Method for recycling phosphorus element in sludge gasification slag

Abstract

The invention relates to the technical field of sludge resource utilization, in particular to a method for recycling phosphorus in sludge gasification slag. According to the method disclosed by the invention, the sludge gasification slag is subjected to acid leaching treatment, and the sludge gasification slag is subjected to acid leaching by adopting a dilute sulfuric acid solution in the process, so that the dissolution of other impurities can be effectively avoided while the phosphorus element is extracted, the extraction efficiency is high, and the purity of the obtained product struvite can be effectively ensured. The method disclosed by the invention is simple in process and low in equipment requirement, can realize extraction of phosphorus in the sludge gasification slag at lower cost, and has very high economic benefits; meanwhile, the obtained struvite is high in purity and can be used as a raw material for producing a phosphate fertilizer or a slow-release fertilizer, solid waste resource utilization and environment-friendly economic benefits are improved, and the struvite has positive significance on sludge reduction, harmlessness, stabilization and recycling.

Description

Technical Field

[0001] The invention relates to the technical field of sludge resource utilization, and in particular to a method for recycling phosphorus in sludge gasification residue. Background Art

[0002] Sludge is the main byproduct of sewage treatment plants. It contains a large amount of organic and inorganic substances, as well as a large number of pathogens, heavy metals and other harmful substances. Sludge treatment and disposal is an important environmental issue worldwide. Sludge contains a large amount of phosphorus, which is an essential nutrient in agricultural production. It is a non-renewable resource with decreasing reserves. The shortage of phosphorus resources has gradually attracted people's attention. As global phosphate rock resources are gradually depleted, it is of great significance to recover phosphorus from waste.

[0003] Sludge gasification residue is the solid waste remaining after the sewage treatment plant treats the sludge through high-temperature gasification. Gasification treatment technology is an efficient sludge treatment method that can reduce the volume and weight of waste and recover energy at the same time. Gasification residue contains rich inorganic minerals, among which phosphorus exists in the form of inorganic phosphate. Existing phosphorus recovery technologies include chemical precipitation, biological treatment and adsorption, but these methods have the disadvantages of high cost, complex treatment process, long treatment time and limited adsorption capacity, making them difficult to promote and apply on a large scale. In order to overcome these shortcomings, the present invention proposes a process for extracting phosphorus from sludge gasification residue and preparing struvite by acid leaching. Summary of the invention

[0004] The purpose of the present invention is to provide a method for recovering phosphorus in sludge gasification residue to solve the problems of high cost, complex treatment process, long treatment time, limited adsorption capacity and difficulty in large-scale promotion and application in existing methods.

[0005] To achieve the above object, the present invention adopts the following technical solution: a method for recovering phosphorus in sludge gasification slag, comprising the following steps:

[0006] S1, taking the pre-treated sludge gasification residue and subjecting it to acid leaching treatment with a dilute sulfuric acid solution;

[0007] S2, taking the supernatant after acid leaching in S1, adding a magnesium source and an ammonium source thereto;

[0008] S3. Take the mixed solution of S2, adjust the pH to alkaline, separate the solid and the liquid, and then you can get struvite crystals.

[0009] Furthermore, in the above S1, the sludge gasification slag is pretreated before acid leaching, and the pretreatment method includes grinding, magnetic separation and screening. The particle size of the sludge gasification slag obtained after the pretreatment is 300-800 meshes.

[0010] Furthermore, in the S1, the concentration of the dilute sulfuric acid solution is 0.1-0.3 mol / L, and the solid-liquid ratio of the sludge gasification residue to the dilute sulfuric acid solution is 1:5-10.

[0011] Furthermore, in the S1, the stirring intensity during the acid leaching treatment is 60-120 r / min, the temperature is room temperature, and the time is 6-12 h; after the acid leaching treatment is completed, the supernatant is allowed to stand for separation for 1-3 h.

[0012] Further, in the S2, PO4 in the supernatant 3- Mg 2+ With NH4 + ; The magnesium source is magnesium chloride solution, and the ammonium source is ammonium chloride solution.

[0013] Furthermore, in S3, the pH of the mixed solution is adjusted to 10.

[0014] Furthermore, the pH is adjusted by using a NaOH solution and a sulfuric acid solution, firstly adjusting the pH to slightly greater than 10 using a NaOH solution, and then counter-adjusting the pH to 10 using a sulfuric acid solution.

[0015] Furthermore, in the S3, after the pH is adjusted to alkaline, the reaction is continued at room temperature for 12 to 24 hours, and the stirring intensity during the reaction is 60 to 120 r / min.

[0016] Furthermore, after the reaction is completed, the struvite crystals can be obtained by filtering, washing and drying.

[0017] Furthermore, the drying temperature is 55-65° C., and the drying time is 12-24 hours.

[0018] Beneficial effects of the present invention:

[0019] 1. The method of the present invention is simple and easy to extract phosphorus, the crystal form is controllable, the equipment requirements are low, the investment cost is low, the energy consumption is small, the reaction efficiency is high, and it can effectively save resources, protect the environment, and improve economic benefits;

[0020] 2. The process conditions of the method of the present invention are controllable, and phosphate can be selectively dissolved to avoid dissolving other impurities, thereby improving the extraction purity;

[0021] 3. The method of the present invention realizes the treatment of gasification slag solid waste, and the struvite obtained can be used as a raw material for phosphate fertilizer production or a slow-release fertilizer, which has significant economic and environmental benefits and also has broad application prospects, and has positive significance for sludge reduction, harmlessness, stabilization and resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the XRD analysis diagram of the sludge and gasification slag involved in Example 1 of the present invention;

[0023] Figure 2 1 is an EDS and XEM analysis diagram of the gasified slag involved in Example 1 of the present invention;

[0024] Figure 3 It is a comparison chart of XRD of the products obtained in Example 1 of the present invention and Comparative Examples 1-3. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0026] Example 1

[0027] Take the sludge and sludge gasification residue from a sewage treatment plant and analyze them. The results are shown in the attached figure. Figure 1-2 shown.

[0028] Attached Figure 1 XRD analysis diagram of sludge and gasification slag.

[0029] It can be seen that the phosphorus in the gasification slag mainly exists in the form of phosphates, etc. Therefore, the acid leaching method can efficiently dissolve the phosphates in the gasification slag and improve the extraction efficiency of phosphorus. The operation process is simple and easy to control and industrially apply.

[0030] Attached Figure 2 EDS and SEM analysis images of gasified slag.

[0031] It can be seen that the sludge gasification slag has no obvious mineral phase embedding characteristics due to the high temperature and strong impregnation in the sludge gasification process. The bright spots are mainly SiO2 mineral phases. However, the EDS image provides element distribution information, which can help identify the distribution pattern of the main elements. Through EDS energy spectrum analysis, it can be seen that the phosphorus content is relatively high and there is a certain enrichment state.

[0032] The sludge gasification slag is ground and magnetically separated, and then passed through a 500-mesh sieve to obtain the pretreated sludge gasification sludge.

[0033] Take 100 kg of the above-mentioned sludge gasification slag and place it in a reactor, add 800 L of dilute sulfuric acid solution thereto at a liquid-to-solid ratio of 8:1 (the liquid-to-solid ratio in the technical solution of the present invention is the ratio of liquid volume to solid mass), the concentration of the dilute sulfuric acid solution is 0.2 mol / L, stir the reaction at a stirring intensity of 100 r / min for 10 hours, then let it stand for 2 hours, extract the upper liquid and filter to obtain 782 L of supernatant, and the phosphate ion concentration in the supernatant is tested to be 0.103 mol / L.

[0034] Take 1 mol / L MgCl2 solution and 1 mol / L NH4Cl solution, and add 80.5 L of each to the supernatant; then use NaOH solution and H2SO4 solution to adjust the pH to 10, wherein the concentration of NaOH solution is 1 mol / L, and the concentration of H2SO4 solution is 0.5 mol / L.

[0035] The reaction was continued at 100 r / min for 20 h, the reaction solution was filtered, the filter cake was washed, and dried at 60° C. for 16 h to obtain struvite crystals.

[0036] Example 2

[0037] Take the sludge gasification slag from Example 1.

[0038] In this embodiment, the pretreatment method is different from that in Embodiment 1. Only the sludge gasification slag is subjected to grinding treatment. The rest is the same as in Embodiment 1.

[0039] Example 3

[0040] Take the sludge gasification slag from Example 1.

[0041] In this embodiment, the pretreatment method is different from that in Embodiment 1. Only grinding and magnetic separation are performed on the sludge gasification slag. The rest is the same as in Embodiment 1.

[0042] The acid leaching phosphorus recovery rates of Examples 1-3 are compared as shown in the following table:

[0043]

[0044] By comparison, it can be found that the phosphorus recovery rates in the acid leaching solutions obtained by different pretreatments of the gasified slag are very different. For the gasified slag that has been crushed and ground but not magnetically separated and then directly subjected to acid leaching for phosphorus extraction, the phosphorus recovery rate of the acid leaching solution is only 58.07%, while it can reach 87.78% by the method of the present invention.

[0045] Comparative Example 1

[0046] In this comparative example, 0.5 mol / L sulfuric acid solution was used for acid leaching, and the rest was the same as in Example 1.

[0047] Comparative Example 2

[0048] In this comparative example, 0.4 mol / L hydrochloric acid solution was used for acid leaching, and the rest was the same as in Example 1.

[0049] Comparative Example 3

[0050] In this comparative example, 0.4 mol / L nitric acid solution was used for acid leaching, and the rest was the same as in Example 1.

[0051] The XRD diffraction patterns of Example 1 and Comparative Examples 1-3 are as follows: Figure 3 shown.

[0052] It can be seen that in Example 1, by analyzing the XRD of the product prepared by acid leaching with a H2SO4 solution with a concentration of 0.2 mol / L, it can be seen that there are obvious diffraction peaks at 2θ=15.81°, 20.85°, 21.45°, 30.60° and 33.28°, which coincide with the PDF card of struvite (MgNH4PO4·6H2O), and it can be verified that the struvite product is successfully synthesized and prepared.

[0053] The precipitated products recovered in Comparative Examples 1-3 showed no obvious diffraction peaks, indicating that the precipitated products were mainly amorphous substances. This indicates that the acid leaching concentration is high and the types of acid solutions are different, and there are too many impurity ions in the solution that can form precipitates, generating a large number of crystal nuclei, thereby forming a large number of fine crystals, making the precipitate amorphous.

[0054] Therefore, the type and concentration of acid during acid leaching have a critical impact on the product. The gasified slag is pretreated by grinding and magnetic separation and its tailings are screened, and then acid-leached under low concentration H2SO4 solution conditions. The synthesized struvite has high purity, high whiteness, and good crystallinity, thus realizing the extraction and resource utilization of phosphorus in the gasified slag.

[0055] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A method for recovering phosphorus from sludge gasification residue, It is characterized in that The following steps are involved: S1, taking the pre-treated sludge gasification residue and subjecting it to acid leaching treatment with a dilute sulfuric acid solution; S2, taking the supernatant after acid leaching in S1, adding a magnesium source and an ammonium source thereto; S3. Take the mixed solution of S2, adjust the pH to alkaline, separate the solid and the liquid, and then you can get struvite crystals.

2. The method for recovering phosphorus from sludge gasification slag according to claim 1, Features: In the above-mentioned S1, the pretreatment method includes grinding, magnetic separation and screening, and the particle size of the sludge gasification slag obtained after the pretreatment is 300-800 meshes.

3. The method for recovering phosphorus from sludge gasification slag according to claim 1, Features: In the S1, the concentration of the dilute sulfuric acid solution is 0.1-0.3 mol / L, and the solid-liquid ratio of the sludge gasification residue to the dilute sulfuric acid solution is 1:5-10.

4. The method for recovering phosphorus from sludge gasification slag according to claim 1, Features: In the S1, the stirring intensity during the acid leaching treatment is 60-120 r / min, the temperature is room temperature, and the time is 6-12 h; after the acid leaching treatment is completed, the supernatant is allowed to stand for separation for 1-3 h.

5. The method for recovering phosphorus from sludge gasification slag according to claim 1, Features: In the S2, PO in the supernatant is 4 3- Mg 2+ With NH 4 + ; The magnesium source is magnesium chloride solution, and the ammonium source is ammonium chloride solution.

6. The method for recovering phosphorus from sludge gasification slag according to claim 1, Features: In the step S3, the pH of the mixed solution is adjusted to 10.

7. The method for recovering phosphorus from sludge gasification slag according to claim 6, Features: The pH is adjusted by using a NaOH solution and a sulfuric acid solution. The pH is first adjusted to be slightly greater than 10 by using a NaOH solution, and then the pH is counter-adjusted to 10 by using a sulfuric acid solution.

8. The method for recovering phosphorus from sludge gasification slag according to claim 1, Features: In the S3, after the pH is adjusted to alkaline, the reaction is continued at room temperature for 12 to 24 hours, and the stirring intensity during the reaction is 60 to 120 r / min.

9. The method for recovering phosphorus from sludge gasification slag according to claim 8, Features: After the reaction is completed, the struvite crystals can be obtained by filtering, washing and drying.

10. The method for recovering phosphorus from sludge gasification slag according to claim 9, Features: The drying temperature is 55-65° C., and the drying time is 12-24 hours.

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