LIX®63 stability in the presence of Versatic 10 under proposed commercial extract and strip conditions, part III: Effect of manganese and cobalt loading on oxime stability at 30 °C

The combination of LIX (R) 63 with the carboxylic acid Versatic 10 exhibits synergistic properties, enabling direct separation of Co and Zn from Mn, Mg and Ca, a process of interest to the proposed El Boleo copper/cobalt project. Previous work on the chemical stability of this system had revealed the potential for rapid degradation of LIX (R) 63 oxime ('oxime') at high temperature (40, 50 degrees C) when extracting cobalt and zinc from El Boleo solutions. The present study under extract conditions at 30 degrees C found increased manganese loading, achieved by increasing operating pH from 4.5 to 6.0, facilitated increased rates of oxime degradation and 'irreversible' loading of cobalt. This cobalt was able to be reductively stripped using zinc metal, yielding anti oxime and 'keto-oxime'. Operation at pH 4.5 resulted in low manganese loading (about 0.2 g/L) and a calculated oxime half life of 67 weeks. Increasing the pH to 6.0 resulted in manganese loading of 2.5 g/L and a decrease in oxime half life to 24 weeks. Operation at pH 6.0 in the absence of manganese gave an oxime half life of 66 weeks. Zinc loading, cobalt loading and changes in pH between 4.5 and 6.0 (excluding the resulting impact on manganese loading) did not appear to have any adverse effect on oxime stability. At a given pH (5.0), 'irreversible' Co loading increased with increasing Co concentration in the aqueous solution. This did not have any noticeable effect on oxime half life. The metal:oxime:carboxylic acid stoichiometries of the Zn, Mn and Co synergist complexes were determined by continuous variation and maximum loading studies to be 1:3:2 for all three metals although 1:2:2 remained a possibility for manganese. Inter-conversion of syn oxime to anti oxime was observed to occur via two different mechanisms under the conditions used: a rapid process facilitated by manganese complexation; and a slower, temperature-based isomer re-equilibration process which occurred in the absence of manganese. This inter-conversion process, which resulted in increased manganese and zinc loading occurring relative to fresh organic (cobalt already being fully loaded), also opens up the possibility of decreasing the amount of LIX (R) 63 required in the El Boleo process. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.