Method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode

Abstract

The invention discloses a method for preparing silicon carbide from a silicon waste material and a waste lithium ion battery graphite anode. The method specifically comprises the following steps: (1) respectively carrying out ball milling and mixing on the diamond wire cutting silicon waste material and the crushed and screened waste lithium ion battery graphite anode; (2) high-temperature smelting, ball milling and roasting; and (3) placing in an acid, stirring, leaching, centrifuging, washing, drying and ball-milling to obtain the high-efficiency leaching agent. According to the method, the diamond wire cutting silicon waste and the waste lithium ion battery graphite anode are used as preparation raw materials, silicon carbide is prepared and purified through the processes of ball milling, material mixing, smelting, roasting, acid leaching, centrifuging, drying and the like, and finally high-purity nanoscale silicon carbide particles are obtained. The recycling of the diamond wire cutting silicon waste and the graphite anode of the waste lithium ion battery not only can reduce resource waste and environmental pollution and improve the utilization rate of the waste, but also can generate considerable economic benefits.

Description

Technical Field

[0001] The invention relates to the technical field of silicon carbide preparation, and more particularly to a method for preparing silicon carbide from silicon waste and waste lithium battery graphite anodes. Background Art

[0002] Silicon carbide (SiC), also known as corundum, has a density of 3.2g / cm 3 , natural SiC is very rare and is mainly synthesized artificially. SiC is a Group IV-IV compound semiconductor material composed of Si and C, with a variety of allotropic types. The third-generation semiconductor materials represented by SiC have the advantages of large bandgap, high breakdown electric field, high thermal conductivity, high electron saturation rate and strong radiation resistance. Therefore, semiconductor devices prepared using third-generation semiconductor materials can not only operate stably at higher temperatures, but are also suitable for high voltage and high frequency scenarios. In addition, higher operating capabilities can be achieved with lower power consumption.

[0003] With the introduction of the concepts of carbon peak and carbon neutrality, the photovoltaic industry has developed rapidly. During the silicon rod cutting process, about 35% of crystalline silicon enters silicon cutting waste (SCW) in the form of high-purity silicon powder and is lost. At present, the recycling of SCW mainly focuses on purification to obtain high-purity silicon, and there is little research on other potential applications. At the same time, with the explosive growth of waste lithium-ion batteries (LIBs), the mass ratio of graphite in lithium-ion batteries is about 10% to 20%. More than 78% of the graphite in lithium-ion batteries can be separated by simple ultrasonic vibration and screening, and the purity of the separated graphite exceeds 99.5%. The effective recycling of graphite as a key anode material has become economically attractive and environmentally significant. With the year-on-year growth of SCW and LIBs, it has caused great waste of resources and serious environmental pollution.

[0004] Therefore, how to synthesize high-quality nano-silicon carbide using diamond wire-cut silicon waste and waste lithium-ion battery graphite anodes as raw materials is a technical problem that technicians in this field urgently need to solve. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for preparing silicon carbide from silicon waste and waste lithium battery graphite anodes to solve the deficiencies in the prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode, characterized in that it specifically comprises the following steps:

[0008] (1) firstly ball-milling the silicon waste cut by diamond wire and the waste lithium-ion battery graphite anode after crushing and screening respectively, and then mixing them to obtain a mixed material;

[0009] (2) placing the mixed material in a crucible and placing it in a high-temperature reaction furnace for high-temperature smelting to obtain a silicon carbide crystal block, then ball milling to obtain silicon carbide powder, and then placing it in a resistance furnace in an air atmosphere for roasting to remove the remaining carbon in the product;

[0010] (3) First, the calcined silicon carbide powder is placed in an acid, stirred and leached or ultrasonic-assisted stirred and leached under heating conditions, and then centrifuged to achieve solid-liquid separation, washed, dried, and ball-milled in sequence to obtain nano-silicon carbide particles.

[0011] Furthermore, in the above step (1), the mass ratio of diamond wire cut silicon waste to waste lithium ion battery graphite anode is 1:(1-2.5).

[0012] Furthermore, in the above step (1), the ball milling device is a planetary ball mill, the speed is 100-400 rpm, and the time is 0.5-5 hours; the mixing device is a planetary ball mill, the speed is 100-600 rpm, and the time is 0.5-20 hours. Before mixing, a catalyst of 1% to 10% by mass can be added to the mixture, specifically at least one of NaCl, KCl, and LiCl.

[0013] A further beneficial effect of adopting the above method is that the present invention uses a planetary ball mill for mixing and activates the silicon source and the carbon source in advance, which can effectively reduce the reaction temperature in the smelting process, effectively reduce the energy consumption in the smelting process, reduce the loss of the high-temperature reactor, and extend the service life of the high-temperature reactor equipment and the crucible.

[0014] Furthermore, in the above step (1), a pressing step is also included after mixing. The pressing equipment is a high-pressure pelletizing machine with a pressure of 5 to 40 MPa to obtain pellets with a diameter of 15 to 50 mm and a thickness of 3 to 8 mm. The holding time is 30 to 180 seconds.

[0015] Furthermore, in the above step (2), the material of the crucible is graphite, alumina, zirconia, boron nitride or silicon nitride; the high-temperature reaction furnace is a vacuum induction furnace, a box-type resistance furnace, a tubular resistance furnace or an arc furnace; the high-temperature smelting temperature is 1000-2500°C, and the insulation time is 0.5-4h.

[0016] Furthermore, in the above step (2), the ball milling equipment is a planetary ball mill, the rotation speed is 100-400 rpm, and the time is 0.5-5 h; the resistance furnace is a box-type resistance furnace or a tubular resistance furnace; the heating rate of roasting is 5-10°C / min, the roasting temperature is 650-850°C, and the holding time is 0.5-4 h.

[0017] Furthermore, in the above step (3), the acid is at least one of nitric acid, hydrochloric acid, sulfuric acid and hydrofluoric acid, and the total concentration is 5 to 30 wt%; the heating rate of the stirring leaching is 1 to 5°C / min, the temperature is 30 to 120°C, the stirring speed is 0 to 600 rpm, and the time is 5 to 180 min; the heating rate of the ultrasonic-assisted stirring leaching is 1 to 5°C / min, the temperature is 30 to 120°C, the ultrasonic frequency is 30 to 180 kHz, the ultrasonic power is 0 to 300 W, the stirring speed is 0 to 600 rpm, and the leaching time is 5 to 180 min.

[0018] A further beneficial effect of the above method is that the present invention uses ultrasound-assisted stirring leaching to acid-leach and purify the obtained silicon carbide powder. The ultrasound generates local high temperature and pressure and more effective oscillation, which can promote the separation of agglomerates, promote the transfer of the solution, and effectively promote the removal of impurities in the obtained silicon carbide product.

[0019] Furthermore, in the above step (3), the centrifugal device is a high-speed centrifuge with a rotation speed of 2000-5000 rpm; the washing reagent is deionized water, and the mixture is centrifuged again after shaking, and this operation is repeated 3-5 times until the supernatant after centrifugation is neutral.

[0020] A further beneficial effect of the above method is that the present invention uses a high-speed centrifuge to perform solid-liquid separation and washing on the silicon carbide particles after acid leaching, which can effectively reduce the raw material loss caused by traditional filter paper filtration and prevent the silicon carbide particles from entering the waste liquid through the gaps in the filter paper due to their small size.

[0021] Furthermore, in the above step (3), the drying equipment is a vacuum drying oven with a vacuum degree of 0.05 to 0.09 MPa, a temperature of 60 to 120° C., and a drying time of 2 to 10 h.

[0022] Furthermore, in the above step (3), the ball milling equipment is a planetary ball mill, the rotation speed is 100 to 400 rpm, and the time is 0.5 to 5 hours.

[0023] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. The present invention directly uses the diamond wire cutting silicon waste generated in the process of slicing single crystal silicon rods as the silicon source, and the crushed and screened waste lithium ion battery graphite anode as the carbon source, and does not need to treat the raw materials for impurities, simplifies the entire process flow, and is lower in cost than the traditional industrial preparation of silicon carbide. At the same time, it can effectively reduce environmental pollution and resource waste, realize the high added value utilization of the two waste materials of diamond wire cutting silicon waste and waste lithium ion battery graphite anode, and provide a new idea for the recycling of the two waste materials.

[0025] 2. The diamond wire cutting silicon waste produced in the process of slicing the single crystal silicon rod used in the present invention and the graphite anode of the waste lithium ion battery after crushing and screening have the characteristics of small particles, low impurity content, non-toxic and harmless. At the same time, since the diamond wire cutting silicon waste is a sheet structure, the contact area between the silicon source and the carbon source is increased, making the reaction more sufficient. Therefore, the diamond wire cutting silicon waste and the graphite anode of the waste lithium ion battery are ideal raw materials for preparing silicon carbide materials. The present invention prepares nano silicon carbide by carbothermal reduction method, which can achieve efficient conversion of diamond wire cutting silicon waste and graphite anode of waste lithium ion battery.

[0026] 3. The present invention uses silicon waste cut by diamond wire and graphite anodes of waste lithium-ion batteries as raw materials for preparation, and prepares and purifies silicon carbide through processes such as ball milling, mixing, smelting, roasting, acid leaching, centrifugation and drying, and finally obtains high-purity nano-scale silicon carbide particles. The recycling of silicon waste cut by diamond wire and graphite anodes of waste lithium-ion batteries can not only reduce resource waste, alleviate environmental pollution, and improve the utilization rate of waste materials, but also produce considerable economic benefits. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Example 1

[0029] The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode specifically comprises the following steps:

[0030] (1) Raw material ball milling: 5 g of diamond wire cut silicon waste and 15 g of crushed and sieved waste lithium ion battery graphite anode were respectively placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain ball milled materials;

[0031] (2) Raw material mixing: The ball milled materials were fully mixed in a planetary ball mill at a speed of 500 rpm for 5 h to obtain a mixed material;

[0032] (3) Smelting: placing the mixed material in an alumina crucible and placing it in a vacuum induction furnace for high temperature smelting at 1500° C. for 1 h to obtain a silicon carbide crystal block;

[0033] (4) Calcination: The silicon carbide crystal block is placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain silicon carbide powder; the silicon carbide powder is then placed in a box-type resistance furnace for calcination in an air atmosphere at a heating rate of 5°C / min, a calcination temperature of 650°C, and a holding time of 1 h;

[0034] (5) Acid leaching: The calcined silicon carbide powder was placed in a beaker containing 5 wt% hydrochloric acid and stirred for leaching under heating conditions at a heating rate of 1°C / min, a temperature of 30°C, a stirring speed of 100 rpm, and a time of 30 min;

[0035] (6) Centrifugation: The mixed solution after acid leaching is placed in a high-speed centrifuge for centrifugation at a speed of 2000 rpm;

[0036] (7) Washing: Pour deionized water into the centrifuge tube after centrifugation, shake and centrifuge again, and repeat this operation 4 times until the supernatant after centrifugation is neutral;

[0037] (8) Drying: The centrifuged product was placed in a vacuum drying oven for drying at a vacuum degree of 0.07 MPa, a temperature of 60°C, and a time of 3 h;

[0038] (9) Ball milling: The dried product is placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain nano-silicon carbide particles.

[0039] Example 2

[0040] The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode specifically comprises the following steps:

[0041] (1) Raw material ball milling: 5 g of diamond wire cut silicon waste and 10 g of crushed and sieved waste lithium ion battery graphite anode were respectively placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain ball milled materials;

[0042] (2) Raw material mixing: The ball milled materials were fully mixed in a planetary ball mill at a speed of 500 rpm for 10 h to obtain a mixed material;

[0043] (3) Pressing pellets: The mixture is placed in a high-pressure pellet press and pressed at a pressure of 10 MPa to obtain pellets with a diameter of 20 mm and a thickness of 5 mm. The pressure holding time is 60 s.

[0044] (4) Smelting: placing the pellets in a graphite crucible and placing it in a vacuum induction furnace for high temperature smelting at 1500° C. for 0.5 h to obtain a silicon carbide crystal block;

[0045] (5) Calcination: The silicon carbide crystal block is placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain silicon carbide powder; the silicon carbide powder is then placed in a box-type resistance furnace for calcination in an air atmosphere at a heating rate of 5°C / min, a calcination temperature of 650°C, and a holding time of 2 h;

[0046] (6) Acid leaching: The calcined silicon carbide powder was placed in a beaker containing 10 wt% hydrochloric acid and stirred for leaching under heating conditions at a heating rate of 1°C / min, a temperature of 30°C, a stirring speed of 100 rpm, and a time of 30 min;

[0047] (7) Centrifugation: The mixed solution after acid leaching is placed in a high-speed centrifuge for centrifugation at a speed of 2000 rpm;

[0048] (8) Washing: Pour deionized water into the centrifuge tube after centrifugation, shake and centrifuge again, and repeat this operation 4 times until the supernatant after centrifugation is neutral;

[0049] (9) Drying: The centrifuged product was placed in a vacuum drying oven for drying at a vacuum degree of 0.07 MPa, a temperature of 60°C, and a time of 3 h;

[0050] (10) Ball milling: The dried product was placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain nano-silicon carbide particles.

[0051] Example 3

[0052] The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode specifically comprises the following steps:

[0053] (1) Raw material ball milling: 10 g of diamond wire cut silicon waste and 15 g of crushed and sieved waste lithium ion battery graphite anode were respectively placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain ball milled materials;

[0054] (2) Raw material mixing: The ball milled materials were fully mixed in a planetary ball mill at a speed of 500 rpm for 15 h to obtain a mixed material;

[0055] (3) Pressing pellets: The mixture is placed in a high-pressure pellet press and pressed at a pressure of 20 MPa to obtain pellets with a diameter of 30 mm and a thickness of 5 mm. The pressure holding time is 60 s.

[0056] (4) Smelting: The pellets are placed in an alumina crucible and placed in a box-type resistance furnace for high-temperature smelting at 1600° C. for 1 h to obtain a silicon carbide crystal block;

[0057] (5) Calcination: The silicon carbide crystal block is placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain silicon carbide powder; the silicon carbide powder is then placed in a box-type resistance furnace for calcination in an air atmosphere at a heating rate of 8°C / min, a calcination temperature of 700°C, and a holding time of 3 h;

[0058] (6) Acid leaching: The calcined silicon carbide powder was placed in a beaker containing 10 wt% nitric acid and stirred for leaching under heating conditions at a heating rate of 1°C / min, a temperature of 40°C, a stirring speed of 120 rpm, and a time of 60 min;

[0059] (7) Centrifugation: The mixed solution after acid leaching is placed in a high-speed centrifuge for centrifugation at a speed of 3000 rpm;

[0060] (8) Washing: Pour deionized water into the centrifuge tube after centrifugation, shake and centrifuge again, repeat this operation 3 times until the supernatant after centrifugation is neutral;

[0061] (9) Drying: The centrifuged product was placed in a vacuum drying oven for drying at a vacuum degree of 0.07 MPa, a temperature of 70° C., and a time of 4 h;

[0062] (10) Ball milling: The dried product was placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain nano-silicon carbide particles.

[0063] Example 4

[0064] The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode specifically comprises the following steps:

[0065] (1) Raw material ball milling: 7 g of diamond wire cut silicon waste and 14 g of crushed and sieved waste lithium ion battery graphite anode were respectively placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain ball milled materials;

[0066] (2) Raw material mixing: The ball milled materials were fully mixed in a planetary ball mill at a speed of 600 rpm for 20 h to obtain a mixed material;

[0067] (3) Pressing pellets: The mixture is placed in a high-pressure pellet press and pressed at a pressure of 15 MPa to obtain pellets with a diameter of 20 mm and a thickness of 5 mm. The pressure holding time is 120 s.

[0068] (4) Smelting: The pellets are placed in an alumina crucible and placed in a tubular resistance furnace for high-temperature smelting at 1600° C. for 3 h to obtain a silicon carbide crystal block;

[0069] (5) Calcination: The silicon carbide crystal block is placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain silicon carbide powder; the silicon carbide powder is then placed in a box-type resistance furnace for calcination in an air atmosphere at a heating rate of 8°C / min, a calcination temperature of 700°C, and a holding time of 4 h;

[0070] (6) Acid leaching: The calcined silicon carbide powder was placed in a beaker containing 5 wt% nitric acid and sulfuric acid and 10 wt% hydrofluoric acid, and ultrasonic-assisted stirring leaching was performed under heating conditions, with a heating rate of 5°C / min, a temperature of 80°C, an ultrasonic frequency of 50 kHz, an ultrasonic power of 120 W, a stirring speed of 200 rpm, and a leaching time of 80 min;

[0071] (7) Centrifugation: The mixed solution after acid leaching is placed in a high-speed centrifuge for centrifugation at a speed of 4000 rpm;

[0072] (8) Washing: Pour deionized water into the centrifuge tube after centrifugation, shake and centrifuge again, repeat this operation 3 times until the supernatant after centrifugation is neutral;

[0073] (9) Drying: The centrifuged product was placed in a vacuum drying oven for drying at a vacuum degree of 0.09 MPa, a temperature of 80°C, and a time of 4 h;

[0074] (10) Ball milling: The dried product was placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain nano-silicon carbide particles.

[0075] Example 5

[0076] The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode specifically comprises the following steps:

[0077] (1) Raw material ball milling: 5 g of diamond wire cut silicon waste and 10 g of crushed and sieved waste lithium ion battery graphite anode were respectively placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain ball milled materials;

[0078] (2) Raw material mixing: The ball milled materials were fully mixed in a planetary ball mill at a speed of 500 rpm for 15 h to obtain a mixed material;

[0079] (3) Pressing pellets: The mixture is placed in a high-pressure pellet press and pressed at a pressure of 20 MPa to obtain pellets with a diameter of 20 mm and a thickness of 5 mm. The pressure holding time is 60 s.

[0080] (4) Smelting: The pellets are placed in an alumina crucible and placed in a tubular resistance furnace for high-temperature smelting at 1600° C. for 2 h to obtain a silicon carbide crystal block;

[0081] (5) Calcination: The silicon carbide crystal block is placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain silicon carbide powder; the silicon carbide powder is then placed in a box-type resistance furnace for calcination in an air atmosphere at a heating rate of 8°C / min, a calcination temperature of 750°C, and a holding time of 3 h;

[0082] (6) Acid leaching: The calcined silicon carbide powder was placed in a beaker containing 5 wt% hydrochloric acid and 10 wt% hydrofluoric acid, and ultrasonic-assisted stirring leaching was performed under heating conditions, with a heating rate of 5°C / min, a temperature of 60°C, an ultrasonic frequency of 30 kHz, an ultrasonic power of 100 W, a stirring speed of 20 rpm, and a leaching time of 80 min;

[0083] (7) Centrifugation: The mixed solution after acid leaching is placed in a high-speed centrifuge for centrifugation at a speed of 4000 rpm;

[0084] (8) Washing: Pour deionized water into the centrifuge tube after centrifugation, shake and centrifuge again, and repeat this operation 4 times until the supernatant after centrifugation is neutral;

[0085] (9) Drying: The centrifuged product was placed in a vacuum drying oven for drying at a vacuum degree of 0.09 MPa, a temperature of 80°C, and a time of 4 h;

[0086] (10) Ball milling: The dried product was placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain nano-silicon carbide particles.

[0087] Example 6

[0088] The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode specifically comprises the following steps:

[0089] (1) Raw material ball milling: 5 g of diamond wire cut silicon waste and 10 g of crushed and sieved waste lithium ion battery graphite anode were respectively placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain ball milled materials;

[0090] (2) Raw material mixing: The ball milled materials were fully mixed in a planetary ball mill at a speed of 600 rpm for 20 h to obtain a mixed material;

[0091] (3) Pressing pellets: The mixture is placed in a high-pressure pellet press and pressed at a pressure of 20 MPa to obtain pellets with a diameter of 20 mm and a thickness of 5 mm. The pressure holding time is 120 s.

[0092] (4) Smelting: The pellets are placed in a zirconia crucible and placed in a vacuum induction furnace for high-temperature smelting at 1800° C. for 3 h to obtain a silicon carbide crystal block;

[0093] (5) Calcination: The silicon carbide crystal block is placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 3 hours to obtain silicon carbide powder; the silicon carbide powder is then placed in a box-type resistance furnace for calcination in an air atmosphere at a heating rate of 5 to 10°C / min, a calcination temperature of 750°C, and a holding time of 4 hours;

[0094] (6) Acid leaching: The calcined silicon carbide powder was placed in a beaker containing 7 wt % sulfuric acid and 13 wt % hydrofluoric acid, and ultrasonic-assisted stirring leaching was performed under heating conditions, with a heating rate of 5 ° C / min, a temperature of 80 ° C, an ultrasonic frequency of 50 kHz, an ultrasonic power of 120 W, a stirring speed of 300 rpm, and a leaching time of 80 min;

[0095] (7) Centrifugation: The mixed solution after acid leaching is placed in a high-speed centrifuge for centrifugation at a speed of 4000 rpm;

[0096] (8) Washing: Pour deionized water into the centrifuge tube after centrifugation, shake and centrifuge again, and repeat this operation 4 times until the supernatant after centrifugation is neutral;

[0097] (9) Drying: The centrifuged product was placed in a vacuum drying oven for drying at a vacuum degree of 0.09 MPa, a temperature of 80° C., and a time of 5 h;

[0098] (10) Ball milling: The dried product was placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain nano-silicon carbide particles.

[0099] Example 7

[0100] The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode specifically comprises the following steps:

[0101] (1) Raw material ball milling: 10 g of diamond wire cut silicon waste and 20 g of crushed and sieved waste lithium ion battery graphite anode were respectively placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain ball milled materials;

[0102] (2) Raw material mixing: The ball milled materials were fully mixed in a planetary ball mill at a speed of 500 rpm for 20 h to obtain a mixed material;

[0103] (3) Pressing pellets: The mixture is placed in a high-pressure pellet press and pressed at a pressure of 15 MPa to obtain pellets with a diameter of 20 mm and a thickness of 5 mm. The pressure holding time is 150 s.

[0104] (4) Smelting: The pellets are placed in a boron nitride crucible and placed in an electric arc furnace for high-temperature smelting at 2000° C. for 3 h to obtain a silicon carbide crystal block;

[0105] (5) Calcination: The silicon carbide crystal block is placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain silicon carbide powder; the silicon carbide powder is then placed in a tubular resistance furnace for calcination in an air atmosphere at a heating rate of 10 °C / min, a calcination temperature of 750 °C, and a holding time of 4 h;

[0106] (6) Acid leaching: The calcined silicon carbide powder was placed in a beaker containing 7 wt% sulfuric acid and 13 wt% hydrofluoric acid, and ultrasonic-assisted stirring leaching was performed under heating conditions, with a heating rate of 5°C / min, a temperature of 100°C, an ultrasonic frequency of 70 kHz, an ultrasonic power of 150 W, a stirring speed of 400 rpm, and a leaching time of 120 min;

[0107] (7) Centrifugation: The mixed solution after acid leaching is placed in a high-speed centrifuge for centrifugation at a speed of 4000 rpm;

[0108] (8) Washing: Pour deionized water into the centrifuge tube after centrifugation, shake and centrifuge again, and repeat this operation 4 times until the supernatant after centrifugation is neutral;

[0109] (9) Drying: The centrifuged product was placed in a vacuum drying oven for drying at a vacuum degree of 0.09 MPa, a temperature of 100 °C, and a time of 4 h;

[0110] (10) Ball milling: The dried product was placed in a planetary ball mill for thorough ball milling at a speed of 300 rpm for 2 h to obtain nano-silicon carbide particles.

[0111] Performance Testing

[0112] The nano-SiC particle samples prepared in Examples 1-7 were taken to test their purity and average particle size. The results are shown in Table 1.

[0113] Table 1 Purity and average particle size of nano silicon carbide particle samples of Examples 1-7

[0114] Nano-SiC particle samples purity / % Average particle size / nm Example 1 97.6 14.6 Example 2 97.3 12.2 Example 3 97.7 11.4 Example 4 98.3 7.5 Example 5 98.1 7.8 Example 6 98.5 5.7 Example 7 98.7 5.2

[0115] As shown in Table 1, the following conclusions can be drawn based on the experimental conditions and results of Examples 1-7:

[0116] 1. The purpose of increasing the activity of the reactants and refining the grain size can be achieved by extending the ball milling time, increasing the rotation speed and other ball milling mixing conditions.

[0117] 2. The purpose of promoting silicon carbide synthesis and refining grain size can be achieved by increasing smelting temperature, extending smelting time and other smelting conditions.

[0118] 3. By increasing the acid leaching temperature, extending the acid leaching time, increasing the ultrasonic and stirring power and other acid leaching conditions, silicon carbide particles with higher purity can be obtained.

[0119] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode, characterized in that: The specific steps include: (1) firstly ball-milling the silicon waste cut by diamond wire and the waste lithium-ion battery graphite anode after crushing and screening respectively, and then mixing them to obtain a mixed material; (2) placing the mixed material in a crucible and placing it in a high-temperature reaction furnace for high-temperature smelting to obtain a silicon carbide crystal block, then ball milling to obtain silicon carbide powder, and then placing it in a resistance furnace for roasting in an air atmosphere; (3) Firstly, the calcined silicon carbide powder is placed in an acid, and stirred and leached or ultrasonic-assisted stirred and leached is performed under heating conditions, and then centrifuged, washed, dried, and ball-milled in sequence to obtain the nano-silicon carbide particles.

2. The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode according to claim 1, characterized in that: In step (1), the mass ratio of the diamond wire cut silicon waste to the waste lithium ion battery graphite anode is 1: (1 to 2.5).

3. The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode according to claim 1, characterized in that: In step (1), the ball milling device is a planetary ball mill with a rotation speed of 100 to 400 rpm and a time of 0.5 to 5 h; the mixing device is a planetary ball mill with a rotation speed of 100 to 600 rpm and a time of 0.5 to 20 h.

4. The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode according to claim 1, characterized in that: In step (1), after mixing, a pressing step is also included. The pressing equipment is a high-pressure ball press. The pressure is 5 to 40 MPa, and the obtained balls are 15 to 50 mm in diameter and 3 to 8 mm in thickness. The holding time is 30 to 180 s.

5. The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode according to claim 1, characterized in that: In step (2), the material of the crucible is graphite, alumina, zirconia, boron nitride or silicon nitride; the high-temperature reaction furnace is a vacuum induction furnace, a box-type resistance furnace, a tubular resistance furnace or an arc furnace; the temperature of the high-temperature smelting is 1000-2500°C, and the insulation time is 0.5-4h.

6. The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode according to claim 1, characterized in that: In step (2), the ball milling equipment is a planetary ball mill with a rotation speed of 100 to 400 rpm and a holding time of 0.5 to 5 h; the resistance furnace is a box-type resistance furnace or a tubular resistance furnace; the heating rate of the roasting is 5 to 10°C / min, the roasting temperature is 650 to 850°C, and the holding time is 0.5 to 4 h.

7. The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode according to claim 1, characterized in that: In step (3), the acid is at least one of nitric acid, hydrochloric acid, sulfuric acid and hydrofluoric acid, and the total concentration is 5-30wt%; the heating rate of the stirring leaching is 1-5°C / min, the temperature is 30-120°C, the stirring speed is 0-600rpm, and the time is 5-180min; the heating rate of the ultrasonic-assisted stirring leaching is 1-5°C / min, the temperature is 30-120°C, the ultrasonic frequency is 30-180kHz, the ultrasonic power is 0-300W, the stirring speed is 0-600rpm, and the leaching time is 5-180min.

8. The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode according to claim 1, characterized in that: In step (3), the centrifugal device is a high-speed centrifuge with a rotation speed of 2000-5000 rpm; the washing reagent is deionized water, and the mixture is centrifuged again after shaking, and this operation is repeated 3-5 times until the supernatant after centrifugation is neutral.

9. The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode according to claim 1, characterized in that: In step (3), the drying equipment is a vacuum drying oven with a vacuum degree of 0.05 to 0.09 MPa, a temperature of 60 to 120° C., and a drying time of 2 to 10 hours.

10. The method for preparing silicon carbide from silicon waste and waste lithium battery graphite anode according to claim 1, characterized in that: In step (3), the ball milling equipment is a planetary ball mill with a rotation speed of 100 to 400 rpm and a time of 0.5 to 5 hours.