Research On Properties And Mechanism Of Sulfidated Zero-valent Iron During Leaching Remediation Of Cr(Ⅵ) Contaminated Soil

In the process of industrial development,a large number of chromium-containing wastewater,waste residue and waste gas were produced by chromium mining,electroplating and other industrial activities,and soil was contaminated by chromium when the chromium infiltrated into the soil.Chromium pollution in soil can cause great harm to animals,plants,microorganisms and human health.The remediation techniques for chromium-contaminated soil include solidification/stabilization,leaching,chemical reduction,biological,and electric technologies.Although some techniques have been mature,there are some limitations in the practical application of single remediation technology.The emergence of combined soil remediation techniques effectively solves the problem.In this paper,the combined application of leaching and chemical reduction remediation technology makes up for the shortcomings of single remediation technology and improves the remediation effect of contaminated soil.Zerovalent iron(ZVI)is commonly used as reducing agent in soil remediation.However,ZVI has some disadvantages,such as easy passivation and poor electron selectivity.Sulfidation modification is an effective method to improve the selectivity and reactivity of ZVI to pollutants.Sulfidated zero-valent iron(S-ZVI)has the advantages of high electron transfer efficiency and fast removal rate of pollutants and is a research hotspot in the field of chemical reduction.The performance and mechanism of SZVI in the leaching remediation process of chromiumcontaminated soil were studied to provide theoretical support for the field application of chromium-contaminated soil remediation technologies.In this paper,simulated chromium-contaminated soil was used to conduct oscillation leaching and reduction experiments in the laboratory.The effects of H2O and CA as leaching eluent on the remediation of Cr(Ⅵ)contaminated soil by SZVI were systematically studied,and the factors affecting Cr(Ⅵ)removal during soil remediation were analyzed by single factor experiment.The changes of soil surface morphology and material composition were analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy(SEM-EDS)and X-ray photoelectron spectroscopy(XPS).The morphological changes of Cr in the soil were investigated.The results showed that the removal rate of Cr(Ⅵ)was better and was less affected by the pH of soil environment under the condition of H2O as eluent.It has obvious promoting effect when CA was used as eluent,and the removal rate of Cr(Ⅵ)by SZVI was related to CA concentration and SZVI dosage.The removal effect of Cr(Ⅵ)was the best when CA concentration was 0.003 mol/L and SZVI dosage was 1.0 wt.%.The combined technology of leaching and SZVI reduction can effectively reduce the content of weak acid extracted Cr in soil and achieve Cr immobilization.In this paper,citric acid modified sulfidated zero-valent iron(CA-SZVI)was prepared,and the performance of CA-SZVI in leaching remediation process of Cr(Ⅵ)-contaminated soil was studied.The mechanism of removing Cr(Ⅵ)by CA-SZVI were analyzed by analyzing the morphological structure and substance composition changes of SZVI and CA-SZVI.The effect of aging on CA-SZVI and the long-term stability of the treated soil were investigated.The results showed that CA-SZVI had the best performance when the CA addition time was 5 min after adding Na2S and the dosage was 10 mmol,and the Cr(Ⅵ)removal rate of CA-SZVI was higher than that of SZVI under different dosages.Compared with SZVI,the surface roughness,specific surface area and the proportion of FeS content of CA-SZVI were increased,and more-OH was anchored on the surface of CA-SZVI,so the removal effect of CA-SZVI was improved.Aging has a great negative effect on the surface morphology and material composition of CASZVI,but the aged CA-SZVI still has a higher Cr(Ⅵ)removal rate,and the Cr(Ⅵ)removal rate of CA-SZVI was higher than that of SZVI under different aging time.After treated by leaching and reduction,the leaching concentrations of Cr(Ⅵ)and total Cr met the requirements of leaching and the leaching risk was low.The repaired soil has better long-term stability.