Determination of induction time and primary nucleation kinetics for batch reactive crystallization of calcium carbonate

This paper is focus on nucleation and metastability with the objective of defining ranges of optimal supersaturation with respect to product quality. For batch reactive crystallization, a new definition of critical metastable zone width (CMSZW) was proposed. The induction time for batch reactive crystallization of calcium carbonate from unseeded aqueous supersaturated CaCl2–(NH4)2CO3 system were measured at different supersaturation ratios under 10 oC using focused beam reflectance measurement (FBRM). The determination of critical metastable zone width depended on the induction time. The induction time data was analyzed to calculate interfacial energy and various nucleation parameters, such as the radius of critical nucleus (rc), the critical free energy of nucleus (∆Gcrit), etc. Experimental results demonstrated that homogeneous nucleation predominated at high supersaturation and the heterogeneous nucleation prevailed at low supersaturation. It was recommended to maintain an optimum supersaturation everywhere and all the time in the crystallizer with respect to the mean crystal size and the purity of the crystals and when the concentration of initial CaCl2 solution, ranged from 0.1 mol/L to 0.5 mol/L, was 0.4 mol/L, the rc and ∆Gcrit achieved the maximum value.