The impact of the electrical potential gradient on limestone dissolution under wet flue gas desulfurization conditions

Abstract

The flux of an ion in an ionic solution is due to a concentration gradient and an electrical potential gradient. The latter is a result of differences in the diffusion constants of the diffusing ions. Even though it is possible to express the electrical potential gradient in terms of concentrations and concentration gradients, it results in a complicated system to solve if more than two species diffuse. In this study the dissolution rate of limestone has been modeled with the flux equations, including the electrical potential gradient and assuming that the electrical potential gradient is zero. Under wet flue gas desulfurization (WFGD) conditions which correspond to a rather high ionic strength, > 100 mM, it was found that the impact of the potential gradient is insignificant when the pH of the slurry is above 3. Furthermore, it has been shown that when neglecting the potential gradient, the mass balances must be combined with a flux of charge condition and not a condition of electroneutrality.