Electric vehicles and various clean energy technologies are powered by metal-based batteries known as
lithium
. The rising demand for lithium has turned lithium mining into a booming industry. This vital resource is predominantly found in volcanic formations called
pegmatite
. Ongoing research aims to determine the carbon and water consumption in pegmatite mining, but the impact on local water quality remains uncertain.
Mining pegmatites not only yields lithium but also other trace metals like rubidium and cesium. While the environmental effects and potential human toxicity of these trace metals are not well documented, the EPA has associated elevated lithium levels with detrimental health risks, including kidney dysfunction, impaired neurodevelopment, and thyroid issues. Currently, no safe threshold for lithium in drinking water has been established, although the
United States Geological Survey
suggests a preliminary safe level of 10 micrograms per liter (μg/L).
Researchers at Duke University recently investigated how pegmatite mining affects lithium concentrations in nearby water sources and the duration of these effects post-mining. Their study involved measuring metal concentrations in water downstream of two lithium mines and a connected processing plant. The researchers hypothesized that mining activities could alter the interactions between the rock and surrounding water, thereby influencing lithium levels.
The team collected 99 water samples from surface streams and 93 samples from groundwater wells in a 40-kilometer (25-mile) stretch along the South Carolina-North Carolina border, particularly near the Kings Mountain and Holman Beam lithium mines. They compared 51 surface water samples collected upstream of the mines to 48 samples taken downstream that were influenced by mining activities.
Using an
inductively coupled plasma mass spectrometer
, the researchers measured lithium alongside trace elements such as rubidium, cesium, arsenic, and strontium. Their findings revealed that lithium concentrations in surface water skyrocketed from baseline levels of 0.2 μg/L to between 785 and 1,249 μg/L within 10 kilometers (6.2 miles) of mines. Groundwater wells showed lithium levels between 4,500 and 47,000 μg/L in mining areas, contrasted with unaffected downstream wells measuring between 0.5 and 890 μg/L.
The research suggested that the lithium found in groundwater downstream was primarily due to natural interactions between pegmatite rocks and water rather than direct mining activities. This was evidenced by rising lithium levels in groundwater following rainfall, which intensified water-rock interactions.
Moreover, the team analyzed ions such as calcium, sulfate, and chloride using an
ion chromatograph
. They observed spikes in calcium and sulfate concentrations in surface waters within 10 kilometers downstream of the processing facility, measuring 50 to 120 milligrams per liter (mg/L) of calcium and 100 to 300 mg/L of sulfate. In comparison, background surface waters contained only 5 to 20 mg/L of calcium and 3 to 10 mg/L of sulfate. These ions are by-products of pegmatite processing and arise from waste composed of calcium sulfate or
plaster
.
The researchers highlighted that active mining ceased at this site around three decades ago, and the lithium levels documented reflect a long-term release from dormant mining operations and waste. Historical data indicates that during its active years, the mine may have discharged 10 to 30 times more trace metals than currently recorded.
Ultimately, the researchers concluded that processing pegmatite has a more significant impact on downstream metal and ion concentrations than mining activities themselves. As lithium mining expands, further research is essential to explore lithium toxicity and the implications of co-occurring metals like rubidium and cesium. There is also a pressing need to develop strategies to mitigate trace metals and dissolved gypsum from infiltrating water systems.
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Source: sciworthy.com
