A method for preparing Al-Si-Ca alloy, AlF3 and MgF2 by cutting silicon waste and CaF2-MgO waste residue

Abstract

The application discloses a method for preparing low-oxygen Al-Si-Ca alloy, AlF3 and MgF2 by recycling diamond wire cutting silicon waste and CaF2-MgO waste slag, and belongs to the technical field of secondary utilization of solid waste resources. The method comprises the following steps: (1) uniformly mixing diamond wire cutting silicon waste, CaF2-MgO waste slag and metal Al particles to obtain a mixture; (2) placing the mixture obtained in step (1) in a micro-negative pressure condition formed by inert atmosphere adjustment, performing electromagnetic induction heating to melt the mixture, and performing constant-temperature reduction smelting to obtain uniform Al-Si-Ca alloy melt, molten residue and volatile products AlF3 and MgF2; and (3) condensing and collecting the volatile products AlF3 and MgF2, and obtaining low-oxygen Al-Si-Ca alloy ingots and reduction residue after the Al-Si-Ca alloy melt and the molten residue are cooled and separated from the slag. The application comprehensively utilizes various waste materials in a simple, efficient and clean manner to obtain diversified high-value-added products, and is helpful to saving resource consumption and reducing environmental pollution.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary utilization of solid waste resources, and relates to a method for preparing Al-Si-Ca alloy, AlF3 and MgF2 from cutting silicon waste and CaF2-MgO slag. BACKGROUND

[0002] With the rapid development of the photovoltaic industry, solar energy is widely used as a clean energy source, and the demand for solar-grade crystalline silicon wafers has increased significantly. However, during the manufacturing process of silicon wafers, about 35% to 40% of the crystalline silicon becomes diamond wire cutting silicon waste. Since its particle size is smaller than that of PM2.5 particulate matter, it is considered to be a solid waste harmful to the environment and human health. Diamond wire cutting silicon waste is mainly composed of Si and O elements, with oxygen usually existing in the form of SiO2. If not recycled and treated in time, it will not only cause environmental pollution but also waste valuable Si resources. At present, various methods have been explored for the recycling of diamond wire cutting silicon waste, such as vacuum refining, induction melting, Al-Si alloying, H2SO4 or HCl pickling, etc. However, the existing methods have limited effect on removing O impurities (removing the SiO2 layer on the surface of diamond wire cutting silicon waste), and have not been widely used in industrial production.

[0003] At present, fluorine-containing slag is widely used in steel ladle metallurgy, secondary metallurgy, and electroslag refining (ESR) and other metallurgical processes. Among them, CaF2-MgO slag and CaF2-CaO-MgO slag can effectively remove S and P impurities during steelmaking. After steelmaking, the slag containing impurities will form CaF2-MgO slag containing F elements. If the slag is not recycled and utilized, it will not only cause environmental pollution but also waste Ca and Mg resources.

[0004] Al-Si-Ca alloy has the advantages of corrosion resistance, heat resistance, and endurance strength, and has been widely used in the fields of aerospace, electrical appliances, and building structural materials. However, the production of Al-Si-Ca alloy usually requires high-purity Al, Si, and Ca raw materials to be melted, which is costly. AlF3, as a flux, can lower the melting point of Al2O3, enhance the conductivity of the electrolyte, and improve the efficiency and quality of aluminum production. MgF2 has excellent corrosion resistance and optical properties, and is suitable for manufacturing infrared windows and resonators. AlF3 is generally prepared by low-temperature heat treatment growth method, while MgF2 is synthesized by dissolving magnesium chloride in hydrofluoric acid (HF) and deionized water through fluorination. The above methods for preparing AlF3 and MgF2 will produce waste acid, causing environmental problems.

[0005] At present, there is no method for cleaning and efficiently recycling diamond wire cutting silicon waste and CaF2-MgO slag to prepare low-oxygen Al-Si-Ca alloy, AlF3, and MgF2.

[0006] Therefore, it is necessary to provide a method for preparing low-oxygen Al-Si-Ca alloy, AlF3 and MgF2 from diamond wire cutting silicon waste and CaF2-MgO waste residue, so as to efficiently and cleanly recycle multiple waste materials, obtain rich and diversified recycling resources, and provide a new approach for reducing resource consumption and saving resources, and a new idea for reducing environmental pollution and truly realizing waste treatment. SUMMARY

[0007] In order to overcome the problems in the background art, the present application uses Si in diamond wire cutting silicon waste as a Si source for preparing Al-Si alloy, and uses CaF2-MgO waste residue to deoxidize the diamond wire cutting silicon waste, introduces Ca in the waste residue into the alloy, and fixes F in the waste residue by Al and Mg, so as to simultaneously realize deoxidization, Ca doping and F fixation, thereby preparing low-oxygen Al-Si-Ca alloy, AlF3 and MgF2. The present application simultaneously utilizes multiple waste materials in a clean, simple and efficient manner to obtain diversified recycling resources, which helps to save resource consumption and improve environmental friendliness, and truly realizes waste treatment.

[0008] In order to achieve the above-mentioned purpose, the present application realizes the following technical scheme:

[0009] The method comprises the following steps:

[0010] (1) uniformly mixing diamond wire cutting silicon waste, CaF2-MgO waste residue and metal Al particles to obtain a mixture;

[0011] (2) placing the mixture obtained in step (1) in a micro-negative pressure condition formed by adjusting an inert atmosphere, and performing electromagnetic induction heating to melt the mixture, and constant temperature reduction smelting to obtain a uniform Al-Si-Ca alloy melt, a molten residue and volatile products AlF3 and MgF2.

[0012] (3) condensing and collecting the volatile products AlF3 and MgF2, and after the Al-Si-Ca alloy melt and the molten residue are cooled to room temperature, the low-oxygen Al-Si-Ca alloy ingot and the reduction residue are obtained after slag-gold separation.

[0013] As a preferred, in step (1), the mass of the diamond wire cutting silicon waste accounts for 25-40% of the total mass of the mixture, the mass of the CaF2-MgO waste residue accounts for 15-30% of the total mass of the mixture, and the mass of the metal Al particles accounts for 45-50% of the total mass of the mixture.

[0014] Preferably, the content of MgO in the CaF2-MgO waste residue is 12-30% of the total mass of the CaF2-MgO waste residue.

[0015] Preferably, in step (2), the reduction smelting temperature is 1450-1500 DEG C, and the reduction smelting time is 2h.

[0016] Preferably, in step (2), the inert atmosphere is adjusted to form a micro-negative pressure in the range of 6.5x10 3 ~4x10 4 Pa.

[0017] Preferably, in step (3), the volatile products AlF3 and MgF2 are condensed and collected at 700-850 DEG C.

[0018] Preferably, in step (3), the Al-Si-Ca alloy ingot and the reduction residue are separated by mechanical cutting or wire cutting.

[0019] Preferably, the diamond wire cutting silicon waste material contains SiO2 and Si, and the SiO2 is wrapped on the surface of the elemental Si.

[0020] At high temperature, a reduction reaction occurs among Al, CaF2 and SiO2 to generate Si and Ca, which are melted into the alloy to form an Al-Si-Ca alloy, and AlF3 is volatilized, and Al2O3 is melted into the slag; then, the formed Ca reduces MgO to obtain Mg and CaO, and Mg acts as a reducing agent to reduce CaF2 to form CaO and MgF2, which can be collected by volatilization; finally, CaO and Al2O3 further react to generate CaAl2O4 slag. In addition, induction heating is used in the reduction smelting process to apply electromagnetic force to the reduction process, and because the electrical conductivity of the Al-Si-Ca alloy is much greater than that of the slag, the alloy melt moves along the direction of the electromagnetic force, while the slag migrates in the opposite direction of the electromagnetic force, promoting the separation of the alloy and the slag.

[0021] The beneficial effects of the present application are:

[0022] 1. The present application can utilize diamond wire cutting silicon waste material and CaF2-MgO waste residue material to prepare Al-Si-Ca alloy, AlF3 and MgF2 three high value-added products by Al reduction smelting, simultaneously recycling a variety of waste materials, and producing relatively abundant high value-added products, and the comprehensive utilization effect is excellent, and the waste treatment effect is good.

[0023] 2. In the method of the present application, the alloy melt is subjected to Lorentz force, electromagnetic stirring is generated in the container, Si and Ca are uniformly distributed in the alloy during the heat and mass transfer process, the alloy melt and the slag are subjected to different electromagnetic forces during the smelting process, and good separation can be achieved, and under the condition of micro negative pressure, combined with induction heating, reduction smelting is carried out, which is beneficial to the volatilization of products AlF3 and MgF2 and the collection in the condenser.

[0024] 3. The present application realizes low-cost and environmentally friendly recycling of diamond wire cutting silicon waste and CaF2-MgO waste slag.

[0025] 4. The method of the present application is simple, has high utilization rate of waste, good quality of high value-added products, and is suitable for industrialization and application. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a process flow diagram of the present application;

[0027] Figure 2 is a longitudinal macroscopic physical diagram of the separation of the alloy and the slag after electromagnetic induction smelting in Example 1 of the present application;

[0028] Figure 3 is the EDS-Mapping of the separation interface of the Al-Si-Ca alloy and the residue in Example 1 of the present application;

[0029] Figure 4 is the XRD analysis result diagram of the volatilization in Example 1 of the present application;

[0030] Figure 5 is the EDS-Mapping of the separation interface of the Al-Si-Ca alloy and the residue in Example 2 of the present application;

[0031] Figure 6 is the XRD analysis result diagram of the oxygen-rich residue in Example 2 of the present application. DETAILED DESCRIPTION

[0032] The present application will be further described in detail below in combination with the drawings and specific examples, but the scope of protection of the present application is not limited to the described content.

[0033] In the examples of the present application, commercially available analytical pure chemicals are used for experiments.

[0034] In the examples of the present application, the mass of the diamond wire cutting silicon waste, CaF2-MgO waste slag and metal Al particles is shown in Table 1.

[0035] Table 1

[0036]

[0037] Example 1

[0038] A method for cutting silicon waste, CaF2-MgO waste slag, and regenerating Al-Si-Ca alloy, AlF3, and MgF2 (see Figure 1 ), and the specific steps are as follows:

[0039] (1) The diamond wire cutting silicon waste (oxygen content is 4.7%) with a purity of 94.3% and the CaF2-MgO waste slag (MgO content is 12 wt.%) are mixed uniformly using a vibration mill, and then metal Al particles (purity is 99.9%) are added to obtain a mixture.

[0040] (2) The mixture is placed in a 1×10 4 Pa micro-negative pressure condition (inert atmosphere adjustment) and is heated to a temperature of 1450℃ by electromagnetic induction to completely melt it, and then is reduced and smelted for 2h at a constant temperature to obtain an Al-Si-Ca alloy melt, a molten residue, and volatile products AlF3 and MgF2.

[0041] (3) The volatile products AlF3 and MgF2 are condensed to 700℃, and then are collected in a condenser, and the Al-Si-Ca alloy melt and the molten residue are cooled to room temperature, and then are separated by mechanical cutting or wire cutting to obtain low-oxygen Al-Si-Ca alloy ingots and a reduction residue.

[0042] The macrograph of the separation of the Al-Si-Ca alloy from the molten residue after electromagnetic induction smelting is shown in Figure 2 , and it can be seen from Figure 2 that the oxygen impurities in the diamond wire cutting silicon waste are enriched in the residue, and no oxygen-rich residue is observed in the alloy.

[0043] The EDS-Mapping analysis results of the interface between the Al-Si-Ca alloy and the residue in this example are shown in Figure 3 , and it can be seen from Figure 3 that the oxygen element is not obviously detected in the alloy, and the oxygen impurities in the diamond wire cutting silicon waste are enriched in the residue; the F element is enriched in the same position as the oxygen impurities, proving that F does not enter the alloy to contaminate it; and the Ca element is not only enriched in the residue but also distributed in the alloy.

[0044] The XRD analysis results of the volatile products in this example are shown in Figure 4 , and it can be seen from Figure 4 that the volatile products in this example are indeed AlF3 and MgF2.

[0045] The main components of the Al-Si-Ca alloy in the embodiment are Al, Si and Ca, and the contents are Al: 72.99 wt.%, Si: 17.98 wt.% and Ca: 9.03 wt.% respectively; the oxygen content is 0.0065 wt.%. The purity of the mixture of AlF3 and MgF2 is 98.2 wt.%, and the main components are F: 37.23 wt.%, Mg: 13.62 wt.% and Al: 47.31 wt.% respectively; the main impurities and the contents are Si: 0.54 wt.% and Ca: 1.30 wt.% respectively.

[0046] It can be seen from the above component detection results that the high value-added products (Al-Si-Ca alloy, AlF3 and MgF2) prepared from waste materials have very low impurity content and high product quality.

[0047] Embodiment 2

[0048] A method for preparing Al-Si-Ca alloy, AlF3 and MgF2 by cutting silicon waste and CaF2-MgO waste residue, and the specific steps are as follows:

[0049] (1) The diamond wire cutting silicon waste (the oxygen content is 4.7%) with a purity of 94.3% and the CaF2-MgO waste residue (the MgO content is 15 wt.%) are mixed uniformly using a vibration mill, and then metal Al particles (the purity is 99.9%) are added to obtain a mixture.

[0050] (2) The mixture is placed in a 6.5×10 3 Pa micro-negative pressure condition (inert atmosphere adjustment, the inert atmosphere is Ar gas) and is heated to 1470℃ by electromagnetic induction to completely melt, and then is reduced and smelted for 2h to obtain uniform Al-Si-Ca alloy melt, molten residue and volatile product AlF3.

[0051] (3) The volatile product AlF3 is condensed to 800℃, and then is collected in a condenser; the Al-Si-Ca alloy melt and the molten residue are cooled to room temperature, and then are separated by mechanical cutting or wire cutting to obtain low-oxygen Al-Si-Ca alloy ingot and reduction residue.

[0052] The EDS-Mapping analysis results of the Al-Si-Ca alloy and the residue separation interface in the embodiment are shown in Figure 5 , and it can be seen from Figure 5 that the oxygen element is not obviously detected in the alloy, and a large amount of oxygen impurities are detected in the residue; the F element is enriched in the same position as the oxygen impurities, which proves that F does not enter the alloy and cause alloy pollution; the Ca element is not only enriched in the residue, but also distributed in the alloy.

[0053] The XRD analysis results of the oxygen-enriched residue in this embodiment are shown below. Figure 6 ,pass Figure 6 It can be seen that the main phases in the oxygen-rich residue are CaF2 and CaAl2O4, indicating that oxygen impurities in the silicon waste from diamond wire cutting were separated into the residue through the reduction smelting process.

[0054] The alloy ingot was cut and separated along the slag-gold interface to obtain an Al-Si-Ca alloy and oxygen-rich residue. Analysis showed that the main components of the Al-Si-Ca alloy in this embodiment were Al, Si, and Ca, with contents of Al: 73.53 wt.%, Si: 18.52 wt.%, and Ca: 7.95 wt.%, respectively; the oxygen content was 0.0035 wt.%. The mixture of AlF3 and MgF2 had a purity of 97.7 wt.%, with main components of F: 38.21 wt.%, Mg: 10.02 wt.%, and Al: 49.49 wt.%, respectively; the main impurities and their contents were Si: 0.40 wt.% and Ca: 1.88 wt.%, respectively.

[0055] Example 3

[0056] A method for preparing Al-Si-Ca alloys, AlF3, and MgF2 from silicon waste and CaF2-MgO waste residue, the specific steps of which are as follows:

[0057] (1) Diamond wire cutting silicon waste with a purity of 94.3% (oxygen content of 4.7%) and CaF2-MgO waste residue (MgO content of 18wt.%) were mixed evenly using a vibratory mill, and metal Al particles (purity of 99.9%) were added to obtain a mixture.

[0058] (2) The mixture is placed in a 4×10 4 Under a slight negative pressure (inert atmosphere conditioning), the material was electromagnetically induction heated to 1480℃ to completely melt it, and then constant temperature reduction smelting was carried out for 2 hours to obtain a uniform Al-Si-Ca alloy melt, molten residue, and volatile products AlF3 and MgF2.

[0059] (3) After the volatile products AlF3 and MgF2 are condensed to 850°C, they are collected in a condenser. After the Al-Si-Ca alloy melt and molten residue are cooled to room temperature, they are separated by mechanical cutting or wire cutting to obtain low-oxygen Al-Si-Ca alloy ingots and reduction residues.

[0060] The main components of the Al-Si-Ca alloy in this embodiment are Al, Si and Ca, and the contents are Al: 73.94 wt.%, Si: 19.21 wt.% and Ca: 6.85 wt.% respectively; the oxygen content is 0.0031 wt.%. The purity of the mixture of AlF3 and MgF2 is 99.3 wt.%, and the main components are F: 33.92 wt.%, Mg: 19.48 wt.% and Al: 45.93 wt.% respectively; the main impurities and their contents are Si: 0.29 wt.% and Ca: 0.38 wt.%.

[0061] Example 4

[0062] A method for preparing Al-Si-Ca alloy, AlF3 and MgF2 by cutting silicon waste, CaF2-MgO waste residue, and the specific steps are as follows:

[0063] (1) The diamond wire cutting silicon waste (oxygen content is 4.7%) with a purity of 94.3% and the CaF2-MgO waste residue (MgO content is 24 wt.%) are mixed uniformly using a vibration mill, and then metal Al particles (purity is 99.9%) are added to obtain a mixture.

[0064] (2) The mixture is placed in a 9x10 3 cm crucible under a micro-negative pressure condition (inert gas atmosphere adjustment) and is heated to a temperature of 1490°C by electromagnetic induction to completely melt, and then is reduced and smelted for 2 h at a constant temperature to obtain an Al-Si-Ca alloy melt, a molten residue and volatile products AlF3 and MgF2.

[0065] (3) The volatile products AlF3 and MgF2 are condensed to 750°C, and then are collected in a condenser; the Al-Si-Ca alloy melt and the molten residue are cooled to room temperature, and then are separated by mechanical cutting or wire cutting to obtain low-oxygen Al-Si-Ca alloy ingots and reduction residues;

[0066] The main components of the Al-Si-Ca alloy in this embodiment are Al, Si and Ca, and the contents are Al: 74.42 wt.%, Si: 20.25 wt.% and Ca: 5.33 wt.% respectively; the oxygen content is 0.0022 wt.%. The purity of the mixture of AlF3 and MgF2 is 99.4 wt.%, and the main components are F: 28.02 wt.%, Mg: 23.64 wt.% and Al: 47.79 wt.% respectively; the main impurities and their contents are Si: 0.08 wt.% and Ca: 0.47 wt.%.

[0067] Example 5

[0068] A method for cutting silicon waste, CaF2-MgO waste residue, and preparing Al-Si-Ca alloy, AlF3, and MgF2 by regeneration, the specific steps are as follows:

[0069] (1) The diamond wire cutting silicon waste (oxygen content is 4.7%) with a purity of 94.3% and the CaF2-MgO waste residue (MgO content is 30wt.%) are mixed uniformly by using a vibration mill, and then the mixed material is obtained after adding metal Al particles (purity is 99.9%).

[0070] (2) The mixed material is placed in a 2×10 4 Pa micro-negative pressure condition (inert atmosphere adjustment) is heated to a temperature of 1500 DEG C by electromagnetic induction to completely melt, and the temperature is kept constant for 2h to obtain uniform Al-Si-Ca alloy melt, molten residue, and volatile products AlF3 and MgF2.

[0071] (3) The volatile products AlF3 and MgF2 are condensed to 780 DEG C, and then collected in a condenser, and the Al-Si-Ca alloy melt and the molten residue are cooled to room temperature, and then separated by mechanical cutting or wire cutting to obtain low-oxygen Al-Si-Ca alloy ingots and reduction residues.

[0072] After detection and analysis, the main components of the Al-Si-Ca alloy in the embodiment are Al, Si, and Ca, and the contents are Al: 74.35wt.%, Si: 20.39wt.%, and Ca: 4.26wt.%, respectively; the oxygen content is 0.0020wt.%. The purity of the mixture of AlF3 and MgF2 is 96.7wt.%, and the main components are F: 26.50wt.%, Mg: 34.96wt.%, and Al: 35.32wt.%, respectively; and the main impurities and their contents are Si: 2.71wt.%, and Ca: 0.51wt.%.

[0073] In summary, the present application can fully utilize the diamond wire cutting silicon waste and CaF2-MgO waste residue by a simple, efficient, and clean method, and obtain high-quality Al-Si-Ca alloy, AlF3, and MgF2 products, and truly realize waste treatment with waste.

[0074] Finally, it should be pointed out that the above preferred embodiments are only used to illustrate the technical solutions of the present application and are not limiting, and although the present application has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present application.

Claims

1. A method for preparing Al-Si-Ca alloy, AlF3, and MgF2 by cutting silicon waste and regenerating CaF2-MgO waste residue, characterized in that: The method includes the following steps: (1) Mix the silicon waste from diamond wire cutting and CaF2-MgO waste residue evenly and add metal Al particles to obtain a mixture; (2) The mixture obtained in step (1) is placed under a slight negative pressure condition formed by an inert atmosphere and subjected to electromagnetic induction heating to melt the mixture. Then, it is subjected to constant temperature reduction smelting to obtain a uniform Al-Si-Ca alloy melt, molten residue and volatile products AlF3 and MgF2. (3) The volatile products AlF3 and MgF2 are collected by condensation. After the Al-Si-Ca alloy melt and molten residue are cooled to room temperature, low-oxygen Al-Si-Ca alloy ingots and reduction residues are obtained by slag-gold separation.

2. The method according to claim 1, characterized in that: In step (1), the mass of silicon waste from diamond wire cutting accounts for 25-40% of the total mass of the mixture, the mass of CaF2-MgO waste slag accounts for 15-30% of the total mass of the mixture, and the mass of metallic Al particles accounts for 45-50% of the total mass of the mixture.

3. The method according to claim 2, characterized in that: In the CaF2-MgO waste residue, the MgO content accounts for 12-30% of the total mass of the CaF2-MgO waste residue.

4. The method according to claim 1, characterized in that: In step (2), the reduction melting temperature is 1450-1500℃ and the reduction melting time is 2h.

5. The method according to claim 1, characterized in that: In step (2), the micro-negative pressure range formed by the inert atmosphere adjustment is 6.5 × 10⁻⁶. 3 ~4×10 4 Pa.

6. The method according to claim 1, characterized in that: In step (3), the volatile products AlF3 and MgF2 are collected when condensed to 700-850°C.

7. The method according to claim 1, characterized in that: In step (3), the Al-Si-Ca alloy ingot and the reduction residue are separated by mechanical cutting or wire cutting.

8. The method according to any one of claims 1-7, characterized in that: The silicon waste from diamond wire cutting contains both SiO2 and Si, with SiO2 coating the surface of elemental Si.

Images