Separating Cadmium (?) From Water With Ion Exchange Membrane Based On Donnan Dialysis

In recent years,with the rapid development of mining,metallurgy,machinery manufacturing,chemical,electronics,instrumentation and other industries,a large number of heavy metal-containing pollutants are emitted into the environment,of which cadmium pollution is particularly prominent.This paper uses a homogeneous cation exchange membrane to separate Cd???in water based on Donnan dialysis.In this paper,the cation exchange membrane separation device was first constructed and optimized.Then,the single-factor batch experiment method was used to investigate the type and concentration of the desorbed solution,the pH value of the feed phase,the stirring intensity,the feed water flow rate and other operating conditions under the operating conditions of the Donnan separation experiment.The membrane separates the properties of Cd???in water.The optimum separation operation conditions of Cd???were determined by orthogonal optimization test method.Finally,possible pollutants such as inorganic substances?SiO₂ and Al₂O₃?,natural organic substances?humic acid?,and Cd???could be added by adding,Complex-forming substances?EDTA?,surfactants?anionic surfactants,cationic surfactants and nonionic surfactants?and easily hydrolyzable substances?FeCl₃?,etc,to explore the separation of the above pollutants on the ion exchange membrane separation device the effect of Cd???.By comparing the homogeneous cation exchange membranes produced by Hangzhou Lvhe Environmental Protection Technology corporation and Shandong Tianwei Membrane Technology corporation,the homogeneous cation exchange membrane produced by Hangzhou Lvhe Environmental Protection Technology corporation with better separation effect was selected.The performance parameters:thickness?wet state?0.28�0.02 mm,dry and wet state expansion 5¹2%,water content 35%?wet?,bursting strength 6?kg/cm²?,exchange capacity 2 meq/g?dry?),the transmittance is?98%,the film surface resistance is 3.5??�cm²?,the current density is<150 mA/cm²,and the temperature resistance is<60??short-term is80??.Through the use of pre-treated and unpretreated membranes,it was found that the pretreated membrane had better separation and removal of contaminants.It was considered that the pretreatment process cleaned the membrane surface and impurities in the membrane and passed through NaCl.The membrane immersed in the solution for a long time,and a large amount of compensating ion Na⁺is adsorbed in the membrane,and both of these effects improve the separation and removal effect.Comparing the two analytical solutions of NaCl solution and KCl solution,it was found that the NaCl solution had better effect on separating and removing Cd²⁺from the cation exchange membrane separation device.Through the study of the stirring speed,it is found that the separation and removal rate of Cd²⁺in the feed fluid and the ion flux are proportional to the stirring speed.The concentration of the acceptor solution has a great influence on the test results.When the concentration of the acceptor solution is increased from 0 mol/L to 0.001 mol/L,the separation and removal rate and ion flux of Cd²⁺in the donor pool are greatly improved.The concentration of the acceptor solution continues to increase,and the separation and removal rates and ion fluxes continue to rise.The separation and removal rate of Cd²⁺in the feed fluid decreased with the increase of the initial concentration of the body fluid.Since most of the cadmium ions exist in the form of free Cd²⁺when the pH value of the solution is less than 8.0,the precipitation of Cd?OH?₂ begins to occur when the pH value is greater than 8.0.Therefore,when the pH value of the body fluid is below 8.0,the test results have little effect.The influent flow rate of the donor tank affects the test results by changing the hydraulic retention time of the pollutants.The larger the influent flow rate of the donor tank,the shorter the hydraulic retention time,and the more unfavorable the separation and removal of pollutants in the donor pool.Through orthogonal test and analysis of variance,it was found that the optimal operating conditions of the test were stirring speed of 6.37�10⁹?Kgf�m?/s,feed water flow rate of 1.0 ml/min,and acceptor concentration of 0.1 mol/L.By adding various pollutants to the feed phase,it is found that inorganic substances such as SiO₂ and Al₂O₃ and nonionic surfactants do not ionize in water,and do not have physical and chemical interaction with the Cd²⁺,so the effect on the test results is not significant.Natural organic matter such as humic acid and anionic surfactants reduce the concentration of Cd²⁺in the feed fluid.The humic acid also adheres to the surface of the cation exchange membrane formed by the black floc formed by Cd²⁺,which hinders the Donnan dialysis.Therefore,the humic acid inhibits the Cd???in the cation exchange membrane.EDTA reacts with Cd²⁺to form complex cadmium ions with a large radius that cannot pass through the cation exchange membrane.The Cd???in the feed fluid cannot be separated.Hydrolyzable substances such as FeCl₃ can cause"iron poisoning"phenomenon in the cation exchange membrane,and the hydrolysis reaction of FeCl₃ will increase the concentration of H⁺in the solution.The above phenomenon will inhibit the entry of Cd²⁺into the cation exchange membrane.