Selective separation of Cu(II), Zn(II), and Cd(II) by solvent extraction

An experimental investigation was presented on the separation of Cu(II), Zn(II), and Cd(II) from a rich sulfate leachate of zinc slag by solvent extraction. The results of orthogonal experiments indicate that LIX 984N is highly selective and very efficient in the extraction of Cu(II), and the analysis of variance indicates that the sequence of parameters according to their influence on the separation efficiency is phase ratio > LIX 984N concentration > pH value > extraction time. The optimal condition for copper extraction is obtained as 25% of LIX 984N concentration, 7 min of extraction time, 3:2 of phase ratio O/A, and pH = 1.7. The separation of Zn(II) and Cd(II) was performed after the copper extraction from the raffinate. Comparative analysis of the separation with di-2-ethylhexyl phosphoric acid (D2EHPA), D2EHPA- tributylphosophate (TBP) synergistic extracting system, and 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (HEHEHP) was made at pH = 2.0. It is demonstrated that the extraction efficiency with D2EHPA is improved after being saponified by sodium hydroxide, and D2EHPA-TBP synergistic extracting, as well as HEHEHP, has a superior selectivity to Zn(II) over Cd(II).