Preparation And Arsenic Removal Performance Of Graphene-siderite Composites

High arsenic groundwater is an environmental issueworldwidely,which affects the health of hundreds of millions of people around the world.The commonly used methodsto remove arsenic from groundwaterinclude adsorption,chemical precipitation,flocculation,ion exchange and membrane filtration.Adsorption is the most widely used technology for groundwaterarsenic removal.As an adsorbent,siderite synthesized under high temperature and high pressure(SID-HTP)has high arsenic adsorption capacity.However,whether the SID-HTP can form a composite material with graphene to further improve its adsorption performance is still unknown.Based on the preparation of the optimum composite for arsenic removal,this study investigates characteristics and mechanism of arsenic adsorption on the optimum composite,which has certain theoretical and practical significance.The main achievements are obtained as follows:(1)Composites of graphene and siderite were successfully synthesized.When the mass ratio of siderite to graphene is 4:3,the composite shows the best performance of arsenic removal(the optimum composite),and the adsorption capacity of As(?)is greater than that of As(?).(2)The kinetic rate of As(?)adsorption is higher than that of As(?)adsorption on the optimum composite.The adsorption of As(?)reached equilibrium at 12 h,with the equilibrium adsorption capacity around 67 mg/g,while the adsorption of As(?)reached equilibrium at about8 days,with the equilibrium adsorption capacity of 35 mg/g.The pseudo second order kinetic equation can well describe the adsorption kinetics of As(?)and As(?).(3)Compared with the Freundlich isothermal adsorption model,the Langmuir isothermal adsorption model is more suitable for the adsorption of As(?)and As(?)on the optimum composites.The adsorption reactions are endothermic and spontaneous.(4)pH has different effects on the adsorption of As(?)and As(?)on the optimum composite.When p H is in the range of 4-9,the capacityof As(?)adsorption is 66-70 mg/g,which decreases significantly when p H increases to 10.p H has little effect on the adsorption of As(?),and the amount of As(?)adsorbed on the composite is 26-30 mg/g at p H of 4-10.The adsorption of As(?)on the composite is affected by the coexisting anions such as PO₄^3-,Si O₃^2-and HCO₃^-,and PO₄^3-showed the greatest competition adsorption,followed by Si O₃^2-and HCO₃^-.In relative to As(?)adsorption,PO₄^3-,Si O₃^2-showed competition adsorption to As(?).PO₄^3-inhibited the adsorption of As(?)more greatly than Si O₃^2-.(5)Arsenic adsorption on the composite belongs to chemical adsorption and specific adsorption.During reaction,hydroxyl groups are formed onthe iron-bearing minerals.Arsenic is complexed with hydroxyl groups on the surface of the minerals,with the formation of As-O-Fe bonds.