Method for producing carbide powder

Abstract

The present invention relates to a method for producing cemented carbide powder from cemented carbide scrap, wherein the cemented carbide scrap is subjected to an acid treatment to dissolve the metal binder, thereby forming a carbide residue comprising a carbide skeleton, which is then crushed into cemented carbide powder. The present invention also relates to the powder produced according to the method, and to cemented carbides produced using the cemented carbide powder.

Description

[Technical Field]

[0001] The present invention relates to a method for producing carbide powder from cemented carbide scrap. The present invention also relates to the carbide powder produced according to such a process, and to the cemented carbide produced from such carbide powder. [Background technology]

[0002] Recycling of cemented carbide has been known for a long time and several processes are used in the art for recycling. One of the most common processes is the Zn process, in which the Co binder in the cemented carbide scrap is dissolved in molten Zn, which is then removed by distillation.

[0003] There is a growing demand for recycling of hard metals for both environmental and economic reasons. The availability of primary raw materials is limited and their extraction is resource intensive.

[0004] Although the Zn process is considered efficient, it is not environmentally friendly and has high energy requirements. The final carbide product from the Zn process contains a significant amount of the metal binder (usually Co), but other metals present in the scrap, such as grain growth inhibitors (e.g., Cr, V, etc.), also remain to a large extent in the final carbide product.

[0005] In recent years, the proportion of recycled materials in the production of cemented carbide has increased, which has led to increased demands on the quality of the recycled carbide powder. Due to the increased proportion of recycled materials, repeated recycling of cemented carbide can cause certain elements to accumulate in the recycled material over time. If not removed during recycling, some elements from the coating and / or residues (e.g., brazing residues) can cause defects in the cemented carbide microstructure if they are present in large quantities.

[0006] The object of the present invention is to obtain an environmentally friendly and energy-efficient recycling method for cemented carbide scrap, whereby the carbide powder is of high quality.

[0007] Another object of the present invention is to provide a method for recycling cemented carbide scrap that reduces the amount of grain growth inhibitors (e.g., Cr, V, etc.).

[0008] The object of the present invention is to provide a method for removing residues and / or coatings from hardmetal scrap, whereby the remaining hardmetal scrap is recycled. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows a flow sheet of one embodiment of the present invention. [Figure 2] 1 shows an optical microscope image of the sintered cemented carbide of Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention relates to a method for producing carbide powder from cemented carbide scrap comprising tungsten carbide and a metal binder, the method comprising the following steps: a) subjecting the cemented carbide scrap to an acid treatment at atmospheric pressure and a temperature between 15 and 99°C for a period of at least 24 hours to dissolve the metal binder in the acid solution, wherein the acid is H2SO4 having a concentration between 0.4 and 10N, and the cemented carbide scrap being in a quiescent state during the acid treatment to form an acid solution containing the dissolved metal binder and a solid fraction containing a carbide skeleton, the carbide skeleton being formed by dissolving the metal binder in at least an outer portion of the original cemented carbide scrap; b) separating the acid solution from the solid fraction; c) if the solid fraction comprises a portion of the original cemented carbide scrap in which the metal binder is still present as a cemented carbide residue, separating the carbide skeleton from the cemented carbide residue, d) crushing the carbide skeleton into a carbide residue; and e) grinding the carbide residue to form carbide powder. Includes.

[0011] As used herein, cemented carbide scrap refers to solid pieces of cemented carbide in the form of cutting inserts, drills, end mills, mining buttons, rolls, and the like.

[0012] By hardmetal herein is meant a sintered material comprising grains of a hard phase embedded in a metallic binder, wherein the hard phase contains at least 50 wt% WC. Other hard phase constituents that may be present are carbides, nitrides or carbonitrides of one or more of Nb, Ti, Ta, Cr, V, etc.

[0013] The metal binder may be any metal binder used in the field of cemented carbides, such as any one of Fe, Co and Ni, or alloys thereof. The most commonly used binder is Co.

[0014] If necessary, the cemented carbide scrap undergoes one or more sorting steps, which have several purposes, one of which is to reject scrap that is not cemented carbide, such as cermets (whose hard phases are mainly TiCN or TIC), steels, ceramics, etc.

[0015] Once the non-hardmetal scrap is removed from the remainder, the hardmetal pieces are also separated into various classifications based on size, shape, etc.

[0016] In one embodiment of the present invention, cemented carbide scrap is sorted using markings already present on the cutting tool / cemented carbide piece. An example of such markings is described in U.S. Patent Application Publication No. 2021 / 0229175 (US2021 / 0229175). Such markings can provide information regarding chemical composition, coating type, etc., allowing the scrap to be processed in batches, thereby producing a more predictable composition for the final carbide powder.

[0017] In one embodiment of the present invention, the cemented carbide scrap is crushed into smaller pieces prior to the following process steps. Crushing can be carried out using any mechanical means suitable for the purpose, such as a crusher, shredder, hammer mill, (gravity) drop hammer, etc. Crushing the crushed cemented carbide scrap into small enough pieces before the acid treatment will result in the metal binder being dissolved throughout the pieces. How small the pieces need to be after crushing to allow the metal binder to be dissolved throughout will depend on the type of scrap.

[0018] In one embodiment of the present invention, when the cemented carbide scrap is crushed before being subjected to the acid treatment, no other process steps / treatments are performed on the crushed material before being subjected to the acid treatment, i.e., the acid treatment is applied immediately after the crushing step.

[0019] If a washing and / or decoating step is required, crushing may be carried out before or after the washing and / or decoating step.

[0020] In one embodiment of the present invention, the cemented carbide scrap is not very suitable for shredding, and the scrap is directly subjected to an acid treatment.

[0021] Whether or not hardmetal scrap is suitable for shredding depends on the type of scrap, the size of the pieces, and the physical properties of the scrap (e.g., hardness and toughness). Also, if the hardmetal pieces are small enough to completely dissolve the metal binder, no shredding step is necessary.

[0022] To dissolve the metal binder, the cemented carbide scrap is subjected to an acid treatment by placing it in an acid solution containing sulfuric acid (H2SO4) and water, the concentration (normality) of which is between 0.2 and 10N, preferably between 0.3 and 6N, to dissolve the binder.

[0023] The temperature of the acidic solution is between 15 and 99°C, preferably between 50 and 90°C.

[0024] During the acid treatment, the cemented carbide scrap is in a stationary state, which means in this specification that the cemented carbide scrap pieces are at rest during leaching, i.e., no mechanical interference is applied to the cemented carbide scrap, for example, continuous grinding. Since it is desirable to maintain the grain size of the WC particles, mechanical interference during the leaching process would result in some of the WC particles being broken, limiting the use of the recycled carbide powder.

[0025] The acid treatment is carried out at atmospheric pressure, which means in this specification that no pressure is applied.

[0026] In one embodiment of the invention, the acid treatment is carried out without applying an electric current.

[0027] The cemented carbide pieces remain in the acid solution for between 24 hours and 100 days, preferably between 3 and 50 days.

[0028] After the acid treatment, the dissolved metal binder is present in the acid solution and the remaining cemented carbide scrap forms the solid fraction.

[0029] The solid fraction includes the portion of the cemented carbide scrap from which the metal binder has been removed by acid treatment, and is referred to herein as the carbide skeleton portion. This means herein that the portion still retains its original shape, but the absence of the metal binder means that the carbide particles are held together loosely enough to be easily broken using mechanical means such as crushing. The solid fraction may also include a powder fraction of carbide derived from the naturally disintegrated carbide skeleton.

[0030] If the cemented carbide scrap is subjected to a crushing process prior to acid treatment, the acid will dissolve the metal binder throughout the fragments, causing the fragments to form a carbide skeleton.

[0031] If the cemented carbide scrap is subjected to an acid treatment without being subjected to a crushing process, the binder may not be dissolved throughout the pieces in one acid treatment step.

[0032] If no crushing step is performed before the acid treatment, the solid fraction after the acid treatment also contains parts where the metal binder still remains, the so-called hardmetal residue. Typically, the metal binder remains in the inner part of the original hardmetal scrap, while the outer part is the carbide skeleton from which the metal binder was removed during the acid treatment.

[0033] The carbide skeleton can be further liberated from the hardmetal residue (i.e., inner portion) by mechanical means (i.e., vibration, sieving, etc.), if necessary. The hardmetal residue portion is then removed from the carbide skeleton and acid solution, preferably by sieving and / or magnetic separation. The hardmetal residue portion, which still contains the metal binder, is still magnetic due to the presence of the metal binder, while the skeleton is non-magnetic since the metal binder has been removed.

[0034] The remaining hardmetal portion is then treated as hardmetal scrap and subjected to one or more additional acid treatments until all of the metal binder has dissolved.

[0035] After the acid treatment, the metal binder is present as ions in the acid solution. The acid solution is removed and the carbide framework is washed to remove any remaining acid, usually with water.

[0036] The metal binder dissolved in the acid solution is preferably recovered by precipitation after the carbide residue has been separated from the acid solution.

[0037] Thereafter, the washed carbide skeleton is preferably dried.

[0038] To make the carbide skeleton suitable for comminution, it is usually necessary to break the carbide skeleton into smaller pieces using mechanical means to make it suitable for the comminution process, which is preferably done by crushing to form a carbide residue.

[0039] The grinding can be carried out by any grinding technique common in the field of carbides (for example, ball mill, attritor mill, bead mill, jet mill, etc.).

[0040] In one embodiment of the present invention, the cemented carbide scrap is subjected to a cleaning and / or de-coating process to remove residues and / or coatings from the cemented carbide scrap before recycling. This method comprises the following steps: subjecting the cemented carbide scrap to a preliminary acid treatment in an acid solution having a concentration between 0.2 and 10 N at a temperature between 15 and 99°C for a time period between 30 minutes and 72 hours; Removal of residues and / or coatings by mechanical means Includes.

[0041] The most common type of coated cemented carbide scrap is cutting tools (e.g., inserts, drills, end mills, etc.). Typical coatings are deposited using conventional PVD (physical vapor deposition) and CVD (chemical vapor deposition) processes. Recently, more advanced deposition techniques, such as the PVD technique HIPIMS (high power impulse magnetron sputtering), have become more common.

[0042] Cutting tools such as inserts are typically deposited with either PVD or CVD techniques, whereas cutting tools such as drills or end mills are usually coated using PVD techniques.

[0043] Residue, as used herein, refers to any undesirable particles or elements that are useful to remove from cemented carbide scrap before recycling the cemented carbide. Examples of residue include brazing residue, rock residue, residue of workpiece material welded to the cutting tool during machining operations, etc.

[0044] Cemented carbide mining tools and wear parts are typically brazed to holders, drill heads, etc. Before being recycled, the cemented carbide parts are separated from the holders and some of the solder may still remain on the cemented carbide parts. Mining tools may also contain pieces of rock that have been wedged into the mining tool during operation. Cutting tools may also contain brazed parts, which may leave behind brazing residues.

[0045] The acid used in the acid solution in the preliminary acid treatment to remove residues and / or coatings may be any acid capable of dissolving the metal binder beneath the residues and / or coatings, and is preferably one or more of sulfuric acid (H2SO4), hydrochloric acid (HCl), acetic acid (CH3COOH), or phosphoric acid (H3PO3), more preferably one or more of sulfuric acid (H2SO4) and hydrochloric acid (HCl), and most preferably sulfuric acid (H2SO4). If the cemented carbide scrap contains brazing residues (e.g., solder), the solder may also be at least partially dissolved in the acid. The concentration of the acid solution may be 0.2 to 10 N, preferably 0.3 to 6 N, more preferably 0.5 to 5 N. The temperature of the acid solution may be between 15 and 99°C, preferably between 50 and 90°C. The time for which the cemented carbide is subjected to the preliminary acid treatment is between 30 minutes and 72 hours, preferably between 10 and 48 hours. This time depends on the concentration and temperature of the acid solution.

[0046] In one embodiment of the present invention, the pre-acid treatment is carried out without the application of pressure or electrical current.

[0047] The cemented carbide pieces are preferably washed after the pre-acid treatment to remove any remaining acid, primarily to avoid corrosion of the equipment.

[0048] The acid used in the previous acid treatment can be reused, for example, when producing the carbide powder according to the present invention.

[0049] Although residues and / or coatings may still be present after the prior acid treatment, they will be less adherent because the acid treatment has dissolved the metal binder in the outermost part of the cemented carbide, allowing the residues and / or coatings to be removed.

[0050] After the prior acid treatment, the residue and / or coating is removed from the cemented carbide scrap by mechanical means. By mechanical means herein is meant any type of mechanical treatment capable of removing the residue and / or coating. The residue and / or coating is preferably removed by blasting or tumbling. Following the mechanical treatment, the removed residue and / or coating residue is separated from the cemented carbide scrap by suitable means such as sieving, magnetic means, etc.

[0051] In one embodiment of the present invention, after a prior acid treatment, residues and / or coatings are removed from the cemented carbide scrap by blasting. Blasting can be used with any type of cemented carbide scrap, but is particularly useful for drills and end mills with flutes. If a coating is present within the flutes, it may be difficult to reach with other types of mechanical removal methods. The exact parameters of the blasting process, i.e., type of blasting media, blasting pressure, wet or dry blasting, nozzle size, etc., may depend on several things (e.g., the type of blasting equipment used), and it is up to the skilled artisan to adjust the parameters to achieve the desired results.

[0052] In one embodiment of the present invention, after the prior acid treatment, residues and / or coatings are removed from the hardmetal scrap by tumbling. The most common type of tumbling involves placing pieces in a rotating drum, where the pieces collide with each other and with the drum walls. Tumbling is particularly suitable when processing large amounts of hardmetal scrap. The parameters of the tumbling process (e.g., drum load, rotation speed, etc.) are set by a person skilled in the art depending on the type and size of the drum, the size of the hardmetal scrap, etc.

[0053] In one embodiment of the present invention, the cemented carbide scrap is subjected to a mechanical treatment before the preliminary acid step. The mechanical treatment can be any technique that can cause defects (e.g., cracks) in the coating or even break down the cemented carbide scrap into smaller pieces. Examples of such techniques include tumbling, blasting, and crushing. Creating defects or breaking down the scrap can make it easier for the acid in the acid treatment to penetrate the coating in order to dissolve the metal binder. This step can be useful when the coating thickness is too thick and / or when the coating is of a very dense type, such as a HIPIMS coating.

[0054] In one embodiment of the present invention, the method relates to a method for producing carbide powder from coated cemented carbide scrap, the method comprising the steps of: a) subjecting the cemented carbide scrap to a cleaning and / or decoating process and a crushing process; b) subjecting the crushed cemented carbide scrap to an acid treatment at atmospheric pressure and a temperature between 15 and 99°C for a time period of at least 24 hours to dissolve the metal binder in the acid solution, wherein the acid is HSO having a concentration between 0.2 and 10N, and the cemented carbide scrap is in a quiescent state during the acid treatment to form an acid solution containing the dissolved metal binder and a solid fraction containing a carbide skeleton, the carbide skeleton being formed by dissolving the metal binder; c) separating the acid solution from the solid fraction containing the char framework; d) crushing the carbide skeleton into a carbide residue; and e) grinding the carbide residue to form carbide powder. Includes.

[0055] In one embodiment of the present invention, the method relates to a method for producing carbide powder from uncoated cemented carbide scrap, the method comprising the steps of: a) subjecting the cemented carbide scrap to a washing process and a crushing process; b) subjecting the crushed cemented carbide scrap to an acid treatment at atmospheric pressure and a temperature between 15 and 99°C for a time period of at least 24 hours to dissolve the metal binder in the acid solution, wherein the acid is HSO having a concentration between 0.2 and 10N, and the cemented carbide scrap is in a quiescent state during the acid treatment to form an acid solution containing the dissolved metal binder and a solid fraction containing a carbide skeleton, the carbide skeleton being formed by dissolving the metal binder; c) separating the acid solution from the solid fraction containing the char framework; d) crushing the carbide skeleton into a carbide residue; and e) grinding the carbide residue to form carbide powder. Includes.

[0056] In one embodiment of the present invention, the method relates to a method for producing carbide powder from uncoated cemented carbide scrap, the method comprising the steps of: a) subjecting the cemented carbide scrap to an acid treatment at atmospheric pressure and a temperature between 15 and 99°C for a time period of at least 24 hours to dissolve the metal binder in the acid solution, wherein the acid is H2SO4 having a concentration between 0.2 and 10N, and the cemented carbide scrap is in a quiescent state during the acid treatment to form an acid solution containing the dissolved metal binder and a solid fraction containing a carbide skeleton, the carbide skeleton being formed by dissolving the metal binder in at least an outer portion of the original cemented carbide scrap; b) separating the cemented carbide fraction in which the metal binder still remains from the cemented carbide fraction in which the binder has dissolved; c) the binder-dissolved cemented carbide fraction forms a carbide residue; d) separating the carbide residue from the acid solution and the metal binder; e) subjecting the carbide residue to a grinding process to form carbide powder. Includes.

[0057] The present invention also relates to carbide powders made according to the above-described methods.

[0058] The final carbide powder contains less than 1 wt% metal binder, preferably less than 0.5 wt% metal binder, more preferably less than 0.2 wt% metal binder.

[0059] In one embodiment of the invention, the final carbide powder contains at least 40%, preferably 50% less Cr than originally present in the cemented carbide scrap.

[0060] In one embodiment of the invention, the final carbide powder contains at least 20%, preferably 30% less V than originally present in the cemented carbide scrap.

[0061] The WC grains pass through the process almost completely unchanged, so that the WC grain size in the final carbide powder will be consistent with the WC grain size in the cemented carbide scrap.

[0062] The present invention also relates to the use of recycled carbide powder for making sintered cemented carbide, wherein the hard phase in the cemented carbide is at least 50 wt. %, preferably at least 70 wt. %, more preferably at least 90 wt. %, and most preferably 100 wt. % recycled carbide powder as described above. The recycled carbide powder is used in the same way as conventional WC raw material, and the cemented carbide is produced according to standard practice in the art, i.e., mixing the input raw materials, for example, by wet grinding, slurry formation, spray drying, pressing, and sintering.

[0063] drawing FIG. 1 shows a flow sheet of one embodiment of the present invention, where A is a washing and / or decoating process, B is a crushing process, C is an acid treatment, D is a process where the acid solution is separated from the solid fraction, E is a process where if not all the metal binder is dissolved in the acid treatment, the cemented carbide scrap still containing the metal binder is separated to be recycled for further acid treatment, F is a step where the cemented carbide skeleton is crushed, and G is a grinding process.

[0064] FIG. 2 shows an optical microscope image of the sintered cemented carbide of Example 7.

[0065] Example 1 (invention) Uncoated cemented carbide scrap in the form of indexable inserts was crushed into smaller pieces and screened to reduce the size to less than 8 mm. The scrap pieces were then placed in a container. Acid treatment was carried out in 12 wt% H2SO4 (2.6 N) at 80°C. The acid concentration was continuously adjusted during the acid treatment to maintain the acid concentration in the container. The total acid treatment time was 17 days.

[0066] At the end of the acid treatment process, the acid was removed and the remaining carbide framework was washed with four washing cycles to remove any remaining acid residue.

[0067] The remaining carbide framework was broken down to a size of less than 1 mm and then ball milled to form carbide powder.

[0068] The final carbide powder was analyzed and its elemental analysis and grain size are shown in Table 1. The remaining elements are W and impurities, and all values ​​are in wt%. The oxygen and carbon content were analyzed using a LECO instrument (WC-600), and the other elements were analyzed by XRF (X-ray fluorescence) using a Panalytical Axios Max Advanced instrument.

[0069] Table 1 TIFF2026500363000001.tif27170

[0070] Example 2 (invention) Pre-broken cemented carbide rods were used as starting material for cemented carbide scrap.

[0071] The scrap pieces were then placed in a vessel. Leaching was carried out in 12 wt% H2SO4 (2.6N) at 60 °C. The acid concentration was kept as stable as possible. The acid concentration was continuously adjusted during the acid treatment to maintain the acid concentration in the vessel. The total acid treatment time was 20 days.

[0072] At the end of the leaching process, the acid was removed and the remaining char framework was washed through three washing cycles to remove any remaining acid residue.

[0073] After leaching, the Co content of the carbide framework was 0.1%.

[0074] The remaining carbide framework was deagglomerated (<1 mm) and then ball milled to form carbide powder.

[0075] The final carbide powder was analyzed and its properties are shown in Table 2.

[0076] Table 2 TIFF2026500363000002.tif27170 1 FSSS as Fisher subsieve sizer: commercially available

[0077] Example 3 (invention) The coated batches were subjected to an acid treatment in 12 wt% HSO (2.6N) at 70°C for 24 hours. After the acid treatment, the inserts were washed with water, and then 1500 g of the inserts were placed in an 800 ml mill and subjected to a tumbling process, filling the mill two-thirds full with water. The mill was then run for 36 hours.

[0078] After tumbling, the cemented carbide scrap and fine coating residue were separated by a sieve (1 mm).

[0079] Comparing the cemented carbide scrap before and after the decoating process, it was concluded by visual inspection that more than 70% of the coating was removed.

[0080] Example 4 (invention) 13.75 tons of coated inserts were treated in 12 wt% HSO (2.6N) at 80°C for 24 hours. After acid treatment, the inserts were washed and subjected to a tumbling process using a large mill (1 ton). The mill was then operated for 36 hours.

[0081] After tumbling, the cemented carbide scrap and fine coating residue were separated by a sieve (3 mm).

[0082] Comparing the cemented carbide scrap before and after the decoating process, it was concluded by visual inspection that more than 70% of the coating was removed.

[0083] Example 5 (comparison) For comparison, a batch of coated inserts was subjected to a tumbling process in water for 36 hours. The inserts were washed and examined, and after visual inspection, more than 60% of the coating was still remaining.

[0084] The inserts were then subjected to a recycling process (Zn process) to form recycled cemented carbide powder, which was analyzed to detect coating flakes and coating residues.

[0085] Example 6 Drills and end mills with PVD coatings were prepared.

[0086] One batch was subjected to acid treatment in 12 wt% H2SO4 (2.6N) for 24 hours at 60° C. This batch is hereafter referred to as Invention 1.

[0087] For comparison, the coated cutting tool portions that were not subjected to acid treatment were divided into three batches (Comparative 1-3).

[0088] Invention 1 and Comparative Examples 1-3 were subjected to dry blasting in a suction blast cabinet "Boy 100" equipped with a filtration unit using an injection blasting system with manual movement of the blast gun. The blasting media was Al2O3 (mesh 120). The pressure was 5 bar, the nozzle diameter was 8 mm, and the nozzle distance was 70 mm. The blasting times were varied and are shown in Table 1. The cutting tools were visually inspected and the results are shown in Table 3.

[0089] Table 3 TIFF2026500363000003.tif91170

[0090] As can be seen from these examples, blasting alone does not provide sufficient coating removal, even with long blasting times, whereas the process according to the present invention shows a high removal rate.

[0091] Example 7 Sintered cemented carbides were fabricated using the recycled carbide powder prepared according to Example 1. The carbide powder was mixed with 6.5 wt% Co and 2 wt% PEG (amounts based on the total weight of the powder) to form a powder blend. The powder blend was mixed with a grinding liquid (ethanol / water) to form a slurry, which was then dried in a pan and then pressed into a green body.

[0092] The green bodies were debindered at 310°C for 120 minutes and then sintered in vacuum at 1450°C for 60 minutes.

[0093] The microstructure of the sintered cemented carbide was examined by optical microscope (LOM). Figure 2 shows the LOM image, which shows that the microstructure is completely dense.

Claims

1. 1. A method for producing carbide powder from cemented carbide scrap comprising tungsten carbide and a metal binder, comprising the steps of: a) subjecting the cemented carbide scrap to an acid treatment at a temperature between 15 and 99°C at atmospheric pressure for a period of at least 24 hours to dissolve the metal binder in the acid solution, wherein the acid is a H2O solution having a concentration between 0.4 and 10N; ２ SO ４ wherein the cemented carbide scrap is kept quiescent during the acid treatment to form an acid solution containing a dissolved metal binder and a solid fraction containing a carbide skeleton, the carbide skeleton being formed by dissolving the metal binder in at least an outer portion of the original cemented carbide scrap. b) separating the acid solution from the solid fraction; c) if the solid fraction comprises a portion of the original cemented carbide scrap in which the metal binder is still present as a cemented carbide residue, separating the carbide skeleton from the cemented carbide residue; d) crushing the carbide skeleton into a carbide residue; and e) grinding the carbide residue to form carbide powder. A method comprising:

2. 10. The method of claim 1, wherein the cemented carbide residue is separated from the carbide skeleton using magnetic means.

3. 3. The method of claim 2, wherein the hardmetal residue, on which the metal binder still remains, is treated as hardmetal scrap and repeatedly subjected to the method of claim 1 until all the metal binder has dissolved.

4. 4. The method according to any one of claims 1 to 3, wherein the concentration of the acid solution is between 1 and 6N.

5. 5. The method according to any one of claims 1 to 4, wherein the cemented carbide scrap is subjected to an acid treatment at a temperature between 50 and 90°C for a period of 1 to 100 days.

6. 6. The method according to any one of claims 1 to 5, wherein the cemented carbide scrap is subjected to a crushing step before the acid treatment, and the acid treatment is applied immediately after the crushing step.

7. 7. The method according to any one of claims 1 to 6, wherein the cemented carbide scrap is sorted using information from markings already present on the cemented carbide scrap pieces.

8. 8. The method according to any one of claims 1 to 7, wherein the cemented carbide scrap is subjected to a cleaning and / or decoating step before the acid treatment.

9. 9. The method according to claim 8, wherein the cleaning and / or decoating step comprises subjecting the coated cemented carbide scrap to a preliminary acid treatment in an acid solution having a concentration between 0.2 and 10 N at a temperature between 15 and 99°C for a time between 30 minutes and 72 hours, after which the coating is removed using mechanical means.

10. 10. The method of claim 9, wherein the mechanical means is selected from tumbling or blasting.

11. 11. The method according to any one of claims 8 to 10, wherein the prior acid treatment is preceded by a mechanical pretreatment, the mechanical pretreatment being selected from tumbling, blasting and crushing.

12. 12. Carbide powder made from recycled cemented carbide scrap produced by the method of any one of claims 1 to 11, wherein the powder has a metal binder content of less than 1 wt%.

13. 13. The carbide powder of claim 12, wherein the metal binder content is less than 0.5 wt%.

14. 14. Use of the carbide powder according to claim 12 or 13 for making a sintered cemented carbide body, wherein at least 50 wt% of the hard phase consists of the carbide powder.

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