Study On The Removal Of Cr(?)from Water By Sulfurized Nano-zero-valent Iron And Its Modification

With the development of extensive industrialization and rapid urbanization,Cr(VI)pollution caused by improper treatment and discharge of Cr(VI)-containing wastewater produced in industries such as mining,pharmaceuticals,tanning,and stainless steel manufacturing,is harmful through various means to human health.Nano-zero-valent iron(nZVI)has the characteristics of large specific surface area,strong reducibility,and abundant raw materials.It is considered to be an excellent material for removing Cr(?),but it is easy to agglomerate,passivate,and lose during the process of sewage treatment.To this end,many modifications have been made to nZVI.In the past ten years,sulfurized nano-zero-valent iron(S-nZVI)produced by sulfide-modified nZVI has become a research hotspot because it improves the reactivity,dispersibility,oxidation resistance,and service life of nZVI.In the research,it was found that the dispersibility of S-nZVI can be achieved through biochar,carboxymethyl cellulose,clay minerals,etc.In this experiment,three materials,nZVI,S-nZVI,and S-nZVI supported on active carbon(S-nZVI@AC)were prepared to study the mechanism of nZVI vulcanization modification to improve the Cr(?)removal effect,and to explore whether the activated carbon loading can be further Improve the activity of S-nZVI.The specific research content is as follows:(1)SEM characterization results show that nZVI is granular particles,the outer layer is smooth,the outer layer is rough after vulcanization,and the shell layer with flaky structure is formed;the BET characterization results show that the specific surface area of nZVI is 25.6 m²·g^-1,S-nZVI(S/Fe molar ratio=0.5)has a specific surface area of 48.32 m²·g^-1;the analysis results of a vibrating sample magnetometer show that the saturation magnetization of nZVI decreases drastically as the degree of vulcanization increases,reducing the inter-particle Agglomeration;FTIR and XRD characterization results show that Fe S_x is formed after nZVI vulcanization,Fe Sx prevents Fe^o oxidation and promotes the formation of Fe^o crystal form;XPS characterization results show that S-nZVI adsorbs Cr(?)and undergoes a redox reaction,Fe S_x participates in the reduction of Cr(?).The experimental results show that the S/Fe molar ratio,p H,temperature,and coexisting anions and cations will all affect the removal effect of Cr(?).When the S/Fe molar ratio is 0.5,the removal effect of Cr(?)is the best.The material is acidic.The removal effect of Cr(?)will be better under high temperature and high temperature.Anions in the water can inhibit its removal rate,and cations can promote it.Kinetic analysis shows that the removal of Cr(?)by S-nZVI is mainly controlled by chemical adsorption.The adsorption process includes two stages of molecular diffusion and intra-particle diffusion.The aging experiment shows that the removal rate of S-nZVI after aging for7 days has dropped by 8%,while nZVI has dropped by 12%.S-nZVI has much less iron outflow than nZVI.Sulfuration has a great effect on the reactivity and service life of nZVI.improve.The aging experiment shows that the removal rate of S-nZVI is only reduced by 12%after 4 times of repeated use,and it has good reusability.(2)Different proportions of S-nZVI@AC were prepared by adjusting different mass ratios of C/Fe and S/Fe molar ratios.The results showed that the removal effect of Cr(?)was the best when the mass ratio of C/Fe was 1 and the molar ratio of S/Fe was 0.4.SEM results showed that S-NZVI was uniformly dispersed on AC surface.BET characterization showed that the specific surface area was 165.09 m²·g^-1,which was 3.42 times that of S-NZVI(S/Fe molar ratio=0.5).FTIR characterization results showed that there was S-Fe peak in S-nZVI@AC infrared spectrum,indicating that S-NZVI was successfully loaded.Kinetic analysis shows that the removal of Cr(?)by S-nZVI@AC is mainly chemisorption,and the adsorption process includes two stages:molecular diffusion and intra-particle diffusion.The aging experiment showed that the removal rate of S-nZVI@AC decreased by 2.5%after 7 days of aging,and the iron flux was 0.3 mg·L^-1.Compared with S-NZVI,it had better reactivity and service life.According to the above analysis,the S-nZVI@AC prepared in this study can efficiently remove Cr(?)from water,which provides a feasible choice for the removal of wastewater containing Cr(?).