"Editor's note in January 29th 20, literature and intelligence concerned the research of Li Shiyin's team of Nanjing Normal University Environmental Science Institute on humic acid modified nano iron sulfide to enhance the removal of six valent chromium in water. Specially invited Li wrote the highlight of this research for the official account, on the one hand, he enriched the research field of natural organic matter, especially the research field of water body restoration, and the other side. In addition, we hope that the research results of the team can inspire and inspire the followers, and promote the research of natural organic matter. "
Guide reading
Among the heavy metal pollutants in water, hexavalent chromium is considered as the priority pollutant. Because of the high toxicity of hexavalent chromium in water, chemical reduction is considered as an efficient and economic means for the removal of hexavalent chromium in water. Nanosized ferrous sulfide is considered to be a very excellent environmental remediation material for heavy metal pollution, not only because of the excellent reducibility of Fe2 + and S2 -, but also because of its higher reactivity and larger specific surface area. Although nano FES has a good effect on the removal of hexavalent chromium from water, it is easy to be oxidized and agglomerated in air, soil or water, which limits its application in the treatment of polluted environment. Humic acid can exchange, adsorb, complexate and chelate with heavy metal ions, and act as polyelectrolyte to disperse and stabilize. Therefore, this study intends to use humic acid as a modifier and stabilizer to modify nano ferrous sulfide to improve its adsorption and reduction capacity of hexavalent chromium, and to explore the process and mechanism of removing hexavalent chromium from water by humic acid modified ferrous sulfide.
In this study, humic acid was used as a modifier and stabilizer to coat the surface of nano-sized ferrous sulfide to reduce the agglomeration of nano-sized ferrous sulfide. First of all, the stability of ha-fes is 330.4%, 145.0%, 1157.1% and 384.6% higher than that of unmodified FES. Compared with the unmodified FES, the stability of nano FES modified by HA is significantly improved. Through the measurement of ferrous sulfide particles and the hydraulic diameter of ha-fes, it is found that under different pH conditions, the hydraulic diameter of ha-fes is significantly lower than that of unmodified ferrous sulfide, because the humic acid coating on the surface of ferrous sulfide particles improves the electrostatic repulsion on the surface of particles and the dispersion of ferrous sulfide nanoparticles.
▲ precipitation characteristics of unmodified FES and ha FES (a) within 120 min. The hydraulic diameters of unmodified FES and ha FES at different pH (b) and zeta potential (c)
The removal efficiency of hexavalent chromium by ferrous sulfide, humic acid and ha-fes was compared and analyzed. It was found that the maximum removal amount of hexavalent chromium by ha-fes was about 7.7 times of humic acid and 2.3 times of ferrous sulfide. In addition, the rate limiting step for the removal of hexavalent chromium by ha-fes is chemical adsorption, that is, the electronic exchange or sharing between adsorbate and adsorbent. The unmodified FES nanoparticles are easy to agglomerate and oxidized in the aerobic environment, thus reducing their reactivity to hexavalent chromium. Humic acid modification improves the removal efficiency of hexavalent chromium in water by ferrous sulfide, not only because humic acid can reduce the agglomeration of nano ferrous sulfide, but also humic acid can provide rich functional groups for adsorption and reduction of hexavalent chromium on the surface of nano ferrous sulfide.
The quasi primary and quasi secondary model fitting of Cr (VI) removal by HA FES. The initial concentration of hexavalent chromium is 40, 60 and 80 mg / L respectively, and that of humic acid modified ferrous sulfide is 100 mg / L
In order to further reveal the mechanism of hexavalent chromium removal by ha-fes, it was found by XPS and XRD that 95.03% of Cr was reduced from Cr (VI) to Cr (III), and 4.97% of hexavalent chromium was adsorbed on the surface of ha-fes. Therefore, the removal of hexavalent chromium in water by ha-fes mainly depends on its reducibility, and the adsorption also plays an auxiliary role. Finally, the removal process of hexavalent chromium by ha-fes was studied under different pH, Ca2 +, Mg2 + concentration and actual water conditions. It was found that ha-fes has good stability and reactivity, and can be well applied to the removal of hexavalent chromium in real water.
This study provides an effective method to improve the stability and reactivity of nano FES, which can provide practical guidance for the rapid remediation of hexavalent chromium polluted water.
The XPS spectrum of ferrous sulfide modified by humic acid before and after reaction with hexavalent chromium
Reference
[1] Yao, Y. R., Mi, N. He, C., He, H.,Zhang, Y., Zhang, Y. C., Yin, L., Li, J., Yang, S. G., Li, S. Y., Ni, L. X.2020. Humic acid modified nano-ferrous sulfide enhances the removal efficiencyof Cr(VI). Sep. Purif. Technol., 240: 116623.[2] Yao, Y. R., Mi, N., He, C., Yin, L., Zhou, D. B., Zhang, Y., Sun, H. G., Yang, S. G., Li, S. Y., He, H. 2020. Transport of arsenic loaded by ferric humate colloid in saturated porous media. Chemosphere: 240: UNSP 124987.
Contact author
Li Shiyin, Professor, School of environment, Nanjing Normal University, email: lishiyin@njnu.edu.cn
Extended reading
[viewpoint] Study on the mechanism of hexavalent chromium removal by magnetic ferric tetrasulfide / biochar composite -- Wenzhou Medical University Wang Xuedong (Liu Wei)
[viewpoint] Study on remediation of cadmium and lead contaminated soil by pyrite humic acid coprecipitation -- Lanzhou University -- Zhao zhuanjun (Xu Miaomiao)
[viewpoint] mechanism of humic acid affecting persulfate / Fe (II) remediation of groundwater: Li Xiaodong (Gu Qingbao), Chinese Academy of Environmental Sciences
Editor: Wang Yuqin
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