Preparation Of Novel Polyvinyl Alcohol Hybrid Chitosan Anion Exchange Membrane And Its Application In Waste Acid Recovery

Pickling process is widely used in iron and steel,electroplating and other industrial processes,resulting in a large number of pickling waste liquid.The waste pickling solution contains a large amount of metal ions and has a high acidity,which needs to be treated in order to be discharged.The current waste acid treatment methods are complicated in operation,large in waste water discharge,and produce a large amount of sludge in the treatment process,which do not meet the needs of sustainable development.Therefore,it is of great practical significance to develop a kind of waste acid treatment method which can efficiently recover the acid from the waste liquid,which is green and environmental friendly and easy to operate.Diffusion dialysis is a membrane separation method based on ion exchange membrane,which can effectively separate metal ions and acid in waste acid to achieve the purpose of recovering acid,and has the advantages of low energy consumption,easy automation and environmental protection.However,the commercial membrane DF120 has the disadvantages of low acid dialysis rate（U_H=0.009 m/h）and separation coefficient(S(H⁺/Fe²⁺)=18.5)between acid and ferrous ion,which makes it less efficient in treating spent acid,and is generally used for treating waste acid containing ferrous ions.In response to these shortcomings,the main research contents of this paper are as follows:1、Preparation of novel polyvinyl alcohol hybrid chitosan anion exchange membraneThe polyvinyl alcohol（PVA）was used as the membrane material,chitosan（CS）was used as the raw material to prepare the quaternary ammonium salt chitosan active material,and tetraethoxysilane（TEOS）was used as the linking agent and crosslinking agent to prepare a series of chitosan-based polyvinyl alcohol（Q_nCS-PVA,n=1⁴）hybrid anion exchange membrane.The hydroxyl groups on chitosan and polyvinyl alcohol can promote the penetration of hydrogen ions through hydrogen bonding,and the coordination ability of chitosan with metal ions and the electrostatic repulsion of quaternary amine groups can block metal ions from permeable to the membrane.Tetraethoxysilane introduces inorganic silicon into the organic polymer membrane,which makes the Q_nCS-PVA hybrid anion exchange membrane have better chemical and thermal stability.In particular,the acid dialysis rate（U_H=0.0273 m/h）and the separation coefficient(S(H⁺/Fe²⁺)=51.26)of Q₃CS-PVA hybrid anion exchange membrane are much larger than that of commercial membrane DF120 and partial anion exchange membranes reported in the literature.2、Study on diffusion dialysis of Q₃CS-PVA hybrid anion exchange membrane for hydrochloric acid pickling waste liquidHydrochloric acid has good solubility to metals such as Fe,Ni,Zn,etc.,so it is a commonly used acid cleaning agent,which will produce a large amount of hydrochloric acid pickling waste liquid containing different metal ions.In this chapter,the diffusion dialysis process of hydrochloric acid pickling waste liquid containing Fe²⁺,Fe³⁺,Ni²⁺and Zn²⁺ions was studied by using the prepared Q₃CS-PVA hybrid anion exchange membrane.The results show that becauseNi²⁺、Zn²⁺and other metal ions form different complexing ions in hydrochloric acid solution,the membranes have the best dialysis separation effect on HCl+NiCl₂ system(U_H=0.0294 m/h,S(H⁺/Ni²⁺)=55.48)and the worstdialysis separation effect on HCl+ZnCl₂ system(U_H=0.0258m/h,S(H⁺/Zn²⁺)=49.24).At the same time,the effects of temperature,metal ion concentration and hydrochloric acid concentration on the diffusion dialysis results were also studied.The results showed that for the four systems of HCl+FeCl₂,HCl+FeCl_3,HCl+NiCl₂ and HCl+ZnCl₂,the U_H increases with the increase of temperature,while S increases first and then decreases with the increase of temperature,and both U_H and S decrease with increasing metal ion concentration or hydrochloric acid concentration.3、Study on diffusion dialysis of Q₃CS-PVA hybrid anion exchange membrane for sulfuric acid pickling waste liquidSulfuric acid is also widely used as an acid cleaning agent due to its wide range of sources and low cost,thus producing a large amount of sulfuric acid pickling waste liquid.In this chapter,the diffusion dialysis process of sulfuric acid pickling waste liquid containing different metal ions was studied by using the prepared Q₃CS-PVA hybrid anion exchange membrane,and compared with the diffusion dialysis process of hydrochloric acid pickling waste liquid.The results showed that the salt effect in the hydrochloric acid pickling waste liquid,that is,the addition of FeCl₂,FeCl₃ and other salts in hydrochloric acid can promote the penetration of hydrochloric acid into the membrane.Therefore,the membrane has good dialysis separation effect on hydrochloric acid pickling waste liquid.At the same time,for the four systems of H₂SO₄+FeSO₄,H₂SO₄+Fe₂（SO₄）₃,H₂SO₄+NiSO₄ and H₂SO₄+ZnSO₄,the corresponding U_H and S decrease with the increase of metal ion concentration or sulfuric acid concentration.