THE DISSOLUTION KINETICS OF ICELAND SPAR SINGLE-CRYSTALS

The dissolution of Iceland spar has been studied using a rotating disk method. This allows measurements to be made under conditions of well-defined mass transport and with single crystals prepared with surfaces having reproducible characteristics. The dissolution reaction was studied in the pH range 3.0-6.2 and with varying partial pressures of carbon dioxide. In general the flux of dissolving Ca2+ is given by the equation jCa2+/mole cm-2 sec-1 = k1[H+] + k2 + k3[H2CO3], where we find k2 to be 2.1 × 10-9 mole cm-2 sec-1 at 25°C (in citrate buffers) and k1 and k3 are given by the rate of transport of H+ and H2CO3, respectively, to the disk surface. In the presence of weak acids such as acetic acid which can rapidly dissociate on the rotating disk time scale then [H+] should be replaced by [weak acid] in the above equation and the diffusion coefficient used in calculating k1 should be that of the weak acid. © 1984