Scheelite weathering and tungsten (W) mobility in historical oxidic-sulfidic skarn tailings at Yxsjöberg, Sweden

Abstract

More knowledge of the geochemical behavior of tungsten (W) and associated contamination risks is needed. Therefore, weathering of scheelite (CaWO 4) and secondary sequestration and transport of W to groundwater in historical skarn tailings and surface water downstream of the tailings were studied. The tailings contained 920 mg/kg W, primarily in scheelite. Mineralogical and geochemical analyses were combined to elucidate the geochemical behavior of W in the tailings, and water samples were taken monthly during 2018 to monitor its mobility. In the tailings, a large peak of W was found at 1.5 m depth. There, 30 wt%. of W was present in easily reducible phases, indicating former scheelite weathering. Currently, W is being released from scheelite to water-soluble phases at 2.5 m depth. The release of WO 4 2− is hypothetically attributed to anion exchange with CO 3 2− released from calcite neutralizing acid produced from pyrrhotite oxidation in the upper tailings and transported downwards to pH conditions > 7. Higher concentrations of dissolved W were found in the groundwater and particulate W in downstream surface water than in reference water, but they were lower than current contamination thresholds. Tungsten showed correlations with hydrous ferric oxides (HFO) in both the tailings and surface water.

The Dynamics of Tungsten in Soil: An Overview

“…Even though the Wenzel's SEP is the most used for tungsten, it is not the only one. A different sequential extraction has been used to define tungsten speciation in mining soils [59]. This procedure, originally used by Dold [60], subdivided tungsten forms into seven fractions: (1) poly-tungstates water-soluble phase, (2) exchangeable phase, (3) easily reducible minerals, (4) resistant reducible minerals, (5) easily oxidizable minerals, (6) resistant oxidizable minerals, and (7) residues and silicates.…”

A simple model for evaluating isotopic (18O, 2H and 87Sr/86Sr) mixing calculations of mine – Impacted surface waters

“…On the other hand, Al, Be, Ca, Sr, SO 4 2− and W concentrations range from 0.05-37 mg/L, 1-4671 μg/L, 498-642 mg/L, 168-242 μg/L, 455-639 mg/L and 0.5-24 μg/L, respectively. The (Hällström et al, 2019). The high pH in the groundwater despite the influence of sulphide oxidation is due to the relatively high carbonate (calcite) content (~6%) of the tailings.…”

“…Previous ground and surface water sampling campaigns in the tailings and downstream, respectively (e.g. Höglund et al, 2004;Hällström et al, 2019), reported of W and other elemental contamination in some of the surface waters. These authors hypothesised that the groundwater from the tailings could be the source of these contaminants to the surface waters.…”

Pollution and Ecological Risk Evaluation of Heavy Metals in the Soil and Sediment around the HTM Tailings Pond, Northeastern China

“…Liu et al found that Cu, Zn, and Cd were the main pollutants in the sediment around the copper mine areas [13]. Lina et al found that higher concentrations of particulate tungsten were found in the surface water downstream of a scheelite tailings pond [14]. The oxidation of sulfide tailings was the source of the mine environmental pollution [15,16].…”