Effect of temperature on Mn–Ca selectivity with organophosphorus acid extractants

The effect of temperature on manganese recovery by solvent extraction was studied for the production of high purity MnSO4 from hydrometallurgical tailings solutions. Two commercially available organophosphorus cation exchange reagents, di-(2-ethylhexyl)phosphoric acid (D2EHPA) and bis(2,4,4-trimethylpentyl)phosphinic acid (CYANEX 272) as the active main components, were chosen. Among these regents, CYANEX 272 is selective for Mn over Ca while D2EHPA is selective for Ca over Mn. CYANEX 272 would therefore be the choice if the aim is to have good Mn/Ca selectivity. It was found, however, that at subambient temperatures the Ca–Mn selectivity of D2EHPA improves remarkably although the extraction order (Ca before Mn) still remains unchanged. As a cheaper reagent D2EHPA would be attractive, but lowering the temperature causes also an increase in viscosity and slower phase separation. The choice in the current case was therefore CYANEX 272 and a temperature of 40 °C. A three-stage Mn extraction followed by two-stage scrubbing and a two-stage sulfuric acid stripping led to a very pure MnSO4 solution.