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 4 ) 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 Re 2 S 7 in this process. Mechanistic experiments showed that the intermediate Re-S species (i.e., HReO 3 S) was the dominant limitation responsible for Re(VII) precipitation in the dark, and UV irradiation dramatically accelerated the generation and conversion of HReO 3 S by inducing the formation of HS• and H•. The H• produced from the photodissociation of H 2 S promoted HReO 4 transformation to H 2 ReO 4 •, which rapidly reacted with HS• to produce HReO 3 S, accelerating the conversion of HReO 4 . The radical-induced acceleration can also take place during the HReO 3 S conversion by slowly introducing H 2 S 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.
In this study, nanoscale zero-valent iron was successfully soldered onto graphene oxide to synthesize nZVI/rGO nanocomposite by an improved modified Hummers' method. The nZVI/rGO nanocomposite was used to remove Re(VII) in water remediation , which was utilized as a replacement for the radioactive element of Technetium-99 (99Tc). The results showed that nZVI/rGO could effectively remove Re(VII) at pH = 13 with a removal efficiency of 99.1 %. rGO can effectively inhibit the aggregation of nZVI and significantly improve the removal performance. The removal capacity of nZVI minus the removal capacity of rGO in the composite was as high as 468.8 and 474.9 mg/g, respectively, corresponding to the mass ratio of Fe 0 :rGO = 1:1 and 1:2. However, the removal capacity of pure nZVI was only 33.5 mg/g, and that of the pure rGO was 42.6 mg/g. The removal capacity of Re(VII) by nZVI/rGO was not affected by cations of Na + , Ca 2+ , K + , and Mg 2+ ions. The removal efficiency of Fe 0 :rGO with a mass ratio of 1:1 and 1:2 was still higher than 60 % (63.5 % and 67.1 %, respectively). The results of this study demonstrate that the graphene oxide-based zerovalent iron nanocomposite under an appropriate mass ratio, can economically and efficiently remediate rhenium heavy metal ions in high pH water environments.
It is urgently needed to develop highly efficient and selective adsorbents for enrichment and separation of Re(VII) from Mo(VI) to obtain metallic rhenium. By tuning cross-link of chitosan, ionic gel capsules (CSN) were prepared, which had a core-shell structure and wrapped N263 (methyl trioctyl ammonium chloride) as an extractant. After being characterized, the CSN capsules were used as a green adsorbent for separation of ReO 4 − from MoO 4 2− . It was found that the gel yielded good adsorption capacities for Re(VII) in a wide pH range from pH 2 to 12. The adsorption of Re(VII) on the gel followed the Langmuir model, exhibiting a maximum adsorption capacity of 222 mg g −1 for Re. The adsorbent showed good adsorption capacities for Mo(VI) at pH < 2, but little at pH > 3.5. Therefore, the enrichment and separation of Re(VII) from Mo(VI) could be easily achieved by using the gel adsorbent in a wide pH range from 4 to 12, showing a separation factor β Re/Mo with values of 10 3 –5 × 10 4 . A mechanism was proposed for the selective adsorption of Re(VII). The extractant N263 wrapped in the capsule core provides excellent extractive adsorption ability for Re(VII) through ion association extraction, generating ion association complex R 4 N + ∙ReO 4 − in the adsorbent. The gel shell was composed of cross-linked chitosan induced by sodium tripolyphosphate, and functioned as a blocking layer for the adsorption of Mo(VI), being possibly related to a special interaction between Mo and P as observed in the formation of phosphorus molybdenum heteropolyacid and/or the crosslinking with Mo and chitosan. The CSN gel was successfully applied to separate ReO 4 − from a practical alkaline solution.
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