Separation of nickel and copper by solvent extraction using di-2 ethylhexylphosphoric acid-based synergistic mixture

Solvent extraction of copper(II) and nickel(II) from aqueous acetate solutions with di(2-ethylhexyl)phosphoric acid (D2EHPA), dissolved in n-heptan has been investigated. The extraction of Cu(II) was found to be quantitative in neutral, acetic acid, and acetate buffer media 96%, 95%, and 85% respectively. On the other hand, the extraction efficiency of Cu(II) decreases with the increase of the salt concentration in the aqueous solution. The extraction of Ni(II) in acetate buffer media is better than in neutral, 94% and 83% respectively. In addition, mechanisms of copper(II) and nickel(II) extraction have been established in neutral, acid, salt, and acetate buffer media. The results obtained are in good agreement with the speciation calculations given by the Cheaqs v. L20.1 (A Program for Calculating Chemical Equilibria in Aquatic Systems, RIVM, Bilthoven, The Netherlands). A study of the extraction kinetics of the copper-D2EHPA system was carried out. The mass transfer resistance was found to have a significant influence on the overall rate of the extraction of copper. At first, the extraction of an equimolar mixture of these two metals (Cu2+, Ni2+) was carried out in order to determine the optimum conditions for their separation from each other by the D2EHPA. The results showed that the selective extraction of copper(H) over nickel(II) 93% and 83%, respectively takes place at pH(s) = 5.71 using 4.8 mmol dm(-3) D2EHPA in n-heptan. Then, the same study was performed with tributyl phosphate (TBP) organophosphorus co-extractants. Synergistic effect has been observed on the yield of extraction of copper over nickel at 0.76 of TBP onto D2EHPA ratio in extractants mixture.