# Heap leach process



## alshangiti (10 فبراير 2010)

Heap leaching means leaching ores that have been mined, crushed, and transported on impervious pads for leaching by sprinkling and percolation of the solution through the ore. Barrick's Pierina Mine in Peru uses heap leaching to extract gold. Pierina is expected to produce more than 800,000 ounces of gold at a total cash cost of less than $50 per ounce in 1999, making it the world's lowest-cost major gold mine. 
The facilities consist of a valley-fill heap leach pad and a conventional Merrill-Crowe gold and silver recovery plant. The ore is stacked in a lined containment area behind a retention dam. A leach solution is applied to the top of the ore and allowed to percolate through the heap. As the solution migrates through the ore, it leaches the gold and silver from the rock and holds it in a solution. The gold-bearing solution ("pregnant solution") is collected at the base of the leach pad in the pore space within the heap. The pregnant solution is pumped to the gold recovery plant where suspended solids are removed and the solution is then treated in a conventional Merrill-Crowe precious metal circuit. The same valley-fill system was successfully used at Barrick's Mercur Mine in Utah.







Precious metals method
The crushed ore is irrigated with a dilute cyanide solution. The solution percolates through the heap and leaches out the precious metal. This can take several weeks.
The solution containing the precious metals ("pregnant solution") continues percolating through the crushed ore until it reaches the liner at the bottom of the heap where it drains into a storage (pregnant solution) pond. After separating the precious metals from the pregnant solution, the dilute cyanide solution (now called "barren solution") is normally re-used in the heap-leach-process or occasionally sent to an industrial water treatment facility where the residual cyanide is treated and residual metals are removed. The water is then discharged to the environment, posing possible water pollution.[_citation needed_]
The production of one gold ring, through this method, generated 20 tons of waste material.[]
During the extraction phase, the gold ions form complex ions with the cyanide:




Recuperation of the gold is readily achieved with a reaction:




*[ Copper method*

The method is similar to the cyanide method, above, except sulfuric acid is used to dissolve copper from its ores. The acid is recycled from the solvent extraction circuit (see solvent extraction-electrowinning, SX/EW) and reused on the leach pad. A byproduct is iron(II) sulfate, jarosite, which is produced as a byproduct of leaching pyrite, and sometimes even the same sulfuric acid that is needed for the process.
Although the heap leaching is a low cost-process, it normally has recovery rates of 60-70%, although there are exceptions. It is normally most profitable with low-grade ores. Higher-grade ores are usually put through more complex milling processes where higher recoveries justify the extra cost. The process chosen depends on the properties of the ore.
*[] Sulfuric acid heap leaching of nickel*

The method is an acid heap leaching method like that of the copper method in that it utilises sulfuric acid instead of cyanide solution to dissolve the target minerals from crushed ore. The method has been developed by European Nickel PLC for the rock laterite deposits of Turkey and the Balkans


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