Degradation in hydroxyoxime solvent extraction systems

Abstract

The factors that influence the loss of oxime extractants by degradation mechanisms have been studied under conditions chosen so as to magnify these effects but far from those pertaining to present commercial practice. No decisions vis-à-vis choice of a commercial extractant should therefore be based upon these results. The reaction of mineral acid with oximes is shown to be a major factor in the degradation of oximes. LIX 63 degrades in the organic phase, probably by the hydrolysis of an acidic species such as HLIX63 +HSO 4 − · nH 2O. The process is enhanced by aqueous phase additives which increase the proton activity, reduced by copper complexation of the oxime, and is largely unaffected by diluents and other organic phase additives (except nonylphenol). There is also evidence of degradation occurring even in the absence of added acid when LIX 63 is complexed with copper at pH values around 2–3. SME529 also decomposes in the bulk organic phase; the degradation is faster than for LIX63. In contrast, LIX65N and P5100 degrade by an interfacial process, which can be accelerated by factors (such as alteration of the nature of the diluent or the addition of a second oxime) which increase water or acid uptake into the organic phase. Degradation of P5100 is faster than that of LIX65N. The degradation of kerosene (Escaid 100) is also shown to affect kinetic performance in solvent extraction adversely.