China develops system to recover critical minerals from lithium ores

Chinese scientists have built the world's first industrial extraction column system for recovering and separating rubidium and cesium from low-grade resources associated with lithium ores, with the technology achieving stable production of high-purity products and commercial products already entering the market.

The breakthrough is expected to strengthen China's ability to make use of these two critical minerals, which are in short supply but have important applications in aerospace, precision instruments, 6G communications and quantum technologies.

Rubidium and cesium are highly dispersed metals that rarely occur in deposits large enough to be mined economically on their own. Only a handful of economically viable pollucite mines, a major source of cesium, are known to exist globally, including in Canada and Zimbabwe. Rubidium is found mainly in minerals such as lepidolite and in salt lake brines.

For years, rubidium and cesium have largely been discarded during the processing of more abundant minerals because their concentrations are relatively low and they are difficult to separate.

"The new process recovers rubidium and cesium, which were previously discarded, as byproducts of lithium ore processing," said Wang Yong, a researcher at the Institute of Process Engineering of the Chinese Academy of Sciences who led the project.

In a typical lithium concentrate, 1 metric ton contains about 25 kilograms of lithium oxide, 7.8 kilograms of rubidium oxide and 1.8 kilograms of cesium oxide, Wang said.

Although the amounts of rubidium and cesium are relatively small, the new technology makes it possible to recover them efficiently during lithium extraction. The demonstration line produces cesium carbonate, rubidium carbonate and other compounds, including chlorides, oxides and sulfates. These compounds can then be further processed into metallic rubidium and cesium for use in various industries, Wang said.

The key breakthrough was replacing conventional extraction tanks, in which organic solvents are exposed to the air, with compact extraction columns.

"The columns operate as a fully enclosed system, markedly reducing solvent vapor emissions and odors as well as associated fire risks," Wang said.

A single extraction column can achieve the separation efficiency of up to 15 conventional stages, while reducing solvent consumption by 40 percent and cutting the equipment footprint by more than half, he said.

The conventional process would have required more than 70 tanks to handle the same amount of material. The new plant uses only 17 extraction columns across four sections — extraction, scrubbing, stripping and de-oiling — allowing the entire process to operate continuously and automatically.

Wang said the main technical challenge was that rubidium and cesium have very similar chemical properties and are present in relatively small amounts in the material being processed.

"Achieving both high recovery and high product purity therefore requires exceptionally precise control of how the liquids come into contact, how substances move between them and how rubidium and cesium are separated," he said.

The demonstration line was jointly developed by the Institute of Process Engineering and Ganfeng Lithium Group Co, the world's largest lithium salt producer, headquartered in Xinyu, Jiangxi province. The project builds on nearly two decades of research into extraction column technology.

The demonstration line has an annual production capacity of 500 tons and produces cesium carbonate and rubidium carbonate with purities exceeding 99.9 percent, according to the project team.

The overall recovery rate for cesium exceeds 98 percent, while that for rubidium exceeds 95 percent, the team said.

"The entire system was designed and manufactured in China," Wang said.

The technology has already been applied in the industrial separation of zirconium and the purification of phosphoric acid, and is being further developed for processes used to extract nickel, cobalt and lithium from ores and other raw materials.