A method and system for selective recovery of hydroxyapatite from sewage sludge incineration ash

Abstract

A method and system for selectively recovering hydroxyapatite from sludge incineration ash, comprising the following steps: by setting the concentration of hydrochloric acid solution, the phosphorus in the sludge incineration ash is extracted into the sludge leaching solution, and the mixture is separated into the sludge leaching solution and the acid leaching residue by a solid-liquid separation process; the sludge leaching solution is used for subsequent phosphorus extraction solution, and the acid leaching residue is used as a carrier to prepare a Zr adsorbent by coprecipitation with a Zr reagent; the concentration of phosphorus elements in the desorption solution is used as a basis for adding a calcium source, and hydroxyapatite products are generated in the desorption solution. It has the advantages of simple operation, high phosphorus recovery efficiency and low cost. The prepared adsorbent utilizes solid waste (acid leaching residue), and the prepared adsorbent has good stability, can selectively adsorb phosphorus elements directly from strong acid sludge leaching solution, and has good selective adsorption effect on phosphorus in the sludge leaching solution.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sewage resource recovery, and more particularly relates to a method for preparing a zirconium adsorbent and a method for selectively recovering hydroxyapatite from incineration ash of sludge. BACKGROUND

[0002] Phosphorus, as one of the essential nutrients for plant growth, is of great significance to the development of modern agriculture. However, phosphorus mainly flows from phosphorus-rich phosphate rock to the natural environment in a one-way manner, hindering the circulation of phosphorus in the biosphere. The huge demand for phosphorus fertilizer in modern agriculture is continuously depleting the reserves of phosphate rock, which is expected to be exhausted within 50-100 years, which will lead to a serious phosphorus crisis for humans, and in turn, severely affect the development of modern agriculture. Therefore, it is necessary to find a phosphorus source that can replace phosphate rock.

[0003] At present, a large part of the phosphorus discharged by human activities will enter the sewage treatment plant through the urban drainage network, and will eventually be enriched in sludge. Therefore, sludge is rich in phosphorus elements. Therefore, the recovery of phosphorus elements from sludge not only resources the sludge, but also promotes the circulation of phosphorus in the biosphere, which is of great significance to alleviate the phosphorus crisis that humans will face.

[0004] Sludge, as a hazardous pollutant, poses a huge potential risk to the environment due to its high content of organic pollutants, heavy metals, pathogens and water, and therefore needs to be harmlessly treated and disposed of before being discharged into the environment. Sludge incineration, as a harmless treatment and disposal method for sludge, has been widely used for sludge treatment and disposal in European Union countries and Japan.

[0005] After sludge incineration, the volume of sludge is greatly reduced, and the phosphorus in the sludge is further enriched in incineration ash of sludge (ISSA), accounting for about 4.9-11.9% of the mass of incineration ash of sludge. However, the heavy metal elements in the sludge are also enriched, and the concentration thereof will exceed the relevant national standards for the use of phosphorus fertilizer, resulting in that the incineration ash of sludge cannot be directly applied to the environment soil as phosphorus fertilizer. Therefore, reducing the concentration of heavy metal elements in the incineration ash of sludge is an indispensable process for utilizing phosphorus in the incineration ash of sludge.

[0006] At present, wet chemical technology is generally considered as a promising technology for recovering phosphorus elements from incineration ash of sludge. Wet chemical technology needs to extract phosphorus elements in incineration ash of sludge into leaching solution by acidic reagent, and then produce phosphorus products through crystallization or precipitation process. However, the heavy metal elements in the incineration ash of sludge will also be extracted into the sludge leaching solution during the acid leaching process, increasing the difficulty of recovering high-purity phosphorus products from the sludge leaching solution, which requires pretreatment technology to reduce the concentration of impurity ions in the sludge leaching solution, and then produce high-purity phosphorus products.

[0007] Pretreatment technology based on cation exchange resins adsorbs metal cations in sludge leachate through ion exchange, and then separates the cation exchange resin from the sludge leachate through a solid-liquid separation process, thereby reducing the concentration of heavy metals in the sludge leachate and consequently reducing the impurity content in the subsequently generated phosphorus products. However, this technology faces challenges such as secondary pollution from the subsequent treatment and disposal of cation exchange resins and relatively high costs, hindering its large-scale application in phosphorus recovery from sludge incineration ash. Therefore, a more efficient technology for recovering phosphorus from sludge leachate needs to be developed.

[0008] Chinese patent application CN116143094A discloses a method for cyclically extracting phosphorus from sludge ash. This invention uses a method that adjusts the pH of the phosphorus-containing sludge leachate to acidity, heats the leachate, adds iron salts, and causes phosphorus in the leachate to precipitate as ferric phosphate hydrate, which is then recovered. However, this invention suffers from low phosphorus recovery efficiency, and even after phosphorus recovery, a certain amount of phosphorus remains in the sludge leachate. Multiple continuous recovery processes are needed to improve the efficiency of phosphorus recovery from the sludge leachate, making the operation complex. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a method for selectively recovering hydroxyapatite from sludge incineration ash, which has the advantages of simple operation, high phosphorus recovery efficiency, and low cost.

[0010] The present invention adopts the following technical solution. The first aspect of the present invention provides a method for selectively recovering hydroxyapatite from sludge incineration ash, comprising the following steps:

[0011] Phosphorus in sludge incineration ash is extracted into sludge leachate by using a hydrochloric acid solution of a set concentration, and the mixture is separated into sludge leachate and acid leaching residue through a solid-liquid separation process.

[0012] The sludge leachate is used as the subsequent phosphorus extraction solution, and the acid leaching residue is used as a carrier to prepare Zr adsorbent through co-precipitation with Zr reagent;

[0013] A calcium source is added based on the phosphorus concentration in the desorption solution, resulting in the production of hydroxyapatite in the desorption solution.

[0014] A second aspect of the present invention provides a method for selectively recovering hydroxyapatite from sludge incineration ash, comprising the following steps:

[0015] Step 1: Add the sludge incineration ash to an HCl solution for mixing, and then perform solid-liquid separation of the mixture into sludge leachate and acid leaching residue.

[0016] Step 2: Mix the acid leaching residue obtained in Step 1 with zirconium oxychloride solution, adjust the pH to the set value, let stand, and then separate the solid and liquid components of the mixture to obtain the solid substance, thus obtaining the Zr adsorbent.

[0017] Step 3: Add the Zr adsorbent prepared in step 2 to the sludge leachate obtained in step 1 and mix thoroughly. Then, perform solid-liquid separation on the mixture to obtain the adsorbent. The adsorbent will selectively adsorb phosphorus elements in the sludge leachate.

[0018] Step 4: Add the phosphorus-adsorbent obtained in Step 3 to NaOH solution. The phosphorus on the adsorbent will be desorbed into the solution. After the phosphorus desorption is completed, the mixture is subjected to solid-liquid separation to obtain the adsorbent.

[0019] Step 5: Add calcium source based on the phosphorus concentration of the desorption solution to generate hydroxyapatite product in the desorption solution.

[0020] Preferably, step 1 includes:

[0021] Step 1.1: The dewatered sludge from the wastewater treatment plant is dried in an oven and then incinerated in a muffle furnace at 850°C to obtain sludge incineration ash.

[0022] Step 1.2: Add the sludge incineration ash to a 0.2 mol / L HCl solution at a liquid-to-solid ratio of 50 mL / g and mix.

[0023] Step 1.3: After phosphorus is extracted from the sludge incineration ash, the mixture is subjected to solid-liquid separation to obtain sludge leachate and acid leaching residue.

[0024] Preferably, step 2 includes:

[0025] Step 2.1: Mix 1-5g of acid leaching residue with 100mL of 0.1-0.5mol / L zirconium oxychloride solution and shake thoroughly in a shaking incubator for 12h;

[0026] Step 2.2: Adjust the pH of the mixture to approximately 7-12 and continue to shake thoroughly in a shaking incubator for 12 hours;

[0027] Step 2.3: After the mixture is allowed to stand and age for 12 hours, the mixture is separated into solid and liquid components to obtain solid substances, which are then washed with deionized water.

[0028] Step 2.4: Place the solid material in an oven to dry, and obtain the Zr adsorbent.

[0029] Preferably, in step 3, 1.5g of the prepared Zr adsorbent is added to 50mL of sludge leachate and placed in a shaking incubator for thorough shaking and mixing for 4h.

[0030] Preferably, in step 4, the adsorbent that adsorbs phosphorus is added to a 0.5-4 mol / L NaOH solution and thoroughly shaken and mixed in a shaking incubator for 4 hours, so that the phosphorus on the adsorbent will be desorbed into the solution.

[0031] Preferably, before performing step 5, the selective adsorption and desorption processes of phosphorus in steps 3 and 4 are repeated 5 times consecutively.

[0032] Preferably, during the continuous repetition of steps 3 and 4, the regenerated adsorbent obtained in step 4 is used in step 3 and added to the sludge leachate obtained in step 1.

[0033] The Zr adsorbent that selectively adsorbs phosphorus in step 3 is added again to the 1 mol / L NaOH solution in step 4. The adsorbent will desorb phosphorus in the 1 mol / L NaOH solution and be regenerated for recycling.

[0034] Preferably, step 5 includes:

[0035] After repeatedly performing steps 3 and 4, the pH of the desorption solution remains strongly alkaline. Without adjusting the pH of the desorption solution, adding a calcium source at a calcium-to-phosphorus molar ratio of 2.0:1 can produce a high-purity hydroxyapatite product in the desorption solution.

[0036] A third aspect of the present invention provides a system for selectively recovering hydroxyapatite from sludge incineration ash, comprising the method for selectively recovering hydroxyapatite from sludge incineration ash, and including:

[0037] The separation module is used to add sludge incineration ash to an HCl solution for mixing, and then perform solid-liquid separation of the mixture into sludge leachate and acid leaching residue.

[0038] The pH adjustment module mixes the acid leaching residue obtained from the separation module with the zirconium oxychloride solution, adjusts the pH to the set value, and after standing, separates the solid and liquid components of the mixture to obtain solid substances, thus obtaining the Zr adsorbent.

[0039] The adsorption module adds the Zr adsorbent prepared by the pH adjustment module to the sludge leachate obtained by the separation module, performs solid-liquid separation on the mixture and obtains the adsorbent, which selectively adsorbs phosphorus from the sludge leachate.

[0040] The desorption module adds the phosphorus-adsorbent obtained from the adsorption module to a NaOH solution. The phosphorus on the adsorbent will be desorbed into the solution. After the phosphorus desorption is completed, the mixture is subjected to solid-liquid separation to obtain the adsorbent.

[0041] The recovery module adds a calcium source based on the phosphorus concentration in the desorption solution, resulting in the production of hydroxyapatite in the desorption solution.

[0042] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0043] This invention proposes a method for selectively recovering hydroxyapatite from sludge incineration ash. This method has the advantages of simple operation, high phosphorus recovery efficiency and low cost. Moreover, the recovered hydroxyapatite can not only be used as a slow-release phosphate fertilizer to promote plant growth, but also as a widely used functional material. Therefore, this method has great economic advantages and market prospects.

[0044] Compared to other methods for recovering phosphorus products from sludge incineration ash, this method utilizes solid waste (acid leaching residue) to prepare an adsorbent. Furthermore, the prepared adsorbent can selectively adsorb phosphorus directly from strongly acidic sludge leachate, exhibiting excellent selective adsorption of phosphorus in the sludge leachate. This invention provides a simple phosphorus product recovery method, and the adsorbent exhibits good stability, which is beneficial for the market application of this method. Attached Figure Description

[0045] Figure 1 This is a flowchart of the method for selectively recovering hydroxyapatite products from sludge incineration ash in this invention;

[0046] Figure 2 The surface morphology of sludge incineration ash before and after phosphorus extraction from sludge incineration ash in this invention.

[0047] Figure 3 This refers to the amount of phosphorus selectively adsorbed from the sludge leachate by the adsorbent in this invention.

[0048] Figure 4 This invention involves multiple phosphorus adsorption and desorption cycles of the adsorbent from sludge leachate.

[0049] Figure 5 This is a phase analysis of the adsorbent used in this invention to selectively recover phosphorus products from sludge incineration ash. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0051] like Figure 1 As shown, Embodiment 1 of the present invention provides a method for selectively recovering hydroxyapatite from sludge incineration ash, comprising the following steps:

[0052] Step 1: Add the sludge incineration ash to an HCl solution for mixing, and then perform solid-liquid separation of the mixture into sludge leachate and acid leaching residue.

[0053] In a preferred but non-limiting embodiment of the present invention, step 1 specifically includes:

[0054] Step 1.1: The dewatered sludge from the wastewater treatment plant is dried in an oven and then incinerated in a muffle furnace at 850°C to obtain sludge incineration ash.

[0055] Step 1.2: Add the sludge incineration ash to a 0.2 mol / L HCl solution at a liquid-to-solid ratio of 50 mL / g and mix. Preferably, place the mixture in a shaking incubator and shake for 12 hours to fully extract phosphorus from the sludge incineration ash.

[0056] Step 1.3: After extraction, the sludge incineration ash mixture undergoes solid-liquid separation to obtain sludge leachate and acid leaching residue. The sludge leachate is used for subsequent phosphorus recovery, while the acid leaching residue contains a rich porous structure, such as... Figure 2 As shown, after cleaning and drying, it can be used as a carrier material for the subsequent preparation of adsorbents.

[0057] After phosphorus is extracted from sludge incineration ash using wet chemical processes, the acid leaching residue, as a major byproduct, requires further treatment. After acid leaching, the heavy metal content in the sludge incineration ash is significantly reduced, and the porosity of the acid leaching residue is significantly increased, indicating that the acid leaching residue can be used as a carrier for preparing Zr-modified adsorbents. Significantly different from existing technologies, this invention uses zirconium-modified acid leaching residue, a solid waste, to prepare a Zr-modified adsorbent with high selectivity for phosphorus.

[0058] Zr-modified adsorbents have attracted much attention for phosphorus recovery from wastewater due to their high selectivity for phosphorus, effectively adsorbing low concentrations of phosphorus in wastewater without any purification pretreatment even in the presence of heterogeneous ions. Furthermore, Zr-modified adsorbents also exhibit good phosphorus adsorption performance and stability in acidic wastewater, making them suitable for phosphorus recovery from acidic sludge leachate.

[0059] As one of the beneficial technical effects of this invention, it provides a zirconium adsorbent prepared by co-precipitation of porous acid leaching residue and zirconium reagent, used to selectively recover phosphorus from strongly acidic sludge leachate and produce a high-purity hydroxyapatite product. This method utilizes the acid leaching residue after acid leaching of sludge incineration ash as a carrier to load zirconium into the zirconium adsorbent. The prepared adsorbent can directly and selectively recover phosphorus from strongly acidic sludge leachate. Then, phosphorus is desorbed in an alkaline solution. Finally, a calcium source is added without adjusting the pH of the desorption solution to produce a high-purity hydroxyapatite product, thereby achieving the selective recovery of hydroxyapatite from sludge incineration ash.

[0060] It is worth noting that the specific equipment or values ​​involved in step 1 are merely preferred options and not limitations on the technical solution. For example, to obtain sludge incineration ash from dewatered sludge in a wastewater treatment plant, those skilled in the art can use equipment other than an oven or muffle furnace to dry and incinerate it at a set temperature. Any means of obtaining sludge incineration ash from dewatered sludge in a wastewater treatment plant falls within the scope of this invention.

[0061] Similarly, the proportion of sludge incineration ash added to the HCl solution for mixing is preferred rather than a limitation on the technical solution. Those skilled in the art can adjust or convert the proportion according to actual needs. In the subsequent steps of this invention, the equipment and figures involved are merely preferred examples to clearly illustrate the technical solution of this invention, and not the only implementation of the technical concept of this invention.

[0062] Step 2: Mix the acid leaching residue obtained in Step 1 with zirconium oxychloride solution, adjust the pH to the set value, let it stand, and then separate the solid and liquid components of the mixture to obtain the solid substance, thus obtaining the Zr adsorbent.

[0063] In a preferred but non-limiting embodiment of the present invention, step 2 specifically includes:

[0064] Step 2.1: Mix 1-5g of acid leaching residue with 100mL of 0.1-0.5mol / L zirconium oxychloride solution and shake thoroughly in a shaking incubator for 12h. The preferred method is to mix 3g of acid leaching residue with 0.2mol / L zirconium oxide solution.

[0065] Step 2.2: Adjust the pH of the mixture to around 7-12 and continue to shake it thoroughly in a shaking incubator for 12 hours. A more preferred pH is 10.0.

[0066] Step 2.3: After the mixture is left to stand and age for 12 hours, the mixture is separated into solid and liquid components to obtain solid substances, which are then washed with deionized water.

[0067] Step 2.4: Place the solid material in an oven to dry, and obtain the Zr adsorbent.

[0068] Step 3: Add the Zr adsorbent prepared in step 2 to the sludge leachate obtained in step 1, perform solid-liquid separation on the mixture and obtain the adsorbent. The adsorbent will selectively adsorb phosphorus from the sludge leachate.

[0069] In a preferred but non-limiting embodiment of the present invention, different doses of the prepared Zr adsorbent are weighed and added to the sludge leachate, which is then placed in a shaking incubator and thoroughly shaken for 6 hours. The mixture is then subjected to solid-liquid separation to obtain the adsorbent. The adsorbent selectively adsorbs phosphorus from the sludge leachate, with a maximum phosphorus adsorption capacity reaching 53.1 ± 0.8 mg / g. Figure 3 As shown.

[0070] In a further preferred but non-limiting embodiment, preferably 1.5 g of the prepared Zr adsorbent is added to 50 mL of sludge leachate and placed in a shaking incubator for 4 h to mix thoroughly. The mixture is then subjected to solid-liquid separation to obtain the adsorbent, which selectively adsorbs phosphorus from the sludge leachate.

[0071] Step 4: Add the phosphorus-adsorbent obtained in Step 3 to the NaOH solution. The phosphorus on the adsorbent will be desorbed into the solution. After the phosphorus desorption is completed, the mixture is subjected to solid-liquid separation to obtain the adsorbent.

[0072] In a preferred but non-limiting embodiment of the present invention, step 4 specifically includes: adding the phosphorus-adsorbent to a 0.5-4 mol / L NaOH solution, preferably 1 mol / L, and thoroughly shaking and mixing in a shaking incubator for 4 hours, so that the phosphorus on the adsorbent will be desorbed into the solution. After the phosphorus desorption is completed, the mixture is subjected to solid-liquid separation to obtain the adsorbent.

[0073] In a further preferred but non-limiting embodiment, steps 3 and 4 are repeated multiple times before step 5. Preferably, the selective adsorption and desorption processes of phosphorus in steps 3 and 4 are repeated five times consecutively. As one of the beneficial technical effects of this invention, the adsorption and desorption ratios of phosphorus by the adsorbent are consistently above 90%, indicating that after the phosphorus adsorption process, the adsorbent is regenerated in an alkaline solution, and the regenerated adsorbent has the same performance as the initial adsorbent. Figure 4 As shown.

[0074] In a further preferred but non-limiting embodiment, the regenerated adsorbent can selectively adsorb phosphorus again from the sludge leachate and re-desorb phosphorus in a 1 mol / L NaOH solution. Specifically, during the continuous repetition of steps 3 and 4, the regenerated adsorbent obtained in step 4 is used in step 3 by adding it to the sludge leachate obtained in step 1. The Zr adsorbent that selectively adsorbed phosphorus in step 3 is then added again to the 1 mol / L NaOH solution in step 4. The adsorbent will desorb phosphorus in the 1 mol / L NaOH solution and be regenerated, thus achieving recycling and phosphorus enrichment.

[0075] As one of the beneficial technical effects of the present invention, the selective adsorption and desorption process of phosphorus in sludge leachate is repeated in steps 3 and 4. After 5 phosphorus adsorption and desorption processes, phosphorus in sludge incineration ash is enriched in 1 mol / L NaOH solution. The desorbed solution has a high phosphorus content and extremely low impurity content, which is conducive to the production of high-purity phosphorus products.

[0076] Step 5: Add calcium source based on the phosphorus concentration of the desorption solution to generate hydroxyapatite product in the desorption solution.

[0077] In a preferred but non-limiting embodiment of the present invention, step 5 specifically includes: after multiple cumulative desorption cycles, preferably but not limited to, after 5 cumulative desorption cycles, the pH of the desorption solution is still greater than 13. Without adjusting the pH of the desorption solution, using the phosphorus concentration of the desorption solution as a baseline and adding a calcium source according to a calcium / phosphorus molar ratio of 2, a high-purity hydroxyapatite product can be produced in the desorption solution, such as... Figure 5 As shown.

[0078] Compared with existing technologies, the method provided by this invention mainly extracts phosphorus from sludge incineration ash into sludge leachate using a hydrochloric acid solution of a set concentration, such as, but not limited to, 0.2 mol / L hydrochloric acid solution. The mixture is then separated into sludge leachate and acid leaching residue through a solid-liquid separation process. The sludge leachate is used as the subsequent phosphorus extraction solution, and the acid leaching residue serves as a carrier to prepare a Zr adsorbent through co-precipitation with a Zr reagent.

[0079] The prepared Zr adsorbent can selectively adsorb phosphorus from complex sludge leachate, with a theoretical maximum adsorption capacity of 53.1 ± 0.8 mg / g. Adding an appropriate amount of Zr adsorbent can almost completely adsorb phosphorus from the sludge leachate. Then, the adsorbed phosphorus is desorbed into the solution in an alkaline solution (1 mol / L NaOH), thus regenerating the adsorbent. The regenerated adsorbent can selectively adsorb phosphorus again from the sludge leachate and re-desorb phosphorus in the 1 mol / L NaOH solution.

[0080] Furthermore, a 1 mol / L NaOH solution can repeatedly desorb phosphorus from the Zr adsorbent, achieving phosphorus enrichment. After the adsorbent undergoes five cumulative desorption cycles in the 1 mol / L NaOH solution, there is no need to adjust the pH of the desorption solution. Adding a calcium source at a calcium-to-phosphorus molar ratio of 2.0:1 can produce a high-purity hydroxyapatite product in the desorption solution.

[0081] Embodiment 2 of the present invention provides a system for selectively recovering hydroxyapatite from sludge incineration ash, which performs a method for selectively recovering hydroxyapatite from sludge incineration ash as described in Embodiment 1, and includes: a separation module, a pH adjustment module, an adsorption module, a desorption module and a recovery module.

[0082] The separation module is used to add sludge incineration ash to an HCl solution for mixing, and then perform solid-liquid separation of the mixture into sludge leachate and acid leaching residue.

[0083] The pH adjustment module mixes the acid leaching residue obtained from the separation module with the zirconium oxychloride solution, adjusts the pH to the set value, and after standing, separates the solid and liquid components of the mixture to obtain solid substances, thus obtaining the Zr adsorbent.

[0084] The adsorption module adds the Zr adsorbent prepared by the pH adjustment module to the sludge leachate obtained by the separation module, performs solid-liquid separation on the mixture and obtains the adsorbent, which selectively adsorbs phosphorus from the sludge leachate.

[0085] The desorption module adds the phosphorus-adsorbent obtained from the adsorption module to a NaOH solution. The phosphorus on the adsorbent will be desorbed into the solution. After the phosphorus desorption is completed, the mixture is subjected to solid-liquid separation to obtain the adsorbent.

[0086] The recovery module adds a calcium source based on the phosphorus concentration in the desorption solution, resulting in the production of hydroxyapatite in the desorption solution.

[0087] It is worth noting that, compared with the phosphorus recovery technology represented by existing technology document 1, the present invention, through the developed adsorbent, can selectively recover phosphorus from sludge leachate, and by adjusting the dosage of the adsorbent, can almost completely adsorb phosphorus from the sludge leachate. Furthermore, the operation is simple and the conditions are mild. In addition, the phosphorus product recovered by the present invention is hydroxyapatite, which is more suitable as a phosphate fertilizer to promote plant growth.

[0088] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for selectively recovering hydroxyapatite from sludge incineration ash, characterized in that, Includes the following steps: Phosphorus in sludge incineration ash is extracted into sludge leachate by using a hydrochloric acid solution of a set concentration, and the mixture is separated into sludge leachate and acid leaching residue through a solid-liquid separation process. The sludge leachate is used as the subsequent phosphorus extraction solution, and the acid leaching residue is used as a carrier to prepare Zr adsorbent through co-precipitation with Zr reagent; A calcium source is added based on the phosphorus concentration in the desorption solution, and hydroxyapatite is produced in the desorption solution. Specifically, the following steps are included: Step 1: Add the sludge incineration ash to an HCl solution for mixing, and then perform solid-liquid separation of the mixture into sludge leachate and acid leaching residue. Step 2: Mix the acid leaching residue obtained in Step 1 with zirconium oxychloride solution, adjust the pH to the set value, let stand, and then separate the solid and liquid components of the mixture to obtain the solid substance, thus obtaining the Zr adsorbent. Step 3: Add the Zr adsorbent prepared in step 2 to the sludge leachate obtained in step 1, perform solid-liquid separation on the mixture and obtain the adsorbent. The adsorbent will selectively adsorb phosphorus elements in the sludge leachate. Step 4: Add the phosphorus-adsorbent obtained in Step 3 to NaOH solution. The phosphorus on the adsorbent will be desorbed into the solution. After the phosphorus desorption is completed, the mixture is subjected to solid-liquid separation to obtain the adsorbent. Before performing step 5, steps 3 and 4 are repeated multiple times. After the phosphorus adsorption and desorption process, the phosphorus element in the sludge incineration ash is enriched in the solution. Step 5: Add calcium source based on the phosphorus concentration of the desorption solution to generate hydroxyapatite product in the desorption solution.

2. The method for selectively recovering hydroxyapatite from sludge incineration ash as described in claim 1, characterized in that: Step 1 includes: Step 1.1: The dewatered sludge from the wastewater treatment plant is dried in an oven and then incinerated in a muffle furnace at 850°C to obtain sludge incineration ash. Step 1.2: Add the sludge incineration ash to a 0.2 mol / L HCl solution at a liquid-to-solid ratio of 50 mL / g and mix. Step 1.3: After phosphorus is extracted from the sludge incineration ash, the mixture is subjected to solid-liquid separation to obtain sludge leachate and acid leaching residue.

3. The method for selectively recovering hydroxyapatite from sludge incineration ash as described in claim 1, characterized in that: Step 2 includes: Step 2.1: Mix 1-5g of acid leaching residue with 100mL of 0.1-0.5mol / L zirconium oxychloride solution and shake thoroughly in a shaking incubator for 12h; Step 2.2: Adjust the pH of the mixture to approximately 7-12 and continue to shake thoroughly in a shaking incubator for 12 hours; Step 2.3: After the mixture is allowed to stand and age for 12 hours, the mixture is separated into solid and liquid components to obtain solid substances, which are then washed with deionized water. Step 2.4: Place the solid material in an oven to dry, and obtain the Zr adsorbent.

4. The method for selectively recovering hydroxyapatite from sludge incineration ash as described in claim 1, characterized in that: In step 3, 1.5g of the prepared Zr adsorbent was added to 50mL of sludge leachate and placed in a shaking incubator to mix thoroughly for 4h.

5. The method for selectively recovering hydroxyapatite from sludge incineration ash as described in claim 1, characterized in that: In step 4, the phosphorus adsorbent is added to a 0.5-4 mol / L NaOH solution and thoroughly shaken and mixed in a shaking incubator for 4 hours. The phosphorus on the adsorbent will be desorbed into the solution.

6. The method for selectively recovering hydroxyapatite from sludge incineration ash as described in claim 1, characterized in that: Before performing step 5, repeat the selective adsorption and desorption processes of phosphorus in steps 3 and 4 five times consecutively.

7. The method for selectively recovering hydroxyapatite from sludge incineration ash as described in claim 1, characterized in that: During the continuous repetition of steps 3 and 4, the regenerated adsorbent obtained in step 4 is used in step 3 and added to the sludge leachate obtained in step 1. The Zr adsorbent that selectively adsorbs phosphorus in step 3 is added again to the 1 mol / L NaOH solution in step 4. The adsorbent will desorb phosphorus in the 1 mol / L NaOH solution and be regenerated for recycling.

8. The method for selectively recovering hydroxyapatite from sludge incineration ash as described in claim 1, characterized in that: Step 5 includes: After repeatedly performing steps 3 and 4, the pH of the desorption solution remains strongly alkaline. Without adjusting the pH of the desorption solution, adding a calcium source at a calcium-to-phosphorus molar ratio of 2.0:1 can produce a high-purity hydroxyapatite product in the desorption solution.

9. A system for selectively recovering hydroxyapatite from sludge incineration ash, comprising performing a method for selectively recovering hydroxyapatite from sludge incineration ash as described in any one of claims 1 to 8, characterized in that: The separation module is used to add sludge incineration ash to an HCl solution for mixing, and then perform solid-liquid separation of the mixture into sludge leachate and acid leaching residue. The pH adjustment module mixes the acid leaching residue obtained from the separation module with the zirconium oxychloride solution, adjusts the pH to the set value, and after standing, separates the solid and liquid components of the mixture to obtain solid substances, thus obtaining the Zr adsorbent. The adsorption module adds the Zr adsorbent prepared by the pH adjustment module to the sludge leachate obtained by the separation module, performs solid-liquid separation on the mixture and obtains the adsorbent, which selectively adsorbs phosphorus from the sludge leachate. The desorption module adds the phosphorus-adsorbent obtained from the adsorption module to a NaOH solution. The phosphorus on the adsorbent will be desorbed into the solution. After the phosphorus desorption is completed, the mixture is subjected to solid-liquid separation to obtain the adsorbent. The recovery module adds a calcium source based on the phosphorus concentration in the desorption solution, resulting in the production of hydroxyapatite in the desorption solution.

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