United States Patent Office 3,305,322
Patented Feb. 21, 1967
1 2
is made by oxidizing the vanadium to the +5 state, adjusting
the acidity. to a pH at which ferric vanadate will
precipitate and heating to near boiling. The pH used
is normally above about 1.5 but this will depend upon
5 the amount of iron present. Iron is separated from the
precipitated ferric vanadate by heating the precipitate at
elevated temperatures with a'basic solution such as sodium
carbonate or sodium hydroxide, or roasted with sod£um
'carbonate or sodium chloride to convert the vanadium
10 to soluble sodium vanadate, leaving the iron undissolved
as hydrated ferric oxide. The last step for the recovery
or vanadium is essentially like that described for the
process above, 1. e., the solution is acidified to about
pHI and heated to precipitate the vanadium as vanadium
15 oxide.
In both of the procedures described above, the final
step is drying and fusing the vanadium oxide in a furnace
at high temperature. The melt is then discharged on a
cooling plate to form dense black flakes which is the
20 common item of commerce known as "black flake."
Both of the methods described above employ an oxidation
step and this is one of the largest items of chemical
cost. The least expensive of the commercially available
oxidants in terms of cost per equivalent weight is sodium
25 chlorate. Stoichiometrically, 0.22 lb. sodium chlorate per
lb. V20 5 is required and greater amounts are required
if other oxidizable materials are present in solution. The
total 'cost of sodium chlorate necessary for the oxidation
step is relatively high.
It would be highly advantageous to provide a method
using a solvent extraction or ion exchange pmcedure
which permits extraction of vanadium in the presence of
ferric iron. It is known that certain amines will extract +5 vanadium in the presence of ferric iron. Amines
35 which may be used are re'Presented by those disclosed in
U.S. Patents 2,877,250 and 2,455,019. Preferred amines
are the tri-'capryl and the tri-lauryl amines. However, the
use of oxidizing agents such as sodium chlorate to effect
the oxidation results in contamination and loss of ef-
40 ficiency of the solvent extraction or ion exchange agent.
More important, the use of amine and other extractants
to extract +5 vanadium has not been practical because
oxidation of the vanadiumprior to extraction in a solution
containing other oxidizable materials has been too expen-
45 sive. Prior attempts to find a ,cheapter oxidation process
for vanadium have included the use of S02 in procedures
similar to those used for oxidizing uranium as disclosed
in U.S. Patent 2,863,716. For various reasons these
attempts ha've met with failure.
Liquors which contain relatively low concentrations of
vanadium (less than 0.5 g. V20 5 per liter) are being discarded
because it is uneconomical to process them for the
recovery ,of vanadium by present methods. In most instances,
the reduction of ferric iron prior to vanadium
55 recovery by extraction with alkyl phosphates is the prohibitive
cost item.
Accordingly, it is 'an object of this invention to provide
an improved process for the oxidation of vanadium which
is more economical than present processes.
It is another object of this invention to provide a method
for the recovery of vanadium from its ores which is more
economical than prior art methods.
It is a further object of the invention to provide an
economical method for the oxidation of vanadium in the
65 recovery from its ores so that ,it can be recovered as V20 5•
I}t is still another object of. this invention to provide a
method for the recovery of vanadium with amine solvents
f!'Om leach solutions containing ,ferric i!'On.
70 It is another object of this invention to p!'Ovide a
method for recovery of vanadium from low-grade ores
which is economically· feasioble.
3,305,322
VANADIUM RECOVERY PROCESS EMPLOYING
802 GAS AS THE OXIDIZER
Angus V. Henrickson, Golden, Colo., assignor to Hazen
Research Inc., Golden, Colo., a corporation of
Colorado
No Drawing. Filed Dec. 23, 1963, Ser. No. 332,936
13 Claims. (Cl. 23-322)
This invention relates to a new process for the recovery
of vanadium; more particularly, it relates to a new method
for the oxidation of vanadium for recovery purposes.
The invention is illustrated herein by its application to
the oxidation of vanadium to its highest valence state for
recovery from its ores, and particularly, for recovery from
leach and strip liquor solutions. However, the invention
is not limited to this application as it is applicable to the
oxidation of vanadium for recovery purposes irrespective
of the type of solution in which it exists.
Vanadium is marketed almost exdusively as the oxide
vanadium pentoxide in which the metal has a valence of
5. This is largely because V20 5 is an insoluble compound
and conveniently recovered as such. Accordingly,
practically all methods for its recovery include the step
of oxidizing vanadium to the +5 state to permit its
recovery as V20 5•
Uranium and vanadium commonly exist together in
ores, such as, carnotite, or vanadium exists in ores in
which no uranium is present. In recovering vanadium
from both ,typeS of ores, the are is leached with sulfuric 30
add to dissolve vanadium in the +4 valence state ,and
the solution separated from the solid barren gangue material.
If a uranium-bearing ore is being treated, the
uranium is selectively recovered by ion e:1echange or solvent
extraction. The vanadium-containing solution in
either case also contains impurities such as iron, aluminum
and other soluble ore constituents. The solutions from
direct leaching to dissolve vanadium, or acid tailings from
uranium processing which contain vanadium ,are eSSen,
tially identical. In each 'case, a major part of the vana·
d£um exists in the +4 valence state and regardless of the
method used for its recovery from solution, ,an oxidation
step must be performed before it can be recovered
as V20 5•
The preferred method today for recovering vanadium
from leach liquors is by solvent extraction with an alkyl
phosphoric acid compound, such as, alkyl phosphoric
acid, dissolved in an appropriate diluent such as kerosene.
Vanadium is extracted by the solvent as an organic soluble
+4 vanadium alkyl phosphate complex. The pH of the 50
solution is maintained at 1.5-2.0 because this is the most
favorable range for extraction of 'Plus 4 vanadium. The
chief disadvantage of this process is the' fact that ferric
iron dissolved in the liquor is extracted by alkyl phosphoric
acid solvents under the same conditions as vanadium,
and contaminates the vanadium product as well as
seriously impairs the efficiency of the solvent in terms of
vanadium capacity. .To prevent the interference of ferric
iron with the recovery process, it is necessary to reduce
it to the ferrous state with a reducing agent such as 60
metallic iron prior to extraction. After extraction, vanadium
is ordinarily stripped from the solvent with a 10-15
percent solution of sulfuric acid and recovered from the
sulfuric acid solution by oxidation to the +5 valence state
followed by pH adjustment to about 1 and heating' to
precipitate a hydrated vanadium oxide. There are a
number of variants to the recovery process after extraction,
but in all of them the vanad£um is oxidized to the
+5 state before recovery as vanadium pentoxide.
Another method for recovering vanadium from acid
leach liquors or uranium tailings is based on the precipitation
of vanadium. as ferric vanadate. The precipitation
3,305,322
3
It has been found that the above and other objectives
can be accomplished by an 'improved process for the
oxidation of vanadium in solution in which the solution
is treated with sulphur dioxide and an oxy,gen"containing
gas such as air, in the presence 'Of iron. Sulphur dioxide 5
may be added in gaseous form or as sulphurous acid.
Oxidation of vanadium in solution can be accomplished
inexpensively with air with the use of techniques which
provide good gas and liquid contact. It ,is required that
,a small 'amount 'Of S02 be ,introduced with the air stream 10
or into the solution and that the solution contain iron as
a catalyst. A preferred pH range for the aeration process
is between about 1 and 3. The a'ir and S02 are introduced
by conventional means. Waste gases containing
oxygen, as well as other oxygen-containing gases can, of 15
course, be used. Oxygen alone in ,combination with sulphur
dioxide can be used but, of course, the cost is considered
prohibitive for most applications.
The time over which the air and 802 are introduced is,
of course, not critical; however, increase in the rate of 20
introduction up to a certain point will increase the speed
of the oxidation. The oxidation ,can be performed at
room temperatures.
The ratio of S02 to oxygen containing gas must be
maintained below a maximum as too large a ratio will 25
permit the 802 to act as a reducing agent. The upper
mole percent of 802 when used with air is about 7 and 8
mole percent. At concentrations greater than about 3
mole percent oxidation is incomplete. The lower limit
of the range is governed by what is practicable, as minute 30
amounts of S02 are operative; however the rate decreases
proportionally.
Likewise, the amount of iron present as a catalyst is
not critical; however, it has been found that an amount
of about 50 mg. per liter .and above is preferred in actual 35
practice.
The application of the process to the recovery of
vanadium from its 'Ores is as follows. The ore is crushed
and ground to the required fineness and digested with
sulfuric acid by conventional milling techniques. The 40
solution containing the dissolved vanadium in the +4
valence state is then separated from the solid barren
gangue material by filtration or countercurrent decantation
to produce a clear liquor which contains, in addition
to vanadium, impurities such as iron, aluminum, and 45
other soluble ore constituents. The same general dissolv,
ing method is 'applicable if the ore contains uranium.
If the are contains uranium, this metal is selectively reo
covered by conventional methods, such as ion exchange
or solvent extraction methods, and vanadium is left in 50
soluti'On along with impurities. Air is bubbled vigorously
through the leach solution with addition of 802 and incremental
replenishment of 802 by ,addition of 6 percent
sulfurous acid solution at a rate such that the mol ratio 55
of 802 to air is less than 3: 100. The pH of the solution
is maintained below the precipitation point of ferric
v,anadate and when the vanadium has 'all been oxidized
to the +5 state, it is extracted with tri-capryl amine solvent
and stripped with a base such as amm'Onium or 60
sodium hydroxide, or sodium carbonate. The pH of the
strip solution is then 'adjusted to .about 1 and heated to
precipitate vanadium as hydrated VzOs in the conventional
manner. Alternative precipitations well known to
the art can be used, such as the precipitation of vanadium 65
as ammonium vanadate or other saleable product.
In application of the process to recovery of vanadium
by the prior art ferric vanadate precipitation described
above, air and 802 in the presence of iron are again used
to perform the ·oxidation rather than sodium chlorate. 70
The pH of the solution is maintained within the precipitation
range of ferr.ic vanadate. Ordinarily, sufficient iron
is present in the leach solution to catalyze the reaction.
The following example was ,conducted as a study of 75
4
effective ·concentration 'Of 802 ,for oxidation of vanadium
in the presence 'Of iron.
Example I
500 ml. of solvent extraction raffinate containing 1.5
grams of reduced vanadium expressed as V20 S and approximately
0.75 gram of ferrous iron was used for the
test. Air was bubbled vigorously through the solution
at about 500 cc. per minute. S02 was added to the solution
and replenished incrementally by addition 'Of 6 percent
sulfurous acid solution. The pH of the solution was
maintained at about 1.5, this being below the precipitation
point of ferric vanadate for this solution. Change in
oxidation of iron and vanadium was followed by measurement
of E.M.F. with a platinum electrode and a calomel
reference electrode. The E.M.F. reading rose rapidly
from -390 to -450, a point indicating complete oxidation
of iron. Then the rate decreased significantly and
tended to drop to a lower negative value on each addition
of 802 and then gradually inoreased as the 802 was
purged. At this point the method of 802 addition was
changed so that the S02 was introduced in the air stream
through an aspirating stirrer. A low concentration of
802 was introduced through the impeller by placing the
mouth of a flask containing 6 percent 802 at the intake
of the impeller. The E.M.F. then rose steadily to -790.
At this point a sample of the solution was titrated potentiometrically
with permanganate to determine the extent
'Of oxidation. This indicated that the vanadium was 65
percent oxidized. This preliminary test was made without
measurement of absolute S02 concentration or rate of
air flow. However, it did show conclusively that iron
is oxidized rapidly at relatively high 802 concentrations
but that in order to oxidize vanadium, low concentrations
of 802 are necessary.
The following test was made as a study of the effect
of pH value on oxidation.
Example II
500cc. of a solvent extraction raffinate containing 1.15
grams of reduced vanadium expressed as V20 S and approximately
0.25 gram of ferric and ferrous iron per liter
expressed as ferric iron was treated in a reactor with 3
mol percent 802 in air at a rate of 100 cc. per minute.
The temperature was held constant at 50° C. and the acidity
was held constant at pH 2.0. The 'Oxidation was followed
by E.M.F. measurement using a platinum electrode
and a calomel reference electrode. In three hours the
E.M.F. rose from -319 to -540. At an £.M.F. of
-522, a slight precipitate of ferric vanadate started to
form indicating conclusively that oxidation of vanadium
was proceeding. At E.M.F. -540 the solution was
checked quantitatively with dilute permanganate and
showed that oxidation of vanadium was complete. The
test was repeated using a pH 'Of 1.5 with oxidation being
completed after three hours.
The above tests indicate that complete oxidation can
be obtained at pH 1.5 and 2.0. It was found that ferric
vanadate precipitates from the raffinate at a pH of about
2 or above while if the pH was held below about 2 no
ferric vanadate precipitated. If the solvent extracti'On
procedure is used the pH must be held below about 2 in
order to prevent the precipitation of ferric vanadate.
The following test was conducted to determine the
effect of 802 concentration on oxidation.
Example III
One liter 'Of tailings solution from a uranium recovery
operation containing about 1.5 grams of reduced vanadium
expressed as V20 S and approximately 0.75 gram
of ferrous and ferric iron per liter expressed as ferric iron
was treated 'with 3.0 mol. percent 802 in air at 500 cc;
per minute, at 50-60° C. The oxidation was followed by
E.M.F. measurement with a platinum elecrode and a calomel
reference electrode. After :90 minutes the E.M.F.
,
3,305,322
(References on following page)
6
The pro~ed~res described herein provide a new process
for the oXldatIOn of vanadium to its +5 state which is
~ighly efficient and. economical. The process makes posslble
the use of amme solvent extraction agents represented
by those disclosed above for recovering vanadium
from leach solutions in the presence of ferric iron. The
low cost of the reagents used for oxidizing the vanadium
makes the process economically attra'ctive. The process
is applicable to the recovery of vanadium from its ores or
lQ for reclaiming it from scrap metal, and is highly compatible
with the recovery of vanadium as V20 5•
Although the invention has been illustrated and described
with reference to the preferred embodiments
thereof, it is to be understood that it is in no way limited
15 to the details of such embodiments, but is capable of numerous
modifications within the scope of the appended
claims.
What is claimed is:
1. The process for the oxidation of vanadium in solu20
tion which comprises treating the solution with sulphur
dioxide and a medium containing oxygen gas in the presence
of ferric iron.
2. The process of claim 1 in which the medium containing
oxygen gas is air.
3. The process of claim 2 in which the percentage of
S02 in air extends up to about 7 mole percent.
4. The process of claim 3 in which the oxidation is
performed at a pH between 'about 1 and about 3.
5. The process of claim 3 in which sulphur dioxide is
30 added in the form of sulfurous acid.
6. The process for the recovery of vanadium from
leach solutions of its ores which comprises oxidizing the
vanadium to the plus five state with 802 and a medium
containing oxygen gas in the presence of ferric iron, and
35 recovering the vanadium in the plus five state.
7. The process of daim 6 in which the oxidation step
is performed at a pH below the precipitation point of
ferric vanadate, the vanadium in the plus five state is solvent
extracted from the leach solution, stripped from the
40 solvent and recovered from the strip solution as vanadium
pentoxide.
8. The process of claim 6 in which the oxidizing step
is conducted at a pH within the range for the precipitation
of ferric vanadate,and vanadium is recovered from the
45 ferric vanadate as V20 5•
9. The process of claim 6 in which the oxygen containing
gas is air and sulphur dioxide is present in amounts
extending up to about 7.5 mole percent.
10. The process of claim 9 in which sulphur dioxide
50 is added in the form of sulphurous acid.
11. The process for the recovery of vanadium from
material in which part of the vanadium exists in the
+4 state which comprises: comminuting the material;
leaching the material to form a leach solution of the
55 vandium; contacting the leach solution with air and 802
in a ratio of not more than about 7 mole percent of S02
to air at a pH between 1 and 3 in the presence of ferric
iron in solution to oxidize the vanadium to the +5 state;
and recovering the vanadium in the +5 state.
12. The process for the recovery of vanadium from
material in which at least part of the vanadium exists
in the +4 state which comprises: comminuting the material;
leaching the material to form a leach solution of the
vanadium; contacting the leach solution with air and S02
65 in a ratio of not more than about 7 mole percent of S02
to air at a 'pH between about 1 and the precipitation point
of ferric vanadate in the presence of ferric iron in solution
to oxidize the vanadium to the +5 state; extracting the
vanadium from the leach solution with an amine extract-
70 ant; stripping the vanadium from the extractant; and
recovering the vanadium in the +5 state.
13. The process of claim 12 in which the mole percent
of 802 to air is between about 3 and about 5.
75
so, concentra- Percent vanatioll,
lual per- E.M.F. dium oxidized
cent
3.0 736 100
3.5 690 90
4.6 670 75
5.6 630 50
7.6 500 0
5
rose from -440 to -736. A check of the solution at
this point showed no reduced vanadium was present in
the solution. At this point different samples of the solution
.were tested with different concentrations of 802,
holdmg at each concentration until the E.M.F. remained 5
stable. The degree of oxidation was then estimated from
the E.M.F. reading corrected to the pH of the control
at 3.0 mol percent 802' These data are given in the following
table.
The above data indicates that the concenration of S02
at which no oxidation occurs is between 7 and 8 mol percent,
and that in order to get complete oxidation the 802
cencentration must be less than about 3 to 3.5 mole percent.
The following test was run as a study of the lower
limit of S02 concentration in the oxidation process. 25
Example IV
A test run was made using 350 ml. of a synthetic vanadium
(IV) solution containing 100 mg. per Uter of ferric
iron.. Air containing no 802 was bubbled through the
solutIOn at 350 cc. per minute at 50° C. The oxidation
was followed /by measurement of E.M.F. with a platinum
electrode and a calomel reference electrode. After one
hour no change in the E.M.F has occurred. Titration
with permanganate verified the finding that no oxidation
of vanadium had occurred. Sulphur dioxide was then introduced
into the air stream at a concentration of 0.14
mol percent per liter. The E.M.F. started to rise. Samples
were removed at intervals of one-half hour, one
hour and two hours and titrated for oxidized vanadium.
At one-half hour, one hour and two hours 9.4 percent, 28
percent, and 47 percent, respectively, of the vanadium was
oxidized.
This test indicated that oxidation will proceed with the
use of incremental amounts of sulphur dioxide.
The following test was run to study the iron reqUirement
for the oxidationprocess.
Example V
350 ml. of a synthetic vanadium (IV) solution containing
no iron was used. 3 mol percent of S02 in air
was bubbled through the solution at a rate of 350 cc. per
minute at 50° C. The oxidation was followed by measurement
of E.M.F. with a platinum electrode and a calomel
reference electrode. The operation was continued
for two hours and the vanadium oxidation then checked
by titration with potassium permanganate. No oxidation
of vanadium had occurred. At this point ferric iron was
added to a concentration of 100 mg. per liter of solution.
The E.M.F. immediately started to rise from -380 and 60
leveled off at -640. The solution was then checked by
titration with permanganate and it was found that all
of the vanadium was oxidized.
This test indicates that the oxidation will not proceed
without the presence of ferric il'on. While incremental
amounts of iron will produce some catalytic effect,
amounts of 50 mg. per liter and above are preferred from
a practical standpoint.
Methods for the recovery of vanadium from leach solutions
once it has been oxidized to the +5 state are well
known to the art and are illustrated by such methods in
the prior art processes disclosed above. These methods
are used with the oxidation process described herein to
constitute a combined process for the recovery of vanadium
from its ores.
3,305,322
1,540,154
1,733,700
2,211,119
2,863,716
7
References Cited by the Examiner
UNITED STATES PATENTS
6/1925 Wittig 23-19
10/1929 Stevens et al. 23-23 5
8/1940 Hixson 23-19
12/1958 Thunaes et al.
8
FOREIGN PATENTS
157,555 1/1921 Great Britain.
CARL D. QUARFORTH, Primary Examiner.
BENJAMIN R. PADGETI, Examiner.
S. TRAUB, Assistant Examiner.