Hydroxyl-rich defective carbon nitride rare earth adsorbent as well as preparation method and application thereof

Abstract

The invention relates to a hydroxyl-rich defective carbon nitride rare earth adsorbent as well as a preparation method and application thereof. The hydroxyl-rich defective carbon nitride rare earth adsorbent is prepared from the following raw materials: a precursor, alkali metal chloride, ammonium chloride and water, a precursor, alkali chloride, ammonium chloride and water are mixed to obtain a mixture, the obtained mixture is subjected to an ion-induced thermal polymerization strategy, and the hydroxyl-rich defective carbon nitride rare earth adsorbent is prepared and has an expanded nanopore structure; the hydroxyl-rich defective carbon nitride rare earth adsorbent has the advantages of high adsorption capacity, rapid adsorption kinetics, high selectivity and good cycle stability, the recovery efficiency of rare earth ions in ore leaching tail liquid is high, the preparation raw materials are low in price, and the preparation process is simple.

Description

Technical Field

[0001] The present invention relates to the technical field of material preparation, and in particular to a hydroxyl-rich defective carbon nitride rare earth adsorbent and a preparation method and application thereof. Background Art

[0002] Rare earth elements are recognized as key strategic metal resources and are widely used in defense, military industry, electronic information, aerospace, new energy materials and other fields. Due to the incomplete leaching process of the current technology, a large number of rare earth waste tailings are left behind, and a large amount of leaching tailings and leaching wastewater are generated, resulting in serious loss 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 to maintaining the sustainable development of the rare earth economy and ecological environment. However, the rare earth ion concentration in most leaching tailings and leaching wastewater is low, the impurity ions are of many types and high content, and the system is complex. Selective enrichment and recovery of rare earths is still extremely challenging.

[0003] At present, various methods have been developed to recover rare earths from complex low-concentration rare earth wastewater. Among these methods, the adsorption method is widely used due to its simple operation, low cost and energy consumption, no need to use organic solvents, and clean and green characteristics, and has made great progress in the separation and recovery of rare earths. At present, conventional adsorbents include ion exchange resins, clays, porous organic polymers, metal organic frameworks, covalent organic frameworks, etc. According to the theory of hard and soft acids and bases, rare earth ions, as Lewis hard acids, usually have a strong binding effect with hard base groups containing O electron donors. Therefore, introducing a large number of hydroxyl groups into the adsorbent skeleton can be used to greatly improve the adsorption capacity of materials for rare earth ions. At present, various hydroxyl functionalized adsorbents have been developed and show 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 rare earth extraction applications.

[0004] As a two-dimensional layered material, graphitic carbon nitride (g-C3N4) has the advantages of stable physicochemical properties, simple preparation and environmental friendliness, and therefore has potential application value in the field of rare earth adsorption and separation. However, bulk graphitic carbon nitride has the disadvantages of narrow nanopores, small specific surface area, low density of oxygen-containing functional groups, poor hydrophilicity and dispersibility in solvents, resulting in insufficient exposure of available active sites and hindered diffusion of rare earth ions. Therefore, through the ion-induced thermal polycondensation strategy, alkali metal ions induce defects in the heptazine structural unit of carbon nitride and rearrange it, thereby forming an in-plane extended defect nanopore to optimize the microstructure of the material, and introduce abundant hydroxyl and cyanide groups, to achieve efficient adsorption performance for rare earths.

[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] In order to solve the above technical problems, the purpose of the present invention is to provide a hydroxyl-rich defective carbon nitride rare earth adsorbent and a preparation method and use thereof. 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, has high efficiency in recovering rare earth ions in leaching tailings, and has low price of raw materials and simple preparation process.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a hydroxyl-rich defective carbon nitride rare earth adsorbent, wherein the preparation raw materials of 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 nanopore structure and hydroxyl and cyano groups;

[0009] The specific surface area of ​​the hydroxyl-rich defective carbon nitride rare earth adsorbent is 100-120 m 2 / g, for example, it can 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 is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[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 helps the 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 provided by the present invention has abundant hydroxyl groups and electron-rich cyanide groups, providing abundant adsorption sites and having strong interactions 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. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[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 preparation method comprising the following steps:

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

[0014] The present invention prepares a defective carbon nitride rare earth adsorbent rich in hydroxyl groups and extended nanopores through an ion-induced thermal polymerization strategy under molten salt confined conditions. Among them, alkali metal chloride acts as a hard template agent to play a role of structural induction. Its addition can introduce alkali metal ions to destroy the covalent bonds between the precursors C and N, reduce the hydrogen bonding and van der Waals forces within the plane and between the layers, and help to form extended triangular nanopores composed of six heptazine structural units. At the same time, water molecules form hydroxyl groups at the broken bonds under thermal decomposition, and the porogen ammonium chloride produces gas under thermal decomposition, which helps to increase the specific surface area of ​​the material. This material is used for selective adsorption and separation of adsorbed rare earths, and has the advantages of high adsorption capacity, fast adsorption kinetics and high selectivity.

[0015] The defective carbon nitride rich in hydroxyl groups and expanded nanopores prepared by the present invention does not require complicated processing steps during the preparation process, avoids the high energy consumption generated by the secondary reaction grafting group in the conventional method, and is suitable for large-scale production. The one-step alkalization melt calcination method provided by the present invention is different from the hydrothermal synthesis method. If an oil bath combined with a hydrothermal synthesis method is used, not only the preparation method is more complicated and requires high temperature and high pressure conditions, but more importantly, it cannot prepare the defective expanded triangular nanopore structure of the present application. It cannot provide the sealing conditions of the molten salt for ion-induced structural defects, so it can only form a narrow nanopore structure densely bound by three heptazine 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, and other unlisted values ​​within the numerical range are also applicable.

[0017] The molar ratio of the precursor, alkali chloride, ammonium chloride and water in the present invention affects the morphology of the prepared hydroxyl-rich defective carbon nitride rare earth adsorbent, wherein the alkali chloride can introduce alkali metal ions to destroy the covalent bond between C and N, and the amount of the alkali chloride added affects the rearrangement of the heptazine unit structure and the degree of construction of defective extended nanopores in the thermal polycondensation process of the precursor. The water content directly affects the hydroxyl content in the final product. When it is too little, rich hydroxyl groups cannot be formed, and when it is too much, it will affect the formation of a molten state of alkali metal ions; the content of the porogen ammonium chloride will affect the specific surface area of ​​the adsorbent. When it is too little, a loose and porous morphological structure cannot be formed, and when it is too much, the degree of polymerization of the material will be reduced.

[0018] Preferably, the precursor comprises any one of melamine, urea or thiourea or a combination of at least two of them, 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, preferably melamine.

[0019] Preferably, the mixing comprises grinding mixing.

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

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

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

[0023] In the present invention, the precursor undergoes an ionic thermal polycondensation reaction during the calcination stage, and the calcination temperature directly affects the degree of the thermal polycondensation reaction of the precursor. If the temperature is too low, the alkali metal cannot form a molten state, which is not conducive to the sufficient mixing reaction of the precursor. If the temperature is too high, the material may be carbonized, resulting in a decrease in yield.

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

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

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

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

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

[0029] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0030] Melamine, alkali metal chloride, ammonium chloride and water are 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, and the obtained mixture is heated to 500-600°C in a tubular furnace at a heating rate of 2-10°C / min for calcination reaction for 3-5h, followed by solid-liquid separation and washing, and dried at 40-80°C for 6-12h to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

[0031] In a third aspect, the present invention provides a 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 the present invention is used for selectively adsorbing and separating rare earths, 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≥145 mg / 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, and other unlisted values ​​within the numerical 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 numerical range are also applicable.

[0035] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists 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) The present invention adopts an ion-induced thermal polycondensation strategy, wherein alkali metal chloride acts as a hard template agent to play a structural induction role. Its addition can introduce alkali metal ions to destroy the covalent bonds between C and N in the precursor, reduce the hydrogen bonding and van der Waals forces within the plane and between the layers, and help to form an extended triangular nanopore composed of six heptazine structural units. At the same time, water molecules form hydroxyl groups at the broken bonds under thermal decomposition, and the porogen ammonium chloride generates gas under thermal decomposition, which helps to increase the specific surface area of ​​the material, and is applied to selective adsorption separation adsorption, and 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 heptazine structural units, and its pore size is 1.107nm, which helps the 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 cyanide groups, providing abundant adsorption sites and having strong interactions 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a preparation flow chart of Example 1 of the present invention using an ion-induced thermal polycondensation strategy;

[0041] Figure 2 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 is a bar graph of the adsorption amount of rare earth neodymium, dysprosium and lutetium by the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 of the present invention at different pH values;

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

[0044] Figure 5 The embodiment 1 of the present invention provides a graph showing the variation of the adsorption amount of neodymium, dysprosium and lutetium of a hydroxyl-rich defective carbon nitride rare earth adsorbent at different equilibrium concentrations;

[0045] Figure 6 The present invention provides a bar graph of lutetium separation factors of a hydroxyl-rich defective carbon nitride rare earth adsorbent under different interfering ions in Example 1;

[0046] Figure 7 The rare earth extraction rate bar graph 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 The nitrogen adsorption-desorption curve diagram of the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 of the present invention;

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

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

[0050] Fig.12The C1s full spectrum of the hydroxyl-rich defective carbon nitride rare earth adsorbent before and after adsorbing neodymium, dysprosium and lutetium ions provided in Example 1 of the present invention;

[0051] Fig.13 The embodiment 1 of the present invention provides the full O1s spectrum of the hydroxyl-rich defective carbon nitride rare earth adsorbent before and after adsorbing neodymium, dysprosium and lutetium ions. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only 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 shall be subject to the claims.

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

[0054] Example 1

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

[0056] Melamine, potassium chloride, ammonium chloride and water are ground and mixed in a molar ratio of 1:0.5:0.06:0.008 to obtain a mixture, the obtained mixture is placed in a covered crucible, and the temperature is increased to 550°C in a tube furnace at a heating rate of 5°C / min for calcination reaction for 4 hours. After the reaction, the product is transferred to a conical flask, washed with deionized water for 3 times, and dried at 60°C for 10 hours to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

[0057] The hydroxyl-rich defective carbon nitride rare earth adsorbent has an extended triangular nanopore microstructure constructed by six heptazine units; and its specific surface area is 116.79 m 2 / g.

[0058] from Figure 1 It can be seen that Example 1 adopts an ion-induced thermal polycondensation strategy to prepare a defective carbon nitride rare earth adsorbent rich in hydroxyl groups and with expanded nanopores, wherein the molten salt provides a closed liquid environment to accelerate the polymerization process and regulate the reorganization of structural units. In this process, the positively charged K +The ions will destroy the CN=N covalent bonds in the heptazine units, reduce the hydrogen bonds and van der Waals forces in the plane and interlayer regions, and thus promote the rearrangement of the structural units and form an extended nanopore formed by six heptazine units. At the same time, water molecules promote the formation of hydroxyl groups at the broken bonds of the defective heptazine units under thermal decomposition, accompanied by the generation of cyano groups. In addition, the generation of gas by thermal decomposition of the porogen ammonium chloride helps to increase the specific surface area of ​​the material. Therefore, the successful preparation of defective carbon nitride rare earth adsorbents rich in hydroxyl groups and extended nanopores will be conducive to 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 flaky solid.

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

[0061] from Figure 4 It can be seen that the adsorption kinetic data of neodymium / dysprosium / lutetium on the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 conforms to the pseudo-second-order kinetic model, belongs to chemical adsorption, and can reach equilibrium within 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 amounts of 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 a high selectivity (SF=57-774) for the rare earth ion lutetium in the presence of different interfering ions other than aluminum.

[0064] from Figure 7 It can be seen that the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 has a single rare earth ion removal rate of 72-100%, and a total rare earth ion removal rate of up to 89% according to calculations, and thus has good practical application potential.

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

[0066] from Fig. 9 It can be seen that the characteristic peaks of BCN at 13.05 and 27.51° belong to the (100) crystal plane and (002) crystal plane of g-C3N4, respectively, corresponding to the in-plane repeating unit and interlayer stacking structure of the heptazine ring. According to Bragg's law, BCN has narrow triangular nanopores formed by three heptazine units, and its pore diameter is 0.678nm. In the XRD spectrum of DGCN-K, the (100) crystal plane is reduced to 7.98°, which proves that after ion-induced defects, an extended triangular nanopore formed by six heptazine units is formed, and its pore diameter is 1.107nm. The (002) crystal plane increases to 28.36°, proving that K ions are inserted into the carbon nitride interlayer, causing a slight contraction of the interlayer distance; DGCN-K is before adsorption.

[0067] from Fig.10 It can be seen that in the infrared spectrum of DGCN-K, at 3300cm -1 ~3500cm -1 Area, 1200-1700cm -1 Area and 808cm -1 The absorption peaks at 2179cm-1 belong to the stretching vibration peak of NH / -OH, the stretching vibration peak of CN=C heterocyclic ring of triazine ring, and the bending vibration peak of triazine ring. -1 and 1151cm -1 They belong to the stretching vibrations of 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 shift, which indicates that there is interaction between cyanide and hydroxyl groups and neodymium / dysprosium / lutetium ions; among them, DGCN-K is before adsorption, and Nd / Dy / Lu-DGCN-K is after adsorption.

[0068] from Fig.11 It can be seen that after the adsorption of DGCN-K, Nd-DGCN-K has new binding energy peaks at 1005.73 eV and 983.23 eV, which are characteristic peaks of neodymium ions and are attributed to Nd 3d 3 / 2 and Nd 3d 5 / 2 Dy-DGCN-K shows new binding energy peaks at 1334.84 eV and 1296.26 eV, which are characteristic peaks of dysprosium ions and are attributed to Dy 3d 3 / 2 and Dy 3d 5 / 2 Lu-DGCN-K has new binding energy peaks at 206.75eV and 197.08eV, which are characteristic peaks of lutetium ions and are attributed to Lu4d 3 / 2 and Lu 4d 5 / 2In addition, the binding energy peak intensities of K 2s and K 2p of Nd / Dy / Lu-DGCN-K were reduced to zero, where DGCN-K was before adsorption and Nd / Dy / Lu-DGCN-K was after adsorption.

[0069] from Fig.12 It can be seen that the C1s spectrum of DGCN-K is composed 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 undergo obvious blue shifts, and the binding energy decreases; among them, DGCN-K is before adsorption, and Nd / Dy / Lu-DGCN-K is after adsorption.

[0070] from Fig.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 undergoes an obvious red shift, and the binding energy increases; DGCN-K is before adsorption, and Nd / Dy / Lu-DGCN-K is after adsorption.

[0071] Based on the above results, it is proved that rare earth ions have strong interactions with cyano and hydroxyl groups, and ion exchange and coordination are the main mechanisms of adsorption of Nd / Dy / Lu by the hydroxyl-rich defective carbon nitride rare earth adsorbent provided by the present invention.

[0072] Example 2

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

[0074] Melamine, sodium chloride, ammonium chloride and water are ground and mixed in a molar ratio of 1:0.4:0.05:0.007 to obtain a mixture, the obtained mixture is placed in a covered crucible, and the temperature is increased to 500°C in a tube furnace at a heating rate of 3°C / min for calcination reaction for 5 hours. After the reaction, the product is transferred to a conical flask, washed with deionized water for 3 times, and dried at 75°C for 12 hours to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

[0075] The defective carbon nitride rare earth adsorbent rich in hydroxyl groups and having extended nanopores has an extended triangular nanopore structure constructed by six heptazine units; its specific surface area is 109.73 m 2 / g.

[0076] Example 3

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

[0078] Melamine, potassium chloride, ammonium chloride and water are ground and mixed in a molar ratio of 1:1.2:0.1:0.01 to obtain a mixture, the obtained mixture is placed in a covered crucible, and the temperature is increased to 600°C in a tube furnace at a heating rate of 10°C / min for calcination reaction for 3 hours. After the reaction, the product is transferred to a conical flask, washed with deionized water 4 times, and dried at 55°C for 12 hours to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

[0079] The defective carbon nitride rare earth adsorbent rich in hydroxyl groups and having extended nanopores has an extended triangular nanopore structure constructed by six heptazine units; its specific surface area is 113.26 m 2 / g.

[0080] Example 4

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

[0082] Example 5

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

[0084] Example 6

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

[0086] Example 7

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

[0088] Comparative Example 1

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

[0090] Comparative Example 2

[0091] This comparative example provides a method for preparing a carbon nitride rare earth adsorbent, which is different from Example 1 only in that, when preparing the carbon nitride rare earth adsorbent, ammonium chloride is not added, and the reduced mass is distributed to melamine, potassium chloride and water according to 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 using a scanning electron microscope (Sigma 300, Zeiss, UK).

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

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

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

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

[0098] ② Determination of the 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 value of the neodymium / dysprosium / lutetium stock solution to between 1 and 7 with 0.1 mol / L HNO3 and 0.1 mol / L NaOH, add 20 mL of a 50 mg / L pH-adjusted neodymium / dysprosium / lutetium solution, place in a constant temperature shaking shaker (25°C, 200 rpm) and shake at constant temperature for 30 min to reach adsorption equilibrium, take the supernatant with a syringe, filter with a 0.22 μm water filter, and use an inductively coupled plasma optical emission spectrometer (ICP-OES) to determine the lutetium concentration of the solution before and after adsorption and calculate the adsorption amount, the adsorption amount Q e =(C0-C e) / m×V, where C0 (mg / L) is the concentration of Nd / Dy / Lt ​​in the initial solution, C e (mg / L) is the concentration of neodymium / dysprosium / lutetium in the solution at adsorption equilibrium, V(L) is the volume of the solution, and m(g) is the mass of the adsorbent added; the bar graph of the adsorption amount of neodymium / dysprosium / lutetium of the hydroxyl-rich defective carbon nitride rare earth adsorbent prepared in Test Example 1 at different pH values ​​is shown in Figure 3 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, 120 mL of a 50 mg / L neodymium / dysprosium / lutetium solution with a pH of 5.0 was added, and the mixture was placed in a constant temperature shaking shaker (25° C., 200 rpm) for constant temperature shaking. Samples were taken 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 taken with a syringe and filtered with a 0.22 μm water filter. The neodymium / dysprosium / lutetium concentration of the solution before and after adsorption was determined by ICP-OES and the adsorption amount was calculated. The obtained neodymium / dysprosium / lutetium rare earth adsorption amount of the hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 at different times was as shown in the figure below. Figure 4 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 a 0-700 mg / L neodymium / dysprosium / lutetium solution with a pH of 5.0, place in a constant temperature shaking shaker (25°C, 200 rpm) and shake at constant temperature for 30 min to reach adsorption equilibrium, take the supernatant with a syringe, filter with a 0.22 μm water filter, and use an inductively coupled plasma optical emission spectrometer (ICP-OES) to measure the neodymium / dysprosium / lutetium concentration of the solution before and after adsorption and calculate the adsorption amount, and obtain the change of neodymium / dysprosium / lutetium adsorption amount of the rare earth adsorbent provided in Example 1 at different equilibrium concentrations as shown in Figure 5 As shown;

[0101] According to the above test method, the simulated maximum adsorption capacity of lutetium of the rare earth adsorbents provided in Examples 2-5 and Comparative Examples 1-2 was tested respectively. The test results are shown in Table 1.

[0102] (5) Effect of competing ions: 5 mg of the hydroxyl-rich defective carbon nitride rare earth adsorbent prepared in Example 1 was weighed into a 50 mL centrifuge tube, and 50 mg / L of lutetium and other coexisting metal ions (Al 3+ , Ba 2+ , Mn 2+ 、Co 2+、Ni 2+ , Ca 2+ Mg 2+ , K + 、Na + ) in a binary mixed solution with a pH of 5.0, placed in a constant temperature shaking shaker (25°C, 200 rpm) and shaken at constant temperature for 30 minutes to reach adsorption equilibrium, the supernatant was taken with a syringe, filtered with a 0.22 μm water filter, and the lutetium concentration and interfering ion concentration of the solution before and after adsorption were determined using an inductively coupled plasma optical emission spectrometer (ICP-OES), and the separation factor bar graph of the rare earth adsorbent provided in Example 1 under different interfering ions was obtained as shown in Figure 6 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, and 20 mL of actual rare earth leaching tailings (pH = 5.2) was added and placed in a constant temperature shaking shaker (25°C, 200 rpm) for constant temperature shaking for 30 min to reach adsorption equilibrium. The supernatant was taken with a syringe and filtered with a 0.22 μm water filter. The rare earth concentration and interfering ion concentration of the solution before and after adsorption were determined using an inductively coupled plasma optical emission spectrometer (ICP-OES), and a bar graph 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 was obtained. Figure 7 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, The Netherlands). The XRD spectra obtained by the test are shown in FIG. Fig. 9 As shown; wherein 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 spectrum test: The hydroxyl-rich defective carbon nitride rare earth adsorbent provided in Example 1 was tested before and after adsorbing neodymium, dysprosium and lutetium ions using an infrared spectrum tester (Bruker, Germany, Tensor 27). The infrared spectrum obtained by the test is shown in FIG. Fig.10 As shown, DGCN-K is before adsorption and Nd / Dy / Lu-DGCN-K is after adsorption.

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

[0107] Table 1

[0108]

[0109]

[0110] The test results show that: (1) Examples 1-3 show that the defective carbon nitride rare earth adsorbent rich in hydroxyl and extended nanopores 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. No complicated processing steps are required in the preparation process, which avoids the high energy consumption generated by the secondary reaction grafting group in the conventional method, is suitable for large-scale production, and 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.

[0111] (2) By comparing Example 1 with Examples 4-7, it can be seen that the present invention further controls the molar ratio of the precursor, alkali metal chloride, ammonium chloride and water to be 1: (0.4-1.2): (0.05-0.1): (0.007-0.01). The molar ratio between the raw materials affects the morphology of the prepared hydroxyl-rich defective carbon nitride rare earth adsorbent, and the alkali metal chloride affects the rearrangement of the heptazine unit structure and the degree of construction of defective extended nanopores in the thermal polycondensation process of the precursor. The content of ammonium chloride affects the specific surface area of ​​the material. When it is too little, a loose and porous morphological structure cannot be formed, and when it is too much, the degree of polymerization of the material is reduced.

[0112] (3) It can be seen from Example 1 and Comparative Examples 1-2 that the present invention adopts a precursor, an alkali metal chloride, ammonium chloride and water to prepare a hydroxyl-rich defective carbon nitride rare earth adsorbent through a one-step alkalization and calcination method. When alkali metal chloride or ammonium chloride is lacking in the reaction process, the hydroxyl-rich defective carbon nitride rare earth adsorbent with a defective nanopore structure of the present invention cannot be prepared.

[0113] In summary, the present invention adopts a precursor, an alkali metal chloride, ammonium chloride and water to prepare a hydroxyl-rich defective carbon nitride rare earth adsorbent with a defective nanopore structure. It is specifically prepared by a one-step alkalization and calcination method. No complicated processing steps are required during the preparation process, and the high energy consumption generated by the secondary reaction grafting group in the conventional method is avoided. It is suitable for large-scale production. The obtained hydroxyl-rich defective carbon nitride rare earth adsorbent can be used for selective adsorption and separation of rare earths, and has the advantages of high adsorption capacity, fast adsorption kinetic rate and high selectivity.

[0114] The applicant declares that the above is only a specific implementation mode 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 thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope 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 nanopore structure and hydroxyl and cyano groups; The specific surface area of ​​the hydroxyl-rich defective carbon nitride rare earth adsorbent is 100-120 m 2 / g.

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

3. The preparation method according to claim 2, characterized in that: 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); Preferably, the precursor includes any one of melamine, urea or thiourea, or a combination of at least two thereof, preferably melamine.

4. The preparation method according to claim 2 or 3, characterized in that: The mixing includes grinding mixing.

5. The preparation method according to any one of claims 2 to 4, characterized in that: The alkali metal chloride includes any one of lithium chloride, sodium chloride, potassium chloride, rubidium chloride or cesium chloride, or a combination of at least two thereof.

6. The preparation method according to any one of claims 2 to 5, characterized in that: The heating rate of the calcination is 2-10°C / min; Preferably, the calcination temperature is 500-600°C; Preferably, the calcination time is 3-5 hours.

7. The preparation method according to any one of claims 2 to 6, characterized in that: The calcination further includes solid-liquid separation, washing and drying; Preferably, the washing comprises washing with deionized water; Preferably, the drying temperature is 40-80°C; Preferably, the drying time is 6-12 hours.

8. The preparation method according to any one of claims 2 to 7, characterized in that: The preparation method comprises the following steps: Melamine, alkali metal chloride, ammonium chloride and water are 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, and the obtained mixture is heated to 500-600°C in a tubular furnace at a heating rate of 2-10°C / min for calcination reaction for 3-5h, followed by solid-liquid separation and washing, and dried at 40-80°C for 6-12h to obtain the hydroxyl-rich defective carbon nitride rare earth adsorbent.

9. 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 efficient and selective enrichment and recovery of rare earth ions in leaching tailings.

10. The use of the hydroxyl-rich defective carbon nitride rare earth adsorbent according to claim 9, characterized in that: The hydroxyl-rich defective carbon nitride rare earth adsorbent has an adsorption capacity of Qe≥145 mg / g for rare earth ions neodymium, dysprosium and lutetium in the pH range of 4-7; Preferably, the total rare earth ion removal rate of the hydroxyl-rich defective carbon nitride rare earth adsorbent is ≥80%.

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