Effect of baffles on solid-liquid mass transfer coefficient in high solid concentration mixing

Suspension of solids plays an important role in promoting mass transfer between solids and liquid in mechanically agitated vessels employed in mineral and chemical industries. This becomes especially important when high solids concentrations are used for the purpose of process intensification. In mineral industry, there is a strong demand 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 study aims to investigate the effect of baffling conditions on solid-liquid mass transfer in slurries with high solids concentration up to 30 % (v/v) at just off-bottom solid suspension condition. Experiments were carried out in a 0.2 m diameter vessel equipped with a six-bladed Rushton turbine. Four rectangular equally spaced baffles were used to study the effect of baffling condition on mass transfer. Aqueous NaOH solution and cationic ion-exchange resins were used as the liquid and solid phases, respectively. Experimental results show that solid-liquid mass transfer coefficient (kSL) increases rapidly with an increase in CV from 5 to 20 % (v/v). This study also indicates that kSL values at Njs under unbaffled conditions are greater than those under baffled condition. Operating the vessel under unbaffled condition was found to be more energy efficient compared to baffled condition. These results imply that it is possible to intensify the process and still achieve significant improvement in mass transfer simply by removing the baffles and increasing the solids concentration in the system.