DISSOLUTION OF CALCIUM-CARBONATE CRYSTALS - A CONSTANT-COMPOSITION KINETIC-STUDY

A highly reproducible constant-composition technique has been used to study the rates of dissolution of calcium carbonate crystals over a range of undersaturation. The technique can be used even at very low undersaturation. Over a range of relative undersaturation, 0.05-0.33, the dissolution reaction appears to be controlled by a surface process which, in contrast to a bulk diffusion reaction, is markedly inhibited by the presence of additives. The influence of a number of polyphosphonates on the rate of reaction has been investigated. The reduction in dissolution rates can be interpreted in terms of a Langmuir-type adsorption isotherm. The effect of the pK(a) values of phosphonates on their inhibition of dissolution rates of calcite crystals has been discussed.