The Dissolution of CaMg(SiO3)2 in Acid Solutions

Abstract

Abstract The dissolution phenomena of synthesized diopside, CaMg(SiO3)2, and a glassy material of the same composition in an acid solution were studied. The results observed in the dissolution of the glass were as follows; the molar concentrations of Ca dissolved in the solution are equal to those of Mg throughout the dissolution of the glass. The rate at which the cations go into solutions are proportional to the surface area up to about a 60% dissolution. The dissolution behavior of silica is similar to that of cations. A residual layer rich in silica is formed, one which is no longer dissolved after the removal of the cations. The results observed in the dissolution of the crystalline diopside were as follows; there is an initial rapid dissolution of the components, followed by another process. The molar ratios of the Ca ions to the Mg ions, and of each cation to silica in the solutions, are larger than those in the solid during the course of the reaction; they are especially large in the initial dissolution stage. An essential feature of diopside dissolution is that the Ca ions are more readily removed from the crystal than are the Mg ions. This fact is also confirmed in the natural diopside crystal. While the rates of the dissolution of the cations are not affected by the concentrations of HCl and HClO4, the concentration of H2SO4 does have an influence. Diopside cannot be dealt with as a single species participating in the heterogeneous reaction because its various components show selective dissolution. The mechanism of the dissolution of diopside will be discussed in connection with its structure.