The effect of carboxylic acids on the dissolution of calcite in aqueous solution. Part 2.—d-, l- and meso-Tartaric acids

Abstract

The effects of the dianions (A2–) of d-, l- and meso-tartaric acids on the dissolution reaction which takes place between calcite and the corresponding monoanions (HA–) has been investigated: (a) by using channel-electrode shielding measurements and (b) through the characterization of the resulting dissolution etch-pit morphologies. For the d- and l-tartaric acid system, under conditions where A2– is present at a concentration of 20 × 10–3 mol dm–3, dissolution is found to be described by the following rate law: jCa2+= 0.01 cm s–1[HA–]0 where [HA–]0 is the concentration (mol dm–3) of HA– at the calcite/water interface and jCa2+ is in mol s–1 cm–2. This demonstrates partial inhibition of the dissolution reaction as compared to the rate of dissolution in mineral acids. This is attributed to the adsorption of A2–. The shape of the etch pits resulting from treatment of calcite with A2–/HA– was used to infer the likely adsorption sites for the dianion. In the meso-tartaric acid system, much stronger inhibition is found and the rate of dissolution is strongly dependent on the concentration of A2– present, the rate law being given by: j[graphic omitted] = 0.04 cm s–1[HA–]0//1 +K[A2–] where K= 1.4 × 103 dm3 mol–1. Etch-pit morphologies indicated inhibition of both the lateral dissolution and the etch-pit nucleation process at dislocations on the calcite surface.