1070-4272/02/7510-1572 $27.00 C 2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 10, 2002, pp. 1572!1576. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 10, 2002,
Original Russian Text Copyright + 2002 by Lokshin, Vershkova, Vershkov, Tareeva.
AND INDUSTRIAL INORGANIC CHEMISTRY
Efficiency of Sulfuric Acid Leaching of Lanthanides
in Relation to Quality of Phosphosemihydrate
Obtained from Khibiny Apatite Concentrate
E. P. Lokshin, Yu. A. Vershkova, A. V. Vershkov, and O. A. Tareeva
Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials,
Kola Scientific Center, Russian Academy of Sciences, Apatity, Russia
Received May 13, 2002
Abstract-Reasons for a decrease in recovery of lanthanides by sulfuric acid leaching from separate lots of
phosphosemihydrate produced by Voskresenskie Mineral’nye Udobreniya joint-stock company were studied.
Khibiny apatites are one of the most promising
Russian raw sources of lanthanides [1, 2]. The sum
of lanthanides in the apatite concentrate (AC) ob-
tained from ores mined at the Khibiny field is about
1 wt % , with the relative contents of elements
being close to the optimal in the pattern of consump-
In 1996, more than 80% of the 4.82 million tons of
AC supplied to Russian plants were processed by the
sulfuric acid technology. This technology was imple-
mented in the form of semihydrate and dihydrate pro-
cesses, which produce as a recrement, together with
, either [phosphosemihydrate] 2CaSO
(PSH) or [phosphodihydrate] CaSO
The semihydrate process is used at two largest
Russian fertilizer plants: Ammofos joint-stock com-
pany (Cherepovets) and Voskresenskie Mineral’nye
Udobreniya joint-stock company (Voskresensk, Mos-
cow oblast). This method is more economical and
will gradually replace the dihydrate process at other
Russian plants. With the semihydrate process, up to
95% of lanthanides is extracted to PSH from the apa-
tite concentrate [5, 6].
An efficient technology for recovery of lanthanides
from PSH has been developed at the Ammofos joint-
stock company . According to this scheme,
the same H
solution is used for leaching of sev-
eral PSH portions. In each leaching stage, concentrated
sulfuric acid (93.5 wt %) is added to the solution to
maintain its concentration. Lanthanides are extracted
from the sulfate solution by ionic flotation.
In the case of acid leaching, only lanthanides form-
ing independent phases in PSH can pass into solution.
Part of lanthanides in PSH do not crystallize iso-
morphically with hydrated calcium sulfate, but form
independent phases precipitating on celestine (SrSO
grains. The most probable compounds of lanthanides
in these phases are phosphates and binary sulfates of
rare-earth and alkali metals .
Some authors  believe that the limiting con-
centration of lanthanides in solutions (1.131.2 g l
is determined by the salting-out action of H
which lowers the solubility of lanthanide sulfates.
However, the solubility of lanthanide sulfates is an
order of magnitude higher in H
the concentrations under study, compared with that
reached in leaching solutions.
Phosphoric acid is accumulated in leaching solu-
tions [7, 9, 17] because of the dissolution of lan-
thanide and calcium phosphates in H
because of its inflow from unwashed PSH.
The solubility of lanthanide orthophosphates in
acid sulfate-phosphate solutions grows with increas-
ing concentration of sulfuric acid and falls with in-
creasing concentration of orthophosphoric acid .
The use of more concentrated acidic sulfate solutions
allowed the sum of lanthanides in the leaching solu-
tion to be raised to 3 g l
and more . As a result,
the volume of solutions decreased to a level permitt-
ing their utilization in manufacture of fertilizers with-
out disturbing the water balance and carrying out their
concentration by evaporation.