Get enough engineers on a problem, and in this age of innovation, you will likely solve it.
The US has pledged that 100 per cent of its electricity will be generated from clean energy technology by 2035. Achieving that will require many of the dynamic dozen. But there are long-standing worries about their global supply and the environmental damage of their extraction. Much of the resource is in China, Indonesia and the Democratic Republic of the Congo, which the International Energy Agency has described as “a concern from a geopolitical point of view”.
Enter Old King Coal. Coal waste (in the US at least) contains absolutely tonnes of the stuff. Coal ash alone contains an estimated 288,000 tonnes of lithium, enough to supply the US market for 130 years. It is also rich in cobalt, neodymium, dysprosium, platinum, iridium, gallium and germanium. The last two of these are needed for the semiconductors that will be used in sensors and controllers for the clean tech.
“It’s significant enough to meet some of these clean energy targets that we have,” said Wilcox in the webinar. “I’m really excited.”
There are other reasons to be excited. Not only does coal waste contain those crucial elements, some of it is rich in magnesium and calcium. These aren’t being lined up for extraction, but as a material for negative emissions tech. Coal waste containing magnesium and calcium reacts with carbon dioxide and locks it away as solid carbonates.
Coal waste is also often situated in communities blighted by the loss of jobs in mining. They need new jobs and often have the skills that will be required to develop a minerals extraction industry. Win, win, win, win.
But there is a way to go. The purity of the elements is typically modest, said Wilcox, and the separation technologies to recover and refine them are in their infancy. The cost of doing so is also unknown. But the US Department of Energy is burning the midnight coal to work out how to do it.
And if coal doesn’t work out, there are other unconventional feedstocks that could be tapped. These include asbestos mine tailings, “red mud” from aluminium production, brines from geothermal power plants, phosphogypsum wastes from phosphoric acid and fertiliser production, e-waste, conventional landfills and even sewage sludge.
Of course, if the US does develop a coal waste separation industry, it is unlikely to share the bounty. But many other countries, including the UK and Germany, have plenty of slag of their own. Coal may be on its way out, but its legacy could help to save us from the storms of our own making.
As I’ve reported before, Rice University has been working on exactly this problem for some time.
The Rice lab of chemist James Tour reports it has successfully extracted valuable rare earth elements (REE) from waste at yields high enough to resolve issues for manufacturers while boosting their profits.
The lab’s flash Joule heating process, introduced several years ago to produce graphene from any solid carbon source, has now been applied to three sources of rare earth elements — coal fly ash, bauxite residue and electronic waste — to recover rare earth metals, which have magnetic and electronic properties critical to modern electronics and green technologies.
The researchers say their process is kinder to the environment by using far less energy and turning the stream of acid often used to recover the elements into a trickle.
The study appears in Science Advances.
Rare earth elements aren’t actually rare. One of them, cerium, is more abundant than copper, and all are more abundant than gold. But these 15 lanthanide elements, along with yttrium and scandium, are widely distributed and difficult to extract from mined materials.
“The U.S. used to mine rare earth elements, but you get a lot of radioactive elements as well,” Tour said. “You’re not allowed to reinject the water, and it has to be disposed of, which is expensive and problematic. On the day the U.S. did away with all rare earth mining, the foreign sources raised their price tenfold.”
So there’s plenty of incentive to recycle what’s been mined already, he said. Much of that is piled up or buried in fly ash, the byproduct of coal-fired power plants. “We have mountains of it,” he said. “The residue of burning coal is silicon, aluminum, iron and calcium oxides that form glass around the trace elements, making them very hard to extract.” Bauxite residue, sometimes called red mud, is the toxic byproduct of aluminum production, while electronic waste is from outdated devices like computers and smart phones.