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

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) (HReO) 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 ReS in this process. Mechanistic experiments showed that the intermediate Re-S species (i.e., HReOS) was the dominant limitation responsible for Re(VII) precipitation in the dark, and UV irradiation dramatically accelerated the generation and conversion of HReOS by inducing the formation of HS• and H•. The H• produced from the photodissociation of HS promoted HReO transformation to HReO•, which rapidly reacted with HS• to produce HReOS, accelerating the conversion of HReO. The radical-induced acceleration can also take place during the HReOS conversion by slowly introducing HS 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.