Note: Descriptions are shown in the official language in which they were submitted.
1()~;~5~7~
The present invention relates to the hydrometallurgy
of rare metals, and more particularly to a process for separa-
tion of tungsten and molybdenum by extraction from aqueous solu-
tions of chemical compoùnds thereof.
The separation of tungsten and molybdenum in aqueous
solutions of salts thereof is one of the most complicated prob- `
lems in the production of pure chemical compounds of tungsten,
such as ammonium paratungstate and tungstic acid, and hence, -
metallic tungsten.
At present only one commercial process for separation
of tungsten and molybdenum from aqueous solutions obtained after
the alkali decomposition of molybdenum-containing tungsten con-
centrate is known. This process, which is referred to as tri-
sulphide purification involves a precipitation of hardly solukle
molybdenum trisulphide from solutions containing sodium tung-
state and molybdate.
In this process, tungsten mainly remains in the aqueous
solution.
However, the process of trisulphide purification cannot
provide for a desired separation of tungsten and molybdenum with
a high content of molybdenum in tungsten concentrate, such as
with 4 - 5 w.% of molybdenum contained in scheelite concentrate.
About 0.1 w.% of molybdenum remains in tungstic acid, whereas
tungsten used for electronic and vacuum electronic techniques
should contain less than 0.02 w.% of molybdenum as impurity.
In addition, a considerable quantity of tungsten up
to 1 - 1.5 w.% of the starting content thereof in the aqueous
solution is lost with molybdenum sulphide precipitate.
The disadvantages of this process also include contam-
ination of environment with noxious sulphydrates formed in theproduction liquors during the trisulphide purification of tung-
sten from molybdenum.
During the decomposition of scheelite concentrates
10~35~;~2
with hydrochloric acid a separation of tungsten and molybdenum
also occurs. In this case, tungsten substantially completely
precipitates in the form of tungstic acid, and the main part of
molybdenum remains in the aqueous solution. It should be, how-
ever, noted that tungstic acid obtained after decomposition of
such concentrates with hydrochloric acid contains generally from
0.1 to 0.3 w.% of molybdenum, which is undesirable.
It is known the process of separation of tungsten and
molybdenum by extracting molybdenum with an organic extracting
13 agent - methyl isobutyl ketone or acetophenon from a sludge of
tungstic acid containing also hydrochloric acid. This method
permits to reduce the content of molybdenum in tungstic acid up
to 0.02 w.%.
The process conducted by this method requires, however,
a high consumption of hydrochloric acid of up to 8 tons per 1 ton
of tungsten concentrate so that such method cannot have any indus-
trial application.
Rapid and widespread development of such important
industries as electronic engineering, and electrovacuum technol-
ogy, production of pure compounds and the like impose stringentrequirements on the purity of metallic tungsten and molybdenum
and their compounds.
Necessity for complex, economic and rational utilization
of deposits of difficultly available tungsten and molybdenum con-
centrates and products makes very urgent the solution of the
problem of the provision of a new efficient process for separa-
tion of these metals.
The main difficulty lies in that molybdenum is a perman-
ent and difficultly separated impurity in tun~sten ores and pro-
duction liquors containing tungsten.
Difficulties in separating tungsten and molybdenum areassociated with the affinity of these metals. This circumstance
-- 2 --
1~4~5t7~
explains the fact that none of the above-described processes of
separating tungsten and molybdenum can provide for complete sep-
aration of the metals.
The attempts to separate tungsten and molybdenum by
extraction with organic extracting agents from aqueous solutions
of salts thereof have not gained expected results due to affinity
of tungsten and molybdenum.
The difficulties become still more serious due to the
fact that at pH less than 2 tungstic acid precipitates from aqu-
eous solutions containing tungsten, and molybdenic acid is pre-
cipitated therewith, while at pH from 2 to 7 tungsten and molyb-
denum form polyanions, for example, of the type
[H(W,M)6~21-a9]
and of another composition.
It is obvious, that over a large range of pH of an ~-
aqueous solution tungsten and molybdenum either precipitate or
are strongly bound into polymeric complexes. The both circum-
stances witness the impossibility of selecting the conditions for
complete separation of tungsten and molybdenum by extraction from
conventional aqueous solutions.
On the basis of theoretical and experimental tests, it
has been found that the process for separation of tungsten and
molybdenum by extraction should be carried out under qualitative-
ly new conditions, wherein these metals could be retained in the
solution over a wide range of pH without formation common com-
plexes in between them and have different chemical properties
and extraction ability.
The theoretical and experimental tests have shown that
the both conditions are provided by adding to a solution contain-
ing tungsten and molybdenum a complexing agent - hydrogen per-
oxide and preferably also water-soluble phosphorus compounds.
It has been found,that peroxide complexes of tungsten
io435q;~
and molybdenum formed after adding hydrogen peroxide to the 901u-
tion exhibit different chemical and extraction properties.
Tungstic acid will never precipitate at a~y pH of an
aqueous solution in the presence of hydrogen peroxide.
In addition, the degree of polymerization of tungsten
and molybdenum in an aqueous solution and their capability of
forming combined polymeric complexes are reduced.
Separation of tungsten and molybdenum by extraction
from such solutions is possible using neutral and ion-exchange
organic extracting agents.
It is the main object of the invention to provide a
process for separation of tungsten and molybdenum by extraction
which permits to obtain a solution of chemical compounds of tung-
sten containing substantially no mol~bdenum~from an aqueous
solution of chemical compounds thereof.
An important object of the invention is to increase the
degree of extraction of tungsten from 5 to 10 w.% into the high
quality end product - tungsten trioxide containing less than
0.005 w.% of molybdenum.
Still another object of the invention is to increase
the degree of extraction of molybdenum from 2 to 3 w.% as com-
pared to that obtained with the trisulphide purification.
It is also an object of the invention to simplify the
process for separation of tungsten and molybdenum and provide
the conditions for automation of the process.
A not least important object of the invention is to
eliminate contamination of environment with noxious production
wastes occurring with t~e trisulphide purification of tungsten
from molybdenum.
These objects are accomplished by the provision of a
process for separation of tungsten and molybdenum by extraction
with organic extracting agents from an aqueous solution of chem-
1(1~3S72
ical compounds thereof, wherein, according to the invention to
said solution there is added a complexing agent-hydrogen peroxide
in an amount from 1.5 to 2 mol per 1 g-atom of the total content
of tungsten and molybdenum and then an inorganic acid selected
from the group consisting of nitric, hydrochloric and sulphuric
acid to obtain pH of the solution from 0.5 to 1.8, whereafter
molybedenum is extracted from the resulting solution with neutral
or ion-exchange extracting agents with the volumetric ratio of
the aqueous solution to the organic solution of 1:1.5.
The process for separation by extraction according to
the invention provides for obtaining a solution containing chemi-
cal compounds of tungsten with molybedenum impurity from 0.001 to
0.003 w.%.
Besides, it has been found that it is necessary to
strictly maintain the above-described operating conditions in con-
ducting the separation of tungsten and molybdenum by extraction.
A decrease in the consumption of hydrogen peroxide below 1.5 mol
per 1 g-atom of the total content of tungsten and molybdenum re-
sults in a rapid destruction of peroxide complex of tungsten and,
hence, in a more rapid precipitation of tungstic acid and hampered
extraction conditions. An increase in the consumption of hydro-
gen peroxide above 2 mol per 1 g-atom of the total content of
tungsten and molybdenum is technologically unreasonable and may
only result in a needless consumption of hydrogen peroxide.
The above-specified range of pH provides for the most
complete separation of tungsten and molybdenum since maximum ex-
traction of molybdenum and minimum extraction of tungsten are
obtained within this range.
It has been found that the above-specified ratio be-
tween the volumes of organic and aqueous solutions (Vorg :Vfrom 1 to 1.5) is the optimal one since with a lower ratio the
coefficient of molybdenum distribution Emo is reduced resulting
-- 5 --
104~5'7Z
in an increased number of extraction stages and volume of ex-
traction equipment, and with an increase in this ratio the con-
sumption of organic extracting agent becomes greater and the con-
centration of molybdenum in organic extracting agent is lower.
The above-described complexing agent may be used with
water-soluble phosphorus compounds taken in an amount from 0.002
to 0.005 mol/l.
This permits to carry out the separating of tungsten
and molybdenum by extraction from production liquors containing
silicon, arsenic and phosphorus impurities.
It has also been found that a decrease or increase in
the amount of water~soluble phosphorus compounds added to the
production liquor as compared to the range from 0.002 to 0.005
mol/l results in an increased rate of destruction of hydrogen
peroxide and reduced efficiency of separation of tungsten and
molybdenum by extraction.
The separation of tungsten and molybdenum by extrac-
tion is preferably conducted using neutral extracting agents,
-such as tri-n-butylphosphate or tributylphosphineoxide from
aqueous solutions in the presence of nitric acid at pH from 0.5
to 1Ø
This permits to obtain maximum efficiency of purifica-
tion of tungsten from molybdenum with minimum number of produc-
tion stages.
The separation of tungsten and molybdenum by extrac-
tion from aqueous solutions using an ion-exchange extracting
agent, such as trioctylamine is preferably conducted in the pre-
sence of nitric acid within the pH range from 0.5 to 1.8 since
in this pH range an optimal separation of the metals is achieved.
The separation of tungsten and molybdenum by extrac-
tion from aqueous solutions using trin-butylphosphate is prefer-
ably effected in the presence of hydrochloric acid within the
-- 6 --
104;~5'7~
pH range from 1.5 to 1.8 to obtain an efficient separation and
sufficient stability of hydrogen peroxide.
The separation of tungsten and molybdenum by extraction
from aqueous solutions using trin-butylphosphate may be conduct-
ed in the presence of sulphuric acid within the pH range from
0.5 to 1.5 since it is in this range that a satisfactory separa-
tion of the metals takes place.
The invention will now be illustrated by examples of
specific embodiments of the process according to the invention.
Example 1
From an artificially prepared aqueous solution contain-
ing 19 g/l of tungsten and 1 g/l of molybdenum and acidified with
nitric acid to pH = 0.5 with a preliminary addition of hydrogen
peroxide used in an amount of 1.5 mol per 1 g-atom of the total
content of the metals 79 w.% of molybdenum were extracted at one
stage with tri-n-butylphosphate with the volumetric ratio of the
aqueous to organic solution of 1:1. Substantially no tungsten was
extracted.
After three sequential extraction stages with fresh
tri-n-butylphosphate with the volumetric ratio of the aqueous to
organic solution of 1:1 the content of molybdenum in the aqueous
solution was reduced to 0.01 g/l, the content of tungsten being
as high as 18.5 g/l.
The separation of tungsten and molybdenum by extraction
may be effected with an ion-exchange extracting agent such as a
salt of quaternary ammonium base from an aqueous solution in the
presence of nitric acid at pH from 2.5 to 2.8 or in the presence
of sulphuric acid at pH = 4.3.
In this example the separation by extraction may be
effected using an organic extracting agent comprising tri-butyl-
phosphineoxide with the same efficiency.
-- 7 --
\
1U43S7Z
Exam~le 2
0.003 mol/l of sodium pyrophosphate were added to an
artificially prepared aqueous solution of sodium tungstate and
sodium molybdate containing 78.65 g/l of tungsten trioxide,
4.7 g/l of molybdenum and 0.1 g/l of silicon. Then hydrogen
peroxide was added to the solution in an amount of 2 mol per
1 g-atom of the total content of tungsten and molybdenum and
nitric acid to obtain pH of 0.9. Subsequently the extraction
was conducted using trin-butylphosphate with the volumetric ratio
of the aqueous to organic solution of 1:1.
The test results have shown that the coefficient of
tungsten distribution DW was below 0.0045, whereas the coeffic-
ient of distribution for molybdenum DMo was equal to 4. 78.3 g/l
of tungsten trioxide and only 0.9 g/l of molybdenum were found
in the tungsten solution after the extraction. .
Example 3
0.005 mol/l of sodium pyrophosphate were added to a
production liquor obtained after decomposition of scheelite con-
centrate with soda containing 109.8 g/l of tungsten trioxide,
9.103 g/l of molybdenum, 0.15 g/l of silicon dioxide, 0.0045 g/l
of phosphorus, 0.003 g/l of arsenic, 25 g/l of sodium nitrate
and 3.5 g/l of sodium hydroxide. Then nitric acid was added to
the resulting solution to obtain pH of 0.5, and hydrogen peroxide
in an amount of 2 mol per 1 g-atom of the total content of tung-
sten and molybdenum.
The extraction was conducted with tri-n~butylphosphate
in a mixing and settling apparatus continuously in counter-cur-
rent with the ratio of flows of aqueous and organic solutions
of 1:1.5.
Throughput capacity of the apparatus was 6 l/hour of
the total flow of the organic and aqueous solutions, with the
~()435r~Z
volume of one section of the apparatus being equal to 2.5 1.
After eight extraction stages in an equilibrium aqueous
solution the content of tungsten trioxide was 102.8 g/l and the
content of molybdenum was lowered to 0.0033 g/l. The content of
tungsten in the organic solution was 7.0 g/l and the content of
molybdenum - 9.1 g/l.
The tests of re-extraction of molybdenum and tungsten
have shown that the both metals are extracted from tri-n-butyl-
phosphate in an aqueous solution containing 10 w.% of water and
about 8 w.% of sodium nitrate with four stages with continuous
counter-current operation and with the volumetric ratio of aque-
ous to organic solution of 1~
The resulting re-extracts contained from 14 to 16 g/l
of tungsten trioxide and from 18 to 20 g/l of molybdenum. 0.2 g/l
of tungsten trioxide and 0.002 g/l of molybdenum remained in the
organic solution.
Example 4
From a production liquor obtained after decomposition
of scheelite concentrate with soda containing 120 g/l of tungsten
20 trioxide, 5.8 g/l of molybdenum, 0.15 g/l of silicon dioxide, 0.005
g/l of phosphorus and 0.003 g/l of arsenic, after adding thereto
0.005 mol/l of sodium pyrophosphate, and 1.8 mol of hydrogen per-
oxide per 1 g-atom of the total content of tungsten and molybdenum
and hydrochloric acid to obtain pH of the solution about 1.5,
molybdenum was extracted with tri-n-butylphosphate continuously in
counter-current in a mixing and settling apparatus as described
; in Example 3.
With six extraction stages with the volumetric ratio
of aqueous to organic solution of 1:1.3 substantially the total
content of molybdenum was extracted from the solution. The con-
tent of molybdenum in the aqueous solution was lowered to 0.0035
g/l, and the content of tungsten trioxide in the aqueous solution
10435~2
was 113.2 g/l.
6.8 g/l of tungsten trioxide and 5.78 g/l of molybdenum
remained in the organic solution.
The re-extraction was conducted as de~cribed above.
Exam~le 5
Hydrogen peroxide was added to an artificially prepared
solution containing 98.5 g/l of tungsten and 9.6 g/l of molybdenum
in an amount of 2 mol per 1 g-atom of the total content of tung-
sten and molybdenum, and hydrochloric acid was then added to ob-
tain pH about 1.8. Molybdenum was extracted from the resultingsolution with tri-n-butylphosphate with the volumetric ratio of
the aqueous to organic solution of 1:1.86 w.% of moIybdenum and
only 2 w.% of tungsten were extracted in a single stage.
With four sequential re-extraction stages with a fresh
extracting agent the content of molybdenum in the aqueous solu-
tion of tungsten was lowered to 0.0016 g/l.
Example 6
Hydrogen peroxide in an amount of 1.5 mol per 1 g-atom
of the total content of tungsten and molybdenum was added to an
artificially prepared solution containing 19 g/l of tungsten
- and 1 g/l of molybdenum, and then sulphuric acid was added to
obtain pH - 0.65. Molybdenum, and partially tungsten were select-
ively extracted from the resulting solution using tri-n-butylphos-
; phate. Coefficient of molybdenum distribution was DMo = 3, co-
efficient of tungsten distribution was DW ~ 0.18. 80 w.% of
molybdenum and 15 w.% of'tungsten were transferred into the or-
ganic solution at a single extraction stage.
Molybdenum content in the aqueous solution was lowered
to 0.2 g/l, and the content of tungsten was as high as 16.5 g/l.
Example 7
~ itric acid was added to an artificially prepared solu-
tion containing 20 g/l of tungsten and 1 g/l of molybdenum to
-- 10 --
10435\7;~
obtain p~ , and then hydrogen peroxide was ad~ed to the solu-
tion in an amount of l.S mol per l g-atom of the total content
of tungsten and molybdenum.
Subsequently the extraction was effected with 15% solu-
tion of trioctylamine in kerosene with the volumetric ratio of
the aqueous to organic solution of l:l. Up to 80 w.% of molyb-
denum and about 3 w.% of tungsten were extracted in a single
stage.
We have also conducted physical and chemical studies
on the chemical states of molybdenum and tungsten in the pre-
sence of hydrogen peroxide and on the mechanism governing the
extraction of molybdenum from peroxide solutions.
We have found that, independently of the kind of in-
organic acid used, diperoxidemolybdenic acid and diperoxide-
tungstic acid of the general formula H2Me20ll(H20)2 are formed
in weakly acidic solutions.
It has been shown that the extraction of molybdenum
proceeds in conformity with the hydronium mech~nism. Molybdenum
is converted into the organic phase in the body of hydrosolvate
of the formula
[H30 tH2o) 3 3 TBP] 2 [M2ll (H20) 2 ]
Example 8
From an artificially prepared aqueous solution contain-
ing 19.6 g/l of tungsten and 0.9 g/l of molybdenum acidified with
sulfuric acid to obtain pH = 4.3, to which there was preliminarily
added hydrogen peroxide in the amount of 1.5 mole per l g-atom of
total content of metals, more than 90 w.% of rnolybdenum and 15
w.% of tungsten were extracted in a single stage with 0.1 molar
solution of quaternary ammonium tetraoctylammonium sulfate com-
pound in toluene. Coefficient of separation of metals was
~ = 73. Ratio of volumes of aqueous and organic solutions was
43~72
In this example, the separation of the above mentioned
metals may be as well carried out from their aqueous solutions of
nitric acid with pH from 2.5 to 2.8
