Hexagonal system hydroxyapatite as well as synthesis method and application thereof in groundwater remediation

Abstract

The invention provides hexagonal system hydroxyapatite, a synthesis method thereof and application of the hexagonal system hydroxyapatite in groundwater remediation, the synthesis method comprises the following steps: S1, raw material preparation: taking a high-calcium leachate as a calcium source, adding soluble phosphorus salt into the leachate, and synthesizing a hydroxyapatite precursor through a coprecipitation reaction, wherein the concentration of Ca < 2 + > in the leachate is greater than or equal to 500mg / L; s2, magnetocaloric crystal form regulation and control: uniformly mixing magnetic nanoparticles into the hydroxyapatite precursor, and heating the system to 40-80 DEG C by utilizing an alternating magnetic field to excite a magnetocaloric effect, so as to obtain hexagonal system hydroxyapatite. The crystal form of hydroxyapatite is regulated and controlled based on magnetic heat, hexagonal system hydroxyapatite is prepared through an efficient and low-cost synthesis method, the capacity of neutralizing acid wastewater and adsorbing heavy metal of hydroxyapatite is improved, and in-situ remediation of mining area underground water is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental remediation, in particular to a hexagonal hydroxyapatite and a synthesis method thereof and an application of groundwater remediation. BACKGROUND

[0002] Acid in-situ leaching of uranium ore is a strategic technology for natural uranium mining in China, which has important strategic significance for ensuring national energy security and nuclear industry development. This technology can efficiently extract uranium resources by injecting sulfuric acid and oxidizing agent into the ore-bearing aquifer as leaching agent, with the advantages of less capital investment, low operating cost, and relatively small environmental disturbance. However, during the leaching process, the continuous deepening of the acid leaching solution leads to a significant decrease in the pH of the groundwater in the mining area, accompanied by the dissolution of heavy metal ions, which not only long-term affects the ecological environment, but also poses a potential threat to human health. In the in-situ neutralization and remediation of groundwater in the acid in-situ leaching mining area, the neutralization method is the most widely used chemical remediation technology due to its direct operation and rapid reaction. However, the traditional neutralization method requires continuous addition of reagents, has high operation and maintenance cost, and is prone to cause stratum plugging, which limits its long-term application.

[0003] Therefore, there is an urgent need for a new remediation technology that is low-cost, long-term stable, and can avoid stratum plugging, to solve the current difficulties in the remediation of groundwater pollution in the retired mining area of acid in-situ leaching. Hydroxyapatite has good calcium-phosphorus stability and heavy metal adsorption capacity, making it an optimal material for in-situ remediation of acid-contaminated groundwater. However, the crystal form of hydroxyapatite directly affects its reactivity and stability. Existing synthesis methods rely on laboratory conditions and are difficult to directly utilize industrial waste liquid resources, and the crystal form control means is complex. Therefore, there is an urgent need to develop an efficient and low-cost crystal form control method to improve the neutralization and adsorption performance of hydroxyapatite and achieve in-situ remediation of groundwater in the mining area. SUMMARY

[0004] Therefore, the present application provides a hexagonal hydroxyapatite and a synthesis method thereof and an application of groundwater remediation, mainly aiming to solve the problem that in the in-situ remediation of groundwater in the retired mining area of acid in-situ leaching, hydroxyapatite has good calcium-phosphorus stability and heavy metal adsorption capacity, but its crystal form directly affects its reactivity and stability. Therefore, an efficient and low-cost crystal form control method of hydroxyapatite is needed to improve the neutralization and adsorption performance of hydroxyapatite and achieve in-situ remediation of groundwater in the mining area.

[0005] To achieve the above-mentioned purpose, the technical scheme of the present application provides a synthesis method of a hexagonal hydroxyapatite, which comprises the following steps: S1, raw material preparation: taking high-calcium leaching solution as calcium source, the concentration of Ca 2+ in the leaching solution is ≥500 mg / L, soluble phosphorus salt is added to the leaching solution, and hydroxyapatite precursor is synthesized by coprecipitation reaction; S2. Magnetothermic crystal form control: Magnetic nanoparticles are uniformly mixed into the hydroxyapatite precursor, and the system is heated to 40-80℃ by stimulating the magnetocaloric effect using an alternating magnetic field to obtain hexagonal hydroxyapatite.

[0006] In some embodiments, the soluble phosphate salt is Na2HPO4 and / or NH4H2PO4.

[0007] In some embodiments, the pH of the leachate is 5-8.

[0008] In some embodiments, in step S1, the calcium source and the soluble phosphate salt are added at a Ca to P molar ratio of (1.4-1.7):1.

[0009] In some embodiments, the magnetic nanoparticles are Fe3O4.

[0010] In some embodiments, in step S2, the average particle size of the hexagonal hydroxyapatite is 4-6 μm.

[0011] In some embodiments, a hexagonal hydroxyapatite is prepared by any of the synthesis methods described herein.

[0012] In some embodiments, the application of hexagonal hydroxyapatite in groundwater remediation involves injecting the hydroxyapatite into the groundwater layer to neutralize the acidic water through alkaline release, thereby bringing the pH value of the acidic water to between 6.5 and 8.5.

[0013] In some embodiments, the application of hexagonal hydroxyapatite in groundwater remediation involves injecting the hydroxyapatite into the groundwater layer to adsorb and fix heavy metal ions in the groundwater through adsorption.

[0014] In some embodiments, the heavy metal ions include uranium, cadmium, and lead.

[0015] Compared with existing technologies, the hexagonal hydroxyapatite, its synthesis method, and its application in groundwater remediation described in this application have the following beneficial effects: (1) Precise control of crystal form by magnetocaloric: The magnetocaloric effect of magnetic nanoparticles is excited by alternating magnetic field to achieve controllable crystal form of hydroxyapatite, forming a stable hexagonal crystal form with a hexagonal crystal system ratio of ≥90%; (2) Dual remediation mechanism: Hydroxyapatite plays a dual role in neutralizing acid and adsorbing and fixing metals, which can improve the groundwater remediation efficiency of acid leaching mining areas by more than 30%. (3) Waste liquid resource utilization: using ground leaching waste liquid as a calcium source reduces raw material costs and solves the problem of waste liquid treatment. Attached Figure Description

[0016] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 SEM images of hydroxyapatite particles provided in embodiments of this application are shown.

[0017] Figure 2 The XRD image of hydroxyapatite particles provided in the embodiments of this application is shown.

[0018] Figure 3 The figures show the changes in pH and heavy metal concentration in groundwater before and after the use of hydroxyapatite particles provided in this application for groundwater remediation.

[0019] In the attached diagram: "Intensity" means "strength"; "Composite" means "compound"; "2theta" means "2θ". Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0022] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0023] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0024] The present application discloses a method for synthesizing hexagonal hydroxyapatite, which includes the following steps: S1. Raw material preparation: Using high-calcium leachate as the calcium source, the calcium in the leachate... 2+ With a concentration ≥500 mg / L, soluble phosphate salts are added to the leachate, and hydroxyapatite precursors are synthesized through a co-precipitation reaction. The high-calcium leachate is derived from the neutral high-calcium leachate produced during the decommissioning phase of the acid leaching mining area, with a pH of 5-7. The soluble phosphate salts are Na₂HPO₄ and NH₄H₂PO₄, and the calcium source and soluble phosphate salts are mixed at a Ca:P molar ratio of 1.67:1. The hydroxyapatite particles synthesized through co-precipitation reaction have a particle size of 1-10 μm.

[0025] S2. Magnetothermic crystal form control: Magnetic nanoparticles are uniformly mixed into the hydroxyapatite precursor, and the system is heated to 40-80℃ by stimulating the magnetocaloric effect using an alternating magnetic field to obtain hexagonal hydroxyapatite.

[0026] The magnetic nanoparticles are Fe3O4; in the step of stimulating the magnetocaloric effect using an alternating magnetic field, the temperature is gradually increased to 40-80℃. The hydroxyapatite crystal structure is hexagonal. Through magnetocaloric effect regulation, hydroxyapatite preferentially forms highly stable hexagonal hydroxyapatite, with the hexagonal crystal system accounting for ≥90%, avoiding the energy consumption problem of traditional high-temperature calcination and achieving controllable crystal structure.

[0027] Example 1 This embodiment describes a method for synthesizing hydroxyapatite, which specifically includes the following steps: S1. Raw material preparation: For the groundwater in the final mining area of ​​acidic uranium leaching, a neutral uranium leaching high-calcium leachate is selected. The Ca content of the leachate is... 2+ A hydroxyapatite precursor was synthesized by adding Na2HPO4 at a concentration of 600 mg / L and pH=7.5, with a Ca / P molar ratio of 1.67, via a co-precipitation reaction. S2. Magnetothermal crystal form control: 5wt% Fe3O4 magnetic nanoparticles were uniformly mixed into the hydroxyapatite precursor and reacted under an alternating magnetic field for 2 hours. The frequency of the alternating magnetic field was 100kHz and the magnetic field strength was 20kA / m, forming hexagonal hydroxyapatite particles with an average particle size of 5μm.

[0028] The scanning electron microscope image of the hexagonal hydroxyapatite particles synthesized in Example 1 is shown below. Figure 1 As shown, the corresponding XRD image is as follows: Figure 2 As shown. By Figure 1 It can be seen that the hexagonal hydroxyapatite particles exhibit agglomerated nanoscale particle characteristics, composed of a large number of particles of similar size, with a porous structure between the particles. Figure 2 It can be seen that the hydroxyapatite particles synthesized in Example 1 showed characteristic peaks of the hexagonal hydroxyapatite crystal system, and the total intensity of these characteristic peaks accounted for 90%, indicating that the hydroxyapatite in the product is mainly hexagonal and has good crystallinity.

[0029] Example 2 This embodiment describes a method for synthesizing hydroxyapatite, which specifically includes the following steps: S1. Raw material preparation: For the groundwater in the final mining area of ​​acidic uranium leaching, a neutral uranium leaching high-calcium leachate is selected. The Ca content of the leachate is... 2+ A hydroxyapatite precursor was synthesized by adding Na2HPO4 at a concentration of 600 mg / L and pH=7.5, with a Ca / P molar ratio of 1.4, via a co-precipitation reaction. S2. Magnetothermal crystal form control: 5wt% Fe3O4 magnetic nanoparticles were uniformly mixed into the hydroxyapatite precursor and reacted under an alternating magnetic field for 2 hours. The frequency of the alternating magnetic field was 100kHz and the magnetic field strength was 20kA / m, forming hydroxyapatite particles with an average particle size of 5μm.

[0030] Example 3 This embodiment describes a method for synthesizing hydroxyapatite, which specifically includes the following steps: S1. Raw material preparation: For the groundwater in the final mining area of ​​acidic uranium leaching, a neutral uranium leaching high-calcium leachate is selected. The Ca content of the leachate is... 2+ A hydroxyapatite precursor was synthesized by adding Na2HPO4 at a concentration of 600 mg / L and pH=7.5, with a Ca / P molar ratio of 1.67, via a co-precipitation reaction. S2. Magnetothermal crystal form control: 2wt% Fe3O4 magnetic nanoparticles were uniformly mixed into the hydroxyapatite precursor and reacted under an alternating magnetic field for 2 hours. The frequency of the alternating magnetic field was 100kHz and the magnetic field strength was 20kA / m, forming hydroxyapatite particles with an average particle size of 5μm.

[0031] Application Example 1 The hexagonal hydroxyapatite particles synthesized in Example 1 were used for groundwater remediation in the final mining area of ​​uranium mined by acid leaching.

[0032] Hydroxyapatite particles were injected into the groundwater in a simulated mining area. The initial pH of the groundwater was 2.0, and U(VI) was 5 mg / L. The pH and uranium concentration of the groundwater were tested, and the results are shown in the table below.

[0033]

[0034] The curves showing the changes in groundwater pH and heavy metal concentration before and after remediation are as follows: Figure 3 As shown, by Figure 3 As shown in the table above, after 7 days, the pH of the groundwater in the simulated mining area rose to 6.1, and the uranium concentration decreased to below 0.1 mg / L. This indicates that the hexagonal hydroxyapatite particles synthesized in Example 1 of this application have good adsorption and fixation capacity for uranium ions. Meanwhile, Ca... 2+ The concentration decreased by only 180 mg / L after 7 days, indicating that the hydroxyapatite particles did not dissolve rapidly during aging, but rather released Ca slowly. 2+ This demonstrates the characteristic of "long-term release," which meets the requirements of long-term material performance for in-situ groundwater remediation.

[0035] Application Example 2 The hexagonal hydroxyapatite particles synthesized in Example 1 of this application were injected into the groundwater of a simulated mining area, wherein the initial pH of the groundwater was 2.0, and the Cd content was [missing information]. 2+ The initial concentration was 20 mg / L. The pH and cadmium ion concentration of the groundwater were tested, and the test results are shown in the table below.

[0036]

[0037] The results in the table above show that as the reaction time increases, the pH value of the simulated groundwater gradually increases, while the cadmium ion concentration continuously decreases. After 7 days, the Cd concentration... 2+ When the concentration decreased to below 0.3 mg / L, the results showed that the hexagonal hydroxyapatite particles synthesized in Example 1 of this application had a good adsorption and fixation capacity for cadmium ions.

[0038] Application Example 3 The hexagonal hydroxyapatite particles synthesized in Example 1 of this application were injected into groundwater in a simulated mining area, wherein the initial pH of the groundwater was 2.0, and the Pb content was... 2+ The initial concentration was 30 mg / L. The pH and lead ion concentration of the groundwater were tested, and the test results are shown in the table below.

[0039]

[0040] The results in the table above show that the lead ion concentration decreased significantly over time, and after 7 days, Pb... 2+ When the concentration decreased to below 0.2 mg / L, the results showed that the hydroxyapatite particles synthesized in Example 1 also had a strong adsorption and fixation capacity for lead ions.

[0041] Application Example 4 The hydroxyapatite particles synthesized in Example 2 of this application were injected into the groundwater of a simulated mining area. The initial pH of the groundwater was 2.0 and the U(VI) concentration was 5 mg / L. The pH and uranium ion concentration of the groundwater were tested, and the test results are shown in the table below.

[0042]

[0043] As can be seen from the results in the table above, after 7 days, the pH of the groundwater in the simulated mining area rose to 5.1 and the uranium concentration dropped to below 0.5 mg / L. Compared with Example 1, the hydroxyapatite synthesized in Example 2 showed a significant decrease in its ability to adsorb and fix uranium ions.

[0044] Application Example 5 The hydroxyapatite particles synthesized in Example 3 of this application were injected into the groundwater of a simulated mining area. The initial pH of the groundwater was 2.0 and the U(VI) concentration was 5 mg / L. The pH and uranium ion concentration of the groundwater were tested, and the test results are shown in the table below.

[0045]

[0046] The results in the table above show that after 7 days, the pH of the groundwater in the simulated mining area rose to 5.6, and the uranium concentration dropped below 0.3 mg / L. Compared with Example 1, the hydroxyapatite synthesized in Example 3 showed a significantly weakened adsorption and fixation capacity for uranium ions.

[0047] This application utilizes ground leaching wastewater as a calcium source, achieving resource utilization of waste, reducing raw material costs, and solving the problem of wastewater treatment. The localized heating effect of magnetic nanoparticles enables controllable crystal structure of hydroxyapatite, avoiding the energy consumption problem of traditional high-temperature calcination. Through crystal structure control, the hexagonal crystal structure of the hexagonal hydroxyapatite particles is ≥90%. The synthesized hydroxyapatite simultaneously neutralizes acidic groundwater and adsorbs and fixes heavy metals, raising the pH value of acidic groundwater to between 6.5 and 8.5. Furthermore, it can adsorb and fix heavy metal ions such as uranium, cadmium, and lead in groundwater, improving groundwater remediation efficiency by more than 30%.

[0048] Those skilled in the art will understand that the steps, measures, and solutions in the various operations, methods, and processes discussed in this application can be alternated, modified, combined, or deleted. Furthermore, other steps, measures, and solutions in the various operations, methods, and processes discussed in this application can also be alternated, modified, rearranged, decomposed, combined, or deleted. Furthermore, steps, measures, and solutions in the prior art that are similar to those disclosed in this application can also be alternated, modified, rearranged, decomposed, combined, or deleted.

[0049] The above description is only a partial embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for synthesizing hexagonal hydroxyapatite, characterized in that, Includes the following steps: S1. Raw material preparation: Using high-calcium leachate as the calcium source, the calcium in the leachate... 2+ With a concentration ≥500 mg / L, soluble phosphate salts are added to the leachate, and hydroxyapatite precursors are synthesized through a co-precipitation reaction. S2. Magnetothermic crystal form control: Magnetic nanoparticles are uniformly mixed into the hydroxyapatite precursor, and the system is heated to 40-80℃ by stimulating the magnetocaloric effect using an alternating magnetic field to obtain hexagonal hydroxyapatite.

2. The method for synthesizing hexagonal hydroxyapatite according to claim 1, characterized in that, The soluble phosphate salt is Na2HPO4 and / or NH4H2PO4.

3. The method for synthesizing hexagonal hydroxyapatite according to claim 1, characterized in that, In step S1, the pH of the leachate is 5-8.

4. The method for synthesizing hexagonal hydroxyapatite according to claim 1, characterized in that, In step S1, the calcium source and the soluble phosphate salt are added at a Ca to P molar ratio of (1.4-1.7):

1.

5. The method for synthesizing hexagonal hydroxyapatite according to claim 1, characterized in that, The magnetic nanoparticles are Fe3O4.

6. The method for synthesizing hexagonal hydroxyapatite according to claim 1, characterized in that, In step S2, the average particle size of the hexagonal hydroxyapatite is 4-6 μm.

7. A hexagonal hydroxyapatite, characterized in that, It is prepared by the synthesis method according to any one of claims 1-6.

8. The application of the hexagonal hydroxyapatite according to claim 7 in groundwater remediation, characterized in that, The hydroxyapatite is injected into the groundwater layer, and the acidic water is neutralized by alkaline release, so that the pH value of the acidic water is between 6.5 and 8.

5.

9. The application according to claim 8, characterized in that, The hydroxyapatite is injected into the groundwater layer, where it adsorbs and fixes heavy metal ions in the groundwater through adsorption.

10. The application according to claim 9, characterized in that, The heavy metal ions include uranium, cadmium, and lead.

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