Method and system for combined treatment of bayer red mud and low-grade bauxite

Abstract

This invention relates to a method and system for the combined processing of Bayer process red mud and low-grade bauxite. The method includes: separately detecting the aluminum and silicon content in the red mud and bauxite, mixing the red mud and bauxite according to the detection results to achieve an aluminum-to-silicon ratio greater than 1 in the resulting raw material, adding a calcination aid, and calcining to obtain clinker. The clinker undergoes multiple cycles of water leaching and primary desilication treatment until the aluminum-to-silicon ratio in the solution is greater than 300 and the vanadium content reaches 2 g / L, at which point deep desilication is performed. The deep desilication solution is then carbonated to extract aluminum. Ammonium salts are added to the resulting solution to further extract vanadium. The final solution is crystallized and used as a calcination aid. The water leaching residue from the water leaching treatment is acid-leached, aged, and hydrolyzed to polymerize, yielding calcium sulfate, silica gel, and a water purification agent, respectively. This invention effectively utilizes both major and rare elements, solving the problems of red mud accumulation and the ineffective utilization of low-grade bauxite.

Description

Technical Field

[0001] This invention relates to the field of red mud recycling technology, specifically to a method and system for the combined treatment of Bayer process red mud and low-grade bauxite. Background Technology

[0002] Currently, there are many methods for extracting valuable metals from red mud, such as reduction roasting. Magnetic separation is used to separate iron, and wet processes can also be used to extract iron and aluminum. Some methods, such as acid leaching, stepwise extraction, and melting, are used to extract various rare metals like vanadium, titanium, scandium, and lanthanum, as illustrated in existing technologies CN112011691A, CN103898330B, CN107083485B, CN110066923A, CN108751142A, and CN107385197B. However, some of these methods introduce other impurity ions during the extraction of aluminum, iron, and vanadium, resulting in low purity of the extracted elements, which is unfavorable for industrial applications. Others require specialized roasting, magnetic separation, acid leaching, and melting equipment, placing excessive demands on the equipment and hindering industrial production. Although there are some existing technologies for extracting rare metal vanadium, such as CN102732727A, these are mainly for raw materials with high vanadium content and are obviously not suitable for direct application to red mud with extremely low vanadium content.

[0003] In addition, in the smelting of metallic aluminum, because the aluminum and silicon content in low-grade bauxite is relatively low, it is difficult to extract aluminum from it using existing metallic aluminum smelting methods. In order to increase aluminum production, some higher-quality bauxite is usually preferred as raw material, and low-quality bauxite is shelved and cannot be effectively utilized.

[0004] It is evident that neither Bayer process red mud nor low-grade bauxite can be efficiently utilized in isolation, thus reducing their economic value. Although the applicant has proposed a method for the comprehensive utilization of red mud and bauxite in existing technology CN113860343B, this method mainly focuses on the extraction of major elements from the two raw materials. Rare metal elements in the raw materials cannot be purified separately, especially vanadium. Pure vanadium is extremely valuable and has a wide range of applications. Therefore, the applicant has made further improvements based on existing technology CN113860343B. Summary of the Invention

[0005] Based on the above situation, the main objective of this invention is to provide a method and system for the combined processing of Bayer process red mud and low-grade bauxite, which enables the effective utilization of major and rare elements and solves the problems of red mud accumulation and the inability to effectively utilize low-grade bauxite.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention provides

[0008] A method for the combined processing of Bayer process red mud and low-grade bauxite, wherein both the red mud and bauxite contain aluminum, silicon, iron, calcium, and vanadium; comprising the following steps:

[0009] S10: Detect the aluminum and silicon content in the red mud and bauxite respectively, determine the mixing ratio of red mud and bauxite based on the detection results, mix the red mud and bauxite according to the mixing ratio to obtain raw material, wherein the mixing ratio makes the aluminum-silicon content ratio in the raw material greater than 1;

[0010] S20: Add an alkaline calcination aid to the raw material and calcine it to obtain clinker;

[0011] S30: The clinker is subjected to water leaching treatment, followed by solid-liquid separation to obtain a first water leaching solution and a first water leaching residue; the red mud is added to the first water leaching solution, aged, and filtered to obtain sodium silicate slag and primary desiliconization solution; the first water leaching residue is subjected to acid leaching treatment to obtain calcium sulfate and acid leaching solution, the acid leaching solution is aged and filtered to obtain silica gel and aged desiliconization solution, and the sodium silicate slag is added to the aged desiliconization solution to obtain polyaluminum ferric sulfate flocculant;

[0012] S40: Return the primary desilication solution to step S30 for water immersion treatment, and repeat the water immersion desilication multiple times until the Al2O3 concentration in the primary desilication solution reaches 100~130g / L and the aluminum-silicon content ratio is greater than 300, and then proceed to step S50.

[0013] S50: Determine the silicon content in the primary desilication solution. Add magnesium salt or lime slurry to the primary desilication solution, filter, and obtain a deep desilication solution and magnesium silicate or calcium silicate. The amount of magnesium salt or lime slurry added is determined based on the measured silicon content to ensure that the aluminum-silicon ratio in the deep desilication solution is greater than 3000. - The concentration is greater than 2 g / L;

[0014] S60: Carbon dioxide is introduced into the deep desilication solution for carbonation decomposition, and solid-liquid separation is performed to obtain aluminum hydroxide and a second aqueous extract; then ammonium salt is added to the second aqueous extract and stirred, filtered to obtain NH4VO3 and a third aqueous extract, the NH4VO3 is calcined to obtain V2O5, and the ammonia gas generated during calcination is recovered; the crystals obtained by concentrating the third aqueous extract are returned to step S20 as an alkaline calcination aid.

[0015] Preferably, in step S50, magnesium salt or lime milk is added and stirred, and the reaction temperature is set to be greater than 90°C to produce precipitation. After precipitation stops, the mixture is allowed to stand for at least 0.5 hours and then filtered to obtain the deep desilication liquid and the magnesium silicate or calcium silicate.

[0016] Preferably, in step S50, magnesium salt is added to the primary desilication solution at a magnesium salt to silicon molar ratio of 1 to 1.5.

[0017] Preferably, in step S60, carbon dioxide is stopped during carbonation decomposition when the concentration of aluminum oxide in the solution is less than 20 g / L.

[0018] Preferably, in step S60, the ammonium salt is added according to a molar ratio of ammonium salt to vanadium of (1~2):1, and the reaction temperature is set to 20~30℃;

[0019] The ammonium salt is selected from NH4Cl.

[0020] Preferably, in step S60, the calcination temperature of NH4VO3 is 450~600℃.

[0021] Preferably, in step S30, the acid leaching treatment is performed with sulfuric acid until no precipitate is produced and the addition of sulfuric acid is stopped; sodium silicate slag is added to the aged desiliconization solution until the mixture becomes weakly acidic and then stops.

[0022] Preferably, in step S61, the aluminum hydroxide obtained in step S60 is calcined to obtain aluminum oxide, wherein the calcination temperature of the aluminum hydroxide is 600~800℃ and the calcination time is 4~5 hours.

[0023] Preferably, in step S10, the red mud and the bauxite are mixed in a mass ratio of 0.5 to 3:1 to obtain a mixed raw material, and then ground to obtain the raw meal of 300 to 500 mesh; the alkaline calcining aid is selected from at least one of sodium hydroxide and sodium carbonate; the mass ratio of the raw meal to the alkaline aid is 1:(0.5 to 2), the calcination temperature is 700 to 1100°C, and the calcination time is 0.5 to 1.5 hours.

[0024] Preferably, in step S30, the solid-liquid mass ratio of the raw material in the water immersion treatment is 3-15, the water immersion treatment temperature is 20-90℃, and the immersion time is 5-30 minutes.

[0025] Preferably, in step S30, the red mud is added to the first aqueous solution while stirring until the concentration of the red mud in the solution is 10~40g / L, at which point the addition of the red mud is stopped. The reaction temperature is 105~130℃, and the reaction time is 1~3 hours.

[0026] A second aspect of the present invention provides a combined processing system for Bayer process red mud and low-grade bauxite, for implementing the combined processing method described in any of the preceding claims; comprising:

[0027] A mixing device for mixing raw materials in steps S10, S20, and S70.

[0028] Calcination apparatus used for calcination in steps S10, S20, and S70;

[0029] A mixing reaction apparatus for mixing and reacting raw materials in steps S30, S40, S50, S60, and S70;

[0030] Filtration separation device for solid-liquid separation in steps S30, S40, S50, S60, and S70;

[0031] The mixing device, the calcining device, the mixing reaction device, and the filtration and separation device are connected by a conveying device or a pipeline.

[0032] Preferably,

[0033] The mixing device includes a mixer;

[0034] The calcination apparatus includes a rotary kiln;

[0035] The mixing reaction apparatus includes a pressure reactor having a first stirring component and a heating component;

[0036] The filtration and separation device includes a filter press, a vacuum filter, and / or a centrifuge.

[0037] The combined processing method of this invention, on the one hand, increases the detection of aluminum and silicon elements in red mud and bauxite and ensures that the aluminum-silicon content ratio is greater than 1 when mixing to obtain raw materials. It also simultaneously cycles through water leaching and primary desilication steps to reduce silicon content and enrich aluminum and vanadium. Furthermore, it adds a deep desilication step to further reduce silicon content. Specifically, by setting the aluminum-silicon ratio in the raw materials, the silicon index in the primary desilication step can more easily reach a preset value, or even be significantly lower than the preset silicon index in primary desilication. This results in more complete silicon separation during deep desilication, improving the purity of aluminum extraction and reducing the influence of silicon on vanadium extraction, thus increasing the purity of vanadium extraction. Therefore, the entire combined processing method not only improves the extraction purity of major elements in the treatment of red mud waste from aluminum smelting but also extracts high-quality aluminum and vanadium. This process extracts high-purity rare metal vanadium, effectively utilizing low-grade bauxite that had previously lacked efficient utilization methods. It achieves high-purity extraction of abundant aluminum, silicon, iron, and trace amounts of rare metal vanadium. The resulting products, including calcium sulfate, aluminum hydroxide, polyaluminum ferric sulfate flocculant, hydrated sodium aluminosilicate, and vanadium pentoxide, are directly usable industrial products. For example, calcium sulfate can be directly used in cement, gypsum, and paper industries; aluminum hydroxide can be directly used in flame-retardant materials, dye abrasives, and pharmaceutical industries; polyaluminum ferric sulfate flocculant can be directly used in water purification agents; hydrated sodium aluminosilicate can be used in phosphorus-free detergents, exhibiting strong surface adsorption capacity and serving as an ideal adsorbent and desiccant; and vanadium pentoxide can be used in metallurgy and chemical industries. These products have a wide range of applications, which will not be listed here.

[0038] On the other hand, the entire processing method of the present invention generates no solid or liquid waste, does not cause secondary pollution, is environmentally friendly, and all added additives can be effectively utilized. For example, the added alkaline calcining aid can be recycled, the added ammonium salt can be recovered into ammonia, and the added magnesium salt or lime milk can be used to generate magnesium silicate or calcium silicate. The hydrated sodium aluminosilicate produced in the process can not only be used directly as a raw material for other industries, but can also be used to form polyaluminum ferric sulfate water purification agent by adding the intermediate product aluminum ferric sulfate acid leaching residue.

[0039] As can be seen, the processing method of this invention not only achieves full-scale treatment of red mud and low-grade bauxite, reducing the amount of red mud stockpiled and discharged, but also effectively utilizes the low-grade bauxite. The entire process generates no secondary waste, achieving harmless treatment of the red mud. Furthermore, the process is simple, requires no special equipment, and is easily industrialized. The comprehensive utilization rate of major and trace elements in red mud and low-grade bauxite is high, reaching a level of complete extraction. These elements or mixtures can be used as raw materials in industrial production, generating good economic benefits. This truly achieves comprehensive and highly integrated treatment of red mud and low-grade bauxite, greatly improving their overall utilization value.

[0040] 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

[0041] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. In the drawings:

[0042] Figure 1 A schematic flowchart of a preferred embodiment of the method for the combined utilization of Bayer red mud and low-grade bauxite provided by the present invention.

[0043] Figure 2 This is a schematic diagram illustrating the generation of products in each step of a preferred embodiment of the method for the combined utilization of Bayer red mud and low-grade bauxite provided by the present invention.

[0044] Figure 3 The infrared spectrum of the aluminum ferric sulfate flocculant obtained by a preferred embodiment of the method for the combined utilization of Bayer red mud and low-grade bauxite provided by the present invention. Detailed Implementation

[0045] 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.

[0046] 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.

[0047] Unless the context explicitly requires it, the words "comprising," "including," or 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."

[0048] 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.

[0049] In the description of this invention, "content" refers to a percentage by mass.

[0050] To address the problems of existing technologies, this invention provides a combined processing method for Bayer process red mud and low-grade bauxite. Both Bayer process red mud and bauxite contain elements such as aluminum, silicon, iron, calcium, and vanadium, with the content of aluminum, silicon, iron, and calcium being significantly higher than that of vanadium. In other words, aluminum, silicon, iron, and calcium are major elements in both Bayer process red mud and low-grade bauxite, and their content is relatively high, while vanadium is a trace element and a rare metal, and its content is relatively low. Typically, the aluminum and silicon content in Bayer process red mud is similar, differing by less than 15%, while the difference in aluminum and silicon content in low-grade bauxite, although also relatively small, is greater than the difference in Bayer process red mud, generally exceeding 20%. The main forms of these major elements are Al2O3, SiO2, Fe2O3, and CaO, while vanadium is mainly V2O5. Of course, it cannot be ruled out that these elements may also exist in other forms, and there may also be other elements in Bayer process red mud and low-grade bauxite.

[0051] refer to Figure 1 and Figure 2 The combined processing method of the present invention includes the following steps:

[0052] S10: Detect the aluminum and silicon content in Bayer process red mud and low-grade bauxite respectively. Based on the determined mixing ratio of red mud and bauxite, mix Bayer process red mud and low-grade bauxite according to the mixing ratio to obtain raw material, wherein the mixing ratio makes the aluminum-silicon content ratio in the raw material greater than 1.

[0053] Specifically, the content of aluminum and silicon in Bayer process red mud and low-grade bauxite is first tested. Then, Bayer process red mud and low-grade bauxite are mixed at a certain mass ratio to obtain a mixed raw material in which the aluminum-silicon content ratio is greater than 1.

[0054] In this step, the main focus is on detecting the aluminum and silicon content in Bayer process red mud and low-grade bauxite. Specifically, these two elements are calculated as Al2O3 and SiO2, respectively, to determine the mass ratio in the red mud-bauxite mixture. The goal is to ensure the aluminum-silicon ratio in the mixed raw material is greater than 1, facilitating desilication in the subsequent desilication step, resulting in a deeply desilication solution that is essentially free of silicon. Of course, the content of other elements, such as iron and vanadium, can also be detected simultaneously during this process.

[0055] S20: Add an alkaline calcination aid to the raw material obtained in step S10 and calcinate it to obtain clinker.

[0056] The purpose of roasting is to convert Al₂O₃ into sodium aluminosilicate, which is easily soluble in water or dilute alkaline solutions; to convert Fe₂O₃ into sodium ferrite, which is easily hydrolyzed; and to convert SiO₂ and CaO into compounds that are sparingly soluble in water or dilute alkaline solutions. The chemical reactions that occur during this roasting process vary depending on the alkaline roasting aids added. However, for the major elements aluminum, silicon, and calcium, roasting will result in sodium aluminosilicate (such as Na₂O₃). 1.95 Al 1.95 Si 0.05 O4, Na 1.75 Al 1.75 Si 0.25 Iron exists as sodium silicate, calcium silicate, and sodium silicate (O4), while iron exists as sodium ferrite or is dissolved in sodium aluminosilicate. The trace element vanadium exists as sodium vanadate.

[0057] For example, when sodium hydroxide is selected as the alkaline additive, the main chemical reactions that occur during the calcination process include:

[0058] 1.95Al2O3+0.1SiO2+3.9NaOH=2Na 1.95 Al 1.95 Si 0.05 O4 + 1.95H2O;

[0059] 1.75Al2O3+0.5SiO2+3.5NaOH=2Na 1.75 Al 1.75 Si 0.25 O4 + 1.75H2O;

[0060] 2NaOH + SiO2 = Na2SiO3 + H2O;

[0061] 2CaO + SiO2 = 2CaSiO3;

[0062] 2NaOH + V₂O₅ = 2NaVO₃ + H₂O;

[0063] For example, when sodium carbonate is chosen as the alkaline additive, the main chemical reactions that occur during the calcination process include:

[0064] 1.95Al2O3+0.1SiO2+1.95Na2CO3=2Na 1.95 Al 1.95 Si 0.05 O4 + 1.95CO2;

[0065] 1.75Al2O3+0.5SiO2+1.75Na2CO3=2Na 1.75 Al 1.75 Si 0.25 O4 + 1.75CO2;

[0066] SiO2 + CaO = CaSiO3;

[0067] 2Na2CO3+SiO2=Na2SiO3+ CO2↑;

[0068] Na2CO3 + V2O5 = NaVO3 + CO2↑;

[0069] Fe2O3+Na2CO3=Na2O· Fe2O3+CO2↑;

[0070] In this step, the addition of sintering aids is to convert Al2O3 into sodium aluminosilicate, so that more and purer aluminum powder can be extracted in subsequent steps, thereby improving the purification efficiency of major elements from Bayer red mud and low-grade bauxite.

[0071] S30: Water leaching step, which involves leaching the clinker obtained in step S20 with water, followed by solid-liquid separation to obtain a first water leaching solution and a first water leaching residue; Primary desilication step, which involves adding Bayer red mud to the first water leaching solution, aging it, and filtering it to obtain silicon slag and primary desilication solution. In other words, the clinker in step S20 is first leached with water, and then the filtrate obtained after water leaching is subjected to primary desilication.

[0072] Water leaching step: Specifically, the clinker obtained in step S20 is mixed with a certain amount of water and stirred to fully dissolve the clinker. Then, solid-liquid separation is performed, and the mixture is filtered to obtain the first water leaching solution and the first water leaching residue. Since calcium silicate is insoluble in water, sodium aluminosilicate (Na...) 1.95 Al 1.95 Si 0.05 O4, Na 1.75 Al 1.75 Si 0.25 The NaAlSiO4 obtained from the hydrolysis of O4 is also insoluble in water. Therefore, this step can separate calcium and NaAlSiO4, meaning the first water leaching residue contains a mixture of calcium silicate and NaAlSiO4. Iron also enters the first water leaching residue along with sodium aluminosilicate. The first water leaching solution mainly contains AlO2.- SiO3 2- VO3 - At this point, the aluminum-to-silicon ratio in the first immersion solution is less than 20, meaning the silicon content is still relatively high. The chemical reactions occurring during this immersion process mainly include:

[0073] Na 1.95 Al 1.95 Si 0.05 O4+3.8H2O+aq=1.9NaAl(OH)4+0.05NaAlSiO4+aq;

[0074] Na 1.75 Al 1.75 Si 0.25 O4+3H2O+aq=1.5NaAl(OH)4+0.25NaAlSiO4+aq.

[0075] Primary desilication step: In this process, Bayer red mud is added to the first aqueous leachate obtained in step S30. The red mud from step S10 can be used. To promote the reaction, ground red mud is preferred, causing sodium silicate (Na2SiO3) in the first aqueous leachate to precipitate as hydrated sodium aluminosilicate (Na2O·Al2O3·1.7SiO2·nH2O). The filter residue obtained after solid-liquid separation is sodium silicate slag (i.e., hydrated sodium aluminosilicate). The main components of the primary desilication solution are aluminum ions, sodium ions, and a small amount of silicate ions, as well as vanadium ions, to separate most of the silicon from the first aqueous leachate. The separated hydrated sodium aluminosilicate can be used in phosphorus-free detergents; it has strong surface adsorption capacity and is an ideal adsorbent and desiccant. In this process, even if the first aqueous leachate obtained in step S30 contains a small amount of NaAlSiO4, it will precipitate along with the sodium silicate slag. It is worth noting that although red mud is added in this step, it will not undergo further calcination in step S20, and the amount added is relatively small. It mainly acts as a seed crystal / reaction initiator to promote more efficient precipitation of hydrated sodium aluminosilicate. Therefore, it has virtually no impact on the aluminum-silicon ratio prepared in the initial step S10. The main chemical reactions occurring in the primary desilication solution step include:

[0076] 1.7Na2SiO3+2NaAl(OH)4+aq=Na2O·Al2O3·1.7SiO2·nH2O+3.4NaOH+aq.

[0077] S40: Aluminum and vanadium enrichment step. The primary desilication solution is returned to step S30 for water immersion treatment. The water immersion desilication is repeated multiple times until the Al2O3 concentration in the primary desilication solution reaches 100~130g / L and the aluminum-silicon content ratio is greater than 300. Then, step S50 is performed.

[0078] In this step, the primary desilication liquid is returned to step S30 and mixed with the clinker in step S20. The mixture is then cyclically subjected to water immersion and primary desilication treatment until the Al2O3 concentration in the primary desilication liquid reaches 100~130 g / L, such as 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L, 126 g / L or 130 g / L, and the aluminum-silicon content ratio is greater than 300, such as 301, 350, 380, 400 or 440, in order to enrich aluminum and vanadium elements and further reduce the silicon content. Specifically, after each primary desilication step, most of the silicon in the resulting primary desilication solution is separated. During the return to the water leaching step, since some solids in the solution originate from the primary desilication solution, the aluminum and vanadium content in the same mass of solids relatively increases. This allows the aluminum and vanadium content in the recycled primary desilication solution to gradually increase, while the silicon content gradually decreases, achieving an aluminum-to-silicon ratio greater than 300, meaning a very low silicon content. This reduces the difficulty of separating aluminum and vanadium in subsequent steps and improves the purity of vanadium extraction. Compared to first circulating water leaching (i.e., only circulating water leaching) followed by Bayer red mud desilication, this invention, through simultaneous circulating water leaching and primary desilication steps, significantly reduces the content of the main element silicon in the solution, enriches the main element aluminum and the trace element vanadium, and reduces the number of cycles.

[0079] S50: Deep desilication step. The silicon content in the primary desilication solution is determined. Magnesium salts or lime slurry are added to the primary desilication solution. After filtration, deep desilication solution and deep desilication slag are obtained. The deep desilication slag is magnesium silicate (when magnesium salts are added) or calcium silicate (when lime slurry is added). The amount of magnesium salts or lime slurry added is determined based on the measured silicon content to ensure that the aluminum-silicon ratio in the deep desilication solution is greater than 3000. VO3 - The concentration is greater than 2 g / L.

[0080] Specifically, magnesium salts or lime slurry are added to the primary desilication liquid obtained after circulating water immersion and primary desilication, and the mixture is stirred to allow the residual silicon in the primary desilication liquid to fully react. Afterwards, solid-liquid separation is performed to obtain magnesium silicate (when magnesium salts are added) or calcium silicate (when lime slurry is added) as deep desilication slag and deep desilication liquid. Magnesium silicate can be used in pharmaceuticals, the production of deodorizing and decolorizing agents, ceramics, rubber, and other industries, and can also be used as insulation materials in construction. Calcium silicate is a commonly used safe heat insulation material to replace asbestos and can also be used in fireproofing materials. After this step, the aluminum-silicon content ratio in the deep desilication liquid is greater than 3000, which is significantly higher than the aluminum-silicon content ratio in the first water immersion liquid or even the primary desilication liquid, increasing the content difference between the two. For example, the aluminum-silicon content ratio can be 3001, 3100, 3500, 3800, 4000, or 4300, etc., and further increases the concentration of vanadium ions and VO3. - The concentration of aluminum is greater than 2 g / L, such as 2.1 g / L, 2.3 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L, or 5 g / L, thus further increasing the content difference between aluminum and silicon and reducing the content of silicon. This improves the purity of subsequent aluminum extraction and reduces the impact of silicon on vanadium extraction. The main chemical reactions in this process include:

[0081] SiO3 2- +Mg 2+ = MgSiO3, or

[0082] SiO3 2- +Ca 2+ =CaSiO3.

[0083] It is worth noting that although adding red mud can further reduce the silicon content in the primary desilication solution, the time cost of adding red mud is too high. However, adding magnesium salts or lime slurry for deep desilication can accelerate the generation of deep desilication slag, reduce reaction time, speed up the process, and save costs.

[0084] S60: Carbonation decomposition step, carbon dioxide is introduced into the deep desilication solution for carbonation decomposition, and solid-liquid separation yields aluminum hydroxide and a second aqueous leachate; Vanadium extraction step, ammonium salt is added to the second aqueous leachate and stirred, filtered to obtain NH4VO3 and a third aqueous leachate, NH4VO3 is calcined to obtain V2O5, and ammonia gas generated during calcination is recovered. The crystals obtained from the concentrated third aqueous leachate are returned to step S20 as an alkaline calcination aid. In other words, the deep desilication solution first undergoes a carbonation decomposition step, and the resulting second aqueous leachate is then used to extract vanadium in the vanadium extraction step.

[0085] In the carbonation decomposition step, CO2 is introduced into the deep desilication solution to carry out carbonation decomposition. During this process, aluminum ions in the deep desilication solution are converted into aluminum hydroxide and precipitated. Solid-liquid separation yields aluminum hydroxide precipitate and a second aqueous leachate. The second aqueous leachate is mainly a sodium carbonate solution, and the trace element vanadium exists in the solution as vanadate ions. Because the major element is separated, the concentration of vanadium in the solution is further increased, which is beneficial for subsequent vanadium extraction. The main chemical reactions occurring in the carbonation decomposition step include:

[0086] AlO2 - +OH - +CO2 + aq = Al(OH)3 + CO3 2- +O2+aq;

[0087] 2AlO2 - +CO2 + 3H2O + aq = 2Al(OH)3 + CO3 2- +aq.

[0088] The vanadium extraction process begins by adding ammonium salts, such as NH4Cl, to the second aqueous leaching solution, which also contains NH4. + An ammonium salt solution containing ions is stirred to precipitate NH4VO3. The precipitate is filtered to obtain a second aqueous extract, which is a sodium carbonate solution. This second aqueous extract, after concentration, can be used as an alkaline calcination aid in step S20. The resulting precipitated NH4VO3 is calcined to obtain V2O5, and the generated ammonia gas can be recovered in this process. The main chemical reactions occurring during the addition of the ammonium salt include:

[0089] VO3 - +NH4 + =NH4VO3;

[0090] The main chemical reactions that occur during the calcination of ammonium vanadate include:

[0091] 6NH4VO3=(NH4)2V6O 16 +4NH3+2H2O;

[0092] (NH4)2V6O 16 =2V₂O₄ + N₂ + 4H₂O;

[0093] 2V₂O₄ + O₂ = 2V₂O₅.

[0094] In this invention, aluminum is first extracted by carbonation decomposition (i.e., step S60), and then ammonium salt is added to extract vanadium. This process can remove some of the water in the solution during aluminum extraction, further increasing the vanadium content, which is beneficial for the precipitation of NH4VO3 in the vanadium extraction step. Furthermore, since the silicon content in the deep desilication solution is already very low or even non-existent, no silicon will precipitate along with the ammonium vanadate during the addition of ammonium salt. Therefore, the vanadium oxide obtained is of extremely high purity and can be directly used as a raw material in industrial products.

[0095] Step S30 above further includes: acid leaching the first water-leached residue to obtain calcium sulfate and acid leaching solution; the acid leaching solution is first aged and then filtered to obtain silica gel and aged desiliconization solution; sodium silicate obtained in step S30 is added to the aged desiliconization solution and polymerized to obtain polyaluminum ferric sulfate flocculant. In other words, the first water-leached residue can sequentially produce calcium sulfate, silica gel, and polyaluminum ferric sulfate flocculant through acid leaching, aging and silica extraction, and the polymerization step does not require the addition of any other external materials; the sodium silicate from step S30 can be used directly.

[0096] Specifically, in the acid leaching step, an acid solution is added to the first aqueous leaching residue and stirred. Calcium in the residue is converted to calcium sulfate precipitate, aluminum and iron are converted to aluminum sulfate and ferric sulfate, and silicon is mainly converted to orthosilicic acid. After filtration, acid leaching solution and acid leaching residue are obtained. The acid leaching solution mainly contains aluminum sulfate, ferric sulfate, and orthosilicic acid, while the acid leaching residue is calcium sulfate, which can be used as gypsum in various industries. The main chemical reactions occurring in the acid leaching step include:

[0097] Al 3+ +3H2SO4+aq=Al2(SO4)3+3H2O+aq;

[0098] Fe 3+ +3H2SO4+aq=Fe2(SO4)3+3H2O+aq;

[0099] CaSiO3+ H2SO4+aq =CaSO4↓+ H2O + SiO2+aq;

[0100] SiO2 + 2H2O + aq = H4SiO4 + aq.

[0101] The aging and silica extraction step involves aging the aforementioned acid leaching solution. In the acidic solution, the orthosilicic acid (H4SiO4) generated during the acid leaching process gradually polymerizes and condenses into dimers, trimers, and cyclic polymers, until a three-dimensional network structure with silica and a continuous aqueous medium as its framework is formed, i.e., silica hydrogel. After filtration, silica gel and the aging and desiliconizing solution are obtained. The silica gel obtained in this way has high purity and can be directly used in industry, such as the electronics industry. The aging and desiliconizing solution mainly includes aluminum sulfate and ferric sulfate. The chemical equations occurring in this process include:

[0102] H4SiO4→H2SiO3+H2O;

[0103] H2SiO3+mH2O→SiO2·(m+1)H2O.

[0104] In the hydrolysis polymerization step, sodium silicate slag from step S30 is added to the aged desiliconization liquor to adjust its acidity, thereby reducing the acidity and facilitating the hydrolysis polymerization reaction of aluminum ferric sulfate, ultimately yielding aluminum ferric sulfate flocculant. Specifically, the main reactions occurring during the hydrolysis stage include:

[0105] 2Fe₂(SO₄)₃ + 2nH₂O → 2Fe₂(OH)₃ n (SO4) 3-2n + nH2SO4;

[0106] 2 Al2(SO4)3 + 2nH2O → 2Al2(OH) n (SO4) 3-2n + nH2SO4;

[0107] The main reactions that occur during the aggregation phase include:

[0108] m[Fe2(OH)] n (SO4) 3-2n →[Fe2(OH)] n (SO4) 3-2n ] m ;

[0109] m[Al2(OH)] n (SO4) 3-2n →[Al2(OH)] n (SO4) 3-2n ] m .

[0110] The aluminum ferric sulfate flocculant obtained through the above steps meets the requirements of water purification agents and can be directly applied in industry. The infrared spectrum of the obtained aluminum ferric sulfate flocculant is shown below. Figure 3 As shown.

[0111] This invention mixes red mud and bauxite based on elemental content detection results, ensuring an aluminum-to-silicon ratio (A / S) greater than or equal to 1:1. Subsequent steps include calcination, water leaching, primary desilication, and deep desilication to extract high-purity calcium sulfate, a water purification agent, and silica gel. The process involves cyclical water leaching and primary desilication to minimize silicon content in the primary desilication solution, enriching aluminum and vanadium elements until the Al₂O₃ concentration in the primary desilication solution reaches 100-130 g / L and the A / S ratio is greater than 300 before proceeding to the deep desilication step. The deep desilication step includes a step to detect silicon content in the solution, adding magnesium salts or lime slurry based on the silicon content to convert silicon in the primary desilication solution into magnesium silicate or calcium silicate for separation. The resulting filtered deep desilication solution has an A / S content greater than 3000 and a VO₃ content of [missing information]. - The concentration of vanadium is greater than 2 g / L, so the aluminum element can be extracted more purely in the subsequent extraction process. The vanadium extraction process is not affected by silicon element. The remaining water extract after vanadium extraction is a sodium carbonate solution, which can be used as a calcining aid in the calcination of raw materials after concentration.

[0112] On the one hand, the combined treatment method for Bayer process red mud and low-grade bauxite provided by this invention comprehensively utilizes the waste red mud from aluminum smelting and low-grade bauxite. This not only improves the extraction purity of major elements in the treatment of the waste red mud from aluminum smelting, but also extracts high-purity rare metal vanadium. Simultaneously, it effectively utilizes low-grade bauxite, which has lacked effective utilization methods, allowing for the high-purity extraction of abundant aluminum, silicon, iron, and trace amounts of rare metal vanadium. The entire treatment process yields calcium sulfate, alumina, hydrated sodium aluminosilicate, and polyaluminum ferric sulfate flocculants. Chemicals such as calcium sulfate, silica gel, and vanadium pentoxide are directly usable industrial products. For example, calcium sulfate can be directly used in the cement, gypsum, and paper industries; alumina can be directly used in flame-retardant materials, dyes, abrasives, and pharmaceuticals; hydrated sodium aluminosilicate can be used in phosphorus-free detergents, and its strong surface adsorption capacity makes it an ideal adsorbent and desiccant; polyaluminum ferric sulfate flocculant can be directly used in water purification agents; silica gel can be used in the beer, edible oil, and electronics industries; and vanadium pentoxide can be used in metallurgy and chemical industries. These products have a wide range of applications, which will not be listed here.

[0113] On the other hand, the entire processing method of the present invention generates no solid or liquid waste, does not cause secondary pollution, is environmentally friendly, and all added additives can be effectively utilized. For example, the added alkaline calcining aid can be recycled, the added ammonium salt can be recovered into ammonia, and the added magnesium salt or lime milk can be used to generate magnesium silicate or calcium silicate. The hydrated sodium aluminosilicate produced in the middle can not only be used directly as a raw material for production in other industries, but can also be used to form polyaluminum ferric sulfate water purification agent by adding the intermediate product aluminum ferric sulfate acid leaching residue.

[0114] As can be seen, the processing method of this invention not only achieves full-scale treatment of red mud and low-grade bauxite, reducing the amount of red mud stockpiled and discharged, but also effectively utilizes the low-grade bauxite. The entire process generates no secondary waste, achieving harmless treatment of the red mud. Furthermore, the process is simple, requires no special equipment, and is easily industrialized. The comprehensive utilization rate of major and trace elements in red mud and low-grade bauxite is high, reaching a level of complete extraction. These elements or mixtures can be used as raw materials in industrial production, generating good economic benefits. This truly achieves comprehensive and highly integrated treatment of red mud and low-grade bauxite, greatly improving their overall utilization value.

[0115] It should be noted that although sodium aluminosilicate in the clinker is filtered out by water leaching as much as possible in S30, a small portion may still remain in the first water leaching solution. By using the combined treatment method of the present invention, the sodium aluminosilicate remaining in the first water leaching solution can be further separated in the primary desilication step and the deep desilication step, so as to better reduce the silicon content in the deep desilication solution and improve the purity of the subsequent vanadium extraction.

[0116] Preferably, in step S10, after Bayer red mud and low-grade bauxite are mixed in a certain proportion, they are ground to ensure that the two are fully and evenly mixed.

[0117] Specifically, Bayer process red mud and low-grade bauxite can be mixed in a mass ratio ranging from 0.5 to 3:1. That is, the preferred mass ratio of Bayer process red mud to low-grade bauxite is 0.5, 0.8, 1, 1.5, 1.8, 2.0, 2.3, 2.5, 2.8, or 3. Within this range, while ensuring an aluminum-to-silicon ratio greater than 1, it also allows the aluminum and silicon elements in the raw material to be converted into Na as much as possible during roasting. 1.95 Al 1.95 Si 0.05 O4, Na 1.75 Al 1.75 Si 0.25 In the form of O4, most of the aluminum element exists as aluminum ions during water leaching, so that more aluminum powder can be extracted by the subsequent generation of aluminum hydroxide. The remaining aluminum element can be separated out as NaAlSiO4 to form a water purification agent. At the same time, more low-grade bauxite can be used in the mixed raw materials, so that the low-grade bauxite can be utilized more effectively and the accumulation of red mud can be reduced.

[0118] In a preferred embodiment, the raw material is ground to obtain a mesh size of 300-500, such as 300, 320, 350, 370, 400, 430, 450, 480, or 500 mesh. Using raw material within this mesh range allows for sufficient reaction of the various elements during subsequent roasting and increases the reaction rate. Specifically, after grinding the mixed raw materials, a 300-500 mesh sieve can be used for sieving.

[0119] In a more preferred embodiment of the present invention, Bayer red mud and low-grade bauxite are mixed in a mass ratio of 0.5 to 3 to obtain a mixed raw material, which is then ground and sieved to obtain a raw material of 300 to 500 mesh.

[0120] In step S20, if quicklime is used as the alkaline calcination aid, the calcium content will increase, leading to an increase in the mass of calcium silicate generated during calcination. This affects the ratio of silicon to aluminum, reducing the subsequent desilication process. Furthermore, the generated calcium silicate will significantly increase the amount of acid used in the subsequent acid leaching process. In a preferred embodiment of the present invention, the alkaline calcination aid in step S20 is selected from at least one of sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate; more preferably, it is selected from at least one of sodium hydroxide and sodium carbonate. Using these alkaline calcination aids will not significantly affect the desilication process in subsequent steps, and can further improve the purity of the hydrated sodium aluminosilicate obtained from the desilication process. When the alkaline calcination aid includes sodium hydroxide, the iron in the raw material exists in the Na... 1.95 Al 1.95 Si 0.05 O4, Na 1.75 Al 1.75 Si 0.25 O4, sodium ferrite; when the alkaline calcination aid includes sodium carbonate, the iron element in the raw meal exists in Na. 1.95 Al 1.95 Si 0.05 O4, Na 1.75 Al 1.75 Si 0.25 O4.

[0121] To ensure that elements such as aluminum, silicon, calcium, and vanadium in the raw material can be transformed into their existing forms through the aforementioned chemical reaction, in step S20, the preferred mass ratio of raw material to alkaline additive is 1:(0.5~2), such as 1:0.5, 1:1, 1:1.5, or 1:2. To ensure sufficient chemical reaction of each element during calcination and to improve reaction efficiency, in step S20, the calcination temperature is 700~1100℃, and the calcination time is 0.5~1.5 hours. For example, the calcination temperature can be 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, or 1100℃, and the calcination time can be 0.5 hours, 0.8 hours, 1.0 hour, 1.2 hours, or 1.5 hours. In a preferred embodiment of the present invention, in step S20, the mass ratio of raw material to alkaline additive is 1:(0.5~2), the calcination temperature is 700~1100℃, and the calcination time is 0.5~1.5 hours. Preferably, after mixing the raw material and alkaline additive, the mixture is also sieved to obtain a 300~500 mesh mixture, which is then calcined.

[0122] In the water immersion step S30, the solid-liquid mass ratio of the raw materials is preferably 3-15, that is, the mass of the clinker and water in step S20 is mixed in a ratio of 3-15, such as a solid-liquid mass ratio of 3, 5, 8, 10, 12, 14, or 15, and then stirred. Using a mixing ratio within this range can not only make Na 1.95 Al 1.95 Si 0.05 O4, Na 1.75 Al 1.75 Si 0.25 The O4 fully hydrolyzes, allowing the two mixtures in the clinker to be leached out as much as possible in the form of NaAlSiO4. This also ensures that the concentrations of aluminum and vanadium in the first leaching solution are within a high range, which is beneficial for the subsequent separate extraction of aluminum and vanadium. More preferably, the leaching temperature is 20–90°C, and the leaching time is 5–30 minutes, such as leaching temperatures of 20°C, 25°C, 30°C, 40°C, 50°C, 60°C, 75°C, 80°C, or 90°C, and leaching times of 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes.

[0123] In the primary desilication step S30, red mud is added to the first aqueous leaching solution while stirring until the concentration of red mud in the solution reaches 10-40 g / L, at which point the addition of red mud is stopped. For example, the concentration of red mud can be 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, or 40 g / L, to separate a larger amount of silicon element through the red mud. The reaction temperature is set to 105-130℃, and the reaction time is 1-3 hours, such as 105℃, 110℃, 115℃, 120℃, 125℃, or 130℃, and the reaction time is 1 hour, 1.5 hours, or 3 hours, etc.

[0124] In step S50, magnesium salt or lime slurry is added and stirred, with the reaction temperature set above 90℃, such as 90℃, 95℃, 100℃, or 110℃. Heating can be done while stirring to ensure a complete reaction and precipitation. After precipitation stops, the mixture is allowed to stand for at least 0.5 hours, such as 30 minutes, 40 minutes, 50 minutes, 1 hour, 1.5 hours, or 2 hours. Finally, the mixture is filtered to obtain a deep desilication liquid and sodium silicate slag. By setting these conditions, almost all the remaining silicon in the primary desilication liquid can be converted into magnesium silicate or calcium silicate, thereby separating the silicon and better reducing the silicon content in the deep desilication liquid to ensure a silicon-to-aluminum ratio greater than 3000.

[0125] In step S50, after determining the silicon content in the primary desilication solution, magnesium salt is added to the primary desilication solution at a ratio of 1 to 1.5, such as a magnesium salt to silicon molar ratio of 1, 1.1, 1.2, 1.3, 1.4 or 1.5, to further separate the silicon element more thoroughly.

[0126] In step S60, the carbonation decomposition step, carbon dioxide is stopped when the concentration of aluminum oxide in the solution is less than 20 g / L. For example, if the concentration of aluminum oxide is 20 g / L, 18 g / L, 17 g / L, 15 g / L, 13 g / L, or 12 g / L, the carbon dioxide is stopped. This indicates that the aluminum element in the deep desilication solution is basically precipitated in the form of aluminum hydroxide. Using this method, it is possible to more directly determine that all the aluminum element in the solution has been converted. In step S60, the vanadium extraction step involves adding ammonium salt at a molar ratio of (1~2):1 to vanadium, and setting the reaction temperature to 20~30℃. For example, a molar ratio of 1:1, 1.5:1, or 2:1 can be selected to ensure that there is enough ammonium salt to convert vanadium into ammonium vanadate and precipitate. At the same time, a reaction temperature of 20℃, 23℃, 25℃, 28℃, or 30℃ can be set to provide the most suitable conditions for the reaction between ammonium salt and vanadium, so that the two can react fully, increase the content of ammonium vanadate produced, and better improve the utilization rate of vanadium in red mud.

[0127] In step S70, the calcination temperature of NH4VO3 is 450~600℃, such as 450℃, 480℃, 500℃, 530℃, 550℃, 580℃ or 600℃.

[0128] In step S31, acid leaching is performed using sulfuric acid until no precipitate is formed, at which point the addition of sulfuric acid is stopped. The concentration of sulfuric acid can be selected to be approximately 5 mol / L. In the hydrolysis-polymerization step, sodium silicate slag is added to the aged desilication solution mainly to adjust the pH value of the solution, which is beneficial to the hydrolysis-polymerization reaction. Specifically, the addition of sodium silicate slag is stopped when the mixture is weakly acidic. That is, the pH value of the solution is tested while adding silicate slag, and the addition of sodium silicate slag is stopped when the pH value is detected to be 4-6, such as 4, 5, or 6.

[0129] The aluminum hydroxide obtained in step S60 can be directly used in various industrial and pharmaceutical fields, or it can be further used to extract alumina. In a preferred embodiment of the present invention, the combined processing method further includes step S61: calcining the aluminum hydroxide obtained in step S60 to obtain alumina. Specifically, calcining the obtained aluminum hydroxide to obtain alumina can be used directly as an industrial raw material. The reactions that occur during calcination mainly include:

[0130] 2Al(OH)3 == Al2O3 + 3H2O↑.

[0131] In step S61, the preferred calcination temperature of aluminum hydroxide is 600~800℃, and the calcination time is 4~5 hours, such as 600℃, 650℃, 700℃, 750℃ or 800℃, and the calcination time is 4 hours, 4.5 hours or 5 hours.

[0132] The present invention also provides a combined processing system for Bayer process red mud and low-grade bauxite, used to implement the combined processing method described in any of the above embodiments; the combined processing system includes: a mixing device for mixing raw materials in steps S10, S20, S70, and S61; a calcining device for calcination in steps S10, S20, and S61; a mixing and reaction device for mixing and reacting raw materials in steps S30, S40, S50, S60, and S31; and a filtration and separation device for solid-liquid separation in steps S30, S40, S50, S60, and S31; wherein the mixing device, calcining device, mixing and reaction device, and filtration and separation device are connected by a conveying device or pipeline, and the products obtained in each step can be conveyed sequentially through the conveying device or pipeline, so that the entire system can achieve automated processing.

[0133] Specifically, the mixing device may include a mixer; the calcination device may include a rotary kiln; the mixing reaction device may include a pressure reactor with a first stirring component and a heating component to better control the temperature of the reaction environment during the reaction; and the filtration and separation device may include a filter press, a vacuum filter, and / or a centrifuge.

[0134] The above-described combined processing method of the present invention will now be described with reference to specific embodiments.

[0135] Example 1

[0136] In this embodiment, the red mud sample was taken from a location in Henan Province. The main chemical components of the red mud, determined by conventional chemical analysis methods, were: Al₂O₃ 21.27%, SiO₂ 17.42%, Fe₂O₃ 9.97%, CaO 22.27%, Na₂O 4.89%, MgO 1.96%, and V₂O₅ 0.085%. The main phase compositions were perovskite-ABO₃, brookite-TiO₂, hematite-Fe₂O₃, dolomite-CaMg(CO₃)₂, garnet-A₃B₂(SiO₄)₃, quartz-SiO₂, and muscovite-KAl₂(AlSi₃O₃). 10 Vanadium exists in a isomorphous form within the muscovite lattice as )(OH)₂. The main chemical components of low-grade bauxite are: Al₂O₃ 34.93%, SiO₂ 19.17%, TFe 23.25%, TiO₂ 3.14%, and CaO 0.43%.

[0137] The combined processing method in this embodiment includes the following steps:

[0138] S10: Detect the aluminum and silicon content in the red mud and bauxite respectively, mix the red mud and bauxite in a 1:1 ratio, and grind them through a 300-mesh sieve to obtain raw material.

[0139] S20: Mix the mixture with sodium carbonate at a ratio of 1:0.5 and calcine at 900℃ for 1 hour to obtain the cooked material.

[0140] S30: With a solid-liquid mass ratio of clinker to water of 7, stir at room temperature for 10 minutes, filter and separate to obtain the first water leaching solution and the first water leaching residue. Then add Bayer red mud to the first water leaching solution and stir until the concentration of the red mud in the solution is 10 g / L. Stop adding red mud, age, and filter to obtain sodium silicate slag and primary desilication liquid.

[0141] S40: The primary desilication liquid is used as part of the liquid in the water immersion treatment in step S30. It is mixed with the clinker in the same proportion as in S30 and the water immersion step and primary desilication step are repeated. When the Al2O3 concentration in the primary desilication liquid after the cyclic treatment reaches 100g / L and the aluminum-silicon content ratio is 3:10, the cyclic treatment is stopped. After 2 cycles, the process proceeds to step S50.

[0142] S50: The silicon content in the primary desilication solution was determined. Based on the determined silicon content, magnesium salt was added to the primary desilication solution. After filtration, a deep desilication solution and magnesium silicate were obtained. The aluminum-silicon ratio in the deep desilication solution was tested again and found to be 3500. VO3 - The concentration is 3 g / L;

[0143] S60: Carbon dioxide is introduced into the deep desilication solution for carbonation decomposition. The process is stopped when the concentration of aluminum oxide in the solution reaches 20 g / L. Then, solid-liquid separation is performed to obtain aluminum hydroxide and a second aqueous extract. NH4Cl is then added to the second aqueous extract and stirred. The solution is filtered to obtain NH4VO3 and a third aqueous extract. NH4VO3 is calcined at 450°C to obtain V2O5, while recovering the ammonia gas generated during calcination. The crystals obtained from the concentrated third aqueous extract are used as the alkaline calcination aid in step S20.

[0144] S31: Add 5 mol / L sulfuric acid to the first water leaching residue obtained in step S30 for acid leaching treatment to obtain calcium sulfate and acid leaching solution. After aging treatment, the acid leaching solution is filtered to obtain silica gel and aged desiliconization solution. Add the sodium silicate slag obtained in step S30 to the aged desiliconization solution to hydrolyze and polymerize aluminum ferric sulfate in the solution to obtain polyaluminum ferric sulfate flocculant.

[0145] S61: The aluminum hydroxide obtained in step S60 is calcined at 600°C for 5 hours to obtain aluminum oxide.

[0146] Analysis and testing showed that the calcium sulfate, sodium aluminosilicate hydrate, silica gel, aluminum ferric sulfate flocculant, and aluminum oxide obtained in the combined treatment method of Example 1 all met the relevant industry standards; the purity of vanadium pentoxide obtained from the trace element vanadium was above 95%, which also reached the industrial grade of metallic vanadium.

[0147] Those skilled in the art will understand that, without conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0148] 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 the combined processing of Bayer process red mud and low-grade bauxite, wherein both the red mud and bauxite contain aluminum, silicon, iron, calcium, and vanadium; characterized in that, Including the following steps: S10: Detect the aluminum and silicon content in the red mud and bauxite respectively, determine the mixing ratio of red mud and bauxite based on the detection results, mix the red mud and bauxite according to the mixing ratio to obtain raw material, wherein the mixing ratio makes the aluminum-silicon content ratio in the raw material greater than 1; S20: Add an alkaline calcination aid to the raw material and calcine it to obtain clinker; S30: The clinker is subjected to water leaching treatment, followed by solid-liquid separation to obtain a first water leaching solution and a first water leaching residue; the red mud is added to the first water leaching solution, aged, and filtered to obtain sodium silicate slag and primary desiliconization solution; the first water leaching residue is subjected to acid leaching treatment to obtain calcium sulfate and acid leaching solution, the acid leaching solution is aged and filtered to obtain silica gel and aged desiliconization solution, and the sodium silicate slag is added to the aged desiliconization solution to obtain polyaluminum ferric sulfate flocculant; S40: Return the primary desilication solution to step S30 for water immersion treatment, and repeat the water immersion desilication multiple times until the Al2O3 concentration in the primary desilication solution reaches 100~130g / L and the aluminum-silicon content ratio is greater than 300, and then proceed to step S50. S50: Determine the silicon content in the primary desilication solution. Add magnesium salt or lime slurry to the primary desilication solution, filter, and obtain a deep desilication solution and magnesium silicate, or a deep desilication solution and calcium silicate. The amount of magnesium salt or lime slurry added is determined based on the measured silicon content to ensure that the aluminum-silicon ratio in the deep desilication solution is greater than 3000. - The concentration is greater than 2 g / L; S60: Carbon dioxide is introduced into the deep desilication solution for carbonation decomposition, and solid-liquid separation is performed to obtain aluminum hydroxide and a second aqueous extract; then ammonium salt is added to the second aqueous extract and stirred, filtered to obtain NH4VO3 and a third aqueous extract, the NH4VO3 is calcined to obtain V2O5, and the ammonia gas generated during calcination is recovered; the crystals obtained by concentrating the third aqueous extract are returned to step S20 as an alkaline calcination aid.

2. The method according to claim 1, characterized in that, In step S50, magnesium salt or lime milk is added and stirred, and the reaction temperature is set to be greater than 90°C to produce precipitation. After the precipitation stops, the mixture is allowed to stand for at least 0.5 hours and then filtered to obtain the deep desilication liquid and the magnesium silicate, or to obtain the deep desilication liquid and calcium silicate.

3. The method according to claim 1, characterized in that, In step S50, magnesium salt is added to the primary desilication solution at a ratio of magnesium salt to silicon of 1 to 1.

5.

4. The method according to claim 1, characterized in that, In step S60, carbon dioxide is stopped during carbonation decomposition when the concentration of aluminum oxide in the solution is less than 20 g / L.

5. The method according to claim 1, characterized in that, In step S60, the ammonium salt is added according to a molar ratio of ammonium salt to vanadium of (1~2):1, and the reaction temperature is set to 20~30℃. The ammonium salt is selected from NH4Cl.

6. The method according to claim 1, characterized in that, In step S60, the calcination temperature of NH4VO3 is 450~600℃.

7. The method according to claim 1, characterized in that, In step S30, the acid leaching treatment is carried out with sulfuric acid until no precipitate is produced and the addition of sulfuric acid is stopped; sodium silicate slag is added to the aged desiliconization liquid until the mixture becomes weakly acidic and then stops.

8. The method according to claim 1, characterized in that, It also includes the following steps: S61, the aluminum hydroxide obtained in step S60 is calcined to obtain aluminum oxide, wherein the calcination temperature of the aluminum hydroxide is 600~800℃ and the calcination time is 4~5 hours.

9. The method according to claim 1, characterized in that, In step S10, the red mud and bauxite are mixed in a mass ratio of 0.5 to 3:1 to obtain a mixed raw material, which is then ground to obtain a raw meal of 300 to 500 mesh. In step S20, the alkaline calcining aid is selected from at least one of sodium hydroxide and sodium carbonate. The mass ratio of the raw meal to the alkaline calcining aid is 1:(0.5 to 2), the calcination temperature is 700 to 1100°C, and the calcination time is 0.5 to 1.5 hours.

10. The method according to claim 1, characterized in that, In step S30, the solid-liquid mass ratio of the raw material in the water immersion treatment is 3~15, the water immersion treatment temperature is 20~90℃, and the immersion time is 5~30 minutes.

11. The method according to any one of claims 1-10, characterized in that, In step S30, the red mud is added to the first aqueous solution while stirring until the concentration of the red mud in the solution is 10~40g / L, at which point the addition of the red mud is stopped. The reaction temperature is 105~130℃ and the reaction time is 1~3 hours.

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