The role of the diffuse double layer in leaching of calcium from the surface of flyash particles

Abstract

A 1:25 ratio of flyash:water was stirred in an unbaffled reactor and the calcium that was leached into the bulk solution was measured over time. This experiment was conducted for two different flyashes differing in surface charge and calcium content. In both cases calcium accounted for nearly 92% of the total ions leached into the bulk phase. Since flyash particles are negatively charged, the overall mass transfer coefficient for the leaching of calcium from the surface of flyash into the bulk was calculated assuming the ions diffuse across a diffuse double layer. A steady state was assumed to exist across the diffuse double layer–bulk interface and the calcium is partitioned between the two phases. It was found that the overall mass transfer coefficient was influenced by the mass transfer from the flyash surface to the diffuse double layer. This novel approach explains the role of the diffuse double layer in leaching of calcium from flyashes