A new process makes lithium extraction from hard rock cheaper, easier and more environmentally friendly. Instead of heat and strong acids or alkalis, this method only requires an aqueous solution of an ammonium fluoride salt and room temperature. Lithium, aluminum and silicate can be almost completely extracted from the lithium-containing mineral spodumene – and even the solvent is recycled, as researchers report in “Science”. This could also make lithium production profitable in Europe.
The raw material lithium is indispensable for many of our technologies, because the alkali metal is the main component of lithium-ion batteries. But the coveted resource is becoming increasingly scarce because global demand is increasing rapidly due to the expansion of electromobility. To date, a large part of the lithium compounds used industrially comes from the salt lakes of South America, where this raw material can be extracted at relatively low cost. However, this extraction has significant ecological and social consequences.
Another source of lithium are lithium-containing ores such as the mineral spodumene. Their big advantage: “Such rocks can be found almost everywhere,” explains co-author Camden Hunt from the Massachusetts Institute of Technology (MIT). There are deposits of these ores in Australia, North America and Africa, but also here in Europe. In Germany, rocks containing lithium can be found, for example, in the Ore Mountains.
Lithium extraction without heat and wastewater
But extracting lithium from the ores is complex and two to three times more expensive than extracting lithium from salt lakes. To do this, the rock must be heated to around 1000 degrees, treated with strong acids and then neutralized. This requires a lot of energy, generates high CO2 emissions and leaves behind large amounts of acidic or highly alkaline wastewater, as the researchers explain. Because of this effort, a large part of the lithium-containing ores has so far been processed in China – but given political conflicts and possible bottlenecks, this is becoming a problem.
However, there is a solution, as Hunt, first author Benjamin Mowbray from MIT and their colleagues report. They have developed a process with which the lithium compounds required for batteries etc. can be extracted from spodumene without great heat and harmful wastewater. In addition to lithium, the process also separates the raw materials aluminum and silicate from the ore and minimizes overburden. “However, the key feature of our process is the recovery of the reaction solution and the used water,” emphasizes the team.
Common process turned upside down
The new process works in exactly the opposite way to conventional processes: These specifically remove the desired metals from the silicate structure of the spodumene because the chemical bond between silicon and oxygen in the silicate is difficult to break. Mowbray and his team turn this on its head: “Our process dissolves the aluminosilicate matrix of spodumene, releasing lithium, aluminum and silicon in the form of fluorinated salts,” they explain.
This is made possible by the salt ammonium hydrogen difluoride (NH4HF2). In an aqueous solution, it can break the stable bonds in the silicate at room temperature and react with the metals contained in the ore, as the researchers explain. The result is the metal-containing fluorine salts lithium fluoride (LiF), ammonium cryolite (NH4)3AlF6 and ammonium hexafluorosilicate (NH4)2SiF6). These can be separated using simple means or isolated directly through filtration.
Efficient raw material extraction in the circulatory system
In initial tests, the team was able to extract more than 99 percent of the lithium contained in spodumene using this process, and after 48 hours their extraction even reached 100 percent – without strong heating or other complex process steps. “The lithium fluoride can then be filtered off, purified by recrystallization, and defluorinated using sulfurous acid and converted into lithium hydroxide or lithium carbonate,” write Mowbray and his team. These lithium compounds are the raw materials for lithium-ion batteries.
But the team also obtained other valuable raw materials from the spodumene: The ammonium cryolite can be converted into aluminum oxide in several steps, from which aluminum can be obtained. In another secondary process, silicon dioxide is created from the ammonium hexafluorosilicate. “For this we only need ammonium fluoride, nitric acid and water as additives,” report the researchers. As they emphasize, in their process – unlike strong heating – no toxic hydrogen fluoride is released from the ammonium hydrogen difluoride.
Another advantage: The water and ammonium hydrogen difluoride used for the process can be almost completely recovered – an almost closed cycle is created. “We achieve this by using the ammonium fluoride solution (NH.) remaining after lithium extraction4F) heat and reintroduce the ammonia gas released during the process. This causes ammonium hydrogen difluoride to form again,” the researchers write. “We demonstrated this recycling cycle over five cycles.”
“The most energy-saving and cheapest way to extract lithium”
The crucial question, however, is how much the whole thing costs. Is it competitive with current methods? Mowbray and his team investigated this in a technical-economic model analysis. Their result: “For the total production costs we come to 5160 US dollars per ton of lithium carbonate equivalent – that is half as much as for the common extraction process from spodumene,” report the researchers. The extraction of lithium from rock would then hardly cost more than from the salt lakes.
Then factoring in the value of the co-products would bring the cost down to around $3,900 per ton of lithium carbonate equivalent. This is 56 percent less than current ore processing and 20 percent less than lithium extraction from concentrated brines, the team writes. “In our opinion, this is the most energy-efficient and cheapest way to extract lithium – not just from ore, but anywhere,” says senior author Yet-Ming Chiang from MIT.
Opportunity for decentralization
According to the researchers, their process opens up a real opportunity to make lithium production cheaper and more decentralized. Chemists Gang San Lee and Karthish Manthiram from the California Institute of Technology, who were not involved in the study, also see it this way: “Because kilns for high temperatures are becoming superfluous, large-scale systems are no longer necessary and the costs for the infrastructure are falling,” they write in an accompanying commentary in “Science”.
This would allow the spodumene to be processed decentrally directly at the mines, instead of transporting the raw ore halfway around the world by ship. China’s monopoly position in the processing of spodumene could also be broken in this way because local extraction would be worthwhile even from smaller deposits.
Source: Benjamin Mowbray (Massachusetts Institute of Technology, Cambridge, USA) et al., Science, 2026; doi: 10.1126/science.aec4652