REMOVAL OF CADMIUM BY ANION EXCHANGE IN A WET PHOSPHORIC ACID PROCESS. PART 2: EQUILIBRIA,KINETICS AND REGENERATION |
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| Authors: | TT Tjioe P Weij JA Wesselingh GM van Rosmalen |
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| Affiliation: | Department of Chemical Engineering , Delft University of Technology , De Vries van Heystplantsoen 2, 2628 RZ Delft, The Netherlands |
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| Abstract: | The removal of cadmium by anion exchange from 55 w% H3PO4 (black acid from a Nissan H process) at 90°C in the presence of small amounts of halides (Cl-, Br-, I-) was investigated. Cadmium distribution coefficients, CD]resin/CD]acid (concentrations in mol/1), larger than 250 were obtained with HBr equilibrium concentrations of more than 0.10 w% in the phosphoric acid solution or with HI concentrations of more than 150 ppm. The regeneration of the Cd loaded resin was performed with a very dilute phosphoric acid solution (< 1 w% H3PO4). The excess of iodide in the phosphoric acid solution could also be- removed by anion exchange. A value of about 90 was obtained for the iodide distribution coefficient of a weakly basic resin. This resin could be regenerated with an 1 M NH3 solution at 50°C. The rate of adsorption and desorption of both cadmium and iodide were mainly determined by the diffusion in the resin|particle. Effective diffusivities of about 3*10-13 mZ/s and 1.3*10-11mZ/s were obtained for the adsorption of cadmium in the presence of HI and for the adsorption of iodide respectively. |
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