| With the improvement of people’s living standard and the acceleration of urbanization,the output of kitchen waste increases gradually.Because kitchen waste is rich in organic matter and high in water content.So hydrothermal carbonization of kitchen waste to produce biochar.In our country,electroplating and leather industries will produce a large quantity of wastewater containing chromium,which causes the groundwater pollution.nZVI has a large surface area and strong oxidation ability,but nZVI is easy to agglomerate and be oxidized by oxygen.Therefore,nZVI is loaded onto biochar.Three different modifiers were used for modification treatment to prevent oxidation of nZVI.Comparing the effect of the three modifiers,it was found that the modification effect of sodium thiosulfate was better.Single factor experiment was carried out with the S-modified material and the reaction kinetics was explored.Firstly,food waste was prepared into biochar by hydrothermal carbonization.The yield of biochar was 27.41%,and biochar could provide a site for nZVI loading.Sodium thiosulfate（S）,polyacrylic acid（PAA）and Xanthan gum（XG）were selected as modifiers.Three materials,S/BC/nZVI,PAA/BC/nZVI and XG/BC/nZVI,were prepared by liquid phase reduction.The distribution of S/BC/nZVI was more uniform through SEM.BET indicates that S/BC/nZVI has a large specific surface area,XRD indicates that S/BC/nZVI has the largest peak of zero-valent iron and the highest content of zero-valent iron.Iron content is controlled by determination of iron content in the three materials,and the removal rate of Cr（Ⅵ）is explored under the condition of consistent iron content.The results show that the removal efficiency of Cr（Ⅵ）is the highest in S/BC/nZVI,which indicates that sodium thiosulfate has a good protective effect on zero-valent iron.Through static sequencing batch experiment,the influences of S/BC/nZVI dosage,initial p H,initial concentration,Na Cl concentration and humic acid concentration on Cr（Ⅵ）removal are studied.The larger S/BC/nZVI dosage is,the higher the removal rate is.In order to save finished products,0.75g/l S/BC/nZVI is selected for the following experiment.When the concentration of Cr（Ⅵ）is 30mg/l and the dosage of S/BC/nZVI is 0.75g/l,the removal rate of Cr（Ⅵ）is 94.34%,and the acidic condition is conducive to the removal of Cr（Ⅵ）.The higher the initial concentration is,the lower the removal rate is.The presence of Na Cl and humic acid have a great influence on the removal of Cr（Ⅵ）.However,with the doubling of Na Cl concentration and humic acid concentration,the removal rates are also decreasing.Finally,the dosage of S/BC/nZVI,initial p H,initial concentration,Na Cl concentration and humic acid concentration all conform to the quasi-second-order kinetic model.The fitting curve of particle diffusion model can be roughly divided into three stages,and the slopes of each stage from the first to the third gradually decrease.The results show that,The main reason affecting the adsorption of Cr（Ⅵ）is the obstruction of the adsorption of solute to nZVI.According to the XPS map results of the newly prepared S/BC/nZVI and the reacted S/BC/nZVI,the removal of Cr（Ⅵ）by S/BC/nZVI is mainly the reduction of Cr（Ⅵ）to Cr（Ⅲ）,and then the formation of Cr2O3and Cr（OH）3precipitation attached to the material surface.In order to achieve the removal of Cr（Ⅵ）and total chromium in water. |
