Effect Mechanism And Treatment Efficiency Of Ultrafiltration For Heavy Metals Complexed By Palygorskite

Because of the heavy metal waste water produced by the mining and electroplating industry,it is also a serious threat to the health of natural ecosystems and the safety of human drinking water.The treatment method and technology application of heavy metal wastewater has always been the research focus of environmental engineering,municipal engineering,chemical engineering and other disciplines.Among them,the complextion-ultrafiltration coupling process has become a key technology for many scholars because of its good processing effect and low processing cost.In this study,the palygorskite ore of Tianshui,Gansu Province was selected,and the high-purity palygorskite was obtained by crushing,sieving,acid-modifying,and ball milling.Then,the palygorskite colloidal solution was prepared by high-speed stirring and ultrasonication.The dynamic ultrafiltration enrichment experiment of palygorskite-heavy metal ion colloid solution was conducted under the conditions of the addition of 5 g/L of palygorskite,the concentration of Cu²⁺,Zn²⁺,and Cd²⁺ of 40,30,and 10 mg/L,respectively.To investigate the effects of heavy metals on the membrane specific flux and rejection coefficient of the complexation-ultrafiltration of heavy metals by palygorskite in the four membrane pore sizes,four temperature conditions,and five operating pressures;and effects of five p H values,two ionic strength,two competitive complexing agent on rejection coefficient of heavy metals.Through the analysis of variance and multiple comparison methods,the results are as follows:The removal of heavy metals by palygorskite complexation-ultrafiltration was carried out through hollow fiber ultrafiltration membrane with molecular weights of 6000,10000,50000 and 100000 Da,respectively.Comprehensive analysis of the rejection coefficient and normalization membrane specific flux,10000 Da ultrafiltration membrane was selected as the pore size of Cu²⁺ and Zn²⁺,and 6000 Da ultrafiltration membrane was used as the pore size of Cd²⁺.The pseudo first-order reaction rate equation can better represent the reaction behavior of complexation-ultrafiltration of heavy metals by palygorskite in four membrane molecular weight cutoffs.When the feed liquid temperature was 288,293,298,and 303 K respectively,the increase in temperature increases the rejection coefficient of heavy metals,significantly.Under the condition of low temperature（288 K）,the increase of temperature significantly decreased the concentration of Cu²⁺,Zn²⁺ and Cd²⁺ permeate.Under high temperature conditions（293,298,303 K）,the increase of temperature significantly decreased the concentration of Cu²⁺ and Zn²⁺ permeate.The permeate concentration has no significant effect.The higher the temperature,the smaller the normalization membrane,and the increased temperature aggravated the contamination of the ultrafiltration membrane.The pseudo first-order reaction rate equation can better represent the reaction behavior of complexation-ultrafiltration of heavy metals by palygorskite in four temperature conditions.When operating pressures were 0.05,0.075,0.1,0.125,and 0.15 MPa,respectively,the rejection coefficient of heavy metals was minimally affected by the operating pressure.As the operating pressure increases,the permeate flux increases almost linearly and the normalization membrane specific flux decreases significantly.With the increase of p H value,the rejection of three heavy metals increased significantly.In the p H range of 3 to 5,the p H is increased by one unit,and the Cu²⁺ rejection coefficient increases 8.91% on average,and the p H range of 6 to 7,no significant increase of heavy metal Cu²⁺ rejection coefficient.In the p H range of 3 to 4,the p H value increased by one unit,and the rejection coefficient of heavy metal Zn²⁺ and Cd²⁺ increased by an average of 9.42% and 4.40%,and the p H range of 5 to 7,with the p H value increases,the rejection coefficient of heavy metals Zn²⁺ and Cd²⁺ increases slightly.As the ionic strength increases,the rejection of three heavy metals decreases slightly.The three heavy metal rejection rates were not significantly affected by 0.01 mol/L Na Cl.The 0.1 mol/L Na Cl significantly reduced the Cu²⁺ rejection rate of the heavy metals and had slightly less effect on the rejection of Zn²⁺ and Cd²⁺.The three heavy metal rejection rates are severely affected by low molecular weight competing complexing agents.The effect of sodium tartrate on the three heavy metals is greater than that of triethanolamine.The effect on Zn²⁺ and Cd²⁺ is much greater than that of Cu²⁺.In this study,the palygorskite nanomaterials are preferably used as inorganic complexing agents in the process of complexation-ultrafiltration coupled process for the removal of heavy metal wastewater through the purification,acid-modified,and the crystal-bundles dispersing.This study has solved the disadvantages of expensive and secondary pollution of organic complexing agents.By screening suitable pore size of the ultrafiltration membrane and the influence mechanism of the ultrafiltration process,it is possible to industrialize the removal of heavy metals with complex-ultrafiltration by palygorskite.This study promotes the improvement of heavy metal removal by complexation-ultrafiltration coupled technology.