THE EFFECT OF COMPLEXING AGENTS ON THE PRECIPITATION AND REMOVAL OF COPPER AND NICKEL FROM SOLUTION

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Abstract
This paper addresses the effect of the complexing agents citrate, tartrate, ammonia, phosphate, and EDTA on the removal of copper and nickel from solution using both hydroxide and sulfide precipitation. Both batch and continuous metal sulfide precipitation experiments were performed. Results are presented for the removal of heavy metals and the resulting particle size distributions. The presence of weak complexing agents (citrate, tartrate, ammonia, and phosphate) had a minimal effect on the removal of copper and nickel, while the presence of a strong complexing agent (EDTA) resulted in the residual metal concentration being 1-2 orders of magnitude greater than the case with no complexing agents present. In an open system, the residual nickel concentration increased with increasing reaction time, due to the oxidation of nickel sulfide co nickel sulfate. For copper sulfide precipitation, the presence of complexing agents reduced the precipitate growth rate, nuclei density, and nucleation rate, resulting in a decrease of the dominant particle size (as compared to copper sulfide precipitation with no complexing agents present). The value of the kinetic order, i, decreased, while the kinetic rate constant, kN, increased in the presence of EDTA.

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