Electric vehicles and sustainable energy systems rely heavily on metal-based batteries, primarily made of lithium. The surge in lithium usage has led to the rapid growth of the lithium mining industry. This vital metal is predominantly found in volcanic rocks known as pegmatite. While researchers are assessing the carbon and water consumption in pegmatite mining, the implications for local water quality remain unclear.
Mining pegmatites not only extracts lithium but also other metals commonly present, like rubidium and cesium. Despite limited studies on these trace elements and their environmental impact or potential toxicity, the EPA has associated elevated lithium levels with negative health outcomes, particularly concerning kidney function, neurodevelopment, and thyroid activity. Currently, there is no established safe level of lithium in drinking water, although a preliminary safe limit is suggested to be 10 micrograms per liter (μg/L) according to the United States Geological Survey.
Researchers from Duke University recently investigated how pegmatite mining influences lithium concentrations in local water bodies and the duration of these effects post-mining. This was achieved by measuring metal concentrations in water downstream from two lithium mines and an adjacent processing facility. The hypothesis was that mining activities may enhance interaction between the rock and surrounding surface and groundwater, thereby affecting lithium concentrations.
A total of 99 water samples were collected from surface streams, alongside 93 samples from groundwater wells across the Kings Mountain and Holman Beam lithium mines, covering an area of about 40 kilometers (25 miles) along the South Carolina-North Carolina border. To assess natural metal levels, 51 surface water samples were taken upstream of the mines, compared to 48 downstream samples influenced by mining activities.
Employing an Inductively Coupled Plasma Mass Spectrometer, the researchers analyzed lithium and trace elements such as rubidium, cesium, arsenic, and strontium in the water. Results revealed that lithium levels in surface water surged from background levels of 0.2 μg/L to concentrations ranging from 785 to 1,249 μg/L within a 10-kilometer (6.2 miles) radius of mines. Groundwater samples from mine wells exhibited significantly higher lithium concentrations, reaching 4,500 to 47,000 μg/L, while downstream wells showed much lower levels, between 0.5 to 890 μg/L.
The study indicated that the lithium detected in groundwater downstream likely originated from the natural interaction between pegmatite rocks and water, rather than directly from mining operations. This idea was reinforced when researchers observed increased lithium levels in groundwater following rainfall, indicating enhanced water-rock interactions.
Additionally, researchers measured ions like calcium, sulfate, and chloride in the water using an ion chromatograph. Findings showed elevated calcium and sulfate concentrations in surface waters within 10 kilometers downstream of the treatment facility, with levels of 50 to 120 milligrams per liter (mg/L) of calcium and 100 to 300 mg/L of sulfate, compared to background levels of 5 to 20 mg/L of calcium and 3 to 10 mg/L of sulfate. This increase is attributed to pegmatite processing waste composed of calcium sulfate, also known as plaster.
The researchers noted that mining activities at the site ceased roughly 30 years ago, and the measured lithium concentrations reflect a long-term release from dormant mines and associated waste. Historical data estimates indicate that the mine was likely releasing 10 to 30 times more trace metals when active compared to present measurements.
In conclusion, the researchers found that processing pegmatite has a more significant impact on downstream metal and ion concentrations than the mining process itself. As lithium mining operations continue to expand, future studies should focus on lithium toxicity as well as the potential environmental effects of co-occurring metals such as rubidium and cesium. The need to develop strategies to eliminate trace metals and dissolved gypsum from water systems or prevent their contamination is imperative.
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Source: sciworthy.com