Study On The Removal And Mechanism Of Bromate In Drinking Water Using Activated Carbon Supported β-FeOOH

Currently,Ozone disinfection technology has been widely used in water treatment industry.Bromate（BrO₃^-）is a toxic disinfection byproduct that is caused by the oxidation of bromide（Br^-）during the ozonation of bromide-containing water.many countries have set the maximum contaminant level for bromate in drinking water at 10μg/L（0.078μmol/L）.Activated carbon can adsorb and reduce bromate in water treatment unit,but it has some disadvantages such as low efficiency and short service cycle.akaganeite（β-FeOOH）is a promising material for bromate adsorption,but its loose structure and easy hydrolysis significantly reduces adsorption capacity for bromate.Loadedβ-FeOOH onto activated carbon to form composite adsorbent in this topic,it not only changed the physical and chemical properties of activated carbon,but also improved the loose structure and easy hydrolysis ofβ-FeOOH.it also enhanced the adsorption ability of activated carbon andβ-FeOOH for bromate.Activated carbon was treated with an FeCl₃ solution under heat to form composite adsorbent（FAC）,and bromate removal rate as indicators of the evaluation criteria.Over the response surface method to determine the various factors in the process of the of FAC,to obtain the best technological parameters for FAC,those were:the FeCl₃ concentration of 0.3mol/L,impregnation time of 15 h,impregnation temperature of 135℃,in the optimum condition bromate removal was 58.12%。By Field emission scanning electron microscope,Fourier transform infrared spectroscopy,N₂ adsorption analyzer,and Zeta potentiometer to characterization surface physicochemical properties and hole structure of FAC.specific surface area and total pore volume decreased,and the average pore size and Zeta potential of activated carbon significantly increased after modification by FeCl₃ solution under heat.The modified activated carbon was covered with numerousβ-FeOOH particles,iron content was 82.30mgFe/g,the amount of iron dissolved in the solution was less than 5%,which indicated that FAC had high physicochemical stability,β-FeOOH supported on the surface of activated carbon is not easy to fall off and hydrolyze.Study on removal of bromate by FAC via a series of batch experiments,and the effects of the initial concentration,the pH,temperature,and organics were evaluated.The repetitive regeneration of FAC was carried out.The experimental results show that the adsorption capacity of activated carbon,β-FeOOH and FAC for bromate in the following order:FAC>β-FeOOH>>activated carbon under the same condition.The bromate adsorption capacity of the FAC increased as the initial bromate concentration and contact time increased.The removal rate of bromate by FAC was up to 99.33%at pH 3-7,and the iron concentration in solution was acceptable at pH 4-11（<0.3 mg/L,the China drinking water standard）,which indicated that the physicochemical stability of FAC was high.The bromate removal percentage remained higher than 50%after 3 cycles for the FAC,and the removal rate of bromate by FAC-1,FAC-2 and FAC-3 were 92.34%,83.28%,72.67%respectively after repeated regeneration of FAC treated with an FeCl₃ solution under heat,This result indicated that the FAC is an efficient material with high reusability for bromate removal.The adsorption kinetics,isotherm and thermodynamics of bromate removal by FAC was discussed in this study,to analysis characteristics of bromate on FAC.The experimental results show that the pseudo-second-order model was the best fit for the dynamic bromate sorption behaviour on FAC at different initial bromate concentrations;Intraparticle diffusion and film diffusion occured during the entire sorption process,and the adsorption rate was controlled by film diffusion rather than intraparticle diffusion.Langmuir model and Redlich-peterson were better fit for the FAC bromate removal data at different temperature.Thermodynamic parameters indicated that bromate removal by FAC was an endothermic and spontaneous process.ion exchange effect ofβ-FeOOH for bromate played a major role during the entire sorption process for the activation energy value was 23.64 kJ/mol.Finally,the mechanism of bromate removal by FAC was discussed combined with adsorption products,and found that the bromate removal by FAC involves electrostatic attraction,ion exchange and reduction.Firstly bromate moves to the FAC surface and then the80%bromate adsorbed onto the active sites is reduced to bromide,activated carbon can quickly reduce bromate to bromide and improve reduction rate in the presence of Fe³⁺/Fe²⁺.