MASS-TRANSFER BETWEEN A FIXED-BED OF LIMESTONE PARTICLES AND ACID-SOLUTIONS

Limestone dissolution in acid solutions was experimentally studied by means of a fixed-bed reactor. A diffusive model was proposed to descri be experimental results. The model, based on the film theory, takes in to account the effect of the electric potential of diffusion on the di ssolution rate. In order to validate the model, experiments were carri ed out to study the effect of both particle size and liquid-solid rela tive velocity on the dissolution rate. Furthermore, the limestone diss olution rate in aqueous solutions of SO2(aq), HCl, and H2SO4 was measu red at different acid concentrations. The results showed that the diff usive model, associated with the correlation proposed by Chu et al. [C hu, J. C.; Kalil, J.; Wetteroth, W. A. Chem. Eng. Prog. 1953, 49 (3), 141] for the evaluation of the liquid-solid mass-transfer coefficient, is capable of describing the dependence of the dissolution rate on bo th the size of the limestone particles and the liquid-solid relative v elocity. In addition, it was found that, in agreement with the physica l meaning of the film theory, the thickness of the liquid film is not dependent on the kind of acid present in the solution nor on its conce ntration but only on the fluid dynamic conditions of the liquid-solid system.