QuEra, a U.S. quantum computer startup, recently received $230 million (about 330 billion won) in investment from Google and SoftBank Vision Fund. This is the largest amount raised in a single investment for a quantum computer corporation. QuEra is developing a neutral atom-based quantum computer, using rubidium as the atom.
Rubidium is a byproduct generated during the production of lithium, which has mostly been discarded due to a lack of practical applications. However, recent uses of rubidium in advanced technologies such as quantum computers, atomic clocks, and Global Positioning Systems (GPS) are changing the situation. Technologies to efficiently obtain rubidium have been developed successively.
Researchers at Tianjin University announced in November of last year that they had developed a method to extract rubidium from solid potassium chloride crystals, as reported in a Nature sister journal. Like lithium, rubidium can be mined from rocks or extracted from salt lakes. The conventional method is costly due to the significant amount of water and chemicals required, and it is also environmentally unfriendly. Corporations that mine lithium have discarded rubidium without extracting it, given this burden.
The researchers at Tianjin University developed a technique to extract rubidium from solid potassium chloride crystals left after evaporating saltwater, instead of extracting it directly from saltwater. They explained that this method significantly reduces the energy, water, and chemicals used in the extraction process compared to when it is in a brine state. They successfully lowered energy consumption by 98% and increased recovery efficiency by 22% compared to conventional methods.
A new method for extracting rubidium from rocks has also emerged. Everest Metals, a mining corporation in Australia, announced that it found a location with abundant rubidium deposits approximately 400 kilometers northeast of Perth, Australia, at the end of last year. Everest Metals is assessing the commercial viability of rubidium extraction from pegmatite rock samples collected in this area, in collaboration with researchers from Edith Cowan University.
Researchers in Australia recovered rubidium with a 91% efficiency from rock samples using a new technology distinct from conventional methods. The technique involves crushing the rock samples, dissolving them in an acidic solution, and then purifying rubidium and lithium from that state.
Lithium and rubidium are bonded with oxygen within pegmatite. The acidic solution dissolves pegmatite, similar to how hot water dissolves sugar. When this dissolved solution passes through an ion exchange device, rubidium adheres to the resin inside. By pouring dilute acid, rubidium can be removed from the resin. Adam Simon, a professor at the University of Michigan, remarked that this is "the method used for decades to separate uranium."
According to the U.S. Geological Survey, the price of a solution containing 1 gram of rubidium was $121 as of September 2023. This represents an increase of about 20% from a year ago due to the growing usage of rubidium in advanced industries. Rubidium is utilized not only in QuEra's quantum computers but also in atomic clocks that leverage regular oscillations.
Despite the increasing demand for rubidium and rising prices, there are currently no places commercially mining rubidium. There are only estimates that rubidium mining occurs in China. Experts predict that existing lithium corporations will shift their focus toward rubidium.
Brent Elliott, a professor at the University of Texas, noted in Spectrum, published by the Institute of Electrical and Electronics Engineers (IEEE), that considering the potential profits from rubidium mining, it seems reasonable for lithium mining corporations to include rubidium in their ongoing mining developments and that as lithium extraction technology advances, there will be more mining efforts focused on the recoverable rubidium.
References
Nature Sustainability (2024), DOI: https://doi.org/10.1038/s41893-024-01449-w