MXPA97005395A

MXPA97005395A - Recovery process for carbide detungsteno / cobalto using digestion with ac

Info

Publication number: MXPA97005395A
Application number: MXPA/A/1997/005395A
Authority: MX
Inventors: Seegopaul Furnesh; Wu Li
Original assignee: Nanodyne Incorporated
Priority date: 1996-07-17
Filing date: 1997-07-16
Publication date: 1998-04-01

Abstract

The present invention relates to a method for recycling a tungsten / cobalt composition, which comprises oxidizing the tungsten / cobalt composition at a temperature greater than 850 ° C to form an oxidized composition, digesting a portion of the oxidized composition in an acidic solution. water, to form a paste of the dissolved cobalt composition combined with the solid tungsten species, neutralize the paste to an effective pH to cause the cobalt hydroxide and the cobalt oxychloride to precipitate and separate the liquid components from the solid components from this country

Description

RECOVERY PROCESS FOR TUNGSTEN CARBIDE / COBALT USING ACID DIGESTION BACKGROUND OF THE INVENTION Tungsten carbide is widely used today in cutting tools, mining tools, and wear parts. The material can be produced through a variety of different manufacturing processes. Several preferred methods for forming tungsten carbide grains embedded in a cobalt matrix are described in Polizotti, U.S. Patent No. 4,581,041, as well as in McCandlish, U.S. Patent Nos. 5,230,729 and 5,352,269. Tungsten and tungsten carbide products are relatively expensive, and there is an extreme need to recover the waste through the recycling of spent and unused tungsten carbide and tungsten-based products, both for environmental and cost reasons. . There are several processes that are currently used to recycle tungsten carbide and tungsten products. These processes include the zinc process, the cold stream process, an alkaline leaching process, the chlorination, electrolysis, and high temperature fusion systems. With the exception of zinc and cold stream processes, the other methods involve numbers of conversion, extraction, and precipitation steps that increase cycle time and cost. Many of these chemical methods involve the use of acids, bases, and different inorganic salts. The zinc and cold stream processes allow direct conversion to a usable powder, but the purity of the material is a problem, and consequently, the application of this type of recovered material is extremely limited. Typically, the most common zinc process involves heating, sublimation, and grinding processes to recover the WC-Co powder. A key difference is that the zinc process leaves the size of the grain intact, causing the successive growth of the grain in each cycle.

SUMMARY OF THE INVENTION The present invention has its premise in the realization that tungsten carbide and tungsten carbide materials can be recovered in a relatively inexpensive manner. In accordance with the present invention, tunsgtene carbide scrap, tungsten, and scrap of materials containing tunqstene, are oxidized to form tetragonal and octahedral tungsten trioxide which is insoluble in water at a neutral pH. This is digested in an acid solution to dissolve the cobalt, but not the tungsten. The pH of the combined solution / slurry is raised to between 6 and 10 to precipitate the cobalt as cobalt hydroxide, cobalt oxychloride, and traces of other cobalt compounds. The solids, i.e. the tungsten and cobalt compounds, are separated from the slurry, and re-dissolved in an aqueous solution having a pH > 11. This can be spray dried to form a precursor composition for another carburization and the formation of tungsten carbide, or tungsten carbide maintained in a cobalt matrix. If desired, the cobalt can be separated after precipitation by its redissolution once separated from the chloride solutes. The objects and advantages of the present invention will be further appreciated in light of the following description.

Detailed Description In the present invention, the tungsten-containing materials are recycled to form a precursor composition suitable for the formation of tungsten carbide and other composite materials. The tungsten material that can be used in the present invention includes elemental tungsten, tungsten carbide, tungsten oxides, tungsten-copper, tungsten-silver, tungsten nitride, tungsten boride, tungsten selenide, tungsten sulfide, silicon tungsten, and tungsten carbide, with a binder such as cobalt, nickel, or iron. This material will generally be waste material, and is referred to in the industry as "hard waste" or "soft waste". The hard waste would be the previously sintered material, and the soft waste would be the non-sintered powder. With respect to hard waste, it must be shredded to a small size suitable for loading in a rotary kiln. Although it is preferred that the crushed size be reduced to a few millimeters to increase the speed of the reaction, fragments can also be used in the range of 2.54 to 15.24 centimeters. The tungsten-based materials are oxidized at temperatures in the range of 850 ° C to 1,200 ° C, preferably to about 950 ° C. This is done by heating the tungsten-based material in an oxidizing atmosphere with air or oxygen-air mixtures. The oxidation time will vary depending on the size of the lot. A lot size of 4,536 kilograms will require approximately 2-3 lfm of air, taking approximately 12 hours for complete oxidation. Different types of high temperature furnaces can be used for oxidation. However, it is preferable to conduct the work in a rotary kiln, where the oxidized surfaces are continuously eroded to give new and fresh surfaces for efficient processing. This high temperature oxidation of the tungsten materials produces tetragonal and orthorhombic tungsten oxide species that are not normally soluble in the aqueous medium. The binder metal, such as cobalt, if present, forms a complex of cobalt, such as tungstates, and in this case cobalt tungstate. The products of the oxidation are then subjected to an acid digestion. Preferably, this will be an aqueous acid solution having a pH of 2.0 to 1.0 or less. Preferably, the pH should be less than 1. The aqueous acid solution is preferably formed from hydrochloric acid. However, other strong acids such as phosphoric acid, sulfuric acid, and nitric acid may be employed. In this digestion, tungsten oxide basically remains as tungsten oxide, while metal tungstates become a kind of chlorine such as cobalt chloride, and tungsten is converted to tungstic acid or hydrated tungstic acids such as 03 * H20 and W03 »2H20. Other additives present in the material will be converted into chloride species or complex chloride species, and most will be solubilized with the metal chlorides which, in this case, would be cobalt chloride. The tungsten species will remain insoluble. Accordingly, digestion with acid produces a paste containing undissolved tungsten compounds and dissolved cobalt species. This paste can be dried to precipitate cobalt chloride in the presence of tungstate and W03 * H20. Then the cobalt chloride can be redissolved to form a solution, and can be treated separately, if necessary. Alternately and preferably, this mixture will be treated with alkali to increase its pH to about 6.0 to 8.5. This can be done by bubbling ammonia gas into the paste, or with an ammonium hydroxide solution. In this stage, cobalt is precipitated as a hydroxide or an oxychloride, while tungsten remains as an insoluble species, W03 and W03 «H20. Then it is filtered and washed. Impurities, such as cobalt amine and other chloride species, will be separated and discarded. The filtrate or residue is then redissolved in an ammonia-based solution having a pH greater than 11. Again, ammonia gas can be bubbled into the aqueous medium to obtain the desired pH. This will cause the cobalt and tungsten to dissolve, forming primarily a complex of cobalt / amine and ammonium tungstate. Species such as iron, titanium, tantalum, chromium, aluminum, and magnesium will all remain insoluble, or will be precipitated during this procedure if there are some present. The concentration of tungsten and the binding elements can be measured by any suitable analytical method, such as absorption spectroscopy and atomic emission (ICP) techniques. If desired, the proportion of the binder metal to tungsten can then be adjusted by the addition of a water-soluble binder salt such as cobalt nitrate or ammonium metatungstate to the solution. This solution can then be spray dried to form a precursor powder which is suitable for the formation of tungsten carbide, subjecting it to elevated temperatures in the presence of a carburizing gas, as is now well known in the industry. This method greatly simplifies the steps required to recycle the tungsten / cobalt compositions. It is particularly suitable for the subsequent reuse of tungsten and cobalt to form tungsten-cobalt carbide complexes.

This has been a description of the present invention, together with a preferred method for practicing the present invention. However, the invention itself should only be defined by the appended claims, wherein we claim:

Claims

NOVELTY OF THE INVENTION Having described the above invention, it is considered as a novelty, and therefore, the content of the following is claimed as property: CLAIMS

1. A method for recycling a tungsten / cobalt composition, which comprises oxidizing the tungsten / cobalt composition at a temperature greater than 850 ° C to form an oxidized composition; digesting a portion of the oxidized composition in an aqueous acid solution, to form a paste of the dissolved cobalt composition combined with the solid tungsten species; neutralize the paste to an effective pH to cause the cobalt hydroxide and the cobalt oxychloride to precipitate, and separate the liquid components from the solid components of this paste.

2. The method according to claim 1, characterized in that it further comprises dissolving the solid components in an aqueous medium having a pH greater than 11.0, and filtering this aqueous medium to remove any undissolved particulate matter.

3. The method according to claim 2, characterized in that it also comprises spraying the aqueous medium.

4. The method according to claim 3, characterized in that the aqueous medium is an aqueous solution of ammonia.

5. The method according to claim 1, characterized in that the oxidation of high temperature is conducted from 850 ° C to 1,200 ° C in the presence of oxygenate.

6. The method according to claim 5, characterized in that it further comprises forming tungsten carbide by spray drying the aqueous medium and carburizing the formed particles.

7. The method according to claim 6, further comprising adding a soluble salt of a carrier metal to the aqueous basic solution, to establish a desired proportion of the carrier metal to tungsten, and spray drying and carburizing the aqueous solution to form a carrier metal / tungsten carbide complex. The method according to claim 1, characterized in that the acid solution is an aqueous solution of an acid selected from the group consisting of sulfuric acid, phosphoric acid, and nitric acid. 9. The method according to claim 3, characterized in that it further comprises adding a soluble salt of cobalt to the aqueous medium, to establish a desired ratio of cobalt to tungsten, and spray drying and carburizing this aqueous solution to form a cobalt matrix / tungsten carbide. 10. The method according to claim 3, characterized in that it further comprises dissolving additional soluble tungsten salt in the aqueous medium, to establish a desired ratio of cobalt to tungsten. 11. The method according to claim 1, characterized in that it also includes filtering the insoluble material from the paste. 12. The method according to claim 1, characterized in that it also includes adding chelating agents to the paste.