Journal
SEPARATION AND PURIFICATION TECHNOLOGY
Volume 275, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.seppur.2021.118915
Keywords
Cr(VI) removal; Sodium borohydride; Oxalate; Turbidity; Membrane filtration
Categories
Funding
- National Natural Science Foundation of China [52000047]
- Fundamental Research Funds for the Central Universities
- NSRIF [2020027]
- National Key R&D Program of China [2019YFD1100104]
- Reform of Graduate Teaching Research in Harbin Institute of Technology [JGYJ-2018029]
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The treatment of industrial wastewater containing Cr(VI)-organic compounds has been a long-term concern in the field of environment. Researchers developed a novel catalytic chemical reduction/membrane filtration method for efficient removal of total Cr (TCr) in a system with coexisting Cr(VI) and oxalate (Ox). The study investigated the effects of Ox, Fe(III), and Al(III) concentrations, NaBH4 dosage, and sedimentation time on the removal of Cr(VI) containing Ox by NaBH4.
The treatment of industrial wastewater containing Cr(VI)-organic compounds is a long-term concern in the field of environment. In order to realize the high-efficient reduction of Cr(VI) and solve the problem of Cr(III) residue in water environment, a novel catalytic chemical reduction/membrane filtration method was developed for the removal of total Cr (TCr) in a system with coexisting Cr(VI) and oxalate (Ox). The effects of the concentrations of Ox, Fe(III), and Al(III), the dosage of NaBH4, and sedimentation time on the removal of Cr(VI) containing Ox by NaBH4 were investigated. Additionally, the simultaneous removal of turbidity and TCr using a microfiltration membrane was investigated, and the reason for the enhanced TCr removal was clarified. The results of ion chromatography (IC), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) suggested that when Cr(VI) and Ox coexist, low concentrations (0.3 mM) of Fe(III) or Al(III) contributed significantly to the high turbidity caused by the formation of suspended solids (SS) following the reduction of Cr(VI) by NaBH4. However, almost all the Cr(III) could be removed by a 1-mu m microfiltration membrane. The high turbidity system formed by Ox and Cr(III) is unstable, and some Ox will gradually release their binding sites with Cr(III) with the extension of the natural settling time. For 24 h, 53.75% of Ox was involved in the formation of SS, while in the presence of Fe(III) or Al(III), only 11.28% and 6.30% of Ox were involved, respectively. High concentrations of Fe(III) and Al(III) enhanced the reduction of Cr(VI) by NaBH4. The removal of TCr was close to 100% after natural sedimentation for 15 mM and combined with a microfiltration membrane. This result is caused because Fe(III)-Cr(III) or Al(III)-Cr(III) can form larger SS, which is easily intercepted by the microfiltration membrane. The development of a novel combined method of catalytic chemical reduction and membrane filtration will be beneficial for reducing the retention of TCr in the environment.
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