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UBC Theses and Dissertations

The kinetics zinc removal from cobalt electrolytes by Ion exchange Swami, Nathan S.


The removal of trace zinc concentrations from the INCO (Port Colborne) cobalt advance electrolyte by solvent impregnated ion exchange, was studied in column and batch tests. The solvent impregnated resins containing the extractants D2EHPA, Cyanex 272 and Cyanex 302, were com pared in terms of zinc loading and selectivity. D2EHPA impregnated OC 1026 resin demonstrated superior zinc loading and selectivity charac teristics, but retained objectionably high amounts of cobalt, which were lost in the zinc elution process. Cobalt loading, was found to be closely related to the electrolyte pH drop across the column and could be reduced by a resin pre-treatment with the advance electrolyte at a pH of 3 or by an increase in the feed electrolyte pH to 5, along with operation at a temperature of 40°C and a flow rate of 10 BV/hr.; all of which act to diminish the pH drop. The kinetics of zinc loading on each of the resins was found to be comparable, and the rate controlling mechanism in batch tests was found to be particle diffusion in the first fifteen minutes, while film diffusion became rate controlling at later time intervals. Pre-treatment enhanced the diffusion coefficient inside the resin phase by nearly an order of magnitude, improved exchange kinetics by allowing a lower pH reduction during the loading process, and improved Co²⁺/Zn²⁺ exchange in a mathx of the cobalt complex. An analysis of the breakthrough curves for the resins was done to determine the mass transfer coefficients inside the column, and a range of other parameters useful in the design of ion exchange columns. The rate controlling regime in the column was a mixture of the particle and film diffusion steps, with the former being the dominant control mechanism at the operating flow rate. Further work is needed in the X-ray microprobe analysis of resin samples from the top, middle and bottom portions of the columns, and of samples from batch tests, to aid in understanding the mechanism of ion exchange. The use of zinc selective electrodes in batch tests could also be undertaken to obtain a more accurate estimate of the diffusion and mass transfer coefficients.

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