Sulfuric acid injection in copper heap leaching

Heap leaching is the use of percolating chemical solutions to leach out metals. Following mining, transporting and crushing to a consistent gravel-size, the ore is piled into a heap on top of an impenetrable layer on a slight slope. The leaching reagent (dilute sulfuric acid) is sprayed through sprinklers on top of the heap pile and allowed to trickle down through the heap, where it dissolves the copper from the ore. The resulting solution of sulfuric acid and copper sulfate is collected in a small pool. Copper concentration is around 65%.

Next step is solvent extraction. The leach solution is mixed vigorously with a solvent. The copper migrates from the leach solution into the solvent. The two liquids are then allowed to separate based on solubility, with copper remaining in solution in the solvent, and impurities remaining in the leach solution. 

The leftover leach solution is then recycled by adding additional acid – the LEWA pump application – and sent back to the sprinklers in the heap leaching process.

The last step is electro winning. An electrical current passes through an inert anode (positive electrode) and through the copper solution from the previous step, which acts as an electrolyte. Positively-charged copper ions (called cations) come out of solution and are plated onto a cathode (negative electrode) as 99.99% pure copper.