Review of Emerging Extraction Technologies for Treatment of Low Concentration Cr(VI) in Wastewater

With the rapid development of national economy, the chromium resources usage is increasing day by day, and the discharge of wastewater containing Cr(VI) is also increasing greatly. Cr(VI) has the characteristics of carcinogenicity, teratogenicity and mutagenicity. If it is not well treated, Cr(VI) will seriously pollute the ecological environment and threaten human health. In this review, the research progress of low concentration Cr(VI) treatment in wastewater by emerging extraction technologies was systematically summarized, and the technical difficulties and the research trends in the future were summarized and prospected. The analysis showed that the traditional extractants were easily emulsified, volatile and at low selectivity, and it was extremely urgent to develop a new economical, efficient and green extractants. Compared with the traditional solvent extraction (mixed-settler extraction, centrifugal extraction and tower extraction), chemical precipitation, electrochemistry, membrane separation, ion exchange, photocatalysis, adsorption, etc., these emerging extraction technologies, such as liquid membrane extraction, solid phase extraction, magnetic extraction and microfluid extraction, not only can remove low concentration Cr( VI) from wastewater, but also can obtain high quality chromium products. They were consistent with the concept of sustainable development. However, the above emerging extraction technologies are still in the laboratory research stage, a major research breakthrough of green extraction agents and new extraction equipments must be made in the future for achieving industrial application.