KINETICS AND MECHANISM OF CONGRUENT AND I NCONGRUENT DISSOLUTION OF ALBITE IN 0.1 M POTASSIUM BICARBONATE AT 300-DEGREES-C AND PH 9

Initial congruent and the subsequent incongruent stages of albite diss olution were controlled by surface reactions on primary albite and sec ondary sanidine, respectively, and not diffusion in solution. An equat ion to describe the rate of the congruent stage as a function of Gibbs free energy of reaction was deduced. It implies a complex reaction me chanism, which involves crystal imperfections and a few rate-controlli ng elementary reactions. Incongruent albite dissolution was controlled by the growth of secondary sanidine crystals on seeds and nuclei on t he albite surface, according to the rate equation deduced, The recipro cal effect of albite dissolution and sanidine precipitation was govern ed by a mechanism more strict than the one acting through the activiti es of common aqueous species in the relevant rate equations: it equali zed the reaction rates despite great changes in the surface ratio betw een the primary and secondary minerals.