Selective separation of lanthanides by supported liquid membranes containing Cyanex 925 as a carrier

The work describes in detail the transport of lanthanides between chloride solutions by a facilitated transport through a supported liquid membrane (SLM) containing Cyanex 925 (a mixture of alkylphosphine oxides, Cyanamid). The chemical nature of this carrier requires a strong difference of chloride content between the two sides of the membrane which leads to a strong rise in the osmotic pressure. The influence of physical and chemical parameters affecting the transport of neodymium was determined including stirring rate and the chemical composition of the feed and stripping solutions. The highest permeability coefficients (cm min(-1)) were obtained under the following conditions: 1.0 M Cyanex 925 in kerosene (membrane), stirring rate 1200 rpm, feed solution of 2.5 M NaCl at pH 4.0 and a stripping solution of 0.8 M HCl. Under these conditions, the SLM is shown to be effective for the transport and separation of neodymium. Separation of lanthanide mixtures is possible. The selectivity of the system is such that Yb is the most favourably transported and La the least favoured, following the correlation Yb>Tb>Nd much greater than La. (C) 1999 Elsevier Science B.V. All rights reserved.