The interactions between calcite particles and aqueous solutions of magnesium, barium or zinc chlorides

Abstract

The interactions between calcite particles and solutions containing MgCl 2, BaCl 2 or ZnCl 2 were investigated in two different systems. In one system the solution was percolating through a column of ground calcite. In the second system the solution was equilibrated with calcite powder and the suspension was thoroughly shaken. The solid sediment was then examined by X-ray diffraction, IR spectroscopy, SEM, microprobe analysis and thermal analysis. During the percolation, the reaction which occurred at the solid-liquid interface predominated. With BaCl 2, witherite was obtained; with ZnCl 2, Zn 5(OH) 8Cl 2 was obtained. Under equilibration conditions, the products dependent on the reaction which occurred in the aqueous phase. With BaCl 2, witherite enriched with Ca was obtained, together with small amounts of alstonite. Very small amounts of calcite recrystallized to aragonite as well. With ZnCl 2, only traces of smithsonite were obtained, while there were no new phases with MgCl 2. In addition, the following reactions, which do not lead to the formation of new phases, also occurred: (1) sorption of the metallic cation onto the calcite surface, either by cation exchange or by surface hydrolysis; (2) topochemical substitution of Ca by the metallic cation inside the calcite crystal. The first was favored in the percolation system, whereas the second occurred in both.