The basic parameters used in ball mill design (power calculations), rod mill or anytumbling millsizing are; material to be ground, characteristics, Bond Work Index, bulk density, specific density, desired mill tonnage capacity DTPH, operating % solids or pulp density, feed size as F80 and maximum chunk size, productsize as P80 and maximum and finally the type of circuit open/closed you are designing for.
In extracting fromNordberg Process Machinery Reference ManualI will also provide 2 Ball Mill Sizing (Design) example done by-hand from tables and charts. Today, much of this mill designing is done by computers, power models and others. These are a good back-to-basics exercises for those wanting to understand what is behind or inside the machines.
W = power consumption expressed in kWh/short to (HPhr/short ton = 1.34 kWh/short ton) Wi = work index, which is a factor relative to the kwh/short ton required to reduce a given material from theoretically infinite size to 80% passing 100 microns P = size in microns of the screen opening which 80% of the product will pass F = size in microns of the screen opening which 80% of the feed will pass
Open circuit grinding to a given surface area requires no more power than closed circuit grinding to the same surface area provided there is no objection to the natural top-size. If top-size must be limited in open circuit, power requirements rise drastically as allowable top-size is reduced and particle size distribution tends toward the finer sizes.
A wet grinding ball mill in closed circuit is to be fed 100 TPH of a material with a work index of 15 and a size distribution of 80% passing inch (6350 microns). The required product size distribution is to be 80% passing 100 mesh (149 microns). In order to determine the power requirement, the steps are as follows:
The ball mill motorpower requirement calculated above as 1400 HP is the power that must be applied at the mill drive in order to grind the tonnage of feed from one size distribution. The following shows how the size or select thematching mill required to draw this power is calculated from known tables the old fashion way.
The value of the angle a varies with the type of discharge, percent of critical speed, and grinding condition. In order to use the preceding equation, it is necessary to have considerable data on existing installations. Therefore, this approach has been simplified as follows:
A = factor for diameter inside shell lining B = factor which includes effect of % loading and mill type C = factor for speed of mill L = length in feet of grinding chamber measured between head liners at shell- to-head junction
Many grinding mill manufacturers specify diameter inside the liners whereas othersare specified per inside shell diameter. (Subtract 6 to obtain diameter inside liners.) Likewise, a similar confusion surrounds the length of a mill. Therefore, when comparing the size of a mill between competitive manufacturers, one should be aware that mill manufacturers do not observe a size convention.
In Example No.1 it was determined that a 1400 HP wet grinding ball mill was required to grind 100 TPH of material with a Bond Work Index of 15 (guess what mineral type it is) from 80% passing inch to 80% passing 100 mesh in closed circuit. What is the size of an overflow discharge ball mill for this application?
Max Feeding size <25mm Discharge size0.075-0.4mm Typesoverflow ball mills, grate discharge ball mills Service 24hrs quotation, custom made parts, processing flow design & optimization, one year warranty, on-site installation.
Ball mill, also known as ball grinding machine, a well-known ore grinding machine, widely used in the mining, construction, aggregate application. JXSC start the ball mill business since 1985, supply globally service includes design, manufacturing, installation, and free operation training. Type according to the discharge type, overflow ball mill, grate discharge ball mill; according to the grinding conditions, wet milling, dry grinding; according to the ball mill media. Wet grinding gold, chrome, tin, coltan, tantalite, silica sand, lead, pebble, and the like mining application. Dry grinding cement, building stone, power, etc. Grinding media ball steel ball, manganese, chrome, ceramic ball, etc. Common steel ball sizes 40mm, 60mm, 80mm, 100mm, 120mm. Ball mill liner Natural rubber plate, manganese steel plate, 50-130mm custom thickness. Features 1. Effective grinding technology for diverse applications 2. Long life and minimum maintenance 3. Automatization 4. Working Continuously 5. Quality guarantee, safe operation, energy-saving. The ball grinding mill machine usually coordinates with other rock crusher machines, like jaw crusher, cone crusher, to reduce the ore particle into fine and superfine size. Ball mills grinding tasks can be done under dry or wet conditions. Get to know more details of rock crushers, ore grinders, contact us!
Ball mill parts feed, discharge, barrel, gear, motor, reducer, bearing, bearing seat, frame, liner plate, steel ball, etc. Contact our overseas office for buying ball mill components, wear parts, and your mine site visits. Ball mill working principle High energy ball milling is a type of powder grinding mill used to grind ores and other materials to 25 mesh or extremely fine powders, mainly used in the mineral processing industry, both in open or closed circuits. Ball milling is a grinding method that reduces the product into a controlled final grind and a uniform size, usually, the manganese, iron, steel balls or ceramic are used in the collision container. The ball milling process prepared by rod mill, sag mill (autogenous / semi autogenous grinding mill), jaw crusher, cone crusher, and other single or multistage crushing and screening. Ball mill manufacturer With more than 35 years of experience in grinding balls mill technology, JXSC design and produce heavy-duty scientific ball mill with long life minimum maintenance among industrial use, laboratory use. Besides, portable ball mills are designed for the mobile mineral processing plant. How much the ball mill, and how much invest a crushing plant? contact us today! Find more ball mill diagram at ball mill PDF ServiceBall mill design, Testing of the material, grinding circuit design, on site installation. The ball grinding mill machine usually coordinates with other rock crusher machines, like jaw crusher, cone crusher, get to know more details of rock crushers, ore grinders, contact us! sag mill vs ball mill, rod mill vs ball mill
How many types of ball mill 1. Based on the axial orientation a. Horizontal ball mill. It is the most common type supplied from ball mill manufacturers in China. Although the capacity, specification, and structure may vary from every supplier, they are basically shaped like a cylinder with a drum inside its chamber. As the name implies, it comes in a longer and thinner shape form that vertical ball mills. Most horizontal ball mills have timers that shut down automatically when the material is fully processed. b. Vertical ball mills are not very commonly used in industries owing to its capacity limitation and specific structure. Vertical roller mill comes in the form of an erect cylinder rather than a horizontal type like a detachable drum, that is the vertical grinding mill only produced base on custom requirements by vertical ball mill manufacturers. 2. Base on the loading capacity Ball mill manufacturers in China design different ball mill sizes to meet the customers from various sectors of the public administration, such as colleges and universities, metallurgical institutes, and mines. a. Industrial ball mills. They are applied in the manufacturing factories, where they need them to grind a huge amount of material into specific particles, and alway interlink with other equipment like feeder, vibrating screen. Such as ball mill for mining, ceramic industry, cement grinding. b. Planetary Ball Mills, small ball mill. They are intended for usage in the testing laboratory, usually come in the form of vertical structure, has a small chamber and small loading capacity. Ball mill for sale In all the ore mining beneficiation and concentrating processes, including gravity separation, chemical, froth flotation, the working principle is to prepare fine size ores by crushing and grinding often with rock crushers, rod mill, and ball mils for the subsequent treatment. Over a period of many years development, the fine grinding fineness have been reduced many times, and the ball mill machine has become the widest used grinding machine in various applications due to solid structure, and low operation cost. The ball miller machine is a tumbling mill that uses steel milling balls as the grinding media, applied in either primary grinding or secondary grinding applications. The feed can be dry or wet, as for dry materials process, the shell dustproof to minimize the dust pollution. Gear drive mill barrel tumbles iron or steel balls with the ore at a speed. Usually, the balls filling rate about 40%, the mill balls size are initially 3080 cm diameter but gradually wore away as the ore was ground. In general, ball mill grinder can be fed either wet or dry, the ball mill machine is classed by electric power rather than diameter and capacity. JXSC ball mill manufacturer has industrial ball mill and small ball mill for sale, power range 18.5-800KW. During the production process, the ball grinding machine may be called cement mill, limestone ball mill, sand mill, coal mill, pebble mill, rotary ball mill, wet grinding mill, etc. JXSC ball mills are designed for high capacity long service, good quality match Metso ball mill. Grinding media Grinding balls for mining usually adopt wet grinding ball mills, mostly manganese, steel, lead balls. Ceramic balls for ball mill often seen in the laboratory. Types of ball mill: wet grinding ball mill, dry grinding ball mill, horizontal ball mill, vibration mill, large ball mill, coal mill, stone mill grinder, tumbling ball mill, etc. The ball mill barrel is filled with powder and milling media, the powder can reduce the balls falling impact, but if the power too much that may cause balls to stick to the container side. Along with the rotational force, the crushing action mill the power, so, it is essential to ensure that there is enough space for media to tumble effectively. How does ball mill work The material fed into the drum through the hopper, motor drive cylinder rotates, causing grinding balls rises and falls follow the drum rotation direction, the grinding media be lifted to a certain height and then fall back into the cylinder and onto the material to be ground. The rotation speed is a key point related to the ball mill efficiency, rotation speed too great or too small, neither bring good grinding result. Based on experience, the rotat
ion is usually set between 4-20/minute, if the speed too great, may create centrifuge force thus the grinding balls stay with the mill perimeter and dont fall. In summary, it depends on the mill diameter, the larger the diameter, the slower the rotation (the suitable rotation speed adjusted before delivery). What is critical speed of ball mill? The critical speed of the ball mill is the speed at which the centrifugal force is equal to the gravity on the inner surface of the mill so that no ball falls from its position onto the mill shell. Ball mill machines usually operates at 65-75% of critical speed. What is the ball mill price? There are many factors affects the ball mill cost, for quicker quotations, kindly let me know the following basic information. (1) Application, what is the grinding material? (2) required capacity, feeding and discharge size (3) dry or wet grinding (4) single machine or complete processing plant, etc.
The final fineness of the product mainly depends on the number of times the ore particles pass through the grinder. The longer the grinding, the smaller the particle size. Separate crushing and grinding steps are necessary, the ball mill can only receive the broken ore particle, and then grind to the grinding fineness required for flotation.
In order to separate the concentrate from the ore, the ore should be ground fine enough to release the target mineral from the non-mineral grains. The degree of grinding required for this depends on the size of the mineral particles in the ore. A laboratory-scale flotation test is usually required on materials of different particle sizes to determine the grinding particle size required to release the target minerals.The fineness of the ore particles produced by grinding is crucial to recover the minerals by flotation. The most common grinding machines are semi-automatic (SAG) and automatic (AG) mills and ball mills.
Determining an optimal grinding size can maximize the recovery of target minerals in the subsequent flotation process.The grinding size is too large, and some ore particles and non-ore particles cannot be separated, thus preventing their flotation. If the particle size is too fine, the bubbles that rise during the flotation will push the very fine ore-containing particles away, preventing them from contacting the bubbles, thereby reducing their ability to be recovered into the concentrate.In addition, extremely fine rock and iron sulfide particles may agglomerate with extremely fine sulfide ore particles, preventing the ore particles from floating.
According to the test, the particles usually need to be ground to a diameter of about 100 mm to release minerals from each other. When the particles are less than about 10 mm, this is not conducive to the flotation effect.Grinding operations are very power-hungry, which is another reason to avoid excessive grinding.
The crushed products are ground in SAG or AG mills. The self-grinding machine can grind ore without grinding media such as iron ball, or steel rod, as long as the hardness of the ore is sufficient for the rolling ore to grind by itself.A large vibrating screen is used to sieve the ground products to separate the oversized particles. A small cone crusher to recover the oversized material, and then sent them return to the SAG or AG mill for re-grinding. The correct size material is sent to the ball mill for final grinding.
The ball mill is the fine grinding machine connect the SAG or AG mill and flotation machine. Ball mills produce fine particles with a uniform size for flotation, its grinding medias commonly are steel ball. The ball mill rolls grinding media together with the ore, as the ore grinds, these balls initially 5-10 cm in diameter but gradually wear out.Grinding is always carried out under wet conditions, with about 70% solid mixture in water.This procedure maximizes ore production and minimizes power consumption.
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You can read all the details of this now Biblical grinding power requirement calculation formula in Fred Bonds original paper. You can also review the step-by-step Bond Work Index Test Procedure I posted here.
For any circuit, whether a crushing circuit, a rod mill, or a closed ball mill circuit, the Work Index always means the equivalent amount of energy to reduce one ton of the ore from a very large size to 100 um.
The sample was received crushed appropriately for the ball mill test. Ball Mill Grindability Testwas conducted by standard practice using 100-mesh (150 pm) closingscreens.The ball mill work index is shown below.
Any improvement in the accuracy of commercial comminution calculations under the Third Theory must be accomplished either by increased precision in energy input measurements, or by a better evaluation of the total new crack length produced, as indicated by the feed and product size distributions. Since at the present time feed and product sizes are approximated solely by the microns 80% passes, the most promising opportunity for increased accuracy lies in consideration of their plotted size distribution characteristics. This paper shows how more accuracy can be obtained over an increased range of feed and product sizes from size distribution studies.
where W is the work input required in kilowatt hours per short ton to grind from 80% passing F microns to 80% passing P microns, and Wi is the work index, or the grinding resistance parameter. It represents the energy input required in kilowatt hours to reduce a short ton from theoretically infinite feed size to 80% passing 100 microns. This simple equation has been extremely useful in analyzing and grinding operations, and in predicting the performance of new installations.It can be written in the following form:
The work index Wi can be determined from plant operations and from laboratory ball mill grindability, rod mill grindability, and impact crushing tests. The laboratory test results are used to check the efficiency of commercial operations and to compute the proper machine sizes for new installations.
where Pi is the opening in microns of the sieve mesh tested, and Gbp is the net grams of mesh undersize produced per revolution of the 12 x 12 test ball mill. The closed circuit 80% passing size P averages P1/log 20 for all sizes larger than 150 mesh. For 150 mesh the average P value is 76 microns, for 200 mesh it is 50, for 270 mesh it is 32.3, and for 325 mesh it is 26.7. These average values can be used when P cannot be determined from screen analyses.
where Sg is the specific gravity and C is the impact crushing strength of the twin pendulum weights in foot-pounds per inch of rock thickness. No size distribution measurements are made in the impact test.
The trend of the particle size distribution line is shown by plotting its screen analysis in, such a manner that a complete homogeneous crushed or ground product will form a straight line; any curvature then indicates a natural or induced grain size. Semi-log paper is used with the percent cumulative retained plotted on the vertical logarithmic scale Y. Straight lines which each represent one mesh sieve size of P1 microns are drawn radiating from the upper left hand corner of the plot; each crosses the 20% retained, or 80% passing, line at w = 10/P1 where w is the horizontal lineal X value at Y = 20. The total work input to the sample in KWH/ton divided by the work index Wi is w. The straight plotted distribution line follows the exponential equation:
The exposure ratio Er is the quantity that expresses the line trend, or the fine size distribution. Er equals X2/W where X2 is the value of x at the top of the chart with Y = 100%. It has the following relationship to b.
When the exposure ratio Er is zero only one particle size is present and there has been no exposure of fines to the grinding media. The fines present increase as Er increases, and when Er is unity b is infinite.
When natural or induced grain sizes cause the plotted distribution line to curve in the region of 80% passing, the straight line determining Er is drawn through w at the average slope from Y = 10 to Y = 40, or is estimated to avoid the curvature. The exposure, ratio of the feed is Erf and that of the product is Erp.
It is apparent that the specific work input required, as represented by the new crack length Cr produced in centimeters per cc of solid (Crp Crf), will be decreased at large product sizes and will increase at fine product sizes when Crf and Erf are increased. In this case the work index Wi will increase as the product size P becomes smaller. Conversely, when the feed contains little fines and Erf and Crf are small, the work index will increase as P increases. These conditions are largely responsible for the observed work index variations at different product sizes which were formerly thought to require an exponent different from .
In a recent publication fifteen different ores each had grindability tests made at 28, 35, 48, 65 and 100 mesh, with many work index variations at the different product sizes. These tests are used here to develop empirical equations from which the work index at different product sizes can be computed from a grindability test at one size. In each of the 15 ores the data from the grindability test at 48 mesh alone were used to calculate the Wi values at 28, 35, 65, and 100 mesh, and these were compared with the actual values obtained by testing. In the calculation the exposure ratio Erp of each mesh product size was considered to be that determined by testing at 48 mesh, and Crp was determined from that value and the average P for each mesh size.
However, an equation is desired which uses the exposure ratios and does not require calculation of the crack lengths, Eq. (8) was derived to give the work index Wi at any 80% passing product size P from the work index Wio found from a single grindability test with a product size Po and exposure ratios Erf and Erp. It is
The work index values calculated from Eq. (7) and Eq. (8) are listed in Table I. Comparison with the actual Wi values shows that Eq. (8) is slightly more accurate than Eq. (7), and it is much simpler to use. Eq. (8) is suitable for determining the work index at various product sizes from one ball mill grindability test made at product size Po. It can be checked by grindability tests made at other product sizes.
The exposure ratio of the prepared minus 6 mesh feed Erf is regularly somewhat larger than that of the closed circuit product Erp, and Eq. (8) indicates that when Erf/Erp equals 1.29 the work index continues constant at all product sizes. When Erf/Erp is greater than 1.29, the work index increases as the product size decreases, and when Erf/Erp is less than 1.29 the work index decreases.
When Wi100 is calculated by Eq. (9) from the data at 48 mesh for each of the 15 ores listed, then Wip found by Eq. (10) for each of these ores at 28, 35, 65, and 100 mesh is essentially the same as the Wi value found from Eq. (8).
Comparison of the Wi100 values from Eq. (9) for different ores furnishes a measure of the relative grindability unaffected by size distribution differences; and comparison of the Wi100 values for the same ore calculated from the data at different mesh sizes gives a measure of the actual experimental errors involved in testing, plus any error in measuring the plotted Er values, and any error resulting from natural grain sizes causing curved plotted lines.
The standard work index Wi100 values calculated from Eq. (9) for each ore at each mesh size are included in Table I. Comparison for each ore shows a reasonable agreement among the tests made at various mesh sizes, and indicates that Eq. (9) and Eq. (10) can be used with confidence. The data show that the ball mill grindability tests at 28 mesh are somewhat less accurate than the others; this is expected because of the low ratio of reduction and the short retention time in the mill, when grinding prepared minus 6 mesh feed.
The total crack length Cr in centimeters per cubic centimeter of solids is most conveniently found from log-log charts prepared from a previously published table. However, in the absence of these chart the crack length of a crushed or ground product can be calculated for any 80% passing size P in microns and any exposure ratio Er by the following equation:
In the standard ball mill and rod mill grindability tests the specific crack lengths of the product Crp and of the feed Crf are found from their Erp, P, Erf, and F values. Where Y is the cumulative fraction of the feed retained on the mesh size tested the centimeters of new crack length produced per mill revolution are found from:
The average useful work input to the standard ball mill is 65 joules/Rev. with 115 joules/Rev. to the rod mill. The crack energy Ce of the sample tested is found by dividing joules/Rev. by Cm/Rev. The standard work index can then be found by transposing Eq. (16) and solving for Wi100.
In commercial grinding mills the operating work index is found by Eq. (19). However, when exposure ratios of the feed and product are obtained by plotting the screen analyses, their specific crack lengths Crf and Crp can be found. This furnishes the crack energy Ce in joules/Cm from:
The standard work index Wi100 can then be found from transposed Eq. (16). Comparison with the plant operating work index at product size P may show that the coefficients .018 and .014 in the last term of Eq. (9) should be altered slightly for the commercial grind. With the proper coefficients Eq. (9) can be used to evaluate the plant grinding operation at different product sizes with considerable accuracy.
The common types of ball mill used in the mineral processing mainly include cement ball mill, tubular ball mill, ultra-fine laminating mill, cone ball mill, ceramic ball mill, intermittent ball mill, overflow ball mill, grid ball mill, wind discharge ball mill, double bin ball mill, energy-saving ball mill. But the types of ball mill are also varying according to the different sorting conditions.
Short cylinder ball mill: the cylinder length(L) is less than two times of the cylinder diameter(D), that is, the ball mill with L2D is the short cylinder ball mill. It is usually a single-bin structure, mainly used for coarse grinding or first-stage grinding. Because of its high operation efficiency, two or three ball mills can be used in series at the same time, which has a wide application.
The grinding medium in the gravel ball mill mainly includes pebbles, gravel, sand, porcelain balls, etc. The gravel ball mill adopts porcelain material or granite as the lining board, which is widely used in the field of colored cement, white cement and ceramics.
Center driving ball mill: The driving power end of this ball mill is in the center of the ball mill. And the motor realizes the operation of the ball mill through reducer. During the operation, the hollow shaft in the center of the ball mill drives the mill body to rotate under the driving of the power system.
Wet ball mill: Adding water when feeding, the discharging material is discharged when it is in a certain concentration of slurry. The wet ball mill forms the closed circuit operation with the hydraulic classification equipment in the closed circuit system.
I went thru the same problem of ball mill scats over production last week. I need to ask you, is the 10mm something you saw yourself or something you were told it was? This is important as if you have not seen if yourself, you can not trust it is really 10mm. There should be no scats at 10 mm unless you are using much too small a grinding ball or the mill charge is much too low.
For example, I was told by a client his ball mill feed was P80 = 9mm but when I went to look at the feed belt, I saw this below. The conveyor belt is 15 mm thick, therefore the rocks on it are more like 20-30mm.
The last stages of vibrating screening is 12 mm D80=de to 10 mm measured by exploitation team The ball mill size added: 2/3 is of 100mm and 75 mm 1/3 Actually the initial work index changed and we tried to calculate the operational work index according to a follow-up of the parameters below but I dont have any conclusionsaccording to this follow-up for an absorbed power and for the same tonnage I find a scats production is different (the feed ore coming the same area)
Hi think your ball mill trommel has its holes too small. What you are discharging is small and smaller than fresh feed. It should/would go to the cyclone feed pump if your holes were larger. Also, reviewing the conversation above; you should eliminate that 100 mm ball and increase your mill's power-draw.
Furthermore, your 100 mm ball needs to be eliminated. By using a 75 mm ball instead of 100 mm you will effectively 2X the number of balls you load. Well if you are at 50/50 100 and 75, you will double on 50% therefore a net of 33% in "good hammers". This change should not go unnoticed.
I think that to increase the aperture to 15 mm knowing that the ore feeding d100 = 10 mm all the scats is going not to outside of trammel but its going to pass towards the pump and the hydro cyclone, the pump of and hydrocyclone lining will be destroyed, hydro cyclone Under flow will be blocked and we are going to find afterward these scat in the flotation cells
I would suggest that you firstly study your feed PSDvs ball charge size distribution before opting for the alternative. Plus I'm not sure if a grate discharge will give you the same grind as the overflow could give you.
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Ore ball mill sometimes called ore grinding mill, is generally used in mineral processing concentrator, processing materials include iron ore, copper ore, gold ore, molybdenum ore and all kinds of nonferrous metal ore. The core function of the ore ball mill is to grind the materials, and also to separate and screen different mineral materials, and to separate the tailings, which is very important to improve the quality of the selected mineral materials.
The ore ball mill designed by our company, which is represented by gold ore ball mill and iron ore ball mill, is manufactured with high-quality materials and advanced technology. They have the characteristics of high efficiency, energy-saving, green environmental protection, simple operation, stable operation, and low failure rate, and have a good reputation in the industry.
The crushing ratio of the ore grinding mill is very large, and it is easy to adjust the fineness of the grinding product. The ore grinding mill has strong sealing performance and can be operated under negative pressure. It is widely used in chemical industry, metallurgy, new building materials and other fields.
We offer different types of ore ball mills for customers to choose from. There are energy-saving ore ball mill, dry and wet ball mill,wet grate ball mill, andwet overflow ball mill. Customers can choose to purchase according to material conditions.
Mineral processing is the most important link in the entire production process of mineral products. It is a process of separating useful minerals from useless minerals (usually called gangue) or harmful minerals in a mineral raw material by physical or chemical methods, or a process of separating multiple useful minerals The process is called mineral processing, also known as ore processing.
The first step in the ore processing is to select the useful minerals. In order to select useful minerals from ore, the ore must be crushed first. Sometimes, in order to meet the requirements of subsequent operations on the particle size of materials, it is necessary to add a certain ore grinding operation in the process.
The preparation before beneficiation is usually carried out in two stages: crushing screening operation and mineral classification operation. Crusher and ore ball mill are the main equipment in these two stages.
As a ball mills supplier with 22 years of experience in the grinding industry, we can provide customers with types of ball mill, vertical mill, rod mill and AG/SAG mill for grinding in a variety of industries and materials.
The ball mill is a tumbling mill that uses steel balls as grinding media. Ball mills can be used in wet or dry systems for bulk and continuous milling, and are most widely used in small or large-scale beneficiation plant.The feed can be dry with a water content of less than 3% to minimize the coverage of the ball, or it can be a slurry with a water content of 20-40%. The ball mill can be used for primary or secondary grinding applications. In the primary application, they receive feed from the crusher, and in the secondary application, they receive feed from the rod mill, autogenous mill or semi-autogenous mill.
Main partsThe mill includes motor, reducer, slow drive, power distribution control cabinet, feeding device, main bearing, rotary part, discharging device, transmission part, lubrication system (mainly including high-pressure pump station and low-pressure thin oil station) and other parts.The main working part of the ball mill is a rotary cylinder mounted on two large bearings and placed horizontally. The cylinder body is divided into several compartments by a partition plate, and a certain shape and size of grinding body is installed in each compartment. The grinding bodies are generally steel balls, steel forgings, steel rods, pebbles, gravel and porcelain balls. In order to prevent the barrel from being worn, a liner is installed on the wall of the barrel. The length of a cylindrical shell is usually 11.5 times the diameter of the shell.The grinding elements including grinding media and material in the ball mill move at different speeds. Therefore, the collision force, direction and kinetic energy between two or more elements vary greatly in the ball charge. Friction and wear or friction and collision energy all act on the particles. These forces come from the rotating motion of the ball and the particle motion in the mill and the contact area of the collision ball.
High chromium cast ballHigh chromium cast ball is an alloy white cast iron ball with high chromium content (more than 10% Cr), which is wear-resistant, heat-resistant and corrosion-resistant, and has considerable toughness. The martensitic matrix high-chromium cast iron ball surface hardness HRC can reach 58-66. The wear resistance of high chromium cast iron balls is 8 to 12 times that of ordinary carbon steel ballsLiner plateThe cylinder is lined with high-manganese steel lining and multi-element alloy wear-resistant lining, which has good impact resistance and wear resistance.
Wide applicability and high capacity Maintain a certain capacity for a long time to achieve the durability of the specified grinding fineness (add balls regularly to compensate for its wear)Reliability and safety, easy maintenance.The machine runs smoothly and works reliably. The internal structure can be adjusted according to customer requirements.Suitable for batch grinding, continuous grinding, open circuit grinding and closed circuit grinding, suitable for all kinds of hardness materials.
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Mining thickener is mainly used for dewatering the wet concentrate during the ore dressing process. Our thickener is mostly located between cleaning beneficiation process and filtration equipment. Thickener is applied to both the concentrate and tailings to recover water. The thickener could be used to recover immediately reusable water back to mineral processing plant, as 
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Fine grinding, to P80 sizes as low as 7m, is becoming increasingly important as mines treat ores with smaller liberation sizes. This grinding is typically done using stirred mills such as the Isamill or Stirred Media Detritor. While fine grinding consumes less energy than primary grinding, it can still account for a substantial part of a mills energy budget. Overall energy use and media use are strongly related to stress intensity, as well as to media size and quality. Optimization of grinding media size and quality, as well as of other operational factors, can reduce energy use by a factor of two or more. The stirred mills used to perform fine grinding have additional process benefits, such as polishing the mineral surface, which can enhance recovery.
Fine grinding is becoming an increasingly common unit operation in mineral processing. While fine grinding can liberate ores that would otherwise be considered untreatable, it can entail high costs in terms of energy consumption and media use. These costs can be minimized by performing adequate test work and selecting appropriate operating conditions. This paper reviews fine grinding technology, research, and plant experience and seeks to shed light on ways in which operators can reduce both operating costs and the environmental footprint of their fine grinding circuit.
This paper will begin by giving an overview of fine grinding and the equipment used. It will then discuss energyproduct size relationships and modeling efforts for stirred mills in particular. The paper will go on to cover typical test work requirements, the effect of media size, and the contained energy in media. In closing, specific case studies will be reviewed.
Grinding activities in general (including coarse, intermediate, and fine grinding) account for 0.5pct of U.S. primary energy use, 3.8pct of total U.S. electricity consumption, and 40pct of total U.S. mining industry energy use. Large energy saving opportunities have been identified in grinding in particular.
TableI shows a very large disparity between the theoretical minimum energy used in grinding and the actual energy used. More interestingly, a fairly large difference remains even between Best Practice grinding energy use and current energy use. This suggests that large savings in grinding energy (and associated savings in maintenance, consumables, and capital equipment needed) could be obtained by improving grinding operations.
As fine grinding is typically used on regrind applications, the feed tonnages to fine grinding circuits are small compared to head tonnages, typically 10 to 30tph. However, the specific energies are often much larger than those encountered in intermediate milling and can be as high as 60kWh/t. Total installed power in a fine grinding circuit can range from several hundred kW to several MW; for example, the largest installed Isamill has 3MW installed power. This quantity is small compared to the power used by a semi-autogenous mill and a ball mill in a primary grinding circuit; a ball mill can have an installed power of up to 15MW, while installed power for a SAG mill can go up to 25MW. However, the energy used for fine grinding is still significant. Moreover, as this paper seeks to demonstrate, large energy reduction opportunities are frequently found in fine grinding.
Grinding can be classified into coarse, intermediate, and fine grinding processes. These differ in the equipment used, the product sizes attained, and the comminution mechanisms used. The boundaries between these size classes must always be drawn somewhat arbitrarily; for this paper, the boundaries are as given in TableII. As shown in the table, coarse grinding typically corresponds to using an AG or SAG mill, intermediate grinding to a ball mill or tower mill, and fine grinding to a stirred mill such as an Isamill or Stirred Media Detritor (SMD). Of course, various exceptions to these typical values can be found.
In fine grinding, a material with an F80 of less than 100m is comminuted to a P80 of 7 to 30m. (P80s of 2m are at least claimed by equipment manufacturers.) The feed is typically a flotation concentrate, which is reground to liberate fine particles of the value mineral.
The three modes of particle breakage are impact; abrasion, in which two particles shear against each other; and attrition, in which a small particle is sheared between two larger particles or media moving at different velocities. In fine grinding, breakage is dominated by attrition alone. In stirred mills, this is accomplished by creating a gradient in the angular velocity of the grinding media along the mills radius.
Fine grinding is usually performed in high-intensity stirred mills; several manufacturers of these stirred mills exist. Two frequently used stirred mills include the Isamill, produced by Xstrata Technology, and the SMD, produced by Metso (Figure1). A third mill, the KnelsonDeswik mill (now the FLS stirred mill), is a relative newcomer to the stirred milling scene, having been developed through the 1990s and the early 2000s. In all these mills, a bed of ceramic or sand is stirred at high speed. Ceramic media sizes in use range from 1 to 6.5mm.
The Isamill and the SMD have very similar grinding performance. Grinding the same feed using the same media, Nesset et al. found that the Isamill and SMD had very similar specific energy use. Gao et al. observed that an Isamill and SMD, grinding the same feed with the same media, produced very similar product particle size distributions (PSDs). This similarity in performance has also been observed in other operations.
Nevertheless, there are important differences. In the Isamill, the shaft is horizontal and the media are stirred by disks, while in the SMD, the stirring is performed by pins mounted on a vertical shaft. In an SMD, the product is separated from the media by a screen; the Isamill uses an internal centrifugation system. This means that the screens in an SMD constitute a wear part that must be replaced, while for the Isamill, the seals between the shaft and body constitute important wear parts. Liner changes and other maintenance are claimed by Xstrata Technology to be much easier than in an SMD: While an SMDs liner is removed in eight parts, the Isamills liner can be removed in two pieces, with the shell sliding off easily. The KnelsonDeswik mill is top stirred and can therefore be considered to be similar to an SMD.
An important difference among the Isamill, the SMD, and the KnelsonDeswik mill is that of scale. The largest Isamill installed at time of writing had 3MW of installed power; an 8MW Isamill is available, but appears not to have yet been installed. The largest SMD available has 1.1MW of installed power; one 1.1-MW SMD has been installed. The next largest size SMD has 355kW of installed power. Thus, several SMDs are often installed for a fine grinding circuit, while the same duty would be performed by a single Isamill. SMDs are typically arranged in series, with the product of one becoming the feed for the other. This has the advantage that each SMD in the line can have its media and operating conditions optimized to the particle size of its particular feed. The largest installed power in a KnelsonDeswik mill is 699kW; this places it in an intermediate position between the 355-kW and 1.1-MW SMDs.
In 2012, FLSmidth reported that it had acquired the KnelsonDeswik mill; the mill is now known as the FLSmidth stirred mill. An FLSmidth stirred mill will be installed to perform a copper concentrate regrind in Mongolia. It is speculated that the mill will continue to be scaled up under its new owners to allow it to effectively compete against the SMD and Isamill.
Gravity-induced stirred (GIS) mills include the Tower mill, produced by Nippon Eirich, and the Vertimill, produced by Metso. Grinding to below 40m in GIS mills or ball mills is usually not recommended. In their product literature, Metso give 40m as the lower end of the optimal P80 range for Vertimills. At lower product sizes, both tower mills and ball mills will overgrind fines. At Mt. Isa Mines, a GIS mill fed with material of F80 approximately 50m lowered the P80 size by only 5 to 10m, at the same time producing a large amount of fines. Similarly, in ball mills, it is known that grinding finer than approximately 40m will result in overgrinding of fines as well as high media consumption. However, it must be noted that the product size to which a mill can efficiently grind depends on the feed material, the F80, and media type and size. A Vertimill has been used to grind to sizes below 10m.
The phenomenon of overgrinding is largely the result of using media that are too large for the product size generated. The smallest ball size typically charged into ball mills and tower mills is inch (12.5mm), although media diameters as small as 6mm have been used industrially in Vertimills.
In a laboratory study by Nesset et al., a GIS mill charged with 5-mm steel shot, and with other operating conditions similarly optimized, achieved high energy efficiencies when grinding to less than 20m. This appears to qualitatively confirm the notion that fine grinding requires smaller media sizes. In the case of the Nesset study, the power intensity applied to the laboratory tower mill was lowthat is, the shaft was rotated slowly in order to obtain this high efficiency, leading to low throughput. This suggests that charging GIS mills with small media may not be practicable in plant operation.
Millpebs have been used as grinding media to achieve fine grinding in ball mills. These are 5- to 12-mm spherical or oblong cast steel pellets, charged into ball mills as a replacement of, or in addition to, balls. While Millpebs can give significantly lower energy use when grinding to finer sizes, they also can lead to high fines production and high media use.
Millpebs were tested for fine grinding at the Brunswick concentrator. The regrind ball mills at the concentrator used 25-mm slugs to produce a P80 of 28m. In one of the regrind mills, the slugs were replaced by Millpebs; these were able to consistently maintain a P80 of 22m while decreasing the power draw by 20pct. However, media use increased by 50pct and the production of fines of less than 16m diameter increased by a factor of 5. The observed drop in specific energy may be due to the fact that Millpebs had smaller average diameters than the slugs and so were more efficient at grinding to the relatively small product sizes required. It is therefore unclear whether the performance of Millpebs would be better than that of conventional 12-mm steel balls. To the best of the authors knowledge, no performance comparison between Millpebs and similarly sized balls has been performed.
A host of other technologies exist to produce fine grinding, including jet mills, vibrating mills, roller mills, etc. However, none of these technologies has reached the same unit installed power as stirred mills. For example, one of the largest vibrating mills has an installed power of 160kW. Therefore, these mills are considered as filling niche roles and are not treated further in this review. A fuller discussion of other fine grinding technologies can be found in a review by Orumwense and Forssberg.
Neese et al. subjected 50- to 150-m sand contaminated with oil to cleaning in a stirred mill in the laboratory. The mill operated at low stress intensities: A low speed and small-size media (200- to 400-m quartz or steel beads) were used. These conditions allowed the particles to be attrited without being broken. As a result, a large part of the oil contaminants was moved to the 5-m portion of the product. This treatment may hold promise as an alternative means of processing bituminous sands, for example, in northern Alberta.
The Albion process uses ultrafine grinding to enhance the oxidation of sulfide concentrates in treating refractory gold ores. In the process, the flotation concentrate is ground to a P80 of 10 to 12m. The product slurry is reacted with oxygen in a leach tank at atmospheric pressure; limestone is added to maintain the pH at 5 to 5.5. The leach reaction is autothermal and is maintained near the slurry boiling point. Without the fine grinding step, an autoclave would be required for the oxygen leaching process. It is hypothesized that the fine grinding enhances leach kinetics by increasing the surface area of the particles, as well as by deforming the crystal lattices of the particles.
Numerous researchers, for example, Buys et al., report that stirred milling increases downstream flotation recoveries by cleaning the surface of the particles. The grinding media used in stirred mills are inert, and therefore corrosion reactions, which occur with steel media in ball mills, are not encountered. Corrosion reactions change the surface chemistry of particles, especially with sulfide feeds, and hamper downstream flotation.
Further increases in flotation recoveries are obtained by limiting the amount of ultrafine particles formed; stirred mills can selectively grind the larger particles in the feed with little increase in ultrafines production. Ultrafine particles are difficult to recover in flotation.
In intermediate grinding to approximately 75m, the Bond equation (Eq. ) is used to relate feed size, product size, and mechanical energy applied. Below 75m, correction factors can be applied to extend its range of validity.
No general work index formula governing energy use over a range of conditions, like the Bond equation for intermediate grinding, has yet been found for the fine grinding regime. Instead, the work-to-P80 curve is determined in the laboratory for each case. The energy use usually fits an equation of the form
Signature plot (specific energy vs P80 curve) for Brunswick concentrator Zn circuit ball mill cyclone underflow; F80=63m. The plots give results for grinding the same feed using different mills and media. After Nesset et al.
Values for the exponent k have been found in the range 0.7 to 3.5, meaning that the work to grind increases more rapidly as grind size decreases than in intermediate grinding. The specific energy vs product size curve has a much steeper slope in this region than in intermediate grinding.
The values of k and A are specific to the grinding conditions used in the laboratory tests. Changes in feed size, media size distribution, and in other properties such as media sphericity and hardness can change both k and A, often by very large amounts. Media size and F80 appear to be the most important determinants of the signature plot equation.
The connections (if any) between k and A and various operating conditions remain unknown. Because of the relatively recent advent of stirred milling in mineral processing, fine grinding has not been studied to the same extent as grinding in ball mills (which of course entail much larger capital and energy expenditures in any case). One of the research priorities in the field of stirred milling should be the investigation of the effects of F80 and media size on the position of the signature plots. If analogous formulas to the Bond ball mill work formula and the Bond top ball size formula can be found, the amount of test work required for stirred milling would be greatly reduced.
Larson et al. found that when specific energy is plotted against the square of the percent particles in the product passing a given size (a proxy for particle surface area), a straight line is obtained. This is demonstrated in Figure3.
In contrast to the conventional signature plot, this function gives zero energy at the mill feed. It is therefore hypothesized that if a squared function plot is obtained by test work for one feed particle size, the plot for another feed particle size can be obtained simply by changing the intercept of the line while keeping the slope the same. Therefore, the squared function plot allows the effect of changes in both F80 and P80 to be modeled.
While the Squared Function Plot is intriguing, experimental validation of its applicability has not yet been published. It nevertheless remains an interesting topic for further investigation and if validated may be used in the future as an alternative measure of specific energy.
A similar analysis has been performed by Musa and Morrison, who developed a model to determine the surface area within each size fraction of mill product. They defined a marker size below which 70 to 80pct of the product surface area was contained; the marker size thus served as a proxy for surface area production. Specific energy use was then defined as kWh of power per the tonne of new material generated below the marker size. Musa and Morrison found that by defining specific energy in this way, it was possible to accurately predict the performance of full-scale Vertimills and Isamills from laboratory tests.
Blecher and coworkers[22,23] found that stress intensity combines the most important variables determining milling performance. Stress intensity for a horizontal stirred mill, with media much harder than the mineral to be ground, is defined as in Eq. .
Note that the stress intensity is strongly sensitive to changes in media diameter (to the third power), is less sensitive to stirrer tip speed (to the second power), and is relatively insensitive to media and slurry density.
For vertical stirred mills such as the SMD and tower mill, both SIs and SIg are non-zero. For horizontal stirred mills such as the Isamill, net gravitational SI is zero due to symmetry along the horizontal axis. Therefore, for horizontal stirred mills, only SIs need be taken into consideration.
Kwade and coworkers noted that, at a given specific energy input, the product P80 obtainable varies with stress intensity and passes through a minimum. Product size at a given energy input can be viewed as a measure of milling efficiency; therefore, milling efficiency reaches a maximum at a single given stress intensity. This idea was experimentally validated by Jankovic and Valery (Figure 4).
The stress intensity is defined by parameters that are independent of mill size or type. According to Jankovic and Valery, once the optimum SI has been determined in one mill for a given feed, the same SI should also be the point of optimum efficiency in any other mill treating that feed. Therefore, the optimum SI need only be determined in one mill (e.g., a small test mill); the operating parameters of a full-scale mill need only be adjusted to produce the optimum SI.
Stress frequency multiplied by stress intensity is equal to mill power; therefore, stress intensity could in theory be used to predict mill specific energy. However, to the authors knowledge, a comprehensive model linking stress intensity, stress frequency, and specific energy has not yet been developed. Therefore, there is not yet any direct link between stress intensity and specific energy.
The definition of SIs as given in Eq.  is valid only for cases where the grinding media are much harder than that of the material ground (for example, the grinding of limestone with glass beads). Becker and Schwedes determined that, in a collision between media and a mineral particle, the fraction of energy transferred to the product is given by Eq. :
To maintain high efficiency in milling, the media must be chosen so as to be much harder (higher Youngs modulus) than the product material, keeping E p,rel close to unity. Where the Youngs modulus of the product is similar to that of the media, much of the applied energy goes into deformation of the media instead of that of the particle to be ground. The energy used to deform the media is lost, lowering the amount of energy transferred to the product. This fact explains why steel media, with a relatively low Youngs modulus, tend to perform poorly in stirred milling, even though the media are much more dense than silica or alumina media.
The previous sections indicated that stress intensity is independent from individual millsi.e., the optimal stress intensity when using Mill A will also be the optimal stress intensity when using Mill B. However, this does not seem to be the case when actually scaling up mills.
Four-liter Isamills are commonly used for grindability test work. It can be assumed that operating parameters of the test mill (including media type, media size, and slurry density) are adjusted so far as possible to give the optimum SI. These parameters are then used in the full-scale mill as well. However, the 4-L test mills have a tip speed of approximately 8m/s, while full-scale Isamills have tip speeds close to 20m/s. If the same media size, media density, and slurry density are used in the test mill as in the full-scale mill, the stress intensity of the full-scale mill will be approximately 6.25 times larger than that of the test mill. This implies that the full-scale mill is operating outside of the optimum SI and will be grinding less efficiently. That is to say that the operating point of the full-scale mill will be above the signature plot determined by test work.
In reality, however, the operating points of full-scale stirred mills are generally found to lie on the signature plots generated in test work. Therefore, the full-scale mills and test mills have the same milling efficiency, even though the full-scale mill operates at a different stress intensity than the test mill.
This question remains unresolved. One possible answer arises from the observation that two of the P80 vs SI curves in Figure4 appear to have broad troughs, covering almost an order of magnitude change in SI. In this case, even a sixfold increase in SI might not create a noticeable difference in performance, considering experimental and measurement error.
Product size vs stress intensity at three different specific energies for a zinc regrind. Note optimum stress intensity at which the lowest product size is reached. Figure used with permission from Jankovic and Valery
The SMD test unit appears from photographs to have a bed depth of around 30cm, while the full-scale SMD355 has a bed depth of approximately one meter. This represents a change in the gravitational stress intensity of almost two orders of magnitude. As has been previously noted, however, laboratory and full-scale SMDs scale-up with a scale-up factor of approximately unity, with no apparent change in the optimum stress intensity. This observation suggests that the gravitational stress intensity, SIg, is unimportant in SMDs compared to the stirring stress intensity, SIs. By contrast, in GIS mills, where full-size units have bed depths of ten meters or more, gravitational stress intensity can be expected to be much more important in full-size units than in test units, adding a complicating factor to GIS mill scale-up.
Factorial design experiments were performed by Gao et al. and Tuzun and Loveday to determine the effect of various operating parameters on the power use of laboratory mills. Power models were determined giving the impact of different parameters as power equations with linear and nonlinear terms. The derived models did not appear to be applicable to mills other than the particular laboratory units being studied.
In ball milling, the Bond ball mill work index can be used to determine specific energy at a range of feed and product sizes. The Bond top size ball formula can be used to estimate the media size required. No such standard formulas exist in fine grinding. Energy and media parameters must instead be determined in the laboratory for every new combination of operating conditions such as feed size, media size, and media type.
For the Isamill, test work is usually performed with a 4-L bench-scale Isamill. Approximately 15kg of the material to be ground is slurried to 20pct solid density by volume. The slurry is then fed through the mill and mill power is measured. The products PSD is measured, additional water is added if needed, and the material is sent through the mill again. This continues until the target P80 is reached; typically, there will be 5 to 10 passes through the mill. The test work will produce a signature plot and media consumption data as the deliverables.
In contrast to laboratory-scale testing for ball mills and AG/SAG mills, test work results for stirred mills can be used for sizing full-size equipment with a scale-up factor close to one. Larson et al.[19,20] found a scale-up factor for the Isamill of exactly 1, while Gao et al. imply that the scale-up factor for SMDs is 1.25.
A common error in test work is using monosize media (e.g., fresh 2-mm media loaded into in the mill) as opposed to aged media with a distribution of particle sizes. The aged media will grind the smaller feed particles more efficiently. Therefore, using fresh media will give a higher specific energy than in reality.
Another pitfall is coarse holdup in the mill. If the mill is not sufficiently flushed, coarse particles will be kept inside the mill. The mill product then appears finer than it in reality is. This leads to lower estimates of specific energy than reality.
In ball milling, the product particle size distribution (PSD) can usually be modeled as being parallel to the feed PSD on a log-linear plot. When grinding to finer sizes in ball mills, the parallel PSDs mean that large amounts of ultrafine particles are produced. This consumes a large amount of grinding energy while producing particles which are difficult to recover in subsequent processing steps such as flotation.
As shown in the figure, at the left end of the graph, the product PSD is very close to the feed PSD; at the right, the two PSDs are widely spaced. This indicates that the mill is efficiently using its energy to break the top size particles and is spending very little energy on further grinding of fine particles. Thus, the overall energy efficiency of the fine grinding can be expected to be good. As a bonus, the tighter PSD makes control of downstream processes such as flotation easier.
In an experimental study, Jankovic and Sinclair subjected calcite and silica to fine grinding in a laboratory pin stirred mill, a Sala agitated mill (SAM), and a pilot tower mill. The authors found that for each mill, the PSD of the product was narrower (steeper) than that of the feed. In addition, when grinding to P80s below approximately 20m in any of the three mills tested, the PSD became more narrow (as measured by P80/P20 ratio) as the P80 decreased. (When the width of the PSD was calculated using an alternative formula, the PSD was only observed to narrow with decreasing P80 when using the pin stirred mill.) The authors concluded that the width of the PSD was strongly affected by the material properties of the feed, while not being significantly affected by the media size used.
In stirred milling, the most commonly used media are ceramic balls of 1 to 5mm diameter. The ceramic is usually composed of alumina, an alumina/zirconia blend, or zirconium silicate. Ceramic media exist over a wide range of quality and cost, with the lower quality/cost ceramic having a higher wear rate than higher quality/cost ceramic. Other operations have used sand as media, but at the time of writing, only two operations continue to use sand.[8,27,33] Mt Isa Mines has used lead smelter slag as media; however, it is now using sand media.[10,27] Mt Isa is an exception in its use of slag, as a vast majority of operations do not have a smelter on-site to provide a limitless supply of free grinding media. However, in locations where slag is available, it should be considered as another source of media.
Media use in fine grinding is considered to be proportional to the mechanical energy applied. Typical wear rates and costs are given in TableIII and Figure6; these figures can of course vary significantly from operation to operation.
Contained energy refers to the energy required to produce and transport the media, and is distinct from the mechanical (electrical) energy used to drive the mill. Hammond and Jones estimated the contained energy in household ceramics (not taking account of transportation). Hammond and Jones estimates range from 2.5 to 29.1MJ/kg, with 10MJ/kg for general ceramics and 29MJ/kg for sanitary ceramics. Given that ceramic grinding media require very good hardness and strength, especially compared to household ceramics, it is appropriate to estimate its contained energy at the top end of Hammond and Jones range, at 29MJ/kg.
Using 29MJ/kg for the contained energy of ceramic media and a wear rate of 35g/kWh of mechanical energy gives a contained energy consumption of 0.28kWh contained per kWh of mechanical energy applied. A wear rate of 7g/kWh gives a contained energy consumption of 0.06kWh contained per kWh of mechanical energy applied. Therefore, 6 to 20pct of the energy use in fine grinding using ceramic media can be represented by contained energy in the grinding media itself.
Sand media have much lower contained energy than ceramic media as the media must simply be mined or quarried rather than manufactured. Hammond and Jones report a contained energy of 0.1MJ/kg. Blake et al. reported that switching a stirred mills media from sand to ceramic results in a mechanical energy savings of 20pct. Therefore, using sand rather than ceramic media would produce savings in contained energy, but would cost more in mechanical energy. Likewise, Davey suggests that poor-quality media will increase mechanical energy use in stirred milling. It is speculated that this is due to the lower sphericity of sand media. On the other hand, the work of Nesset et al. suggests that the energy use between ceramic and sand media of the same size is the same. Slag media, where a smelter is on-site, would probably have the lowest contained energy consumption of the different media types. There is very little transportation, and for accounting purposes, almost no energy has gone into creating the media as the granulated slag is a by-product of smelter operation.
Becker and Schwedes point out that with poor-quality media, a significant part of the product will consist of broken pieces of media, which will affect the measured product PSD. Clearly, more information on the relationships between contained energy in media and media wear rates is desirable.
Of the different operating parameters for stirred mills, media size probably has the biggest influence on overall energy consumption. The appropriate media size for a mill appears to be a function of the F80 and P80 required. The grinding media must be large enough to break up the largest particles fed to the mill and small enough to grind the material to the product fineness desired. As demonstrated by the experience of Century mine, an inappropriate media size choice can result in energy consumption double that of optimum operation.
In their laboratory study, Nesset et al. varied a number of operating parameters for stirred mills and identified media size as having the largest impact on energy use. It was also noted that the trials which produced the sharpest product PSD were also the ones which resulted in the lowest specific energy use.
Gao et al. report that at Century mine, the grinding media in SMDs performing regrind duty were changed from 1 to 3mm. This resulted in a drop in energy use of approximately 50pct; the signature plot shifted significantly downward (Figure7).
Figure8 shows the product PSD for laboratory SMD tests using 1- and 3-mm media. The PSD for the test using 1-mm media shows that the SMD produced a significant amount of fines (20pct below 4m). The mill also had difficulty breaking the top size particlesthe 100pct passing size appears to be almost the same for both the feed and the product. In contrast, the PSD using 3-mm media shows less fines production (20pct below 9m) and effective top size breakage, with all the particles above 90m broken. This is in line with the observation of Nesset et al. that low energy use is associated with tight product size distributions.
Gao et al. tested copper reverberatory furnace slag (CRFS, SG 3.8) and heavy media plant rejects (HMPR, SG 2.4) in a laboratory stirred mill at two sizes: 0.8/+0.3mm, and 1.7/+0.4mm. For both CRFS and HMPR, the smaller size media gave a lower specific energy than the larger size media. At the same size, both CRFS and HMPR had similar specific energy use. However, the CRFS ground the material much faster than HMPR. Possibly, this was due to its higher density.
Data on F80, P80, and media size were compiled from the literature in order to allow benchmarking against existing operations. The sources are listed in Table IV. F80 and P80 were plotted against media size; the results are given in Figure9.
F80 plotted against media size (blue diamonds); P80 plotted against media size (red crosses). Century UFG=Century ultrafine grind; Century Regr.=Century regrind. Data are taken from Case studies table (Color figure online)
It can be seen from the figure that as the P80 achieved decreases, the media size does as well, from 3mm to achieve 45m to 1mm to achieve under 10m. The F80 decreases with media size in a similar way, from 90m at 3mm to 45m at 1mm. Dotted lines have been added to Figure7 to define the region of operation of mills; these delimit a zone in which the stirred mill can be expected to operate efficiently.
In general, for a particular media size, limits on both F80 and P80 must be respected. For example, the figure suggests that a mill operating with an F80 of 100m should use 3-mm media, while a mill grinding to below 10m would need to use 1-mm media. To reduce a feed of 90m F80 to 10m P80, Figure9 suggests that comminution be done in two stages (two Isamills or SMDs in series) for optimal efficiency. The first stage would grind the feed from 90m to perhaps 45m using 3-mm media, while the second would grind from 45 to 10m using 1- or 2-mm media.
A number of opportunities exist to reduce the energy footprint of fine grinding mills. There are no general formulas, such as the Bond work formula and Bond top size ball formula in ball milling, to describe the performance of stirred mills. Therefore, improvement opportunities must be quantified by performing appropriate test work.
In addition to obtaining the signature plot, the specific energy as a function of new surface area should be determined during test work. This could be done either by the method of Larsen or by that of Musa and Morrison. Defining specific energy as a function of new surface area may constitute a superior means of predicting the performance of full-scale mills, as opposed to defining specific energy as a function of feed tonnage.
Media size should be chosen with care. It is recommended that test work be done with several media sizes in order to locate the stress intensity optimum. Media size can be benchmarked against other operations using Figure9.
There are indications that lower-quality media, apart from degrading faster, require more mechanical energy for grinding due to factors such as lower sphericity. It is recommended to perform test work using media of different quality to determine the effect of media quality on energy use. Slag and sand media may also be considered. Subsequently, a trade-off study involving media cost, electricity cost, improvement in energy efficiency, and contained energy in media should be performed to identify the best media from an economic and energy footprint standpoint.
D. Rahal, D. Erasmus, and K. Major: KnelsonDeswick Milling Technology: Bridging the Gap Between Low and High Speed Stirred Mills, Paper presented at the 43rd Canadian Mineral Processors Meeting, Ottawa, 2011.
Metso: Stirred milling: Vertimill grinding mills and Stirred Media Detritor (product brochure), 2013, available at http://www.metso.com/miningandconstruction/MaTobox7.nsf/DocsByID/F58680427E2A748F852576C4005210AC/$File/Stirred_Mills_Brochure-2011_LR.pdf, accessed April 21, 2013.
J. Nesset, P. Radziszewski, C. Hardie, and D. Leroux: Assessing the Performance and Efficiency of Fine Grinding Technologies, Paper presented at the 38th Canadian Mineral Processors Meeting, Ottawa, 2006.
FLSmidth: Acquisition enhances our precious metals offerings, 2012, FLSmidth eHighlights April 2012, available at http://www.flsmidth.com/en-US/eHighlights/Archive/Minerals/2012/April/Acquisition+enhances+our+precious+metals+offerings, accessed 17 April 2013.
S. Buys, C. Rule, and D. Curry: The Application of Large Scale Stirred Milling to the Retreatment of Merensky Platinum Tailings, Paper presented at the 37th Canadian Mineral Processors Meeting, Ottawa, 2005.
D. Curry, M. Cooper, J. Rubenstein, T. Shouldice, and M. Young: The Right Tools in the Right Place: How Xstrata Nickel Australasia Increased Ni Throughput at Its Cosmos Plant, Paper presented at the 42nd Canadian Mineral Processors conference, Ottawa, 2010.
G. Davey: Fine Grinding Applications Using the Metso Vertimill Grinding Mill and the Metso Stirred Media Detritor (SMD) in Gold Processing, Paper presented at the 38th Canadian Mineral Processors Meeting, Ottawa, 2006.
Because the method used to grind the fine material in the beneficiation equipment was an early mine mill, and later developed into a ball mill. Nowadays, there is a finer with a larger output, and the speed of replacement is very fast. Some people in the industry say that the ball mill will soon be replaced by the fine crusher, just like it replaced the ore mill. We believe that at least, in the next ten years, the ball mill will not disappear, and the fine crusher will not be the only one. , Then lets analyze the advantages and disadvantages of using a ball mill:
1.The output of ball mill is much larger than that of mineral mill. Although it is smaller than fine crusher, it is a moderate product. A production line group requires suitable machines. The current production efficiency ball mill is fully capable, and the fast work of the fine crusher causes other supporting machines to fail to keep up. So this is also an important reason for its failure to enter the market in large quantities. the reason.
2.The ball mill is a slow machine with low power consumption. After more than ten years of development, the technology has become quite mature. This is an important point. Many manufacturers use this equipment, rest assured.
3.The ball mill has been developed for so many years, and there are fixed maintenance points in many places. If the machine has a problem, it can be solved quickly. But the fine crusher is much worse. There is a small problem, and not many people know it, which causes the maintenance delay.
1.The machine is cumbersome. Think about a machine with a diameter of more than ten meters. It is two or three meters in diameter. It takes a lot of effort to move the house. The fine crusher belongs to the crusher equipment. A small trailer can solve it. For some Manufacturers who do not have fixed production will mostly choose the latter.
3.The requirements for factory buildings are relatively high. Generally, ball mills cannot be used on the land, because the foundation is not up to standard, and the machine will sink into the ground during production.
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