Determination of nucleation kinetics of cobalt sulfate by measuring metastable zone width and induction time in pure and sulfuric acid solution

Abstract

The metastable zone width (MSZW) and induction time of CoSO4 in the presence of H2SO4 were measured at various operating conditions by polythermal and isothermal methods, respectively. Raman spectroscopy and UV–Vis have been successfully adopted for measuring the solubility of CoSO4. The nucleation parameters were estimated with a self-consistent Nývlt-like approach and classical 3D theory approach. The results show a decrease in the solubility of CoSO4 with an increase in the concentration of H2SO4. MSZW decreased when raising the saturation temperature, mixing speed, and H2SO4 concentration, and decreasing the cooling rate. The induction time measurement indicated that the system showed homogeneous nucleation at high supersaturation (>1.15) and heterogeneous nucleation at low supersaturation (<1.15). The crystallized product was CoSO4⋅7H2O which has an octahedron shape and cubic shape with and without H2SO4, respectively. Moreover, the particle sizes are smaller with increased H2SO4 concentration and cooling rate.