| Human increasing demand for mineral resources,mining activities frequently caused serious ecological destruction and environmental pollution.The rich chrome ore resources in the western region of Inner Mongolia have led to serious chromium pollution in the soil environment around the mine,threatening the health of animals,plants and humans,so there is an urgent need to develop rapid and effective soil chromium pollution remediation technology.Nanoscale materials are often used to remove heavy metals from soil due to their high specific surface area effect,superior small size effect,and strong reducing,adsorbing and complexing abilities,which also do not cause secondary pollution.In recent years,many studies have shown that nano zero-valent iron materials are effective for remediation of chromium contamination in soil,but there are fewer studies on the application in calcareous contaminated soil.In order to explore the feasibility of nanometer zero-valent iron in the remediation of cr-contaminated calcareous soil,in this study we prepared stable nanometer zero-valent iron PVP-NZVI using polyethylene pyrrolidone(PVP k-30)and ethanol solution.Study the remediation effect and transformation mechanism of PVP-nZVI on calcareous Cr(Ⅵ)contaminated soil by static soil sample incubation and dynamic soil column drenching experiments.The main results are as follows:(1)PVP-NZVI prepared by PVP and anhydrous ethanol through improved liquid phase reduction method has stable properties,is not easy to agglomeration and oxidation,and can be stored in ethanol solution for a long time.Its specific surface area is 40m2/g,pore volume is 0.2135cm3/g,and average pore size is 21.1366 nm.The SEM characterization results showed that the PVP-nZVI particles were spherical in shape and uniformly dispersed,with interparticle connections forming chains and an average particle size of about 30 nm.The XRD pattern showed a complete main peak around 2θ= 44°,which proved that the material was zero-valent iron.the EDS and XPS characterization results showed that the prepared PVP-nZVI material had a complete core-shell structure.(2)Static soil incubation experiments were conducted to investigate the effects of addition amount,reaction time,temperature and soil-water ratio on the effect of PVP-nZVI on the removal of Cr(Ⅵ)from calcareous soils,and to explore the optimal conditions.The results showed that the optimal PVP-nZVI addition amount was 3%,the removal amount was 99.9 mg/kg,and the removal rate reached 87.3%.The best removal effect was achieved at 16 h with the removal amount of 93.3mg/kg and the removal rate reached81.6%;the best removal effect was achieved at 35℃ with the removal amount of 108mg/kg and the removal rate reached 94.4%;the best removal amount was 99.1mg/kg and the removal rate reached 87.6% when the soil and water ratio was 1:5.Moreover,the removal of Cr(Ⅵ)from soil in water-soluble state by PVP-nZVI material is in accordance with pseudo primary kinetics with apparent reaction rate Kobs=0.0124 min-1.(3)Study of Cr(Ⅵ)removal from calcareous soils by PVP-nZVI and the effect on soil properties through dynamic soil column drenching experiments.The results showed that the concentration of Cr(Ⅵ)in the leachate showed a decreasing trend,and the concentration of Cr(Ⅵ)in the leachate was basically undetectable on the fifth day,and the p H value of the leachate showed a state of first increasing,then decreasing and finally stabilizing with the decreasing concentration of Cr(Ⅵ),and the conductivity and redox potential of the leachate showed a decreasing trend with the decreasing concentration of Cr(Ⅵ)in the leachate.It can be seen that PVP-nZVI can reduce the conductivity and REDOX potential in a certain range when repairing soil,but the change range of p H is small,which basically has no influence on the properties of soil column leachate. |
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