5,882,620 Pyrometallurgical process for forming tungsten carbide

Patent Number/Link:

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

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"'"

'JJ. =~

~....

o....,

Tilting Furnace

110

Schematic Diagram of the Pilot·scale Siagging System

Fig. 3 ...U. l

...N.

'JJ. =~

~....

d•

'JJ.

•

~.....

~=.....

o....,

:-'l

~'"~"'"

''"0"'"

To Atmosphe..re '0

138

Baghouse

Fugitive Exhaust

Capture

Dust

.................. .................. ..................

150 i , < To Atmosph:re

142

Cooling Air

Intake

Cooling

Coil

i8'

Flowmeter

°2 144

C2H4

Or 128

CH4

127

Liquid N2

120 Tilting Furnace

110

Schematic Diagram of the Pilot-scale Sparging System

Fig. 4

...U. l

...N.

5,882,620

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

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

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.

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

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

Si 0.21 19.50

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%.

TABLE III

Comparative Tests D, E. F and G

Test 0

Charge Composition for Test 0

TABLE VI

Compound

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

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

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.

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

(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.

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. 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;

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;

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

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;

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.

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

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;

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.

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