Two-stage countercurrent solvent extraction of copper from cuprous chloride solution: Cu(II) loading coupled with Cu(I) oxidation by oxygen and iron scrubbing

This study was conducted as part of the development of a novel process for copper recovery from copper sulfide concentrates by chloride leaching, simultaneous cuprous oxidation and cupric solvent extraction to transfer copper to a conventional sulfate electrowinning circuit and hematite precipitation to reject iron. Four LIX reagents (LIX84-I, LIX612N-LV, XI-04003 and LIX984N) were used as extractants while kerosene was used as a diluent. Copper was effectively extracted into LIX reagent organic solution from chloride solution. However, iron co-extraction exceeded 0.5 g/L. Two-stage countercurrent solvent extraction is proposed to reduce iron extraction. In the first stage, copper-loaded organic solution was pre-scrubbed by contacting with the cuprous and ferrous chloride pregnant leach solution. The extent of iron removal increased from 78 to 91 to 95% with decreasing pH from 1.0 to 0.5 to 0.0 while the extent of copper removal increased from 1 to 17 to 36%. Although more iron was removed at a pH below 0.5, copper was removed to an unacceptable level. Therefore, it is recommended that pH should be controlled around 1.0 to remove the bulk of the loaded iron while avoiding excessive copper stripping. In the second solvent extraction stage, copper is loaded into the organic solution by simultaneous cuprous oxidation by oxygen and cupric extraction. After two-stage counter current solvent extraction, the organic solution was further scrubbed by contacting with copper sulfate (4 g/L Cu) and sulfuric acid (15 g/L) solution. The iron extraction was reduced to a satisfactory level at an A/O ratio of 1/40 to 1/20 while the copper extraction practically did not change. The Cu/Fe ratio in the copper-loaded organic solution can meet the industrial requirement.