1110
RYABTSEV et al.
solutions of LiOH. A solution was evaporated to a
LiOH concentration in solution of 170 180 g l .
Then, the evaporated solution was cooled in a closed
flask to room temperature and the crystals formed
were rapidly filtered off. The product was dried in
a desiccator at room temperature and then analyzed
for the content of impurities and subjected to washing.
the whole amount of PbO quantitatively dissolved.
2
1
The concentration of lead in solution was determined
by EDTA titration, with Xylenol Orange as indicator,
at pH 5.5 [15]. The concentrations of Cl and O
2
3
in the gas phase were determined by photocolorimetry
on a KFK-2MP instrument [16].
The procedure for obtaining high-purity LiOH
H O from technical-grade Li CO is shown in
The mother liquor, which is a saturated solution of
LiOH with impurities, was recycled into the stage
of evaporation and crystallization, and so on. This
yielded, each time, crystals and mother liquors in-
creasingly contaminated with impurities. A total of
five different samples were obtained.
2
2
3
Scheme 1.
According to the scheme suggested, a Li SO
2
4
solution is obtained from H SO and Li CO [reac-
2
4
2
3
+
+
tions (1), (2)]. In the process, impurities of Na , K ,
2+
2+
3+
3+
2
Ca , Mg , Al , Fe , SiO , and Cl ions will also
3
The resulting LiOH H O samples were, each
2
pass into solution from technical-grade Li CO . Some
2
3
separately, washed to remove impurities with a pure
saturated solution of LiOH in accordance with a
scheme of three-stage batch washing with phase mix-
ing; the l : s ratio was 1 : 1 for each stage.
of these impurities can impair the quality of the result-
ing LiOH solution and disturb the course of elec-
trolysis to the point of its complete termination. This
primarily refers to cations that tend to form poorly
soluble compounds on coming in contact with alkali
formed in the cathode chamber. Therefore, prior to
delivering the Li SO solution to electrochemical
The washed LiOH H O samples were dried, and
2
the residual content of impurities in them was deter-
mined.
2
4
conversion, it should be alkalized to pH 11 12 in
order to precipitate these impurities in the form of
poorly soluble compounds [reactions (4) (9)]. The
purified Li SO solution is fed into the anode
A mother liquor formed after crystallization, which
is a saturated LiOH solution contaminated with Na, K,
and Ca ions, was placed in a vessel for carbonation,
into which CO was fed from a cylinder at a rate of
2
4
2
1
chamber of the electrolyzer. In the course of electroly-
sis, water is oxidized electrochemically at the anode to
0.3 l min through a gas-distribution unit. The carbo-
nation was performed in the bubbling mode to pH
12.3 to prevent formation of lithium hydrocarbonate.
+
give gaseous O and H ions by reaction (10).
2
The cathode space is filled with a dilute LiOH
solution, with the electrochemical reduction of water
The resulting suspension was separated by filtra-
tion, after which the precipitate was washed on the
filter with a threefold volume of distilled water, dried
in a desiccator, and analyzed for the content of im-
purities.
occurring at the cathode to give gaseous H and OH
2
ions by reaction (12). The cation-exchange membrane
separating the cathode and anode spaces of the elec-
+
trolyzer ensures free transfer of cations (mainly Li )
The conventional analytical techniques were used
in the study. The concentration of Li, K, and Na ions
was determined by the spectral method on a Philips
AAS-SP-9 atomic-absorption spectrophotometer [10];
that of calcium and magnesium ions, by EDTA titra-
from the anode space of the electrolyzer into its cath-
ode space under the action of an electric field and
precludes transfer of anions. As a result, a fairly pure
LiOH solution concentrates in the cathode chamber
[reaction (13)]. The main ingredients that contaminate
+
tion [11]; that of OH and H ions, by titration with
+
+
LiOH will be Na and K , which are present in the
anolyte and cannot be removed from the anolyte in
the stage of its alkaline purification preceding the
electrolysis. Therefore, these cations will also freely
a 0.1 N solution of HCl or KOH, respectively [12];
and that of chloride ions, by mercurimetric titration,
with nitroprusside as indicator [13]. Sulfate ions were
determined in solutions with their concentration ex-
+
pass, together with Li cations, into the cathode
1
ceeding 1 g l by volumetric EDTA titration [14],
chamber and thereby contaminate the product [reac-
tions (14), (15)].
and in cases when the concentration of these ions was
1
lower than 1 g l , by the nephelometric method on a
KFK-1 photocolorimeter [12]. The accuracy of deter-
The thus obtained LiOH solution containing a cer-
+
+
mination was 5%. The formation of PbO in the sys-
tain amount of Ba and K impurities is delivered to
the stage of evaporation and crystallization of LiOH
H O and is, in part, used to alkalize the Li SO solu-
2
tem under study was monitored as follows. The pre-
cipitate was filtered off and then boiled, together with
the filter, in a mixture of HNO with H O , with
2
2
4
tion before the electrochemical conversion.
3
2 2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 77 No. 7 2004
Ryabtsev
