Heap leaching process was developed as a mineral processing low-grade metal that is more efficient and minimal cost. Compared with conventional cyanidation process of the mineral leaching process with stirred tank Heap leaching has several advantages in the form of designs that use a very simple, operating costs are also minimal, and in requiring less investment, because the heap leaching recovery is around 60% to 80 %. In large-scale process technology was first used and applied to the mining of gold ore at Carlin Nevada USA in 1970. This process has really made a lot of mines that can easily take on geological resources that have a low grade and transforming them into the category of proven ore. Ore value as low as 0.01 oz Au can be processed by heap leaching system is economically.
Besides gold and silver, cyanidation is also often used to recover copper content in the rock, due to the nature of this metal is very easily soluble in both the cyanide. And sometimes too much copper in the rocks encountered in the content of gold and silver cyanidation method on the rocks so that it is still economical given. Heap leaching generally requires 60 to 90 days for processing of ore that can be leached in 24 hours in a conventional agitated leach process. Gold recovery is usually 70% compared with 90% in agitated leach plant. Even with this low performance, the heap leaching process has facilitated the processing of natural resources, because the processing cost is much reduced compared with agitated leaching.
The process involves the leaching of rocks and placed as well as the destruction of rock minerals that contain metal ore in a heap on the building on a floor stand. The foundations of leaching (leaching pad) can be made permanently using a hardening of the concrete floor or foundation and geo-coated membrane (high density polyethylene) cyanide solution is distributed at the top of the stack and then the liquid seeps down through the pile of ore and dissolves the gold through a pile interrupted. Gold laden minerals flowing out from the bottom of the pile and is collected for gold recovery by carbon adsorption either with or zinc precipitation. Barren solution is then recycled to the next pile.
Some of the benefits or advantages from the use of heap leaching system are as follows:
- Extraction from the heap leaching is usually carried out on the rocks -3 / 4 inches, whereas extraction in agitated leaching in stirred tank requires a reduction to -200 mesh size of 100 mesh or need.
- Solid liquid separation step is not necessary to heap leaching on the heap leaching system.
- Tailings disposal costs are high enough for the modern agitated leach plant. Large dam expensive fluid retention is required. For comparison, heap leach pads can generally be left in place after reclamation.
Some Disadvantages heap leaching system, in addition to a lower recovery compared with agitated leaching heap leaching, including:
- Ore stacked must be porous enough to allow solution to drip or drain water solution through the slit pore. There are plenty of recovery failure due to inability to obtain the flow solution. It's a lot of experience when the ore has high clay content or in rocks containing clay very much. This problem is often solved by agglomeration prior to stacking piles.
- In areas of high rainfall, the solution of balance problems can arise, so it requires a lot of care and discharge processes.
- In areas where extremely cold, freezing the pile can result in low recovery period. Modification of operational procedures such as subsurface application solutions has been reduced, but not eliminated this concern.
Quite often, the mine will use the washing agitated for high grade ores and heap leaching for marginal grade ore that would otherwise be considered waste rock. A common recovery plant is often used for both operations.
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