Stripping of copper from CYANEX® 301 extract with thiourea–hydrazine–sodium hydroxide solution

The stripping of copper from the organic extract of bis(2,4,4-trimethylpentyl) phosphinodithioic acid, CYANEX® 301, using an aqueous mixture of thiourea, hydrazine and sodium hydroxide has been investigated. The optimal concentrations of the aqueous solution were found to be 1.0 M, 5 × 10− 2 M and 5.0 M, respectively which led to 95% stripping of copper from CYANEX 301 with concomitant regeneration of the extractant. The characterization of the stripped copper product was done using a combination of microanalyses, cyclic voltammetry and X-ray diffractometry (XRD). The product was made up of two non-stoichiometric copper sulfides, CuxS with x = 1.60 and 1.77. Cu1.60S was the major product. Hydrazine appears to play the role of reducing the disulfide species of CYANEX 301, R2P(S)S–S(S)PR2, formed during the extraction step, back into CYANEX 301, whereas thiourea provides a source of sulfur in the formation of the stripping products.