Rubidium Can Be More Than a Lithium Cast-Off

Lithium has been the apple of the mining industry’s eye as demand for electric vehicle batteries has skyrocketed. Now, the investment in lithium extraction is spilling over to include rubidium, another element on the leftmost column of the periodic table. Rubidium is found in the earth’s crust alongside lithium and is used in technologies such as atomic clocks, motion sensors, signal generators, and GPS equipment—technologies that all rely on the hyperfine transition of electrons in rubidium atoms to keep time.

Rubidium, like lithium, is mined from rock or pumped to the surface in briny groundwater. Previously, rubidium was often seen as an impurity that needed to be removed from a lithium deposit. Now, new research on extracting rubidium is opening the possibility of a greater supply of the once-overlooked metal, which could then be put to wider use in high-tech industries.

Researchers from Tianjin University in China have developed a technique to extract rubidium from solid potassium chloride salt, which forms after brine has dried. They detail their results in a study published in November in Nature Sustainability. By extracting rubidium from solid salts and limiting the amount of water in the process, the researchers report using 98 percent less energy than the techniques that extract rubidium directly from watery brine.

But, similar to lithium, rubidium exists in much higher concentrations in chunks of a rock called pegmatite than in brine water, says Brent Elliott, an economic geologist at the University of Texas at Austin who was not involved in the research.

A mining company in western Australia claims to have hit the rubidium jackpot while searching for lithium about 400 kilometers northeast of Perth, Western Australia (and around 700 kilometers north of the world’s largest hard-rock lithium mine). Researchers at Edith Cowan University (ECU) have teamed up with the company Everest Metals Corporation to pull rubidium from the rocky samples collected at the Mt. Edon pegmatite field. And, by using a new direct rubidium extraction technique, the team reported in December recovering 91 percent of the rubidium from rock samples.

Mined pegmatite is later processed to extract rubidium and lithium from the mineral. Everest Metals

The technique recycles water through the process, says Amir Razmjou, the lead investigator on the project and an associate professor at ECU. Water recycling is what makes the extraction method more sustainable than other extraction techniques. It’s an adaptation of membrane technology used for water desalination, which Razmjou, whose background is in chemical engineering, specialized in before refocusing on minerals.

An Easier Way to Extract Rubidium

Scant information is available about the specific chemicals used in the extraction technique—Everest Metals and ECU are in the process of filing a patent—but, in general, the method follows three main steps: crushing the rock samples, dissolving the mineral in acid, and purifying rubidium and lithium from the acidic slurry.

Adam Simon, a professor of earth and environmental sciences from the University of Michigan and uninvolved in the work, pieced together what he believes is the most likely methodology.

Lithium and rubidium are both naturally bonded to oxygen within pegmatite. Acids can dissolve the pegmatite, similar to how hot water dissolves sugar in a cup of coffee, Simon says. The acid solution is passed through an ion exchanger, which is a column lined with a resin to which the element of interest (rubidium, in this case) will stick. Then, dilute acid is poured through the column in order to pull the rubidium off the resin, flushing a solution of only rubidium out the other side of the column.

This process is not necessarily new. “We’ve done this for decades” to separate out uranium, Simon says.

The unique, patentable aspect of the project, Simon says, might be the use of a weakly acidic solution that pulls out only rubidium, or rubidium plus lithium. Sulfuric acid is the most commonly used acid in extraction, which is safe but requires a lot of storage and cleanup at industrial scales.

But a less acidic solution could minimize the cost to neutralize water and recycle it, Simon says. Reducing the amount of acid needed would be great for the mining industry. Simon is not aware of anyone else doing this for rubidium.

“I’m intrigued by the process if they can demonstrate that it works for rubidium and lithium,” Simon says. “It has the potential to work for other metals in other minerals.”

What’s the Market for Rubidium, Anyway?

As of now, there are no active mining sites of rubidium, according to the latest data from the U.S. Geological Survey, published in 2024. But China is a blind spot on the world’s mining map because it is so difficult to obtain information, says Candice Tuck, a mineral commodity specialist for the USGS’s National Minerals Information Center, who wrote the latest rubidium report. While there are indications that rubidium is being produced in China, there is no definitive evidence, she says.

Everest Metals, however, seems to think that demand will rise: The company expects the rubidium market to grow from 6.36 tonnes in 2023 to 7.94 tonnes in 2028.

This is the chicken-or-the-egg problem of the mining industry, says Gavin Mudd, director of the Critical Minerals Intelligence Centre at the British Geological Survey. Demand for rubidium, as of now, is low, and low demand spurs little action from mining companies. A mine near Cornwall in the United Kingdom, run by the company Cornish Lithium, for example, throws out the rubidium and caesium that it extracts along with lithium. But sometimes a new, consistent supply of one element creates demand, Mudd says.

In September 2023, the price for one vial containing a solution of 1 gram of rubidium was going for US $121, and a vial of 100 grams in solution went for $2,160, a nearly 20 percent jump up from 2022, according to the 2024 USGS report.

“That is a lot of money for a little vial of rubidium oxide,” says Elliott, of the University of Texas. Given the potential profit, it makes sense for lithium mining companies to include another output to an existing mining operation.

“I think we are going to see a lot more happening only because the lithium extraction technologies are getting better and it just makes sense to have another stream to get another commodity out that you can sell,” Elliott says.