Study On Remediation And Mechanism Of Green-tea Impregnated Attapulgite On Cr(Ⅵ) Contaminated Soil

With the rapid development of industry,our country’s environmental pollution has become increasingly serious.In the process of remediation of polluted environment,soil pollution is the most difficult problem.Unlike organic pollutants that can be degraded by microorganisms,the heavy metals in the soil can only be extracted artificially（such as leaching,electric remediation）or adding stabilizers to the soil,so that the heavy metals with high toxicity and strong migration ability can be transformed into the form of low toxicity or non-toxicity and weak migration ability.Among them,chromium-contaminated soil requires special attention,not only because of the carcinogenicity and high toxicity of Cr（VI）,but also because of its different properties（such as changes in valence state under different p H values,changes in anion form,etc.）.The Cr（VI）remediation agents currently studied（such as nano-zero-valent iron,biochar,etc.）,although they have a good remediation effect on Cr（VI）,they are expensive and change the inherent physical and chemical properties of the soil after being used,harmful to plants and microorganisms,etc.Therefore,the purpose of this research is to prepare a cost-effective,environmental-friendly and efficient solution in remediating the Cr（VI）contaminated soils.The combination of natural clay mineral attapulgite（ATP）and natural antioxidant tea polyphenols can provide an economical,environmental-friendly and efficient solution in remediating the Cr（VI）contaminated soils.In this study,ATP and green tea were used as raw materials to prepare green tea impregnated attapulgite（GATP）for the remediation of Cr（VI）contaminated soil.The main results obtained are as follows:（1）In aqueous solution,GATP has a strong adsorption and reduction effect on Cr（VI）.Without changing the mineral structure of attapulgite,the green tea extract（tea polyphenol）was successfully combined with attapulgite.（2）After restoration,The content of Cr（VI）in the soil of different treatment groups decreased to different degrees.The greater the amount of material added,the better the fixation effect of Cr（VI）,and GATP showed a better fixation effect on Cr（VI）.The tea polyphenols on GATP have strong reducing ability to Cr（VI）,reducing Cr（VI）to Cr（III）.GATP can convert the chromium originally combined with organic matter into chromium combined with materials or into other forms.（3）The physical and chemical properties of the soil basically did not fluctuate greatly after the restoration.The soil enzyme activity has increased in different degrees.The more the material is added,the higher the degree of enzyme activity is improved,and the effect of adding GATP is better than that of ATP.GATP not only reduces Cr（VI）to Cr（III）,which is less toxic,and greatly reduces the toxicity to soil microorganisms.The green tea extract on GATP can be used as a substrate for soil microorganism respiration,which is not only conducive to the reproduction of soil microorganisms.It is of great help to the improvement of soil fertility and the restoration of soil ecosystem.（4）The state and valence state of C,O,Si and Cr in the soil before and after restoration were analyzed by XPS,and the mechanism of GATP restoration of Cr（VI）contaminated soil was studied.The phenolic hydroxyl group on GATP undergoes redox reaction with Cr（VI）to produce Cr（III）.Under alkaline conditions,Cr（OH）₃,Cr₂O₃ and Cr-Si oxides were more stable in the soil.（5）After remediation,the bioavailability of Cr in the soil of different treatment groups was reduced to varying degrees.The greater the amount of material added,the lower the biological toxicity of the soil.Compared with ATP,GATP showed better fixation of Cr.After the restoration,the content of bioavailable Cr in the soil was significantly reduced,and the soil toxicity was significantly weakened.Moreover,the bioavailability of Cr depends on the content of Cr（VI）,and has nothing to do with the total Cr content in the soil.