Method for recovering glass and silicon powder from waste photovoltaic module

Abstract

The invention belongs to the field of photovoltaic module recovery, and particularly relates to a method for recovering glass and silicon powder from a waste photovoltaic module. The method comprises the following steps: (S1) crushing the waste photovoltaic module, and mixing the obtained powder with water to form slurry; (S2) adjusting the pH value of the slurry to be alkaline to obtain alkaline slurry; (S3) the alkaline slurry is mixed with a collecting agent, an inhibitor and a foaming agent, then flotation separation is conducted, and coarse silicon powder and a glass foam layer are obtained; (S4) cleaning the coarse silicon powder to obtain a silicon powder product; and (S5) sequentially carrying out defoaming, solid-liquid separation and washing on the glass foam layer to obtain a glass product. By optimizing the slurry pH, flotation reagent combination, washing and other process conditions, the separation effect of the silicon powder and the glass powder is improved, the problem that separation is not thorough due to similar surface properties in a traditional physical separation method is solved, the reagent residual quantity on the surface of the silicon powder is reduced, and the subsequent purification cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic module recycling technology, specifically relating to a method for recovering glass and silicon powder from waste photovoltaic modules. Background Technology

[0002] With the rapid development of the photovoltaic industry, the recycling of waste photovoltaic modules has become an important issue in the field of resource recycling. In waste photovoltaic modules, silicon powder and glass powder (containing SiO2 and metal oxides such as CaO and Na2O) form a fine mixture during the crushing process. The two materials have similar particle sizes and small density differences (silicon powder is approximately 2.33 g / cm³). 3 The glass content is approximately 2.5 g / cm³. 3 Furthermore, their surfaces are all hydrophilic, making separation extremely difficult.

[0003] Traditional separation technologies have significant limitations: physical methods such as gravity separation and magnetic separation rely on differences in density or magnetic properties. Since the surface properties and physical parameters of the two are similar, the purity of silicon powder after separation is only 50% to 70%, the glass removal rate is less than 60%, and the mechanical entrainment loss of silicon material is serious. Methods such as vibrating sieving and electrostatic separation are affected by particle agglomeration and cannot effectively distinguish between fine silicon powder and glass particles, resulting in low resource recovery rate (silicon powder recovery rate ≤75%), which is difficult to meet the requirements of high-value regeneration.

[0004] Reverse flotation, as a targeted separation technology, achieves selective separation of silicon powder and glass powder through reagent control, thus improving the separation effect to some extent. However, existing reverse flotation technologies still have shortcomings in practical applications: the reagent system has limited selective differentiation ability between silicon powder and glass powder, easily resulting in glass particle residue or silicon powder entrainment, leading to unsatisfactory separation efficiency; at the same time, the existing process is not very adaptable to changes in the silicon to glass ratio in the raw materials. When the raw material composition fluctuates, the separation effect is prone to significant fluctuations, making it difficult to consistently obtain high-purity silicon powder and glass products.

[0005] In summary, existing technologies cannot meet the requirements for efficient and stable separation of silicon powder and glass powder in waste photovoltaic modules, resulting in low silicon resource recycling rates and difficulty in directly reusing glass resources, thus limiting the resource value of waste photovoltaic modules. Therefore, developing a recycling method that can achieve efficient separation of silicon powder and glass powder with strong process stability has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the efficient separation and recycling of silicon powder and glass powder.

[0007] Based on the above considerations, the present invention provides a method for recovering glass and silicon powder from waste photovoltaic modules, the method comprising the following steps:

[0008] (S1) The waste photovoltaic modules are crushed and the crushed powder is mixed with water to form a slurry;

[0009] (S2) Adjust the pH of the slurry to alkaline to obtain an alkaline slurry;

[0010] (S3) The alkaline slurry is mixed with a collector, an inhibitor, and a foaming agent, and then separated by flotation to obtain a glass foam layer and coarse silica powder collected at the bottom of the tank;

[0011] (S4) The coarse silicon powder is cleaned to obtain the silicon powder product;

[0012] (S5) The glass foam layer is sequentially defoamed, separated into solid and liquid and washed to obtain the glass product;

[0013] The execution of steps (S4) and (S5) is not in any particular order.

[0014] Preferably, the method further includes the following steps:

[0015] (S6) The silica powder washing wastewater obtained in step (S4) is subjected to pH adjustment to 6-8, solid-liquid separation and COD adsorption to obtain purified water.

[0016] (S7) The glass washing wastewater obtained in step (S5) is subjected to demulsification, COD removal by adsorption and nanofiltration membrane concentration treatment in sequence to obtain nanofiltration permeate and nanofiltration concentrate.

[0017] More preferably, the suspended solids content and COD content in the purified water are <20mg / L and <30mg / L, respectively, and are reused in step (S1);

[0018] More preferably, the inhibitor used in step (S3) is sodium silicate, and the sodium silicate content in the nanofiltration concentrate is ≥95%, which is recycled for step (S3).

[0019] The beneficial effects of this invention are as follows:

[0020] I. This invention achieves efficient separation and recovery of glass and silicon powder through reagent-assisted flotation, solving the problem of incomplete separation caused by similar surface properties in traditional physical separation methods, and avoiding mechanical entrainment loss of high-value silicon materials.

[0021] Second, this invention achieves a silicon powder purity >98.5% and a glass removal rate >90% by selectively activating glass powder and inhibiting silicon powder flotation through a controlled reagent system, combined with a multi-stage cleaning and wastewater recycling process. Simultaneously, this invention reduces the amount of reagent residue on the silicon powder surface through a three-stage washing process (countercurrent water washing + acid washing + ultrasonic cleaning) during the purification of crude silicon powder, thereby avoiding the impact of reagent residue on silicon powder purity and reducing subsequent purification costs.

[0022] Third, this invention achieves efficient separation and green recycling by optimizing the reagent combination, cleaning process, and wastewater recycling system. Especially when sodium silicate is used as an inhibitor, a closed-loop process is formed through low-temperature operation (≤25℃) in conjunction with the demulsification and adsorption stages. Detailed Implementation

[0023] The technical solution and its effects of the present invention will be further described below with reference to specific embodiments / examples. The following embodiments / examples are merely illustrative of the present invention and are not intended to limit it. Simple modifications made to the present invention based on the concept of the present invention are all within the scope of protection claimed by the present invention.

[0024] The method for recovering glass and silicon powder from waste photovoltaic modules provided by this invention includes the following steps:

[0025] (S1) The powder from the crushed waste photovoltaic modules is mixed with water to form a slurry;

[0026] (S2) Adjust the pH of the slurry to alkaline to obtain an alkaline slurry;

[0027] (S3) The alkaline slurry is mixed with a collector, an inhibitor, and a foaming agent, and then separated by flotation to obtain a glass foam layer and coarse silica powder collected at the bottom of the tank;

[0028] (S4) The coarse silicon powder is cleaned to obtain the silicon powder product;

[0029] (S5) The glass foam layer is sequentially defoamed, separated into solid and liquid and washed to obtain the glass product;

[0030] The execution of steps (S4) and (S5) is not in any particular order.

[0031] Step S1: Slurry preparation

[0032] In some embodiments, in step (S1), the waste photovoltaic modules are first crushed, and then the crushed powder is mixed with water to form a slurry. The powder is dispersed by water medium to make it uniformly suspended, laying the material basis for subsequent flotation separation.

[0033] Preferably, the mass ratio of silicon powder to glass in the waste photovoltaic module is 1:(0.5-2), which is suitable for the composition ratio of most waste photovoltaic modules.

[0034] Preferably, the particle size of the powder is ≤100μm, and it is more likely to pass through a 100-300 mesh sieve (e.g., a 200 mesh sieve, preferably with a particle size ≤74μm) to facilitate flotation separation.

[0035] Preferably, the solid content of the slurry is 12% to 25%, more preferably 15% to 20%, for example, 16%, 17%, 18% or 19%. This range is beneficial for the full suspension of particles and can reduce the consumption of subsequent reagents.

[0036] Step S2: pH adjustment

[0037] In some embodiments, in step (S2), alkali is added to the slurry to adjust the pH to alkaline to obtain an alkaline slurry; the alkaline environment can enhance the selective adsorption of the collector on the glass surface in the subsequent step (S3), while inhibiting the hydrophilicity of the silicon powder surface.

[0038] Preferably, the alkali used to adjust the pH is selected from at least one of alkali metal hydroxides such as NaOH and KOH or alkaline earth metal hydroxides such as Ca(OH)2.

[0039] Preferably, the pH of the adjusted alkaline slurry is 8-12 (more preferably 9.5-10.5). The advantages of this range are: ① enhanced adsorption activity of the glass surface and the collector, while suppressing the hydrophilicity of the silica powder surface, maximizing the difference in surface properties between the glass and the silica powder; ② promotion of hydroxylation of the silica powder surface and its binding with the inhibitor, improving the efficiency of the inhibitor; ③ increased recovery rate of the inhibitor (especially sodium silicate) in subsequent wastewater treatment, reducing wastewater treatment costs.

[0040] Step S3: Flotation Separation

[0041] In some embodiments, step (S3) achieves selective separation of glass and silicon powder through the synergistic effect of collector, inhibitor and frother. Specifically, the above-mentioned agents (preferably collector, inhibitor and frother added in sequence) are added to alkaline slurry and mixed thoroughly before flotation, so that glass particles float with the foam to form a glass foam layer and silicon powder settles to form a coarse silicon powder layer.

[0042] (1) Collecting agent

[0043] Preferably, the collector is selected from at least one of fatty acids (oleic acid, linoleic acid, stearic acid), sulfonates (sodium dodecylbenzene sulfonate (SDBS), sodium petroleum sulfonate, and α-olefin sulfonate), and amines (at least one of dodecylamine (DDA), octadecylamine, and N-dodecyl-1,3-propanediamine (ND13)); the amount of collector added is 100-300 g / t (e.g., 150 g / t, 200 g / t, or 250 g / t) based on the mass of the alkaline slurry.

[0044] More preferably, the collector includes fatty acids and sulfonates. The order of addition is to first add the fatty acid collector and stir evenly (e.g., stir for 2-5 minutes), and then add the sulfonate collector and stir (e.g., stir for 1-3 minutes). This stepwise adsorption enhances the collector coverage on the glass surface and improves the separation efficiency.

[0045] More preferably, the fatty acid collector is oleic acid, and the sulfonate collector is sodium dodecylbenzenesulfonate, with a mass ratio of (3-5):1, to suit the glass surface properties (containing Ca). 2+ / Na + (e.g., metal ions) thus synergistically capture glass powder, improving the separation effect.

[0046] (2) Inhibitors

[0047] Preferably, the inhibitor includes an inorganic silicate inhibitor (at least one of sodium silicate, potassium silicate, and sodium hexametaphosphate) and / or an anionic polymeric dispersant (at least one of sodium polyacrylate (PAAS), sodium carboxymethyl cellulose (CMC-Na), and polyacrylamide (PAA)) to inhibit silica powder flotation; based on the mass of the alkaline slurry, the amount of the inhibitor added is 200-500 g / t (e.g., 150 g / t, 200 g / t, 250 g / t, 300 g / t, 400 g / t).

[0048] More preferably, the inhibitor includes an inorganic silicate inhibitor and an anionic polymeric dispersant.

[0049] More preferably, the inhibitor includes sodium silicate and sodium polyacrylate in a mass ratio of (4-5):1. The combination of the two can form a hydrophilic film on the surface of silica powder to better inhibit its floating and disperse the slurry to avoid particle agglomeration, thereby improving the flotation effect. Sodium silicate can be recycled and reused through subsequent steps (S7).

[0050] (3) Foaming agent

[0051] Preferably, the foaming agent is selected from at least one of methyl isobutyl methanol (MIBC), polyethylene glycol ether, and triethoxybutane, which can generate easily broken brittle foam to reduce silica powder entrainment; based on the mass of alkaline slurry, the amount of foaming agent added can be 10-30 g / t (e.g., 15 g / t, 20 g / t, or 25 g / t).

[0052] (4) Flotation operating conditions

[0053] Preferably, the flotation is carried out in a flotation machine, and the operating conditions include: flotation time of 10-20 min, stirring speed of 1000-1500 rpm, and the height of the slurry liquid level is kept stable at 70% to 80% of the tank volume to ensure that the bubbles and particles are in full contact and the foam layer is stably discharged.

[0054] Step S4: Cleaning of coarse silica powder

[0055] In some embodiments, in step (S4), the coarse silicon powder at the bottom of the tank is collected and then washed, centrifuged, dehydrated, and dried in sequence to remove residual agents and fine impurities, thereby obtaining a silicon powder product with a purity >98.5%.

[0056] Preferably, the washing method includes a three-stage design of "countercurrent water washing → acid washing → ultrasonic cleaning". Through the synergistic effect of physical dissolution, chemical bond breaking, and mechanical stripping, it can not only reduce the residues of agents and fine stripping particles on the silicon powder surface to below 0.1%, but also achieve the effects of reducing acid consumption, improving silicon powder flowability, and reducing equipment corrosion. The specific washing conditions are as follows:

[0057] Countercurrent water washing: The water washing temperature is 40-70℃, and the mass ratio of water to coarse silica powder is (2-4):1. Water washing can remove soluble salts and loosely attached agents from the surface, and at the same time preheat the surface to improve the efficiency of subsequent acid washing.

[0058] Pickling: Pickling is performed using an acid solution (e.g., dilute hydrochloric acid or dilute sulfuric acid) at a concentration of 0.5-2 wt% (e.g., 1.0 wt% ± 0.1 wt% acid solution). The pickling time is 3-10 minutes, and the mass ratio of acid solution to coarse silicon powder (based on the mass of acid solution) is (3-10):1, such as 5:1 or 8:1. Pickling can destroy the collector adsorption film remaining on the surface of silicon powder. Pickling can also selectively dissolve metal oxides in coarse silicon powder without damaging the silicon powder product.

[0059] Ultrasonic cleaning: cleaning temperature 40-50℃, cleaning time 5-30 min, ultrasonic power density (1-5) kW / m 3 The frequency is 30-50kHz. Ultrasonic cleaning uses ultrasonic vibration to peel off fine glass particles, thoroughly removing nanoscale residues, allowing silicon powder to be directly used in photovoltaic applications, saving the cost of secondary purification.

[0060] Step S5: Glass foam layer treatment

[0061] In some embodiments, in step (S5), the glass foam layer is sequentially defoamed, separated into solid and liquid, and washed to remove the foam carrier and residual agents, and the glass powder is recovered to obtain the glass product.

[0062] Preferably, the defoaming method includes at least one of adding a defoamer, mechanical stirring defoaming, and heating defoaming; wherein the defoamer is selected from at least one of silicone defoamers, polyether defoamers, and mineral oil defoamers, and the amount added is 0.01-1 wt.% of the glass foam layer, for example, 0.05 wt.%, 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, 0.5 wt.%, 0.8 wt.%, or 0.9 wt.%.

[0063] Preferably, the solid-liquid separation temperature is ≤25°C. When the inhibitor in step (S3) contains sodium silicate, this low-temperature operation can also inhibit the hydrolysis of sodium silicate in glass washing wastewater (avoiding the formation of silica gel that contaminates glass products), laying the foundation for sodium silicate recovery in the subsequent step (S7).

[0064] Preferably, after washing, the metal oxide (e.g., CaO, Na2O) content in the glass product is >85%, and it can be directly reused as raw material for glass melting furnaces.

[0065] Step S6: Treatment of silicon powder washing wastewater

[0066] In some embodiments, the silicon powder washing wastewater generated in step (S4) contains residual acid washing waste liquid, trace amounts of inhibitors, and fine silicon particles, and needs to be treated in step (S6) for reuse. Therefore, the method provided by the present invention may further include step (S6): adjusting the pH of the silicon powder washing wastewater to 6-8, performing solid-liquid separation, and adsorbing to remove COD, to obtain purified water.

[0067] Preferably, step (S6) includes:

[0068] (S6a) Add alkaline solution to the silicon powder washing wastewater to adjust the pH to 6-8, so that high-valence metal ions (e.g., divalent Cu) can be added. 2+ Mg 2+ Zn 2+ and trivalent Fe 3+ Al 3+ (and higher valence metal ions) form hydroxide precipitates, while neutralizing acidic substances. After solid-liquid separation, the precipitate and supernatant are obtained.

[0069] (S6b) The supernatant is adsorbed by activated carbon or resin to remove residual organic inhibitors and small molecule impurities generated by acid washing, thus obtaining purified water;

[0070] (S6c) If the suspended solids content in the purified water is <20mg / L and COD <30mg / L, it can be reused in step (S1) to ensure that the properties of the slurry are not affected.

[0071] More preferably, the solid-liquid separation temperature in step (S6a) is ≤25°C; when the inhibitor in step (S3) contains sodium silicate, this low temperature condition can prevent trace amounts of sodium silicate in the wastewater from hydrolyzing to generate silica gel, preventing it from mixing with heavy metal hydroxide precipitates, and improving the convenience of subsequent sludge treatment.

[0072] Step S7: Glass washing wastewater treatment

[0073] In some embodiments, the glass washing wastewater obtained in step (S5) contains residual collectors, inhibitors, foaming agents, and defoamers (especially when the inhibitor in step (S3) contains sodium silicate, the wastewater also contains a high concentration of sodium silicate), and needs to be treated in step (S7) to achieve resource recovery or recycling. Step (S7) specifically involves: sequentially subjecting the glass washing wastewater to demulsification, COD removal by adsorption, and nanofiltration membrane concentration treatment to obtain nanofiltration permeate and nanofiltration concentrate.

[0074] Preferably, when the inhibitor in step (S3) comprises sodium silicate, step (S7) includes:

[0075] (S7a) The residual foam is broken by adding a demulsifier (e.g., polyaluminum chloride, at a dosage of 50-100 mg / L) or heating (e.g., 50-60°C), causing the organic agents (e.g., oleic acid, MIBC) to coagulate and separate.

[0076] (S7b) Use activated carbon (e.g., coconut shell activated carbon with a particle size of 0.5-1mm, added at a rate of 5-10g / L) or resin adsorption to remove dissolved organic pollutants in the water, reduce the COD of the wastewater, and reduce the burden on subsequent membrane treatment.

[0077] (S7c) The adsorbed wastewater is passed through an alkali-resistant nanofiltration membrane at a temperature ≤25℃, a pressure of 1.5-2.0MPa, and a membrane flux ≥20L / (m³). 2 Sodium silicate is concentrated by retention under h).

[0078] Especially when the inhibitor in step (S3) includes sodium silicate, low-temperature (≤25℃) operation is the core of efficient sodium silicate recovery and membrane system stability, which is reflected in:

[0079] ① Inhibit sodium silicate hydrolysis: Sodium silicate is easily hydrolyzed at high temperatures to form silica gel particles. Low temperatures can prevent the formation of silica gel, thus preventing it from clogging the nanofiltration membrane pores and ensuring that the sodium silicate rejection rate is ≥95% (the rejection rate will decrease at high temperatures).

[0080] ② Reduce membrane fouling: Inhibit the polymerization and deposition of oleic acid with organic matter such as SDBS and calcium. 2+ Fe 3+ Metal ions react with silicates to form insoluble precipitates, reducing the risk of organic deposition and inorganic scaling.

[0081] ③ Protective membrane material: Nanofiltration membranes are easily oxidized and degraded at high temperatures, while low temperatures can extend the membrane's operating cycle.

[0082] Preferably, the sodium silicate content in the nanofiltration concentrate is ≥95%, and after simple treatment (such as impurity removal and concentration adjustment), it can be reused in step (S3) as an inhibitor to reduce the cost of reagent replenishment; the nanofiltration permeate can be reused in the washing process of step (S5) to achieve water resource recycling.

[0083] In some embodiments, the precipitated sludge generated in steps (S6) and (S6) is dewatered and then centrally treated to avoid secondary pollution; furthermore, the nanofiltration membrane system is regularly cleaned and maintained to ensure a membrane flux ≥20 L / (m²). 2 ·h).

[0084] The present invention will be described in detail below with reference to embodiments and comparative examples.

[0085] Example 1 (IE)

[0086] (S1) The waste photovoltaic modules are crushed into powder with a particle size of <100μm, and then water is added to prepare a slurry with a solid content of 18%;

[0087] (S2) Add NaOH solution to the slurry to adjust the pH to 10.0 to obtain an alkaline slurry.

[0088] (S3) Collector, inhibitor, and frother are added sequentially to the alkaline slurry, and the mixture is mechanically stirred and floated in a flotation machine for 13 minutes to form a glass foam layer and a coarse silica powder layer at the bottom of the tank; among which,

[0089] The collector is 150 g / t of oleic acid and 50 g / t of SDBS; when adding, first add oleic acid and stir for 3 min, then add SDBS and stir for 2 min;

[0090] The inhibitor is 300 g / t sodium silicate and 80 g / t PAAS;

[0091] The foaming agent is 20 g / t MIBC;

[0092] (S4) The coarse silicon powder layer in step (S3) is subjected to three-stage cleaning (60℃ countercurrent water washing, 1% HCl acid washing, 40kHz ultrasonic cleaning), followed by centrifugal drying to obtain silicon powder product and silicon powder washing wastewater.

[0093] (S5) Add 0.1% organosilicon defoamer to the glass foam layer in step (S3), mix thoroughly, let stand for separation, and wash with water to obtain glass products and glass washing wastewater;

[0094] (S6) Add NaOH solution to the silicon powder washing wastewater in step (S4) to adjust the pH to 7, so that heavy metal ions precipitate. After filtration, the supernatant is obtained. The supernatant is adsorbed by activated carbon to obtain purified water, which is reused in the preparation process of step (S1).

[0095] (S7) Under continuous stirring, the glass washing wastewater in step (S5) is heated to 55°C and maintained for 20 min. Then it is filtered, and 5 g / L of coconut shell activated carbon (particle size 0.5-1 mm) is added to adsorb the organic matter in the wastewater for 30 min. The adsorbed wastewater is then passed through a polyamide composite nanofiltration membrane under an operating pressure of 1.8 MPa and a temperature of 25°C to obtain nanofiltration concentrate and nanofiltration permeate. The nanofiltration permeate is then reused in step (S5) to be mixed with the glass foam layer.

[0096] Example 2 (IE2)

[0097] The procedure is the same as in Example 1, except that:

[0098] In step (S1), the solid content of the slurry is 15%.

[0099] In step (S2), the pH of the alkaline slurry is 9.8.

[0100] In step (S3), the flotation time is 15 minutes.

[0101] Example 3 (IE3)

[0102] The procedure is the same as in Example 1, except that:

[0103] In step (S1), the solid content of the slurry is 20%.

[0104] In step (S2), the pH of the alkaline slurry is 10.5.

[0105] In step (S3), the flotation time is 12 minutes.

[0106] Example 4 (IE4)

[0107] The procedure is the same as in Example 1, except that:

[0108] In step (S1), the collector is only 150 g / t of oleic acid.

[0109] Example 5 (IE5)

[0110] The procedure is the same as in Example 1, except that:

[0111] In step (S1), the inhibitor is only 300 g / t of sodium silicate.

[0112] Example 6 (IE6)

[0113] The procedure is the same as in Example 1, except that:

[0114] In step (S1), oleic acid and SDBS in the collector are added simultaneously.

[0115] Comparative Example 1 (CE1)

[0116] The procedure is the same as in Example 1, except that:

[0117] In step (S4), the coarse silicon powder layer is washed only by countercurrent water washing at 60°C.

[0118] The residual amount of silicon powder on the surface of the product is 0.3%.

[0119] Comparative Example 2 (CE2)

[0120] The procedure is the same as in Example 1, except that:

[0121] In step (S4), the washing method for the coarse silica powder layer is only 60°C countercurrent water washing and 1% HCl acid washing.

[0122] The residual amount of silicon powder on the surface of the product is 0.3%.

[0123] Comparative Example 3 (CE3)

[0124] The procedure is the same as in Example 1, except that:

[0125] In step (S4), the coarse silicon powder layer is washed only by 1% HCl acid washing and 40kHz ultrasonic cleaning.

[0126] The residual amount of silicon powder on the surface of the product is 0.4%.

[0127] The above embodiments and comparative examples were characterized, and the results are shown in the table below.

[0128] Silicon powder purity Silicon powder residue Glass recycling rate Sodium silicate recovery rate Example 1 98.8％ <0.1％ 92％ 65％ Example 2 99.1％ <0.1％ 93％ 60％ Example 3 98.3％ 0.1％ 91％ 70％ Example 4 95.2％ 0.6％ 85％ 55％ Example 5 96.8％ 0.4％ 88％ 50％ Example 6 96.8％ 0.5％ 86％ 58％ Comparative Example 1 94.7％ 0.8％ 70％ Same as Example 1 Comparative Example 2 97.5％ 0.3％ 85％ Same as Example 1 Comparative Example 3 96.5％ 0.4％ 88％ Same as Example 1

[0129] in:

[0130] Silicon powder purity refers to the mass fraction of silicon in a silicon powder product;

[0131] Silicon powder residue refers to the mass percentage of reagents and glass particles remaining on the surface of silicon powder products. It is determined using XPS coupled with laser particle size distribution. Reagent residue is calculated as the C1s / O1s peak area ratio, glass particle residue is calibrated using the characteristic peak intensity of SiO2, and the total residue is verified using the loss on ignition method.

[0132] Glass recycling rate refers to the percentage of the mass of glass products relative to the total mass of glass in the raw materials. This ratio can also be considered as the glass removal rate of the raw materials.

[0133] Sodium silicate recovery rate refers to the percentage of sodium silicate mass in the nanofiltration concentrate relative to the initial sodium silicate mass.

[0134] summary:

[0135] Examples 1-3 demonstrate that: the reverse flotation process under medium concentration and alkaline conditions can balance separation efficiency and resource recovery rate, and is suitable for efficient separation of conventional fine particle systems (Example 1); lower pulp concentration and extended flotation time effectively reduce particle agglomeration and optimize glass collection effect, making it suitable for scenarios with higher requirements for silica powder purity (Example 2); using a highly alkaline environment can accelerate the glass activation reaction, while the high recovery rate of sodium silicate reduces reagent replenishment costs, making it suitable for industrial production that pursues resource recycling efficiency (Example 3).

[0136] Compared to Example 1, which used both oleic acid and SDBS as collectors, Example 4 used only oleic acid as a collector, resulting in a slight decrease in the purity of the silicon powder product. This is because the combination of oleic acid and SDBS enhances the collector's adsorption capacity on glass, and the addition of SDBS also improves the selectivity of the collector's adsorption on glass.

[0137] Compared to Example 1, which used both sodium silicate and PAAS as inhibitors, Example 5 used only sodium silicate as an inhibitor, resulting in a slight decrease in the purity of the silicon powder product. This is because the combination of sodium silicate and PAAS enhances the collector's adsorption capacity on glass, and the addition of PAAS also improves the dispersibility of the slurry, reducing the entrainment rate of silicon powder in the glass foam layer.

[0138] Compared to the stepwise addition of the collector in Example 1 (oleic acid first, then SDBS), the simultaneous addition of the collector in Example 6 resulted in a decrease in both glass removal rate and silica powder purity. This is because the oleic acid and SDBS were pre-mixed and added all at once, leading to competitive adsorption between the two agents and uneven coverage. This indicates that stepwise addition of the collector can preferentially adsorb Ca from the glass surface via oleic acid. 2+ / Na + Furthermore, SDBS is used to enhance hydrophobicity and reduce silicon powder entrainment.

[0139] Compared to the three-stage cleaning in Example 1, Comparative Examples 1-3 only used a portion of the three-stage cleaning process, all of which resulted in increased residual silicon powder and decreased silicon powder purity. This is because the lack of acid washing of coarse silicon powder leads to oleic acid film residue; the lack of ultrasonic cleaning leads to fine glass particle residue; and the lack of countercurrent water washing pretreatment leads to increased acid usage during the acid washing process, which also results in soluble salt residue.

Claims

1. A method for recovering glass and silicon powder from waste photovoltaic modules, characterized in that, The method includes the following steps: (S1) The waste photovoltaic modules are crushed and the crushed powder is mixed with water to form a slurry; (S2) Adjust the pH of the slurry to alkaline to obtain an alkaline slurry; (S3) The alkaline slurry is mixed with a collector, an inhibitor, and a foaming agent, and then separated by flotation to obtain a glass foam layer and coarse silica powder collected at the bottom of the tank; (S4) The coarse silicon powder is cleaned to obtain the silicon powder product; (S5) The glass foam layer is sequentially defoamed, separated into solid and liquid and washed to obtain the glass product; The execution of steps (S4) and (S5) is not in any particular order.

2. The method according to claim 1, characterized in that, In step (S1), The particle size of the powder is ≤100μm, preferably ≤74μm; The solid content of the slurry is 12% to 25%, preferably 15% to 20%; Preferably, the mass ratio of silicon to glass in the waste photovoltaic module is 1:(0.5-2).

3. The method according to claim 1 or 2, characterized in that, In step (S2), The pH of the alkaline slurry is 9.5-10.5; Preferably, the alkali used to adjust the pH is selected from at least one of alkali metal hydroxides and alkaline earth metal hydroxides.

4. The method according to any one of claims 1 to 3, characterized in that, In step (S3), The collector is selected from at least one of fatty acid collectors, sulfonate collectors, and amine collectors; wherein the fatty acid collector is selected from at least one of oleic acid, linoleic acid, and stearic acid; the sulfonate collector is selected from at least one of sodium dodecylbenzene sulfonate, sodium petroleum sulfonate, and α-olefin sulfonate; and the amine collector is selected from at least one of dodecylamine, octadecylamine, and N-dodecyl-1,3-propanediamine. The inhibitor includes an inorganic silicate inhibitor and / or anionic polymeric dispersant; wherein the inorganic silicate inhibitor is selected from at least one of sodium silicate, potassium silicate, and sodium hexametaphosphate; and the anionic polymeric dispersant is selected from at least one of sodium polyacrylate, sodium carboxymethyl cellulose, and polyacrylamide. The foaming agent is selected from at least one of methyl isobutyl methanol, polyethylene glycol ether, and triethoxybutane; Based on the mass of the alkaline slurry, the amount of collector added is 100-300 g / t; the amount of inhibitor added is 200-500 g / t; and the amount of foaming agent added is 10-30 g / t.

5. The method according to claim 4, characterized in that, In step (S3), during mixing, a collector, an inhibitor, and a foaming agent are added to the slurry in sequence; wherein, The collectors include fatty acid collectors and sulfonate collectors; when adding the collectors, the fatty acid collectors are added first and stirred evenly, and then the sulfonate collectors are added.

6. The method according to claim 5, characterized in that, In step (S3), the fatty acid collector is oleic acid, the sulfonate collector is sodium dodecylbenzenesulfonate, and the mass ratio of oleic acid to sodium dodecylbenzenesulfonate is (3-5):

1.

7. The method according to any one of claims 1 to 6, characterized in that, In step (S3), The inhibitor comprises sodium silicate and sodium polyacrylate, wherein the mass ratio of sodium silicate to sodium polyacrylate is (4-5):

1.

8. The method according to any one of claims 1 to 7, characterized in that, In step (S4), the cleaning includes sequential counter-current water washing, acid washing, and ultrasonic cleaning; wherein, The conditions for the countercurrent water washing are: the water washing temperature is 40-70℃, and the mass ratio of water to coarse silicon powder is (2-4):1; The pickling conditions are as follows: pickling is performed using dilute hydrochloric acid and / or dilute sulfuric acid for 3-10 minutes, and the mass ratio of acid solution to crude silica powder is (3-10):

1. The conditions for ultrasonic cleaning are: cleaning temperature of 40-50℃, cleaning time of 5-30 min, and ultrasonic power density of 1-5 kW / m². 3 The frequency is 30-50kHz.

9. The method according to any one of claims 1 to 8, characterized in that, In step (S3), the conditions for flotation separation include: The flotation time is 10-20 minutes; The stirring speed of the flotation machine is 1000-1500 rpm; The slurry level in the flotation machine is 70% to 80% of the flotation tank volume; and / or In step (S5), the defoaming method is selected from at least one of adding a defoaming agent, mechanical stirring defoaming, and heating defoaming; wherein, The defoamer is selected from at least one of silicone defoamers, polyether defoamers, and mineral oil defoamers, and the amount added is 0.01-1 wt.% of the glass foam layer.

10. The method according to any one of claims 1 to 9, characterized in that, The method further includes the following steps: (S6) The silica powder washing wastewater obtained in step (S4) is subjected to pH adjustment to 6-8, solid-liquid separation and COD adsorption to obtain purified water. (S7) The glass washing wastewater obtained in step (S5) is subjected to demulsification, COD removal by adsorption and nanofiltration membrane concentration treatment in sequence to obtain nanofiltration permeate and nanofiltration concentrate. Preferably, the suspended solids content in the purified water is <20mg / L and the COD content is <30mg / L, and the water is reused in step (S1). Preferably, the inhibitor used in step (S3) is sodium silicate, the solid-liquid separation temperature in step (S6) is ≤25°C, the nanofiltration membrane concentration treatment temperature in step (S7) is ≤25°C, and the sodium silicate content in the nanofiltration concentrate is ≥95%, which is recycled for step (S3).