5,882,620
Mar. 16, 1999
[11]
[45]
111111111111111111111111111111111111111111111111111111111111111111111111111
US005882620A
Patent Number:
Date of Patent:
United States Patent [19]
Downey et al.
[54] PYROMETALLURGICAL PROCESS FOR
FORMING TUNGSTEN CARBIDE
5,372,797 12/1994 Dunmead et al. 423/439
FOREIGN PATENT DOCUMENTS
[75] Inventors: Jerome P. Downey, Parker; Peter W.
Siewert, Littleton, both of Colo.
[73] Assignee: International Carbitech Industries,
Inc., Vancouver, Canada
223726
476496
808370
954472
WO 90/08103
A
8/1958 Australia 423/440
8/1951 Canada 423/440
2/1981 U.S.S.R 423/61
8/1982 U.S.S.R 423/61
7/1990 WIPO.
Re.32,612
667,705
1,839,518
3,012,877
3,077,385
3,256,057
3,266,875
3,330,646
3,373,097
3,589,987
3,676,105
3,716,627
3,800,025
4,190,439
4,353,881
4,402,737
4,489,044
4,504,461
4,534,956
4,603,043
4,629,503
4,752,456
5,096,689
5,102,646
5,188,810 36 Claims, 4 Drawing Sheets
(List continued on next page.)
Primary Examiner~teven Bos
Attorney, Agent, or Firm~heridan Ross, Pc.
ABSTRACT
OTHER PUBLICATIONS
[57]
Kirk-Othmer Encyclopedia of Chemical Technology, Edition
3, vol. 23, 1987, Wiley & Sons, New York
XP002062951, pp. 417-419.
John M. Gomes, Kenji Uchida, Don H Baker, Jr., "A
High-temperature, Two-phase Extraction Technique for
Tungsten Minerals", United States Department of the Interior,
Bureau of Mines, Report of Investigations 7106, 1968,
no month.
J.M. Gomes, A.E. Raddatz, T.G. Carnahan, "Preparation of
Tungsten Carbide by Gas Sparging Tungstate Melts", Reno
Research Center, Bureau of Mines, United States Department
of the Interior, Presented at the 3rd International
Tungsten Symposium, Madrid, Spain, May 13-17, 1985.
J.M. Gomes, A.E. Raddatz, T.G. Carnahan, "Preparation of
Tungsten Carbide by Gas Sparging Tungstate Melts", Journal
of Metals, pp. 29-32, Dec., 1985.
A process for forming a salt, such as sodium tungstate, using
a pyrometallurgical operation is provided. A slagging operation
is performed in which a metal-containing material is
melted in the presence of slag formers such as sodium
metasilicate and silica. The metal predominantly reports to
a denser metal-containing phase. The denser metalcontaining
phase may then be subjected to gas sparging with
a carbon-containing gas in order to form metal carbide,
preferably tungsten carbide.
2/1988 Gomes et al. .
2/1901 Holloway et al. 423/61
1/1932 Woods et al. 423/440
12/1961 Foos et al. 75/622
2/1963 Robb 423/440
6/1966 Burwell.
8/1966 Romeo 423/440
7/1967 Heinen et al. 423/439
3/1968 Gomes et al. .
6/1971 Gomes et al. .
7/1972 McLeod et al. 75/10.18
2/1973 Middelhoek 423/440
3/1974 Fox 423/61
2/1980 Gortsema 423/439
10/1982 Quatrini et al. 423/58
9/1983 Kronenwetter et al. .
12/1984 Gomes et al. .
3/1985 Carpenter et al. .
8/1985 Arendt et al. 423/DIG. 12
7/1986 Douglas et al. 423/61
12/1986 Fruchter et al. 423/61
6/1988 Yoda et al. 423/439
3/1992 Terry et al. 423/DIG. 12
4/1992 Bienvenu 423/439
2/1993 Sommers 423/439
Appl. No.: 482,129
Filed: Jun. 7, 1995
Int. CI.6 COlB 31/34; C22B 34/00
U.S. CI. 423/440; 423/439; 423/53;
423/61
Field of Search 423/DIG. 12, 439,
423/440, 53, 61; 75/10.15, 10.18, 612,
622,623
U.S. PATENT DOCUMENTS
References Cited
[21]
[22]
[51]
[52]
[58]
[56]
5,882,620
Page 2
OlliER PUBLICATIONS
John M. Gomes, M.M. Wong, "Preparation of Tungsten
Carbide by Electrodeposition", United States Department of
the Interior, Bureau of Mines Report ofInvestigations 7247,
1969, no month.
John H. Gomes, Kenji Uchida, M.M. Wong, "Electrolytic
Preparation of Tungsten Metal and Tungsten Carbide from
Wolframite", United States Department of the Interior,
Bureau of Mines Report of Investigations 7344, 1970, no
month.
S. Hessel, B. Shpigler, O. Botstein, "A New Process for
Production of Tungsten , Tungsten Carbide, and Tungsten
Oxide Powders", Reviews in Chemical Engineering, vol. 9,
pp. 345-364, No. 3-4, 1993, no month.
E. Vil'nianski and Z.L. Persits, "The Theory of the SodaSilica
Process for the Production of Sodium Tungstate From
Scheelite", Journal of Applied Chemistry of the USSR, vol.
21, No.5, pp. 663-667, May, 1958.
Metallurgy of Rare Metals, 2nd Ed., pp. 12-18,24,25,1964,
no month.
u.s. Patent Mar. 16, 1999 Sheet 1 of 4 5,882,620
PARTICULATES 48
PARTICULATE
CONTROL 46
SPARGED
SPENT SALT 51
TUNGSTEN·CONTAINING 1-.-......-(
CONCENTRATE 12
COMMINUTED AND ACID LEACHED WC SUSPENSION 74
SOLIDILIQUID
SEPARATION 76
NEUTRALIZATIONJ
PRECIPITATION 82
Fig. 1
u.s. Patent Mar. 16, 1999 Sheet 2 of 4 5,882,620
1Liquid
W03
738'
625'
A=825t3'C
B= 78StS'C
System Na20-Si02-W03' (A) 1200'C; (B) liquidus.
Fig. 2
Air Compressor
126 ~122
r 15< 0 I To Atmosph:re
Draft Fan
I ! Bubbling Scrubber
140
142
Cooling Air
Intake
d•
'JJ.
•
~
~.....
~=.....
~
~
:-'l
~'"~"'"
''"0"'"
'0
'0
'JJ. =~
~....
~
o....,
~
Tilting Furnace
110
Schematic Diagram of the Pilot·scale Siagging System
Fig. 3 ...U. l
00
00
...N.
0\
N=
'JJ. =~
~....
d•
'JJ.
•
~
~.....
~=.....
~
o....,
~
~
~
:-'l
~'"~"'"
''"0"'"
'0
To Atmosphe..re '0
138
Baghouse
Fugitive Exhaust
Capture
Dust
.................. .................. ..................
150 i , < To Atmosph:re
142
Cooling Air
Intake
Cooling
Coil
i8'
6
Flowmeter
°2 144
C2H4
Or 128
CH4
N2
127
Liquid N2
120 Tilting Furnace
110
Schematic Diagram of the Pilot-scale Sparging System
Fig. 4
...U. l
00
00
...N.
0\
N=
5,882,620
2
SUMMARY OF IRE INVENTION
In accordance with one embodiment of the invention, a
method is provided for concentrating the metal in a metalcontaining
material by employing a pyrometallurgical
operation. The pyrometallurgical operation includes a heating
step in which the metal-containing material is heated in
the presence of at least one sodium or potassium compound
40 to melt the metal-containing material and form a high
density metal-containing phase and a low density slag phase.
The majority of the metal reports to the high density
metal-containing phase. The two phases are immiscible and
the high density metal-containing phase separates by gravity
from the low density slag phase. Because of its higher
density the high density metal-containing phase will settle to
the bottom of a furnace crucible. The two phases can then be
separated. Preferably, the high density metal-containing
phase is subjected to a second pyrometallurgical operation,
i.e., sparging with a carbon-containing gas, to form metal
carbide.
Although the methods of the present invention have been
found particularly applicable to tungsten-containing
materials, the methods can be employed to recover other
metals from metal-containing materials. Examples of such
other metals are Group III-B metals (e.g., thorium), Group
IV-B metals (e.g., titanium, zirconium, hafnium), Group V-B
metals (e.g., vanadium, niobium, tantalum), Group VI-B
metals (e.g., tungsten) and Group VII-B metals (e.g., manganese
and rhenium). More preferred are refractory metals
such as tungsten, titanium and tantalum. Most preferred are
tungsten-containing materials. Examples of tungstencontaining
materials include tungsten ores such as huebnerite
(MnW04), scheelite (CaW04), ferberite (FeW04 ) and
wolframite ((Fe,Mn)W04 ). Additionally, the method of the
present invention can be effective with other tungstencontaining
materials such as flue dusts and various secondare
rejected to the slag phase. The viscous slag is more dense
than the salt and settles to the bottom of the furnace crucible.
The salt phase, which chiefly consists of sodium chloride
and sodium tungstate, is forwarded to a second stage for
5 processing into tungsten carbide.
A problem with the methods described above is that the
lower density tungsten-containing phase also includes a
halide salt (e.g., sodium chloride). During subsequent sparging
operations, this halide salt volatilizes and deposits within
10 various components of the gas handling system. This accretion
of salt eventually leads to downtime in order to clear the
obstructions. The sodium chloride also represents an operating
cost. Additionally, the sodium chloride is extremely
corrosive and its presence increases the cost of the materials
15 due to the need to employ corrosion resistant materials and
results in higher operating costs due to the corrosion.
Furthermore, the sodium chloride dilutes the sodium tungstate
in the sparging operation, effectively reducing the
chemical activity of the tungstic oxide (W03 ).
It would be advantageous to provide a method for forming
metal carbide (e.g., tungsten carbide) from a metalcontaining
mineral using a pyrometallurgical process.
Additionally, it would be advantageous to form metal (e.g.,
tungsten) carbide without the need for forming a fused
25 metal-halide salt. It would be advantageous to provide a
process in which a majority of the tungsten input to the
system is converted to tungsten carbide. It would be advantageous
to provide a process in which tungsten carbide can
be formed efficiently and economically without a large
30 amount of system downtime.
BACKGROUND OF THE INVENTION
1
PYROMETALLURGICAL PROCESS FOR
FORMING TUNGSTEN CARBIDE
FIELD OF THE INVENTION
The present invention is directed to the pyrometallurgical
treatment of metal-containing materials and, in a preferred
embodiment, the formation of tungsten carbide using a two
stage pyrometallurgical process.
Two stage processes for producing tungsten carbide (We)
are known. For example, in U.S. Pat. No. 3,373,097 entitled
"Method For Separation Of A Metal-Containing Halide
Phase From A Gangue-Containing Silicate Phase and Electrolysis
of Halide Phase To Obtain The Metal" by Gomes et
aI., issued Mar. 12, 1968, a process for producing tungsten
carbide is disclosed. The process involves a molten phase
separation employing sodium chloride (NaCI) in which the
tungsten reports to a less dense upper halide phase while 20
impurity elements such as calcium, manganese and iron are
recovered in a denser lower silicate phase. The separation is
effected by heating a mixture of halide salts, concentrates of
either scheelite (CaWO4) or wolframite ((Fe,Mn)WO4)' and
a slag former such as sodium silicate to 900° C. to 1,100° C.
After fifteen minutes to an hour at the elevated temperature,
the phase separation is completed and the halide phase is
decanted for processing by molten salt electrolysis.
U.S. Pat. No. 4,489,044 entitled, "Formation Of Tungsten
Monocarbide From A Molten Tungstate-Halide Phase By
Gas Sparging" by Gomes et aI., issued Dec. 18, 1984,
reissued as Re 32,612 on Feb. 23, 1988, discloses a process
for producing tungsten carbide. The process involves the
formation of a sodium chloride/sodium tungstate (Na2WO4)
phase by molten phase separation, similar to the process 35
described above. The tungsten monocarbide is produced by
sparging the melt of sodium chloride and sodium tungstate
with a hydrocarbon gas, particularly methane (CH4 ) or
natural gas. According to the disclosure, other alkali halides
can be substituted for sodium chloride.
In May, 1985, Gomes, Raddatz and Caranahan made a
presentation at the Third Tungsten Symposium in Madrid,
Spain (May 13-17, 1985) regarding a two step technique for
producing a granular tungsten carbide powder directly from
scheelite or wolframite concentrates. The concentrates were 45
first reacted at 1,050° C. with a sodium chloride/sodium
metasilicate (Na2Si03 ) melt. The reaction produces two
immiscible liquids: a lighter tungstate-halide (NaClNa
2W04) phase containing 99 percent of the input tungsten
and a denser silicate slag phase containing 90 to 96 percent 50
of the iron, manganese and calcium oxides. After phase
separation, the tungstate-halide phase is sparged with methane
gas in a second step to yield granular tungsten carbide.
The tungsten carbide is recovered from the reactor by
decanting excess salt, cooling, water leaching and scraping. 55
See "Preparation of Tungsten Carbide by Gas Sparging
Tungstate Melts", Gomes et aI., Journal ofMetals, December
1985, pps. 29-32.
The processes described above all include an initial
slagging operation in which a tungsten concentrate is com- 60
bined with a siliceous flux and sodium chloride (other halide
sources can be substituted). The tungsten compounds contained
in the concentrate (e.g., calcium, iron, or manganese
tungstates) react with the sodium chloride and the sodium
silicate to produce two immiscible phases: a molten salt and 65
a molten silicate slag. The tungsten preferentially reports to
the molten salt phase, while the majority of the impurities
5,882,620
3 4
centrate 12 together with silica 14 and sodium silicate 16 are
introduced into a slagging furnace 18. The slagging furnace
18 is heated to a temperature in the range from about 900°
C. to about 1,200° c., preferably from about 1,050° C. to
about 1,150° C. and more preferably to approximately
1,050° C. for approximately 0.5 to 2.0 hours. The feed
materials separate into two immiscible phases. A higher
density tungsten-containing phase (tungstate) 20 settles to
the bottom of the furnace crucible due to gravity and a less
dense slag phase (silicate) 22 segregates to the upper portion
of the furnace crucible. The higher density tungstencontaining
phase 20 is introduced into a sparging furnace 24.
The lower density slag phase 22 can be disposed of, or
subjected to further treatment. The higher density tungstencontaining
phase 20 can be separated from the lower density
slag phase 22 by any number of appropriate processes. For
example, the higher density phase 20 and lower density
phase 22 can be poured sequentially from the mouth of a
tilting or rotating furnace into separate appropriate vessels
such as ladles. Alternatively, an outlet can be provided in the
crucible to draw off the higher density tungsten-containing
phase 20. Gas 26 from the slagging furnace 18 can be
subjected to particulate control 28. The recovered particulate
matter 30 can be recycled to the slagging furnace 18 and the
treated gas 32 can be vented to the atmosphere.
The higher density tungsten-containing phase 20 is introduced
into a sparging furnace 24. The higher density
tungsten-containing phase 20 is heated to a temperature in
the range of from about 1,050° C. to about 1,200° c.,
30 preferably from about 1,050° C. to about 1,150° C. and more
preferably to a temperature of approximately 1,100° C. A
carbon-containing gas 34, such as methane, is introduced
into the sparging furnace 24. The carbon-containing gas 34
is cracked at the sparging furnace temperatures and the
35 carbon is available for the formation of tungsten carbide.
Gas 36 from the sparging furnace 24 can be subjected to an
afterburner 38 with the addition of an oxygen-containing gas
such as air 40 and a hydrocarbon, such as methane 42. The
afterburner gas 44 can be subjected to particulate control 46.
40 Recovered particulate matter 48 can be recycled to the
slagging furnace 18 and treated gas 50 can be vented to the
atmosphere. Sparged, spent salt 51 can be recycled to the
slagging furnace 18.
The sparging step 24 results in a crude tungsten carbide
45 product 52 which resembles a gray sintered material. The
crude tungsten carbide product 52 is subjected to a water
leaching step 54 after addition of water 55, followed by
solidlliquid separation 56. The liquid portion 58 is fed to a
crystallizer 60 and the crystals 62 can be recycled to the
50 sparging furnace 24. The solid crude tungsten carbide crystals
64 are comminuted 66 in water 68 and subjected to acid
leaching 70 with a suitable acid 72 (e.g., HCI). In a preferred
embodiment, the comminution 66 and acid leaching 70 take
place in a single operation. The comminution 66 is prefer-
55 ably conducted in a ball mill using tungsten carbide grinding
media. The crude tungsten carbide crystals 64 are first
slurried in a dilute aqueous 68 solution of hydrochloric acid
72, and the comminution 66 is continued for a period of time
sufficient to liberate and solubilize impurities. The commi-
60 nuted and acid leached suspension 74 is subjected to solidi
liquid separation 76. The solid high purity tungsten carbide
78 preferably has a purity level of at least 90 percent
tungsten carbide, more preferably at least 95 percent tungsten
carbide, and more preferably at least 99 percent tung-
65 sten carbide. The liquor 80 is subjected to neutralization and
precipitation 82 of solid materials 84. The solid precipitate
84, after drying, can be recycled to the slagging furnace 18.
DETAILED DESCRIPTION OF THE
INVENTION
BRIEF DESCRIPTION OF THE DRAWINGS
In accordance with one embodiment of the present
invention, a pyrometallurgical process is provided for forming
a tungstate salt, for example, sodium tungstate or potassium
tungstate and preferably sodium tungstate, from a
tungsten-containing material. Preferably, the tungstencontaining
material is a tungsten ore such as huebnerite
(MnW04), scheelite (CaW04 ), ferberite (FeW04) and wolframite
((Fe,Mn)WO4) or a tungsten-containing material
such as flue dust and various secondary materials (e.g., slag
and scrap). The pyrometallurgical slagging process comprises
heating the tungsten-containing material in the presence
of a slag forming silicate (preferably silica and an alkali
metal silicate). The melt separates into two immiscible
phases, a denser tungsten-containing phase, preferably
sodium or potassium tungstate, and a less dense slag phase.
In accordance with another embodiment of the present
invention, a process for forming tungsten carbide from a
tungsten-containing material is provided. Preferably, the
process includes two pyrometallurgical stages, a first slagging
stage and a second sparging stage.
FIG. 1 illustrates a flow diagram of a preferred embodiment
of the present invention. A tungsten-containing conary
materials (e.g., slag and scrap). While the methods of the
present invention are useful in connection with a number of
materials, for purposes of clarity, the following description
will be of a preferred embodiment employing a tungstencontaining
material. It is to be expressly understood that 5
other materials, such as those listed above, can also be
employed.
In accordance with another embodiment of the present
invention, tungsten carbide is formed from a tungsten mineral
concentrate. The tungsten mineral concentrate is heated 10
in the presence of a sodium or potassium compound to a
temperature from about 900° C. to about 1,200° C. in order
to obtain a first melt. The first melt is maintained at temperature
until it separates into a higher density tungstencontaining
phase and a lower density slag phase. The higher 15
density tungsten-containing phase is then separated from the
lower density slag phase. The higher density tungstencontaining
phase is heated to a temperature of about 1,050°
C. to about 1,200° C. to obtain a second melt. Methane gas
is then sparged through the second melt to form tungsten 20
carbide. The tungsten carbide enriched portion of the second
melt is removed and purified in order to obtain purified
tungsten carbide. Preferably, the first melt is formed in the
substantial absence of sodium chloride. In a preferred
embodiment, a portion of a sparged, spent salt-containing 25
material is recycled from the second melt to the first melt in
order to aid in the separation of the higher density tungstencontaining
phase from the lower density slag phase and to
recycle tungsten not converted to tungsten carbide in the
sparging stage.
FIG. 1 is a flow diagram of one embodiment of the
process of the present invention.
FIG. 2 is a ternary phase diagram of the W03-Na20Si0
2 system at 1,200° C.
FIG. 3 is an illustration of a pilot scale slagging system in
accordance with an embodiment of the present invention.
FIG. 4 is an illustration of a pilot scale sparging system in
accordance with an embodiment of the present invention.
5,882,620
6
The hydrogen gas and much of the elemental carbon are
oxidized in the afterburner. However, some of the carbon
re~~in.s a.s a contaminant within the salt phase. Thus,
mIlllmizatlon of excess carbon formation in the sparging
5 furnace is desirable.
Other hydrocarbon gases, such as propane or ethylene
(C2H4), can be used in place of methane. For instance, the
~se of ethylen~ might enhance the sparging efficiency (i.e.,
mcrease the yIeld of tungsten carbide per unit of carbon
10 added to the melt).
After separation of the free-flowing spent salt phase, the
resultant tungsten carbide crystals are contained in a separate
p.hase h.aving a g~ay, sintered appearance. The gray
matenal retams apprecIable quantities of salt. The salt and
other impurities are removed via a process of dry and/or wet
15 grind~ng and sequential leaching in hydrochloric acid,
caustlc, and water. After this treatment, the resultant crystals
can ~ssay between approximately 99.3 and 99.4% tungsten
carbIde. However, the tungsten carbide produced in preliminary
tests contains substantially higher impurity concentra-
20 tions. The elevated impurity concentrations, mainly chromium
and nickel, are believed to result from chemical attack
of the fused salt on the reaction crucible.
An example of a suitable system for slagging (FIG. 3) and
sparging (FIG. 4) includes a tilting furnace 110 with a cover
25 at the top which has room for two sparging lances 112, 114,
two thermocouples 116, 118, one dedicated nitrogen line
120, one exhaust line 122, and one pressure gauge 124. The
main component is a 12.9 kW resistance-heated furnace 110.
The furnace 110 has a hot zone 0.914 meter long by 12.7 cm
30 diameter; it can attain a maximum operating temperature of
about 1,200° C. Within the furnace shell, the process reaction
vessel, or crucible 126, is constructed of 10.2 cm
diameter Inconel 600 pipe; the maximum bath depth is about
45.7 cm. The crucible 126 may be removed for cleaning or
35 maintenance by opening the hinged split shell furnace.
The same furnace can be employed for slagging (FIG. 3)
and sparging (FIG. 4). In either slagging or sparging
operations, the initial charge is typically added to the cold
crucible 126, and then power is applied to the furnace 110
40 in order to elevate the bath temperature to the desired target.
Subsequent charges can be made to the hot furnace 110. To
facilitate removal of molten products, the furnace 110 can be
tilted a full 180 degrees from its vertical operating position
to pour products into ladles.
For operation in the gas sparging mode (FIG. 4), a facility
was designed with the capability to purge the crucible 126
with nitrogen 127 and sparge the molten bath with methane,
propane, ethylene or any mixture of these hydrocarbon
source gases 128. Seven access ports are located in the
50 reactor lid. Two of the ports admit gas lances 112, 114 during
sparging operations. Hydrocarbon gases 128 are injected
into the crucible 126 through one of the lances 112, with the
other lance 114 held in reserve in case the first lance 112
becomes obstructed. Preferably, the lances 112, 114 have a
55 relatively small inner diameter (e.g., 0.14 cm) to provide
relatively high velocity flow, thus minimizing cracking in
the lances 112, 114. The inlet hydrocarbon gases 126 are
directly injected into the melt at a point approximately 5 cm
a~ove the crucible 126 bottom. During each sparging test,
60 llltrogen 120 can also be injected through a third inlet port
at a point approximately 2.5 cm below the reactor lid. The
dedicated nitrogen lance 120 assures positive pressure inside
the freeboard to prevent air from entering the crucible 126.
All of the inlet gas flows are controlled by flow meters 130,
65 132, 134. Three other lid ports serve as thermocouple wells,
and the main (central) port 122 serves as the process gas
offtake.
5
In the first pyrometallurgical operation, a furnace charge
consisting of a blend of tungsten concentrate and siliceous
flux is treated at approximately 1,050° C. The tungsten
compounds contained in the concentrate (e.g., calcium, iron,
or manganese tungstates) react with the siliceous flux
(preferably sodium silicate and silica) to produce two
immiscible phases: a molten salt and molten silicate slag.
The tungsten is preferentially segregated in the molten salt
phase, while the majority of the impurities are rejected in the
slag. The salt is more dense than the slag and settles to the
bottom of the furnace crucible. The salt phase, which chiefly
consists of sodium tungstate, is then forwarded to the second
stage of pyrometallurgical processing, i.e., sparging.
The concentrate used in the examples contained huebnerite
(MnW04) as the primary tungsten mineral. When a
blended charge is treated as described above, the following
chemical reaction ensues:
4CH4(g)+Na2W04(0~WC(,)+3CO(g)+8H2(g)+Na20(0
Because a large stoichiometric excess of hydrocarbon gas
is needed, some of the excess gas also cracks to produce
carb~n and hydrogen gas, as illustrated by the following
reactlon:
Segregation of the salt and slag phases is predicated upon the
exploitation of the immiscibility region existing within the
tungstic oxide-sodium oxide-silica system shown in FIG. 2.
When the tungsten concentrates enter the 1,050° C. melt,
they react with the sodium silicate to produce sodium
tungstate and slag. At this temperature, the slag and tungstate
are immiscible, and they separate by gravity.
The precise chemistry of the slag will depend upon the
relative amounts of excess silica and sodium oxide in the
system. Sodium oxide is a desirable slag constituent because
its presence reduces the slag melting point sufficiently to
ensure the formation of a completely liquid phase. In the
absence of sodium oxide or another flux compound which
will effectively lower the slag's melting point, a liquid slag
cannot be formed in the manganese oxide-silica system at
temperatures below approximately 1,250° C.
An example of a slagging system is illustrated in FIG. 3.
With the exception of a gas injection system, the same basic
furnace configuration useful in the sparging operation
(described below) can be employed for the slagging operation.
Because the slagging operation is simply a melting and
separating exercise, no gas lances or nitrogen purge lines are
required.
The second pyrometallurgical process effects the crystallization
of tungsten carbide within the molten salt phase.
This feat is accomplished by heating the tungsten-bearing 45
molten salt from the first stage to within the range of
approximately 1,080° to 1,100° C. and then sparging with a
large stoichiometric excess of hydrocarbon gas, such as
methane or propane. Under these conditions, the hydrocarbon
gas cracks and provides the reductant and carbon source
necessary for forming the tungsten carbide. The tungsten
carbide phase forms as micron-sized crystals, which are
insoluble in the molten salt phase. The crystals are also
denser than the salt and are segregated near the bottom of the
reactor. At the conclusion of the sparging operation, the
spent salt is decanted from the crystals.
When methane is employed as the hydrocarbon source,
the net chemical reaction leading to the formation of the
tungsten carbide (We) product is believed to be:
5,882,620
7 8
TABLE I
Charge Compositions for Comparative Slagging
Tests A, Band C
Comparative Tests A, Band C
Three comparative slagging tests, designated as A, Band
C, were completed within a 5 kW induction furnace system.
In view of the huebnerite mineralogy of the concentrate
sample, the tests were performed to obtain a preliminary
indication of the behavior of the MnO-Na20-Si02 system
slag. The charge components included varying amounts
of concentrate, sodium chloride, and slag-formers sodium
silicate and silica. These were added according to the
respective charge compositions detailed in Table I.
During these experiments, excessive salt fumes were
evident at times, and thin layers of salt condensed on the
internal surface of the dome of the bell j ar induction furnace
containment.
Visual inspection of the slag and salt products indicated
no problems with phase separation. The three slag samples
had a vitreous appearance and were tinted green, ranging
from light green in Test A to emerald green in Test C. Most
of the sodium chloride was volatilized during the first test,
leaving a deposit of dark solids on the slag surface. In the
other two tests, the halide phase was off-white with a yellow
tint on each surface. The slag and halide phase samples
produced in each test were recovered and submitted for XRF
analysis; the amount of halide phase recovered from Test A
was insufficient for XRF analysis.
The XRF data, summarized in Table II, suggest that a
favorable partitioning of the tungsten between the slag and
65 the halide phase occurred in two of the three tests. The
tungstic oxide (W03) concentrations in the slag samples
generated in Tests A and C were 0.5 and 0.7%, respectively,
together prior to initiating any testing. Approximately half of
the sample was stored in a plastic-lined 55-gallon drum. The
remaining half of the sample was split into lots of approximately
45 kg. Subsamples were drawn from three of the lots
5 for comparative analysis to ascertain the efficiency of the
blending operation. Duplicate samples were retained on
inventory for verification analyses. The blended master
samples were then stored in sealed containers pending their
use in the various tests.
The three subsamples of the tungsten concentrate were
initially screened by semiquantitative analytical methods,
such as x-ray diffraction (XRD), x-ray fluorescence (XRF),
and emission spectrography, to approximate its mineralogy
and chemical composition. Subsequently, all major and
15 minor components detected by the screening methods were
analyzed by more exacting techniques, including wet quantitative
analytical chemistry, atomic absorption spectroscopy
(AA), and inductively-coupled plasma spectroscopy (ICP).
In some cases, multiple analytical techniques were
20 employed in order to firmly establish the chemical composition
of the concentrate sample. In addition to the chemical
analysis, the tungsten concentrate sample characterization
also included a limited amount of physical characterization.
EXAMPLES AND COMPARATIVE TESTS
The tungsten concentrate sample used in the following
examples was shipped from a commercial source. The 817
kg sample was packed in two unlined 30 gallon metal drums.
The contents of both drums were thoroughly blended
A primary concern in the system design is to ensure
efficient transport of the nascent hydrogen, which is formed
by cracking or as a product of the sparging reaction to the
afterburner 136. Preferably, in one embodiment, the pressure
inside the furnace 110 is first adjusted to 0.25 to 0.50
millimeters (mm) of water by balancing the flow of reacting
gas with the extraction draft. Then the pressure is increased
to 2.5 to 5.0 mm of water by adjusting the flow of the
dedicated nitrogen lance 120. Note that the tip of this lance
120 is positioned only about 5 cm from the top of the 10
crucible 126 so that most of the draft is utilized to extract the
reaction product gases and not nitrogen. In this way, most of
the nitrogen flows through the top cover, maintaining an
inert atmosphere at the top of the crucible 126 and preventing
any air from contacting the product gases inside the
furnace 110. The reaction gases are drawn into the afterburner
136 and combusted to H2 0 and CO2 , Carryover salt
can be collected at the baghouse 138 or scrubber 140. The
afterburner 136 offgases can be air cooled 142° to 120° C.
before reaching the baghouse 138 or scrubber 140. When the
baghouse 138 is employed, the gases go through the scrubbing
system; then they can be discharged into the atmosphere.
In the embodiment shown in FIG. 4, the afterburner
136 offgas passes through the scrubber 140, while the
baghouse 138 is used to treat possible fugitive emissions 25
from the furnace 110.
Process gases exit the crucible 126 through the single exit
port 122 leading to the gas handling system. The gases are
fed directly into a 20.3 cm diameter by 55.9 cm long natural
gas-fired, stainless steel afterburner 136 through a 5 cm 30
diameter pipe. The afterburner 136 is designed to operate
with a pressure pilot burner which remains ignited throughout
the tests. Oxygen 144 is fed into the afterburner 136 at
a controlled rate for combustion of the nascent hydrogen,
residual hydrocarbon gases, and carbon fines entrained in 35
the offgas stream. After exiting the afterburner 136, the gases
pass through a ball valve 146 (used to balance the system gas
pressure profile) and then into the scrubber 140.
The scrubber 140 is constructed of a 208-liter polymer
drum and polyvinyl chloride (PVC) piping. The scrubber is 40
filled with approximately 114 liters of water; the afterburner
discharge gases are bubbled into the reservoir to condense
and remove any soluble material in the gas stream. The
afterburner exhaust gases are cooled by air dilution 142 and
by an external chiller coil system 148 before entering the
scrubber 140. Gases are pulled through the scrubbing system
by a 25 cm diameter blower 150. Exit gases from the blower
150 can be vented to the atmosphere.
An external baghouse 138 and blower assembly was set
up to collect fugitive emissions from the crucible lid. The
baghouse 138 was fitted with two inlet hoses, each 10.2 cm
in diameter, that were placed near the crucible lid. Fugitive
emissions were thus drawn into the baghouse 138, filtered,
and then blown into the atmosphere.
Temperature was monitored at several key points through- 55
out the system. Readings were measured by two thermocouples
116, 118 which are placed through two separate lid
ports. One thermocouple 116 measured the melt temperature
near the point of gas injection, while the other thermocouple
118 was used to monitor the temperature of the head space, 60
or freeboard, in the crucible 126 above the melt.
5,882,620
As shown in Table III, the halide phase samples from
Tests Band C consisted primarily of chlorine, sodium, and
tungsten. According to the XRF data, the halide phase 20
samples from Tests Band C contained 39 and 40% tungstic
oxide, respectively. The iron and manganese concentrations
were each below 0.1% in both halide samples. Trace levels
of several other elements were also detected.
Analytical Results from Example I
TABLE V
10
Example 1 was conducted without difficulty and phase
separation was excellent. The products of this experiment
were submitted for analysis to determine their respective
tungsten and manganese distribution between the two prod-
S uct phases. As shown in Table V, the analytical results for
Example 1 confirmed the feasibility of favorable tungsten
and manganese distributions between the slag and salt
phases. Judging from these results, the separation of tungsten
from the concentrate as sodium tungstate, in the absence
10 of sodium chloride, presents an attractive alternative.
Charge Composition Chemical Analysis
Species Weight % Element % in Salt % in Slag
Na2Si03 41.45 Mg 0.06 0.34
Sio2 14.17 Na 12.80 16.70
MnW04 44.38 W 59.25 0.10
Mn 2.05 12.40
CI
Si 0.21 19.50
15
9
TABLE II
XRF Analysis of Slag Samples from Comparative Slagging Tests
A B C
Compound Weight % Weight % Weight %
NaCI 7.1 8.7 3.1
Al20 3 3.5 2.6 1.2
FeO 0.7 0.5 0.9
MnO 14.4 10.2 28.7
Na20 22.7 21.2 14.4
Si02 47.7 51.2 42.4
W03 0.5 1.8 0.7
Total 96.6 96.2 91.4
while the tungstic oxide concentration in the B slag was
1.8%.
25
TABLE III
Comparative Tests D, E. F and G
Test 0
Charge Composition for Test 0
TABLE VI
Compound
55
Variation of the Manganese-to-Sodium Silicate Ratio in
the Charge
The objective of Comparative Test D is to evaluate the
30 effect of a high manganese-to-sodium silicate (Mn:Na2Si03 )
ratio on the distribution of tungsten and manganese between
the slag and salt phases. While not wishing to be bound by
any theory, it is believed that is important to maintain a
certain level of sodium in the system. In conducting tests
35 where the slag composition was the independent variable,
the respective distribution of manganese between the salt
and slag phases was adversely affected as the manganese
oxide level of the slag increased. This problem became
apparent when the molar ratio of manganese to sodium
40 silicate in the charge was raised above 1. It is believed that
this phenomena occurred because an insufficient amount of
sodium was present to complete the following reaction:
If Mn:Na2Si03 molar ratios of greater than one are
desired to reduce flux consumption, additional sources of
sodium are needed to maximize the formation of sodium
tungstate and minimize the dissolution of unreacted man-
50 ganese tungstate into the salt phase. The additional source of
sodium utilized in this experiment was sodium hydroxide
(NaOH) according to the composition presented in Table VI.
66.57
o
62.16
21.27
150.00
Example 1
TABLE IV
XRF Analysis of Halide Phase Samples from
Preliminary Slagging Tests
Charge Component
and Mass
Concentrate, grams
NaCI, grams
Na2Si03 , grams
Si02 , grams
Total, grams
B C
Element Weight % Weight %
CI 46.5 44.5
Na 23.0 23.3
W 31.0 32.0
Total 100.5 99.8
Charge Components and Masses for Sodium Tungstate
Production
Example 1
Sodium Tungstate Production
Example 1 is designed to demonstrate the feasibility of
forming a discrete sodium tungstate phase in the absence of
sodium chloride in the charge. For the test to be successful,
it is necessary that the sodium tungstate and slag would be
present as immiscible liquids at the temperature of interest.
This test was conducted in a 5 kW induction furnace. This 45
charge composition is presented in Table IV.
Although two distinct phases were again formed, the
appearance of the slag was different than that observed in
previous experiments. The slag in this test had a sandy
appearance which, when observed under the microscope (30
Visual inspection of the test products indicates the for- 60
mation of two distinct phases, sodium tungstate and slag.
The slag phase has a dark green appearance and is at the top,
while the sodium tungstate phase is off-white and located at
the bottom of the crucible. The fact that the sodium tungstate
phase is located at the bottom of the crucible is due to its 65
higher density and its immiscibility with the lower density
slag phase.
Concentrate, grams
NaCI, grams
Na2Si03 , grams
NaOH, grams
Total, grams
41.23
64.33
12.26
3.24
121.06
5,882,620
TABLE VIII
Mass Balance for Slagging Example 2
Material In Kilograms Material Out Kilograms
Concentrate 4.43 Halide Phase 3.94
Silica 1.41 Slag 5.74
Sodium Metasilicate 4.15
Total 10.00 Total 9.68
12
Example 2
In Example 2, no sodium chloride was included in the
charge. The slag composition was selected to ensure the
formation of two immiscible liquids. The formation of the
two immiscible phases, as well as the favorable distributions
of tungsten and manganese in the salt and slag, was predicted
by the results of Example 1.
The mass balance for Example 2 is shown in Table VIII.
The mass closure for this Example was 96.8%. A tungsten
mass balance indicates that 92.9% of the charged tungsten
reported to the halide phase and 3.3% to the slag. Only 3.8%
of the tungsten in the charge was unaccounted.
The tungsten distribution for Example 2, as calculated
from the analytical data, indicates that approximately 97%
of the input tungsten was segregated in the tungstate phase,
with the difference reporting to the slag. While these results
suggest that an efficient slagging operation in the absence of
sodium chloride is indeed possible, those skilled in the art
can improve the tungsten distribution without undue experimentation.
Entrainment of salt from the reactor walls during
slag pouring may have contributed to the relatively high
tungsten concentration in the slag from Example 2.
From an operational point of view, although the sodium
tungstate phase was segregated below the slag in the reactor
(due to the higher density of the salt), it poured first, due to
its lower viscosity and the geometry of the reactor. There
were only a few minor traces of slag entrained in the salt,
40 and these had floated to the surface before the salt solidified
in the ladle.
11
TABLE VII
Analytical Results for Comparative Tests D. E. F. and G
x magnification), gave evidence of different phases and
incomplete fusion of the charge. The halide phase had the
same appearance as in the previous tests. As evidenced from
the analytical results given in Table VII, the use of sodium
hydroxide yielded unsatisfactory tungsten and manganese 5
distributions in both the slag and salt phases.
Three additional induction furnace tests were conducted
to further explore the effect of altering the Mn:Na2Si03 ratio
in the furnace charge, and to investigate the use of alternative
sources of sodium and silica. The specific objective of 10
Test E was to study the effects of a slag composition with a
Mn:Na2Si03 molar ratio of one on the distributions of
tungsten and manganese between the halide and slag phases.
As indicated in Table VII, the 0.55% concentration of
tungsten in the slag and the 0.14% concentration of man- 15
ganese in the halide indicate that reduction in flux consumption
to realize a slag molar ratio of Mn:Na2Si03 of less than
or equal to one is feasible and worth pursuing.
In Test F, an attempt was made to increase the manganese:
silicon ratio to 1.35, under conditions similar to those of 20
Test D but using sodium carbonate (Na2C03) instead of
sodium hydroxide as the additional sodium source. The
objective was to determine whether the choice of additional
sodium source had any significant effect on the tungsten and
manganese distributions. As seen in Table VII, a tungsten 25
concentration of 1.08% in the slag suggests, when compared
to 3.9% from Test D, that the source of additional sodium
can have an effect on the distribution of tungsten in the
halide phase.
In Test G the objective was to study the feasibility of using 30
silica and sodium carbonate as the sole sources of sodium
and silica in an attempt to substitute less expensive raw
materials for sodium metasilicate. As shown in Table VII,
the 0.13% tungsten concentration in the slag and the 0.03%
manganese concentration in the halide suggested that the 35
substitution is feasible.
Weight Ele- % in %/in
Test Species % ment Salt Slag Comments
Comparative Na2Si03 10.13 Mg 0.01 1.35 NaOH used
Test 0 Si02 0.00 Na 34.90 5.82 as
MnW04 34.05 W 17.50 9.44 additional
NaCl 53.14 Mn 0.22 33.60 sodium
NaOH 2.68 Cl 46.00 0.75 source for
Si 0.19 11.90 a basic
slag.
Comparative Na2Si03 20.24 Mg 0.01 0.69 Mn:Na2Si03
Test E Si02 0.00 Na 30.70 14.80 molar ratio
MnW04 31.40 W 25.60 0.55 of one in
NaCl 48.36 Mn 0.14 24.50 the slag.
Cl 37.00 0.06
Si 0.12 12.30
Comparative Na2Si03 13.89 Mg 0.01 0.39 Na2C03 used
Test F Si02 0.00 Na 30.30 11.10 as
MnW04 32.56 W 23.40 1.08 additional
NaCl 50.28 Mn 0.10 32.70 sodium
Na2C03 3.27 Cl 38.00 0.39 source
Si 0.31 12.40 (basic slag).
Comparative Na2Si03 0.00 Mg 0.03 0.72 Si02 and
Test G Si02 18.85 Na 30.50 15.60 Na2C03 as
MnW04 24.20 W 23.60 0.13 sole
NaCl 37.36 Mn 0.03 13.20 sources of
Na2C03 19.59 Cl 40.50 0.10 silicon and
Si 0.17 16.95 sodium.
Charge
Composition Chemical Analysis Example 3
Recycling Sparged, Spent Salt to the Slagging Operation
45 This Example is designed to demonstrate the effectiveness
of recycling the spent salt from the sparging unit operation
to the slagging unit operation. This practice is desirable for
two reasons. First, the spent salt typically contains an
appreciable concentration of tungsten (approximately 15%
50 by weight) which is not converted to tungsten carbide during
the sparging step. Returning the salt to the slagging operation
keeps the tungsten within the processing circuit and is
useful in achieving economic levels of tungsten recovery in
the overall operation. Second, it is believed that the sodium
55 oxide in the sparged salt can serve as the sodium source in
the production of sodium tungstate during the slagging
operation. Therefore, recycling the spent salt is expected to
reduce the consumption of raw materials. This Example was
designed to determine whether recycling the spent salt
60 would affect the distribution of tungsten between the salt and
slag phases.
The Example consists of three charging cycles conducted
sequentially. The Cycle 1 charge represents a typical slagging
operation charge without salt recycled from the sparg65
ing operation and consists of a 5 kg blend of 26.3%
huebnerite concentrate, 24.7% sodium metasilicate
(Na2Si03), 8.4% silica (Si02 ) and 40.6% sodium chloride
5,882,620
13
(NaCI). The Cycle 2 charge consisted of 1 kg of spent salt
(generated during a previous sparging test) plus 4 kg of the
same components used in Cycle 1, mixed in the identical
proportions. The Cycle 3 charge contained 2 kg of spent salt
plus 4 kg of the components used in Cycle 1, again mixed 5
according to the Cycle 1 proportions.
At the beginning of each test cycle, the charge materials
were blended together, added to the furnace, and processed
at a nominal temperature of 1,050° C. for one hour. The
fused salt was then removed by tilting the furnace and 10
pouring the melt into a ladle where it was allowed to solidify.
The furnace was restored to its vertical operating position,
and the process was repeated with the next charge. The slag
phase was not removed until all three cycles had been
completed. The slag was then poured into a ladle and 15
allowed to solidify. Samples of the slag and of each of the
three salt products were prepared and submitted for chemical
analysis.
The analyses of the slag and salt products are summarized
in Table IX. As calculated from the measured product 20
weights and associated tungsten analyses, approximately
99.1%of the tungsten reported to the salt. Comparison of the
salt analyses from Cycles 1, 2 and 3 indicates favorably low
concentrations of impurities in all three cycles.
14
unidentified crystalline phase. More significantly, the dense
graph phase was found to contain sodium tungstate, with
lesser concentrations of tungsten carbide (WC) and ditungsten
carbide (W2C) and trace concentrations of metallic
tungsten and the same unidentified crystalline phase that
occurred in the white salt.
Although those skilled in the art will be able to further
optimize the process, the x-ray diffraction results demonstrate
that it is possible to form tungsten carbide via the
methane sparging method.
While various embodiments of the present invention have
been described in detail, it is apparent that modifications and
adaptations of those embodiments will occur to those skilled
in the art. It is to be expressly understood, however, that such
modifications and adaptations are within the scope of the
present invention, as set forth in the following claims:
List of Reference Numerals
Tungsten-Containing Concentrate 12
Silica 14
Silicate 16
Slagging Furnace 18
Tungstate Salt 20
TABLE IX
Analytical Data from Spent Salt Recycling Tests
Example 3 Sample
Sample Description Mass, kg AI% CI% Cr % Fe % Mn% Na % Ni% Si % w%
Cycle 1 Salt 3.01 0.01 36 <0.002 <0.01 0.09 29.4 0.007 <0.1 28.4
Cycle 2 Salt 3.57 <0.01 40 0.003 <0.01 0.04 31.5 <0.002 <0.1 21.9
Cycle 3 Salt 4.62 0.01 41 <0.002 <0.01 0.04 31.6 <0.002 <0.1 22.8
Slag 4.21 0.09 2.5 0.08 0.34 13.9 17.1 0.13 24.8 0.6
Examples 4 and 5
Sparging Sodium Tungstate to Produce Tungsten Carbide 40
It has been demonstrated that tungsten carbide of reasonably
high purity can be obtained by sparging a molten
mixture of sodium tungstate and sodium chloride with
methane. However, elimination of the sodium chloride from
the operation improves the process for several reasons. 45
Consequently, two additional Examples are presented to
demonstrate whether crystalline tungsten carbide powder
can be produced by sparging molten sodium tungstate with
methane gas.
In each Example, the initial melt consists of sodium 50
tungstate produced in previous slagging tests. During the
Examples, the sodium tungstate bath is maintained at
approximately 1,100° c., while methane gas is injected
below its surface at a flow rate of approximately 11.4 liters
per minute. Methane sparging is continued for three hours in 55
Example 4 and for 90 minutes in Example 5. At the
conclusion of each Example, the molten products are poured
into a steel ladle and allowed to solidify.
After the products have solidified and cooled sufficiently,
two separate phases are observed: a white "spent ash" and a 60
denser, medium gray phase. The two phases are separated
and prepared for x-ray diffraction (XRD) analysis. The
products from Example 4 were selected for the XRD analysis
because they were more easily and cleanly separated
after cooling. XRD analysis of the white spent salt indicates 65
that it is predominantly composed of unreacted sodium
tungstate (Na2W04) with trace concentration of another
Slag 22
Sparging Furnace 24
Slagging Furnace Gas 26
Particulate Control 28
Particulates 30
Treated Gas 32
Carbon-Containing Gas 34
Sparging Furnace Gas 36
Afterburner 38
Oxygen-Containing Gas 40
Methane 42
Afterburner Gas 44
Particulate Control 46
Particulates 48
Treated Gas 50
Sparged, Spent Salt 51
Crude Tungsten Carbide Product 52
Water Leaching Step 54
Water 55
Solid/Liquid Separation 56
Liquid Portion 58
Crystallizer 60
Crystals 62
Solid Crude Tungsten Carbide Crystals 64
Comminution 66
5,882,620
15 16
5
30
5. The method of claim 1, wherein said alkali metal
compound is selected from the group consisting of sodium
silicate, sodium carbonate, sodium hydroxide and mixtures
thereof.
6. The method of claim 1, wherein said heating step (a)
takes place at a temperature from about 900° C. to about
1,200° C.
7. The method of claim 1, wherein said heating step (a)
takes place at a temperature from about 1,050° C. to about
10 1,150° C.
8. The method of claim 1, wherein said sparging step (d)
takes place at a temperature from about 1,050° C. to about
1,200° C.
9. The method of claim 1, wherein said sparging step (d)
takes place at a temperature from about 1,050° C. to about
15 1,150° C.
10. The method of claim 1, wherein said carboncontaining
gas is a hydrocarbon gas.
11. The method of claim 1, wherein said carboncontaining
gas is selected from the group consisting of
20 methane, ethylene, propane and mixtures thereof.
12. The method of claim 1, wherein said high density
phase is separated from said low density phase by pouring
said high density phase from a crucible.
13. The method of claim 1, wherein said high density
25 phase is removed through an outlet in a crucible containing
said high density phase and said low density phase.
14. The method of claim 1, wherein said tungsten carbide
formed in step (d) is separated from the remainder of
materials and purified.
15. The method of claim 14, wherein said tungsten
carbide is at least 90 percent pure after it is purified.
16. The method of claim 1, wherein said heating step (a)
is performed in the substantial absence of halide salt.
17. The method of claim 5, wherein said salt-containing
35 material which is recycled comprises materials selected
from the group consisting of sodium tungstate, Na2 0 and
mixtures thereof.
18. A method for forming tungsten carbide comprising the
steps of:
(a) heating a tungsten mineral concentrate in the presence
of a sodium or potassium compound to a temperature
from about 900° C. to about 1,200° C. in order to obtain
a first melt;
(b) maintaining said first melt at a temperature of from
about 900° C. to about 1,200° C. until said melt
separates into a higher density tungsten-containing
phase and lower density slag phase, wherein in at least
80% of the tungsten in said tungsten mineral concentrate
reports to said higher density tungsten-containing
phase;
(c) separating said higher density tungsten-containing
phase from said lower density slag phase;
(d) heating said higher density tungsten-containing phase
to a temperature of from about 1,050° C. to about
1,200° C. to obtain a second melt;
(e) sparging methane gas through said second melt to
form a sparged second melt comprising tungsten carbide;
(f) separating a tungsten carbide enriched portion from
said sparged second melt; and
(g) purifying said tungsten carbide enriched portion in
order to obtain purified tungsten carbide.
19. The method of claim 18, wherein said first melt is
65 formed in the substantial absence of sodium chloride.
20. The method of claim 18, wherein a portion of a
salt-containing material is recycled from the second melt to
Water 68
Acid Leaching 70
Acid 72
Comminuted and Acid Leached Suspension 74
SolidlLiquid Separation 76
High Purity Tungsten Carbide 78
Liquor 80
Neutralization and Precipitation 82
Solid Precipitate 84
Tilting Furnace 110
Sparge Lances 112, 114
Thermocouples 116, 118
Nitrogen Line 120
Exhaust Line 122
Pressure Gauge 124
Crucible 126
Nitrogen 127
Hydrocarbon Gas(es) 128
Flow Meters 130, 132, 134
Afterburner 136
Baghouse 138
Scrubber 140
Cooling Air Intake 142
Oxygen 144
Valve 146
Chiller Coil System 148
Blower 150
What is claimed is:
1. A method for forming tungsten carbide comprising the
steps of:
(a) heating the tungsten-containing material in the presence
of an alkali metal compound at a temperature
sufficient to melt said tungsten-containing material and
for a time sufficient for the formation of a high density
phase and a low density phase wherein the majority of 40
said tungsten reports to said high density phase in the
form of tungstate salt;
(b) allowing said high density phase and said low density
phase to separate by gravity wherein said high density 45
phase settles to the bottom;
(c) concentrating said tungsten by separating said high
density phase from said low density phase;
(d) producing tungsten carbide by subjecting said high
density phase to sparging with a carbon-containing gas 50
at an elevated temperature in order to form tungsten
carbide; and
(e) recycling a portion of a salt-containing material from
the sparged high density phase of step (d) to a melt
comprising tungsten-containing material in the pres- 55
ence of an alkali metal compound as described in step
(a).
2. The method of claim 1, wherein said tungstencontaining
material is selected from the group consisting of
huebnerite (MnWO4), scheelite (CaWO4), ferberite 60
(FeW04 ), wolframite ((Fe,Mn)W04 ) and mixtures thereof.
3. The method of claim 1, wherein said tungstencontaining
material is selected from the group consisting of
flue dusts, slags, scrap and mixtures thereof.
4. The method of claim 1, wherein said alkali metal
compound is selected from the group consisting of sodium
compounds and potassium compounds.
5,882,620
30
17
a first melt as described in step (a) in order to aid in the
separation of said higher density tungsten-containing phase
from said lower density slag phase.
21. The method of claim 18, wherein said higher density
tungsten-containing phase comprises a tungsten oxide salt. 5
22. The method of claim 18, wherein said higher density
tungsten-containing phase comprises sodium tungstate salt.
23. The method of claim 18, wherein said lower density
slag phase comprises a silicate.
24. The method of claim 18, wherein said lower density 10
slag phase comprises manganese silicate, iron silicate or
aluminum-calcium silicates.
25. The method of claim 18, wherein said tungsten
carbide is produced in a fine size with at least 90 percent of
said tungsten carbide having an average diameter of less 15
then 10 microns.
26. The method of claim 18, wherein at least 95 percent
of the tungsten in said tungsten mineral concentrate reports
to said higher density tungsten-containing phase.
27. The method of claim 18, wherein at least 97 percent 20
of the tungsten in said tungsten mineral concentrate reports
to said higher density tungsten-containing phase.
28. The method of claim 18, wherein at least a portion of
said sodium compound is in a form selected from the group
consisting of: (i) sodium silicate (Na2Si03 ); or (ii) sodium 25
carbonate (Na2C03) in the presence of silica (Si02).
29. The method of claim 18, wherein said purifying step
(g) comprises:
(a) dry grinding, air elutriation and dry separation of melt
from tungsten carbide;
(b) water leaching said dry purified material;
(c) subjecting said water leached material to solidlliquid
separation to form crude tungsten carbide crystals;
(d) comminuting and acid leaching said crude tungsten 35
carbide crystals; and
(e) subjecting said comminuted and acid leached crude
tungsten carbide crystals to solidlliquid separation to
obtain high purity tungsten carbide.
30. The method of claim 18, wherein said purified tung- 40
sten carbide is at least 90 percent tungsten carbide.
31. The method of claim 20, wherein said salt-containing
material which is recycled comprises materials selected
from the group consisting of sodium tungstate, Na2 0 and
mixtures thereof.
18
32. The method of claim 29 wherein liquid which is
separated in step (c) is fed to a crystallizer and the crystals
are recycled to said second melt.
33. A method for forming tungsten carbide comprising the
steps of:
(a) heating a tungstate salt to a temperature greater than its
melting temperature to form a melt in the substantial
absence of any halide salt such that the melt separates
into a high density phase and a low density phase
wherein the majority of the tungsten reports to said
high density phase;
(b) sparging a hydrocarbon gas through said high density
phase to form tungsten carbide; and
(c) separating said tungsten carbide from the remainder of
said high density phase.
34. The method of claim 33, wherein said tungstate salt
comprises sodium tungstate.
35. The method of claim 34 wherein a portion of said
remainder of said high density phase of step (e) is recycled
to a melt as set forth in step (a).
36. A method for forming tungsten carbide comprising the
steps of:
(a) heating a tungsten mineral concentrate in the presence
of a sodium or potassium compound and in the substantial
absence of sodium chloride to a temperature
from about 900° C. to about 1,200° C. in order to obtain
a first melt;
(b) maintaining said first melt at a temperature of from
about 900° C. to about 1,200° C. until said melt
separates into a higher density tungsten-containing
phase and lower density slag phase;
(c) separating said higher density tungsten-containing
phase from said lower density slag phase;
(d) heating said higher density tungsten-containing phase
to a temperature of from about 1,050° C. to about
1,200° C. to obtain a second melt;
(e) sparging methane gas through said second melt to
form a sparged second melt comprising tungsten carbide;
(f) separating a tungsten carbide enriched portion from
said sparged second melt; and
(g) purifying said tungsten carbide enriched portion in
order to obtain purified tungsten carbide.
* * * * *