Origin and significance of the deviations from a pseudo first order rate law in the coupled transport of metal species through supported liquid membran

Abstract

A new equation describing the permeation rate of metal species in the coupled transport through supported liquid membranes (SLM) was derived. The equation assumes that the concentration profile within the membrane never goes to zero and contains the independently measurable distribution ratios of the permeating metal species between the organic liquid membrane and the aqueous feed and strip solutions. The equation was experimentally verified by measuring the distribution ratios and the permeation rates of Eu 3+ through SLMs consisting of a 0.1 F solution of bis(2-ethylhexyl)phosphoric acid (carrier) in n-dodecane absorbed on a thin microporous polypropylene film. The conclusion was reached that the deviations from a pseudo first order rate law, often observed when measuring the coupled transport of metal species at low concentration through SLMs, originate in the non-negligible value of the distribution ratio at the SLM—strip solution interface. Nevertheless, these deviations can easily be taken into account in a quantitative way and, by an appropriate linearization of the permeation data, information can be obtained on two, newly defined, permeability coefficients of the SLM.