Liquid – Liquid Equilibrium between Aqueous and Organic Copper Solutions

With the depletion of rich ore resources, hydrometallurgy is becoming more popular since it is suitable for lean ores as well as metal containing wastes. Taking place at normal temperature, it consumes less fuel, emits less gas and poses less risk of fire and explosion. In hydrometallurgy, solvent extraction is a typical technique to concentrate and/or purify the leachate obtained from ore leaching step. Although developments such as membrane contact extraction or electrically enhanced extraction can speed up the process and eliminate some technical obstacles such as phase separation, important performance indicators such as recovery or extract concentration are inherently dictated by liquid – liquid equilibrium (LLE). In this paper, we investigated the LLE between D2EHPA and feed solvent contains copper, a metal commonly found in e-waste. The equilibrium curves at well controlled pH were obtained. Although the importance of pH in equilibrium is well known, this is the first time its effect on the degree of polymerization (DoP) of copper complex is recognized and quantified: ten times reduction of proton concentration resulted in nearly ten times increase of DoP. The relationship between copper concentrations in aqueous and organic phase was strictly linear (in log scale), allowing accurate prediction of extraction efficiency. The pH of aqueous phase between 3.5 and 4 was found to be the appropriate condition for copper recovery.