A Study of copper recovery by liquid membrane containing a chelating agent

Abstract

The liquid membrane process is being used on a small commercial scale for the recovery of copper and other heavy metals from mine waste waters, specially from leach solutions. The process used to give pure concentrated solutions which are suitable as a feed to a conventional tankhouse to recover equivalent grade of metals to those produced by solvent extraction. This study is concerned with copper recovery by unsupported liquid membrane containing a chelating agent. The objectives of this research study are: 1) to study the transfer process of copper ion across a liquid membrane containing a chelating agent; 2) to investigate the parameters that affect this transfer process. The investigated parameters are: copper concentration in feed solution, mixing speed, and the chelate concentration in the liquid membrane phase. The data obtained were then interpreted in terms of the above variables. In this study, an experimental setup was designed specially for copper recovery by LIX reagent-containing membranes. Most of the work was devoted on utilization of LIX64N reagent as a cation carrier, dissolved in kerosene at different concentrations. Different quantities of CuSO₄ were dissolved in deionized water to form variety of feeds. The copper concentrations in the aqueous phases were analysed by an Atomic Adsorption Spectrophotometer. The amount of copper complex in the organic phase can be calculated from mass balance of copper. Results show briefly that, the extraction process of copper can be modeled in terms of series resistances; first mass transfer resistance due to diffusion of copper ions in bulk of aqueous phase and then, kinetic resistance due to pseudo first order reaction (extraction reaction) at the interface. Based on results also, the stripping process is modeled in terms of active sites distributed evenly at the other interface. The number of active sites is assumed to be related to the feed concentration while the stripping reaction is considered under pseudo zero order reaction rate. In addition, the copper concentration appeared in the organic phase is modeled as the intermediate product of a series reaction. Furthermore, the chelates studied were classified in terms of their performance with copper extraction rate alone, and with respect to their effectiveness on the overall process of copper recovery based on the maximum copper yield obtained from experimental results. Explanations due to changes in copper feed concentration and changes in mixing speed were also given. Finally the equilibrium data of copper distribution between the aqueous phases and the organic phase, for the chelates used, were obtained. In addition, a simple diffusion experiment to obtain the diffusion coefficient of copper in aqueous feed was performed in a Diffusion Cell unit.