Method for preparing hydroxyapatite from solid waste by ammonia-alkali method

Abstract

The application provides a method for preparing hydroxyapatite from solid waste by ammonia alkaline method, and belongs to the field of comprehensive utilization of solid waste resources and synthesis of inorganic materials. First, ammonia distillation waste clear liquid and alkali residue of the ammonia alkaline method are prepared into slurry, and the slurry is reacted with concentrated hydrochloric acid, then calcium-containing alkaline solid substances are added to adjust pH, remove impurities and increase concentration, so that a calcium chloride solution with a concentration of 25.08-32.02% is obtained; then hydroxyapatite seeds, crystal formation inducer and crystal extraction agent are added, finally, the solution is reacted with a phosphoric acid trisalt solution, and after washing and purification, high-yield (>99%) and high-purity (>=99%) hydroxyapatite is prepared. The application significantly improves the resource utilization rate, the utilization rate of alkali residue reaches 85.01-87.00%, and the effective component extraction rate is more than 96.60%. Meanwhile, the total amount of alkali residue emission is greatly reduced, the ammonia distillation waste clear liquid is reused, the hydroxyapatite is rapidly prepared, and the product added value is improved.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization of solid waste resources and synthesis of inorganic materials, specifically relating to a method for preparing hydroxyapatite from ammonia-soda solid waste. Background Technology

[0002] The solid waste resource utilization industry is an important sub-sector of the green and environmentally friendly industry. It can save a significant amount of resources and energy, and has the advantages of recycling, energy conservation, and carbon reduction. It is of great significance for promoting and accelerating the formation of green and low-carbon production and lifestyles. In particular, the "three wastes" of the ammonia-soda process have always been a pain point for the industry. Achieving their comprehensive utilization will help to conserve energy and reduce emissions, thereby realizing the green development of the soda ash industry.

[0003] The domestic ammonia-soda process has a production capacity of approximately 14 million tons per year, resulting in the annual discharge of about 126 million tons of ammonia stripping waste liquor and 3.78 million tons of alkali residue. These large quantities of waste liquor and residue have become a major problem for enterprises. Furthermore, the surge in natural soda ash production has significantly impacted chemical soda ash production. Therefore, the comprehensive utilization of ammonia stripping waste liquor and alkali residue to reduce operating costs and enhance enterprise competitiveness is urgently needed. The main components of ammonia stripping waste liquor are CaCl2 (8-10%) and NaCl (4-6%); the main components of alkali residue are CaCO3 (46-48%), Mg(OH)2 (9-11%), NaCl (10-17%), CaCl2 (7-13%), Fe2O3 (0.5-1.5%), and acid-insoluble matter (11-15%, mainly SiO2 and CaSO4, with SiO2 being the primary component).

[0004] Because ammonia stripping waste liquid and alkaline residue contain a large amount of calcium, they have recycling value. The main components of ammonia stripping waste liquid are shown in the table below:

[0005]

[0006] Currently, the mainstream technology for the resource utilization of ammonia stripping waste liquid from the ammonia-soda process, both domestically and internationally, is the evaporation crystallization process to produce calcium chloride. The traditional method involves introducing the liquid into salt fields for natural evaporation, and then using it in production once the concentration reaches approximately 20°Bé. This process is inefficient, time-consuming, and requires a large area. Furthermore, the instability of natural evaporation makes it difficult to guarantee the quality and supply of concentrated calcium chloride, leading to significant fluctuations in production costs. For the alkaline residue generated during the ammonia-soda process, common treatment methods include direct discharge or use as a filler material in the construction industry. However, direct discharge not only incurs high treatment costs but also frequently faces multiple risks such as environmental penalties and resource waste. When used as a filler material, its low proportion in building materials results in limited consumption and poor economic efficiency. Overall, neither domestic nor international efforts have achieved ideal results in the resource utilization of ammonia stripping waste liquid and alkaline residue. Therefore, achieving efficient and value-added comprehensive utilization of ammonia stripping waste liquid and alkaline residue is imperative.

[0007] Currently, hydroxyapatite can be prepared using solid-state reaction, hydrothermal, sol-gel, microemulsion, and chemical precipitation methods. Solid-state reaction requires high-temperature blending, resulting in high energy consumption and long processing times, limiting its widespread application. Hydrothermal methods utilize high temperature and pressure for chemical reactions, but these methods are prone to side reactions, have long reaction times, and require sophisticated equipment, making them unsuitable for large-scale production. The sol-gel method offers relatively mild reaction conditions, simple equipment, and produces products with good crystallinity and high dispersion, but suffers from drawbacks such as expensive alkoxide raw materials, highly toxic organic solvents, and low yields. Microemulsion preparation of hydroxyapatite involves complex processes including microemulsion preparation, precipitation reaction, separation and washing, drying, and calcination, requiring high-temperature calcination, resulting in high energy consumption and low product yields. Chemical precipitation, with its simple operation, low equipment requirements, and low cost, has become a focus of research.

[0008] Chinese invention patent document CN114159963A discloses a method for producing calcium chloride solution from waste residue in the ammonia-soda process. The method involves preparing a slurry from the alkali residue with water or dilute hydrochloric acid, then reacting it with hydrogen chloride gas to obtain a completed reaction liquid. This completed reaction liquid is then heated with the slurry to obtain an alkaline solution and a residue slurry. After clarification and filtration, concentrated hydrochloric acid is added to adjust the pH, yielding a calcium chloride solution. In this technique, the alkali residue is prepared into a slurry, which is then fed into two-stage reactors, each containing slurry from the alkali residue. A portion of the slurry in the first-stage reactor reacts with hydrogen chloride gas. After the reaction is complete, the completed reaction liquid from the first-stage reactor is forced into a second-stage reactor for further reaction. The slurry in the second-stage reactor undergoes an acid-base neutralization reaction with the completed reaction liquid from the first-stage reactor. The primary purpose of the second-stage reactor is to adjust the pH of the completed reaction liquid from the first-stage reactor for impurity removal (removal of magnesium and iron). Because the pH of the slurry in the secondary reactor is generally between 10 and 11, the amount of reaction solution from the primary reactor (pH = 1-5.5) entering the secondary reactor is limited. Therefore, the utilization rate of the alkali residue is significantly reduced, resulting in low practicality. Furthermore, the pH adjustment in the primary and secondary reactors limits the increase in calcium chloride solution concentration. Additionally, the reaction of hydrogen chloride gas with the alkali residue slurry is problematic because water has limited absorption capacity for hydrogen chloride gas, requiring a continuous supply of excess hydrogen chloride gas to complete the reaction. This excess hydrogen chloride necessitates environmentally unfriendly transportation.

[0009] Chinese invention patent document CN105129822A discloses a system and method for treating salt mud, a byproduct of chlor-alkali production. The method involves adding the salt mud to a reactor containing 22-29% hydrochloric acid for acidification. The carbon dioxide produced during the acidification process is absorbed by an alkaline solution. The resulting solution is used for primary brine purification (removing magnesium and iron) in the chlor-alkali industry. Then, caustic soda is added to the reactor once to adjust the pH and remove iron. The impurities remaining after iron removal are used in cement plants. A second addition of caustic soda removes magnesium. The impurities remaining after magnesium removal are calcined to prepare magnesium oxide, ultimately yielding a clear calcium chloride solution, thus achieving comprehensive utilization of the salt mud. This method involves adding 37% hydrochloric acid to water to adjust it to 22-29% hydrochloric acid. The amount of water introduced is approximately 0.27-0.68 times the volume of hydrochloric acid. However, due to the small amount of water added, the concentration of hydrochloric acid is high. The excess hydrochloric acid reacts violently with oxides such as calcium carbonate in the salt mud, producing a large amount of carbon dioxide gas and intense heat. With the interaction of water evaporation, the generation of a large number of bubbles, and the fact that the calcium chloride generated during the reaction process easily absorbs water, the reaction system forms a state with a high solid content, making it difficult to carry out the acidification reaction. Consequently, the utilization of the salt mud decreases sharply.

[0010] Chinese invention patent document CN105000541A discloses a method for preparing nano-hydroxyapatite. This method involves reacting calcium nitrate solution, trisodium phosphate solution, and acetamide in a packed bed at a low to medium temperature of 40-80°C via rotational reaction. The precipitate is then aged at room temperature for 36 hours, and finally centrifuged and washed to obtain hydroxyapatite. This process combines chemical precipitation and gravity methods to prepare hydroxyapatite; however, the resulting mixed-phase hydroxyapatite is not pure-phase hydroxyapatite and is primarily composed of calcium hydrogen phosphate. We refer to the appendix to the specification... Figure 1 XRD analysis revealed a high-intensity diffraction angle (the main diffraction peak of calcium hydrogen phosphate) at around 10°, and this diffraction angle was much larger than that of hydroxyapatite at around 32° (the main diffraction peak of hydroxyapatite). This indicates that the main product is a mixed phase of calcium hydrogen phosphate and the secondary product is hydroxyapatite. Summary of the Invention

[0011] The technical problem this invention aims to solve is to provide a method for preparing hydroxyapatite from solid waste generated during the ammonia-soda process. This method can simply and rapidly prepare hydroxyapatite with high yield and high purity. Compared with traditional preparation methods, it effectively overcomes the drawbacks of long reaction time, high energy consumption during medium- and high-temperature operation, and low product yield. Simultaneously, it solves the problems of long evaporation, re-drying, and concentration of traditional ammonia stripping waste liquid, as well as the high energy consumption of high-temperature concentration processes. Furthermore, this method achieves comprehensive utilization of both alkali residue and ammonia stripping waste liquid, solving the problems of high cost and environmental hazards associated with their separate utilization.

[0012] To address the above problems, the present invention provides a method for preparing hydroxyapatite from ammonia-soda solid waste, specifically comprising the following steps:

[0013] (1) Crush / grind the alkali residue into fine particles, add ammonia stripping waste liquid to adjust the slurry, and obtain alkali residue slurry; add acidification aid to the slurry to obtain the first mixed solution;

[0014] (2) Add concentrated hydrochloric acid to the first mixed solution and react at 40-75℃ for 1-3 hours. After filtration / centrifugation, the first residue and the first clear liquid are obtained.

[0015] (3) Add calcium-containing alkaline solids to the first clear liquid to adjust the pH to 10-12, stir the reaction for 0.3-0.5 h, filter / centrifuge to obtain the second residue and the second clear liquid, and recycle the second residue.

[0016] (4) Add hydroxyapatite seed crystals, adipic acid or succinic acid, and quaternary ammonium salt surfactant to the second clear liquid, stir and mix evenly to obtain the second mixed solution; add triphosphate aqueous solution to the second mixed solution, and adjust the pH to 10-12 with alkaline solution, stir and react at room temperature for 0.5-1h. After the reaction is completed, filter / centrifuge to obtain crude hydroxyapatite and the third clear liquid, and recover and reuse the third clear liquid;

[0017] (5) The crude hydroxyapatite was cleaned with a cleaning solution composed of pure water and proton organic solvent, and then dried to obtain hydroxyapatite.

[0018] Further, in step (1), the particle size of the fine alkaline residue is 100-300 mesh; the ratio of alkaline residue to ammonia stripping waste liquid in the alkaline residue slurry is 1g:4-10mL; the acidification aid is allyl polyoxyalkyl epoxy ether or allyl alcohol polyoxyalkyl ether or nonylphenol polyoxyethylene ether.

[0019] Furthermore, in step (1), the ratio of the amount of acidifying agent added to the amount of ammonia waste liquid added in the first mixed solution is 0.003-0.008g:1mL.

[0020] Further, in step (2), the concentration of concentrated hydrochloric acid is 31-37%; the ratio of the amount of concentrated hydrochloric acid used (calculated as hydrogen ions) to the amount of alkali residue added to the alkali residue slurry is 0.02-0.024 mol: 1g.

[0021] Furthermore, in step (3), the calcium-containing alkaline solid substance is calcium oxide or calcium hydroxide; the particle size of the calcium-containing alkaline solid substance is 200-300 mesh.

[0022] Furthermore, in step (3), the second residue can be recycled by using it to prepare cement raw materials.

[0023] Further, in step (4), the ratio of the amount of hydroxyapatite seed crystals added to the amount of the second clarifying liquid is 0.01-0.05 g: 1 mL; the ratio of the amount of adipic acid or succinic acid added to the amount of the second clarifying liquid is 0.01-0.03 g: 1 mL; and the ratio of the amount of quaternary ammonium salt surfactant added to the amount of the second clarifying liquid is 0.02-0.04 g: 1 mL.

[0024] Further, in step (4), the quaternary ammonium salt surfactant is alkyl dimethyl benzyl ammonium chloride or alkyl dimethyl ethyl ammonium bromide; the triphosphate is trisodium phosphate or tripotassium phosphate or triammonium phosphate; and the alkaline solution is saturated sodium hydroxide solution or saturated potassium hydroxide solution or ammonia water.

[0025] Furthermore, in step (4), the molar ratio of calcium ions in the triphosphate to the second clarified liquid is 0.582-0.599:1; the volume ratio of water content in the triphosphate aqueous solution to the volume of the second clarified liquid is 0.5-1:1.

[0026] Furthermore, in step (4), the third clarified solution is recycled by returning it to step (1) to be used as ammonia stripping waste liquid.

[0027] Further, in step (5), the proton organic solvent is methanol, ethanol, or isopropanol; the volume ratio of pure water to proton organic solvent in the cleaning solution is 1:0.3-0.5; the cleaning conditions are: two to four cleanings; the drying conditions are: temperature 60-80℃, time 2-4h.

[0028] The first residue obtained by the inventors in step (2) is solid waste such as silicon dioxide and calcium sulfate. The first residue is mainly silicon dioxide and can be used for road paving.

[0029] The second residue obtained by the inventors in step (3) is a solid waste of magnesium hydroxide and iron hydroxide. The second residue is mainly composed of magnesium hydroxide and can be used as a raw material for cement production.

[0030] During the experiment in step (4), the inventors discovered that when the pH was below 10, the reaction conditions did not yield pure hydroxyapatite, and the product was mainly calcium hydrogen phosphate; when the pH was above 12, the reaction conditions also failed to yield pure hydroxyapatite, and the product was mainly calcium hydroxide. Therefore, to obtain pure hydroxyapatite, the pH of the reaction system needs to be appropriately controlled.

[0031] The beneficial effects of this invention are as follows:

[0032] (1) The technical solution of this invention provides a comprehensive utilization method for the treatment of ammonia stripping waste liquid and alkali residue solid waste in the ammonia-soda process soda ash industry. By introducing ammonia stripping waste liquid as a reaction solvent and controlling the reaction conditions such as the particle size of alkali residue (100-300 mesh) and the amount of hydrochloric acid added, the utilization rate of alkali residue reaches 85.01-87.00%, the extraction of effective components reaches over 96.60%, and only insoluble substances such as SiO2 and CaSO4 are discharged. This technical solution not only reduces the total discharge of alkali residue but also realizes the utilization of ammonia stripping waste liquid. The entire process generates almost no waste, saving energy and reducing emissions, turning waste into treasure, and guiding the healthy development of the soda ash industry. It also significantly improves resource utilization efficiency, increases product added value, and powerfully promotes the sustainable development of the soda ash industry, showing broad industrial application prospects.

[0033] (2) The technical solution of this invention is a simple and rapid method for preparing high-yield and high-purity hydroxyapatite, with a yield of over 99% and a purity of over 99%. This method optimizes specific triphosphates through extensive experiments, controlling the reaction time to within 1 hour, resulting in a fast reaction rate. Furthermore, it eliminates the need for prolonged aging or high-temperature calcination for secondary crystallization, thus possessing the characteristics of simple preparation method, fast reaction rate, and low energy consumption.

[0034] (3) The acidification aid (allyl polyoxyalkyl epoxy ether or allyl alcohol polyoxyalkyl ether or nonylphenol polyoxyethylene ether) used in this invention can suppress carbon dioxide gas bubbles generated during the acidification process, prevent the overflow of the reaction solution, reduce the danger of the acidification reaction, and enable the continuous addition of concentrated hydrochloric acid, laying the foundation for industrial continuous acidification reaction.

[0035] (4) This invention prepares a high-concentration calcium chloride solution of 25.08-32.02% by adjusting the solid-liquid ratio, the amount of concentrated hydrochloric acid added, and introducing calcium-containing alkaline solid substances. Compared with traditional methods, this method does not require time-consuming evaporation and re-drying concentration of ammonia stripping waste liquid, nor does it rely on energy-intensive high-temperature concentration processes to obtain the target concentration of calcium chloride solution, significantly saving time and energy. In addition, hydrochloric acid is one of the products of the chlor-alkali industry, which has long faced the dilemma of price inversion, seriously restricting the development of the chlor-alkali industry. This method consumes a large amount of hydrochloric acid by-product of chlor-alkali production, effectively alleviating its price inversion pressure, thereby promoting the coordinated development of the chlor-alkali and soda ash industries.

[0036] (5) The calcium-containing alkaline solid material (CaO / Ca(OH)2) used in this invention has a particle size of 200-300 mesh, which can effectively reduce the amount of calcium-containing alkaline solid material used, improve the effective utilization rate of resources and the dissolution rate in water, thereby shortening the time required for the impurity removal process and improving the removal efficiency of impurities such as iron and magnesium. In addition, the waste residue after impurity removal can be used as raw material for cement preparation, which helps to promote the circular economy. At the same time, the calcium-containing alkaline solid material (CaO / Ca(OH)2) also has the effect of increasing the concentration of calcium chloride solution.

[0037] (6) This invention uses hydroxyapatite seed crystals, adipic acid or succinic acid as crystal formation inducing agents, quaternary ammonium salt surfactants as crystal-raising agents, and alkaline solutions as pH adjusters. Hydroxyapatite seed crystals, adipic acid, or succinic acid can all effectively increase the nucleation rate of hydroxyapatite. When used together, they produce a synergistic effect, significantly reducing the nucleation energy barrier and thus increasing the overall reaction rate. The quaternary ammonium salt surfactant, as a crystal-raising agent, not only increases the crystallinity and nucleation rate of hydroxyapatite but also effectively inhibits hydroxyapatite agglomeration. Furthermore, the quaternary ammonium salt surfactant also has a synergistic effect with the hydroxyapatite seed crystals, adipic acid, or succinic acid, jointly promoting the increase in reaction rate.

[0038] (7) This invention uses a cleaning solution composed of pure water and a proton-containing organic solvent to purify crude hydroxyapatite. This cleaning solution not only effectively removes impurities but also reduces the drying conditions, allowing the drying process to be carried out at a lower temperature, thereby significantly reducing energy consumption. In addition, the wastewater generated after cleaning recovers the proton-containing organic solvent through evaporation. The residual wastewater after distillation contains sodium chloride, which can be directly transported to the salt field for salt production, realizing resource recycling. Attached Figure Description

[0039] Figure 1 The X-ray diffraction (XRD) structure diagram of the hydroxyapatite obtained in step (5) of Examples 1-4;

[0040] Figure 2 The XRD structure diagram of the hydroxyapatite obtained in step (5) of Comparative Example 4 is shown.

[0041] Figure 3 The XRD structure diagram of the product obtained in step (5) of Comparative Examples 6-9 is shown.

[0042] Figure 4 The XRD structure diagram of the product obtained in step (5) of Comparative Example 10;

[0043] Figure 5 The XRD structure diagram of the product obtained in step (5) of Comparative Example 11;

[0044] Figure 6 The XRD structure diagram of the product obtained in step (5) of Comparative Examples 12-13 is shown. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention is not limited thereto.

[0046] Example 1

[0047] (1) Grind the alkali residue using a ball mill and pass it through a 200-mesh sieve to obtain 200-mesh alkali residue particles. Take 50g of the ground alkali residue particles and add 300mL of ammonia-evaporized waste liquid. Stir and adjust the slurry to obtain alkali residue slurry. Add 1.80g of allyl polyoxyalkyl epoxy ether to the slurry to obtain the first mixed solution.

[0048] (2) 1.1 mol of 37% concentrated hydrochloric acid (calculated as hydrogen ions) was added to the first mixed solution and reacted at 60°C for 2 hours. After the reaction was completed, the first residue and the first clear liquid were obtained by filtration.

[0049] (3) Add calcium oxide with a particle size of 250 mesh to the first clarified liquid, adjust the pH to 11, stir for 0.4 h, and then filter to obtain the second residue and the second clarified liquid;

[0050] (4) Take 200 mL of the second clarified liquid and add 7.0 g of hydroxyapatite seed crystals, 4.0 g of succinic acid and 6.0 g of alkyl dimethyl benzyl ammonium chloride to it. Stir and mix evenly to obtain the second mixed solution. Add 0.437 mol of trisodium phosphate (trisodium phosphate) with a ratio of 0.592:1 to the total amount of calcium ions in the second clarified liquid to 140 mL of pure water to prepare a trisodium phosphate aqueous solution. Add the trisodium phosphate aqueous solution to the second mixed solution and adjust the pH to 11 with saturated sodium hydroxide solution. Stir the reaction at room temperature for 0.7 h. After the reaction is completed, filter to obtain crude hydroxyapatite and the third clarified liquid. Return the third clarified solution to step (1) as a waste liquid for ammonia stripping and reuse.

[0051] (5) The crude hydroxyapatite was washed three times with a washing solution composed of pure water and ethanol in a volume ratio of 50:20, and then dried at 70°C for 3 hours to obtain hydroxyapatite (HAP). The washing wastewater was distilled to recover ethanol.

[0052] In step (1), the utilization rate of alkali residue and the extraction rate of effective components in alkali residue were tested. The test results are shown in Table 1.

[0053] In step (3), the second clarified liquid was subjected to Ca2+ spectroscopy using an inductively coupled plasma optical transilluminator (ICP). 2+ Concentration test results are shown in Table 1.

[0054] In step (5), the hydroxyapatite was subjected to X-ray diffraction (XRD) to determine its structure, yield, and purity. The test results are shown in the figure below. Figure 1 Table 1.

[0055] The utilization rate test procedure for alkali residue is as follows: Place the first residue in an oven at 80℃ or higher, and after drying, weigh its mass. The calculation formula is: Y 总 = (m0-m1) / m0×100%, Y 总 The alkali residue utilization rate is %; m0 is the amount of alkali residue added (g); m1 is the mass of the first residue after drying (g). Where m0 is 50g.

[0056] The procedure for testing the extraction rate of effective components in alkali residue is as follows: Place the first residue in an oven at 80℃ or higher and dry for 12 hours. After drying, weigh its mass. The calculation formula is: Y 有效 = (m0-m1) / (m0×(1-X)) 酸性不溶物 ))×100%, Y 有效X represents the extraction rate of effective components from the alkali residue, %; m0 represents the amount of alkali residue added, g; 酸性不溶物 The content of acid-insoluble matter is %; m1 is the mass of the first residue after drying, in g. Wherein, X 酸性不溶物 It is 12%.

[0057] Ca 2+ Concentration testing method: Standard curves of calcium chloride solutions of different concentrations were prepared using calcium chloride and deionized water, with an average error ≤0.999. The Ca concentration of the test sample was determined based on the standard curve of the calcium chloride solution. 2+ Concentration. Among them, the mass fraction of calcium chloride is related to Ca... 2+ The concentration relationship is: W = C × M / (1000 × ρ) × 100%, where W is the mass fraction of CaCl2, and %; C is the mass fraction of CaCl2. 2+ Concentration, mol / L; M is the relative molecular mass of CaCl2, g / mol; ρ is the density of the calcium chloride solution at this concentration, g / L.

[0058] The yield test of hydroxyapatite is performed as follows: Weigh the hydroxyapatite from step (5) to obtain m2; according to the Ca in the second clarified liquid from step (4) 2+ The concentration and dosage were used to calculate the corresponding amount (mol) of hydroxyapatite (HAP), and then the theoretical mass (m) of HAP was obtained. max The formula is: Y HAP =(m2-m 晶种 ) / m max ×100%, Y HAP m is the yield of HAP, %; m2 is the total mass of HAP, g; m 晶种 The mass of hydroxyapatite seed crystals in the first mixed solution is expressed in g; m max For Ca in the second clarified liquid 2+ The entire theory is converted into the mass of HAP, g.

[0059] The purity test procedure for hydroxyapatite is as follows: Weigh 1g of sample and dissolve it in hydrochloric acid solution, dilute to 100mL in a volumetric flask, and measure the Ca in the solution using ICP. 2+ Concentration, from Ca 2+ The concentration of hydroxyapatite was calculated from the concentration of Ca. 2+ The relationship between concentration and purity is: X 纯度 =C Ca2+ ×a×M HAP / 10b×100%, X 纯度 denoted as hydroxyapatite (HAP), %; a is the volume of the solution, 0.1 L; M HAP It is hydroxyapatite (molecular formula Ca) 10The relative molecular mass of (PO4)6(OH)2 is 1004; b is the mass of the product when dissolved in hydrochloric acid, 1g.

[0060] As shown in Table 1, the mass of the first residue after drying in step (1) is 6.5g, and the Ca content in the second clarified liquid in step (3) is... 2+ The concentration was 3.69 mol / L, and the mass of HAP in step (5) was 81.07 g. Calculations showed that after acidifying the alkali residue and ammonia-removed waste liquid with 37% hydrochloric acid, the concentration of CaCl2 was 32.02% by mass, the utilization rate of the alkali residue reached 87.00%, the extraction rate of effective components from the alkali residue reached 98.86%, with only 1.04% loss of effective components, and the yield of hydroxyapatite reached 99.97%.

[0061] Depend on Figure 1 It can be seen that the standard card 09-0432 for hydroxyapatite contains only the diffraction peaks of hydroxyapatite, indicating that the substance is a pure phase and does not contain other phases.

[0062] As shown in Table 1, the hydroxyapatite (HAP) product contains 99.5% hydroxyapatite, meaning the product purity is 99.5%. Example 2

[0063] (1) After the alkali residue is crushed by a pulverizer, it is sieved through a 100-mesh sieve to obtain 100-mesh alkali residue particles. Take 50g of the crushed alkali residue particles and add 500mL of ammonia stripping waste liquid. Stir and adjust the slurry to obtain alkali residue slurry. Add 1.5g of allyl alcohol polyoxyalkylene ether to the slurry to obtain the first mixed solution.

[0064] (2) Add 1.0 mol of 31% concentrated hydrochloric acid (calculated as hydrogen ions) to the first mixed solution and react at 75°C for 1 h. After the reaction is complete, centrifuge to obtain the first residue and the first clear liquid. Transport the first residue.

[0065] (3) Add calcium hydroxide with a particle size of 200 mesh to the first clarified liquid to adjust the pH to 10, stir the reaction for 0.5 h, and then centrifuge to obtain the second residue and the second clarified liquid;

[0066] (4) Take 200 mL of the second clarified liquid and add 2.0 g of hydroxyapatite seed crystals, 2.0 g of succinic acid and 4.0 g of alkyl dimethyl ethyl ammonium bromide to it. Stir and mix evenly to obtain the second mixed solution. Add 0.332 mol of tripotassium phosphate (i.e., 0.599:1) to 100 mL of pure water to prepare a tripotassium phosphate aqueous solution. Add the tripotassium phosphate aqueous solution to the second mixed solution and adjust the pH to 12 with saturated potassium hydroxide solution. Stir the reaction at room temperature for 0.5 h. After the reaction is completed, centrifuge to obtain crude hydroxyapatite and the third clarified liquid. Return the third clarified solution to step (1) as a waste liquid for ammonia stripping and reuse.

[0067] (5) The crude hydroxyapatite was washed twice with a washing solution composed of pure water and methanol in a volume ratio of 50:15, and then dried at 80°C for 4 hours to obtain hydroxyapatite. The washing wastewater was distilled to recover methanol.

[0068] In step (1), the utilization rate of alkali residue and the extraction rate of effective components in alkali residue were tested. The test methods were the same as in Example 1, and the test results are shown in Table 1.

[0069] In step (3), the second clarified liquid is subjected to ICP Ca2+. 2+ Concentration testing was conducted using the same method as in Example 1, and the results are shown in Table 1.

[0070] In step (5), the hydroxyapatite was subjected to XRD structure, yield, and purity tests. The test methods were the same as in Example 1, and the test results are shown in [the table below]. Figure 1 Table 1.

[0071] As shown in Table 1, the mass of the first residue after drying in step (1) is 7.495g, and the Ca content in the second clarified liquid in step (3) is... 2+ The concentration was 2.77 mol / L, and the mass of hydroxyapatite in step (5) was 56.57 g. Calculations showed that after acidifying the alkali residue and ammonia-removed waste liquid with 31% hydrochloric acid, the concentration of CaCl2 was 25.08% by mass, the utilization rate of the alkali residue reached 85.01%, the extraction rate of effective components from the alkali residue reached 96.60%, with only 3.40% loss of effective components, and the yield of hydroxyapatite reached 98.11%.

[0072] Depend on Figure 1 It can be seen that the standard card 09-0432 for hydroxyapatite contains only the diffraction peaks of hydroxyapatite, indicating that the substance is a pure phase and does not contain other phases.

[0073] As shown in Table 1, the hydroxyapatite content in the hydroxyapatite product is 99.0%, that is, the purity of the product is 99.0%. Example 3

[0074] (1) After grinding the alkali residue with a ball mill, it is sieved through a 300-mesh sieve to obtain 300-mesh alkali residue particles. Take 50g of the ground alkali residue particles and add 200mL of ammonia-evaporized waste liquid. Stir and adjust the slurry to obtain alkali residue slurry. Add 1.6g of nonylphenol polyoxyethylene ether to the slurry to obtain the first mixed solution.

[0075] (2) Add 1.2 mol of 35% concentrated hydrochloric acid (calculated as hydrogen ions) to the first mixed solution and react at 40°C for 3 hours. After the reaction is complete, filter to obtain the first residue and the first clear liquid. Transport the first residue.

[0076] (3) Add calcium oxide with a particle size of 300 mesh to the first clarified liquid to adjust the pH to 12, stir the reaction for 0.3 h, and then filter to obtain the second residue and the second clarified liquid;

[0077] (4) Take 200 mL of the second clarified liquid and add 10.0 g of hydroxyapatite seed crystals, 6.0 g of adipic acid and 8.0 g of alkyl dimethyl benzyl ammonium chloride to it. Stir and mix evenly to obtain the second mixed solution. Add 0.360 mol of triammonium phosphate (triammonium phosphate) with a ratio of 0.582:1 to the total calcium ion molar ratio in the second clarified liquid to 200 mL of pure water to prepare a triammonium phosphate aqueous solution. Add the triammonium phosphate aqueous solution to the second mixed solution and adjust the pH to 10 with ammonia water. Stir and react at room temperature for 1 h. After the reaction is completed, centrifuge to obtain crude hydroxyapatite and the third clarified liquid. Return the third clarified solution to step (1) as a waste liquid for ammonia stripping and reuse.

[0078] (5) The crude hydroxyapatite was washed four times with a washing solution consisting of pure water and isopropanol in a volume ratio of 50:25, and then dried at 60°C for 2 hours to obtain hydroxyapatite. The washing wastewater was distilled to recover isopropanol.

[0079] In step (1), the utilization rate of alkali residue and the extraction rate of effective components in alkali residue were tested. The test methods were the same as in Example 1, and the test results are shown in Table 1.

[0080] In step (3), the second clarified liquid is subjected to ICP Ca2+. 2+ Concentration testing was conducted using the same method as in Example 1, and the results are shown in Table 1.

[0081] In step (5), the hydroxyapatite was subjected to XRD structure, yield, and purity tests. The test methods were the same as in Example 1, and the test results are shown in [the table below]. Figure 1 Table 1.

[0082] As shown in Table 1, the mass of the first residue after drying in step (1) is 6.895g, and the Ca content in the second clarified liquid in step (3) is... 2+ The concentration was 3.09 mol / L, and the mass of hydroxyapatite in step (5) was 71.47 g. Calculations showed that after acidifying the alkali residue and ammonia-removed waste liquid with 35% hydrochloric acid, the concentration of CaCl2 was 27.98% by mass, the utilization rate of the alkali residue reached 86.21%, the extraction rate of effective components from the alkali residue reached 97.97%, with only 2.03% loss of effective components, and the yield of hydroxyapatite reached 99.07%.

[0083] Depend on Figure 1 It can be seen that the standard card 09-0432 for hydroxyapatite contains only the diffraction peaks of hydroxyapatite, indicating that the substance is a pure phase and does not contain other phases.

[0084] As shown in Table 1, the hydroxyapatite content in the hydroxyapatite product is 99.5%, that is, the purity of the product is 99.5%. Example 4

[0085] (1) After grinding the alkali residue with a ball mill, it is sieved through a 200-mesh sieve to obtain 200-mesh alkali residue particles. Take 50g of the ground alkali residue particles and add 400mL of ammonia stripping waste liquid. Stir and adjust the slurry to obtain alkali residue slurry. Add 1.6g of allyl polyoxyalkyl epoxy ether to the slurry to obtain the first mixed solution.

[0086] (2) 1.1 mol of 37% concentrated hydrochloric acid (calculated as hydrogen ions) was added to the alkaline residue slurry and reacted at 65°C for 1 hour. After the reaction was completed, the residue and the clarified liquid were obtained by filtration.

[0087] (3) Add calcium oxide with a particle size of 200 mesh to the first clarified liquid to adjust the pH to 11. After stirring and reacting for 0.5 h, filter to obtain the second residue and the second clarified liquid.

[0088] (4) Take 200 mL of the second clarified liquid and add 5.0 g of hydroxyapatite seed crystals, 3.0 g of succinic acid and 5.0 g of alkyl dimethyl benzyl ammonium chloride to it. Stir and mix evenly to obtain the second mixed solution. Add 0.402 mol of trisodium phosphate (trisodium phosphate) with a ratio of 0.588:1 to the total amount of calcium ions in the second clarified liquid to 120 mL of pure water to prepare a trisodium phosphate aqueous solution. Add the trisodium phosphate aqueous solution to the second mixed solution and adjust the pH to 11.5 with saturated potassium hydroxide solution. Stir and react at room temperature for 1 h. After the reaction is completed, filter to obtain crude hydroxyapatite and the third clarified liquid. Return the third clarified solution to step (1) as a waste liquid for ammonia stripping and reuse.

[0089] (5) The crude hydroxyapatite was washed three times with a washing solution composed of pure water and ethanol in a volume ratio of 50:20, and then dried at 70°C for 3 hours to obtain hydroxyapatite. The washing wastewater was distilled to recover ethanol.

[0090] In step (1), the utilization rate of alkali residue and the extraction rate of effective components in alkali residue were tested. The test methods were the same as in Example 1, and the test results are shown in Table 1.

[0091] In step (3), the second clarified liquid is subjected to ICP Ca2+. 2+ Concentration testing was conducted using the same method as in Example 1, and the results are shown in Table 1.

[0092] In step (5), the hydroxyapatite was subjected to XRD structure, yield, and purity tests. The test methods were the same as in Example 1, and the test results are shown in [the table below]. Figure 1 Table 1.

[0093] As shown in Table 1, the mass of the first residue after drying in step (1) is 6.660 g, and the Ca content in the second clarified liquid in step (3) is... 2+ The concentration was 3.42 mol / L, and the mass of hydroxyapatite in step (5) was 73.38 g. Calculations showed that after acidifying the alkali residue and ammonia-removed waste liquid with 37% hydrochloric acid, the concentration of CaCl2 was 27.98% by mass, the utilization rate of the alkali residue reached 86.21%, the extraction rate of effective components from the alkali residue reached 97.97%, with only 2.03% loss of effective components, and the yield of hydroxyapatite reached 99.57%.

[0094] Depend on Figure 1 It can be seen that the standard card 09-0432 for hydroxyapatite contains only the diffraction peaks of hydroxyapatite, indicating that the substance is a pure phase and does not contain other phases.

[0095] As shown in Table 1, the hydroxyapatite content in the hydroxyapatite product is 99.4%, that is, the purity of the product is 99.4%. Comparative Example 1

[0096] The difference between Comparative Example 1 and Example 1 is that the amount of ammonia waste liquid added in step (1) is different. 300 mL of ammonia waste liquid is replaced with 100 mL of ammonia waste liquid, while the other steps remain unchanged.

[0097] During the experiment, it was found that when the solid-liquid ratio of the alkali residue to the ammonia stripping waste liquid was less than 1 g:4 mL, the addition of concentrated hydrochloric acid caused a violent reaction between the alkali residue and the concentrated hydrochloric acid, producing a large number of bubbles and rapid exothermic reaction. After stirring for a period of time, the reaction system essentially became a viscous solid agglomerate, making acidification impossible. The formation of the viscous solid agglomerate is likely due to the violent reaction causing solution evaporation, the generation of a large number of bubbles, and the hygroscopic nature of calcium chloride. The interaction of these three factors led to the reaction system becoming a viscous solid agglomerate. Therefore, proper control of the amount of ammonia stripping waste liquid added is necessary to obtain a high-concentration calcium chloride solution. Comparative Example 2

[0098] The difference between Comparative Example 2 and Example 1 is that the amount of ammonia stripping waste liquid added in step (1) is different. 300 mL of ammonia stripping waste liquid is replaced with 750 mL, while the other steps remain unchanged.

[0099] In step (3), the second clarified liquid is subjected to ICP Ca2+. 2+ Concentration testing was conducted using the same method as in Example 1, and the results are shown in Table 1.

[0100] In step (5), the yield of hydroxyapatite was tested using the same method as in Example 1. The test results are shown in Table 1.

[0101] As shown in Table 1, the Ca in the second clarified liquid in step (3) 2+ The concentration was 1.57 mol / L, and the mass of hydroxyapatite in step (5) was 31.78 g. Calculations showed that after acidifying the alkali residue and ammonia stripping waste liquid with 37% concentrated hydrochloric acid, the mass fraction of CaCl2 obtained was 15.33%. Due to the low concentration of the obtained calcium chloride solution, the yield of hydroxyapatite was 78.60%, far lower than the effect in Example 1. Therefore, it is necessary to appropriately control the amount of ammonia stripping waste liquid added to ensure a high utilization rate of the alkali residue while obtaining a high concentration of calcium chloride solution, thereby improving the yield of hydroxyapatite. Comparative Example 3

[0102] The difference between Comparative Example 3 and Example 1 is that no acidifying agent was added in step (1), while the other steps remained the same.

[0103] During the experiment, it was found that without the addition of an acidifying agent, the acidification reaction was violent, producing a large amount of carbon dioxide gas bubbles that caused the solution to overflow, making the reaction dangerous. Therefore, the acidifying agent is a key factor in ensuring the safe and gentle conduct of the acidification reaction. Comparative Example 4

[0104] The difference between Comparative Example 4 and Example 1 is that the pH adjusted by calcium oxide in step (3) is different. The pH is changed from 11 to 9, while the other steps remain the same.

[0105] During the experiment, it was found that no precipitate appeared when the pH was less than 10, meaning that the purification of the reaction solution was not completed.

[0106] In step (3), the second clarified liquid is subjected to Ca... 2+ Concentration testing was conducted using the same method as in Example 1, and the results are shown in Table 1.

[0107] In step (5), the hydroxyapatite was subjected to XRD structure and yield tests, using the same methods as in Example 1. The test results are shown in [reference needed]. Figure 2 Table 1.

[0108] As shown in Table 1, the Ca in the second clarified liquid in step (3) 2+ The concentration was 2.50 mol / L, and the mass of hydroxyapatite in step (5) was 51.78 g. Calculations showed that the mass fraction of CaCl2 was 24.71%. Due to the low concentration of the obtained calcium chloride solution, the yield of hydroxyapatite was 87.37%, far lower than the effect in Example 1. Therefore, calcium oxide can not only adjust pH and remove impurities, but also serve as a calcium source to supplement calcium, thereby increasing the concentration of the calcium chloride solution and thus improving the yield of hydroxyapatite.

[0109] Depend on Figure 2 It is known that hydroxyapatite contains impurities, with the impurity peak being magnesium hydroxyphosphate (Mg2(PO4)OH), corresponding to standard card 97-004-0828. This is because the magnesium impurities in the calcium chloride solution were not completely removed, resulting in the appearance of magnesium-based impurity peaks in the product. Comparative Example 5

[0110] The difference between Comparative Example 5 and Example 1 is that the mesh size of calcium oxide in step (3) is different, with 250 mesh replaced by 50 mesh, while the other steps remain unchanged.

[0111] During the experiment, it was found that when the mesh size of calcium oxide was below 200 mesh, the large particle size made it difficult to dissolve in water, and the particles tended to agglomerate upon contact with water, further increasing in size and resulting in a very slow dissolution rate, making it difficult to remove impurities from the reaction system. Therefore, selecting a calcium-containing alkaline solid with an appropriate particle size can help improve the impurity removal efficiency. Comparative Example 6

[0112] The difference between Comparative Example 6 and Example 1 is that no hydroxyapatite seed crystals were added in step (4), while the other steps remained the same.

[0113] The product from step (5) underwent XRD structural testing, and the test results are shown in [the table below]. Figure 3 .

[0114] Depend on Figure 3It is known that the product is a mixed phase of hydroxyapatite and calcium phosphate dihydrate, with a phase ratio of 2:8 between calcium phosphate dihydrate and hydroxyapatite. The standard card for calcium phosphate dihydrate is 97-001-6132. This is because, without the addition of hydroxyapatite seed crystals, pure hydroxyapatite cannot be obtained within a short reaction time. Therefore, hydroxyapatite seed crystals act as crystallization inducers, accelerating the reaction rate. Comparative Example 7

[0115] The difference between Comparative Example 7 and Example 1 is that no succinic acid and hydroxyapatite seed crystals were added in step (4), while the other steps remained unchanged.

[0116] The product from step (5) underwent XRD structural testing, and the test results are shown in [the table below]. Figure 3 .

[0117] Depend on Figure 3 It is known that the product is a mixed phase of hydroxyapatite and calcium hydrogen phosphate dihydrate, with a phase ratio of 7:3. This is because, without the addition of succinic acid and hydroxyapatite seed crystals, pure hydroxyapatite cannot be obtained within a short reaction time. Therefore, succinic acid and hydroxyapatite seed crystals act as crystallization inducers, accelerating the reaction rate, and the two have a synergistic effect. Comparative Example 8

[0118] The difference between Comparative Example 8 and Example 1 is that no quaternary ammonium salt surfactant alkyl dimethyl benzyl ammonium chloride was added in step (4), while the other steps remained unchanged.

[0119] The product from step (5) underwent XRD structural testing, and the test results are shown in [the table below]. Figure 3 .

[0120] Depend on Figure 3 It is known that the product is a mixed phase of hydroxyapatite and calcium hydrogen phosphate dihydrate, with a phase ratio of 1:9 for calcium hydrogen phosphate dihydrate and hydroxyapatite, and the hydroxyapatite exhibits low crystallinity. This is because, without the addition of the quaternary ammonium salt surfactant alkyl dimethyl benzyl ammonium chloride, highly crystalline hydroxyapatite cannot be obtained within a short reaction time. Therefore, the quaternary ammonium salt surfactant alkyl dimethyl benzyl ammonium chloride, as a crystallizing agent, not only improves the crystallinity of hydroxyapatite but also increases the reaction rate. Comparative Example 9

[0121] The difference between Comparative Example 9 and Example 1 is that in step (4), there is no addition of hydroxyapatite seed crystals, succinic acid, and quaternary ammonium salt surfactant alkyl dimethyl benzyl ammonium chloride, while the other steps remain unchanged.

[0122] The product from step (5) underwent XRD structural testing, and the test results are shown in [the table below]. Figure 3.

[0123] Depend on Figure 3 It is known that the product is dicalcium phosphate dihydrate. Without hydroxyapatite seed crystals, succinic acid, and quaternary ammonium salt surfactants, hydroxyapatite cannot be obtained within a short reaction time. Therefore, hydroxyapatite seed crystals, succinic acid, and quaternary ammonium salt surfactants have a synergistic effect, jointly accelerating the reaction rate and promoting the transformation of dicalcium phosphate into hydroxyapatite, which is an important factor in the preparation of pure-phase hydroxyapatite. Comparative Example 10

[0124] The difference between Comparative Example 10 and Example 1 is that there is no alkaline solution to adjust the pH in step (4), while the other steps remain the same.

[0125] The product from step (5) underwent XRD structural testing, and the test results are shown in [the table below]. Figure 4 .

[0126] Depend on Figure 4 It is known that the product is pure-phase calcium hydrogen phosphate dihydrate, corresponding to standard card PDF#97-001-6132. Without pH adjustment, hydroxyapatite is difficult to form within a short reaction time. Therefore, pH is another important factor in the formation of hydroxyapatite.

[0127] The price of dicalcium phosphate is much lower than that of hydroxyapatite, and dicalcium phosphate has fewer applications, mainly in the field of feed additives, while hydroxyapatite can be used in adsorbents, oral care, catalysis and other fields. Therefore, hydroxyapatite has a broader market prospect. Comparative Example 11

[0128] The difference between Comparative Example 11 and Example 1 is that no protonated organic solvent ethanol is added in step (5), while the other steps remain unchanged. The operation method of step (5) is as follows:

[0129] The crude hydroxyapatite was washed three times with 5 mL of pure water and then dried at 70 °C for 8 h to obtain hydroxyapatite.

[0130] The product from step (5) underwent XRD structural testing, and the test results are shown in [the table below]. Figure 5 .

[0131] Depend on Figure 5 and Figure 1 The comparison shows that the product is mainly hydroxyapatite, but it contains some impurity peaks located at 14.2°, 35.5°, and 55.7°. This is because the addition of the protonated organic solvent ethanol cannot completely remove the impurities, resulting in the presence of impurity phases in the hydroxyapatite. Furthermore, the addition of the protonated organic solvent ethanol can reduce the drying time. Comparative Example 12

[0132] The difference between Comparative Example 12 and Example 1 is that the trisodium phosphate in step (4) is replaced with disodium hydrogen phosphate, while the other steps remain unchanged.

[0133] The product from step (5) underwent XRD structural testing, and the test results are shown in [the table below]. Figure 6 .

[0134] Depend on Figure 6 , Figure 1 and Figure 3 The comparison shows that the product is mainly a mixed phase of calcium hydrogen phosphate dihydrate and hydroxyapatite, but calcium hydrogen phosphate dihydrate is dominant. This is because the hydrolysis rate of triphosphate is greater than that of diphosphate, allowing it to quickly combine with calcium ions. After a period of reaction, the target product, hydroxyapatite, is obtained. Therefore, triphosphate is another necessary condition for the rapid preparation of hydroxyapatite. Comparative Example 13

[0135] The difference between Comparative Example 13 and Example 1 is that the trisodium phosphate in step (4) is replaced with sodium dihydrogen phosphate, while the other steps remain unchanged.

[0136] The product from step (5) underwent XRD structural testing, and the test results are shown in [the table below]. Figure 6 .

[0137] Depend on Figure 6 and Figure 1 as well as Figure 3 The comparison shows that the product is mainly a mixed phase of calcium hydrogen phosphate dihydrate and hydroxyapatite, but calcium hydrogen phosphate dihydrate is dominant. This is because the hydrolysis rate of triphosphate is greater than that of dihydrogen phosphate, allowing it to quickly combine with calcium ions. After a period of reaction, the target product, hydroxyapatite, is finally obtained. Therefore, triphosphate is another necessary condition for the rapid preparation of hydroxyapatite. Comparative Example 14

[0138] The difference between Comparative Example 14 and Example 1 is that the particle size of the alkali residue grinding in step (1) is 500 mesh, while the other steps remain unchanged.

[0139] In step (1), the utilization rate of alkali residue and the extraction rate of effective components in alkali residue were tested. The test methods were the same as in Example 1, and the test results are shown in Table 1.

[0140] During our experiments, we found that when the particle size of the alkali residue is too small, the alkali residue powder will float on the surface of the solution, causing the alkali residue to react with the acid in a timely manner, resulting in a decrease in the utilization rate of the alkali residue.

[0141] As shown in Table 1, the mass of the first residue after drying was 13.756 g. Calculations show that the utilization rate of the alkali residue and the extraction rate of its effective components were 72.49% and 82.37%, respectively, far lower than the test results of Example 1. Therefore, it is necessary to appropriately control the grinding particle size of the alkali residue.

[0142]

[0143] As can be seen from the above, compared with Comparative Examples 1-2, Example 1 could not obtain a high concentration of calcium chloride solution when the amount of ammonia stripping waste liquid was low or high. Similarly, controlling the ratio of ammonia stripping waste liquid to alkaline residue is a key factor in obtaining a high concentration of calcium chloride solution, thereby achieving a high yield of hydroxyapatite. Compared with Comparative Example 3, the acidification aid is a key factor for the safe conduct of the acidification reaction. Compared with Comparative Example 4, calcium oxide, a calcium-containing alkaline solid, can not only adjust the pH to remove impurities but also serve as a calcium source to supplement calcium, increasing the concentration of the calcium chloride solution and thus improving the yield of hydroxyapatite. This is another key factor in the preparation of pure-phase hydroxyapatite. Compared with Comparative Example 5, the mesh size of the calcium-containing alkaline solid affects the impurity removal efficiency. This is because larger-sized calcium oxide particles have limited solubility in water, and the surface of calcium oxide easily absorbs water, leading to calcium oxide agglomeration and further increasing the particle size, making impurity removal difficult. Therefore, selecting an appropriate particle size of the calcium-containing alkaline solid helps to improve the impurity removal efficiency. Compared to Comparative Examples 6-9, hydroxyapatite seed crystals, succinic acid, and quaternary ammonium salt surfactants all accelerated the reaction rate, and the three synergistically accelerated the reaction rate, promoting the transformation of calcium hydrogen phosphate to hydroxyapatite. Hydroxyapatite and succinic acid were the main factors accelerating the reaction rate and worked synergistically, while the quaternary ammonium salt surfactant alkyl dimethyl benzyl ammonium chloride was a secondary factor accelerating the reaction rate and also a decisive factor in improving the crystallinity of hydroxyapatite. Compared to Comparative Example 10, adjusting the pH of the reaction system to 10-12 was a necessary condition for obtaining hydroxyapatite; pH has a significant impact on hydroxyapatite. Compared to Comparative Example 11, the protonated organic solvent ethanol could both purify the target product and reduce drying requirements. Compared to Comparative Examples 12-13, the triphosphate exhibited a faster reaction rate than the dihydrogen phosphate and dihydrogen phosphate, which was a necessary condition for the rapid preparation of hydroxyapatite. Compared with Comparative Example 14, the particle size of the alkali residue was too small, which was not conducive to the acidification reaction of the alkali residue. Therefore, the grinding treatment of alkali residue should appropriately control the particle size range.

Claims

1. A method for preparing hydroxyapatite from ammonia-alkali solid waste, characterized in that, The method comprises the following steps: (1) crushing or grinding the alkali residue into fine particles, adding the ammonia distillation waste liquor to adjust the slurry, obtaining the alkali residue slurry, adding acidification aids to obtain the first mixed solution; (2) adding concentrated hydrochloric acid into the first mixed solution, reacting at 40-75 DEG C for 1-3h, and separating by filtration or centrifugation to obtain the first residue and the first clear solution; (3) adding calcium-containing alkaline solid material into the first clear solution to adjust the pH to 10-12, stirring for 0.3-0.5h, and separating to obtain the second residue and the second clear solution; (4) adding hydroxyapatite crystal seeds, adipic acid or succinic acid, and quaternary ammonium salt surfactant into the second clear solution, stirring to obtain the second mixed solution; adding the phosphoric acid trisalt aqueous solution into the second mixed solution, adjusting the pH to 10-12 by using alkaline solution, stirring at room temperature for 0.5-1h, and separating to obtain the hydroxyapatite crude product and the third clear solution; (5) washing the hydroxyapatite crude product with the washing liquid composed of pure water and protic organic solvent, and drying to obtain the hydroxyapatite. In the step (1), the particle size of the alkali residue fine particles is 100-300 mesh; the ratio of the amount of the alkali residue to the amount of the ammonia distillation waste liquor in the alkali residue slurry is 1g:4-10mL; the acidification aids are allyl polyoxyalkyl epoxy ether, allyl alcohol polyoxyalkyl ether or nonylphenol polyoxyethylene ether. In the step (3), the calcium-containing alkaline solid material is calcium oxide or calcium hydroxide; the particle size of the calcium-containing alkaline solid material is 200-300 mesh.

2. The process for the preparation of hydroxyapatite from ammonia-alkali solid waste as claimed in claim 1 wherein, In the step (1), the ratio of the amount of the acidification aids to the amount of the ammonia distillation waste liquor in the first mixed solution is 0.003-0.008g:1mL.

3. The process for the preparation of hydroxyapatite from ammonia-alkali solid waste according to claim 1, characterized in that, In the step (2), the concentration of the concentrated hydrochloric acid is 31-37%; the ratio of the amount of the concentrated hydrochloric acid to the amount of the alkali residue in the alkali residue slurry is 0.02-0.024moL:1g.

4. The process for the preparation of hydroxyapatite from ammonia-alkali solid waste as claimed in claim 1 wherein, In the step (4), the ratio of the amount of the hydroxyapatite crystal seeds to the amount of the second clear solution is 0.01-0.05g:1mL; the ratio of the amount of the adipic acid or succinic acid to the amount of the second clear solution is 0.01-0.03g:1mL; the ratio of the amount of the quaternary ammonium salt surfactant to the amount of the second clear solution is 0.02-0.04g:1mL.

5. The process for the preparation of hydroxyapatite from ammonia-alkali solid waste as claimed in claim 4, wherein, In the step (4), the quaternary ammonium salt surfactant is alkyl dimethyl benzyl ammonium chloride or alkyl dimethyl ethyl ammonium bromide; the phosphoric acid trisalt is trisodium phosphate or tripotassium phosphate or triammonium phosphate; the alkaline solution is saturated sodium hydroxide solution or saturated potassium hydroxide solution or ammonia water.

6. The process for the preparation of hydroxyapatite from ammonia-alkali solid waste as claimed in claim 1 wherein, In the step (4), the molar ratio of the phosphoric acid trisalt to calcium ions in the second clear solution is 0.582-0.599:1; the volume ratio of the water content in the phosphoric acid trisalt aqueous solution to the second clear solution is 0.5-1:

1.

7. The process for the preparation of hydroxyapatite from ammonia-alkali solid waste as claimed in claim 1 wherein, In the step (5), the protic organic solvent is methanol or ethanol or isopropyl alcohol; the volume ratio of the pure water to the protic organic solvent in the washing liquid is 1:0.3-0.5; the washing condition is: washing for 2-4 times; the drying condition is: temperature 60-80 DEG C, time 2-4h.

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