Recovery of Re(VII) from strongly acidic wastewater using sulphide: Acceleration by UV irradiation and the underlying mechanism

Abstract Strongly acidic wastewater generated from the molybdenum and copper smelting process is of great value for recycling sulfuric acid and valuable metals, such as rhenium (Re). Herein, a high Re(VII) (HReO4) recovery efficiency of 99% within 35 min from strongly acidic wastewater was successfully achieved by using sulphide coupled with ultraviolet (UV) light, and soluble Re(VII) precipitated as Re2S7 in this process. Mechanistic experiments showed that the intermediate Re-S species (i.e., HReO3S) was the dominant limitation responsible for Re(VII) precipitation in the dark, and UV irradiation dramatically accelerated the generation and conversion of HReO3S by inducing the formation of HS• and H•. The H• produced from the photodissociation of H2S promoted HReO4 transformation to H2ReO4•, which rapidly reacted with HS• to produce HReO3S, accelerating the conversion of HReO4. The radical-induced acceleration can also take place during the HReO3S conversion by slowly introducing H2S into the strongly acidic wastewater to continuously produce H• and HS•. This work offers an insight into the improvement of Re(VII) recovery by UV light, which can be potentially applied into resource recovery from strongly acidic wastewater.