MONOLAYER STUDIES OF SOLVENT EXTRACTION REAGENTS (HYDROMETALLURGY, FILM BALANCE, LIX63, LIX65N, INTERFACIAL CHEMISTRY

Efforts to elucidate solvent extraction mechanisms in hydrometallurgical systems have generally been hindered by a lack of physico-chemical data pertaining to the interfacial properties of organic soluble extractants and their metal complexes. In an effort to address this situation, a Langmuir film balance was used to characterize the interfacial properties of purified metal extractants spread as monomolecular films at the air/water interface. Both equilibrium and dynamic film properties of single component and mixed monolayers were examined. This included the measurement of pressure-area isotherms and the kinetics of monolayer dissolution into the aqueous substrate.;The kinetics of dissolution from sodium dinonylnaphthalene sulfonate (NaDNNS) monolayers followed a diffusion-controlled model from which the aqueous solubility of NaDNNS was estimated to be 0.7 (mu)mol dm('-3) at pH 6.0.;Pressure-area isotherms of 2-hydroxy-5-nonylbenzophenone oxime (HBPO, active reagent in LIX65N), and 5,8-diethyl-7-hydroxy-6-dodecanone oxime (DEDO, active reagent in LIX63) indicated that these extractants form liquid-condensed and liquid-expanded monolayer films respectively. The only extractant to show evidence of a phase transition in its pressure-area isotherm was DEDO in which a gaseous/liquid transition was observed.;The dissolution kinetics of HBPO followed a diffusion-controlled model. From the influence of pH on the dissolution rate, the surface pKa for HBPO was estimated to be 11.5. Because of deprotonation of the hydroxyoxime group, the aqueous solubility of HBPO was pH dependent. At pH 2.0, the solubility was 0.1 (mu)mol dm('-3) and increased to 4.0 (mu)mol dm('-3) at pH 12.;The collapse pressures of HBPO and mixed monolayers of DEDO/HBPO were inversely related to copper concentration in the aqueous substrate. Copper complexation apparently lead to the formation of reaction products which were less surface active than the unreacted oximes.