ISSN 1070-4272, Russian Journal of Applied Chemistry, 2015, Vol. 88, No. 4, pp. 567−573. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © E.P. Lokshin, O.A. Tareeva, 2015, published in Zhurnal Prikladnoi Khimii, 2015, Vol. 88, No. 4, pp. 534−540.
INORGANIC SYNTHESIS AND INDUSTRIAL
Production of High-Quality Gypsum Raw Materials
E. P. Lokshin and O. A. Tareeva
Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, Kola Science Center,
Russian Academy of Sciences, Apatity, Akademgorodok 26a, Apatity, 184209 Russia
Received March 5, 2015
Abstract—Possibility of obtaining high-quality gypsum products from phosphogypsums produced in sulfuric acid
processing of the Khibiny apatite concentrate was examined. A variant of phosphogypsum processing including the
sulfuric acid leaching of rare-earth elements and admixtures of phosphorus and ﬂ uorine compounds, neutralization
of the puriﬁ ed gypsum product, and utilization of phosphates and ﬂ uorides released from phosphogypsum was
considered. It was experimentally demonstrated that the agitation sulfuric acid leaching is inefﬁ cient for puriﬁ ca-
tion of phosphogypsums. It was conﬁ rmed that combining a percolation sulfuric acid leaching of phosphogypsums
with their preliminary washing with water is promising for obtaining high-quality gypsum raw materials.
Annually, more than 6 million tons of phosphogypsum,
phosphodihydrate (PDH) and phosphohemihydrate
(PHH), are produced at Russia’s plants in processing of
the Khibiny apatite concentrate into mineral fertilizers by
the sulfuric acid method. Hundreds of millions of tons
of this technogenic raw material have been accumulated
in decades at plant dumps. These wastes contain 0.4–
0.6 wt % rare-earth elements (REE) in terms of their
oxides. For economically feasible recovery of REEs from
phosphogypsums, their integrated use is necessary. Large
amounts of gypsum can be consumed in manufacture
of gypsum building materials and cement (as a cement
setting retarder and for production of cement clinker).
Depending on the application area, raw materials should
contain not more than (wt %): 0.5–0.6 water-insoluble
, 0.4–0.6 water-insoluble ﬂ uorine compounds, and
0.02–0.1 water-soluble P
and ﬂ uorides (each) .
Phosphogypsums contain up to 1.3 wt % P
0.4 wt % ﬂ uorine , which requires their preliminary
puriﬁ cation, especially in manufacture of cement clinker,
in which ﬂ uorine compounds are nearly inadmissible .
One of the most promising approaches to economically
feasible processing of phosphogypsum is that in which a
concentrate of rare-earth elements and a puriﬁ ed gypsum
product are obtained. The approach includes the sulfuric
acid leaching of REEs, recovery of Res from the leaching
solution, and neutralization of the purified gypsum
process to the pH value required by regulations.
The percolation sulfuric acid leaching provides
a high degree of purification to remove compounds
of phosphorus (to ≤0.5 wt % P
) and ﬂ uorine (to
0.001 wt %) for both PDH  and PHH . It is
recommended here to saturate phosphogypsum with
water and then displace the aqueous solution into which a
considerable part of phosphorus and ﬂ uorine compounds
passes with a sulfuric acid leaching solution and, at the
end of the process, displace the residual amount of the
leaching solution with water .
The agitation leaching with 26 wt % H
for 25 min at a ratio between the volume of the liquid
phase and the phosphogypsum mass, V
: s = 2 : 1, enables
effective puriﬁ cation of PHH to remove phosphates
. However, the efﬁ ciency of REE recovery into the
concentrate from a solution of this kind is insufﬁ cient .
Recently, it has been suggested to use the agitation
leaching of REEs with solutions containing ≤4 wt %
[8–11], from which REES can be quantitatively
sorbed by the sulfonic cation exchanger. However, the