Key words: supercritical fluid extraction, microwave radiation, rare earth elements, thorium, uranium, carbon dioxide, monazite concentrate, phosphogypsum, tributyl phosphate, di-(2-ethylhexyl)phosphoric acid
Supercritical fluid extraction (SCFE) using carbon dioxide containing tributyl phosphate
(TBP) and di-(2-ethylhexyl)phosphoric acid (D2EHPA) or their adducts with HNO3
is proposed as a method to extract rare earth elements (REE), Th and U from monazite
concentrate (MC) and phosphogypsum (PG). On the first stage, the product of baking
the MC with Na2CO3 (MCS) is obtained in the presence of coal under microwave
irradiation, in which phosphates of REE, Th and U present in the MC are converted
into their oxides. Up to 50 % of REE can be recovered from the powdered MCS by
the adducts of TBP and D2EHPA with HNO3 in SCFE conditions, whereas Th and U
remain in the solid phase. After a complete dissolution of the MCS residue in the
mixture of 4 M HCl and 0.05 M HF, Th and U are quantitatively extracted using
supercritical carbon dioxide containing D2EHPA and thus separated from the REE
that remain in an acidic solution. The conditions of quantitative isolation of REE, Th
and U from PG are determined and the schemes for complex processing of MC and
PG targeted to the recovery of REE separated from Th and U are suggested.
doi:10.1134/S1990793116070186