Kinetic studies on cadmium ions by Amberlite XAD7 impregnated resins containing di(2-ethylhexyl) phosphoric acid as extractant

The extractive behaviour of the di(2-ethylhexyl) phosphoric acid (DEHPA) adsorbed on the large specific area solid support (Amberlite XAD7) is investigated. Firstly, the retention of this extractant on the solid support is examined. It is shown that the extractant impregnation content varies significantly with the hydrophobicity of the impregnated solvent. Secondly, the kinetics measurements on the extraction of cadmium ions from aqueous sulphate solution with this impregnated resin were conducted. Experiments were carried out while varying the initial pH from 2.5 to 4, cadmium concentrations in the aqueous solution from 10 to 150 ppm and DEHPA content in the Amberlite XAD7 from 0.84 to 1.55 mmol/g SIR. Analysis of the rate data in accordance with two theoretical models used to explain the metal extraction kinetics showed that the process is always controlled by the rate diffusion of the cadmium ions through the liquid/liquid interface (aqueous solution/extractant) inside the pores resin. Particle diffusion coefficients were determined from the graphical representation of the proposed models. The results show that the homogenous diffusion model predicts a cadmium diffusion coefficient in the order of 10(-12) m(2)/s under the range of parameters studied. These values are lower than those calculated by the shrinking core model, which have an order of magnitude of 10(-7) m(2)/s. (C) 2007 Elsevier B.V. All rights reserved.