The influence of impurities on the growth rate of calcite

The effects of 34 different additives on the growth rate of calcite were investigated. An initial growth rate of about one crystal monolayer (3 × 10-8 cm) per minute was adjusted at a constant supersaturation which was maintained by a control circuit. Then the impurity was added step by step and the reduction of the growth rate was measured. The impurity concentration necessary to reduce the initial growth rate by a certain percentage increased in the order Fe2+, ATP, P3O5-10, P2O4-7, (PO3)6-6, Zn2+, ADP, Ce3+, Pb2+, carbamyl phosphate, Fe3+, PO3-4, Co2+, Mn2+, Be2+, β-glycerophosphate, Ni2+, Cd2+, “Tris”, phenylphosphate, chondroitine sulphate, Ba2+, citrate, AMP, Sr2+, tricarballylate, taurine, SO2-4, Mg2+ by 4 orders of magnitude. The most effective additives halved the initial growth rate in concentrations of 2 × 10-8 mol/1. For Fe2+ the halving concentration was nearly proportional to the initial rate. The mechanism of inhibition by adsorption of the impurities at growth sites (kinks) is discussed.