Title of Invention	"AN IMPROVED PROCESS FOR THE RECOVERY OF TUNGSTEN VALUES FROM THE SCRAPS OF TUNGSTEN HEAVY ALLOYS"
Abstract	An improved process for the recovery of tungsten metal from the scraps of tungsten heavy alloys. A process has been developed to recover tungsten as its ammonium salt by subjecting the scraps of heavy tungsten alloy to electrolytic dissolution. The process provides a method for direct conversion of tungsten from tungsten alloy into its ammonium salt from which Ammonium Para Tungstate (APT) can be obtained. Metallic tungsten can be recovered from Ammonium Para Tungstate.

Title of Invention

"AN IMPROVED PROCESS FOR THE RECOVERY OF TUNGSTEN VALUES FROM THE SCRAPS OF TUNGSTEN HEAVY ALLOYS"

Abstract

An improved process for the recovery of tungsten metal from the scraps of tungsten heavy alloys. A process has been developed to recover tungsten as its ammonium salt by subjecting the scraps of heavy tungsten alloy to electrolytic dissolution. The process provides a method for direct conversion of tungsten from tungsten alloy into its ammonium salt from which Ammonium Para Tungstate (APT) can be obtained. Metallic tungsten can be recovered from Ammonium Para Tungstate.

Full Text	The present invention relates to an improved process for the recovery of tungsten metal from the scraps of tungsten heavy alloys The present -invention particularly relates to recovering tungsten as its ammonium salt by subjecting the scraps of heavy tungsten alloy to electrolytic dissolution. The importance of reclamation can be understood from the fact that secondary source provides about 34% of the tungsten input. The process provides a method for direct conversion of tungsten into its ammonium salt from which Ammonium Para Tungstate(APT) can be obtained. Hitherto it has been proposed to recover tungsten values from such scraps by adopting methods like oxidation -reduction, sodium nitrate alkali fusion (moltexclusion), electrolysis in acid and alkaline medium. In air oxidation - reduction process [D.Chait, R.Gero and S.Nadir , J.R&HM,4(1985)40], the scraps after cleaning are subjected to oxidation at temperatures of 900 - 10000 C and reduced with H at the same temperature range. Though this process produces a product having the same composition of original alloy, inclusion of even small impurities such as Al, Ca, Si and Cr oxides have an extremely adverse effect on the final properties of the alloy. Moreover, the alloys containing copper, forms cuprous oxide during oxidation and protects copper from further attack resulting in lower efficiency. The moltexclusion technique suffers from the disadvantage of strong contamination by nitrogen or precipitated nitrates. This route is problematic for environment conscious industrialised nations even when suitable catalysts are used [Dai Enzog, Proc. Recycling of Metal1iferrous materials, IMM, UK, Apr.1990, 63]. Also the rate of the process is affected by the over sized scraps. Moreover this method is economically viable for W-Cu/W-Ag alloys only [B.F.Kieffer and E.Lassner, J.R&HM (1988) 63]. Under selective electrolytic dissolution method, a mineral acid like nitric or sulphuric or hydrochloric acid is employed in which certain oxidative additives are added to precipitate tungsten as tungstic acid while impurities are passed on to the electrolyte. However this method suffers from the chronic anode passivation problem. In caustic soda or ammoniacal medium tungsten dissolves with the formation of tungstate and anodic current depends upon the alkali concentration. If sodium hydroxide is used as electrolyte, one has to process the tungstate for the preparation of ammonium para tungstate (APT) only after the precipitation of tungstic acid. According to the process of present invention, tungsten heavy alloy scrap containing 0-5% Fe, 0 5% Ni and 90 - 95% tungsten can be processed through electrolytic dissolution. The main object of present invention is to provide an improved process for the recovery of tungsten values from the scraps of tungsten heavy alloys which obviates the drawbacks as detailed above. The tungsten heavy alloy scrap is dissolved directly in ammoniacal medium in the presence of additives such as ammonium nitrate, ammonium chloride, sodium chloride, which can improve the conductivity of the electrolyte. Tungsten in the alloy forms ammonium tungstate with ammonia. APT can be obtained from saturated ammonium tungstate solution by control of pH of the solution around 7 and subsequent evaporation. Iron gets precipitated during operation whereas impurities like nickel which can complex with ammonia goes into the solution. The tungstate solution thus obtained may be purified by the addition of ammonium sulphide to remove nickel and cobalt and APT can be crystallized from the resultant purified solution. Accordingly the present invention provides an improved process for the recovery of tungsten metal from the scraps of tungsten heavy alloys which comprises of anodic dissolution of the above said tungsten heavy alloy at an anodic current density of 250 - 800 Am"2 in an ammoniacal electrolyte such as herein described optionally containing additives such as urea, sodium/ammonium oxalate having concentration such as herein described, with a current efficiency in the range of 25-98% and recovering tungsten metal from ammonium tungstate solution by known methods. To these ends, the invention broadly consists of dissolving the tungsten in the tungsten heavy alloy scrap pieces/turnings in a suitable electrolyte under the influence of direct current. The electrolyte consists of ammoniacal solution (10- 35% V/V) with ammonium chloride (15-30 gdm-3), ammonium nitrate (10-30 gdm-3) and also additives like urea, oxalate ( 5 -20 dm-3) or ammonia and carbonate ( NH3 -15 to 35% V/V ) and CO32- 15 -35 gdm-3) . The heavy alloy scraps form the anode and titanium plates ad cathodes. Electrolysis is carried out at anodic current densities ranging from 250 - 800Am-2. The temperature of the electrolyte is maintained around 30°C. Under these conditions tungsten present in the scrap dissolves with a current efficiency of 70 - 97%. The ammonium tungstate formed can be processed for the preparation of APT. The following examples are given by way of illustration of the present invention and should not be Tungsten heavy alloy scrap. Composition: Fe 3.00% Ni 1.86% Co 0.08% W Rest Titanium plate 35% V/V -3 NH 30 gdm NH Cl 4 NH NO 4 3 -2 400Am -3 30 gdm 2.8 - 3.6 V o 30 - 35 C 82.6% 65 g dm Tungsten heavy alloy scrap Composition: Fe 3.00% Ni 1.86% Co 0.08% W Rest Titanium plate.Isl 35% V/V -3 NH 20 gdm NH Cl 4 NH NO 4 3 -3 20 gdm -2 250 Am 2.4 - 3.2 V the scope of the present construed to limit invention. EXAMPLE -1 Anode Cathode Electrolyte Anodic current density Cell voltage Temperature Current efficiency 'W concentration in ammonium tungstate solution Sulphide added as ammonium sulphide •XAMPLE -2 Anode Cathode Electrolyte Anodic current density Cell voltage Temperature 30 - 35 C Current efficiency 79.3% -3 'W concentration in ammonium 63 g dm tungstate solution Sulphide added as ammonium sulphide 1 g EXAMPLE -3 AnodeTungsten heavy alloy scrap Composition: Fe Ni Co W3.00% 1.86% 0.08% Rest Cathode Electrolyte Anodic current density Cell voltage Temperature Current efficiency 'W concentration in ammonium tungstate solution Sulphide added as ammonium sulphide Titanium plate.1sl 35% V/V -3 NH Cl 30 gdm -3 4 -3 NH NO 30 gdm 4 3 Urea 20 gdm — 2 250 Am 2.4 - 2.6 V o 30 - 35 C 98.0% -3 71 g dm 1 g EXAMPLE -4 AnodeTungsten heavy alloy scrap Composition: Cathode ElectrolyteAnodic current density Cell voltage Temperature Current efficiency 'W concentration in ammonium tungstate solution Sulphide added as ammonium sulphide Fe 3.00% Ni 1.86% Co 0.08% W Rest Titanium plate NH 35% V/V 3 -3 NH Cl 20 gdm 4 -3 NH NO 20 gdm 4 3 -3 Oxalate 5 gdm -2 250 Am 2.2 - 2.4 V O 30 - 35 84.4% -3 60 g dm i g EXAMPLE - 5 AnodeTungsten heavy alloy scrap Composition: Fe Ni Co W 3.00% 1.86% 0.08% Rest Cathode Electrolyte Anodic current density Cell voltage Temperature Current efficiency Titanium plate.1sl 35% V/V -3 2- (CO ) 15 gdm 3 -2 250 Am 5.5 - 8.1 V O 30 - 35 C 87.3% 'W concentration in ammonium 70 g dm tungstate solution Sulphide added as ammonium sulphide 1 g The main advantages of the present invention are: 1. No generation of harmful gases and effluents 2. Ease of operation 3. Low energy consumption 4. Simplified flowsheet for the preparation of APT We Claim: 1. An improved process for the recovery of tungsten metal from the scraps of tungsten heavy alloys which comprises of anodic dissolution of the above said tungsten heavy alloy at an anodic current density of 250 - 800 Am-2 in an ammoniacal electrolyte such as herein described optionally containing additives such as urea, sodium/ammonium oxalate having concentration such as herein described, with a current efficiency in the range of 25-98% and recovering tungsten metal from ammonium tungstate solution by known methods. 2. An improved process as claimed in claim 1 wherein an ammoniacal electrolyte used is comprising of NH3 ( 10 - 35% V/V), NH4CI (15-30 g/l, NH4NO3 (10-30 g/l ) or ammonium/sodium carbonate ( 15-35 g/l) ammonia (10 - 35% V/V). 3. An improved process as claimed in claims 1 & 2 wherein concentration of additives used is 5 - 20 gdm"3 4. An improved process for the recovery of tungsten metal from the scraps of tungsten heavy alloys substantially as herein described with reference to the examples.

Full Text

The present invention relates to an improved process for the recovery of tungsten metal from the scraps of tungsten heavy alloys
The present -invention particularly relates to recovering tungsten as its ammonium salt by subjecting the scraps of heavy tungsten alloy to electrolytic dissolution. The importance of reclamation can be understood from the fact that secondary source provides about 34% of the tungsten input. The process provides a method for direct conversion of tungsten into its ammonium salt from which Ammonium Para Tungstate(APT) can be obtained.
Hitherto it has been proposed to recover
tungsten values from such scraps by adopting
methods like oxidation -reduction, sodium nitrate
alkali fusion (moltexclusion), electrolysis in
acid and alkaline medium.
In air oxidation - reduction process [D.Chait, R.Gero and S.Nadir , J.R&HM,4(1985)40], the scraps
after cleaning are subjected to oxidation at
temperatures of 900 - 10000 C and reduced with H
at the same temperature range. Though this process produces a product having the same composition of original alloy, inclusion of even small impurities such as Al, Ca, Si and Cr oxides have an extremely adverse effect on the final properties of the alloy.

Moreover, the alloys containing copper, forms cuprous oxide during oxidation and protects copper from further attack resulting in lower efficiency.
The moltexclusion technique suffers from the disadvantage of strong contamination by nitrogen or precipitated nitrates. This route is problematic for environment conscious industrialised nations even when suitable catalysts are used [Dai Enzog, Proc. Recycling of Metal1iferrous materials, IMM, UK, Apr.1990, 63]. Also the rate of the process is affected by the over sized scraps. Moreover this method is economically viable for W-Cu/W-Ag alloys only [B.F.Kieffer and E.Lassner, J.R&HM (1988) 63].
Under selective electrolytic dissolution method, a mineral acid like nitric or sulphuric or hydrochloric acid is employed in which certain oxidative additives are added to precipitate tungsten as tungstic acid while impurities are passed on to the electrolyte. However this method suffers from the chronic anode passivation problem.
In caustic soda or ammoniacal medium tungsten dissolves with the formation of tungstate and anodic current depends upon the alkali concentration. If sodium hydroxide is used as electrolyte, one has to process the tungstate for the preparation of ammonium para tungstate (APT) only after the precipitation

of tungstic acid.
According to the process of present invention, tungsten heavy alloy scrap containing 0-5% Fe, 0 5% Ni and 90 - 95% tungsten can be processed through electrolytic dissolution.
The main object of present invention is to provide an improved process for the recovery of tungsten values from the scraps of tungsten heavy alloys which obviates the drawbacks as detailed above. The tungsten heavy alloy scrap is dissolved directly in ammoniacal medium in the presence of additives such as ammonium nitrate, ammonium chloride, sodium chloride, which can improve the conductivity of the electrolyte. Tungsten in the alloy forms ammonium tungstate with ammonia. APT can be obtained from saturated ammonium tungstate solution by control of pH of the solution around 7 and subsequent evaporation. Iron gets precipitated during operation whereas impurities like nickel which can complex with ammonia goes into the solution. The tungstate solution thus obtained may be purified by the addition of ammonium sulphide to remove nickel and cobalt and APT can be crystallized from the resultant purified solution.

Accordingly the present invention provides an improved process for the recovery of tungsten metal from the scraps of tungsten heavy alloys which comprises of anodic dissolution of the above said tungsten heavy alloy at an anodic current density of 250 - 800 Am"2 in an ammoniacal electrolyte such as herein described optionally containing additives such as urea, sodium/ammonium oxalate having concentration such as herein described, with a current efficiency in the range of 25-98% and recovering tungsten metal from ammonium tungstate solution by known methods.
To these ends, the invention broadly consists of dissolving the tungsten in the tungsten heavy alloy scrap pieces/turnings in a suitable electrolyte under the influence of direct current. The electrolyte consists of ammoniacal solution (10- 35% V/V) with ammonium chloride (15-30 gdm-3), ammonium nitrate (10-30 gdm-3) and also additives like urea, oxalate ( 5 -20 dm-3) or ammonia and carbonate ( NH3 -15 to 35% V/V ) and CO32- 15 -35 gdm-3) . The heavy alloy scraps form the anode and titanium plates ad cathodes. Electrolysis is carried out at anodic current densities ranging from 250 - 800Am-2. The temperature of the electrolyte is maintained around 30°C. Under these conditions tungsten present in the scrap dissolves with a current efficiency of 70 - 97%. The ammonium tungstate formed can be processed for the preparation of APT.
The following examples are given by way of illustration of the present invention and should not be

Tungsten heavy alloy
scrap.
Composition:
Fe 3.00%
Ni 1.86%
Co 0.08%
W Rest
Titanium plate
35% V/V -3
NH
30 gdm
NH Cl
4
NH NO 4 3
-2 400Am
-3
30 gdm
2.8 - 3.6 V
o 30 - 35 C
82.6%
65 g dm
Tungsten heavy alloy
scrap
Composition:
Fe 3.00%
Ni 1.86%
Co 0.08%
W Rest
Titanium plate.Isl
35% V/V -3
NH
20 gdm
NH Cl
4
NH NO
4 3
-3
20 gdm
-2
250 Am
2.4 - 3.2 V
the scope of the present
construed to limit invention.
EXAMPLE -1
Anode
Cathode Electrolyte
Anodic current density Cell voltage Temperature Current efficiency
'W concentration in ammonium tungstate solution
Sulphide added as ammonium sulphide
•XAMPLE -2
Anode
Cathode Electrolyte
Anodic current density Cell voltage

Temperature 30 - 35 C
Current efficiency 79.3%
-3
'W concentration in ammonium 63 g dm
tungstate solution
Sulphide added as ammonium sulphide 1 g
EXAMPLE -3

AnodeTungsten heavy alloy scrap
Composition:

Fe Ni Co W3.00% 1.86% 0.08% Rest

Cathode Electrolyte
Anodic current density Cell voltage Temperature Current efficiency
'W concentration in ammonium tungstate solution
Sulphide added as ammonium sulphide
Titanium plate.1sl
35% V/V -3
NH Cl 30 gdm
-3
4
-3
NH NO 30 gdm 4 3
Urea 20 gdm
— 2
250 Am
2.4 - 2.6 V
o 30 - 35 C
98.0%
-3
71 g dm
1 g
EXAMPLE -4
AnodeTungsten heavy alloy scrap
Composition:
Cathode ElectrolyteAnodic current density Cell voltage Temperature Current efficiency
'W concentration in ammonium tungstate solution
Sulphide added as ammonium sulphide

Fe 3.00%
Ni 1.86%
Co 0.08%
W Rest
Titanium plate
NH 35% V/V 3
-3
NH Cl 20 gdm 4
-3
NH NO 20 gdm 4 3
-3 Oxalate 5 gdm
-2 250 Am
2.2 - 2.4 V
O 30 - 35
84.4%
-3 60 g dm
i g

EXAMPLE - 5

AnodeTungsten heavy alloy scrap
Composition:

Fe Ni Co W
3.00% 1.86% 0.08% Rest
Cathode Electrolyte
Anodic current density Cell voltage Temperature Current efficiency
Titanium plate.1sl
35% V/V -3
2-
(CO ) 15 gdm 3
-2 250 Am
5.5 - 8.1 V
O 30 - 35 C
87.3%

'W concentration in ammonium 70 g dm
tungstate solution
Sulphide added as ammonium sulphide 1 g
The main advantages of the present invention are:
1. No generation of harmful gases and effluents
2. Ease of operation
3. Low energy consumption
4. Simplified flowsheet for the preparation of APT

We Claim:
1. An improved process for the recovery of tungsten metal from the scraps of tungsten heavy alloys which comprises of anodic dissolution of the above said tungsten heavy alloy at an anodic current density of 250 - 800 Am-2 in an ammoniacal electrolyte such as herein described optionally containing additives such as urea, sodium/ammonium oxalate having concentration such as herein described, with a current efficiency in the range of 25-98% and recovering tungsten metal from ammonium tungstate solution by known methods.
2. An improved process as claimed in claim 1 wherein an ammoniacal
electrolyte used is comprising of NH3 ( 10 - 35% V/V), NH4CI (15-30
g/l, NH4NO3 (10-30 g/l ) or ammonium/sodium carbonate ( 15-35
g/l) ammonia (10 - 35% V/V).
3. An improved process as claimed in claims 1 & 2 wherein concentration
of additives used is 5 - 20 gdm"3
4. An improved process for the recovery of tungsten metal from the
scraps of tungsten heavy alloys substantially as herein described with
reference to the examples.

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Patent Number

216541

Indian Patent Application Number

285/DEL/1999

PG Journal Number

13/2008

Publication Date

28-Mar-2008

Grant Date

14-Mar-2008

Date of Filing

19-Feb-1999

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG. NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	GAJAVALLI NAGARAJARAO SRINIVASAN	CENTRAL ELECTRO-CHEMICAL RESEARCH INSTITUTE, KARAIKUDI 630 006, TAMILNADU, INDIA.
2	KUNNISSERI VENKATACHALAM VENKATESWARAN	CENTRAL ELECTRO-CHEMICAL RESEARCH INSTITUTE, KARAIKUDI 630 006, TAMILNADU, INDIA.
3	ARIYANAN MANI	CENTRAL ELECTRO-CHEMICAL RESEARCH INSTITUTE, KARAIKUDI 630 006, TAMILNADU, INDIA.

PCT International Classification Number

C25B 1/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA