Improved reduction efficiency, cycling performance, and removal rate of hexavalent chromium by adding water-soluble salts

• Published in: Environmental science and pollution research international 2023-11, Vol.30 (53), p.113553-113560
• Main Authors: He, Junfeng, Liang, Yuheng, Huang, Hao, Zhai, Wangjian, He, Qinyu
• Format: Article
• Language: English
• Subjects: Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Chromium; Chromium - chemistry; Earth and Environmental Science; Ecotoxicology; Efficiency; Electromagnetic coupling; Electromagnetism; Electron transfer; Electrons; Environment; Environmental Chemistry; Environmental Health; Environmental science; Ferric Compounds; Ferric oxide; Heavy metals; Hexavalent chromium; Iron - chemistry; Iron oxides; Photoelectron spectroscopy; Photoelectrons; Reagents; Redox reactions; Research Article; Salt; Salts; Shells (structural forms); Sodium; Sodium acetate; Sodium chloride; Sodium sulfate; Toxicity; Waste Water Technology; Wastewater; Water Management; Water Pollutants, Chemical - analysis; Water Pollution Control; X ray photoelectron spectroscopy; X-ray diffraction
• ISSN: 1614-7499; 0944-1344; 1614-7499
• DOI: 10.1007/s11356-023-30138-y

Recently, the reaction speed and cycle performance of hexavalent chromium reduction over microsized zero-valent iron (ZVI) with an Fe 0 core and iron oxide (FeO x ) shell structure have been improved by activating the Fe 0 -core electrons through electromagnetic coupling between Fe 0 -core electrons and charges (hexavalent chromium in solution, double-charge layers of the ZVI/solution interface). Herein, the abovementioned electromagnetic coupling was greatly increased by adding salt (CH 3 COONa, NaCl, NaNO 3 , and Na 2 SO 4 ) in the hexavalent chromium solution to increase the charge response. Adding salt greatly improved the reaction speed and cycle performance of hexavalent chromium reduction. It took 8 min to reduce hexavalent chromium with CH 3 COONa to below the discharge standard of wastewater in the first cycle and 20 min after reducing for 20 cycles. The best apparent rate of constant value (0.416 (min) -1 ) is nearly four times larger than those without salts. X-ray diffraction and X-ray photoelectron spectroscopy revealed the production of amorphous iron oxide shell with salt. The salt improves the hexavalent chromium reduction speed and cycle performance and impedes the Fe 0 -core-electron transfer via the produced Fe 2 O 3 , resulting in existence of an optimized salt dosage. This work aims to provide an effective route for enhancing the removal efficiency and cycle performance of heavy-metal–ion reduction via Fe 0 . And this work also proposes a novel viewpoint that adding salt in waste water would increase the electromagnetic coupling between the charges in solution and Fe 0 -core electrons which could finally activate the redox reaction.