In-situ Sr isotopic measurement of scheelite using fs-LA-MC-ICPMS

Experiments on metasomatism in a system comprising huebnerite and aqueous CaCl2 solution were performed at 130, 150, and 170 °C. SEM observations revealed the formation of euhedral crystals of scheelite replacing huebnerite in all experiments. The replacement texture of huebnerite by scheelite was classified as rim replacement texture. Although the molar volume ratio of replacing mineral to replaced mineral was 1.12 for the present study, huebnerite was replaced by scheelite. This suggests that the influence of molar volume ratio is small on the metasomatism of huebnerite to scheelite, which has not been expected in previous studies. Our results also suggest that the metasomatism of huebnerite to scheelite can be achieved if the CaCl2 concentration in the solution and the reaction temperature are sufficiently high. The apparent rate constant k for huebnerite dissolution in the metasomatism is approximately 10-9-10-6 mol l-1 s-1; the activation energies are 9.6, 20.7, and 31.2 kJ/mol for CaCl2 concentrations of 0.01, 0.10, and 1.00 mol/l, respectively. The precipitation of scheelite can be the rate-determining process of the metasomatism during the initial stage when the W concentration in the solution is high.

Scheelite

Metasomatism

Volume fraction

10.2465/jmps.080414

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Hydrocalumite as well as the Formation of Scheelite Induced by Its Dissolution, Removing Aqueous Tungsten with Varying Concentrations

International Journal of Environmental Research and Public Health (2022)

Yang Chen Qinghai Guo Yaowu Cao G. A. Chelnokov

As a toxic element, tungsten (W) in elevated concentrations, originating from human activities or geological sources, poses a severe threat to the environment. However, there has been a lack of robust remediation techniques focusing on aqueous tungsten contamination with varying initial concentrations, because only recently have the toxicity and the environmental threat of tungsten been fully realized. In this study, the removal of tungsten from an aqueous solution by hydrocalumite was investigated for the first time. Systematic removal experiments were carried out at designated contact time, temperature, and initial tungsten concentration. The results showed that hydrocalumite is capable of effectively removing tungsten under various conditions, especially at high initial tungsten concentrations, with the maximum uptake capacity being up to 1120.5 mg (tungsten)/g (hydrocalumite). The mechanisms of tungsten removal were studied based on the measured chemical compositions of the solution samples and their PHREEQC simulations as well as the solid sample characterization by XRD, SEM-EDX, and XPS. At low initial tungsten concentrations (below 1 mmol/L), anion exchange between the tungsten in solution and the Cl in the hydrocalumite interlayers played a critical role in tungsten removal. At high initial tungsten concentrations (higher than 5 mmol/L), the removal of W from the solution was solely caused by the precipitation of scheelite (CaWO4), facilitated by the substantial release of Ca2+ from hydrocalumite dissolution. At moderate tungsten concentrations (1-5 mmol/L), however, both mechanisms were responsible for the uptake of tungsten, with scheelite precipitation being more important. Hydrocalumite is promising for wide use in the treatment of high-tungsten natural waters or wastewaters.

Scheelite

10.3390/ijerph19148630

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