A survey study of the kinetics of wollastonite dissolution in H 2 O-CO 2 and buffered systems at 25 degrees C

Abstract

The aqueous dissolution of wollastonite was examined at 25°C in two types of systems: (I) systems of approximately constant pH, and (2) systems evolving under different partial pressures of carbon dioxide. In all cases calcium, silica, and pH were determined as a function of time. Results indicate that the decomposition is by hydrogen ion attack. Rates of appearance of calcium, and perhaps silica, in the bulk solution may be governed by diffusion through an aqueous surface film. The calcium gradient through the film is a function of the pH of the system and is larger for lower pH values. In solutions under dilferent partial pressures of carbon dioxide, the overall reaction appears to be one of decreasing rate of calcium release with increasing pH and a corresponding decrease in calcium gradient in the surface film. Eventually, a state is reached at which the pH and rate of calcium release become approximately constant.