MASS-TRANSFER AND KINETIC-BEHAVIOR OF CHELATED CADMIUM SOLUTIONS

The effect of the chelating agents nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) on the electrodeposition of cadmium from solutions was studied. Experimental results show that the presence of a chelating agent severely inhibits cadmium reduction. The mass transfer and kinetic behaviour of cadmium ions in chelated solutions (NTA and EDTA) were investigated. The observed overall diffusion coefficients of the chelated cadmium solutions, using the simple Levich equation, were found to be a function of the solution pH and the chelating agent. The relevant kinetic properties, such as the reaction order, alphaz, k(f)0 and the equilibrium potential, were measured for cadmium ions in the chelated solutions. The diffusion coefficients of the more stable chelated cadmium species were found to be less than those of the less stable chelated cadmium species, thus causing more interference in the diffusion step.