The crushing and screening stage in the industry is mainly composed of three-stage and a closed-circuit process. Gold ores need to go through coarse, medium, and fine crushing processes to be minimized into smaller pieces. The screening equipment is used to sieving the smaller gold ores into the proper size for the next steps.
The grinding operation usually adopts one or two ball mills with types of lattice and overflow. The second stage grinding operation forms a closed circuit with a spiral classifier or a hydro cyclone to ensure the grinding fineness.
Since traditional ball milling equipment appears some shortcomings such as fast wear and large energy consumption, many manufacturers adopt new wear-resisting rubber lining boards, sliding bearing to improve a mill operation efficiency and prolong a machine's service life.
The beneficiation stage is a crucial part of gold extraction during the whole gold ore processing plant. Placer gold mine and rock gold mine are most widely processed to extract gold concentration.
The gold slurry process of the carbon slurry method (CIP and CIL) is to put activated carbon into cyanide ore slurry, adsorb dissolved gold on activated carbon, and finally to extract gold from activated carbon.
Equipment required for carbon slurry gold mining process: Leaching mixing tank, activated carbon screen, Two-layer (three-layer) washing and thickening machine, fast desorption electrolysis system with high-efficiency and low-consumption, high-frequency dewatering screen.
It means that by ion exchange resin, gold also can be extracted from ore pulp. Like carbon, the process makes gold absorbed onto solid spherical polystyrene resin beads instead of activated carbon grains.
According to different physical and chemical properties of different types of gold ores, flotation separation utilizes various reagents to make the gold attached to the bubbles then scraping these gold particles from blades to get the concentrate.
A jigger is one of the main pieces of equipment in the gravity separation process. The jigging process mixes gold ore particles of different specific gravity together, then stratifying these particles. The minerals with small specific gravity will be on the upper layer while the minerals with large specific gravity will be on the lower layer.
A shaking table is used to process gold ores in the horizontal medium flow. The motor drives the surface of the shaker to perform the longitudinal reciprocating motion, as well as the differential motion of the washing stream and the surface of the bed. Gold ore particles are stratified perpendicular to the surface of the bed, then being separated parallel to the surface of the bed in reciprocating motion which allows gold ores with different particle sizes to be discharged from different parts to achieve separation.
It adopts lope water flow to achieve separation. With the effect of the combined force of water flow, mineral gravity, the friction created by the bottom of the tank, and ore particles, the gold ore particles will settle in different areas of the tank. The ore particles with small specific gravity will flow away with the water, while ore particles with larger specific gravity would stay.
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Henan Fote Heavy Machinery Co., Ltd. (FTM) has more than 40-year experience in the design of gold mining equipment processes. Its beneficiation equipment and plants sales to many countries including Tanzania, India, South Africa, the United Kingdom and other regions. According to the actual needs of customers, all machines can be customized here.
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Placer mining and lode mining are very different. Whereas placer gold has been released from within the rock and is generally free from any significant matrix, lode gold presents different challenges. While gold may be present in ore, it must somehow be released for proper extraction.
As a result, a number of machines have been invented to bring about maximum results with regard to obtaining the much needed resource, gold. One of such equipment is the ball mill. Below is the write-up of how a ball mill works, is used to crush ore and an explanation regarding its effectiveness in gold mining.
First of all, in order to get the best out of how this particular equipment is used it is important to get acquainted with knowledge on what it is, and is made of. Hence, a mill is a piece of equipment used to grind ores. Its major purpose is to perform the grinding and blending of rocks and ores to release any free-gold that is contained within them.
At major mines, the mill was the critical equipment that was required to process the ores that were extracted from deep underground. Many early mines used stamp mills, but many operations today find that ball mills are more functional for smaller operations and perform well with the modern equipment we have available now such as combustion engines.
To perform its functions, the ball mill operates on the principle of impact and attrition. This principle entails that the balls are dropped from near the top of the shell in order to bring about size reduction impact.
The major components of the ball mill include a shell that is hollow and is suspended on its axis to bring about rotation. The axis of the shell can be suspended horizontally or at an angle to the horizontal.
The shell is filled with quite few, but reasonable amount of balls which do the grinding process, and can be made of steel such as chrome steel and stainless steel. They can also be made of ceramic or rubber depending on their targeted material to be ground.
Its major operations are categorized into two, namely the dry and wet processes. Through those processes the machine is able to perform its functions of grinding the crushed materials. One of such functions, is that which is witnessed when grinding different types of ore, such as gold ore.
Now here is what one must know with regard to how the ball mill operates. The drum of the mill (shell) is suspended on two self-aligned rollers. Then the material to be worked on is loaded through the hopper.
From there, the mill is driven using a motor with a clutch, gearbox and the flexible coupling. The mill is then lifted to a certain level of height as it rotates. It is from that height that the balls begin to freely fall or roll down in order to grind the material that has been loaded.
After the material is ground, it is then removed from the mill depending on the discharge method used on the machine. For example, there are center unloading mills as well as unloading through the grille mills.
For the center unloading mills, the ground material is discharged through a hollow unloading trunnion using a free sink. To make it more efficient the pulp level in the drum should at least be above the level of the lower generating trunnion for unloading.
On the other hand, mills whose unloading is done using the grid consist of a lifting device which helps to unload the crushed material. For this reason, in such a mill the slurry level is likely to be lower compared to the unlading trunnion level. In such a mill, a grid with openings used for unloading crushed material is located in the unloading end of the drum.
To crush the gold ore in order to obtain pure gold, the large ore of gold is fed into a jaw crusher or mobile jaw crusher for the primary crushing process. The crushing process acts as a medium of screening the fine gold ore. It is then sieved using the vibrating screen and later sent through the use of a conveyer belt.
The ore is sent into a single-cylinder hydraulic cone crusher for the secondary crushing. Thereafter, the gold ore is transferred to a multi-cylinder hydraulic cone crusher, where the ore is crushed further into finer material. From there, the crushed gold ore is sent to a ball mill, evenly as it passes through a vibrating screen for grinding.
From the ball mill, the gold ore powder is subjected to the process known as beneficiation for further crushing before classification and floatation processes. Most commonly, professional mining operations will use a shaker table at this point. These are extremely effective at capturing tiny particles of free-gold that has been released from the ores.
Good working conditions can strengthen the grinding outcomes of overflow type ball mills. Therefore, in practical operation, workers need to continuously adjust overflow type ball mills working conditions so that they can work at optimal state. Then, what are the working conditions influencing the overflow ball mills outcome?
Overflow ball millsrotary speed influences the motion state of steel balls. Under the low-speed circumstance, steel balls drop after rising to a certain level, with grinding as main acting force supplemented by the impact. If increasing the speed, steel balls are thrown and fallen, with impact as main acting force supplemented by grinding. At higher speed, steel balls will do centrifugal exercise instead of grinding work. When at lower rotary speed, overflow ball mills have a better grinding outcome. It does the same when the steel balls filling ratio is among 40% to 50%.
Under a certain filling ratio, the smaller steel balls are, the better the grinding outcome is. However, as steel balls size becomes smaller, the impact between steel balls and ore particles will accordingly get weaker, which hinders the grinding effect. Consequently, as to materials with certain particle size, there always exists an optimal steel balls size capable of achieving a perfect grinding outcome.
Increasing pulp density in a certain condition, the viscosity of ore pulp will strengthen, making it easier to adhere to ball mills, thus enhance the mill productivity to improve the grinding outcome. But when the pulp density is too high, the ropy ore slurry will have buffer action on ball mills grinding operation. Higher feeding speed can contribute to timely ore discharge, while excessively fast speed likely leads to the over-load phenomenon. Therefore, it is necessary to set appropriate pulp density and feeding speed for the sake of better grinding performance.
Properly increase the mill circulating speed is conducive to the discharge of ore particles and improve the mill grinding performance. Usually, the suitable value for mill circulating load is 150% to 600%.
Xinhai is committed to adjusting the mills grinding performance to the best state. And it can change overflow ball mills working conditions like rotary speed and filling ration in accordance with customer requirement, thus increasing the interests of customers by increasing concentrate grade and recovery rate in subsequent separating process.
Prominer maintains a team of senior gold processing engineers with expertise and global experience. These gold professionals are specifically in gold processing through various beneficiation technologies, for gold ore of different characteristics, such as flotation, cyanide leaching, gravity separation, etc., to achieve the processing plant of optimal and cost-efficient process designs.
Based on abundant experiences on gold mining project, Prominer helps clients to get higher yield & recovery rate with lower running cost and pays more attention on environmental protection. Prominer supplies customized solution for different types of gold ore. General processing technologies for gold ore are summarized as below:
For alluvial gold, also called sand gold, gravel gold, placer gold or river gold, gravity separation is suitable. This type of gold contains mainly free gold blended with the sand. Under this circumstance, the technology is to wash away the mud and sieve out the big size stone first with the trommel screen, and then using centrifugal concentrator, shaking table as well as gold carpet to separate the free gold from the stone sands.
CIL is mainly for processing the oxide type gold ore if the recovery rate is not high or much gold is still left by using otation and/ or gravity circuits. Slurry, containing uncovered gold from primary circuits, is pumped directly to the thickener to adjust the slurry density. Then it is pumped to leaching plant and dissolved in aerated sodium cyanide solution. The solubilized gold is simultaneously adsorbed directly into coarse granules of activated carbon, and it is called Carbon-In-Leaching process (CIL).
Heap leaching is always the first choice to process low grade ore easy to leaching. Based on the leaching test, the gold ore will be crushed to the determined particle size and then sent to the dump area. If the content of clay and solid is high, to improve the leaching efficiency, the agglomeration shall be considered. By using the cement, lime and cyanide solution, the small particles would be stuck to big lumps. It makes the cyanide solution much easier penetrating and heap more stable. After sufficient leaching, the pregnant solution will be pumped to the carbon adsorption column for catching the free gold. The barren liquid will be pumped to the cyanide solution pond for recycle usage.
The loaded carbon is treated at high temperature to elute the adsorbed gold into the solution once again. The gold-rich eluate is fed into an electrowinning circuit where gold and other metals are plated onto cathodes of steel wool. The loaded steel wool is pretreated by calcination before mixing with uxes and melting. Finally, the melt is poured into a cascade of molds where gold is separated from the slag to gold bullion.
Prominer has been devoted to mineral processing industry for decades and specializes in mineral upgrading and deep processing. With expertise in the fields of mineral project development, mining, test study, engineering, technological processing.