Performance Estimation of Tubular Supported Liquid Membrane for Heavy Metal Removal Processes

Modeling studies are carried out to estimate the performance of the processes for the removal and recovery of heavy metal ions in aqueous solutions using the shell-and-tube type modules of supported liquid membranes. The mathematical model includes the boundary mass transfer resistance in the bulk solutions, the interfacial reaction between metal ions and impregnated chelating agents, and the diffusion in the membrane pores. Analytic solutions are obtained for coccurrent and countercurrent flows of feed and strip solutions respectively, when the hydrogen ion concentration(pH) is constant. The metal ion removal efficiency of the membrane modules is examined when the feed side pH is constant and when changed. Results show that the performances of cocurrent and countercurrent operations of feed and strip solutions have similar trends, when the dimensionless length is less than 0.2 under the given conditions. However, the effluent metal concentration for the countercurrent flow of feed decreases to zero value for the dimensionless membrane module length greater than 0.2, while the feed concentration approaches to equilibrium for the coccurrent flow. It is also found that the metal ion flux is decreased by slow interfacial reaction rate which results from decreasing pH of the feed when the feed is operated without pH adjustment. The selectivity and removal rate of the metal ion could be increased by constant pH operation in the feed side. The effects of interfacial reaction rate constants and diffusivities of metal-complex ions on the performance of membrane modules are studied. The results would provide a basis for the design and operation of tubular supported liquid membrane modules to select chelating agents and operation conditions.