A method for preparing struvite from porous silicon waste solution

Abstract

The present application belongs to the technical field of wastewater treatment, and relates to a method for preparing struvite from porous silicon waste liquid, comprising the following steps: step 1: preparing a reaction product one; step 2: preparing ant nest-like porous silicon; step 3: adjusting the PH value of the first filtrate to 9.5-11, stirring and standing to obtain a precipitate; step 4: filtering and collecting the precipitate obtained in step 3, rinsing the wet cake with deionized water, suction-filtering to recover white solids, and drying to obtain struvite. The present application adopts a coprecipitation method, successfully separates out ant nest-like porous silicon by adjusting the ratio of Mg and P and the PH value, can be used as a commercial negative electrode material, and obtains struvite with high crystallinity, which has commercial value; and the synthesis is simple, the process flow is short, the environment is friendly, and mass production can be promoted; the waste liquid of the ant nest-like porous silicon of the present application does not contain Ca 2+ , Zn 2+ , etc., does not interfere with the crystallization of struvite, and the obtained struvite is more stable.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and in particular relates to a method for preparing struvite from porous silica waste liquid. Background Technology

[0002] With the continuous development of science and technology, the recycling and utilization of renewable resources has become a common concern for the whole society. Industrial waste recycling is costly, and improper handling can lead to environmental pollution. Reusing resources can not only alleviate resource pressure but also protect the environment. Therefore, providing a green development and resource-saving path plays a vital role in sustainable economic development. Establishing an effective recycling and utilization system for renewable resources is an effective way to protect the environment, improve resource utilization, develop a circular economy, and build a resource-saving and environmentally friendly society.

[0003] Currently, the method for removing phosphorus from wastewater using physicochemical methods such as lime, aluminum, and iron salts is orthophosphate precipitation. However, this produces difficult-to-manage chemical precipitates that are often disposed of in landfills. Therefore, struvite (MgNH4PO4·6H2O) precipitation is an economical method for recovering phosphorus from phosphorus-containing wastewater, and struvite is easy to handle and does not have sludge treatment problems. Furthermore, struvite has commercial value as a fertilizer. Heraldy et al. studied the preparation process of struvite using seawater desalination wastewater (brine) as a magnesium source; Crutchik et al. prepared well-crystallized struvite using untreated wastewater or secondary treated wastewater (generated from a frozen fish processing plant located on the coast). How to prepare well-crystallized struvite from wastewater while simultaneously preparing porous silica remains to be investigated. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides a method for preparing struvite from porous silica waste liquid. The specific technical solution is as follows:

[0005] A method for preparing struvite from porous silica waste liquid includes the following steps:

[0006] Step 1: Grind magnesium silicide evenly and place it in a reaction vessel. Then place the reaction vessel in an inert atmosphere tube furnace, heat it to 750-780℃ and start to introduce ammonia gas to keep it at that temperature for 5-7 hours. After the holding time is over, stop introducing ammonia gas and remove the vessel as it cools down in the furnace to obtain reaction product one. Keep the inert gas flowing through the furnace during the reaction process.

[0007] Step 2: Grind the reaction product obtained in Step 1 into powder, add it to phosphoric acid solution and wash it with acid for 3-5 hours, filter and separate the first filtrate for recovery, then filter until neutral, and freeze dry under vacuum to obtain ant nest-like porous silica.

[0008] Step 3: Add ammonia to the first filtrate recovered in Step 2 to adjust the pH value to 9.5-11, then stir for more than 2 hours and let it stand for 9-11 hours to obtain the precipitate;

[0009] Step 4: Collect the precipitate obtained in Step 3 by filtration, wash the wet cake with deionized water, recover the white solid by vacuum filtration, and dry to obtain struvite.

[0010] Furthermore, in step 1, the reaction vessel is an alumina crucible, and the inert gas is argon.

[0011] Furthermore, in step 1, the heating rate of the inert atmosphere tube furnace is 5°C / min.

[0012] The inert atmosphere tube furnace heats up at a rate of 5℃ / min to prevent damage to the furnace resistance wire due to excessive heating and to precisely control the temperature of the inert atmosphere tube furnace.

[0013] Furthermore, in step 2, the molar ratio of P to Mg is greater than or equal to 2:1, preferably 2:1.

[0014] In step 2, if the amount of phosphoric acid added is insufficient, other impurities will be generated in the product, and silicon cannot be successfully separated.

[0015] Furthermore, in step 3, the pH value is preferably 10.

[0016] In step 3, a pH value that is too high or too low is not conducive to the formation of struvite and may also lead to the formation of byproducts.

[0017] Furthermore, in step 4, the precipitate is collected by filtration through a 0.22 μm membrane filter.

[0018] Furthermore, in step 4, a white solid is obtained by centrifugation at 2000-3000 rpm for 10-20 minutes.

[0019] Furthermore, in step 4, the white solid is dried in a vacuum oven at 50-60°C for 20-28 hours to obtain struvite.

[0020] When drying white solids, while improving drying efficiency, the drying and heat preservation temperatures should not be too high, otherwise it will lead to the decomposition of the struvite.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention employs a co-precipitation method, successfully separating ant-nest porous silicon by controlling the ratio of Mg and P and the pH value. This silicon can be used as a commercial anode material, and yields highly crystalline struvite, which has commercial value. The synthesis of this invention is simple, the process is short, and it is environmentally friendly, making it suitable for mass production. The waste liquid from the ant-nest porous silicon produced by this invention does not contain Ca. 2+ Zn 2+ This process does not interfere with the crystallization of struvite, and the resulting struvite is more stable. This is because calcium can interfere with struvite crystallization by forming amorphous calcium phosphate, while zinc is more easily adsorbed onto struvite (Zn(NH3)x). 2+ Its stability is relatively low, and the supersaturation ratio (Sa) of zinc-containing precipitates is greater than that of struvite. Attached Figure Description

[0023] Figure 1 The image shows the XRD pattern of the ant-nest porous silicon obtained in Example 1 of this invention.

[0024] Figure 2 The image shown is a scanning electron microscope (SEM) image of the porous silicon described in Example 1 of this invention.

[0025] Figure 3 This is the XRD pattern of the struvite obtained in Example 1 of this invention;

[0026] Figure 4 XRD pattern of the ant-nest porous silicon obtained in Example 2 of this invention;

[0027] Figure 5 This is a scanning electron microscope image of the porous silicon described in Embodiment 2 of the present invention;

[0028] Figure 6 This is the XRD pattern of the struvite obtained in Example 2 of this invention;

[0029] Figure 7 This is the XRD pattern of the struvite obtained in Example 3 of the present invention;

[0030] Figure 8 XRD pattern of the ant-nest porous silicon obtained in Comparative Example 1 of this invention;

[0031] Figure 9 This is the XRD pattern of the struvite obtained in Comparative Example 1 of this invention;

[0032] Figure 10 This is the XRD pattern of the struvite obtained in Comparative Example 2 of this invention;

[0033] Figure 11 This is the XRD pattern of the guanostone obtained in Comparative Example 3 of this invention. Detailed Implementation

[0034] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0035] Example 1:

[0036] A method for preparing struvite from porous silica waste liquid includes the following steps:

[0037] Step 1: Grind 3g of magnesium silicide evenly (particle size of 3-5 micrometers) and place it in a corundum crucible. Then place the reaction vessel in an inert atmosphere tube furnace and heat it to 750-780℃ at a heating rate of 5℃ / min. Then start to introduce ammonia gas and keep it at this temperature for 6 hours for nitriding. During nitriding, NH3:Ar = 3:1, NH3: 90ml / min, Ar: 30ml / min. After the holding time is over, stop the introduction of ammonia gas and take it out with the furnace to cool. The reaction product 1 is obtained. During the reaction, the inert gas argon gas is introduced.

[0038] Step 2: Take 4 ml of phosphoric acid with a concentration of 85% or higher, mix it with deionized water to make 100 ml of acid solution, take 1.42 g of the reaction product obtained in Step 1, grind it into powder, dissolve it in the acid solution (Mg:P = 1:2), and stir magnetically at room temperature for 4 hours; grinding is to prevent the formation of clumps of magnesium nitride after nitriding, so that it can react more easily and completely with the phosphoric acid solution; take the stirred solution and filter it, recover the first filtrate, then add deionized water and filter until neutral to remove any residual impurities, and then transfer the obtained sample to a freeze dryer and freeze dry (cold trap temperature -40℃) for 24 hours to obtain sample A1;

[0039] Step 3: Add 25% ammonia water to the first filtrate recovered in Step 2 to adjust the pH value to 10, then stir for more than 2 hours and let stand for 10 hours to promote struvite crystallization.

[0040] Step 4: Take the solution after standing and filter it. Rinse the wet cake with deionized water to remove any residual impurities. Filter and recover the white solid. Dry it in a vacuum oven at 55°C for 24 hours to obtain sample B1, which will be used for subsequent characterization.

[0041] Sample A1 was analyzed using a Rigaku D / max-2500 X-ray diffractometer (Japan), and the results are as follows: Figure 1 As shown, this indicates that silicon was successfully isolated. The sample was observed using a NovaNano SEM 230 scanning electron microscope from FEI (USA), and the results are as follows. Figure 2 As shown, sample A1 has porous silicon with an ant nest-like structure.

[0042] like Figure 3As shown, all diffraction peaks of sample B1 correspond to Mg(NH4)PO4·6H2O, and no other impurity peaks were found, indicating that the material has high purity, and the strong peak intensities indicate that the material has good crystallinity.

[0043] Example 2:

[0044] A method for preparing struvite from porous silica waste liquid includes the following steps:

[0045] Step 1: Same as Example 1, and will not be repeated here;

[0046] Step 2: Take 8 ml of phosphoric acid with a concentration of 85% or higher, mix it with deionized water to make 100 ml of acid solution, grind 1.42 g of the reaction product obtained in Step 1 into powder, dissolve it in the acid solution (Mg:P = 1:4), and stir magnetically at room temperature for 4 h; take the stirred solution and filter it, recover the first filtrate, then add deionized water and filter until neutral to remove any residual impurities, then transfer the obtained sample to a freeze dryer and freeze dry (cold trap temperature -40℃) for 24 hours to obtain sample A2;

[0047] Step 3: Same as Example 1, and will not be repeated here;

[0048] Step 4: After the solution has been allowed to stand, filter it and rinse the wet cake with deionized water to remove any residual impurities. Filter the white solid back to obtain sample B2 by drying it in a vacuum oven at 55°C for 24 hours. This sample will be used for subsequent characterization.

[0049] Sample A2 was analyzed using a Rigaku D / max-2500 X-ray diffractometer (Japan), and the results are as follows: Figure 4 As shown, pure silicon phase was successfully isolated. The sample was observed using a NovaNano SEM 230 scanning electron microscope (FEI, USA), and the results are as follows. Figure 5 As shown, sample A2 was found to have porous silicon with an ant nest-like structure.

[0050] like Figure 6 As shown, all diffraction peaks of sample B2 correspond to Mg(NH4)PO4·6H2O, and no other impurity peaks were found, indicating that the guanostone has high purity, and the strong peak intensities indicate that the material has good crystallinity.

[0051] Example 3:

[0052] A method for preparing struvite from porous silica waste liquid includes the following steps:

[0053] Step 1: Same as Example 1, and will not be repeated here;

[0054] Step 2: Same as in Example 1, and will not be repeated here, to obtain sample A3;

[0055] Step 3: Add 25% ammonia water to the first filtrate recovered in Step 2 to adjust the pH value to 11, then stir for more than 2 hours and let it stand for 10 hours to promote the crystallization of struvite to obtain a precipitate;

[0056] Step 4: Filter the settled solution, rinse the wet cake with deionized water to remove any residual impurities, and filter to recover the white solid, such as... Figure 11 As shown, sample B3 was obtained by drying in a vacuum oven at 55°C for 24 hours and used for subsequent characterization.

[0057] Silicon was successfully separated from sample A3 obtained by analysis using a Rigaku D / max-2500 X-ray diffractometer (Japan). Further examination of the sample using a FEI NovaNano SEM 230 (USA) revealed that sample A3 contained porous silicon resembling an anthill.

[0058] like Figure 7 As shown, all diffraction peaks of sample B3 correspond to Mg(NH4)PO4·6H2O, with no other impurity peaks observed, indicating high material purity. The strong peak intensities also indicate good crystallinity. However, comparison revealed that the XRD peak intensity at pH=11 is weaker than at pH=10, suggesting that crystallinity at pH=11 is worse than at pH=10. Therefore, a pH value should not be too high, as it is detrimental to crystallization and increases costs.

[0059] Comparative Example 1:

[0060] A method for preparing struvite from porous silica waste liquid includes the following steps:

[0061] Step 1: Same as Example 1, and will not be repeated here;

[0062] Step 2: Take 2 ml of phosphoric acid with a concentration of 85% or higher, mix it with deionized water to make 100 ml of acid solution, grind 1.42 g of the reaction product obtained in Step 1 into powder, dissolve it in the acid solution (Mg:P = 1:1), and stir magnetically at room temperature for 4 h; take the stirred solution and filter it, recover the first filtrate, then add deionized water and filter until neutral to remove any residual impurities, then transfer the obtained sample to a freeze dryer and freeze dry (cold trap temperature -40℃) for 24 hours to obtain sample A4;

[0063] Step 3: Add 25% ammonia water to the first filtrate recovered in Step 2 to adjust the pH value to 10, then stir for more than 2 hours and let it stand for 10 hours to promote the crystallization of struvite to obtain a precipitate;

[0064] Step 4: After the solution has been allowed to stand, filter it and rinse the wet cake with deionized water to remove any residual impurities. Filter the white solid back to obtain sample B4 by drying it in a vacuum oven at 55°C for 24 hours. This sample will be used for subsequent characterization.

[0065] Sample A4 was analyzed using a Rigaku D / max-2500 X-ray diffractometer (Japan), and the results are as follows: Figure 8 As shown, silicon could not be successfully separated and contained MgHPO4·3H2O. The P:Mg ratio was too low, which would produce MgHPO4·3H2O impurities that were difficult to separate from silicon. MgHPO4·3H2O is soluble in acid, so excess phosphoric acid should be added during the experiment.

[0066] like Figure 9 As shown, all diffraction peaks of sample B4 correspond to Mg(NH4)PO4·6H2O. No other impurity peaks were found, indicating high material purity, while the strong peak intensities indicate good crystallinity.

[0067] Comparative Example 2:

[0068] A method for preparing struvite from porous silica waste liquid includes the following steps:

[0069] Step 1: Same as Example 1, and will not be repeated here;

[0070] Step 2: Same as Example 1, and will not be repeated here; obtain sample A5;

[0071] Step 3: Add 25% ammonia water to the first filtrate recovered in Step 2 to adjust the pH value to 7, then stir for more than 2 hours and let stand for 10 hours to promote the crystallization of struvite to obtain a precipitate;

[0072] Step 4: Take the solution after standing and filter it. Rinse the wet cake with deionized water to remove any residual impurities. Filter and recover the white solid. Dry it in a vacuum oven at 55°C for 24 hours to obtain sample B5, which will be used for subsequent characterization.

[0073] like Figure 10 As shown, sample B5 exhibited diffraction peaks of Mg(NH4)PO4·6H2O and MgHPO4·3H2O, indicating that pure-phase struvite could not be obtained.

[0074] Comparative Example 3:

[0075] A method for preparing struvite from porous silica waste liquid includes the following steps:

[0076] Step 1: Same as Example 1, and will not be repeated here;

[0077] Step 2: Same as Example 1, and will not be repeated here; obtain sample A6;

[0078] Step 3: Add 25% ammonia water to the first filtrate recovered in Step 2 to adjust the pH value to 9, then stir for more than 2 hours and let stand for 10 hours to promote the crystallization of struvite to obtain a precipitate;

[0079] Step 4: After the solution has been allowed to stand, filter it and rinse the wet cake with deionized water to remove any residual impurities. Filter the white solid back to obtain sample B6 by drying it in a vacuum oven at 55°C for 24 hours. This sample will be used for subsequent characterization.

[0080] like Figure 11 As shown, sample B6 exhibited diffraction peaks of Mg(NH4)PO4·6H2O and MgHPO4·3H2O, indicating that pure-phase struvite could not be obtained.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing struvite from porous silica waste liquid, characterized in that, Includes the following steps: Step 1: Grind magnesium silicide evenly and place it in a reaction vessel. Then place the reaction vessel in an inert atmosphere tube furnace, heat it to 750-780℃ and start to introduce ammonia gas to keep it at that temperature for 5-7 hours. After the holding time is over, stop introducing ammonia gas and remove the vessel as it cools down in the furnace to obtain reaction product one. Keep the inert gas flowing through the furnace during the reaction process. Step 2: Grind the reaction product obtained in Step 1 into powder, add it to phosphoric acid solution and wash it with acid for 3-5 hours. Filter and separate the first filtrate for recovery. Then filter until neutral, freeze dry under vacuum to obtain ant nest-like porous silicon; the molar ratio of P:Mg is greater than or equal to 2:

1. Step 3: Add ammonia to the first filtrate recovered in Step 2 to adjust the pH value to 9.5-11, then stir for more than 2 hours and let it stand for 9-11 hours to obtain the precipitate; Step 4: Collect the precipitate obtained in Step 3 by filtration, wash the wet cake with deionized water, recover the white solid by vacuum filtration, and dry to obtain struvite.

2. The method for preparing struvite from porous silica waste liquid according to claim 1, characterized in that, In step 1, the reaction vessel is an alumina crucible, and the inert gas is argon.

3. The method for preparing struvite from porous silica waste liquid according to claim 1, characterized in that, In step 1, the heating rate of the inert atmosphere tube furnace is 5°C / min.

4. The method for preparing struvite from porous silica waste liquid according to claim 1, characterized in that, In step 3, the pH value is 10.

5. The method for preparing struvite from porous silica waste liquid according to claim 1, characterized in that, In step 4, the precipitate is collected by filtration through a 0.22 μm membrane filter.

6. The method for preparing struvite from porous silica waste liquid according to claim 1, characterized in that, In step 4, a white solid is obtained by centrifugation at 2000-3000 rpm for 10-20 minutes.

7. The method for preparing struvite from porous silica waste liquid according to claim 1, characterized in that, In step 4, the white solid is dried in a vacuum oven at 50-60°C for 20-28 hours to obtain struvite.

8. The method for preparing struvite from porous silica waste liquid according to claim 4, characterized in that, In step 2, the molar ratio of P:Mg is 2:1.

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