Study On The Treatment Of Ammonium Chloride Wastewater And The Preparation Of Polyferric Sulfate With High Basicity By The Bipolar Membrane Electrodialysis

Many industries,such as nano-sized superfine calcium carbonate?NSCC?industry and soda ash industry,can produce the NH₄Cl wastewater.Discharging it directly will not only waste a lot of recyclable resources,but also result in some environmental problems,such as eutrophication and algae excessive propagation.Hence,it is necessary to deal with it.Some existing treatment methods include crystallization,evaporation,decomposition,nano-filtration,and biodegradation as well.However,these methods have some drawbacks,such as causing secondary salt pollution and high process cost.In addition,with the continuous development of Chinese chemical industry and the improvement of people's living level,the discharging of industrial wastewater and domestic wastewater is increasing.How to treat the industrial and domestic wastewater to recycle the water resources effectively has received widespread attention and it also raises a claim for the flocculant with high performance.Polyferric sulfate is an iron-based polymer coagulant with a molecular weight up to 10⁵.It has the superior removal efficiency of COD,BOD,turbidity,heavy metal,and it is also insensitive to temperature and pH.Generally speaking,the higher basicity the polyferric sulfate has,the higher flocculation performance it will have.Bipolar membrane electrodialysis is an organic combination of bipolar membranes and electrodialysis.Among them,bipolar membrane,is a kind of composite membrane,consists of an anion exchange membrane layer,a cation exchange membrane layer and an intermediate layer.Under a reverse bias of direct current field,water molecule in the intermediate layer of bipolar membrane can be dissociated to H⁺and OH^-ions.Here,BMED is used to treat the ammonium chloride wastewater and prepare the polyferric sulfate with high basicity.The research works concerned are described as follows:1.Bipolar membrane electrodialysis?BMED?with BP-A stack configuration was employed to convert the ammonium chloride wastewater into hydrochloric acid and ammonium hydroxide,in order to overcome the shortcomings of conventional treatment methods.First,different commercial anion exchange membranes ?TWEDA2,AMV,JAM-II and CJMA-2?and bipolar membranes?BP-1,BPM-I and FBM?were used to conduct the BMED process.Results show that AMV and BPM-I are regarded as the optimum membranes in consideration of process performance(the final HCl concentration,the final solution conductivity in salt compartment,process energy consumption and process cost comprehensively.Second,BMED process is optimized by changing the current density,initial NH₄Cl solution concentration and initial volume ratio of acid solution and NH₄Cl solution.Results indicate that as the current density increases from 70 to 90 mA/cm²,the energy consumption and the final acid concentration can increase from 1.51 to 2.83 kW·h/kg HCl and 2.45 to 2.84 mol/L respectively,and the total process cost of 70 mA/cm² is the highest?0.80$/kg HCl?;meanwhile,increasing the initial NH₄Cl concentration can increase the energy consumption,the final acid concentration and the total process cost;in addition,with the increment of the initial volume ratio of acid solution and NH₄Cl solution from 0.5 to 1.0,the energy consumption varies between 1.46 and 1.62 kW·h/kg HCl and the final acid concentration improves from 1.95 to 2.71 mol/L,while the total process cost decreases from 0.63 to 0.42$/kg HCl.In short,based on these results,the optimum operation condition is that the current density is 80 mA/cm²,the initial NH₄Cl concentration is 1 mol/L and the initial volume ratio of acid solution and NH₄Cl solution is 0.67⁰.83.2.BMED with BP-A stack configuration is used to study the continuous process of preparing PFS with high basicity.Effect of current density,molar ratio of FeSO₄ to H₂SO₄ in feed and feed flow rate on the PFS properties?basicity,total iron content,pH,density,etc.?and process energy consumption was investigated.Results show that when the current density increased from 10 to 20 mA/cm²,the basicity and turbidity removal ratio increased from 8.59%to 11.32%and from 84.31%to 95.34%,respectively.However,when the current density was greater than 20 mA/cm²,the turbidity removal ratio and basicity decreased slightly,while the process energy consumption increased up to 4.26 kW·h/kg H₂SO₄ and the final acid concentration in acid compartment is up to 0.45 mol/L.In addition,as the molar ratio of FeSO₄ to H₂SO₄ in the feed increased from 2.01 to 4.08,the basicity increased from 8.69%to 11.38%and the turbidity removal ratio increased gradually from 94.96%to 95.88%,while the process energy consumption changed in a small range of 3.05³.15 kW·h/kg H₂SO₄ and the final acid concentration is⁰.38 mol/L. Finally,as the feed flow rate increased from 1 to 3 mL/min,the basicity reduced from 11.52%to 6.75%,the turbidity removal ratio decreased gradually from 95.92%to 75.61%and the process energy consumption decreased from 3.09 to 2.77 kW·h/kg H₂SO₄.In conclusion,a simple,green and efficient method for treating the ammonium chloride wastewater and preparing the PFS with high basicity was proposed in this thesis.On a laboratory scale,some ammonium chloride wastewater has been dealt with and the qualified PFS products have been prepared successfully.In order to apply the method to industrial production,on the one hand,it is necessary to develop the new excellent ion exchange membranes with high performance cost ratio;on the other hand,the pilot production study should also be indispensable.