A comprehensive recycling method for red mud

Abstract

This invention relates to a comprehensive recycling method for red mud, comprising the following steps: S100: grinding red mud to obtain red mud powder; S200: adding a first acid solution to the red mud powder and stirring to dissolve it to obtain a first reactant; the concentration of the first acid solution is 1-6 mol / L; the first reactant includes the corresponding salts generated by the reaction of Al2O3, Fe2O3, and SiO2 with the first acid solution; S300: performing solid-liquid separation on the first reactant to obtain an acid leaching solution and an acid leaching residue; the corresponding salts are separated into the acid leaching solution, and the various rare earth elements are separated into the acid leaching residue; S400: treating the acid leaching solution to obtain silica powder and a water purification agent; S500: treating the acid leaching residue to obtain scandium oxide, other rare earth element oxides, and other rare earth mixed precipitates. This invention provides a comprehensive recycling method for red mud, which has low overall cost, good environmental benefits, and is industrially feasible.

Description

Technical Field

[0001] This invention relates to the field of metallurgical waste treatment, and in particular to a comprehensive recycling method for red mud. Background Technology

[0002] Red mud is a solid waste discharged by alumina plants during the production of alumina from bauxite. It is named for its high iron content, which typically gives it a reddish color. However, depending on the production process and the grade of the bauxite, some red mud can also appear gray or grayish-white. Statistics show that 0.5-2.0 tons of red mud are generated for every ton of alumina produced, with a global annual output of 60-80 million tons. The treatment of red mud requires significant investment of manpower, resources, and capital, placing a heavy economic burden on alumina plants and causing a series of environmental problems, including occupying large amounts of land, polluting the air, and contaminating water bodies.

[0003] Besides containing significant amounts of metallic elements such as Fe and Al, red mud also contains small amounts of rare earth metals like Sc, Y, and La, making it a valuable resource with considerable potential economic value. Scandium, in particular, is increasingly in demand due to the rapid development of emerging industries such as aerospace and new energy vehicles. The high reserves and relatively high scandium content of red mud make it a promising direct source of scandium in the future. Currently, Sc is mainly extracted from red mud through extraction processes. While this can recover scandium from red mud, it also causes additional environmental pollution and resource waste, limiting its industrial application due to the combined costs and environmental benefits. Summary of the Invention

[0004] To address the issues of high overall cost and poor environmental benefits in the extraction of scandium from red mud using extraction processes, this invention provides a comprehensive and industrially feasible method for the recycling and utilization of red mud that is cost-effective and environmentally friendly.

[0005] A comprehensive recycling method for red mud, the method comprising the following steps:

[0006] S100: Red mud is ground to obtain red mud powder; the red mud contains Al2O3, Fe2O3, SiO2 and various rare earth elements, including scandium.

[0007] S200: A first acid solution is added to the red mud powder and stirred to dissolve it, thereby obtaining a first reactant; the concentration of the first acid solution is 1-6 mol / L, and the first acid solution and the red mud powder are added at a liquid-to-solid ratio of 4-15:1; the first reactant includes the corresponding salts generated by the reaction of Al2O3, Fe2O3, and SiO2 with the first acid solution.

[0008] S300: The first reactant is subjected to solid-liquid separation to obtain an acid leaching solution and an acid leaching residue; the corresponding salt is separated into the acid leaching solution, and the various rare earth elements are separated into the acid leaching residue;

[0009] S400: The acid leaching solution is treated to obtain silicon micro powder and water purification agent;

[0010] S500: The acid leaching residue is treated to obtain scandium oxide, other rare earth element oxides and other rare earth mixed precipitates;

[0011] Step S500 includes:

[0012] S501: A second acid solution is added to the acid leaching residue, and the mixture is stirred to dissolve and heap leaching to obtain a second reactant. The concentration of the second acid solution is greater than 10 mol / L, and the second acid solution and the acid leaching residue are added at a liquid-to-solid ratio of 4-20:1. The second reactant includes scandium compounds generated by the reaction of scandium with the second acid solution, and other rare earth element compounds generated by the reaction of other rare earth elements (excluding scandium) with the second acid solution.

[0013] S502: The second reactant is calcined at a first temperature to obtain a calcined product, wherein the first temperature is 0-15°C lower than the decomposition temperature of the scandium compound; during the calcination process, a portion of the other rare earth element compounds decomposes to generate corresponding other rare earth element oxides.

[0014] S503: Add water to the calcined product and grind it to remove the other rare earth element oxides, and obtain the first filtrate;

[0015] S504: Add NaOH to the first filtrate and adjust the pH value to 8-10. The other rare earth element compounds that were not decomposed in step S502 react with the NaOH to form other rare earth mixed precipitates.

[0016] S505: Filter out the other rare earth mixed precipitates to obtain a second filtrate;

[0017] S506: Add the third acid solution to the second filtrate, adjust the pH to 0-2, and then add oxalic acid to precipitate scandium oxalate;

[0018] S507: Calcining the scandium oxalate yields scandium oxide.

[0019] Preferably, in step S100, the red mud powder is obtained by grinding and sieving through a 200-300 mesh sieve; the red mud is any one, two or more of Bayer process red mud, sintering process red mud or combined process red mud; the rare earth elements other than scandium among the various rare earth elements include one or more of Y, La, Ce, Pr, Nd, Gd, Dy, Er and Yb.

[0020] Preferably, step A is included before step S200: repeatedly washing the adhering alkali in the red mud powder with water until the pH value of the washing water is 6.9-7.2.

[0021] Preferably, in step S200, the stirring dissolution is carried out in a water bath, the stirring dissolution is controlled at 20-60°C, and the stirring dissolution time is 1-10 min.

[0022] Preferably, in step S501, the stirring dissolution is carried out in a water bath, and the stirring dissolution is controlled at 30-100°C for 3-15 min; the heap leaching is carried out in a vacuum oven at 100-140°C for 12-16 h.

[0023] Preferably, the second acid solution is sulfuric acid, and in step S502, the calcination temperature is higher than 690°C and lower than 700°C.

[0024] Preferably, in step S502, SO3 gas is generated by calcination, and the SO3 gas is recovered.

[0025] Preferably, step 503 specifically includes: adding water to the calcined product and then ball milling; the water and the calcined product are added at a liquid-solid ratio of 20-50:1, and the ball milling time is 20-40 minutes.

[0026] Preferably, the first acid solution is sulfuric acid; step S400 specifically includes the following steps:

[0027] S401: The acid leaching solution is aged to obtain silicon micro powder;

[0028] S402: Filter out the silica powder in the acid leaching solution to obtain the third filtrate;

[0029] S403: Concentrate the volume of the third filtrate to 30%-60% of its original volume;

[0030] S404: The concentrated third filtrate is allowed to crystallize naturally at 10℃-20℃, and then filtered through an 800-900 mesh sieve to obtain aluminum ferric sulfate crystals;

[0031] S405: Dissolve the aluminum ferric sulfate crystals in deionized water at a solid-liquid ratio of 1:1.5-10 g / ml, then adjust the pH of the solution to 1.0-5.0 with a Ca(OH)2 emulsion with a mass concentration of 10-40%, and filter through a 400-600 mesh to obtain a fourth filtrate. Stir the fourth filtrate in a water bath at a temperature of 50℃-100℃ to obtain the polyaluminum ferric sulfate water purifier.

[0032] This invention provides a method for the comprehensive utilization of red mud. Through dilute acid stirring and dissolution, acid leaching residue and acid leaching solution are obtained. The main elements are largely separated into the acid leaching solution, while rare earth elements are separated into the acid leaching residue. The acid leaching solution is used to extract silica powder and generate a water purification agent. The acid leaching residue is subjected to concentrated acid leaching, roasting, filtration, precipitation, re-filtration, and further precipitation, followed by roasting to extract scandium, achieving efficient recovery and utilization of red mud. This method has low requirements for raw materials and equipment, is easily industrialized, meets environmental protection requirements, and offers considerable economic benefits, opening up new avenues for the comprehensive utilization of red mud.

[0033] Other beneficial effects of the present invention will be explained in detail through the introduction of specific technical features and technical solutions in specific embodiments. Those skilled in the art should be able to understand the beneficial technical effects brought about by these technical features and technical solutions through the introduction of these technical features and technical solutions. Attached Figure Description

[0034] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. In the drawings:

[0035] Figure 1 This is a process flow diagram of a comprehensive recycling method for red mud according to the present invention.

[0036] Figure 2 for Figure 1 Detailed process flow diagram of step S500. Detailed Implementation

[0037] The present invention is described below based on embodiments, but the present invention is not limited to these embodiments. In the following detailed description of the present invention, some specific details are described in detail, but well-known methods, processes, procedures, and elements are not described in detail in order to avoid obscuring the essence of the present invention.

[0038] Furthermore, those skilled in the art should understand that the accompanying drawings provided herein are for illustrative purposes only and are not necessarily drawn to scale.

[0039] Unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as encompassing rather than being exclusive or exhaustive; that is, meaning "including but not limited to."

[0040] In the description of this invention, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0041] Please see Figure 1 The present invention provides a comprehensive recycling method for red mud, the method comprising steps S100 to S500.

[0042] In step S100, the red mud is ground to obtain red mud powder; the red mud powder includes Al2O3, Fe2O3, SiO2 and various rare earth elements, including scandium.

[0043] In step S200, a first acid solution is added to the red mud powder and stirred to dissolve it, thereby obtaining a first reactant. The concentration of the first acid solution is 1-6 mol / L, and the first acid solution and the red mud powder are added at a liquid-to-solid ratio of 4-15:1. The first reactant includes the corresponding salts generated by the reaction of Al2O3, Fe2O3, and SiO2 with the first acid solution.

[0044] In step S300, the first reactant is subjected to solid-liquid separation to obtain an acid leaching solution and an acid leaching residue; the corresponding salts are separated into the acid leaching solution, and the various rare earth elements are separated into the acid leaching residue.

[0045] In step S400, the acid leaching solution is treated to obtain silicon micro powder and water purification agent;

[0046] In step S500, the acid leaching residue is treated to obtain scandium oxide, other rare earth element oxides and other rare earth mixed precipitates.

[0047] Specifically, in step S100, the red mud is ground to obtain red mud powder.

[0048] As one embodiment, the red mud is any one, two, or a mixture of more than one of the following: Bayer process red mud, sintered process red mud, or combined process red mud. The red mud contains Al₂O₃, Fe₂O₃, SiO₂, and various rare earth elements, and may also include other components such as CaO. The various rare earth elements include scandium (Sc) and other rare earth elements, including one or more of Y, La, Ce, Pr, Nd, Gd, Dy, Er, and Yb. It is understood that the types of rare earth elements are not limited, and may include one or more not listed. Rare earth elements generally exist in combined states as by-products.

[0049] As one embodiment, the main components of red mud include Al2O3, Fe2O3, SiO2, and CaO, while its non-main components include scandium and other rare earth elements. This invention uses red mud containing Al2O3, Fe2O3, SiO2, CaO, scandium, and other rare earth elements as an example for illustration.

[0050] As another embodiment, the red mud powder is composed of Al2O3, Fe2O3, SiO2, CaO, scandium and other rare earth elements (some components are present in very low amounts and can be ignored).

[0051] As one example, the red mud powder is obtained by grinding and sieving through a 200-300 mesh sieve.

[0052] As one embodiment, the red mud powder may contain adhering alkali. Before step S200, step A is included: repeatedly washing the red mud powder with water to remove the adhering alkali until the pH value of the washing water is 6.9-7.2, that is, removing the adhering alkali from the red mud powder. Preferably, the pH value of the washing water is 7.

[0053] Specifically, in step S200, a first acid solution is added to the red mud powder and stirred to dissolve it to obtain a first reactant; the concentration of the first acid solution is 1-6 mol / L, and the first acid solution and the red mud powder are added at a liquid-solid ratio of 4-15:1; the first reactant includes the corresponding salts generated by the reaction of Al2O3, Fe2O3, and SiO2 with the first acid solution.

[0054] It is understandable that step S200 mainly involves adding dilute acid to separate the main elements such as aluminum, iron, and silicon to prepare silicon powder and water purification agent.

[0055] It is understandable that in step S200, the first reactant does not specifically refer to the product that reacts with the first acid solution, but rather refers generally to the entire solution after the red mud powder is added to the first acid solution and stirred to dissolve, which includes both reacting and unreacted substances.

[0056] As one embodiment, the first acid solution is sulfuric acid, hydrochloric acid, or nitric acid, preferably sulfuric acid. This invention will use sulfuric acid as an example. The concentration of sulfuric acid is 1-6 mol / L. After the sulfuric acid is added to the red mud powder at a liquid-to-solid ratio of 4-15:1, the following reaction occurs ("aq" indicates that the reaction takes place in solution):

[0057] Al2O3+3H2SO4+aq=Al2(SO4)3+3H2O+aq

[0058] Fe2O3+3H2SO4+aq=Fe2(SO4)3+3H2O+aq

[0059] CaO+H2SO4+aq=CaSO4↓+H2O+aq

[0060] SiO₂ + 2H₂O + aq = H₄SiO₄ + aq

[0061] That is, under sulfuric acid concentrations of 1-6 mol / L (dilute sulfuric acid), Al2O3, Fe2O3, SiO2, and CaO react with sulfuric acid to form the corresponding salts (Al2(SO4)3, Fe2(SO4)3, H4SiO4, and CaSO4), while rare earth elements do not react with (dilute) sulfuric acid.

[0062] As one example, the concentration of sulfuric acid is 3-4.5 mol / L, corresponding to a liquid-to-solid ratio of sulfuric acid to red mud powder of 10-15:1. The concentration of sulfuric acid is 4-5 mol / L, corresponding to a liquid-to-solid ratio of sulfuric acid to red mud powder of 8-12:1. The concentration of sulfuric acid is 5-6 mol / L, corresponding to a liquid-to-solid ratio of sulfuric acid to red mud powder of 4-8:1. It can be understood that the concentration of sulfuric acid can be 3 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, or 6 mol / L, corresponding to liquid-to-solid ratios of sulfuric acid to red mud powder of 15:1, 12:1, 10:1, 8:1, 6:1, or 4:1.

[0063] As one embodiment, in step S200, the stirring and dissolving process is carried out in a water bath at a temperature of 20-60°C for a duration of 1-10 minutes. Further, the stirring and dissolving process is carried out at a temperature of 50-60°C for a duration of 1-4 minutes.

[0064] Specifically, in step S300, the first reactant undergoes solid-liquid separation to obtain an acid leaching solution and an acid leaching residue. Using the above embodiment as an example, Al2(SO4)3, Fe2(SO4)3, and H4SiO4 are soluble and are separated into the acid leaching solution. Rare earth elements are separated into the acid leaching residue. When the major element in red mud includes CaO, the CaSO4 precipitate in the first reactant is separated into the acid leaching residue; that is, the soluble salt obtained from the reaction with dilute sulfuric acid is separated into the acid leaching solution, and the insoluble salt is separated into the acid leaching residue.

[0065] Specifically, in step S400, the acid leaching solution is treated to obtain silicon micro powder and water purification agent; in step S500, the acid leaching residue is treated to obtain scandium oxide, other rare earth element oxides and other rare earth mixed precipitates.

[0066] It is understood that in the comprehensive recycling method of red mud provided by the present invention, the major elements (aluminum, iron, silicon) of red mud are separated to extract silicon micro powder and made into water purification agent. Scandium in rare earth elements is extracted and other rare earth elements are enriched in the form of a mixture. The major elements and rare earth elements are fully recycled and utilized, and the red mud is turned from waste into treasure as a whole.

[0067] In step S500, other rare earth elements are removed by acid heap leaching, roasting, filtering, and precipitation of the acid leaching residue. Scandium oxalate is then obtained by further filtering and precipitation, and scandium oxalate is roasted to obtain scandium oxide. Specifically, step S500 includes steps S501 to S507.

[0068] In step S501, a second acid solution is added to the acid leaching residue, and the mixture is stirred to dissolve and heap leaching to obtain a second reactant. The concentration of the second acid solution is greater than 10 mol / L, and the second acid solution and the acid leaching residue are added at a liquid-to-solid ratio of 4-20:1. The second reactant includes scandium compounds generated by the reaction of scandium with the second acid solution, and other rare earth element compounds generated by the reaction of other rare earth elements (excluding scandium) with the second acid solution.

[0069] In step S502, the second reactant is calcined at a first temperature to obtain a calcined product. The first temperature is 0-15°C lower than the decomposition temperature of the scandium compound. During the calcination process, a portion of the other rare earth element compounds decomposes to generate corresponding other rare earth element oxides.

[0070] In step S503, water is added to the calcined product for grinding, and the other rare earth element oxides are filtered out to obtain the first filtrate.

[0071] In step S504, NaOH is added to the first filtrate to adjust the pH value to 8-10. The other rare earth element compounds that were not decomposed in step S502 react with the NaOH to form other rare earth mixed precipitates.

[0072] In step S505, the other rare earth mixed precipitates are filtered out to obtain a second filtrate.

[0073] In step S506, a third acid solution is added to the second filtrate to adjust the pH value to 0-2, and then oxalic acid is added to precipitate scandium oxalate.

[0074] In step S507, scandium oxalate is calcined to obtain scandium oxide.

[0075] It is understood that in step S501, the second reactant does not specifically refer to the product that reacts with the second acid solution, but rather generally includes substances that have reacted and those that have not.

[0076] As one embodiment, the second acid solution is sulfuric acid, hydrochloric acid, or nitric acid, preferably sulfuric acid. This invention will use sulfuric acid as an example. The concentration of sulfuric acid is greater than 10 mol / L. After sulfuric acid is added to red mud powder at a liquid-to-solid ratio of 4-20:1, various rare earth elements react with the sulfuric acid to generate corresponding sulfates.

[0077] Taking rare earth elements Sc, Ce, and Yb as examples, they react with sulfuric acid as follows: XJKD003CN1

[0078] 2Sc 3+ +3SO4 2- =SC2(SO4)3

[0079] 2Ce 4+ +3SO4 2- =Ce2(SO4)4

[0080] 2Yb 3+ +3SO4 2- =Yb2(SO4)3

[0081] That is, the second reactant includes scandium compound SC2(SO4)3 generated by the reaction of scandium with sulfuric acid, and other rare earth element compounds such as Ce2(SO4)4 and Yb2(SO4)3 generated by the reaction of other rare earth elements with sulfuric acid.

[0082] It is understandable that rare earth elements generally exist in combined forms within associated compounds. As an example, rare earth elements (represented by "RE") exist in REFCO3 and REPO4, and react with sulfuric acid as follows:

[0083] 2REFCO3+3H2SO4=RE2(SO4)3+2CO2↑+2HF↑+2H2O↑

[0084] 2REPO4+3H2SO4=RE2(SO4)3+2H3PO4

[0085] It is understood that the above reaction is merely an illustrative representation of the reaction that occurs when rare earth elements in their combined state are added to concentrated sulfuric acid. In reality, their combined state is not limited to the example above.

[0086] As one example, the concentration of sulfuric acid is 10-16 mol / L, corresponding to a liquid-to-solid ratio of sulfuric acid to red mud powder of 4-20:1. The concentration of sulfuric acid is 10-12 mol / L, corresponding to a liquid-to-solid ratio of sulfuric acid to red mud powder of 15-20:1. The concentration of sulfuric acid is 12-14 mol / L, corresponding to a liquid-to-solid ratio of sulfuric acid to red mud powder of 10-15:1. The concentration of sulfuric acid is 14-16 mol / L, corresponding to a liquid-to-solid ratio of sulfuric acid to red mud powder of 4-10:1. It can be understood that the concentration of sulfuric acid can be 10 mol / L, 12 mol / L, 13 mol / L, 14 mol / L, 15 mol / L, or 16 mol / L, corresponding to liquid-to-solid ratios of sulfuric acid to red mud powder of 20:1, 15:1, 12:1, 10:1, 7:1, or 4:1.

[0087] As one embodiment, in step S200, the stirring and dissolving process is carried out in a water bath at a temperature of 20-60°C for a duration of 1-10 minutes. Further, the stirring and dissolving process is carried out at a temperature of 50-60°C for a duration of 1-4 minutes.

[0088] As one embodiment, in step S501, the water bath stirring and dissolving process is carried out at 30-100°C for 3-15 minutes. Further, the stirring and dissolving process is carried out at 80-100°C for 3-5 minutes.

[0089] As one embodiment, heap leaching is carried out in a vacuum oven at a temperature of 100-140°C for 12-16 hours. Further, heap leaching is carried out in a vacuum oven at a temperature of 100-110°C for 12-13 hours.

[0090] As one embodiment, in step S502, the roasting temperature is appropriately controlled to thermally separate some of the other rare earth elements.

[0091] As one example, when the second acid solution is sulfuric acid, the calcination temperature is above 690°C and below 700°C.

[0092] Following the example above, the second reactants include SC2(SO4)3, Ce2(SO4)4, Yb2(SO4)3, etc. The second reactants are calcined at temperatures above 690℃ and below 700℃. Since the decomposition temperature of Ce2(SO4)4 is lower than the calcination temperature, it undergoes the following decomposition reaction:

[0093] Ce2(SO4)4=2CeO2+4SO3↑

[0094] Other rare earth element compounds with decomposition temperatures higher than the roasting temperature do not decompose.

[0095] Calcination can alter the internal structure of red mud and improve the properties of rare earth elements, which are difficult to extract. Therefore, the second reactant after calcination can better extract the elements contained in the red mud.

[0096] As one example, the SO3 gas generated during roasting is recovered. It is understood that concentrated sulfuric acid can also decompose to produce SO3 gas at the roasting temperature, which can then be recovered and reused.

[0097] As one embodiment, in step S503, water addition and grinding can be performed either by adding water first and then grinding, or by grinding first and then adding water. As one embodiment, step 503 specifically includes: adding water to the calcined product, and then ball milling. The water and the calcined product are added at a liquid-to-solid ratio of 20-50:1, and the ball milling time is 20-40 minutes. Further, the calcined product is added at a liquid-to-solid ratio of 40-50:1, and the ball milling time is 30-40 minutes.

[0098] As an example, in step S503, other rare earth element oxides generated during roasting in step S502 are removed by filtration. The oxides corresponding to rare earth elements in red mud are usually insoluble in water, such as CeO2. Therefore, CeO2 can be removed by filtration, which means that some rare earth elements are separated.

[0099] In step S504, the other rare earth element compounds that did not decompose in step S502 react with the NaOH to form other rare earth mixed precipitates, thereby separating the other rare earth elements. The reaction equation is as follows:

[0100] RE+xOH - =RE(OH) X ↓

[0101] For example, precipitates such as Yb(OH)3 and Pr(OH)3 are formed; rare earth elements (such as Y, La, Nd, Gd, Dy, Er, etc.) contained in red mud can be quantitatively precipitated. Filtering out the precipitates can separate other rare earth elements.

[0102] In step S504, Sc 3+ With OH - The reaction produces Sc(OH)3, which is amphoteric. With continuous addition of NaOH until the pH of the filtrate reaches 8-10, Sc(OH)3 exhibits significant solubility. Therefore, under these pH conditions, other rare earth elements besides scandium can be separated. Preferably, the pH is adjusted to 8-9, 8.5-9.5, or 9-10; further values ​​of 8, 8.5, 9, 9.5, and 10 are also acceptable.

[0103] In step S506, a third acid solution is added to the second filtrate to adjust the pH value to 0-2, and then oxalic acid is added to precipitate scandium oxalate.

[0104] As one example, the third acid solution is sulfuric acid, hydrochloric acid, or nitric acid, preferably sulfuric acid.

[0105] The reaction that occurs in step S506 is as follows:

[0106] 2Sc(OH)3+3H2C2O4=SC2(C2O4)3+6H20

[0107] Finally, scandium oxide was obtained by calcining scandium oxalate.

[0108] As one embodiment, in step S506, the pH value can be adjusted to 0.5-1.5, preferably pH=1.

[0109] When the first acid solution is sulfuric acid, as an example, step S400 specifically includes steps S401 to S405.

[0110] In step S401, the acid leaching solution is aged to obtain silicon micropowder. It is understood that the specific aging time can be adjusted according to the aging conditions; alternatively, the aging time can be controlled within 1-2 hours.

[0111] In step S402, the silicon powder in the acid leaching solution is filtered out to obtain a third filtrate.

[0112] In step S403, the volume of the third filtrate is concentrated to 30%-60% of its original volume. It is understood that the concentration ratio to the original volume of the third filtrate is not limited. To accelerate crystallization efficiency and improve crystallization effect, the volume of the third filtrate is concentrated to 40%-60%, 50%-60%, or 45%-55% of its original volume, with 55%-60% being more preferred.

[0113] In step S404, the concentrated third filtrate is allowed to crystallize naturally at 10℃-20℃, and then filtered through an 800-900 mesh sieve to obtain aluminum ferric sulfate crystals.

[0114] In step S405, the aluminum ferric sulfate crystals are dissolved in deionized water at a solid-liquid ratio of 1:1.5-10 g / ml. The pH of the solution is then adjusted to 1.0-5.0 with a Ca(OH)2 emulsion with a mass concentration of 10-40%, and filtered through a 400-600 mesh filter to obtain a fourth filtrate. The fourth filtrate is then stirred in a water bath at a temperature of 50℃-100℃ to obtain the polyaluminum ferric sulfate water purifier.

[0115] It is understood that the first acid solution is not sulfuric acid, but another acid. The acid leaching solution can also be aged to obtain silica powder. After filtering out the silica powder, the corresponding water purification agent can be obtained through concentration, crystallization, and polymerization. If the first acid solution is hydrochloric acid, polyaluminum ferric chloride water purification agent can be obtained through appropriate treatment.

[0116] As one example, hydrolysis occurred spontaneously in the third filtrate. The reaction equation for the hydrolysis stage is:

[0117] 2Al2(SO4)3+2nH2O+aq=2Al2(OH)n(SO4)3-n / 2+nH2SO4+aq

[0118] 2Fe2(SO4)3+2nH2O+aq=2Fe2(OH)n(SO4)3-n / 2+nH2SO4+aq

[0119] Regarding the comprehensive recycling method for red mud provided by this invention, two sets of experimental data are provided as follows.

[0120] Experimental group 1

[0121] The red mud used in this experimental group was sintered red mud from an alumina plant in Shanxi Province. Its main chemical components were determined by conventional chemical analysis methods as follows: Al2O3: 23.6%, Fe2O3: 4.18%, CaO: 20.24%, SiO2: 17.44%, and other non-major components: 34.54%. The non-major components include Sc, Y, La, Ce, Pr, Nd, Gd, Dy, Er, and Yb.

[0122] Step S100: Grind the red mud and then pass it through a 200-mesh sieve to obtain red mud powder.

[0123] Step S101: Wash the red mud powder repeatedly with water to remove the attached alkali in the red mud. Stop washing after the pH of the washing water is neutral. After filtration, discard the filtrate to obtain the washed red mud powder.

[0124] Step S200: Add a 6 mol / L sulfuric acid solution to the cleaned red mud powder at a liquid-to-solid ratio of 4:1. Stir the solution in a water bath at 30°C for 1 minute to dissolve the red mud powder.

[0125] Step S300: The solution obtained after step S200 is subjected to solid-liquid separation to obtain acid leaching solution and acid leaching residue.

[0126] Step S400: The acid leaching solution is treated to obtain silicon micro powder and water purification agent; Step S400 specifically includes steps S401 to S405.

[0127] Step S500: The acid leaching residue is treated to obtain scandium oxide, other rare earth element oxides, and other rare earth mixed precipitates. Step S500 specifically includes steps S501 to S505.

[0128] Step S501: Add 10 mol / L sulfuric acid to the acid leaching residue at a liquid-to-solid ratio of 20:1. In a water bath at 30°C, stir the solution for 3 minutes to dissolve it. Then place it in a vacuum oven at 120°C and keep it warm for 14 hours.

[0129] Step S502: The second reactant obtained in step S501 is calcined in a tube furnace at 700°C for 1 hour.

[0130] Step S503: Add water and calcined product at a liquid-solid ratio of 50:1, ball mill for 30 minutes, and filter to obtain filtrate.

[0131] Step S504: Adjust the pH of the filtrate obtained in step S503 to 8 using NaOH, and remove other rare earth mixed precipitates formed during the pH adjustment process by filtration. The filtrate is obtained after removing other rare earth mixed precipitates.

[0132] Step S505: Adjust the pH of the filtrate obtained in step S504 to 1 using concentrated sulfuric acid, then precipitate scandium oxalate by adding solid oxalic acid, and then calcine the scandium oxalate to obtain scandium oxide.

[0133] Step S401: Aging the acid leaching solution for 2 hours to obtain silicon micro powder.

[0134] Step S402: Filter out the silica powder to obtain the filtrate.

[0135] Step S403: Concentrate the filtrate obtained in step S402 to 60% of its original volume;

[0136] Step S404: Allow the concentrated filtrate to crystallize naturally at 10°C, and filter through an 800-mesh sieve to obtain aluminum ferric sulfate crystals.

[0137] Step S405: Dissolve the aluminum ferric sulfate crystals obtained in step S404 in deionized water at a solid-liquid ratio of 1:10 g / ml, adjust the pH of the solution to 4 with a 10% Ca(OH)2 emulsion, filter the solution through a 400-mesh sieve to obtain the filtrate, and stir the filtrate in a water bath at 50°C for 5 hours to obtain polyaluminum ferric sulfate water purifier.

[0138] In this experimental group, the scandium oxide obtained had a high purity (up to 93%), and the resulting water purification agent had an Al2O3 and Fe2O3 content of 15.2%, a basicity of 35%, a density of 1300 g / mL at room temperature, and a pH of 1.8; all of the above products met the relevant industry standards. TXRF analysis of other rare earth mixed precipitates confirmed that the formed solids contained only trace amounts of Sc.

[0139] Experimental group 2

[0140] The red mud used in this experimental group was taken from an aluminum plant in Guangxi. Its main chemical components were determined by conventional chemical analysis methods as follows: Al2O3: 19.05%, Fe2O3: 23.13%, CaO: 12.64%, SiO2: 9.87%, Na2O: 4.87%, and other non-major components: 30.44%, including Sc, Y, La, Ce, Pr, Nd, Gd, Dy, Er, and Yb.

[0141] Step S100: Grind the red mud and then pass it through a 250-mesh sieve to obtain red mud powder.

[0142] Step S101: Wash the red mud powder repeatedly with water to remove the attached alkali in the red mud. Stop washing after the pH of the washing water is neutral. After filtration, discard the filtrate to obtain the washed red mud powder.

[0143] Step S200: Add a 3 mol / L sulfuric acid solution to the cleaned red mud powder at a liquid-to-solid ratio of 15:1. Stir the solution in a water bath at 30°C for 10 minutes to dissolve the mud.

[0144] Step S300: The solution obtained after step S200 is subjected to solid-liquid separation to obtain acid leaching solution and acid leaching residue.

[0145] Step S400: The acid leaching solution is treated to obtain silicon micro powder and water purification agent; Step S400 specifically includes steps S401 to S405.

[0146] Step S500: The acid leaching residue is treated to obtain scandium oxide, other rare earth element oxides, and other rare earth mixed precipitates. Step S500 specifically includes steps S501 to S505.

[0147] Step S501: Add 12 mol / L sulfuric acid to the acid leaching residue at a liquid-to-solid ratio of 4:1. In a water bath at 50°C, stir the solution for 3 minutes to dissolve it. Then place it in a vacuum oven at 100°C and keep it warm for 12 hours.

[0148] Step S502: The second reactant obtained in step S501 is calcined in a tube furnace at 690°C for 1 hour.

[0149] Step S503: Add water and calcined product at a liquid-solid ratio of 30:1, ball mill for 30 minutes, and filter to obtain filtrate.

[0150] Step S504: Adjust the pH of the filtrate obtained in step S503 to 9 using NaOH, and remove other rare earth mixed precipitates formed during the pH adjustment process by filtration, and obtain the filtrate after removing other rare earth mixed precipitates.

[0151] Step S505: Adjust the pH of the filtrate obtained in step S504 to 2 using concentrated sulfuric acid, then precipitate scandium oxalate by adding solid oxalic acid, and then calcine the scandium oxalate to obtain scandium oxide.

[0152] Step S401: Aging the acid leaching solution for 2 hours to obtain silicon micro powder.

[0153] Step S402: Filter out the silica powder to obtain the filtrate.

[0154] Step S403: Hydrolyze the filtrate from step S402, and then concentrate its volume to 50% of the original volume;

[0155] Step S404: Allow the concentrated filtrate to crystallize naturally at 20°C, and filter through a 900-mesh sieve to obtain aluminum ferric sulfate crystals.

[0156] Step S405: Dissolve the aluminum ferric sulfate crystals obtained in step S404 in deionized water at a solid-liquid ratio of 1:1.5 g / ml, adjust the pH of the solution to 2 with a 40% Ca(OH)2 emulsion, filter the solution through a 600-mesh sieve to obtain the filtrate, and stir the filtrate in a water bath at 100°C for 1 hour to obtain polyaluminum ferric sulfate water purifier.

[0157] In this experimental group, the scandium oxide obtained was a high-purity product (purity up to 99%), and the resulting water purification agent had an Al2O3 and Fe2O3 content of 6.14%, a basicity of 47%, a density of 1340 g / mL at room temperature, and a pH value of 4.5; all of the above products meet the relevant industry standards.

[0158] Experimental group 3:

[0159] The red mud used in this experimental group was taken from an aluminum plant in Guangxi. Its main chemical components were determined by conventional chemical analysis methods as follows: Al2O3: 19.05%, Fe2O3: 23.13%, CaO: 12.64%, SiO2: 9.87%, Na2O: 4.87%, and other non-major components: 30.44%, including Sc, Y, La, Ce, Pr, Nd, Gd, Dy, Er, and Yb.

[0160] Step S100: Grind the red mud to obtain red mud powder; the red mud contains Al2O3, Fe2O3, SiO2 and various rare earth elements, including scandium and cerium (Ce).

[0161] Step S200: A first acid solution is added to the red mud powder and stirred to dissolve it, yielding a first reactant; the concentration of the first acid solution is 3 mol / L, and the first acid solution and the red mud powder are added at a liquid-to-solid ratio of 10:1; the first reactant includes the corresponding salts generated by the reaction of Al2O3, Fe2O3, and SiO2 with the first acid solution; the various rare earth elements, including scandium and cerium, do not react with the first acid solution;

[0162] Step S300: The first reactant is subjected to solid-liquid separation to obtain an acid leaching solution and an acid leaching residue; the corresponding salts are separated into the acid leaching solution, and the various rare earth elements, including scandium and cerium, are separated into the acid leaching residue;

[0163] Step S400: The acid leaching solution is treated to obtain silicon micro powder and water purification agent; Step S400 may specifically include the same steps S401 to S405 as Experimental Group 2.

[0164] Step S500: The acid leaching residue is treated to obtain scandium oxide, other rare earth element oxides, and other rare earth mixed precipitates. Step S500 specifically includes steps S501 to S505.

[0165] Step S501: Add a second acid solution to the acid leaching residue, stir to dissolve, and heap leaching to obtain a second reactant. The concentration of the second acid solution is greater than 10 mol / L, and the second acid solution and the acid leaching residue are added at a liquid-to-solid ratio of 12:1. The second reactant includes scandium and cerium compounds generated by the reaction of scandium and cerium with the second acid solution, as well as other rare earth element compounds generated by the reaction of other rare earth elements (excluding scandium and cerium compounds) with the second acid solution.

[0166] Step S502: The second reactant is calcined at a first temperature to obtain a calcined product, wherein the first temperature is 5°C lower than the decomposition temperature of the scandium compound; during the calcination process, the Ce compound decomposes to obtain cerium oxide (CeO2), and further, a portion of the other rare earth element compounds decomposes to generate corresponding other rare earth element oxides.

[0167] Step S503: Add water to the calcined product and grind it to remove cerium oxide and other rare earth element oxides, and obtain the first filtrate;

[0168] Step S504: Add NaOH to the first filtrate and adjust the pH value to 8-10. The other rare earth element compounds that were not decomposed in step T502 react with the NaOH to form other rare earth mixed precipitates. Filter out the other rare earth mixed precipitates to obtain the second filtrate.

[0169] Step S505: Add a third acid solution to the second filtrate, adjust the pH value to 1, and then add oxalic acid to precipitate scandium oxalate; calcine the scandium oxalate to obtain scandium oxide.

[0170] In this experimental group, scandium oxide was obtained as a high-purity product (purity up to 99%), and the resulting water purification agent had an Al2O3 and Fe2O3 content of 6.2%, a basicity of 46%, a density of 1320 g / mL at room temperature, and a pH value of 4.3; all of the above products meet the relevant industry standards.

[0171] This invention provides a comprehensive utilization method for red mud. Through dilute acid stirring and dissolution, acid leaching residue and acid leaching solution are obtained. The main elements are largely separated into the acid leaching solution, while rare earth elements are separated into the acid leaching residue. The acid leaching solution is used to extract silica powder and generate a water purification agent. Scandium is extracted from the acid leaching residue through a process involving concentrated acid leaching, roasting, filtration, and precipitation. This achieves efficient recycling of red mud, resulting in significant economic benefits and effectively reducing the stockpiling and discharge of red mud. Compared with existing methods for recovering scandium from red mud, the method provided by this invention has a higher scandium recovery rate (greater than 75%), lower raw material requirements (scandium content greater than 1%), and higher scandium oxide recovery grade (purity greater than 88%). It also has advantages such as simple process, no special equipment requirements, and easy industrialization. The extraction process does not discharge toxic or harmful solid waste, nor does it discharge acidic, alkaline, or heavy metal-containing solutions, meeting environmental protection requirements and opening up new avenues for the comprehensive utilization of red mud.

[0172] It should be noted that the use of step numbers (letters or numbers) to refer to certain specific method steps in this invention is merely for the purpose of convenience and brevity in description, and is by no means intended to restrict the order of these method steps. Those skilled in the art will understand that the order of the relevant method steps should be determined by the technology itself and should not be unduly restricted by the existence of step numbers. Those skilled in the art can determine various permissible and reasonable orderings of steps based on the technology itself.

[0173] Those skilled in the art will understand that, without conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0174] It should be understood that the above embodiments are merely exemplary and not restrictive. Various obvious or equivalent modifications or substitutions that can be made by those skilled in the art regarding the above details without departing from the basic principles of the present invention will be included within the scope of the claims of the present invention.

Claims

1. A method for comprehensive recycling of red mud, characterized by, The method comprises steps of: S100: grinding the red mud to obtain red mud powder; the red mud comprises Al2O3, Fe2O3, SiO2 and multiple rare earth elements, and the multiple rare earth elements comprise a scandium element; S200: adding a first acid solution to the red mud powder to stir and dissolve to obtain a first reactant; the concentration of the first acid solution is 1-6 mol / L, the first acid solution is added to the red mud powder at a liquid-solid ratio of 4-15:1; the first reactant comprises corresponding salts generated by the Al2O3, Fe2O3 and SiO2 respectively reacting with the first acid solution; the first acid solution is sulfuric acid; S300: performing solid-liquid separation on the first reactant to obtain an acid leaching liquid and an acid leaching residue; the corresponding salts are separated into the acid leaching liquid, and the multiple rare earth elements are separated into the acid leaching residue; S400: processing the acid leaching liquid to obtain silicon powder and a water purifying agent; the water purifying agent is a polyaluminum ferric sulfate water purifying agent; S500: processing the acid leaching residue to obtain scandium oxide, other rare earth element oxides and other rare earth mixed precipitates respectively; The step S500 comprises: S501: adding a second acid solution to the acid leaching residue to stir and dissolve to obtain a second reactant; the concentration of the second acid solution is greater than 10 mol / L, and the second acid solution is added to the acid leaching residue at a liquid-solid ratio of 4-20:1; the second reactant comprises a scandium compound generated by the scandium reacting with the second acid solution, and other rare earth element compounds generated by other rare earth elements in the multiple rare earth elements except the scandium reacting with the second acid solution; S502: roasting the second reactant at a first temperature to obtain a roasting product; the first temperature is 0-15 ℃ lower than the decomposition temperature of the scandium compound; in the roasting process, part of the other rare earth element compounds decomposes to generate corresponding other rare earth element oxides; S503: adding water to the roasting product to grind, and filtering out the other rare earth element oxides to obtain a first filtrate; S504: adding NaOH to the first filtrate to adjust the pH value to 8-10; the other rare earth element compounds that are not decomposed in the step S502 react with the NaOH to form other rare earth mixed precipitates; S505: filtering out the other rare earth mixed precipitates to obtain a second filtrate; S506: adding a third acid solution to the second filtrate to adjust the pH value to 0-2, and then adding oxalic acid to precipitate scandium oxalate; S507: roasting the scandium oxalate to obtain scandium oxide.

2. The method for comprehensive recycling of red mud according to claim 1, characterized in that, In the step S100, the red mud powder is obtained after being ground and sieved through a 200-300 mesh sieve; the red mud is any one or a mixture of multiple of Bayer process red mud, sintering process red mud or combined process red mud; The other rare earth elements in the multiple rare earth elements except the scandium comprise one or more of Y, La, Ce, Pr, Nd, Gd, Dy, Er and Yb.

3. The method for comprehensive recycling of red mud according to claim 1, characterized in that, Before the step S200, a step A is included: repeatedly washing attached alkali in the red mud powder with water until the pH value of the washing water is 6.9-7.

2.

4. The method for comprehensive recycling of red mud according to claim 1, characterized in that, In step S200, the stirring dissolution is carried out in a water bath, and the stirring dissolution is controlled to be carried out at 20-60℃, and the stirring dissolution time is 1-10 min.

5. The method for comprehensive recycling of red mud according to claim 1, characterized in that, In step S501, the stirring dissolution is carried out in a water bath, and the stirring dissolution is controlled to be carried out at 30-100℃, and the stirring dissolution time is 3-15 min; the heap leaching is carried out in a vacuum oven at a temperature of 100-140℃, and the heap leaching time is 12-16 h.

6. The method for comprehensive recycling of red mud according to claim 1, characterized in that, The second acid solution is sulfuric acid, and in step S502, the roasting temperature is higher than 690℃ and lower than 700℃.

7. The method for comprehensive recycling of red mud according to claim 6, characterized in that, In step S502, roasting produces SO3 gas, and the SO3 gas is recovered.

8. The method for comprehensive recycling of red mud according to claim 1, characterized in that: The step 503 specifically comprises: adding water to the roasting product, and then carrying out ball milling; the water is added to the roasting product at a liquid-solid ratio of 20-50:1, and the ball milling time is 20-40 min.

9. The comprehensive red mud recycling method according to any one of claims 1 to 8, characterized in that, The step S400 specifically comprises steps of: S401: aging the acid leaching solution to obtain silicon micro powder; S402: filtering out the silicon micro powder in the acid leaching solution to obtain a third filtrate; S403: concentrating the third filtrate to 30%-60% of the original volume; S404: naturally crystallizing the concentrated third filtrate at 10-20℃, and filtering through a 800-900 mesh screen to obtain aluminum-iron sulfate crystals; S405: dissolving the aluminum-iron sulfate crystals with deionized water at a solid-liquid ratio of 1:1.5-10 g / ml, adjusting the solution pH value to 1.0-5.0 with Ca(OH)2 emulsion with a mass concentration of 10-40%, and filtering through a 400-600 mesh screen to obtain a fourth filtrate, and stirring the fourth filtrate at a water bath temperature of 50-100℃ to obtain the polymeric aluminum-iron sulfate water purifying agent.

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