Deep salt separation of zero discharge nanofiltration concentrate from steel industry wastewater
Water,as an important natural resource,is an indispensable resource for human life and production.Industrial water usage accounts for a large proportion of the total water consumption in the country,with the steel industry being one of the water-intensive industrial processes.The production of steel from raw materials requires a large amount of water,so the full utilization of the wastewater generated in the steel industry process is of great practical significance.For the nanofiltration concentrated wastewater generated in the steelmaking process,selective electrodialysis can not only greatly remove Cl-to obtain water for slag flushing,but obtain a high-purity and concentrated NaCl solution.In this study,selective anion and cation exchange membranes are replaced in the membrane stack,with the anion exchange membrane playing a key role in the system by separating Cl-and SO42-.The effects of different operating modes,voltages,volume ratios,and temperatures on the separation efficiency of Cl-and SO42-are explored,and pilot-scale long-term verification experiments are conducted.The experimental results indicate that constant voltage operation mode is more suitable for deep separation of Cl-and stable membrane operation.Under different voltages,membranes exhibit a high SO42-rejection rate,exceeding 97％,and reduces Cl-concentration below 1000 mg/L in the diluted chamber,resulting in a mass ratio of SO42-to Cl-greater than 10.Pilot-scale selective electrodialysis operated under 20 V at room temperature for 2 months demonstrates that the selective electrodialysis method has strong adaptability to fluctuations in wastewater concentration.It can effectively remove Cl-ions,stabilizing the concentration of Cl-in the desalination chamber to below 1000 mg/L.The mass ratio of SO42-to Cl-exceeds 10 by far,achieving a sulfate retention rate of over 94.5％.The energy consumption remains relatively stable,ranging from 0.254 to 0.278 kW·h/kg NaCl.
waste liquid of in iron and steel industryselective electrodialysisselective separation of monovalent anionspilot-scale long-term operation
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