A US group has carried out the primary thorough chemical evaluation of wastewater related to mining the lithium brine on the Salar de Uyuni, in Bolivia. Their findings might inform methods to handle future mining operations and keep away from the groundwater depletion and different issues which have affected websites just like the Salar de Atacama in Chile.
The Salar de Uyuni is the situation of the world’s largest identified lithium deposit, and is an enormous salt pan stretching for hundreds of sq. miles atop a excessive, dry Andean plateau in Bolivia. For a lot of the yr, salt crystals encrust the terrain, white as confectioner’s sugar. Through the moist season, pooling rainwater mirrors surrounding mountains and sky.
“The Salar is a magical place for travellers from all over the world who come to see the colors, the reflections, in this endless white landscape,” mentioned Avner Vengosh, Nicholas Chair of Environmental High quality on the Duke College Nicholas College of the Setting.
What most vacationers don’t see is the huge reserve of lithium dissolved in extremely saline, or salty, brine just under their sneakers. Contained inside sediments and salts that descend a number of toes to greater than 160 toes beneath the floor, this untapped trove might doubtlessly be a key useful resource for the renewable power sector.
For the previous few years, Vengosh, who can also be chair of the Division of Earth and Local weather Sciences on the Nicholas College, and PhD pupil Gordon Williams have been working to know the potential environmental well being implications of lithium mining, each within the US and overseas.
Printed in Environmental Science & Expertise Letters in January, the duo reported their findings from the chemical evaluation of wastewater related to mining the lithium brine on the Salar de Uyuni.
Lithium-brine mining at the moment entails a multi-step course of, whereby brine is pumped from beneath the floor right into a sequence of shallow, above-ground evaporation ponds. As liquid evaporates in successive ponds, undesirable salts precipitate out. Lithium, nonetheless, turns into extra concentrated within the brine at every stage. The concentrated lithium is finally moved from the evaporation ponds to a close-by facility for processing into lithium carbonate — the fabric that goes into rechargeable batteries.
Lithium extraction on the Salar de Uyuni is within the preliminary phases of being developed. Nevertheless, analysis has proven that long-term mining of lithium brines in different salt pans, such because the Salar de Atacama in Chile, may cause groundwater ranges to say no and land to subside, or sink. Such impacts might have an effect on the way forward for lithium mining on the Salar de Uyuni, in line with Vengosh.
Williams and Vengosh analyzed the chemistry of lithium brine and waste supplies related to a pilot mining operation on the Salar de Uyuni. Particularly, they have been thinking about figuring out acidity and the presence of hint parts, reminiscent of arsenic. Samples from the mine web site included pure brine pumped from underground; brine from eight evaporation ponds; and wastewater from the lithium processing facility.
In pure brine samples, the group measured arsenic ranges between 1 and 9 ppm, in addition to comparatively impartial acidity. Compared, evaporation-pond brine grew to become more and more acidic because it grew to become extra concentrated.
Arsenic ranges additionally dramatically elevated from pond to pond. For instance, the final pond revealed arsenic ranges at practically 50 elements per million — about 1,400 occasions greater than the benchmark thought of ecologically acceptable by the US Environmental Safety Company.
“This arsenic level is extremely high,” mentioned Vengosh. “My group has worked all over the world — in Africa, Europe, Vietnam, India — and I don’t think we ever measured that level of arsenic.”
Because the authors famous, leaking or intentional discharge of brine from the evaporation ponds to the encircling salt pan might negatively have an effect on wildlife.
“There’s a risk for bioaccumulation,” mentioned Williams, referring to the method by which chemical compounds construct up in organisms over time, with doubtlessly dangerous penalties. Flamingos, as an example, feed on native brine shrimp, that are delicate to arsenic at ranges above 8 elements per million.
The group additionally discovered that ranges of boron — which may doubtlessly trigger well being results relying on the character of publicity — elevated from evaporation pond to evaporation pond. In contrast, wastewater from the lithium processing plant confirmed comparatively low ranges of boron and arsenic much like, and in some circumstances decrease than, ranges discovered within the pure brines.
Moreover, Williams and Vengosh investigated the potential repercussions of taking spent brine — that’s, brine left over after lithium is eliminated — or wastewater from lithium processing and injecting it again into the lithium deposit. The lithium-mining trade has indicated these approaches can counteract land subsidence.
The group discovered that each injection strategies would have undesirable penalties. For instance, the spent brine would doubtless combine poorly with pure brine, hindering the circulate of brine beneath the floor and doubtlessly interfering with pumping. Alternatively, injecting wastewater again into the deposit might dilute the lithium useful resource.
One potential answer to stopping land subsidence could be to fastidiously mix spent brine with wastewater to realize a chemical stability with the pure brine. Nevertheless, future research ought to additional examine the environmental implications of that technique, they added.
Williams and Vengosh are turning their consideration to the origin of lithium on the Salar de Uyuni.
“We’re building a geochemical model to understand why lithium is enriched in those brines,” Williams defined. “What’s the source? And what’s the mechanism causing this concentration?”
The group can also be trying to know how lithium-brine mining on the Salar de Uyuni might have an effect on the well being and well-being of neighboring Indigenous communities.
“We see lithium as the future for energy security, so we’re trying to analyze it from different angles to ensure sustainable development and supplies,” Vengosh mentioned.
