Hydroxyoxime stability and unusual cobalt loading behaviour in the LIX 63-Versatic 10-tributyl phosphate synergistic system under synthetic laterite conditions

The chemical stability of LIX (R) 63 (hydroxyoxime) in the presence of the carboxylic acid Versatic 10 and tributyl phosphate (TBP) was assessed under synthetic nickel laterite extract (pH 5.5) and strip conditions in the absence and presence of organic additive TXIB (the diester 22,4-trimethyl-1,3-pentanediol diisobutyrate). Anomalous cobalt extraction behaviour resulted in lower than expected cobalt uptake. Hydroxyoxime half lives were found to range from 26 to 68 weeks and 102 to 229 weeks under extract conditions at 45 and 35 degrees C, respectively, and 72 to 86 and >200 weeks under strip conditions. Decreasing hydroxyoxime half life under extract conditions appeared to be associated primarily or solely with increasing copper complexation. The presence of TXIB had no appreciable effect on hydroxyoxime stability. Investigation into the unexpectedly poor cobalt loading observed in the stability study samples resulted in the observation of unusual, 'N'-shaped cobalt extraction isotherms. This phenomenon was found to be attributable to ongoing displacement of complexed cobalt by nickel when insufficient anti-hydroxyoxime was available. Increasing the hydroxyoxime concentration overcame this issue. (C) 2011 Elsevier B.V. All rights reserved.