DOE OSTI2017
Southern Research, as the primary awardee, with sub-awardees ArcSec Technologies, LLC (ArcSec) and Reaction Engineering International (REI) have investigated a plasma arc based thermal process intended to concentrate rare earth elements (REE) from coal fly ash. Successful demonstration of the technology would contribute to the effort for realizing a competitive, domestic REE value chain thereby reducing U.S. dependence on foreign supply, maintaining national security interests, and creating opportunities for economic growth. The originally proposed concept included two technology options – 1) a smelting process and 2) a smelting plus vaporization and condensation process. For both options, coal fly ash would be smelted in a plasma arc heated furnace under reducing conditions to separate ash into molten slag and reduced metal (primarily iron) phases. During smelting, it was expected that the REE would also be reduced to metals and partition mostly to the iron phase. During the first year of work, sample coal ash feedstocks were acquired and characterized, feasibility of the smelting process was evaluated in bench-scale experiments, and the vaporization/condensation process was investigated through equilibrium and CFD modeling studies. From the feedstock characterization, REE content for the coal ash samples obtained was measured to be in the range of 302 – 1219 ppm with average at 537 ppm. Though it was successfully demonstrated that ash could be separated into slag and metal phases, the bench-scale experiments were only marginally successful at collecting REE in the metal phase. Producing REE concentrates near the DOE goal of 2%, however, has not been achieved. From the modeling studies, the vaporization/condensation process was predicted to be effective for separating individual REE and producing enriched metal fractions with total REE content higher than 2%, provided the smelting process performed as intended. Supplemental smelting experiments and thermodynamic modeling studies, conducted during the second year of work, indicated a number of technical modifications that could lead to producing higher REE concentrates from coal ash. The strategy shifted to reducing as much of the ash oxides to metals as possible, leaving the REE more concentrated in the remaining slag. Results from later experiments based on the modified approach showed improvements in REE recovery and concentration levels in smelted products. SEM-EDS analyses on product specimens showed agglomerations of reduced metal REE crystals at much larger length-scales as compared to REE content in raw ash.
01 COAL, LIGNITE, AND PEAT↗