Title of Invention

AN IMPROVED PROCESS FOR THE RECOVERY OF TUNGSTEN FROM TUNGSTEN ALLOY SCRAPS"

Abstract

An Improved process for the recovery of tungsten from tungsten alloy scraps which comprises: i) drying tungsten scraps at a temperature in the range of 100 to 250°C for a period from 4 to 6 hours and washing with trichloroethylene, benzine or acetone to free it from oil and grease, ii) characterized in that mixing the said cleaned tungsten scraps with sodium chloride in the range of 5-10% by, weight of tungsten scraps, iii) curing the resultant tungsten scraps at ambient temperature with nitric acid of strength is in the range from 65 to 72% solution in the range of greater than stoichiometric amount of acid, for a period of 8 to 30 hours iv) diluting the slurry with water after curing, decanting and filtering for solid/liquid separation, v) washing the residue thoroughly with water to free it from acid, vi) drying the residue & reducing at a temperature in the range of 600 to 850°C for a period of 1 to 6 hours, followed by cooling under inert atmosphere to obtain pure tungsten.

Full Text

This invention relates an improved process for the recovery of tungsten from tungsten alloy scraps. Tungsten is a metal of great importance. Cemented carbides with valuable metals like nickel, cobalt, iron etc. as the binding medium are widely used in hard metal industry for manufacture of cutting tools, drilling tools and high wear resistance parts. During processing, the tungsten industry are generating about 30-40% scraps of its inputs per year either as hard scraps of discarded cutting tips, buttons, bits, hot rolls, dies etc. or as soft scraps produced from discarded pre-sintered parts, grinding sludges,dust collector fines, floor sweeps and spent catalysts. Tungsten scraps generated usually contains valuable metals like nickel, cobalt,iron etc. Therefore, these scraps may be considered as a potential source of high value tungsten, nickel and cobalt. The reclaimed tungsten metal can be recycled in preparation of tungsten carbide for hardfacing. In the hitherto known cold stream process (Blasko, M.J.,1976, Recent developments in hard metals, Metal powder Rep 12: 452-453) which uses high-velocity stream of air at mach 2 to shatter the cemented carbide into a fine well-distributed powder. In another hitherto zinc process (Keiffor, B.F., 1983 Recycling Systems with Particular reference to the Zinc Process. Metal power Rep., 38 667-672) which recovers tungsten carbide by alloying with zinc. Yet in another process (Hartline, A.G. III, Campbell J.A. and Maget T.T (1980). Reclaiming cemented tungsten carbide. In L.H. Yaverpallm (Ed). Technology of metal powders, Recent Developments. Noyes Data Corporation, N.J., pp.309-311), to recover tungsten, cemented carbide are fused with sodium nitrate to yield soluble sodium tungstate which is leached with water. In an another process (Jonsson, K. 1968. South African Patent 25, 40) where tungsten values are recovered from scrap by conversion of tungsten to tungsten hexachloride. In an another electrolytic method (Nutzel, H.G. and Kuhl, R. 1982, process for decomposing hard metal scrap. U.S. Patent 4- 349-423) where nitric acid is used to dissolve the binder at current density of 2-10 Amp per kg. of scrap. Yet in another electrochemical dissolution method (Gandehari, M.H., Faulkner, J.K. and Schussler M. 1982. "Selective dissolution of the binder phase alloy (Co-W) from WC-Co cemented carbide in particulate bed electrode system. J. of electrochem Soc., 129-2666-2668) where active dissolution of binder phase is occured in phosphoric acid medium. The hitherto known processes have the following drawbacks: In the Cold stream process the cemented carbides with high cobalt can not be processed because of their high toughness. Moreover, the tungsten powder is contaminated with oxygen and elements of the surface of the blast chamber (iron). Zinc process has no purifying action and the chemical composition of the input scrap and of the output powder are practically the same. Thus, the scraps must be cleaned and sorted. Moreover, the process requires pure zinc since any-nonvolatile impurity contained in the zinc will remain in the reclaimed powder. Also the repeated use of this process results in a progressive enrichment in impurities. This process needs heat energy also. The nitrate process consumes more heat energy for fusion/melting. The number of unit operation is more. Moreover, the product is in the form of CaWO which needs further processing to get tungsten in powder form thereby increasing the cost of production. The chlorination process consumes more heat energy. The process also corrodes the processing equipments. The process of electro-chemical dissolution needs electric energy for recovery of tungsten. The main object of the present invention is to provide an improved process for the recovery of tungsten and by products such as nickel and cobalt from tungsten alloy scraps which is generally considered as rejects. Another object of the present invention is to provide an improved process for the recovery of tungsten value whereby processing cost of tungsten is reduced. Yet another object of the present invention is to provide an improved process whereby tungsten powder is produced without loss of tungsten value. Still another object of the present invention is to provide an improved process whereby costly binding metals such as nickel, cobalt are recovered as by-product. In the process of the present invention cleaned tungsten scraps containing nickel, cobalt, iron etc. are subjected to curing at ambient temperature with nitric acid solution where nickel, cobalt, iron etc. present in the scraps are chemically reacted with nitric acid producing water soluble nitrate of nickel, cobalt, iron etc. leaving the unreacted tungsten in the residue. The chemical reactions occuring during curing may be represented as follows : Ni + 4 HNO2 = Ni(NO3)2 + 2 NO2 + 2 H O2 Co + 4HNO3 = Co(NO3)2 + 2 NO2 + 2 H O2 Fe + 2 HNO3 = FeNO3 + NO2 + H2O After curing, the solid/liquid separation is done by dilution and decantation. The tungsten containing residue is repeatedly washed with water to free it from entrapped soluble nickel, cobalt and iron salts followed by filtration. The product after removal of binding metals is reduced under hydrogen atmosphere in the range of 600 to 850oC to remove the oxide films. The possible chemical reactions during reduction are as follows : WO3 + 3H2 ----> W+3H2O The reclaimed pure tungsten powder thus produced can be used for making cemented tungsten carbide and other powder metallurgy applications in the tungsten industry. After curing treatment, the liquor containing nickel, cobalt and iron is further processed fro recovery of nickel and cobalt by conventional processes. Accordingly, the present invention provides an improved process for the recovery of tungsten from tungsten alloy scraps which comprises: i) drying tungsten scraps at a temperature in the range of 100 to 250°C for a period from 4 to 6 hours and washing with trichloroethylene, benzine or acetone to free it from oil and grease, ii) characterized in that mixing the said cleaned tungsten scraps with sodium chloride in the range of 5-10% by weight of tungsten scraps, iii) curing the resultant tungsten scraps at ambient temperature with nitric acid of strength is in the range from 65 to 72% solution in the range of greater than stoichiometric amount of acid, for a period of 8 to 30 hours iv) diluting the slurry with water after curing, decanting and filtering for solid/liquid separation, v) washing the residue thoroughly with water to free it from acid, vi) drying the residue & reducing at a temperature in the range of 600 to 850°C for a period of 1 to 6 hours, followed by cooling under inert atmosphere to obtain pure tungsten. According to a feature of this invention, the tungsten scraps employed may be selected from tungsten scrap having the following composition range: W = 70-90% Ni = 3-10% Fe = 5-10% Co = 0.1-5% The tungsten scraps may be dried at a temperature in the range of 100 to 120°C for a period of 4 to 6 hours. The nitric acid used may be commercial grade. Strength of nitric acid solution used for curing may vary from 65-72%. The sodium chloride used as additive may be commercial grade. The pure tungsten powder may be dried at a temperature in the range of 110 to 250oC for a period of 4 to 6 hours. According to feature of this invention, the leach-liquor produced on curing contains valuable metals like nickel and cobalt which on further processing by conventional methods produce nickel and cobalt as by-product. By the process of present invention most of the binding metals like nickel, cobalt and iron etc. are removed and tungsten powder of 99.9% purity is produced which may be recycled in the tungsten industry. The following examples are given by way of illustration and should not be construed to the limit the scope of the invention. The tungsten scraps treated were of the following composition: W = 87.0% Ni = 5.14% Fe - 3.40% Co = 0.19% The strenth of nitric acid used in the examples is in the range of 65-72% and additive like sodium chloride is used of commercial grade. Example-1 50 gm. of tungsten scrap sample was dried at 12p C and then was washed with trichloroethylene to free it from oil and grease. The dry washed sample was cured at ambient temperature with 0 to 100 percent excess of stoichiometric amount of nitric acid for 24 hours. After curing, the solid/liquid separation was done by dilution and decantation. The tungsten containing residue was washed with water and then dried at 110 C. The results of reclaimed tungsten after removal of nickel, cobalt and iron are given in Table-1. (Table Removed) Example-2 50 gm. of tungsten scraps were subjected to curing with 0 to 10 percent by weight of additive like sodium chloride for 24 hrs. at ambient temperature as per Table-2. The results are given in Table-2. (Table Removed) Example-3 50 gm. of tungsten scrap was mixed with 5% sodium chloride and 100% excess of stoichiometric amount of nitric acid. The mix was then allowed for curing for different time as per Table-3. The result of reclaimed tungsten powder after removal of nickel, cobalt and iron are given in Table-3. (Table Removed) Example-4 The reclaimed tungsten obtained after removal of nickel, cobalt and iron has been subjected to reduction in the temperature range of 650-850°C for 6 hours under hydrogen atmosphere to remove the oxide film from the enriched tungsten as per Table-4. The results of reduction tests are given in Table-4. (Table Removed) The main advantages of the present invention are : 1) In the present invention binding metals like nickel, cobalt and iron have been removed at ambient temperature without any extra heat or electric energy. Where as in the existing processes extra energy is required. 2) The present invention produces pure tungsten powder which can be re-used where as the existing processes have no purifying action and the chemical compositions of input scrap and output powder remains unchanged leading to further purification to produce pure tungsten powder. 3) The present process enables to remove nickel and cobalt without any loss of tungsten value where as in the existing processes some loss of tungsten has been taking place. 4) In the present invention the process steps are less when compared to the existing processes leading to less operating cost. 5) In the present process chemicals used are cheaper than the existing processes. 6) In the present invention the valuable metals like nickel and cobalt is obtained as by-product recovery We Claim: 1. An improved process for the recovery of tungsten from tungsten alloy scraps which comprises: i) drying tungsten scraps at a temperature in the range of 100 to 250°C for a period from 4 to 6 hours and washing with trichloroethylene, benzine or acetone to free it from oil and grease, ii) characterized in that mixing the said cleaned tungsten scraps with sodium chloride in the range of 5-10% by weight of tungsten scraps, iii) curing the resultant tungsten scraps at ambient temperature with nitric acid of strength Is in the range from 65 to 72% solution in the range of greater than stoichiometric amount of acid, for a period of 8 to 30 hours iv) diluting the slurry with water after curing, decanting and filtering for solid/liquid separation, v) washing the residue thoroughly with water to free it from acid, vi) drying the residue & reducing at a temperature in the range of 600 to 850°C for a period of 1 to 6 hours, followed by cooling under inert atmosphere to obtain pure tungsten. 2. An improved process as claimed in claims 1 wherein the tungsten scraps are dried at a temperature in the range of 100 to i20°C . 3. An improved process as claimed in the claims 1 wherein the pure tungsten powder is dried at a temperature in the range of 110 to 250°C for a period of 4 to 6 hours. 4. An improved process for the recovery of tungsten and by-products such as nickel and cobalt from tungsten alloy scraps substantially as herein described with reference to the examples.

Documents:

645-DEL-1996-Abstract.pdf

645-DEL-1996-Claims.pdf

645-del-1996-complete specification (granted).pdf

645-DEL-1996-Correspondence-Others.pdf

645-DEL-1996-Correspondence-PO.pdf

645-DEL-1996-Description (Complete).pdf

645-DEL-1996-Descripton (Provisional).pdf

645-DEL-1996-Form-1.pdf

645-DEL-1996-Form-2.pdf

645-DEL-1996-Form-3.pdf

645-DEL-1996-Form-4.pdf

645-DEL-1996-Form-6.pdf