Method for leaching ion-type rare earth ore by using distillation by-product waste liquid of vetiver essential oil

Abstract

The application relates to the technical field of rare earth extraction and processing, and particularly discloses a method for leaching ion-type rare earth ore by using waste liquid byproduct of vetiver essential oil distillation. The method uses the waste liquid byproduct of vetiver essential oil distillation as a leaching medium, realizes selective separation of rare earth and impurity ions such as aluminum and iron by pH regulation, effectively reduces the impurity content in the leaching liquid, solves the problem of poor selectivity of organic acid leaching, and lays a foundation for obtaining high-purity rare earth oxides; meanwhile, the method realizes resource utilization of the waste distillation liquid by treating the waste liquid byproduct of vetiver essential oil distillation as ore.

Description

Technical Field

[0001] This application relates to the field of rare earth extraction and processing technology, and more specifically, it relates to a method for leaching ion-adsorption rare earth ores using waste liquid from the distillation of vetiver essential oil. Background Technology

[0002] Ion-adsorption rare earth deposits (also known as weathering crust leaching rare earth deposits) are an important strategic resource in my country. They are rich in medium and heavy rare earth elements such as praseodymium, neodymium, dysprosium, and terbium, and are widely used in permanent magnet materials, luminescent materials, catalysis, and high-end manufacturing. In these deposits, rare earth elements are mainly present on the surface of clay minerals such as kaolinite and hydrous kaolinite in the form of hydrated or hydroxyl hydrated cations through ion adsorption. Ion exchange or desorption must be carried out with the help of cations or protons in the leaching agent to transfer the rare earth elements from the mineral phase to the liquid phase for recovery.

[0003] The most widely used leaching methods in early and current industrial applications are in-pond leaching or heap leaching with inorganic ammonium salts (such as ammonium sulfate and ammonium chloride). These methods use ammonium ions to exchange rare earth cations on the surface of clay minerals, resulting in a simple process and high leaching efficiency. However, ammonium salt leaching agents such as ammonium sulfate generate large amounts of ammonia-nitrogen-containing wastewater during leaching and subsequent treatment. This wastewater seeps into surface and groundwater bodies with the leachate, easily causing environmental problems such as eutrophication and soil acidification. Furthermore, ammonium ions remain in the ore body and are difficult to completely leach, and long-term in-situ injection poses a risk of inducing secondary geological disasters such as landslides. Therefore, developing environmentally friendly alternative leaching systems has become a research direction in this field.

[0004] To reduce ammonia nitrogen pollution from inorganic ammonium salts, existing technologies have gradually developed leaching routes using organic acids as leaching agents. For example, patent application CN116949287A discloses a method for leaching ion-adsorption rare earth ores using organic acids with enhanced coupled ion exchange. This method uses an organic acid solution with a pH of 0.5–3.0 as the leaching agent, mixed with the ion-adsorption rare earth ores, to obtain a leaching solution and a leaching residue. The leaching solution is recycled. Subsequently, a salt solution with a mass fraction of 1.0–5.0 wt% and a pH of 3.0–5.5 is used to perform a secondary ion exchange on the leaching residue. After solid-liquid separation, an exchange solution and an exchange residue are obtained. The salt solution includes inorganic salts such as aluminum sulfate, ammonium sulfate, and ammonium chloride. This method utilizes the proton exchange and carboxyl chelation of organic acids to leach rare earths, thus reducing the introduction of ammonia nitrogen during the leaching stage to a certain extent.

[0005] However, organic acids have a strong proton exchange and complexation ability on rare earth ions and impurity ions such as aluminum and iron in clay mineral phases. When leaching under low pH conditions, impurities such as aluminum and iron are dissolved in large quantities along with rare earths, resulting in high impurity content in the leachate, high subsequent impurity removal load, and loss of rare earths due to entrainment. Summary of the Invention

[0006] In order to reduce the impurity content in the leachate and solve the problem of poor selectivity in organic acid leaching, this application provides a method for leaching ion-adsorption rare earth minerals using waste liquid from the distillation of vetiver essential oil.

[0007] This application provides a method for leaching ion-adsorption rare earth ores using by-product waste liquid from vetiver oil distillation, employing the following technical solution: A method for leaching ion-adsorption rare earth minerals using waste liquid from vetiver oil distillation includes the following steps: S1, adjust the pH of the by-product waste liquid from the distillation of vetiver essential oil to 3.8-4.2 and heat it to 45-72℃ to obtain the extract; S2, mix the leachate with ion-adsorption type rare earth ore for heap leaching or pool leaching, and collect the leachate and tailings. S3. Adjust the pH of the leachate to 5.0-5.5 to cause impurity ions to form hydroxide precipitates. Remove the precipitates by solid-liquid separation to obtain purified solution. S4. Oxalic acid is added to the above purified solution as needed to precipitate rare earth ions, and solid-liquid separation is performed to obtain rare earth oxalate and precipitate mother liquor. S5. Rare earth oxalate is washed and then calcined at 750-850℃ for 1-3 hours to obtain rare earth oxides.

[0008] By adopting the above technical solution, this application uses the by-product waste liquid from vetiver oil distillation as the core medium, utilizing the dual effects of acidolysis and complexation of its natural organic acids to achieve efficient leaching of ionic rare earth elements under mild acidic conditions. The mechanism is as follows: under pH 3.8–4.2 conditions, the carboxyl anions of small-molecule organic acids (oxalic acid, citric acid, malic acid, phenolic acid, etc.) in the waste liquid form stable monodentate or bidentate complexes with rare earth cations, significantly reducing the adsorption energy of rare earth ions on the surface of clay minerals, thereby achieving efficient leaching of ionic rare earth elements at lower pH levels. + Highly efficient ion exchange and desorption can be achieved at the specified concentration. Simultaneously, step S3 adjusts the pH of the leachate to 5.0–5.5, utilizing the preferential hydrolysis of impurity ions such as aluminum and iron to form hydroxide precipitates within this pH range, thus achieving selective separation of rare earth elements from the main impurities. This impurity removal step effectively reduces the content of interfering ions such as aluminum and iron in the leachate, significantly mitigating impurity entrainment losses in the subsequent oxalic acid precipitation process, laying the foundation for obtaining high-purity rare earth oxides.

[0009] Preferably, in S1, the preparation method of the by-product waste liquid from the distillation of vetiver essential oil includes the following steps: taking the underground fibrous roots of 12-18 month old vetiver, washing and removing mud, drying until the moisture content is less than 10%, cutting them into 2-5 cm root segments, and soaking them in clean water for 10-20 hours; mixing the soaked root segments with water at a mass ratio of 1:9 to 1:14, and distilling at 95-99°C under normal pressure for 8-18 hours; filtering the mixture at the bottom of the vessel after distillation, and collecting the filtrate as the by-product waste liquid from the distillation of vetiver essential oil; and collecting the aqueous phase obtained after condensing and separating the oil and water from the distilled vapor during the distillation process separately for later use.

[0010] By adopting the above technical solution, the optimal raw material source and preparation process of the waste liquid are defined. By selecting vetiver roots of a specific age and precisely controlling the parameters of washing, drying, cutting, soaking and distillation, the content of active organic acids, flavonoids and polysaccharides in the obtained waste liquid can be kept within the range required for efficient leaching, thus ensuring the stability and repeatability of the subsequent leaching effect.

[0011] Preferably, in S1, the total amount of small-molecule organic acids in the by-product waste liquid from the distillation of vetiver essential oil is 8-18 g / L, the total flavonoid content is 0.6-1.4 g / L, and the water-soluble polysaccharide content is 2.2-4.5 g / L; the oxalic acid content in the small-molecule organic acids is 2.0-4.5 g / L.

[0012] By adopting the above technical solution, high-content small-molecule organic acids provide sufficient H+. + Together with complexing ligands, flavonoids help enhance the selectivity for medium and heavy rare earth elements, while polysaccharide components help inhibit the dissolution of impurities and regulate solution properties. The three work synergistically to endow the waste liquid with excellent selective leaching ability and biodegradability.

[0013] Preferably, before adjusting the pH in S1, an enzymatic pretreatment is further included: adding a compound biological enzyme agent to the by-product waste liquid from the distillation of vetiver essential oil, adjusting the pH to 4.5-5.0 with citric acid or sodium hydroxide, enzymatically hydrolyzing at 35-40°C for 2-4 hours, and then adjusting the pH back to 3.8-4.2 after enzymatic hydrolysis; the compound biological enzyme agent contains 0.05-0.2 g / L of pectinase and 0.1-0.3 g / L of cellulase.

[0014] By adopting the above technical solution, a compound biological enzyme is introduced for enzymatic pretreatment before the leachate is prepared, and the pH is adjusted to the optimal range of pectinase and cellulase (4.5-5.0). This can effectively destroy plant cell wall fragments and macromolecular cross-linking structures in the waste liquid, and fully release bound organic acids and flavonoid aglycones into free active forms, significantly improving the available concentration and reactivity of effective components in the leachate.

[0015] Preferably, in S2, the liquid-to-solid ratio of a single cycle of heap leaching or pool leaching is 3-8 mL / g, where the liquid-to-solid ratio refers to the ratio of the volume of the leaching solution to the mass of the ore during each batch of cycles. The heap leaching or pool leaching employs a two-stage variable-temperature countercurrent leaching process: the first stage involves circulating spray leaching at 45-50°C for 3-5 hours, and the first stage enriched solution is collected for the recovery of medium and heavy rare earth elements; subsequently, the ore heap is heated to 65-72°C for the second stage of deep leaching, and the second stage leaching solution is collected. The endpoint of the circulating spray is determined by the rare earth concentration in the mother liquor; when the difference in rare earth concentration measured between two adjacent samples is ≤10 mg / L, the cycle is stopped.

[0016] By adopting the above technical solution, a two-stage variable temperature countercurrent leaching process is used. The low-temperature front stage preferentially releases complexing components with high affinity for medium and heavy rare earth elements, achieving preliminary grouping and enrichment of light and heavy rare earth elements at the leaching source, obtaining a high-value medium and heavy rare earth enriched solution, and significantly reducing the cost of subsequent full-element separation. The high-temperature back stage leverages the strong complexing ability of oxalic acid at higher temperatures to deeply recover residual light rare earth elements and improve the overall recovery rate.

[0017] Preferably, vetiver oil distillation by-product waste liquid is added to the first enrichment solution, and air is introduced for aeration. The reaction is carried out at pH 4.0–4.5 and temperature 50–60°C for 1–1.5 hours. Under aeration (oxygen) conditions, Ce… 3+ Oxidized to Ce 4+ Flavonoids in the waste liquid act as coordination promoters and react with Ce. 4+ A stable complex is formed, which promotes its preferential hydrolysis under weakly acidic conditions to generate Ce(OH)4 precipitate. After solid-liquid separation to remove the precipitate, the filtrate is combined with the second-stage leachate and enters S3.

[0018] By adopting the above technical solution, some undigested waste liquid is added to the first enrichment solution, utilizing the flavonoids therein to react with Ce under aeration conditions. 4+ The strong coordination complexation of cerium enables highly selective pre-separation of cerium. This method eliminates the cumbersome steps of additional flavonoid extract preparation, achieving cerium extraction at zero cost and with zero added complexity. It produces high-purity cerium-rich products and reduces the amount of cerium doping in rare earth oxalate, thus improving the quality of the final product.

[0019] Preferably, in S3, the pH is adjusted using the aqueous phase obtained by oil-water separation during the distillation of vetiver essential oil (i.e., the lower aqueous phase obtained after condensation and oil-water separation of the distilled vapor during the atmospheric distillation of vetiver essential oil, which is weakly acidic due to the presence of volatile organic acids extracted from the root segments, with a pH of 3.5 to 4.5).

[0020] By adopting the above technical solution, the distilled aqueous phase of vetiver grass is used in the impurity removal and acidification process to avoid the introduction of foreign ions such as sodium, calcium or ammonia nitrogen, ensuring that inorganic impurities do not accumulate throughout the process and maintaining the complete biodegradability of the waste liquid system.

[0021] Preferably, in step S4, before rare earth ion precipitation, vetiver essential oil distillation by-product waste liquid is added to the purification liquid, ultrasonically dispersed for 5-10 minutes (ultrasonic power 200-400W, frequency 40-60kHz), and then oxalic acid is added as needed under stirring for precipitation; the initial addition of oxalic acid does not exceed 15% of the mass of oxalic acid in the purification mother liquor.

[0022] By adopting the above technical solution, a portion of untreated raw waste liquid is directly added before the oxalic acid precipitation step to introduce natural water-soluble polysaccharides. The steric hindrance effect of the polysaccharide macromolecules is used to regulate the crystallization process of rare earth oxalate. This method produces ultrafine rare earth oxalate precursors with uniform particle size and excellent dispersibility with simple operation, laying the foundation for subsequent low-temperature calcination to obtain nanoscale high-value-added rare earth oxides.

[0023] Preferably, the process further includes step S6: adjusting the pH of the precipitate mother liquor obtained from the solid-liquid separation in S4 to 8.5–9.0 with lime milk to generate calcium oxalate precipitate; separating the solid and liquid to obtain calcium oxalate solid and filtrate; adding dilute sulfuric acid to the obtained calcium oxalate solid to acidify, recovering the oxalic acid solution, and reusing it for the oxalic acid replenishment step in S4; the clear liquid after decalcification of the filtrate (with controlled Ca) 2+ (Concentration ≤ 50 mg / L), to be reused in the preparation of the next batch of leachate.

[0024] By adopting the above technical solution, a closed-loop regeneration circuit for oxalic acid in the precipitate mother liquor was constructed. Through a two-step treatment of calcification and acidification, residual oxalate in the mother liquor is efficiently recovered as oxalic acid and directly replenished to the precipitation stage, solving the problem of precipitation wastewater discharge. The decalcified liquor is reused to prepare the leaching agent, achieving full-component recycling of the liquid phase.

[0025] Preferably, in step S2, the tailings slag is adjusted to pH 6.0–7.0 with lime, and then mixed with vetiver oil distillation residue and Bacillus subtilis inoculant (live count ≥ 1 × 10⁻⁶). 8 (CFU / g, inoculum amount of 0.3% to 0.8% of the total mass of the mixture) are mixed and stacked for in-situ bioremediation.

[0026] By adopting the above technical solution, the pH of the leaching tailings is first adjusted to a neutral range suitable for microbial growth, and then it is co-piled with vetiver essential oil distillation residue and Bacillus subtilis inoculum for in-situ bioremediation. The organic matter and polysaccharides in the residue provide carbon and energy sources for microorganisms, accelerating the tailings soilification process and promoting vegetation restoration.

[0027] In summary, this application has at least one of the following beneficial technical effects: 1. This application uses the by-product waste liquid from the distillation of vetiver essential oil as the core leaching medium. By utilizing the dual effects of acidolysis and complexation of its natural small molecule organic acids, it can achieve efficient leaching of ionic rare earth elements under mild acidic conditions.

[0028] 2. This application employs a series of optimized technical solutions, including enzymatic pretreatment, two-stage variable-temperature countercurrent leaching, in-situ flavonoid coordination oxidation for cerium extraction, and polysaccharide-regulated precipitation. Among these, enzymatic decomposition releases bound organic acids, improving the uniformity and stability of the leaching agent; variable-temperature leaching utilizes the thermodynamic differences of different complexing agents to achieve in-situ preliminary grouping of light and heavy rare earth elements at the leaching source; and the waste liquid itself utilizes flavonoids and polysaccharides to achieve selective pre-separation of cerium and regulation of rare earth oxalate nanocrystals, respectively. These optimizations are all achieved by "directly adding part of the original waste liquid," significantly improving the selectivity of the target rare earth elements without sacrificing process simplicity.

[0029] 3. This application further constructs a complete material closed loop from leaching to end-of-pipe treatment by optimizing schemes such as oxalic acid closed-loop regeneration, aluminum-iron slag reuse, full recycling of precipitate mother liquor, and in-situ bioremediation of tailings. The entire process forms a closed loop covering the entire life cycle from plant cultivation, extraction, leaching to land remediation. Detailed Implementation

[0030] The present application will be further described in detail below with reference to preparation examples and embodiments.

[0031] Unless otherwise specified, the raw materials used in the preparation examples, embodiments, and comparative examples of this application are all commercially available.

[0032] The total amount of small molecule organic acids was determined by high performance liquid chromatography (HPLC). The chromatographic conditions were as follows: Agilent Zorbax SB-Aq column (250 mm × 4.6 mm, 5 μm), mobile phase of 40 mmol / L KH2PO4 solution (pH adjusted to 2.7 with phosphoric acid) and methanol at a volume ratio of 95:5, detection wavelength of 210 nm, flow rate of 1.0 mL / min, and column temperature of 30 °C. The oxalic acid content was qualitatively determined and quantitatively determined by the retention time and peak area of ​​the oxalic acid standard under the above chromatographic conditions. The total flavonoid content was determined by AlCl3 colorimetry at a wavelength of 510 nm, using rutin as a reference standard. The water-soluble polysaccharide content was determined by phenol-sulfuric acid method at a wavelength of 490 nm, using glucose as a reference standard.

[0033] Preparation Example 1 This preparation example discloses a method for preparing waste liquid from the distillation of vetiver essential oil, as detailed below: Take 5 kg of fibrous roots from 12-month-old fragrant root grass, rinse thoroughly with running water to remove surface soil and impurities; spread the cleaned roots on a ventilated mesh rack and air dry naturally in a shaded environment at 25℃ and 55% humidity, turning them over every 2 hours and testing with a halogen moisture analyzer until the root moisture content drops below 10%; cut the dried roots into 2 cm long uniform root segments using a herb cutter, take all the root segments, add 40 L of deionized water, and let them soak for 10 hours; after soaking, transfer the root segments and soaking water together to an atmospheric pressure distillation kettle, add water until the mass ratio of root segments to water in the total material is 1:9, seal the distillation kettle, heat to 95℃ and maintain this temperature for atmospheric pressure distillation. Distillation was carried out for 8 hours. During the distillation process, the distillate vapor was condensed in a condenser and then separated into oil and water. The upper layer of vetiver essential oil was collected, and the lower aqueous phase (vetiver distillation aqueous phase) was collected separately for later use. After distillation, the remaining mixture at the bottom of the vessel was filtered through a 200-mesh stainless steel screen while still hot. The filtrate was collected and naturally cooled to room temperature to obtain approximately 45 L of vetiver essential oil distillation by-product waste liquid with a pH of 3.8. HPLC analysis showed that the total amount of small molecule organic acids in the waste liquid was 8 g / L (of which oxalic acid content was 2.0 g / L). AlCl3 colorimetric method (based on rutin equivalent) showed that the total flavonoid content in the waste liquid was 0.6 g / L. Phenol-sulfuric acid method showed that the water-soluble polysaccharide content in the waste liquid was 2.2 g / L.

[0034] Preparation Example 2 This preparation example discloses a method for preparing waste liquid from the distillation of vetiver essential oil, as detailed below: Take 5 kg of fibrous roots from 15-month-old fragrant root grass, rinse thoroughly with running water to remove surface soil and impurities; spread the cleaned roots on a ventilated mesh rack and air dry naturally in a shaded environment at 25℃ and 55% humidity, turning them over every 2 hours and testing with a halogen moisture analyzer until the root moisture content drops below 10%; cut the dried roots into uniform 3.5 cm long segments using a herb cutter, take all the segments, add 50 L of deionized water, and let them soak for 15 hours; after soaking, transfer the root segments and soaking water to an atmospheric pressure distillation kettle, add water until the mass ratio of root segments to water in the total material is 1:11.5, seal the distillation kettle, heat to 97℃ and maintain this temperature for distillation. The mixture was distilled at atmospheric pressure for 13 hours. During the distillation process, the distillate vapor was condensed in a condenser and then separated into oil and water. The upper layer of vetiver essential oil was collected, and the lower aqueous phase (vetiver distillation aqueous phase) was collected separately for later use. After distillation, the remaining mixture at the bottom of the vessel was filtered through a 200-mesh stainless steel screen while still hot. The filtrate was collected and allowed to cool naturally to room temperature, yielding approximately 55 L of vetiver essential oil distillation by-product waste liquid with a pH of 4.0. High performance liquid chromatography (HPLC) analysis showed that the total amount of small molecule organic acids in the waste liquid was 13 g / L (of which oxalic acid content was 3.2 g / L). AlCl3 colorimetric method (based on rutin equivalent) showed that the total flavonoid content in the waste liquid was 1.0 g / L. Phenol-sulfuric acid method analysis showed that the water-soluble polysaccharide content in the waste liquid was 3.3 g / L.

[0035] Preparation Example 3 This preparation example discloses a method for preparing waste liquid from the distillation of vetiver essential oil, as detailed below: Take 5 kg of fibrous roots from 18-month-old fragrant root grass, rinse thoroughly with running water to remove surface soil and impurities; spread the cleaned roots on a ventilated mesh rack and air dry naturally in a shaded environment at 25℃ and 55% humidity, turning them over every 2 hours and testing with a halogen moisture analyzer until the root moisture content drops below 10%; cut the dried roots into 5 cm long uniform root segments using a herb cutter, take all the root segments, add 60 L of deionized water, and let them soak for 10 hours; after soaking, transfer the root segments and soaking water together to an atmospheric pressure distillation kettle, add water until the mass ratio of root segments to water in the total material is 1:14, seal the distillation kettle, heat to 99℃ and maintain this temperature for atmospheric pressure distillation. Distillation was carried out for 18 hours. During the distillation process, the distillate vapor was condensed in a condenser and then separated into oil and water. The upper layer of vetiver essential oil was collected, and the lower aqueous phase (vetiver distillation aqueous phase) was collected separately for later use. After distillation, the remaining mixture at the bottom of the vessel was filtered through a 200-mesh stainless steel screen while still hot. The filtrate was collected and naturally cooled to room temperature to obtain approximately 70 L of vetiver essential oil distillation by-product waste liquid with a pH of 4.2. HPLC analysis showed that the total amount of small molecule organic acids in the waste liquid was 18 g / L (of which oxalic acid content was 4.5 g / L). AlCl3 colorimetric method (based on rutin equivalent) showed that the total flavonoid content in the waste liquid was 1.4 g / L. Phenol-sulfuric acid method showed that the water-soluble polysaccharide content in the waste liquid was 4.5 g / L.

[0036] Example 1 This embodiment discloses a method for leaching ion-adsorption rare earth minerals using waste liquid from the distillation of vetiver essential oil, specifically including the following steps: S1. The by-product waste liquid from the distillation of vetiver essential oil obtained in Example 2 is heated to 60°C in a water bath to be used as an extract and kept warm for later use. S2: Take 200g of ion-adsorption type rare earth ore (particle size 60-80 mesh, REO grade 0.12%, moisture content 12%) and load it into an organic glass leaching column with an inner diameter of 5cm. A 200-mesh filter screen is laid at the bottom of the column, and a porous distribution plate is laid on top of the ore. Preheat the leaching solution obtained in S1 to 60℃, and spray it evenly from the top of the column at a single circulation liquid-solid ratio of 5mL / g (i.e., 1000mL per batch) and a spraying rate of 15mL / min. The leaching solution seeps through the ore layer under the action of gravity, and the effluent is collected from the bottom of the column and sprayed again. When the rare earth concentration difference between two adjacent samples is ≤10mg / L, the circulation is stopped. Combine all the effluent to obtain the leaching mother liquor, and collect the tailings after leaching. S3, add 1 mol / L sodium hydroxide solution to the leachate mother liquor, adjust the pH to 5.2, stir for 30 min, let stand and settle for 2 h, filter with medium-speed qualitative filter paper, collect the filtrate, and obtain the purified liquid; S4. The concentration of oxalate in the purified solution was determined to be 1.6 g / L by ion chromatography and the total concentration of rare earth ions was determined to be 0.95 g / L by ICP-OES. 0.8 g / L of purified solution of oxalate was added, stirred and dissolved, and allowed to stand for 4 hours to precipitate. The solution was filtered with slow quantitative filter paper, and the oxalate rare earth precipitate and the mother liquor were collected separately. The filter cake was washed twice with deionized water, 50 mL each time, to obtain rare earth oxalate. S5. Rare earth oxalate is placed in a muffle furnace and heated to 800°C at a rate of 5°C / min. It is then calcined at this temperature for 2 hours and cooled with the furnace to obtain mixed rare earth oxides.

[0037] Example 2 This embodiment discloses a method for leaching ion-adsorption rare earth minerals using waste liquid from the distillation of vetiver essential oil, specifically including the following steps: S1, the vetiver oil distillation by-product waste liquid obtained in Preparation Example 2 was adjusted to pH 4.8 with citric acid, and 0.1 g / L of pectinase and 0.2 g / L of cellulase were added. The mixture was stirred at 38℃ for 3 hours for enzymatic hydrolysis. After enzymatic hydrolysis, the pH of the waste liquid was 4.5. The pH was adjusted to 4.0 with citric acid. The solution was heated to 60℃ in a water bath and used as the extract. The extract was kept warm for later use. The extract was analyzed by high performance liquid chromatography. The total amount of small molecule organic acids was 26 g / L (of which the oxalic acid content was 6.5 g / L). The total flavonoid content was 1.5 g / L by AlCl3 colorimetric method (calculated as rutin equivalent). The water-soluble polysaccharide content was 5.6 g / L by phenol-sulfuric acid method. S2: Take 200g of ion-adsorption type rare earth ore (particle size 60-80 mesh, REO grade 0.12%, moisture content 12%) and put it into an organic glass leaching column with an inner diameter of 5cm. A 200-mesh filter screen is laid at the bottom of the column and a porous distribution plate is laid on top of the ore. Preheat the leaching solution obtained from S1 to 48℃ and spray it evenly from the top of the column at a liquid-solid ratio of 4mL / g per cycle (i.e., 800mL per batch) and a spraying rate of 12mL / min. The leachate seeped through the ore layer under gravity, and the effluent was collected from the bottom of the column. The leaching was then circulated and sprayed for 3 hours. All of the first-stage effluent was collected as the first enrichment solution. The leaching column was heated to 70℃, and fresh leachate was added. The effluent was sprayed evenly from the top of the column at a liquid-to-solid ratio of 4 mL / g per cycle (800 mL per batch) and a spraying rate of 15 mL / min, and the cycle was repeated. The endpoint was reached when the rare earth concentration difference in the effluent measured between two adjacent samples was ≤10 mg / L. Leaching was then stopped, and all of the second-stage effluent was collected as the second enrichment solution. The tailings were also collected. The tailings were adjusted to pH 6.5 with lime and then mixed evenly with the remaining vetiver oil distillation residue after S1 enzymatic hydrolysis. The mixture was then inoculated with Bacillus subtilis inoculum (2 × 10⁻⁶ viable cells). 8(CFU / g, inoculation amount is 0.5% of the total mass of the mixture), adjust the moisture content to 55% to 60%, pile in a ventilated and rainproof place, the pile height is about 30cm, the surface is covered with breathable non-woven fabric, turn the pile once every 7 days, and maintain the pile for 60 days; S3, 400 mL of the vetiver oil distillation by-product waste liquid obtained in Preparation Example 2 was added to the first enrichment liquid to obtain a mixed liquid with a pH of 4.1. The mixture was aerated with compressed air, the temperature was maintained at 55°C, and the reaction was carried out for 1.2 h. After filtration and separation, the filter residue was washed and calcined at 800°C to obtain cerium oxide. The filtrate was mixed with the second enrichment liquid, and the pH was adjusted to 5.2 using the vetiver distillation aqueous phase collected in Preparation Example 2. After stirring for 30 min, the mixture was allowed to stand for 2 h to settle. The mixture was then filtered with medium-speed qualitative filter paper, and the filtrate was collected to obtain the purified liquid. At the same time, the aluminum iron hydroxide precipitate was collected and could be returned to the vetiver distillation pretreatment section in S1 as a filter aid dispersant for recycling. S4, the concentration of oxalate in the purified solution was determined to be 2.1 g / L by ion chromatography, and the total concentration of rare earth ions was determined to be 0.88 g / L by ICP-OES; 750 mL of the vetiver oil distillation by-product waste liquid obtained in Example 2 was added, and the mixture was ultrasonically dispersed for 8 min (ultrasonic power 300 W, frequency 50 kHz), stirred for 30 min, and allowed to stand for 4 h to precipitate; after filtration, the rare earth oxalate precipitate and the mother liquor were collected separately, washed twice with deionized water to obtain ultrafine rare earth oxalate; S5. Rare earth oxalate was placed in a muffle furnace and heated to 800°C at a rate of 5°C / min. The temperature was maintained for 2 hours and then cooled with the furnace to obtain mixed rare earth oxides. S6: Collect the precipitate mother liquor obtained from the solid-liquid separation of S4. Slowly add 10% lime milk (by mass) while stirring to adjust the pH to 8.8, generating calcium oxalate precipitate. After settling for 1 hour, filter using slow-speed quantitative filter paper. Wash the filter cake twice with 50 mL of deionized water each time. Add 0.5 mol / L dilute sulfuric acid to the filter cake and stir to acidify for 1 hour to pH 2.0. Filter, and collect the filtrate as the regenerated oxalic acid solution, which is reused in the oxalic acid replenishment stage of the next batch of S4. The decalcified clear liquid is tested for Ca... 2+ Once the concentration is ≤50mg / L, it can be reused to prepare the next batch of S1 leachate.

[0038] Example 3 This embodiment discloses a method for leaching ion-adsorption rare earth minerals using waste liquid from the distillation of vetiver essential oil, specifically including the following steps: S1, the by-product waste liquid from the distillation of vetiver essential oil obtained in Example 1 was adjusted to pH 4.5 with citric acid, and 0.05 g / L of pectinase and 0.1 g / L of cellulase were added. The mixture was stirred at 35°C for 2 hours for enzymatic hydrolysis. After enzymatic hydrolysis, the pH of the waste liquid was 4.2. The pH was adjusted back to 4.0 with citric acid. The solution was heated to 45°C in a water bath and used as the extract. The extract was kept warm for later use. The total amount of small molecule organic acids in the extract was 14 g / L (of which oxalic acid content was 3.6 g / L) by high performance liquid chromatography. The total flavonoid content was 0.9 g / L by AlCl3 colorimetric method (calculated as rutin equivalent). The water-soluble polysaccharide content was 3.5 g / L by phenol-sulfuric acid method. S2: Take 200g of ion-adsorption type rare earth ore (particle size 60-80 mesh, REO grade 0.08%) and pack it into an organic glass leaching column with an inner diameter of 5cm. A 200-mesh filter screen is placed at the bottom of the column, and a porous distribution plate is placed above the ore. Preheat the leaching solution obtained in S1 to 45℃, and spray it evenly from the top of the column at a liquid-to-solid ratio of 3mL / g per cycle (i.e., 600mL per batch) and a spraying rate of 8mL / min. The leaching solution seeps through the ore layer under gravity, and the effluent is collected from the bottom of the column. Circulate and spray leaching for 3 hours. Collect all the first stage effluent as the first enrichment solution. The leaching column was heated to 65℃, and leaching solution was added. A single cycle liquid-to-solid ratio of 3 mL / g (600 mL per batch) and a spraying rate of 10 mL / min were used to uniformly spray from the top of the column. The cycle was repeated. Leaching was stopped when the rare earth concentration difference between two adjacent samples was ≤10 mg / L. All of the second-stage effluent was collected as the second enrichment solution, and the leaching tailings were also collected. The tailings were adjusted to pH 6.0 with lime and then mixed evenly with the remaining vetiver oil distillation residue after S1 enzymatic hydrolysis. The mixture was then inoculated with Bacillus subtilis inoculum (1×10⁻⁶ viable cells). 8 (CFU / g, inoculation amount is 0.3% of the total mass of the mixture), adjust the moisture content to 55% to 60%, pile in a ventilated and rainproof place, the pile height is about 30cm, the surface is covered with breathable non-woven fabric, turn the pile over every 7 days, and maintain the pile for 60 days; S3, 225 mL of the vetiver oil distillation by-product waste liquid obtained in Preparation Example 1 was added to the first enrichment liquid to obtain a mixed liquid with a pH of 3.95. The pH was adjusted to 4.0 with citric acid. The mixture was aerated with compressed air, the temperature was maintained at 50°C, and the reaction was carried out for 1.0 h. After filtration, the filter residue was washed and calcined at 800°C to obtain cerium oxide. The filtrate was mixed with the second enrichment liquid, and the pH was adjusted to 5.0 with the vetiver distillation aqueous phase collected in Preparation Example 1. After stirring for 30 min, the mixture was allowed to stand for 2 h to settle. The mixture was then filtered with medium-speed qualitative filter paper, and the filtrate was collected to obtain the purified liquid. At the same time, the aluminum iron hydroxide precipitate was collected and could be returned to the vetiver distillation pretreatment section in S1 as a filter aid dispersant for recycling. S4, the concentration of oxalate in the purified solution was determined to be 2.8 g / L by ion chromatography, and the total concentration of rare earth ions was determined to be 0.42 g / L by ICP-OES. The concentration of water-soluble polysaccharides in the purified solution was 1.0 g / L, which met the target values, so no waste liquid needed to be added. Since the oxalate was sufficient, there was no need to add exogenous oxalate. The solution was stirred for 30 min and allowed to stand for 4 h to precipitate. After filtration, the rare earth oxalate precipitate and the mother liquor were collected separately and washed twice with deionized water to obtain rare earth oxalate. S5. Rare earth oxalate was placed in a muffle furnace and heated to 750°C at a rate of 5°C / min. The temperature was maintained for calcination for 1 hour, and then cooled with the furnace to obtain mixed rare earth oxides. S6: Collect the precipitate mother liquor obtained from the solid-liquid separation of S4. Slowly add 10% lime milk (by mass) while stirring to adjust the pH to 8.5, generating calcium oxalate precipitate. After settling for 1 hour, filter using slow-speed quantitative filter paper. Wash the filter cake twice with deionized water, 40 mL each time. Add 0.5 mol / L dilute sulfuric acid to the filter cake and stir to acidify for 1 hour to pH 2.0. Filter, and collect the filtrate as the regenerated oxalic acid solution, which is reused in the oxalic acid replenishment stage of the next batch of S4. The decalcified clear liquid is tested for Ca... 2+ Once the concentration is ≤50mg / L, it can be reused to prepare the next batch of S1 leachate.

[0039] Example 4 This embodiment discloses a method for leaching ion-adsorption rare earth minerals using waste liquid from the distillation of vetiver essential oil, specifically including the following steps: S1, the by-product waste liquid from the distillation of vetiver essential oil obtained in Preparation Example 3 was adjusted to pH 5.0 with citric acid, and 0.2 g / L of pectinase and 0.3 g / L of cellulase were added. The mixture was stirred at 40°C for 4 hours for enzymatic hydrolysis. After enzymatic hydrolysis, the pH of the waste liquid was 4.6, and the pH was adjusted back to 4.0 with citric acid. The solution was heated to 72°C in a water bath and used as the extract. The extract was then kept warm for later use. The total amount of small molecule organic acids in the extract was 30 g / L (of which the oxalic acid content was 7.8 g / L) by high performance liquid chromatography. The total flavonoid content was 2.0 g / L by AlCl3 colorimetric method (calculated as rutin equivalent). The water-soluble polysaccharide content was 7.2 g / L by phenol-sulfuric acid method. S2: Take 200g of ion-adsorption type rare earth ore (particle size 60-80 mesh, REO grade 0.15%) and pack it into an organic glass leaching column with an inner diameter of 5cm. A 200-mesh filter screen is placed at the bottom of the column, and a porous distribution plate is placed above the ore. Preheat the leaching solution obtained in S1 to 50℃, and spray it evenly from the top of the column at a liquid-to-solid ratio of 8mL / g per cycle (i.e., 1600mL per batch) and a spraying rate of 25mL / min. The leaching solution seeps through the ore layer under gravity, and the effluent is collected from the bottom of the column. Circulate and spray for leaching for 5 hours. Collect all the effluent from the first stage as the first enrichment solution. Then, place the leaching column... The temperature was raised to 72℃, and the leachate was replenished. The solution was sprayed evenly from the top of the column at a liquid-to-solid ratio of 8 mL / g per cycle (1600 mL per batch) and a spraying rate of 30 mL / min. The cycle was repeated. Leaching was stopped when the difference in rare earth concentration in the effluent between two adjacent samples was ≤10 mg / L. All of the second-stage effluent was collected as the second enrichment solution, and the leaching tailings were also collected. The tailings from S2 leaching were adjusted to pH 7.0 with lime and then mixed evenly with the remaining vetiver oil distillation residue after enzymatic hydrolysis of S1. The mixture was then inoculated with Bacillus subtilis inoculum (5 × 10⁶ viable cells). 8 (CFU / g, inoculation amount is 0.8% of the total mass of the mixture), adjust the moisture content to 55% to 60%, pile in a ventilated and rainproof place, the pile height is about 30cm, the surface is covered with breathable non-woven fabric, turn the pile over every 7 days, and maintain the pile for 60 days; S3, 603 mL of the vetiver oil distillation by-product waste liquid obtained in Preparation Example 3 was added to the first enrichment liquid to obtain a mixed liquid with a pH of 4.05, which is within the target range and does not require additional acid adjustment. The mixture was aerated with compressed air, the temperature was maintained at 60°C, and the reaction was carried out for 1.5 h. After filtration and separation, the filter residue was washed and calcined at 800°C to obtain cerium oxide. The filtrate was mixed with the second stage leachate, and the pH was adjusted to 5.5 using the vetiver distillation aqueous phase collected in Preparation Example 3. After stirring for 30 min, the mixture was allowed to stand for 2 h to settle. The mixture was then filtered with medium-speed qualitative filter paper, and the filtrate was collected to obtain the purified liquid. At the same time, the aluminum iron hydroxide precipitate was collected and can be returned to the vetiver distillation pretreatment section in S1 as a filter aid dispersant for recycling. S4, the concentration of oxalate in the purified solution was determined to be 1.2 g / L by ion chromatography, and the total concentration of rare earth ions was determined to be 1.15 g / L by ICP-OES. 467 mL of the vetiver oil distillation by-product waste liquid obtained in Preparation Example 3 was added to the purified solution (to make the water-soluble polysaccharide concentration reach 3.0 g / L), and ultrasonically dispersed for 10 min (ultrasonic power 400 W, frequency 60 kHz). If the oxalate was insufficient, 6.0 g of exogenous oxalic acid was added, stirred for 30 min, and allowed to stand for 4 h to precipitate. After filtration, the rare earth oxalate precipitate and the mother liquor were collected separately, washed twice with deionized water to obtain ultrafine rare earth oxalate. S5. Rare earth oxalate was placed in a muffle furnace and heated to 850°C at a rate of 5°C / min. The temperature was maintained for calcination for 3 hours, and then cooled with the furnace to obtain mixed rare earth oxides. S6: Collect the precipitate mother liquor obtained from the solid-liquid separation of S4. Slowly add 10% lime milk (by mass) while stirring to adjust the pH to 9.0, generating calcium oxalate precipitate. After settling for 1 hour, filter using slow-speed quantitative filter paper. Wash the filter cake twice with deionized water (60 mL each time). Add 0.5 mol / L dilute sulfuric acid to the filter cake and stir to acidify for 1 hour to pH 2.0. Filter, and collect the filtrate as the regenerated oxalic acid solution, which is reused in the oxalic acid replenishment stage of the next batch of S4. The decalcified supernatant is tested for Ca2+. 2+ Once the concentration is ≤50mg / L, it can be reused to prepare the next batch of S1 leachate.

[0040] Performance testing The following tests were performed on each embodiment, and the test results are recorded in Table 1.

[0041] (1) Total rare earth leaching rate: The total rare earth concentration in the mother liquor obtained from S2 was determined by ICP-OES after being brought to a constant volume, and the total amount of rare earth in the mother liquor was calculated. After drying, the tailings slag from S2 were digested in a closed system at 180℃ for 12 hours with hydrofluoric acid-perchloric acid-nitric acid (volume ratio 1:1:3). After being brought to a constant volume, the residual rare earth content was determined by ICP-OES. Leaching rate = Rare earth content in mother liquor ÷ (Rare earth content in mother liquor + Residual rare earth content in tailings) × 100%.

[0042] (2) Total content of rare earth oxides: Take 0.1g of S5 product, dissolve it in hydrochloric acid and make up to 100mL. ICP-OES is used to determine the content of each rare earth element (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) and convert it into the sum of oxide masses. Divide by the sample weight × 100% to obtain the total content of rare earth oxides (referred to as "product purity" in Table 1).

[0043] (3) Cerium oxide content in the product: The Ce element in the above ICP-OES determination results is converted into the mass fraction of cerium oxide.

[0044] (4) Product particle size D50: Take an appropriate amount of S5 product, ultrasonically disperse it in anhydrous ethanol, and measure it with a laser particle size analyzer. The measured value is the equivalent particle size of the secondary agglomerates.

[0045] (5) Oxalic acid regeneration rate: Take the precipitate mother liquor obtained from solid-liquid separation in S4, record the volume, and determine the oxalate concentration in it by ion chromatography. Calculate the total residual oxalic acid in the mother liquor M1. In S6, adjust the pH of the precipitate mother liquor to 8.5-9.0 with lime milk to generate calcium oxalate precipitate. After filtration, add dilute sulfuric acid to the filter cake for acidification, collect the regenerated oxalic acid solution, record the volume, determine the oxalate concentration in the same way, and calculate the amount of oxalic acid recovered M2. Oxalic acid regeneration rate (%) = M2 ÷ M1 × 100%.

[0046] Table 1 Performance test data for Examples 1-4 As shown in Table 1, this application achieves efficient and selective leaching of ion-adsorption rare earth ores through the synergistic effect of a series of techniques, including enzymatic pretreatment, two-stage variable-temperature countercurrent leaching, flavonoid-coordinated oxidation for cerium extraction, and polysaccharide-regulated precipitation. Compared to the basic scheme, the optimized process significantly improves the total rare earth leaching rate and the total content of rare earth oxides in the product. Simultaneously, it achieves pre-recovery of cerium, reduces the cerium oxide content in the mixed rare earth oxide product, and yields an ultrafine mixed rare earth oxide product with controllable particle size.

Claims

1. A method for leaching ion-adsorption rare earth ores using waste liquid from vetiver oil distillation, characterized in that, Includes the following steps: S1, adjust the pH of the by-product waste liquid from the distillation of vetiver essential oil to 3.8-4.2 and heat it to 45-72℃ to obtain the extract; S2, mix the leachate with ion-adsorption type rare earth ore for heap leaching or pool leaching, and collect the leachate and tailings. S3. Adjust the pH of the leachate to 5.0-5.5 to cause impurity ions to form hydroxide precipitates. Remove the precipitates by solid-liquid separation to obtain purified solution. S4. Oxalic acid is added to the above purified solution as needed to precipitate rare earth ions, and solid-liquid separation is performed to obtain rare earth oxalate and precipitate mother liquor. S5. Rare earth oxalate is washed and then calcined at 750-850℃ for 1-3 hours to obtain rare earth oxides.

2. The method for leaching ion-adsorption rare earth minerals using vetiver oil distillation by-product wastewater according to claim 1, characterized in that, In S1, the preparation method of the by-product waste liquid from the distillation of vetiver essential oil includes the following steps: taking the underground fibrous roots of 12-18 month old vetiver, washing and removing mud, air-drying until the moisture content is less than 10%, cutting them into 2-5 cm root segments, and soaking them in clean water for 10-20 hours; mixing the soaked root segments with water at a mass ratio of 1:9 to 1:14, and distilling at 95-99℃ under normal pressure for 8-18 hours; after distillation, filtering the mixture at the bottom of the vessel and collecting it, which is the by-product waste liquid from the distillation of vetiver essential oil.

3. The method for leaching ion-adsorption rare earth minerals using vetiver oil distillation by-product wastewater according to claim 1, characterized in that, In S1, the total amount of small-molecule organic acids in the by-product waste liquid from the distillation of vetiver essential oil is 8-18 g / L, the total flavonoid content is 0.6-1.4 g / L, and the water-soluble polysaccharide content is 2.2-4.5 g / L; the oxalic acid content in the small-molecule organic acids is 2.0-4.5 g / L.

4. The method for leaching ion-adsorption rare earth minerals using vetiver oil distillation by-product wastewater according to claim 1, characterized in that, In step S1, before adjusting the pH, the process further includes: adding a compound biological enzyme to the by-product waste liquid from the distillation of vetiver essential oil, adjusting the pH to 4.5–5.0, enzymatically hydrolyzing at 35–40°C for 2–4 hours, and then adjusting the pH back to 3.8–4.2; the compound biological enzyme contains 0.05–0.2 g / L of pectinase and 0.1–0.3 g / L of cellulase.

5. The method for leaching ion-adsorption rare earth minerals using vetiver oil distillation by-product wastewater according to claim 1, characterized in that, In S2, the liquid-to-solid ratio of a single cycle of heap leaching or pool leaching is 3-8 mL / g; the heap leaching or pool leaching adopts a two-stage variable temperature countercurrent leaching: the first stage is leaching by circulating spraying at 45-50℃ for 3-5 hours, and the first stage enriched solution is collected; then the ore heap is heated to 65-72℃ for the second stage deep leaching, and the second stage leachate is collected.

6. The method for leaching ion-adsorption rare earth minerals using vetiver oil distillation by-product wastewater according to claim 5, characterized in that, Vetiver oil distillation by-product waste liquid is added to the first enrichment solution and aerated with air. The reaction is carried out at pH 4.0-4.5 and temperature 50-60℃ for 1-1.5 hours. After solid-liquid separation to remove the precipitate, the filtrate is combined with the second leachate and enters S3.

7. The method for leaching ion-adsorption rare earth minerals using vetiver oil distillation by-product wastewater according to claim 1, characterized in that, In S3, the pH is adjusted using the aqueous phase obtained from the oil-water separation process during the distillation of vetiver essential oil.

8. The method for leaching ion-adsorption rare earth minerals using vetiver oil distillation by-product wastewater according to claim 1, characterized in that, In S4, before rare earth ion precipitation, vetiver essential oil distillation by-product waste liquid is added to the purification solution, ultrasonically dispersed for 5-10 minutes, and then oxalic acid is added as needed under stirring to precipitate.

9. The method for leaching ion-adsorption rare earth minerals using vetiver oil distillation by-product wastewater according to claim 1, characterized in that, It also includes S6: adjusting the pH of the precipitate mother liquor obtained from the solid-liquid separation in S4 to 8.5-9.0 with lime milk to generate a precipitate, and separating the solid and liquid to obtain calcium oxalate solid and filtrate; adding dilute sulfuric acid to the obtained calcium oxalate solid to acidify, recovering the oxalic acid solution, and reusing it for the oxalic acid replenishment step in S4; the filtrate is decalcified and used to prepare the next batch of leachate.

10. The method for leaching ion-adsorption rare earth minerals using vetiver oil distillation by-product wastewater according to claim 1, characterized in that, In S2, the tailings slag is adjusted to pH 6.0-7.0 with lime, then mixed with vetiver oil distillation residue and Bacillus subtilis inoculant and piled up for in-situ bioremediation.

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