Method for selective leaching of scandium from rare earth iron-rich minerals

Abstract

This invention belongs to the field of rare earth resource recovery, specifically relating to a method for selective leaching of scandium from rare earth iron-rich minerals. The method involves adding a reducing agent A and a sodium-based activator B to the rare earth iron-rich minerals, followed by calcination at a temperature T for a holding time t. This reduces the iron in the rare earth iron-rich minerals to metallic iron, simultaneously activating scandium and converting rare earth elements into insoluble complex salts. The reducing agent A can be lignite, etc.; the sodium-based activator can be sodium carbonate, etc.; the temperature T is 950-1100℃; and the time t is 1-2 hours. This invention also includes a scheme for separating iron through grinding and magnetic separation of the calcined minerals and an acid leaching scheme for the activated scandium-containing rare earth materials. The activation method of this invention can achieve iron reduction and efficient scandium leaching while simultaneously promoting the conversion of rare earth elements into insoluble forms, thereby achieving efficient separation of scandium from other rare earth elements and significantly reducing the difficulty of subsequent separation.

Description

Technical Field

[0001] This invention belongs to the field of combined fire-hydrometallurgical technology, specifically relating to the recovery and separation of scandium and other rare earth resources. Background Technology

[0002] Scandium has an average abundance of 36 ppm in the Earth's crust, but it is extremely dispersed. Currently, few independent scandium-bearing mineral reserves have been discovered, making it difficult to meet the raw material requirements for large-scale industrial extraction and recovery of scandium. In contrast, scandium is largely dispersed in other minerals, such as bauxite, rare earth elements, phosphate rock, ilmenite, tungsten ore, zircon, and coal. Scandium can be recovered as a byproduct of processing these minerals. In recent years, the scandium-bearing raw materials most frequently studied are nickel ore, titanium ore, bauxite, and rare earth ores. Nickel ore is a high-value scandium-bearing resource; typical laterite nickel ore contains nickel (1%-2%), cobalt (0.05%-0.10%), iron (15%-50%), aluminum (2%-5%), and trace amounts of scandium (0.005%-0.006%). Due to the rapid development of ternary lithium batteries, the processing volume of laterite nickel ore has been increasing year by year. Laterite nickel ore has become one of the main sources of scandium oxide in industry in recent years. Scandium mainly exists as an isomorphous compound of iron and aluminum in goethite and silicate minerals. Currently, hydrometallurgical processes for laterite nickel ore can be divided into high-pressure acid leaching, atmospheric pressure acid leaching, reduction roasting-ammonia leaching, chlorination roasting-water leaching, and sulfation roasting-water leaching. Industrially, high-pressure sulfuric acid leaching is still the main method, and scandium in the leachate is recovered by extraction-oxalic acid precipitation. The leaching temperature is as high as 180℃ or above.

[0003] Bauxite is the most common aluminum ore, containing alumina and hydroxides, and usually contains impurities such as iron oxide. In the global aluminum industry, the Bayer process is the main process for processing bauxite, which involves digesting the bauxite in an alkaline solution at 140-300°C to dissolve the aluminum. Typically, for every ton of alumina produced, an equal amount of red mud is generated as a byproduct / waste. Compared to primary bauxite ore, scandium enrichment in red mud is almost double. Therefore, recovering scandium oxide from red mud is of significant research value compared to primary bauxite. Scandium in red mud is generally found in hematite, goethite, and certain iron silicates and aluminosilicates, and has very poor acid solubility. Numerous studies have been conducted on scandium recovery processes from red mud, including sulfation roasting and water leaching, reduction roasting and phosphoric acid leaching and extraction, and sulfuric acid leaching-extraction. Some researchers have also proposed using scandium-containing titanium dioxide waste acid to leach red mud to further increase the scandium content in the leachate, but the leaching effect on scandium from red mud has not been ideal. Currently, industrial recovery of scandium from red mud has not yet been achieved.

[0004] Scandium recovery from titanium ore has been a research hotspot in recent years. Scandium recovery from titanium ore can be divided into recovery from primary scandium-containing titanium ore and recovery from scandium-containing industrial wastewater. Because scandium is located in a sparingly soluble phase, the extraction process is costly, and scandium recovery from primary scandium-containing titanium ore has remained at the laboratory stage. Industrially, scandium recovery from titanium ore mainly comes from waste acid generated after the sulfuric acid process for titanium dioxide production. Scandium in titanium dioxide waste acid exists in liquid form and can be directly extracted using an oxalic acid precipitation method to obtain scandium oxide, eliminating the need for leaching and significantly reducing recovery costs. However, this method only applies to liquid scandium-containing raw materials and does not solve the problem of high scandium leaching costs.

[0005] In existing technologies, although some companies have proposed using laterite nickel ore as raw material for high-pressure sulfuric acid leaching to recover scandium oxide, this process suffers from problems such as high pressure, high temperature, high acidity, and high energy consumption. Furthermore, the acid leaching solution has an extremely high iron content, leading to high costs for subsequent iron-scandium separation. In addition, for scandium-containing minerals that also contain rare earth elements, traditional activation roasting often uses chloride salts such as sodium chloride and calcium chloride, relying on the volatility and complexation of chloride ions to promote scandium conversion and leaching. While chloride salts are effective in disrupting mineral structures, these processes suffer from inherent drawbacks such as severe equipment corrosion, chlorine gas pollution, and limited selective separation of scandium from other rare earth elements. In contrast, this invention uses sodium-based activators such as sodium carbonate and sodium bicarbonate, which, at high temperatures, utilize sodium ions (Na+) to leach scandium. + The solid-phase reaction of sodium ions effectively disrupts the crystal structure of scandium-containing silicates (such as nepheline), releasing the scandium and converting it into an acid-soluble form. Simultaneously, sodium ions react with rare earth elements, transforming them into active precursors that readily form insoluble sodium sulfate rare earth double salts (NaRE(SO4)2·xH2O) during subsequent sulfuric acid leaching. This dual mechanism of "activating scandium and immobilizing rare earths" based on sodium ions enables highly efficient scandium leaching (leaching rate >90%) and effective rare earth inhibition (leaching rate <30%) under normal pressure and mild leaching conditions. This significantly improves the selective separation efficiency of scandium from other rare earth elements, providing a new approach for the clean and efficient utilization of complex scandium-rare earth ores. Summary of the Invention

[0006] To address the problems of poor acid solubility of scandium-bearing phases in scandium-bearing raw materials, high leaching costs due to associated rare earth elements, high iron content in leachate, and difficulty in rare earth separation, the primary objective of this invention is to provide a method for solid-state reduction magnetic separation of iron in complex iron-scandium rare earth ores, synergistic activation of scandium, and conversion of rare earth elements. The aim is to reduce iron in iron-rich rare earth minerals to metallic iron, simultaneously activate scandium from insoluble components, and transform rare earth elements into insoluble complex salt forms.

[0007] The second objective of this invention is to provide a method for selective leaching of scandium-containing rare earth nonmagnetic materials under normal pressure, which aims to efficiently leach scandium under mild conditions and inhibit the leaching of rare earth elements, thereby achieving efficient separation of the two.

[0008] Scandium in rare earth iron-rich minerals mainly exists as an isomorphous form of iron in a sparingly soluble silicate, nepheline. To address this issue, this invention provides the following improvement: A method for selectively leaching scandium from rare earth iron-rich minerals involves adding a reducing agent A and a sodium-based activator B to the rare earth iron-rich minerals, mixing them thoroughly, and then subjecting them to a heat-preserving roasting treatment at temperature T for a time t. This reduces the iron in the rare earth iron-rich minerals to metallic iron, simultaneously activating scandium and converting rare earth elements to sodium, yielding a reduction-roasting activated product. This product is then subjected to magnetic separation to separate metallic iron from the roasted ore, obtaining a metallic iron product and scandium-containing rare earth non-magnetic material. The scandium-containing rare earth non-magnetic material is then acid-leached to obtain a scandium-containing leachate.

[0009] The reducing agent A is selected from at least one of lignite, anthracite, coke, pulverized coal, graphite, and biochar; the sodium-based activator B is selected from at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, and sodium sulfate; preferably, the sodium-based activator B is at least one of sodium carbonate and sodium bicarbonate.

[0010] The temperature T is 950-1100℃;

[0011] The time t mentioned is 1-2 hours.

[0012] This invention innovatively mixes rare earth iron-rich minerals with appropriate amounts of reducing agent A and sodium-based activator B, then presses the mixture into lumps under pressure and holds it at a temperature T. This process promotes the reduction of iron in the rare earth iron-rich minerals from iron oxide to metallic iron, which can then be separated by magnetic separation to obtain metallic iron products, reducing the difficulty of iron-scandium separation in subsequent leaching solutions. Furthermore, at high temperatures, under the action of the sodium-based activator, scandium present in the insoluble nepheline phase is also activated, while associated rare earth elements undergo sodium conversion, forming insoluble rare earth complex salts in subsequent acid leaching, thereby achieving efficient separation of scandium from other rare earth elements. This study demonstrates that, under the synergistic effect of the reducing agent and sodium-based activator at high temperatures, effective activation of scandium present in the insoluble phase of rare earth iron-rich minerals and the transformation of other rare earth elements can be achieved, significantly improving the selective acid leaching behavior of scandium. This invention employs an appropriate amount of reducing agent for internal agglomeration. During calcination, the internally formulated solid reducing agent slowly generates reducing gases such as CO, forming and maintaining a locally strong reducing atmosphere within the agglomerates. This ensures the complete reduction of iron oxides and the decomposition of scandium-containing phases. The gases produced by the decomposition of the solid reducing agent generate bubbles and pores in the liquid phase, which facilitates the migration, collision, and growth of metallic iron grains, forming metallic iron particles that are easier to separate magnetically. Furthermore, compared to systems requiring a continuous flow of gaseous reducing agents such as CO and H2, the internally formulated solid reducing agent process is simpler, requires less equipment, and is safer. It eliminates the need for complex gas delivery, preheating, and other processing systems, making it suitable for large-scale industrial applications. Simultaneously, the internally formulated solid reducing agent and sodium-based activator used in this invention, in conjunction with subsequent processes, also facilitate the selective leaching and recovery of Sc.

[0013] In this invention, the rare earth iron-rich mineral can be any raw material containing iron, scandium, and rare earth elements. There are no particular requirements for the content of each element in the rare earth iron-rich mineral described in this invention; for example, the iron content can be 20-40 wt%, the scandium oxide content can be 50-1000 ppm, and the total rare earth oxide (REO) content can be 0.1-10%.

[0014] The rare earth iron-rich minerals described in this invention mainly consist of aegirine, quartz, hematite, and rare earth-containing silicate phases.

[0015] In this invention, scandium mainly exists as an isomorphous form of iron in the silicate mineral nepheline, which has very poor acid solubility. Rare earth elements are also commonly found in similar silicate or phosphate minerals. In this invention, the particle size of the rare earth-rich iron mineral is less than or equal to 80 μm, preferably 20-80 μm, and more preferably 30-50 μm. In this invention, excessively coarse particle size of the rare earth-rich iron mineral will restrict mass transfer during roasting, affecting the effects of iron reduction, scandium activation, and rare earth conversion; excessively fine particle size will increase pretreatment costs and is detrimental to agglomeration operations.

[0016] In this invention, the main iron-bearing phase in the rare earth iron-rich mineral is hematite, and the main scandium-bearing phase is aegirine, a silicate mineral with very poor acid solubility. Through the innovative activation process and mechanism described in this invention, effective activation of scandium and its selective separation from rare earth elements can be achieved.

[0017] In this invention, the combination of reducing agent A, sodium-based activator B, and temperature T is key to the synergistic activation of scandium by solid-state reduced iron and the conversion of rare earth elements, thereby improving the selective acid leaching behavior of scandium. Preferably, the amount of reducing agent A is 2-15 wt% of rare earth iron-rich minerals, more preferably 2.5-12 wt%, further preferably 5-12 wt%, and even more preferably 6-8 wt%.

[0018] Preferably, the amount of sodium-based activator B is 4-15 wt% of rare earth iron-rich minerals, more preferably 5-12 wt%, and even more preferably 8-11 wt%.

[0019] Preferably, the roasting temperature T is 950~1100℃, and more preferably 1000~1050℃. In this invention, the roasting method for rare earth iron-rich minerals can effectively reduce iron in the rare earth iron-rich minerals from iron oxide to metallic iron. Grinding and magnetic separation of the roasting product can separate the metallic iron from the roasting product.

[0020] In this invention, the grinding and magnetic separation experiment is based on the characteristic that the metallic iron in the roasting product contains magnetism. The metallic iron is separated by magnetic separation to obtain metallic iron products and scandium-containing rare earth non-magnetic materials.

[0021] Preferably, the grinding equipment is a cone ball mill, the grinding time is 10-50 minutes, and the slurry concentration is 40%-60%.

[0022] Preferably, the magnetic separation device is a magnetic separator tube with a magnetic field strength of 500-1500 Gs; preferably, the iron content of the metallic iron product is greater than 90 wt%.

[0023] Preferably, the scandium oxide content in the scandium-containing rare earth non-magnetic material is 100-2000 ppm. This invention also provides a method for selective leaching of scandium-containing rare earth non-magnetic materials under normal pressure. Using the roasting and activation method described in this invention, rare earth-rich iron minerals are treated, and the scandium oxide in the scandium-containing rare earth non-magnetic material obtained by magnetic separation is effectively activated, while other rare earth elements are converted into insoluble forms. Subsequently, the material is subjected to acid leaching to obtain a scandium-containing leachate with high scandium and low rare earth content.

[0024] In this invention, the leaching method for scandium-containing rare earth non-magnetic materials uses an inorganic strong acid aqueous solution, preferably a sulfuric acid solution, in the acid leaching stage.

[0025] Preferably, the solute concentration of the acid solution is 0.2M or higher, and more preferably 0.5~3M;

[0026] The leaching liquid-to-solid ratio is 3~10 mL / g, preferably 4~7 mL / g. In the leaching method for scandium-containing rare earth non-magnetic materials of the present invention, the temperature of the acid leaching stage is above 5°C, preferably 10~95°C, and further preferably 25~45°C.

[0027] In this invention, the acid leaching stage is carried out under normal pressure.

[0028] In this invention, the leaching method for scandium-containing rare earth non-magnetic materials involves an acid leaching stage lasting at least 10 minutes, preferably 30 minutes to 2 hours, and more preferably 1 hour to 2 hours. As a preferred embodiment, when the amount of reducing agent A is 7.5 wt% of the rare earth-rich iron mineral and the amount of sodium-based activator B is 10 wt% of the rare earth-rich iron mineral, after calcination at 1100°C for 2 hours, magnetic separation is performed to obtain scandium-containing rare earth non-magnetic materials. The scandium-containing rare earth non-magnetic materials are then acid-leached to obtain a scandium-containing leachate. The acid leaching uses 2 mol / L sulfuric acid, the leachate solid-to-solid ratio is 7.5 mL / g, the leaching temperature is 35°C, and after leaching for 30 minutes, the scandium leaching rate is greater than 95%, while the leaching rate of other rare earth elements is less than 5%.

[0029] This invention achieves iron reduction and selective and efficient leaching of scandium, while significantly reducing the content of iron and other rare earth elements in the leachate and making the scandium morphology suitable for extraction, thus creating favorable conditions for the subsequent efficient separation and enrichment of scandium using a fluorine-containing extraction system.

[0030] Beneficial effects

[0031] 1. This invention innovatively uses sodium-based activators (such as Na2CO3, Na2O, NaHCO3) to replace traditional chloride salts. During high-temperature roasting, sodium ions destroy the structure of scandium-containing silicates, efficiently activating scandium. At the same time, it promotes the transformation of associated rare earth elements into insoluble sulfate double salts and other forms, achieving selective separation of scandium from other rare earth elements at the source and avoiding equipment corrosion and environmental pollution problems caused by chloride salt processes.

[0032] 2. By using a reduction roasting-magnetic separation process, while activating scandium and other rare earth elements, the iron in the raw materials is efficiently reduced to metallic iron and separated. This not only yields high-grade iron products but also greatly reduces the iron content in the subsequent leachate, simplifying the scandium extraction and enrichment process.

[0033] 3. Scandium-containing rare earth non-magnetic materials treated by the method of this invention can achieve efficient leaching of scandium (leaching rate >90%) under mild conditions of normal pressure, low acid and low temperature, while the leaching rate of other rare earths is significantly reduced (usually <30%). The leaching selectivity is high, the acid consumption is low, and the cost advantage is obvious.

[0034] 4. The final scandium-containing leachate has the characteristics of high scandium concentration and low iron and other rare earth impurities, making it particularly suitable for direct entry into a fluorine-containing extraction system using P2O4, P5O7, etc. as extractants for high-purity scandium extraction, forming a complete, efficient, and clean scandium resource recovery process chain. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments.

[0036] The rare earth iron-rich minerals used are common complex minerals containing iron, scandium, and rare earth elements. For example, as an example, in the following cases, unless otherwise stated, the iron content is 23-28 wt%, the scandium oxide content is 230-250 ppm, and the total rare earth oxide (REO) content is 3.5-4.1%; in the rare earth iron-rich minerals, the main iron-bearing phase is hematite, the main scandium-bearing phase is aegirine, and other rare earth elements are mostly found in the silicate phase.

[0037] Example 1

[0038] Step (1): Roasting

[0039] Rare earth iron-rich minerals (iron content 25.4wt%, scandium oxide content 242ppm, REO content 1180ppm, particle size d) 50 The mixture of lignite (approximately 35 μm) with reducing agent A (lignite, 7.5 wt%, particle size less than 74 μm) and sodium-based activator B (sodium carbonate, 10 wt%, particle size less than 74 μm) was uniformly mixed, pressed into pellets, and then calcined at 1100℃ (temperature T) for 2 hours to obtain the calcined product.

[0040] Step (2): Grinding and selection

[0041] The roasted product was crushed and milled in a conical ball mill for 15 minutes (slurry concentration 50%). Magnetic metallic iron and scandium-containing rare earth non-magnetic material were separated by a magnetic separator (magnetic separation intensity 1000 Gs). The iron content in the obtained magnetic material was 91.2%, and the iron recovery rate was 85.0%. The scandium oxide content in the scandium-containing rare earth non-magnetic material was 385 ppm, and the scandium recovery rate was 97.1%.

[0042] Step (3): Acid leaching

[0043] Scandium-containing rare earth non-magnetic materials were leached in a sulfuric acid solution with an initial sulfuric acid concentration of 2 mol / L, a leaching liquid-to-solid ratio of 7.5 mL / g, a leaching temperature of 35℃, and a leaching time of 30 min. The leaching rate of scandium was 96.5%, and the leaching rate of other rare earth elements was 4.3%.

[0044] The scandium-containing leachate obtained by the above acid leaching treatment has significantly reduced iron and other rare earth content. It can be directly or after simple conditioning into an extraction system using fluoride ions as a regulator and P2O4 or P5O7 as an extractant for efficient separation and enrichment of scandium.

[0045] Example 2

[0046] Compared with Example 1, the only difference is that the amount of activator B is 8wt%, the calcination holding time is 1.5h, and the sulfuric acid leaching time is 60min; after treatment in steps (1) and (2), the iron content in the obtained magnetic material is 90.6%, and the iron recovery rate is 84.3%; the scandium oxide content in the scandium-containing rare earth non-magnetic material is 378ppm, and the scandium recovery rate is 95.5%. After treatment in step (3), the scandium leaching rate is 94.8%, and the leaching rate of other rare earths is 4.7%.

[0047] Example 3

[0048] Compared with Example 1, the only difference is that the amount of reducing agent A is 10 wt% and the amount of activator B is 5 wt%; after treatment in steps (1) and (2), the iron content in the obtained magnetic material is 90.1% and the iron recovery rate is 85.9%; the scandium oxide content in the scandium-containing rare earth non-magnetic material is 379 ppm and the scandium recovery rate is 96.3%. After treatment in step (3), the scandium leaching rate is 93.1% and the leaching rate of other rare earths is 3.4%.

[0049] Example 4

[0050] Compared with Example 1, the only difference is that the calcination temperature is 1000℃; after treatment in steps (1) and (2), the iron content in the obtained magnetic material is 88.6%, and the iron recovery rate is 82.4%; the scandium oxide content in the scandium-containing rare earth non-magnetic material is 361ppm, and the scandium recovery rate is 93.6%. After treatment in step (3), the scandium leaching rate is 92.2%, and the leaching rate of other rare earths is 4.8%.

[0051] Example 5

[0052] Compared with Example 1, the only difference is that the sodium-based activator B is sodium bicarbonate (10wt%); after treatment in steps (1) and (2), the iron content in the obtained magnetic material is 90.0%, and the iron recovery rate is 85.8%; the scandium oxide content in the scandium-containing rare earth non-magnetic material is 380ppm, and the scandium recovery rate is 96.2%. After treatment in step (3), the scandium leaching rate is 97.2%, and the leaching rate of other rare earths is 4.2%.

[0053] Example 6

[0054] Compared with Example 1, the only difference is that the rare earth iron-rich minerals have a higher REO content, approximately 1850 ppm; after treatment in steps (1) and (2), the magnetic material has an iron content of 90.2% and an iron recovery rate of 86.5%; the scandium oxide content in the scandium-containing rare earth non-magnetic material is 382 ppm and the scandium recovery rate is 96.8%. After treatment in step (3), the scandium leaching rate is 95.1%, and the leaching rate of other rare earth elements is 4.6%.

[0055] Example 7

[0056] Compared with Example 1, the amount of reducing agent A was 12.0 wt%; after treatment in steps (1) and (2), the iron content in the obtained magnetic material was 90.5%, and the iron recovery rate was 86.9%; the scandium oxide content in the scandium-containing rare earth non-magnetic material was 383 ppm, and the scandium recovery rate was 96.7%. After treatment in step (3), the scandium leaching rate was 93.8%, and the leaching rate of other rare earth elements was 3.6%.

[0057] Example 8

[0058] Compared with Example 1, the amount of reducing agent A was 5.0 wt%; after treatment in steps (1) and (2), the iron content in the obtained magnetic material was 89.8%, and the iron recovery rate was 84.5%; the scandium oxide content in the scandium-containing rare earth non-magnetic material was 376 ppm, and the scandium recovery rate was 95.4%. After treatment in step (3), the scandium leaching rate was 92.9%, and the leaching rate of other rare earth elements was 4.8%.

[0059] Example 9

[0060] Compared with Example 1, the only difference is that the reducing agent A is anthracite (5.0 wt%, particle size less than 74 μm); after treatment in steps (1) and (2), the iron content in the obtained magnetic material is 90.1%, and the iron recovery rate is 85.9%; the scandium oxide content in the scandium-containing rare earth non-magnetic material is 379 ppm, and the scandium recovery rate is 96.1%. After treatment in step (3), the scandium leaching rate is 94.5%, and the leaching rate of other rare earths is 3.7%.

[0061] Example 10

[0062] Compared with Example 1, the amount of reducing agent A was 3.0 wt%, and the sulfuric acid concentration was 1.5 mol / L. After treatment in steps (1) and (2), the iron content in the obtained magnetic material was 88.5%, and the iron recovery rate was 80.9%. The scandium oxide content in the scandium-containing rare earth non-magnetic material was 371 ppm, and the scandium recovery rate was 94.0%. After treatment in step (3), the scandium leaching rate was 91.3%, and the leaching rate of other rare earth elements was 4.4%.

[0063] Comparative Example 1

[0064] Compared with Example 1, the difference is that the rare earth iron-rich minerals that have not undergone the roasting treatment in step 1 are directly subjected to acid leaching. The acid leaching conditions are the same as in Example 1, with a scandium leaching rate of 10.2% and other rare earth leaching rates of 65.8%.

[0065] Comparative Example 2

[0066] Compared with Example 1, the difference is that the rare earth iron-rich minerals that have not undergone the roasting treatment in step 1 are directly subjected to acid leaching treatment. The acid leaching conditions are: initial sulfuric acid concentration of 4 mol / L, leaching liquid-to-solid ratio of 10 mL / g, leaching temperature of 35℃, and leaching time of 1 h. Under these conditions, the scandium leaching rate is 14.6%, and the leaching rate of other rare earths is 78.5%.

[0067] Comparative Example 3

[0068] Compared with Example 1, the difference is that the rare earth iron-rich minerals that have not undergone the roasting treatment in step 1 are directly subjected to acid leaching treatment. The acid leaching treatment conditions are: initial sulfuric acid concentration of 4 mol / L, leaching liquid-to-solid ratio of 10 mL / g, leaching temperature of 185℃, and leaching time of 2 h. Under these conditions, the scandium leaching rate is 52.3%, and the leaching rate of other rare earths is 89.6%.

[0069] Comparative Example 4

[0070] Compared with Example 1, the difference is that sodium-based activator B was not added. Other conditions were the same. After treatment in steps (1) and (2), the iron content in the obtained magnetic material was 88.8%, and the iron recovery rate was 81.3%; the scandium oxide content in the scandium-containing rare earth non-magnetic material was 310 ppm, and the scandium recovery rate was 84.1%. After treatment in step (3), the scandium leaching rate was 38.7%, and the leaching rate of other rare earth elements was 38.2%. The results show that without the addition of sodium-based activator B, it is difficult to achieve efficient activation of scandium by reduction roasting alone, nor can it promote the conversion of rare earth elements into insoluble complex salts, resulting in low leaching rates of both scandium and rare earth elements and poor separation effect.

[0071] Comparative Example 5

[0072] Compared with Example 1, the difference is that solid reducing agent A is not added, and a reducing gas (a mixture of CO and N2, with a CO volume fraction of 30% and a total flow rate of 500 mL / min) is introduced during the calcination process. Other conditions are the same. After treatment in steps (1) and (2), the iron content in the obtained magnetic material is 84.8%, and the iron recovery rate is 77.6%; the scandium oxide content in the scandium-containing rare earth non-magnetic material is 358 ppm, and the scandium recovery rate is 90.5%. After treatment in step (3), the scandium leaching rate is 74.2%, and the leaching rate of other rare earths is 58.9%. When using a gaseous reducing agent, the activation efficiency of scandium and the inhibition effect of rare earths both decrease significantly, and the process complexity and safety risks increase.

[0073] Comparative Example 6

[0074] Compared with Example 1, the difference is that the amount of reducing agent A added is 20 wt / %. After treatment in steps (1) and (2), the iron content in the obtained magnetic material is 86.3%, and the iron recovery rate is 82.1%; the scandium oxide content in the scandium-containing rare earth non-magnetic material is 373 ppm, and the scandium recovery rate is 94.2%. After treatment in step (3), the scandium leaching rate is 80.8%, and the leaching rate of other rare earths is 48.5%. Excessive addition of reducing agent will lead to an increase in carbon inclusions in the metallic iron product, a decrease in iron grade, and an excessively strong reducing atmosphere is not conducive to the sodiumization reaction of scandium and the directional conversion of other rare earths, which will subsequently lead to a significant decrease in the scandium leaching rate.

[0075] Comparative Example 7

[0076] Compared to Example 1, the difference lies in the addition amount of sodium-based activator B, which is 20 wt%. During calcination, the product severely agglomerated, making crushing and grinding difficult. After barely managed treatment and magnetic separation, the iron content of the magnetic material was 84.5%, with an iron recovery rate of 76.8%. The scandium-containing rare earth non-magnetic material exhibited severe agglomeration, and the scandium oxide content was uneven. The acid leaching process resulted in a dramatic increase in acid consumption, with a scandium leaching rate of only 71.5% and other rare earth leaching rates of 41.2%.

Claims

1. A method for selective leaching of scandium from rare earth iron-rich minerals, characterized in that: A reducing agent A and a sodium-based activator B are added to rare earth iron-rich minerals, and then the minerals are subjected to heat-preserving roasting at a temperature T for a time t. This reduces the iron in the rare earth iron-rich minerals to metallic iron, simultaneously activating scandium and converting rare earths to sodium, thus obtaining a reduction roasting activation product. The activated product from the reduction roasting process is then ground and magnetically separated to separate metallic iron from the roasted ore, yielding metallic iron products and scandium-containing rare earth non-magnetic materials. The scandium-containing rare earth non-magnetic materials are then acid-leached to obtain a scandium-containing leachate. The reducing agent A is selected from at least one of lignite, anthracite, coke, pulverized coal, graphite, and biochar; the amount of reducing agent A is 5-12 wt% of the rare earth iron-rich mineral. The sodium-based activator B is selected from at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, and sodium sulfate; the amount of sodium-based activator B is 5-12 wt% of the rare earth iron-rich mineral. The temperature T is 1100℃; The time t mentioned is 2 hours; The grinding equipment is a cone ball mill, with a grinding time of 10-50 minutes and a slurry concentration of 40%-60%. The magnetic separator is a magnetic separator tube with a magnetic field strength of 500-1500 Gs; Scandium-containing rare earth non-magnetic materials were leached with acid to obtain a scandium-containing leachate. The acid leaching was carried out using 2 mol / L sulfuric acid, with a solid-liquid ratio of 7.5 mL / g and a leaching temperature of 35℃. After leaching for 30 min, the scandium leaching rate was greater than 95%, while the leaching rate of other rare earth elements was less than 5%. Scandium was extracted from the scandium-containing leachate using a fluorine-containing extraction system with P2O4 and P5O7 as extractants.

2. The method for selective leaching of scandium from rare earth iron-rich minerals as described in claim 1, characterized in that: The rare earth iron-rich mineral contains 20-40 wt% iron, 50-1000 ppm scandium oxide, and 0.1 wt% to 10 wt% rare earth oxides; the particle size of the rare earth iron-rich mineral is 20-80 μm.

3. The method for selective leaching of scandium from rare earth iron-rich minerals as described in claim 1, characterized in that: The amount of reducing agent A is 7.5 wt% of the rare earth iron-rich mineral; The amount of sodium-based activator B is 10 wt% of the rare earth iron-rich mineral.

4. The method for selective leaching of scandium from rare earth iron-rich minerals as described in claim 1, characterized in that: Metallic iron is separated from the reduction roasting activation products by grinding and magnetic separation.

5. The method for selective leaching of scandium from rare earth iron-rich minerals as described in claim 4, characterized in that: The obtained metallic iron product has an iron content greater than 90 wt%; The scandium oxide content in the obtained scandium-containing rare earth non-magnetic materials is 100-2000 ppm.