Effect of added complexing agents on extraction of Cu(II) from sulfate solutions by di(2-ethylhexyl)phosphoric acid

The efficiencies of Cu(II) extraction from 0.5 mol/dm(3) (Na,H)SO4 solutions by di(2-ethylhexyl)phosphoric acid (D2EHPA) in kerosene were measured in the presence of complexing agents EDTA, nitrilotriacetic acid (NTA), and citric acid. All experiments were performed in solution at pH 1.8-4.1; Cu(II) concentration of 0.005, 0.01, and 0.02 mol/dm(3); the concentration of complexing agent to Cu(II) as 0, 0.1, 0.2, 0.5; and a D2EHPA concentration of 0.01-0.5 mol/dm(3). The extraction efficiency of Cu(II) decreased with the addition of EDTA and NTA, but not with citric acid. The presence of complexing agents resulted in a change of reaction stoichiometry of Cu(II) and D2EHPA, likely due to the mutual interaction of Cu(II)-D2EHPA complexes and the complexing agents. The coextraction of citric acid into the organic phase could explain the increase in extraction efficiency with increasing citric acid concentration.