ABSTRACT
The growth of calcium oxalate monohydrate (CaOx) on colloidal oxide particles has been studied to investigate the role of ion adsorption in heterogeneous nucleation and growth of crystalline phases from aqueous solutions. Electrosonic amplitude (ESA) titrations of colloidal suspensions of SiO2, TiO2 and AI2O3 were used to characterize native particle surface charges and to detect adsorption of Ca2+ and Ox2−(C2O4 2−). For all three oxides, the results suggest that adsorption of divalent ions occurs on surfaces with opposite charges. The kinetics of CaOx nucleation on the colloidal oxides were determined using constant composition methods. Results indicate that induction times for CaOx nucleation are shortened by the presence of colloidal oxide particles. Analysis of the induction times as a function of solution supersaturation using classical nucleation theory suggests that at pH 6.5 SiO2 and TiO2 lower the surface energy barriers to nucleation while Al2O3 does not.
