A bipolar membrane electrodialysis metathesis process for N-methyldiethanolamine regeneration, sulfate high-value conversion and resourcelization of NH4Cl wastewater

The treatment of wastewater and exhaust gas is the main issues in the environment protection field. A bipolar membrane electrodialysis metathesis (BP-EDM) process was proposed for the regeneration of MDEA and resourcelization of NH 4 Cl wastewater in the rare earth ores industry. The operating voltage had a favorable impact on augmenting both the MDEA regeneration rate and the desalination rate, accompanied by an increase in energy consumption. The increase in C(S):C(N) could reduce system energy consumption and enhance current efficiency when the ratio of C(S):C(N) was lower than 1:3.5. The increase of concentration of SO 4 2− in spent MDEA solution was advantageous for elevating the concentrations of (NH 4 ) 2 SO 4 and HCl solution, but accompanied by a decline in both the regeneration rate of MDEA and the desalination rate. The regeneration rate of MDEA and removal rate of HSS could reach 94.57 % and 93.11 %, respectively. Meanwhile, 43.83 g/L (NH 4 ) 2 SO 4 and 22.77 g/L HCl solutions could be produced. The energy consumption was only 0.33 kWh/kg MDEA, and the product cost was only 0.22 $/kg MDEA. The BP-EDM has shown great prospects as a cost-effective method for treatment and reclamation of wastewater and exhaust gas, and will play a pivotal role in the stable, efficient, and low-consumption operation of the absorption process by the regeneration and utilization of the MDEA absorbent.