Method for recovering silicon from silicon-containing waste and high-purity silicon powder for plasma spraying

Abstract

The invention belongs to the technical field of waste recovery, and discloses a method for recovering silicon from silicon-containing waste and high-purity silicon powder for plasma spraying, the method for recovering silicon from the silicon-containing waste comprises the following steps: step 1, crushing, crushing and cyclone grading the silicon-containing waste in sequence to obtain powder; 2, the powder is demagnetized for the first time, and non-magnetic powder is obtained; and 3, the non-magnetic powder is sequentially subjected to vacuum degreasing, hydrogen reduction and secondary demagnetization, and the silicon powder is obtained. According to the method, magnetic metal simple substances are removed through first-time demagnetization, so that the purity of silicon in the silicon waste is improved, then hydrogen reduction is carried out to reduce metal oxides into magnetic metal simple substances, and part of silicon oxide is reduced into silicon simple substances; and then secondary demagnetization is carried out to remove the reduced magnetic metal elementary substance and reduce the oxygen content in the obtained silicon powder, so that the purity of the silicon is improved while the recovery rate of the silicon is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of waste recycling, and in particular to a method for recycling silicon from silicon-containing waste and high-purity silicon powder for plasma spraying. Background Art

[0002] Silicon waste is the waste generated in the production process of crystalline silicon. Crystalline silicon, i.e. silicon cylinder, is made from silicon ingots through processes such as cutting, boring, and polishing. In the production process of silicon cylinders, 85% of silicon is wasted in the processing process and becomes silicon waste. The utilization rate of the product is only about 15% of the silicon ingot. In addition, a cooling emulsion is required during the processing, so the silicon waste contains a large amount of grease.

[0003] Existing silicon waste is mainly treated by stockpiling or as an additive in construction, but the consumption is limited and there is a lack of effective treatment methods. In addition, silicon waste, especially ultrafine silicon waste generated during the processing of silicon ingots, has a large specific surface area and high activity. It is easy to cause combustion when piled up in the air for a long time. At the same time, the dust will also pollute the environment, making the recycling and reuse of silicon waste particularly necessary.

[0004] Prior art 1: Chinese patent application 201911401134.3 discloses a method for preparing high-purity micro-nano silicon powder using silicon waste from the photovoltaic industry, including S10) selecting a specific diamond wire saw and resin plate to make the impurity elements in the silicon waste controllable; S20) online gravity filtration of the silicon waste liquid from S10 to remove large impurities such as diamonds that fall off the wire saw; at the same time, online magnetic separation of the silicon waste liquid to remove magnetic iron and nickel impurities, and filter pressing to obtain silicon slurry after the silicon ingot is sliced. S30) acid-washing the silicon slurry from S20 to remove oxygen elements, washing with deionized water and centrifuging to obtain silicon slurry; filter pressing to obtain silicon waste slurry; S40) high-temperature treatment of the silicon slurry from S30 under an inert atmosphere to remove organic matter such as polyethylene glycol in the resin plate chips and chip liquid to obtain high-purity silicon millimeter-level agglomerated particles. S50) physically crushing the silicon millimeter-sized particles of S40 to obtain dispersed silicon micro-nano particles.

[0005] Prior art 1 recovers silicon powder from silicon waste by controlling the content of impurity elements, and can fully obtain high-purity silicon powder. However, the impurity removal process is to remove oxygen elements through acid washing. According to its manual, "Step 5, the silicon slurry is corroded by hydrofluoric acid solution to react with silicon oxide, and then washed with deionized water to obtain silicon slurry with silicon oxide removed."

[0006] It can be seen from this that although the prior art 1 obtains high-purity silicon powder, hydrofluoric acid is highly corrosive and will produce acid mist. The hydrofluoric acid in the acid wastewater not only reacts with silicon oxide but also reacts with silicon element, and will also dissolve part of the silicon element and remove part of the silicon element. The silicon recovery rate of the prior art 1 is low, which is not conducive to the recycling and reuse of silicon. Summary of the invention

[0007] One of the purposes of the present invention is to provide a method for recovering silicon from silicon-containing waste, which can efficiently recover silicon element with a high recovery rate of silicon element, and obtain high-purity silicon powder through a combination of multi-step demagnetization and hydrogen reduction.

[0008] Another object of the present invention is to provide a high-purity silicon powder for plasma spraying, which is obtained by the method of recovering silicon from silicon-containing waste materials of the present invention and has the advantages of high purity, uniform particle size and high Hall flow rate.

[0009] To achieve the above object, the present invention provides a method for recovering silicon from silicon-containing waste, comprising the following steps:

[0010] Step 1: crushing, pulverizing and cyclone classification of silicon-containing waste to obtain powder;

[0011] Step 2: Demagnetize the powder for the first time to obtain non-magnetic powder;

[0012] Step 3: vacuum degreasing, hydrogen reduction and secondary demagnetization of the non-magnetic powder are performed in sequence to obtain silicon powder;

[0013] The heating temperature of the vacuum degreasing in step 3 is 400-500°C, and the insulation time is 2-3h; the heating temperature of the hydrogen reduction is 950-1000°C, and the insulation time is 2-3h.

[0014] Furthermore, the specific operation of step 1 is: putting the silicon waste into a crusher for crushing to obtain particles with a particle size of less than 2 mm, putting the particles into a pulverizer to obtain pulverized materials, and classifying the pulverized materials through an air flow classifier to obtain powder.

[0015] In the technical solution of the present invention, the air flow classifier is used for classification in order to obtain a higher concentration of the target powder, reduce the pressure of the back-end equipment, and facilitate the removal of impurities such as iron and manganese; and some impurities with small particle sizes in the crushed material will be separated during the friction with the air flow classifier, which are generally impurity particles larger than 600 mesh.

[0016] More preferably, the pulverizer used in the present invention is a jet pulverizer, and the pulverized material obtained by pulverizing with a jet pulverizer classifier will have a higher Hall flow rate.

[0017] Preferably, the method for recovering silicon from silicon-containing waste materials of the present invention further comprises step 11: sieving the powder to obtain a powder with a particle size distribution of 70 mesh to 400 mesh.

[0018] Furthermore, the specific operation of step 2 is: putting the powder into a dry powder magnetic separator to remove the magnetic elements in the powder to obtain non-magnetic powder.

[0019] Furthermore, the specific operation of vacuum degreasing in step 3 is: heating the non-magnetic powder to 400-500° C. under a vacuum degree of -100Pa to -500Pa, and keeping the temperature for 2-3 hours.

[0020] As an optional technical solution, the heating temperature for vacuum degreasing in step 3 may be selected to be 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, or 500°C.

[0021] Furthermore, the specific operation of hydrogen reduction in step 3 is: heating to 950-1000° C. in an atmosphere of a mixture of hydrogen and inert gas, and keeping the temperature for 2-3 hours.

[0022] Furthermore, in the atmosphere of the mixture of hydrogen and inert gas, the gas pressure is 0.2-0.3Mpa.

[0023] As an optional technical solution, the heating temperature for hydrogen reduction in step 3 can be selected to be 950°C, 960°C, 970°C, 980°C, 990°C, or 1000°C.

[0024] Preferably, in the atmosphere of the mixture of hydrogen and inert gas, the volume proportion of hydrogen is 3-5%.

[0025] Furthermore, the method further comprises step 4: putting the silicon powder into a mixer for homogenization.

[0026] The invention also discloses high-purity silicon powder for plasma spraying, which is obtained by adopting the above method for recovering silicon from silicon-containing waste materials.

[0027] Beneficial Effects

[0028] Compared with the prior art, the present invention has at least the following advantages:

[0029] (1) The present invention removes magnetic metal elements through the first demagnetization, thereby improving the purity of silicon in silicon waste, and then performs hydrogen reduction to reduce metal oxides to magnetic metal elements and partially reduce silicon oxide to silicon elements, and then performs a second demagnetization to remove the reduced magnetic metal elements and reduce the oxygen content in the obtained silicon powder, thereby effectively improving the recovery rate of silicon and improving the purity of silicon;

[0030] (2) The present invention first performs vacuum degreasing between the first demagnetization and hydrogen reduction, thereby removing a large amount of grease and preventing some grease from reacting with hydrogen to produce other substances during the subsequent hydrogen reduction process, thereby effectively ensuring the purity of the recovered silicon powder;

[0031] (3) The present invention discloses a method for recovering silicon from silicon-containing waste materials, which does not require the use of acid to remove impurities, effectively avoids the generation of sewage during the pickling process, and reduces environmental treatment costs. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the embodiments, but it does not constitute any limitation to the present invention. Any limited number of modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0033] In order to explain the technical content of the present invention in detail, further description is given below in conjunction with the implementation modes.

[0034] In the following examples and comparative examples, the crusher is a vertical shaft impact crusher, and the pulverizer is a jet pulverizer classifier.

[0035] Example 1

[0036] A method for recovering silicon from silicon-containing waste comprises the following steps:

[0037] Step 1: 500 kg of silicon waste is put into a crusher to be crushed to obtain particles with a particle size of less than 2 mm, the particles are put into a pulverizer to obtain pulverized materials, and the pulverized materials are classified by an air flow classifier to obtain powder;

[0038] Step 2: Put the powder into a dry powder magnetic separator to remove the magnetic metal in the powder to obtain non-magnetic powder;

[0039] Step 3: Place the non-magnetic powder in a vacuum sintering furnace and heat it to 450°C under a vacuum degree of -300Pa, keep it warm for 3 hours to obtain a degreased material, then introduce a mixed gas of 3% volume of hydrogen and 97% volume of argon to 0.3Mpa, heat it to 950°C, maintain the pressure of 0.3Mpa and keep it warm for 2 hours to obtain a reduced material, then put the reduced material into a dry powder magnetic separator to remove the magnetic metal in the reduced material to obtain silicon powder.

[0040] Example 2

[0041] A method for recovering silicon from silicon-containing waste comprises the following steps:

[0042] Step 1: 500 kg of silicon waste is put into a crusher to be crushed to obtain particles with a particle size of less than 2 mm, the particles are put into a pulverizer to obtain pulverized materials, and the pulverized materials are classified by an air flow classifier to obtain powder;

[0043] Step 2: Sieve the powder to obtain a powder with a particle size distribution of 70 mesh to 400 mesh;

[0044] Step 3: Put the powder obtained in step 2 into a dry powder magnetic separator to remove the magnetic metal in the powder to obtain non-magnetic powder;

[0045] Step 4: Place the non-magnetic powder in a vacuum sintering furnace and heat it to 450°C at a vacuum degree of -300Pa, keep it warm for 3 hours to obtain a degreased material, then introduce a mixed gas of 3% volume of hydrogen and 97% volume of argon to 0.3Mpa, heat it to 950°C, maintain the pressure of 0.3Mpa and keep it warm for 2 hours to obtain a reduced material, then put the reduced material into a dry powder magnetic separator to remove the magnetic metal in the reduced material to obtain silicon powder;

[0046] Step 5: Add the silicon powder into the mixer for homogenization.

[0047] Comparative Example 1

[0048] A method for recovering silicon from silicon-containing waste comprises the following steps:

[0049] Step 1: 500 kg of silicon waste is put into a crusher to be crushed to obtain particles with a particle size of less than 2 mm, the particles are put into a pulverizer to obtain pulverized materials, and the pulverized materials are classified by an air flow classifier to obtain powder;

[0050] Step 2: Put the powder into a dry powder magnetic separator to remove the magnetic metal in the powder to obtain non-magnetic powder;

[0051] Step 3: Place the non-magnetic powder in a vacuum sintering furnace and heat it to 450°C under a vacuum degree of -300Pa, keep it warm for 3 hours to obtain a degreased material, and then put the degreased material into a dry powder magnetic separator to remove the magnetic metal in the degreased material to obtain silicon powder.

[0052] Comparative Example 2

[0053] A method for recovering silicon from silicon-containing waste comprises the following steps:

[0054] Step 1: 500 kg of silicon waste is put into a crusher to be crushed to obtain particles with a particle size of less than 2 mm, the particles are put into a pulverizer to obtain pulverized materials, and the pulverized materials are classified by an air flow classifier to obtain powder;

[0055] Step 2: Put the powder into a dry powder magnetic separator to remove the magnetic metal in the powder to obtain non-magnetic powder;

[0056] Step 3: In a vacuum sintering furnace, introduce a mixed gas of 3% volume of hydrogen and 97% volume of argon into the non-magnetic powder to 0.3Mpa, heat it to 950°C, maintain the pressure of 0.3Mpa for 2 hours to obtain a reduced material, then heat the reduced material to 450°C under a vacuum degree of -300Pa, and keep it warm for 3 hours to obtain a degreased material, put the degreased material into a dry powder magnetic separator to remove the magnetic metal in the degreased material to obtain silicon powder.

[0057] The silicon powder obtained in Example 1-2 and Comparative Example 1-2 was subjected to impurity element detection and Hall flow rate test, and the results are shown in Table 1;

[0058] The impurity element detection and silicon powder purity are obtained by ICP / MS mass spectrometer detection, and the Hall flow rate is obtained by Hall flow meter testing.

[0059] Table 1 Silicon powder data results obtained from Examples 1-2 and Comparative Examples 1-2

[0060]

[0061]

[0062] According to the results in Table 1, we can see that:

[0063] According to the data comparison between Example 1 and Example 2, it can be seen that the addition of a screening step in the process of silicon waste recycling in the present invention can effectively reduce the content of Mn element and further improve the purity of silicon powder and product performance.

[0064] According to the data comparison between Example 1 and Comparative Example 1, it can be seen that the present invention can effectively remove a large amount of impurity elements through the hydrogen reduction step. The reason is that a large amount of impurities exist in the form of oxides after the first demagnetization. The oxides can be effectively reduced to simple substances through hydrogen reduction, and the impurities can be further effectively removed in combination with the second magnetic separation. Although the purity of the silicon powder is not significantly improved on the surface, the total amount of impurities in the silicon powder is greatly reduced (the total amount of impurities in Comparative Example 1 is 764ppm, and the total amount of impurities in Example 1 is 385ppm). The use of the silicon powder for subsequent high-purity plasma spraying will result in very different effects due to the differences in impurity content and magnetic element content, and cannot meet the high performance requirements of customers.

[0065] According to the data comparison between Example 1 and Comparative Example 2, if hydrogen reduction is performed first and then vacuum degreasing is performed during the silicon waste recovery process, a large amount of oil will be hydrogenated, making it difficult to remove the subsequent S element and C element, thereby causing a significant decrease in the purity of the recovered silicon powder.

[0066] The embodiments presented herein are only embodiments selected according to the combination of all possible embodiments. The appended claims should not be limited by the embodiments describing the present invention. Some numerical ranges used in the claims include sub-ranges therein, and the changes in these ranges should also be covered by the appended claims.

Claims

1. A method for recovering silicon from silicon-containing waste, characterized in that: The steps include: Step 1: crushing, pulverizing and cyclone classification of silicon-containing waste to obtain powder; Step 2: Demagnetize the powder for the first time to obtain non-magnetic powder; Step 3: vacuum degreasing, hydrogen reduction and secondary demagnetization of the non-magnetic powder are performed in sequence to obtain silicon powder; The heating temperature of the vacuum degreasing in step 3 is 400-500°C, and the insulation time is 2-3h; the heating temperature of the hydrogen reduction is 950-1000°C, and the insulation time is 2-3h.

2. The method for recovering silicon from silicon-containing waste according to claim 1, characterized in that: The specific operation of step 1 is: putting the silicon waste into a crusher to crush it to obtain particles with a particle size of less than 2 mm, putting the particles into a pulverizer to obtain pulverized materials, and classifying the pulverized materials through an air flow classifier to obtain powder.

3. The method for recovering silicon from silicon-containing waste according to claim 2, characterized in that: The method further comprises step 11: sieving the powder to obtain a powder with a particle size distribution of 70 meshes to 400 meshes.

4. The method for recovering silicon from silicon-containing waste according to any one of claims 1 to 3, characterized in that: The specific operation of step 2 is: putting the powder into a dry powder magnetic separator to remove the magnetic elements in the powder to obtain non-magnetic powder.

5. The method for recovering silicon from silicon-containing waste according to any one of claims 1 to 3, characterized in that: The specific operation of vacuum degreasing in step 3 is: heating the non-magnetic powder to 400-500° C. under a vacuum degree of -100 Pa to -500 Pa, and keeping the temperature for 2-3 hours.

6. The method for recovering silicon from silicon-containing waste according to any one of claims 1 to 3, characterized in that: The specific operation of hydrogen reduction in step 3 is: heating to 950-1000° C. in an atmosphere of a mixture of hydrogen and inert gas, and keeping the temperature for 2-3 hours.

7. The method for recovering silicon from silicon-containing waste according to claim 6, characterized in that: In the atmosphere of the mixture of hydrogen and inert gas, the volume proportion of hydrogen is 3-5%.

8. The method for recovering silicon from silicon-containing waste according to claim 1, characterized in that: The step 4 is also included: putting the silicon powder into a mixer for homogenization.

9. A high-purity silicon powder for plasma spraying, characterized in that: The silicon is obtained by the method for recovering silicon from silicon-containing waste as described in any one of claims 1 to 8.

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