Efficient Bromate And Roxarsone Removal In Water With Micro-nano Zero-valent Iron

With the rapid development of social economy,severe water pollution becomes a major obstacle to human health,social sustainable development.Developing environment friendly,economic and effective methods to remove the pollutants of water is important.Iron content is rich in the crust,and zero-valent iron can be used as reducing agent,adsorbent,flocculant,Fenton oxidant to remove a variety of inorganic anions,heavy metals,organics and so on.Nano zero-valent iron has high activity,but its instability,easy to spontaneous combustion and difficult to store,there are many difficulties in practical applications.Therefore,the development of wide applicability,stability,high activity of zero-valent iron has become the common goal of many researchers.In the preliminary work,our research group independently designed and synthesized a micron nanometer multi-level structure of zero-valent iron(hereinafter referred to as micro-nano zero-valent iron,expressed as mnZVI).The mnZVI is a zero-valent iron ball with loose porous submicron size by assembled in situ with nanostructure unit.The nanostructured units are not completely exposed to the air,and have both the high activity of the nanometer zero-valent iron and the stability of the ordinary zero-valent iron.In this paper we apply mnZVI to remove two typical pollutants and study the removal mechanism in depth.1.The mnZVI reduction of removing by-product bromate(BrO3-)in drinking water:The mnZVI can quickly and efficiently remove BrO3-.In the air atmosphere,0.1 g/L mnZVI to remove 1000 ppb BrO3-takes 5 min(4 times faster than the reported nZVI in the literature),the removal reaction is accordance with the first order kinetics,the removal reaction in argon atmosphere takes only 3 min,and the reaction rate is 2.18 times of the air atmosphere.The reasons for the reduction of dissolved oxygen are as follows:In the Ar atmosphere,the proportion of ferrous ions on the surface of the mnZVI is higher than the air atmosphere,so the reduction reaction is promoted.The air atmosphere can form iron oxide layer to hinder the reduction reaction.In the system,ferrous ions are involved in the reduction of bromate,the contribution rate of 14%.The system does not produce bromine intermediates,so does not cause secondary pollution,the mnZVI does not adsorb bromine and the total solution bromine recovery rate of more than 94%.The cation exchange resin can effectively remove the by-product iron ions in the solution,and the dynamic chromatographic column can be used to simulate the small water purifier to remove the bromate.2.The mnZVI removal of roxarsone(ROX):The mnZVI can quickly removal of ROX.In the air atmosphere,0.75 g/L mnZVI remove 20 mg/L ROX,when time up to 2.5 min,the removal rate up to 98.6%,the removal reaction is accordance with the first order kinetics.The ROX process is first rapidly reduced to 3-amino-4-hydroxyphenylarsinic acid(HAPA),·H plays a vital role in this process.The main degradation path of HAPA is·OH attack As-C bond to form As(V)and 2-aminophenol,in addition,·H also can degradation of HAPA to form As(?)and 2-aminophenol,As(?)can be further oxidized to As(V)by ·OH.The immobilization process of inorganic arsenic is the FeO(OH)and As(V)form coprecipitation adsorption on the surface of mnZVI.HAPA degradation rate is slow,this is due to the less ·OH generated in the system,the undegraded HAPA is adsorbed by the mnZVI.