Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 11, pp. 1919−1924.
Pleiades Publishing, Ltd., 2010.
Original Russian Text © E.P. Lokshin, O.A. Tareeva, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 11, pp. 1787−1792.
INORGANIC SYNTHESIS AND INDUSTRIAL
Treatment of Rare-Earth Concentrate
to Remove Phosphorus and Fluorine Compounds
E. P. Lokshin and O. A. Tareeva
Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials,
Kola Scientiﬁ c Center, Russian Academy of Sciences, Apatity, Murmansk oblast, Russia
Received February 26, 2010
Abstract—It was suggested to purify poor lanthanide concentrate precipitated from the extraction orthophosphoric
acid produced by the dihydrate process to remove phosphorus and ﬂ uorine compounds by heating a mixture of
the concentrate with sulfuric acid in the presence of hydrated silica followed by water leaching of water-soluble
sulfates and phosphates. The treatment conditions for the separation of the bulk of phosphorus(V) and the entire
ﬂ uorine in the form of SiF
were determined, ensuring approximately 3.5-fold increase in lanthanide concentration.
The introduction of sodium compounds and sulfuric
acid into the extraction orthophosphoric acid (EPA) pro-
duced by the dihydrate method leads allows precipita-
tion of the concentrate of rare-earth elements (REEs),
which contains as major components double sulfates
of REE and sodium, calcium sulfate dihydrate, and so-
dium hexaﬂ uorosilicate . It was established that the
ratio of sodium hexaﬂ uorosilicate and double sulfates
of REE with sodium in the concentrate depends on the
order, at which the reagents are introduced into EPA.
If sodium compound is introduced ﬁ rst, then most of
containing only traces of REEs is precipitated
and may be separated by ﬁ ltration. At subsequent intro-
duction of sulfuric acid, there is precipitated the REE
concentrate, into which a minority of sodium hexaﬂ uo-
rosilicate, precipitated from EPA, passes. Such run of
the process ensures the higher concentration of REEs
in the concentrate (10.5–19.5 wt % ΣLn
on the sodium compound used), whereas requires two
ﬁ ltrations. If sulfuric acid and sodium compound are
introduced into EPA simultaneously, all Na
precipitated passes into the REE concentrate, thus de-
creasing the content of lanthanides in it by a factor of
2.5–4.0. This method requires only one ﬁ ltration, makes
crystallization time of the REE concentrate several-fold
lesser, and ensures somewhat increase in REE extrac-
tion. The forming concentrates capture the mother EPA.
In processing of the above REE concentrates, the
separation of captured mother EPA and ﬂ uorine ions
is the important procedure, because in the course of its
further treatment by the previously suggested methods
 the presence of orthophosphate and ﬂ uorine ions may
lead to formation of difﬁ cultly-soluble and difﬁ cult to
process REE phosphates and ﬂ uorides. In this study, we
searched for the methods of treatment of the concentrates
obtained to remove phosphorus and ﬂ uorine.
The concentrate and the products obtained in the
experiment were analyzed by the following methods:
the content of REEs and calcium was determined by
the mass-spectrometric method (ELAN 9000 DRC-e
system). Solid products were preliminarily dissolved
in a chemically pure hydrochloric acid [GOST(State
Standard) 3118-77]. The content of sodium was
determined by the ﬂ ame atomic emission spectrometry,
the content of phosphorus, photocolorimetrically from
the color intensity of phosphorus-molybdenum blue, and
the ﬂ uorine content, by distillation with potentiometric
end point detection.
Because the concentration of REEs in EPA used in
experiments was low, their concentration in the precipi-