In all ore dressing and milling Operations, including flotation, cyanidation, gravity concentration, and amalgamation, the Working Principle is to crush and grind, often with rob mill & ball mills, the ore in order to liberate the minerals. In the chemical and process industries, grinding is an important step in preparing raw materials for subsequent treatment.In present day practice, ore is reduced to a size many times finer than can be obtained with crushers. Over a period of many years various fine grinding machines have been developed and used, but the ball mill has become standard due to its simplicity and low operating cost.
A ball millefficiently operated performs a wide variety of services. In small milling plants, where simplicity is most essential, it is not economical to use more than single stage crushing, because the Steel-Head Ball or Rod Mill will take up to 2 feed and grind it to the desired fineness. In larger plants where several stages of coarse and fine crushing are used, it is customary to crush from 1/2 to as fine as 8 mesh.
Many grinding circuits necessitate regrinding of concentrates or middling products to extremely fine sizes to liberate the closely associated minerals from each other. In these cases, the feed to the ball mill may be from 10 to 100 mesh or even finer.
Where the finished product does not have to be uniform, a ball mill may be operated in open circuit, but where the finished product must be uniform it is essential that the grinding mill be used in closed circuit with a screen, if a coarse product is desired, and with a classifier if a fine product is required. In most cases it is desirable to operate the grinding mill in closed circuit with a screen or classifier as higher efficiency and capacity are obtained. Often a mill using steel rods as the grinding medium is recommended, where the product must have the minimum amount of fines (rods give a more nearly uniform product).
Often a problem requires some study to determine the economic fineness to which a product can or should be ground. In this case the 911Equipment Company offers its complete testing service so that accurate grinding mill size may be determined.
Until recently many operators have believed that one particular type of grinding mill had greater efficiency and resulting capacity than some other type. However, it is now commonly agreed and accepted that the work done by any ballmill depends directly upon the power input; the maximum power input into any ball or rod mill depends upon weight of grinding charge, mill speed, and liner design.
The apparent difference in capacities between grinding mills (listed as being the same size) is due to the fact that there is no uniform method of designating the size of a mill, for example: a 5 x 5 Ball Mill has a working diameter of 5 inside the liners and has 20 per cent more capacity than all other ball mills designated as 5 x 5 where the shell is 5 inside diameter and the working diameter is only 48 with the liners in place.
Ball-Rod Mills, based on 4 liners and capacity varying as 2.6 power of mill diameter, on the 5 size give 20 per cent increased capacity; on the 4 size, 25 per cent; and on the 3 size, 28 per cent. This fact should be carefully kept in mind when determining the capacity of a Steel- Head Ball-Rod Mill, as this unit can carry a greater ball or rod charge and has potentially higher capacity in a given size when the full ball or rod charge is carried.
A mill shorter in length may be used if the grinding problem indicates a definite power input. This allows the alternative of greater capacity at a later date or a considerable saving in first cost with a shorter mill, if reserve capacity is not desired. The capacities of Ball-Rod Mills are considerably higher than many other types because the diameters are measured inside the liners.
The correct grinding mill depends so much upon the particular ore being treated and the product desired, that a mill must have maximum flexibility in length, type of grinding medium, type of discharge, and speed.With the Ball-Rod Mill it is possible to build this unit in exact accordance with your requirements, as illustrated.
To best serve your needs, the Trunnion can be furnished with small (standard), medium, or large diameter opening for each type of discharge. The sketch shows diagrammatic arrangements of the four different types of discharge for each size of trunnion opening, and peripheral discharge is described later.
Ball-Rod Mills of the grate discharge type are made by adding the improved type of grates to a standard Ball-Rod Mill. These grates are bolted to the discharge head in much the same manner as the standard headliners.
The grates are of alloy steel and are cast integral with the lifter bars which are essential to the efficient operation of this type of ball or rod mill. These lifter bars have a similar action to a pump:i. e., in lifting the product so as to discharge quickly through the mill trunnion.
These Discharge Grates also incorporate as an integral part, a liner between the lifters and steel head of the ball mill to prevent wear of the mill head. By combining these parts into a single casting, repairs and maintenance are greatly simplified. The center of the grate discharge end of this mill is open to permit adding of balls or for adding water to the mill through the discharge end.
Instead of being constructed of bars cast into a frame, Grates are cast entire and have cored holes which widen toward the outside of the mill similar to the taper in grizzly bars. The grate type discharge is illustrated.
The peripheral discharge type of Ball-Rod Mill is a modification of the grate type, and is recommended where a free gravity discharge is desired. It is particularly applicable when production of too many fine particles is detrimental and a quick pass through the mill is desired, and for dry grinding.
The drawings show the arrangement of the peripheral discharge. The discharge consists of openings in the shell into which bushings with holes of the desired size are inserted. On the outside of the mill, flanges are used to attach a stationary discharge hopper to prevent pulp splash or too much dust.
The mill may be operated either as a peripheral discharge or a combination or peripheral and trunnion discharge unit, depending on the desired operating conditions. If at any time the peripheral discharge is undesirable, plugs inserted into the bushings will convert the mill to a trunnion discharge type mill.
Unless otherwise specified, a hard iron liner is furnished. This liner is made of the best grade white iron and is most serviceable for the smaller size mills where large balls are not used. Hard iron liners have a much lower first cost.
Electric steel, although more expensive than hard iron, has advantage of minimum breakage and allows final wear to thinner section. Steel liners are recommended when the mills are for export or where the source of liner replacement is at a considerable distance.
Molychrome steel has longer wearing qualities and greater strength than hard iron. Breakage is not so apt to occur during shipment, and any size ball can be charged into a mill equipped with molychrome liners.
Manganese liners for Ball-Rod Mills are the world famous AMSCO Brand, and are the best obtainable. The first cost is the highest, but in most cases the cost per ton of ore ground is the lowest. These liners contain 12 to 14% manganese.
The feed and discharge trunnions are provided with cast iron or white iron throat liners. As these parts are not subjected to impact and must only withstand abrasion, alloys are not commonly used but can be supplied.
Gears for Ball-Rod Mills drives are furnished as standard on the discharge end of the mill where they are out of the way of the classifier return, scoop feeder, or original feed. Due to convertible type construction the mills can be furnished with gears on the feed end. Gear drives are available in two alternative combinations, which are:
All pinions are properly bored, key-seated, and pressed onto the steel countershaft, which is oversize and properly keyseated for the pinion and drive pulleys or sheaves. The countershaft operates on high grade, heavy duty, nickel babbitt bearings.
Any type of drive can be furnished for Ball-Rod Mills in accordance with your requirements. Belt drives are available with pulleys either plain or equipped with friction clutch. Various V- Rope combinations can also be supplied.
The most economical drive to use up to 50 H. P., is a high starting torque motor connected to the pinion shaft by means of a flat or V-Rope drive. For larger size motors the wound rotor (slip ring) is recommended due to its low current requirement in starting up the ball mill.
Should you be operating your own power plant or have D. C. current, please specify so that there will be no confusion as to motor characteristics. If switches are to be supplied, exact voltage to be used should be given.
Even though many ores require fine grinding for maximum recovery, most ores liberate a large percentage of the minerals during the first pass through the grinding unit. Thus, if the free minerals can be immediately removed from the ball mill classifier circuit, there is little chance for overgrinding.
This is actually what has happened wherever Mineral Jigs or Unit Flotation Cells have been installed in the ball mill classifier circuit. With the installation of one or both of these machines between the ball mill and classifier, as high as 70 per cent of the free gold and sulphide minerals can be immediately removed, thus reducing grinding costs and improving over-all recovery. The advantage of this method lies in the fact that heavy and usually valuable minerals, which otherwise would be ground finer because of their faster settling in the classifier and consequent return to the grinding mill, are removed from the circuit as soon as freed. This applies particularly to gold and lead ores.
Ball-Rod Mills have heavy rolled steel plate shells which are arc welded inside and outside to the steel heads or to rolled steel flanges, depending upon the type of mill. The double welding not only gives increased structural strength, but eliminates any possibility of leakage.
Where a single or double flanged shell is used, the faces are accurately machined and drilled to template to insure perfect fit and alignment with the holes in the head. These flanges are machined with male and female joints which take the shearing stresses off the bolts.
The Ball-Rod Mill Heads are oversize in section, heavily ribbed and are cast from electric furnace steel which has a strength of approximately four times that of cast iron. The head and trunnion bearings are designed to support a mill with length double its diameter. This extra strength, besides eliminating the possibility of head breakage or other structural failure (either while in transit or while in service), imparts to Ball-Rod Mills a flexibility heretofore lacking in grinding mills. Also, for instance, if you have a 5 x 5 mill, you can add another 5 shell length and thus get double the original capacity; or any length required up to a maximum of 12 total length.
On Type A mills the steel heads are double welded to the rolled steel shell. On type B and other flanged type mills the heads are machined with male and female joints to match the shell flanges, thus taking the shearing stresses from the heavy machine bolts which connect the shell flanges to the heads.
The manhole cover is protected from wear by heavy liners. An extended lip is provided for loosening the door with a crow-bar, and lifting handles are also provided. The manhole door is furnished with suitable gaskets to prevent leakage.
The mill trunnions are carried on heavy babbitt bearings which provide ample surface to insure low bearing pressure. If at any time the normal length is doubled to obtain increased capacity, these large trunnion bearings will easily support the additional load. Trunnion bearings are of the rigid type, as the perfect alignment of the trunnion surface on Ball-Rod Mills eliminates any need for the more expensive self-aligning type of bearing.
The cap on the upper half of the trunnion bearing is provided with a shroud which extends over the drip flange of the trunnion and effectively prevents the entrance of dirt or grit. The bearing has a large space for wool waste and lubricant and this is easily accessible through a large opening which is covered to prevent dirt from getting into the bearing.Ball and socket bearings can be furnished.
Scoop Feeders for Ball-Rod Mills are made in various radius sizes. Standard scoops are made of cast iron and for the 3 size a 13 or 19 feeder is supplied, for the 4 size a 30 or 36, for the 5 a 36 or 42, and for the 6 a 42 or 48 feeder. Welded steel scoop feeders can, however, be supplied in any radius.
The correct size of feeder depends upon the size of the classifier, and the smallest feeder should be used which will permit gravity flow for closed circuit grinding between classifier and the ball or rod mill. All feeders are built with a removable wearing lip which can be easily replaced and are designed to give minimum scoop wear.
A combination drum and scoop feeder can be supplied if necessary. This feeder is made of heavy steel plate and strongly welded. These drum-scoop feeders are available in the same sizes as the cast iron feeders but can be built in any radius. Scoop liners can be furnished.
The trunnions on Ball-Rod Mills are flanged and carefully machined so that scoops are held in place by large machine bolts and not cap screws or stud bolts. The feed trunnion flange is machined with a shoulder for insuring a proper fit for the feed scoop, and the weight of the scoop is carried on this shoulder so that all strain is removed from the bolts which hold the scoop.
High carbon steel rods are recommended, hot rolled, hot sawed or sheared, to a length of 2 less than actual length of mill taken inside the liners. The initial rod charge is generally a mixture ranging from 1.5 to 3 in diameter. During operation, rod make-up is generally the maximum size. The weights per lineal foot of rods of various diameters are approximately: 1.5 to 6 lbs.; 2-10.7 lbs.; 2.5-16.7 lbs.; and 3-24 lbs.
Forged from the best high carbon manganese steel, they are of the finest quality which can be produced and give long, satisfactory service. Data on ball charges for Ball-Rod Mills are listed in Table 5. Further information regarding grinding balls is included in Table 6.
Rod Mills has a very define and narrow discharge product size range. Feeding a Rod Mill finer rocks will greatly impact its tonnage while not significantly affect its discharge product sizes. The 3.5 diameter rod of a mill, can only grind so fine.
Crushers are well understood by most. Rod and Ball Mills not so much however as their size reduction actions are hidden in the tube (mill). As for Rod Mills, the image above best expresses what is going on inside. As rocks is feed into the mill, they are crushed (pinched) by the weight of its 3.5 x 16 rods at one end while the smaller particles migrate towards the discharge end and get slightly abraded (as in a Ball Mill) on the way there.
We haveSmall Ball Mills for sale coming in at very good prices. These ball mills are relatively small, bearing mounted on a steel frame. All ball mills are sold with motor, gears, steel liners and optional grinding media charge/load.
Ball Mills or Rod Mills in a complete range of sizes up to 10 diameter x20 long, offer features of operation and convertibility to meet your exactneeds. They may be used for pulverizing and either wet or dry grindingsystems. Mills are available in both light-duty and heavy-duty constructionto meet your specific requirements.
All Mills feature electric cast steel heads and heavy rolled steelplate shells. Self-aligning main trunnion bearings on large mills are sealedand internally flood-lubricated. Replaceable mill trunnions. Pinion shaftbearings are self-aligning, roller bearing type, enclosed in dust-tightcarrier. Adjustable, single-unit soleplate under trunnion and drive pinionsfor perfect, permanent gear alignment.
Ball Mills can be supplied with either ceramic or rubber linings for wet or dry grinding, for continuous or batch type operation, in sizes from 15 x 21 to 8 x 12. High density ceramic linings of uniform hardness male possible thinner linings and greater and more effective grinding volume. Mills are shipped with liners installed.
Complete laboratory testing service, mill and air classifier engineering and proven equipment make possible a single source for your complete dry-grinding mill installation. Units available with air swept design and centrifugal classifiers or with elevators and mechanical type air classifiers. All sizes and capacities of units. Laboratory-size air classifier also available.
A special purpose batch mill designed especially for grinding and mixing involving acids and corrosive materials. No corners mean easy cleaning and choice of rubber or ceramic linings make it corrosion resistant. Shape of mill and ball segregation gives preferential grinding action for grinding and mixing of pigments and catalysts. Made in 2, 3 and 4 diameter grinding drums.
Nowadays grinding mills are almost extensively used for comminution of materials ranging from 5 mm to 40 mm (3/161 5/8) down to varying product sizes. They have vast applications within different branches of industry such as for example the ore dressing, cement, lime, porcelain and chemical industries and can be designed for continuous as well as batch grinding.
Ball mills can be used for coarse grinding as described for the rod mill. They will, however, in that application produce more fines and tramp oversize and will in any case necessitate installation of effective classification.If finer grinding is wanted two or three stage grinding is advisable as for instant primary rod mill with 75100 mm (34) rods, secondary ball mill with 2540 mm(11) balls and possibly tertiary ball mill with 20 mm () balls or cylpebs.To obtain a close size distribution in the fine range the specific surface of the grinding media should be as high as possible. Thus as small balls as possible should be used in each stage.
The principal field of rod mill usage is the preparation of products in the 5 mm0.4 mm (4 mesh to 35 mesh) range. It may sometimes be recommended also for finer grinding. Within these limits a rod mill is usually superior to and more efficient than a ball mill. The basic principle for rod grinding is reduction by line contact between rods extending the full length of the mill, resulting in selective grinding carried out on the largest particle sizes. This results in a minimum production of extreme fines or slimes and more effective grinding work as compared with a ball mill. One stage rod mill grinding is therefore suitable for preparation of feed to gravimetric ore dressing methods, certain flotation processes with slime problems and magnetic cobbing. Rod mills are frequently used as primary mills to produce suitable feed to the second grinding stage. Rod mills have usually a length/diameter ratio of at least 1.4.
Tube mills are in principle to be considered as ball mills, the basic difference being that the length/diameter ratio is greater (35). They are commonly used for surface cleaning or scrubbing action and fine grinding in open circuit.
In some cases it is suitable to use screened fractions of the material as grinding media. Such mills are usually called pebble mills, but the working principle is the same as for ball mills. As the power input is approximately directly proportional to the volume weight of the grinding media, the power input for pebble mills is correspondingly smaller than for a ball mill.
A dry process requires usually dry grinding. If the feed is wet and sticky, it is often necessary to lower the moisture content below 1 %. Grinding in front of wet processes can be done wet or dry. In dry grinding the energy consumption is higher, but the wear of linings and charge is less than for wet grinding, especially when treating highly abrasive and corrosive material. When comparing the economy of wet and dry grinding, the different costs for the entire process must be considered.
An increase in the mill speed will give a directly proportional increase in mill power but there seems to be a square proportional increase in the wear. Rod mills generally operate within the range of 6075 % of critical speed in order to avoid excessive wear and tangled rods. Ball and pebble mills are usually operated at 7085 % of critical speed. For dry grinding the speed is usually somewhat lower.
The mill lining can be made of rubber or different types of steel (manganese or Ni-hard) with liner types according to the customers requirements. For special applications we can also supply porcelain, basalt and other linings.
The mill power is approximately directly proportional to the charge volume within the normal range. When calculating a mill 40 % charge volume is generally used. In pebble and ball mills quite often charge volumes close to 50 % are used. In a pebble mill the pebble consumption ranges from 315 % and the charge has to be controlled automatically to maintain uniform power consumption.
In all cases the net energy consumption per ton (kWh/ton) must be known either from previous experience or laboratory tests before mill size can be determined. The required mill net power P kW ( = ton/hX kWh/ton) is obtained from
Trunnions of S.G. iron or steel castings with machined flange and bearing seat incl. device for dismantling the bearings. For smaller mills the heads and trunnions are sometimes made in grey cast iron.
The mills can be used either for dry or wet, rod or ball grinding. By using a separate attachment the discharge end can be changed so that the mills can be used for peripheral instead of overflow discharge.
Company revises 2021 production guidance and maintains 2022 2023 production guidance Mining activities and project work have resumed at Tasiast TORONTO, June 21, 2021 Kinross Gold Corporation today provided an update regarding the temporary suspension of milling operations at its Tasiast mine due to a fire that occurred on June 15, 2021. Mining activities and project work have resumed Kinross confirms there were
TORONTO, June 21, 2021 (GLOBE NEWSWIRE) Kinross Gold Corporation (TSX:K; NYSE:KGC) (Kinross and the Company) today provided an update regarding the temporary suspension of milling operations at its Tasiast mine due to a fire that occurred on June 15, 2021.
Kinross confirms there were no injuries as a result of the fire. Mining activities have resumed at Tasiast, including stripping to access higher grade ore. Construction work on the Tasiast 24k expansion project has also resumed and the Company is evaluating opportunities to optimize the project while milling operations are suspended.
Kinross is drawing on resources from across the Company to expedite actions to reduce the SAG mills downtime and to review all potential strategies to mitigate the expected production deferral. With mining activities continuing at Tasiast, Kinross expects to process stockpiles of higher grade ore when the mill restarts.
Based on the initial estimate of the mills downtime and with ongoing work on the 24k project, Tasiasts throughput capacity is now expected to reach 21,000 tonnes per day during Q1 2022, compared with the previous estimate of year-end 2021. Throughput capacity is expected to increase to 24,000 tonnes per day by mid-2023, which is unchanged from the original 24k project estimate.
Despite the mill incident at Tasiast, the Company remains in a strong financial position and is committed to evaluating options to further enhance shareholder returns, which is supported by Kinross Board of Directors.
All of our people are safe and accounted for at Tasiast, which is our most important priority. Our site team responded quickly to the fire, which limited the main impacts to the mill discharge area. While we are continuing to assess the impact and are investigating the cause of the incident, we are pleased to report that mining and project work have now resumed at site. We are now focused on restarting milling operations at Tasiast and are mobilizing technical resources from across the Company to expedite actions and achieve this goal.
Although this unfortunate incident is expected to impact our annual production guidance, our financial position and longer-term outlook remain very strong. We continue to expect production to increase to 2.7 and 2.9 million ounces in 2022 and 2023, respectively, and drive our robust free cash flow profile. The strength of our investment grade balance sheet, free cash flow position and growing production from our global portfolio underpin our commitment to further enhancing shareholder returns, including a potential share buyback program.
In connection with this news release, Kinross will hold a conference call and audio webcast on Tuesday, June 22, 2021at 8:00 a.m. ET to discuss the update, followed by a question-and-answer session. The call-in numbers are as follows:
Kinross is a Canadian-based senior gold mining company with mines and projects in the United States, Brazil, Russia, Mauritania, Chile and Ghana. Our focus is on delivering value based on the core principles of operational excellence, balance sheet strength, disciplined growth and responsible mining. Kinross maintains listings on the Toronto Stock Exchange (symbol:K) and the New York Stock Exchange (symbol:KGC).
All statements, other than statements of historical fact, contained or incorporated by reference in this news release including, but not limited to, any information as to the future financial or operating performance of Kinross, constitute forward-looking information or forward-looking statements within the meaning of certain securities laws, including the provisions of the Securities Act (Ontario) and the provisions for safe harbor under the United States Private Securities Litigation Reform Act of 1995 and are based on expectations, estimates and projections as of the date of this news release. Forward-looking statements include future events and opportunities including, without limitation, statements with respect to: the potential impact of the mill fire on operations at Tasiast; our estimates, expectations, forecasts and updated guidance for production at Tasiast, our revised production guidance across all of our assets, our expectations regarding potential enhancements to shareholder returns, all-in sustaining cost and capital expenditures, cost savings, project economics (including net present value and internal rates of return); the impact of the fire on the mineral reserve and mineral resource estimates at Tasiast, the timing and amount of estimated future production, capital expenditures, the costs and timing of the development of the 21k and 24k projects, and the proposed timing of re-commencing mining and processing activities. The words anticipate, estimate, expect, opportunity, and option or variations of or similar such words and phrases or statements that certain actions, events or results may, could, will or would occur, and similar expressions identify forward-looking statements. Forward-looking statements are necessarily based upon a number of estimates and assumptions that, while considered reasonable by Kinross as of the date of such statements, are inherently subject to significant business, economic and competitive uncertainties and contingencies. The estimates, models and assumptions of Kinross referenced, contained or incorporated by reference in this news release, which may prove to be incorrect, include, but are not limited to, the various assumptions set forth herein and in our Annual Information Form dated March 30, 2021 and our full-year 2020 and first-quarter 2021 Managements Discussion and Analysis as well as: (1) the estimated cost and projected timing of repairing and re-starting the SAG mill being consistent with the Companys current expectations; (2) the Companys estimates regarding the timing of completion of the 21k project; (3) the Companys ability to successfully recover under its insurance policies being consistent with managements expectations; (4) the impact of the incident on the Companys current production guidance, mineral reserve and mineral resource estimates, and estimated overall value of Tasiast; (5) the estimated duration of the suspension of the SAG mill being consistent with Kinross current expectations; (6) the construction of the 24k project being unaffected by the suspension or re-start of the SAG mill; (7) the estimated impact on the timing of completion of the 21k project being consistent with the Companys expectations; and (8) the viability of options to enhance shareholders returns and the Companys ability to obtain the necessary consents and approvals related to such options. Known and unknown factors could cause actual results to differ materially from those projected in the forward-looking statements. These uncertainties and contingencies can directly or indirectly affect, and could cause, Kinross actual results to differ materially from those expressed or implied in any forward-looking statements made by, or on behalf of, Kinross. There can be no assurance that forward-looking statements will prove to be accurate, as actual results and future events could differ materially from those anticipated in such statements. Forward-looking statements are provided for the purpose of providing information about managements expectations and plans relating to the future. All of the forward-looking statements made in this news release are qualified by these cautionary statements and those made in our other filings with the securities regulators of Canada and the United States including, but not limited to, the cautionary statements made in the Risk Factors section of our Annual Information Form dated March 30, 2021 and the Risk Analysis section of our full-year 2020 and first-quarter 2021 Managements Discussion & Analysis. These factors are not intended to represent a complete list of the factors that could affect Kinross. Kinross disclaims any intention or obligation to update or revise any forward-looking statements or to explain any material difference between subsequent actual events and such forward looking statements, except to the extent required by applicable law.
Where we say we, us, our, the Company, or Kinross in this news release, we mean Kinross Gold Corporation and/or one or more or all of its subsidiaries, as may be applicable. The technical information about the Companys mineral properties contained in this news release has been prepared under the supervision of Mr. John Sims who is a qualified person within the meaning of National Instrument 43-101. Mr. Sims was an officer of Kinross until December 31, 2020. Mr. Sims remains the Companys qualified person as an external consultant.
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CABORCA, Mexico, Oct. 05, 2020 (GLOBE NEWSWIRE) -- Mexus Gold US (OTCQB: MXSG) (Mexus or the Company) announced that its ball mill gravity gold recovery system is now operational. This system will allow the company to run high grade material from the Julio quartz vein at its Santa Elena mine located in Caborca, MX.
In addition, the company announced an important discovery concerning gold recovery from its heap leach pad at the mine site. Mexus has been and continues to recover gold from the mineralized material placed on the heap leach pad. The resulting gold production from this work has been variable leading to an analysis of the heap leach pad. It has been found that the salt placed on the pad by the prior operator continues to limit gold recovery. Assays of the cyanide solution returning to the pregnant pond are not representative of the material being placed on the pad. The company decided to remove the material from the top of the heap leach pad down to 2 meters from the bottom and have it assayed. These assays showed that salt is causing issues with gold recovery. The silver in this material, when coming into contact with salt, turns to silver chloride. Cyanide solution with gold reacts with silver chloride and turns the gold to a metallic state inhibiting recovery. The silver chloride found in the bottom 2 meters was assayed and showed an extremely high level of gold value (ounces to the ton). Mexus CEO, Paul Thompson, along with Chief Geologist, Cesar Lemas, determined that the bottom 2 meters of the heap leach pad needs to be removed and run through the ball mill gravity system. Tests have shown that 95% of the gold in the silver chloride material can be recovered using the companys gravity ball mill circuit. This work has already begun. These efforts accomplish two things for the company. First, this allows for gold recovery of highly assayed material at the bottom of the heap leach pad. Secondly, it fixes the heap leach pad allowing for normal and consistent recovery of gold going forward.
Mexus will continue to produce gold in the last quarter of 2020. The company was looking to give guidance for the 4th quarter of 2020 but determined that the recent findings have made it difficult to give an estimate. In the near future, shareholders of Mexus can expect an update on both the heap leach and ball mill gravity gold recovery circuits. Mexus CEO, Paul Thompson added, Im excited for gold production in the coming weeks. We believe that a substantial amount of gold trapped on the pad is now going to be recovered.
Mexus Gold US is an American based mining company with holdings in Mexico. The fully owned Santa Elena mine is located 54km NW of Caborca, Mexico. Mexus also owns rights to the Ures property located 80km N of Hermosillo, Mexico. This property contains 6900 acres and has both gold and copper on the property. Founded in 2009, Mexus Gold US is committed to protecting the environment, mine safety and employing members of the communities in which it operates.
Forward looking Statement: Statements in this press release may constitute forward-looking statements and are subject to numerous risks and uncertainties, including the failure to complete successfully the development of new or enhanced products, the Company's future capital needs, the lack of market demand for any new or enhanced products the Company may develop, any actions by the Company's partners that may be adverse to the Company, the success of competitive products, other economic factors affecting the Company and its markets, seasonal changes, and other risks detailed from time to time in the Company's filings with the Securities and Exchange Commission. The actual results may differ materially from those contained in this press release. The Company disclaims any obligation to update any statements in this press release.
Save to read list Published by Jessica Casey, Editorial Assistant Global Mining Review, Wednesday, 07 October 2020 12:05
Mexus Gold US has announced that its ball mill gravity gold recovery system is now operational. This system will allow the company to run high grade material from the Julio quartz vein at its Santa Elena mine located in Caborca, Mexico.
In addition, the company announced an important discovery concerning gold recovery from its heap leach pad at the mine site. Mexus has been and continues to recover gold from the mineralised material placed on the heap leach pad. The resulting gold production from this work has been variable leading to an analysis of the heap leach pad.
It has been found that the salt placed on the pad by the prior operator continues to limit gold recovery. Assays of the cyanide solution returning to the pregnant pond are not representative of the material being placed on the pad. The company decided to remove the material from the top of the heap leach pad down to 2 m from the bottom and have it assayed. These assays showed that salt is causing issues with gold recovery.
The silver in this material, when coming into contact with salt, turns to silver chloride. Cyanide solution with gold reacts with silver chloride and turns the gold to a metallic state inhibiting recovery. The silver chloride found in the bottom 2 m was assayed and showed an extremely high level of gold value (oz to the t).
Mexus CEO, Paul Thompson, along with Chief Geologist, Cesar Lemas, determined that the bottom 2 m of the heap leach pad needs to be removed and run through the ball mill gravity system. Tests have shown that 95% of the gold in the silver chloride material can be recovered using the companys gravity ball mill circuit. This work has already begun. These efforts accomplish two things for the company. First, this allows for gold recovery of highly assayed material at the bottom of the heap leach pad. Secondly, it fixes the heap leach pad allowing for normal and consistent recovery of gold going forward.
In this webinar, Chris Pearson, Group Business Development Director at MMD Group, will discuss in detail their Fully Mobile Surge Loader (FMSL), its key requirements, and implementation considerations.
Gold mining news Silver mining news
In this webinar, Chris Pearson, Group Business Development Director at MMD Group, will discuss in detail their Fully Mobile Surge Loader (FMSL), its key requirements, and implementation considerations.
WINNIPEG, MB / ACCESSWIRE / June 4, 2021 / Winston Gold Corp. ("Winston Gold" or the "Corporation") (CSE:WGC) (OTCQB:WGMCF) is pleased to announce that the necessary upgrades to the Paradine Mill Facility, near Radersburg, Montana, are nearing completion, despite staffing, material acquisition and delivery challenges.
"Naturally, with any re-commissioning activity, unforeseen challenges inevitably arise," commented Mr. Murray Nye, CEO and Director of Winston Gold Corp. "I must commend our staff at the Paradine Mill facility for their perseverance and dedication during this period. The overall advantages of renovating an old mill still significantly outweigh building and permitting a new one."
Work at the mill is now focused on installing critical new parts (delayed due to shipping issues), in addition to re-configuring and optimizing the floatation circuits. The following points summarize the progress achieved to date:
The Paradine mill facility is being developed into a turn-key mineral processing plant," stated Mr. Joseph Carrabba, Executive Chairman of Winston Gold. "The mill lies in the heart of a region blessed with precious metal endowment, and the future value opportunities are significant."
Towards that end, Winston Gold recently formed a joint venture with Bond Resources (CSE:BJB) to test the near-term cash-flow viability of another past producer, the Hard Cash Mine. (Refer to news release dated May 13th 2021). The Hard Cash property is located just 4.3 miles from the Paradine Mill and an initial drill program should commence shortly.
The Paradine mill located just 35 miles (56 km) by paved road from the Company's wholly owned Winston Gold project which is situated near Helena, Montana. The Mill has a nameplate capacity of 150 tons per day and hosts a ball milling circuit as well as both a gravity and flotation circuit. A new lined settling pond has been constructed for tailings disposal with a 35,000-ton capacity and two additional ponds are also being built.
The scientific and technical content and interpretations contained in this news release have been reviewed, verified and approved by Dr. Criss Capps PhD. P.Geol., an independent consultant to Winston Gold Corp. Dr. Capps is a Qualified Person as defined in National Instrument 43-101 Standards of Disclosure for Mineral Projects.
Winston Gold is a junior mining company focused on advancing high-grade, low-cost mining opportunities into production. Towards that end, the Corporation has acquired the under-explored and under-exploited Winston Gold project near Helena, Montana.
The CSE has neither approved nor disapproved the information contained herein. This news release does not constitute an offer to sell or a solicitation of an offer to buy any of the securities in the United States. The securities have not been and will not be registered under the United States Securities Act of 1933, as amended (the "U.S. Securities Act"), or any state securities laws and may not be offered or sold within the United States or to U.S. Persons unless registered under the U.S. Securities Act and applicable state securities laws or an exemption from such registration is available.
This release includes certain statements that may be deemed "forward-looking statements". All statements in this release, other than statements of historical facts, that address events or developments that Winston Gold Mining Corp. (the "Company") expects to occur, are forward-looking statements. Forward-looking statements are statements that are not historical facts and are generally, but not always, identified by the words "expects", "plans", "anticipates", "believes", "intends", "estimates", "projects", "potential" and similar expressions, or that events or conditions "will", "would", "may", "could" or "should" occur. Although the Company believes the expectations expressed in such forward-looking statements are based on reasonable assumptions, such statements are not guarantees of future performance and actual results may differ materially from those in the forward-looking statements. Factors that could cause the actual results to differ materially from those in forward-looking statements include regulatory actions, market prices, exploitation and exploration successes, and continued availability of capital and financing, and general economic, market or business conditions. Investors are cautioned that any such statements are not guarantees of future performance and actual results or developments may differ materially from those projected in the forward-looking statements. Forward-looking statements are based on the beliefs, estimates and opinions of the Company's management on the date the statements are made. Except as required by applicable securities laws, the Company undertakes no obligation to update these forward-looking statements in the event that management's beliefs, estimates or opinions, or other factors, should change.
Golden Minerals Company is a Colorado-based precious metals producer with a pipeline of exploration projects in Mexico, Argentina and Nevada. With the commencement of gold and silver production at its Rodeo project in January... LEARN MORE
Ball mill and rod mill are the common grinding equipment applied in the grinding process. They are similar in appearance and both of them are horizontal cylindrical structures. Their cylinders are equipped with grinding medium, feeder, gears, and transmission device.
The working principle of ball mill and rod mill machine is similar, too. That is, the cylinder drives the movement of the grinding medium (lifting the grinding medium to a certain height then dropping). Under the action of centrifugal force and friction, the material is impacted and ground to required size, so as to realize the operation of mineral grinding.
Grate discharge ball mill can discharge material through sieve plate, with the advantage of the low height of the discharge port which can make the material pass quickly so tha t to avoid over-grinding of material. Under the same condition, it has a higher capacity and can save more energy than other types of mills;
It is better to choose a grate discharge ball mill when the required discharge size is in the range of 0.2 to 0.3 mm. Grate discharge ball mill is usually applied in the first grinding system because it can discharge the qualified product immediately.
Overflow discharge ball mill can grind ores into the size under 0.2 mm, so it is very suitable for the second grinding system. The capacity of it is about 15% lower than grate discharge ball mill in the same specification, and the loaded grinding medium is also less than that one.
It can be divided into three types of rod mills according to the discharge methods, center and side discharge rod mill, end and side discharge rod mill and shaft neck overflow discharge rod mill.
It is fed through the shaft necks in the two ends of rod mill, and discharges ore pulp through the port in the center of the cylinder. Center and side discharge rod mill can grind ores coarsely because of its structure.
This kind of rod mill can be used for wet grinding and dry grinding. "A rod mill is recommended if we want to properly grind large grains, because the ball mill will not attack them as well as rod mills will."
It is fed through one end of the shaft neck, and with the help of several circular holes, the ore pulp is discharged to the next ring groove. The rod mill is mainly used for dry and wet grinding processes that require the production of medium-sized products.
The diameter of the shaft neck is larger than the diameter of the feeding port about 10 to 20 centimeters, so that the height difference can form a gradient for ore pulp flow. There is equipped with a spiral screen in the discharge shaft neck to remove the impurities.
It has high toughness, good manufacturability and low price. The surface layer of high manganese steel will harden rapidly under the action of great impact or contact. The harder index is five to seven times higher than other materials, and the wear resistance is greatly improved.
It has high toughness, good manufacturability and low price. The surface layer of high manganese steel will harden rapidly under the action of great impact or contact. The harder index is five to seven times higher than other materials, and the wear resistance is greatly improved.
It is made of several elements such as chromium and molybdenum, which has high hardness and good toughness. Under the same work condition, the service of this kind of ball is one time longer than the high manganese steel ball.
After the professional technology straightening and quenching processing process, a high carbon steel rod has high hardness, excellent performance, good wear resistance and outstanding quality.
The steel ball of ball mill and the mineral material are in point contact, so the finished product has a high degree of fineness, but it is also prone to over-grinding. Therefore, it is suitable for the production with high material fineness and is not suitable for the gravity beneficiation of metal ores.
The steel rod and the material are in line or surface contact, and most of the coarse particles are first crushed and then ground. Therefore, the finished product is uniform in quality, excellent in particle size, and high in qualification rate.
The cylinder shape of the rod mill and the ball mill is different: the cylinder of the rod mill is a long type, and the floor area is large. The ratio of the length to the diameter of the cylinder is generally 1.5 to 2.0;
The cylinder of the ball mill is a barrel or a cone. And the ratio of the length to the diameter of the cylinder is small, and in most cases the ratio is only slightly larger than 1, and the floor area is small, too.
The above is the main content of this article. The ball mill and the rod mill are the same type of machine on the appearance, but there are still great differences in the interior. It is very necessary to select a suitable machine for the production to optimize the product effect and maximize its efficiency.
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A mill is a grinder used to grind and blend solid or hard materials into smaller pieces by means of shear, impact and compression methods. Grinding mill machine is an essential part of many industrial processes, there are mainly five types of mills to cover more than 90% materials size-reduction applications.
Do you the difference between the ball mill, rod mills, SAG mill, tube mill, pebble mill? In the previous article, I made a comparison of ball mill and rod mill. Today, we will learn about the difference between SAG mill vs ball mill.
AG/SAG is short for autogenous mill and semi-autogenous mill, it combines with two functions of crushing and grinding, uses the ground material itself as the grinding media, through the mutual impact and grinding action to gradually reduce the material size. SAG mill is usually used to grind large pieces into small pieces, especially for the pre-processing of grinding circuits, thus also known as primary stage grinding machine. Based on the high throughput and coarse grind, AG mills produce coarse grinds often classify mill discharge with screens and trommel. SAG mills grinding media includes some large and hard rocks, filled rate of 9% 20%. SAG mill grind ores through impact, attrition, abrasion forces. In practice, for a given ore and equal processing conditions, the AG milling has a finer grind than SAG mills.
The working principle of the self-grinding machine is basically the same as the ball mill, the biggest difference is that the sag grinding machine uses the crushed material inside the cylinder as the grinding medium, the material constantly impacts and grinding to gradually pulverize. Sometimes, in order to improve the processing capacity of the mill, a small amount of steel balls be added appropriately, usually occupying 2-3% of the volume of the mill (that is semi-autogenous grinding).
High capacity Ability to grind multiple types of ore in various circuit configurations, reduces the complexity of maintenance and coordination. Compared with the traditional tumbling mill, the autogenous mill reduces the consumption of lining plates and grinding media, thus have a lower operation cost. The self-grinding machine can grind the material to 0.074mm in one time, and its content accounts for 20% ~ 50% of the total amount of the product. Grinding ratio can reach 4000 ~ 5000, more than ten times higher than ball, rod mill.
Ball mills are fine grinders, have horizontal ball mill and vertical ball mill, their cylinders are partially filled with steel balls, manganese balls, or ceramic balls. The material is ground to the required fineness by rotating the cylinder causing friction and impact. The internal machinery of the ball mill grinds the material into powder and continues to rotate if extremely high precision and precision is required.
The ball mill can be applied in the cement production plants, mineral processing plants and where the fine grinding of raw material is required. From the volume, the ball mill divide into industrial ball mill and laboratory use the small ball mill, sample grinding test. In addition, these mills also play an important role in cold welding, alloy production, and thermal power plant power production.
The biggest characteristic of the sag mill is that the crushing ratio is large. The particle size of the materials to be ground is 300 ~ 400mm, sometimes even larger, and the minimum particle size of the materials to be discharged can reach 0.1 mm. The calculation shows that the crushing ratio can reach 3000 ~ 4000, while the ball mills crushing ratio is smaller. The feed size is usually between 20-30mm and the product size is 0-3mm.
Both the autogenous grinding mill and the ball mill feed parts are welded with groove and embedded inner wear-resistant lining plate. As the sag mill does not contain grinding medium, the abrasion and impact on the equipment are relatively small.
The feed of the ball mill contains grinding balls. In order to effectively reduce the direct impact of materials on the ball mill feed bushing and improve the service life of the ball mill feed bushing, the feeding point of the groove in the feeding part of the ball mill must be as close to the side of the mill barrel as possible. And because the ball mill feed grain size is larger, ball mill feeding groove must have a larger slope and height, so that feed smooth.
Since the power of the autogenous tumbling mill is relatively small, it is appropriate to choose dynamic and static pressure bearing. The ball bearing liner is made of lead-based bearing alloy, and the back of the bearing is formed with a waist drum to form a contact centering structure, with the advantages of flexible movement. The bearing housing is lubricated by high pressure during start-up and stop-up, and the oil film is formed by static pressure. The journal is lifted up to prevent dry friction on the sliding surface, and the starting energy moment is reduced. The bearing lining is provided with a snake-shaped cooling water pipe, which can supply cooling water when necessary to reduce the temperature of the bearing bush. The cooling water pipe is made of red copper which has certain corrosion resistance.
Ball mill power is relatively large, the appropriate choice of hydrostatic sliding bearing. The main bearing bush is lined with babbitt alloy bush, each bush has two high-pressure oil chambers, high-pressure oil has been supplied to the oil chamber before and during the operation of the mill, the high-pressure oil enters the oil chamber through the shunting motor, and the static pressure oil film is compensated automatically to ensure the same oil film thickness To provide a continuous static pressure oil film for mill operation, to ensure that the journal and the bearing Bush are completely out of contact, thus greatly reducing the mill start-up load, and can reduce the impact on the mill transmission part, but also can avoid the abrasion of the bearing Bush, the service life of the bearing Bush is prolonged. The pressure indication of the high pressure oil circuit can be used to reflect the load of the mill indirectly. When the mill stops running, the high pressure oil will float the Journal, and the Journal will stop gradually in the bush, so that the Bush will not be abraded. Each main bearing is equipped with two temperature probe, dynamic monitoring of the bearing Bush temperature, when the temperature is greater than the specified temperature value, it can automatically alarm and stop grinding. In order to compensate for the change of the mill length due to temperature, there is a gap between the hollow journal at the feeding end and the bearing Bush width, which allows the journal to move axially on the bearing Bush. The two ends of the main bearing are sealed in an annular way and filled with grease through the lubricating oil pipe to prevent the leakage of the lubricating oil and the entry of dust.
The end cover of the autogenous mill is made of steel plate and welded into one body; the structure is simple, but the rigidity and strength are low; the liner of the autogenous mill is made of high manganese steel.
The end cover and the hollow shaft can be made into an integral or split type according to the actual situation of the project. No matter the integral or split type structure, the end cover and the hollow shaft are all made of Casting After rough machining, the key parts are detected by ultrasonic, and after finishing, the surface is detected by magnetic particle. The surface of the hollow shaft journal is Polished after machining. The end cover and the cylinder body are all connected by high-strength bolts. Strict process measures to control the machining accuracy of the joint surface stop, to ensure reliable connection and the concentricity of the two end journal after final assembly. According to the actual situation of the project, the cylinder can be made as a whole or divided, with a flanged connection and stop positioning. All welds are penetration welds, and all welds are inspected by ultrasonic nondestructive testing After welding, the whole Shell is returned to the furnace for tempering stress relief treatment, and after heat treatment, the shell surface is shot-peened. The lining plate of the ball mill is usually made of alloy material.
The transmission part comprises a gear and a gear, a gear housing, a gear housing and an accessory thereof. The big gear of the transmission part of the self-grinding machine fits on the hollow shaft of the discharge material, which is smaller in size, but the seal of the gear cover is not good, and the ore slurry easily enters the hollow shaft of the discharge material, causing the hollow shaft to wear.
The big gear of the ball mill fits on the mill shell, the size is bigger, the big gear is divided into half structure, the radial and axial run-out of the big gear are controlled within the national standard, the aging treatment is up to the standard, and the stress and deformation after processing are prevented. The big gear seal adopts the radial seal and the reinforced big gear shield. It is welded and manufactured in the workshop. The geometric size is controlled, the deformation is prevented and the sealing effect is ensured. The small gear transmission device adopts the cast iron base, the bearing base and the bearing cap are processed at the same time to reduce the vibration in operation. Large and small gear lubrication: The use of spray lubrication device timing quantitative forced spray lubrication, automatic control, no manual operation. The gear cover is welded by profile steel and high-quality steel plate. In order to enhance the stiffness of the gear cover, the finite element analysis is carried out, and the supporting structure is added in the weak part according to the analysis results.
The self-mill adopts the self-return device to realize the discharge of the mill. The self-returning device is located in the revolving part of the mill, and the material forms a self-circulation in the revolving part of the mill through the self-returning device, discharging the qualified material from the mill, leading the unqualified material back into the revolving part to participate in the grinding operation.
The ball mill adopts a discharge screen similar to the ball mill, and the function of blocking the internal medium of the overflow ball mill is accomplished inside the rotary part of the ball mill. The discharge screen is only responsible for forcing out a small amount of the medium that overflows into the discharge screen through the internal welding reverse spiral, to achieve forced discharge mill.
The slow drive consists of a brake motor, a coupling, a planetary reducer and a claw-type clutch. The device is connected to a pinion shaft and is used for mill maintenance and replacement of liners. In addition, after the mill is shut down for a long time, the slow-speed transmission device before starting the main motor can eliminate the eccentric load of the steel ball, loosen the consolidation of the steel ball and materials, ensure safe start, avoid overloading of the air clutch, and play a protective role. The slow-speed transmission device can realize the point-to-point reverse in the electronic control design. When connecting the main motor drive, the claw-type Clutch automatically disengages, the maintenance personnel should pay attention to the safety.
The slow drive device of the ball mill is provided with a rack and pinion structure, and the operating handle is moved to the side away from the cylinder body The utility model not only reduces the labor intensity but also ensures the safety of the operators.
M CABORCA, Mexico, October 5th, 2020 (GLOBE NEWSWIRE) Mexus Gold US (OTCQB: MXSG) (Mexus or the Company) announced that its ball mill gravity gold recovery system is now operational. This system will allow the company to run high grade material from the Julio quartz vein at its Santa Elena mine located in Caborca, MX. In addition, the company announced an important discovery concerning gold recovery from its heap leach pad at the mine site. Mexus has been and continues to recover gold from the mineralized material placed on the heap leach pad. The resulting gold production from this work has been variable leading to an analysis of the heap leach pad. It has been found that the salt placed on the pad by the prior operator continues to limit gold recovery. Assays of the cyanide solution returning to the pregnant pond are not representative of the material being placed on the pad. The company decided to remove the material from the top of the heap leach pad down to 2 meters from the bottom and have it assayed. These assays showed that salt is causing issues with gold recovery. The silver in this material, when coming into contact with salt, turns to silver chloride. Cyanide solution with gold reacts with silver chloride and turns the gold to a metallic state inhibiting recovery. The silver chloride found in the bottom 2 meters was assayed and showed an extremely high level of gold value (ounces to the ton). Mexus CEO, Paul Thompson, along with Chief Geologist, Cesar Lemas, determined that the bottom 2 meters of the heap leach pad needs to be removed and run through the ball mill gravity system. Tests have shown that 95% of the gold in the silver chloride material can be recovered using the companys gravity ball mill circuit. This work has already begun. These efforts accomplish two things for the company. First, this allows for gold recovery of highly assayed material at the bottom of the heap leach pad. Secondly, it fixes the heap leach pad allowing for normal and consistent recovery of gold going forward. Mexus will continue to produce gold in the last quarter of 2020. The company was looking to give guidance for the 4th quarter of 2020 but determined that the recent findings have made it difficult to give an estimate. In the near future, shareholders of Mexus can expect an update on both the heap leach and ball mill gravity gold recovery circuits. Mexus CEO, Paul Thompson added, Im excited for gold production in the coming weeks. We believe that a substantial amount of gold trapped on the pad is now going to be recovered.
About Mexus Gold US Mexus Gold US is an American based mining company with holdings in Mexico. The fully owned Santa Elena mine is located 54km NW of Caborca, Mexico. Mexus also owns rights to the Ures property located 80km N of Hermosillo, Mexico. This property contains 6900 acres and has both gold and copper on the property. Founded in 2009, Mexus Gold US is committed to protecting the environment, mine safety and employing members of the communities in which it operates. For more information on Mexus Gold US, visit www.mexusgoldus.com. Mexus Gold US (775) 721-9960 Cautionary Statement Forward looking Statement: Statements in this press release may constitute forward-looking statements and are subject to numerous risks and uncertainties, including the failure to complete successfully the development of new or enhanced products, the Companys future capital needs, the lack of market demand for any new or enhanced products the Company may develop, any actions by the Companys partners that may be adverse to the Company, the success of competitive products, other economic factors affecting the Company and its markets, seasonal changes, and other risks detailed from time to time in the Companys filings with the Securities and Exchange Commission. The actual results may differ materially from those contained in this press release. The Company disclaims any obligation to update any statements in this press release.
This ball mill is typically designed to grind mineral ores and other materials with different hardness, and it is widely used in different fields, such as ore dressing, building material field, chemical industry, etc. Due to the difference of its slurry discharging method, it is divided to two types: grid type ball mill and overflow type ball mill.
Compared with grid type ball mill, overflow type ball mill can grind materials finer even though its grinding time is usually longer. So it can make finer particle products. Hence the grid type ball mill is mainly used for primary stage of grinding while overflow type ball mill is mainly used for the secondary grinding.
Ball mill Advantages: 1Jack-up device, easy maintenance; 2The hydrostatic and hydrodynamic bearings ensure the smooth operation; 3Low speed transmission is easy for starting and maintenance; 4The oil-mist lubrication device guarantees reliable performance of bearings; 5The air clutch adopts the flexible start-up model./5According to the customer demand, manganese steel liner and wear-resistant rubber liner can be customized with good wear resistance, long service life and easy maintenance.
The grinding system uses either 'open circuit' or 'closed circuit'. In an open circuit system, the feed rate of materials is adjusted to achieve the desired fineness of the product. In a closed circuit system, coarse particles are separated from the finer ones and sent back for further grinding.
Prominer has been devoted to mineral processing industry for decades and specializes in mineral upgrading and deep processing. With expertise in the fields of mineral project development, mining, test study, engineering, technological processing.
For thousands of years the word gold has connoted something of beauty or value. These images are derived from two properties of gold, its colour and its chemical stability. The colour of gold is due to the electronic structure of the gold atom, which absorbs electromagnetic radiation with wavelengths less than 5600 angstroms but reflects wavelengths greater than 5600 angstromsthe wavelength of yellow light. Golds chemical stability is based on the relative instability of the compounds that it forms with oxygen and watera characteristic that allows gold to be refined from less noble metals by oxidizing the other metals and then separating them from the molten gold as a dross. However, gold is readily dissolved in a number of solvents, including oxidizing solutions of hydrochloric acid and dilute solutions of sodium cyanide. Gold readily dissolves in these solvents because of the formation of complex ions that are very stable.
Gold (Au) melts at a temperature of 1,064 C (1,947 F). Its relatively high density (19.3 grams per cubic centimetre) has made it amenable to recovery by placer mining and gravity concentration techniques. With a face-centred cubic crystal structure, it is characterized by a softness or malleability that lends itself to being shaped into intricate structures without sophisticated metalworking equipment. This in turn has led to its application, from earliest times, to the fabrication of jewelry and decorative items.
The history of gold extends back at least 6,000 years, the earliest identifiable, realistically dated finds having been made in Egypt and Mesopotamia c. 4000 bc. The earliest major find was located on the Bulgarian shores of the Black Sea near the present city of Varna. By 3000 bc gold rings were used as a method of payment. Until the time of Christ, Egypt remained the centre of gold production. Gold was, however, also found in India, Ireland, Gaul, and the Iberian Peninsula. With the exception of coinage, virtually all uses of the metal were decorativee.g., for weapons, goblets, jewelry, and statuary.
Egyptian wall reliefs from 2300 bc show gold in various stages of refining and mechanical working. During these ancient times, gold was mined from alluvial placersthat is, particles of elemental gold found in river sands. The gold was concentrated by washing away the lighter river sands with water, leaving behind the dense gold particles, which could then be further concentrated by melting. By 2000 bc the process of purifying gold-silver alloys with salt to remove the silver was developed. The mining of alluvial deposits and, later, lode or vein deposits required crushing prior to gold extraction, and this consumed immense amounts of manpower. By ad 100, up to 40,000 slaves were employed in gold mining in Spain. The advent of Christianity somewhat tempered the demand for gold until about the 10th century. The technique of amalgamation, alloying with mercury to improve the recovery of gold, was discovered at about this time.
The colonization of South and Central America that began during the 16th century resulted in the mining and refining of gold in the New World before its transferal to Europe; however, the American mines were a greater source of silver than gold. During the early to mid-18th century, large gold deposits were discovered in Brazil and on the eastern slopes of the Ural Mountains in Russia. Major alluvial deposits were found in Siberia in 1840, and gold was discovered in California in 1848. The largest gold find in history is in the Witwatersrand of South Africa. Discovered in 1886, it produced 25 percent of the worlds gold by 1899 and 40 percent by 1985. The discovery of the Witwatersrand deposit coincided with the discovery of the cyanidation process, which made it possible to recover gold values that had escaped both gravity concentration and amalgamation. With E.B. Millers process of refining impure gold with chlorine gas (patented in Britain in 1867) and Emil Wohlwills electrorefining process (introduced in Hamburg, Ger., in 1878), it became possible routinely to achieve higher purities than had been allowed by fire refining.
The major ores of gold contain gold in its native form and are both exogenetic (formed at the Earths surface) and endogenetic (formed within the Earth). The best-known of the exogenetic ores is alluvial gold. Alluvial gold refers to gold found in riverbeds, streambeds, and floodplains. It is invariably elemental gold and usually made up of very fine particles. Alluvial gold deposits are formed through the weathering actions of wind, rain, and temperature change on rocks containing gold. They were the type most commonly mined in antiquity. Exogenetic gold can also exist as oxidized ore bodies that have formed under a process called secondary enrichment, in which other metallic elements and sulfides are gradually leached away, leaving behind gold and insoluble oxide minerals as surface deposits.
Endogenetic gold ores include vein and lode deposits of elemental gold in quartzite or mixtures of quartzite and various iron sulfide minerals, particularly pyrite (FeS2) and pyrrhotite (Fe1-xS). When present in sulfide ore bodies, the gold, although still elemental in form, is so finely disseminated that concentration by methods such as those applied to alluvial gold is impossible.
Native gold is the most common mineral of gold, accounting for about 80 percent of the metal in the Earths crust. It occasionally is found as nuggets as large as 12 millimetres (0.5 inch) in diameter, and on rare occasions nuggets of native gold weighing up to 50 kilograms are foundthe largest having weighed 92 kilograms. Native gold invariably contains about 0.1 to 4 percent silver. Electrum is a gold-silver alloy containing 20 to 45 percent silver. It varies from pale yellow to silver white in colour and is usually associated with silver sulfide mineral deposits.
Gold also forms minerals with the element tellurium; the most common of these are calaverite (AuTe2) and sylvanite (AuAgTe4). Other minerals of gold are sufficiently rare as to have little economic significance.
Of the worlds known mineral reserves of gold ore, 50 percent is found in South Africa, and most of the rest is divided among Russia, Canada, Australia, Brazil, and the United States. The largest single gold ore body in the world is in the Witwatersrand of South Africa.Get in Touch with Mechanic