Source: {"pile_set_name": "USPTO Backgrounds"}

Recovery of copper from oxidic copper bearing raw materials can be realized by leaching the raw materials with sulfuric acid at pH 1 to 2.5 followed by copper recovery by electrowinning after solvent extraction. However, especially with primary sulfide minerals, copper can be leached with sulfuric acid only at high temperatures and pressures resulting in a pregnant leach solution containing high sulfuric acid concentration due to high level of oxidation of elemental sulfur. This makes solvent extraction of copper expensive as excessive amount of acid in the solution has to be neutralized prior to the solvent extraction stage.
There are several discloses in the literature for the recovery of metals, in particular copper, from a copper-bearing sulfide ores where either hydrochloric acid or high chloride concentration has been utilized. Although leaching can be performed in reduced pressure and temperature as compared to sulfuric acid processes a high chloride concentration in pregnant leach solution decreases copper extraction yield in solvent extraction and makes the process more unattractive.
WO2004035840 for example relates to a method for the recovery of metals, in particular copper, from a copper-bearing raw material, whereby the material is leached into a chloride-containing solution. The leaching of the raw material is performed oxidatively and at a sufficiently high redox potential that the copper in the copper chloride solution from leaching is mainly divalent. The chloride solution obtained, which contains copper and potentially other valuable metals, is fed to liquid-liquid extraction. In the extraction the copper is first transferred to the organic phase with extraction and then to a sulphate solution in stripping, which is fed to copper electrowinning.
US2010/0031779A1 on the other hand discloses a process for recovering copper from an acid aqueous solution containing cupric chlorides and alkali metal and/or alkali earth metal chlorides by a solvent extraction with a cation exchange extractant, comprising the step of processing a solvent extraction in the presence of sulfate ions.