纳米MnFe2O4@DE复合材料对重金属钒的钝化稳定化效果

Immobilizing and stabilizing effect of nano-MnFe2O4@DE composite on heavy metal vanadium

为获得能够有效减少日益严重的土壤钒污染的稳定剂,该文合成了纳米铁锰氧化物@硅藻土复合材料(MnFe2O4@DE),并通过模拟试验研究该复合材料对土壤钒的稳定化效果及机理,通过植物试验探究了该复合材料对土壤钒生物有效性的影响。试验结果表明,MnFe2O4@DE的最佳投加量为7%,此时其对钒的稳定化率分别约为硅藻土(DE)和MnFe2O4的16.87及1.24倍;时间和pH值单因素试验证明MnFe2O4@DE对土壤钒的稳定化效果能保持较长时间,酸性及中性pH有利于复合材料对钒的稳定。表征与钒形态分析结果表明,复合材料的稳定化效果较好与其较大比表面积和孔体积、钒的残渣态含量增加以及钒价态降低有关。植物萌发试验表明,添加复合材料可使钒污染组的油菜幼苗发芽率、株高和根长较未加钒的对照组无明显差异,植物中钒含量减少约80%。因此,MnFe2O4@DE复合材料在重金属污染土壤修复中具有较好应用前景。

In order to obtain a stabilizing material for treatment of soil vanadium pollution, based on the functional complementarity between different materials, iron-manganese oxide @ diatomite composite(MnFe2O4@DE) was synthesized. Through XRD, SEM and BET characterization, it can be seen that MnFe2O4 nanoparticles were uniformly deposited on the surface of diatomite, resulting in larger specific surface area and pore volume of composite. Besides, MnFe2O4@DE presented much larger specific surface area(112.3 m2/g) and pore volume(0.244 cm3/g) than DE and MnFe2O4, respectively.. This was mainly because the MnFe2O4 nanoparticles can disperse well on the surface of diatomite support restraining the self-agglomeration, which can effectively reduce the grain size of MnFe2O4 nanoparticles. Generally, smaller grain size would lead to a larger specific surface area of materials. The larger specific surface area as well as pore volume could provide more surface active sites for adsorption of the contaminant molecules, which was beneficial to improve the removal performance of the composite for pollutants. The stabilizing effect and mechanism of the composite on soil vanadium were studied by simulation experiments. Results indicated that as-synthesized MnFe2O4@DE composite had better soil vanadium stabilizing effect than the monomer stabilizer(DE, MnFe2O4) at the optimal dosage(7%), and its stabilizing rate of vanadium was about 16.87 and 1.24 times as much as that of diatomite(DE) and MnFe2O4, respectively. MnFe2O4@DE(7% dosage, 30 days of stabilizing) had the best stabilizing effect on vanadium in soil, and the stabilization rate was 94.81%±2.5%. Stabilizing time and pH experiments proved that the stabilizing effect of MnFe2O4@DE composite on soil vanadium can be maintained for a long time, and acidic as well as neutral conditions were beneficial to the stability of vanadium by composite. The stabilizing rate of vanadium in soil by MnFe2O4@DE decreased with the increase of pH value. This phenomenon could be attributed to the greater pH value, which increased in the electrostatic repulsion between the negative charge on the surface of the composite and the vanadium anion in the soil. The XPS and vanadium form analysis showed that the composite had excellent stabilizing effect on vanadium in soil, which related to the larger specific surface area and pore volume as well as the reduce of vanadium valence. Compared with the form of vanadium without added stabilizer, the content of residual state of vanadium in soil increased after adding the MnFe2O4@DE stabilizer, which increased from 19.70% to 30.69%. XPS analysis demonstrated that vanadium could be reduced to low valence vanadium with low toxicity by MnFe2O4@DE composite. Effects of the composite on the bioavailability of soil vanadium were also investigated through the plant experiments. Plant germination experiment indicated that the germination rate, plant height and root length of rapeseed(Brassica napus) seedlings in vanadium-contaminated group with the addition of composite were higher than those of the other two monomer stabilizers, and which had no significant difference compared with the control group without vanadium. The vanadium content of plants in the vanadium-contaminated group after adding the composite was also lower than that in the vanadium-contaminated group with the addition of only monomer. Besides, the composite reduced the vanadium content in the plants by about 80% compared to the vanadium-contaminated group without stabilizers. Therefore, MnFe2O4@DE composite had a good application prospect in the remediation of heavy metal contaminated soil.