Removal Of Hexavalent Chromium And Bromate From Water By Iron Modified Lotus Biochar

With the rapid development of China's economy and industry,the increasing pollution of Cr?VI?and BrO₃^-in water has led to potential dangers for human health,which cannot be ignored.Compared with other water treatment technologies,adsorption method has been known for the advantages of low cost,high treatment effect and short reaction time,and has been widely used in various water treatment processes.However,most of the adsorbents for removing Cr?VI?and BrO₃^-have several disadvantages,including low efficiency,high cost and poor environmental adaptability.In this study,Cr?VI?and BrO₃^-were taken as target pollutants,FeCl₃ and lotus stem were used to prepare Fe modified lotus biochar by impregnation calcination method.The effect of influential factors on adsorption performance were tested.Additionally,the mechanism of Cr?VI?and BrO₃^-removal was revealed by Brunauer-Emmett-Teller?BET?method,X-ray photoelectron spectroscopy?XPS?,Fourier transform infrared?FTIR?spectroscopy,X-ray diffraction?XRD?and Zeta potential.When Cr?VI?was the target pollutant,the preparation conditions of the material were optimized by orthogonal design:the carbonization condition was:500?,1 hour;the activation condition was:700?,1.5 hours;the mass ratio of Lotus biochar to FeCl₃was 1:4.When BrO₃^-was the target pollutant,the preparation conditions were optimized by single factor variable method:the carbonization condition was:500?,1hour;the activation condition was 700?,1.5 hours;the impregnation quality ratio of Lotus biochar to FeCl₃ was 1:5.At the same time,the BET characterization results showed that the specific surface and total pore volume of biochar was increased significantly by the modification of FeCl₃.The study on the effect of influential factors on adsorption performance showed that,the best removal efficiency on Cr?VI?and BrO₃^-could be observed when the pH ranges from 2.0 to 10.0.The adsorption process of Cr?VI?and BrO₃^-on the materials conformed to pseudo-second-order kinetic model,which indicated that chemical adsorption is the main speed-controlling step in the adsorption process.Langmuir-Freundlich isotherm fitting curves showed the maximum adsorption capacity of the materier for Cr?VI?was 26.16 m/g.Langmuir isotherm fitting curves showed the maximum adsorption capacity of the materier for BrO₃^-was 212.30 m/g.FTIR and XPS showed that C=C,C-O and C=O groups on the surface of the material participated in the reduction process of Cr?VI?and BrO₃^-and the reduction was the main mechanism for Cr?VI?and BrO₃^-removal.In the process of removing Cr?VI?,the reduced Cr?III?is adsorbed on the surface of the material by three ways:electrostatic attraction,ion exchange and complexation.In the process of BrO₃^-removal,Fe³⁺/Fe²⁺on the surface of the material acted as an electronic shuttle to accelerate and improve the removal of BrO₃^-and the order of functional groups involved in BrO₃^-reduction was:C-OH>C=O>COOH>C-H.The results show that the iron modified lotus biochar adsorbent can be used to remove Cr?VI?and BrO₃^-,which provides technical support for the remediation of Cr?VI?and BrO₃^-polluted water.