Investigating the Potential for Recovering REEs from Coal Fly Ash and Power Plant Wastewater with an Engineered Sorbent

摘要

The global demand for rare earth elements (REE) has increased significantly in the past 20 years due to their extensive use in electronics and other applications. Although many recent studies related to quantifying rare earth elements in coal and coal combustion byproducts have been published, methods of extracting rare earth elements are still not economically feasible. The objective of our study is to investigate the potential extraction of the REEs from coal ash and from wastewater sludge collected from a power plant near Detroit, MI. The collected ash and sludge will undergo a hydrothermal extraction process developed by Los Alamos National Laboratory to extract REEs from the sludge or coal ash, resulting in a liquid enriched in dissolved REEs. Batch experiments were conducted using an organosilica adsorbent (Osorb) and a ligand [P-di(2-ethylhexyl) methanediphosphonic acid (DIPEX)] to extract neodymium from a synthetic hydrothermal extraction solution. DIPEX-associated Osorb media was produced by first dissolving DIPEX into a solvent (e.g., methanol). Different amounts of DIPEX-methanol solution were then added to 0.2 g of Osorb to determine the maximum sorption capacity. The methanol was evaporated and, after a rinse step, the DIPEX-Osorb sorbent was used in sorption experiments. A 300 ppm neodymium (Nd) synthetic ash/sludge leachate was tested with the various DIPEX-Osorb media. Results show that DIPEX-Osorb ratios of 4.3, 1.1, 0.5, and 0.05 mL/g sorbed 60, 51, 25, and 7 mg Nd per g media, respectively. Since the 4.3 mL DIPEX/g Osorb media sorbed 100% of the Nd in the solution, a higher capacity is expected and these experiments are ongoing. Breakthrough curve for of the sorption of Nd to Osorb was conducted and showed a higher sorption ratio when the Nd concentration increased. We are also investigating the reusability of the DIPEX-Osorb media by measuring how many cycles the media can be regenerated by extracting the Nd with nitric acid and reusing the sorbent for another cycle.