Preparation And Application Of Monovalent Selective Cation Exchange Membrane

Compared with the ordinary cation exchange membrane,the monovalent selective cation exchange membrane has a wider range of applications because of its selective permeation performance for monovalent cations.In this paper,a monovalent selective cation exchange membrane(modified membrane)was prepared,and electrodialysis experiments,characterization and basic performance tests were carried out to prove the feasibility of modified materials and modification methods,and it was applied to the treatment of acid heavy metal wastewater to provide guidance for its industrial application The specific research results are as follows:(1)Using polypyrrole as the modified material,the ordinary homogeneous cation exchange membrane was impregnated and surface modified to prepare a monovalent selective cation exchange membrane.Adopting single factor experiment and orthogonal experiment method,taking the selective separation performance of the modified membrane for Na+/Ca2+ system as the evaluation index,the optimal preparation conditions of the modified membrane were determined as follows:the type of oxidant was ferric chloride,and the immersion time was 6.5 h,The immersion temperature was 35℃,the concentration of pyrrole and oxidant were 0.2 mol/L and 0.8 mol/L,and the concentration of proton acid was 0.06 mol/L.(2)The static electrodialysis experiment was carried out on the modified membrane prepared under the optimal conditions.The experimental results showed that the permeability of the modified membrane to Na+ and the leakage rate of Ca2+ were 60.2%and 7.3%respectively.The selective permeability coefficient PCa2+Na+ and the selective separation efficiency S(Na+/Ca2+)were respectively 8.3%and 78.4%,and the selective separation performance of the modified membrane was better than ordinary homogeneous cation exchange membrane(unmodified membrane)and commercial monovalent selective cation exchange membrane(commercial membrane).(3)Conduct membrane surface characterization and membrane basic performance test on the modified membrane prepared under the optimal conditions.Scanning electron microscopy(SEM)results showed that the surface of the modified film was smoother than before.The basic performance test results of the modified membrane showed that the water content,swelling degree,contact angle,and ion exchange capacity of the modified membrane were respectively 17.3%,8.88%,88.5°,0.78 mmol/g;the mechanical properties and chemical properties of the modified membrane improved stability;modified membrane had high selective separation performance for Na+/Ca2+system under the conditions of different electrodialysis operating current density,total ion concentration and relative ion concentration,and has high stability in use;modified membrane was resistant to H+/Zn2+system had high selective separation performance,showing strong acid resistance and applicability to different separation systems.(4)The modified membrane prepared under optimal conditions was used for dynamic electrodialysis to treat acidic heavy metal wastewater,and the selective separation performance of the modified membrane for H+and heavy metal ions(Zn2+and Cd2+)was used as the evaluation index to determine the electrodialysis the best operating conditions were:the current density was 20 mA/cm2,and the inlet water flow rate was 25 L/h.Under the best operating conditions,the leakage rates of Zn2+and Cd2+at the end of the electrodialysis operation were respectively 8.33%and 7.28%;at this time,the selective permeability coefficients of the modified membrane PZn2+H+ and PCd2+H+ were respectively 27.18 and 33.26,and the selective separation efficiency S(H+/Zn2+)andS(H+/Cd2+)were respectively 81.15%and 83.17%,and the current efficiency was72.25%.Its treatment effect can meet the treatment requirements of acidic heavy metal wastewater,and was better than the treatment effect of commercial membrane-electrodialysis.