St. Petersburg Mining University (St. Petersburg, Russia):
Cheremisina O. V., Head of Chair, Doctor of Engineering Sciences, ovcheremisina@yandex.ru
Sergeev V. V., Assistant Lecturer, Candidate of Engineering Sciences, sergeev.spmi@yandex.ru
Fedorov A. T., Postgraduate, bers10@bk.ru
Lukyantseva E. S., Student, lukyantseva_lena@inbox.ru

More integrated processing of apatite ores may be achieved through the isolation of rare-earth elements (REE) as an independent product using the sulfuric acid technology for the treatment of phosphate raw materials. For the associated recovery and separation of rareearth metals (REM), it is proposed to introduce staged solvent extraction into the basic acid recovery process for the apatite concentrate. This work focuses on establishing the factors governing the concentration recovery of heavy group rare-earth metals from apatite concentrate processing products and their separation at the extraction stage. The effect of the concentration of the extracting agent (di-2-ethylhexylphosphoric acid or D2EGPA) on the concentration recovery of individual rare-earth metals from phosphate products has been established. The values of D2EGPA molecules solvated with REM ions have been calculated. The proportionality between the distribution coefficients and the rates of REM recovery into the organic phase has been established based on the element atomic number, which is associated with an increase in the chemical affinity between the organic acid molecules and the rare-earth ions in the series of lanthanides. The ultimate capacity of the extracting agent with respect to ytterbium at 298 K was determined, equal to 0.045 mol/l, which is several orders of magnitude higher than its initial content in the process solutions. An increase in the number of extraction stages leads to higher relative contents of ytterbium in the organic solvent, with the Yb/Y separation coefficient growing up to 36. It is most practical to isolate erbium and dysprosium after the extraction of ytterbium and yttrium. In order to achieve the dysprosium recovery of over 90 %, three to six stages of extraction will be required with an increase in the ratio of aqueous and organic phases from two to five.
The work was carried out with the financial support of the Russian Science Foundation (project No. 19-19-00377).

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