Effect of monothiophosphinic acid and phosphine sulfide impurities on the solvent extraction behavior of bis(2,4,4-trimethylpentyl)dithiophosphinic acid from sulfate and methanesulfonate media

Abstract

A crude, synthesized mixture of bis(2,4,4-trimethylpentyl)dithiophosphinic acid (DTPhos), was evaluated as a functional alternative to the discontinued Cyanex® 301 extractant. This study enabled the assessment of the influence of common impurities, such as bis(2,4,4-trimethylpentyl)monothiophosphinic acid (MTPhos) and phosphine sulfides, on metal extraction performance from methanesulfonate (MSA) and sulfate media. Both extractants exhibited nearly quantitative extraction of Ni(II), Co(II), and Zn(II) under non-saponified conditions. In contrast to Cyanex 301, synthesized DTPhos-based mixtures did not give rise to third-phase formation at elevated pH values in methanesulfonate media. Additionally, Mn(II) was extracted at lower pH values with the DTPhos mixtures than with Cyanex 301. Regression analysis of distribution ratios confirmed comparable cobalt(II) extraction efficiencies and revealed a moderate reduction in separation from nickel(II) for the least-enriched DTPhos formulation. Overall, the effect of the DTPhos impurity on the extraction properties was limited under the investigated conditions. Furthermore, variations in extraction mechanisms were suggested by pH-dependent behavior, particularly in sulfate-based systems. These findings support the use of synthesized DTPhos as a viable alternative to Cyanex 301, offering practical benefits such as stability against third-phase formation and flexibility in extractant composition.