Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 11, pp. 1925−1929.
Pleiades Publishing, Ltd., 2010.
Original Russian Text © L.A. Voropanova, L.G. Baratov, V.N. Kovalev, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 11, pp. 1793−1797.
INORGANIC SYNTHESIS AND INDUSTRIAL
Dehydration of Zinc Hydroxide Precipitate Produced
by Neutralization of Weakly Concentrated Zinc Sulfate Solutions
with Aqueous Ammonia
L. A. Voropanova
, L. G. Baratov
, and V. N. Kovalev
North-Caucasian Institute of Mining and Smelting (State Technological University),
Vladikavkaz, Ossetia, Russia
Polymetal Engineering Private Company, St. Petersburg, Russia
Received November 11, 2008
Abstract—Method for dehydration of zinc-containing products is suggested. The method makes lower the energy
expenditure in ﬁ ltration, drying, and calcination, diminishes the expenditure of reagents, and improves ecological
characteristics of the process.
Precipitation of zinc hydroxide with aqueous
ammonia yields a poorly ﬁ lterable precipitate. Even
after two or three washings, the thus obtained precipitate
(moisture content 400–500%) contains a large amount
of water-soluble impurities captured together with
the mother liquor in precipitation of the hydroxide.
Dehydration of such a precipitate requires calcination in
a rotating tubular furnace (900–950°C) .
Treatment of concentrated zinc sulfate solutions
containing 100 g dm
of Zn(II) with 25% aqueous
ammonia leads to precipitation of zinc hydroxo sulfates
OH = 3Zn(OH)
Even on being twice washed with water, the precipitate
contains a large amount of the SO
ion (up to 20%)
in the compound 3Zn(OH)
, and, therefore, the
calcination temperature should be raised to 900–950°C.
To avoid this difﬁ culty, the precipitate of basic zinc
sulfate salts is treated with a solution of ammonium
carbonate or hydrocarbonate, with a concentration of
40–100 g dm
. In this case, the exchange reaction
results in that the content of the sulfate ion in the
precipitated basic zinc carbonate decreases from 20 to
3%. Replacement of sulfate ions with carbonate ions
makes lower the calcination temperature. At a <3%
content of the SO
ion in the precipitate, it was dried
and calcined at 750°C.
Precipitation from weakly concentrated solutions
yields, together with basic zinc sulfate, a poorly
ﬁ lterable amorphous precipitate of zinc hydroxide,
which involves difﬁ culties in its further treatment with
ammonium carbonate or hydrocarbonate and leads to
a gross expenditure of these reagents; drying of the
precipitate and its calcination at 750°C are accompanied
by release of a large amount of carbon(IV) oxide and
In the present study, we demonstrated the possibility
of a fast and efﬁ cient dehydration of zinc hydroxide
produced from weakly concentrated zinc sulfate
Zinc hydroxide is precipitated from a solution
containing 100 mg dm
of the Zn(II) ion with aqueous
ammonia added to pH 8–9. The precipitated zinc