A recent report has revealed that in the Salar de Uyuni, also known as salar de Tunupa and located in the southwestern part of Bolivia, there are 21 million tons of lithium, making it the world’s largest reserve of this mineral.
The challenge now is to determine what the environmental impact of exploiting this resource will be, so a group of scientists has started researching to prevent potential damages.
Lithium Extraction in Bolivia
The world’s largest lithium deposit is located in the Salar de Uyuni, a vast salt flat that extends for thousands of square kilometers on top of an Andean plateau in Bolivia.
For most of the year, salt crystals cover the terrain, white as powdered sugar. During the rainy season, the accumulated water reflects the surrounding mountains and sky.
“The Salar is a magical place for travelers from all over the world who come to see the colors and reflections in this infinite white landscape,” said Avner Vengosh, Nicholas Professor of Environmental Quality at the Nicholas School of the Environment at Duke University.
What most tourists do not perceive is the enormous reserve of lithium dissolved in the highly saline brine just below the surface. This untapped treasure could become a key resource for the renewable energy sector. Over the past years, Vengosh and Ph.D. student Gordon Williams have been working to understand the potential environmental implications of lithium mining, both in the U.S. and abroad.
Implications for Environmental Health
In a report published in Environmental Science & Technology Letters in January, Vengosh and Williams conducted the first comprehensive chemical analysis of the wastewater associated with lithium brine extraction in the Salar de Uyuni. Their findings could help manage future mining operations more sustainably and protect the fragile environment of the salt flat.
Lithium brine extraction currently involves a multi-step process: brine is pumped from underground to a series of evaporation ponds. As the liquid evaporates, unwanted salts precipitate, but lithium becomes more concentrated in the brine at each stage. Finally, the concentrated brine is moved to a nearby facility to be processed into lithium carbonate, the material used in rechargeable batteries.
Lithium extraction in the Salar de Uyuni is still in its early stages. However, research has shown that prolonged extraction of brines in other salt flats, such as the Salar de Atacama in Chile, can lead to decreased groundwater levels and land subsidence. These impacts could affect the future of lithium mining in Uyuni, according to Vengosh.
In their study, Williams and Vengosh analyzed the chemistry of the brine and waste from a pilot mining operation in the Salar de Uyuni. They were interested in the acidity and the presence of elements like arsenic, a toxic metal that can cause health problems in exposed humans and wildlife. The samples included natural subsurface brine, brine from evaporation ponds, and wastewater from the processing plant.
Lithium in the Salt Flat Brine
In the natural brine samples, they measured arsenic levels between 1 and 9 parts per million and relatively neutral acidity. In comparison, the brine from the ponds became more acidic as it concentrated.
Arsenic levels increased dramatically from one pond to another, reaching nearly 50 parts per million in the last pond, approximately 1,400 times higher than the ecologically acceptable standard set by the EPA.
According to the authors, the leakage or intentional discharge of brine from the ponds into the surrounding salt flat could negatively impact wildlife. “There is a risk of bioaccumulation,” explained Williams, referring to the process by which chemicals accumulate in organisms over time, with potentially harmful consequences. For example, flamingos feed on local brine shrimp, which are sensitive to arsenic at levels higher than 8 parts per million.
The team also found that boron levels increased from one pond to another. Conversely, plant wastewater showed relatively low levels of boron and arsenic, similar to natural brines and, in some cases, lower.
Additionally, Williams and Vengosh investigated the repercussions of injecting used brine or wastewater back into the lithium deposit. The mining industry has suggested that this could counteract land subsidence. However, they found that both methods would have undesirable consequences, such as poor mixing with natural brine or diluting the lithium resource.
A possible solution would be to carefully mix the used brine with wastewater to balance the chemistry with natural brine. However, future studies should further investigate the environmental implications of this strategy.
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