AGI/AIPG SUMMER INTERNS
quantities maintain monopolies in the market, giving them tremendous power and control over global supply and prices.
Harvesting critical REEs from coal ash has the potential to lessen the 3000-ton global supply-demand imbalance because it contains relatively high concentrations of critical REEs. It also is less labor-intensive, costly, and environmentally haz- ardous than mining elements from unprocessed coal ore. At some utility plants, the coal combustion process has even been shown to enrich the critical REE concentration when compared to raw coal deposits.11 Standard reference materials for coal ash, NIST SRM 1633b and IRANT EOP, average 420 mg/kg and 806 mg/kg for REEs, respectively.12
The Duke University study may provide a solution to simul- taneously address critical REE scarcity and the cost of coal ash cleanup operations. The geoscientists found that critical REE composition is unique to each source of coal ash, and that coal ash from the Appalachian Mountains has the highest critical REE content identified in the United States. Additionally, they documented sources of coal ash with lower compositions of critical REEs than Appalachian coal ash, but with higher extractable yields. Despite its high concentration, Appalachian coal actually had the lowest amount of recoverable critical REEs. This has been a problem that has garnered much attention among the research community as developing and refining extraction techniques have continuously improved recovery rates over the last 30 years.
The extraction process generally involves the following steps: (1) acid leaching of coal ash with a low-PH acid (e.g., hydrochloric, sulfuric, or nitric), (2) removal of undesirable
materials using chelating resins or other precipitates (e.g., calcium sulfate), and (3) purification using solvent extraction. Depending on which combination of acids and extractants are used and the concentration of other metals in the ash, recovery rates vary greatly between 50 to 99 percent.13
Unfortunately, these studies have only been completed on a laboratory scale because according to Dr. Heileen Hsu-Kim, the lead investigator of the Duke University study, the reagents used are currently too expensive to be used on an indus- trial scale.14 However, Dr. Hsu-Kim is optimistic that higher yields can be achieved with alternative, cheaper extraction techniques, making this process an economically attractive investment for entrepreneurs, since commercial plants are estimated to cost upwards of hundreds of millions of dollars.
Intrigued by this opportunity, the DOE has already invested $20 million into research projects on extraction technologies for coal wastes beginning in 2015.15 Additionally, numerous local utilities and government grants have provided invest- ments to help cover the capital costs of building pilot plants. Others are investigating ways to reduce the chemical and water intensiveness of the process.16 All of these efforts are rapidly improving the state and understanding of critical REE potential in the U.S. Much is still to be learned, but the potential to reduce waste and avoid catastrophic impoundment spills, while also limiting reliance on foreign suppliers, are key reasons to suggest that critical REE extraction from coal ash may be an important technology that should reframe how we think about coal ash: from harmful waste to vital resource.
13. Coal Ash: Waste or Resource. (2015). North Carolina Coal Ash Management Coalition. Web. 14. Kingery, Ken. (2016). Appalachian Coal Ash Richest in Rare Earth Elements. Duke University School of Engineering. Web. 15. DOE Selects Projects to Enhance Its Research Into Recovery of Rare Earth Elements from Coal and Coal Byproducts. (2015). Department of Energy. Web. 16. Coal Ash: Waste or Resource. (2015). North Carolina Coal Ash Management Coalition. Web.
Tales from the Field: We Are Not Alone Jim Burnell, CPG-11609
It was the summer of 1975 in northern Wisconsin. The recent discovery of the huge Crandon massive sulfide had stirred interest in the Precambrian terrain of the Lake Superior District. Our exploration director (for a major mining company) sent us out to do some baseline exploration. Lincoln County, Wisconsin, is an area of undeveloped drainage. Underlain by glacial deposits, it is mostly lakes and swamps. An outcrop is a dream. In fact, that’s how the story develops.
References on the geology of the area were as scarce as outcrops. Several years before, an M.S. student at an in-state university had done his thesis in the Lincoln County area. One feature of his thesis was an outcrop map. Yes, for those of us working recently in the Rocky Mountains, this was a map that located all the outcrops in his thesis area.
We decided one morning to track down what was identified as a large bedrock outcrop. We needed to see some bedrock, right? It was difficult to access. We planned a three-mile hike (one way) from the end of a desolate road. As we anticipated,
the walk was mostly through swampy ground. Wilderness. I can’t impress on you how desolate the area appeared for the Lower 48. No civilization, no sign of anybody or anything.
Finally, in the distance through scattered tamaracks, we saw the outcrop. And it was, in fact, large – some twenty feet long rising six feet out of the swamp. We got to the outcrop, poised to take samples and notes when we noticed right there in front of us a cigarette butt. It was freshly stubbed out and still smoldering.
Now where in the world …?!? We looked around through the trees, called out, but nothing. Silence. Apparently some other geologist had also tracked down this famous outcrop at the same time as we did. Where was he? A spooky experience.
Editor’s note: Got an interesting field experience? Of course you do! Send in your field (or office) story and we’ll share it in TPG.
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