Customizing copper-iron selectivity using modified aldoxime extractants

In most copper solvent-extraction operations, an important consideration in the choice of extractant is the requirement for high selectivity of copper over iron. Ester-modified aldoxime extractants presently offer the best Cu:Fe selectivity. In some plants, however, the process feed liquors contain significant amounts of manganese but little iron. Although manganese is not chemically extracted by oximes, trace amounts are carried over to the electrowinning circuit by physical entrainment. This may result in anodic oxidation of manganese which, in turn, can cause oxidative degradation of the organic phase when returned to the solvent-extraction circuit in the spent electrolyte. Many of these operations prefer to operate with higher levels of iron reporting to the advance electrolyte as appropriate control of the Fe(II)/Fe(III) couple will ensure that manganese remains in the benign Mn(II) form. A new reagent, ACORGA® LS4202, offers the possibility of tailoring the iron co-extraction, so that appropriate Cu:Fe selectivity can be achieved in the solvent-extraction operation to maintain an electrolyte Fe:Mn mass ratio of >10:1, while retaining the other benefits offered by ester-modified aldoximes. The results of an integrated solvent extraction-electrowinning pilot-plant trial are presented, in which the performances of the conventional extractants ACORGA® M5774 and LIX® 984N are compared with ACORGA® LS4202. The Cu:Fe selectivity is demonstrated, along with results on the transfer of other impurities to the advance electrolyte.