Extraction of Rare Earth Oxides Using Supercritical Carbon Dioxide Modified with Tri-n-Butyl Phosphate–Nitric Acid Adducts

Abstract

A new tri-n-butylphosphate−nitric acid (TBP−HNO 3 ) adduct was prepared by combining TBP and fuming (90%) HNO 3 . The adduct was characterized, and its phase-equilibrium behavior in supercritical carbon dioxide is reported. Supercritical carbon dioxide (sc-CO 2 ) was modified with this new adduct [TBP(HNO 3 ) 5.2 (H 2 O) 1.7 ], and the extraction efficacies of selected rare earth oxides (Y, Ce, Eu, Tb, and Dy) at 338 K and 34.5 MPa were compared with those obtained using an adduct formed from concentrated (70%) HNO 3 and TBP [TBP(HNO 3 ) 1.7 (H 2 O) 0.6 ]. All rare earth oxides tested with both adduct species could be extracted with the exception of cerium oxide. The water and acid concentrations in the different adducts were found to play a significant role in rare earth oxide extraction efficiency.

Rare earth element extraction from pretreated bastnäsite in supercritical carbon dioxide

“…Supercritical CO 2 with TBP has been used to extract REEs (and actinides) from aqueous nitrate solutions [8][9][10] and from solid nitrate salts [11][12][13]. Another option is to premix TBP and HNO 3 to form a liquid adduct, dissolve this adduct in supercritical CO 2 , and use this modified CO 2 to extract REEs from acid-soluble mineral phases such as oxides [14][15][16][17][18][19]. In the latter configuration, the extraction mechanism involves three sequential steps in a single reaction vessel: reaction of REE minerals with nitric acid to form REE nitrates, complexation of the nitrate salt with TBP, and dissolution of the metal complex in CO 2 .…”

“…The TBP/HNO 3 adducts were prepared by shaking dry TBP (<300 ppm H 2 O) with fuming HNO 3 at various volume ratios for five minutes, following the procedure from previous studies [16,28]. All of the adduct compositions used in this study resulted in a single phase.…”

“…A note of caution should be given with regard to mixing, handling, use, and storage of TBP and nitric acid mixtures. Mixtures comprised of concentrated (70%) nitric acid and TBP have previously been characterized and widely reported in literature without mishap [14][15][16][17][18][19]. Care should be taken not to formulate mixtures of TBP and fuming nitric acid which would result in a mixture having greater than approximately 10 M H + in the organic phase because such mixtures have been found to be unstable and can undergo rapid exothermic decomposition (hydrolysis).…”

“…The extraction pressure was set at 34 MPa to dissolve the full range of adduct compositions by a comfortable margin [16] and a reaction column temperature of 65°C because extractions near this temperature had achieved high recoveries in previous studies [14,15].…”

Alkylation and pre-organisation of diglycolamide ligands on flexible platforms for nuclear waste treatment

“…305 The performance of the TBP-HNO3 complex, however, was negatively affected by the increasing amount of water and acid. 306 …”