A method for preparing zinc-iron double metal hydroxide phosphorus-loving adsorbent using sewage sludge ash and its application

Abstract

The invention discloses a method and application of a zinc-iron bimetallic hydroxide phosphorus-loving adsorbent prepared from sludge ash, wherein the specific operation process is to subject the sludge ash to ball milling treatment and primary chemical wet treatment to obtain insoluble solid residue and acid extract, and then subject the insoluble solid residue to secondary chemical wet treatment, pH adjustment and modification to obtain Zn / Fe-LDHs modified sludge ash, which is placed in an acid extract to absorb phosphorus as a phosphorus adsorbent, and then desorbed using sodium hydroxide, and finally calcium hydroxide is added for chemical precipitation to obtain a hydroxyapatite product. The invention takes sludge ash as a starting point, realizes the resource utilization of sludge ash, and solves the problem of secondary pollution caused by sludge ash to urban environmental sanitation; the prepared phosphorus adsorbent has a high adsorption capacity for phosphate and has strong stability and recyclability, and can be repeatedly used to treat phosphorus.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection and resource recovery, and specifically relates to a method for preparing a zinc-iron double metal hydroxide phosphorus-philic adsorbent by utilizing sewage sludge ash and an application thereof. Background Art

[0002] Phosphorus plays a vital role in the growth of plants and animals, is essential in cell structure and metabolism, and is widely present in the biosphere. Phosphorus in nature mainly exists in the form of phosphate ore, but the reserves of phosphate ore are finite.

[0003] Incineration is a relatively complete method for treating sludge, which meets the requirements of volume reduction, harmlessness and resource utilization, and can reduce the original volume by more than 80%. After the sludge is incinerated, the non-volatile phosphorus is enriched in the sludge ash and can be recycled as a source for producing fertilizers and other phosphate products, which can alleviate the current shortage of phosphorus resources.

[0004] At present, the main technologies for extracting phosphorus from sludge ash include thermochemical method, electrodialysis method, ion exchange method, adsorption method, biological method and wet chemical method. Among them, thermochemical method, electrodialysis method, ion exchange method, adsorption method and biological method all have bottlenecks in industrial application. The reaction conditions of thermochemical method are harsh, energy consumption is large, and only volatile metals can be removed, while non-volatile harmful metals (such as As, Ni, etc.) cannot be removed. The wet chemical method currently has corresponding industrial applications and is operable and has a sound theoretical basis. However, the current research on wet chemical methods has the following problems: 1) The research on wet chemical methods mainly focuses on sulfuric acid and hydrochloric acid extraction. Sulfuric acid easily reacts with calcium in sludge ash to form gypsum, which adheres to the surface of sludge ash, hindering the further reaction between the two and resulting in a decrease in phosphorus extraction rate; 2) The wet chemical method not only extracts phosphorus, but also leaches a large amount of heavy metals. The low purity of phosphorus will limit the recovery and further use of phosphorus; 3) After the phosphorus in sludge ash is extracted by wet chemical methods, there is a lack of research on the subsequent utilization of residues, which are mostly used for landfill treatment, which is not conducive to the formation of a complete resource utilization pathway. One of the reasons for the above problems is that the current development of phosphorus recovery and utilization technology for phosphorus in phosphorus-rich extracts is not perfect. Among them, the struvite crystallization method and the blue iron ore recovery method have relatively strict requirements on operating conditions, and the phosphorus recovery rate is not high, especially for sewage treatment plants in my country that generally use aluminum salts as flocculants. It is even more useless. The calcium phosphate crystallization method is greatly interfered by coexisting ions and is not easy to form pure and large-size crystals, so the phosphorus recovery rate is also limited. In addition, the patents in the prior art on the use of phosphorus in sludge to prepare phosphate fertilizer mainly include methods of using fresh sludge to leach phosphorus to make fertilizer and using phosphorus in sludge ash obtained after drying and incineration of sludge to prepare phosphate fertilizer. The above methods generally have complex operation procedures and difficult to control operating conditions; many chemical agents are added, and a lot of waste liquid is generated, resulting in high energy consumption and high costs. At the same time, due to the complex and diverse components contained in the sludge itself, there is a risk of leaching of harmful elements such as heavy metals in the process of preparing phosphate fertilizer, so the generally adopted operating conditions are relatively harsh, such as calcination, ion exchange and other technical means, which greatly increases the production cost of the product. Summary of the invention

[0005] In view of the above problems, the object of the present invention is to provide a method for preparing a zinc-iron double hydroxide phosphorus-philic adsorbent using sludge ash and its application.

[0006] The specific technical solutions are as follows:

[0007] A method for preparing a zinc-iron double metal hydroxide phosphorus-philic adsorbent using sludge ash, comprising:

[0008] 1) The pretreatment unit of sludge ash mainly includes ball milling treatment of sludge ash and primary chemical wet treatment for phosphorus extraction. The sludge ash is ball milled to a particle size of 50-80 microns with a rotation speed of 1000-1200 r / min, the co-grinding time is 10min, and ball milling can fully reduce the particle size of the sludge ash material, so that the subsequent chemical wet treatment can be more effectively carried out; the specific method of the primary chemical wet treatment is: the sludge ash and dilute hydrochloric acid / nitric acid (0.2-1mol / L) are fully mixed and shaken at a solid-liquid ratio of 1:5-1:20g / mL for 2-5 hours, so that more than 95% of the phosphorus in the sludge ash is released into the supernatant in the form of orthophosphate ions and part of the metals, and then filtered and separated to obtain the insoluble solid residue and the acid extract, the insoluble solid residue is dried in a 65-80℃ forced air drying oven for 24h, and most of the phosphate is extracted from the acid extract, and it contains a small amount of impurities such as metal ions; this step plays the role of extracting phosphorus from the sludge ash and removing some impurities in the sludge ash.

[0009] 2) Activation and modification of insoluble solid slag to prepare zinc-iron double hydroxide phosphorus adsorbent (Zn / Fe-LDHs modified sludge ash). This step mainly includes secondary chemical wet treatment, pH adjustment, modification and stirring. The secondary chemical wet treatment mainly involves placing the insoluble solid slag and concentrated hydrochloric acid (5-8 mol / L) in a magnetic stirrer and mixing them thoroughly for 2 h at 60°C and a solid-liquid ratio of 1:10 g / mL. The secondary chemical wet treatment can not only surface activate the sludge ash and increase its specific surface area, but also leach the iron (mainly in the form of hematite) in the sludge ash, laying the foundation for subsequent reconstruction and regeneration into Zn / Fe-LDHs modified sludge ash, which is beneficial to improve the adsorption capacity of modified sludge ash for orthophosphate. Wait for the upper layer of liquid after the secondary chemical wet treatment to change from transparent to yellow, and then add ZnCl 2 (Zn: Fe molar ratio is 1:1-3:1) and evenly mixed, 2-5mol / L NaOH solution is slowly added to the above solid-liquid mixture to adjust the solution pH value to be stable at 11-12, so that the solid-liquid ratio is between 1:10-2:5. Use a magnetic stirrer to heat to 60-80 °C, stir vigorously at 200-500 rpm for 4h-6h, and after the reaction is complete, centrifuge to obtain Zn / Fe-LDHs modified sludge ash, and rinse the modified sludge ash with deionized water until neutral. The obtained solid is freeze-dried, ground, and sieved (<200μm) to obtain a phosphorus-philic adsorbent, namely Zn / Fe-LDHs modified sludge ash.

[0010] An application of the prepared zinc-iron double metal hydroxide phosphorus-philic adsorbent comprises the following steps:

[0011] 1) A phosphorus recovery adsorption desorption purification unit, including adsorption treatment and desorption treatment, wherein the acid extract is introduced from bottom to top into a leaching device filled with the prepared phosphorus-affinity adsorbent, and is fully and evenly mixed to adsorb phosphorus, the liquid-solid ratio of the acid extract to the adsorbent is 0.025-0.05 L / g, the adsorption temperature is 25-35°C, and the adsorption time is 2-6 h. After the adsorption is completed, the adsorption filtrate is extracted, and the reflux of the adsorption filtrate can be used as an acid leaching liquid in a chemical wet process; an industrial-grade sodium hydroxide aqueous solution (0.1-1 mol / L) is introduced into the phosphorus-affinity adsorbent after phosphorus adsorption, and is fully mixed to desorb phosphorus, the liquid-solid ratio of the sodium hydroxide aqueous solution to the phosphorus-affinity adsorbent is 0.1-0.2 L / g, the desorption temperature is 25-35°C, and the desorption time is 2-6 h; after the desorption is completed, the desorption filtrate is extracted. The desorption filtrate is a phosphorus-rich solution from which heavy metal impurities have been removed. The phosphorus adsorption, desorption and purification unit in the method can be completely completed in a leaching device. The steps can adsorb phosphorus in the acid extract onto the zinc-iron double hydroxide phosphorus adsorbent without adsorbing impurities such as heavy metals in the acid extract, thereby further purifying the phosphorus product.

[0012] 2) Preparation of hydroxyapatite product. Calcium hydroxide is added to the desorption filtrate, and the P:Ca molar ratio is maintained at 1:2-1:4 for reaction. After sufficient reaction, the filter residue and the filtrate are separated by filtration. The filter residue is washed and dried to obtain the hydroxyapatite product. The filtration separation is performed by vacuum filtration.

[0013] The beneficial effects of the present invention are mainly manifested in:

[0014] 1) Taking sewage sludge ash as the starting point, the resource utilization of sewage sludge ash is realized, solving the problem of secondary pollution caused by sewage sludge ash to urban environmental sanitation;

[0015] 2) The prepared zinc-iron double hydroxide phosphorus adsorbent - Zn / Fe-LDHs modified sludge ash, which forms a special metal plate structure, is conducive to phosphate ion exchange, and contains a large number of hydroxyl radicals on the surface, which can provide multi-channel adsorption sites for phosphate. It has a high adsorption capacity for phosphate and has strong stability and recyclability. The phosphorus adsorption capacity can reach 540 mg-P kg -1 , can be reused to treat phosphorus. After 10 cycles of adsorption / regeneration experiments, the adsorption capacity can still reach 88% of the original;

[0016] 3) The zinc-iron double hydroxide-based phosphorus-loving adsorbent can eliminate the interference of other elements in sludge ash to obtain high-quality hydroxyapatite products. It can also be used as a phosphorus-loving adsorbent to adsorb phosphate in actual agricultural runoff water, river water and lake water, solve the problem of eutrophication hazards in water bodies, and achieve the purpose of treating waste with waste;

[0017] 4) The method of phosphorus adsorption, phosphorus desorption and hydroxyapatite precipitation has a simple process flow and is easy to operate. It can recover at least 70% of the phosphate in the sludge ash to produce high-value and high-purity hydroxyapatite products. It has a wide range of uses, good market potential, and significant economic and environmental benefits. This method can achieve the recycling of wet chemical leaching agents, reducing the use of leaching agents and the generation of excess waste liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0019] Figure 2 Schematic diagram of the modified sludge ash structure. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited thereto.

[0021] Example 1

[0022] refer to Figure 1 The iron-rich sludge ash is first ball-milled, the speed of the ball mill is 1100r / min, the co-milling time is 10min, the particle size of the sludge ash ball-milled is 50-80 microns, and the sludge ash after ball milling is subjected to primary chemical wet treatment. The specific steps of the primary chemical wet treatment are: the sludge ash after ball milling is mixed with 0.5mol / L dilute hydrochloric acid / nitric acid, the solid-liquid ratio of sludge ash to dilute hydrochloric acid / nitric acid is 1:10g / mL, and it is fully mixed and shaken for 4h, and then filtered and separated by a solid-liquid separator to obtain insoluble solid residue and acid extract. The insoluble solid residue is dried in an 80℃ blast drying oven for 24h, and then a secondary chemical wet treatment is carried out. The specific operation steps are: the dried insoluble solid residue and 6mol / L concentrated hydrochloric acid are placed in a magnetic stirrer and fully mixed and stirred for 2h at 60℃ and a solid-liquid ratio of 1:10g / mL, and the upper layer liquid changes from transparent to yellow, and then ZnCl is added. 2 (Zn:Fe molar ratio is 2:1) and evenly mixed, 5 mol / LNaOH was slowly added to the above solid-liquid mixture to adjust the solution pH value to be stable at 11, so that the solid-liquid ratio was between 1:10, heated to 80 °C using a magnetic stirrer, and vigorously stirred at 300 rpm for 4 h. After the reaction was complete, centrifuged to obtain Zn / Fe-LDHs modified sludge ash, and the modified sludge ash was rinsed with deionized water to neutrality. The obtained solid was freeze-dried, ground, and sieved (<200 μm) to obtain a phosphorus-philic adsorbent, namely Zn / Fe-LDHs modified sludge ash, with a structure such as Figure 2 As shown in the figure, a large number of densely packed multi-sided laminated plate structures are attached to the surface of the modified sludge ash, showing representative LDH nanosheets ([Zn 2+(1-x) Fe 3+ x (OH) 2 ] x+ [Cl n- ] x / n ∙mH2O). The Zn / Fe-LDHs nanosheets make the surface of the modified ceramsite rougher and more pores appear. The porosity and overlapping structure are significantly increased, indicating that the heterogeneity is improved, so that the modified sludge ash has more abundant ion diffusion channels. The kinetic phosphorus adsorption capacity of the Zn / Fe-LDHs modified sludge ash can reach 540 mg-P·kg -1 The theoretical maximum phosphorus adsorption capacity is 14430 mg-P·kg -1 .

[0023] The acid extract is introduced from bottom to top into the leaching device filled with the prepared phosphorus-affinity adsorbent, and fully mixed to adsorb phosphorus. The liquid-solid ratio of the acid extract to the adsorbent is 0.01L / g, the adsorption temperature is 25°C, and the adsorption time is 6h. After the adsorption is completed, the adsorption filtrate is extracted, and the adsorption filtrate reflux can be used as an acid leaching solution in the primary chemical wet treatment; an industrial-grade sodium hydroxide aqueous solution (0.5mol / L) is introduced into the phosphorus-affinity adsorbent after phosphorus adsorption, and fully mixed to desorb phosphorus. The liquid-solid ratio of the sodium hydroxide aqueous solution to the phosphorus-affinity adsorbent is 0.1L / g, the desorption temperature is 25°C, and the desorption time is 6h. After the desorption is completed, the desorption filtrate is extracted, and calcium hydroxide is added to the desorption filtrate to keep the P:Ca molar ratio at 1:2 for reaction. After sufficient reaction, the filter residue and the filtrate are separated by filtration. The filter residue is washed and dried to obtain a hydroxyapatite product (the main component is Ca 5 (PO 4 ) 3 OH and CaPO 3 OH·2H 2 The recovery rate of phosphorus in sludge ash reached 93%. After repeating the adsorption experiment for ten times, the recovery rate of phosphorus in sludge ash could still reach 78%. The purity of the hydroxyapatite product could still reach 93%.

[0024] Example 2

[0025] refer to Figure 1The iron-rich sludge ash is first ball-milled, the speed of the ball mill is 1000r / min, the co-milling time is 10min, the particle size of the sludge ash ball-milled is 50-80 microns, and the sludge ash after ball milling is subjected to primary chemical wet treatment. The specific steps of the primary chemical wet treatment are: the sludge ash after ball milling is mixed with 0.2mol / L dilute hydrochloric acid / nitric acid, the solid-liquid ratio of sludge ash to dilute hydrochloric acid / nitric acid is 1:20g / mL, and it is fully mixed and shaken for 2h, and then filtered and separated by a solid-liquid separator to obtain insoluble solid residue and acid extract. The insoluble solid residue is dried in a 65℃ blast drying oven for 24h, and then a secondary chemical wet treatment is carried out. The specific operation steps are: the dried insoluble solid residue and 5mol / L concentrated hydrochloric acid are placed in a magnetic stirrer and fully mixed and stirred for 2h at 60℃ and a solid-liquid ratio of 1:10g / mL. When the upper layer liquid changes from transparent to yellow, ZnCl is added. 2 (Zn: Fe molar ratio is 1:1) and evenly mixed, 2 mol / L NaOH was slowly added to the solid-liquid mixture to adjust the solution pH to 11, so that the solid-liquid ratio was between 1:5, heated to 60 ° C with a magnetic stirrer, and stirred vigorously at 300 rpm for 4 hours. After the reaction was complete, centrifuged to obtain Zn / Fe-LDHs modified sludge ash, and rinsed the modified sludge ash with deionized water until neutral, and the obtained solid was freeze-dried, ground, and sieved (<200 μm) to obtain a phosphorus-philic adsorbent, namely Zn / Fe-LDHs modified sludge ash. The kinetic phosphorus adsorption capacity of the Zn / Fe-LDHs modified sludge ash can reach 490 mg-P·kg-1. The theoretical maximum phosphorus adsorption capacity is 11370 mg-P·kg-1.

[0026] The acid extract is introduced from bottom to top into a leaching device filled with the prepared phosphorus-philic adsorbent and mixed thoroughly and evenly to adsorb phosphorus. The liquid-to-solid ratio of the acid extract to the adsorbent is 0.025 L / g, the adsorption temperature is 25°C, and the adsorption time is 2h. After the adsorption is completed, the adsorption filtrate is extracted, and the adsorption filtrate reflux can be used as an acid leaching solution for primary chemical wet treatment; an industrial-grade sodium hydroxide aqueous solution (0.1 mol / L) is introduced into the phosphorus-philic adsorbent after the phosphorus adsorption, and the phosphorus is fully mixed to desorb the phosphorus. The liquid-solid ratio of the sodium hydroxide aqueous solution to the phosphorus-philic adsorbent is 0.1L / g, the desorption temperature is 25°C, and the desorption time is 2h. After the desorption is completed, the desorption filtrate is extracted, and calcium hydroxide is added to the desorption filtrate to keep the P:Ca molar ratio at 1:2 for reaction. After sufficient reaction, the filter residue and the filtrate are obtained by filtration and separation. The filter residue is washed and dried to obtain a hydroxyapatite product (with a purity of 90%), and the recovery rate of phosphorus in the sludge ash reaches 85%. The adsorption experiment is repeated ten times, and the recovery rate of phosphorus in the sludge ash can still reach 73%. The purity of the hydroxyapatite product obtained repeatedly can still reach 88%.

[0027] Example 3

[0028] refer to Figure 1 The iron-rich sludge ash is first ball-milled, the speed of the ball mill is 1200r / min, the co-milling time is 10min, the particle size of the sludge ash ball-milled is 50-80 microns, and the sludge ash after ball milling is subjected to primary chemical wet treatment. The specific steps of the primary chemical wet treatment are: the sludge ash after ball milling is mixed with 1mol / L dilute hydrochloric acid / nitric acid, the solid-liquid ratio of sludge ash to dilute hydrochloric acid / nitric acid is 1:5g / mL, and the mixture is fully mixed and shaken for 5h, and then filtered and separated by a solid-liquid separator to obtain insoluble solid residue and acid extract. The insoluble solid residue is dried in an 80℃ forced air drying oven for 24h, and then subjected to secondary chemical wet treatment. The specific operation steps are: the dried insoluble solid residue and 8mol / L concentrated hydrochloric acid are placed in a magnetic stirrer. The mixture was stirred for 2 h at 60 °C and a solid-liquid ratio of 1:10 g / mL. When the upper liquid turned from transparent to yellow, ZnCl2 (Zn:Fe molar ratio of 3:1) was added and mixed evenly. 5 mol / L NaOH was slowly added to the solid-liquid mixture to adjust the pH value of the solution to 11, so that the solid-liquid ratio was between 2:5. The mixture was heated to 80 °C with a magnetic stirrer and stirred vigorously at 500 rpm for 6 h. After the reaction was complete, the mixture was centrifuged to obtain Zn / Fe-LDHs modified sludge ash, and the modified sludge ash was rinsed with deionized water until neutral. The solid was freeze-dried, ground, and sieved (<200 μm) to obtain a phosphorus-philic adsorbent. The kinetic phosphorus adsorption capacity of the Zn / Fe-LDHs modified sludge ash can reach 510 mg-P·kg-1. The theoretical maximum phosphorus adsorption capacity is 12430 mg-P·kg-1.

[0029] The acid extract was introduced from bottom to top into a leaching device filled with the prepared phosphorus-philic adsorbent and mixed thoroughly and evenly to adsorb phosphorus. The liquid-to-solid ratio of the acid extract to the adsorbent was 0.05 L / g, the adsorption temperature was 35°C, and the adsorption time was 6 h. After the adsorption is completed, the adsorption filtrate is discharged, and the adsorption filtrate reflux can be used as an acid leaching solution for primary chemical wet treatment; an industrial-grade sodium hydroxide aqueous solution (1 mol / L) is introduced into the phosphorus-philic adsorbent after the phosphorus adsorption, and the mixture is fully mixed to desorb the phosphorus, the liquid-solid ratio of the sodium hydroxide aqueous solution to the phosphorus-philic adsorbent is 0.2 L / g, the desorption temperature is 35° C., and the desorption time is 6 hours. After the desorption is completed, the desorption filtrate is discharged, and calcium hydroxide is added to the desorption filtrate to keep the P:Ca molar ratio at 1:4 for reaction. After sufficient reaction, filter residue and filtrate are obtained by separation through filtration. After the filter residue is washed and dried, a hydroxyapatite product is obtained, and the purity reaches 91%. The recovery rate of phosphorus in the sludge ash reaches 94%. The adsorption experiment is repeated ten times, and the recovery rate of phosphorus in the sludge ash can still reach 90%, and the purity of the hydroxyapatite product obtained repeatedly can still reach 88%.

Claims

1. A method for preparing a zinc-iron double hydroxide phosphorus-loving adsorbent using sludge ash, characterized in that The steps include: 1) Ball milling the sludge ash, then thoroughly mixing and oscillating the ball-milled sludge ash with dilute hydrochloric acid / nitric acid, filtering to obtain insoluble solid residue and acid extract, and drying the insoluble solid residue; 2) The insoluble solid residue dried sample from step 1) and concentrated hydrochloric acid are placed in a magnetic stirrer and thoroughly mixed and stirred. After the upper liquid turns from transparent to yellow, ZnCl2 is added and uniformly mixed. NaOH solution is dropwise added to the solid-liquid mixture to adjust the pH value of the solution to be stable at 11-12, so that the solid-liquid ratio is between 1:5 and 2:

5. The mixture is heated and stirred with a magnetic stirrer. After the reaction is complete, the mixture is centrifuged, washed to neutrality, freeze-dried, ground and sieved to obtain a zinc-iron double hydroxide-supported phosphorus-philic adsorbent. Step 2) The concentration of concentrated hydrochloric acid is 5-8 mol / L, the solid-liquid ratio of the dried insoluble solid residue sample to concentrated hydrochloric acid is 1 g:10 mL, and the mixture is thoroughly mixed and stirred at 60°C for 2 hours. After adding ZnCl2, the molar ratio of Zn to Fe is 1:1-3:1; In step 2), the concentration of the NaOH solution is 2-5 mol / L. After the NaOH solution is added dropwise, the magnetic stirrer is heated to 60-80° C. and vigorously stirred at 200-500 rpm for 4-6 hours.

2. The method according to claim 1, wherein The specific operation process of the ball milling treatment in step 1) is as follows: the rotation speed of the ball mill is 1000-1200 r / min, the co-milling time is 10 minutes, and the particle size of the obtained sludge ash is 50-80 microns.

3. The method according to claim 1, wherein The concentration of dilute hydrochloric acid / nitric acid is 0.2-1 mol / L, the solid-liquid ratio of sludge ash in dilute hydrochloric acid / nitric acid is 1g:5-20mL, the oscillation time is 2-5 hours, and the insoluble solid residue is dried in a forced air drying oven at 65-80°C.

4. An application of a zinc-iron double hydroxide phosphorus adsorbent prepared by the method according to any one of claims 1 to 3, characterized in that The steps include: 1) The acid extract is introduced from bottom to top into a leaching device filled with zinc-iron double hydroxide phosphorus adsorbent, and after being thoroughly mixed, phosphorus adsorption is carried out. After the adsorption is completed, the adsorption filtrate is discharged. The adsorbent after phosphorus adsorption is introduced into a sodium hydroxide aqueous solution, and after being thoroughly mixed, phosphorus is desorbed. After the desorption is completed, the desorption filtrate is discharged. 2) adding calcium hydroxide to the desorption filtrate, maintaining a molar ratio of phosphorus to calcium of 1:2-1:4 for reaction, and filtering and separating to obtain a filter residue and a filtrate after sufficient reaction, and washing and drying the filter residue to obtain a hydroxyapatite product.

5. The use according to claim 4, characterized in that In step 1), the liquid-to-solid ratio of the neutralized acid extract to the adsorbent is 0.025-0.05 L / g, the adsorption temperature is 25-35° C., and the adsorption time is 2-6 h.

6. The use according to claim 4, characterized in that The concentration of the sodium hydroxide aqueous solution in step 1) is 0.1-1 mol / L, the liquid-solid ratio of the sodium hydroxide aqueous solution to the adsorbent is 0.1-0.2 L / g, the desorption temperature is 25-35° C., and the desorption time is 2-6 h.

Images