(658g) Economic Extraction and Recovery of Rees and Production of Clean Value-Added Products from Low-Rank Coal Fly Ash
The University of North Dakota Energy & Environmental Research Center (EERC), with assistance from Pacific Northwest National Laboratory and the U.S. Department of Energyâs National Energy Technology Laboratory, is developing economically viable and tailorable rare-earth element (REE) extraction and concentration methods for low-rank coal fly ash. These methods are tailored based on a detailed understanding of fly ash formation mechanisms, fly ash properties, the form of the REEs in the fly ash and, to some degree, the mode of occurrence of the REEs in the coal. These new methods were applied to high-calcium-containing fly ash materials derived from the combustion of subbituminous coals from the Powder River Basin (PRB) and North Dakota lignite coal from the Fort Union region, the resource of which has the potential to far exceed the current U.S. REE demand. The EERC evaluated several simple and environmentally benign pretreatment approaches that can 1) alter the physical structure of the fly ash by increasing porosity or decreasing particle size; 2) alter the chemical composition of the fly ash to improve solubility, allowing the use of a much milder leaching process to extract REEs; and 3) enrich the metals/elements of interest on the surface of the ash particles, making them more accessible by solvents. This approach was used to take advantage of the high alkali/alkaline-earth content in PRB and lignite fly ashesâa significant REE recovery advantage over eastern bituminous coals. In addition, the EERC will present results from the development of improvements to existing supercritical CO2-based extraction of metals from ash and other solid waste materials. This involves a lower-cost method of compressed CO2 processing that utilizes both traditional and novel, inexpensive metal chelating agents.