LIX®63 stability in the presence of Versatic 10 under proposed commercial extract and strip conditions, part II: Oxime isomer inter-conversion and the effect of oxime degradation products on selected physical properties

Although combining Versatic 10 with LIX®63 oxime (‘oxime’) results in desirable synergistic solvent extraction properties, it can also promote oxime degradation, resulting in products which could potentially have an adverse effect on physical properties. Degradation of eight organic solutions under different operating conditions typically in excess of those expected at the proposed El Boleo operation, resulted in the generation of 5,8-diethyl-6,7-dodecanedione monooxime (keto-oxime), 5,8-diethyl-6,7-dodecanedione (diketone) and 5,8-diethyl-7-hydroxydodecan-6-one (acyloin) to varying degrees in the different samples. None of the degradation products were found to have an adverse effect on metal selectivity or phase disengagement. A previously mooted possibility of 5,8-diethyl-6,7-dodecanedione monooxime having a beneficial effect by acting as a synergist was found to be unsustained.A chromatographic (HPLC) method was developed to enable the observation of discrete syn and anti isomers of LIX®63 oxime and to investigate possible isomer inter-conversion in this synergistic system. Conversion of ‘inactive’ syn oxime to the ‘active’ anti form occurred readily under extract conditions at 30 °C. Subsequent conversion of some anti oxime back to syn under strip conditions was also observed.