Kinetics of crystallisation of calcite from calcium bicarbonate solutions

Abstract

The kinetics of calcite crystal growth from supersaturated and metastable dilute solutions of Ca(HCO₃)₂ has been measured at 298.15 K using a seeding technique. The results are expressed as reduced growth curves against growth affinity and are consistent with a mechanistic growth model in which the CO₂ concentration in the layer adjacent to the surface is greater than in the bulk of solution. As the reaction proceeds to equilibrium, the dissolved CO₂ concentration gradient across the boundary layer decreases tending to unity at equilibrium. Models of crystal growth that have previously been used with varying degrees of success for growth from CaCl₂+ Na₂CO₃/NaHCO₃ mixtures are found to be in disagreement with these data. The results are consistent with the mechanistic model suggested by Plummer et al. based on the results of dissolution experiments. The growth model of Davies and Jones leads to good agreement when the extent of precipitation is between 0.1 and 0.45.