Photoinduced fluorescence modulation through controllable intramolecular [2+2] photocycloaddition in single molecules and molecular aggregates.

We report a general molecular design strategy of spatial proximity, which allows intramolecular [2+2] photocycloaddition reaction to take place in both single molecules and molecular aggregates. Sharply contrasting photoinduced fluorescence changes in solution and in the solid state were found and attributed to the aggregation-induced quenching property of the monomers and the aggregation-induced emission nature of the photodimers.

Accelerating bioleaching of tungsten mining wastes using indigenous acidophilic bacteria.

The growing amount of W mining waste produced globally is of concern for its proven hazard to the environment and to human health. While uncontrolled biooxidation can result in environmental harm, bioleaching, where pregnant leach solutions are controlled, has been widely used in the mining industry for valuable metals recovery, often from low-grade materials. This bioleaching study was developed to evaluate whether the biogeochemical reprocessing of W tailings could be employed for the decontamination of W-bearing mine waste, combined with valuable metals recovery, i.e., turning a waste into a resource. Using an in-vitro laboratory model, the susceptibility of wolframite [(Fe,Mn)WO4] to acid dissolution during the concomitant oxidation of co-localized sulfidic minerals represented the basic strategy for enhanced W recovery. Encouragingly, geochemistry and synchrotron-based X-ray absorption near edge structure of weathered W tailings demonstrated that early-stage wolframite dissolution occurred. However, W dissolution was limited by the formation of secondary W minerals; weathering produced two secondary W minerals i.e., gallium-rich tungstate and minor sanmartinite [(Zn,Fe)WO4]. The dissolution and re-precipitation of W minerals may provide a strategy for W waste reprocessing if the two processes can be separated by initially putting W into solution, and allowing for its extraction from tailings, followed by its' recovery by secondary W mineral formation.

Microbially influenced tungsten mobilization and formation of secondary minerals in wolframite tailings.

Wolframite [(Fe,Mn)WO4] tailings represent a hazardous waste that can pose a threat to the environment, humans, animals and plants. The present study aims to conduct a high-resolution depth profile characterization of wolframite tailings from Wolfram Camp, North Queensland, Australia, to understand the biogeochemical influences on W mobilization. Several indigenous Fe- and S-oxidizing bacteria (e.g., Streptococcus pneumoniae and Thiomonas delicata) in wolframite tailings were found highly associated with W, As, and rare earth elements. Biooxidation of metal sulfides, i.e., pyrite, molybdenite and bismuthinite, produced sulfuric acid, which accelerated the weathering of wolframite, mobilizing tungstate (WO42-). Using synchrotron-based X-ray fluorescence microscopy (XFM) and W L-edge X-ray absorption near-edge spectroscopy (µ-XANES) analysis, wolframite was initially transformed into Na- and Bi- tungstate as well as tungstic acid (partial weathering) followed by the formation of Ga- and Zn- tungstate after extensive weathering, i.e., the wolframite had disappeared. While W (VI) was the major W species in wolframite tailings, minor W(0) and W(II), and trace W(IV) were also detected. The major contaminant in the Wolfram Camp tailings was As. Though wolframite tailings are hazardous waste, the toxicity of W was unclear. Tungsten waste still has industrial value; apart from using them as substitution material for cement and glass production, there is interest in reprocessing W waste for valuable metal recovery. If the environmental benefits are taken into consideration, i.e., preventing the release of toxic metals into surrounding waterways, reprocessing may be economic.