1070-4272/05/7810-1571 C 2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 10, 2005, pp. 1571!1575. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 10, 2005,
Original Russian Text Copyright + 2005 by Litvinov, Poilov.
AND INDUSTRIAL INORGANIC CHEMISTRY
Reduction of Sulfates with Oil Coke
in a Carnallite Melt
A. V. Litvinov and V. Z. Poilov
Perm State Technical University, Perm, Russia
Received April 7, 2005
Abstract-Purification of flotation carnallite to remove sulfates by their reduction in a melt was studied.
The optimal parameters of the reduction and the effect of various factors on this process were determined.
The mechanism of the process is suggested, and the results of industrial tests are given.
When passing to new raw materials for electrolytic
production of metallic magnesium and, in particular,
to flotation carnallite, brucite, or serpentinite, a neces-
sity arises for additional purification of the molten
magnesium electrolyte to remove sulfates. It is known
that sulfate admixtures contained in the electrolyte sub-
stantially impair the current efficiency by magnesium
and disrupt the operating mode [1, 2]. At a sulfate
content in anhydrous carnallite exceeding 0.05 wt %,
the current efficiency sharply decreases. A froth ap-
pears on the electrolyte surface and the electrolyte
circulation is enhanced, which results in that the slime
is stirred up and passivates the cathodes .
The procedures developed for purification of the
molten magnesium electrolyte to remove sulfate ad-
mixtures by reduction with natural gas, carbon oxide,
and magnesium  have been only implemented
on laboratory installations. Their commercial use
appeared to be unfeasible owing to the high fire
and explosion hazard. In this study, we developed
an efficient commercial procedure for removing sul-
fate admixtures from the melt of flotation carnal-
We used as a raw material for laboratory studies
four batches of flotation carnallite produced in labora-
tory by the flotation technique (VNIIG, St. Petersburg).
They contained different amounts of calcium sulfate
(0.07, 0.39, 0.55, and 0.68 wt %). We also used arti-
ficially contaminated halurgic carnallite containing
0.531.0 wt % sulfate ions.
When studying the removal of sulfate ions from
an electrolyte melt, we simulated the processes oc-
curring in the chambers of an industrial chlorinator:
in the melting pot, in chlorinating chambers, and in
the mixer (settling tank). We studied the removal of
sulfate ions from the melt at 5003800oC (temperature
profile of the chlorinator) in a reactor into which
chlorine was fed to simulate the operation of chlori-
nating chambers, and argon, for a more complete
mixing of the components. We determined the resid-
ual content of sulfate ions by photocolorimetry or
We used as reducing agents activated carbon and
oil coke, and metallic magnesium for comparison.
The data obtained for a model carnallite melt with
various reducing additives are presented in Figs. 1
Fig. 1. Concentration c of sulfate ions in the carnallite
melt vs. the weight ratio A between the amount of the re-
ducing additive and CaSO
. Process duration 1 h, T =
C, initial content of sulfate ions 1.0 wt %. Reducing
agent: (1) oil coke, (2) metallic magnesium, (3) activated
carbon; the same for Fig. 2.