Effect of solid concentration on solid-liquid mass transfer in a mixing vessel

Solid-liquid mixing vessels are employed widely in mineral processing industry for carrying out operations such as leaching, digestion, adsorption, precipitation and other chemical processes. Efficiency of these operations depends on physical processes such as mixing and mass transfer between the solid and liquid phases. Previous studies on mixing and mass transfer in solid-liquid agitated systems were often on systems with low concentration of solids. However, there is a strong demand in mineral industry for intensifying existing mixing operations so that more materials can be processed without significant increase in energy consumption and major changes in the geometry of the existing infrastructure. This work investigates the effect of increasing the throughput on solid-liquid mass transfer in a mixing vessel. Experiments were carried out in a fully baffled 0.2 m diameter cylindrical mixing vessel equipped with a 6-bladed Rushton turbine. Aqueous HCl solution and cationic ion-exchange resin were used as the liquid and solid phases, respectively. Mass transfer rate was determined at various intervals by measuring the changes in the conductivity of the liquid phase due to the transfer of cations from the liquid to solid phase. Mass transfer coefficient was then calculated from the measured mass transfer rate and correlated with impeller speed and specific impeller power input. Current results show that the mass transfer coefficient increases with increasing solid concentration in the slurry. It was also found that there is no significant increase in the mass transfer coefficient with increasing solute concentration in the liquid phase.