Combination of continuous diffusion dialysis and electrodialysis for separating NaOH/NaAlO_2 solution

摘要

Diffusion dialysis (DD), driven by concentration gradient, has inherent defects such as significant water osmosis, low transport rate, and recovery ratio. Meanwhile, electrodialysis (ED) is driven by electric field, which has high transport rate but consumes significant energy. Hence, the DD and ED processes are combined here to separate NaOH/NaAlO2 solution. The continuous DD process is first used to separate the alkaline solution, which is equipped with self-prepared polyvinyl alcohol (PVA)-based cation exchange membrane. The running condition is optimized at feed flow rate of 0.83 L m(-1) h(-1) and water flow rate of 1.0 L m(-1) h(-1), which can obtain recovered NaOH of 0.66 mol L-1 (M), recovery ratio of 44.4%, and rejection ratio of 91.2%. The residual liquor is further separated by ED process. The ED process running at 20 mA cm(-2) for 2 h can recover 0.40 M NaOH. The current efficiency is 79.4% and the energy consumption is 2.2 kWh kg(-1). The combination of DD and ED processes can remove 97.9% NaOH with the AlO2-rejection ratio of 85.4%. The energy is greatly saved due to insignificant energy consumption in DD process. Hence, the combination can elevate separation efficiency and save energy.