Russian Journal of Applied Chemistry, 2013, Vol. 86, No. 5, pp. 623−628.
Pleiades Publishing, Ltd., 2013.
Original Russian Text © E.P. Lokshin, O.A. Tareeva, I.R. Elizarova, 2013, published in Zhurnal Prikladnoi Khimii, 2013, Vol. 86, No. 5, pp. 673−679.
AND INDUSTRIAL INORGANIC CHEMISTRY
Recovery of Rare Earth Elements from Wet Process Extraction
E. P. Lokshin, O. A. Tareeva, and I. R. Elizarova
Tananaev Institute of Chemistry and Technology
of Rare Elements and Mineral Raw Materials, Apatity, Russia
Received March 27, 2013
Abstract—It is shown that an increase in the recovery of rare earth elements in ﬂ uorophosphate concentrates,
which are obtained by treating the wet process phosphoric acid by ammonium ﬂ uoride, is achieved by prior partial
neutralization of H
by ammonia. Therewith the consumption of ammonium ﬂ uoride is reduced that provides
almost complete precipitation of rare earth elements.
A fraction of rare earth elements (REE) of Khibine
apatite concentrate (AC), which is included in the wet
process extraction phosphoric acid (EPA), is estimated
at 30% [1, 2], but, likely, this value is overstated. Indeed,
a yield of a production EPA containing 28 wt% of P
(~38.6 wt% of H
) and 1.3–1.4 kg m
of REE is
approximately 1.05 m
from 1 ton of AC. Thus, by the
EPA no more than 13.5–15% of REE contained therein
comes in a fertilizer produced from AC.
Furthermore, at least 2.5 m
of EPA containing 0.9–
1.0 kg m
of REE is used in feedback for decomposition
of 1 ton AC. Both the production and feedback acid, into
which, respectively, 2470–2660 and 4275–4750 tons from
sum of REE oxides (ΣTr
) go at plants in Russia, can
be used REE recovery.
An important advantage of EPA is the high content in
the REE sum of middle and yttrium groups as compared
with both the original AC and even more loparite
concentrate, the only Russian industrial source of REE
that determines the increased interest in developing
methods for recovery of REE from EPA. These methods
should be compatible with the main production of mineral
fertilizers that necessitates their operating availability at
elevated temperatures (75–80°C), moreover, a relatively
small production area should be occupied in their
implementation. It is important to ensure high recovery
of most valuable REE of the middle and yttrium groups.
For a long time a method of spontaneous crystallization
of REE on seeds was considered as promising [3–10]. It
was based on the assumption that EPA is supersaturated by
REE, mainly, by cerium [3–8]. Phosphates or ﬂ uorides of
rare earth elements were proposed as seeds, also gypsum
may be used . However, the fact that in the presence
of gypsum, which is recommended as a possible seed
material , EPA remained supersaturated by REE, is
misunderstood. Therewith in the course of EPA producing
gypsum crystals were maintained a long time in a hot
sodium phosphate solution of relatively low viscosity.
This and other reasons discussed in  cast doubt on
the reliability of the results of [3–10].
Rare earth elements of EPA may be precipitated in the
form of a ﬂ uorophosphate concentrate by introduction of
compounds containing ﬂ uoride ion . The method is
based on the assumption that in the presence of ﬂ uorine
REE will form ﬂ uorides poorly soluble in hot phosphoric
acid solution. Although EPA of Khibine AC always
contains relatively high concentrations of ﬂ uorine, REE
ﬂ uorides are not formed, since in EPA ﬂ uorine is bound in
strong anionic complexes with silica and, possibly, with
aluminum, titanium, and iron. However, if the content
of ﬂ uoride ion in EPA exceeds those required to form
anionic complexes, REE ﬂ uorides will be formed and