A method for recovering scandium from red mud

Abstract

This invention provides a method for recovering scandium from red mud, the method comprising the following steps: reducing and roasting the red mud, followed by magnetic separation to obtain iron-removed red mud; mixing hydrochloric acid and fluoride to obtain a composite leachate, using the composite leachate to perform pressure leaching on the iron-removed red mud, and separating the solid and liquid to obtain a scandium-rich leachate and a titanium-containing leaching residue; mixing the scandium-rich leachate with oxalic acid to perform oxalic acid precipitation treatment to obtain scandium oxalate precipitate; roasting the scandium oxalate precipitate to obtain crude scandium oxide; mixing the crude scandium oxide with an acid solution to obtain a crude scandium salt solution; and sequentially extracting and back-extracting the crude scandium salt solution to obtain a scandium-rich salt solution. After removing iron from the red mud in advance, the present invention uses a hydrochloric acid-fluoride composite leaching system to separate scandium from most of the impurity ions. Scandium is then further purified by oxalic acid precipitation, calcination, acid dissolution and extraction to prepare a high-purity scandium-rich salt solution.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology and relates to a method for recovering scandium from red mud. Background Technology

[0002] Scandium is a scarce strategic rare and dispersed metal with characteristics such as high melting point, low density, and excellent electrical conductivity and catalytic performance. It has irreplaceable application value in high-end alloys, aerospace, new energy materials, electronic ceramics, catalysts, and other fields. Red mud solid waste generated during aluminum industry production is rich in trace scandium resources and is one of the core secondary resources for industrial scandium extraction. Compared with primary scandium ore, red mud scandium extraction has outstanding advantages such as large raw material reserves, low acquisition cost, and the ability to realize the resource utilization of solid waste. It is currently a research hotspot and key development direction in the field of rare and dispersed metal recycling.

[0003] Red mud has a complex mineral structure and diverse composition. In addition to trace amounts of scandium, it also contains a large number of associated impurities such as iron, titanium, aluminum, silicon, calcium, and magnesium. Scandium is mostly embedded in the mineral lattice in an isomorphous form, exhibiting an extremely stable state. Conventional processing methods are insufficient for efficient and selective separation and recovery, significantly increasing the technical difficulty of scandium extraction from red mud. Currently, existing red mud scandium extraction processes mostly employ conventional technical routes such as direct acid leaching, single extraction, and stepwise precipitation, which generally have many technical defects, hindering the efficient and low-cost industrial production of high-purity scandium products.

[0004] Most existing conventional scandium extraction processes do not include a specific iron removal pretreatment step. A large amount of iron oxide components in red mud will dissolve simultaneously during acid leaching. A large amount of iron ions enter the leachate system, which not only competes for leaching agents, increases agent consumption, and reduces scandium leaching selectivity, but also seriously interferes with the separation and enrichment of scandium in subsequent precipitation and extraction purification processes. This results in problems such as scandium oxalate precipitation carrying a large amount of iron impurities, emulsification of the extraction system, difficulty in two-phase separation, and low scandium recovery rate, which greatly reduces the purity and resource utilization rate of the final scandium product.

[0005] Meanwhile, traditional single hydrochloric acid and sulfuric acid leaching systems lack a specific titanium-suppressing mechanism, allowing titanium in red mud to dissolve simultaneously with large amounts of scandium. Since titanium and scandium ions have similar physicochemical properties, subsequent separation is extremely difficult. Existing technologies typically require multiple titanium and impurity removal steps, resulting in lengthy, complex, and cumbersome processes. Furthermore, these multi-stage impurity removal processes lead to significant scandium loss, further reducing the overall scandium recovery rate and increasing energy consumption and waste treatment pressures, making them poorly adaptable to industrial applications. In addition, conventional leaching processes exhibit poor selectivity, producing leachate with a wide variety and high concentration of impurity ions. Subsequent purification using only single extraction methods is insufficient to completely remove trace amounts of residual impurities such as titanium and iron, resulting in scandium salt products with limited purity that cannot meet the high-purity scandium material application requirements of advanced fields. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for recovering scandium from red mud. In this invention, after removing iron from the red mud in advance, a hydrochloric acid-fluoride composite leaching system is used to separate scandium from most of the impurity ions. Then, scandium is further purified by oxalic acid precipitation, calcination, acid dissolution, and extraction to prepare a high-purity scandium-rich salt solution.

[0007] To achieve this objective, the present invention adopts the following technical solution: This invention provides a method for recovering scandium from red mud, the method comprising the following steps: After the red mud is subjected to reduction roasting treatment, it is then subjected to magnetic separation treatment to obtain iron-removed red mud; Hydrochloric acid and fluoride were mixed to obtain a composite leachate. The composite leachate was used to perform pressure leaching treatment on iron-removed red mud. Solid-liquid separation was performed to obtain scandium-rich leachate and titanium-containing leaching residue. The scandium-rich leachate was mixed with oxalic acid and subjected to oxalic acid precipitation to obtain scandium oxalate precipitate. Scandium oxalate precipitate was roasted to obtain crude scandium oxide. The crude scandium oxide was mixed with an acid solution to obtain a crude scandium salt solution. The crude scandium salt solution was then subjected to extraction and back-extraction treatments to obtain a scandium-rich salt solution.

[0008] This invention pre-converts Fe2O3 in red mud into Fe3O4, followed by magnetic separation to remove Fe. Then, a pressure leaching treatment of the iron-removed red mud is performed using an HCl-fluoride composite leaching system, where fluoride ions react with Sc... 3+ Formation of stable complexes (such as ScF6) 3- Meanwhile, fluoride ions and impurity ions (such as Ti) 4+ ) forms insoluble fluorotitanate precipitates (such as TiF6) 2- (Salt precipitation) effectively suppresses impurity ions in the leaching residue, preventing them from entering the solution. Subsequent oxalic acid precipitation followed by calcination yields crude scandium oxide. The crude scandium oxide is then acid-dissolved and extracted to remove Sc. 3+ A high-purity scandium-rich salt solution can be obtained by separating it from impurity ions.

[0009] Preferably, before the reduction roasting treatment, the red mud is subjected to drying and ball milling activation treatment in sequence.

[0010] This invention significantly enhances the activity of subsequent leaching reactions by mechanically activating and disrupting the dense structure of red mud.

[0011] Preferably, the atmosphere of the reduction roasting treatment includes a mixture of reducing gas and nitrogen.

[0012] Preferably, in the mixture of reducing gas and nitrogen, the volume percentage of reducing gas is 5% to 15%, for example: 5%, 8%, 10%, 12% or 15%, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0013] This invention involves reducing and roasting Fe2O3 under a suitable reducing atmosphere to convert it into Fe3O4, which has strong magnetic properties. Iron impurities can then be removed by magnetic separation, avoiding interference from iron ions in scandium extraction and reducing the load on subsequent separation processes.

[0014] Preferably, the reducing gas includes hydrogen and / or carbon monoxide.

[0015] Preferably, the temperature of the reduction calcination treatment is 550℃~750℃, for example: 550℃, 600℃, 650℃, 700℃ or 750℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the reduction calcination treatment time is 1.5h to 3h, for example: 1.5h, 1.8h, 2h, 2.5h or 3h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] Preferably, the magnetic field strength of the magnetic separation process is 0.15T~0.3T, for example: 0.15T, 0.18T, 0.2T, 0.25T or 0.3T, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the molar concentration of the hydrochloric acid is 3 mol / L to 6 mol / L, for example: 3 mol / L, 3.5 mol / L, 4 mol / L, 5 mol / L or 6 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the fluoride includes any one or a combination of at least two of NaF, NH4F, or HF. Typical but non-limiting combinations include combinations of NaF and HF, NaF and NH4F, or NH4F and HF, etc.

[0020] This invention uses a hydrochloric acid-fluoride composite leaching system, in which fluoride ions react with scandium to form a stable hexafluoroscandium complex ion, ensuring a high scandium leaching rate; at the same time, titanium is converted into insoluble fluorotitanate precipitate and fixed in the slag, achieving scandium dissolution and titanium barrier in one step, eliminating the need for a separate titanium removal process and simplifying the process.

[0021] Preferably, the liquid-to-solid volume ratio of the composite leachate to the iron-removing red mud is (4~8) mL / 1g, for example: 4mL / 1g, 5mL / 1g, 6mL / 1g, 7mL / 1g or 8mL / 1g, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the molar ratio of fluoride ions in the composite leachate to metal ions in the iron-removing red mud is (6~8):1, for example: 6:1, 6.5:1, 7:1, 7.5:1 or 8:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] The metal ions in the iron-removing red mud described in this invention mainly include scandium ions and titanium ions.

[0024] Preferably, the temperature of the pressure leaching treatment is 80℃~110℃, for example: 80℃, 85℃, 90℃, 100℃ or 110℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, the pressure of the pressure leaching treatment is 0.2MPa to 0.5MPa, for example: 0.2MPa, 0.25MPa, 0.3MPa, 0.4MPa or 0.5MPa, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, the pH of the pressure leaching treatment is 0.5 to 1, for example: 0.5, 0.6, 0.8, 0.9 or 1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, the pressure leaching treatment time is 2h to 5h, for example: 2h, 2.5h, 3h, 4h or 5h, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] Preferably, before mixing the scandium-rich leachate with oxalic acid, the pH of the scandium-rich leachate is adjusted to 0.5~2, for example: 0.5, 0.8, 1, 1.5 or 2, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0029] Preferably, the temperature for the oxalic acid scandium precipitation treatment is 40℃~70℃, for example: 40℃, 45℃, 50℃, 60℃ or 70℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] In this invention, after oxalic acid precipitation, the resulting scandium oxalate precipitate is subjected to multi-stage washing with dilute acid and pure water to remove adsorbed salts and impurities.

[0031] Preferably, the calcination temperature is 500℃~700℃, for example: 500℃, 550℃, 600℃, 650℃ or 700℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the roasting time is 2h to 4h, for example: 2h, 2.5h, 3h, 3.5h or 4h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the acid solution includes a hydrochloric acid solution.

[0034] Preferably, the extractant comprises P227 and / or P204.

[0035] Preferably, the O / A ratio of the extraction process is 1:(1.5~2.5), for example: 1:1.5, 1:1.8, 1:2, 1:2.2 or 1:2.5, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the pH of the extraction process is 1 to 2, for example: 1, 1.2, 1.5, 1.8 or 2, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, the stripping agent in the stripping treatment includes a hydrochloric acid solution with a molar concentration of 1 mol / L to 2 mol / L, such as 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, or 2 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0039] Compared with the prior art, the present invention has the following beneficial effects: (1) After removing iron from the red mud in advance, the present invention uses a hydrochloric acid-fluoride composite leaching system to separate scandium from most of the impurity ions therein. Then, scandium is further purified by oxalic acid precipitation, calcination, acid dissolution and extraction to prepare a high-purity scandium-rich salt solution.

[0040] (2) The method for recovering scandium from red mud described in this invention can obtain a scandium-rich salt solution with a purity of over 94.8%, a scandium recovery rate of over 87.6%, a scandium leaching rate of over 92%, a titanium content of less than 0.05 g / L and an iron content of less than 0.1 g / L in the scandium-rich leachate, and a separation coefficient of scandium from titanium and iron that is greater than 200. Detailed Implementation

[0041] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0042] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0043] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0044] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed-ended features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various locations throughout the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth," etc., used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0045] In this invention, the order in which the steps are written in the methods described in each embodiment does not imply a strict execution order. The actual execution order of each step should be determined according to its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order in which they are written or in any order that does not conflict with the technology.

[0046] The mass percentages of various metal elements in the red mud used in the embodiments and comparative examples of this invention are as follows: The mass percentages of the main metallic elements in the red mud are as follows: Fe2O3: 40%, Al2O3: 20%, TiO2: 12%, SiO2: 15%, CaO: 8%, MgO: 3%, Sc2O3: 0.03%.

[0047] Example 1 This embodiment provides a method for recovering scandium from red mud, the method comprising the following steps: After drying, the red mud was ball-milled at 200 rpm for 4 hours to obtain activated red mud. The activated red mud was then subjected to reduction roasting at 650℃ for 2 hours in a mixed atmosphere of CO and nitrogen (CO volume percentage of 10%). After that, it was subjected to 0.2T magnetic separation to obtain iron-removed red mud. A composite leachate was prepared by mixing 4.5 mol / L hydrochloric acid with NaF. The composite leachate was then mixed with iron-removing red mud at a liquid-to-solid volume ratio of 6 mL / 1 g. The molar ratio of fluoride ions in the composite leachate to metal ions in the iron-removing red mud was controlled at 7:1. The mixture was subjected to pressure leaching at 95 °C, 0.35 MPa, and pH 0.8 for 3.5 h. Solid-liquid separation was performed to obtain scandium-rich leachate and titanium-containing leaching residue. The pH of the scandium-rich leachate was adjusted to 1, and the scandium-rich leachate was mixed with oxalic acid. The oxalic acid was then used to precipitate scandium at 60°C to obtain scandium oxalate precipitate. Scandium oxalate precipitate was sequentially acid-washed and washed with pure water, and then calcined at 600℃ for 3 hours to obtain crude scandium oxide. The crude scandium oxide was mixed with hydrochloric acid solution to dissolve it and obtain a crude scandium salt solution. Using P227 (10% P227 + 90% sulfonated kerosene by volume), with the O / A ratio controlled at 1:2 and the pH at 1.5, the crude scandium salt solution was extracted to obtain a scandium-rich organic phase. The scandium-rich organic phase was back-extracted using a hydrochloric acid solution with a molar concentration of 1.5 mol / L to obtain a scandium-rich salt solution.

[0048] Example 2 This embodiment provides a method for recovering scandium from red mud, the method comprising the following steps: After drying, the red mud was ball-milled at 200 rpm for 4 hours to obtain activated red mud. The activated red mud was then subjected to reduction roasting at 550℃ for 3 hours in a mixed atmosphere of CO and nitrogen (CO volume percentage of 5%). After that, it was subjected to 0.3T magnetic separation to obtain iron-removed red mud. A composite leachate was prepared by mixing 3 mol / L hydrochloric acid with NaF. The composite leachate was then mixed with iron-removing red mud at a liquid-to-solid volume ratio of 4 mL / 1 g. The molar ratio of fluoride ions in the composite leachate to metal ions in the iron-removing red mud was controlled at 6:1. The mixture was subjected to pressure leaching at 80 °C, 0.2 MPa, and pH 1 for 5 h. Solid-liquid separation was then performed to obtain scandium-rich leachate and titanium-containing leaching residue. The pH of the scandium-rich leachate was adjusted to 2, and the scandium-rich leachate was mixed with oxalic acid. The oxalic acid was then used to precipitate scandium at 70°C to obtain scandium oxalate precipitate. Scandium oxalate precipitate was sequentially acid-washed and washed with pure water, and then calcined at 500℃ for 4 hours to obtain crude scandium oxide. The crude scandium oxide was mixed with hydrochloric acid solution to dissolve and obtain crude scandium salt solution. Using P2O4 (10% P2O4 + 90% sulfonated kerosene by volume), with O / A ratio controlled at 1:1.5 and pH at 2, the crude scandium salt solution was extracted to obtain scandium-rich organic phase. The scandium-rich organic phase was back-extracted using hydrochloric acid solution with a molar concentration of 1 mol / L to obtain scandium-rich salt solution.

[0049] Example 3 This embodiment provides a method for recovering scandium from red mud, the method comprising the following steps: After drying, the red mud was ball-milled at 200 rpm for 4 hours to obtain activated red mud. The activated red mud was then subjected to reduction roasting at 750℃ for 1.5 hours in a mixed atmosphere of CO and nitrogen (CO volume percentage of 15%). After that, it was subjected to magnetic separation at 0.15T to obtain iron-removed red mud. A composite leachate was prepared by mixing 6 mol / L hydrochloric acid with NH4F. The composite leachate was then mixed with iron-removing red mud at a liquid-to-solid volume ratio of 8 mL / 1 g. The molar ratio of fluoride ions in the composite leachate to metal ions in the iron-removing red mud was controlled to be 8:1. The mixture was subjected to pressure leaching at 110 °C, 0.5 MPa, and pH 0.5 for 2 h. Solid-liquid separation was then performed to obtain scandium-rich leachate and titanium-containing leaching residue. The pH of the scandium-rich leachate was adjusted to 0.5, and the scandium-rich leachate was mixed with oxalic acid. The oxalic acid was then used to precipitate scandium at 40°C to obtain scandium oxalate precipitate. Scandium oxalate precipitate was sequentially acid-washed and washed with pure water, and then calcined at 700℃ for 2 hours to obtain crude scandium oxide. The crude scandium oxide was mixed with hydrochloric acid solution to dissolve it and obtain a crude scandium salt solution. Using P2O4 (10% P2O4 + 90% sulfonated kerosene by volume), with O / A ratio controlled at 1:2.5 and pH at 1, the crude scandium salt solution was extracted to obtain a scandium-rich organic phase. The scandium-rich organic phase was back-extracted using a 2 mol / L hydrochloric acid solution to obtain a scandium-rich salt solution.

[0050] Example 4 The only difference between this embodiment and Embodiment 1 is that the temperature of the reduction roasting treatment is 500℃, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0051] Example 5 The only difference between this embodiment and Embodiment 1 is that the temperature of the reduction roasting treatment is 800℃, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0052] Example 6 The only difference between this embodiment and Embodiment 1 is that the molar ratio of fluoride ions in the composite leachate to metal ions in the iron-removing red mud is 5:1. All other conditions and parameters are exactly the same as in Embodiment 1.

[0053] Example 7 The only difference between this embodiment and Embodiment 1 is that the molar ratio of fluoride ions in the composite leachate to metal ions in the iron-removing red mud is 9:1. All other conditions and parameters are exactly the same as in Embodiment 1.

[0054] Example 8 The only difference between this embodiment and Embodiment 1 is that the pH of the pressure leaching treatment is 0.3, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0055] Example 9 The only difference between this embodiment and Embodiment 1 is that the pH of the pressure leaching treatment is 1.2, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0056] Comparative Example 1 The only difference between this comparative example and Example 1 is that sodium fluoride is not added; all other conditions and parameters are exactly the same as in Example 1.

[0057] Performance testing: The purity and scandium recovery rate of the scandium-rich salt solution were determined, and the test results are shown in Table 1. Table 1 As shown in Table 1, the scandium-rich salt solutions of Examples 1-3 all had a purity of over 94.8% and a scandium recovery rate of over 87%, showing similar results. However, due to parameters deviating from the preferred range, the purity of Examples 4-9 decreased to 89.7%-93.1%, and the recovery rate decreased to 81.3%-85.0%, which was slightly worse than Examples 1-3 but significantly better than Comparative Example 1 (purity 78.5%, recovery rate 65.3%).

[0058] A comparison of Examples 1 and 4-5 shows that, in the method for recovering scandium from red mud described in this invention, the temperature of the reduction roasting treatment affects the recovery effect. Controlling the temperature of the reduction roasting treatment at 550℃~750℃ results in a better recovery effect. If the temperature of the reduction roasting treatment is too low, the reduction of Fe2O3 will be insufficient, and the magnetic separation for iron removal will be ineffective. If the temperature of the reduction roasting treatment is too high, energy consumption will increase and scandium may be encapsulated in the insoluble phase, leading to a decrease in the leaching rate.

[0059] Comparing Examples 1 and 6-7, it can be seen that in the method for recovering scandium from red mud according to the present invention, the amount of fluoride added affects the recovery effect. The recovery effect is better when the molar ratio of fluoride ions in the composite leachate to metal ions in the iron-removed red mud is controlled at (6-8):1. If the amount of fluoride added is too low, the titanium inhibition is insufficient, impurities enter the leachate, and the scandium purity decreases. If the amount of fluoride added is too high, the fluoride consumption increases, the cost increases, and too many scandium fluoride complexes may be formed, affecting the efficiency of subsequent scandium oxalate precipitation.

[0060] A comparison of Examples 1 and 8-9 shows that in the method for recovering scandium from red mud described in this invention, the pH of the pressure leaching treatment affects the recovery effect. Controlling the pH of the pressure leaching treatment at 0.5-1 results in a better recovery effect. If the pH of the pressure leaching treatment is too low, the titanium inhibition effect decreases, and impurities enter the leachate. If the pH of the pressure leaching treatment is too high, the scandium leaching rate decreases significantly, and other impurities compete for dissolution.

[0061] Comparing Example 1 and Comparative Example 1, it can be seen that the present invention uses an HCl-fluoride composite leaching system to perform pressure leaching treatment on iron-removing red mud, where fluoride ions react with Sc... 3+ Formation of stable complexes (such as ScF6) 3- Meanwhile, fluoride ions and impurity ions (such as Ti) 4+ ) forms insoluble fluorotitanate precipitates (such as TiF6) 2- (Salt precipitation) effectively suppresses impurity ions in the leaching residue, preventing them from entering the solution, thereby achieving the separation of scandium from impurity ions.

[0062] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method of recovering scandium from red mud, characterised in that, The method includes the following steps: After the red mud is subjected to reduction roasting treatment, it is then subjected to magnetic separation treatment to obtain iron-removed red mud; Hydrochloric acid and fluoride were mixed to obtain a composite leachate. The composite leachate was used to perform pressure leaching treatment on iron-removed red mud. Solid-liquid separation was performed to obtain scandium-rich leachate and titanium-containing leaching residue. The scandium-rich leachate was mixed with oxalic acid and subjected to oxalic acid precipitation to obtain scandium oxalate precipitate. Scandium oxalate precipitate was roasted to obtain crude scandium oxide. The crude scandium oxide was mixed with an acid solution to obtain a crude scandium salt solution. The crude scandium salt solution was then subjected to extraction and back-extraction treatments to obtain a scandium-rich salt solution.

2. The method of claim 1, wherein, Before the reduction roasting treatment, the red mud is subjected to drying and ball milling activation treatment in sequence.

3. The method of claim 1 or 2, wherein, The atmosphere for the reduction roasting process includes a mixture of reducing gas and nitrogen. Preferably, in the mixture of reducing gas and nitrogen, the volume percentage of reducing gas is 5% to 15%. Preferably, the reducing gas includes hydrogen and / or carbon monoxide; Preferably, the temperature of the reduction calcination treatment is 550℃~750℃; Preferably, the reduction calcination treatment time is 1.5h to 3h; Preferably, the magnetic field strength of the magnetic separation process is 0.15T~0.3T.

4. The method according to any one of claims 1 to 3, characterized in that, The molar concentration of the hydrochloric acid is 3 mol / L to 6 mol / L; Preferably, the fluoride includes any one or a combination of at least two of NaF, NH4F, or HF.

5. The method according to any one of claims 1 to 4, wherein The liquid-to-solid volume ratio of the composite leachate to the iron-removing red mud is (4~8) mL / 1g; Preferably, the molar ratio of fluoride ions in the composite leachate to metal ions in the iron-removing red mud is (6~8):

1.

6. The method according to any one of claims 1 to 5, wherein, The temperature for the pressure leaching treatment is 80℃~110℃; Preferably, the pressure of the pressure leaching treatment is 0.2 MPa to 0.5 MPa; Preferably, the pH of the pressure leaching treatment is 0.5~1; Preferably, the pressure leaching treatment lasts for 2 to 5 hours.

7. The method according to any one of claims 1 to 6, wherein Before mixing the scandium-rich leachate with oxalic acid, the pH of the scandium-rich leachate is adjusted to 0.5-2. Preferably, the temperature for the oxalic acid scandium precipitation treatment is 40℃~70℃.

8. The method according to any one of claims 1 to 7, wherein, The calcination temperature is 500℃~700℃; Preferably, the roasting time is 2h to 4h.

9. The method according to any one of claims 1-8, characterized in that, The acid solution includes a hydrochloric acid solution; Preferably, the extractant comprises P227 and / or P204; Preferably, the O / A ratio in the extraction process is 1:(1.5~2.5); Preferably, the pH of the extraction process is 1 to 2.

10. The method of any one of claims 1-9, wherein, The stripping agent for the stripping process includes a hydrochloric acid solution with a molar concentration of 1 mol / L to 2 mol / L.

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