Photovoltaic waste acid solution treatment method and system

Abstract

The invention provides a photovoltaic waste acid solution treatment method and system.The method comprises the steps that potassium hydroxide is added into a photovoltaic waste acid solution, a reaction is conducted under the stirring condition, a reaction solution is obtained, and then a potassium fluosilicate filter cake and mixed acid mother liquor are obtained through filtering and washing; the mixed acid mother liquor is evaporated in a reduced pressure evaporation mode, and mixed steam and evaporation residual liquor are obtained; and fractionating the mixed steam. The photovoltaic waste acid is recycled into mixed acid containing hydrofluoric acid, the recycling process is simple, the recycled acid can be reused for an original photovoltaic etching production line and can be used for etching treatment of ultrathin display screens at the same time, and the market capacity is large.

Description

Technical Field

[0001] The present invention relates to the technical field of waste liquid treatment, and in particular to a method and system for treating photovoltaic waste acid liquid. Background Art

[0002] During the production of silicon-based photovoltaic cells, HF or mixed acid (HF+HCl or HF+HNO3) is required for high-purity cleaning many times, including cleaning after alkali texturing, cleaning after boron or phosphorus diffusion, cleaning of quartz boats and other tools, and the waste acid after cleaning is sent to the sewage treatment station for harmless treatment. The concentration of HF in the pickling solution used by each manufacturer varies according to demand, and the general content is 5%~22%. After cleaning, the waste acid components will increase fluorosilicic acid and soluble metal salts, of which the fluorosilicic acid content is generally 0.82%~5.96%, and the metal salt content is ≤0.01%.

[0003] Hydrogen fluoride (Hydrogen Fluoride), with the chemical formula of HF and molecular weight of 20.01, is easily soluble in water and ethanol. Anhydrous hydrogen fluoride (AHF for short) is a colorless transparent liquid at low temperature or pressure, with a boiling point of 19.4°C, a melting point of -83.37°C, and a density of 1.008g / cm3 (water = 1). It is very easy to evaporate into white smoke at room temperature and normal temperature. Its chemical properties are extremely active and can react with alkalis, metals, oxides, and silicates. Hydrogen fluoride is the basis of modern fluorine chemical industry and is the most basic raw material for the preparation of elemental fluorine, various fluorine refrigerants, new fluorine-containing materials, inorganic fluoride salts, various organic fluorides, etc. Hydrogen fluoride and water can be mixed in any mass ratio to become hydrofluoric acid (HF for short).

[0004] Potassium fluorosilicate is an inorganic compound with the chemical formula K2SiF6. It is a white crystalline powder, almost insoluble in cold water, insoluble in liquid ammonia and alcohol, but soluble in hydrochloric acid. It is mainly used in wood preservation, pesticides, ceramic enamel manufacturing, aluminum and magnesium smelting, and the manufacture of optical glasses such as potassium fluorochlorate and potassium glass, as well as raw materials for synthetic mica and welding electrodes.

[0005] Publication No. CN116692874A provides a semiconductor waste acid recycling method, which uses soluble potassium salt to precipitate fluorosilicic acid, and removes fluorosilicic acid by solid-liquid separation. Urea is reacted with nitric acid to generate urea nitrate precipitation, and nitric acid is extracted by solid-liquid separation. The solution from which nitric acid is removed is distilled and fractionated by distillation to obtain a hydrofluoric acid solution. However, since urea nitrate has a large solubility in acidic conditions, especially in hydrofluoric acid, the purity of the hydrofluoric acid solution obtained is limited.

[0006] Therefore, it is necessary to propose a method and system for treating photovoltaic waste acid liquid so that the effective resources of photovoltaic waste acid liquid can be better recycled and utilized. Summary of the invention

[0007] The present invention provides a photovoltaic waste acid liquid treatment method and system, which solves the problem of resource waste in the harmless treatment of waste acid.

[0008] The technical solution of the present invention is achieved in this way: A method for treating photovoltaic waste acid liquid comprises the following steps: S1 Potassium Fluorosilicate Reaction Potassium hydroxide is added to the photovoltaic waste acid liquid, and the reaction is carried out under stirring to obtain a reaction liquid; then the reaction liquid is introduced into a sedimentation tank, and then filtered and washed to obtain a potassium fluorosilicate filter cake and a mixed acid mother liquor; the photovoltaic waste acid liquid is a waste acid liquid containing hydrofluoric acid and nitric acid from a photovoltaic production line; S2 mother liquor evaporation The mixed acid mother liquor is evaporated by reduced pressure evaporation to obtain mixed steam and evaporation residue; the KNO3 or KCl content in the evaporation residue is controlled to be higher than 10% and the potassium fluorosilicate content is controlled to be lower than 5%, and the evaporation residue is cooled to room temperature and then returned to the potassium fluorosilicate reaction step; S3 fractionation and concentration The mixed steam is fractionated to control the HF content of the top condensate to be ≤1%, and the bottom of the tower is used to concentrate the mixed acid, wherein the HF content is ≥15%.

[0009] In some embodiments, the molar amount of potassium hydroxide added is twice the molar amount of fluorosilicic acid added in the original waste acid; and the reaction is carried out at normal temperature and pressure.

[0010] In some embodiments, the amount of the evaporated residual liquid added is determined according to the concentration of fluorosilicic acid in the photovoltaic waste acid liquid and the amount of waste acid.

[0011] The mixed steam is HF, HNO3 or HCl, and water evaporated from the mixed acid solution. The evaporated mixed steam is subjected to a fractionation and concentration process. The evaporation pressure is ≤-0.085MPa, and the evaporation temperature is 58°C to 70°C.

[0012] In some embodiments, during the fractionation process, the operating pressure of the fractionation tower is ≤-0.09 MPa, and the temperature is 55°C~65°C.

[0013] A treatment system for photovoltaic waste acid liquid, comprising: a reaction kettle, a filter, an evaporator, a fractionation tower, and a condenser connected in sequence; The reactor comprises a dosing port and a drain port, photovoltaic waste liquid and potassium hydroxide are added in sequence through the dosing port, and the reaction liquid obtained after sufficient stirring and reaction is discharged from the drain port; The filter is connected to the liquid discharge port to filter the reaction liquid and separate the potassium fluorosilicate precipitate and the filtered solution; The evaporator is connected to the filter and is used to evaporate the filtered solution to obtain mixed steam and evaporated residual liquid; The fractionation tower is connected to the upper part of the evaporator to fractionate the mixed steam to obtain concentrated hydrofluoric acid and waste water; The wastewater is condensed by the condenser and then sent to the sewage treatment equipment.

[0014] In some embodiments, a filter press device is further included, which is located behind the filter and is used to dry and filter the potassium fluorosilicate precipitate to obtain a potassium fluorosilicate filter cake.

[0015] In some embodiments, the evaporator is connected to the reactor through a pipeline, and the evaporation residue is refluxed and added into the reactor.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This method recycles photovoltaic waste acid into mixed acid containing hydrofluoric acid. The recycling process is simple. The recycled acid can not only be reused in the original photovoltaic etching production line, but also can be used for etching of ultra-thin display screens. The market capacity is large. Using electronic grade potassium hydroxide as the potassium source, the recycled mixed acid solution can be reused in the photovoltaic cell production line; ultra-thin display panel glass is currently a major trend. The main formula of the etching acid solution for ultra-thin display screens is a mixed acid solution of hydrofluoric acid and nitric acid (or hydrochloric acid). Using ordinary reagent grade potassium hydroxide to recycle photovoltaic fluorine-containing waste acid into mixed acid containing hydrofluoric acid can be used for etching of ultra-thin display screens. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in 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 only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 This is a process diagram of the photovoltaic waste acid liquid treatment process of the present invention; Figure 2 This is a schematic diagram of the structure of the photovoltaic waste acid liquid treatment system of Example 1; wherein: Reactor 10 , filter 20 , evaporator 30 , fractionation tower 40 , condenser 50 , filter press equipment 60 . DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Example 1 Reference Figure 1-2 As shown, a treatment system for photovoltaic waste acid liquid includes: a reactor 10, a filter 20, an evaporator 30, a fractionation tower 40, and a condenser 50 connected in sequence. The reactor 10 includes a dosing port and a drain port, through which photovoltaic waste liquid and potassium hydroxide are added in sequence, and the reaction liquid obtained after sufficient stirring and reaction is discharged from the drain port. The filter 20 is connected to the drain port to filter the reaction liquid and separate the potassium fluorosilicate precipitate and the filtered solution. The evaporator 30 is connected to the filter 20 to evaporate the filtered solution to obtain mixed steam and evaporated residual liquid.

[0021] The fractionation tower 40 is connected to the upper part of the evaporator 30 to fractionate the mixed steam to obtain concentrated hydrofluoric acid and waste water. The waste water is condensed by the condenser 50 and then sent to the sewage treatment equipment.

[0022] The present invention further comprises a filter press device 60, which is located behind the filter 20 and is used to dry and filter the potassium fluorosilicate precipitate to obtain a potassium fluorosilicate filter cake.

[0023] The evaporator 30 of the present invention is connected to the reactor 10 through a pipeline, and the evaporation residual liquid is refluxed and added into the reactor 10.

[0024] The specific process is as follows: Photovoltaic waste liquid and potassium hydroxide are added successively through the feeding port of the reactor 10, and reacted under stirring conditions. The reaction liquid is introduced into the filter 20, and then filtered and washed to separate the potassium fluorosilicate precipitate and the filter solution; the potassium fluorosilicate precipitate passes through the filter press 60 to obtain the potassium fluorosilicate filter cake.

[0025] The filtered solution enters the evaporator 30 for evaporation to obtain mixed steam and evaporation residue. The fractionation tower 40 is connected to the upper part of the evaporator 30 to fractionate the mixed steam to obtain concentrated hydrofluoric acid and wastewater; the wastewater is condensed by the condenser 50 and sent to the sewage treatment equipment, and the concentrated hydrofluoric acid is recovered in the storage tank for subsequent use.

[0026] The evaporator 30 is connected to the reactor 10 through a pipeline, so that the evaporated residual liquid can be refluxed into the reactor 10 for further treatment.

[0027] Example 2 The waste acid liquid used in this embodiment is the waste acid liquid containing hydrofluoric acid and nitric acid from the photovoltaic production line, and the other reagents used are commercially available. The composition of the photovoltaic waste acid liquid is shown in Table 1. The system used is the system in Example 1.

[0028] Table 1 Composition of raw materials photovoltaic waste acid liquid .

[0029] A method for treating photovoltaic waste acid liquid comprises the following steps: 1. At room temperature, add photovoltaic waste acid liquid to the potassium fluorosilicate reactor at a rate of 1000Kg / hr, start the agitator, and when the liquid level in the reactor reaches 50%, according to the concentration and flow rate of fluorosilicic acid in the photovoltaic waste acid liquid, continuously add 40% potassium hydroxide solution to the reactor at a certain speed. After the reaction liquid reaches the overflow port, the reaction liquid overflows into the sedimentation tank and settles naturally.

[0030] When the residual liquid tank of the evaporation system reaches the liquid level that can operate continuously, the potassium fluorosilicate reactor increases the residual liquid feed, starts the residual liquid delivery pump, and pumps the residual liquid into the potassium fluorosilicate reactor at a certain flow rate after cooling. The delivery of potassium hydroxide is not affected by the residual liquid feed.

[0031] 2. Allow the supernatant in the sedimentation tank to overflow into the mother liquor tank. When the sedimentation tank begins to overflow, turn on the centrifuge. When the centrifuge is operating normally, open the discharge valve at the bottom of the sedimentation tank and introduce the potassium fluorosilicate slurry into the fully automatic centrifuge. Use ultrapure water to wash the filter cake in the washing process (the washing time needs to be controlled to facilitate the control of the amount of washing water), and the washing liquid is discharged into the mother liquor tank; the filter cake is packaged and sold.

[0032] 3. When the mother liquid tank reaches the liquid level for continuous operation of the evaporation system (after the potassium fluorosilicate centrifuge has been running for 8 to 10 hours), start the vacuum pump and open the condenser at the top of the fractionation tower; adjust the vacuum valve to control the top pressure of the tower to ≤-0.09MPa; 4. Pump the filtered mother liquor into the mother liquor evaporator at a certain flow rate. When the mother liquor level reaches 60% of the evaporator level, start the jacket heating steam to start evaporating the mother liquor; 5. When liquid appears in the extraction pipe at the top of the distillation tower (introduced into the acidic wastewater collection tank and sent to the sewage treatment station for treatment), slightly open the reflux valve. According to the increase of the extraction flow, slowly open the reflux valve. Regularly analyze the HF content in the produced acidic wastewater and control the HF content of the produced acidic wastewater to ≤1%. When the HF content in the produced wastewater stabilizes at a certain value below 1%, it is considered that the reflux ratio has been adjusted; 6. When the liquid level in the bottom of the distillation tower rises to a certain height (controlled at about 60%), start to extract the acid from the bottom of the tower, and introduce it into the recovery acid collection tank after cooling. Control the opening degree of the regulating valve to control the liquid level in the bottom of the tower at a certain stable position. Recover the mixed acid and sell it or send it to the etching production line for acid preparation; 7. When the liquid level of the evaporator reaches 80%, take samples to analyze the component content of the evaporation residual liquid of the evaporator, control the potassium fluorosilicate content in the residual liquid to be no higher than 5%, and the potassium nitrate content to be no lower than 10%, start to adjust the residual liquid discharge valve, and introduce the residual liquid into the residual liquid tank after cooling. When the residual liquid tank reaches the state where it can run stably, use a pump to pump the residual liquid into the potassium fluorosilicate reactor; 8. When the waste acid is used up, stop the waste acid delivery pump, stop the potassium hydroxide feed pump, stop the residual liquid delivery pump, and pump the used reaction liquid into the centrifuge for separation; when the mother liquid tank is full, stop the mother liquid delivery pump, stop the evaporator heating steam, stop the vacuum pump, break the vacuum of the evaporation and fractionation system, stop the condenser cooling water; guide the evaporator residual liquid into the residual liquid collection tank, and pump the fractionation tower bottom liquid into the recovery acid collection tank. The parking is completed.

[0033] The logistics data and component analysis results after the test device was operated continuously for 3 days are shown in Tables 2~6.

[0034] Table 2 Material flow data table .

[0035] Table 3 Potassium Fluorosilicate Filter Cake Composition Table .

[0036] Table 4 Composition of evaporation residue .

[0037] Table 5 Recovered acid composition and recovery rate .

[0038] Table 6 Composition of acidic wastewater .

[0039] 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 replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating photovoltaic waste acid liquid, characterized in that: The steps include: S1 Potassium Fluorosilicate Reaction Potassium hydroxide is added to the photovoltaic waste acid liquid, and the reaction is carried out under stirring to obtain a reaction liquid; then the reaction liquid is introduced into a sedimentation tank, and then filtered and washed to obtain a potassium fluorosilicate filter cake and a mixed acid mother liquor; the photovoltaic waste acid liquid is a waste acid liquid containing hydrofluoric acid and nitric acid from a photovoltaic production line; S2 mother liquor evaporation The mixed acid mother liquor is evaporated by reduced pressure evaporation to obtain mixed steam and evaporation residue; the KNO3 or KCl content in the evaporation residue is controlled to be higher than 10% and the potassium fluorosilicate content is controlled to be lower than 5%, and the evaporation residue is cooled to room temperature and then returned to the potassium fluorosilicate reaction step; S3 fractionation and concentration The mixed steam is fractionated to control the HF content of the top condensate to be ≤1%, and the bottom of the tower is used to concentrate the mixed acid, wherein the HF content is ≥15%.

2. A method for treating photovoltaic waste acid liquid according to claim 1, characterized in that: The molar amount of potassium hydroxide added is twice the molar amount of fluorosilicic acid of the original waste acid added.

3. The method for treating photovoltaic waste acid liquid according to claim 1, characterized in that: The amount of the evaporated residual liquid added is determined according to the concentration of fluorosilicic acid in the photovoltaic waste acid liquid and the amount of waste acid.

4. The method for treating photovoltaic waste acid liquid according to claim 1, characterized in that: The mixed steam is HF, HNO3 or HCl and water evaporated from the mixed acid solution.

5. The method for treating photovoltaic waste acid liquid according to claim 1, characterized in that: The evaporation pressure is ≤-0.085MPa, and the temperature is 58°C~70°C.

6. The method for treating photovoltaic waste acid liquid according to claim 1, characterized in that: During the fractionation process, the operating pressure of the fractionation tower is ≤-0.09MPa and the temperature is 55°C~65°C.

7. A treatment system for photovoltaic waste acid liquid, characterized in that: include: A reaction kettle, a filter, an evaporator, a fractionation tower, and a condenser connected in sequence; The reactor comprises a dosing port and a drain port, photovoltaic waste acid liquid and potassium hydroxide are added in sequence through the dosing port, and the reaction liquid obtained after sufficient stirring and reaction is discharged from the drain port; The filter is connected to the liquid discharge port to filter the reaction liquid and separate the potassium fluorosilicate precipitate and the filtered solution; The evaporator is connected to the filter and is used to evaporate the filtered solution to obtain mixed steam and evaporated residual liquid; The fractionation tower is connected to the upper part of the evaporator to fractionate the mixed steam to obtain concentrated hydrofluoric acid and waste water; The wastewater is condensed by the condenser and then sent to the sewage treatment equipment.

8. A treatment system for photovoltaic waste acid liquid according to claim 7, characterized in that: The method also comprises a filter pressing device, which is located behind the filter and is used for drying and filtering the potassium fluorosilicate precipitate to obtain a potassium fluorosilicate filter cake.

9. A treatment system for photovoltaic waste acid liquid according to claim 7, characterized in that: The evaporator is connected to the reactor through a pipeline, and the evaporation residual liquid is refluxed and added into the reactor.

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