Enhanced mechanical stirring by eccentric impeller stirring system in zinc hydrometallurgy process for cadmium removal

Abstract The fluid in the reactor can be poorly mixed, so an eccentric impeller is proposed to improve the fluid mixing efficiency. In this investigation, numerical simulations and cadmium removal experiments for the purification of zinc sulfate solution were conducted. The effect of eccentric impellers on the purification efficiency was discussed. The mechanism of the effect of concentric and eccentric arrangement of stirring impellers on mixing in the stirred tank was elucidated. The results showed that the average axial velocity of the eccentric impeller stirring system (EIS) was 131.52% of that of the concentric stirring system (CS) and 134.23% of that of the eccentric stirring system (ES). In the purification and removal of cadmium in the zinc hydrometallurgy experiment, unit ion purification energy was introduced to quantify the energy consumed for each 1% of Cd2+ removed. The eccentric impeller shortens the reaction time by 40% and reduces the reaction energy consumption by 31.8% compared to the non-eccentric impeller. Compared to CS and ES, EIS disrupts the periodicity of fluid flow and facilitates the destruction of isolated mixing regions. EIS can enhance mechanical stirring to improve purification efficiency.