Analysis of the pH-stat and pH-drift seeded precipitation of calcite

Crystal growth of calcium carbonate (calcite) has been carried out using pH -stat and pH-drift methods at 15, 25 and 40 degrees C. The slope "m" of the linear relationship between the logarithm of the linear growth rate, lnG, and the logarithm of supersaturation, ln(S-1), in the experiments carried o ut at pH-stat varied from 2.9 at 15 degrees C to 0.95 at 40 degrees C, indi cating a change in the factors controlling the growth mechanism. If a parab olical law, m = 2, is assumed, for the sake of comparison with previous res ults of the literature, the activation energy calculated is 53 kJ/mol, whic h is comparable with these results. When experiments are carried out at pH- drift the relationship between lnG and In (S-1) is nonlinear. This result i s interpretated by a simultaneous process of growth units incorporation at some kinks of the surface, progressive increase of the H+ concentration on the surface and local H+ adsorption at kink sites, inhibiting the growth un its incorporation at these sites.