Reduction Characteristics And Mechanism Of Ascorbic Acid Modified Nano-FeS On Cr（Ⅵ）

Nano-ferrous sulfide has a large specific surface area and good adsorption and reduction performance,which is often used in the remediation of inorganic polluted soil.In order to improve the utilization and stability of nano-ferrous sulfide,ascorbic acid-modified nano-ferrous sulfide（VC-n Fe S）was synthesized by chemical coprecipitation method after the preference of modifier,and the nanomaterials before and after modification were characterized and their antioxidant performance were compared.Firstly,the influencing factors and reaction mechanism of VC-n Fe S on Cr（VI）reduction were investigated by solution experiments and product characterization;secondly,the changes of soil Cr（VI）reduction rate,soil p H and Cr forms were studied by adding VC-n Fe S to the Cr（VI）-contaminated soil.The research conclusions are as follows:（1）SEM,Zeta potential,XRD and FTIR analysis showed that the n Fe S was successfully synthesized after the VC modification.The oxidation of the material surface was effectively inhibited,thus improving the stability and reactivity of the nanoparticles.VC-n Fe S has excellent reduction effect on Cr（VI）in water,and the reduction rate can reach more than99%.The reduction rate increased with increasing dosage or increasing reaction temperature,acidic and neutral environment is more conducive to the reduction of,VC-n Fe S can maintain excellent reduction rate of Cr（Ⅵ）in a wide p H（3-8）.（2）The reduction process could be described by the pseudo-second-order model,indicating that the chemisorption is dominant mechanism of Cr（Ⅵ）reduction.The Langmuir model fitted by the adsorption isotherms satisfies the condition of 0L<1,thereby indicating strong adsorption of the material on Cr（VI）,and the maximum adsorption capacity of VC-n Fe S for Cr（VI）is 595.24 mg/g.In addition,the main products are Cr₂O₃、Cr（OH）₃and Fe（III）-Cr（III）complex,and the oxygen-containing functional groups（C=O,O-H,C-O,etc.）on the material surface are important in the reaction.The mechanism of reduction of Cr（VI）by VC-n Fe S includes adsorption,reduction and precipitation.（3）After 60 d of treatment by adding VC-n Fe S to the Cr（VI）-contaminated soil,the treatment of 4:1 for soil 1 had the highest reduction rate（80.35%）,except for the significantly lower reduction rate of 1.5:1 treatment（62.89%）,the other groups（2:1,3:1,4:1）had better treatment effects（above 95%）.Compared with CK,the soil p H value of each treatment decreased.The soil p H value of soil 1 decreased by 0.06～0.57 p H units,and the minimum p H value was 7.56（1.5:1,60 d）;the soil p H value of soil 2 decreased by 0.01～0.10 p H units,and the minimum p H value was 8.01（4:1,60 d）.（4）The treatment of 4:1 for both soil had the best repair and stability effect,after 60 d of treatment,the HOAc-extractable Cr and reducible state Cr of soil 1 decreased by 8%and20%,and the oxidizable state Cr and residue state Cr increased by 22%and 5%.The content of oxidizable state Cr and residual Cr of soil 2 increased most significantly（44%,7%）,which was mainly converted to HOAc-extractable Cr（46%）and residue state Cr（5%）.