Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 8, pp. 1494−1497.
Pleiades Publishing, Ltd., 2009.
Original Russian Text
I.J. Kostiv, O.J. Ivanyuk, 2009, published in Zhurnal Prikladnoi Khimii, 2009, Vol. 82, No. 8, pp. 1394−1397.
Kinetics of the Carnallite Synthesis
I. J. Kostiv and O. J. Ivanyuk
Research Institute of Halurgy, Kalush, Ukraine
Vasily Stefanik Subcarpathian National University, Ivano-Frankovsk, Ukraine
Received October 23, 2008
Abstract— The kinetics of the carnallite synthesis from crystalline KCl and a MgCl
solution at temperatures from
20 up to 100ºC was studied. The temperature dependence of the conversion degree was determined. The activation
energy and the rate constant of the carnallite synthesis in the temperature range of 30−60ºC were determined.
Carnallite (KCl· MgCl
O) is used as a raw
material for the electrolytic production of magnesium
. It is synthesized from natural and anthropogenic
magnesium chloride raw material by the reaction
= KCl· MgCl
+ (n − 6)H
The limiting stage of the process is the KCl dissolution
in a concentrated solution with the composition point
located in the crystallization ﬁ eld of the system K
It is known  that the duration of particles
dissolution increases as their size increases, whereas
the dissolution rate and KCl solubility decrease as the
concentration increases. In its 35.5% solution the
solubility of KCl at 80°C is 1.8%.
Dissolved KCl reacts with excess MgCl
with a partial
carnallite formation on a surface of KCl crystals, which
hinders the further KCl dissolution. Intensive stirring
results in the destruction of the carnallite layer, which
has formed on the surface of KCl crystals .
To study the kinetics of the carnallite synthesis, we
used a solution of natural bischoﬁ te of the composition
(wt %): K
1.04, and Н
О 71.82 and also recrystallized
potassium chloride. We prepared a saturated solution
from pure-grade KCl, which was slowly dried in natural
conditions to form large crystals. They were separated,
crushed, and the fractions of size −0.5 and 0.2−0.315 mm
were sifted out. A solution of natural bischoﬁ te was
preliminarily desulfated by a 25% СаСl
precipitate of calcium sulfate was filtrated, and the
resulting solution was evaporated and ﬁ ltrated.
A solution of the composition (wt %): K
30.35 %), Cl
22.82, and Н
О 69.27 was
obtained. Its density was 1290 g dm
. The process
of carnallite synthesis was studied under isothermal
conditions at temperatures from 20 up to 100°C with
permanent stirring in a laboratory two-wall glass
temperature-controlled reactor with a stirrer. We ﬁ lled
250 ml of the solution in the reactor, heated it up to
a required temperature, and added 100 g of crystalline
KCl at permanent stirring. Samples of the suspension
were taken in 10, 20, 30, 45, 60, and 90 min, and ﬁ ltered
through a paper ﬁ lter in vacuum on a Buchner funnel.
The contents of K
in the resulting solid phases
and solutions were determined by the ﬂ ame-photometric
method, those of Mg
, by the chelatometric, and
, by the mercurymetric methods. Material balances
and mineral compositions of the obtained solid phases
were calculated on a PC by the results of the analyses.
The degree of KCl conversion in carnallite α (%) was
calculated by the formula