Heap Leaching

Heap leaching is an industrial mining method to dig out precious metals and copper compounds from ore.

Process of heap leaching

The mined ore is crushed into tiny chunks and heaped on an impermeable plastic and/or clay lined leach pad where it may be irrigated with a leach solution to melt the valuable metals. Sprinklers, or frequently drip irrigation, are used to minimize evaporation. The solution then percolates through the heap and leaches out the precious metal. This can take many weeks. The leach solution having the dissolved metals is then accumulated.

Precious metals method

The crushed ore is irrigated with a dilute cyanide solution. The solution percolates through the heap and leaches out the valuable metal. This may take many weeks.

The solution containing the precious metals ("pregnant solution") carries on percolating through the crushed ore awaiting it reaches the liner at the underneath of the heap where it drains into a storage space (pregnant solution) pond. After unraveling the precious metals from the pregnant solution, the dilute cyanide solution (presently known as "barren solution") is usually re-used in the heap-leach-method or infrequently sent to an industrial water treatment ability where the residual cyanide is treated and residual metals are taken out. The water is then released to the environment, posing likely water pollution.

Copper method

The method is akin to the cyanide technique, above, except sulfuric acid is utilized to dissolve copper from its ores. The acid is recycled from the solvent withdrawal circuit and is used again on the leach pad. A byproduct is iron (II) sulfate, jarosite, which is manufactured as a byproduct of leaching pyrite, and at times even the same sulfuric acid that is needed for the procedure.

 

Although the heap leaching is a low cost-method, it usually has recovery rates of 60-70%, though there are exceptions. It is usually most profitable with low-grade ores. Higher-grade ores are normally put through more complex milling processes where elevated recoveries justify the extra cost. The method chosen depends on the properties of the ore.

Sulfuric acid heap leaching of nickel

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