INFLUENCE OF MG2+ ON THE KINETICS OF CALCITE PRECIPITATION AND CALCITE CRYSTAL MORPHOLOGY

Abstract

The kinetics of calcite growth in the presence of Mg2 has been studied by both a pH free drift method and by visual observation. Our experiments show that the calcite growth rate is reduced by the presence of Mg2+. The higher the Mg/Ca ratio in the solution, the lower the growth rate in a CaCO3 supersaturated solution. The inhibition of calcite growth by the presence of Mg2+ is caused by Mg2+ being incorporated into the original calcite seed surfaces and developing new crystal surfaces. The Mg2+ distribution on the calcite surfaces is not uniform as there is likely to be different Mg2+ densities on the newly developed surfaces than on the original surfaces of the calcite seeds. This causes the calcite crystal morphology to change. The significance of creating error in using the initial rate data rather than the equilibrium rate data for the prediction of the calcite precipitation kinetics is discussed.