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

The interactions between calcite particles and solutions containing MgCl₂, BaCl₂ or ZnCl₂ 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 BaCl₂, witherite was obtained; with ZnCl₂, Zn₅(OH)₈Cl₂ was obtained. Under equilibration conditions, the products dependent on the reaction which occurred in the aqueous phase. With BaCl₂, witherite enriched with Ca was obtained, together with small amounts of alstonite. Very small amounts of calcite recrystallized to aragonite as well. With ZnCl₂, only traces of smithsonite were obtained, while there were no new phases with MgCl₂. 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.