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ore dressing ore gold ore ball milling

ore dressing ore gold ore ball milling

Using Ball Mills to Extract Raw Gold from Ores ...

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.

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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. Meanwhile, the surface of the inner part of the shell is in most instances coated with an abrasion resistant material which may include manganese steel. 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 grin...

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Now here is what one must know with regard to how the ball mill operates. The drum of the mill 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 u...

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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 tableat this point. These are extremely effective at capturing tiny particles of free gold that has been released from the ores.

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Ore Dressing Methods

The fact that a product of high value and small bulk can be produced at a gold mine, often by relatively simple milling processes, has made it possible to operate gold mines successfully in remote and inhospitable regions where high costs of transportation, fuel, and power would make it impossible to exploit profitably base metal ores of equal dollar value. As a result, in many instances gold mine development has been the advance guard of civilization in regions where other mineral resources were developed later and agriculture and industry followed.

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In the milling of gold ores, as with other kinds of ores, the treatment that will give the best metallurgical and economic results in any particular instance is determined primarily by the character of the ore, although other factors previously mentioned must be considered also. The principal ore characteristics that govern the selection of the milling method are grade of ore and uniformity of tenor, the size of the gold particles, the nature of the associated minerals, and the degree to which the gold particles are locked within them. The details of the process also will be determined by these characteristics and to a considerable extent by the crushing and grinding qualities of the ore. Ores of very low grade usually can be exploited successfully only when treated on a large scale in plants of high capacity, which involve heavy initial capital outlay. Higher grade ores may be treated profitably in smaller plants with lower initial outlay per dollar of output, unless the ore is ref...

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There are two principal methods of amalgamationplate amalgamation and barrel amalgamation. In plate amalgamation the ore is crushed wet in stamp mills or ground in ball mills and the resulting pulp flows over copper plates , which are coated with amalgam and mercury. Particles of free gold and silver coming in contact with the mercury alloy with it to form gold silver amalgam, which adheres to the plates. Where stamps are employed, the screen openings range from about 12 to 40 mesh as a rule, which determines the maximum size of ore particles in the pulp passing over the plates. Mercury sometimes is introduced into the stamp mortar, also, especially if there is much coarse free gold in the ore. The plates are dressed every few hours, the interval depending on the grade of the ore, amount of sickening that takes place, the scouring action of the pulp, and degree of discoloration of the plates by chemical action. Dressing usually comprises brushing the plates from the...

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Concentration is employed for the purpose of segregating the gold in a product of relatively small bulk for direct shipment to a smelter or for further treatment in the mill. For many years gravity concentration was virtually the only concentrating method employed in gold mills, but in recent years flotation methods have been used widely, especially in the flow sheets of new mills. As an adjunct to other methods, concentration may effect marked savings in operating costs. Thus, it is often possible to produce a concentrate containing most of the gold after relatively coarse grinding, then fine grind the concentrate preparatory to extracting the gold by cyanidation or amalgamation. Since fine grinding usually is the most costly operation in gold milling, it is obvious that where it can be restricted to a concentrate, the bulk of which is only a fraction of that of the original ore, the saving in cost is appreciable. Furthermore, the constituents of t...

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The cyanide process is based on the work of MacArthur and the Forrests and involves the leaching of gold and silver from alkaline pulps with dilute solutions of sodium or potassium cyanide, the filtering and clarification of the gold silver bearing solution, and precipitation of metals from solution. Oxygen is essential to the solution reaction, and in practice oxygenation is accomplished by violent agitation of the pulp by the injection of compressed air. Precipitation usually is by means of zinc shavings or zinc dust and is improved if the solution be first de aerated. Aluminum is used instead of zinc under some unusual conditions. Nearly all gold ores are amenable to cyanidation, although, as previously pointed out, certain constituents of some ores cause excessive consumption of cyanide and other reagents, or the fouling of solutions, with resultant high costs. A few are so difficult to treat by direct cyanidation that costly preliminary treatment must be employe...

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The data in table 57 have been obtained from various sources as noted. In view of the frequent changes in practice that take place in most mills due to changes in ore characteristics, in methods and equipment brought about by research and improved machines, and increases or decreases in capacity, these data should be understood to apply specifically to the period covered and only generally to long time operations. However, they represent broadly current practices and results obtained in milling various types of gold ores.

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