The precipitation of transition metal oxalate powders from aqueous solution. Crystal numbers and final sizes

Abstract

AbstractThe precipitation of manganous, ferrous, cobalt, nickel and copper oxalate hydrates was studied from equivalent solutions of concentrations from 0.001 to 0.3 M at pHs 7 to 6, by optical microscopy and other methods. Crystals growth started after induction periods: the precipitations were heterogeneously nucleated at low supersaturations and homogeneously nucleated at medium to high supersaturations. The crystal numbers of the final precipitates depended on the number of nuclei (and crystallites) formed during the induction periods. At medium to high supersaturations, crystal numbers increased with increasing initial metal oxalate complex ion concentrations according to the relation. N = N1Cmoxβ, where β was 5. The N values increased in the order Mn ≪ Fe < Co < < Ni < Cu.The final crystal lengths, in this range, then decreased with increasing metal oxalate complex ion concentrations according to the relation lfin = l1/Cmoxγ, where γ was 1.3. For precipitations from solution of any concentration, smaller crystals were generally obtained in the precipitates of the metal oxalate of lower solubility; nickel oxalate precipitations were the exception to this.