Scientists from the Institute of Minerals and Materials Technology (IMMT), Bhubaneswar, have estimated the quantity of rare earth elements that can be recovered from a toxic byproduct of aluminium extraction that India produces in copious amounts.
Rare earth elements (REEs) are crucial components of electronic and electric systems, from the devices used to produce ‘green hydrogen’ to electric vehicles.
IMMT Bhubaneswar is a facility of the Council of Scientific and Industrial Research.
The study, published in Current Science on March 25, reported that fine-grained content of red mud at the National Aluminium Company (NALCO) facility in Damanjodi, Odisha, contains 433 ppm of REEs like cerium, neodymium, and scandium. These metals have applications in catalytic converters, LEDs, electric motors, and high-intensity lamps.
Scientists have known that red mud contains REEs. But the quantity of elements present depends on the location of the bauxite ore and how it is processed.
In fact, “red mud recycling around the world is [undertaken] with scandium as the prime target, whose oxide cost $367/gram as of December 2022,” Pratima Meshram, principal scientist at the Metal Extraction and Recycling Division, CSIR-National Metallurgical Laboratory, Jamshedpur, told The Hindu by email.
Dr. Meshram said previous work by her and others was the first to report that scandium is associated not with iron in red mud, as was believed, but with calcium titanate.
IMMT researchers obtained samples of red mud from the site, whose bauxite originates from a deposit in the state’s south.
In the Bayer process, bauxite ore is mixed with a solution of sodium hydroxide and heated in a pressurised vessel. When the resulting sodium aluminate is filtered out, what’s left is the toxic residue called red mud.
According to Sasmita Prusty, a senior scientist at IMMT and the paper’s sole author, a representative sample of red mud weighing 1 kg was prepared. Grains in the sample were classified by size, and chemically analysed to elucidate their molecular contents. Parts of the sample were also analysed under a spectrometer and a scanning electron microscope.
She found that in parts of the sample ground to smaller than 45 µm, there were 433 ppm of REEs; 206 ppm in the 45-75 µm samples; and 180 ppm in the 75+ µm samples. In them, scandium was present to the tune of 41.5 ppm, 42.5 ppm, and 41.5 ppm respectively.
“The value of 433 ppm is lower than that in Central Indian red mud, which contains 700-800 ppm of REEs,” Dr. Meshram said. She added that Indian red mud overall has lower REE concentration than that in “Greece, Jamaica, Canada, and Australia”.
But India also produces large quantities of red mud. According to the Jawaharlal Nehru Aluminium Research Development and Design Centre, an autonomous institute under the Ministry of Mines, as of September 2019, Europe produced 6.8 million tonnes of red mud a year whereas India alone produced 9 million tonnes.
There are two strategies to recover REEs from red mud: extract only REEs or extract all metals (such as iron, titanium, and sodium) including REEs. “Only extracting REEs is never economical,” according to Dr. Meshram. “Now we are processing red mud by the second route, so as to extract all metals of value, like iron, alumina, titania, and REEs.”
“Extraction of REEs from red mud has two facets. Either you focus only on extracting REEs or process red mud holistically so as to extract all metals including REEs,” according to Dr. Meshram. “Only extracting REEs is never economical, which we have attempted as an Indian patent in 2015-2016. But now we are processing red mud by second route, so as to extract all valuable metals like iron, alumina, titania and REEs, which is also partnered by all prime aluminium industries”. This project is happening with the help of NITI Aayog, she said.
“The important thing to be considered is what do we do with the rest – more than 95% of the red mud – after concentrating or extracting the REEs. Some uses must be explored,” Dr. Prusty said.
Note: This article was updated at 2:04 pm on May 18, 2023, to clarify Dr. Meshram’s comments.
Published - April 03, 2023 01:46 pm IST
