Clean process for selective simultaneous extraction of aluminum and vanadium from bayer red mud

Abstract

The application provides a clean process for selectively and synchronously extracting aluminum and vanadium from Bayer red mud, comprising the following steps: pretreating the Bayer red mud to obtain red mud powder; uniformly mixing the red mud powder with a sodiumizing agent and a fluorine-containing activator, and performing medium-low temperature calcination activation to obtain sodiumized clinker; performing hot alkali leaching on the sodiumized clinker, and then performing solid-liquid separation to obtain a leaching solution and a leaching tailing; performing multi-stage countercurrent extraction on the leaching solution by using a composite organic phase, selectively extracting vanadate into the organic phase, and obtaining a vanadium-rich organic phase and a vanadium-removed sodium aluminate aqueous phase after phase separation; performing carbonization decomposition on the vanadium-removed sodium aluminate aqueous phase, precipitating aluminum hydroxide, and calcining to obtain aluminum oxide; performing stripping on the vanadium-rich organic phase by using a dilute alkali solution, obtaining a sodium vanadate aqueous solution, and preparing vanadium pentoxide by ammoniation, vanadium precipitation and calcination. The application realizes efficient and collaborative recovery of aluminum and vanadium by coupling medium-low temperature calcium fluoride activation and sodiumizing calcination with direct extraction of vanadium in an alkaline system.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and hydrometallurgical technology in the alumina industry, and in particular to a clean process for selective and simultaneous extraction of aluminum and vanadium from Bayer red mud. Background Technology

[0002] Bayer red mud is a highly alkaline industrial waste generated during alumina production. my country's annual discharge exceeds 100 million tons, with a cumulative stockpile of over 1.6 billion tons. Long-term stockpiling has led to serious environmental problems such as soil salinization and groundwater pollution. Red mud is rich in valuable components such as Al2O3 (12%–22%) and V2O5 (0.1%–0.3%), possessing significant secondary resource recovery value. However, an economically feasible, clean, and efficient industrial extraction process has not yet been developed.

[0003] Existing technologies for recovering aluminum and vanadium from red mud mainly fall into two categories. One is the "sodium roasting-alkali leaching aluminum extraction" route, where aluminum enters the alkaline solution in the form of sodium aluminate, while vanadium mostly remains in the dealuminizing slag, requiring separate acid leaching extraction. The mother liquors from the two processes are incompatible, resulting in double the consumption of alkali and acid. The other is the "direct acid leaching" route, which can dissolve aluminum and vanadium in one step, but the free alkali in the red mud consumes a large amount of acid, and the generated gypsum gel severely degrades filtration performance, leading to high investment in equipment corrosion protection. Neither route can achieve closed-loop circulation of the leaching mother liquor, resulting in large volumes of wastewater discharge.

[0004] In the roasting and activation stage, conventional sodium roasting temperatures reach as high as 850-950℃, with energy consumption accounting for over 40% of the total process cost. Furthermore, because vanadium is hosted in stable phases such as perovskite and andradite, even with high-temperature roasting, only 30%-45% of the vanadium is converted into water-soluble sodium vanadate. A large amount of vanadium is lost with the dealumination slag, making industrial-scale recovery difficult. In the vanadium separation stage, the vanadate and aluminate ions in the sodium aluminate concentrate obtained from alkaline leaching have similar properties, making high-selectivity separation difficult using conventional precipitation, ion exchange, and solvent extraction methods. During carbon or seed fractionation to prepare aluminum hydroxide, vanadium is entrained and co-precipitated, resulting in a V₂O₅ content in the product alumina generally exceeding 0.01%, far higher than the metallurgical grade standard (<0.005%). Therefore, in industry, sodium aluminate solution must be acidified to pH 2-3 before vanadium extraction is carried out using amine extractants. However, the acidification process consumes a large amount of sulfuric acid, and subsequent neutralization produces a large amount of sodium sulfate / gypsum mixed salt residue. For every ton of red mud treated, 0.3-0.5 tons of solid waste are added, which seriously weakens the environmental benefits of red mud reduction. In addition, acidification causes sodium aluminate to decompose and release aluminum hydroxide colloid, resulting in aluminum entrainment loss and emulsification of the extraction system.

[0005] In summary, existing technologies lack an integrated process that simultaneously achieves efficient low-temperature activation and leaching of aluminum and vanadium under alkaline conditions throughout the entire process, selective separation of vanadate without acidification, and closed-loop recycling of the sodium carbonate mother liquor. Developing a low-carbon, clean, and economical method for the co-extraction of aluminum and vanadium from Bayer red mud is urgently needed.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a clean process for the selective and simultaneous extraction of aluminum and vanadium from Bayer red mud, which solves at least one of the problems mentioned in the background art.

[0008] In one aspect, this invention provides a cleaning process for the selective and simultaneous extraction of aluminum and vanadium from Bayer red mud, comprising the following steps: S1: Pre-treat Bayer red mud to obtain red mud powder; S2: The red mud powder is mixed evenly with sodium-forming agent and fluorine-containing activator, and the resulting mixture is activated by medium-low temperature roasting at 350~550℃ to obtain sodium-formed clinker; S3: The sodium-treated clinker is subjected to hot alkaline leaching with alkaline mother liquor. After leaching, solid and liquid are separated to obtain an aluminum-vanadium mixed alkaline leaching solution and leaching tailings enriched with titanium and iron. S4: A composite organic phase consisting of a tertiary amine extractant, a neutral phosphorus extractant, and a diluent is used to perform multi-stage countercurrent extraction on the aluminum-vanadium mixed alkaline leachate, selectively extracting vanadate into the organic phase, and obtaining a vanadium-rich organic phase and a sodium aluminate devanadium aqueous phase after phase separation. S5: Carbonize and decompose the aqueous phase of the sodium aluminate devanadiumate to precipitate aluminum hydroxide, and calcine to obtain metallurgical grade alumina with low vanadium impurities. S6: The vanadium-rich organic phase is back-extracted using a dilute alkaline solution to obtain an aqueous solution of sodium vanadate, which is then ammonified to precipitate vanadium and calcined to obtain industrial vanadium pentoxide.

[0009] The present invention has at least the following beneficial effects: (1) Aluminum and vanadium are recovered simultaneously, alkaline medium throughout the process, sodium carbonate mother liquor generated by carbonization can be recycled and reused, no acidification and neutralization are required, sodium salt solid waste is greatly reduced, wastewater is recycled in a closed loop, clean and low carbon. (2) Using medium-low temperature sodium calcination at 350~550℃, combined with calcium fluoride activator, energy consumption is reduced by more than 40% compared with traditional high temperature calcination above 850℃. (3) Alkaline selective extraction for vanadium removal solves the problem of difficult separation of aluminum and vanadium co-solution and the problem of excessive vanadium in alumina; (4) The sodium carbonate mother liquor is entirely internally circulated, reducing the consumption of soda ash reagent by 30%; (5) The process is highly flexible. Enterprises can put only the aluminum and vanadium extraction unit into operation at this stage, and retain the aluminum and vanadium slag to build titanium, iron and scandium extraction processes later, which is suitable for phased plant construction planning. Attached Figure Description

[0010] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0011] Figure 1 This is a flowchart of the cleaning process for selective and simultaneous extraction of aluminum and vanadium from Bayer red mud in an embodiment of the present invention. Detailed Implementation

[0012] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0013] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form includes the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0014] It should be noted that if the text uses terms such as "first" or "second", these terms are only used to distinguish similar objects and should not be interpreted as indicating or implying their relative importance, order of precedence, or implicitly indicating the number of technical features indicated. It should be understood that the data in the descriptions of "first" and "second" can be interchanged where appropriate.

[0015] Throughout the accompanying drawings, identical elements are represented by the same or similar reference numerals. Conventional structures or configurations may be omitted where they might cause confusion in understanding the invention. Furthermore, the shapes, dimensions, and positional relationships of the components in the drawings do not reflect actual size, scale, or actual positional relationships. Additionally, any reference symbols placed within parentheses in this invention should not be construed as limiting the scope of the invention.

[0016] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] This invention provides a cleaning process for the selective and simultaneous extraction of aluminum and vanadium from Bayer red mud, such as... Figure 1 As shown, it includes the following steps: S1: Pre-treat Bayer red mud to obtain red mud powder; S2: The red mud powder is mixed evenly with the sodium-containing agent and the fluorine-containing activator. The resulting mixture is then subjected to medium-low temperature roasting activation at 350~550℃, for example, 355℃, 370℃, 395℃, 420℃, 450℃, 490℃, 530℃, etc. At low temperature, the fluorine-containing activator destroys the dense lattice of vanadium perovskite, causing the aluminum and vanadium in the red mud to be converted into soluble sodium aluminate and sodium vanadate, respectively, to obtain sodium-containing clinker. S3: The sodium-treated clinker is subjected to hot alkaline leaching with alkaline mother liquor. After leaching, solid and liquid are separated to obtain an aluminum-vanadium mixed alkaline leaching solution and leaching tailings enriched with titanium and iron. S4: A composite organic phase consisting of a tertiary amine extractant, a neutral phosphorus extractant, and a diluent is used to perform multi-stage countercurrent extraction on the aluminum-vanadium mixed alkaline leachate, selectively extracting vanadate into the organic phase, and obtaining a vanadium-rich organic phase and a sodium aluminate devanadium aqueous phase after phase separation. S5: Carbonize and decompose the aqueous phase of the sodium aluminate devanadiumate to precipitate aluminum hydroxide, and calcine to obtain metallurgical grade alumina with low vanadium impurities. S6: The vanadium-rich organic phase is back-extracted using a dilute alkaline solution to obtain an aqueous solution of sodium vanadate, which is then ammonified to precipitate vanadium and calcined to obtain industrial vanadium pentoxide.

[0018] To overcome the shortcomings of existing technologies such as stepwise aluminum and vanadium recovery, acid-base switching for salt production, low vanadium leaching rate, excessive alumina impurities, and high roasting energy consumption, this invention provides an integrated process of full-process alkaline medium, medium-low temperature composite sodium activation-alkali leaching-alkali extraction, which simultaneously recovers metallurgical grade alumina and industrial vanadium pentoxide with high yield, and the sodium carbonate mother liquor is recycled in a closed loop, resulting in a significant reduction in waste.

[0019] The present invention discloses a clean process for the simultaneous recovery of aluminum and vanadium from Bayer red mud. First, red mud is prepared with a sodium-containing agent and a fluorine-containing activator (such as soda ash and calcium fluoride) and subjected to low-temperature sodium roasting at 350-550°C. This low-temperature activation simultaneously dissolves aluminum and vanadium, significantly reducing energy consumption compared to traditional high-temperature sodium roasting above 850°C. The aluminum leaching rate is ≥86%, and the vanadium alkali leaching rate is ≥82%. Hot alkali leaching yields a mixed alkaline mother liquor of aluminum and vanadium. Vanadium is selectively extracted in a strongly alkaline system using an N235-TBP composite extractant. Aqueous phase carbonization produces a recycled sodium carbonate mother liquor, which is then used to prepare high-purity alumina. Organic phase reverse extraction precipitates vanadium to produce V2O5. The entire process involves a closed-loop recycling of the sodium carbonate mother liquor, eliminating the need for acid-base neutralization to produce salt. Roasting energy consumption is extremely low, and aluminum and vanadium recovery rates are high. The process can be implemented in stages, and the dealuminized vanadium slag is enriched with titanium and iron, facilitating subsequent multi-metal comprehensive extraction. This method is suitable for the industrial application of red mud resource utilization in alumina plants.

[0020] In particular, the in-situ selective extraction of vanadium-free sodium aluminate mother liquor in an alkaline system directly uses a tertiary amine-modified neutral phosphorus composite extractant to selectively extract vanadate in a strongly alkaline sodium aluminate solution, with sodium aluminate remaining completely in the aqueous phase; this solves the problems of salt production and alumina co-extraction loss in acidic extraction, with a vanadium single-stage extraction rate ≥91% and aluminum entrainment loss <1.2%.

[0021] In some embodiments, step S1, the Bayer red mud pretreatment includes drying, crushing, and grinding; the particle size of the red mud powder is 200 mesh or less (e.g., particle size less than 0.074 mm). By drying, crushing, and grinding the Bayer red mud and controlling the particle size to 200 mesh or less, the specific surface area and reactivity of the red mud particles are effectively increased, making the solid-phase reaction between the sodium-oxidizing agent and the red mud components more complete and uniform during the subsequent sodium-oxidizing roasting process, thus laying a raw material foundation for the efficient leaching of valuable metals. The contents of components Al2O3, V2O5, CaO, and TiO2 can be detected for later use.

[0022] In some embodiments, in step S2, the sodizing agent is one or more of sodium carbonate, sodium hydroxide, and sodium bicarbonate, and the fluorine-containing activator is one or two of calcium fluoride and sodium fluoride. Using sodium carbonate or similar substances as the sodizing agent in combination with calcium fluoride and / or sodium fluoride as the fluorine-containing activator can significantly reduce the decomposition temperature of silicate minerals during roasting, promote the directional conversion of valuable metals such as aluminum and vanadium in red mud into soluble sodium salts, and simultaneously, the introduction of calcium fluoride and / or sodium fluoride can effectively disrupt the stable aluminosilicate crystal structure, thereby improving subsequent leaching efficiency.

[0023] In some embodiments, in step S2, the mass ratio of red mud powder, sodium leaching agent, and fluorine-containing activator is 100:(18~24):(1.2~2.5), for example, 100:20:1.5, 100:22:2.1, 100:19:2.4, etc., preferably 100:(20~22):(1.5~2.0). By optimizing the mass ratio of the three components, the waste of raw materials and the burden of subsequent mother liquor treatment caused by excessive sodium leaching agent and activator are avoided while ensuring sufficient activation of aluminum and vanadium. Under the preferred ratio, the aluminum leaching rate can reach more than 90% and the vanadium leaching rate can reach more than 86%, achieving the best balance between recovery rate and production cost.

[0024] Appropriately extending the roasting time helps to fully dissociate the sparingly soluble mineral phase in the red mud and to carry out the sodiumization reaction completely. However, in order to balance the activation effect and production efficiency, in some embodiments, the low-temperature roasting activation time in step S2 is 40~180 min, preferably 150~180 min.

[0025] In some embodiments, the low-temperature calcination activation temperature in step S2 is 480~520℃. At this temperature, calcium fluoride exhibits the most significant activation effect, effectively disrupting the aluminosilicate structure while preventing the volatilization loss of valuable metals.

[0026] In some embodiments, in step S2, the low-temperature calcination activation is carried out in an air atmosphere. Calcination in an air atmosphere eliminates the need for additional atmosphere control or the introduction of protective gases, simplifying operation, reducing equipment costs, and facilitating large-scale industrial production. Simultaneously, the air atmosphere is sufficient to meet the oxygen requirements of the sodium sulfonation reaction, ensuring the smooth progress of the activation reaction.

[0027] In some embodiments, the low-temperature calcination activation in step S2 is carried out in a rotary kiln or a tunnel kiln, which confirms that the method of the present invention has good feasibility for industrial scale-up.

[0028] In some embodiments, in step S3, the alkaline mother liquor is, preferably, sodium carbonate mother liquor. Using sodium carbonate mother liquor as the circulating leaching medium effectively extracts sodium aluminate and sodium vanadate from the roasted clinker, while also achieving the recycling of the mother liquor, significantly reducing wastewater discharge and alkali consumption. This recycling system forms a closed-loop alkali cycle with the upstream sodium roasting process, significantly reducing the raw material consumption and environmental burden of the entire process.

[0029] In some embodiments, in step S3, the liquid-to-solid ratio during leaching is (4~6):1, for example, 4.5:1, 5.2:1, 5.8:1, etc. A suitable liquid-to-solid ratio ensures good fluidity and mass transfer efficiency in the leaching system, allowing valuable metals to fully dissolve into the liquid phase, while avoiding the problems of excessively large leaching solution volume and increased energy consumption for subsequent concentration caused by an excessively high liquid-to-solid ratio. Within the above-mentioned liquid-to-solid ratio range, the leaching rates of aluminum and vanadium can reach ideal levels.

[0030] In some embodiments, in step S3, the leaching temperature is 85-95°C, and the leaching time is 90-120 min. Under the above temperature and time conditions, the soluble sodium aluminate and sodium vanadate in the calcined clinker can be fully dissolved into the liquid phase, and the leaching reaction tends to be complete. Too low a temperature or too short a time will result in insufficient leaching, while too high a temperature or too long a time will increase energy consumption and have limited effect on improving the leaching rate. The above-mentioned range of the present invention takes into account both leaching effect and energy consumption control.

[0031] In some embodiments, in step S3, leaching is carried out under stirring, which can enhance the mass transfer and mixing effect between the solid and liquid phases, avoid the sedimentation and agglomeration of solid particles, ensure that the soluble components in the roasted clinker are in full contact with the leachate, thereby improving the leaching rate and leaching percentage and shortening the leaching time.

[0032] In some embodiments, in step S3, after leaching is completed, solid-liquid separation is achieved by plate and frame filtration, which has the advantages of high separation efficiency, good filtrate clarity, and suitability for large-scale production.

[0033] In some embodiments, in step S4, the volume composition of the composite organic phase is: 12%~18% tertiary amine extractant, for example 13%, 15%, 15.9%, 17%, etc.; 6%~10% neutral phosphorus extractant, for example 6.8%, 7.5%, 8.6%, 9.5%, etc.; and the remainder is diluent. This composite extraction system utilizes the high selective extraction capability of tertiary amine extractants for vanadate anions, combined with the synergistic effect of neutral phosphorus extractants, to achieve highly efficient and selective separation of vanadium and aluminum in a strongly alkaline system. By controlling the extractant ratio, the co-extraction of aluminum and other impurity ions can be effectively suppressed while ensuring the vanadium extraction rate (≥90%), thus ensuring the purity of the alumina product obtained in the subsequent carbonization process.

[0034] In some embodiments, in step S4, the ratio of the extracted organic phase to the aqueous phase (O / A) is 1:(3~5), for example, 1:3.5, 1:4.2, 1:4.8, etc. Optimized ratio conditions ensure efficient vanadium extraction with low organic phase usage, reducing organic phase input and loss. Too low a ratio (too little organic phase) leads to incomplete vanadium extraction, while too high a ratio (too much organic phase) increases costs and may cause emulsification. A preferred ratio balances extraction efficiency and economy.

[0035] In some embodiments, in step S4, countercurrent extraction is performed at room temperature. Room temperature extraction eliminates the need for heating, significantly reducing energy consumption and operating costs. It also avoids potential degradation of the extractant and the formation of a third phase under high-temperature conditions, which is beneficial for the long-term stable operation and recycling of the organic phase.

[0036] In some embodiments, in step S4, the countercurrent extraction has 3 to 5 stages, which can achieve efficient vanadium recovery with reasonable equipment investment and operating costs.

[0037] In some embodiments, in step S4, the total alkali concentration of the aluminum-vanadium mixed alkaline leaching solution is 180~240 g / L, for example, 185 g / L, 196 g / L, 205 g / L, 215 g / L, 224 g / L, 235 g / L, etc. Within the above-mentioned total alkali concentration range, vanadium is mainly present as VO3. - and V2O7 4- The presence of sodium aluminate in extractable forms facilitates efficient extraction by tertiary amine extractants. Simultaneously, suitable alkalinity ensures the stability of sodium aluminate in solution, preventing hydrolysis and precipitation, thus creating favorable conditions for subsequent carbonization and decomposition to produce high-purity aluminum hydroxide.

[0038] In some embodiments, in step S4, the tertiary amine extractant is trioctylamine (N235), the neutral phosphorus extractant is tributyl phosphate (TBP), and the diluent is sulfonated kerosene. Trioctylamine (N235) exhibits excellent selective extraction capability for vanadate, tributyl phosphate (TBP), as a synergistic extractant, can significantly improve extraction efficiency and phase separation performance, and sulfonated kerosene, as a diluent, has the characteristics of high flash point, low toxicity, and good stability. The composite organic phase formed by the combination of these three components exhibits good extraction performance and cycle life in a strongly alkaline system.

[0039] In some embodiments, in step S5, carbonization decomposition is carried out by introducing CO2. Using CO2 gas for carbonization decomposition allows for precise adjustment of the solution pH to the target range by controlling the amount of CO2 introduced, achieving selective decomposition of sodium aluminate and precipitation of aluminum hydroxide, while avoiding the introduction of other impurity ions.

[0040] In some embodiments, in step S5, the carbonization decomposition temperature is 50~65℃, for example 53℃, 58℃, 63℃, etc., and the final pH value of carbonization is 10.5~11.5, for example 10.8, 11, 11.3, etc. At a temperature of 50~65℃, the carbonization decomposition reaction rate is moderate, and the aluminum hydroxide grains grow well, facilitating subsequent filtration and washing. Controlling the final pH value to 10.5~11.5 ensures sufficient precipitation of aluminum ions while effectively inhibiting the co-precipitation of impurities such as silicon and iron, which is a key control parameter to ensure the purity of the alumina product (vanadium impurities <0.005%).

[0041] In some embodiments, in step S5, the obtained aluminum hydroxide is washed and then calcined at 1100-1300°C to produce metallurgical-grade alumina with a vanadium impurity content of <0.005%. At the high-temperature calcination of 1100-1300°C, the aluminum hydroxide is completely converted to α-Al₂O₃, and residual volatile components and trace impurities are further removed. The vanadium impurity content in the obtained product is less than 0.005%, fully meeting the quality standards for metallurgical-grade alumina, thus achieving high-value recovery of aluminum resources from red mud.

[0042] In some embodiments, in step S5, the sodium carbonate mother liquor obtained from carbonation decomposition is concentrated and then returned to steps S2 and / or S3 for recycling. The carbonation mother liquor contains a large amount of sodium carbonate; after concentration, it is returned to the sodium roasting process and / or alkaline leaching process for recycling, achieving internal recycling and zero discharge of alkali resources. This recycling strategy significantly reduces the amount of sodium carbonate required for external replenishment, lowers raw material costs, and avoids the discharge of high-salt wastewater, embodying the design concept of green chemical engineering.

[0043] In some embodiments, in step S6, the dilute alkaline solution is a dilute sodium hydroxide solution. Sodium hydroxide solution is used as the stripping agent, through OH... - The ion exchange reaction with vanadate ions in the supported organic phase allows for efficient back-extraction of vanadium from the organic phase to the aqueous phase, generating a sodium vanadate solution. The sodium hydroxide back-extraction system is simple, efficient, and compatible with subsequent ammoniation precipitation of vanadium; furthermore, the back-extracted organic phase is easily regenerated and recycled.

[0044] In some embodiments, in step S6, the concentration of the dilute sodium hydroxide solution is 1.5~2.5 mol / L, for example, 1.8 mol / L, 2.2 mol / L, etc. Sodium hydroxide solutions within this concentration range can provide sufficient OH-. - The concentration was optimized to ensure sufficient vanadium back-extraction (back-extraction rate ≥ 96%) while avoiding increased alkali consumption and subsequent acid consumption due to excessively high concentrations. The optimized concentration range achieved a good balance between back-extraction efficiency and reagent consumption.

[0045] In some embodiments, in step S6, countercurrent back-extraction is employed, with two or more stages. Multi-stage countercurrent back-extraction enables efficient vanadium transfer and deep regeneration of the organic phase with fewer stages. Two or more stages of countercurrent back-extraction ensure that the residual vanadium content in the organic phase is minimized after back-extraction, which is beneficial for the recycling of the organic phase and the overall improvement of vanadium recovery rate.

[0046] In some embodiments, in step S6, the back-extraction ratio O / A is (3~5):1, for example, 3.5:1, 4:1, 4.5:1, etc. Controlling the ratio O / A to (3~5):1 during the back-extraction process allows for vanadium enrichment with a smaller aqueous phase volume, resulting in a higher concentration of sodium vanadate solution, which is beneficial for subsequent ammoniation precipitation of vanadium. Under this ratio condition, the back-extraction efficiency is high, the two-phase separation effect is good, and emulsification is avoided.

[0047] In some embodiments, in step S6, the organic phase after back-extraction is washed and regenerated and then recycled for the extraction process in S4, thereby significantly reducing the consumption cost of the extractant.

[0048] In some embodiments, step S6, vanadium precipitation by ammonium salt and calcination, includes: adding ammonium salt to an aqueous sodium vanadate solution to precipitate vanadium; washing the resulting vanadium precipitate and calcining it at 500-600°C to obtain a vanadium pentoxide product with a purity ≥98.5%. Through the process route of ammonium salt precipitation—washing—calcination, an aqueous sodium vanadate solution can be converted into a high-purity vanadium pentoxide product. Under calcination conditions of 500-600°C, ammonium vanadate completely decomposes into V₂O₅, while removing residual ammonium salt and moisture. The resulting product has a purity of over 98.5%, meeting the quality standards for industrial-grade vanadium pentoxide and realizing high added value from vanadium resources in red mud.

[0049] In some embodiments, the leaching tailings enriched with ferrotitanium obtained in step S3 are stored separately as raw materials for subsequent stepwise extraction of titanium and iron. Valuable metals such as titanium and iron are significantly enriched in the leaching tailings. Separate storage avoids resource dispersion and environmental pollution caused by mixing with large amounts of red mud, while also preserving high-grade raw materials for subsequent stepwise extraction of titanium and iron. This strategy achieves graded recovery and full resource utilization of multiple metals such as aluminum, vanadium, titanium, and iron in red mud, aligning with the core concept of a circular economy.

[0050] This invention addresses two key aspects. First, it involves roasting red mud with soda ash and a small amount of calcium fluoride as an activator at a low to medium temperature of 350-550°C. Under these low-temperature conditions, calcium fluoride disrupts the dense lattice of vanadium perovskite, simultaneously converting aluminum and vanadium into soluble sodium aluminate and sodium vanadate. Compared to traditional high-temperature sodium roasting above 850°C, this significantly reduces energy consumption, achieving an aluminum leaching rate of ≥86% and a vanadium alkali dissolution rate of ≥82%. Second, it utilizes in-situ selective extraction of vanadium in an alkaline system, without acidifying the sodium aluminate mother liquor. A tertiary amine-modified neutral phosphorus composite extractant (N235 + TBP + sulfonated kerosene) is directly used to selectively extract vanadate in a strongly alkaline sodium aluminate solution, ensuring that sodium aluminate remains entirely in the aqueous phase. This solves the problems of salt production during acidic extraction and alumina co-extraction losses, achieving a vanadium single-stage extraction rate of ≥91% and aluminum entrainment loss of <1.2%.

[0051] Furthermore, a fully closed-loop circulation coupling of sodium carbonate mother liquor was achieved. After vanadium extraction, sodium aluminate in aqueous phase is directly carbonized to prepare aluminum hydroxide. The decomposition mother liquor, mainly composed of dilute sodium carbonate, is evaporated and concentrated, then supplemented with a small amount of soda ash and returned to the S2 sodium roasting and S3 hot alkali leaching processes for recycling. The vanadium-rich organic phase is back-extracted with dilute alkali to obtain pure sodium vanadate solution, which is then recycled for ore blending. The entire process involves no acid-base neutralization, reducing sodium salt solid waste by more than 90%. The final alkali leaching tailings, after removing aluminum and vanadium, are enriched with titanium and iron, which can be used as raw materials for subsequent titanium and iron extraction, achieving step-by-step resource utilization. This aligns with the company's production plan of first focusing on aluminum and vanadium extraction and then expanding to multi-metal comprehensive extraction in the long term.

[0052] The technical solution of the present invention will be described in detail below through specific embodiments, but the present invention is not limited to the following embodiments.

[0053] Experimental methods not specified in the examples are generally performed under conventional conditions or in accordance with common knowledge in the art. The typical chemical composition of the Bayer red mud used in the examples is as follows: Bayer red mud components: Al2O3 16.7%, V2O5 0.21%.

[0054] Example 1 A cleaning process for selective and simultaneous extraction of aluminum and vanadium from Bayer red mud includes the following steps.

[0055] S1: Place Bayer red mud in an oven and dry it to constant weight at 105~110℃. After coarse crushing with a jaw crusher, grind it with a planetary ball mill until it all passes through a 200-mesh standard sieve (particle size ≤0.074 mm) to obtain red mud powder.

[0056] S2: Take 100 parts by weight of the above-mentioned red mud powder, add 21 parts by weight of sodium carbonate (Na2CO3) as a sodicizing agent, and add 1.8 parts by weight of calcium fluoride (CaF2) as a fluorine-containing activator. Mix the mixture evenly in a mixer. Place the mixture into a corundum crucible, put it in a muffle furnace, and heat it to 500°C at a heating rate of 5°C / min under air atmosphere. Hold the temperature for 180 min. After calcination, cool it to room temperature with the furnace to obtain the sodic clinker.

[0057] S3: Add the above-mentioned sodium-treated clinker to the circulating sodium carbonate mother liquor (total alkali concentration approximately 200 g / L), controlling the liquid-to-solid ratio at 5:1, and leach at 90°C with stirring for 100 min. After leaching, use a plate and frame filter press for solid-liquid separation to obtain a mixed alkaline leachate of aluminum and vanadium and leaching tailings enriched with titanium and iron. The leaching tailings are stored separately as raw materials for subsequent stepwise extraction of valuable titanium and iron metals.

[0058] S4: A composite organic phase was prepared using trioctylamine (N235), tributyl phosphate (TBP), and sulfonated kerosene at a volume ratio of 15:8:77. The aluminum-vanadium mixed alkaline leachate obtained in S3 (total alkali concentration approximately 210 g / L) was mixed with the composite organic phase at a ratio O / A = 1:4 in a separatory funnel, and subjected to four stages of countercurrent extraction at room temperature. After extraction, the phases were separated to obtain a vanadium-rich organic phase and a sodium aluminate-devanadium aqueous phase.

[0059] S5: Industrial CO2 gas is introduced into the aqueous phase of sodium aluminate obtained in S4 for carbonization decomposition. The decomposition temperature is controlled at 60℃, and the endpoint is monitored with a pH meter. Gas introduction is stopped when the solution pH drops to 11.0. Aluminum hydroxide precipitate is obtained by filtration, washed with deionized water until neutral, and then calcined at 1200℃ for 2 h to obtain metallurgical grade alumina product. The sodium carbonate mother liquor obtained from carbonization decomposition is evaporated and concentrated, and then returned to the S2 sodium roasting process and / or the S3 hot alkaline leaching process for recycling.

[0060] S6: Using a 2.0 mol / L sodium hydroxide solution as the back-extraction agent, a two-stage countercurrent back-extraction was performed on the vanadium-rich organic phase obtained in S4, with an O / A ratio of 4:1. After back-extraction, the phases were separated to obtain an aqueous sodium vanadate solution. The back-extracted organic phase was regenerated by washing with water and then recycled for the S4 extraction process. Ammonium chloride (molar ratio of ammonium ions to vanadium of 3:1) was added to the sodium vanadate aqueous solution to adjust the pH to 8.0-8.5. The mixture was heated to 90°C with stirring to precipitate vanadium. After filtration, ammonium polyvanadate precipitate was obtained, washed with deionized water, and calcined at 550°C for 2 h to obtain industrial vanadium pentoxide product.

[0061] Results of this embodiment: Al leaching rate 87.3%, V dissolution rate 83.6%; vanadium extraction rate 93.2%; vanadium impurities in alumina 0.0042%; V2O5 purity 98.7%; sodium carbonate mother liquor recycling rate 91%.

[0062] Example 2 The difference between this embodiment and Embodiment 1 lies in the material ratio and calcination conditions in step S2, in order to verify the feasibility and effectiveness of the method of the present invention under boundary conditions.

[0063] S2: Take 100 parts by weight of the red mud powder obtained in Example 1, add 18 parts by weight of sodium carbonate as a sodium-forming agent, and add 1.2 parts by weight of calcium fluoride as a fluorine-containing activator. After mixing evenly, place it in a muffle furnace and heat it to 480°C at a heating rate of 5°C / min under air atmosphere, and keep it at that temperature for 40 min. The remaining steps are the same as in Example 1.

[0064] Results of this embodiment: Due to the lower limit of the dosage of sodium-containing agent and fluorine-containing activator (100:18:1.2) within the scope of the claims, and the relatively low roasting temperature (480℃) and short roasting time (40 min), the dissociation of aluminum and silicate minerals in the red mud was not sufficient. Testing showed that the aluminum leaching rate was 82.1%, and the vanadium dissolution rate was 76.3%, which was lower than in Example 1; the vanadium extraction rate was 90.5%, and the vanadium impurity content in the alumina product was 0.0048%, still meeting the metallurgical grade standard (<0.005%); the purity of the vanadium pentoxide product was 98.2%. This embodiment demonstrates that even within the limits of the proportions and roasting conditions, the method of the present invention can still achieve acceptable valuable metal recovery effects and product quality, reflecting a wide process adaptability window.

[0065] Example 3 The difference between this embodiment and Embodiment 1 is that the calcination and activation in step S2 are carried out in a rotary kiln, and some process parameters are adjusted to another boundary of the scope of the claims, in order to verify the applicability of the method of the present invention under industrial continuous production conditions.

[0066] S2: Take 100 parts by weight of the red mud powder obtained in Example 1, add 24 parts by weight of sodium carbonate as a sodium-forming agent, add 2.5 parts by weight of calcium fluoride as a fluorine-containing activator, mix evenly and continuously feed into a rotary kiln, control the kiln temperature at 520°C, the material residence time is about 150 min, and continuously roast under air atmosphere to obtain sodium-formed clinker.

[0067] S3: Add the above-mentioned sodium-treated clinker to the circulating sodium carbonate mother liquor, control the liquid-to-solid ratio at 6:1, and stir and leach at 95°C for 120 min. The remaining steps are the same as in Example 1.

[0068] Results of this embodiment: The aluminum leaching rate of the clinker obtained by continuous roasting in a rotary kiln was 90.8%, and the vanadium leaching rate was 86.1%, which is basically equivalent to the effect of intermittent roasting in a muffle furnace (Example 1), verifying the feasibility of the method of the present invention in continuous production in a rotary kiln. The vanadium extraction rate was 94.1%, the vanadium impurity content in the alumina product was 0.0039%, and the purity of the vanadium pentoxide product was 98.9%. Although the increase in the dosage of sodium thiosulfate and activator (within the upper limit of the claim 100:24:2.5) slightly improved the leaching rate, the increase has become gradual, and further increasing the dosage of activators has limited improvement on the recovery rate, but instead increases the raw material cost. This embodiment further verifies the rationality of the preferred ratio range (100:20~22:1.5~2.0) and the preferred roasting time (150~180 min) in the claims—that is, achieving optimal economic efficiency while ensuring high recovery rate. Comparative Example 1 (Traditional high-temperature sodium roasting, fluorine-free activation aid) The mixture was roasted at 900°C, with only soda ash and no CaF2, and the other parameters were the same as in Example 1.

[0069] Results: Al leaching was 76.1%, and vanadium dissolution was 44.8%; energy consumption was more than 40% higher, the mother liquor had low vanadium content, and had no industrial value.

[0070] Comparative Example 2 (Conventional Acidic Extraction for Vanadium Removal) The sodium leaching solution was acidified with sulfuric acid to pH 2, and vanadium was extracted using N235 acidic solution. The vanadium extraction rate was 90.5%, but neutralization produced a large amount of sodium sulfate residue, the sodium carbonate mother liquor could not be recycled, and the reagent cost increased by 35%.

[0071] A comparison of Example 1 and Comparative Example 1 shows that the present invention achieves an aluminum leaching rate of 87.3% and a vanadium dissolution rate of 83.6% under low-temperature conditions of 500℃ with the addition of calcium fluoride activator. In contrast, the traditional high-temperature fluorine-free roasting at 900℃ only achieves an aluminum leaching rate of 76.1% and a vanadium dissolution rate of only 44.8%. This demonstrates that the calcium fluoride activator can significantly reduce the roasting temperature and greatly improve the vanadium dissolution efficiency, while saving more than 40% of energy. A comparison of Example 1 and Comparative Example 2 further shows that the present invention uses an alkaline system to directly extract vanadium, achieving a vanadium extraction rate of 93.2%, which is comparable to or even better than acidic extraction (90.5%). However, it avoids the large amount of sodium sulfate residue generated by acidification and neutralization, achieving a 91% efficient recycling rate of sodium carbonate mother liquor, and significantly reducing reagent costs. Examples 2 and 3, under boundary conditions and industrial continuous conditions, respectively, verified the feasibility and stability of the method of the present invention, indicating that the present invention has a wide process adaptability window and good prospects for industrial scale-up.

[0072] In summary, this invention directly extracts vanadium through a low-temperature calcium fluoride-assisted sodium roasting coupled with an alkaline system, fundamentally solving the two major industry pain points of traditional processes: "high temperature and high energy consumption" and "salt production by acid-base switching." It achieves efficient synergistic recovery of aluminum and vanadium and closed-loop circulation of the alkaline medium.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cleaning process for the selective and simultaneous extraction of aluminum and vanadium from Bayer red mud, characterized in that, Includes the following steps: S1: Pre-treat Bayer red mud to obtain red mud powder; S2: The red mud powder is mixed evenly with sodium-forming agent and fluorine-containing activator, and the resulting mixture is activated by medium-low temperature roasting at 350~550℃ to obtain sodium-formed clinker; S3: The sodium-treated clinker is subjected to hot alkaline leaching with alkaline mother liquor. After leaching, solid and liquid are separated to obtain an aluminum-vanadium mixed alkaline leaching solution and leaching tailings enriched with titanium and iron. S4: A composite organic phase consisting of a tertiary amine extractant, a neutral phosphorus extractant, and a diluent is used to perform multi-stage countercurrent extraction on the aluminum-vanadium mixed alkaline leachate, selectively extracting vanadate into the organic phase, and obtaining a vanadium-rich organic phase and a sodium aluminate devanadium aqueous phase after phase separation. S5: Carbonize and decompose the aqueous phase of sodium aluminate to precipitate aluminum hydroxide, and calcine to obtain metallurgical grade alumina with low vanadium impurities. S6: The vanadium-rich organic phase is back-extracted using a dilute alkaline solution to obtain an aqueous solution of sodium vanadate, which is then ammonified to precipitate vanadium and calcined to obtain industrial vanadium pentoxide.

2. The cleaning process according to claim 1, characterized in that, In step S1, the Bayer red mud pretreatment includes drying, crushing, and grinding; the particle size of the red mud powder is 200 mesh or less.

3. The cleaning process according to claim 1 or 2, characterized in that, In step S2, the sodium-containing agent is one or more of sodium carbonate, sodium hydroxide, and sodium bicarbonate, and the fluorine-containing activator is one or two of calcium fluoride and sodium fluoride. Preferably, the mass ratio of red mud powder, sodium oxidizing agent, and fluorine-containing activator is 100:(18~24):(1.2~2.5), and more preferably 100:(20~22):(1.5~2.0); Preferably, the low-temperature calcination activation time is 40~180 min, more preferably 150~180 min; Preferably, the low-temperature calcination activation temperature is 480~520℃; Preferably, the low-temperature calcination activation is carried out in an air atmosphere; Preferably, the low-temperature calcination activation is carried out in a rotary kiln or a tunnel kiln.

4. The cleaning process according to any one of claims 1 to 3, characterized in that, In step S3, the alkaline mother liquor is a recycled alkaline mother liquor, preferably a sodium carbonate mother liquor; Preferably, the liquid-to-solid ratio during leaching is (4~6):1; Preferably, the leaching temperature is 85~95℃ and the leaching time is 90~120 min; Preferably, the leaching is carried out under stirring; Preferably, solid-liquid separation is achieved by plate and frame filtration after leaching.

5. The cleaning process according to any one of claims 1 to 4, characterized in that, In step S4, the volume composition of the composite organic phase is: 12%~18% tertiary amine extractant, 6%~10% neutral phosphorus extractant, and the remainder is diluent; Preferably, the ratio of the extracted organic phase to the aqueous phase is O / A = 1:(3~5); Preferably, the countercurrent extraction is performed at room temperature; Preferably, the countercurrent extraction has 3 to 5 stages; Preferably, the total alkali concentration of the aluminum-vanadium mixed alkaline leachate is 180~240 g / L.

6. The cleaning process according to any one of claims 1 to 5, characterized in that, The tertiary amine extractant is trioctylamine, the neutral phosphorus extractant is tributyl phosphate, and the diluent is sulfonated kerosene.

7. The cleaning process according to any one of claims 1 to 6, characterized in that, In step S5, the carbonization decomposition is carried out by introducing CO2; Preferably, the carbonization decomposition temperature is 50~65℃, and the final pH value of carbonization is 10.5~11.5; Preferably, the obtained aluminum hydroxide is washed and then calcined at 1100~1300℃ to produce metallurgical grade aluminum oxide with vanadium impurity content <0.005%; Preferably, the sodium carbonate mother liquor obtained from carbonation decomposition is concentrated and then returned to step S2 and / or S3 for recycling.

8. The cleaning process according to any one of claims 1 to 7, characterized in that, In step S6, the dilute alkaline solution is a dilute sodium hydroxide solution; Preferably, the concentration of the dilute sodium hydroxide solution is 1.5~2.5 mol / L; Preferably, the back-extraction is countercurrent back-extraction, and the number of back-extraction stages is two or more. Preferably, the ratio of O / A in the back-extraction is (3~5):1; Preferably, the organic phase after back-extraction is washed and regenerated with water and then recycled for the S4 extraction process.

9. The cleaning process according to any one of claims 1 to 8, characterized in that, In step S6, the ammonium precipitation and calcination of vanadium includes: adding ammonium salt to the sodium vanadate aqueous solution to precipitate vanadium; washing the obtained vanadium precipitate and calcining it at 500~600℃ to obtain a vanadium pentoxide product with a purity ≥98.5%.

10. The cleaning process according to any one of claims 1 to 9, characterized in that, The leaching tailings enriched with ilmenite obtained in step S3 are stored separately as raw materials for subsequent stepwise extraction of valuable titanium and iron metals.

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