Precipitation kinetics of nickel in the presence of iron

The effect of iron on the precipitation kinetics of industrially produced nickel powder was investigated on a laboratory scale using experimental conditions which, as far as possible simulated industrial scale. Seeded experiments were conducted using a 0.5 L stainless steel autoclave and a synthetic nickel ammine sulphate solution in the presence of a morphology modifier. Iron was introduced into the reduction solution as acidified ferrous sulphate solution (pH 2.5 to prevent oxidation) to give a reduction solution with Fe(2+) concentration of 6mg/L, 20mg/L and 200mg/L. The particle size distribution (PSD) of the powder from each batch reduction (densification) was measured by laser diffraction and the PSD data for each cycle was transformed into moments. Using the moments form of the population balance equation and assuming no breakage and size independent growth and aggregation, the molecular growth rate (G(0)), aggregation kernel (beta), aggregation rate (R(a)) and nucleation rate (J) were calculated. The results for the calculated G(0), B(0) and R(a) are shown below: [GRAPHICS] Iron was found to alter the precipitation kinetics by inducing nucleation and increasing the rate aggregation. There was however, a slight increase in the molecular growth rate.