PRETREATMENT METHODS FOR RARE EARTH ELEMENT EXTRACTION IN
SUPERCRITICAL CARBON DIOXIDE
L.K. Sinclaira, D.L. Baekb, R.V. Foxb
a
Cornell University, Department of Chemical and Biomolecular Engineering. Snee Hall, Cornell
University, Ithaca, New York, 14853 lks82@cornell.edu
b
Idaho National Laboratory, 775 University Boulevard, Idaho Falls, Idaho 83415
ABSTRACT
In this study, rare earth elements were recovered from bastnasite concentrate and waste fluorescent lamp
phosphors using supercritical carbon dioxide extraction with a nitric acid/tributyl phosphate adduct. Several
pretreatment methods were used to alter the crystal structure of the source materials and thus improve rare
earth element recovery. Pretreatment methods included 1) dry roasting of the source material at 730 oC, 2)
decomposition with 50% sodium hydroxide solution at 150 oC for 4 hours, and 3) decomposition with 12 M
sulfuric acid at 300oC for 4 hours. Treated and untreated samples underwent supercritical extraction at 24
MPa and 65oC for 1 hour. Untreated bastnasite and phosphor samples showed <10% rare earth element
recovery, but sodium hydroxide digestion resulted in >60% recovery for most rare earth elements. Dry
roasting of the bastnasite concentrate was also effective, resulting in >60% recovery for cerium.
KEYWORDS
Rare earth elements, supercritical, carbon dioxide, leaching, sulfuric acid, sodium hydroxide, acid adduct