The ball mill is a kind of grinding machine, which is the key milling machine used after the material has been crushed, and it also has a mixing effect. This type of grinding machine has a cylindrical body with spherical grinding mediums and materials.
The centrifugal force and friction generated by the rotation of the fuselage bring the material and the grinding medium to a certain height and then fall. Impact and friction grind the material into fine powders.
It is widely used in cement, silicate, new construction material, refractory material, chemical fertilizer, ferrous metal and non-ferrous as well as ceramics, and widely applied to dry or wet grinding for ores and grindable materials. The wet type is often equipped with a classifier, and the dry type is configured with a suction and separation device.
Both of the dry and wet ball mills are composed of feeding port, discharging port, turning part, and transmission parts such as retarder, small transmission gear, motor, electronic control. The wet grinding can be widely used, because most of the minerals can be wet milled.
The ball mill is equipped with a cylindrical rotating device and two bins, which can rotate by gears. The discharge port is straight, and there are also air intake devices, dust exhaust pipes, and dust collectors.
The material from the feeding device is uniformly fed into the first bin of the mill by the hollow shaft spiral. This bin has stepped lining or corrugated lining, which is filled with steel balls of different specifications.
The rotation of the cylinder generates centrifugal force to bring the steel ball to a certain height, and then fall, which will hit and grind the material. After the material is coarse grinding in the first bin, it will enter the second bin through the single-layer partition plate.
This bin is embedded with a flat liner, and the steel balls inside will further grind the material, then the powder is discharged through the discharge grate to complete the grinding. We can't add water or other liquids during the grinding process.
The material needs to be added water or anhydrous ethanol during the grinding process. We must control the grinding concentration, otherwise, it will affect the grinding efficiency. The amount of water depends on the use of the mud, the amount of clay in the formula, and the water absorption of the clay.
It will be gradually pulverized under the action of impact and grinding. The movement of the ore needs to be driven by the water. The bulk material will be cracked under the impact and grinding of the grinding medium, with the crack gradually increasing and deepening, the final material will be separated from the crack to achieve the effect of bulk material being ground.
The grinding ore will be discharge through the discharge port, and then the discharged mineral will be classified into the qualified product in a spiral classifier, with the coarse sand being returned to the ball mill through the combined feeder to continue grinding.
The feeder feeds material continuously and evenly, the ground material will be continuously discharged from the ball mill. The wet ball mill can be divided into three types according to the motion characteristics: a simple swing type wet ball mill, a complex swing type wet ball mill, and a hybrid swing type wet ball mill.
The dry grinding is suitable for materials that can react with water, which may not be used for wet grinding such as cement, marble and other building materials. Some products which require storage and sale in powder form is suitable for dry grinding, and in some other arid areas, because of the lack of water resources, dry grinding can also be used to save water.
Wet grinding is suitable for most materials, such as all kinds of metal ore, non-metallic ore. As long as it is water-repellent and will not affect the quality of the finished product, the material can be used for wet grinding.
Common ore includes copper ore, iron ore, molybdenum ore, phosphate rock, feldspar mine, fluorite ore, etc. The proportion of steel balls, materials, and water in wet grinding is 4:2:1. The detailed proportion can be determined by grinding experiments.
At the same time, the size of the alumina grinding balls is also required. If the ratio is good, then the ball milling efficiency will be greatly improved. Generally, there are large, medium and small balls, and the better ratio between them can also be obtained through experiments.
The dry milling process may be used when the particle size of the powder is not required to be very fine or when the ball milled product is to be stored or sold in powder form. For example, in the production of cement, it is necessary to choose dry grinding instead of wet grinding, otherwise, it will be difficult to meet our needs.
Wet grinding is generally used in mineral processing, because the wet ball mill has the advantages of strong materials adaptability, continuous production, large grinding ratio, easy to adjust the fineness of the milled products, and it is widely used at present.
Since the dry and wet ball mill equipment has its own advantages, we must find out the suitable grinding type that the material is suitable for so that we can ensure quality and efficiency. Welcome to consult Fote company, where our professionals will give you a satisfactory answer based on your needs.
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Wet Grinding Mills is mainly used for separation of gold, silver, lead, zinc, molybdenum,iron, copper, antimony, tungsten, tin and other minerals selected. With less investment, fast results, small footprint saving power, sturdiness and durability, ease of maintenance and high return on investment. It is the preferred production for alternative ball mill, is ideal for smalland medium enterprises dressing.
4.Undertheeffectionofgrindingrolleroperating,thecrushedmaterialsandthewater mixed intensively to float on it uniformly,then passing through the overflow discharge gate that setting up on the mill basin to discharge,after thatenter intonext operation procedure to process.
XMQ series cone ball mill is a laboratory grinding equipment for wet grinding of ore (150*50 cone ball mill can also be used for dry grinding). It is suitable for mineral feasibility study of laboratories in schools, research institutes and ore beneficiation plants. XMQ cone ball mill can also be used for grinding of a small amount of material in the field of metallurgy, geology, chemistry and construction.
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 Fetekro project, which includes the Lafigu gold deposit, is located in the northern end of the Oum-Fetekro greenstone belt (lower Proterozoc), a North-South elongated belt which is approximately 300 km long and 20 km wide. This belt is composed mainly of Birimian volcanosediments, consisting mainly of mafic to intermediate metavolcanics, felsic metavolcanics, and clastic metasediments, that are bound and intruded by granitoid complexes. Known gold deposits such as Bonikro and Agbaou are hosted within the same belt.Lafigu deposit geology is a birimian volcanic complex mostly composed of mafic rocks, namely metagabbros / metanorites and metabasalts and felsic intrusive (granodiorite or tonalite) that occurs in the western part of the prospect. This volcanic complex is affected by a transpressive deformation and intruded by granodioritic bodies and quartz-porphyry dykes. Regional foliation varies in strike from N-S to N070 with gentle to intermediate / steep dips to the E and S (25-65).The mineralisation is mainly controlled by an ENE-trending brittle-ductile thrust fault dipping 15 to 45 SSE. Mineralisation is mainly hosted by a network of Qz-Cb-To-Py-PoVisible Gold quartz veins within sheared and altered brittle-ductile deformation zones of various thickness (few metres to some 10 metres and so). The alteration assemblage comprises Bt-SerToChlCb (Carbonates) and various amounts of disseminated Pyrrhotite and Pyrite (up to 5% or so).At Lafigu, a prominent deformation zone is typically located at the contact zone between a mafic intrusive (gabbro) and mafic volcanics, whereby the contact also occurs with a felsic intrusive at Lafigu Nord. The shear zones are better developed at or near lithological contact zones, where competency contrasts favour the localisation of brittle-ductile shearing, permeability increase and enhanced hydrothermal fluid flow. However, these shear zones also appear in the core of massive intrusive or metavolcanic units.The mineralisation has been recognised over 2 km along an ENE axis and the down dip extension has been demonstrated over 1 km so far.Two types of mineralisation have been identified:- An overburden mineralisation (transported material composed of quartz blocs and pebbles in a clayish matrix). This portion represents less than 5% of the deposit resources.- Mineralisation is mainly hosted by a network of quartz veins. The succession of hydrothermal events associated with C-plane fracture phases and thrusting resulted in the formation of two ore-bearing, quartz-carbonatetourmaline-(chlorite-biotite-pyrrhotitepyrite-gold) in echelon extension vein generations. The textural and geochemical (minor elements and boron isotopy) features of the distinct tourmaline generations highlight the micro-scale record of fault-valve processes leading to the overall gold endowment of Lafigu deposit. The lodes generally occur on lithological or structural discontinuities, typically at the granodiorite edges, on C-planes or re-opening early Quartz-Carbonate veins. At the deposit scale, the lodes show pinch and swell figures both laterally and longitudinally with thicknesses up to 40 metre.The Ftkro deposit resembles a typical shear zone deposit of the West African granite-greenstone terrane. Lafigue gold mineralisation can be associated with the low-sulphide quartz gold (of 03-077) deposit model of Laurence J. Drew (Drew, L., 2003, Low-Sulfide Quartz Gold Deposit Model. U.S. Geological Survey, p1-24).The Ftkro deposit resembles a typical shear zone deposit of the West African granite-greenstone terrane. The deposit itself is associated with a major regional North South shear zone. The lithologies can be any form of sediment (volcanosediment) or igneous rock with the main feature being a shear zone between the two contrasting lithologies (metabasalt and metagabbro or metabasalt and intrusive).Mineralisation may also be spatially related to the emplacement of intrusives. The gold mineralisation is mesothermal in origin and occurs as free gold in quartz vein stockworks and zones of silicification, associated with tourmaline, calcite, ankerite and pyrite. The gold mineralisation is found in linear zones in or near the contacts between two different rock types (Metabasalt and metagabbro or metabasalt and intrusive). This contact shows evidence of shearing. Alteration is weak to severe depending on the development of the system.The final July 2020 interpretation included twenty-two mineralized zones / domains and four mineralised laterite zones, which collectively make up the deposit. The Lafigu deposits are separated into three main areas, Lafigu South, Lafigu Centre, Lafigu North and mineralised laterite are typical cross-Sections A-B-C-D-E showing the mineralised domains with the drillholes.
The Ftkro prospect has not been mined commercially. Only artisanal mining has been observed. The quartz veins have been manually mined out and sorted.Lafigu Gold Project is intended to be conventional open pit mining using a drill, blast, load, haul and tip mining cycle. Endeavour plan to contract out the mining to a suitable mining contractor whilst maintaining operation oversight. Given the high grades, this does not preclude future underground mining if the orebody extends at depth.The saprolite and laterite is anticipated to be primarily free-dig, potentially requiring ripping. Production drilling of saprock and fresh material will be undertaken by top hammer drills drilling 127 mm diameter holes. As rock strengths increase, blasting will be utilised more regularly in the saprock with powder factors estimated at 0.36 kg/bcm. All the fresh rock will be blasted with powder factors estimated at 0.83 kg/bcm.Loading will be undertaken by hydraulic excavators (100 t and 200 t operating weights) to provide a balance between mining selectively and productivity. Hauling will be undertaken by rigid body dump trucks (90 t capacity).Ore will be tipped on:- Strategic long-term (LT) stockpiles to increase the plant feed grade and for rehandle during later stage pre-strip.- Run-of-mine (ROM) stockpiles for short-term rehandle to the crusher.Waste will be tipped on:- External waste dumps.- Bund and road construction.- Tails dam wall construction.- Inpit backfill may be potentially available but has not been incorporated into the mining schedule.The primary mining equipment will be supported by suitably sized ancillary and support equipment such as, but not limited to, dozers, graders, water carts and wheel loaders. This equipment will be used for activities such as: Clearing and stripping of topsoil. Construction of haul roads and ramps (temporary and long-term). Pit, stockpile and dump floor maintenance. Ripping of free-dig material, if required. Dump face reshaping for rehabilitation, topsoil spreading, ripping, and seeding. Drill pattern preparation. Clean-up of spillage around pit, stockpile and dump working areas and haul roads andramp. Stockpile rehandle. Dust suppression on roads, loading and tipping areas. Fire fighting.
Fresh ore closed circuit secondary crushing with crushed ore storage, closed circuit High Pressure Grinding Rolls (HPGR) crushing with HPGR crushed ore storage and ball milling.Oxide ore open circuit primary crushing with direct feeding of the ball mill.When processing fresh ore, mechanical availabilities of 70% for the closed circuit secondary crushing plant, 86.7% for the closed circuit HPGR crushing plant 91.3% for the remainder of the plant, supported by crushed ore storage and standby equipment in critical areas. When processing oxide ore, mechanical availability of 88.0% with direct feed of primary crushed ore to the ball mill.The treatment plant design incorporates the following unit process operations:- Primary jaw crushing to produce a coarse crushed product.Fresh Ore- Secondary cone crushing in closed circuit with a dry sizing screen to produce an intermediate crushed product- A live secondary crushed ore stockpile, providing coarse crushed ore storage and reclaim to feed the HPGR crushing circuit- Tertiary HPGR crushing in closed circuit with a wet sizing screen with undersize slurry reporting to the milling circuit via the mill discharge hopper. The circuit will achieve the target P80 grind size of 75 m when processing fresh ore.Oxide Ore- Direct feeding of primary crushed ore to the ball mill feed chute.Oxide and Fresh Ores- A ball mill in closed circuit with hydrocyclones to produce a grind size of 80% passing (P80)75 m (micron).The ROM pad will be used to provide a buffer between the mine and the plant. The ROM stockpiles will allow blending of feed stocks and ensure a consistent feed ore type, rate and grade to the plant. The ROM bin will be designed to accommodate both direct tipping from mine trucks and blended feed addition by FEL. A mobile rock breaker will be used to break any oversize rocks on the ROM pad.A primary crushing, milling and downstream plant availability of 88% (454 dry t/h) was selected for when the plant is processing oxide ore. With the potential for ore handling problems due to wet and sticky oxide ore, the ball mill will be direct fed with primary crushed ore, with no surge capacity, resulting in the overall lower plant availability.Closed circuit secondary crushing is required to achieve the fresh ore particle size suitable for downstream HPGR crushing. HPGR are sensitive to feed size and it is important that the top feed size is less than the HPGR operating gap. The feed size to the HPGR impacts on the HPGR tyre wear life with the wear life decreasing as the top size increases. A secondary closing screen aperture of 35 mm was selected for the secondary crushing circuit in order to maximise HPGR tyre wear life.The primary jaw crusher, secondary cone crusher and dry crushing screen were sized by OMC based on the expected crushing circuit throughput rates, crushing and screening efficiencies and recirculating load.An apron feeder was selected to draw material from the ROM bin being suited to both clayey oxides and harder primary ore. The apron feeder will discharge onto a vibrating grizzly which will allow crusher product sized ore to bypass the jaw crusher, reducing the load and wear on the jaw crusher.On oxide ore, primary crushed material will bypass, via a diverter gate, to the oxide feed conveyor and will report directly to the ball mill feed.Secondary crushed ore will report to a live stockpile with sufficient capacity to allow for regular maintenance at the primary and secondary crushers without interrupting feed to the HPGR. The stockpile will be covered to prevent rain increasing the crushed ore moisture and to minimise dust emissions from the crushed ore. The HPGR and wet screen were sized by OMC based on the benchmarked HPGR design parameters,expected HPGR circuit throughput rates, screening efficiency and recirculating load. The HPGR will operate in closed circuit with the wet milling screen with screen oversize reporting back to the HPGR feed (along with new feed) and screen undersize reporting to the milling circuit. All conveyors with material reporting to the HPGR will be covered to prevent rain increasing the HPGR feed moisture. The HPGR product will contain considerable oversize due to the pressure profile across the roll width, with little crushing occurring near the roll edges. Wet screening allows efficient screening down to fine sizes and as the size decreases, the overall process becomes more energy efficient due to reduced ball milling requirement. A closing screen aperture of 4 mm was selected for the HPGR circuit based on OMC experience with other HPGR operations. The HPGR product will be mixed with water in a re-pulping box to assist in de-agglomeration of the HPGR flake product to improve the subsequent wet screening process.When treating fresh ore through the HPGR circuit, the ball mill will be reverse fed via the cyclone underflow. This will remove final product size material generated by the HPGR effectively reducing the new feed rate to the mill. This HPGR advantage has been taken into account when sizing the ball mill. The milling screen undersize will contain significant water (from the wet screening stage) and minimal additional water will be required to the mill discharge hopper. When treating oxide ore, the ball mill will be direct fed via the mill feed spout. Dilution water will be added to the mill feed and mill discharge hopper. The ball mill will be equipped with a variable speed drive and will typically be operated between 60% and 75% of critical speed. The ball mill has been sized based on fresh ore and will typically operate at 75% critical speed when treating fresh ore. When treating oxide ore, the mill will be operated at lower speeds (and lower ball charge) to minimise overgrinding of the softer material.When treating fresh ore, the cyclones will be fed at lower slurry densities due to the high milling screen water addition and reverse feeding of the ball mill.
Centrifugal concentratorCarbon re-activation kilnDewateringSmeltingIntensive Cyanidation Reactor (ICR)Wet ScreeningGravity separationAgitated tank (VAT) leachingCarbon in pulp (CIP)ElutionAARL elutionSolvent Extraction & ElectrowinningCyanide (reagent)
The Lafigu plant will process fresh and oxide ores and is expected to operate on either 100% fresh ore (possibly with a small portion of oxide) or 100% oxide ore. The fresh and oxide ores have different comminution and material handling characteristics with the fresh ore significantly more competent than the oxide ore. The ore types require different comminution flowsheets.The plant design is based on a nominal capacity of 3.0 Mtpa of fresh ore and is expected to process 3.5 Mtpa of oxide ore. The plant will process either 100% fresh ore (possibly with a small portion of oxide) or 100% oxide ore. The plant feed schedule indicates that the life of mine (LOM) plant feed is 8% oxide / transition ore and 92% % fresh ore, with the majority of oxide ore processed in the first two years of operation.Gravity ConcentrationGravity testwork indicated that 20 to 90% of the contained gold in the Lafigu ores is recoverable through gravity gold methods. The gravity cir ........
Reserves at July 31, 2020: Resources are reported using cut-off grade 0.5 g/t Au.Reserves are reported using cut-off grades of 0.34 g/t Au for laterite and saprolite, 0.38 g/t Au for saprock and 0.43 g/t Au for fresh ore.
Grid ball mill is widely used in smashing all kinds of ores and other materials, ore dressing and national economic departments like building and chemical industries etc. The size of ore shall not exceed 65mm and the best feed size is under 6mm. The effect in this job is better than coarse grinding. Grid ball mill consists of the shell, feeding part, discharging part, main bearing, lubricating system, driving system and other parts. There is wearing a liner inside the shell, and both ends of the shell are provided with a flange. The end cover of the mill is connected with the flange plate. The feeding part consists of the head, trunnion and feeding device. The discharge part includes the grid plate, head, and discharge trunnion.
Wet Grid ball mill is mainly used for mixing and grinding materials in two types: dry grinding and wet grinding .It has advantages of fineness uniformity and power saving. The machine uses different types of liner to meet different customer needs. The grinding fineness of material can be controlled by grinding time. The electro-hydraulic machine is auto-coupled and decompressed to reduce the starting current, and its structure is divided into integral type and independent type.
Compared with similar products,Wet Grid ball mill has the characteristics of low investment, low energy consumption, novel structure, simple operation, stable and reliable performance. It is suitable for mixing and grinding ordinary and special materials. The users can choose the right type, liner and medium type by considering the specific gravity, hardness, yield and other factors. The grinding medium is Wet Grid ball.
1.The ball mill is composed of a horizontal cylinder, a hollow shaft for feeding and discharging, and a grinding head. The main body is a long cylinder made of steel. The cylinder is provided with an abrasive body, and the steel lining plate is fixed to the cylinder body. The grinding body is generally a steel ball and is loaded into the cylinder according to different diameters and a certain proportion, and the grinding body can also be used with a steel section.
2.According to the particle size of the grinding material, the material is loaded into the cylinder by the hollow shaft of the wet grid ball mill feeding end. When the ball mill cylinder rotates, the grinding body acts on the cylinder liner due to the action of inertia and centrifugal force and friction. It is carried away by the cylinder. When it is brought to a certain height, it is thrown off due to its own gravity. The falling abrasive body crushes the material in the cylinder like a projectile.
3.The material is uniformly fed into the first chamber of the mill by the feeding device through the hollow shaft of the feeding material. The chamber has a step liner or a corrugated liner, and various steel balls are loaded therein. The rotation of the cylinder generates centrifugal force to bring the steel ball to a certain extent. The height drops and then hits and grinds the material. After the material reaches the rough grinding in the first bin, it enters the second bin through the single-layer partition plate. The bin is embedded with a flat liner with steel balls inside to further grind the material. The powder is discharged through the discharge raft to complete the grinding operation.
The main function of the steel ball in the ball mill is to impact crush the material and also play a certain grinding effect. Therefore, the purpose of grading steel balls is to meet the requirements of these two aspects. The quality of the crushing effect directly affects the grinding efficiency, and ultimately affects the output of the ball mill. Whether the crushing requirement can be achieved depends on whether the grading of the steel ball is reasonable, mainly including the size of the steel ball, the number of ball diameters, and the ball of various specifications. Proportion and so on.
The ball mill is composed of the main part such as a feeding part, a discharging part, a turning part, a transmission part (a reduction gear, a small transmission gear, a motor, and electric control). The hollow shaft is made of cast steel, the inner lining can be replaced, the rotary large gear is processed by casting hobbing, and the barrel is embedded with wear-resistant lining, which has good wear resistance. The machine runs smoothly and works reliably.
The Mutanda copper-cobalt deposit lies with the lower part of the Neoproterozoic Katangan sedimentary succession which extends over more than 700 km from Zambia through the Katanga province of the DRC and is up to 150km wide. It is part of a thrust-and-fold belt known as the Lufilian Arc. It shares the same characteristics of most of the deposits within the Copperbelt in that it is stratiform and associated with carbonate or carbon-rich lithologies (Cailteux, et. al. 2005).The main copper oxide minerals present are malachite and pseudomalachite, with heterogenite, the main Cobalt mineral. Quartz and chlorite dominate the gangue component in all the samples.The sulphide minerals have yet to be subjected to a laboratory mineralogical analysis.Four mineralised bodies have been delineated at Mutanda. The largest of these lies in the East Zone which extends along an east-west strike for 900m and down dip for 500m. It lies within the R4 dolomites and dolomitic shales and is up to 50m thick near surface. This body dips at 35 to the south and plunges towards to southeast. Although sulphides have been intersected at depth these are more sparsely drilled and have yet to be investigated in detail. The down-plunge extensions of this mineralisation have yet to be drilled. A second carbonaceous shale-hosted mineralised zone lies stratigraphically above the main mineralisation (some 60m vertically below) and has been intersected in only seven drillholes. It appears to be variable in thickness and intensity of the mineralisation but visually the grades for both copper and cobalt appear to be higher than those in the carbonate hosted sulphide zone.
The mining method applied is conventional open pit mining, consisting of drilling, blasting, loading and hauling.All future mining is planned based on contractor mining. Pit designs were created based on the current mining methodology that includes mining at 5m or 10m benches. Ramp and pit access designs considered the largest envisaged hauler dimension specifications ensuring safe and practical execution. Pit designs were conducted based on the optimum pit shell. All pit designs adhere to current geotechnical requirements.
The ROM ore will be tipped into a ROM tip bin equipped with a static grizzly which will ensure that oversize material will not report to the primary crusher (oversize material can choke the crusher). Ore will be withdrawn from the ROM tip bin using a variable speed apron feeder to a vibrating grizzly feeder (to scalp off fines) ahead of the primary crusher. A single toggle jaw crusher will be sized for the purpose of primary crushing.Ore from the primary crusher will be scrubbed ahead of secondary and tertiary crushing to remove clay associated with the ore. The scrubber will be equipped with a trommel screen and oversize material from this screen will be crushed using an open circuit secondary impact crusher while trommel undersize will be wet screened on a double deck screen. Oversize from this screen will be crushed using a tertiary impact crusher, intermediate product will be conveyed to the mill feed bin and the undersize slurry pumped to the mill discharge sump. Both products from secondary and tertiary crushers will be screened on a single deck screen, with the oversize recycled to the tertiary crusher for further size reduction and the undersize reporting to the mill feed bin. A feed bin will be installed ahead of each impact crusher to ensure consistent feed to the crushers.Milling and classification of the crushed ore will be through an overflow discharge wet ball mill operating in closed circuit with a hydrocyclone cluster. Crushed ore will be fed to the ball mill using a variable speed belt feeder and mill feed conveyor. The primary screen undersize will be pumped to the mill discharge sump to join the ball mill discharge. The mill discharge together with the primary screen undersize will be pumped to a hydrocyclone cluster. The overflow from the hydrocyclone cluster will be the circuit product and will gravitate to pre leach thickening while the underflow from the hydrocyclone cluster will gravitate to the ball mill for further size reduction.
The concentrate operations consist of a crusher, a small dense media separator plant, and a spiral plant. These operations produce more than 20,000 metric tons each year. The two older Mutanda copper plants consist of four tank houses, commissioned between September of 2010 and January 2012. They use two-stage metallurgical process of solvent extraction and electro winning to process a combined 110,000 metric tons of copper each year. The expansion completed at the end of 2013 included the addition of: Increasing crushing, milling, leaching and CCD capacity to 200 ktpa (kilo-tonnes per annum) at design feed grades. 54 ktpa HG SX and 46 ktpa LG SX. Adding Electro winning sections EW5 to EW7 of 30 ktpa each.The sulfuric acid and liquid sulfur dioxide plant was commissioned in early 2012 and has an expected daily capacity of 390 MT of sulfuric acid and 73 MT of liquid sulfur dioxide. The production of sulfur dioxide a reagent used in cobalt leaching, enables significant savings in reagent costs. Leaching, using acidified raffinate and/or sulphuric acid, will take place in four mechanically agitated tanks operating in a series overflow cascade configuration under atmospheric conditions. A 25% W/w Sodium Metabisulphite solution will be also added to the leach tanks to facilitate the leaching of the Co3+ species by reducing the Co3+ to Co2+. The slurry from the final leach tank will be washed, with cobalt effluent solution topped up with return dam solution, and then thickened in a series of five counter current decantation CCD thickeners. Alternate wash water will be sourced in order of preference from process water, raw water or raffinate. The overflow from the first CCD thickener will be treated in a clarifier to reduce the amount of suspended solids in the pregnant leach solution (PLS). Overflow from the clarifier will gravitate to the PLS pond while the underflow from the final CCD thickener will be pumped to the tailings disposal tank. The clarifier underflow will be pumped back to the CCD circuit or the clarifier feed tank. Due to the need to further dilute the discharge from the final leach tank in the CCD thickeners before thickening to ensure optimum settling of solids, high rate thickeners with auto feed dilution will be incorporated into the design. The PLS (aqueous phase) will be pumped to two extraction mixer settlers where it will be mixed with an organic solvent solution consisting of an extractant and diluent (organic phase). The solvent solution will extract the copper from the PLS producing a copper loaded organic stream (loaded organic) and a copper depleted aqueous stream (raffinate).The loaded organic will be mixed with a solution from electrowinning (spent electrolyte) in two stripping mixer settlers where it will be stripped of the copper producing an advance electrolyte. This advance electrolyte will be filtered using dual media filters to remove entrained organic solution, to prevent organic burn on the deposited copper. The advance electrolyte will then be heated using a heat exchanger prior to it being fed to electrowinning. The stripped solvent solution (stripped organic) will be returned to the extraction mixer settlers.Advance electrolyte will be pumped to 16 polishing cells before being pumped to 66 commercial cells. Each cell will have 48 cathodes and 49 anodes. Copper will plate onto the cathodes by the process of electroplating. Blank stainless steel cathodes and lead anodes will be used in the cells. The spent electrolyte from the electrowinning banks will be pumped back to the strip section of solvent extraction. After the plating cycle, the cathodes will be removed from the electrowinning cells, washed in a hot water tank, the deposited copper stripped from the cathodes using a semi automatic stripping machine and the blank cathodes returned to the cells. The copper stripped from the cathodes will be the finished copper product.
The Iron Ore Industry has perhaps seen more varied and drastic changes in its approach to crushing and grinding in the last 5 years than any of the other mineral industries. Multimillion ton per year plants have become common place. Centralized control and computers have become an established benefit. Autogenous grinding along with a variety of rod and ball grinding flowsheets are in use.
The most common control in a primary crusher installation begins with sensing of the bin level below the crusher discharge. This is usually done using a gamma ray source and detector. High level sensors trigger the no-dump lights and protect the crusher from damage due to an overloaded bin. Low level sensors not only actuate the dumping lights, but can be used to control the discharge feeder to protect it from direct blows of large ore chunks. Hydraulic mantle positioning devices with remote positions indicators are included on most modern primary gyratory crusher installations.
These control devices have served to protect equipment and maintain operating availability. In most cases the crusher operators job has not been eliminated because of the necessity of operating the rock hook or lowering the mantle when large chunks bridge the crusher cavity.
Most of the rod mill ball mill circuit controls in the Iron Ore Industry are patterned after a scheme developed by Erie Mining Company.This control is based upon the premise that constant volume, and structure of feed to the cyclone will result in a controlled sizing of the cyclone overflow by varying the density of the cyclone feed.
Prior to the introduction of automatic density control on cyclone feed, a manual method on cyclone overflow was used. This consisted of manual adjustment of dilution water to the cyclone feed sump and manual adjustment of the tonnage set point on the automatic feed controller. The cyclone feed pressure was varied to maintain the feed sump at a constant level. This was accomplished automatically through the use of a sump level sensor controlling a vari-speed cyclone feed pump.
Grinding control circuitry is still based upon cyclone feed density controlling rod mill feed tonnage. This scheme permits the selective grinding of the low grade coarse fraction. This results in the advantage of obtaining either a coarser overall grind with the same grade and an increase in throughput, or a better grade at the same grind and throughput.
Controls for a plant having two rod mills followed by three ball mills, have also been developed.The principle of grind control is based upon the cyclone feed density controlling the magnetic tons of feed to the rod mill. Magnetic tons were chosen because of a wide variation in magnetic iron of the feed.
A problem area in any two stage flowsheet is the utilization of the maximum power capability in each grinding stage. This is particularly true of autogenous grinding, where mill power draw is a direct function of the charge level within the mill.
Controls for a plant with wet autogenous ball mill grinding incorporate the use of a nuclear density gauge on the ball mill cyclone feed line. The density set point controls the tonnage feed rate to the autogenous mill. An optional control by autogenous mill power is also provided,
In a successful attempt to gain a finer grind in the primary autogenous mill, a 100 ton charge of 1- diameter steel balls was added to the primary mills by one operator. The use of these small balls made up for a lack of grinding media and doubled the mill power draw. This balancing of power and grind allowed the plant to reach design tonnage.
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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.
The Ahafo mine is composed of three orogenic gold deposits that have oxide and primary mineralization. The gold is hosted in brittle shear zones cutting granitic intrusives that have kilometer-scale vertical and lateral extent. Gold occurs primarily in pyrite and secondarily as native gold in quartz veins.Regionally, there are 12 known deposits in the Ahafo district, localized along multiple northeaststriking structural zones. Discrete mineralization styles are recognized within the Ahafo district, which are termed Kenyasi-style, Subika-style, and Subenso-style. The Kenyasistyle and Subika-style mineralization are identified within the Ahafo South Operations area and Subenso-style mineralization is identified within the Ahafo North area.The Kenyase style is hosted in structures on or parallel to the regional Belt boundary separating basinal metasediments from Dixcove type granodiorite. High-grade zones occur in hydrothermal breccia and quartz veins accompanied by intense silica-albite-carbonate-sericite-pyrite alteration. Teekyere type deposits occur solely within folded metasediments intensely altered by carbonate, quartz, feldspar, pyrite, chlorite and sericite. They lack veins, instead occurring in pervasive alteration. Yamfo style deposits are similar to Teekyere type but occur in discrete veins. Newmont geologists Enders (2004) and Williams (2005) lump the Teekyere and Yamfo deposits together calling them Subenso type. Grades within the deposits are consistent, with the gold occurring with very fine disseminated pyrite. Arsenopyrite is absent; the ore is non-refractory above and below oxidation, which generally occurs to a depth of 50-75 metres (Griffis, 2004).All of the shear zone deposit types appear to be part of the same mineralized system. As with many deposits located in tropical climates, a saprolite zone, typically between 550 m thick, is developed at surface. The saprolite zone gives way at depth to a sulfide zone, within which gold occurs in structurally-controlled zones of hydrothermal alteration.Ahafo South Operations area.The Apensu deposit is located on the main Kenyasi Thrust Fault zone at the southern edge of the Ahafo trend. It is considered to be a Kenyasi-style deposit. When open pit mining commenced, the deposit had dimensions of 3.8 km x 600 m and had been tested to 500 m vertical depth.Mineralization was developed in mylonitic to cataclasite units along the sheared contact between footwall Birimian volcanosedimentary units and hanging wall granodiorite. Footwall units included phyllonite (PHY), meta-volcanosedimentary units (MV) and mixed mylonitic volcano sedimentary units (GVM). Late-stage fine-grained aplite dikes that are sub-parallel to the Kenyasi Thrust Fault were logged but could represent fine-grained mylonite zones.Mineralization is characterized by an association of silicaalbitecarbonatewhite micapyrite alteration, quartz veining and brittle chlorite-filled fractures. Better gold mineralization is developed in quartzcalcite veins associated with pyrite grains that can vary from fine disseminations to 1.5 mm in size. Gold occurs as single grains 120 m in diameter but also commonly occurs in clusters of grains from 510 m. There does not appear to be an association of gold with either arsenopyrite or rutile, and the gold is generally silver-poor, with <5 ppm Ag.Visible gold occurs in the veined cataclasite. Locally, 0.22.0 cm wide quartz veins can return assays with more than 32 g/t Au from coarse gold. In the oxide zone, gold is associated with coarse goethite pseudomorphs after euhedral pyrite. Gold grains in the oxidized zone range from 510 m. Manganese oxides are also observed in oxide mineralization.Apensu DeepsApensu Deeps has dimensions of 3.9 km x 600 m and is tested to about 800 m vertical depth. The Apensu Deeps area is subdivided into four zones, Apensu South, Apensu Gap, Apensu Main, and Apensu North. Mineralization remains open at depth in all zones, and to the north in Apensu North.Shear zone fabrics and fault geometries were inherited from early compressional deformation and include a strong cataclastic deformation of the hanging wall granitoids interpreted to be analogous to a crush breccia. The Apensu Gap area is different to the Apensu South and Apensu Main zones, as the area lacks the mafic unit that is associated with Apensu South, and the cataclasis is very weak. In this area, it appears that low-angle faults control and limit the extent of better grade gold mineralization. Subika The Subika deposit is located about 2 km southeast of the Apensu Main deposit. It is developed in the hanging wall of the Kenyasi Thrust Fault but lies on a separate and parallel fracture zone (MFZ) to the fracture that hosts the Kenyasi-style deposits. The Subika deposit has horizontal dimensions of approximately 2.2 km x 400 m, and is tested to about 1 km in vertical depth. Subika mineralization remains open at depth and along strike. There is little development of either duricrust or saprolite, due to erosion associated with the old Tanoso River. Oxidation is limited to a thin (515 m) zone of complete oxidation of bedrock, followed by an irregular zone of partial oxidation extending as much as 20 m into primary bedrock.Better grades of gold mineralization occur in dilatant zones (MFZ), ranging in width from 160 m. Hanging wall lower-grade mineralization tends to extend only about 30 m from the dilatant zones. Higher grade shoots within the dilatant zones plunge south at 20 to 70. The high-grade zones appear to be controlled by dilatant left jogs in the MFZ created by offsets across the mylonite zones. Four granitoid subset lithologies are recognized: diorite, gabbro, microdiorite, and dioritegabbro mixed. Aplite and pegmatite dikes cross-cut the granitoid material.Mineralization is hosted in the MFZ, which typically contains >25 g/t Au over widths of 550 m. Quartz and carbonate veinlets are common with thickness between 150 mm. They form stockworks in some instances and most of the veins are impregnated with pyrite, and in some cases with sparse visible gold at the contact with the host rock.Awonsu The Awonsu deposit is located approximately 1 km to the northeast of the Apensu deposit in a right-hand jog of the Kenyasi Thrust Fault and is a continuation of the Apensu mineralizing system. The Awonsu deposit had horizontal dimensions of approximately 1,800 m x 150 m, and was tested to 450 m vertical depth. The mineralization remains open at depth and towards the north along strike.The primary lithological units in the Awonsu deposit were altered to a depth of 40 m to saprolite, intensely oxidized, leached, and mottled and contain saprolite clay and quartz fragments.Awonsu mineralization was typically more disseminated than that at Apensu. AmomaThe deposit has horizontal dimensions of 1,500 m x 170 m, and is tested to approximately 300 m vertical depth. Mineralization remains open at depth.Footwall rocks comprise a mixture of mafic volcanic units, and pelitic to turbiditic sedimentary units of the Birimian succession. Granitoids of dioritic to tonalitic composition comprise the hanging wall. Overlying the deposit is a layer of duricrust, which can be 8 m thick, comprising iron pisolites and transported alluvial cobbles. Saprolite is from 2050 m thick.Gold mineralization is developed primarily in the cataclasite unit. Mineralized zones that host gold grades >0.5 g/t Au range in width from 10110 m. Higher-grade material (>1.5 g/t Au) is developed in the cataclasite, but lower-grade (0.51.5 g/t Au) mineralization locally occurs as a 2050 m wide halo in the hanging wall granitoids. A narrower, lower-grade halo also occurs in the footwall mixed mylonite units, ranging from 030 m in width.
Ahafo has two active open pits, Subika and Awonsu. Subika added an underground operation, which reached commercial production in November 2018, and Awonsu completed a layback in November 2019. Open pit mining is conducted at Ahafo South using conventional techniques and an Owneroperated conventional truck and shovel fleet.Underground mining is currently conducted using conventional stoping methods, and conventional mechanized equipment. Underground mining is conducted by contractor African Underground Mining Services (AUMS). The Subika underground mining operations are split into two areas: The Upper mining zone, above the 840 relative level (RL); also known as the upper Yoda area; The Central mining zone (corridor) below the 840 RL; also referred to as the Central area.The mine plan assumes the use of a number of different mining methods, including: Sub-level open stope (SLOS): to be used above 840 RL; Long-hole open stope retreat (LHOSR): to be used above the 750 RL in the Central zone; Long-hole retreat with rockfill (LHSRF): to be used in the transition zone between the 750 and 665 RLs in the Central zone; Single lens retreat (SLR): to be used below the 665 RL in the Central zone, and in the North and South mining zones; stopes will be paste-filled.Mining operations in the Sub level open stope (SLOS) zone will use existing infrastructure and spirals created on a 40 m level spacing to access the stopes. These stopes are mined from the lowest stope level upward in stope groups to create large open stopes. The ore on these levels is loaded directly from the mining extraction level to trucks and hauled up the existing main decline to the surface, and placed on stockpiles. Surface haulage equipment transports stockpiled material to the process plant.To access the lower ore, below the 840 RL, a set of twin declines will be developed off the existing main haulage decline. The twin declines will be developed as a figure eight or elongated spiral configuration with one full rotation at 50 m intervals. The declines will be connected via a link drive that will act as a ventilation, escapeway and haulage connection between the two declines.Both declines will act as a primary ventilation circuit with fresh air. Additional ventilation will be sourced through fresh air ventilation raises connected at the link drives and the foot wall drives below the 750 RL. The fresh air raise will deliver refrigerated air from the surface refrigeration system. The return air will be taken from the access drives above the 750 RL and from the ends of the foot wall drives below the 750 RL, using return air raises connected to the main fans at the surface and Portal 2.Level accesses will be created off the decline at 25 m intervals to cross the ore zone from levels 800 to 700 RL. Below the 700 RL, the level interval will be increased to 35m.Above the 750 RL, infrastructure such as substations, pump cuddies and sumps will be developed on these access drives. On these levels the ore drives will be developed from the access drives along the ore lenses identified as containing the mineralization for eventual stoping. The ore drives will be driven to the extents of the defined mining corridor and stoping will retreat from the end of the orebody towards the accesses. These stopes will be mined top-down. Stopes will be mined from the end of the ore drives back to the level access. Pillars will be left between stopes along the mine level for regional stability. Stopes will be mucked using remote mucking equipment back to an ore pass created between levels. Trucks will be loaded from the level below the mining extraction level via the material placed in the ore pass. The trucks will travel up the spiral declines to the main haulage decline and exit and enter via the North portal.Below the 725 RL, the access drive from the decline will connect to a footwall drive that will be offset from the ore zone by 30 m. Stope access drives will be driven off the footwall drives to develop the stopes in the mineralized zone. The footwall drive will be used for infrastructure to connect ventilation returns, ore passes, substations, sumps and other infrastructure to support the mining on the levels. The mining direction for stopes in the areas below the 750 RL is centerout. Thus, stopes will be mined from a specified centralized location out to the extents of the orebody. These stopes will be mined bottom-up.For stopes between the 750 and 665 RL, pillars will be left between stopes along the mine level for regional stability. Stopes will be mucked using conventional and remote mucking equipment back to the foot wall drive. Trucks will be loaded from the level below the mining extraction level via the material placed in the ore pass. When stope mining is completed, the stopes will be backfilled with rockfill using truck tips and remote loading. Stopes must be backfilled before adjacent stopes can be mined in the sequence.For stopes below the 665 RL, no pillars will be left between stopes along the mine level for regional stability. Stability will be provided by backfilling the stopes with paste fill after the stopes have been mined. Stopes must be mined in sequence from a center-out, bottom-up approach with the mine sequencing a critical factor in controlling the high stress potential of these stopes. Stopes will be mucked using conventional and remote mucking equipment back to the footwall drive.Trucks will be loaded from the level below the mining extraction level via the material placed in the ore pass. When stope mining is completed, the stopes will be backfilled with paste fill from a surface plant facility. Paste fill will be directed to the stopes through fill pipes from the surface to underground. Once a stope is filled and the backfill cured for the time required, the adjacent stope can be mined.The daily production rate is approximately 95,000. tonnes.The primary source of ore for 2019 will be from stockpiles and Subika, which will produce significant tonnes of high-grade ore. Three 9400 diggers will be located in Subika from May 2019 to the last quarter of 2019, when mining is planned to start in Awonsu Phase 3. Subika mining will constitute stripping of large quantities of waste from pit Phase 4. Mining will be completed in Subika by 2024, while Awonsu Phase 4 will be the last pit to be completed in 2029.
The Ahafo Mill Expansion was completed in October 2019 that expanded the existing plant by approximately 3.5 million tonnes per year through the installation of a new crusher, a single stage SAG mill and two leach tanks. Crushing Circuit ROM ore is dumped from haul trucks or a front-end loader into a feed hopper which feeds a 54- inch x 75-inch gyratory crusher. Primary crushed material is discharged into a surge hopper directly underneath the crusher. From the surge hopper, the primary crushed material is withdrawn to a reclaim stockpile via an apron feeder, conveyors and a transfer station. Where oxide ore is available, the oxide ore is loaded onto the tail end of the SAG mill feed conveyer. Primary ore from the reclaim stockpile is discharged to the SAG mill feed conveyor through apron feeders. A regulated amount of lime from a lime silo is also added to the SAG mill feed conveyor.Grinding Circuit The grinding circuit consists of a single 10.36 m diameter () x 5.00 m effective grinding length (EGL) SAG mill followed by a ball mill in closed circuit with hydrocyclones. The SAG mill and two MP800 pebble crushers are in a closed circuit. The SAG mill discharge is classified via a pebble dewatering screen. The oversize from the screen is crushed via the pebble crushing circuit and returned to the SAG mill.The undersize from the pebble dewatering screen reports to the cyclone feed hopper and is pumped to a cluster of classification cyclones. The cyclone underflow reports to the ball mill for regrinding. The cyclone overflow reports to the pre-leach thickener via the trash screens.
The processing plant was commissioned in 2006 to process 7.5 million tonnes of primary and oxide ore per year. With the depletion of oxide ore, the current plant throughput has decreased to 6.5 million tonnes per year. The processing plant consists of a crushing plant, a grinding circuit, carbon in leach tanks, elution circuit, counter current decantation circuit and a tailings disposal facility.The Ahafo Mill Expansion which was completed in October 2019, expanded the plant capacity to process approximately 11 million tonnes per year through the installation of a new crusher, a single stage SAG mill and two leach tanks. Wet Circuit The undersize of the trash screens reports to the 42 m pre-leach thickener with the thickener overflow recycled to the milling circuit as process water. The pre-leach thickener underflow is pumped to CIL leach and adsorption tanks in series. Carbon is added to the CIL tanks and flow countercurrent to the process slurry. The CIL tailings is discharge onto the carbon safety screens before being pumped to the countercurrent decantation (CCD) circuit.The CCD circuit consist of two 42 m thickeners. The overflow from the thickeners is recycled back to the process as process water while the underflow is pumped to the tailings disposal tank. Tailings are discharged via a spigot system into the TSF.Stripping and Dore Production The loaded carbon is recovered via a carbon recovery screen and treated in the elution and electrowinning circuit. Loaded carbon is acid washed with dilute hydrochloric acid in an 18 t acid wash column prior to transfer into an elution column where it is presoaked in a cyanide/caustic solution for 30 minutes to elute gold. The pregnant eluate is then rinsed from the carbon by as many as 10 bed volumes of water heated to 130 C. The resultant pregnant solution is pumped to electrowinning cells in which the gold is deposited on cathodes. The gold sludge on the cathodes is washed, dried and smelted in a furnace to produce dor. Dor is shipped to Switzerland to be refined to bullion at Valcambi.A CCD circuit was commissioned in 2008 to recover cyanide from CIL tailings prior to discharge to the TSF. Recovered cyanide is effectively re-used in the CIL circuit and weakly acid-dissociable cyanide (CNWAD) levels in the plant tailings are effectively controlled to ensure the discharge limit of 50 ppm CNWAD is not exceeded.A gravity circuit that was initially included in the plant was decommissioned in 2010.
Reserves at December 31, 2020: Ahafo South Open Pits: Cut-off grade utilized in 2020 reserves not less than 0.67 gram per tonne. Ahafo South Underground: Cut-off grade utilized in 2020 reserves not less than 3.10 gram per tonne.Ahafo North: Cut-off grade utilized in 2020 reserves not less than 0.50 gram pertonne.
UNTIL THE THIRD THEORY OF COMMINUTION of Work Index method of determining crushing and grinding mill size was introduced, there was no way of accurately figuring the most applicable, most economical size of crushing and grinding mill.
Naturally, with little or no factual operating data correlated in useful form, it was easy enough, even for the most experienced, to arrive at an incorrect size of crusher or grinding mill, especially when a slightly smaller unit carried an advantage in initial investment.
The Work Index method, frequently referred to as the Bond* method, is based on extensive field operating data and equally extensive laboratory data covering wide varieties of materials, ranges of reduction sizes and types of equipment.The correlation of all this factual material enabled the establishment of a consistent common factor, known as the Work Index, for accurately determining crushing and grinding mill sizes.
Knowing the Work Index, one has but to apply the proper given equation to determine the power input required. The calculated power input in turn enables you to select the proper crusher or grinding mill unit. Selection of various sizes of machines is made from the power requirements listed in equipment manufacturers published bulletins. The following example will help clarify the above procedure.
Assume a capacity of 2000 short tons of average material per day. A Work Index of 13 over the entire size range. A feed 80% passing 3 and a final desired product of 80% passing 100 mesh. These, then, work out as follows:
By referring to equipment manufacturers bulletin on crushers, Fig. 1, a crusher producing 80% passing 3/4 requires a close side setting of approximately 5/8. Since the selected crusher capacity must be in excess of 143 tons per hour, the next higher figure (159) is chosen. The 159 indicates a 548 crusher size with 1 eccentric throw. With 1-in. eccentric throw, the motor hp allowed on the crusher is a maximum of 125. However, since only 90.3 hp is required for this average material, a 100-hp motor is sufficient.
Fig. 2, taken from manufacturers bulletin, lists horsepower requirements and Rod Mill sizes. The calculatedpower input or horsepower in the above example is 316. Therefore, a 350-hp motor is required and this in turn indicates that an 812 (8 x 12) Rod Mill is required.
For your convenience, this manual lists over 1200 work indexes. Table I lists the Work Indexes alphabetically by company and deposit. Table II lists the Work Indexes alphabetically by materials. Table III lists the average Work Indexes alphabetically by different types of materials. In the event these 1200 listings of Work Indexes do not include the particular one that applies to your particular material, you can readily determine it, since the WorkIndex expresses the resistance or a material to crushing and grinding and the relative efficiency of any machine.
Let W represent the work input in Kwhr/T, F the feed size or diameter in microns of the square hole which 80% of the feed passes, P the product size or microns which 80% of the product passes, and Rr the reduction ratio F/P. To find the Work Index (IF/) use Equation 1.
The 80% passing size in microns is a convenient term for expressing the fineness of a crushed or ground product. It is also a convenient base for calculating the reduction ratio and the work required for reduction. It is readily found by plotting the percent passing on log-log paper, as in Fig. 5, to determine the size distribution curve.
When the size distribution curves of the feed and product are parallel, the reduction ratio remains constant for all particle sizes, and the Work Index calculated from the 80% passing size is equivalent to that calculated on the basis of any other selected percent passing size.
Small differences between the slopes of the plotted feed and product lines have only a slight effect on the Work Index, proportional to the square root of the effect upon the surface areas. However, when the feed has had the fines removed the feed size is changed and the Work Index may be considerably in error. In cases where a crusher feed is scalped by passing over a grizzly screen, with openings equal to or smaller than the crusher openings, the tonnage and size distribution of the fines removed are rarely known. It is preferable, therefore, to consider the feed to the grizzly as being equivalent to the feed to the crusher and calculate the Work Index on this basis.
Several methods (2) have been used to correct the calculated Work Index for large differences between the product and feed slopes, when plotted as in Fig. 5. A newer method is the use of the average reduction ratio Rra. This can be obtained by averaging the reduction ratios at 90, 70, 50, 30 and 10% passing. The reduction ratio, at any percent passing, can be obtained quickly. Place a piece of the log- log paper (the same as used in plotting) along the percent passing line as indicated by the dotted lines A and B, Fig. 5. With point A coinciding with 100 on the micron scale and B coinciding with 773 on the same scale, 7.73 is the reduction ratio at that percent passing.
The Work Index values listed in Table I and II apply directly to a wet grinding overflow type rod mill 7.5 feet in diameter in open circuit; and to a wet grinding overflow type ball mill 7.5 feet in diameter in closed circuit with a rake classifier at 250% circulating load, and with 80% or more of the feed passing 4 mesh. Correction factors should be applied for over-size feed and other operating conditions which change the grinding efficiency. When Work Index values at several different product sizes are available (see Tables I and II), the value nearest the actual product size should be used. The Work Index represents the total work input necessary in installations of average efficiency.How to Find Work Index From Impact Crushing Tests
The Work Index is found from the first stage of the wet open circuit grinding tests (1) by multiplying the grinding index Iw by 0.0082, and from the first stage of the dry open circuit grinding tests by multiplying the dry grinding index Id by 0.00546.
The Work Index is found from the second stage of the wet open circuit grinding tests(1) by multiplying the grinding index IIw by 0.0022, and from the second stage of the dry open circuit grinding tests by multiplying the dry grinding index IId by 0.00147. The second stage dry open circuit grinding tests may show an increased Work Index because of ball coating, and are not reliable if ball coating exists.
The Work Index can be calculated by Equation 1 from commercial crushing or grinding data or from pilot mill tests, and compared with the listed Work Indexes in Tables I and II to obtain the relative mechanical efficiency.
In cases where the capacity is found to vary more than this amount, some condition causing inefficient operation should be suspected. These may include packing in a crusher, oversize feed or improper ball and rod sizes in a tumbling mill, and coating dry in grinding.
Impact crushing tests, as well as rod mill and ball mill grindability tests, can be made at cost by thewww.911metallurgist.com Laboratories. To run a proper test, a representative sample of 50 pounds minimum is required. The sample for an impact crushing test should be no finer than 2. The sample for a rod mill grindability test should be no finer than 80% passing 0.5, and the sample for a ball mill grindability test should be no finer than 80% passing 6 mesh.
FRED C. BOND Special Engineer with Allis-Chalmers Mfg. Co. Standard Grindability Tests Tabulated, Trans. AIME (1949) vol. 183, page 313, TP 2180, Mining Technology, July 1947. FRED C. BONDThe Third Theory of Comminution, Trans. AIME, TP 3308B, Mining Engineering, May 1952.Get in Touch with Mechanic