Effect of carboxylic acids on the dissolution of calcite in aqueous solution. Part 3.—Polymaleic acid

The kinetics of calcite dissolution in polymaleic acid (PMA) solution (pH 2.70) have been determined using channel-electrode shielding measurements. Initially, the dissolution reaction proceeded with a rate constant (k′0= 0.02–0.04 cm s–1) similar in magnitude to that for the H+/calcite reaction in the absence of PMA. However, the reaction rate slowly decreased with time. This was attributed to the reversible adsorption of PMA at reactive sites on the calcite surface and a kinetic model for the adsorption–desorption processes was developed, for which the corresponding rate constants were deduced. The steady-state dissolution rate constant (k′) was found to depend on the concentration of PMA according to the following equation (k′)–1=(k′0)–1+ 1.4 × 108 cm2 s mol–1[PMA].The likely adsorption sites for the polymer were inferred from interference light microscopy studies of the dissolution etch-pit morphologies.