Preparation Of Nanoscale Zero Valent Iron Microcapsule And The Removal Of Hexavalent Chromium From Groundwater

With the continuous progress of people's life and the rapid development of social economy,the problem of water pollution is becoming more and more serious.Due to the random discharge of industrial wastewater,hexavalent chromium enters into the groundwater environment,which will cause serious harm to human health and the balance of water ecosystem.As the filling material of permeable reactive barrier(PRB),nanoscale Zero-Valent Iron(nZVI)has been widely used in the removal of pollutants in groundwater due to its large specific surface area and strong reducibility.However,the removal ability of pollutants is reduced due to its easy agglomeration,which restricts its application in permeable reactive barrier remediation technology.In this study,embedded nZVI/ABS microcapsules were prepared by using acrylonitrile butadiene styrene copolymer resin(ABS)as shell material.SEM,XPS,XRD and other characterization methods confirmed the successful preparation of nZVI/ABS microcapsules.nZVI was successfully embedded in ABS,which improved the dispersion of nZVI particles and inhibited the agglomeration of nZVI particles to a certain extent.The kinetic fitting results show that the pseudo second order kinetic model can better describe the adsorption and removal process of Cr(?)by nZVI/ABS microcapsules,and the core-shell ratio and the viscosity of silicone oil have limited control range on the reaction rate constant.In order to effectively control the reaction rate constant,the porous nZVI/(ABS+EC)microcapsules were prepared by using ethyl cellulose(EC)which is easily soluble in ethanol.SEM and BET results confirmed the effect of ethanol impregnation on the formation of pores in the matrix.After pore forming,the specific surface area of nZVI/(ABS+EC)microcapsules increased from 26.772 m²/g to 43.462 m²/g,the total pore volume increased from 0.0462 cm³/g to 0.0642cm³/g,and the average pore size increased from 5.767 nm to 11.40 nm.Compared with nZVI,the equilibrium time of the reaction between nZVI/(ABS+EC)microcapsules and Cr(?)increased from 12 h to 24 h,which indicated that nZVI/(ABS+EC)microcapsules also played a sustained-release role in a certain extent,making the reaction activity of nZVI sustained.The kinetic fitting results show that the pseudo second order kinetic model can better describe the adsorption and removal process of Cr(?)by nZVI/(ABS+EC)microcapsules;in addition,the effective regulation of rate constant can be achieved by controlling the amount of EC and nZVI,and then the reaction rate of Cr(?)removal by nZVI/(ABS+EC)microcapsules can be controlled to achieve the purpose of activity persistence control.In the process of Cr(?)removal by nZVI/(ABS+EC)microcapsules,the unit removal amount decreased with the increase of material dosage,and increased with the increase of initial Cr(?)concentration.The results showed that nZVI/(ABS+EC)microcapsules showed good Cr(?)removal performance in a wide p H range(3-7),with removal efficiency of 90%-95%;the coexisting anions(CO₃^2-,NO₃^-,SO₄^2-)inhibited the removal of Cr(?)by nZVI/(ABS+EC)microcapsules,and the inhibition degree of CO₃^2-was the largest.nZVI/(ABS+EC)microcapsules remove Cr(?)from the solution by reduction.nZVI acts as an electron donor to reduce Cr(?)to Cr(?),and Cr(?)is adsorbed and fixed on the surface of the material in the form of chromium(hydrogen)oxide and chromium iron oxide coprecipitation.