Surface alteration of dolomite in dedolomitization reaction in alkaline media

The phases precipitated on the dolomite surface and the influence of alkalis on the properties of this surface were characterized. Experiments consisted of the immersion of single crystals of dolomite in saturated portlandite solutions with different alkalinity, temperature, and silica content. Most calcite forms in the solution as {104} rhombohedra. Brucite crystallizes as platelets, piles of platelets, sponge-like and {001} truncated ditrigonal pyramids attached to the dolomite surface. The morphology of brucite crystals depends on the pH of the solution. Apparent dissolution rate constants for dolomite at 75 degreesC are one order of magnitude higher than at room temperature. Initially, calcite grows on the dolomite surface with the same structural orientation {104}. In a second stage, when calcite has reached equilibrium with the solution, the new-formed {104} calcite surface starts playing an important role on the precipitation of brucite, while calcite continues crystallizing in the bulk solution. The calcite surface, negatively charged, can adsorb specifically metal cations. Mg2+, liberated by the dissolution of dolomite, would move attached to the surface, until they are trapped on these negatively charged surfaces, while OH- supplied by the alkaline solution favors the nucleation and growth of brucite. The attachment of Mg2+ to the surface controls the place where brucite grows. (C) 2003 Elsevier Ltd. All rights reserved.