Institute of Chemistry and Chemical Technology, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russia

S. N. Kalyakin, Senior Researcher, Candidate of Chemical Sciences
M. A. Mulagaleeva, Junior Researcher, e-mail: maral7508@mail.ru
V. I. Kuzmin, Chief Researcher, Doctor of Chemical Sciences

O. A. Epov, Junior Researcher

Physicochemical regularities of extraction of chlorides, sulfates, nitrates of heavy lanthanides (HREE) were investigated using binary extractants (BE) based on di-(2-ethylhexyl)phosphoric acid (DEHPA), mono-2-ethylhexyl ester of 2-ethylhexylphosphonic acid (HEHEHP), capric acid (RCOOH), tri-n-octylammine (TOA), dioctylamine (DOA) and solvating additives – tri-n-octylamine nitrate (TOA·HNO₃), dioctylamine nitrate (DOA·HNO₃). Introduction of solvating additives into the organic phase eliminates formation of precipitates therein during extraction of lanthanides. Equations of the main heterogeneous reactions are proposed, allowing to describe extraction in a wide range of component concentrations. The presented isotherms of heavy group lanthanide extraction using BE in the presence of a solvating additive of amine nitrates have an S-shape. Based on the isotherms, the concentration constants of binary extraction of chlorides, sulfates and nitrates of heavy group lanthanides were calculated. It is shown that the lanthanide extraction process can be described quantitatively based on the equations of concentration constants of binary extraction in a wide range of lanthanide concentrations and extractant compositions. BE compositions with the required properties based on phosphorus-containing organic acids – HEHEHP, DEHPA, high-molecular organic amine TOA and the solvating additive TOA·HNO₃ are proposed. It was found that HEHEHP-based extractants are effective for separating heavy group lanthanides within the group. In addition, the selectivity of DOA-based extractants is higher than for TOA ones. Mathematical models of heavy group lanthanide extraction processes using BE and countercurrent extraction cascades with BE have been developed. A rational scheme of extraction cascades for the sequential isolation of heavy group lanthanides has been proposed. When using the proposed BE, a countercurrent cascade system containing more than 400 individual extraction stages is required to separate all heavy group lanthanides.
The work was carried out within the framework of the state assignment of the Institute of Chemistry and Chemical Technology SB RAS (project FWES-2021-0014) using the equipment of the Krasnoyarsk Regional Center for Collective Use of the FRC KSC SB RAS.

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