LX-SX-EW aims to concentrate the aqueous copper solution from a few g/l to around 40-50 g/l and to eliminate the chloride, ferrous, manganese and other impurities that may cause problems in the downstream electrowinning process.
There are six different methods for leaching: heap, dump, in-situ, agitation, autoclave and vat. The leaching method used at each processing plant varies based on the ore chemistry and local conditions. Heap and vat leaching are common leaching methods.
In vat leaching, the process starts with the crushing, grinding and separation circuit followed by thickening. The slurry then enters vat leaching tanks and moves to solvent extraction through dewatering.
Heap leaching starts with the sprinkling of a low concentration sulfuric acid and water solution on a stockpile (leach pad) of low-grade ore.
The liquid percolates through the stockpile and dissolves copper minerals, producing an approx. 60% copper concentration called pregnant leach solution (PLS). The PLS then flows to a collection reservoir and to the solvent extraction plant; the copper is then transferred from the mildly acid aqueous leach solution to an organic solution.
After extraction, the copper-loaded extractant is fed to the stripping unit, where it is transferred from the organic solution to a strongly acid aqueous electrolyte solution.
This is followed by the final stage, electrowinning, where metal is recovered from the acid solution as it deposits to the cathode plates. In this step, an electric current is passed through a bath of the extracted material causing the copper to deposit onto metal plates and results in a pure form of the metal.