A hydroxyl-rich defective carbon nitride rare earth adsorbent, a preparation method and use thereof

Abstract

The present application relates to a kind of rich hydroxyl defective carbon nitride rare earth adsorbent and its preparation method and purposes, the preparation raw material of the rich hydroxyl defective carbon nitride rare earth adsorbent includes precursor, alkali metal chloride, ammonium chloride and water;The present application is obtained by mixing precursor, alkali metal chloride, ammonium chloride and water mixture, the mixture obtained by ion-induced thermal polymerization strategy, preparation obtains the rich hydroxyl defective carbon nitride rare earth adsorbent, and has extended nanopore structure;The rich hydroxyl defective carbon nitride rare earth adsorbent of the present application has high adsorption capacity, fast adsorption kinetics and higher selectivity and good cycle stability, is used in the recovery efficiency of rare earth ion in leaching tail liquid, and preparation raw material is low in price, and preparation process is simple.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, and in particular to a hydroxyl-rich defective carbon nitride rare earth adsorbent, its preparation method, and its applications. Background Technology

[0002] Rare earth elements are recognized as critical strategic metal resources, widely used in defense, electronics, aerospace, and new energy materials. Due to incomplete leaching processes in current methods, a large amount of rare earth waste tailings are left behind, generating substantial amounts of leaching tailings and leaching wastewater, causing serious losses of rare earth resources and environmental pollution. Therefore, the selective and efficient enrichment and separation of rare earth elements from complex, low-concentration rare earth wastewater is crucial for maintaining the sustainable development of the rare earth economy and the ecological environment. However, most leaching tailings and leaching wastewater contain low concentrations of rare earth ions, with a wide variety and high content of impurity ions, and complex systems, making the selective enrichment and recovery of rare earths extremely challenging.

[0003] Currently, various methods have been developed to recover rare earth elements from complex, low-concentration rare earth wastewater. Among these methods, adsorption is widely used due to its simple operation, low cost and energy consumption, lack of organic solvents, and clean and environmentally friendly characteristics, and has made significant progress in rare earth separation and recovery. Conventional adsorbents include ion exchange resins, clay, porous organic polymers, metal-organic frameworks, and covalent organic frameworks. According to the hard-soft acid-base theory, rare earth ions, as Lewis hard acids, typically exhibit strong binding interactions with hard base groups containing O electron donors. Therefore, introducing a large number of hydroxyl groups into the adsorbent framework can significantly improve the material's adsorption capacity for rare earth ions. Various hydroxyl-functionalized adsorbents have been developed and exhibit good adsorption capacity for rare earth ions. However, their disordered pore structure, harsh synthesis conditions, and high cost hinder the large-scale production of adsorbents and their application in rare earth extraction.

[0004] Graphitic carbon nitride (g-C3N4), as a two-dimensional layered material, possesses advantages such as stable physicochemical properties, simple preparation, and environmental friendliness, thus showing potential application value in the field of rare earth adsorption and separation. However, bulk graphitic carbon nitride suffers from drawbacks such as narrow nanopores, small specific surface area, low density of oxygen-containing functional groups, and poor hydrophilicity and dispersibility in solvents, resulting in insufficient exposure of available active sites and hindered diffusion of rare earth ions. Therefore, an ion-induced thermal polycondensation strategy is employed to induce defects and rearrangements in the heptaazine structural units of carbon nitride by alkali metal ions, thereby forming an in-plane extended defect nanopore optimized material microstructure and introducing abundant hydroxyl and cyano groups to achieve highly efficient rare earth adsorption performance.

[0005] Therefore, it is of great significance to develop a hydroxyl-rich defective carbon nitride rare earth adsorbent with high adsorption capacity, high selectivity, fast adsorption rate, low cost, and simple preparation process. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a hydroxyl-rich defective carbon nitride rare earth adsorbent, its preparation method, and its applications. The hydroxyl-rich defective carbon nitride rare earth adsorbent of the present invention has high adsorption capacity, rapid adsorption kinetics, high selectivity, and good cycle stability. It has high recovery efficiency for rare earth ions in leaching tailings, and the raw materials used for its preparation are inexpensive and the preparation process is simple.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a hydroxyl-rich defective carbon nitride rare earth adsorbent, wherein the raw materials for preparing the hydroxyl-rich defective carbon nitride rare earth adsorbent include a precursor, an alkali metal chloride, ammonium chloride, and water; the hydroxyl-rich defective carbon nitride rare earth adsorbent has an extended nanoporous structure and hydroxyl and cyano groups.

[0009] The specific surface area of ​​the hydroxyl-rich defective carbon nitride rare earth adsorbent is 100-120 m². 2 / g, for example, could be 100m 2 / g、101m 2 / g、102m 2 / g、103m 2 / g, 104m 2 / g, 105m 2 / g, 106m 2 / g, 107m 2 / g, 108m 2 / g、109m 2 / g、110m 2 / g、111m 2 / g、112m 2 / g、113m 2 / g、114m 2 / g、115m 2 / g、116m 2 / g、117m 2 / g、118m 2 / g、119m 2 / g or 120m 2 / g, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0010] The hydroxyl-rich defective carbon nitride rare earth adsorbent has a high specific surface area and a defective extended nanopore structure with a nanopore size of 1.107 nm, which facilitates the efficient diffusion of rare earth ions in the solution between material layers and their interaction with active sites. At the same time, the hydroxyl-rich defective carbon nitride rare earth adsorbent provided by this invention has abundant hydroxyl groups and electron-rich cyano groups, providing abundant adsorption sites and strong interaction with rare earth ions.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0012] In a second aspect, the present invention provides a method for preparing a hydroxyl-rich defective carbon nitride rare earth adsorbent as described in the first aspect, the method comprising the following steps:

[0013] A mixture of a precursor, an alkali metal chloride, ammonium chloride, and water is obtained. The mixture is then calcined to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

[0014] This invention prepares a defective carbon nitride rare earth adsorbent rich in hydroxyl groups and with extended nanopores through an ion-induced thermal polymerization strategy under molten salt closed conditions. Alkali metal chlorides act as hard templates, inducing structural changes. Their addition introduces alkali metal ions to break the covalent bonds between the precursor C and N, reducing in-plane and interlayer hydrogen bonding and van der Waals forces, thus facilitating the formation of extended triangular nanopores composed of six heptaazine structural units. Simultaneously, the thermal decomposition of water molecules forms hydroxyl groups at bond breaks, and the thermal decomposition of the pore-forming agent ammonium chloride generates gas, further increasing the material's specific surface area. When applied to the selective adsorption and separation of rare earth elements, this material exhibits advantages such as high adsorption capacity, fast adsorption kinetics, and high selectivity.

[0015] The hydroxyl-rich and extended nanopore defective carbon nitride prepared by this invention requires no complex processing steps, avoiding the high energy consumption caused by secondary reactions and grafting groups in conventional methods. This makes it suitable for large-scale production. The one-step alkali-melting-calcination method provided by this invention differs from hydrothermal synthesis. Using an oil bath combined with hydrothermal synthesis is not only more cumbersome, requiring high temperature and pressure conditions, but more importantly, it cannot produce the extended triangular nanopore structure with defects as described in this application. It cannot provide the sealed conditions of molten salt for ion-induced structural defects, thus only forming a narrow nanopore structure with three densely bonded heptaazine units.

[0016] Preferably, the molar ratio of the precursor, alkali metal chloride, ammonium chloride, and water is 1:(0.4-1.2):(0.05-0.1):(0.007-0.01), for example, it can be 1:0.4:0.05:0.007, 1:0.8:0.05:0.009, 1:0.8:0.07:0.009, 1:0.4:0.08:0.01, 1:0.4:0.1:0.01, 1:1.2:0.08:0.009, or 1:1.2:0.1:0.01, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] In this invention, the molar ratio of the precursor, alkali metal chloride, ammonium chloride, and water affects the morphology of the prepared hydroxyl-rich defective carbon nitride rare earth adsorbent. The alkali metal chloride introduces alkali metal ions to break the covalent bonds between C and N, and its amount affects the degree of heptaazine unit structure rearrangement and defective extended nanopore construction during the thermal polycondensation process of the precursor. The water content directly affects the hydroxyl content in the final product; too little water prevents the formation of abundant hydroxyl groups, while too much water hinders the formation of alkali metal ions in a molten state. The content of the pore-forming agent ammonium chloride affects the specific surface area of ​​the adsorbent; too little water prevents the formation of a loose and porous morphology, while too much water reduces the degree of polymerization.

[0018] Preferably, the precursor comprises any one or a combination of at least two of melamine, urea, or thiourea, wherein typical but non-limiting combinations include a combination of melamine and urea, a combination of urea and thiourea, a combination of melamine and thiourea, a combination of melamine, urea, and thiourea, and preferably melamine.

[0019] Preferably, the mixing includes grinding and mixing.

[0020] Preferably, the alkali metal chloride includes any one or a combination of at least two of lithium chloride, sodium chloride, potassium chloride, rubidium chloride, or cesium chloride, wherein typical but non-limiting combinations include combinations of lithium chloride and sodium chloride, combinations of sodium chloride and potassium chloride, combinations of potassium chloride and rubidium chloride, combinations of rubidium chloride and cesium chloride, combinations of lithium chloride, sodium chloride, and potassium chloride, combinations of potassium chloride, rubidium chloride, and cesium chloride, and combinations of lithium chloride, sodium chloride, potassium chloride, and rubidium chloride, preferably lithium chloride.

[0021] Preferably, the heating rate of the calcination is 2-10℃ / min, for example, it can be 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0022] Preferably, the calcination temperature is 500-600℃, for example, it can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃ or 600℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0023] In this invention, the precursor undergoes an ionothermal polycondensation reaction during the calcination stage. The calcination temperature directly affects the extent of the precursor's thermal polycondensation reaction. If the temperature is too low, the alkali metal cannot form a molten state, which is not conducive to the thorough mixing and reaction of the precursor. If the temperature is too high, the material may carbonize, resulting in a decrease in yield.

[0024] Preferably, the calcination time is 3-5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the calcination process further includes solid-liquid separation, washing, and drying.

[0026] Preferably, the washing includes washing with deionized water.

[0027] Preferably, the drying temperature is 40-80℃, for example, it can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0028] Preferably, the drying time is 6-12 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0030] Melamine, alkali metal chloride, ammonium chloride, and water were ground and mixed in a molar ratio of 1:(0.4-1.2):(0.05-0.1):(0.007-0.01) to obtain a mixture. The mixture was then calcined in a tube furnace at a heating rate of 2-10℃ / min to 500-600℃ for 3-5 hours. After solid-liquid separation and washing, the mixture was dried at 40-80℃ for 6-12 hours to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

[0031] Thirdly, the present invention provides the use of the hydroxyl-rich defective carbon nitride rare earth adsorbent as described in the first aspect, wherein the hydroxyl-rich defective carbon nitride rare earth adsorbent is used for the efficient and selective enrichment and recovery of rare earth ions in leaching tailings.

[0032] The hydroxyl-rich defective carbon nitride rare earth adsorbent provided by this invention is used for the selective adsorption and separation of rare earth elements, and has the advantages of high adsorption capacity, fast adsorption kinetic rate and high selectivity.

[0033] Preferably, the hydroxyl-rich defective carbon nitride rare earth adsorbent has an adsorption capacity of Qe≥145mg / g for rare earth ions neodymium, dysprosium and lutetium in the pH range of 4-7. For example, the pH can be 4, 4.5, 5, 5.5, 6, 6.5 or 7, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the total rare earth ion removal rate of the hydroxyl-rich defective carbon nitride rare earth adsorbent is ≥80%, for example, it can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0035] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0036] Compared with the prior art, the present invention has at least the following beneficial effects:

[0037] (1) This invention employs an ion-induced thermal polycondensation strategy, in which alkali metal chlorides act as hard templates, playing a structural induction role. Their addition introduces alkali metal ions to break the covalent bonds between C and N in the precursor, reducing in-plane and interlayer hydrogen bonding and van der Waals forces, which helps to form extended triangular nanopores composed of six heptaazine structural units. Simultaneously, the thermal decomposition of water molecules forms hydroxyl groups at the bond-breaking sites, and the thermal decomposition of the pore-forming agent ammonium chloride generates gas, which helps to increase the specific surface area of ​​the material. When applied to selective adsorption and separation, it has the advantages of high adsorption capacity, fast adsorption kinetics, and high selectivity.

[0038] (2) The hydroxyl-rich defective carbon nitride rare earth adsorbent provided by the present invention has a high specific surface area and a defective extended nanopore structure. The extended triangular nanopore is composed of six heptaazine structural units with a pore size of 1.107 nm, which helps rare earth ions in the solution to diffuse efficiently between material layers and interact with active sites. At the same time, the hydroxyl-rich defective carbon nitride rare earth adsorbent has abundant hydroxyl groups and electron-rich cyano groups, providing abundant adsorption sites and strong interaction with rare earth ions.

[0039] (3) The hydroxyl-rich defective carbon nitride rare earth adsorbent provided by the present invention is used for selective adsorption and separation of rare earths, and has the advantages of high adsorption capacity, fast adsorption kinetic rate and high selectivity. Attached Figure Description

[0040] Figure 1 This is a flowchart of the preparation process using the ion-induced thermal polycondensation strategy in Example 1 of the present invention;

[0041] Figure 2 This is a scanning electron microscope image of the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 of the present invention.

[0042] Figure 3 This is a bar chart showing the adsorption capacity of rare earth neodymium, dysprosium, and lutetium at different pH values ​​for the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 of this invention.

[0043] Figure 4 This is a graph showing the changes in the adsorption capacity of neodymium, dysprosium, and lutetium of the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 of the present invention at different times.

[0044] Figure 5 This is a graph showing the changes in the adsorption capacity of neodymium, dysprosium, and lutetium of a hydroxyl-rich defective carbon nitride rare earth adsorbent at different equilibrium concentrations, provided in Example 1 of the present invention.

[0045] Figure 6 This is a bar chart of the lutetium separation factor of the hydroxyl-rich defective carbon nitride rare earth adsorbent under different interfering ions provided in Example 1 of the present invention;

[0046] Figure 7 This is a bar chart showing the rare earth extraction rate of the hydroxyl-rich defective carbon nitride rare earth adsorbent in an actual leaching tailings system provided in Example 1 of the present invention.

[0047] Figure 8 This is a nitrogen adsorption-desorption curve of the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 of the present invention.

[0048] Figure 9 This is the XRD pattern of the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 of the present invention; Figure 10 The infrared spectra of the hydroxyl-rich defective carbon nitride rare earth adsorbent before and after adsorbing neodymium, dysprosium, and lutetium ions are provided in Example 1 of this invention.

[0049] Figure 11 This is the XPS full spectrum of the hydroxyl-rich defective carbon nitride rare earth adsorbent before and after adsorption of neodymium, dysprosium, and lutetium ions provided in Example 1 of the present invention;

[0050] Figure 12This is the C1s full spectrum of the defective carbon nitride rare earth adsorbent rich in hydroxyl groups before and after adsorption of neodymium, dysprosium, and lutetium ions provided in Example 1 of the present invention.

[0051] Figure 13 This is the O1s full spectrum of the defective carbon nitride rare earth adsorbent rich in hydroxyl groups before and after adsorption of neodymium, dysprosium, and lutetium ions provided in Example 1 of the present invention. Detailed Implementation

[0052] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0053] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used are conventional methods and techniques in the art.

[0054] Example 1

[0055] This embodiment provides a hydroxyl-rich defective carbon nitride rare earth adsorbent and its preparation method, the preparation method comprising the following steps:

[0056] Melamine, potassium chloride, ammonium chloride, and water were ground and mixed in a molar ratio of 1:0.5:0.06:0.008 to obtain a mixture. The mixture was placed in a covered crucible and calcined in a tube furnace at a heating rate of 5℃ / min to 550℃ for 4 hours. After the reaction was completed, the product was transferred to an Erlenmeyer flask, washed three times with deionized water, and dried at 60℃ for 10 hours to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

[0057] The hydroxyl-rich defective carbon nitride rare earth adsorbent possesses an extended triangular nanoporous microstructure constructed from six heptaazine units; and its specific surface area is 116.79 m². 2 / g.

[0058] from Figure 1 As can be seen, Example 1 employs an ion-induced thermal polycondensation strategy to prepare a defective carbon nitride rare earth adsorbent rich in hydroxyl groups and with expanded nanopores. The molten salt provides a closed liquid environment to accelerate the polymerization process and regulate the recombination of structural units. In this process, the positively charged K... +Ions disrupt the CN=N covalent bonds in the heptaazine units, reducing hydrogen bonds and van der Waals forces in both in-plane and interlayer regions. This promotes structural unit rearrangement and the formation of extended nanopores composed of six heptaazine units. Simultaneously, the thermal decomposition of water molecules promotes the formation of hydroxyl groups at bond-breaking sites in the defective heptaazine units, accompanied by the formation of cyano groups. Furthermore, the gas generated by the thermal decomposition of the pore-forming ammonium chloride helps increase the specific surface area of ​​the material. Therefore, the successful preparation of a defective carbon nitride rare earth adsorbent rich in hydroxyl groups and with extended nanopores will facilitate the efficient diffusion of rare earth ions and their interaction with adsorption active sites.

[0059] from Figure 2 It can be seen that the apparent morphology of the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 is a loose, porous, curved sheet-like solid.

[0060] from Figure 3 It can be seen that the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 has good adsorption capacity for neodymium / dysprosium / lutetium in a wide pH range of 4-7. Therefore, pH 5.0 was selected as the representative and used in subsequent adsorption experiments.

[0061] from Figure 4 It can be seen that the Nd / dysprosium / lutetium adsorption kinetics data of the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 conform to the pseudo-second-order kinetic model, which belongs to chemisorption, and equilibrium can be reached in 30 minutes.

[0062] from Figure 5 It can be seen that the isotherm data of the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 conforms to the Langmuir adsorption isotherm model, and the simulated maximum adsorption capacities for neodymium, dysprosium, and lutetium are 146.25 mg / g, 180.82 mg / g, and 204.34 mg / g, respectively.

[0063] from Figure 6 It can be seen that the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 has high selectivity for rare earth ion lutetium in the presence of different interfering ions other than aluminum (SF = 57-774).

[0064] from Figure 7 It can be seen that the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 achieves a removal rate of 72-100% for individual rare earth ions, and the calculated total rare earth ion removal rate can reach 89%, thus showing good potential for practical application.

[0065] from Figure 8 It can be seen that the hydroxyl-rich and expanded nanopore-rich defective carbon nitride rare earth adsorbent provided in Example 1 has a high pore volume, and its BET specific surface area is calculated to be 116.79 m². 2 / g.

[0066] from Figure 9 As can be seen, the characteristic peaks of BCN at 13.05° and 27.51° belong to the (100) and (002) crystal planes of g-C3N4, respectively, corresponding to the in-plane repeating unit and interlayer stacking structure of the heptaazine ring. According to Bragg's law, BCN has a narrow triangular nanopore formed by three heptaazine units with a channel diameter of 0.678 nm. In the XRD pattern of DGCN-K, the (100) crystal plane decreases to 7.98°, confirming that after ion-induced defects, it forms an extended triangular nanopore formed by six heptaazine units with a channel diameter of 1.107 nm. The (002) crystal plane increases to 28.36°, proving that K ions insert into the carbon nitride interlayer, causing a slight contraction of the interlayer distance; DGCN-K is before adsorption.

[0067] from Figure 10 It can be seen that in the infrared spectrum of DGCN-K, at 3300 cm⁻¹... -1 ~3500cm -1 Area, 1200-1700cm -1 area and 808cm -1 The absorption peaks appearing at [location] belong to the stretching vibration peak of NH / -OH, the CN=C heterocyclic stretching vibration peak of the triazine ring, and the bending vibration peak of the triazine ring, respectively. Additionally, at 2179 cm⁻¹... -1 and 1151cm -1 The stretching vibrations belong to C≡N and C-OH, respectively. In the infrared spectrum of Nd / Dy / Lu-DGCN-K, both C≡N and C-OH show obvious red shifts, indicating that there is an interaction between the cyano group and the hydroxyl group and the neodymium / dysprosium / lutetium ions. DGCN-K represents the pre-adsorption state, and Nd / Dy / Lu-DGCN-K represents the post-adsorption state.

[0068] from Figure 11 It can be seen that after DGCN-K adsorption, Nd-DGCN-K exhibits new binding energy peaks at 1005.73 eV and 983.23 eV, which are characteristic peaks of neodymium ions and are attributed to Nd3d+ ions, respectively. 3 / 2 and Nd 3d 5 / 2 Dy-DGCN-K exhibits new binding energy peaks at 1334.84 eV and 1296.26 eV, which are characteristic peaks of the dysprosium ion and are attributed to Dy 3d ions, respectively. 3 / 2 and Dy 3d 5 / 2 The Lu-DGCN-K exhibits new binding energy peaks at 206.75 eV and 197.08 eV, which are characteristic peaks of the lutetium ion and are attributed to Lu4d, respectively. 3 / 2 and Lu 4d 5 / 2In addition, the binding energy peak intensities of K 2s and K 2p for Nd / Dy / Lu-DGCN-K both decreased to the point of disappearing; where DGCN-K represents the state before adsorption and Nd / Dy / Lu-DGCN-K represents the state after adsorption.

[0069] from Figure 12 It can be seen that the C1s spectrum of DGCN-K consists of four binding energy peaks at 288.31 eV, 286.48 eV, 285.88 eV, and 284.8 eV, which are attributed to NC=N, CO, C≡N, and CC, respectively. After adsorption, the CO and C≡N peaks of Nd / Dy / Lu-DGCN-K show a significant blue shift, and the binding energy decreases. Among them, DGCN-K is before adsorption, and Nd / Dy / Lu-DGCN-K is after adsorption.

[0070] from Figure 13 It can be seen that the O1s spectrum of DGCN-K consists of two binding energy peaks at 531.76 eV and 5331.63 eV, which are attributed to H2O and CO, respectively. After adsorption, the CO peak of Nd / Dy / Lu-DGCN-K shows a significant red shift, indicating an increase in binding energy; DGCN-K represents the peak before adsorption, while Nd / Dy / Lu-DGCN-K represents the peak after adsorption.

[0071] In summary, the above results demonstrate that rare earth ions interact strongly with cyano and hydroxyl groups, and that ion exchange and coordination are the main mechanisms by which the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in this invention adsorbs Nd / Dy / Lu.

[0072] Example 2

[0073] This embodiment provides a hydroxyl-rich defective carbon nitride rare earth adsorbent and its preparation method, the preparation method comprising the following steps:

[0074] Melamine, sodium chloride, ammonium chloride, and water were ground and mixed in a molar ratio of 1:0.4:0.05:0.007 to obtain a mixture. The mixture was placed in a covered crucible and calcined in a tube furnace at a heating rate of 3℃ / min to 500℃ for 5 hours. After the reaction was completed, the product was transferred to an Erlenmeyer flask, washed three times with deionized water, and dried at 75℃ for 12 hours to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

[0075] The hydroxyl-rich and extended nanopore-rich defective carbon nitride rare earth adsorbent possesses an extended triangular nanopore structure constructed from six heptaazine units; its specific surface area is 109.73 m². 2 / g.

[0076] Example 3

[0077] This embodiment provides a hydroxyl-rich defective carbon nitride rare earth adsorbent and its preparation method, the preparation method comprising the following steps:

[0078] Melamine, potassium chloride, ammonium chloride, and water were ground and mixed in a molar ratio of 1:1.2:0.1:0.01 to obtain a mixture. The mixture was placed in a covered crucible and calcined in a tube furnace at a heating rate of 10℃ / min to 600℃ for 3 hours. After the reaction was completed, the product was transferred to an Erlenmeyer flask, washed four times with deionized water, and dried at 55℃ for 12 hours to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

[0079] The hydroxyl-rich and extended nanopore-rich defective carbon nitride rare earth adsorbent possesses an extended triangular nanopore structure constructed from six heptaazine units; its specific surface area is 113.26 m². 2 / g.

[0080] Example 4

[0081] This embodiment provides a method for preparing a carbon nitride rare earth adsorbent. The only difference from Example 1 is that the molar ratio of melamine, potassium chloride, ammonium chloride and water is 1:1.8:0.06:0.008 when preparing the carbon nitride rare earth adsorbent.

[0082] Example 5

[0083] This embodiment provides a method for preparing a carbon nitride rare earth adsorbent. The only difference from Example 1 is that the molar ratio of melamine, potassium chloride, ammonium chloride and water is 1:0.05:0.06:0.008 when preparing the carbon nitride rare earth adsorbent.

[0084] Example 6

[0085] This embodiment provides a method for preparing a carbon nitride rare earth adsorbent. The only difference from Example 1 is that the molar ratio of melamine, potassium chloride, ammonium chloride and water is 1:0.5:0.2:0.008 when preparing the carbon nitride rare earth adsorbent.

[0086] Example 7

[0087] This embodiment provides a method for preparing a carbon nitride rare earth adsorbent. The only difference from Example 1 is that the molar ratio of melamine, potassium chloride, ammonium chloride and water is 1:0.5:0.005:0.008 when preparing the carbon nitride rare earth adsorbent.

[0088] Comparative Example 1

[0089] This comparative example provides a method for preparing a carbon nitride rare earth adsorbent. The only difference from Example 1 is that potassium chloride is not added when preparing the carbon nitride rare earth adsorbent, and the reduced mass is distributed to melamine, ammonium chloride and water in the original proportion.

[0090] Comparative Example 2

[0091] This comparative example provides a method for preparing a carbon nitride rare earth adsorbent. The only difference from Example 1 is that, when preparing this carbon nitride rare earth adsorbent, ammonium chloride is not added, and the reduced mass is distributed to melamine, potassium chloride and water in the original proportion.

[0092] Test method:

[0093] (1) The morphology of the hydroxyl-rich defective carbon nitride rare earth adsorbent prepared in Example 1 was characterized by scanning electron microscopy (Zeiss Sigma 300, UK).

[0094] (2) ① Preparation of rare earth stock solution:

[0095] Accurately weigh 1.5195g of Nd(NO3)3·6H2O into a 50mL beaker, add deionized water, transfer to a 500mL volumetric flask and make up to volume. Shake well. At this point, the concentration of Nd(III) in the solution is 1000mg / L.

[0096] Accurately weigh 1.4050g of Dy(NO3)3·6H2O into a 50mL beaker, add deionized water, transfer to a 500mL volumetric flask and make up to volume. Shake well. At this point, the concentration of Dy(III) in the solution is 1000mg / L.

[0097] Accurately weigh 1.3404 g of Lu(NO3)3·6H2O into a 50 mL beaker, add deionized water, transfer to a 500 mL volumetric flask and make up to volume. Shake well. At this point, the concentration of Lu(III) in the solution is 1000 mg / L.

[0098] ② Determination of optimal pH: Weigh 5 mg of the hydroxyl-rich defective carbon nitride rare earth adsorbent prepared in Example 1 into a 50 mL centrifuge tube. Adjust the pH of the Nd / dysprosium / lutetium stock solution to between 1 and 7 using 0.1 mol / L HNO3 and 0.1 mol / L NaOH. Add 20 mL of a 50 mg / L Nd / dysprosium / lutetium solution with adjusted pH. Place the solution in a constant-temperature shaking incubator (25°C, 200 rpm) and shake for 30 min until adsorption equilibrium is reached. Collect the supernatant with a syringe and filter it through a 0.22 μm aqueous filter. Use inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the lutetium concentration in the solution before and after adsorption and calculate the adsorption amount Q. e =(C0-C e) / m×V, where C0 (mg / L) is the initial concentration of Nd:N ... e (mg / L) represents the Nd:N / D:D:L concentration in the solution at adsorption equilibrium, V(L) is the solution volume, and m(g) is the mass of the adsorbent added. The bar chart showing the Nd:N / D:D:L adsorption capacity of the hydroxyl-rich defective carbon nitride rare earth adsorbent prepared in Example 1 at different pH values ​​is shown below. Figure 3 As shown.

[0099] (3) Determination of kinetic equilibrium time: 30 mg of the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 was weighed into a 150 mL plastic bottle, and 120 mL of a Nd:Y / Dys:Y / L solution with a pH of 5.0 and a concentration of 50 mg / L was added. The bottle was placed in a constant-temperature shaking shaker (25℃, 200 rpm) and shaken at different adsorption time points of 2 min, 4 min, 6 min, 8 min, 10 min, 15 min, 20 min, 30 min, 60 min, 120 min, and 180 min. The supernatant was collected with a syringe and filtered through a 0.22 μm aqueous filter. The Nd:Y / Dys:Y / Lynthium concentrations of the solution before and after adsorption were determined using ICP-OES, and the adsorption capacity was calculated. The change in the Nd:Y / Dys:Y / Lynthium adsorbent adsorbent provided in Example 1 at different times is shown in the figure below. Figure 4 As shown.

[0100] (4) Weigh 10 mg of the hydroxyl-rich defective carbon nitride rare earth adsorbent prepared in Example 1 into a 5 mL centrifuge tube, add 4 mL of Nd:Y / D:Y / Lt:Nd:Y / ... Figure 5 As shown;

[0101] The simulated maximum adsorption capacity of rare earth adsorbents for lutetium provided in Examples 2-5 and Comparative Examples 1-2 were also tested according to the above test methods. The test results are shown in Table 1.

[0102] (5) Influence of competing ions: 5 mg of the hydroxyl-rich defective carbon nitride rare earth adsorbent prepared in Example 1 was weighed into 50 mL centrifuge tubes, and 50 mg / L of lutetium and other coexisting metal ions (Al) were added. 3+ Ba 2+ Mn 2+ Co 2+Ni 2+ Ca 2+ Mg 2+ K + Na + The rare earth adsorbent provided in Example 1 was placed in a binary mixed solution with a pH of 5.0 and placed in a constant-temperature shaking shaker (25℃, 200 rpm) for 30 min to reach adsorption equilibrium. The supernatant was collected using a syringe and filtered through a 0.22 μm aqueous filter. The concentrations of lutetium and interfering ions in the solution before and after adsorption were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The separation factor histogram of the rare earth adsorbent under different interfering ions was obtained as shown in the figure. Figure 6 As shown.

[0103] (6) Adsorption effect of the actual system: 10 mg of the hydroxyl-rich defective carbon nitride rare earth adsorbent obtained in Example 1 was weighed into a 50 mL centrifuge tube. 20 mL of actual rare earth leaching tailings (pH = 5.2) was added, and the tube was placed in a constant-temperature shaking incubator (25℃, 200 rpm) for 30 min to reach adsorption equilibrium. The supernatant was collected with a syringe and filtered through a 0.22 μm aqueous filter. The rare earth concentration and interfering ion concentration of the solution before and after adsorption were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). The bar chart of the rare earth removal rate of the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 in the actual leaching tailings is shown below. Figure 7 As shown.

[0104] (7) X-ray diffraction test: The rare earth adsorbents provided in Example 1 and Comparative Example 1 were tested using an X-ray diffractometer (Empyrean, PANalytical BV, Netherlands). The obtained XRD patterns are shown below. Figure 9 As shown; where DGCN-K is the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1, and BCN is the pure phase carbon nitride adsorbent of Comparative Example 1.

[0105] (8) Infrared Spectroscopy Test: An infrared spectrometer (Bruker, Tensor 27, Germany) was used to test the adsorption of neodymium, dysprosium, and lutetium ions by the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 before and after adsorption. The infrared spectra obtained are shown below. Figure 10 As shown, DGCN-K represents the state before adsorption, and Nd / Dy / Lu-DGCN-K represents the state after adsorption.

[0106] (9) Elemental Analysis: The adsorption of neodymium, dysprosium, and lutetium ions by the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 was analyzed using an X-ray photoelectron spectroscopy (Thermo, ESCALAB 250Xi) instrument. The obtained XPS full spectra are shown below. Figure 11As shown, the high-resolution C1s spectrum obtained from the test is as follows: Figure 12 As shown, the high-resolution O1s spectrum obtained from the test is as follows: Figure 13 As shown, DGCN-K represents the state before adsorption, and Nd / Dy / Lu-DGCN-K represents the state after adsorption.

[0107] Table 1

[0108]

[0109]

[0110] The test results show that: (1) As can be seen from Examples 1-3, the hydroxyl-rich and extended nanopore defective carbon nitride rare earth adsorbent provided by the present invention has a defective extended nanopore structure, a high specific surface area, and can provide abundant hydroxyl and cyano groups as rare earth adsorption active sites. The preparation process does not require complex processing steps, avoiding the high energy consumption generated by secondary reactions and grafting groups in conventional methods. It is suitable for large-scale production and is used for selective adsorption and separation of rare earths, with advantages of high adsorption capacity, fast adsorption kinetic rate, and high selectivity.

[0111] (2) A comparison of Examples 1 and 4-7 shows that by further controlling the molar ratio of precursor, alkali metal chloride, ammonium chloride, and water to 1:(0.4-1.2):(0.05-0.1):(0.007-0.01), the molar ratio of the raw materials affects the morphology of the prepared hydroxyl-rich defective carbon nitride rare earth adsorbent. The alkali metal chloride affects the degree of rearrangement of the heptaazine unit structure and the construction of defective extended nanopores in the precursor during the thermal polycondensation process. The content of ammonium chloride affects the specific surface area of ​​the material; too little ammonium chloride cannot form a loose and porous morphology, while too much ammonium chloride reduces the degree of polymerization of the material.

[0112] (3) As can be seen from Example 1 and Comparative Examples 1-2, the present invention uses a precursor, alkali metal chloride, ammonium chloride and water to prepare a hydroxyl-rich defective carbon nitride rare earth adsorbent by a one-step alkali calcination method. However, when alkali metal chloride or ammonium chloride is lacking in the reaction process, the hydroxyl-rich defective carbon nitride rare earth adsorbent with defective nanoporous structure of the present invention cannot be prepared.

[0113] In summary, this invention utilizes a precursor, alkali metal chloride, ammonium chloride, and water to prepare a hydroxyl-rich defective carbon nitride rare earth adsorbent with a defective nanoporous structure. Specifically, it is prepared via a one-step alkali calcination method, which eliminates the need for complex processing steps and avoids the high energy consumption associated with secondary reactions and grafting groups in conventional methods. This method is suitable for large-scale production. The resulting hydroxyl-rich defective carbon nitride rare earth adsorbent can be used for the selective adsorption and separation of rare earth elements, exhibiting advantages such as high adsorption capacity, fast adsorption kinetic rate, and high selectivity.

[0114] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A hydroxyl-rich defective carbon nitride rare earth adsorbent, characterized in that, The raw materials for preparing the hydroxyl-rich defective carbon nitride rare earth adsorbent include a precursor, an alkali metal chloride, ammonium chloride, and water. The hydroxyl-rich defective carbon nitride rare earth adsorbent has an extended nanoporous structure and hydroxyl and cyano groups. The specific surface area of ​​the hydroxyl-rich defective carbon nitride rare earth adsorbent is 100-120 m². 2 / g; The hydroxyl-rich defective carbon nitride rare earth adsorbent is obtained by the following preparation method: A mixture of a precursor, an alkali metal chloride, ammonium chloride, and water is obtained. The mixture is then calcined to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent. The molar ratio of the precursor, alkali metal chloride, ammonium chloride, and water is 1:(0.4-1.2):(0.05-0.1):(0.007-0.01); The alkali metal chloride includes any one or a combination of at least two of sodium chloride or potassium chloride.

2. A method for preparing the hydroxyl-rich defective carbon nitride rare earth adsorbent as described in claim 1, characterized in that, The preparation method includes the following steps: A mixture of a precursor, an alkali metal chloride, ammonium chloride, and water is obtained. The mixture is then calcined to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

3. The preparation method according to claim 2, characterized in that, The precursor includes any one or a combination of at least two of melamine, urea, or thiourea.

4. The preparation method according to claim 3, characterized in that, The precursor is melamine.

5. The preparation method according to claim 2, characterized in that, The mixing includes grinding and mixing.

6. The preparation method according to claim 2, characterized in that, The heating rate for calcination is 2-10℃ / min.

7. The preparation method according to claim 2, characterized in that, The calcination temperature is 500-600℃.

8. The preparation method according to claim 2, characterized in that, The calcination time is 3-5 hours.

9. The preparation method according to claim 2, characterized in that, The calcination process also includes solid-liquid separation, washing, and drying.

10. The preparation method according to claim 9, characterized in that, The washing process includes washing with deionized water.

11. The preparation method according to claim 9, characterized in that, The drying temperature is 40-80℃.

12. The preparation method according to claim 9, characterized in that, The drying time is 6-12 hours.

13. The preparation method according to claim 2, characterized in that, The preparation method includes the following steps: Melamine, alkali metal chloride, ammonium chloride, and water were ground and mixed in a molar ratio of 1:(0.4-1.2):(0.05-0.1):(0.007-0.01) to obtain a mixture. The mixture was then calcined in a tube furnace at a heating rate of 2-10℃ / min to 500-600℃ for 3-5 hours. After solid-liquid separation and washing, the mixture was dried at 40-80℃ for 6-12 hours to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

14. The use of the hydroxyl-rich defective carbon nitride rare earth adsorbent according to claim 1, characterized in that, The hydroxyl-rich defective carbon nitride rare earth adsorbent is used for the efficient and selective enrichment and recovery of rare earth ions in leaching tailings.

15. The use of the hydroxyl-rich defective carbon nitride rare earth adsorbent according to claim 14, characterized in that, The hydroxyl-rich defective carbon nitride rare earth adsorbent exhibits an adsorption capacity of Qe≥145mg / g for rare earth ions neodymium, dysprosium, and lutetium within a pH range of 4-7.

16. The use of the hydroxyl-rich defective carbon nitride rare earth adsorbent according to claim 15, characterized in that, The total rare earth ion removal rate of the hydroxyl-rich defective carbon nitride rare earth adsorbent is ≥80%.

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