Solvent extraction of divalent copper, cobalt and zinc from aqueous thiocyanate solutions by tributyl phosphate

The extraction of divalent copper, cobalt and zinc from aqueous solutions containing potassium thiocyanate by tributyl phosphate (TBP) in kerosene has been investigated under different conditions. The distribution coefficient of metals for TBP increases with increasing aqueous thiocyanate concentration. The electronic and infrared spectra of the organic extracts were studied. From the results, it was found that the extraction efficiencies are in the order Zn(II) > Cu(II) > Co(II) for potassium thiocyanate concentrations in the range 0.1-0.2 mol dm(-3), and the extraction systems proceed according to the following reactions in which the thiocyanate ion of the extracted species coordinates to the metals through the nitrogen atom : M-1(2+)(a) + 2NCS(-)(a) + 2TBP (o) (right arrow over left arrow) M-1(NCS)(2)center dot 2TBP(o) where M-1 = Co or Zn and Cu2+ (a) + 2NCS(-)(a) + 3TBP(o) (right arrow over left arow) cu(NCS)(2)center dot 3TBP(o).