Separation of nickel and zinc ions in a synthetic acidic solution by solvent extraction using D2EHPA and Cyanex 272

Solvent extraction was used to recover nickel and zinc from synthetic acidic solution. Many leaching solution and waste waters contain both zinc and nickel at the same time. Bis (2,4,4trimethylpentyl) phosphinic acid (Cyanex 272) and Di(2-ethylhexyl) phosphoric acid (D2EHPA) were used to separate nickel and zinc. In the D2EHPA system, at equilibrium pH of 2, zinc extraction was more than 98% whereas nickel extraction was only 0.36%. The extraction of metals was found to increase with an increase of pH of the aqueous phase. At equilibrium pH 3.5, zinc extraction was completed and higher than 99% zinc was extracted using Cyanex 272. The maximum nickel extractions using D2EHPA and Cyanex 272 were achieved at equilibrium pH 4.5 and 7.5, respectively. Both extractants showed the relatively good separation levels between nickel and zinc. D2EHPA and Cyanex 272 isotherms for single metal solutions showed that the extraction order was Zn2+>Ni2+. ΔpH1/2 value showed that the separation of nickel and zinc using Cyanex 272 was simpler than D2EHPA system. The stripping study was performed using sulphuric acid and it was shown that above 98% zinc and nickel could be extracted. These results demonstrated separation of zinc and nickel from sulphate solutions to be favorable.