On the application of bulk-supported liquid membrane techniques in hydrometallurgy

Abstract

A theory of bulk-supported liquid membrane extraction has been developed. The process is performed sequentially in a series of three-phase mass-transfer stages. In each stage the extractant circulates in a closed circuit and alternately contacts a donor (feed) phase and an acceptor (stripping) phase. Special cases have been analyzed in which the phases in the chambers move countercurrently in plug-flow mode; contact chambers represent perfectly-mixed cells; contact chambers consist of a series of theoretical stages; each contact chamber represents a theoretical stage. Experimental and computational studies on extraction and separation of lanthanide chlorides have been carried out using two schemes of a cascade of mixer-settlers: (1) connected in the usual way with external circulation of the extractant (the extractant first passes through all the stages of extraction and then through all the stripping stages) and (2) based on a bulk-supported liquid membrane (the extractant recycles between each pair of extraction and stripping stages). The effectiveness of the bulk-supported liquid membrane extraction scheme was considerably greater than that of the conventional scheme. Experiments on the extraction of lanthanide chlorides from neutral aqueous solutions in the system involving methyltrioctylammonium di(2-ethylhexyl)phosphate were carried out. The experimental results are in satisfactory agreement with the data calculated, which confirms the agreement between theory and experiment. The bulk-supported liquid membrane extraction can be applied to other systems and heavy metals as well.