SOLID-LIQUID MASS-TRANSFER IN THE PRESENCE OF MICROPARTICLES DURING DISSOLUTION OF IRON IN A MECHANICALLY AGITATED CONTRACTOR

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, alpha, defined as the ratio of the solid-liquid mass transfer coefficient with and without the presence of inert micro-particles (k'(sl)/k(sl), was correlated by the expression (SD = 8.66%). alpha = 1 + betaln phi*/phi(mp) where phi(mp) = the volume fraction of inert micro-particles, phi* the threshold volume fraction below which the inert micro-particles do not influence the mass transfer coefficient; and beta = a mass transfer attenuation factor, beta and phi* are functions of density and size of inert micro-particles and can be expressed as: beta = 4.33 x 10(-5) d(mp)-0.32 rho1.05; phi* = 0.17 d(mp)0.12 rho(mp)-0.52. The ranges of variables covered by the correlation are: 1.0 < d(mp) < 13 mum; 2600 < rho(mp) < 5300 kg/m3; 0 < phi(mp) < 0.06. The relative mass transfer factor, alpha, was found to be independent of the coarse active solid phase hold-up to a volume fraction of 0.04.