Electrolyte slag treatment method

Abstract

The invention discloses an electrolyte slag treatment method which comprises the following steps: pretreatment: grinding electrolyte slag into powder, and then carrying out combustion treatment to obtain residual slag; mixing: grinding the residues into powder, adding the treated medicine powder, and uniformly mixing to obtain mixed powder; heating reaction: heating the mixed powder, collecting generated tail gas, adding water for dissolving after the reaction is finished, and filtering to obtain aluminum-containing precipitate; the treatment powder is acidic powder and contains ammonium ions. The electrolyte slag treatment method provided by the invention has the effects of high treatment efficiency, low cost and simplicity and convenience in operation.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous aluminum smelting and recovery, and in particular relates to a method for treating electrolyte slag. Background Art

[0002] Electrolyte slag is an inevitable solid waste generated in the electrolytic aluminum production process. Its composition is complex and poses a potential threat to the environment and human health. In the aluminum electrolysis operation, the gradual consumption of anode and cathode materials, the chemical reaction and decomposition of the electrolyte, together lead to the formation of a large amount of waste slag. These waste slags mainly contain carbon, Na3AlF6 (sodium fluoroaluminate), NaF (sodium fluoride), CaF2 (calcium fluoride), NaCN (sodium cyanide), Al2O3 (aluminum oxide) and other components.

[0003] Fluoride is highly corrosive and poses a threat to the environment and human health. Therefore, electrolyte slag is a hazardous waste and must be treated harmlessly. Before being treated harmlessly, electrolyte slag is usually first treated by high-temperature roasting.

[0004] During the high-temperature roasting process, the carbonaceous components in the electrolyte slag are converted into carbon dioxide (CO2), and the cyanide is decomposed into non-toxic or low-toxic gas under high temperature conditions, which effectively reduces the volume of waste slag and reduces the cost of subsequent treatment and disposal. The main components of the electrolyte slag after roasting include fluorine, aluminum, sodium, oxygen and other elements. The main components include CaF2, NaF, Na3AlF6, Al2O3, Al3F 14 (sub-cryospar), Fe2O3 (ferric oxide), etc., can be harmlessly treated by removing the fluorine element by adding calcium salts, acid leaching, alkali leaching, etc.

[0005] ① Adding calcium salt: By adding calcium salt, such as limestone or calcium chloride, to the calcined slag, a chemical reaction is carried out to convert fluoride into calcium fluoride (CaF2) precipitate which is insoluble in water, thereby removing the fluorine element.

[0006] ② Acid leaching: Use an acidic iron-containing solution to leach the roasted slag to convert the insoluble fluoride into soluble fluoride, thereby achieving the extraction of fluorine.

[0007] ③Alkali leaching: The calcined slag is treated with alkali leaching to make the fluoride react with the alkali to form soluble fluoride, and then sodium fluoride or calcium fluoride is recovered by evaporation crystallization and other methods.

[0008] However, the above-mentioned methods for removing fluorine have the following shortcomings:

[0009] ① Adding calcium salt: The CaF2 particles produced are relatively small and have a slow sedimentation rate, requiring a long sedimentation time and a large sedimentation space, which directly affects the treatment efficiency. In addition, the effective separation of fine particles also requires efficient filtration or centrifugation technology, which undoubtedly increases the complexity of the equipment and the difficulty of operation, making the overall efficiency of adding calcium salt to remove fluorine unsatisfactory.

[0010] ② Acid leaching: After acid leaching, the leachate needs to be further treated, such as neutralization, precipitation, recovery, etc. These steps not only increase the consumption of chemical reagents, but also introduce additional equipment requirements, thereby raising the processing cost.

[0011] ③Alkali leaching: The alkali leaching process is complicated, covering multiple links such as pretreatment, alkali leaching, filtration, washing, and drying. Each link requires precise control, which significantly increases the complexity of the operation. In addition, the alkali solution (such as sodium hydroxide) used in alkali leaching is expensive, and the entire process consumes a lot of water and energy, which further increases the overall processing cost.

[0012] In summary, the existing defluorination methods have shortcomings in terms of treatment efficiency, cost control and ease of operation. Therefore, it is particularly important to develop a new method that can achieve harmless treatment of electrolyte slag both efficiently and economically. Summary of the invention

[0013] In view of the deficiencies of the prior art, an object of the present invention is to provide a method for treating electrolyte slag.

[0014] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0015] On the one hand, a method for treating electrolyte slag comprises the following steps:

[0016] Pretreatment: Grind the electrolyte slag into powder and then burn it to obtain residual slag;

[0017] Mixing: Grind the residue into powder, add the treated powder, and then mix evenly to obtain a mixed powder;

[0018] Heating reaction: Heat the mixed powder, collect the tail gas generated, add water to dissolve and filter to obtain aluminum-containing precipitate after the reaction is completed;

[0019] The treatment powder is an acidic powder and contains ammonium ions.

[0020] In the present invention, the reaction between the treated powder and the substances in the residue is represented by the following ionic equation:

[0021] F - +NH4 + =NH4F↑,

[0022] AlF63- +3H + =AlF3+3HF,

[0023] Al3F 14 +5H + =3AlF3+5HF,

[0024] Fe2O3+6H + =2Fe 3+ +3H2O,

[0025] Some Al2O3 undergoes the following reaction:

[0026] 6HF+Al2O3=2AlF3+H2O↑.

[0027] In the present invention, the acid powder and the sodium element finally form a sodium salt, and the solubility of the sodium salt is relatively high. At 25° C., the solubility of aluminum fluoride in water is 0.559 g, and the solubility of aluminum fluoride is relatively low. Aluminum fluoride and the sodium salt can be separated by adding water to dissolve and filtering.

[0028] Preferably, the acid ions in the acidic powder include one or more of sulfate ions, hydrogen sulfate ions, phosphate ions, monohydrogen phosphate ions, and dihydrogen phosphate ions.

[0029] In the present invention, sulfate ions and hydrogen sulfate ions are ultimately converted into Na2SO4 (sodium sulfate), and phosphate ions, monohydrogen phosphate ions, and dihydrogen phosphate ions are ultimately converted into Na3PO4 (trisodium phosphate).

[0030] In the present invention, the treated powder is selected from one or more of sulfuric acid / ammonium sulfate, ammonium bisulfate (NH4HSO4), monoammonium hydrogen phosphate ((NH4)HPO4), diammonium phosphate (NH4H2PO4), phosphoric acid / triammonium phosphate ((NH4)3PO4), phosphoric acid / monoammonium hydrogen phosphate, and phosphoric acid / diammonium phosphate.

[0031] Preferably, the treatment powder is ammonium bisulfate powder.

[0032] Preferably, the total amount of negative charges carried by the anions in the treated powder is equal to the amount of sodium ions in the residue.

[0033] In the present invention, the treated powder can just form all the sodium salt, which is beneficial to the separation of the sodium salt and aluminum fluoride.

[0034] Preferably, the heating temperature in the heating reaction is 350°C to 700°C.

[0035] In the present invention, the heating temperature is 350° C. to 700° C., and moisture and ammonium fluoride can be volatilized, which is beneficial to the generation of aluminum fluoride.

[0036] In the present invention, the decomposition temperature of Na2SO4 is about 1000°C or above, the decomposition temperature of Na3PO4 is about 1340°C, and when the heating temperature is 350°C to 700°C, Na2SO4 and Na3PO4 can exist stably.

[0037] In the present invention, at 25°C, the solubility of Na2SO4 is 19.5g, and the solubility of Na3PO4 is 14.5g. The solubility of Na2SO4 and Na3PO4 is greater than that of aluminum fluoride. Aluminum fluoride can be separated by adding water to dissolve and filtering.

[0038] Preferably, the heating time in the heating reaction is 0.5h to 1h.

[0039] Preferably, in the heating reaction step, the pH of the solution obtained by adding water to dissolve after the reaction is completed is 4-6.

[0040] In the present invention, aluminum oxide is relatively stable under the condition of pH 4 to 6, aluminum oxide is difficult to react with acid, and aluminum ions are not easy to dissolve.

[0041] In the present invention, cryolite is easily decomposed in an acidic environment, and the fluorine element and the aluminum element tend to generate aluminum fluoride, which is conducive to the generation of aluminum-containing precipitation.

[0042] In the present invention, after the reaction is completed, the pH of the solution obtained by adding water to dissolve is selected from 4, 4.5, 5, 5.5, and 6.

[0043] In the present invention, the pH of the solution obtained by adding water to dissolve after the reaction is completed is specifically 5.

[0044] Preferably, the aluminum-containing precipitate comprises aluminum fluoride.

[0045] Preferably, the aluminum-containing precipitate comprises aluminum oxide.

[0046] Preferably, the tail gas comprises ammonium fluoride.

[0047] In the present invention, compared with hydrogen fluoride, ammonium fluoride is a toxic gas, which has high reactivity and corrosiveness and has a strong irritating effect on the respiratory tract and eyes; while ammonium fluoride is relatively more stable and easy to handle and store. In addition, ammonium fluoride is a valuable chemical raw material that can be used to prepare other fluorides, such as ammonium hydrogen fluoride, aluminum fluoride, etc. Through the conversion process, the recycling of fluorine resources can be achieved, reducing dependence on natural resources.

[0048] In the present invention, ammonium ions are introduced to combine with excess fluoride ions, so that the emission of hydrogen fluoride is reduced during the reaction process.

[0049] Preferably, the particle size of the residue after being ground into powder is larger than the particle size of the treated powder.

[0050] In the present invention, the particle size of the treated powder is smaller than the particle size of the residue after being ground into powder. The treated powder can fill the gaps in the residue powder and surround the residue powder, which is conducive to the full reaction between the residue and the treated powder.

[0051] Preferably, the particle size of the residue after being ground into powder is 50 mesh to 400 mesh.

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

[0053] (1) In the electrolyte slag treatment method provided by the present invention, the sedimentation rates of aluminum fluoride and aluminum oxide are greater than those of calcium fluoride, which is beneficial to improving the electrolyte slag treatment efficiency;

[0054] (2) The electrolyte slag treatment method provided by the present invention does not produce hydrogen fluoride, does not require high-pressure and corrosion-resistant equipment, and the ammonium fluoride produced is a valuable chemical raw material, and does not require complicated tail gas treatment equipment and processes;

[0055] (3) The present invention provides a method for treating electrolyte slag, which separates soluble substances and insoluble substances by water, and does not produce acidic or alkaline wastewater during the process, which is conducive to reducing production difficulty and cost;

[0056] (4) The present invention provides a method for treating electrolyte slag, which can effectively treat the fluorine element in the electrolyte slag by converting the fluorine element into ammonium fluoride and aluminum fluoride, and convert the harmful fluorine element into valuable ammonium fluoride and aluminum fluoride. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] 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.

[0058] Figure 1 This is a test chart of the residue in Preparation Example 1 of the present invention qualitatively analyzed by X-ray fluorescence. DETAILED DESCRIPTION

[0059] 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.

[0060] 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.

[0061] As used herein, "this application" means "the present invention" or "the present disclosure".

[0062] 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.

[0063] In this document, "or its combination" means "or any combination thereof", and "any one", "any one" means "any one", "any one" or "any one".

[0064] 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".

[0065] 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 sub-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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] In the following descriptions:

[0073] Ammonium bisulfate: content ≥99.5%, chloride ≤0.01%, heavy metal ≤0.01%, 100 mesh;

[0074] Ammonium dihydrogen phosphate: content ≥99%, fluorine content ≤10mg / kg, heavy metal content ≤10mg / kg, 150 mesh.

[0075] Preparation Example

[0076] Preparation Example 1

[0077] The raw materials used in this preparation example include: 5 kg of electrolyte slag.

[0078] The preparation method of this preparation example includes:

[0079] Z1, burning the electrolyte slag in a combustion furnace at a temperature of 800°C to obtain residual slag;

[0080] Z2. Grind the residue into 50 mesh powder to obtain residue powder.

[0081] Table 1 Composition of the residue powder obtained in Preparation Example 1

[0082]

[0083]

[0084] Preparation Example 2

[0085] The difference between this preparation example and preparation example 1 is that in step Z2, the residue is ground into 200 mesh powder.

[0086] Preparation Example 3

[0087] The difference between this preparation example and preparation example 1 is that in step Z2, the residue is ground into 400 mesh powder.

[0088] Example

[0089] Example 1

[0090] The raw materials used in this example include: 1 kg of the residue powder obtained in Preparation Example 1 and 395.1 g of ammonium bisulfate.

[0091] The preparation method of this embodiment includes:

[0092] S1. Mix the residue powder and ammonium bisulfate uniformly at 15° C. to obtain a mixed powder;

[0093] S2, placing the mixed powder in a calcination furnace for calcination at a temperature of 350° C. for 1 h, collecting the generated tail gas to obtain a powder after the reaction; drying the tail gas and passing it into a saturated calcium chloride solution;

[0094] S3. Add water to the powder after the reaction at 15°C to dissolve it so that the pH of the aqueous solution is 5. After standing for 1 hour, filter to obtain an aluminum-containing precipitate.

[0095] Example 2

[0096] The difference between this embodiment and embodiment 1 is that the slag powder in the raw materials used in this embodiment comes from preparation example 2.

[0097] Example 3

[0098] The difference between this embodiment and embodiment 1 is that the ammonium bisulfate in the raw material used in this embodiment is replaced with 417.7 g of ammonium dihydrogen phosphate.

[0099] Comparative Example

[0100] Comparative Example 1

[0101] The difference between this comparative example and Example 1 is that 300 g of ammonium bisulfate is used in the raw materials used in this example.

[0102] Comparative Example 2

[0103] The difference between this comparative example and Example 1 is that the raw material used in this example contains 500 g of ammonium bisulfate.

[0104] Results

[0105] Table 2 Composition of aluminum-containing precipitates obtained in Examples 1 to 3 and Comparative Examples 1 to 2

[0106]

[0107] 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 treating electrolyte slag, characterized in that: The steps include: Pretreatment: Grind the electrolyte slag into powder and then burn it to obtain residual slag; Mixing: Grind the residue into powder, add the treated powder, and then mix evenly to obtain a mixed powder; Heating reaction: Heat the mixed powder, collect the tail gas generated, add water to dissolve and filter to obtain aluminum-containing precipitate after the reaction is completed; The treatment powder is an acidic powder and contains ammonium ions.

2. The method for treating electrolyte slag according to claim 1, characterized in that: The acid ions in the acidic powder include one or more of sulfate ions, hydrogen sulfate ions, phosphate ions, monohydrogen phosphate ions, and dihydrogen phosphate ions.

3. The method for treating electrolyte slag according to claim 2, characterized in that: The treatment powder is ammonium bisulfate powder.

4. The method for treating electrolyte slag according to claim 1, characterized in that: The total amount of negative charges carried by the anions in the treated powder is equal to the amount of sodium ions in the residue.

5. The method for treating electrolyte slag according to claim 1, characterized in that: The heating temperature in the heating reaction is 350°C to 700°C; And / or, the heating time in the heating reaction is 0.5h to 1h.

6. The method for treating electrolyte slag according to claim 1, characterized in that: In the heating reaction step, after the reaction is completed, water is added to dissolve the resulting solution, and the pH value is 4 to 6; and / or, the aluminum-containing precipitate comprises aluminum fluoride; and / or, the aluminum-containing precipitate comprises aluminum oxide; And / or, the tail gas comprises ammonium fluoride.

7. The method for treating electrolyte slag according to claim 1, characterized in that: The particle size of the residue after being ground into powder is larger than the particle size of the treated powder.

8. The method for treating electrolyte slag according to claim 7, characterized in that: The particle size of the residue after being ground into powder is 50 mesh to 400 mesh.

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