The effect of chloride ions on copper solvent extraction from sulfate-chloride medium using LIX 984N

Abstract

The supply of fresh water is becoming an increasingly important issue in hydrometallurgical treatment of mineral ores. The problem may significantly reduce if the extraction process can incorporate the usage of saltwater throughout the whole hydrometallurgical operation. Seawater as the main source of saltwater is a potential alternative to freshwater. In this research, the effect of the chloride ions, in a range of 0 to 40 g/L, on the solvent extraction of copper with LIX 984N was studied. LIX 984N has been commercially used in copper solvent extraction around the world. Increasing the concentration of Cl− was shown to increase the H+ activity and formation of CuCl+ and CuCl2 species. The solution acidity did not have a negative effect on the extent of copper extraction and extraction rate, in the presence and absence of chloride ion, in contrast to recent studies. The chloride addition was even showed to have a positive impact on copper extraction at pHs below 2 and at shorter mixing times. Through thermodynamic studies, it was shown that increasing chloride concentration results in both higher H+ activity and an increase in the activity of copper chloride complexes, of which the latter factor counteracts the former and overall improves the extent of copper extraction. Increasing the chloride concentration was found to negatively affect the copper extraction isotherms. The impact became more significant at lower concentrations of the extractant. It is therefore suggested that cupric chloride complex ion inhibits copper extraction by lowering the extraction driving forces. Also, it was shown that increasing aqueous chloride concentration promotes involvement of more extractant molecules per Cu2+ species in the extraction reaction in contrast to the reaction without chloride ions. The negative effect of chloride ions on copper solvent extraction then is due to the change in the reaction stoichiometry and decrease in the extraction driving force rather than the types of aqueous Cu2+ speciation. The effect of wash stages on the removal of the chloride ion from loaded organic solution was then investigated and the optimum conditions for the wash stage were found at wash solution to loaded organic ratio of 1 to 7 and sulfuric acid concentration of 10 g/L.