Solid-liquid mass transfer in the presence of micro-particles during dissolution of iron in a mechanically agitated contactor

Abstract

Mass transfer between solid particles and liquids frequently occurs in the presence of inert micro-particles during iron removal by precipitation. In this investigation, the influence of inert micro-particles on mass transfer between a coarse active particle and liquid is simulated with the aid of a cementation reaction between cast iron particles and copper sulphate solution in a mechanically agitated contactor. Kaolin, silicon carbide, iron oxide and anatase were used as the inert micro-particles. The reaction was carried out under conditions of mass transfer control. The experimental data agreed well with Sano's semiempirical expression for a solid-liquid mass transfer coefficient based on the specific power group. The presence of inert micro-particles was found to reduce the solid-liquid mass transfer coefficient significantly, depending on volume fraction, size and density. The relative mass transfer factor, α, defined as the ratio of the solid-liquid mass transfer coefficient with and without the presence of inert micro-particles ( κ′ sl / κ′ sl ), was correlated by the expression (SD=8.66%). α = 1 + β ln θ ∗ θ mp where φ mp =the volume fraction of inert micro-particles, φ ∗= the threshold volume fraction below which the inert micro-particles do not influence the mass transfer coefficient; and β=a mass transfer attenuation factor. β and φ ∗ are functions of density and size of inert micro-particles and can be expressed as: β=4.33×10 −5 d mp −0.32 ϱ 1.05; φ ∗=0.17 d mp 0.12 ϱ mp −0.52 . The ranges of variables covered by the correlatiion are: 1.0< d mp<13 μm; 2600< ϱ mp<5300 kg/m 3; 0< φ mp<0.06. The relative mass transfer factor, α, was found to be independent of the coarse active solid phase hold-up up to a volume fraction of 0.04.