INORGANIC SYNTHESIS AND INDUSTRIAL
Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 9, pp. 1461−1469.
Pleiades Publishing, Ltd., 2011.
Original Russian Text © E.P. Lokshin, O.A. Tareeva, I.P. Elizarova, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 9, pp. 1409−1417.
Processing of Phosphodihydrate to Separate
Rare-Earth Elements and Obtain Gypsum Free
from Phosphates and Fluorides
E. P. Lokshin, O. A. Tareeva, and I. P. Elizarova
Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Resources,
Kola Scientiﬁ c Center, Apatity, Murmansk oblast, Russia
Received December 30, 2010
Abstract—Geotechnological complex processing of phosphodihydrate, including sulfuric acid leaching, sorption
extraction of rare-earth elements, recovery of leaching solutions to obtain rare-earth products and gypsum material,
which in the radioactivity and concentration of impurity ﬂ uorides and phosphates is suitable for use in building
and cement industries, is outlined.
In phosphogypsum (PG) formed by sulfuric acid
leaching of the Khibiny apatite concentrate by the
dihydrate technology the rare-earth elements (REEs)
are present in fairly readily soluble and isomorphically
cocrystallized form .
Prolonged static treatment of PDH with sulfuric acid
solutions with a sulfuric acid concentration 0.5–4 wt%
causes leaching of sodium ﬂ uorosilicate, readily soluble
REEs, the bulk of isomorphically cocrystallized REEs,
and phosphate ions. The ﬁ nal products are solutions
with low concentration of REEs and gypsum, which in
the concentration of impurity ﬂ uorides and phosphates
is suitable for use in building and cement industries .
The study is concerned with the leaching efﬁ cicency
for REEs and phosphorus in conditions of a continuous
gravity ﬂ ow of sulfuric acid leaching solution through
the PDH layer. The conditions of the sorption extraction
of REEs from leaching solution and the possibility of
its recovery by removal of impurity phosphates and
ﬂ uorides were determined.
We used in the study main substances and the methods
of the analysis described previously . The installation
for FDH leaching is schematically presented in Fig. 1.
Its main units are made of polyethylene. Leaching is
performed in a 1500-mm high column 1 equipped with
ﬂ anges 2 tightened with vacuum rubber spacers. Initial
sulfuric acid solution is poured into a vessel 3 through
a pipe 4 and leaching solution is collected in a reception
tank 5. The vessel 3 and column 1 are connected through
a silicone rubber pipe equipped with a glass reactor 6
having a hole of about 1 mm in diameter. The inlet and
outlet ﬂ ow velocities of a leaching solution in the column
1 are controlled by the glass reactor 6 and valves 7 at the
top and bottom ﬂ anges of the column. The main units
are assembled on the steel frame over a plastic tray 8,
designed to collect sulfuric acid solution in the case of
occidental depressurization of the installation.
Work on the installation was carried out as follows.
To a column 1, a bottom ﬂ ange was connected.
A prescribed weighed portion of FDH was placed into
the reactor and pretreated in a solution with c
4 wt % at agitation (V
/Т = 2) for 1 h to assist leaching
of REEs in the uncocrystallized isomorphous form.
The solution was separated by ﬁ ltration, a wet PDH
was charged into a column 1, and the top ﬂ ange was
set. The assembly of the installation was complete. The
vessel 3 was ﬁ lled with a sulfuric acid leaching solution.