Coal ash – Lightsources.org

As the world transitions away from fossil fuels, the demand for rare earth elements (REEs) is only going to increase. These elements are vital to the production of technologies that will make the transition to green energy possible. While REEs are not technically rare, large deposits are found in only a few locations around the world – mostly in China – and they are difficult to extract.

“If we want to switch to electric vehicles by 2035 and be net-zero by 2050 we’re going to need new sources of these metals,” says Brendan Bishop, a PhD candidate studying REEs at the University of Regina.

Bishop and his colleagues have been studying one potential new source of these valuable elements: the ash that is produced as waste from coal-fired power plants. Researchers have looked into REEs in coal waste in the United States and China, but there has been little work done on ash from Canadian coal.

The team analyzed samples of ash from coal plants in Alberta and Saskatchewan to determine how much REEs the ashes contained, and how they could be extracted. While the concentration of REEs in Canadian coal ash is on par with that found in ash from other parts of the world, questions remained about whether the REEs are dispersed evenly throughout the ash particles or concentrated in certain minerals found within the ashes.

Using the powerful X-ray beamlines at the Canadian Light Source (CLS) at the University of Saskatchewan (USask), Bishop probed the ash, in search of a rare earth element called yttrium. They found it was distributed in specific mineral phases within the ash particles, most often in the form of silicates or phosphates such as xenotime which remain unchanged when the coal is burned. The work was published in Environmental Science and Technology.

Read more on CLS website

How well toxic elements leach out of coal ash depends on the ash’s nanoscale composition

Everyone knows that burning coal causes air pollution that is harmful to the climate and human health. But the ash left over can often be harmful as well.

For example, Duke Energy long stored a liquified form of coal ash in 36 large ponds across the Carolinas. That all changed in 2014, when a spill at its Dan River site released 27 million gallons of ash pond water into the local environment. The incident raised concerns about the dangers associated with even trace amounts of toxic elements like arsenic and selenium in the ash. Little was known, however, about just how much of these hazardous materials were present in the ash water or how easily they could contaminate the surrounding environment.

Fears of future spills and seepage caused Duke Energy to agree to pay $1.1 billion to decommission most of its coal ash ponds over the coming years. Meanwhile, researchers are working on better ways of putting the ash to use, such as recycling it to recover valuable rare earth elements or incorporating it into building materials such as concrete. But to put any potential solution into action, researchers still must know which sources of coal ash pose a hazardous risk due to its chemical makeup — a question that scientists still struggle to answer.

In a new paper published June 6 in the journal Environmental Science: Nano, researchers at Duke University have discovered that these answers may remain elusive because nobody is thinking small enough. Using one of the newest, most advanced synchrotron light sources in the world — the National Synchrotron Light Source II at Brookhaven National Laboratory — the authors show that, at least for selenium and arsenic, the amount of toxic elements able to escape from coal ash depends largely on their nanoscale structures.

Read more on the BNL website

Image: Leftover sludge from the 2008 coal ash spill at the Kingston TVA power plant. New research indicates that the nanoscale structure of the coal ash plays a large part in whether or not toxic chemicals can leach into the environment from such events

Tag: Coal ash

Recovering rare earth elements from coal ash for clean energy technologies

The problems with coal ash start smaller than anyone thought