Rare-earth elements (REE) make up 17 of the elements in the periodic table and, though the name suggests otherwise, they are actually plentiful in the earth’s crust. What makes them “rare” is the fact that they are not often concentrated in the ore deposits where they can be found. This makes them a challenge to extract, which results in them becoming expensive and unreliable.
This situation is inconvenient since the viability of a renewable energy future relies on the ready supply of REEs. For example, two of these rare-earth elements, neodymium (Nd) and dysprosium (Dy), are crucial for the development of solar and wind technologies and electric vehicles. They are also used to make hard drives, television screens, and modern electronics like the one you may be holding in your hand right now.
However, according to Renewables Consulting Group (RCG), “the use of REEs has faced criticism due to price volatility and political issues surrounding the supply chain.” Not to mention the millions of tons of acidic pollution generated by conventional extraction methods, and the renewable energy industry doesn’t look so green anymore. That is why Paul J. Antonick and Zhichao Hu, members of the thermodynamics team at the Rutgers University School of Engineering, came up with a natural solution.
They discovered a new way to get these elements out of phosphate rock waste – also known as phosphogypsum. They found out that mineral and organic acids – made by naturally occurring bacteria called Gluconobacter oxydanscould – can do the job instead of using harsh chemicals. If they can figure out a way to scale this new method up, it would mean less of a reliance on REE mining, as well as less, toxic chemicals usually deployed to extract the elements from metal ores. It would be a huge boost for clean energy development.
How They Did It
- The researchers tried a number of bio-acid mixtures of mineral and organic acids to extract six REEs – yttrium, cerium, neodymium, samarium, europium and ytterbium.
- They used these natural acids along with a bio-acid mixture, or biolixiviant, to extract six rare-earth elements from synthetic phosphogypsum. They said that “the biolixiviant was more efficient at rare earth element extraction than gluconic acid and phosphoric acid but less efficient than sulfuric acid.”
- So, for the experiments, they primarily using gluconic acid, found naturally in fruits and honey, to tease out the rare earth elements trapped in the waste.
- At first, the phosphate rock waste they were working with was watery; and then, as it dried, it formed a crust.
- The research has been published in the Journal of Chemical Thermodynamics.
What’s Next
This study only looked at synthetic phosphogypsum produced in the lab. Next, they will test if this method also works on waste actually produced by the industry. Phosphogypsum is actually a waste by-product of phosphoric acid production for fertilizers. According to Futurity, “each year, the U.S. mines an estimated 250 million tons of phosphate rock to produce phosphoric acid for fertilizers.”
In other words, there’s a lot of it – about 100,000 tons of these REEs end up in phosphate rock waste every year. Theoretically speaking, the amount of waste produced means the annual production of rare earth oxides could be almost doubled if they can get this to work, even though the elements only make up about 0.1 percent of phosphate rock.
A steady supply of REEs is going to be crucial to supply the populations increasing demand for new smartphones and such, electric vehicles, and renewable energy technologies for electricity, among other things. It will also be good for large wind turbine manufacturers that rely on magnet generators made from neodymium and dysprosium, among other rare-earth elements like praseodymium (Pr) and terbium (Tb). Hopefully, this new research will make the supply easier to get for everyone, and more sustainably, too.
