Lithium extracted from brine, why conventional methods fall short
Is lithium the new oil? In many ways, yes. Global demand continues to surge as this metal remains a strategic raw material for the energy transition, serving as a core component of electric vehicle batteries and stationary energy storage systems.
Today, lithium is obtained through two main extraction methods.
- The first relies on hard-rock mining, a process that is costly, energy-intensive, and associated with significant environmental impacts. During extraction, drinking water sources can be contaminated with heavy metals and hazardous chemicals.
- The second method involves salt flats, where brine is pumped from surface or underground saline lakes and left to evaporate. This approach is extremely slow, with evaporation cycles that can take up to three years. It is also expensive and environmentally damaging, since chemical treatments are required to refine lithium from salt.
Now, a discovery from the University of Michigan in the United States points to a promising alternative for lithium extracted from brine, with potentially far-reaching implications.
Lithium extracted from brine: current limitations
In the conventional process, brine is pumped into large evaporation ponds where sunlight gradually concentrates the salts. Once sodium chloride crystallizes, chemical additives are introduced to separate the remaining lithium. This method requires vast amounts of water, long processing times, and intensive use of chemical reagents, all of which place a heavy burden on surrounding ecosystems.
The main challenge lies in magnesium, an element that is chemically similar to lithium. When the magnesium-to-lithium ratio is high, magnesium forms unwanted solids together with lithium, forcing additional separation steps. This increases costs, waste, and environmental impact, which is why many brine resources are classified as low quality and left untapped.
An unexpected discovery: lithium crosses the membrane first
A chemical engineering team at the University of Michigan identified a surprising separation mechanism, detailed in a study published in Nature Chemical Engineering. According to the researchers, lithium can be selectively separated from magnesium without the use of electricity or added pressure.
At the core of the technology is a negatively charged membrane that separates a brine solution from a compartment containing pure water. Counterintuitively, lithium, which carries a weaker positive charge than magnesium, diffuses through the membrane into the pure water, while magnesium remains trapped in the brine.
This simple approach works even at high salinity levels, unlike many other methods designed to separate lithium while dissolved. It also uses far less water than evaporation ponds, which have long raised concerns for communities living near lithium brine operations.
What is charge balance?
The behavior observed by the researchers is explained by the principle of charge balance. For every positive ion that crosses the membrane, a negative ion, such as chloride, must also move to maintain electrical neutrality. Lithium tends to follow chloride ions to balance their charge in the pure water.
Magnesium, by contrast, carries a double positive charge and is strongly attracted to the negative charges of the membrane itself. This interaction is so intense that magnesium ions attempting to pass through are immediately pulled back. The result is a selective separation that remains effective even under highly saline conditions.
How it differs from conventional methods
Ion separation is typically achieved through electrodialysis, a process that uses an electric current to push ions across selective membranes. In that case, electrical energy gives magnesium enough force to overcome the membrane barrier, contaminating the lithium solution.
By removing the electric current and replacing the electrolyte with pure water, the researchers reversed the expected behavior. Lithium passes through first, while magnesium stays behind. The finding emerged almost by chance but was repeated and validated across multiple experimental conditions.
Lithium extracted from brine in a more sustainable way
The new technique does not separate lithium from ions with the same charge, such as sodium. However, it can be combined with other processes, including controlled evaporation, lithium-selective sorbents, or reagents that selectively precipitate the metal. The next phase of research will focus on techno-economic assessments to identify the most efficient process combinations at industrial scale.
From a circular economy perspective, this technology could mark a paradigm shift. It dramatically reduces water consumption, eliminates or limits chemical reagents, and enables the use of low-quality brines previously considered uneconomic.
Expanding the pool of viable resources would ease pressure on high-impact mines and salt flats, strengthening the resilience of the battery supply chain at a time when, according to S&P Global, demand could outstrip supply as early as 2029.