Identification and characterisation of a Cyanex 272 degradation product formed in the Murrin Murrin solvent extraction circuit

Gas chromatography (GC) analysis of organic solutions in Murrin Murrin Operations' cobalt and zinc solvent extraction (SX) circuits revealed the presence of the same, prominent, unidentified foreign impurity in both circuits. This species, which was both isolated and synthesised, was characterised and identified as the n-butyl ester of the Cyanex 272 phosphinic acid, namely n-butyl-bis(2,4,4-trimethylpentyl)phosphinate. This species is formed in the SX circuits by reaction, either directly or indirectly, of the phosphinic acid with tributylphosphate (TBP). It was found to be present at 3.7–4.1% v/v in the Murrin Murrin Operations' organic solutions. Notwithstanding poisoning by chromium (III), this is the first example of chemical degradation of phosphinic acid under SX operating conditions. This species could potentially be acting as an acid extractant.