Determination of nucleation and crystal growth kinetics of barium carbonate

Abstract

A compact apparatus of specific construction is used for nucleation measurements in accordance with Nielsen's method. Experiments are realized by varying the supersaturation ratio from 35 to 280 and temperature from 10 to 50 °C. Barium carbonate is precipitated by mixing equal volumes of sodium carbonate and barium hydroxide solutions. The experimental data have shown that the nucleation rate of barium carbonate in the supersaturation range cited above is characterized by the primary heterogeneous mechanism and can be expressed by the relation r N= A 0 exp(− E/ RT)exp[− B/((ln S) 2)], where A 0=6.4×10 24 m −3 s −1, E=22,065 J mol −1, and B=58.7. An original method, using a high seed charge in a batch crystallizer, is developed for the determination of crystal growth kinetics in a large range of supersaturation variation. At high supersaturation ratio, the crystal growth rate satisfies a first-order kinetic expression, while at supersaturation ratio values lower than 2, the kinetic expression is second order. These results show that the crystal growth of barium carbonate follows the Burton, Cabrera, and Franck mechanism characterized by the kinetic expression G= αs 2 tanh( β/ s). The fitting of this kinetic expression with all experimental data at 25 °C from low to high supersaturation ratio values using a least-squares technique gives α=9.49×10 −7 m 7 mol −2 s −1 and β=1.35×10 −2 mol m −3.