A defluorination agent suitable for single crystal silicon wastewater and its preparation method

Abstract

The present invention relates to a defluorination agent suitable for monocrystalline silicon wastewater and a preparation method thereof. The raw materials of the defluorination agent of the present invention include graphene, porous magnetic microsphere flocculant, aluminum salt, iron salt, and coagulant. The preparation method is as follows: ball-milling and mixing graphene and porous magnetic microsphere flocculant to obtain powder A; stirring and mixing the powder A with aluminum salt aqueous solution and iron salt aqueous solution under air conditions, heating, filtering, and naturally air-drying to obtain powder B; mixing the powder B with a coagulant to obtain the defluorination agent. The present invention realizes substantial removal of fluorine by using aluminum salt and iron salt to complex with fluoride ions in wastewater to form insoluble precipitates, and then combines the adsorption effect of graphene and porous magnetic microsphere flocculant, and utilizes the magnetism of porous magnetic microsphere flocculant to separate heavy metals in wastewater from wastewater through magnetism, thereby achieving a high standard discharge level of low fluorine content and low heavy metal content in wastewater.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater defluorination, and in particular to a defluorination agent suitable for single crystal silicon wastewater and a preparation method thereof. Background Art

[0002] Single crystal silicon wafers are made by washing, texturing, diffusion, etching, plasma chemical vapor deposition, screen printing and other processes. In the silicon wafer cutting process, in order to improve the cutting efficiency and quality, silicon wafer wire saw cutting technology is usually used. In this process, cutting fluid containing fluorine (such as a mixture of hydrofluoric acid and other additives) plays a key role. However, it will also cause fluorine-containing waste liquid to pollute the environment. The "National Standard of the People's Republic of China Comprehensive Wastewater Discharge Standard" (GB 8978-1996) and industry-specific emission standards (if applicable) stipulate: Direct emission standard: For sewage directly discharged into surface water bodies, the maximum allowable emission concentration of fluoride is 10mg / L. Indirect emission standard: If the sewage is treated in a sewage treatment plant before being discharged, the concentration of fluoride in the sewage entering the sewage treatment plant should meet the treatment capacity of the sewage treatment plant, and the fluoride concentration in the water finally discharged into the surface water body should not exceed the above-mentioned 10mg / L limit.

[0003] During the production of single-crystal silicon wafers, there will be a large amount of heavy metal pollutants, such as copper (Cu), iron (Fe), nickel (Ni), cobalt (Co), lead (Pb), cadmium (Cd), chromium (Cr), gold (Au), silver (Ag) and other heavy metals. If these wastewaters are discharged directly, it will seriously affect the environment. The "National Standard of the People's Republic of China for Comprehensive Wastewater Discharge Standards" (GB 8978-1996) also stipulates that heavy metal pollution must be controlled within a certain range before it can be discharged.

[0004] Therefore, for the existing production process of single crystal silicon wafers, it is necessary to develop a new and efficient method for removing fluorine and heavy metals. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a defluorination agent suitable for single crystal silicon wastewater and a preparation method thereof. The present invention uses aluminum salts and iron salts to form insoluble precipitates with fluoride ions in wastewater to achieve substantial removal of fluorine, and then combines the adsorption effect of graphene and porous magnetic microsphere flocculants, and uses the magnetism of porous magnetic microsphere flocculants to separate heavy metals from wastewater through magnetism, thereby achieving a high standard discharge level of low fluoride content and low heavy metal content in wastewater.

[0006] The first object of the present invention is to provide a defluorination agent suitable for single crystal silicon wastewater, wherein the raw materials of the defluorination agent include graphene, porous magnetic microsphere flocculant, aluminum salt, iron salt, and coagulant aid.

[0007] In some specific embodiments of the present invention, the amount of graphene used is 10-20 parts by mass; the amount of porous magnetic microsphere flocculant used is 5-10 parts; the amount of aluminum salt used is 10-15 parts, the amount of iron salt used is 10-15 parts, and the amount of coagulant aid used is 2-8 parts.

[0008] In some specific embodiments of the present invention, the porous magnetic microsphere flocculant is prepared by the following method:

[0009] providing a magnetic particle;

[0010] In an inert atmosphere, the magnetic particles are dispersed in a mixed solution containing a high molecular weight polymer and a template substance, and spray-dried to obtain a microsphere precursor containing magnetic particles;

[0011] The obtained microsphere precursor containing magnetic particles is added into a sodium hydroxide solution, soaked for 2-10 hours, and then taken out and naturally air-dried to obtain a porous microsphere precursor;

[0012] Under an inert atmosphere, the obtained porous microsphere precursor is subjected to high-temperature calcination treatment, and the high molecular polymer is thermally decomposed to form a carbon layer on the surface of the magnetic particles to obtain the porous magnetic microsphere flocculant.

[0013] In some specific embodiments of the present invention, the magnetic particles are magnetic ferroferric oxide particles;

[0014] And / or, the high molecular polymer is selected from polyvinyl alcohol and / or polymethyl acrylate;

[0015] And / or, the template material is selected from silica gel.

[0016] In some specific embodiments of the present invention, the mass ratio of the magnetic particles, the high molecular polymer and the template material is 1: (2-10): (1-3). By setting a reasonable dosage ratio, the magnetic particles in the porous magnetic microsphere flocculant can be reasonably coated with a carbon layer, so that a porous carbon layer is formed on the surface, which is beneficial to the adsorption of heavy metals and fluoride ions.

[0017] And / or, the concentration of the sodium hydroxide solution is 1-2 mol / L; within this concentration range, silica gel can be well removed to achieve the porous carbon layer wrapping the ferroferric oxide magnetic particles.

[0018] And / or, the temperature of the high temperature calcination is 500-650°C. By setting a reasonable high temperature calcination temperature, the high molecular polymer can be fully carbonized, and the influence of high temperature treatment on the magnetism of ferroferric oxide can be reduced as much as possible, so the temperature range needs to be strictly controlled. If it is less than this range, a carbon layer cannot be formed on the surface of ferroferric oxide, which will have a greater impact on the adsorption of fluorine. If it is greater than this temperature range, the magnetism of the magnetic particles will be greatly weakened, so the removal of heavy metals cannot be completed efficiently.

[0019] In some specific embodiments of the present invention, the aluminum salt is selected from polyaluminum sulfate and polyaluminum chloride.

[0020] In some specific embodiments of the present invention, the iron salt is selected from polyferric chloride and / or polyferric sulfate.

[0021] In some specific embodiments of the present invention, the coagulant aid is selected from activated silicic acid and / or alum.

[0022] The second object of the present invention is to provide a method for preparing a defluorination agent suitable for single crystal silicon wastewater, comprising the following steps:

[0023] The graphene and the porous magnetic microsphere flocculant are ball-milled and mixed to obtain powder A;

[0024] Under air conditions, the powder A is stirred and mixed with an aluminum salt aqueous solution and an iron salt aqueous solution, and heated to 60-80° C., filtered, and naturally air-dried to obtain a powder B; wherein the heating temperature is 60-80° C., and the heating time is 1-2 hours;

[0025] The powder B is mixed with a coagulant to obtain the defluorination agent.

[0026] In the present invention, powder A is mixed with aluminum salt and iron salt and heated at 60-80°C to form a hydrated oxide layer on the surface of the porous magnetic microsphere flocculant by hydrolysis. The oxide layer has a strong affinity for fluoride ions, so fluoride ions can be better removed.

[0027] The above technical solution of the present invention has the following advantages compared with the prior art:

[0028] In the present invention, aluminum salt and iron salt can both play a good adsorption and flocculation role. At the same time, the properties of iron salt can change the floc structure, increase the specific gravity of the floc, obtain better sedimentation efficiency, and lay a solid foundation for high-precision removal of fluoride ions.

[0029] In the present invention, after aluminum salt and iron salt flocculate and precipitate most of the fluoride ions, the graphene and porous magnetic microsphere flocculants are coordinated to further adsorb and flocculate; wherein, on the one hand, the aluminum salt and iron salt on the surface of the porous magnetic microsphere flocculant that have not been oxidized can promote the formation of insoluble precipitation with fluoride, and the porous magnetic microspheres can be used as carriers of these precipitation particles to accelerate the precipitation process, and on the other hand, the aluminum salt and iron salt on the surface of the porous magnetic microsphere flocculant undergo oxidation reaction to obtain a hydrated oxide layer containing metal aluminum on the surface, and these hydrated oxides have a strong affinity for fluoride ions. The microspheres loaded with fluoride precipitation are separated from the wastewater by magnetic separation technology, and this process is both fast and efficient, avoiding the problem that traditional flocculants are difficult to recycle after use, and is conducive to reducing treatment costs and realizing recycling. The most important thing is to achieve efficient removal of fluoride ions, so that the fluoride content in the wastewater is kept within 10 mg / L and meets the discharge standard.

[0030] In the present invention, the porous structure of the porous magnetic microsphere flocculant provides a large amount of surface area, which increases the contact opportunity with heavy metal ions and fluoride ions, thereby improving the adsorption efficiency. Since the surface of the magnetic microspheres uses a high molecular polymer containing multifunctional groups, the surface of the magnetic microspheres contains some specific multifunctional groups (such as amino, carboxyl, etc.), which can be closely combined with heavy metal ions through chemical effects (such as coordination, ion exchange, etc.) or physical effects (such as electrostatic attraction), effectively removing heavy metal pollutants in water. DETAILED DESCRIPTION

[0031] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0032] Example 1

[0033] This embodiment provides a defluorination agent suitable for single crystal silicon wastewater, and the specific preparation method is as follows:

[0034] (1) Raw material dosage: 10 parts of graphene, 10 parts of porous magnetic microsphere flocculant, 15 parts of polyaluminium sulfate, 10 parts of polyferric chloride, and 5 parts of alum as a coagulant aid;

[0035] (2) According to the above amounts, the graphene and the porous magnetic microsphere flocculant are ball-milled to obtain powder A;

[0036] (3) Mix the powder A with an aqueous solution of polyaluminium sulfate and an aqueous solution of polyferric chloride, heat to 60° C. for 2 h, filter, and air-dry to obtain powder B;

[0037] (4) Mix the powder B obtained above with alum as a coagulant to obtain the defluorination agent.

[0038] The porous magnetic microsphere flocculant is prepared by the following method:

[0039] S1, purchasing the obtained ferroferric oxide magnetic particles from the market;

[0040] S2. In a nitrogen atmosphere, the above-mentioned ferroferric oxide magnetic particles are dispersed in a mixed solution containing polyvinyl alcohol and silica gel, and the spray drying temperature is 80°C to obtain a microsphere precursor containing magnetic particles; wherein the mass ratio of the ferroferric oxide magnetic particles, polyvinyl alcohol and silica gel is 1:5:1.

[0041] S3, adding the obtained microsphere precursor containing magnetic particles into a 1 mol / L sodium hydroxide solution, soaking for 4 hours, and then taking it out and air-drying it naturally to obtain a porous microsphere precursor;

[0042] S4, subjecting the obtained porous microsphere precursor to a high-temperature calcination treatment at 500° C., and thermally decomposing the polyvinyl alcohol to form a carbon layer on the surface of the magnetic particles, thereby obtaining the porous magnetic microsphere flocculant.

[0043] Example 2

[0044] This embodiment provides a defluorination agent suitable for single crystal silicon wastewater, and the specific preparation method is as follows:

[0045] (1) Raw material dosage: 12 parts of graphene, 12 parts of porous magnetic microsphere flocculant, 10 parts of polyaluminium sulfate, 15 parts of polyferric chloride, and 5 parts of alum as a coagulant aid;

[0046] (2) According to the above amounts, the graphene and the porous magnetic microsphere flocculant are ball-milled to obtain powder A;

[0047] (3) Mix the powder A with an aqueous solution of polyaluminium sulfate and an aqueous solution of polyferric chloride, heat to 80° C. for 2 h, filter, and air-dry to obtain powder B;

[0048] (4) Mix the powder B obtained above with alum as a coagulant to obtain the defluorination agent.

[0049] The porous magnetic microsphere flocculant is prepared by the following method:

[0050] S1, purchasing the obtained ferroferric oxide magnetic particles from the market;

[0051] S2. In a nitrogen atmosphere, the above-mentioned ferroferric oxide magnetic particles are dispersed in a mixed solution containing polymethyl acrylate and silica gel, and the spray drying temperature is 80°C to obtain a microsphere precursor containing magnetic particles; wherein the mass ratio of the ferroferric oxide magnetic particles, polymethyl acrylate and silica gel is 1:2:3.

[0052] S3, adding the obtained microsphere precursor containing magnetic particles into a 1.5 mol / L sodium hydroxide solution, soaking for 2 hours, and then taking out and air-drying naturally to obtain a porous microsphere precursor;

[0053] S4, subjecting the obtained porous microsphere precursor to a high-temperature calcination treatment at 500° C., and thermally decomposing the polymethyl acrylate to form a carbon layer on the surface of the magnetic particles, thereby obtaining the porous magnetic microsphere flocculant.

[0054] Example 3

[0055] This embodiment provides a defluorination agent suitable for single crystal silicon wastewater, and the specific preparation method is as follows:

[0056] (1) Raw material dosage: 15 parts of graphene, 10 parts of porous magnetic microsphere flocculant, 8 parts of polyaluminium sulfate, 15 parts of polyferric chloride, and 4 parts of alum as a coagulant aid;

[0057] (2) According to the above amounts, the graphene and the porous magnetic microsphere flocculant are ball-milled to obtain powder A;

[0058] (3) Mix the powder A with an aqueous solution of polyaluminium sulfate and an aqueous solution of polyferric chloride, heat to 80° C. for 2 h, filter, and air-dry to obtain powder B;

[0059] (4) Mix the powder B obtained above with alum as a coagulant to obtain the defluorination agent.

[0060] The porous magnetic microsphere flocculant is prepared by the following method:

[0061] S1, purchasing the obtained ferroferric oxide magnetic particles from the market;

[0062] S2. In a nitrogen atmosphere, the above-mentioned ferroferric oxide magnetic particles are dispersed in a mixed solution containing polymethyl acrylate and silica gel, and the spray drying temperature is 80°C to obtain a microsphere precursor containing magnetic particles; wherein the mass ratio of the ferroferric oxide magnetic particles, polymethyl acrylate and silica gel is 1:2:3.

[0063] S3, adding the obtained microsphere precursor containing magnetic particles into a 2 mol / L sodium hydroxide solution, soaking for 2 hours, and then taking it out and air-drying it naturally to obtain a porous microsphere precursor;

[0064] S4, subjecting the obtained porous microsphere precursor to a high-temperature calcination treatment at 500° C., and thermally decomposing the polymethyl acrylate to form a carbon layer on the surface of the magnetic particles, thereby obtaining the porous magnetic microsphere flocculant.

[0065] Example 4

[0066] This embodiment provides a defluorination agent suitable for single crystal silicon wastewater, and the specific preparation method is as follows:

[0067] (1) Raw material dosage: 10 parts of graphene, 15 parts of porous magnetic microsphere flocculant, 10 parts of polyaluminium sulfate, 15 parts of polyferric chloride, and 5 parts of alum as a coagulant aid;

[0068] (2) According to the above amounts, the graphene and the porous magnetic microsphere flocculant are ball-milled to obtain powder A;

[0069] (3) Mix the powder A with an aqueous solution of polyaluminium chloride and an aqueous solution of polyferric sulfate, heat to 60° C. for 2 h, filter, and air-dry to obtain powder B;

[0070] (4) Mix the powder B obtained above with alum as a coagulant to obtain the defluorination agent.

[0071] The porous magnetic microsphere flocculant is prepared by the following method:

[0072] S1, purchasing the obtained ferroferric oxide magnetic particles from the market;

[0073] S2. In a nitrogen atmosphere, the above-mentioned ferroferric oxide magnetic particles are dispersed in a mixed solution containing polymethyl acrylate and silica gel, and the spray drying temperature is 80°C to obtain a microsphere precursor containing magnetic particles; wherein the mass ratio of the ferroferric oxide magnetic particles, polymethyl acrylate and silica gel is 1:2:3.

[0074] S3, adding the obtained microsphere precursor containing magnetic particles into a 2 mol / L sodium hydroxide solution, soaking for 2 hours, and then taking it out and air-drying it naturally to obtain a porous microsphere precursor;

[0075] S4, subjecting the obtained porous microsphere precursor to a high-temperature calcination treatment at 500° C., and thermally decomposing the polymethyl acrylate to form a carbon layer on the surface of the magnetic particles, thereby obtaining the porous magnetic microsphere flocculant.

[0076] Comparative Example 1

[0077] Similar to Example 1, the difference is that no porous magnetic microsphere flocculant is added.

[0078] Comparative Example 2

[0079] Similar to Example 1, the difference is that when preparing the porous magnetic microsphere flocculant, the powder A is stirred and mixed with the aluminum salt aqueous solution and the iron salt aqueous solution, but is not heated.

[0080] Comparative Example 3

[0081] Similar to Example 1, the difference is that the porous magnetic microsphere flocculant is replaced by magnetic microspheres (the magnetic microspheres are polystyrene magnetic microspheres produced by Merck).

[0082] Performance Testing

[0083] Fluorine-containing wastewater was taken from a monocrystalline silicon production plant in Shandong as the fluorine-containing wastewater to be treated, wherein the pH of the fluorine-containing wastewater to be treated was 6.5, the fluorine ion concentration c0 was 45 mg / L, and the copper ion concentration was 53 mg / L. The prepared defluorination agent was used to treat the fluorine-containing wastewater to be treated to investigate the defluorination effect of the defluorination agent. The specific steps are as follows:

[0084] S1. Dissolve the defluorination agents obtained in Examples 1-4 and Comparative Examples 1-3 in deionized water to prepare a solution with a mass fraction of 20 wt.%; prepare 5 portions of the above solution in parallel;

[0085] S2. Add 1L of fluorine-containing wastewater to be treated into each of the five beakers, and then add 1 portion of the solution prepared in step S1 into each of the four beakers. Stir the reaction for 20 minutes and then let it stand for 15 minutes. Take the supernatant and use a spectrophotometer to detect the fluoride ion concentration c x And calculate the defluorination rate η = (c0-c x ) / c0×100%, wherein the detection method of fluoride ion concentration refers to "Determination of fluoride in water quality - fluorine reagent spectrophotometry" (HJ488-2009), and the results are shown in Table 1.

[0086] S3. The content of metallic copper in the supernatant obtained in step S2 was detected by atomic absorption spectroscopy. The experimental results are shown in Table 2.

[0087] Table 1 Removal of fluoride ions by the defluorination agents obtained in Examples 1-4 and Comparative Examples 1-3

[0088] <![CDATA[c0(mg / L)]]> <![CDATA[c x (mg / L)]]> η Example 1 45 0.25 99.4 Example 2 45 0.30 99.3 Example 3 45 0.28 99.4 Example 4 45 0.22 99.5 Comparative Example 1 45 9 80.0 Comparative Example 2 45 4.8 89.3 Comparative Example 3 45 7.2 84.0

[0089] Table 2 Removal of copper metal by defluorination agents obtained in Example 1 and Comparative Examples 1-3

[0090]

[0091]

[0092] As shown in Table 2, when porous magnetic microsphere flocculants are present in Example 1 and Comparative Example 2, due to the presence of magnetic ferroferric oxide particles, copper metal is well adsorbed and heavy metals can be removed well. However, since no porous magnetic microsphere flocculants are added in Comparative Example 1, its adsorption effect on heavy metals is relatively weak.

[0093] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A defluorination agent suitable for single crystal silicon wastewater, characterized in that: The raw materials of the defluorination agent include graphene, porous magnetic microsphere flocculant, aluminum salt, iron salt, and coagulant aid; The porous magnetic microsphere flocculant is prepared by the following method: providing a magnetic particle; In an inert atmosphere, the magnetic particles are dispersed in a mixed solution containing a high molecular weight polymer and a template substance, and spray-dried to obtain a microsphere precursor containing magnetic particles; The obtained microsphere precursor containing magnetic particles is added into a sodium hydroxide solution, soaked for 2-10 hours, and then taken out and naturally air-dried to obtain a porous microsphere precursor; The porous microsphere precursor is subjected to high temperature calcination treatment, and the high molecular polymer is thermally decomposed to form a carbon layer on the surface of the magnetic particles to obtain the porous magnetic microsphere flocculant; The defluorination agent is prepared by the following method: mixing graphene and porous magnetic microsphere flocculant by ball milling to obtain powder A; In air, the powder A is stirred and mixed with an aluminum salt aqueous solution and an iron salt aqueous solution, heated, filtered, and naturally air-dried to obtain a powder B; wherein the heating temperature is 60-80° C. and the heating time is 1-2 hours; The powder B is mixed with a coagulant to obtain the defluorination agent.

2. A defluorination agent suitable for single crystal silicon wastewater according to claim 1, characterized in that: In terms of mass fractions, the amount of graphene used is 10-20 parts; the amount of porous magnetic microsphere flocculant used is 5-10 parts; the amount of aluminum salt used is 10-15 parts, the amount of iron salt used is 10-15 parts, and the amount of coagulant aid used is 2-8 parts.

3. A defluorination agent suitable for single crystal silicon wastewater according to claim 1, characterized in that: The magnetic particles are magnetic ferroferric oxide particles; And / or, the high molecular polymer is selected from polyvinyl alcohol and / or polymethyl acrylate.

4. A defluorination agent suitable for single crystal silicon wastewater according to claim 1, characterized in that: The template material is selected from silica gel.

5. A defluorination agent suitable for single crystal silicon wastewater according to claim 1, characterized in that: The mass ratio of the magnetic particles, the high molecular polymer and the template material is 1:(2-10):(1-3); And / or, the concentration of the sodium hydroxide solution is 1-2 mol / L; And / or, the high temperature calcination temperature is 500-650°C.

6. A defluorination agent suitable for single crystal silicon wastewater according to claim 1 or 2, characterized in that: The aluminum salt is selected from polyaluminum sulfate and / or polyaluminum chloride.

7. A defluorination agent suitable for single crystal silicon wastewater according to claim 1 or 2, characterized in that: The iron salt is selected from polyferric chloride and / or polyferric sulfate.

8. A defluorination agent suitable for single crystal silicon wastewater according to claim 1 or 2, characterized in that: The coagulant aid is selected from activated silicic acid and / or alum.

9. The method for preparing the defluorination agent according to any one of claims 1 to 8, characterized in that: The following steps are involved: The graphene and the porous magnetic microsphere flocculant are ball-milled and mixed to obtain powder A; In air, the powder A is stirred and mixed with an aluminum salt aqueous solution and an iron salt aqueous solution, heated, filtered, and naturally air-dried to obtain a powder B; wherein the heating temperature is 60-80° C. and the heating time is 1-2 hours; The powder B is mixed with a coagulant to obtain the defluorination agent.

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