Kinetics and Mechanisms of Dissolution of Silica at Room Temperature and Pressure

Abstract

Numerous studies have been conducted recently concerning the dissolution kinetics and mechanism of quartz or amorphous silica at various temperatures ranging from 25 to 300~ (see Dove and Elston, 1992 and Bcrgcr et aI., 1994 for reviews). These investigations have been mainly concentrated on the influence of pH and of electrolyte solutions on the dissolution rate, and various mechanisms have then been proposed, mostly in terms of surface complexation models. Although these studies have contributed to a better understanding of the reaction mechanism, there still remain questions which need to be addressed and clarified regarding mainly the existence of a minimum in the rate of dissolution of quartz as a function o fpH and on the nature of surface complexation sites and their quantification. We have therefore s tudied the rate of dissolution of amorphous silica and quartz at close pH intervals especially at low pH's. The influence of concentrations of various cations (Li, Na, K, Cs, Mg, Sr and Ba), anions (Br, CI, SO4 and NO3) and organic acids (acetic, citric and oxalic acids) have also been investigated in detail so that their effects on the rate can be better quantified.