Heterogeneous nucleation rate of calcium carbonate derived from induction period

The induction period, t(ind), in the process of heterogeneous nucleation of CaCO3 in aqueous CaCl2-Na2CO3 solution was investigated. The tind was measured by applying the conductivity method. Diatomaceous earth and zirconium oxide were used as foreign particles to induce heterogeneous nucleation. The experimental results showed that tind decreased with an increase in supersaturation and the solid concentration of foreign particles. The solid concentration of foreign particles had a great influence on tind at low supersaturations; however, the effect of foreign particles was negligible at high supersaturations. A novel model of tind for the heterogeneous nucleation was derived by using the Michaelis-Menten equation. In this model, the heterogeneous nucleation rate, J(h), was considered to be the sum of the bulk nucleation rate, J(b), and the particle-induced nucleation rate, J(p), where J(b) and J(p) were contributed from the bulk of solution and the surface of added foreign particles, respectively. The results showed that Jh could be expressed simply as a function of the supersaturation and the solid concentration of foreign particles. The affinity, Km, between calcium carbonate and foreign particles obtained from the diatomaceous earth was greater than that obtained from the zirconium oxide. A comparison between the calculated and experimental results showed that the Michaelis-Menten equation was satisfactory to describe the experimental data of tind and to derive the nucleation rate for the heterogeneous nucleation of calcium carbonate.