Method for cooperatively extracting iron and enriching scandium oxide from red mud tailings

Abstract

This invention provides a method for co-extracting iron and enriching scandium oxide from red mud tailings, comprising the following steps: S1: Pre-treating the red mud tailings after aluminum and vanadium extraction to obtain tailings powder; S2: Mixing the tailings powder with a reducing agent and an activating agent uniformly to obtain a mixture; S3: Performing low-temperature magnetization reduction roasting of the mixture at 380~550℃ under inert gas protection to obtain roasted clinker; S4: Grinding and slurrying the roasted clinker, followed by gradient magnetic separation to obtain iron concentrate and scandium-rich tailings; S5: Leaching the scandium-rich tailings with acid, and obtaining scandium-rich leachate and silica-calcium tailings after solid-liquid separation; S6: Purifying the scandium-rich leachate to obtain scandium oxide. The technical solution of this invention solves the industry pain points such as difficulty in separating iron and scandium in dense red mud tailings after aluminum and vanadium extraction, passivation of scandium lattice by high-temperature roasting, interference of iron impurities in scandium extraction, process fragmentation, and high energy consumption.

Description

Technical Field

[0001] This invention relates to the cross-technical fields of low-carbon resource utilization of metallurgical solid waste and efficient extraction of rare earth metals, and in particular to a method for synergistic iron extraction and scandium oxide enrichment from red mud tailings by low-temperature magnetization reduction roasting. Background Technology

[0002] Red mud is a highly alkaline industrial solid waste produced by alumina smelting (Bayer process) (hence also called Bayer red mud). Globally, its stockpile is enormous, with a comprehensive utilization rate of less than 10%. Long-term open-air storage easily induces ecological risks such as soil salinization and heavy metal leaching of groundwater. The tailings minerals obtained after multi-stage aluminum and vanadium extraction from Bayer red mud (i.e., red mud tailings) have a dense structure. Iron minerals are finely embedded as weakly magnetic hematite / goethite, while scandium is uniformly dissolved in a silicate and iron oxide composite lattice, presenting technical challenges such as severe mineral encapsulation and difficulty in simultaneous iron-scandium separation.

[0003] Currently, there are many shortcomings in the technology for the co-recovery of iron and scandium from red mud tailings after aluminum and vanadium extraction. Traditional red mud iron extraction generally uses high-temperature deep metallization reduction above 1100℃, relying on high-temperature melting to achieve iron mineral agglomeration and separation. However, under high-temperature conditions, the tailings undergo severe sintering, and scandium ions form stable inert silicate lattices with silicon and aluminum, resulting in irreversible lattice passivation. This leads to a significant drop in scandium leaching rate while iron recovery rate increases, making it impossible to achieve efficient co-recovery of iron and scandium. Existing low-temperature magnetization technology is only developed for primary, unextracted vanadium-aluminum red mud, and the raw material matrix is ​​loose, making it unsuitable for the densified tailings after aluminum and vanadium leaching. If magnetization is skipped and iron removal is carried out directly by acid leaching, a large amount of Fe in the tailings will be lost. 3+ Al 3+ Simultaneous dissolution significantly increases acid consumption, and ferric ions react with Sc... 3+ Competitive adsorption and co-precipitation encapsulation occur, severely reducing scandium leaching rate and product purity. Furthermore, existing technologies either focus solely on iron extraction, completely abandoning scandium resources, or rely solely on scandium leaching, resulting in iron loss with the tailings. These fragmented processes lack an original design for the cascaded coupling and separation of iron and scandium. Magnetizing roasting aids generally employ single carbonaceous reducing agents, offering limited functionality and failing to address the dense encapsulation structure. In summary, current technologies lack a dedicated process adapted to the dense red mud tailings after aluminum and vanadium extraction, necessitating a new, integrated, clean process that achieves low-temperature, low-carbon, and synergistic recovery of iron and scandium.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the synergistic extraction of iron and enrichment of scandium oxide from red mud tailings, thereby solving at least one of the problems mentioned in the background art.

[0006] In a first aspect, the present invention provides a method for co-extracting iron and enriching scandium oxide from red mud tailings, comprising the following steps: S1: Pre-treat the red mud tailings after aluminum and vanadium extraction to obtain tailings powder; S2: Mix the tailings powder with the reducing agent and activating agent evenly to obtain a mixture; S3: The mixture is subjected to low-temperature magnetization reduction roasting at 380~550℃ under inert gas protection to obtain roasted clinker; S4: After grinding and slurry preparation of the roasted clinker, it is separated by gradient magnetic separation to obtain iron concentrate and scandium-rich tailings; S5: The scandium-rich tailings are leached with acid, and after solid-liquid separation, scandium-rich leachate and calcium silicate tailings are obtained. S6: The scandium-rich leachate is purified to obtain scandium oxide.

[0007] The present invention has at least the following beneficial effects: (1) The method of the present invention is the first low-temperature ferromagnetization-scandium lattice activation coupling mechanism. The calcination temperature is controlled below 550℃, which reduces energy consumption by more than 35% compared with the traditional 1100℃ high-temperature reduction. The wear and tear of kiln equipment and maintenance costs are significantly reduced. The process is specifically designed for dense high-iron tailings after aluminum and vanadium extraction, solving the defects of conventional magnetization processes that are only suitable for primary red mud and have low magnetization efficiency. It has unique advantages in raw material compatibility.

[0008] (2) The method of the present invention removes most of the iron impurities from the source through pre-gradient magnetic separation, completely eliminating the interference of iron ions on scandium leaching and extraction purification. The total iron recovery rate is ≥90%, and the scandium leaching rate is ≥92%. It simultaneously realizes the synergistic recovery of bulk iron products and high-value-added high-purity scandium, breaking through the technical barrier that the two cannot be taken into account in the existing process.

[0009] (3) The method of the present invention completely eliminates the sintering of tailings and irreversible passivation of scandium lattice through low-temperature roasting, and retains the leaching activity of scandium to the maximum extent; combined with selective low acid leaching and multi-stage extraction and purification, it can stably prepare high-purity scandium oxide with a purity of over 99.9%, and the product grade is superior to the conventional crude scandium products in the industry, with higher economic added value.

[0010] (4) The carbon-ammonium synergistic activator in the method of the present invention has three functions: reduction, etching looseness and lattice protection. It is different from the single carbon reducing agent system. The scandium leaching rate is increased by more than 20%. The mechanism of action of the activator is proposed for the first time in the industry, and the synergistic effect is significant.

[0011] (5) The method of the present invention has no harmful waste gas emissions, and all acid leaching waste liquid and grinding wastewater are recycled and reused. Finally, all silicon and calcium tailings are used to prepare building materials. There is no new solid waste stockpiling, which completely solves the pollution of red mud tailings stockpiling. It forms a full-element tiered recycling industrial chain of "aluminum-vanadium-iron-scandium". The process is highly flexible and can be matched with the phased resource-based production plan of alumina plants. The industrialization value is outstanding. Attached Figure Description

[0012] 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.

[0013] Figure 1 This is a flowchart of the method for co-extracting iron and enriching scandium oxide from red mud tailings in an embodiment of the present invention. Detailed Implementation

[0014] 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.

[0015] 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 exemplary embodiments of the present 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] To address common industry bottlenecks in existing red mud tailings iron and scandium recovery processes, such as high temperature and energy consumption, mutual interference between iron and scandium elements, high-temperature passivation and leaching of scandium lattice, single-function additives, fragmented processes, and short resource recovery chains, this invention provides a method for the synergistic extraction of iron and enrichment of scandium oxide from red mud tailings. Figure 1 As shown, it includes the following steps: S1: Pre-treat the red mud tailings after aluminum and vanadium extraction to obtain tailings powder; S2: Mix the tailings powder with the reducing agent and activating agent evenly to obtain a mixture; S3: The mixture is subjected to low-temperature magnetization reduction roasting at 380~550℃, such as 390℃, 420℃, 450℃, 490℃, 530℃, etc., under inert gas protection to obtain roasted clinker; following the coupling reaction mechanism of directional isomerization transformation of iron minerals and lossless preservation of scandium silicate lattice activity, only weakly magnetic iron minerals are unidirectionally transformed into strongly magnetic magnetite, and the scandium lattice activity is preserved throughout the process without passivation; at the same time, the air inert micro-reduction buffer atmosphere generated by the reducing agent can realize Fe 3+ Gradient-controlled reduction avoids the formation of metallic iron, which can cause mineral agglomeration and sintering. S4: After grinding and slurry preparation of the roasted clinker, it is separated by gradient magnetic separation to obtain iron concentrate and scandium-rich tailings; S5: The scandium-rich tailings are leached with acid, and after solid-liquid separation, scandium-rich leachate and calcium silicate tailings are obtained. S6: Purify the scandium-rich leachate to obtain scandium oxide.

[0020] The red mud tailings obtained after multi-stage extraction of aluminum and vanadium from Bayer red mud have a dense mineral structure, with iron minerals finely embedded in weakly magnetic hematite / goethite, and scandium uniformly dissolved in a silicate and iron oxide composite lattice in an isomorphous manner. This presents technical challenges such as severe mineral encapsulation, difficulty in simultaneous separation of iron and scandium, passivation of the scandium lattice during high-temperature roasting, and low overall resource utilization. This invention overcomes the limitations of existing single-process recovery methods by constructing a novel integrated technology system: low-temperature directional magnetization—gradient magnetic separation pre-treatment—selective low-acid leaching—and closed-loop co-production of all components. This system enables large-scale recovery of iron resources and efficient enrichment and purification of 99.9% high-purity scandium oxide. It can be directly connected to existing Bayer and vanadium extraction production lines in alumina plants and is suitable for the low-carbon, high-value comprehensive utilization of existing red mud tailings in the alumina industry.

[0021] The specific innovative points of the above embodiments of the present invention are as follows: Existing magnetization roasting methods only focus on the reduction and transformation of iron minerals, neglecting the protection of scandium lattice formation. The high-temperature process directly causes permanent passivation of scandium. This invention reveals for the first time the stepwise unidirectional magnetization microscopic transformation mechanism of Fe2O3 / FeOOH under a micro-reducing atmosphere (generated by the release of a reducing agent such as coal powder) at 380~550℃: Fe is achieved by relying on the micro-reducing atmosphere.3+ Gradient-controlled reduction is employed to directionally convert weakly magnetic iron oxides into single-domain magnetite Fe3O4, avoiding excessive reduction that generates metallic iron and induces particle agglomeration. A coupled theoretical model of "iron mineral heterogeneous magnetization + scandium lattice in-situ protection" is established, filling the gap in the research on the microscopic reaction mechanism of low-temperature magnetization in dense red mud tailings for aluminum-vanadium extraction. This model differs from all-high-temperature metallization reduction and conventional single low-temperature magnetization techniques, possessing independent and original scientific theoretical novelty.

[0022] Furthermore, existing technologies either involve first leaching scandium before iron extraction, resulting in wasted iron resources; or first extracting iron at high temperatures and then passivating scandium; direct acid leaching leads to impurity overload and huge acid consumption. This invention innovatively uses an integrated coupled process of "magnetized roasting—multi-stage gradient wet magnetic separation for pre-removal—low-acid selective scandium leaching," reducing the residual total iron in the tailings to below 1.5% through gradient magnetic separation (e.g., 0.6~1.0 T three-stage gradient magnetic separation), eliminating Fe from a thermodynamic perspective. 3+ With Sc 3+ Competitive adsorption and co-precipitation interference significantly reduce acid consumption and subsequent extraction and impurity removal load; the matching acid solution selectively dissociates scandium, while most of aluminum, calcium, and silicon remain in the solid tailings, forming a new separation and control path of "removing iron and impurities at the source and extracting scandium with low consumption and high efficiency". This breaks through the inherent technical bottleneck of mutual interference between iron and scandium, and the integrated tiered separation coupling process is an original design.

[0023] Furthermore, existing processes only recover a single product, resulting in low resource utilization of waste. This invention constructs a low-carbon closed-loop system for the four-stage production of low-temperature magnetization—high-grade iron concentrate—99.9% high-purity scandium oxide—silicon-calcium building material tailings. It features multiple original low-carbon designs: the roasting temperature is controlled below 550℃, compared to the traditional 1100℃ high-temperature reduction, reducing fuel consumption by more than 35%, significantly reducing kiln heat loss and refractory material corrosion, and adapting to long-term industrial operation of continuous rotary kilns; acid leaching mother liquor neutralizes and regenerates hydrochloric acid for cyclic leaching, and magnetic separation and grinding wastewater is circulated in a closed loop, with no acidic wastewater discharge; the roasting tail gas contains no heavy metals or harmful sulfide components, simplifying tail gas treatment equipment; the scandium-de-scandium inert silicon-calcium tailings can be directly used as permeable bricks and roadbed fillers, achieving 100% resource utilization of all components of red mud tailings, with no additional solid waste accumulation.

[0024] The entire process of this invention can be connected in series with the Bayer process for alumina and the aluminum-vanadium extraction production line to form a complete industrial chain of "aluminum-vanadium-iron-scandium" step-by-step recycling. The integrated low-carbon co-production model of the whole process has not been found in similar publicly available technologies and has industrial originality.

[0025] In some embodiments, in step S1, the red mud tailings are tailings obtained from Bayer red mud after multi-stage extraction of aluminum and vanadium. Limiting the red mud tailings to tailings obtained from Bayer red mud after multi-stage extraction of aluminum and vanadium allows for seamless integration between the process of this invention and the upstream aluminum and vanadium extraction process. This ensures a clear source of raw materials and stable composition, overcoming the limitation of existing magnetization processes, which are only suitable for primary loose red mud and cannot handle dense tailings.

[0026] In some embodiments, pretreatment includes drying, crushing, and sieving to 200 mesh or less, such as particle size less than 0.074 mm. Drying, crushing, and grinding to 200 mesh or less effectively eliminates agglomeration and lumps in the tailings, increases the specific surface area of ​​the mineral particles, and ensures sufficient and uniform contact between subsequent additives and mineral particles, providing a fundamental guarantee for the uniform conduction of the magnetization reduction reaction. The content of TFe, Sc2O3, and silicon-aluminum components in the tailings can also be detected simultaneously to stabilize the raw material matrix and eliminate the impact of batch fluctuations.

[0027] In some embodiments, in step S2, the reducing agent is pulverized coal with a fixed carbon content ≥85%, such as industrial anthracite pulverized coal (fixed carbon ≥85%). Using high-fixed-carbon pulverized coal as the reducing agent allows for the continuous and stable slow release of CO to create a locally weakly reducing atmosphere, thereby achieving Fe... 3+ Gradient controllable reduction and directional conversion into strongly magnetic Fe3O4 avoids excessive reduction to generate metallic iron, which can cause particle agglomeration and ensure magnetic separation efficiency.

[0028] In some embodiments, in step S2, the activating agent is one or both of ammonium chloride and sodium chloride, preferably ammonium chloride.

[0029] This invention abandons the industry's approach of using a single coal powder reducing agent, and instead presents an original dual-functional additive combining coal powder, ammonium chloride, and / or sodium chloride, specifically adapted to dense tailings from high-iron mines. The two components exhibit a novel synergistic reaction pathway, a composite activation logic not found in existing literature or patents. Furthermore, on one hand, a locally weak reducing atmosphere is created through a micro-reducing atmosphere (e.g., slow-release CO from coal powder), achieving efficient magnetization of iron minerals; on the other hand, ammonium chloride undergoes low-temperature pyrolysis to generate HCl and NH3. HCl micro-etches the loose tailings agglomerate structure, exposing embedded scandium active sites, while NH3 passivates the scandium lattice to prevent deactivation during roasting. Compared to a single carbon reduction system, scandium acid leaching efficiency is increased by over 20%, and the magnetization conversion rate remains stable at ≥96%. It is specifically adapted to low-alumina dense tailings after aluminum and vanadium extraction. The additive formulation and synergistic activation mechanism are both innovative solutions of this invention.

[0030] In some embodiments, in step S2, the mass ratio of tailings powder, reducing agent and activating agent is 100:(8~15):(1.0~2.5), for example 100:9:1.5, 100:11:2, 100:14:2.3, etc. If it exceeds this range, the additives will be redundant and increase the cost. If it is below this range, the magnetization conversion rate and scandium leaching rate will both decrease. Preferably, it is 100:12:1.8.

[0031] In step S2, the tailings powder is mixed with the reducing agent and activating agent by strong mechanical stirring to avoid local segregation of the activating agent, thereby ensuring that the reducing-activating composite components are uniformly coated on the particle surface.

[0032] In some embodiments, the inert gas in step S3 is nitrogen. Nitrogen serves as a protective carrier gas / barrier gas, on the one hand replacing the air inside the furnace and venting the initial O2, thus acting as an inert shield; on the other hand, it provides a continuous micro-positive pressure seal, preventing outside air from leaking into the furnace; and it can also carry volatiles and gaseous products out of the furnace.

[0033] The reducing atmosphere in low-temperature magnetized reduction roasting can be achieved by using a reducing agent such as pulverized coal to generate reducing gases. Specifically, at high temperatures, carbon undergoes a typical main reduction reaction, rapidly consuming trace amounts of oxygen and generating a large amount of CO. This trace oxygen is then instantly consumed by the reducing agent, such as pulverized coal, simultaneously producing reducing CO and spontaneously creating a localized reducing environment that meets the reduction conditions required for the material reaction.

[0034] In order to achieve both the directional transformation of iron minerals from weak to strong magnetism and to completely prevent tailings sintering and irreversible passivation of scandium lattice, in some embodiments, the temperature of low-temperature magnetization reduction roasting in step S3 is 380~520℃ and the roasting time is 120~180 min.

[0035] In some embodiments, in step S4, the slurry concentration after conditioning the roasted clinker is 25% to 35%, for example, 28%, 30%, 33%, etc. This slurry concentration range ensures good fluidity and dispersibility of the slurry during magnetic separation, avoiding both excessively high concentrations that could lead to particle agglomeration and affect separation accuracy, and excessively low concentrations that could result in reduced throughput and increased water consumption. This is a suitable operating range for obtaining high-grade iron concentrate.

[0036] The calcination in step S3 can be carried out in a rotary kiln, maintaining an inert, micro-reducing buffer atmosphere, and achieving Fe production through a coupled reaction mechanism. 3+ The directional conversion to Fe3O4 occurs without any sintering or caking, and the scandium lattice remains intact without passivation loss.

[0037] In some embodiments, in step S4, the gradient magnetic separation is a three-stage gradient wet magnetic separation with a magnetic field strength of 0.6~1.0T. Using a three-stage gradient wet magnetic separation combined with a magnetic field strength of 0.6~1.0T allows for the step-by-step separation and enrichment of different magnetic minerals, reducing the residual total iron in the tailings to below 1.5%, thus eliminating Fe from the source. 3+ With Sc 3+ The competitive adsorption and co-precipitation interference in the subsequent acid leaching process is an original process design of this invention.

[0038] In some embodiments, the most preferred magnetic field strength is 0.8 T and the slurry concentration is 30%, so that the magnetite particles in the roasted clinker can be optimally separated under suitable hydrodynamic and magnetic conditions.

[0039] Before grinding and slurry preparation, the roasted clinker can be rapidly water-cooled to room temperature to prevent secondary passivation of the scandium lattice caused by residual heat. Magnetic separation can be performed using a three-stage gradient wet magnetic separator to produce high-grade iron concentrate and low-iron, scandium-rich tailings. Magnetic separation product specifications: TFe grade of iron concentrate ≥ 56%, total iron recovery ≥ 82%; residual iron of scandium-rich tailings ≤ 1.5%, with no solid loss of scandium.

[0040] In some embodiments, in step S5, the acid solution is one or both of dilute hydrochloric acid and dilute sulfuric acid. Using dilute hydrochloric acid and / or dilute sulfuric acid as the leaching agent allows for the selective dissociation of scandium at lower concentrations, while exhibiting weaker solubility for impurities such as aluminum, calcium, and silicon, leaving most impurities in the solid tailings. This is a key media selection method for achieving the effect of "selective low-acid leaching."

[0041] In some embodiments, in step S5, the concentration of the acid solution is 4~6 mol / L, for example, 4.5 mol / L, 5.2 mol / L, 5.9 mol / L, etc. This concentration range of dilute hydrochloric acid ensures efficient scandium leaching (leaching rate ≥92%) while avoiding excessive dissolution of impurities and a surge in acid consumption due to excessively high concentrations. Combined with a pre-treatment iron removal process, efficient scandium leaching can be achieved with lower acid consumption, resulting in significant economic benefits.

[0042] In some embodiments, in step S5, the liquid-to-solid ratio of the leaching solution is (5~7):1, for example, 5.5:1, 6.2:1, 6.8:1, etc. A suitable liquid-to-solid ratio ensures that the slurry has good fluidity and mass transfer efficiency, allowing the acid solution to fully contact and react with the scandium component in the scandium-rich tailings. This ensures sufficient leaching of scandium while avoiding an excessively high liquid-to-solid ratio that would result in an excessively large volume of leaching solution and an increased burden on subsequent concentration.

[0043] In some embodiments, in step S5, the leaching temperature is 80~90°C and the time is 90~120 min. Under these mild leaching conditions, scandium can fully dissociate and enter the liquid phase, while the dense silicon-calcium structure remains largely intact and is retained in the solid tailings. Excessive temperature or time will lead to increased leaching of impurities and increased energy consumption. The above range balances leaching rate and operating cost.

[0044] The optimal balance between leaching rate and operating cost is achieved when the hydrochloric acid concentration is 5 mol / L, the liquid-to-solid ratio is 6:1, the leaching temperature is 85℃, and the leaching time is 100 min.

[0045] Due to the significant reduction of impurities in the system by pre-treatment deep iron removal, the scandium leaching rate is ≥92%; the silicon-calcium tailings have stable chemical properties and can be directly used as building material raw materials.

[0046] In some embodiments, in step S5, the silicon-calcium tailings obtained after solid-liquid separation are used to prepare building material raw materials, such as permeable bricks and roadbed building material raw materials.

[0047] In some embodiments, in step S5, the acid leaching wastewater is neutralized and regenerated before being recycled. Magnetic separation and grinding wastewater can be recycled in a closed loop.

[0048] As can be seen, the technical solution of the present invention constructs a low-carbon closed-loop system for the four-in-one production of iron concentrate, high-purity scandium oxide, and building material tailings, realizing the full-component recycling of solid waste and waste liquid.

[0049] In some embodiments, step S6 includes purification treatment comprising: multi-stage countercurrent extraction using an organic phase, followed by washing, back-extraction, precipitation and calcination to obtain scandium oxide product.

[0050] By adopting a multi-stage purification route of "extraction-washing-back-extraction-oxalic acid precipitation-calcination", trace impurities such as aluminum and calcium can be systematically separated. After multiple purification steps, high-purity scandium oxide products with a purity of ≥99.9% can be stably prepared, and the product grade is significantly better than that of conventional crude scandium products in the industry.

[0051] In some embodiments, in step S6, the organic phase is P204-sulfonated kerosene, and precipitation is carried out using oxalic acid. The P204-sulfonated kerosene organic phase is compared with Sc... 3+ It has selective complexation extraction capability, and oxalic acid precipitation can generate high-purity scandium oxalate crystals. The combination of the two is a key technical means to achieve efficient separation of scandium from other impurity ions and ensure the purity of the final product of more than 99.9%.

[0052] Washing can be performed using dilute hydrochloric acid to remove impurities from the organic phase. Back-extraction can be performed using concentrated NaOH solution (mass fraction, for example, 30%~50%) to obtain a high-purity sodium scandate aqueous solution.

[0053] In some embodiments, the pH value during precipitation in step S6 is 2.5 to 3.5, for example, 2.8 or 3.4. Under weakly acidic conditions of pH 2.5 to 3.5, scandium oxalate has the lowest solubility and the most complete precipitation. Moreover, this pH range can effectively inhibit the co-precipitation of impurity ions such as iron and aluminum, which is a key control parameter to ensure high yield and high purity of scandium oxalate precipitation.

[0054] In some embodiments, in step S6, the calcination temperature is 750~850℃ and the time is 2~3 h to obtain a high-purity product of ≥99.9%.

[0055] In some embodiments, the (micro)reducing atmosphere in step S3 is formed by the slow release of CO from pulverized coal to achieve Fe 3+ Gradient controllable reduction and directional conversion to Fe3O4 avoids the formation of metallic iron and the resulting mineral agglomeration and sintering; ammonium chloride is pyrolyzed at low temperature to generate HCl and NH3, where HCl etches the dense coating layer of the tailings to expose the active sites of scandium, and NH3 is adsorbed on the surface of the scandium lattice to form a coordination buffer layer to inhibit the migration and agglomeration of scandium ions.

[0056] This invention pioneers a crystal chemical mechanism that couples the directional isomerization magnetization of iron minerals in the low-temperature range of 380~550℃ with the in-situ preservation of scandium silicate lattice activity. It is paired with a dual-functional synergistic activation agent system of coal powder and ammonium chloride to construct a new process for gradient magnetic separation with pre-purification and selective low-acid leaching for tiered separation. This enables the construction of a low-temperature, low-carbon, multi-product closed-loop co-production system. It achieves efficient magnetization separation of iron under low-temperature conditions, eliminating the interference of iron impurities on scandium extraction from the source, preserving the activity of scandium lattice throughout the process, and simultaneously producing high-grade iron concentrate and 99.9% high-purity scandium oxide. This significantly reduces roasting energy consumption and acid consumption, and all waste liquid and tailings are recycled. It can be seamlessly connected with the alumina and vanadium extraction process to meet the needs of large-scale green and low-carbon industrial production.

[0057] 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.

[0058] Experimental methods not specified in the examples are generally performed under conventional conditions or in accordance with common knowledge in the art. The examples used red mud tailings after aluminum-vanadium extraction, containing 26.3% TFe and 112 ppm Sc2O3.

[0059] Example 1 A method for synergistic iron extraction and scandium oxide enrichment from red mud tailings by low-temperature magnetization reduction roasting includes the following steps.

[0060] S1: Take dense red mud tailings after multi-stage extraction of aluminum and vanadium as raw material, dry them in an oven at 100~110℃ to constant weight, coarsely crush them with a jaw crusher, and then grind and screen them with a planetary ball mill until all of them pass through a 200-mesh standard sieve (particle size ≤0.074 mm) to obtain uniform tailings powder.

[0061] S2: Place the above tailings powder, industrial anthracite powder (fixed carbon ≥ 85%), and ammonium chloride activator in a V-type mixer at a mass ratio of 100:12:1.8, and mechanically stir and mix them evenly so that the particle surface is uniformly coated with the reduction-activation composite component.

[0062] S3: The mixed material is fed into a rotary kiln and calcined at 450℃ for 150 min under nitrogen protection and an inert, micro-reducing buffer atmosphere. This process utilizes the coupled reaction mechanism of directional isomerization transformation of iron minerals and non-destructive preservation of scandium silicate lattice to achieve Fe... 3+ The directional conversion to Fe3O4 occurs without any sintering or caking, and the scandium lattice remains intact without passivation loss.

[0063] S4: The roasted clinker is rapidly water-cooled to room temperature to prevent secondary passivation of the scandium lattice caused by residual heat; water is added to adjust the slurry concentration to 30%, and a 0.8T three-stage gradient wet magnetic separator is used for separation to produce high-grade iron concentrate and low-iron scandium-rich tailings.

[0064] S5: The scandium-rich tailings were mixed with 5 mol / L dilute hydrochloric acid at a liquid-to-solid ratio of 6:1 to form a slurry, which was then leached at a constant temperature of 85℃ for 100 min. Solid-liquid separation was performed using a plate and frame filter press to obtain scandium-rich leachate and stable inert calcium silicate tailings. The calcium silicate tailings are chemically stable and can be directly used as raw materials for building materials.

[0065] S6: Multi-stage countercurrent extraction using P204-sulfonated kerosene organic phase, selective complexation extraction of Sc 3+ Trace amounts of aluminum and calcium impurities were separated; the organic phase was washed with dilute hydrochloric acid to remove entrained impurities, and high-purity sodium scandate aqueous solution was obtained by back-extraction with concentrated NaOH solution (mass fraction of about 40%); the pH of the system was adjusted to 3.0 to precipitate scandate oxalate crystals, which were then washed, dried, and calcined at 800℃ for 2 h to obtain high-purity scandate oxide product.

[0066] Results of this embodiment: Iron concentrate grade was 65%, iron recovery rate was 95%; scandium leaching rate was 94.3%; final scandium oxide purity was 99.92%.

[0067] Example 2 The difference between this embodiment and Embodiment 1 lies in the different ingredient ratios in step S2, the different roasting conditions in step S3, the different magnetic separation conditions in step S4, and the different acid leaching conditions in step S5, in order to verify the feasibility and effectiveness of the method of the present invention under the lower limit conditions of process parameters.

[0068] S2: Take 100 parts by weight of the tailings powder obtained in Example 1, add 8 parts by weight of industrial anthracite powder with fixed carbon ≥85% as a reducing agent, add 1.0 part by weight of ammonium chloride as an activating agent, and mix evenly.

[0069] S3: Place the mixed material in a rotary kiln, maintain an inert micro-reducing buffer atmosphere under nitrogen protection, and calcine at a constant temperature of 380℃ for 180 min.

[0070] S4: After rapid water cooling of the roasted clinker, water is added to adjust the slurry concentration to 25%, and a 0.6 T three-stage gradient wet magnetic separator is used for separation.

[0071] S5: Mix the iron-removed scandium-rich tailings with 4 mol / L dilute hydrochloric acid at a liquid-to-solid ratio of 5:1 to form a slurry, and leach at a constant temperature of 80°C for 120 min with stirring. The remaining steps are the same as in Example 1.

[0072] The results of this embodiment are as follows: iron concentrate grade is 56.8%, iron recovery rate is 82.9%; scandium leaching rate is 91.8%; and final scandium oxide purity is 99.90%. This embodiment shows that even when the feed ratio, roasting temperature, magnetic separation intensity, and acid leaching conditions are all at the lower limit of the claims, the method of the present invention can still achieve acceptable recovery of valuable metals and product purity, demonstrating a wide process adaptability window.

[0073] Example 3 The difference between this embodiment and Embodiment 1 lies in the different ingredient ratios in step S2, the different roasting conditions in step S3, the different magnetic separation conditions in step S4, and the different acid leaching conditions in step S5, in order to verify the feasibility and effectiveness of the method of the present invention under the upper limit of process parameters.

[0074] S2: Take 100 parts by weight of the tailings powder obtained in Example 1, add 15 parts by weight of industrial anthracite powder with fixed carbon ≥85% as a reducing agent, add 2.5 parts by weight of ammonium chloride as an activating agent, and mix evenly.

[0075] S3: Place the mixed material in a rotary kiln, maintain an inert micro-reducing buffer atmosphere under nitrogen protection, and calcine at a constant temperature of 520℃ for 120 min.

[0076] S4: After rapid water cooling of the roasted clinker, water is added to adjust the slurry concentration to 35%, and a 1.0 T three-stage gradient wet magnetic separator is used for separation.

[0077] S5: Mix the iron-removed scandium-rich tailings with 6 mol / L dilute hydrochloric acid at a liquid-to-solid ratio of 7:1 to form a slurry, and leach at a constant temperature of 90°C for 90 min. The remaining steps are the same as in Example 1.

[0078] Results of this embodiment: Iron concentrate grade was 60.0%, iron recovery rate was 90.0%; scandium leaching rate was 92.7%; final scandium oxide purity was 99.91%.

[0079] This embodiment demonstrates that when the process parameters are at the upper limit of the claims, the method of the present invention can still operate stably and achieve good recovery results.

[0080] The above results show that Example 1 can obtain the optimal comprehensive technical and economic indicators under the preferred process parameters; Examples 2 and 3 respectively verify the feasibility and stability of the present invention under the boundary conditions of process parameters, proving that the method of the present invention has a wide process adaptability window and good prospects for industrial application.

[0081] Comparative Example 1 (Traditional high-temperature metallization reduction roasting, without ammonium chloride additive) The conventional 1100℃ high-temperature deep reduction roasting method was adopted, with only coal powder reducing agent added and no ammonium chloride activating agent. The other pretreatment, magnetic separation and scandium extraction parameters were the same as in Example 1.

[0082] Experimental results: Energy consumption is 36% higher than that of the present invention, tailings are severely sintered, scandium lattice undergoes irreversible passivation, scandium leaching rate is only 68.4%, and iron recovery rate is 81.2%.

[0083] The results show that the high-temperature process cannot achieve the synergistic recovery of iron and scandium, and the scandium activity decreases significantly without composite additives, highlighting the inventiveness of the low-temperature coupling mechanism and bifunctional additives in this invention.

[0084] Comparative Example 2 (no magnetization pretreatment, direct acid leaching for scandium extraction) The red mud tailings were not subjected to magnetization roasting or gradient magnetic separation for pre-iron removal. Instead, scandium was extracted directly by acid leaching with hydrochloric acid of the same concentration. The other purification parameters were the same as in Example 1.

[0085] Experimental results: Acid consumption increased by 42%, a large amount of iron impurities dissolved simultaneously, interfering with extraction and separation, scandium leaching rate was only 70.5%, and the purity of scandium oxide after purification was only 98.2%, which could not reach the high-purity grade.

[0086] This demonstrates the novelty and technical advantages of the new coupled process of "pre-magnetic separation de-ironization-step scandium impregnation" in this invention.

[0087] 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 method for co-extracting iron and enriching scandium oxide from red mud tailings, characterized in that, Includes the following steps: S1: Pre-treat the red mud tailings after aluminum and vanadium extraction to obtain tailings powder; S2: Mix the tailings powder with the reducing agent and activating agent evenly to obtain a mixture; S3: The mixture is subjected to low-temperature magnetization reduction roasting at 380~550℃ under inert gas protection to obtain roasted clinker; S4: After grinding and slurry preparation of the roasted clinker, it is separated by gradient magnetic separation to obtain iron concentrate and scandium-rich tailings; S5: The scandium-rich tailings are leached with acid, and after solid-liquid separation, scandium-rich leachate and calcium silicate tailings are obtained. S6: The scandium-rich leachate is purified to obtain scandium oxide.

2. The method according to claim 1, characterized in that, In step S1, the red mud tailings are tailings obtained from Bayer red mud after multi-stage extraction of aluminum and vanadium. Preferably, the pretreatment includes drying, crushing, and sieving to 200 mesh or below.

3. The method according to claim 1 or 2, characterized in that, In step S2, the reducing agent is pulverized coal with a fixed carbon content of ≥85%; Preferably, the activating agent is one or both of ammonium chloride and sodium chloride, with ammonium chloride being the preferred choice; Preferably, the mass ratio of the tailings powder, reducing agent, and activating agent is 100:(8~15):(1.0~2.5).

4. The method according to any one of claims 1 to 3, characterized in that, In step S3, the inert gas is nitrogen; Preferably, the temperature of the low-temperature magnetization reduction calcination is 380~520℃, and the calcination time is 120~180 min.

5. The method according to any one of claims 1 to 4, characterized in that, In step S4, the slurry concentration of the roasted clinker after slurry preparation is 25%~35%; Preferably, the gradient magnetic separation is a three-stage gradient wet magnetic separation with a magnetic field strength of 0.6~1.0 T.

6. The method according to any one of claims 1 to 5, characterized in that, In step S5, the acid solution is one or both of dilute hydrochloric acid and dilute sulfuric acid; Preferably, the concentration of the acid solution is 4~6 mol / L; Preferably, the liquid-to-solid ratio of the leaching is (5~7):1; Preferably, the leaching temperature is 80~90℃ and the leaching time is 90~120 min.

7. The method according to any one of claims 1 to 6, characterized in that, In step S5, the silicon-calcium tailings obtained after solid-liquid separation are used to prepare building material raw materials; Preferably, the acid leaching waste liquid is recycled after neutralization and regeneration.

8. The method according to any one of claims 1 to 7, characterized in that, In step S6, the purification process includes: multi-stage countercurrent extraction using an organic phase, followed by washing, back-extraction, precipitation, and calcination to obtain scandium oxide product.

9. The method according to claim 8, characterized in that, The organic phase is P204-sulfonated kerosene, and precipitation is carried out using oxalic acid. Preferably, the pH value during precipitation is 2.5 to 3.5; Preferably, the calcination temperature is 750~850℃ and the time is 2~3 h.

10. The method according to any one of claims 1 to 9, characterized in that, The reducing atmosphere in step S3 is formed by the slow release of CO from pulverized coal.

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