320
V. Malyshev et al.
Following separation of Li 2 CO 3 from the solution, tungsten is isolated in the
form of tungstic acid. After leaching of the cathode deposit, the filtrate contains
60–80 g/l tungsten. Prior to deposition, the solution is concentrated by evaporation
to 100 g/l W. Hydrochloric acid is used to produce the deposit. The nature of the
deposit thus obtained depends on the concentration of the initial solution and the
method of deposition employed. Poorly filtered deposits of white tungstic acid, i.e.,
hydrated tungsten trioxide, are obtained from cold and dilute solutions. To obtain
easily filtered yellow tungstic acid (H 2 WO 4 ) heated to T = 60–80 ◦ C, a concentrated
solution of tungstates is poured into a boiling HC1 solution (1:1) to which a small
quantity of HNO 3 is added to prevent partial reduction of the tungsten. The quantity
of hydrochloric acid is calculated on the basis of the fact that the concentration of
free HC1 in the final solution must be in the range 7–10%. After the entire solution
has been mixed together, the pulp is poured through a filter. The H 2 WO 4 deposit
is washed in a filter in a 2% HNO 3 solution until it produces a negative reaction to
chlorine ions.
The washed H 2 WO 4 deposit is dried and calcined to a constant mass at
T = 500 ◦ C. At this temperature, tungstic acid completely loses all water in the
course of being turned into tungstic acid anhydride:
H 2 WO 4 → WO 3 + H 2 O.
(2)
The yield of WO 3 amounts to 97–98% of the computed quantity in the electrolyte
or bulb. Recycled lithium carbonate and tungsten trioxide are employed as reusable
reagents for preparing adjusting addition agents.
19.4 Conclusions
1. It is established that free alkali Li 2 O, a product of thermal decomposition of
lithium carbonate, accumulates in the course of isothermal heating in a Na 2 WO 4 -
Li 2 WO 4 -Li 2 CO 3 melt.
2. In lengthy electrolysis of tungstate-carbonate melts for the purpose of producing
carbide with the stoichiometry of tungsten carbide, a constant concentration of
the carbonate in the melt must be maintained.
3. It is shown that the phase composition of the cathode deposit is determined
largely by the content of lithium carbonate in the melt.
4. Methods were developed in the study for use in washing cathode deposits and in
recovery of tungsten and lithium from spent electrolyte and carbide-salt deposits.
V. Malyshev et al.
Following separation of Li 2 CO 3 from the solution, tungsten is isolated in the
form of tungstic acid. After leaching of the cathode deposit, the filtrate contains
60–80 g/l tungsten. Prior to deposition, the solution is concentrated by evaporation
to 100 g/l W. Hydrochloric acid is used to produce the deposit. The nature of the
deposit thus obtained depends on the concentration of the initial solution and the
method of deposition employed. Poorly filtered deposits of white tungstic acid, i.e.,
hydrated tungsten trioxide, are obtained from cold and dilute solutions. To obtain
easily filtered yellow tungstic acid (H 2 WO 4 ) heated to T = 60–80 ◦ C, a concentrated
solution of tungstates is poured into a boiling HC1 solution (1:1) to which a small
quantity of HNO 3 is added to prevent partial reduction of the tungsten. The quantity
of hydrochloric acid is calculated on the basis of the fact that the concentration of
free HC1 in the final solution must be in the range 7–10%. After the entire solution
has been mixed together, the pulp is poured through a filter. The H 2 WO 4 deposit
is washed in a filter in a 2% HNO 3 solution until it produces a negative reaction to
chlorine ions.
The washed H 2 WO 4 deposit is dried and calcined to a constant mass at
T = 500 ◦ C. At this temperature, tungstic acid completely loses all water in the
course of being turned into tungstic acid anhydride:
H 2 WO 4 → WO 3 + H 2 O.
(2)
The yield of WO 3 amounts to 97–98% of the computed quantity in the electrolyte
or bulb. Recycled lithium carbonate and tungsten trioxide are employed as reusable
reagents for preparing adjusting addition agents.
19.4 Conclusions
1. It is established that free alkali Li 2 O, a product of thermal decomposition of
lithium carbonate, accumulates in the course of isothermal heating in a Na 2 WO 4 -
Li 2 WO 4 -Li 2 CO 3 melt.
2. In lengthy electrolysis of tungstate-carbonate melts for the purpose of producing
carbide with the stoichiometry of tungsten carbide, a constant concentration of
the carbonate in the melt must be maintained.
3. It is shown that the phase composition of the cathode deposit is determined
largely by the content of lithium carbonate in the melt.
4. Methods were developed in the study for use in washing cathode deposits and in
recovery of tungsten and lithium from spent electrolyte and carbide-salt deposits.