Michael H. Barker

Study of kinetics of charge transfer across a supported liquid membrane under transient conditions

Abstract The transfer of a cation across a supported liquid membrane is studied both theoretically and experimentally during a linearpotential scan. The transferring cation was originally present both in the membrane and in the flanking aqueous phases, thusworking as a potential-determining ion in the system. With this set-up, the transfer kinetics of hydrophobic ions which usuallydetermine the limits of the potential window of an ideally polarised liquid liquid interface can be studied, even if the standardpotential of transfer is unknown. The probe cation studied was tetrabutylammonium, and the membrane phase was o -nitropheny-loctyl ether. The observed standard rate constant k 0 took a surprisingly low value of ca. 2˛10 ˝4 cm s ˝1 ; however, this agreeswith the values measured with a rotating diffusion cell under steady-state conditions. It is therefore suggested that the differentvalues obtained with different techniques reflect the structural changes of the liquid liquid interface due to the electric current.© 2001 Elsevier Science B.V. All rights reserved.

Reaction product layer on chalcopyrite in cupric chloride leaching

Abstract During the leaching of chalcopyrite in cupric chloride solutions, a reaction product layer forms on the mineral surface. In the present work, the formation and the composition of the reaction product layer on solid stationary chalcopyrite was studied in a chemical environment similar to that of the HydroCopper® process. The effect of the process parameters on the reaction product layer was investigated. Electrochemical measurements, including A.C. impedance spectroscopy, were carried out and an equivalent circuit was used to estimate the surface parameters of the reaction product layer, such as resistance, capacitance and porosity. Scanning electron microscopy was used to complement the electrochemical measurements. The results suggest that at pH = 1, a fragile more resistive elemental sulphur layer forms, whereas at pH = 3, a porous less resistive FeOOH layer is formed. Lors de la lixiviation de la chalcopyrite en solutions de chlorure cuivrique, une couche de produit de reaction se forme a la surface du mineral. Dans le present travail, on a etudie la formation et la composition de la couche du produit de reaction sur de la chalcopyrite solide stationnaire dans un environnement chimique similaire a celui du procede d’HydroCopper®. On a etudie l’effet des parametres du procede sur la couche de produit de reaction. On a effectue des mesures electrochimiques, incluant la spectroscopie a impedance A.C., et l’on a utilise un circuit equivalent pour estimer les parametres de surface de la couche de produit de reaction, comme la resistance, la capacitance et la porosite. On a utilise la microscopie electronique a balayage pour completer les mesures electrochimiques. Les resultats suggerent qu’a un pH = 1, une couche fragile de soufre elementaire plus resistive se forme, alors qu’a un pH = 3, une couche poreuse moins resistive de FeOOH est formee.