FeS/Biochar Nanoparticles And Their Application In Cr（Ⅵ） Containing Wastewater Treatment

Heavy metal pollution damages the ecological environment and threatens human health.Hexavalent chromium ion（Cr（VI））is a highly toxic and carcinogenic heavy metal.Due to the emission of electroplating,smelting and other industries,China is one of the countries with more serious pollution of Cr（VI）.How to treat Cr（VI）pollution with simple,environmental protection and low cost is of great practical significance.Fe²⁺and S^2-can be used as electron donors to reduce the toxicity of Cr（VI）to Cr（III）.Nanoscale FeS particles also have the advantage of high specific surface area and high activity,which has obvious effect in the treatment of Cr（VI）wastewater.However,when nano-FeS is directly used to treat Cr（VI）wastewater,problems such as particle aggregation,easy oxidation and reduced reactivity will appear.Surface modification and physico-chemical loading are usually used to solve these problems.Biochar has the characteristics of large specific surface area,abundant surface functional groups and porous structure,so it is very suitable to be used as supporting material to load nano-FeS onto its surface.In this paper,nano-FeS was loaded onto the surface of biomass charcoal（Biochar）by activation-pyrolysis method.The prepared FeS/Biochar composite material was characterized,and the performance of FeS/Biochar material for Cr（VI）wastewater treatment was evaluated through batch experiments and continuous flow column experiments.Combined with software simulation and test results,the principle of Cr（VI）removal by FeS/Biochar materials was revealed.The main research contents and conclusions are as follows:（1）Ammonium ferrous sulfate（Fe（NH₄）₂·（SO₄）₂,FAS）was used as iron source,sulfur source and activator,and lignocellulosic biomass was used as carbon source.FeS/Biochar composites were prepared by activation and pyrolysis method.The effects of pyrolysis temperature,biomass types and the ratio of activator to biomass on the composition and structure of the composites were studied.TG-DSC and XRD analysis of the samples showed that the pyrolysis temperature and the mass ratio of ammonium ferrous sulfate to biomass had decisive effects on the composition of FeS/Biochar composites.When the pyrolysis temperature was 700℃and the mass ratio of FAS to biomass was 1:1.5,the pure phase FeS/Biochar composite was obtained.（2）The removal of Cr（VI）from aqueous solution by using jute fiber biochar supported FeS composites was investigated.First,the sample was characterized by XRD,Raman,XPS,FT-IR,SEM,TEM and N₂adsorption-desorption experiments.The results showed that the sample was a porous amorphous carbon loaded FeS nanoparticle composite with a specific surface area of 447.021 m~2/g.There were abundant oxygen,nitrogen and sulfur groups on the surface,and the main atomic contents of the surface were C（62.27%）,Fe（5.44%）and S（5.28%）.In the batch experiment,the optimized experimental conditions were as follows:initial p H of the solution was 2,and FeS/Biochar dosage was 1g/L.Under optimized conditions,the adsorption capacity₀)is 55 mg/g.The isothermal adsorption process of Cr（VI）removal by FeS/Biochar accords with the Langmuir model,and the adsorption kinetics fitting results accords with the intra-particle diffusion model.In the process of adsorption,increasing temperature is beneficial to the removal of Cr（VI）.The experimental study on continuous flow column shows that the lower the amount of adsorbent,the higher the flow rate of chromium solution and the higher the concentration of chromium solution,the shorter the time to reach the point of penetration and depletion in the corresponding penetration curve.In the study of cyclic and desorption properties,FeS/Biochar still maintained good chromium removal performance after three rounds of adsorption-desorption cycles,and the adsorption capacity of FeS/Biochar changed from 7.48 mg/g to 5.94 mg/g.After adsorption equilibrium,Cr（VI）concentration changed from 23.75 mg/L to 18.39 mg/L.（3）Comparing the chromium removal performance of FeS/Biochar materials,pure biochar and commercial FeS materials,it is found that FeS/Biochar materials have the best performance.Using Visual MINITEQ software to simulate the existence of Cr and FeS in solution,combined with XPS characterization,it is found that the chromium removal principle of FeS/Biochar material includes about 20%physical and chemical adsorption and about 80%reduction,and the reduction mechanism is also explained.