A method for classifying and treating phosphorus tailings

Abstract

This invention discloses a graded treatment method for phosphate tailings. The method involves mixing phosphate tailings with a eutectic solvent, introducing CO2 gas, and then performing solid-liquid separation to obtain solid tailings and a mixed liquid phase. The mixed liquid phase is allowed to settle and separate into an extract phase and a solvent phase. The solid tailings are washed and dried to obtain an ecological restoration material. The solvent phase can be recycled after regeneration, and the extract phase can be precipitated to remove heavy metals. The eutectic solvent is composed of hydrogen bond acceptors, hydrogen bond donors, complexing agents, and CO2-responsive basic compounds in a molar ratio of 1:1.8–2.2:0.15–0.25:0.7–0.9. This invention achieves deep purification and eradication of heavy metal pollutants in phosphate mine tailings, and the solvent is regenerable, resulting in an intensive, green, and low-consumption process.

Description

Technical Field

[0001] This invention belongs to the field of phosphorus tailings treatment technology, specifically relating to a method for graded treatment of phosphorus tailings. Background Technology

[0002] Phosphorus is an essential element for agricultural production and life activities, and the phosphate chemical industry plays a vital role in the global economy and food security. However, the development and utilization of phosphate rock resources inevitably generates a huge amount of complex phosphate tailings. The large-scale stockpiling of these tailings not only occupies valuable land resources but also brings environmental problems and resource waste, posing a dual challenge to the sustainable development of the phosphate chemical industry.

[0003] On the one hand, phosphate mining and beneficiation often involve the presence of toxic and harmful elements, which are then concentrated in the tailings. Under the influence of natural weathering and rainwater leaching, these heavy metal pollutants are gradually released from the tailings, seeping into and polluting the soil and groundwater, and posing a serious threat to the ecological environment and human health through bioaccumulation in the food chain. On the other hand, current beneficiation technologies cannot achieve complete recovery of phosphorus resources, resulting in tailings still containing a considerable amount of potentially valuable phosphorus components. However, this residual phosphorus is mostly in the form of insoluble apatite, with extremely low bioavailability, and cannot be directly absorbed and utilized by plants, leading to a serious waste of phosphorus resources.

[0004] To address the aforementioned problems, existing technologies have explored various approaches, but they generally suffer from significant drawbacks. The most common current treatment method employs solidification / stabilization technology, which involves adding solidifying agents such as cement, lime, and fly ash to the tailings to physically encapsulate or chemically fix heavy metal pollutants within an inert matrix. However, this method is essentially a "containment" strategy and does not remove the pollutants at their source. The products still pose a risk of heavy metal leaching and leakage under long-term or extremely acidic environments, failing to completely eliminate environmental safety hazards. Furthermore, while reducing the activity of heavy metals, this method also further reduces the availability of phosphorus components, diminishing its value for resource utilization.

[0005] To achieve the removal of heavy metals, the academic community has also studied acid leaching technology in hydrometallurgy. This method uses strong acids to dissolve heavy metals, but the process often lacks selectivity. While leaching heavy metals, it also dissolves large amounts of calcium, magnesium, and other matrix minerals in the tailings. This not only leads to huge acid consumption and high processing costs, but also produces extremely complex leachates. Subsequent separation, purification, and wastewater treatment processes are exceptionally cumbersome and prone to secondary pollution, making this technology difficult to implement on a large scale for industrial use, both economically and environmentally.

[0006] In summary, existing technological approaches often suffer from trade-offs, failing to achieve a balance between efficient heavy metal removal, synergistic activation of phosphorus nutrients, and the economic and environmental friendliness of the process. These methods either only achieve low-level solidification and stabilization of pollutants, or lack selectivity, are lengthy, and cause secondary pollution. Therefore, there is a need in this field to develop a novel technological solution that can selectively and eradicate heavy metal pollutants from the complex matrix of phosphate rock tailings, synergistically convert insoluble phosphorus nutrients into highly bioavailable forms, and ensure that the entire process is highly integrated, green, low-consumption, and capable of recycling core materials. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a graded treatment method for phosphate tailings, which simultaneously eliminates heavy metal pollution in phosphate tailings and activates their phosphorus nutrients, while achieving a green and low-consumption process.

[0008] To achieve the above objectives, the present invention provides a method for graded treatment of phosphorus tailings, comprising the following steps:

[0009] (1) A mixed system is obtained by mixing and reacting phosphorus tailings with a eutectic solvent;

[0010] (2) CO2 is introduced into the mixed system to obtain a multiphase system;

[0011] (3) The multiphase system is separated into solid tailings and mixed liquid phase. The mixed liquid phase is allowed to stand and separate into extract liquid phase and solvent liquid phase.

[0012] (4) Solid tailings are washed and dried to obtain ecological restoration materials; the solvent is regenerated in the liquid phase and returned to step (1) for recycling as a eutectic solvent, and heavy metals are recovered in the extract liquid phase.

[0013] Preferably, the mass ratio of the phosphorus tailings to the eutectic solvent in step (1) is 1:3-5 on a dry weight basis.

[0014] More preferably, the phosphorus tailings are fine phosphorus tailings mud that have undergone hydraulic classification and concentration dewatering.

[0015] More preferably, the eutectic solvent is composed of hydrogen bond acceptors, hydrogen bond donors, complexing agents, and CO2-responsive basic compounds in a molar ratio of 1:1.8-2.2:0.15-0.25:0.7-0.9.

[0016] More preferably, the hydrogen bond acceptor is choline chloride or betaine, the hydrogen bond donor is any one of lactic acid, citric acid and oxalic acid; the complexing agent is thiourea or cysteine, and the CO2-responsive basic compound is N,N-diisopropylethylamine or triethylamine.

[0017] Furthermore, the hydrogen bond acceptor is choline chloride; the hydrogen bond donor is lactic acid; the complexing agent is thiourea; and the CO2-responsive basic compound is N,N-diisopropylethylamine.

[0018] Preferably, the reaction conditions in step (1) are 65-85℃ for 2.5-4.0h.

[0019] Preferably, the method of introducing CO2 in step (2) is to cool the mixed system to 20-30°C and then introduce CO2 gas at a flow rate of 0.2-0.5 L / min for 20-40 min, with the purity of CO2 gas ≥99%.

[0020] Preferably, the drying conditions in step (4) are vacuum drying at 60-80°C for 15-20 hours; the regeneration method is to heat the solvent liquid phase to 60-80°C and then introduce an inert gas.

[0021] More preferably, the inert gas is any one of nitrogen, helium or argon, the flow rate is 0.3-0.8 L / min, and the regeneration time is 30-60 min.

[0022] Preferably, the method for recovering heavy metals from the extraction liquid phase in step (4) is electrolysis or chemical precipitation.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. A eutectic solvent was formulated using hydrogen bond donors, hydrogen bond acceptors, complexing agents, and CO2-responsive alkaline compounds. The complexing agent exhibits high selectivity for heavy metals, actively and efficiently extracting heavy metal ions from the solid matrix into the liquid phase. This completely overcomes the limitations of traditional technologies that only allow for in-situ solidification of pollutants, achieving deep purification and eradication of heavy metal pollutants in phosphate mine tailings. The CO2-responsive alkaline compound can be triggered by the gentle physicochemical process of introducing CO2 gas, driving controllable phase separation throughout the reaction system. This easily separates the solid product, the heavy metal-enriched extract, and the recyclable solvent, avoiding the complex chemical steps of adding back-extraction agents in traditional hydrometallurgy, making the entire separation process highly efficient and environmentally friendly. The eutectic solvent, through a multifunctional synergistic reaction system, eradicates pollutants through selective complexation and activates phosphorus nutrients in an acidic environment. Both processes are completed simultaneously in a single step, resulting in an ecological restoration material with both high safety and high fertilizer efficiency.

[0025] 2. This invention can not only efficiently remove heavy metals, but the reaction environment it creates can also gently treat the insoluble phosphorus minerals in the tailings, improve the bioavailability of phosphorus nutrients, and achieve simultaneous integration of "detoxification" and "efficiency enhancement" of phosphate tailings.

[0026] 3. The eutectic solvent, after completing the separation process in this invention, can have the bound CO2 removed by simple heating or blasting, restoring it to its initial state and allowing for direct recycling. This closed-loop design throughout the entire process minimizes chemical consumption and wastewater generation, ensuring that the entire phosphorus tailings treatment and resource recovery method meets the requirements of green chemistry and circular economy, demonstrating outstanding sustainability and economic efficiency. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0028] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention.

[0029] In the following embodiments, the phosphorus tailings are derived from the flotation tailings slurry of a phosphate mine in Yichang. The fine slurry remaining after classification by a hydrocyclone is used as the phosphorus tailings. The wet tailings filter cake with a moisture content of 18% after pressure filtration and dewatering is used as the phosphorus tailings. The phosphorus tailings contain 30-40% CaO, 15-25% SiO2, 1-5% MgO, and 8-15% P2O5.

[0030] Example 1

[0031] (1) Choline chloride, L-lactic acid, thiourea and N,N-diisopropylethylamine were stirred at 60°C for 1.5 h in a molar ratio of 1:2.0:0.2:0.8 to obtain a clear and homogeneous eutectic solvent;

[0032] (2) The phosphorus tailings and the eutectic solvent were mixed at a solid-liquid mass ratio of 1:4 (based on the dry weight of the phosphorus tailings) and placed in a reactor. The mixture was stirred (400 rpm) and heated to 75°C. The mixture was kept at a constant temperature for 3 hours to obtain the mixed system.

[0033] (3) Cool the mixture to 25°C, and introduce CO2 gas into the system at a flow rate of 0.35 L / min for 30 min. After the liquid phases are clearly separated, a multiphase system is obtained; the purity of the CO2 gas is ≥99%.

[0034] (4) Centrifuge the multiphase system at 4000×g for 8 min to separate the solid tailings and the mixed liquid phase. After the mixed liquid phase is allowed to stand for 20 min, separate the upper solvent liquid phase and the lower extract liquid phase.

[0035] (5) The solid tailings were washed twice with water and then vacuum dried at 70°C for 18 hours to obtain the ecological restoration material; the upper solvent phase was heated to 70°C and nitrogen gas was bubbled in for 45 minutes to regenerate it, and the regenerated solvent was returned to the eutectic solvent prepared in step (1) for recycling, wherein the nitrogen gas flow rate was 0.5 L / min; the lower extraction phase was heated at a current density of 20 A / m 2 Electrolysis was performed for 1.5 hours under the specified conditions, and solid-liquid separation was carried out to obtain heavy metal precipitate and extract. The extract was neutralized and then discharged.

[0036] Example 2

[0037] (1) Choline chloride, L-lactic acid, thiourea and N,N-diisopropylethylamine were stirred at 50°C for 2 h in a molar ratio of 1:1.8:0.15:0.7 to obtain a clear and homogeneous eutectic solvent.

[0038] (2) The phosphorus tailings and the eutectic solvent were mixed at a solid-liquid mass ratio of 1:3 (based on the dry weight of the phosphorus tailings) and placed in a reactor. The mixture was stirred (400 rpm) and heated to 65°C. The mixture was kept at a constant temperature for 2.5 h to obtain the mixed system.

[0039] (3) Cool the mixture to 20°C, and introduce CO2 gas into the system at a flow rate of 0.2 L / min for 20 min. After the liquid phases are clearly separated, a multiphase system is obtained; the purity of the CO2 gas is ≥99%.

[0040] (4) Centrifuge the multiphase system at 3000×g for 10 min to separate the solid tailings and the mixed liquid phase. After the mixed liquid phase is allowed to stand for 30 min, separate the upper solvent liquid phase and the lower extract liquid phase.

[0041] (5) The solid tailings were washed twice with water and then vacuum dried at 60°C for 24 h to obtain the ecological restoration material; the upper solvent liquid phase was heated to 60°C and nitrogen gas was bubbled in for 60 min to regenerate it, and the solvent was returned to the eutectic solvent prepared in step (1) for recycling, wherein the nitrogen gas flow rate was 0.5 L / min; the lower extraction liquid phase was heated at a current density of 20 A / m 2 Electrolysis was performed for 1.5 hours under the specified conditions, and solid-liquid separation was carried out to obtain heavy metal precipitate and extract. The extract was neutralized and then discharged.

[0042] Example 3

[0043] (1) Choline chloride, L-lactic acid, thiourea and N,N-diisopropylethylamine were stirred at 70 °C for 1 h in a molar ratio of 1:2.2:0.25:0.9 to obtain a clear and homogeneous eutectic solvent.

[0044] (2) The phosphorus tailings and the eutectic solvent were mixed at a solid-liquid mass ratio of 1:5 (based on the dry weight of the phosphorus tailings) and placed in a reactor. The mixture was stirred (400 rpm) and heated to 85°C. The mixture was kept at a constant temperature for 4 h to obtain the mixed system.

[0045] (3) Cool the mixture to 30°C, and introduce CO2 gas into the system at a flow rate of 0.5 L / min for 40 min. After the liquid phases are clearly separated, a multiphase system is obtained; the purity of the CO2 gas is ≥99%.

[0046] (4) Centrifuge the multiphase system at 5000×g for 5 min to separate the solid tailings and the mixed liquid phase. After the mixed liquid phase is allowed to stand for 15 min, separate the upper solvent liquid phase and the lower extract liquid phase.

[0047] (5) The solid tailings were washed with water three times and then vacuum dried at 80°C for 12 h to obtain the ecological restoration material; the upper solvent liquid phase was heated to 80°C and nitrogen gas was bubbled in for 30 min to regenerate it, and the solvent was returned to the eutectic solvent prepared in step (1) for recycling, wherein the nitrogen gas flow rate was 0.5 L / min; the lower extraction liquid phase was heated at a current density of 20 A / m 2 Electrolysis was performed for 1.5 hours under the specified conditions, and solid-liquid separation was carried out to obtain heavy metal precipitate and extract. The extract was neutralized and then discharged.

[0048] Comparative Example 1

[0049] The method and steps are the same as in Example 1, except that thiourea is not added to the eutectic solvent in step (1), and the phosphorus tailings are graded to obtain ecological restoration materials, solvent, heavy metal precipitate and extract.

[0050] Comparative Example 2

[0051] The method and steps are the same as in Example 1, except that the molar ratio of choline chloride, L-lactic acid, thiourea and N,N-diisopropylethylamine in the eutectic solvent in step (1) is changed to 1:2.0:1.5:0.8 to perform grading treatment of phosphorus tailings and obtain ecological restoration materials, solvent, heavy metal precipitate and extract.

[0052] Comparative Example 3

[0053] The method and steps are the same as in Example 1, except that N,N-diisopropylethylamine is not added to the eutectic solvent in step (1), and the phosphorus tailings are graded to obtain ecological restoration materials, solvent, heavy metal precipitate and extract.

[0054] Comparative Example 4

[0055] The method and steps are the same as in Example 1, except that the molar ratio of choline chloride, L-lactic acid, thiourea and N,N-diisopropylethylamine in the eutectic solvent in step (1) is changed to 1:1.8:0.15:1.5 to perform grading treatment of phosphorus tailings and obtain ecological restoration materials, solvent, heavy metal precipitate and extract.

[0056] Comparative Example 5

[0057] The method and steps are the same as in Example 1, except that the eutectic solvent in step (1) is changed to consist of only choline chloride and lactic acid in a molar ratio of 1:2, and the phosphorus tailings are graded to obtain ecological restoration materials, solvent, heavy metal precipitate and extract.

[0058] Comparative Example 6

[0059] The method and steps are the same as in Example 1, except that step (4) is omitted. Phosphorus tailings are graded to obtain ecological restoration materials, solvents, heavy metal precipitates and extracts.

[0060] Comparative Example 7

[0061] The method and steps are the same as in Example 1, except that the reaction temperature in step (2) is changed to 40°C to perform grading treatment of phosphorus tailings and obtain ecological restoration materials, solvents, heavy metal precipitates and extracts.

[0062] Comparative Example 8

[0063] (1) Phosphate tailings and ternary DES were mixed in a solid-liquid mass ratio of 1:4 (based on the dry weight of phosphate tailings) and placed in a reactor. The mixture was stirred (400 rpm) and heated to 75°C for 3 hours. Then thiourea was added, and the mixture was kept at a constant temperature for another 3 hours to obtain a mixed system. The ternary DES was composed of choline chloride, lactic acid, and thiourea in a molar ratio of 1:2:0.2.

[0064] (2) Cool the mixture to 25°C, and introduce CO2 gas into the system at a flow rate of 0.35 L / min for 30 min. After the liquid phases are clearly separated, a multiphase system is obtained; the purity of the CO2 gas is ≥99%.

[0065] (3) Centrifuge the multiphase system at 4000×g for 8 min to separate the solid tailings and the mixed liquid phase. After the mixed liquid phase is allowed to stand for 20 min, separate the upper solvent liquid phase and the lower extract liquid phase.

[0066] (4) The solid tailings were washed twice with water and then vacuum dried at 70°C for 18 hours to obtain the ecological restoration material; the upper solvent liquid phase was heated to 70°C and nitrogen gas was bubbled in for 45 minutes to regenerate it, and the solvent was returned to the eutectic solvent prepared in step (1) for recycling, wherein the nitrogen gas flow rate was 0.5 L / min; the lower extraction liquid phase was heated at a current density of 20 A / m 2 Electrolysis for 1.5 hours and solid-liquid separation yielded heavy metal precipitate and extract. The extract was neutralized and then discharged.

[0067] Comparative Example 9

[0068] Phosphorus tailings, lime, and fly ash were dry-mixed evenly at a mass ratio of 20:1:1, water was added to form granules, and the solidified product was obtained after curing at room temperature for 28 days.

[0069] Example 4

[0070] (1) Take 100g of each of the ecological restoration material or solidified product prepared in the above examples and comparative examples, grind them and pass them through a 100-mesh sieve to obtain powder samples;

[0071] (2) Take 0.2g of powder sample, place it in a polytetrafluoroethylene digestion vessel, add 5mL of nitric acid and 2mL of hydrofluoric acid, tighten the lid and place it in a microwave digestion instrument, and digest it according to the standard soil digestion procedure (EPA method 3051A). After digestion, place the digestion vessel on an acid removal plate and heat it to near dryness. Dilute it to 50mL in a volumetric flask with deionized water, and use an inductively coupled plasma mass spectrometer to determine the concentration of cadmium (Cd) in the solution and convert it to the total content (mg / kg) in the solid sample. The results are shown in Table 1.

[0072] (3) Accurately weigh 2.5g of powder sample, place it in a 250mL conical flask, add 100mL of 2% citric acid solution, shake in a constant temperature shaker at 20℃ for 30min, filter and take the clear filtrate, use the molybdenum blue spectrophotometry to determine the phosphorus concentration in the filtrate at a wavelength of 700nm, and convert it to the effective phosphorus content (mg / kg) in the solid sample. The results are shown in Table 1.

[0073] (4) Accurately weigh 5.0g of powder sample and place it in a 150mL conical flask. Add 100mL of an extractant (simulating acid rain environment) prepared with glacial acetic acid and sodium hydroxide solution with a pH of 2.88±0.05. Shake continuously for 18h at a speed of 30±2 rpm on a rotary shaker. After shaking, filter and collect the leachate. Use inductively coupled plasma mass spectrometry to determine the concentration (mg / L) of cadmium (Cd) in the leachate. The results are shown in Table 1.

[0074] Table 1. Performance Comparison Test Results of Products Obtained by Different Treatment Methods

[0075]

[0076] The results showed that Example 1 significantly reduced the total cadmium content in the ecological restoration material, while Comparative Examples 1 and 5, lacking a key selective complexing agent, almost failed to remove cadmium from the tailings. The underlying mechanism lies in the extremely strong coordination force between thiourea (a soft base) and cadmium ions (a soft acid) in the eutectic solvent of Example 1. This precise identification and binding based on the theory of hard and soft acids and bases is the fundamental reason for selectively "extracting" the target pollutant from the complex solid matrix and transferring it to the liquid phase, thereby achieving deep purification of the tailings.

[0077] The ecological restoration material of Example 1 not only has extremely low heavy metal content, but its effective phosphorus content is also several times higher than that of tailings raw materials. This is due to the mild acid hydrolysis activation effect of the lactic acid component in the solvent system on the insoluble apatite. In contrast, the traditional stabilization method represented by Example 9 showed almost no improvement in phosphorus availability in its product, and the total cadmium content was not reduced. More importantly, the leaching toxicity test results showed that the product of Example 1 showed almost no cadmium leaching under simulated extreme acidic conditions, demonstrating extremely high environmental safety, while the product of Comparative Example 9 still had a significant risk of cadmium leaching. This fully demonstrates that the "source removal" technical concept of this invention is far superior to the traditional "in-situ solidification" containment strategy.

[0078] The results of Comparative Example 2 show that blindly increasing the amount of functional components does not necessarily improve the effect; in fact, excessive thiourea reduces the removal rate of heavy metals. The underlying mechanism is that excessive complexing agent alters the supramolecular structure and physicochemical properties of the eutectic solvent, leading to increased system viscosity and hindering interphase mass transfer. Furthermore, excessive complexing agent undergoes non-specific adsorption on the solid surface, effectively re-"fixing" the already complexed cadmium ions to the tailings surface. This demonstrates that the component ratio range given in this invention is an optimized result that balances reaction kinetics and solvent physical properties.

[0079] The results of Comparative Example 7 confirm the necessity of the process conditions from a reaction kinetics perspective. At excessively low reaction temperatures, the chemical reaction rates of both the acidolysis activation of apatite by lactic acid and the complexation extraction of cadmium ions by thiourea were severely inhibited. The reaction system could not obtain sufficient activation energy to effectively overcome the energy barrier, resulting in very low conversion rates for both core chemical processes. The final product was far inferior to that of Example 1 in both detoxification efficiency and phosphorus activation. This strongly demonstrates that the reaction temperature range defined in this invention is the fundamental guarantee for ensuring the efficient and simultaneous execution of the two key reactions.

[0080] The results of Comparative Example 8, from the opposite perspective, prove that Example 1 integrates the two steps of detoxification and activation into a simultaneous "one-pot" reaction, which reduces the core reaction time by half, makes the process highly integrated, greatly simplifies the operation, shortens the production cycle, and significantly reduces the process energy consumption.

[0081] Example 5

[0082] (1) Take the mixed system of Example 1, Comparative Example 3 (lacking N,N-diisopropylethylamine) and Comparative Example 6 (omitting the CO2 introduction step) after the completion of the integrated reaction step, before any separation operation has been performed;

[0083] (2) Take 50 mL of the mixture system in Example 1 and Comparative Example 3 and place it in a 500 mL glass beaker. After standing at room temperature for 1 h, CO2 gas is introduced into the bottom of the beaker through a gas distributor. No gas is introduced into the beaker containing the mixture system in Comparative Example 6. Observe continuously for 30 min and record whether the liquid phase in each beaker shows stratification and observe its macroscopic morphology. The flow rate of CO2 gas is 0.35 L / min and the introduction time is 30 min.

[0084] (3) When the sample of Example 1 showed obvious stratification, about 10 mL of the upper layer liquid and the lower layer liquid were carefully pipetted and diluted 10 times with deionized water. The concentration of cadmium (Cd) in the solution was determined by inductively coupled plasma mass spectrometry (ICP-MS). At the same time, 10 mL of homogeneous liquid phase sample was randomly taken from the mixed system of Comparative Example 3 and Comparative Example 6 that did not stratify. The concentration of cadmium (Cd) in the solution was determined by inductively coupled plasma mass spectrometry (ICP-MS). The results are shown in Table 2.

[0085] Table 2 Comparison of phase separation behavior and cadmium distribution in the liquid phase

[0086]

[0087] The results showed that in Example 1, the liquid phase rapidly and clearly split into two independent liquid phases after CO2 was introduced, while Comparative Examples 3 and 6 did not undergo phase separation at all under the same or similar conditions. This indicates that N,N-diisopropylethylamine in the eutectic solvent can trigger a reversible chemical reaction with CO2 gas. When CO2 is introduced, it reacts with CO2 to form ionic bicarbonate, leading to a fundamental rearrangement of the polarity and hydrogen bond network of the entire solvent system, thereby driving macroscopic phase separation. Comparative Example 3, lacking this crucial response "switch," and Comparative Example 6, lacking a trigger "signal," both failed to initiate this process, thus demonstrating the completeness and necessity of the intelligent separation design.

[0088] In Example 1, over 99% of the cadmium was highly enriched in the relatively small lower extract phase, while the cadmium concentration in the upper solvent phase was extremely low. The underlying mechanism is that the newly formed lower polar phase after phase separation has a stronger ability to dissolve and stabilize the polar cadmium-thiourea complex generated during the reaction stage, thus acting like a magnet to "adsorb" and aggregate the target pollutant from the bulk solvent. This is not merely a simple phase separation, but a highly efficient concentration process that transfers pollutants from a large-volume, low-concentration system to a small-volume, high-concentration system, creating extremely favorable conditions for subsequent resource recovery.

[0089] Example 6

[0090] (1) The regenerated solvent prepared in Example 1 was directly used as the eutectic solvent, and the new phosphorus tailings were repeatedly treated according to the method and steps described in Example 1 to obtain ecological restoration material - cycle 1 and second regenerated solvent;

[0091] (2) Take the second regeneration solvent and repeat step (1) 4 times to obtain ecological restoration material-cycle 2, ecological restoration material-cycle 3, ecological restoration material-cycle 4 and ecological restoration material-cycle 5 respectively;

[0092] (3) Accurately weigh the ecological restoration materials prepared by different cycles, and test the final total content of heavy metal cadmium (Cd) according to step (2) of Example 4. The results are shown in Table 2:

[0093] Table 2 Test data on the recycling performance of regenerated solvent

[0094]

[0095] The results showed that even after five consecutive cycles, the final product treated with the regenerated solvent maintained an extremely low cadmium content, showing no significant difference compared to the effect of using fresh solvent. The fundamental mechanism behind this result lies in the complete reversibility of the separation process in this invention; the phase separation of the solvent is driven by the chemical reaction between N,N-diisopropylethylamine and CO2, a typical reversible equilibrium. By heating or introducing inert gas, the equilibrium can be easily shifted towards the reactants, causing the bound CO2 to disintegrate, thereby restoring the physicochemical properties of the tertiary amine molecules and the entire solvent system to their initial state before the reaction, laying the material foundation for the next efficient cycle.

Claims

1. A method for graded treatment of phosphorus tailings, characterized in that: Includes the following steps: (1) A mixed system is obtained by mixing and reacting phosphorus tailings with a eutectic solvent; (2) CO2 is introduced into the mixed system to obtain a multiphase system; (3) The multiphase system is separated into solid tailings and mixed liquid phase. The mixed liquid phase is allowed to stand and separate into extract liquid phase and solvent liquid phase. (4) Solid tailings are washed and dried to obtain ecological restoration materials; The solvent phase is regenerated and reused, and the extraction phase is used to recover heavy metals. The eutectic solvent is composed of hydrogen bond acceptors, hydrogen bond donors, complexing agents, and CO2-responsive basic compounds in a molar ratio of 1:1.8-2.2:0.15-0.25:0.7-0.

9. The hydrogen bond acceptor is choline chloride or betaine, and the hydrogen bond donor is any one of lactic acid, citric acid, and oxalic acid; the complexing agent is thiourea or cysteine, and the CO2-responsive basic compound is N,N-diisopropylethylamine or triethylamine.

2. The method for graded treatment of phosphorus tailings according to claim 1, characterized in that: The mass ratio of the phosphorus tailings to the eutectic solvent in step (1) is 1:3-5, based on dry weight.

3. The method for graded treatment of phosphorus tailings according to claim 2, characterized in that: The phosphorus tailings are fine phosphorus tailings mud that have undergone hydraulic classification and concentration dewatering.

4. The method for graded treatment of phosphorus tailings according to claim 1, characterized in that: The reaction conditions described in step (1) are 65-85℃ for 2.5-4.0h.

5. A method for graded treatment of phosphorus tailings according to claim 1, characterized in that: The method for introducing CO2 in step (2) is to cool the mixed system to 20-30℃ and then introduce CO2 gas at a flow rate of 0.2-0.5L / min for 20-40min, with CO2 gas purity ≥99%.

6. The method for graded treatment of phosphorus tailings according to claim 1, characterized in that: The drying conditions described in step (4) are vacuum drying at 60-80℃ for 15-20h; the regeneration method is to heat the solvent liquid phase to 60-80℃ and then introduce an inert gas.

7. A method for graded treatment of phosphorus tailings according to claim 6, characterized in that: The inert gas is any one of nitrogen, helium or argon, with a flow rate of 0.3-0.8 L / min and a regeneration time of 30-60 min.

8. A method for classifying and treating phosphorus tailings according to claim 1, characterized in that: The method for recovering heavy metals from the extraction liquid phase in step (4) is electrolysis or chemical precipitation.

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