Characteristics of Novel Extraction and Photoinduced Precipitation Approach by PEG/SA and Fluorescence Monitoring of Cr(VI)

A novel route based on biohydrogel sodium alginate (SA) for extraction by an aqueous two-phase system (ATPS), recovery of chromium by a photoinduced precipitation process, and monitoring of the process by fluorescence spectroscopy (F-S) was developed. The processes were explored by means of FTIR, micro-FTIR, XPS, and F-S, and the roles of polyethylene glycol and sodium alginate (PEG/SA) in the process were analyzed. Results showed that SA acted as an extractant to form a complex with Cr­(VI). The maximum extraction point appeared at pH 5.50, and its kinetic equation showed that CCr(VI) was the key point that controls the reaction. Cr­(VI) was reduced to Cr­(III) within 10 min of 300 W solar irradiation in the presence of PEG. Then coprecipitation of water-insoluble polynuclear complexes consisting of SA and trivalent and hexavalent chromium was completed. The biohydrogel from SA underwent a static quenching process, and the extraction process and phase diagram can be monitored by F-S. It belongs to the transform π–π structure from SA. This work may provide a promising and attractive approach to realize a high-rate and low-cost process for recovery of chromium.