Mobility of Be, Bi, F, Ga, Ge and W in Surface Water and the Water Quality Impact on Epilithic Diatoms Downstream of the Historical Yxsjöberg Mine Site, Sweden

Abstract

There is a potential risk that the geochemical cycles of several critical metals will be affected when mining of these metals increases to meet the demand of green technology. The geochemistry of Be, Bi, Ga, Ge, and W, herewith called CM5, is lacking, yet is necessary to ensure responsible mine waste and water management. Beryllium, Bi, and W are all considered immobile, but in previous studies of skarn tailings in Yxsjöberg, Sweden, all three elements were mobilized. The tailings are enriched in CM5, together with pyrrhotite, calcite, and fluorite. The mobility and environmental impact of CM5 and F in surface waters downstream of the Yxsjöberg mine site, Sweden, were studied using monthly water samples from seven locations and analysis of diatoms at five of these locations. Bismuth, Ge, and W were present at low concentrations, transported in the particulate phase, and likely settled in the sediments hundreds of meters from the tailings. Beryllium and F were present at high concentrations and dominantly transported in the dissolved phase. At these pH conditions (5.6), Be should form insoluble hydroxides; however, elevated concentrations of dissolved Be were observed more than 5 km from the mine site. Diatoms downstream of the mine site were negatively affected by the mine drainage. The release of low quality neutral mine drainage will continue for hundreds of years if remediation actions are not undertaken since only a small portion of the tailings have weathered during 50–100 years of storage.

The Source, Mobility and Fate of Bismuth (Bi) in Legacy Mine Waste, Yxsjöberg, Sweden

“…The suspended matter with Bi adsorbed to Fe (hyrd)oxides settled to the sediments a few 100 m from the Yxsjöberg mine site. Thus, the concentrations of suspended Bi and Fe were elevated in the surface water close to the Yxsjöberg Mine site (average: 0.6 µg/L and 2.8 mg/L, respectively) compared to a reference (average: 0.1 µg/L and 0.9 mg/L) that was sampled by [26] in a nearby stream that belonged to another catchment area. After approximately 1 km, at C14, the Bi and Fe concentrations had decreased to concentrations below the reference value (0.1 µg/L and 0.5 mg/L).…”

“…The Smaltjärnen tailings have been open to the atmosphere for more than 30 years, resulting in sulfide oxidation decreasing the pH from 8 to 4 in the upper parts of the tailings, with a subsequent release of Fe and sulfate (SO4) [25]. Calcite in the tailings has buffered the pH, generating neutral mine drainage and formation of Fe (hydr)oxides in the tailings cores, the tailings shore and in the downstream surface water [26,32,39]. Dissolved Ca, F and Fe and sulfate (with an average concentration of 588 ± 64, 37 ± 36, 39 The concentrations of Bi were low but still higher than the detection limit (0.005 µg/L) in all groundwater wells, and the concentrations varied between the different groundwater wells and over time (Figure 4).…”

“…The small part of Bi that did not adsorb to Fe (hydr)oxides was transported in the dissolved phase more than 5 km from the Yxsjöberg mine site. When correlating surface water data regarding DOC [45] and dissolved concentrations of Bi [26], a likely, but not significant, relationship between the two was observed (p-value 0.08), as can be seen in Figure 9. The lowest concentrations of Bi were detected when the EC levels were at their maximum, and the highest concentrations were detected during the spring flood (Figure 9) when all other elements were diluted by the high water flow [39].…”

“…Including the C7 outlier, the R 2 value between Bi and Fe was 0.36 (Figure 8). The surface water was sampled in 2018 for dissolved and suspended matter (see [26] for a detailed description of the methodology). The suspended matter with Bi adsorbed to Fe (hyrd)oxides settled to the sediments a few 100 m from the Yxsjöberg mine site.…”

“…The tungsten (W) skarn tailings at the Yxsjöberg legacy mine site in Sweden contain a complex matrix including calcite (CaCO 3 ), fluorite (CaF 2 ) and sulfides (e.g., pyrrhotite Fe (1−x) S), together with enriched concentrations of beryllium (Be) (284 mg/kg), Bi (496 mg/kg), copper (Cu) (946 mg/kg) and W (960 mg/kg) [25]. Elevated concentrations of dissolved Bi have been found in the surface water downstream from Yxsjöberg legacy mine waste [26]. For this reason, the historical mine tailings at Yxsjöberg provided an interesting setting for studying the mobility and fate of Bi.…”