Flotation method for separating silicon and glass in waste photovoltaic panel through fluoride-free weak acid method

Abstract

The invention relates to the technical field of silicon and glass flotation, in particular to a flotation method for separating silicon and glass in a waste photovoltaic panel through a fluoride-free weak acid method. According to the technical scheme, the method comprises the following steps: crushing silicon and glass in the waste photovoltaic panel into particles of 100-200 meshes; the crushed particles are pretreated with a nitric acid solution, then washed to be neutral and dried; mixing the dried silicon particles and glass particles according to a mass ratio of 1: 1; and a malonic acid solution is added into the mixed particles, the pH is adjusted to 4-5, and lauryl amine dipropylidene diamine is added as a collecting agent for flotation. According to the method, use of hydrofluoric acid is thoroughly avoided, the risk of virulent safety and environmental pollution caused by hydrofluoric acid is eliminated, extra heating is not needed in the whole flotation process, energy consumption and corrosion to equipment are remarkably reduced, and separation of silicon and glass can be efficiently achieved by selecting a specific flotation agent combination; and a feasible solution is provided for green, low-cost and resource recycling of the waste photovoltaic panel.

Description

Technical Field

[0001] This invention relates to the field of silicon and glass flotation technology, and in particular to a flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method. Background Technology

[0002] Solar energy, as a clean and renewable energy source, plays a crucial role in the global energy structure transformation. Photovoltaic power generation technology is one of the main forms of solar energy utilization. With the rapid development of semiconductor and materials science in recent years, the application scale of solar photovoltaic panels has continued to expand. According to market statistics, its market size has reached billions of yuan, with a significant annual growth rate. my country's photovoltaic industry started in the 1980s, and the first batch of large-scale photovoltaic power plants are now nearing the end of their design life, indicating that the next few years will see a peak in the scrapping of waste photovoltaic panels. Therefore, the development of efficient and environmentally friendly recycling technologies is urgently needed.

[0003] A typical crystalline silicon solar photovoltaic panel mainly consists of silicon wafers, ethylene-vinyl acetate (EVA) film, a glass cover, a backsheet, and metal conductors. The components are tightly bonded together by the EVA film for sealing and protection. This robust composite structure also makes the separation of components during recycling extremely difficult. Currently, for the recycling of photovoltaic panels, the industry typically first performs mechanical crushing pretreatment, followed by pyrolysis or chemical methods to remove EVA, thereby releasing and separating valuable components such as high-purity silicon and glass.

[0004] In existing technologies, Chinese patent CN118988940A proposes a method of mechanical crushing followed by pyrolysis and carbonization, and then sorting and recycling using a color sorter; while patent CN116329256B employs a process combining chemical treatment and calcination. While these methods can achieve a certain degree of recycling, they generally suffer from drawbacks such as long process flows, high energy consumption, and large equipment investments, increasing recycling costs and reducing economic feasibility. Among all components of photovoltaic panels, high-purity silicon is one of the materials with the highest recycling value. Therefore, the core challenge and key objective of recycling technology lies in achieving efficient and high-purity separation of silicon materials from glass.

[0005] Flotation is a mature technology for separating materials based on differences in their surface physicochemical properties (such as hydrophobicity and electrical properties), and it is widely used in the mineral processing field for the separation of coexisting minerals. Since high-purity single-crystal silicon and glass have significantly different surface charge characteristics, theoretically, separation by flotation is feasible. In existing technologies, the hydrofluoric acid (HF) system has been proven to effectively separate silicon and glass by flotation. Hydrofluoric acid can etch the silicate structure on the glass surface, greatly altering its surface properties and thus creating a difference in floatability with silicon. However, hydrofluoric acid is extremely toxic and corrosive, posing a serious threat to the personal safety of operators. Furthermore, the treatment of fluoride-containing wastewater is difficult and costly, and improper disposal can cause persistent environmental damage. This makes the hydrofluoric acid method a significant safety and environmental hazard in industrial applications, especially in the field of solid waste resource utilization for environmental protection. Therefore, this application proposes a fluoride-free weak acid method for the flotation separation of silicon and glass in waste photovoltaic panels. Summary of the Invention

[0006] The purpose of this invention is to address the problems of difficulty and safety hazards in separating silicon materials from glass in existing technologies, and to propose a flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method.

[0007] The technical solution of this invention: A flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method, comprising the following steps:

[0008] S1. Crush the silicon and glass in the waste photovoltaic panels into 100-200 mesh particles;

[0009] S2. Pre-treat the crushed particles with nitric acid solution, then wash with water until neutral and dry.

[0010] S3. Mix the dried silicon particles and glass particles at a mass ratio of 1:1.

[0011] S4. Add malonic acid solution to the mixed particles, and adjust the pH to 4-5 with sodium hydroxide. Stir until the system is stable.

[0012] S5. Add laurylamine dipropylene diamine as a flotation agent and stir to allow the flotation agent to be adsorbed onto the particle surface.

[0013] S6. Introduce gas for flotation. The flotation time is 5-10 minutes. Collect the floating product and the settling product, dry them at 100-110℃ and weigh them.

[0014] Optionally, the concentration of the nitric acid solution in step S2 is 65% to 68%, and 500 ml of nitric acid solution is added for every 250 g of particles.

[0015] Optionally, the concentration of the malonic acid solution in step S4 is 0.8–1.2 mol / L.

[0016] Optionally, in step S4, the stirring speed is 1000-2000 r / min and the stirring time is 2-4 minutes.

[0017] Optionally, the amount of laurylamine dipropylenediamine added in step S5 is 140-420 μl, and its concentration is 0.08-0.12 mol / L.

[0018] Optionally, the concentration of laurylamine dipropylenediamine in the flotation system is 1×10⁻⁶. -5 mol / L~3×10 -5 mol / L.

[0019] Optionally, the inflation volume in step S6 is 0.2 m³. 3 / h~0.6 m 3 / h.

[0020] Optionally, the flotation time in step S6 is 8 to 12 minutes.

[0021] Optionally, the drying temperature in step S6 is 100℃-110℃.

[0022] Optionally, the floating product is mainly glass, and the sinking product is mainly silicon.

[0023] Compared with the prior art, this application includes at least one of the following beneficial technical effects:

[0024] This invention completely eliminates the use of highly toxic and corrosive hydrofluoric acid in traditional methods, fundamentally eliminating the health threats posed by fluorides to operators and the potential environmental pollution. Furthermore, the entire flotation process is conducted under weakly acidic conditions, which are less corrosive to equipment compared to strong acid systems, further reducing safety risks and equipment maintenance costs.

[0025] This invention can be carried out at room temperature without the need for additional heating or high-temperature calcination steps, significantly reducing energy consumption. The flotation agents used (malonic acid and laurylamine dipropylenediamine) have good water solubility and are used in low quantities, which helps control raw material costs and reduce the burden of subsequent wastewater treatment.

[0026] By utilizing the surface charge difference between silicon and glass in a weakly acidic environment and by optimizing a specific combination of flotation agents, this invention can effectively separate silicon and glass. Both the settling product (silicon) and the floating product (glass) achieve high grades, demonstrating the excellent separation effect of this method. Furthermore, the process is simple, easy to operate and control.

[0027] This invention provides a green and sustainable technical path for the recycling of high-value components (high-purity silicon) from waste photovoltaic panels, solves key environmental pain points in current recycling processes, and powerfully promotes the closed-loop circulation of the photovoltaic industry chain.

[0028] In summary, this invention completely avoids the use of hydrofluoric acid, eliminating the risks of its high toxicity, safety hazards, and environmental pollution. The entire flotation process is carried out under weak acid conditions at room temperature, without the need for additional heating, which significantly reduces energy consumption and equipment corrosion. By selecting specific combinations of flotation agents, the separation of silicon and glass can be achieved efficiently. The process is simple, providing a feasible solution for the green, low-cost, and resource-based recycling of waste photovoltaic panels. Detailed Implementation

[0029] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0030] Example 1

[0031] High-purity silicon wafers and glass were crushed to a size of 100-200 mesh. Silica sand and glass sand were placed in a large beaker, and 65% nitric acid was added (specifically, 250g of sand to 500ml of nitric acid). The mixture was acid-washed for 24 hours, followed by water washing until neutral and then dried. The dried sample sand was mixed in a 1:1 ratio (10g silica sand to 10g glass sand) and added to a flotation cell. The pH was then adjusted to 4 using 1mol / L malonic acid and sodium hydroxide, and the mixture was stirred for 3 minutes until stable at a stirring speed of 1000 r / min. 140ul of 0.1mol / L laurylamine dipropylenediamine, a cationic flotation agent, was added to the stable system. The mixture was stirred for 5 minutes until the flotation agent was adsorbed onto the sand surface. Gas flotation was then introduced at a rate of 0.4m³. 3 / h. The flotation time is 10min. After collecting the floating and settling products, they are dried at 100℃, then cooled and weighed.

[0032] Example 2

[0033] High-purity silicon wafers and glass were crushed to a size of 100-200 mesh. Silica sand and glass sand were placed in a large beaker, and 66% nitric acid was added (specifically, 250g of sand to 500ml of nitric acid). The mixture was acid-washed for 24 hours, followed by water washing until neutral and then dried. The dried sample sand was mixed in a 1:1 ratio (10g silica sand to 10g glass sand) and added to a flotation cell. The pH was then adjusted to 4 using 1mol / L malonic acid and sodium hydroxide, and the mixture was stirred for 3 minutes until stable at a stirring speed of 1200 r / min. 420ul of 0.1mol / L laurylamine dipropylenediamine, a cationic flotation agent, was added to the stable system. The mixture was stirred for 5 minutes until the flotation agent was adsorbed onto the sand surface. Gas flotation was then introduced at a rate of 0.4m³. 3 / h. The flotation time is 10min. After collecting the floating and settling products, they are dried at 103℃, then cooled and weighed.

[0034] Example 3

[0035] High-purity silicon wafers and glass were crushed to a size of 100-200 mesh. Silica sand and glass sand were placed in a large beaker, and 67% nitric acid was added (specifically, 250g of sand to 500ml of nitric acid). The mixture was acid-washed for 24 hours, followed by water washing until neutral and then dried. The dried sample sand was mixed in a 1:1 ratio (10g silica sand to 10g glass sand) and added to a flotation cell. The pH was then adjusted to 4.5 using 1mol / L malonic acid and sodium hydroxide, and stirred for 3 minutes until stable at a stirring speed of 1500 r / min. 420ul of 0.1mol / L laurylamine dipropylenediamine, a cationic flotation agent, was added to the stable system. The mixture was stirred for 5 minutes until the flotation agent was adsorbed onto the sand surface. Gas flotation was then introduced at a rate of 0.4m³. 3 / h. The flotation time is 10min. After collecting the floating and settling products, they are dried at 105℃, then cooled and weighed.

[0036] Example 4

[0037] High-purity silicon wafers and glass were crushed to a size of 100-200 mesh. Silica sand and glass sand were placed in a large beaker, and 68% nitric acid was added (specifically, 250g of sand to 500ml of nitric acid). The mixture was acid-washed for 24 hours, followed by water washing until neutral and then dried. The dried sample sand was mixed in a 1:1 ratio (10g silica sand to 10g glass sand) and added to a flotation cell. The pH was then adjusted to 5 using 1mol / L malonic acid and sodium hydroxide, and the mixture was stirred for 3 minutes until stable at a stirring speed of 1800 r / min. 280ul of 0.1mol / L laurylamine dipropylenediamine, a cationic flotation agent, was added to the stable system. The mixture was stirred for 5 minutes until the flotation agent was adsorbed onto the sand surface. Gas flotation was then introduced at a rate of 0.4m³.3 / h. The flotation time is 10min. After collecting the floating and settling products, they are dried at 108℃, then cooled and weighed.

[0038] Example 5

[0039] High-purity silicon wafers and glass were crushed to a size of 100-200 mesh. Silica sand and glass sand were placed in a large beaker, and 68% nitric acid was added (specifically, 250g of sand to 500ml of nitric acid). The mixture was acid-washed for 24 hours, followed by water washing until neutral and then dried. The dried sample sand was mixed in a 1:1 ratio (10g silica sand to 10g glass sand) and added to a flotation cell. The pH was then adjusted to 5 using 1mol / L malonic acid and sodium hydroxide, and the mixture was stirred for 3 minutes until stable at a stirring speed of 2000 r / min. 350ul of 0.1mol / L laurylamine dipropylenediamine, a cationic flotation agent, was added to the stable system. The mixture was stirred for 5 minutes until the flotation agent was adsorbed onto the sand surface. Gas flotation was then introduced at a rate of 0.4m³. 3 / h. The flotation time is 10min. After collecting the floating and settling products, they are dried at 110℃, then cooled and weighed.

[0040] The following is relevant data from the embodiments.

[0041] Table 1. Separation and Recovery Results of Examples

[0042] serial number Mass of floating matter / g Mass of sediment / g Silicon grade / % Glass grade / % Example 1 1.5 17.3 54.66 66.49 Example 2 4.2 13.5 72.11 63.24 Example 3 9.1 10.3 81.12 56.51 Example 4 4.9 13.6 76.09 70.94 Example 5 7.5 10.3 81.73 50.90

[0043] Based on experimental data, the sediment (mainly composed of silicon), the target recovery product, exhibits excellent silicon grade under various conditions. For example, in Examples 3 and 5, the silicon grade of the sediment reached 81.12% and 81.73%, respectively. This indicates that by optimizing parameters such as flotation agent dosage and pH value, this method can effectively enrich high-purity silicon from the mixture, achieving efficient recovery of high-value components.

[0044] Overall, the data from the five examples show that the mass of the sediment was generally greater than that of the floating material, and silicon was the main component of the sediment (silicon grade all above 54%), while glass was the main component of the floating material (glass grade all above 50%). This result clearly confirms that laurylamine dipropylenediamine, as a flotation agent, can selectively adsorb onto the glass surface, causing it to float hydrophobically, while silicon sinks because it is not adsorbed, thus achieving successful separation. Furthermore, by adjusting the flotation conditions (such as the amount of flotation agent), the ratio and grade of the floating and settling products can be controlled. For example, in Examples 2 and 3, increasing the amount of flotation agent under the same pH and aeration rate resulted in more material floating, demonstrating the controllability of the process. All five examples followed the same core process flow (nitric acid pretreatment, malonic acid adjustment to a weakly acidic environment, laurylamine dipropylenediamine flotation), and all successfully achieved the separation of silicon and glass. Although the results fluctuated due to parameter fine-tuning, all cases showed a clear and consistent separation trend, demonstrating that the method has good stability and repeatability and has the potential for industrial scale-up.

[0045] It is worth noting that hydrofluoric acid was not used in any of the embodiments, thus eliminating the safety and environmental risks posed by highly toxic chemicals at the source. The entire flotation process was carried out in a weakly acidic environment with a pH of 4-5, which is less corrosive to equipment and safer to operate compared to strong acid systems. No heating steps were mentioned in the experiments, indicating that it can be carried out effectively at room temperature, avoiding the high energy consumption problems of traditional methods such as pyrolysis or calcination. The amount of laurylamine dipropylenediamine used as the flotation agent was extremely low (in microliters), and its concentration in the system was only 10%. -5 The mol / L level demonstrates its low dosage and high efficiency, helping to reduce costs and alleviate the pressure on subsequent wastewater treatment. The data from the embodiments of this invention strongly prove that the developed fluoride-free weak acid flotation method is a highly efficient, stable, safe, environmentally friendly, and low-energy-consumption recycling technology. It successfully solves the high-risk problems of the traditional hydrofluoric acid method and the energy consumption problems of the pyrolysis method, providing a practical and feasible technical path for the green and economical recycling of high-value silicon materials from waste photovoltaic panels.

[0046] The above specific embodiments are merely several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method, characterized in that, Includes the following steps: S1. Crush the silicon and glass in the waste photovoltaic panels into 100-200 mesh particles; S2. Pre-treat the crushed particles with nitric acid solution, then wash with water until neutral and dry. S3. Mix the dried silicon particles and glass particles at a mass ratio of 1:

1. S4. Add malonic acid solution to the mixed particles, and adjust the pH to 4-5 with sodium hydroxide. Stir until the system is stable. S5. Add laurylamine dipropylene diamine as a flotation agent and stir to allow the flotation agent to be adsorbed onto the particle surface. S6. Introduce gas for flotation. The flotation time is 5-10 minutes. Collect the floating product and the settling product, dry them at 100-110℃ and weigh them.

2. The flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method according to claim 1, characterized in that, The concentration of the nitric acid solution in step S2 is 65% to 68%, and 500 ml of nitric acid solution is added for every 250 g of particles.

3. The flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method according to claim 1, characterized in that, The concentration of the malonic acid solution in step S4 is 0.8–1.2 mol / L.

4. The flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method according to claim 1, characterized in that, In step S4, the stirring speed is 1000-2000 r / min and the stirring time is 2-4 minutes.

5. The flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method according to claim 1, characterized in that, The amount of laurylamine dipropylenediamine added in step S5 is 140-420 μl, and its concentration is 0.08-0.12 mol / L.

6. The flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method according to claim 1, characterized in that, The concentration of laurylamine dipropylenediamine in the flotation system is 1×10⁻⁶. -5 mol / L~3×10 -5 mol / L.

7. The flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method according to claim 1, characterized in that, In step S6, the inflation volume is 0.2 m³. 3 / h~0.6 m 3 / h.

8. The flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method according to claim 1, characterized in that, The flotation time in step S6 is 8 to 12 minutes.

9. The flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method according to claim 1, characterized in that, The drying temperature in step S6 is 100℃-110℃.

10. The flotation method for separating silicon and glass from waste photovoltaic panels using a fluorine-free weak acid method according to claim 1, characterized in that, The floating product is mainly glass, and the sinking product is mainly silicon.