Preparation Of Acid And Alkali From Sodium Sulfate By Coupling Process Of Single-Membrane Electrolysis And Bipolar Membrane Electrodialysis

In industrial production,a large amount of highly saline wastewater is inevitably produced.Among them,sodium sulfate(Na2SO4)is the main salt component in most of the wastewater,and direct discharge will cause waste of resources and serious environmental pollution.The removal and recycling of Na2SO4 in high-salinity wastewater is the research focus and difficulty of wastewater treatment.Single membrane electrolysis technology can electrolyze Na2SO4 solution into corresponding alkali(NaOH)and acid-sodium sulfate(H2SO4-Na2SO4)mixed solution,and bipolar membrane electrodialysis technology can effectively adjust the concentration of H+in the mixture.In this study,single-membrane electrolysis and bipolar membrane electrodialysis technology are coupled to deal with solution containing high concentration of Na2SO4 for generating NaOH and H2SO4.In the H-shaped glass electrolysis cell,the effect of H+ concentration,Na2SO4 concentration,current density,and temperature on the preparation of NaOH by electrolyzing Na2SO4 solution was investigated by using single-membrane electrolysis.The results show that the current efficiency of alkali increases first and then decreases with the increases of current density and electrolysis temperature.Increasing the concentration of Na2SO4 in the salt chamber solution is conducive to enhancing the current efficiency.Moreover,the result of electrolysis is the best when the concentration of H+in the salt chamber reaches at 1 mol/L.For the purpose of coupling with the single-membrane electrolysis,the bipolar membrane electrodialysis technique is used to control the H+concentration in the H2SO4-Na2SO4 mixed solution.In the plate-frame bipolar membrane electrodialysis device,the effects of process conditions such as the type of anion-exchange membrane,H+concentration in the acid chamber,and current density on the current efficiency were studied,and the diffusion phenomenon during the bipolar membrane electrodialysis process was explored.It is found that the current efficiency of AEM-2 membrane is higher than that of AEM-1 membrane.H+ permeates between the salt and acid chamberss under the effect of concentration gradient,the current efficiency will obviously decrease with the increase of the H+concentration in the acid chamber.Increasing the current density can ensure the current efficiency decrease slightly while enhance the purity of the product H2SO4.Under the optimized conditions,Na2SO4 solution was treated by the coupling process of plate-frame type single-membrane electrolysis and bipolar membrane electrodialysis.NaOH was produced in single membrane electrolysis and H2SO4 was generated in bipolar membrane electrodialysis.Compared with traditional two-membrane three-chamber electrolysis,the coupling process increases the current efficiencies of acid and alkali by 22%and 6.2%respectively,significantly reducing the electric energy consumption by 10%.