This data on chemicals, and mixtures of chemicals, commonly known as reagents, is presented for the purpose of acquainting those interested in frothflotation with some of the more common reagents and their various uses.
Flotation as a concentration process has been extensively used for a number of years. However, little is known of it as an exact science, although, various investigators have been and are doing much to place it on a more scientific basis. This, of course, is a very difficult undertaking when one appreciates how ore deposits were formed and the vast number of mineral combinations existing in nature. Experience obtained from examining and testing ores from all over the world indicates that no two ores are exactly alike. Consequently, aside from a few fundamental principles regarding flotation and the use of reagents, it is generally agreed each ore must be considered a problem for the metallurgist to solve before any attempt is made to go ahead with the selection and design of a flotation plant.
Flotation reagents may be roughly classified, according to their function, into the following groups: Frothers, Promoters, Depressants, Activators, Sulphidizers, Regulators. The order of these groups is no indication of their relative importance; and it is common for some reagents to fall into more than one group.
The function of frothers in flotation is that of building the froth which serves as the buoyant medium in the separation of the floatable from the non-floatable minerals. Frothers accomplish this by lowering the surface tension of the liquid which in turn permits air rising through the pulp to accumulate at the surface in bubble form.
The character of the froth can be controlled by the type of frother. Brittle froths, those which break down readily, are obtained by the alcohol frothers. Frothers such as the coal tar creosotes produce a tough bubble which may be desirable for certain separations.
Flotation machine aeration also determines to a certain extent the character of the froth. Finely divided air bubbles thoroughly diffused through the pulp are much more effective than when the same volume of air is in larger bubbles.
In practice the most widely used frothers are pine oil and cresylic acid, although, some of the higher alcohols are gradually gaining favor because of their uniformity and low price. The frothers used depends somewhat upon the location. For instance, in Australia eucalyptus oil is commonly usedbecause an abundant supply is available from the tree native to that country.
Frothers are usually added to the pulp just before its entrance into the flotation machine. The quantity of frother varies with the nature of the ore and the purity of the water. In general from .05 to .20 lbs. per ton of ore are required. Some frothers are more effective if added in small amounts at various points in the flotation machine circuit.
Overdoses of frother should be avoided. Up to a certain point increasing the amount of frother will gradually increase the froth produced. Beyond this, however, further increases will actually decrease the amount of froth until none at all is produced. Finally, as the excess works out of the system the froth runs wild and this is a nuisance until corrected.
Not enough frother causes too fragile a froth which has a tendency to break and drop the mineral load. No bare spots should appear at the cell surface, and pulp level should not be too close to the overflow lip, at least in the cells from which the final cleaned concentrate is removed.
A good flotation frother must be cheap and easily obtainable. It must not ionize to any appreciable extent. It must be an organic substance. Chemically a frother consists of molecules containing two groups having opposite properties. One part of the molecule must be polar in order to attract water while the other part must be non-polar to repel water. The polar group in the molecule preferably should contain oxygen in the form of hydroxyl (OH), carboxyl (COOH), carbonyl (CO); or nitrogen in the amine (NH2) or the nitrile form. All of these characteristics are possessed by certain wood oils such as pine oil and eucalyptus oil, by certain of the higher alcohols, and by cresylic acid.
The function of promoters in flotation is to increase the floatability of minerals in order to effect their separation from the undesirable mineral fraction, commonly known as gangue. Actuallywhat happens is that the inherent difference in wettability among minerals is increased and as a result the floatability of the more non-wettable minerals is increased to the point where they have an attraction for the air bubbles rising to the surface of the pulp. In practical operation the function of promoters may be considered two-fold: namely, to collect and select. Certain of the xanthates, for instance, possess both collective and selective powers to a high degree, and it is reagents such as these that have made possible some of the more difficult separations. In bulk flotation all of the sulphide minerals are collected and floated off together while the gangue remains unaffected and is rejected as tailing. Non- selective promoters serve very well for this purpose. Selective or differential flotation, on the other hand, calls for promoters which are highly selective or whose collecting power may be modified by change in pulp pH (alkalinity or acidity), or some other physical or chemical condition.
The common promoters for metallic flotation are xanthates, aerofloats, minerec, and thiocarbanilide. Soaps, fatty acids, and amines are commonly used for non-metallic minerals such as fluorspar, phosphate, quartz, felpsar, etc.
Promoters are generally added to the conditioner ahead of flotation to provide the time interval required for reaction with the pulp. Some promoters are slower in their action and in such case are added directly to the grinding circuit. Promoters which are fast acting or have some frothing ability are at times added directly to the flotation machine, as required, usually at several points. This practice is commonly known as stage addition of reagents.
The quantity of promoter depends on the character and amount of mineral to be floated, and in general for sulphide or metallic minerals .01 to .20 lbs. per ton of ore are required. Flotation of metallic oxides and non-metallic minerals usually require larger quantities of promoter, and in the case of fatty acids the range is from 0.5 to 2.5 lbs. per ton.
The function of depressants is to prevent, temporarily, or sometimes permanently, the flotation of certain minerals without preventing the desired mineral from being readily floated. Depressants are sometimes referred to as inhibitors.
Lime, sodium sulphite, cyanide, and dichromate are among the best known common depressants. Among organic depressants, starch and glue find widest application. If added in sufficient quantity starch will often depress all the minerals present in an ore pulp. Among the inorganic depressants, lime is the cheapest and best for iron sulphides, while zinc sulphate, sodium cyanide, and sodium sulphite depress zinc sulphide. Sodium silicate, quebracho, and also cyanide are commondepressants in non-metallic flotation.
Depressants are generally added to the grinding circuit or conditioner usually before addition of promoting and frothing reagents. They may also be added direct to the flotation cleaner circuit particularly on complex ores when it is difficult to make a clean cut separation or where considerable gangue may be carried over mechanically into the cleaning circuit as in flotation of fluorspar. Quantity of depressants required depends on the nature of the ore treated and should be determined by actual test. For instance, lime required to depress pyrite may vary from 1 to 10 lbs. a ton.
The function of activators is to render floatable those minerals which normally do not respond to the action of promoters. Activators also serve to render floatable again minerals which have been temporarily depressed in selective flotation. Sphalerite depressed with cyanide and zinc sulphate can be activated with copper sulphate and it will then respond to treatment like a normal sulphide. Stibnite, the antimony sulphide mineral, responds much better to flotation after being activated with lead nitrate.
The theory generally accepted on activation is that the activating substance, generally a metallic salt, reacts with the mineral surface to form on it a new surface more favorable to the action of a promoter. This also applies to non-metallic minerals.
Activators are usually added to the conditioner ahead of flotation and in general the time of contact should be carefully determined. Amounts required will vary with the condition of the ore treated. In the case of zinc ore previously depressed with zinc sulphate and cyanide, from 0.5 to 2.0 of copper sulphate may be required for complete activation. Quantities required should always be determined by test.
The most widely used sulphidizer is sodium sulphide, which is commonly used in the flotation of lead carbonate ores and also slightly tarnished sulphides such as pyrite and galena. In the sulphidization of ores containing precious metals careful control must be exercised as in some instances sodium sulphide has been known to havea depressing effect on flotation of metallics. In such cases it is advisable to remove the precious metals ahead of the sulphidization step.
Sulphidizers are usually fed into the conditioner just ahead of the flotation circuit. The quantity required varies with the characteristics of the ore and may range from .5 to 5 lbs. per ton. Conditioning time should be carefully determined and an excess of sulphidizing reagent avoided.
The function of regulators is to modify the alkalinity or acidity in flotation circuits, which is commonly measured in terms of hydrogen ion concentration, or pH. Modifying the pH of a pulp has a pronounced effect on the action of flotation reagents and is one of the important means of making otherwise difficult separations possible.
Soluble salts may have their source in the ore or water, or both, and in precipitating them out of solution they generally become inert to the action of flotation reagents. Soluble salts have a tendency to combine with promoters thus withdrawing a certain proportion of the reagents from action on the mineral to be floated. Removal of the deleterious salts therefore makes possible a reduction in the amount of reagent, required. Complexing soluble salts by keeping them in solution yet inert to the reagents is in some cases desirable.
Mineral surfaces may vary according to pulp pH conditions as many of the regulators appear either directly or indirectly to have a cleansing effect on the mineral particle. This brings about more effective action on the part of promoters and other reagents, and in turn increases selectivity.
pH control by action of regulators is in some cases very effective in depressing certain minerals. Lime, for instance, will depress pyrite, and sodiumsilicate is excellent for dispersing and preventing quartz from floating. It is necessary, however, to have a definite concentration of the reagents for best results.
The common regulators are lime, soda ash, and sodium silicate for alkaline circuits, and sulphuric acid for acid circuits. Many other reagents are used for this important function. The separation required and character of ore will determine which regulators are best suited. In general, from an operating standpoint, it is preferable to use a neutral or alkaline circuit, but in some instances it is only possible to obtain results in an acid circuit which then will require the use of special equipment to withstand corrosion. Flotation of non-metallic minerals is at times more effective in an acid circuit as in the case of feldspar and quartz. The pulp has to be regulated to a low pH by means of hydrofluoric acid before any degree of selectivity is possible between the two minerals.
Regulators are fed generally to the grinding circuit or to the conditioner ahead of flotation and before addition of promoters and activators. The amounts required will vary with the character of the ore and separation desired. In the event an excessive quantity of regulator is required to obtain the desired pH it may be advisable to consider removing the soluble salts by water washing in order to bring reagent cost within reason.
The tables on the following pages have been prepared to present in brief form pertinent information on a few of the more common reagents now beingused in the flotation of metallic and non-metallic minerals. A brief explanation of the headings in the table is as follows:
Usual Method of Feeding: Whether in dry or liquid form. A large number of reagents are available in liquid form and naturally are best handled in wet reagent feeders, either full strength or diluted for greater accuracy in feeding. Many dry reagents are best handled in solution form and in such cases common solution strengths are specified in percent under this heading. A 10% water solution of a reagent means 10 lbs. of dry reagent dissolved in 90 lbs. of water to make 100 lbs. of solution. Some dry reagents, because of insolubility or other conditions, must be fed dry. This is usually done by belt or cone type feeders designed especially for this service to give accurate and uniform feed rates.
Pasty, viscous, insoluble reagents present a problem in handling and are generally dispersed by intense agitation with water to form emulsions which can then be fed in the usual manner with a wet reagent feederor using a pump.
Price Per Lb.: Prices shown are approximate and in general apply to drum lots and larger quantities F.O.B. factory. This information is very useful whenmaking tests to determine the lowest cost satisfactory reagent combination for a specific ore. Some ores will not justify reagent expenditures beyond a certain limit, and in this case less expensive reagents must be given first consideration.
Uses: General use for each reagent as given is determined from experience by various investigators. Although the Equipment Company uses a large number of these reagents in conducting test work on ores received from all parts of the world, opinion, data, or recommendations contained herein are not necessarily based on our findings, but are data published by companies engaged in the manufacture of those reagents.
The ore testing Laboratory of 911metallurgist, in the selection of reagents for the flotation of various types of ores, uses that combination which gives the best results, irrespective of manufacturer of the reagents. The data presented on the following tables should be useful in selecting reagents for trials and tests, although new uses, new reagents, and new combinations are continually being discovered.
The consumption of flotation reagents is usually designated in lbs. per ton of ore treated. The most common way of determining the amount of reagent being used is to measure or weigh the amount being fed per. unit of time, say one minute. Knowing the amount of ore being treated per unit of time, the amount of reagent may then be converted into pounds per ton.
The tables below will be useful in obtaining reagent feed rates and quantities used per day under varying conditions. The common method of measurement is in cc (cubic centimetres) per minute. The tables are based on one cc of water weighing one gram. A correction therefore will be necessary for liquid reagents weighing more or less than water. Dry reagents may be weighed directly in grams per min. which in the tables is interchangeable with cc per min.
In the table on the opposite page the 100% column refers to undiluted flotation reagents such as lime, soda ash and liquids with a specific gravity of 1.00. Ninety-two per cent is usually used for light pine oils, 27 per cent for a saturated solution of copper sulphate and 14 per cent for TT mixture (thiocarbanilide dissolved in orthotoluidine). The other percentages are for solutions of other frequently used reagents such as xanthates, cyanide, etc.
The action of promoting reagents in increasing the contact-angle at a water/mineral surface implies an increase in the interfacial tension and, therefore, a condition of increased molecularstrain in the layer of water surrounding the particle. If two such mineral particles be brought together, the strain areas enveloping them will coalesce in the reduction of the tensionary system to a minimum. In effect, the particles will be pressed together. Many such contacts normally occur in a pulp before and during flotation, with the result that the floatable minerals of sufficiently high contact-angle are gathered together into flocks consisting of numbers of mineral particles. This action is termed flocculation , and obviously is greatly increased by agitation.
The reverse action, that of deflocculation , takes place when complete wetting occurs, and no appreciable interfacial tension exists. Under these conditions there is nothing to keep two particles of ore in contact should they collide, since no strain area surrounds them ; they therefore remain in individual suspension in the pulp.
Since substances which can be flocculated can usually be floated, and vice versa, the terms flocculated and deflocculated have become more or less synonymous with floatable and unfloatable , and should be understood in this sense, even though particles of ore often become unfloatable in practice while still slightly flocculatedthat is, before the point of actual deflocculation has been reached.
Here is a ListFlotation Reagents & Chemicals prepared to present in brief form pertinent information on a few of the more common reagents now being used in the flotation of metallic and non-metallic minerals. A brief explanation of the headings in the table is as follows:
Usual Method of Feeding: Whether in dry or liquid form. A large number of reagents are available in liquid form and naturally are best handled in wet reagent feeders, either full strength or diluted for greater accuracy in feeding. Many dry reagents are best handled in solution form and in such cases common solution strengths are specified in percent under this heading. A 10% water solution of a reagent means 10 lbs. of dry reagent dissolved in 90 lbs. of water to make 100 lbs. of solution. Some dry reagents, because of insolubility or other conditions, must be fed dry. This is usually done by belt or cone type feeders designed especially for this service to give accurate and uniform feed rates.
Pasty, viscous, insoluble reagents present a problem in handling and are generally dispersed by intense agitation with water to form emulsions which can then be fed in the usual manner with a wet reagent feeder.
The performance of froth flotation cells is affected by changes in unit load, feed quality, flotation reagent dosages, and the cell operating parameters of pulp level and aeration rates. In order to assure that the flotation cells are operating at maximum efficiency, the flotation reagent dosages should be adjusted after every change in feed rate or quality. In some plants, a considerable portion of the operators time is devoted to making these adjustments. In other cases, recoverable coal is lost to the slurry impoundment and flotation reagent is wasted due to operator neglect. Accurate and reliable processing equipment and instrumentation is required to provide the operator with real-time feedback and assist in optimizing froth cell efficiency.
This process of optimizing froth cell efficiency starts with a well-designed flotation reagent delivery system. The flotation reagent pumps should be equipped with variable-speed drives so that the rates can be adjusted easily without having to change the stroke setting. The provision for remotely changing the reagent pump output from the control room assists in optimizing cell performance. The frother delivery line should include a calibration cylinder for easily correlating pump output with the frother delivery rate. Our experience has shown that diaphragm metering pumps of stainless steel construction give reliable, long-term service. Duplex pumps are used to deliver a constant frother-to-collector ratio over the range of plant operating conditions.
In most applications, the flotation reagent addition rate is set by the plant operator. The flotation reagents can be added in a feed-forward fashion based on the plant raw coal tonnage. Automatic feedback control of the flotation reagent addition rates has been lacking due to the unavailability of sensors for determining the quality of the froth cell tailings. Expensive nuclear-based sensors have been tried with limited success. Other control schemes have measured the solids concentrations of the feed, product, and tailings streams and calculated the froth cell yield based on an overall material balance. This method is susceptible to errors due to fluctuations in the feed ash content and inaccuracies in the measurement device.
A series of simple math models have been developed to assist in the engineering analysis of batch lab data taken in a time-recovery fashion. The emphasis is to separate the over-all effect of a reagent or operating condition change into two portions : the potential recovery achievable with the system at long times of flotation, R, and a measure of the rate at which this potential can be achieved, K.
Such patterns in R and K with changing conditions assist the engineer to make logical judgements on plant improvement studies. Standard laboratory procedures usually concentrate on identifying some form of equilibrium recovery in a standard time frame but often overlook the rate profile at which this recovery was achieved. Study has shown that in some plants, at least, changes in the rate, K, are more important relative to over-all plant performance than changes in the lab measured recovery, R. Thus the R-K analysis can serve to improve the engineering understanding of how to use lab data for plant work. Long term plant experience has also shown that picking reagent systems having higher K values associated can be beneficial even when the plant, on the average, is not experiencing rate of mass removal problems. This is due to the cycling or instabilities that can and do exist in industrial circuits.
It is also important to note that the R-K approach does not eliminate the need for surface chemistry principles and characterization. Such principles and knowledge are required to logically select and understand potential reagent systems and conditions of change in flotation. Without this, reagent selection is quickly reduced to a completely Edisonian approach which is obviously inefficient. What the R-K analysis does is to provide additional information on a system in a critical stage of scale-up (from the lab to the plant) in a form (equilibrium recovery and rate of mass removal) which are interpretable to the engineer who has to make the change work.
The influence of operating conditions such as pH, temperature of feed water, degree of grind, air flow rate, degree of agitation, etc. have been characterized using the R-K approach with clear patterns evolving.
The effect of collector type and concentration on a wide variety of ore types have been studied with generally rather clear and sometimes rather significant patterns in R and K. The quantitative ability to analyze collector performance from the lab to the plant using the R-K profiles has been good.
The effect of frother type on various ores has also been undertaken with good success in differentiating between the qualitative directions and effects involved. However, the actual concentrations required in plants have not, in at least some tests, been accurately predicted. Thus further work remains in this area but in almost all cases the qualitative information on frothers that has been gained has proven very valuable in test work as a guide.
Flotation foam is an important but often overlooked component for boat prep. It serves multiple purposes that boat owners often dont consider but it could cost you in the long run. But many boaters only know that flotation foams exists but dont know what its used for and how it can benefit them to have some foam in their boat.
What are the benefits of flotation foam for boats? Flotation foam will provide more-permanent flotation for boats and docks, provide thermal insulation which is important for use in hot and cold extreme that comes with year-round boat care, and for sound deadening. Flotation foam is typically applied to boat hulls either through open or closed-cell mats and blocks or through special marine pour foam which forms a mechanical seal with the hull of boats. Each of these methods has its purposed and benefits for why they should be considered.
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Flotation foam is any type of foam designed or repurposed for use in marine vessels and docks for the purpose of flotation enhancement, thermal insulation, and for sound deadening. You can find specially designed boat flotation options in the form of pourable foam, closed-cell foam mats or blocks, and even boat foam pods that attach to the outside of the boat and rest in the water.
These all serve a purpose and are great options. People also repurpose foam they have for other non-marine projects such as hollow or solid-core swimming noodles and Styrofoam to provide added flotation and sound deadening for their vessels.
I prefer pourable foam because it can form a mechanical bond with aluminum hulls that hold it in place and closed-cell foam sheets because the closed-cell foam is waterproof and wont absorb water as long as it remains in good condition.
I believe a combination of pourable foam and closed-cell foam sheets is the ideal fit for most boats. That is my personal preference based on what Ive seen using some other foam types as time and use passes. I will explain later how to combine these two types of foam for your boat.
To an extent, adding foam to a boat will help it float but perhaps in a way different than many people assume. The common train of thought is that a boat filled with flotation foam will float better than a boat without foam. There may be a shred of truth to that and perhaps more scientific justification than Im giving it credit for.
Foam on board may help a boat sit a smidge higher in the water than one without it, but that is not the purpose of the foam as a flotation device. The foam is there to literally prevent the boat from sinking.
On the other hand, a boat lined with foam will still take on water and will sit progressively lower and lower on top of the water but it will greatly delay the boat from sinking. It should give you enough time to reach safety, radio for help and wait for rescue, or make it to shore before the boat goes under.
First and foremost, you add foam to keep a boat from sinking. As we have already discussed, whether it helps a boat sit higher in the water is debatable, but the foam can literally prevent a boat already taking on water from going under which can save your gear and potentially your life.
Imagining yourself in a small boat in the ocean that is going down quick would have to be one of the loneliest and scariest feelings. I have worked with commercial fishermen who were in a similar situation and managed to get rescued in time. Having a ton of foam on board could literally save your life.
Polyurethane spray or pour foam seems to be the most popular way to insulate spaces aboard a vessel. Thermal insulation is really important on larger boats, especially those with frozen or cool storage areas.
What may sound like an annoying bump from above the water can really amplify and carry underwater. Any footstep, weight shift, and even rocking in the waves will really make it sound so much louder if you dont add foam. Flotation foam not only prevents a boat from sinking but also really dampens or deadens sound.
You could drop your rod on the deck of a well-foamed hull and fish wont even notice but if you did the same thing without foam, you may need to relocate somewhere else to find non-spooked fish. Trust me, you will really benefit from padding the deck of your small aluminum or wooden boat with flotation foam if you are serious about fishing.
Avoid using polystyrene because it soaks up water. Plus, it can easily absorb petrochemicals such as petroleum and a few types of glue. This makes it very dangerous in case a gas leak occurs near this foam. This foamcan soak up the gas becoming a serious fire hazard.
Polyurethane is the better choice because it does not absorb water or petrochemicals. Another advantage of polyurethane is that it is available in liquid form and when you pour it into an air chamber, it can mold perfectly to the boat.
Polyethylene is another great choice for flotation foam. It works as good as polyurethane but without any of the abrasion risk. Polyethylene can be compressed or even bent to fit curved places while polyurethane is rigid.
I have not tested every flotation foam on the market and neither have most people. I have tested the following two pourable foam options and found them easy to use and implement. I would recommend them but the truth is that most pourable foam option will do fine as long as you follow the directions and apply it very quickly after mixing.
Also, I wont make any recommendations for sheet or block foam because you can simply go to your hardware store for that and it will help to see examples in person to make sure you get sheets that are the right density and thickness.
Flotation foam can be an important addition for sink-proofing, thermal insulation, and soundproofing such boats as sailboats, jon boats, aluminum v-hull fishing boats, speed boats, canoes, bass boats, and pontoon boats. It can also help keep floating docks riding higher in the water when loaded down with weight.
The closed-cell foam used on boats is designed to remain water-proof under normal circumstances. There have numerous scientific studies showing that closed-cell foam is better resistant to water permeation than closed-cell including a 2007 study by Sun & Zhang.
But numerous accounts of boaters who replaced closed-cell foam after years of wear and tear show that even this type of foam can absorb water once the protective outer layer is compromised by tiny cuts, abrasions, or sun damage. Long story short, closed-cell foam can absorb water if left submerged in water in a confined space for a long duration of time.
Furthermore, if your boat springs a leak, the foam on-board will keep your boat floating much longer than not having foam which will make it a lot more stable as you motor to safety and also afloat long enough to make shore. For a complete breakdown on how to make a jon boat more stable, check out this link.
I am an avid angler and outdoorsman. I grew up fishing for anything that swims but really cut my teeth fishing for trout, chain pickerel, bass, and bullheads in my teenage years. Since then, I've lived across the country and have really taken that passion for fishing to a new level.
Circle hooks are gaining in popularity across the nation because of their efficiency and effectiveness. But circle hooks have specific applications where they are best suited. Still many others want...
I am an avid angler and outdoorsman. I grew up fishing for anything that swims but really cut my teeth fishing for trout, chain pickerel, bass, and bullheads in my teenage years. Since then, I've lived across the country and have really taken that passion for fishing to a new level.
This site is owned and operated by Eric Matechak. FreshwaterFishingAdvice is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com. FreshwaterFishingAdvice is compensated for referring traffic and business to these companies.
Flotation reagents refer to the agent that used in mineral flotation process, which can adjust the flotation behavior of minerals thus achieving a good effect of mineral separation.Currently using flotation reagents is the most flexible, effective, and convenient method of controlling flotation process.The commonly used flotation reagents can be mainly divided into three types according to their different working principles: flotation collectors, flotation frothers and flotation conditioners.
Among all flotation reagents, the main function of flotation collector is to change the hydrophilicity of the mineral surface, enhance its hydrophobicity, and increase the adhesion of the mineral on the bubble, which can make the minerals more floatable and shorten the induction time.
Since most of the minerals in nature are hydrophilic, the flotation collector is widely used in flotation operations as a kind of flotation reagent. Generally, it can be divided into polar collectors and non-polar collectors. The commonly used collectors for flotation are mainly xanthate, dithiophosphate and thiocarbanilide, etc.
Among all flotation reagents, the main function of the flotation frothers is to promote the formation of uniform bubbles and enhance the elasticity of the surface of the bubble. It can also make the bubbles generated by flotation more stable and not easily deformed. Even when subjected to vibration or other external force, bubbles are less likely to rupture. In addition, the stability of the foam is also affected by the pH of the pulp, the soluble salt content, etc. The commonly used flotation frothers are mainly pine oil, methyl isobutyl carbinol (MIBC) and so on.
Among all flotation reagents, the main function of the flotation conditioners is to adjust the interaction between the collector and the mineral, adjust the pH of the slurry, and promote or inhibit the floatability of the mineral. According to the effect of the conditioners, flotation conditioners can be divided into the following categories: pH modifiers, activators, inhibitors, dispersant, etc.
pH modifiers: It is a kind of reagent mainly used to adjust the pH value of the flotation slurry, control the surface characteristics of the mineral and the chemical composition of the slurry to achieve the conditions required for flotation. Commonly used pH modifiers are lime, sodium carbonate, sulfuric acid and sodium hydroxide, etc.
Activators: It is a kind of reagents mainly used to enhance the floatability of minerals in flotation process, change the composition of the mineral surface, and enhance the effect of the collector. The non-floating minerals can float under the action of the activator. Among the flotation reagents, commonly used activators for flotation are sulfuric acid, sulfurous acid, sodium sulfide, copper sulfate and so on.
Inhibitors: It is a kind of reagents mainly used to increase the hydrophilicity of minerals and to form a hydrophilic film on the surface of the ore particles in flotation process. At the same time, it inhibits the action of the collector on the mineral and reduces the floatability of the mineral. Among the flotation reagents, commonly used inhibitors for flotation are sodium thioglycolate, sodium sulfide, sodium silicate and sodium cyanide.
Dispersant: It is a kind of reagents mainly used to prevent the aggregation of fine-grained minerals and make them in a monomer state in flotation process. The particles can be easily wetted in the medium while remaining in a dispersed state. Commonly used dispersants mainly include sodium silicate and phosphate.
The above describes the principle of action of various flotation reagents in the flotation process. In actual production, the flotation scheme should be formulated according to the nature of the sorted minerals. First we need to determine which minerals need to be inhibited or activated, and choose the right type of flotation reagent. For example, in the flotation of lead-zinc sulfide ore, it is necessary to separate lead, zinc and sulfur. At this time, flotation reagents are used to change the nature of one of the minerals and separate them one by one. In the case of lead-zinc separation, the zinc-inhibited and lead-collected program is usually adopted. That is to say, an inhibitor that inhibits zinc is added to the slurry to preferentially float the lead ore. In the process of zinc-sulfur separation, it is common to use lime to depress iron sulfide, to activate sphalerite with copper sulfate (a kind of activator), and to collect sphalerite with xanthate (a kind of collector). In addition, pH modifiers are used to adjust the pH of the slurry to facilitate flotation.
At the same time, it is necessary to pay attention to the rational preparation of flotation reagents, the order and location of the addition, and the correct method of dosing of flotation reagent, thereby improving the efficiency of flotation.
Archaeological flotation is a laboratory technique used to recover tiny artifacts and plant remains from soil samples. Invented in the early 20th century, flotation is today still one of the most common ways to retrieve carbonized plant remains from archaeological contexts.
In flotation, the technician places dried soil on a screen of mesh wire cloth, and water is gently bubbled up through the soil. Less dense materials such as seeds, charcoal, and other light material (called the light fraction) float up, and tiny pieces of stone called microliths or micro-debitage, bone fragments, and other relatively heavy materials (called the heavy fraction) are left behind on the mesh.
The earliest published use of water separation dates to 1905, when German Egyptologist Ludwig Wittmack used it to recover plant remains from ancient adobe brick. The widespread use of flotation in archaeology was the result of a 1968 publication by archaeologist Stuart Struever who used the technique on the recommendations of botanist Hugh Cutler. The first pump-generated machine was developed in 1969 by David French for use at two Anatolian sites. The method was first applied in southwest Asia at Ali Kosh in 1969 by Hans Helbaek; machine-assisted flotation was first conducted at Franchthi cave in Greece, in the early 1970s.
The Flote-Tech, the first standalone machine to support flotation, was invented by R.J. Dausman in the late 1980s. Microflotation, which uses glass beakers and magnetic stirrers for gentler processing, was developed in the 1960s for use by various chemists but not extensively used by archaeologists until the 21st century.
The reason for the initial development of archaeological flotation was efficiency: the method allows for the rapid processing of many soil samples and the recovery of small objects which otherwise might only be collected by laborious hand-picking. Further, the standard process uses only inexpensive and readily available materials: a container, small-sized meshes (250 microns is typical), and water.
However, plant remains are typically quite fragile, and, beginning as early as the 1990s, archaeologists became increasingly aware that some plant remains split open during water flotation. Some particles can completely disintegrate during water recovery, particularly from soils recovered in arid or semi-arid locations.
The loss of plant remains during flotation is often linked to extremely dry soil samples, which can result from the region in which they are collected. The effect has also been associated with concentrations of salt, gypsum, or calcium coating of the remains. In addition, the natural oxidation process that occurs within archaeological sites converts charred materials which are originally hydrophobic to hydrophilicand thus easier to disintegrate when exposed to water.
Wood charcoal is one of the most common macro-remains found in archaeological sites. The lack of visible wood charcoal in a site is generally considered the result of the lack of preservation of the charcoal rather than the lack of a fire. The fragility of wood remains is associated with the state of the wood on burning: healthy, decayed, and green wood charcoals decay at different rates. Further, they have different social meanings: burned wood might have been building material, fuel for fire, or the result of brush clearing. Wood charcoal is also the main source for radiocarbon dating.
Decayed wood is particularly underrepresented at archaeological sites, and as today, such wood was often preferred for hearth fires in the past. In these cases, standard water flotation exacerbates the problem: charcoal from decayed wood is extremely fragile. Archaeologist Amaia Arrang-Oaegui found that certain woods from the site of Tell Qarassa North in southern Syria were more susceptible to being disintegrated during water processingparticularly Salix. Salix (willow or osier) is an important proxy for climate studiesits presence within a soil sample can indicate riverine microenvironmentsand its loss from the record is a painful one.
Arrang-Oaegui suggests a method for recovering wood samples that begins with hand-picking a sample before its placement in water to see if wood or other materials disintegrate. She also suggests that using other proxies such as pollen or phytoliths as indicators for the presence of plants, or ubiquity measures rather than raw counts as statistical indicators. Archaeologist Frederik Braadbaart has advocated the avoidance of sieving and flotation where possible when studying ancient fuel remains such as hearths and peat fires. He recommends instead a protocol of geochemistry based on elemental analysis and reflective microscopy.
The microflotation process is more time consuming and costly than traditional flotation, but it does recover more delicate plant remains, and is less costly than geochemical methods. Microflotation was used successfully to study soil samples from coal-contaminated deposits at Chaco Canyon.
Archaeologist K.B. Tankersley and colleagues used a small (23.1 millimeters) magnetic stirrer, beakers, tweezers, and a scalpel to examine samples from 3-centimeter soil cores. The stirrer bar was placed at the bottom of a glass beaker and then rotated at 45-60 rpm to break the surface tension. The buoyant carbonized plant parts rise and the coal drops out, leaving wood charcoal suitable for AMS radiocarbon dating.
Froth flotation is a process that selectively separates materials based upon whether they are water repelling (hydrophobic) or have an affinity for water (hydrophilic). Importantly, the word flotation is also used in the literature to describe the process in density separation in which lighter microplastics float to the surface of a salt solution. However, this process is based upon density alone and should not be confused with the process of froth flotation. Thus, the process of froth flotation is not solely dependent upon the density of the material; it is also dependent upon its hydrophobic nature. For example, froth flotation is a technique commonly used in the mining industry. In this technique, particles of interest are physically separated from a liquid phase as a result of differences in the ability of air bubbles to selectively adhere to the surface of the particles, based upon their hydrophobicity. The hydrophobic particles with the air bubbles attached are carried to the surface, thereby forming a froth which can be removed, while hydrophilic materials stay in the liquid phase272 (Fig. 9.8).
Since plastics are generally hydrophobic materials, froth flotation has successfully been used for the separation of plastic materials.5,1375137 For example, two plastic materials which are buoyant in a specific liquid phase can be separated from one another by the addition of a wetting agent which selectively adsorbs to one of the plastics and not the other. Thus, the wetting agent acts as a flotation depressant by selectively adsorbing to the surface of a specific plastic, thereby rendering it hydrophilic. However, adsorption to the other plastic is far less pronounced. Consequently, the hydrophobic plastic will continue to float while hydrophilic plastic will sink to the bottom as a result of depressed flotation. The floating plastic can then be recovered from the surface of the mixture. However, there are many factors to take into account in the process of froth flotation, such as the surface free energy of the microplastics and the surface tension of the liquid in the flotation bath, as well as the critical surface tension, which defines the surface tension at which the liquid completely wets the solid microplastics. Ultimately, the selective separation of inherently hydrophobic microplastics requires that the microplastics are only partially wetted by the liquid in the flotation bath, thereby allowing the bubble to adhere to the surface of the solid phase and bring the microplastics to the surface of the liquid phase to be collected, while the sediment particles are completely wetted and sink. Nevertheless, the technique has rarely been used for the separation of microplastics from sediments.198,436198436 Perhaps the reason for this is that while recovery rates of up to 93% have been reported,436 the technique was found to be negatively influenced by the presence of wetting agents or additives in the plastics.
Froth flotation is a long established technique in mineral processing. Extensive discussion of flotation can be found in the book by Leja (1982); see also recent work by Fecko et al. (2005) and Melo and Laskowski (2006). Basically, particles are either hydrophilic or hydrophobic (Gutierrez-Rodriguez et al., 1984). Surface properties of particles are modified with a surfactant (collector). Bubbles, produced by mechanical (froth flotation) or passive (column flotation) aeration and stabilized by a frother (a surfactant), are used to bring hydrophobic particles to the surface. Macerals, with some variation as will be discussed, and pyrite are hydrophobic and will adhere to the bubbles while clays and other silicates are hydrophilic and will sink. Whether pyrite is truly hydrophobic or entrained by the bubbles or interlocked with floatable particles is a matter of research, but one necessary to develop mechanisms that suppress pyrite from being recovered with clean coal product (Kawatra and Eisele, 1997).
Since froth flotation (and oil agglomeration) relies on the surface properties of coal in separating particles, coal petrology plays an important role in the process. Arnold and Aplan (1989) reported a number of studies which examined maceral partitioning or lithotype partitioning, generally without consideration of the maceral association. In order of decreasing floatability, they noted that liptinite > vitrinite > fusinite and vitrain > clarain > durain > fusain. For an eastern Kentucky coal, Hirt and Aplan (1991) noted the relationship, in order of decreasing floatability: pseudovitrinite (high Rmax) > pseudovitrinite (low Rmax) > vitrinite (high Rmax) > vitrinite (low Rmax) = micrinite = exinite (liptinite) = semifusinite > resinite > fusinite. Note, this differs from the ICCP (1998) maceral definitions, but pseudovitrinite does have a usage precedent in the coal petrology literature (Benedict et al., 1968b). Arnold and Aplan (1989) also examined microlithotype relationships, finding vitrite to be concentrated in the faster floating fractions and inertite in slower floating fractions. In order of decreasing floatability, microlithotypes follow the general order vitrite > inertite > vitrinertite > clarite > duroclarite. A rank relationship exists, with hydrophobicity increasing sharply through the high volatile bituminous rank range (Aplan, 1993). Honaker et al. (1996) investigated differences in maceral partitioning in column flotation related to pH. Since different researchers have used a variety of coals with varying petrographic composition and varying rank, exact comparisons between studies are difficult (Arnold and Aplan, 1989). Overall, the behavior of particles is best understood by understanding the composition of the entire particle (Sarkar et al., 1984; Ofori et al., 2006), although it is really only the outer surface that is important in processing.
Flotation, generally conducted on <0.5 mm particles, is processing particles from the lithotype to microlithotype scale. The maceral and microlithotype composition of the particle can be used as a proxy for the surface interface with the surfactants. Ofori et al. (2006) and O'Brien et al. (2003, 2006) have developed a semiautomated image analysis system to diagnose coal grains by their grain size, composition, and density and relate this directly to flotation performance. Imaging is used to classify grains as liberated (single component) or composite and to derive the density of each grain from maceral and mineral type and abundance (O'Brien et al., 2006). This method provides a tool for tracking behavior in the flotation circuit and for optimizing processes in advance.
Weathering has an influence on hydrophobicity. In a study of Spanish bituminous coals, Garcia et al. (1991) demonstrated that the formation of humic acid complexes and the oxidation of Fe led to poor flotation recovery at the same pH as unweathered coal. Adjustment of the pH towards the basic range did yield some improvement in recovery.
Froth flotation is influenced by several operating factors. The most important of these is pH. Interaction with collector and formation of hydrophobic film at a mineral occurs within certain pH range. In the case of sulfide minerals, at pH above a certain value, called critical pH, the collector uptake does not occur and the mineral ceases to float. This critical pH varies for different minerals and is taken advantage of for selective separation of minerals from slurry containing more than one mineral.
Another influence of pH is in influencing the state of ionization of the collector. Amines are cationic in acidic pH range. In alkaline pH, the long chain amines occur in neutral molecular state and not suitable as cationic reagente. In between the two ranges, within a narrow pH range they occur as ionomolecular complexes comprising ionic and neutral molecule species and they are highly surface active in this form. This also applies to weak acid collectors like sodium oleate, which is anionic in the alkaline pH range, but occurs in neutral molecular state at pH below 4. For further discussion see Rao and Leja (2004).
In froth flotation, the mineral surface plays an important role in the process of reagent adsorption, which determines the geometry and strength of adsorption, and the difference in properties of mineral surfaces is the premise of mineral separation by flotation. We employed the quantum method to model the galena (100) and the pyrite (100) surfaces and investigate the electronic structure and property of the surfaces. The results show that the dissociation of a galena surface results in the breakage of PbS bonds, and the Pb and S atoms are changed from six-coordinated as in the bulk to five-coordinated in the surface. The pyrite Fe and S atoms are five-coordinated and three-coordinated respectively at the surface instead of six in the bulk. The decrease in the coordination number of surface atoms may lead to the variation of their reactivity.
Surface relaxation of galena (100) and pyrite (100) surfaces had been discussed in our previous study , and the results showed that the top three layers of both galena and pyrite surfaces underwent the surface relaxation; however, pyrite underwent greater relaxation than galena.
The Mulliken electron of each layer of PbS (100) and FeS2 (100) surfaces are shown in Fig.6.8. The electron distributions for galena and pyrite are quite different. The outermost layer of both PbS and FeS2 surfaces is electronegative, but PbS carries more negative charge than FeS2 surface.
The DOS of the galena Pb and S atoms and the pyrite Fe and S atoms are shown in Figs.6.9 and 6.10, where the numeral beside the symbol of element represents the layer number. For example, S1 represents S atom in the first layer. Compared with the deep layers (Pb5 and Pb7), the DOS of the surface Pb3 6p state is slightly stronger. It is clearly noted that the DOS of S1 and S3 atoms are quite different from those of S5 and S7 atoms, indicating that electronic properties of surface atoms are different from the deep layer atoms. Moreover, the PbS surface S1 and S3 states dominate around the Fermi level, while the S5 and S7 states have few contributions to the Fermi energy, suggesting that surface Satoms show greater reactivity than the bulk S atoms.
For the pyrite surface, by comparison with the bulk Fe12 layer, the DOS peak of the outermost Fe3 states is obviously enhanced around2.0eV, and Fe 3d state in the conduction band increases from one peak to two peaks. Compared to the deep layer Satoms (S5, S7, and S9), the surface S 3p states (S1 and S4) around2.5 to0eV increase obviously, especially at2.0eV. By comparison to PbS, the Fe atom shows a larger sharp DOS peak at the Fermi level, indicating that the FeS2 Fe atom is more reactive than the PbS Pb atom.
The depressing action of cyanide on pyrite during froth flotation is well known (Sutherland and Wark, 1955) and is widely exploited on many flotation plants to selectively separate copper minerals from pyrite. Depression of pyrite by cyanide during froth flotation appears to take place in solutions containing free cyanide, ferro/ferri cyanide (Sutherland and Wark, 1955), thiocyanate (Plaksin etal., 1949; Adams, 2013), and cuprous cyanide mainly in the form of Cu(CN)32 (Guo etal., 2014). Thedepressing action in the presence of free cyanide seems to be caused by a decrease in the pyrite surface electrochemical activity, leading to lower collector adsorption (Prestige etal., 1993; De Wet etal., 1997). The depressing effect is reversible and is achieved by diluting the pulp with cyanide-free solution. As an illustration of this washing and repulping effect, a cyanide residue from a gold mine with cyanide-free water was sufficient to negate the depressing effect of the cyanide on the pyrite (Hodgkinson etal., 1994). The most widely used method of reversing the depressing effect of cyanide in the past has been to condition the flotation pulp at a pH value in the range 3.54 with sulfuric acid, or bubbling sulfur dioxide into the slurry, and then add copper sulfate to complex the cyanide and subsequently float the pyrite (Clay and Rabone, 1951; Malloy and Tapper, 1978). Amine collectors are also effective at floating cyanide-depressed pyrite in alkaline solutions, although the flotation rate is slow (Ramsay, 1978; Broekman etal., 1987).
The most widely accepted method for upgrading ultrafine coal is froth flotation. Froth flotation is a physicochemical process that separates particles based on differences in surface wettability. Flotation takes place by passing finely dispersed air bubbles through an aqueous suspension of particles (Fig. 17). A chemical reagent, called a frother, is normally added to promote the formation of small bubbles. Typical addition rates are in the order of 0.05 to 0.25 kg of reagent per tonne (0.1 to 0.5 lb per ton) of coal feed. Coal particles, which are naturally hydrophobic (dislike water), become selectively attached to air bubbles and are carried to the surface of the pulp. These particles are collected from a coal-laden froth bed that forms atop the cell due to the frother addition. Most of the impurities that associate with coal are naturally hydrophilic (like water) and remain suspended until they are discharged as dilute slurry waste. Another chemical additive, called a collector, may be added to improve the adhesion between air bubbles and coal particles. Collectors are commonly hydrocarbon liquids such as diesel fuel or fuel oil. In the United States, flotation is typically performed on only the finest fractions of coal (<0.1 mm), although coarse particle flotation (<0.6 mm) is practiced in Australia where coal floatability is high and the contaminants in the process feed low. The removal of clay slimes (<0.03 mm) is carried out ahead of some flotation circuits to minimize the carryover of this high ash material into the froth product. The ultrafine clay slimes are typically removed using large numbers of small diameter (15 mm or 6 inch) classifying cyclones (Fig. 18).
Most of the industrial installations of flotation make use of mechanical (conventional) flotation machines. These machines consist of a series of agitated tanks (four to six cells) through which fine coal slurry is passed. The agitators are used to ensure that larger particles are kept in suspension and to disperse air that enters down through the rotating shaft assembly. The air is either injected into the cell using a blower or drawn into the cell by the negative pressure created by the rotating impeller. Most commercial units are very similar, although some variations exist in terms of cell geometry and impeller design. Industrial flotation machines are now available with individual cell volumes of 28.3 m3 (1000 ft3) or more. Coal flotation is typically performed in a single stage with no attempt to reprocess the reject or concentrate streams. In some cases, particularly where high clay concentrations are present, advanced flotation processes such as column cells have been used with great success. Conventional flotation cells allow a small amount of clay slimes to be recovered with the water that reports to the froth product. A column cell (Fig. 19) virtually eliminates this problem by washing the clay slimes from the froth using a countercurrent flow of wash water. This feature allows columns to produce higher quality concentrate coals at the same coal recovery.
Foam fractionation, also called protein skimming, air stripping and froth flotation, removes surface active (surfactants) dissolved organics and suspended solids, which may be produced in the culture system. If aeration is vigorous, the process can also drive ammonia and volatile components directly to the atmosphere. Additional benefits include the removal of fine particulates and excellent aeration. The process can be very efficient but in some applications has been disappointing. It can be very sensitive to small design details and choices in values of operating variables. The process is believed to be most effective in marine applications, especially in lightly loaded systems. Most seawater applications have been aquarium reuse systems. If it is to be combined with ozonation, some users have strongly recommended, for system control reasons, to separate the two processes by not using ozone in the foam fractionator's gas supply but applying it separately. The equipment, unlike biofilters, does not require much space and maintenance is usually minimal. It is sometimes used in combination with biofilters instead of as a substitute.
Foam fractionation involves agitating aerated seawater to produce a foam rich in dissolved organics and suspended solids. The resulting foam must be collected and discharged to the drain. The performance of this process depends on the organic load and composition, surface tension, temperature, viscosity, pH, salinity, bubble size, air-water ratio, and contact time. Not all these parameters are independent. The ideal bubble size is about a diameter of 0.8 mm (0.03 in.) (Spotte, 1979). High air-water ratios and long bubble contact times increase removal efficiency (Wheaton et al., 1979).
There are a number of configurations for foam fractionators. Some look like airlift pumps and others have a counter-flow arrangement between air and water to increase the contact time (Spotte, 1979; Wheaton et al., 1979). The process water may enter and leave submerged from the bottom or the process water may enter above the surface and counter-flows through the rising foam. In fact, any vigorous diffuser type aerator with an airlift pipe can be used in this manner, if the resulting foam is removed. Probably the most common configuration is the injection of air with a venturi and discharge of the resulting high velocity air-water mixture tangentially near the bottom of a column. This imposes a vigorous circulation, which delays the rise of the small bubbles, increasing contact time. Dimensional design information on the column and venturi (Hagen, 1970) and equations for guidance in optimization are available (Lawson and Wheaton, 1980; Weeks and Timmons, 1992; Timmons et al., 1995). A good review of its use in aquaculture is presented in Timmons (1994). There are indications that small dimensional changes and differences in operating parameters can have large impacts on performance. There is also evidence that prolonged use can lead to depletion of trace materials, especially some metals.
Lead is mostly extracted from galena PbS which is concentrated by a froth flotation process. This concentrated ore is then roasted in a limited supply of air to give lead oxide, which is then mixed with coke and a flux such as limestone and reduced in a blast furnace:
In both cases the obtained lead contains a number of unwanted metal impurities such as copper, silver, gold, zinc, tin, arsenic, and antimony, some of which are clearly valuable in themselves. Lead bullion is melted at a temperature just above its freezing point, then copper rises to the surface as an insoluble solid and therefore copper is the first element to be removed as an impurity. Tin, arsenic, and antimony are removed by oxidation in a reverberatory furnace. The lead may still contain silver, gold, and bismuth. Silver and gold are removed on the basis of their preferential solubility in zinc. The mixed metals are cooled slowly when the Zn solidifies as a crust which is skimmed off; the excess of dissolved zinc is then removed either by a preferential reaction with chlorine or by vacuum distillation or oxidation in a reverberatory furnace. Finally, lead is purified by the process of electrolysis where massive cast leads act as anodes in an electrolyte of acid PbSiF, or a sulfamate; during electrolysis almost 99.99% pure lead is deposited on cathode, which is further purified by zone refining.
Frother -terpineol, MIBC, and DowFroth200 (DF200) together contribute to more than 90% of frother usage in froth flotation industry in the world. Fig.5.19 displays the structure of these three frothers.
DFTB+ module, which is based on the tight-binding method, is used to obtain the initial structures of the interactions between frother molecules and water molecules. For this module, the geometry optimization is built with an algorithm of conjugate gradient. Mio (CHONSP) and divide-conquer are selected as the Slater-Koster library and eigensolver, respectively. The convergence criteria for structure optimization are set to (a)energy tolerance of 0.05kcal/mol, (b)max. force tolerance of 0.5kcal/mol/, and (c)max. iterations of 9999. The smearing is set at 0.005 Ha and all the qualities are under the medium level.
Based on the DFTB+ calculation results, the adsorption of the frother molecule at gasliquid interface is simulated. The interactions between the polar head group of the frother with different numbers of water molecules are performed by Dmol3 module. This module is widely used for its accuracy for not only the molecule structure but also the molecule properties. In this module, no special treatment of core electrons are considered, and all electrons are included. More specifically, spin-unrestricted is performed and the symmetry is also used. The SCF convergence is fixed to 106 Ha, and the convergence criteria for structure optimization are set to (a)energy tolerance of 1.0105 Ha, (b)max. force tolerance of 0.002 Ha/, and (c)max. displacement tolerance of 0.005. The smearing is set at 0.005 Ha, and all kinds of qualities are under the fine level.
For the reason that the exchange-correlation functional and the basis set are the core parameters in DMol3 module, the dOH and HOH of H2O molecule are calculated under different functionals (all with the DNP+ basis set), and the result is shown in Table5.7.
It is clearly shown in Table5.7 that the calculated dOH, HOH, and hydrogen bond energy of the optimized H2O under the functionals of GGA-BP and GGA-VWN-BP are quite close to the experimental values, which are tested at 298K. So in this study, GGA-BP is selected as the exchange-correlation functional.
To find out how the layer of frother molecules absorbs at the gasliquid interface, the molecular dynamics method is used. In the study, the Forcite module is selected, and its temperature, the pressure, and the forcefield are all adjustable. The smart module is chosen as the algorithm, and the convergence criteria are set to (a)energy tolerance of 2.0 105 kcal/mol, (b)max. force tolerance of 0.001kcal/mol/, (c)max. displacement tolerance of 0.005, and (d)max. iterations of 5000. The forcefield of cvff_nocross_nomorse is suitable. In addition, atom-based electrostatic and atom-based van der Waals are selected in simulation method. All the qualities are under the ultrafine level.
where E here is the binding energy; Efrother-nH2O is the total energy of the frother with the water molecules; Efrother is the total energy of the frother molecule; and EH2O is the energy of one water molecule that is calculated under the same condition.
The schematic representation of a foam fractionation column shows a launder foam collection unit that is typical of the foam collection method used in froth flotation. The foam reaches the top of the column and discharges over a weir into a launder vessel around the periphery of the column with a bottom slanted to a discharge tube. Depending on the stability and rheology of the foam at the top of the column, the gas disengages from the foam by drainage and collapses thereby enabling a liquid product to be discharged from the launder, or the foam itself flows out of the discharge line. The major advantage is that launder collection enables relatively large amounts of foam to be collected. The foam handling capacity can be still further enhanced by designing a so-called donut launder that enables discharge around the periphery of the column, as well as into a well in the center. A further idea gained from the design of flotation column is that of a froth crowder which is a solid block that is positioned at the column top to help direct foam over the weir and into the launder.
It should be noted that the launder method of foam handling means that there is a free surface of foam at the column top, and therefore surface coalescence of bubbles is enabled. As mentioned above, coalescence, whether in the bulk or on the foam surface, diminishes the liquid flux but engenders internal reflux. The rate of surface coalescence is currently unpredictable, but it has been shown to be dependent upon environmental humidity,14 and indeed, when the free surface of the foam is open to atmosphere, the environmental humidity is a critical determiner of the performance of a foam fractionation unit: When humidity is low, bubble coalescence is high, meaning that the liquid overflow rate is reduced by the effects of internal reflux are enhanced, meaning that the production rate of the foamate is lower but the enrichment is typically improved.
In general, the collection of foam into a launder is useful for very wet foams (approximately greater than 3% liquid fraction) because these exhibit relatively low viscosity and can therefore flow easily into the launder and discharge. However, relatively dry foams exhibit a high viscosity and therefore tend not to flow easily. Instead, the foam forms a crown on top of the column that can become quite voluminous and bypass the launder vessel. In our laboratory, we can sometimes ameliorate this problem by recycling liquid foamate and using it to spray the foam in the crown to enhance flowability; the spray is targeted to the side on the crown so as not to form a source of external reflux that travels down the column. If antifoams are being used downstream of the launder it is absolutely critical that this spray does not enter the column itself or the process will be killed. The location of spraying should be sufficiently far from the column riser itself so that antifoam cannot travel into the tube by diffusion.
However, a better method for the collection of relatively dry, and therefore viscous, foams is to dispense with the launder and instead pass the foam directly from the top of the column into an inverted U-bend (that can be either solid or a flexible hose) so that the foam is discharged downward into a collection vessel. Such an arrangement is used in the foam fractionation of Nisin described in Section 220.127.116.11.1. The inclined section of the rising in fact sees the Boycott effect of enhanced segregation occur in it, and therefore enhances liquid drainage from the foam (see Section 18.104.22.168).
Thus, the general heuristic is to use a launder collection method if the foam at the top of the column has a liquid fraction of above about 3% and large volumes are to be handled (stripping of surface active material from wastewater falls into this category), whereas for drier foams with lower production volumes (as are typical in bioprocessing) the use of an inverted U-bend circumvents the low flowability of the foam.
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Fecal flotation is a routine veterinary test used to diagnose internal parasites or "worms." The test detects the eggs of mature parasites that live inside the body and pass their eggs to the outside by shedding them into the host's stool. Some of these parasites are worm-like, while others are tiny single-celled organisms called protozoa. Most of the parasites live in the intestine, but a few live elsewhere in the body.
Stool material is mixed with a special liquid that causes the parasite eggs to float to the surface. The eggs are collected from the surface using a glass slide. The slide is examined under a microscope, and the appearance of the eggs identifies what type of adult parasite is present. The number of eggs found may reflect the severity of the infection, but this is not always reliable.
What sample is needed?All that is needed is about a one inch piece of fresh stool. Ideally, the stool sample should be no more than 24 hours old and should be as free as possible of grass, gravel, kitty litter, etc. Your veterinarian may provide a container to collect the sample, but any clean, dry container with a tightly fitting lid can be used, such as a jar or plastic tub. When should fecal flotation be done?Kittens and puppies are frequently infected with intestinal parasites and are susceptible to re-infection. Therefore, multiple fecal flotations are recommended for young animals. Pet owners should bring a fresh stool sample to each appointment for the initial series of veterinary visits. If a pet is found to have parasites, follow-up fecal flotations may be recommended to monitor the response to treatment. Fecal flotation may also be recommended if a pet develops diarrhea or fails to gain weight as expected. Mature pets are less likely to be infected with parasites. A yearly fecal flotation done as part of the annual check-up is usually sufficient to monitor the healthy adult pet. However, more frequent fecal testing will likely be recommended if an adult pet develops diarrhea, exhibits unexplained weight loss, or has a history of recurrent parasitic infections. Does the test work every time?No. Fecal flotation is only a basic screening test and may fail to detect infection in some situations. "Some intestinal parasites just cannot be reliably detected with fecal flotation." A fecal flotation test may fail to detect parasite infection because: 1. The parasites themselves are too young to produce eggs. If no eggs are being shed, then the infection cannot be detected. The fecal flotation will be negative, even though infection is present. This is most common in very young pets, which is why multiple stool tests in puppies and kittens are recommended. 2. The infection is mild and there are only a few adult parasites present. In this case the number of eggs in the stool may be too low to be detected by fecal flotation. 3. Some parasites only produce small numbers of eggs and infection may be missed on a single test. 4. Some parasites just cannot be detected reliably with fecal flotation (see article Fecal Baermann). Are there other tests that can be done?Yes. Fecal flotation is just the first step. If repeat fecal flotation tests are negative and a parasitic infection is still suspected, then your veterinarian may recommend other tests such as doing a fecal wet mount, using concentration methods, using stool preservatives, or doing a fecal Baermann etc. Contributors: Kristiina Ruotsalo, DVM, DVSc, Dip ACVP & Margo S. Tant BSc, DV
All that is needed is about a one inch piece of fresh stool. Ideally, the stool sample should be no more than 24 hours old and should be as free as possible of grass, gravel, kitty litter, etc. Your veterinarian may provide a container to collect the sample, but any clean, dry container with a tightly fitting lid can be used, such as a jar or plastic tub.
When should fecal flotation be done?Kittens and puppies are frequently infected with intestinal parasites and are susceptible to re-infection. Therefore, multiple fecal flotations are recommended for young animals. Pet owners should bring a fresh stool sample to each appointment for the initial series of veterinary visits. If a pet is found to have parasites, follow-up fecal flotations may be recommended to monitor the response to treatment. Fecal flotation may also be recommended if a pet develops diarrhea or fails to gain weight as expected. Mature pets are less likely to be infected with parasites. A yearly fecal flotation done as part of the annual check-up is usually sufficient to monitor the healthy adult pet. However, more frequent fecal testing will likely be recommended if an adult pet develops diarrhea, exhibits unexplained weight loss, or has a history of recurrent parasitic infections. Does the test work every time?No. Fecal flotation is only a basic screening test and may fail to detect infection in some situations. "Some intestinal parasites just cannot be reliably detected with fecal flotation." A fecal flotation test may fail to detect parasite infection because: 1. The parasites themselves are too young to produce eggs. If no eggs are being shed, then the infection cannot be detected. The fecal flotation will be negative, even though infection is present. This is most common in very young pets, which is why multiple stool tests in puppies and kittens are recommended. 2. The infection is mild and there are only a few adult parasites present. In this case the number of eggs in the stool may be too low to be detected by fecal flotation. 3. Some parasites only produce small numbers of eggs and infection may be missed on a single test. 4. Some parasites just cannot be detected reliably with fecal flotation (see article Fecal Baermann). Are there other tests that can be done?Yes. Fecal flotation is just the first step. If repeat fecal flotation tests are negative and a parasitic infection is still suspected, then your veterinarian may recommend other tests such as doing a fecal wet mount, using concentration methods, using stool preservatives, or doing a fecal Baermann etc. Contributors: Kristiina Ruotsalo, DVM, DVSc, Dip ACVP & Margo S. Tant BSc, DV
Kittens and puppies are frequently infected with intestinal parasites and are susceptible to re-infection. Therefore, multiple fecal flotations are recommended for young animals. Pet owners should bring a fresh stool sample to each appointment for the initial series of veterinary visits. If a pet is found to have parasites, follow-up fecal flotations may be recommended to monitor the response to treatment. Fecal flotation may also be recommended if a pet develops diarrhea or fails to gain weight as expected. Mature pets are less likely to be infected with parasites. A yearly fecal flotation done as part of the annual check-up is usually sufficient to monitor the healthy adult pet. However, more frequent fecal testing will likely be recommended if an adult pet develops diarrhea, exhibits unexplained weight loss, or has a history of recurrent parasitic infections.
Does the test work every time?No. Fecal flotation is only a basic screening test and may fail to detect infection in some situations. "Some intestinal parasites just cannot be reliably detected with fecal flotation." A fecal flotation test may fail to detect parasite infection because: 1. The parasites themselves are too young to produce eggs. If no eggs are being shed, then the infection cannot be detected. The fecal flotation will be negative, even though infection is present. This is most common in very young pets, which is why multiple stool tests in puppies and kittens are recommended. 2. The infection is mild and there are only a few adult parasites present. In this case the number of eggs in the stool may be too low to be detected by fecal flotation. 3. Some parasites only produce small numbers of eggs and infection may be missed on a single test. 4. Some parasites just cannot be detected reliably with fecal flotation (see article Fecal Baermann). Are there other tests that can be done?Yes. Fecal flotation is just the first step. If repeat fecal flotation tests are negative and a parasitic infection is still suspected, then your veterinarian may recommend other tests such as doing a fecal wet mount, using concentration methods, using stool preservatives, or doing a fecal Baermann etc. Contributors: Kristiina Ruotsalo, DVM, DVSc, Dip ACVP & Margo S. Tant BSc, DV
1. The parasites themselves are too young to produce eggs. If no eggs are being shed, then the infection cannot be detected. The fecal flotation will be negative, even though infection is present. This is most common in very young pets, which is why multiple stool tests in puppies and kittens are recommended.
Yes. Fecal flotation is just the first step. If repeat fecal flotation tests are negative and a parasitic infection is still suspected, then your veterinarian may recommend other tests such as doing a fecal wet mount, using concentration methods, using stool preservatives, or doing a fecal Baermann etc.
Shopping for a new Life Jacket or more accurately Personal Flotation Device (PFD) can be daunting with all of the types and shapes out there a lot of boaters ask us What PFD should I buy? When you are shopping for your first PFD or one for friends boating with you stick to a type III PFD intended for whitewater use. We have put together a helpful buyers guide at the bottom of the page with some recommendations and you can learn more about basic PFDs below.
The US Coastguard sets the standards in the United States for performance and design characteristics for PFDs. There are 5 categories of PFD and it is important to note that the higher the number does not mean a better PFD. The types designate broad categories of how the PFD is designed to be used. There are 5 categories of PFD and generally 2 subcategories: inflatable and inherent buoyancy. Inflatable PFDs are not designed for river use and are generally designed as emergency PFDs like the type you find on Airplanes. Inherent buoyancy PFDs are generally made from closed cell foam and are effective as long as you are wearing the PFD and often when you are unconscious.
For general boating or the specialized activity that is marked on the device such as water skiing, hunting, fishing, canoeing, kayaking and others. Good for calm, inland waters, or where there is a good chance for fast rescue. Designed so that wearing it will complement your boating activities:
If you are less experienced on whitewater you dont need a PFD with every feature, in fact it is not a good idea to get a rescue vest with every bell and whistlemaybe keep the whistle though. Rescue PFDs have extra hardware integrated into it which can be a danger for people not trained in their use since these PFDs have additional equipment which can snag on things.
If you want to learn more you can check out the Coast Guard PFD Guide. Your local paddling store can help you decide what PFD is best for you and you can try them on to see which best fits your body type since one size definitely doesnt fit all.
Lots of folks ask us how much flotation a person requires to keep them afloat. The USCG minimum recommendations are 15.5 - 22 lbs of flotation for buoyant foam PFDs. This is the minimum amount of flotation needed to keep your head above water in calm conditions. If conditions are rough the USCG recommends even more flotation
Interestingly enough the leaner you are the less buoyant weight you are carrying thus requiring more flotation from your PFD. If you carry more buoyant weight on your body the less lift you require from your PFD.
The formula of your body composition in regards to buoyant and non-buoyant weight will help you to figure out how many ponds of flotation you need. This guideline is a bit of an over simplification since we have to assume some broad generalities for paddlers. According to Dr. Kravitz and Heyward at the University of New Mexico they place the average percentage of water in the human body at 72%.
Because peoples body water content varies throughout the day, and the effects of aerated water vs calm water applying any standard formula will be wildly inaccurate. All of the calculations required being both complex and dynamic creates a headache for new paddlers thus we recommend you stick to the USCG recommendation of 15.5-22 lbs.
If you are running a lot of highly aerated water or big water runs a higher float PFD is recommended. The added flotation will keep you aloft in more turbulent water. Spring runoff seasons are the most common times that you may benefit from a higher float PFD. The downside to these higher float PFDs is that they are often bulky and uncomfortable.
Lower float PFDs are definitely more comfortable, however they provide less flotation and will have a harder time keeping your head above water. This may be less of an issue for more placid rivers like class III fishing trips, but if you have a lot of lean muscle you may need to get a higher float PFD regardless.
Our friends over at MTI Adventure wear came up with this handy guide on PFD care and routine maintenance. Like any piece of gear it is important to clean and maintain your gear as the water can take its toll on wet gear.
Hand wash in mild detergent to help prevent mildew, rinse and hang to dry. We like McNetts Wetsuit and Drysuit Shampoo. McNetts MiraZyme is good if your PFD has developed a funk, or you can use all naturalSurf Remedyto shed the stink!
Inspect PFD for tears and holes, be sure zippers and buckles are working properly. If material is faded the fabric has probably lost strength. Foam deteriorates over time, so test your PFD and be sure it keeps your mouth out of the water. If you notice fraying of fabric or straps, serious UV damage, or crushed foam, please discard and replace with a shiny new PFD.
Comfort is critical in a PFD. Many people purchase PFDs without knowing how they will feel or what they link. Some PFDs are not designed for women and can put a lot of pressure on your chest. Others may be designed for people with long torsos and can feel like a corset if you have a short torso. Some PFDscan feel like a tire around your waist and make it difficult to remount the raft.
Consider the comfort of the PFD and the wearability. Color choice should also be high on your list. The coast guard or transport Canada only authorize certain colors for production in the US and Canada. Many of these standards are also similar in the EU. This does ensure that most PFDs will be highly visible in a variety of conditions. Color choice thus largely comes down to personal preference, however it is important to take note of where you spend most of your time on the river. If youre running mostly hot desert rivers you may want to reconsider black as your PFD choice since it tends to get much hotter in the summer months.
Pockets are also a big this on PFDs. If you are a casual private boater or you are a newer guide, a couple pockets are good for some snacks or a flip line. Its nice to have a few personal effects stowed somewhere close at hand while also following the clean principal.
Protect your PFD from extended Ultraviolet light exposure (sun), and the extremes of hot and cold to minimize premature aging. There are many products available that may be used on the exterior of the vest to help guard against UV degradation.
Since all PFDs manufactured for North American and EU markets meet nearly identical and stringent standards, you can generally expect your PFD from any major manufacturer to last a similar minimum length of time. Some Manufacturers have reputations for longevity among their gear, but in all cases it depends upon how hard you are on your gear.
PFDs should always be in a serviceable condition free from mold or mildew, especially on the floatation elements. It is a good idea to test the flotation of a PFD at the beginning of every season. If you boat 12 months out of the year it is a good idea to check quarterly.
Give the tabs and webbing a good firm tug and if something rips take the PFD out of service immediately. Look for signs of fading and UV damage on the PFD. This can be a sign that the material is weak and has lost strength. Additionally it likely will not be apparent, but UV damage on the outside of the PFD can be a sign that the internal foam also has some UV damage.
The Rocker is the perfect low-profile vest for long days on the water. The comfort and performance of this vest have quickly made it one of our most popular among whitewater boaters and SUP paddlers. Multiple pockets allow you to carry all the needed essentials; While the low cut, offset front-zip makes entry and exit simple.
The Aries PFD offers recreational paddlers the ultimate in comfort, safety, and value. Its low-profile design gives unrestricted freedom of motion, ideal for whitewater or sea kayaking, while its high back with thin PVC-free GAIA foam inserts fit comfortably against the high-back seats of most recreational and sit-on-top kayaks.500 denier Cordura outer shell
Flotation processes are based on the different surface wettability properties of materials (Wang etal., 2015). In principle, flotation works very similarly to a sink and float process, where the density characteristics of the materials, with respect to that of the medium where they are placed are at the base of the separation. Sometimes a centrifugal field is applied to enhance separation. Flotation works in a different way in the sense that in a liquid medium, usually water, a carrier is introduced, air bubbles, responsible to float hydrophobic particles that adhere to the bubbles with respect to the hydrophilic ones that sink. According to surface plastic characteristics, this technique can be profitably applied, in principle, to separate waste polymers (Fraunholcz, 2004). To enhance or reduce plastic surface characteristics (i.e., hydrophobic or hydrophilic) appropriate collectors, conditioners (Singh, 1998; Shen etal., 2002), and flotation cell operative conditions (i.e., air flow rate, agitation) can be utilized. Usually plastic flotation is carried out in alkaline conditions (Takoungsakdakun and Pongstabodee, 2007). Once floated, hydrophobic polymers are recovered as well as the sunk ones (i.e., hydrophilic) at the bottom of the cell. This technique, even if it is well-known (Buchan and Yarar, 1995) and in principle quite powerful is not widely used mainly for three reasons: (1) it is a wet technique, this means that water has to be recovered and processed before reutilization, due to the presence of the reagents and contaminants, (2) polymer surface status (i.e., presence of dirtiness/pollutants and/or of physical/chemical alteration) can strongly affect floatability, and (3) large variation of waste plastics feed in terms of composition. Flotation allows to separate PS, PVC, PET, PC, and mixed polyolefins (MPO).
The flotation process depends on several design and operational variables. We consider a superstructure that includes the following three flotation stages: the rougher, which processes the feed; the cleaner, which generates the final concentrate; and the scavenger, which generates the final tailing, as shown in Fig. (1). This is a simple superstructure but is used here as an example.
The objective is to maximize the total income with respect to the operation conditions and process design. The decision variables to be optimized are divided into design and operating variables. The design variables include equipment dimensions, such as the cell volume and total number of cells for each stage. The operating variables correspond to operating times for each cell at each stage and the directions of tails and concentrate streams. In stochastic problems, the operating variables (second level variables) are able to adapt to each scenario to increase the total income. Moreover, the design variables (first level) are the same for all scenarios.
The flotation process depends on several design and operation variables. We consider a superstructure that includes three flotation stages: rougher, scavenger and cleaner stages, as is shown in figure 1. We allow for the consideration of multiple scenarios. The model consider constraints that enforce the kinetics of flotation and the mass balance on each flotation stage, the behavior at the splitters and mixers, the mass balance at the splitters and mixers, direction choice in the splitters, the penalty the seller must pay for arsenic content in the concentrate, cell volumes, and the costs associated with the flotation cells.
For the deterministic, model we have only a single scenario, and the model then simply maximizes the total income subject to the dynamic and economic constraints. In the stochastic models, we assume we have more than one scenario. Because of this, we need to replace the objective by the maximization of the expected total income. For this, we need the probability of a given scenario. In addition, we know that some of our decision variables can depend on the scenarios. This model corresponds to a stochastic MINLP.
In flotation process, the gas or air bubbles are introduced through culture suspension, and the microalgal biomass get attached to gaseous molecules and accumulated on the liquid surface. This method is particularly effective for thin microalgae suspension that could be simply gravity thickening . The basic variations of this process are dispersed air flotation, dissolved air flotation, electroflotation, and ozone flotation [55,56,57]. The ratio of gaseous molecules to microalgae is one of the most important factors affecting the performance of the flotation efficiency. Several researchers have confirmed that ozone flotation was more effective than other methods [58,59]. Also, ozoflotation could improve lipid recovery yields and modify fatty acid methyl ester (FAME) profiles. The ozone flotation could increase the cell flotation efficiency by modifying the cell wall surface and/or releasing the active agents from microalgal cells . Moreover, the ozone flotation can also improve the quality of water by lowering the turbidity and organic contents of the effluent . Flotation separation efficiency relates to bubble size . Smaller size of gas bubbles has lower rise velocity and higher surface area to volume ratio. This enables their longer retention time and better attachment efficiency with the microalgae cells and leads to the increasing in harvesting efficiency by floatation . Thus, one of the most efficient ways of achieving maximum attachment is by generating as many small bubbles as possible [61,62,63]. Combinations of flocculation with flotation have been also used to increase the harvesting efficiency [64,65,66].
In using these equations, however, one must use parameters with consistent units.(1-3)E=(Ci-Co)/Ci(1-4)E=K/(Qw-K')(1-5)E=(6Kpr2hqg)/(qwdb)whereE = efficiency per cellCi = inlet oil concentrationCo = outlet oil concentrationQw = liquid flow rate, BPDKp = mass transfer coefficientr = radius of mixing zoneh = height of mixing zoneqg = gas flow rateqw = liquid flow through the mixing zonedb = diameter of gas bubble
The froth flotation process is more than a century old and was developed over a long period of time . It takes advantage of the surface chemistry of fine particlesif one particles surface is hydrophobic and another is hydrophilic, upon generation of air bubbles, the hydrophobic particles tend to attach to the air bubbles and float, allowing for a separation between particles in the froth and those in the main body of the liquid.
Typically three different types of chemicals are used in the froth flotation process: collector, frother, and modifier. First, the collector is added to the iron ore slurry to selectively coat the iron oxide particles, making the surface hydrophobic. The slurry then goes to a flotation cell, where air bubbles are generated using an impeller and aerator (Figure 1.2.4). At this step, the frother (for example, fuel oil) is added to the ore slurry to form stable froth and air bubbles. Iron oxide particles stick to the air bubbles and float. Floated and concentrated iron ore slurry is then skimmed from the surface of the bath, and water is removed using a filter press. If the desired iron content is not achieved, the process is repeated. A modifier is added in some cases to enhance the performance of the collector. Frother is the most important chemical that must always be present. Without the generation of stable air bubbles, hydrophobic particles will not have anything to attach to and will not separate from the bulk solution.
Depending on the type of collector, either iron oxide or silica particles can be floated. An anionic collector is added to float the iron oxide particles, a cationic collector for the silica particles . Depending on the situation, the pH of the slurry can be adjusted by adding acid to the solution, which may also enhance the properties of the collector.
The basic objective of a flotation device is to keep the pulp in suspension and provide the air bubbles. The size of air bubbles matters as it controls flotation kinetics as well as the carrying capacity of the bubbles. The design technology determines the characteristics of the machine, resulting in concomitant factors like how the collision and contact between air bubbles and particles takes place. The two resultant products, concentrate and tails, need to be evacuated properly. The most widely used flotation machines can be broadly classified into mechanical and pneumatic depending on various factors. The former use impellers or rotors, which are absent in the latter.
The shape of a mechanical flotation tank is essentially rectangular, U-shaped, conical or cylindrical, according to the cell type and size. It is fitted with an impeller/rotor and stator/diffuser. Air enters into the device through a concentric pipe surrounding the impeller shaft either by self-aspiration or aided by a compressor. The function of the rotating impeller is to keep particles in suspension by thoroughly mixing the slurry and dispersing the injected air into fine bubbles through a diffuser. It also provides conditions for promoting particlebubble collisions.
There is a necessity for the generation of three different hydrodynamic zones for effective flotation. The region near the impeller comprises of a turbulent area required for solids suspension, dispersion of air into bubbles and bubbleparticle interaction. Above the turbulent region lies a quiescent zone where the bubbleparticle aggregates move up in a relatively less turbulent sector. This zone also helps in sinking the amount of gangue minerals that may have been entrained mechanically. The third region overhead the quiescent zone is the froth zone serving as an additional cleaning step, and improves the grade of the concentrate. Particles that do not attach to the bubbles are discharged out from the bottom of the cell (Vazirizadeh, 2015). Fig. 5.33 shows a typical schematic of a mechanical cell.
Mechanical cells are arranged in a series called a bank, having enough cells to assure the required particle residence time for adequate recovery, the subaeration cells are arranged in cell-to-cell flow, while the supercharged machines are placed in an open-flow design.
The strongly hydrophobic and optimised-sized particles are likely to float first in a bank of flotation cells. Sluggish flowing particles float in diminishing order, and so forth, giving rise to total recovery of about 100%. A minimum of four cells is required for coal flotation with a residence time of 5 minutes (Euston et al., 2012). The residence time, pulp volume and flotation kinetics play a vital role in determining the selection of the number of cells required in a flotation circuit. To prevent loss of floatable coal along with tailings, it is advisable to put cells in series. Fig. 5.34 indicates the coal recovery through multiple cells (in series) in a bank. Fig. 5.35 demonstrates arrangement of cells both in series and parallel, the series arrangement gives optimum recovery of combustibles.
The most common examples of pneumatic cells are the column cell and the Jameson cell. As shown in Fig. 5.36, a flotation column is typically a tall vertical cylinder. It is fed with coal pulp at the top third of column. It has no mobile parts or agitators. Air bubbles are injected either through external or internal spargers at the bottom. These bubbles rise up in countercurrent with the descending flow of the pulp. Hydrophobic particles attach to the air bubbles forming bubbleparticle aggregates and move upwards. The zone where this process takes place is called the collection zone. The ascending bubbleparticle aggregates accumulate in the upper part of the column called the cleaning or froth zone, and then overflow into a launder as a concentrate. Wash water is sprinkled at the top of the column to wash off entrained gangue (hydrophilic) particles, which are sent back into the collection zone. The application of wash water helps stabilise the froth and produce high-grade froth concentrates. The hydrophilic particles, along with misplaced hydrophobic particles, are finally released at the bottom of the column.
In spite of improved separation performance, low capital and operational cost, less plant space demand, low maintenance cost, ease of operation, lower energy consumption and adaptability to automatic control (Wills and Napier-Munn, 2006), axial mixing can significantly reduce the overall performance, particularly in larger-diameter columns. Axial mixing can be decreased by different methods (Kawatra and Eisele 1999, 2001):
A Jameson cell is schematically presented in Fig. 5.37. A high-pressure jet, created by pumping feed slurry through the slurry lens orifice, enters a cylindrical device called a downcomer. The downcomer acts as an air entrainment device which sucks air from the atmosphere. The jet of slurry disseminates the entrained air into very fine bubbles after plunging upon the liquid surface. Then, it creates very favourable conditions for collision of bubbles and particles, and their attachment. The particlebubble aggregates move down the downcomer to the cell and float to the top to form the froth. The hydrophilic minerals sink to the bottom and exit as tailings. Tailings recycling is practiced to reduce feed variations to the cell so that the downcomer can operate at a stable feed pressure and flow rate. This helps to ensure steady operation. The downcomer provides an ideal situation for particlebubble contact and minimises the residence time due to rapid kinetics and separate contact zone. Thus, the Jameson cell is of much lower volume compared to equivalent-capacity column or mechanical cells. There is also no requirement for agitators or compressors besides the feed pump.
The dissolved air flotation process takes advantage of the principles described above. Figure 7-104 presents a diagram of a DAF system, complete with chemical coagulation and sludge handling equipment. As shown in Figure 7-104, raw (or pretreated) wastewater receives a dose of a chemical coagulant (metal salt, for instance) and then proceeds to a coagulation-flocculation tank. After coagulation of the target substances, the mixture is conveyed to the flotation tank, where it is released in the presence of recycled effluent that has just been saturated with air under several atmospheres of pressure in the pressurization system shown. An anionic polymer (coagulant aid) is injected into the coagulated wastewater just as it enters the flotation tank.
The recycled effluent is saturated with air under pressure as follows: a suitable centrifugal pump forces a portion of the treated effluent into a pressure holding tank. A valve at the outlet from the pressure holding tank regulates the pressure in the tank, the flow rate through the tank, and the retention time in the tank, simultaneously. An air compressor maintains an appropriate flow of air into the pressure holding tank. Under the pressure in the tank, air from the compressor is diffused into the water to a concentration higher than its saturation value under normal atmospheric pressure. In other words, about 24 ppm of air (nitrogen plus oxygen) can be dissolved in water under normal atmospheric pressure (14.7 psig). At a pressure of six atmospheres, for instance (6 14.7 = about 90 psig), Henry's law would predict that about 6 23, or about 130 ppm, of air can be diffused into the water. In practice, dissolution of air into the water in the pressurized holding tank is less than 100% efficient, and a correction factor, f, which varies between 0.5 and 0.8, is used to calculate the actual concentration.
After being held in the pressure holding tank in the presence of pressurized air, the recycled effluent is released at the bottom of the flotation tank, in close proximity to where the coagulated wastewater is being released. The pressure to which the recycled effluent is subjected has now been reduced to one atmosphere, plus the pressure caused by the depth of water in the flotation tank. Here, the solubility of the air is less, by a factor of slightly less than the number of atmospheres of pressure in the pressurization system, but the quantity of water available for the air to diffuse into has increased by the volume of the recycle stream.
Practically, however, the wastewater will already be saturated with respect to nitrogen, but may have no oxygen, because of biological activity. Therefore, the solubility of air at the bottom of the flotation tank will be about 25 ppm, and the excess air from the pressurized, recycled effluent will precipitate from solution. As this air precipitates in the form of tiny, almost microscopic, bubbles, the bubbles attach to the coagulated solids. The presence of the anionic polymer (coagulant aid), plus the continued action of the coagulant, causes the building of larger solid conglomerates, entrapping many of the adsorbed air bubbles. The net effect is that the solids are floated to the surface of the flotation tank, where they can be collected by some means and thus be removed from the wastewater.
Some DAF systems do not have a pressurized recycle system, but, rather, the entire forward flow on its way to the flotation tank is pressurized. This type of DAF is referred to as direct pressurization and is not widely used for treatment of industrial wastewaters because of undesirable shearing of chemical flocs by the pump and valve.
The behavior of coal in the flotation process is determined not only by a coals natural floatability (hydrophobicity), but also by the acquired floatability resulting from the use of flotation reagents. The general classification of the reagents for coal flotation is shown in Table12.1 (Laskowski, 2001).
The use of liquid hydrocarbons (oils) as collectors in flotation of coal is characteristic for the group of inherently hydrophobic minerals (graphite, sulfur, molybdenite, talc, coals are classified in this group). Since oily collectors are water-insoluble, they must be dispersed in water to form an emulsion. The feature making emulsion flotation different from conventional flotation is the presence of a collector in the form of oil droplets, which must collide with mineral particles in order to enhance the probability of particle- to-bubble attachment. The process is based on selective wetting: the droplets of oil can adhere only to particles that are to some extent hydrophobic. The effect of emulsification on flotation has been studied, and its beneficial effect on flotation is known (Sun et al., 1955).
Coal flotation is commonly carried out with a combination of an oily collector (e.g. fuel oil) and a frother (e.g. MIBC). All coal flotation systems require the addition of a frother to generate small bubbles and to create a stable froth (Table 12.2). Typical addition rates for frothers are in the order of 0.050.3kg of reagent per tonne of coal feed. Depending on the hydrophobic character of the coal particles, an oily collector such as diesel oil or kerosene may or may not be utilized. When required, dosage rates commonly fall in the range of 0.21.0kg of reagent per tonne of coal feed, although dosage levels up to 2kg/t or more have been known to be used for some oxidized coals that are difficult to flotate.
PO stands for propylene oxide (CH2-CH2-CH2-O-), and BO for butylene oxide (CH2-CH2-CH2-CH2-O-) Cresylic acids (mixture of cresols and xylenols) that in the past were commonly used in coal flotation are not in use any more because of their toxicity.
PO stands for propylene oxide (CH2-CH2-CH2-O-), and BO for butylene oxide (CH2-CH2-CH2-CH2-O-) Cresylic acids (mixture of cresols and xylenols) that in the past were commonly used in coal flotation are not in use any more because of their toxicity.
The beneficial effect of a frother on flotation with an oily collector was demonstrated and explained by Melik-Gaykazian et al. (1967). Frother adsorbs at the oil/water interface, lowers the oil/water interfacial tension and hence improves emulsification. However, frother also adsorbs at the coal/water interface (Frangiskos et al., 1960; Fuerstenau and Pradip, 1982; Miller et al., 1983) and provides anchorage for the oil droplets to the coal surface. Chander et al. (1994), after studying various non-ionic surfactants, concluded that the flotation of coal can be improved in their presence because of the increased number of droplets, which leads to an increase in the number of droplet-to-coal particle collisions. While the use of oily collectors and frothers is the most common, also a group of flotation agents known as promoters have found application in coal flotation. In general, these are strongly surface-active compounds and are mostly used to enhance further emulsification of water-insoluble oily collectors in water.
Because of environmental concerns associated with tailing ponds, the method for disposing of fine refuse from coal preparation plants by underground injection has been gaining wide acceptance. Unfortunately, many common flotation reagents, including diesel oil, are not permitted when fine refuse is injected underground into old mine works. This is the main driving force for finding replacement for the crude-oil based flotation collectors (Skiles, 2003). An alternative to fuel oil may be biodiesel, a product created by the esterification of free fatty acids generally from soy oil, with an alcohol such as methanol, and subsequent transesterification of remaining triglycerides. Water, glycerol and other undesirable by-products are removed, to produce a product that has physical characteristics similar to diesel oil. The use of some vegetable oils was demonstrated to provide equivalent (and even superior) flotation results when compared with diesel fuel (Skiles, 2003). These are the results of commercial scale tests on a circuit that has 4.25m in diameter columns. The product concentrate ash was 13.5%. The consumption of the tested vegetable oil was about two times lower from the consumption of diesel oil in these tests.
It features both proven technology and the latest technical innovations at the same time. This flotation cell is highly efficient when it comes to costs and operation. It can be easily scaled to various production levels without compromising performance. In short, OptiCell Flotation enhances the performance of the deinking line cost efficiently and ensures a reliable flotation process. The heart of the flotation process is the injector. In the OptiCell system, this has beendesigned with special care, using the experiences of earlier flotation technologies, modern computational fluid dynamics calculations, and new image analysis methods. The combination of these approaches results in a unique injector that represents the latest technology. This injector differs from traditional injectors in following respects:
OptiCell flotation by Metso is based on computational fluid dynamics and uses new image analysis methods. It is designed to provide smooth-flow velocities that allow unobstructed transfer of bubbles to the surface of the pulp mixture or froth, which improves the efficiency of ink removal. The aeration injector ensures optimal bubble-size distribution. The injector is designed based on the experiences gained with earlier flotation technologies combined with modern computational fluid dynamics calculations and new image analysis methods.
The linear structure of the flotation cells has a large surface area, which has reject separation and fiber loss. This flotation cell design also contributes to high sludge consistency (less water in the sludge) by ensuring smooth drainage of froth (Aksela,2008). The elliptical shape of the flotation cells in this technology is optimal for internal pulp circulation for improved ink removal. Moreover, the flatness of the cells intensifies the rise of air bubbles within the available volume. The first OptiCell Flotation system started operation in September 2008 at Stora Ensos Maxau mill in Germany, which has an approximately 1000 t/day deinking facility (Metso,2012b). According to Metso, the brightness from the complete flotation system has increased by two units. A brightness gain of 13 units from thick stock to accept was obtained with the OptiCell process. Reject ash content also improved and fiber losses decreased. As a result of the flotation performance and corresponding brightness improvement, peroxide consumption has decreased significantly in bleaching. In addition, the stickies content was reduced significantly. It was the lowest ever measured at the deinking line 1 at Maxau mill. The benefits of OptiCell flotation are summarized in Table11.8 (Aksela,2008; Metso,2012b).
Flotation costs are incurred by a publicly-traded company when it issues new securities and incurs expenses, such as underwriting fees, legal fees, and registration fees. Companies must consider the impact these fees will have on how much capital they can raise from a new issue. Flotation costs, expected return on equity, dividend payments, and the percentage of earnings the business expects to retain are all part of the equation to calculate a company's cost of new equity.
Companies raise capital in two ways: debt via bonds and loans or equity. Some companies prefer issuing bonds or obtaining a loan, especially when interest rates are low and because the interest paid on many debts is tax-deductible, while equity returns are not. Other companies prefer equity because it does not need to be paid back; however, selling equity also entails giving up an ownership stake in the company.
There are flotationcosts associated with issuing new equity, or newly issued common stock. These include costs such as investment banking and legal fees, accounting and audit fees, and fees paid to a stock exchange to list the company's shares. The difference between the cost of existing equity and the cost of new equity is the flotation cost.
The flotation cost is expressed as a percentage of the issue price and is incorporated into the price of new shares as a reduction. A company will often use a weighted cost of capital (WACC) calculation to determine what share of its funding should be raised from new equity and what portion from debt.
As an example, assume Company A needs capital and decides to raise $100 million in common stock at $10 per share to meet its capital requirements. Investment bankers receive 7% of the funds raised. Company A pays out $1 in dividends per share next year and is expected to increase dividends by 10% the following year.
The answer is 20.0%. The difference between the cost of new equity and the cost of existing equity is the flotation cost, which is (20.7-20.0%) = 0.7%. In other words, the flotation costs increased the cost of the new equity issuance by 0.7%.
Some analysts argue that including flotation costs in the company's cost of equity implies that flotation costs are an ongoing expense, and forever overstates the firm's cost of capital. In reality, a firm pays the flotation costs one time upon issuing new equity. To offset this, some analysts adjust the company's cash flows for flotation costs.
Flotation is the process of converting a private company into a public company by issuing shares available for the public to purchase. It allows companies to obtain financing externally instead of using retained earnings to fund new projects or expansion. The term "flotation" is commonly used in the United Kingdom, whereas the term "going public" is more widely used in the United States.
Flotation requires careful consideration regarding timing, company structure, the company's ability to withstand public scrutiny, increased regulatory compliance costs, and the time needed to execute the flotation and attract new investors. While flotation provides access to new sources of capital, the extra expenses associated with issuing new stock must be accounted for when considering the switch from a private to a public company.
Companies in mature phases of growth may need additional funding for various reasons including expansion, inventory, research and development, and new equipment.For this reason, the time and monetary costs of becoming a company that is traded publicly are often deemed worth it.
When a company decides to pursue flotation, they typically enlist an investment bank as an underwriter. The underwriting investment bank typically leads the process for conducting an IPO and helps the company determine the amount of money it seeks to raise from the public market issuance.
The investment bank also assists in the documentation requirements for becoming a public company. The bank will develop an investment prospectusand will also market the companys offering in a roadshow prior to the initial stock issuance. A roadshow is a sales pitch to potential investors by the underwriting firm and executive management team of the company about to go public. Gauging demandduring the roadshow is an important step in determining the final IPO share price, as well as in determining the ultimate number of shares to make available for issuance.
When considering flotation as a means of raising capital, companies may also look to other private funding sources before deciding to become a public company. These alternative sources of funding may include small business loans, equity crowdfunding, angel investors, or investment from venture capitalists. However, when seeking additional private funding, companies will still incur legal fees and extra costs for deal structuring and accounting.
Many private companies choose to receive private funds for the benefit of fewer transparency requirements. Private companies may also wish to remain privately funded because of the high costs associated with restructuring and an initial public offering (IPO).
Flotation is the process of issuing and selling shares to public investors. In other words, it is when a company goes public and issues new shares to raise capital. It is a term commonly used in the United Kingdom.
Floating a company allows it to raise capital for the purpose of acquiring external financing for equipment, research and development (R&D)Research and Development (R&D)Research and Development (R&D) is a process by which a company obtains new knowledge and uses itto improve existing products and introduce, or new projects or to expand the business.
There are various methods to float a company. Depending on its objectives and business needs, each company will need to determine which flotation method is the most feasible. Some methods of floating a company will sell securities on a public stock exchange, while other methods will offer securities to private investors.
One way to float a company is to issue an initial public offering (IPO), where a private company will go public by issuing shares for the first time. Floating a company using an IPO typically involves an investment bank that undertakes the underwriting process and determines the specific details of the IPO, such as the share price and the number of shares to be issued.
Additionally, the investment bank will develop the investment prospectusProspectusA prospectus is a legal disclosure document that companies are required to file with the Securities and Exchange Commission (SEC). The document provides information about the company, its management team, recent financial performance, and other related information that investors would like to know. required for the IPO and go on a roadshow to promote the new stock offering to potential investors.
In addition to an IPO, a private company can pursue flotation by offering securities for sale using an intermediary, such as a stockbroker. In this case, the issuance of new shares is not available to the public. Usually, a company that pursues such a flotation method is in its early stages of operations, or it wants to mitigate from issuing shares to the public due to high flotation costs.
A company can also be floated by issuing new shares that are available only to a group of existing investors, who are given the opportunity to purchase new shares before the shares officially get offered to the public.
A private placement is also another way to float a company. Under the private placement, an intermediary would purchase securities from a company at a predetermined price and sell these securities to certain individuals and institutional investors. Again, it helps a company avoid incurring high flotation costs and raise more capital quicker than pursuing an IPO.
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The magnetic separator is the key beneficiation equipment for separating magnetic minerals from non-magnetic minerals or minerals with magnetic differences. The process is based on the different components in the separated materials, which means that in the working magnetic field, the different magnetic field forces and other forces received by different particles are used to separate different materials.
Froth flotation machine is generally used for the concentration of sulphide ores. The principle behind froth flotation process is that sulphide ores are preferentially wetted by pine oil whereas gangue articles are wetted by water.
In this process, the suspension of a powdered ore is made with water. Collectors like pine oil, fatty acids and xanthate are added to it. Froth stabilizers like wrestles and any line stabilized the froth. The mineral particles become wet by oils while gangue particles by water.
A rotating paddle agitates the mixture and draws air in it, as a result, froth is formed which carries the mineral particles. The froth is light and skimmed off, and it is then dried for the recovery of the old particles.
In order to realize the separation of different minerals through magnetic separation, it is necessary to ensure that there is a relatively obvious difference in force between different magnetic materials, especially the difference in magnetic field force.
Minerals in nature, due to their different atomic structures, exhibit different magnetic properties under the action of a magnetic field, and different minerals exhibit large magnetic differences.
Minerals are divided into non-magnetic minerals, weak magnetic minerals and strong magnetic minerals. Among them, strong magnetic minerals are the least. There are dozens of weak magnetic minerals, while non-magnetic minerals are numerous in variety.
Of course, the strength of magnetism between minerals is relative, and it is relative to the strength of the external magnetic field. With the development of magnetic separation technology and magnetic material technology, its definition has always changed.
After crushing to less than 70 mm, the ore need to be washed, sieved and classified, firstly got material with + 30 mm needs manual beneficiation, then 4.5-30 mm ore is dressed by jig, and last ore with -4.5 mm should be processed by roller-type strong magnetic field magnetic separator.
Wolfram ore coarse concentrate magnetic separation process: before separation, the material is crushed to-3 mm by roll crushers, then they are screened into three levels which are 0.83 ~ 3 mm, 0.2 ~ 0.83 mm and 0 ~ 0.2 mm, and finally you can get wolframite concentrate by magnetic classification beneficiation.
Crystalline graphite has good natural floatability, so froth flotation would be best for processing it. Since the size of graphite flakes is one of its most important quality indicators, a multi-stage grinding and multi-beneficiation process is adopted to remove large flake graphite as soon as possible.
Copper is the main valuable recyclable element in ore, and its content is 0.77%. Copper ore contains lightly oxidized sulfide ore, and the copper in the ore is mainly in copper sulfide minerals. For copper ore, there is 0.45% of primary copper sulfide, accounting for 60.57% of the total copper; secondary copper sulfide 0.27%, accounting for the total copper 36.34%; free copper oxide and combined copper content is relatively less.
The recoverable copper in the ore is mainly stored in chalcopyrite, chalcocite and a small amount of copper-bearing sulfide minerals such as copper blue and azurite, with a copper content of about 1.72%.
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Flotation cost is defined as the cost incurred by the company when they issue new stocks in the market as the process involves various stages and participants. It includes audit fees, legal fees, accounting fees, investment banks share out of the issuance, and the fees to list the stocks on the stock exchange that needs to be paid to the exchange.
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This approach includes flotation costs into the cost of capital. Cost of capital consists of the cost of debt and equity. Hence, raising capital via debt or issuance of new stocks would affect the cost of capital.
In 2018, ABC Inc issued common stock in the market to raise $500 million. The current price of a stock in the market is $20. The investment bankers fees would be 6% of the raised capital. ABC Inc paid a dividend of $2 per share in 2019, and an increase of 12% is expected in 2020.
This approach is not accurate and does not depict the actual picture since it includes the flotation costs into the cost of equity Of EquityCost of equity is the percentage of returns payable by the company to its equity shareholders on their holdings. It is a parameter for the investors to decide whether an investment is rewarding or not; else, they may shift to other opportunities with higher returns.read more. The issuance of new stocks in the market involves a one-time expense, and this approach only inflates the cost of capital.
In this approach, it is deducted from the cash flows, which are used for the calculation of Net Present Value (NPV) instead of including the flotation cost in the cost of equity. This approach of deducting it from the cash flows is appropriate and effective than directly including the costs in the cost of capital since this is a one-time expense. Moreover, the cost of capital is not inflated and remains unaffected.
XYZ Inc requires $10,000,000 for a new project, and it expects this project to generate cash flows of $4,500,000 for 3 years. It issues common stock in the market with a price of $30 per share and decides to pay a dividend of $1.25 per share next year. The flotation cost incurred is 9% of the capital raised, and the growth rate is expected to be 7%.
This article has been a guide to what is Flotation Cost and its meaning. Here we discuss how flotation cost impacts the cost of capital calculations along with examples and limitations. You can learn more about financing from the following articles
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