Experimental Study On Removal Of Arsenic And Co-occurreed Components From Groundwater By Combination Of Iron-based Composite Materials And Faujasite

High arsenic groundwater is widely distributed around the world.The drinking water of more than 100 million people in the world has serious safety problems,and most severely affected area by arsenic pollution is South Asia-Southeast Asia region.The typical reduced high arsenic aquifers from South Asia-Southeast Asia and southern China are mainly distributed in floodplains and river deltas where water systems develop.The reduced high arsenic groundwater in lake and river regions has similar water chemical characteristics,and there are widespread water supply safety problems caused by the abnormal water quality of arsenic and associated components,manganese and calcium.Arsenic in reduced groundwater mostly exists in the form of trivalent complex anions,which is high toxic and difficult to fix.Due to the high risk of arsenic exposure and increasing pollution,there is an urgent need to develop detoxified,fixed and more efficient water treatment materials and processes to meet the water quality purification requirements of this type of high arsenic groundwater.According to the characteristics of natural mineral materials,this thesis adjusted and modified them,adjusted the use method,made it highly efficient,environmentally friendly,suitable for high arsenic groundwater concentration and pH working range,and achieved the effect of synergistically removing the associated components in groundwater,providing theoretical support for groundwater quality improvement technology research and water supply safety guarantee.In view of the water quality characteristics and purification requirements of the reduced high-arsenic groundwater in China,the control conditions for preparing hierarchical Faujasite(FAU)by Halloysite(HNT)were explored,and iron-based mineral materials with Halloysite and Faujasite as carriers were synthesized respectively.The adsorption effect and influencing factors of iron-based mineral materials on trivalent arsenic in groundwater were analyzed through static batch experiments and dynamic column experiments.The effect and application method of combined use of iron-based mineral materials and Faujasite to synergistically remove arsenic and associated components are evaluated.It reveals the removal mechanism of the phase change and hydroxyl radical generation in the iron-based mineral material system to the oxidation and fixation of trivalent arsenic.The research content and results mainly included:1.According to the structural characteristics of HNT,Faujasite is prepared hydrothermally by adjusting the alkali leaching concentration and reaction temperature.Combining the difference in ion exchange performances of HNT and Faujasite,adjusting the dosage and concentration of reagents,using HNT and zeolite as carriers respectively to prepare iron-based mineral composite materials.The morphology,chemical structure,element composition and valence state of the prepared material were characterized and analyzed.The zeolite was prepared by hydrothermal reaction:an appropriate amount of HNT was placed in a 2 wt%Na OH solution and reacted hydrothermally at 130°C for 24 h.XRD characterization showed the prepared zeolite material was Faujasite single-phase crystal structure.FT-IR,MNR,TG,and XPS characterizations proved the transformation of HNT structure to Faujasite structure.BET showed that the specific surface area of Faujasite was 61.8 m²/g,which was a mesoporous material.SEM/TEM images showed that the synthetic zeolite had regular flower-like hierarchical structure.The liquid-phase reduction method was used to prepare the nano-zero-valent iron based composite material with HNT as the carrier(O@nZVI-HNT).The sodium borohydride solution used in the preparation process has extremely strong reducibility and may destroy the carrier structure in different concentration ranges.In order to make the obtained composite material maintained the morphological structure of the carrier and the nano-zero-valent iron structure at the same time,the ratio of the use of trivalent iron and sodium borohydride was constantly adjusted,and finally ratios were m _HNT:m _Fe=1:1(mass ratio),M_Fe:M_{Na BH4}=1:3(molar ratio).The characterization analysis of XRD,FT-IR and XPS showed that HNT and n ZVI were effectively combined together.SEM/TEM images showed that n ZVI was uniformly dispersed on the tubular HNT structure and had a shell-core structure with an average particle size of 40-80 nm.The nano-zero-valent iron based composite material with Faujasite as the carrier(O@nZVI-Zeo)is prepared by the liquid-phase reduction method.Due to the different stability and chemical properties of the carrier,the reagent concentration ratio for preparing O@nZVI-Zeo is different from that of O@nZVI-HNT,the final ratios of reagent are m _FAU:m _Fe=1:1(mass ratio),M_Fe:M_{Na BH4}=1:4(molar ratio).The characterization analysis of XRD,FT-IR and XPS explains that the zeolite carrier interacted with ferric ions during the preparation process,and the structure changed to partially Fe-exchange zeolite.SEM/TEM images show that n ZVI was uniformly dispersed and interspersed on the flaky zeolite structure.BET characterization shows that the specific surface area of the composite material increased significantly,which was106.14 m²/g.2.Systematic design of batch experiments and column experiments,discussed the influence of factors such as pH,As(III)initial concentration and coexisting ions on the arsenic removal effect of O@nZVI-HNT,and determined the adsorption type by kinetic model fitting to calculate the adsorption capacity;The effects of flow rate and water chemical composition on the dynamic arsenic removal of O@nZVI-HNT were analyzed,and the effect of O@nZVI-HNT and Faujasite in synergistic removal of arsenic,calcium and manganese in groundwater and the influence of their combined use were evaluated.The initial pH of the solution had a very important effect on the removal of As(III)by O@nZVI-HNT.When the pH of the solution was less than 3,the high hydrogen ion concentration in the solution would dissolve the shell-core structure in the composite material,and the adsorption capacity would be small.At pH 3?10,the adsorption capacity increased without significant changes,which was attributed to the formation of different iron oxides by corrosion of the zero-valent iron structure.The maximum adsorption capacity in this study is 270 mg/g.The reaction reached equilibrium within 50 min.Anions had a certain inhibitory effect on the removal of trivalent arsenic.HCO₃^-,CO₃^2-,and PO₄^3-had obvious effects,and with the increase of anion concentration,the inhibitory effect increased;calcium ions had a certain promotion effect on the removal of arsenic,while divalent manganese had a certain inhibitory effect.Based on the influence of groundwater flow rate on the removal of arsenic by O@nZVI-HNT,a series of experiments were carried out,and it was found that the solution flow rate was 2 ml/min and the amount of adsorbent used was?0.6g,which can effectively remove the arsenic.The arsenic concentration in the solution is consistent with the arsenic content in most reduced high-arsenic groundwater.The presence of characteristic major ions in groundwater water chemistry has an inhibitory effect on the removal of arsenic by O@nZVI-HNT.The different combination with O@nZVI-HNT and Faujasite had no obvious effect on the removal of the three main pollutants,however,they did have a significant purification effect on artificial groundwater.3.Systematic design of batch experiments and column experiments,discussed the influence of factors such as pH,As(III)initial concentration and coexisting ions on the arsenic removal effect of O@nZVI-Zeo,and determined the adsorption type by kinetic model fitting to calculate the adsorption capacity;The effects of flow rate and water chemical composition on the dynamic arsenic removal of O@nZVI-Zeo were analyzed,and the effect of O@nZVI-Zeo and Faujasite in synergistic removal of arsenic,calcium and manganese in groundwater and the influence of their combined use were evaluated.When the pH is 3-11,the adsorption capacity was increased and stable.The maximum adsorption capacity in this study is 240 mg/g.The reaction reached equilibrium within 100 min.Anions had a certain inhibitory effect on the removal of trivalent arsenic.HCO₃^-,CO₃^2-,and PO₄^3-had obvious effects,and with the increase of anion concentration,the inhibitory effect increases;cationic calcium ions and divalent manganese had certain promotion of arsenic removal effect.Based on the influence of groundwater flow rate on the removal of arsenic by O@nZVI-Zeo,a series of experiments were carried out,and it was found that the solution flow rate was 3 ml/min,and the amount of adsorbent used was?0.58g.The removal effect of neutral and weak alkaline arsenic solution is the best,which satisfies Groundwater treatment needs.In addition,the presence of characteristic major ions in groundwater water chemistry can significantly promote the removal of arsenic by O@nZVI-Zeo.The combined use of O@nZVI-Zeo and FAU to purify artificial groundwater showed that O@nZVI-Zeo not only had a significant removal effect on As(III),but also had certain adsorption performance for cations,and the combination with FAU could further remove cations in water.4.Using a series of related characterization methods and experiments,the adsorption mechanism was explained based on the structural changes before and after the adsorption of iron-based mineral materials,the characteristics of iron-based materials producing hydroxyl radicals,and Phreeqc simulation inversion.The adsorption performance of the two iron-based materials was compared,and the suitable removal methods for the two iron-based materials were evaluated.Iron based composites formed a large amount of iron oxide and iron hydroxide during the adsorption process,and the surface contained a large number of metal hydroxyl groups.The adsorption mechanism of trivalent arsenic included oxidation and surface complexation.The intermediate active product·OH produced by the reaction of n ZVI in water oxidizes part of As(III)to As(V).As(III)and As(V)combined with the metal hydroxyl on the surface of the adsorbent produced monodentate and bidentate complexes.Through the comparison of removal effects and experimental evidence,this study found that O@nZVI-HNT was suitable for the static batch removal of As(III),while O@nZVI-Zeo was more suitable for the combined use of FAU to efficiently remove multiple components such as arsenic,calcium,magnesium and manganese.It is indicative of the practical application of groundwater purification.The innovation of this thesis:In response to the water quality characteristics associated with arsenic,calcium,and manganese in the typical aquifer in the floodplain delta area and the demand for water supply security,unique natural clay-iron-based composite materials were synthesized.The influence of factors such as groundwater flow rate and water chemical composition on the arsenic removal effects of iron-based composite materials were identified,and the combination method and applicable conditions of iron-based composite materials and Faujasite were optimized.It provides scientific support for the research and development of economical,green and efficient high-arsenic groundwater purification technology.