A CLEAN PROCESS FOR BAYAN OBO MIXED RARE EARTH CONCENTRATE BASED ON
THE SEPARATION CHEMISTRY OF CERIUM WITH VALENCE VARIATION AND
COMPLEXATION
ZOU Dan, *CHEN Ji, LI Deqian
State Key Laboratory of Rare Earth Resource Utilization
Changchun Institute of Applied Chemistry, Chinese Academy of Science, Changchun 130022, China
(*Corresponding author: jchen@ciac.ac.cn)
ABSTRACT
Bayan Obo mixed RE concentrate is the largest RE source in the world. RE elements occurs dominantly as
bastnaesite and monazite. This paper describes a clean and green technique for processing Bayan Obo
mixed rare earth (RE) concentrate. This two-step oxidation method can recover REs, thorium (Th), fluorine
(F) and phosphorus (P) effectively. Ce has a property of valence change, enabling the separation of it from
other RE(III) elements.
Making use of the interactions between Ce(IV), F and P, a new extraction system was created to separate
Ce(IV) effectively from other REs(III) while recovering F, P and Th by complexing F and P through the
oxidation of Ce(III) to Ce(IV). The method included two parts. Firstly, bastnaesite was oxidized by air
roasting and sulfuric acid leaching and a first leach liquor containing Ce(IV), F and P was obtained.
Secondly, monazite was converted into RE-hydroxide through alkaline attack and then Ce(III) in the REhydroxide was oxidized into Ce(IV) by wet-air oxidation. After sulfuric acid leaching the oxidized REhydroxide, a second leach liquor was obtained. The two parts of leach liquor containing Ce(IV), F and P
were then extracted by the primary amine N1923, and a Th-product was recovered as ThO2. The raffinate
was further extracted by Cyanex923 to obtain CeO2, CeF3 and CePO4 based on the complex of Ce(IV)
with F and P. The RE elements recovery during the whole process is over 92%. The new technique not
only provides a new way for Bayan Obo RE ore utilization, but also avoids resource waste and
environment pollution.
KEYWORDS
Oxidation roast, valence change, Ce(IV), wet-air oxidation, amine extraction of thorium, Cyanex 923
extraction of Ce-P-F complexes