Kinetics and mechanism of extraction of Cu(II) by CYANEX 302 from nitrate medium and oxidative stripping of Cu(I) using Lewis cell technique

The extraction of Cu(II) from nitrate medium using CYANEX 302 (bis(2,4,4-trimethylpentyl) monothiophosphinic acid) in kerosene under equilibrium conditions showed that copper is first extracted as Cu2+ followed by reduction of CuA(2) (HA)(2) to Cu+ while the CYANEX 302 extractant is correspondingly oxidized. The stripping of Cu(II) from loaded organic solutions by using different stripping agents showed that effective stripping is obtained upon using high concentration of nitric acid which oxidizes the extracted Cu(I) to Cu(II). In the present work, the forward extraction kinetics of Cu(II) from nitrate medium using CYANEX 302 in kerosene and kinetics of oxidative stripping of Cu(I)-CYANEX 302 chelate have been investigated using a Lewis cell. Extraction and stripping rates are governed by reactions at liquid-liquid interface rather than in the bulk phase. Extraction and stripping regimes are deduced to be chemical-controlled for Cu(II) and Cu(I). The different parameters affecting the extraction rate were separately studied and the extraction mechanism is discussed according to the dimeric model of CYANEX 302 in non-polar solvent. The stripping of Cu(I) from loaded organic solutions was achieved by using high concentration of nitric acid which oxidizes the extracted Cu(I) to Cu(II). Kinetic studies on the stripping of Cu(I) from loaded CYANEX 302 with nitric acid were also carried out using the same Lewis cell, and the mechanism of stripping process has been also proposed. From the temperature dependence of the rate measurement, the values of activation energy (E), enthalpy change (Delta H) and entropy change (Delta S) are calculated for both systems. (C) 2009 Elsevier B.V. All rights reserved.