Rare earth oxides of gadolinium, praseodymium, cerium, samarium, lanthanum and neodymium. Credit: USDA ARS.

Researchers at Rutgers University–New Brunswick in the US have determined that phosphate rock waste could be a potential new source of rare earth elements.

The researchers also found an environmentally responsible way to explore them and said that the approach could benefit clean energy technology.

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A potential shortage of production of rare earth elements such as neodymium and dysprosium in the US is expected to put the country’s energy security at risk, they added.

Rare earth elements are essential for solar and wind energy and advanced vehicles technologies, along with modern electronics such as smartphones.

Researchers noted that recovering them from phosphogypsum is a potential solution.

Rare earth elements generally amount to less than 0.1% in phosphate rock, however, around 100,000t of these elements can be found in phosphogypsum waste every year across the globe.

Co-lead authors of the study Paul Antonick and Zhichao Hu said instead of using conventional methods to extract the elements, another method might use organic acids produced by bacteria.

The research team was able to extract six rare earth elements yttrium, cerium, neodymium, samarium, europium and ytterbium from synthetic phosphogypsum by exploring use of mineral and organic acids, including a bio-acid mixture.

The bio-acid mixture comprising gluconic acid was produced by scientists led by David Reed at Idaho National Laboratory by growing the bacteria Gluconobacter oxydans on glucose.

“Rare earth elements generally amount to less than 0.1% in phosphate rock, however, around 100,000t of these elements can be found in phosphogypsum waste.”

Based on the results, it was found that the bio-acid did a better job extracting rare earth elements compared to pure gluconic acid at the same pH (2.1), or degree of acidity.

Further, the researchers plan to test bio-acid on industrial phosphogypsum and other wastes generated during phosphoric acid production that also contain rare earth elements.

Initially, they evaluated phosphogypsum made in the lab for their study.

Researchers at OLI Systems in Cedar Knolls, New Jersey; University of California, Davis; and Lawrence Livermore National Laboratory also contributed to the study.