A method for producing cryolite from overhaul slag

Abstract

This invention discloses a method for producing cryolite from overhaul slag. The method includes S1: grinding the overhaul slag finely, mixing it with a treatment liquid, adding sodium hydroxide and a calcium agent, heating and stirring to dissolve the slag, and then filtering to obtain filtrate A; S2: bubbling carbon dioxide gas into filtrate A until no more precipitate forms, and then filtering to obtain the solid cryolite. The calcium agent is selected from one or more of calcium oxide and calcium hydroxide, the treatment liquid includes water, and the pH of filtrate A is >10. This invention provides a method for producing cryolite from overhaul slag that eliminates the need for fluoride addition, has low cost, and is simple to implement.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource treatment technology, specifically, it relates to a method for producing cryolite from overhaul slag. Background Technology

[0002] Overhaul slag is a solid waste generated during the overhaul of aluminum electrolytic cells. It mainly includes waste cathode carbon blocks, refractory materials, insulation materials, paste, and anti-seepage materials. According to the "National Hazardous Waste List (2021 Edition)," overhaul slag is classified as hazardous waste. The main components of overhaul slag include silicon, aluminum, fluorine, and lithium.

[0003] Fluorides, such as sodium fluoride, are usually added during aluminum extraction from overhaul slag, primarily to improve aluminum recovery. Their mechanism of action includes the following:

[0004] ① Fluorides, as fluxes, can lower the melting point of alumina (Al2O3), thereby reducing energy consumption and improving electrolysis efficiency during aluminum electrolysis.

[0005] ② Fluorides help improve the conductivity of electrolytes and the stability of electrolytes, thereby increasing the recovery rate of aluminum.

[0006] ③ The addition of fluorides can help recover valuable substances, such as aluminum and fluorine resources, and achieve high-value utilization.

[0007] However, the practice of adding fluoride during aluminum extraction from overhaul slag has the following drawbacks:

[0008] ① Health Hazards: Fluorides are toxic substances that can pose a threat to the health and safety of workers if not handled properly or if a leak occurs. Furthermore, fluorides can react with other substances to produce toxic or flammable and explosive gases or liquids, further increasing safety risks.

[0009] ② Increased process complexity: The addition of fluoride makes the entire extraction process more complex. Adding fluoride may increase the complexity and cost of the treatment process, and may also be subject to stricter regulations. To effectively control and utilize fluoride, additional process steps and equipment are required, such as precise metering of the amount of fluoride added, control of reaction conditions, and treatment of fluoride-containing wastewater.

[0010] ③ Equipment corrosion and wear: Fluorides are corrosive chemicals. Adding fluorides during the extraction process will increase the corrosion of the equipment, which will not only shorten the service life of the equipment, but also affect the performance and stability of the equipment, thereby increasing the cost of equipment maintenance and replacement. Summary of the Invention

[0011] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for producing cryolite from overhaul slag.

[0012] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0013] A method for producing cryolite from overhaul slag.

[0014] S1. After grinding the overhaul residue into a fine powder, mix it with the treatment liquid, add sodium hydroxide and calcium agent, heat and stir to dissolve, and then filter to obtain filtrate A;

[0015] S2. Pass carbon dioxide gas into filtrate A until no more precipitate is produced, then filter to obtain the solid, which is cryolite;

[0016] The calcium agent is selected from one or more of calcium oxide and calcium hydroxide, the treatment solution includes water, and the pH of the filtrate A is >10.

[0017] In this invention, some aluminum elements in the overhaul slag react with sodium hydroxide to form sodium aluminate (NaAl(OH)4). Taking Al2O3 as an example, the reaction equation is as follows:

[0018] Al2O3+2NaOH+3H2O=2NaAl(OH)4.

[0019] In this invention, the calcium agent dissolves in water to form calcium hydroxide; some aluminum elements in the overhaul slag react with the calcium agent and silicon dioxide to form calcium aluminum silicate (Ca2Al2(SiO3)5). Taking SiO2 as an example, the reaction equation includes the following:

[0020] SiO2 + 2NaOH = Na2SiO3 + H2O;

[0021] 2Ca(OH)2+2NaAl(OH)4+5Na2SiO3=Ca2Al2(SiO3)5↓+4H2O;

[0022] The aforementioned chemical reaction equations can also be combined and written in the following form:

[0023]

[0024] In this invention, fluorine in the overhaul slag is converted into NaF, wherein both NaAl(OH)4 and NaF are soluble in water, and Ca2Al2(SiO3)5 is a precipitate.

[0025] In this invention, the filtrate A obtained in step S1 contains NaAl(OH)4 and NaF.

[0026] In this invention, the filter residue obtained in step S1 contains a compound of Ca2Al2(SiO3)5 and metallic lithium, and the filter residue obtained in step S1 can be used to extract metallic lithium.

[0027] In this invention, carbon dioxide gas in step S2 is an acidic gas, which can lower the pH of filtrate A. When the pH of filtrate A drops below 10, NaAl(OH)4 and NaF in filtrate A will react to form cryolite (Na3AlF6), and the reaction equation is as follows:

[0028] NaAl(OH)4+6NaF+2CO2=Na3AlF6+2H2O+2Na2CO3.

[0029] Preferably, the molar ratio of fluorine to aluminum in the filtrate A is (6-8):1.

[0030] In this invention, the molar ratio of fluorine to aluminum in filtrate A is (6-8):1, which is conducive to the formation of cryolite.

[0031] Preferably, in step S2, carbon dioxide gas is introduced into filtrate A and then filtered to obtain filtrate B;

[0032] The treatment liquid includes filtrate B obtained from other cryolite production processes.

[0033] In this invention, filtrate B contains unreacted sodium hydroxide and NaF. Recycling B can reduce the waste of sodium hydroxide and NaF. At the same time, filtrate B can increase the amount of fluoride ions in the treatment liquid, thereby increasing the proportion of aluminum in the overhaul slag used to convert into cryolite.

[0034] Preferably, the heating temperature in step S1 is 50℃~80℃.

[0035] In this invention, the heating temperature in step S1 is 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C.

[0036] Preferably, the heating and stirring time in step S1 is 0.5h to 3h.

[0037] In this invention, the heating and stirring time in step S1 is 0.5h, 1h, 1.5h, 2h, 2.5h or 3h.

[0038] In this invention, the heating and stirring time in step S1 is specifically 1 hour.

[0039] Preferably, the amount of sodium hydroxide is greater than the sum of the amounts of aluminum and fluorine in filtrate A.

[0040] In this invention, sufficient sodium hydroxide helps to ensure that aluminum and fluorine in the overhaul slag are fully dissolved.

[0041] Preferably, the pH of the filtrate A is 11 to 12.

[0042] In this invention, the pH of filtrate A is 11, 11.2, 11.4, 11.5, 11.6, 11.8 or 12.

[0043] Preferably, in step S2, carbon dioxide gas is introduced into filtrate A until the pH of filtrate A is 8-10.

[0044] In this invention, when the pH value of filtrate A is less than 8, Na3AlF6 is prone to hydrolysis; when the pH value of filtrate A is greater than 10, Na3AlF6 is not prone to sedimentation.

[0045] Preferably, in step S1, silica is added to the overhaul slag, so that the overhaul slag contains silica. n is the amount of substance.

[0046] In this invention, when the overhaul slag contains... At that time, sufficient silicon facilitates the conversion of aluminum into Ca2Al2(SiO3)5.

[0047] Preferably, in step S1, an aluminum agent is added to the overhaul slag, such that the amount of aluminum in the overhaul slag is increased to n. Al >6n F , where n is the amount of substance.

[0048] In this invention, when n in the overhaul slag Al >6n F At that time, sufficient silicon facilitates the conversion of aluminum into NaAl(OH)4.

[0049] In this invention, the aluminum agent is selected from one or more of aluminum metal, aluminum oxide, and aluminum hydroxide.

[0050] In this invention, aluminum oxide is specifically selected as the aluminum agent.

[0051] In this invention, Ca2Al2(SiO3)5 can be used as a concrete filler, which can improve the concrete strength, enhance the concrete durability and impermeability.

[0052] Compared with the prior art, the advantages of the present invention include:

[0053] (1) The present invention provides a method for producing cryolite from overhaul slag. The aluminum element is converted into cryolite and Ca2Al2(SiO3)5 by using the fluorine and aluminum elements contained in the overhaul slag itself. Compared with the existing technology of adding fluoride to obtain cryolite, the present invention does not require the addition of fluoride, thereby avoiding the impact caused by the addition of fluoride.

[0054] (2) The method for producing cryolite from overhaul slag provided by the present invention does not require the addition of fluoride, nor does it require complex reaction equipment and preparation process. The obtained Ca2Al2(SiO3)5 can be used as a filler for concrete, which is beneficial to reducing the treatment cost of overhaul slag.

[0055] (3) The present invention provides a method for producing cryolite from overhaul slag, which uses the filtrate obtained in step S1 to extract lithium element and separate lithium element from aluminum element. The operation is simple and the cost is low. Attached Figure Description

[0056] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0057] Figure 1 This is a test image of cryolite obtained in Example 1 of the present invention, obtained by X-ray fluorescence qualitative analysis. Detailed Implementation

[0058] To enable those skilled in the art to understand the features and effects of this application, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art in this application, and in case of conflict, the definitions in this specification shall prevail.

[0059] The theories or mechanisms described and disclosed herein, whether right or wrong, shall not in any way limit the scope of this application, that is, the content of this application may be implemented without being limited by any particular theory or mechanism.

[0060] In this document, "this application" means "this invention" or "this disclosure".

[0061] The terms “a,” “an,” “a,” or similar expressions are used herein to describe the components and technical features described in this application. Such descriptions are merely for convenience and to provide a general meaning for the scope of this application. Therefore, such descriptions should be understood to include one or at least one, and the singular includes the plural, unless clearly otherwise indicated.

[0062] In this article, "or a combination thereof" means "or any combination thereof", and "any one", "any kind", "any one" means "any one", "any kind", "any one".

[0063] In this document, the terms “comprising,” “including,” “having,” “containing,” or any other similar terms are open-ended transitional phrases, intended to encompass non-exclusive inclusions. For example, a composition or article thereof containing multiple elements is not limited to the elements listed herein, but may also include other elements not explicitly listed but typically inherent to the composition or article thereof. Furthermore, unless explicitly stated to the contrary, the term “or” is inclusive, not exclusive. For example, the condition “A or B” is satisfied in any of the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist). Furthermore, in this article, the interpretation of the terms “contains,” “includes,” “has,” and “contains” should be regarded as having been specifically disclosed and simultaneously covering closed conjunctions such as “composed of,” “consisting of,” and “remaining as,” as well as conjunctions such as “essentially composed of,” “mainly composed of,” “mainly composed of,” “basically containing,” “basically composed of,” “basically composed of,” and “essentially containing.”

[0064] In this document, all features or conditions defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible ranges and individual numerical values ​​(including integers and fractions) within those ranges, especially integer values. For example, range descriptions such as "1.0 to 8.0," "between 1.0 and 8.0," or "between 1.0 and 8.0" should be considered as specifically disclosing all subranges such as 1.0 to 8.0, 1.0 to 7.0, 2.0 to 8.0, 2.0 to 6.0, 3.0 to 6.0, 4.0 to 8.0, 3.0 to 8.0, etc., and should be considered as covering endpoint values, especially subranges defined by integer values, and should be considered as specifically disclosing individual numerical values ​​within those ranges such as 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, etc. Unless otherwise specified, the foregoing interpretation applies to all contents of this application, whether extensive or not.

[0065] If a quantity, concentration, or other numerical value or parameter is expressed as a range, preferred range (or better range), or a series of upper and lower limits, it should be understood that this document has specifically disclosed all ranges consisting of any pair of upper or preferred values ​​(or better values) and lower or preferred values ​​(or better values) of that range, regardless of whether such ranges are disclosed separately. Furthermore, when a range of numerical values ​​is mentioned herein, unless otherwise stated, the range should include its endpoints and all integers and fractions within the range.

[0066] In this document, numerical values ​​are to be understood as having a precision with significant digits, provided that the purpose of the invention can be achieved. For example, the number 40.0 should be understood to cover the range of 39.50 to 40.49.

[0067] Unless otherwise specified, in this application, parts by weight represent the relative number of parts by weight in the composition, and can be any unit of weight, such as, but not limited to, kilograms, grams, pounds, etc. For example, 100 parts by weight of polyphenylene ether resin means that it can be 100 kilograms of polyphenylene ether resin or 100 pounds of polyphenylene ether resin.

[0068] It should be understood that the features disclosed in the various embodiments herein can be arbitrarily combined to form the technical solution of this application, as long as there is no contradiction in the combination of these features.

[0069] The present application will be described below with reference to specific embodiments and examples. It should be understood that these specific embodiments and examples are merely illustrative and are not intended to limit the scope or use of the present application.

[0070] Unless otherwise stated, the methods, reagents, and conditions used in the preparation examples, comparative examples, and embodiments described below are conventional methods, reagents, and conditions in the art.

[0071] The following are the details:

[0072] Overhaul slag sample 1: Fluorine mass fraction 16.4%, aluminum mass fraction 14.8%, silicon mass fraction 14.2%.

[0073] Overhaul slag sample 2: Fluorine mass fraction was 28.1%, aluminum mass fraction was 6.3%, and silicon mass fraction was 19.5%.

[0074] Preparation Example

[0075] Preparation Example 1

[0076] The raw materials used in this preparation example include: 10 kg of overhaul slag sample 1 and 3.56 kg of SiO2.

[0077] The preparation method of this preparation example includes: mixing the overhaul slag sample 1 and SiO2 evenly and then grinding them to 200 mesh to obtain the overhaul slag material.

[0078] Preparation Example 2

[0079] The raw materials used in this preparation example include: 10 kg of overhaul slag sample 2 and 1.49 kg of Al2O3.

[0080] The preparation method of this preparation example includes: mixing the overhaul slag sample 2 and Al2O3 evenly and grinding them to 200 mesh to obtain the overhaul slag material.

[0081] Example

[0082] Example 1

[0083] The raw materials used in this embodiment include: 1 kg of slag material obtained from Preparation Example 1 and 166.9 g of CaO.

[0084] The preparation method of this embodiment includes:

[0085] S1.1 Add CaO to 10L of deionized water in 5 portions and cool to room temperature. Then add the slag-repairing material and stir evenly to obtain the first mixture.

[0086] S1.2 Heat the first mixed solution to 70°C, then add sodium hydroxide solution to the first mixed solution until the pH of the first mixed solution is 12, and start stirring for 1 hour; during the stirring process, keep the temperature of the first mixed solution at 68-72°C and the pH at 11-12.

[0087] S1.3 After the first mixture is stirred, it is cooled to room temperature and then filtered to obtain filtrate A and filter residue B;

[0088] S2. At room temperature, carbon dioxide gas is introduced into filtrate A until the pH reaches 8.5, and then filtered to obtain filtrate B and a solid, which is cryolite.

[0089] Example 2

[0090] The difference between this embodiment and Embodiment 1 is that the amount of CaO used in this embodiment is 174.5g.

[0091] Example 3

[0092] The difference between this embodiment and Embodiment 1 is that the amount of CaO used in this embodiment is 181.8g.

[0093] Example 4

[0094] The raw materials used in this embodiment include: 1 kg of slag material obtained from Preparation Example 1 and 179.5 g of Ca(OH)2.

[0095] The preparation method of this embodiment includes:

[0096] S1.1 Add Ca(OH)2 to 10L of deionized water and cool to room temperature. Then add the slag-repairing material and stir evenly to obtain the first mixture.

[0097] S1.2 Heat the first mixed solution to 70°C, then add sodium hydroxide solution to the first mixed solution until the pH of the first mixed solution is 12, and start stirring for 1 hour; during the stirring process, keep the temperature of the first mixed solution at 68-72°C and the pH at 11-12.

[0098] S1.3 After the first mixture is stirred, it is cooled to room temperature and then filtered to obtain filtrate A and filter residue B;

[0099] S2. At room temperature, carbon dioxide gas is introduced into filtrate A until the pH reaches 8.5. The solid obtained by filtration is cryolite.

[0100] Example 5

[0101] The difference between this embodiment and Embodiment 1 is that the amount of Ca(OH)2 used in this embodiment is 199g.

[0102] Example 6

[0103] The difference between this embodiment and Embodiment 1 is that the amount of Ca(OH)2 used in this embodiment is 219.1g.

[0104] Example 7

[0105] The raw materials used in this embodiment include: 1 kg of slag material obtained in Preparation Example 1, 166.9 g of CaO, and filtrate B obtained in Example 1.

[0106] The preparation method of this embodiment includes:

[0107] S1.1 Add deionized water to filtrate B to a volume of 10L, then add CaO and cool to room temperature, then add slag trimming material and stir evenly to obtain the first mixture.

[0108] S1.2 Heat the first mixed solution to 70°C, then add sodium hydroxide solution to the first mixed solution until the pH of the first mixed solution is 12, and start stirring for 1 hour; during the stirring process, keep the temperature of the first mixed solution at 68-72°C and the pH at 11-12.

[0109] S1.3 After the first mixture is stirred, it is cooled to room temperature and then filtered to obtain filtrate A and filter residue B;

[0110] S2. At room temperature, carbon dioxide gas is introduced into filtrate A until the pH reaches 8.5, and then filtered to obtain the solid, which is cryolite.

[0111] Tests and Results

[0112] (1) The content of each component of the cryolite obtained in Examples 1 to 7 was detected, and the grades were classified in accordance with GB / T 4291-2007;

[0113] (2) The fluoride content of filter residue B obtained in Examples 1 to 7 was measured after drying. The unit is mg / kg.

[0114] The test results are as follows:

[0115] Table 1 shows the cryolite and filter residue B obtained in Examples 1-7.

[0116]

[0117] As shown in Table 1 above, the cryolite obtained in Examples 1 to 7 all meet the Grade 1 standard in GB / T 4291-2007, satisfying the production requirements of cryolite and suitable for industrial production applications.

[0118] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for producing cryolite from overhaul slag, characterized in that: S1. After grinding the overhaul residue into a fine powder, mix it with the treatment liquid, add sodium hydroxide and calcium agent, heat and stir to dissolve, then filter to obtain filtrate A and filter residue B containing CaAl2(SiO4)2. S2. Pass carbon dioxide gas into filtrate A until no more precipitate is produced, then filter to obtain the solid, which is cryolite; The calcium agent is selected from one or more of calcium oxide and calcium hydroxide, the treatment solution includes water, and the pH of the filtrate A is > 10. In step S1, silicon dioxide is added to the overhaul slag to ensure that the silicon, aluminum, and fluorine content in the overhaul slag meets the requirements. , where n is the amount of substance.

2. The method for producing cryolite from overhaul slag according to claim 1, characterized in that: In step S2, carbon dioxide gas is introduced into filtrate A and then filtered to obtain filtrate B; the treated liquid includes filtrate B obtained from other cryolite production processes.

3. The method for producing cryolite from overhaul slag according to claim 1, characterized in that: The heating temperature in step S1 is 50℃~80℃; and / or the heating and stirring time in step S1 is 0.5h~3h.

4. The method for producing cryolite from overhaul slag according to claim 1, characterized in that: In step S1, aluminum agent is added to the overhaul slag, so that the overhaul slag contains aluminum. , where n is the amount of substance.

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