US scientists discover huge amount of rare earth elements in coal ash waste: a treasure trove of clean energy?

Recently CNN.co.jp reported the following:

石炭灰の廃棄物に大量のレアアース、米科学者が発見　クリーンエネルギーの宝庫？

2024.12.07 Sat posted at 13:00 JST

（ＣＮＮ） 石炭を燃焼させた後に残る大量の石炭灰は池や埋め立て地に廃棄されており、水路に流出したり、土壌を汚染させたりする恐れがある。その一方で、こうした有害廃棄物は、クリーンエネルギーの推進に必要な希土類元素（レアアース）の宝庫となる可能性も秘めている。

テキサス大学が主導した最近の研究によると、科学者らは米国各地の発電所から発生した石炭灰を分析し、最大１１００万トンのレアアースを含有していることを発見した。これは米国国内の埋蔵量の８倍近い量で、金額にして約８４億ドル（約１兆２６００億円）に上る。

今回の発見は、新たな採掘の必要なしに米国内でレアアースを調達する大きなポテンシャルを秘めている――。論文を執筆したテキサス大学ジャクソン地球科学大学院の研究教授、ブリジェット・スキャンロン氏はそう語る。「まさに『ゴミを宝に』というスローガンの実例だ」「我々が試みているのは基本的に、サイクルを完結させて廃棄物を利用し、廃棄物の中にある資源を回収することだ」

こうしたいわゆるレアアースは、スカンジウムやネオジム、イットリウムといった地球のコアに存在する金属元素の集合体を指す。レアアースは電気自動車（ＥＶ）や太陽光パネル、風力タービンを含むクリーンテクノロジーにおいて重要な役割を果たす。

その名前とは裏腹に、レアアースは自然界では珍しくない。ただ、周囲の鉱石から抽出・分離するのは難しく、需要に供給が追いついていない状況だ。

世界が地球温暖化を招く化石燃料からの脱却を進める中、今後はさらに多くのレアアースが必要になる見通し。国際エネルギー機関（ＩＥＡ）によると、レアアースの需要は２０４０年までに最大で現在の７倍に跳ね上がるとみられている。

ただ、米国の供給量は依然として少なく、国内にある大規模なレアアース鉱山はカリフォルニア州のマウンテンパスのみだ。米国は現在レアアースの９５％以上を輸入しているが、その大部分は中国から来ており、サプライチェーン（供給網）や安全保障上の問題を突きつけている。

スキャンロン氏はＣＮＮの取材に、「我々は状況を改善する必要がある」と説明。このため、従来とは異なるレアアースの供給源に目を向ける動きが出ており、「こうした供給源の一つが石炭や石炭副産物だ」と指摘した。

地下の鉱床から直接採掘する場合に比べ、石炭灰はレアアースの濃度が比較的低い。長所は入手のしやすさで、米国では毎年約７０００万トンの石炭灰が発生している。

Translation

US scientists discover huge amounts of rare earth elements in coal ash waste: a treasure trove of clean energy?

(CNN) Large amounts of coal ash left over after burning coal were dumped in ponds and landfills, where they risked leaking into waterways and contaminating soil. On the other hand, this hazardous waste could potentially be a treasure trove of rare earth elements needed to promote clean energy.

In a recent study led by the University of Texas, scientists analyzed coal ash from power plants across the US and found that it contained up to 11 million tons of rare earth elements. This was nearly eight times the amount of rare earth elements in the US, worth about $8.4 billion (about 1.26 trillion yen).

The discovery this time noted that hiding in the US was a great potential in sourcing rare earths without the need for new mining, says Bridget Scanlon, a research professor at the University of Texas Jackson School of Geosciences and author of the paper. "It's a perfect example of the slogan 'Trash to Treasure'" ; " What we are trying to do is basically to close the cycle and to use waste, it's about recovering resources from waste."

These so-called rare earths were a collection of metallic elements found in the Earth's core, such as scandium, neodymium and yttrium. Rare earths played an important role in clean technologies, including electric vehicles (EVs), solar panels and wind turbines.

Contrary to their name, rare earths were not uncommon in nature. However, they were difficult to be extracted and separated from the ores around them, and supplies were not keeping up with demand.

As the world is moving away from fossil fuels that caused global warming, more rare earths were expected to be needed in the future. According to the International Energy Agency (IEA), demand for rare earths was expected to jump by seven times higher by 2040.

However, supplies in the United States remained low, with the only large rare earth mine in the country being found in Mountain Pass, California. The US currently imported more than 95% of its rare earths, most of which come from China, posing supply chain and security challenges.

Scanlon told CNN in an interview that "We need to do better," and pointed out that's why there's been a push to look to diverge sources of rare earths, "and one of those sources is coal and coal by-products".

Coal ash had a relatively low concentration of rare earths compared to those extracted directly from underground deposits. The advantage would be its availability; the US produced about 70 million tons of coal ash each year.

So, large amounts of coal ash left over from coal burning could potentially be a treasure trove of rare earth elements needed to promote clean energy. I am interested to know whether people will invest in extracting rare metal from coal ash eventually.

Note:

Bridget R. Scanlon (born 1959) is an Irish and American hydrogeologist known for her work on groundwater depletion and groundwater recharging, and of the effects of climate change and land usage patterns on groundwater. She is a senior research scientist in the Bureau of Economic Geology at the University of Texas at Austin where she is head of the Sustainable Water Resources Program. (Wikipedia)