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THE INFLUENCE OF CATION AND ANION TYPE ON ION EXCHANGE LEACHING OF
LANTHANIDES FROM ION-ADSORPTION CLAYS
Georgiana A. Moldoveanu, Vladimiros G. Papangelakis
Department of Chemical Engineering and Applied Chemistry, University of Toronto
200 College Street, Toronto, ON, M5S 3E5, Canada
[email protected]; [email protected]
ABSTRACT
One of the major commercially viable secondary sources of rare earths elements (REE) are the ionadsorption clays, containing 0.05-0.3 wt% rare earth oxides physically adsorbed on the surface of clay
minerals formed during lateritic weathering of lanthanide-rich rocks. Although ion-adsorption deposits are
substantially lower grade than other types of rare earth sources, this is offset by the easier mining and
processing costs and the low content of radioactive elements. The conventional extraction route involves
ion exchange leaching with monovalent cation solutions (usually ammonium sulphate) under ambient
conditions; during the process, the lanthanides are desorbed and transferred into solution, being replaced by
the exchange cation. While ammonium ions are known to perform best, there is increased environmental
motivation to investigate alternative lixiviants via reducing their concentration without considerable loss in
rare earth extraction.
The objective of the present research was to screen various cations salts (alkaline and alkaline-earth metals
present as sulphates, chlorides and acetates) in order to evaluate lanthanide desorption levels. The overall
aim is to identify more efficient processing routes. The ion exchange ability of the tested cations was
explained in terms of differences in hydration enthalpy. For the anions, it was determined that REE
extraction efficiency follows the order sulphate > acetate > chloride. Finally, various process implications
scenarios are described using mixed cations and anion matrices.
KEYWORDS
Rare earth recovery, ion-adsorption clays, ion exchange leaching, lanthanides, leaching efficiency
COM16 – IMPC2016
Symposium on REE extraction and processing
Quebec City, Canada
September 2016