Method for recycling waste photovoltaic tungsten filament

Abstract

The invention provides a method for recycling waste photovoltaic tungsten filaments. The treatment method comprises the following steps that the photovoltaic tungsten filament waste is subjected to fused salt electrolysis, the formed photovoltaic tungsten filament serves as an anode, a conductive material serves as a cathode, fused salt electrolysis is carried out under the inert atmosphere, and the product is regenerated tungsten powder. According to the scheme, the photovoltaic tungsten filament waste can be recycled in a green and short-process mode, tungsten and lanthanum oxide in the photovoltaic tungsten filament are recycled in one step through molten salt electrolysis, and the prepared regenerated tungsten powder can be directly used as a raw material for producing the photovoltaic tungsten filament.

Description

Technical Field

[0001] The invention relates to the technical field of molten salt electrochemical metallurgy, and in particular to a method for recycling waste photovoltaic tungsten filaments. Background Art

[0002] Under the background of "carbon peak and carbon neutrality", the photovoltaic industry has become an important industry that the country focuses on developing. Tungsten diamond wire (photovoltaic tungsten wire) is an important consumable in the production of photovoltaic silicon wafers, mainly used for cutting photovoltaic silicon wafers. The output of photovoltaic tungsten wire will exceed 16 billion meters in 2023 and about 60 billion meters in 2024. As a result, a large amount of waste photovoltaic tungsten wire is generated, which has important economic and environmental benefits for the recycling of waste tungsten wire.

[0003] At present, the main method used for tungsten resource recycling and regeneration is the oxidation-reduction method. In this method, waste tungsten is oxidized and roasted in air at high temperature, and crude sodium tungstate is obtained by alkaline leaching. The crude sodium tungstate is further subjected to ion exchange and crystallization to obtain APT, and finally APT is calcined and reduced to obtain tungsten powder. The regenerated tungsten powder prepared by this method has the same characteristics as the tungsten powder produced by concentrate, and the product quality is good. However, this method has a long process flow and a large amount of wastewater is discharged during the process. Taking the ion exchange production of APT in this process as an example, 50 tons of wastewater will be discharged for every ton of APT produced. There are various harmful impurities and unreacted NaOH in the wastewater, which need to be treated before discharge. In addition, photovoltaic tungsten filaments are not pure tungsten products. In order to improve the performance, some rare earth oxides (generally lanthanum oxide, La2O3) will be added during the production process of photovoltaic tungsten filaments. These rare earth oxides are distributed in the tungsten filament in a uniformly dispersed form. The traditional tungsten recovery technology does not involve the recovery of rare earth oxides. If the recovery of rare earth elements is taken into account, the process and production cycle will be further extended, and the cost will be increased. Summary of the invention

[0004] The present invention aims to solve one of the technical problems in the prior art at least to a certain extent. To this end, the purpose of the present invention is to provide a method for recycling waste photovoltaic tungsten filaments.

[0005] With the explosive development of the photovoltaic market, a large amount of waste photovoltaic tungsten filaments is bound to be generated. In view of the problems existing in the existing recycling technology, such as complex process, long process, large amount of wastewater discharge and no rare earth element recovery, it is of great strategic significance to develop a short-process, pollution-free photovoltaic tungsten filament waste resource recycling technology. At present, there is no related report on the recycling of photovoltaic tungsten filament waste based on molten salt electrolysis.

[0006] In view of this, the present invention proposes a method for recycling waste photovoltaic tungsten filaments.

[0007] After being formed, the waste photovoltaic tungsten filament is used as the anode, and the conductive material is used as the cathode. The conductive material is used as a container to hold the electrolyte, and molten salt electrolysis is carried out under an inert atmosphere. The product is recycled tungsten powder.

[0008] The formed photovoltaic tungsten wire waste is used as the anode and the conductive material is used as the cathode for molten salt electrolysis. During the electrolysis process, the tungsten wire anode undergoes anode dissolution under the action of electrochemical reaction to generate mobile ions, which are then transferred to the cathode through the molten salt electrolyte to undergo electrochemical deposition reaction to obtain recycled tungsten powder.

[0009] When molten salt electrolysis is performed with tungstate as electrolyte, if a rod-shaped material is used as the cathode, the regenerated tungsten powder produced by electrochemistry will be thermochemically oxidized into sodium tungsten bronze by tungstate after leaving the cathode, which affects the purity of the product. The inventors have found that when a conductive material is used as the cathode and the conductive material is used as a container to hold tungstate, that is, tungstate is placed as the electrolyte in a container formed by a conductive material, such as Figure 1 As shown, the electrochemically generated tungsten powder is in continuous contact with the cathode of the conductive crucible. Since the cathode is in an electron-reducing state, the generated tungsten element can be prevented from being oxidized by tungstate, thereby obtaining pure tungsten powder. Furthermore, molten salt electrolysis is carried out under an inert atmosphere, and lanthanum is dispersed in the waste photovoltaic tungsten wire in the form of lanthanum oxide. After the tungsten wire is dissolved, lanthanum oxide and Na2W2O7 in the molten salt spontaneously react to generate La2(WO4)3, and then the generated La2(WO4)3 migrates to the cathode for electrochemical reduction to obtain W and La2O3, so that lanthanum oxide is evenly dispersed in the generated tungsten powder, and then the prepared photovoltaic tungsten powder has the same raw material composition as the waste photovoltaic tungsten wire. The prepared photovoltaic tungsten powder can be directly used as a raw material for producing photovoltaic tungsten wire, realizing a one-step recycling and regeneration process of molten salt electrolysis from "waste" to "raw material", significantly reducing the process difficulty and recycling cost of recycling waste photovoltaic tungsten wire, and having significant economic benefits.

[0010] In some embodiments of the present invention, the anode is placed in an anode basket, the upper end of the anode basket is open, and the side wall has a through hole. The inventor found that in the process of preparing the regenerated tungsten powder, the waste photovoltaic tungsten wire is electrochemically broken when the anode is dissolved, forming some micron-sized rod-shaped tungsten, which is mixed with the cathode reduction product, affecting the morphology of the regenerated tungsten powder. At the same time, the tungsten powder needs to further react in the anode basket to form Na2W2O7, and then Na2W2O7 and La2O3 generate La2(WO4)3. The through hole on the side wall can ensure the smooth discharge of the generated product.

[0011] It should be noted that, for the anode basket, those skilled in the art can understand that the function of the anode basket is to receive the micron-sized rod-shaped tungsten formed by the falling of the anode; or, to ensure that La2O3 and molten salt generate La2(WO4)3. Therefore, there is no special requirement for its specific shape or material, as long as it can resist molten salt corrosion and ensure the migration of ions. Those skilled in the art can make a choice based on actual conditions, for example, a crucible with a corundum side wall opening can be used.

[0012] The cathode conductive material is a conventional material in the art, and those skilled in the art may select it according to actual conditions. For example, the conductive material includes a conductive crucible, which includes but is not limited to a nickel crucible and a graphite crucible (outer diameter 60 mm, inner diameter 50 mm, height 120 mm).

[0013] It is understood by those skilled in the art that the waste photovoltaic tungsten filaments exist in a filamentary form. If the tungsten filaments are not formed as an anode, it is difficult to use them in the subsequent electrolysis steps. Therefore, it is convenient to shape the filamentary waste photovoltaic tungsten filaments into molten salt electrolysis. The specific shaping method is not particularly limited by those skilled in the art. For example, the tungsten filaments can be forged into a block by forging.

[0014] According to the above-mentioned waste photovoltaic tungsten filament recycling method of the present invention, the above-mentioned waste photovoltaic tungsten filament refers to the photovoltaic tungsten filament that is broken during the production or application process, or cannot be used normally after winding, that is, the waste photovoltaic tungsten filament only changes in physical form compared with the finished tungsten filament.

[0015] According to the above-mentioned method for recycling waste photovoltaic tungsten wires of the present invention, the forging parameters of the waste photovoltaic tungsten wires are: forging pressure 20MPa~40MPa, and pressure holding 10min~40min.

[0016] As for the size of the waste photovoltaic tungsten filament formed by anode forging, technicians in this field can choose it according to actual conditions. For example, the anode forging size is 65×10×6 mm (length×width×height), the weight is 20 g, and the amount of electrolyte salt used is 200g~400g.

[0017] According to the above-mentioned method for recycling waste photovoltaic tungsten filaments of the present invention, the electrolyte includes tungstate, which includes but is not limited to sodium tungstate or potassium tungstate.

[0018] According to the above-mentioned method for recycling waste photovoltaic tungsten filaments of the present invention, the electrolyte is dried at 100° C. for 48 hours before use to completely remove moisture.

[0019] According to the above-mentioned waste photovoltaic tungsten filament recycling method of the present invention, the heating process of the molten salt electrolysis includes the first stage and the second stage in sequence; the first stage includes: evacuating the system, heating from room temperature to 300°C at a heating rate of 10°C / min, and keeping warm for 1 hour; the second stage includes: after the insulation is completed, the system is filled with an inert atmosphere and the inert atmosphere flow is maintained, and the temperature is raised to the working temperature at a heating rate of 10°C / min, and the temperature is kept for 1 hour to ensure that the electrolyte is completely melted, and then the molten salt electrolysis is started. Through the above-mentioned heating and insulation, the moisture in the system can be removed as much as possible.

[0020] According to the above-mentioned method for recycling waste photovoltaic tungsten filaments of the present invention, the time of molten salt electrolysis is not less than 3 hours.

[0021] According to the above-mentioned method for recycling waste photovoltaic tungsten wires of the present invention, in the process of preparing the regenerated tungsten powder, the temperature of the molten salt electrolysis is 750°C to 850°C, and the current is 0.8A to 1.5A. For example, the temperature is 750°C, 770°C, 790°C, 810°C, 830°C, 850°C, etc., or the range between any two of the above values; the current is 0.8A, 1.0A, 1.2A, 1.5A, or the range between any two of the above values.

[0022] According to the above-mentioned method for recycling waste photovoltaic tungsten filaments of the present invention, in the process of preparing the regenerated tungsten powder, the flow rate of the inert atmosphere is 0.2 L / min~0.6 L / min.

[0023] As an example, the inert atmosphere includes at least one of argon and nitrogen.

[0024] According to an embodiment of the present invention, after the electrolysis is completed, after naturally cooling to room temperature relative to the atmosphere, the cathode and the molten salt are taken out, the molten salt and the product on the cathode are repeatedly washed with deionized water to remove the molten salt in the product, and finally the product is dried to obtain the corresponding product.

[0025] In a second aspect of the present invention, the present invention provides a regenerated tungsten powder, which is obtained by processing using the above method.

[0026] In a third aspect of the present invention, the present invention proposes the application of the above-mentioned recycled tungsten powder in the field of photovoltaic silicon wafers.

[0027] The present invention has at least the following technical effects: This application utilizes photovoltaic tungsten filament waste through a short-process resource utilization method of molten salt electrolysis, completely recovers the tungsten and lanthanum oxide in the photovoltaic tungsten filament, and the prepared recycled tungsten powder has a uniform distribution of lanthanum oxide, which can be directly used as a raw material for the production of photovoltaic tungsten filaments, realizing a one-step conversion from "waste" to "raw material". BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 Schematic diagram of the structure of the molten salt electrolytic cell used in Example 1 of the present invention; Figure 2 is the XRD pattern of the product of Example 1 of the present invention; Figure 3 It is the SEM spectrum and EDS mapping spectrum of the product of Example 1 of the present invention; Figure 4 This is the SEM image of the product of Example 2 of the present invention; Figure 5 It is the SEM spectrum and EDS mapping spectrum of the product of Example 2 of the present invention; Figure 6 is the XRD pattern of the product of Example 3 of the present invention; Figure 7 It is the SEM spectrum and EDS mapping spectrum of the product of Comparative Example 1 of the present invention; Figure 8 is the XRD pattern of the product of Comparative Example 2 of the present invention; Fig. 9 It is the XRD spectrum of the product of Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0030] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are only illustrative and do not limit the present invention in any way.

[0031] Example 1 (1) Weigh 20 g of cleaned waste photovoltaic tungsten filaments and place them in a mold. Use a hydraulic press to forge the waste photovoltaic tungsten filaments at a pressure of 30 MPa for 20 min to forge them into a cuboid of 65 × 10 × 6 mm (length × width × height).

[0032] (2) The forged photovoltaic tungsten filament is fixed on the stainless steel current collector and placed in an open anode basket with a corundum side wall and a through hole of 20 mm inner diameter and 300 mm height (see Figure 1), the through hole is opened at 35mm from the bottom and is circular. After sodium tungstate is dried and dehydrated at 100℃ for 48h, 300g is weighed as molten salt electrolyte and placed in a graphite crucible with an inner diameter of 50mm and a height of 120mm. The main body of the graphite crucible is used as the cathode, which is achieved by contact between the stainless steel current collector and the top of the graphite crucible.

[0033] (3) The system was evacuated and the temperature was raised from room temperature to 300°C at a heating rate of 10°C / min and kept at that temperature for 1 h. After the heating was completed, the system was filled with dry argon and the argon flow rate was maintained at 0.6 L / min. The temperature was further raised to 800°C at a heating rate of 10°C / min. After being kept at 800°C for 1 h, electrolysis was performed at a current of 1.2 A for 3 h.

[0034] (4) After the electrolysis is completed, the electrode is raised above the molten salt and naturally cooled to room temperature in an argon atmosphere. The molten salt is taken out and repeatedly washed with pure water, and the precipitate is dried at 100°C to obtain the regenerated tungsten powder.

[0035] The XRD pattern of the product prepared in Example 1 is as follows Figure 2 As shown, from Figure 2 It can be seen that when a graphite crucible cathode is used, the oxidation of tungsten powder by sodium tungstate can be effectively avoided, and the product phase obtained is pure tungsten powder. The SEM spectrum of the product prepared in Example 1 is as follows: Figure 3 As shown, from Figure 3 It can be seen that the prepared tungsten powder has a uniform distribution of lanthanum oxide, which is similar to the traditional preparation of rare earth tungsten alloy powder and can be directly used as a raw material for the production of photovoltaic tungsten wires. The migration process of lanthanum oxide was analyzed by thermodynamic calculation. Lanthanum is dispersed in the tungsten wire in the form of lanthanum oxide. Thermodynamic calculation shows that La2O3 cannot spontaneously react with Na2WO4 to generate La2(WO4)3 ( ), but La2O3 can spontaneously react with Na2W2O7 to generate La2(WO4)3 ( ), while La2(WO4)3 can participate in electrochemical reduction to obtain W and La2O3 (La2(WO4)3→3W + La2O3+ 4.5O2). Therefore, the key to achieving the co-recovery of tungsten and lanthanum oxide is the dissolution of La2O3 in molten salt to form La2(WO4)3. When molten salt electrolysis is carried out under an inert atmosphere, the dissolution of the tungsten anode is divided into two parts, namely electrochemical dissolution (W + 4O 2- → 6 e - + WO4 2- ) and thermochemical reactions ( ), the sodium tungsten bronze produced by the thermochemical reaction can be collected by the anode basket. In the anode basket, the O2 produced during the electrochemical reaction will further oxidize the sodium tungsten bronze to produce WO3 (2 Na x WO3+x / 2 O2→ x Na2WO4+ (2- x ) WO3), at which time WO3 and Na2WO4 will spontaneously react to produce Na2W2O7. Therefore, the design of the anode basket can promote the spontaneous reaction of lanthanum oxide and Na2W2O7 in the molten salt to generate La2(WO4)3, and then the generated La2(WO4)3 migrates to the cathode for electrochemical reduction to obtain W and La2O3 (La2(WO4)3→3W + La2O3+ 4.5O2), so that lanthanum oxide is evenly dispersed in the generated tungsten powder, and the prepared recycled tungsten powder has the same raw material composition as the waste photovoltaic tungsten wire.

[0036] Example 2 The difference between Example 2 and Example 1 is that Example 2 does not use an anode basket.

[0037] The SEM spectrum of the regenerated tungsten powder prepared in Example 2 is as follows: Figure 4 and Figure 5 As shown, from Figure 4 It can be seen that when recycling waste photovoltaic tungsten filaments, if the anode basket is not used, the obtained product contains rod-shaped tungsten. These micron-sized rod-shaped tungsten are produced during the anode dissolution of the photovoltaic tungsten filament. The produced rod-shaped tungsten falls into the graphite crucible and mixes with the product. Therefore, it is preferred to use an anode basket to remove the rod-shaped tungsten. Figure 5 It can be seen that when the anode basket is not used, La exists in the form of oxide particles. This is because when there is no anode basket, La2O3 does not have the conditions to generate La2(WO4)3, so it cannot participate in the electrochemical reaction process, causing the La2O3 in the photovoltaic tungsten filament to fall in the form of anode mud, making it difficult to obtain tungsten powder with uniformly distributed La2O3.

[0038] Example 3 The difference between Example 3 and Example 1 is that the graphite crucible in step (2) is replaced by a nickel crucible.

[0039] The XRD spectrum of the regenerated tungsten powder prepared in Example 3 is as follows: Figure 6 As shown. Figure 6 It can be seen that after the graphite crucible is replaced by a nickel crucible, the obtained product phase is still a single tungsten powder, which further proves that the conductive crucible cathode can effectively prevent the oxidation of tungsten powder and eliminates the influence of graphite on the carbon thermal reduction reaction of sodium tungsten bronze at high temperature.

[0040] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the electrolysis time in step (3) is 2 h.

[0041] The SEM and EDS mapping spectra of the regenerated tungsten powder in Comparative Example 1 are as follows: Figure 7 As shown, from Figure 7 It can be seen that when the electrolysis time is 2 h, there is no dispersed lanthanum oxide distribution in the product. This is mainly affected by the dissolution and deposition process of lanthanum. Lanthanum is dispersed in the tungsten wire in the form of lanthanum oxide. After the tungsten wire is dissolved, lanthanum oxide and Na2W2O7 in the molten salt spontaneously react to generate La2(WO4)3, and then the generated La2(WO4)3 migrates to the cathode for electrochemical reduction. However, La2(WO4)3 has a certain solubility in sodium tungstate. When the electrolysis time is short, the concentration of La2(WO4)3 in the molten salt is low, which is not enough to generate La2O3 by electrochemical reduction.

[0042] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in step (2), the electrolyte is replaced by NaCl-KCl instead of sodium tungstate.

[0043] The XRD pattern of the product prepared in Comparative Example 2 is as follows Figure 8 As shown in FIG. 1 , after sodium tungstate is replaced by NaCl-KCl, the obtained product is pure tungsten powder, but the elemental analysis results show that the product does not contain La2O3. This is because there are no conditions for generating La2(WO4)3 in the NaCl-KCl molten salt, so the recovery of La element cannot be achieved.

[0044] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in step (2), the conductive crucible is replaced by a corundum crucible, and the cathode is replaced by a tungsten rod.

[0045] The XRD pattern of the product prepared in Comparative Example 3 is as follows Fig. 9 As shown, from Fig. 9 It can be seen that the prepared product is a mixture of sodium tungsten bronze (NaWO3) and tungsten powder, of which tungsten accounts for 36.4% and NaWO3 accounts for 63.6%. This is because tungstate is an oxygen-containing acid salt. When a tungsten rod is used as the cathode, the tungsten powder produced by cathode electrochemical deposition is easily converted to tungstate oxide sodium tungsten bronze ( ), resulting in impure products.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recycling waste photovoltaic tungsten filaments, characterized in that: include: After being formed, the waste photovoltaic tungsten filament is used as the anode, and the conductive material is used as the cathode. The conductive material is used as a container to hold the electrolyte, and molten salt electrolysis is carried out under an inert atmosphere to obtain recycled tungsten powder.

2. The method according to claim 1, characterized in that: The anode is placed in an anode basket, the upper end of the anode basket is open, and the side wall has through holes.

3. The method according to claim 1, characterized in that: The conductive material includes a conductive crucible; Preferably, the conductive crucible comprises a graphite crucible or a nickel crucible.

4. The method according to claim 1, characterized in that: The electrolyte includes tungstate.

5. The method according to any one of claims 1 to 4, characterized in that: The time of the molten salt electrolysis is not less than 3 hours.

6. The method according to any one of claims 1 to 4, characterized in that: The temperature of the molten salt electrolysis is 750°C to 850°C.

7. The method according to any one of claims 1 to 4, characterized in that: The current of the molten salt electrolysis is 0.8A~1.5A.

8. The method according to any one of claims 1 to 4, characterized in that: The flow rate of the inert atmosphere is 0.2 L / min~0.6 L / min.

9. A regenerated tungsten powder, characterized in that: The method is prepared by any one of claims 1 to 8.

10. Application of the regenerated tungsten powder according to claim 9 in the field of photovoltaic silicon wafers.

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