A method for producing cryolite from overhaul slag

Abstract

The present invention discloses a method for producing cryolite from overhaul slag, which comprises the following steps: S1, grinding the overhaul slag, mixing it with a treatment liquid, adding sodium hydroxide and a calcium agent, heating and stirring to dissolve, and then filtering to obtain a filtrate A; S2, introducing carbon dioxide gas into the filtrate A until no precipitation is generated, and then filtering to obtain a solid, namely, cryolite; the calcium agent is selected from one or more of calcium oxide and calcium hydroxide, the treatment liquid comprises water, and the pH of the filtrate A is greater than 10. The method for producing cryolite from overhaul slag provided by the present invention has the effects of no need to add fluoride, low cost, and simple process.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste resource treatment, and in particular relates to a method for producing cryolite from overhaul slag. Background Art

[0002] Overhaul slag is solid waste slag produced during the overhaul process of aluminum electrolytic cells, mainly including discarded cathode carbon blocks, refractory materials, thermal insulation materials, pastes, anti-seepage materials and other components. According to the "National List of Hazardous Wastes (2021 Edition)", overhaul slag is classified as hazardous waste. The main components of overhaul slag include silicon, aluminum, fluorine, lithium and other elements.

[0003] Fluorides, such as sodium fluoride, are usually added in the process of extracting aluminum from overhaul slag, mainly to increase the recovery rate of aluminum. Its mechanism of action mainly includes the following points:

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

[0005] ② Fluoride helps to increase the conductivity of the electrolyte, improve the stability of the electrolyte, and thus increase the recovery rate of aluminum.

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

[0007] However, the practice of adding fluoride in the process of extracting aluminum from overhaul slag usually has the following shortcomings:

[0008] ① Health hazards: Fluoride is a toxic substance that may pose a threat to the health and safety of workers if it is not handled properly or leaks. In addition, fluoride may 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 complicated. The addition of fluoride may increase the complexity and cost of the treatment process, and may also be subject to stricter regulatory restrictions. In order to effectively control and utilize fluoride, additional process steps and equipment need to be introduced, such as accurately measuring the amount of fluoride added, controlling reaction conditions, and treating fluoride-containing wastewater.

[0010] ③ Equipment corrosion and wear: Fluoride is a corrosive chemical substance. Adding fluoride during the extraction process will increase the corrosion of fluoride to the equipment, which not only shortens the service life of the equipment, but also affects 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 deficiencies of the prior art, the object of the present invention is to provide a method for producing cryolite from overhaul slag.

[0012] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

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

[0014] S1. Grind the overhaul slag into 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, passing carbon dioxide gas into the filtrate A until no precipitation is produced, and then filtering to obtain a solid, which is cryolite;

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

[0017] In the present invention, part of the aluminum element in the overhaul slag reacts with sodium hydroxide to generate 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 the present invention, the calcium agent is dissolved in water to form calcium hydroxide; part of the aluminum element in the overhaul slag reacts 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 above-mentioned multiple chemical reaction equations can also be written in the following form:

[0023]

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

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

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

[0027] In the present invention, the carbon dioxide gas in step S2 is an acidic gas, which can reduce the pH of the filtrate A; when the pH of the filtrate A drops below 10, the NaAl(OH)4 and NaF in the filtrate A 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 the present invention, the molar ratio of fluorine to aluminum in the 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 treated liquid includes filtrate B obtained from other cryolite production processes.

[0033] In the present invention, the filtrate B contains unreacted sodium hydroxide and NaF, and recycling B can reduce the waste of sodium hydroxide and NaF; at the same time, the filtrate B can increase the amount of fluoride ions in the treatment liquid, thereby increasing the proportion of aluminum in the overhaul slag used for conversion into cryolite.

[0034] Preferably, the heating temperature in step S1 is 50°C to 80°C.

[0035] In the present 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 0.5 h to 3 h.

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

[0038] In the present 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 the filtrate A.

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

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

[0042] In the present invention, the pH of the 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 the filtrate A until the pH of the filtrate A is 8-10.

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

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

[0046] In the present invention, when the overhaul slag When sufficient silicon is present, it is beneficial for the aluminum element to be converted into Ca2Al2(SiO3)5.

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

[0048] In the present invention, when the overhaul slag contains n Al >6n F When sufficient silicon is present, it is beneficial for the aluminum element to be converted into NaAl(OH)4.

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

[0050] In the present invention, the aluminum agent is specifically selected from aluminum oxide.

[0051] In the present invention, Ca2Al2(SiO3)5 can be used as a concrete filler to improve the strength of concrete, enhance the durability and impermeability of concrete, and other advantages.

[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, which converts the aluminum element contained in the overhaul slag into cryolite and Ca2Al2(SiO3)5. Compared with the method of adding fluoride to obtain cryolite in the prior art, the present invention does not require additional 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 additional fluoride, and does not require complicated 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 utilizes the filtrate obtained in step S1 to extract lithium and separate lithium from aluminum. The operation is simple and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the embodiments of the present application 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 recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0057] Figure 1 This is a test chart of the cryolite obtained in Example 1 of the present invention qualitatively analyzed by X-ray fluorescence. DETAILED DESCRIPTION

[0058] In order to enable those skilled in the art to understand the characteristics and effects of the present application, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the common meanings understood by those skilled in the art for the present application. In case of conflict, the definitions in this specification shall prevail.

[0059] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present application in any way, that is, the content of the present application can be implemented without being limited by any specific theory or mechanism.

[0060] As used herein, "this application" means "the present invention" or "the present disclosure".

[0061] The use of "one", "an", "a kind" or similar expressions to describe the components and technical features described in this application is merely for the convenience of expression and to provide a general meaning to the scope of this application. Therefore, such description should be understood to include one or at least one, and the singular also includes the plural, unless it is obvious that it refers to another meaning.

[0062] In this document, "or its combination" means "or any combination thereof", and "any one", "any one" means "any one", "any one" or "any one".

[0063] As used herein, the terms "comprises," "including," "having," "containing," or any other similar terms are open-ended transitional phrases that are intended to cover non-exclusive inclusions. For example, a composition or article containing multiple elements is not limited to the elements listed herein, but may also include other elements that are not explicitly listed but are generally inherent to the composition or article. In addition, unless otherwise expressly stated, the term "or" refers to an inclusive "or" rather than an exclusive "or." For example, any of the following situations satisfies the condition "A or B": 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), and both A and B are true (or exist). In addition, in this article, the terms "comprising", "including", "having", and "containing" should be interpreted as being specifically disclosed and simultaneously covering closed conjunctions such as "consisting of", "consisting of", and "the remainder is", as well as conjunctions such as "consisting essentially of", "mainly consisting of", "mainly consisting of", "basically containing", "essentially consisting of", "essentially consisting of", and "essentially containing".

[0064] In this article, all features or conditions such as numerical values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are only for simplicity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be deemed to have covered and specifically disclosed all possible ranges and individual values ​​within the range (including integers and fractions), especially integer values. For example, the range description of "1.0 to 8.0" or "between 1.0 and 8.0" or "between 1.0 and 8.0" should be deemed to have specifically disclosed all sub-ranges 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 deemed to cover endpoint values, especially sub-ranges defined by integer values, and should be deemed to have specifically disclosed individual values ​​such as 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, etc. Unless otherwise indicated, the foregoing method of interpretation applies to all contents of the entire application, regardless of whether the scope is broad or not.

[0065] If the quantity, concentration or other numerical value or parameter is expressed as a range, a preferred range (or a better range) or a series of upper and lower limits, it should be understood that all ranges consisting of any pair of the upper limit or preferred value (or a better value) of the range and the lower limit or preferred value (or a better value) of the range have been specifically disclosed herein, regardless of whether these ranges are disclosed separately. In addition, if a numerical range is mentioned herein, unless otherwise specified, the range should include its endpoints and all integers and fractions within the range.

[0066] In this document, numerical values ​​should be understood to have the accuracy of the number of significant digits of the numerical value, 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 relative parts by weight in a composition, which may be any weight unit, such as but not limited to kilograms, kilograms, grams, pounds, etc. For example, 100 parts by weight of polyphenylene ether resin may represent 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 may be arbitrarily combined to form the technical solution of the present application, as long as there is no contradiction in the combination of these features.

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

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

[0071] In the following descriptions:

[0072] Overhaul slag sample 1: the mass fraction of fluorine is 16.4%, the mass fraction of aluminum is 14.8%, and the mass fraction of silicon is 14.2%.

[0073] Overhaul slag sample 2: the mass fraction of fluorine is 28.1%, the mass fraction of aluminum is 6.3%, and the mass fraction of silicon is 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 uniformly and grinding them to 200 meshes to obtain a 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 uniformly and grinding them to 200 meshes to obtain a slag material.

[0081] Example

[0082] Example 1

[0083] The raw materials used in this example include: 1 kg of slag repair material obtained in 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 slag repair material and stir evenly to obtain a first mixed solution;

[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, always keep the temperature of the first mixed solution at 68-72°C and the pH at 11-12;

[0087] S1.3, after the stirring is completed, the first mixed solution is cooled to room temperature and filtered to obtain filtrate A and residue B;

[0088] S2. At room temperature, carbon dioxide gas is introduced into the filtrate A until the pH value reaches 8.5, and then the filtrate B and a solid are obtained by filtering. The solid is cryolite.

[0089] Example 2

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

[0091] Example 3

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

[0093] Example 4

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

[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 slag repair material and stir evenly to obtain a first mixed solution;

[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, always keep the temperature of the first mixed solution at 68-72°C and the pH at 11-12;

[0098] S1.3, after the stirring is completed, the first mixed solution is cooled to room temperature and filtered to obtain filtrate A and residue B;

[0099] S2. At room temperature, carbon dioxide gas is introduced into the filtrate A until the pH reaches 8.5, and 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 the raw material 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 the raw material used in this embodiment is 219.1g.

[0104] Example 7

[0105] The raw materials used in this example include: 1 kg of slag repair 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 the filtrate B to a volume of 10L, then add CaO and cool to room temperature, then add the slag repair material and stir evenly to obtain the first mixed solution;

[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, always keep the temperature of the first mixed solution at 68-72°C and the pH at 11-12;

[0109] S1.3, after the stirring is completed, the first mixed solution is cooled to room temperature and filtered to obtain filtrate A and residue B;

[0110] S2. At room temperature, carbon dioxide gas is introduced into the filtrate A until the pH reaches 8.5, and then the solid obtained by filtering is cryolite.

[0111] Test and results

[0112] (1) Detecting the contents of various components of the cryolite obtained in Examples 1 to 7 and classifying them according to GB / T 4291-2007;

[0113] (2) The filter residue B obtained in the test examples 1 to 7 was dried and the fluoride content was measured, unit: mg / kg.

[0114] The test results are as follows:

[0115] Table 1 Cryolite and Filter Residue B Obtained from Examples 1 to 7

[0116]

[0117] According to Table 1 above, the cryolites obtained in Examples 1 to 7 all reach Grade 1 in the GB / T 4291-2007 standard, meet the production requirements of cryolite, and are 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 their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly. It cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, some simple deductions or substitutions can be made without departing from the concept of the present invention. All equivalent changes or modifications made according to the spirit 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. Grind the overhaul slag into 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; S2, passing carbon dioxide gas into the filtrate A until no precipitation is produced, and then filtering to obtain a solid, which is 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 the filtrate A is greater than 10.

2. The method for producing cryolite from overhaul slag according to claim 1, characterized in that: The molar ratio of fluorine to aluminum in the filtrate A is (6-8):

1.

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

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

5. The method for producing cryolite from overhaul slag according to claim 1, characterized in that: The amount of the sodium hydroxide is greater than the sum of the amounts of aluminum and fluorine in the filtrate A; And / or, the pH of the filtrate A is 11-12.

6. The method for producing cryolite from overhaul slag according to claim 1, characterized in that: In the step S2, carbon dioxide gas is introduced into the filtrate A until the pH of the filtrate A is 8-10.

7. The method for producing cryolite from overhaul slag according to claim 1, characterized in that: In step S1, silicon dioxide is added to the overhaul slag so that n is the amount of substance.

8. The method for producing cryolite from overhaul slag according to claim 1, characterized in that: In step S1, aluminum is added to the overhaul slag, so that n Al >6n F , n is the amount of substance.

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