EQUILIBRIUM AND MASS TRANSFER FOR THE EXTRACTION OF COBALT AND NICKEL FROM SULFATE SOLUTIONS INTO BIS (2,4,4-TRIMETHYLPENTYL) PHOSPHINIC ACID - ‘CYANEX 272’.

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Abstract
Single metal and binary equilibrium data have been obtained for the extraction of cobalt and nickel from sulfate solutions into ‘Cyanex 272’. Cobalt extraction was observed to be practically independent of the aqueous phase nickel concentration, however the presence of cobalt in the aqueous phase inhibited nickel extraction. The apparent separation factor was found to be a function of cobalt loading, decreasing sharply at loading values above 60%. Single component isotherms were correlated using semi-empirical and polynomial curve fitting techniques. Binary data were correlated 1) using the deviation from ideal solution behaviour 2) using empirical curve fitting based on initial feed concentrations Mass transfer studies were carried out in a Lewis cell under both extraction and stripping condition. Overall mass transfer coefficients were found to depend on the concentration of the neutralized extractant and the stirrer Reynolds Number indicating both chemical reaction and diffusion effects on extraction rates. At low electrolyte concentrations visible wakes were observed in the aqueous phase due to extraction of the sodium Cyanex salt.