A MATHEMATICAL MODEL TO PREDICT EXTRACTION BEHAVIOR OF METAL IONS BETWEEN A POLYMER GEL AND AN AQUEOUS PHASE

Abstract

ABSTRACT A mathematical model to predict the extraction behavior of metal ion between a polymer gel and an aqueous solution was proposed. It consists of the Flory-Huggins formula for evaluating thermodynamically the physico-chemical properties of polymer gel, the modified Stokes-Einstein equation to evaluate the mass transfer rate of metal ion into polymer gel and the equation to evaluate the extraction equilibrium. The extraction of lanthanide elements, Nd(III), Sm(III) and Gd(III), from an aqueous solution containing nitrate ion was carried out by the use of SDB (styrene-divinylbenzene copolymer) gel swollen with a bidentate organophosphorus compound, CMP (dihexyl-N,N-diethylcarbamoylmethylphosphonate). The binary extraction and the effect of the crosslinking degree of SDB gel on the extraction rate were examined. These experimental results were in agreement with the predictions calculated by the proposed model. It was confirmed that the extraction behavior of lanthanide ions into- the SDB gel was predicted accurately, when the physico-chemical properties of SDB gel, such as the affinity between SDB and CMP ( ϰ ) and the crosslinking degree ( ν ), and a coefficient defined in the modified Stokes-Einstein equation (K0) were known. This model is available as a tool to design an extraction chromatographic process using polymer gel.