Method for microwave oxidizing roasting of waste WC-Co hard alloy

Abstract

The invention belongs to the field of waste hard alloy recovery treatment, and particularly relates to a waste WC-Co hard alloy microwave oxidizing roasting method, the waste WC-Co hard alloy with the particle size below 150 mu m is subjected to oxidizing roasting under the assistance of microwaves, an oxidation product containing tungsten oxide and cobalt tungstate is obtained, the oxidizing roasting temperature is 400 DEG C or above, the oxidizing time is 30 min or above, and the oxidizing product containing tungsten oxide and cobalt tungstate is obtained. And the power of the microwave is more than 600W. According to the method, the waste WC-Co hard alloy is heated for oxidizing roasting by innovatively adopting microwave selective heating, so that the oxidation effect can be remarkably improved based on a brand new mechanism.

Description

Technical Field

[0001] The invention relates to the technical field of recycling secondary resources containing tungsten, and in particular to a method for recycling waste cemented carbide by microwave oxidation. Background Art

[0002] According to data from the United States Geological Survey, my country's tungsten reserves and production ranked first in the world in 2023, at 2.3 million tons and 63,000 tons respectively. The main mineral resources of tungsten include wolframite, scheelite and mixed minerals, with reserves accounting for 23%, 67% and 10% respectively. Wolframite has become the main object of mining and consumption due to its advantages of easy mining and selection, while scheelite has a lower grade, less rich ore content and more difficult to select ore. Therefore, the resource situation is extremely severe, and a large amount of tungsten-containing resources are used without restraint. The reserves of tungsten-containing resources in my country are showing a downward trend year by year. Tungsten waste is an important source of raw materials for the world's tungsten industry. The recycling and utilization of waste cemented carbide is of great significance to solving the problem of non-renewable mineral resources.

[0003] Tungsten-containing secondary resources for recycling include various cemented carbides, tungsten alloys, soft materials and catalysts, etc. The main recycling methods include zinc melting, electrochemical method, acid leaching, mechanical crushing method, molten salt electrolysis, saltpeter smelting-acid leaching and oxidative roasting-alkali leaching. Corrosive chemicals need to be added during the electrolysis recovery process; zinc is easy to remain during the zinc dissolution chemical recovery process; iron is easily doped during the mechanical crushing recovery process; the acid leaching process is simple, low-cost and energy-efficient, but the production scale is small and harmful gases need further treatment; the pyrometallurgical-wet combined process is to acid-leak or alkali-leak the waste cemented carbide that has been smelted by pyrometallurgy, which can significantly improve the metal recovery rate. Therefore, the main recycling method currently used is the pyrometallurgical-wet combined process, which has the advantages of simple equipment, relatively short cycle and low cost.

[0004] The oxidation method is an important step in pyrometallurgy in the pyrometallurgical-hydrometallurgical combined process. The hard phase and bonding phase in the waste cemented carbide are oxidized into tungsten oxide (WO3) and cobalt tungstate (CoWO4), and then converted into ammonium paratungstate (APT) by hydrometallurgical methods to complete recycling.

[0005] In order to fully oxidize the scrap carbide, the traditional tube furnace oxidation process often requires high temperature and long time, which has the disadvantages of slow heating rate, large heat loss, high energy consumption and long process time. Therefore, how to reduce the energy consumption of the traditional tube furnace oxidation process and shorten the oxidation time is a key technical issue in the recycling of scrap carbide.

[0006] The Chinese patent document with publication number CN113403470A discloses a method for recycling cemented carbide waste, which comprises the steps of mixing the cemented carbide waste with sodium silicate and additives to obtain a mixture, roasting the mixture at a temperature of 400°C-1000°C for 1 h-24 h, and reacting the elemental tungsten and / or tungsten carbide in the cemented carbide waste with sodium silicate and additives under high temperature conditions to form sodium tungstate. The Chinese patent document with publication number CN114934169B discloses a method for recycling tungsten-containing waste, wherein the cemented carbide waste and iron powder are placed in a rotary kiln and roasted in air at 1000°C for 1 h, and after cooling, the roasted product is leached with 2 mol / L hydrochloric acid to obtain leached slag, and the leached slag is leached with 2 mol / L hydrogen peroxide and then heated at 190°C for decomposition and separation to obtain pure tungsten oxide. A Chinese patent document with publication number CN116516151A discloses a method for recycling cemented carbide waste. Waste tungsten carbide (containing cobalt) is oxidized into oxides and tungstates at 600-1500°C and 2-50 h, and then leached with alkali at 60-100°C and 1-12 h to convert metal elements such as cobalt into slag phase, and tungsten is dissolved in the solution as sodium tungstate, thereby achieving solid-liquid separation and recovery effect.

[0007] In summary, the traditional method of heating and oxidizing cemented carbide requires high temperature, long time and relatively high energy consumption. Summary of the invention

[0008] In view of the problems existing in the prior art, the first object of the present invention is to provide a method for microwave oxidation roasting of waste WC-Co cemented carbide, aiming to improve the oxidation effect of waste WC-Co cemented carbide based on a new mechanism.

[0009] A method for microwave oxidation roasting of waste WC-Co cemented carbide, wherein waste WC-Co cemented carbide with a particle size of less than 150 μm is subjected to microwave-assisted oxidation roasting to obtain an oxidation product containing tungsten oxide and cobalt tungstate, wherein the oxidation roasting temperature is above 400°C, the oxidation time is above 30 min, and the microwave power is above 600 W.

[0010] The present invention innovatively adopts microwave selective heating to heat the waste WC-Co cemented carbide for oxidation roasting. Different from the traditional heating method, microwave heating can change the heat conduction mode of the waste cemented carbide, so that the temperature inside and outside are almost simultaneously increased, thereby improving the oxidation effect. In addition, the magnetic loss effect caused by the synergistic effect of natural resonance and exchange resonance generated between the Co component in the waste cemented carbide and the microwave can be utilized, so that the binding phase in the waste cemented carbide is preferentially and rapidly oxidized, and oxygen passages are preferentially formed inside, so that thermal oxidation can be achieved from the inside out to disintegrate the alloy structure and improve the oxidation effect. In particular, a good oxidation effect can be obtained at a lower temperature and a shorter time, which is beneficial to the oxidation recovery of the waste cemented carbide; at the same time, the growth and aggregation of metal grains are promoted, and the recovery effect of tungsten and cobalt is improved.

[0011] In the present invention, the waste WC-Co cemented carbide can be any waste cemented carbide with recycling value, for example, it can be at least one of waste worn cemented carbide tools, waste cemented carbide molds, grinding chips, gutter materials, and desktop materials.

[0012] In the present invention, the good induction of microwaves by Co in the metal intermetallic of the waste cemented carbide is the key to strengthening microwave-assisted oxidation. On this basis, further joint control of the particle size, oxidation temperature, microwave power, etc. of the waste cemented carbide is helpful to further strengthen the effect of microwave-assisted oxidation roasting of the cemented carbide.

[0013] In the present invention, the particle size of the waste WC-Co cemented carbide before oxidation roasting is controlled to be below 50 μm. Studies have shown that under optimal conditions, it can exhibit better synergy with the process of the present invention and can further enhance the oxidation effect of microwaves from the inside out.

[0014] In a preferred embodiment, the microwave power is 600-1600 W, preferably 900-1100 W. The inventors found that at this power, it helps to further enhance the selectivity of oxidation and helps to further improve the oxidation effect.

[0015] In the present invention, the average heating rate of microwave heating is 25-100 °C / min.

[0016] In the present invention, the oxidative roasting is carried out in an oxygen-containing atmosphere, which may be, for example, air, oxygen-enriched gas or pure oxygen.

[0017] In the present invention, the temperature of oxidation roasting is 500-950°C, preferably 600-900°C; considering the effect and energy consumption, it can be further 650-750°C. Under the assistance of microwaves, the temperature is further controlled, so that the oxidation effect of cemented carbide can be further enhanced, so that an excellent oxidation treatment effect can be obtained at a relatively low temperature.

[0018] In the present invention, the holding time at the oxidation roasting temperature is more than 30 minutes, and can further be 30 to 95 minutes. Considering the effect and energy consumption, it can be further preferably 45 to 75 minutes, and can further be 55 to 65 minutes. The process of the present invention, based on the special adaptability and synergy of the microwave and cemented carbide, can be based on a special selective oxidation mechanism, and can obtain a better oxidation effect at a lower temperature and a shorter time.

[0019] Beneficial Effects

[0020] The heating oxidation roasting method of the traditional tube furnace first heats the surface of the waste cemented carbide by hot air convection, and then transfers the heat to the inside of the waste cemented carbide through heat conduction to complete the heating. Its heating rate has certain limitations, the heat loss is large, and the oxidation roasting effect of the waste cemented carbide is poor. In the oxidation roasting method of the microwave tube furnace, under the action of the microwave field, the dipoles in the waste cemented carbide are rearranged in the alternating electric field to cause dipole polarization, and the friction between them causes the inside and outside of the waste cemented carbide to heat up almost at the same time, shortening the oxidation roasting reaction time. The microwave external field is used to strengthen the oxidation roasting reaction of the waste cemented carbide. The waste cemented carbide has a strong microwave response characteristic during the heating process, reducing the temperature gradient to achieve rapid heating, reducing heat loss during the oxidation reaction and shortening the process time.

[0021] Cobalt can convert electromagnetic wave energy into heat energy through magnetic loss due to its high magnetic properties. After crushing, the waste cemented carbide has irregular shapes and sizes, which can produce multiple scattering and reflection inside it, increasing the path length of the electromagnetic wave. Since the microwave penetration depth of cobalt in the waste cemented carbide is 2.4062 μm and the microwave penetration depth of tungsten carbide is 22.74 mm, there is a large difference in the ability to absorb microwaves. Therefore, it also has the advantage of selective heating, so that the cobalt as a bonding phase is heated first, and oxygen channels are formed first inside, further improving the effect of recycling waste cemented carbide by oxidation.

[0022] Thanks to the magnetic loss of cobalt, the disintegration degree of waste cemented carbide can be increased. The BET surface area, total pore volume and adsorption average pore size of the microwave oxidized samples are better than those of the conventionally oxidized samples, which is beneficial to increase the contact area between the subsequent wet leaching samples and the leaching solution, and further conducive to the efficient recovery of tungsten and cobalt elements.

[0023] The crushed waste cemented carbide is subjected to oxidation roasting treatment under a microwave field, and the selectivity of the target reaction is further regulated by jointly controlling the waste cemented carbide particle size, oxidation roasting temperature, time and microwave heat treatment power parameters. The study found that the method described in the present invention can regulate the selective heating of the target reaction at a low temperature and in a short time, and can achieve efficient oxidation of tungsten carbide and cobalt in the waste cemented carbide.

[0024] During the experiment, the inventor accidentally discovered that microwave oxidation has an unexpected effect on the porosity and grain growth of waste cemented carbide. The BET surface area, total pore volume and adsorption average pore diameter of the samples oxidized by microwaves are better than those of the samples oxidized by conventional oxidation, which shows that microwaves make the elements in the waste cemented carbide more aggregated, and the degree of disintegration of the waste cemented carbide can be increased due to the magnetic loss properties of cobalt. The increase in its specific surface area and total pore volume is conducive to increasing the contact area between the subsequent wet leaching sample and the leaching solution, which is further conducive to the efficient recovery of tungsten and cobalt elements. The average grain size of the samples after microwave oxidation is significantly larger than that of conventional oxidation, which shows that microwaves can promote the growth and aggregation of tungsten trioxide and cobalt tungstate grains, thereby further improving the recovery rate of tungsten and cobalt. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the BET adsorption / desorption isotherms of the samples after microwave calcination of Example 2A and conventional calcination of Comparative Example 2.

[0026] Figure 2 It is the SEM spectrum of the samples after microwave calcination in Example 2A and conventional calcination in Comparative Example 2. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with an embodiment. A method for recycling waste cemented carbide by microwave oxidation comprises the following steps:

[0028] Remove oil stains from the surface of various types of recycled scrap carbides;

[0029] Crush and dry the waste cemented carbide to a suitable particle size to complete the preliminary sample preparation;

[0030] An appropriate amount of waste cemented carbide samples were placed in a crucible and placed in a microwave tube furnace for oxidation roasting.

[0031] In one embodiment, the waste cemented carbide comprises WC-Co waste cemented carbide, preferably YG8 cemented carbide. In one embodiment, the microwave oxidation roasting temperature is above 400°C, further 500-950°C, and further 650-750°C.

[0032] In one embodiment, the microwave oxidation roasting time is more than 30 min, further 30-95 min, further 45-75 min.

[0033] In one embodiment, the microwave oxidation roasting power is 600-1600 W, further 900-1100 W.

[0034] In one embodiment, the microwave oxidative roasting particle size is less than 150 μm.

[0035] In any of the above embodiments of the present invention, the cleaned and crushed waste cemented carbide is subjected to microwave oxidation roasting in an air atmosphere by utilizing the microwave absorption ability of the cemented carbide itself. Under the action of the microwave external field, the heating time can be controlled to be about 20 minutes, and the hard phase tungsten carbide (WC) and the bonding phase (Co) in the waste cemented carbide are oxidized into tungsten oxide (WO3) and cobalt tungstate (CoWO4).

[0036] The following are specific cases:

[0037] Example 1

[0038] The YG8 type scrap cemented carbide (of which WC accounts for about 92% and Co accounts for about 8%) is cleaned and crushed to less than 48 μm, placed in a microwave tube furnace, and subjected to microwave (microwave power is 1000 W) oxidation roasting in an air atmosphere blown by an air compressor. The temperature is controlled at 500 ° C (marked as T). After constant temperature roasting time of 1 h (marked as t), it is naturally cooled to obtain and take out a mixed powder of tungsten trioxide and cobalt tungstate.

[0039] According to the method of this embodiment, the carbon content of the sample after oxidation is 1.47wt.%, the carbon removal rate is 74.15%, and the weight gain rate reaches 13.86%. Its BET surface area is 5.6154 m 2 / g, and the total pore volume is 0.031906 cm 3 / g, and the average adsorption pore diameter is 17.5679 nm.

[0040] Comparative Example 1

[0041] Compared with Example 1, the only difference is that there is no microwave-assisted oxidation roasting, that is, electric heating is carried out in a conventional tube furnace, and other operations and parameters are the same as in Example 1.

[0042] The carbon content of the sample after oxidation was 2.12 wt.%, the carbon removal rate was 62.67%, and the weight gain rate reached 12.47%. Its BET surface area was 4.3730 m 2 / g, and the total pore volume is 0.021271 cm 3 / g, and the average adsorption pore diameter is 15.5123 nm.

[0043] Example 2

[0044] Compared with Example 1, the only difference is that the temperature T is adjusted. The experimental groups are:

[0045] Group A: temperature T is 600 °C;

[0046] Group B: temperature T is 700 °C;

[0047] Group C: temperature T is 800 °C;

[0048] Group D: temperature T is 900 °C;

[0049] Other operations and parameters are the same as in Example 1; the results of each group are:

[0050] Group A: The carbon content of the oxidized sample is 0.33 wt.%, the carbon removal rate is 94.19%, and the weight gain rate reaches 18.45%. Its BET surface area is 4.8435 m 2 / g, and the total pore volume is 0.046259 cm 3 / g, and the average adsorption pore diameter is 26.4812nm.

[0051] Group B: The carbon content of the oxidized sample was 0.052 wt.%, the carbon removal rate was 99.13%, and the weight gain rate reached 18.85%. Its BET surface area was 4.3435 m 2 / g, and the total pore volume is 0.057344 cm 3 / g, and the average adsorption pore diameter is 29.8724nm.

[0052] Group C: The carbon content of the sample after oxidation was 0.021 wt.%, the carbon removal rate was 99.74%, and the weight gain rate reached 18.94%.

[0053] Group D: The carbon content of the sample after oxidation was 0.0043 wt.%, the carbon removal rate was 99.92%, and the weight gain rate reached 18.91%.

[0054] It can be seen from Examples 1 and 2 that by using the microwave-assisted roasting method of the present invention, an excellent oxidation effect can be obtained at a relatively low temperature.

[0055] Comparative Example 2

[0056] Compared with Example 2A, the only difference is that there is no microwave-assisted oxidation roasting, that is, electric heating is carried out in a conventional tube furnace, and other operations and parameters are the same as in Example 1.

[0057] The carbon content of the oxidized sample was 1.12 wt.%, the carbon removal rate was 80.28%, and the weight gain rate reached 14.67%. Its BET surface area was 4.0881 m 2 / g, and the total pore volume is 0.029366 cm 3 / g, and the average adsorption pore size is 22.5650 nm. Figure 1 The gas adsorption and desorption mass curves of the samples under microwave and conventional oxidation conditions show that the adsorption mass of microwave is significantly higher than that of conventional oxidation, which will be beneficial to the adsorption of the leaching solution by the subsequent sample leaching, and further to the recovery of tungsten and cobalt. Figure 2 The SEM images of the samples after microwave and conventional calcination clearly show that the distance between particles of the sample after microwave calcination is larger and the degree of cracking of the entire particle is more obvious.

[0058] Comparative Example 3

[0059] Compared with Example 2B, the only difference is that there is no microwave-assisted oxidation roasting, that is, electric heating is carried out in a conventional tube furnace, and other operations and parameters are the same as Example 1.

[0060] The carbon content of the oxidized sample was 0.52 wt.%, the carbon removal rate was 90.85%, and the weight gain rate reached 16.87%.

[0061] Example 3

[0062] Compared with Example 2B, the only difference is that the time t is adjusted. The experimental groups are:

[0063] Group A: time t is 30 min;

[0064] Group B: time t was 45 min;

[0065] Group C: time t was 90 min;

[0066] Other operations and parameters are the same as those in Example 2B; the results of each group are:

[0067] Group A: The carbon content of the sample after oxidation was 0.75wt.%, the carbon removal rate was 86.80%, and the weight gain rate reached 16.97%.

[0068] Group B: The carbon content of the sample after oxidation was 0.29wt.%, the carbon removal rate was 94.89%, and the weight gain rate reached 18.13%.

[0069] Group C: The carbon content of the sample after oxidation was 0.031wt.%, the carbon removal rate was 99.45%, and the weight gain rate reached 18.99%.

[0070] It can be seen from Example 3 that by adopting the microwave-assisted roasting method of the present invention, an excellent oxidation effect can be obtained in a relatively short time.

[0071] Example 4

[0072] Compared with Example 2B, the only difference is that the particle size is adjusted. The experimental groups are:

[0073] Group A: particle size 150-74 μm;

[0074] Group B: particle size 74-48 μm;

[0075] Other operations and parameters are the same as those in Example 2B; the results of each group are:

[0076] Group A: The carbon content of the sample after oxidation was 0.26 wt.%, the carbon removal rate was 95.42%, and the weight gain rate reached 18.34%.

[0077] Group B: The carbon content of the sample after oxidation was 0.15wt.%, the carbon removal rate was 97.36%, and the weight gain rate reached 18.85%.

[0078] Example 5

[0079] YG8 type cemented carbide scrap (of which WC accounts for about 92% and Co accounts for about 8%) is placed in a microwave tube furnace and heated using different microwave powers in an air atmosphere blown in by an air compressor.

[0080] Group A: microwave power is 800W;

[0081] Group B: microwave power was 1400W;

[0082] The results are:

[0083] Group A: The temperature reached 900 °C after heating for 25 min, with an average heating rate of 36 °C / min.

[0084] Group B: The temperature reached 1000 °C after 11 min heating, and the average heating rate was 90.2 °C / min. Similar microwave-assisted oxidation roasting effects were obtained at microwave powers ranging from 800 to 1400 W.

[0085] The above is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art of the present invention, several equivalent substitutions or obvious variations can be made without departing from the concept of the present invention, and the performance or use is the same, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for microwave oxidation roasting of waste WC-Co cemented carbide, characterized in that: The waste WC-Co cemented carbide with a particle size of less than 150 μm is subjected to microwave-assisted oxidation roasting to obtain an oxidation product containing tungsten oxide and cobalt tungstate, wherein the oxidation roasting temperature is above 400 ℃, the oxidation time is above 30 min, and the microwave power is above 600 W.

2. The method for microwave oxidation roasting of waste WC-Co cemented carbide according to claim 1, characterized in that: The waste WC-Co cemented carbide is at least one of waste worn cemented carbide tools, waste cemented carbide molds, abrasive chips, gutter materials, and desktop materials.

3. The method for microwave oxidation roasting of waste WC-Co cemented carbide according to claim 1 or 2, characterized in that: The particle size of the waste WC-Co cemented carbide before oxidation roasting is controlled below 50 µm.

4. The method for microwave oxidation roasting of waste WC-Co cemented carbide according to claim 1, characterized in that: The power of microwave is 600~1600 W.

5. The method for microwave oxidation roasting of waste WC-Co cemented carbide according to claim 1, characterized in that: The power of microwave is 900~1100 W.

6. The method for microwave oxidation roasting of waste WC-Co cemented carbide according to claim 1, characterized in that: Oxidative calcination is carried out in an oxygen-containing atmosphere.

7. The method for microwave oxidation roasting of waste WC-Co cemented carbide according to claim 1, characterized in that: The temperature of oxidation roasting is 500~950 ℃.

8. The method for microwave oxidation roasting of waste WC-Co cemented carbide according to claim 1, characterized in that: The temperature of oxidation roasting is 650~750℃.

9. The method for microwave oxidation roasting of waste WC-Co cemented carbide according to claim 1, characterized in that: The holding time at the oxidation roasting temperature is 30~95min.

10. The method for microwave oxidation roasting of waste WC-Co cemented carbide according to claim 9, characterized in that: The holding time at the oxidation roasting temperature is 45~75min.

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