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 may 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 many of the 12 months, 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 around the world who come to see the colours, the reflections, on this limitless white panorama,” stated Avner Vengosh, Nicholas Chair of Environmental High quality on the Duke College Nicholas Faculty of the Surroundings.
What most vacationers don’t see is the huge reserve of lithium dissolved in extremely saline, or salty, brine slightly below their footwear. Contained inside sediments and salts that descend a number of toes to greater than 160 toes beneath the floor, this untapped trove may probably be a key useful resource for the renewable power sector.
For the previous few years, Vengosh, who can be chair of the Division of Earth and Local weather Sciences on the Nicholas Faculty, and PhD scholar Gordon Williams have been working to grasp 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 present 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. Nonetheless, 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 may have an effect on the way forward for lithium mining on the Salar de Uyuni, in response to Vengosh.
Williams and Vengosh analyzed the chemistry of lithium brine and waste supplies related to a pilot mining operation on the Salar de Uyuni. Specifically, they have been serious about figuring out acidity and the presence of hint components, equivalent to 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 workforce 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 almost 50 components per million — about 1,400 instances increased than the benchmark thought of ecologically acceptable by the US Environmental Safety Company.
“This arsenic stage is extraordinarily excessive,” stated Vengosh. “My group has labored all around the world — in Africa, Europe, Vietnam, India — and I don’t suppose we ever measured that stage of arsenic.”
Because the authors famous, leaking or intentional discharge of brine from the evaporation ponds to the encircling salt pan may negatively have an effect on wildlife.
“There’s a threat for bioaccumulation,” stated Williams, referring to the method by which chemical compounds construct up in organisms over time, with probably dangerous penalties. Flamingos, as an example, feed on native brine shrimp, that are delicate to arsenic at ranges above 8 components per million.
The workforce additionally discovered that ranges of boron — which may probably 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 just like, and in some instances 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 business has indicated these approaches can counteract land subsidence.
The workforce discovered that each injection strategies would have undesirable penalties. For instance, the spent brine would possible combine poorly with pure brine, hindering the circulation of brine beneath the floor and probably interfering with pumping. Alternatively, injecting wastewater again into the deposit may dilute the lithium useful resource.
One potential answer to stopping land subsidence can be to rigorously mix spent brine with wastewater to realize a chemical stability with the pure brine. Nonetheless, 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 constructing a geochemical mannequin to grasp why lithium is enriched in these brines,” Williams defined. “What’s the supply? And what’s the mechanism inflicting this focus?”
The group can be making an attempt to grasp how lithium-brine mining on the Salar de Uyuni may have an effect on the well being and well-being of neighboring Indigenous communities.
“We see lithium as the long run for power safety, so we’re making an attempt to research it from totally different angles to make sure sustainable improvement and provides,” Vengosh stated.
