Preparation Of Iron-based Biochar And Application In Chromium Treatment

Chromium is an important industrial raw material.In recent decades,with the development of industry,humans have released a large amount of chromium into the environment through various production activities such as metallurgy,electroplating,and leather tanning.Chromium in the environment mainly exists in the form of Cr(Ⅲ)and Cr(VI).Compared with Cr(Ⅲ),Cr(Ⅵ)is considered to be one of the most carcinogenic metals internationally because of its strong oxidizability,high solubility,easy migration,and greater toxicity to organisms.Chromium pollution environment treatment usually uses chemical reduction technology to reduce Cr(Ⅵ)to Cr(Ⅲ)to reduce the toxicity of Cr(Ⅵ).Among the reducing agents,iron-based materials and sulfur-based materials are widely used.Although nano-ferrous sulfide can be used for Cr(Ⅵ)reduction and passivation,it is difficult to achieve large-scale use due to its defects of easy agglomeration.In order to overcome the application defects of nano-ferrous sulfide,this study used biochar as a support carrier and chitosan as a stabilizer,and prepared a modified composite of nano-ferrous sulfide FeS-CS-BC by a liquid phase reaction method.The reduction effects of FeS-CS-BC on Cr(VI)in aqueous solution and soil were studied respectively,and the reaction mechanism of FeS-CS-BC and Cr(VI)was explored by SEM,XRD,FTIR,XPS and other characterization methods.The main research results obtained are as follows:(1)The SEM image shows that the surface of the FeS-CS-BC modified material is evenly inlaid with a substance with a sheet structure;the XRD pattern of the FeS-CS-BC modified material shows a diffraction peak of FeS;the FTIR pattern shows that FeS-CS-BC modified material appeared a new functional group-NH2.The above results show that the nano-ferrous sulfide particles are successfully and evenly loaded on the biochar,and the content of functional groups on the FeS-CS-BC modified material is higher than that of biochar.(2)The FeS-CS-BC modified material has a good effect of removing Cr(Ⅵ)in the aqueous solution.In 50 mL of Cr(VI)aqueous solution with a concentration of 100 mg·L-1,the experimental results of the removal of Cr(VI)by FeS-CS-BC indicate that the optimal ratio of FeS-CS-BC modified material is FeS:CS:BC=2:2:1;the best dosage of FeS-CS-BC material is 0.1 g,and the removal rate of Cr(VI)can reach 98%;in the range of pH=2～10,the process of removing Cr(VI)by FeS-CS-BC is almost not restricted by pH,and the removal rate of Cr(VI)is basically kept above 96%;FeS-CS-BC is not affected by Cl-and SO42-coexisting ions during the removal of Cr(Ⅵ).NO3-coexisting ions have a certain inhibitory effect on the removal of Cr(Ⅵ),but the removal rate is still 88.58%;the process of removing Cr(Ⅵ)by FeS-CS-BC is a combination of adsorption and reduction,which is in accordance with the pseudo-second-order adsorption kinetic model and the Redlich-Peterson adsorption isotherm model.The above experimental results show that FeS-CS-BC is suitable for removing Cr(Ⅵ)in acidic or neutral aqueous solutions,and the process of removing Cr(Ⅵ)is not affected by the coexisting ions of Cl-and SO42-.(3)The research results of FeS-CS-BC modified materials on the reduction and passivation of Cr(Ⅵ)in soil are as follows:the optimal dosage of FeS-CS-BC modified material is 1.5%of the soil mass,and its reduction and passivation efficiency of Cr(Ⅵ)can reach 99.29%;when the FeS-CS-BC modified material is added to the soil for two weeks of aging,the reduction efficiency of Cr(Ⅵ)can reach more than 90%,and has basically stabilized after four weeks of aging;when the soil repaired by FeS-CS-BC simulated the leaching of groundwater/surface water and acid rain,the leaching concentration of Cr(Ⅵ)was 0.64 mg·L-1 and 1.08 mg·L-1,respectively;compared with the control group,the soil repaired with FeS-CS-BC significantly reduced the leaching concentration of Cr(Ⅵ);compared with the control group,the treatment with 1.5%FeS-CS-BC modified material significantly reduced the toxicity of Cr(Ⅵ)in the soil,and the germination rate of seeds could reach 75%.The above experimental results show that the FeS-CS-BC can effectively reduce and passivate Cr(Ⅵ)in the soil and reduce soil toxicity,improve the locking effect of soil particles on Cr(Ⅵ)and reduce the risk of Cr(Ⅵ)released into the environment.(4)According to the research results of this study,the reaction mechanism of the FeS-CS-BC modified material and Cr(Ⅵ)can be summarized as follows:adsorption and reduction of Cr(Ⅵ)by reducing functional groups such as-NH2,-OH,C-O on the surface of FeS-CS-BC modified material;reduction of Cr(Ⅵ)to Cr(Ⅲ)by the released Fe2+ and S2-;formation of Cr(Ⅲ)-Fe(Ⅲ)precipitate by complex precipitation.