CN114516766B - Method for recycling phosphate in sewage by in-situ generation of calcium carbonate microsphere phosphate fertilizer and application of method - Google Patents

Abstract

The invention discloses a method for generating calcium carbonate microsphere phosphate fertilizer in situ to recover phosphate in sewage and an application thereof. The present invention adds calcium chloride and sodium carbonate solutions to low-phosphate sewage, and utilizes in-situ calcium carbonate microspheres to realize a new strategy for efficient and rapid phosphorus recovery. The in-situ calcium carbonate microsphere phosphate fertilizer technology provided by the present invention can capture phosphate ions very effectively and self-assemble into composite calcium carbonate microspheres; under optimized conditions, 98% of phosphate can be recovered within 30 minutes, and the remaining phosphate The amount is 0.2mg‑P/L, which saves time compared with existing methods. Importantly, a high-quality phosphate fertilizer of 20.8 wt.% was obtained with this novel calcium carbonate in situ recovery strategy, which was 4 times higher than that using the as-prepared calcite calcium carbonate nanoparticles. The fast-growing vegetable pakchoi was increased by 58.9% by using the prepared sodium carbonate in-situ phosphorus fertilizer. This provides a new way for the recycling of low-concentration phosphate fertilizers.

Description

A method for generating calcium carbonate microsphere phosphate fertilizer in situ to recycle phosphate in sewage and its application

technical field

The invention relates to a technology for the removal of low-concentration phosphate and preparation of high-efficiency phosphate fertilizer on the basis thereof, in particular to a method for in-situ generation of calcium carbonate microsphere phosphate fertilizer to recover phosphate in sewage and its application.

Background technique

With the continuous development of the national economy, environmental problems have become increasingly prominent. Rivers, lakes, seas and groundwater are all polluted in different areas and to varying degrees, endangering ecology and even human health. Phosphate is a typical pollutant that causes eutrophication when released into the aquatic environment. And phosphate rock, a non-renewable resource that supports the planet's large and growing population, is being depleted at an alarming rate. Therefore, the recovery of phosphate (P-recovery) from wastewater is becoming an increasingly urgent global environmental issue and plays a key role in the sustainable development of humans (Desmidt et al., 2014).

At present, for high-concentration phosphate wastewater, biological methods, chemical recovery methods and other means are generally used to effectively remove them. Biological phosphorus recovery can capture phosphate and generate phosphorus-containing sludge (Shuai et al., 2021), but the phosphate concentration in the sludge is too low to be used as a phosphorus fertilizer (Egle et al., 2016; Tarayre et al., 2016). Chemical recovery methods (Ye et al., 2017) capture phosphate ions from water quickly and simply by adding calcium (Bouzas et al., 2019), iron (Wilfert et al., 2015), or aluminum (Ma et al., 2018). However, iron and aluminum chemicals are not suitable for agricultural applications because they are too strongly bound to phosphate for uptake by plants (Abel, 2017). Since calcium reagents have been proven safe in soil remediation, calcium chemicals or materials are more suitable for use as phosphate fertilizers. However, the addition of calcium reagents is usually only suitable for treating high-concentration phosphate wastewater, such as the formation of struvite, and the phosphate concentration in municipal wastewater is only at the mg/L level (Desmidt et al., 2013; Kataki et al., 2016). A more efficient strategy for low-concentration phosphorus recovery with calcium reagents is still urgently needed.

Contents of the invention

The primary purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, and provide a method for in-situ generation of calcium carbonate microsphere phosphate fertilizer to recover phosphate in sewage.

Another object of the present invention is to provide the application of the above method for generating calcium carbonate microsphere phosphate fertilizer in situ to recover phosphate in sewage.

The object of the present invention is achieved through the following technical solutions:

A method for generating calcium carbonate microsphere phosphate fertilizer in situ to recycle phosphate in sewage, comprising the following steps:

(1) Add calcium chloride solution to the phosphorus-containing solution under stirring to obtain mixed solution A;

(2) Sodium carbonate is added to the mixed solution A in the stirring state, and the stirring is continued to react to obtain the mixed solution B;

(3) Perform solid-liquid separation on the mixed solution B, and dry the separated solid to obtain calcium carbonate microsphere phosphate fertilizer generated in situ.

The phosphorus-containing solution described in step (1) is preferably a phosphorus-containing solution with a concentration of 1 to 80 mg/L in terms of phosphorus; more preferably a solution with a concentration of ≤ 10 mg/L in terms of phosphorus; most preferably in terms of phosphorus Phosphorus-containing solution with a concentration of 1-10mg/L.

The phosphorus-containing solution described in step (1) is preferably sodium dihydrogen phosphate solution or sewage.

The sewage is preferably urban waste water.

The amount of calcium chloride described in the step (1) is preferably calculated by calcium in calcium chloride: the mol ratio of phosphorus in the solution is 2:1～10:1; more preferably by calcium in calcium chloride: The molar ratio of phosphorus in the solution is calculated as 4:1 to 10:1; the most preferred calculation is based on the molar ratio of calcium in calcium chloride:phosphorus in the solution as 6:1.

The add-on of sodium carbonate described in the step (2) is preferably calculated by the calcium in the calcium chloride in the step (1): the mol ratio of the carbonate radical in the sodium carbonate is 3:1～1:2; More preferably Calcium in calcium chloride in step (1): the mol ratio of the carbonate group in sodium carbonate is 2:1～1:2 Calculation; Most preferably be by the calcium in calcium chloride in step (1): sodium carbonate The molar ratio of the carbonate radicals in the formula is calculated as 1-1.

The reaction time described in step (2) is preferably 0-24h, excluding the endpoint value 0; more preferably 30min-24h; most preferably 30min-2h; most preferably 30min.

The solid-liquid separation method described in step (3) includes filtration, standing or centrifugation.

The filtration is preferably a 0.22 μm microfiltration membrane.

The standing still is to use gravity to settle, so that solid and liquid are separated into layers to obtain solid.

The drying conditions described in step (3) are preferably dried at 50-150°C until completely dry; more preferably dried at 80°C until completely dry.

The application of the above-mentioned method of generating calcium carbonate microsphere phosphate fertilizer in situ to recover phosphate in sewage to recover phosphate in sewage.

Said sewage is preferably urban wastewater; particularly preferably sewage with a phosphorus concentration of ≤ 10 mg/L; most preferably sewage with a phosphorus concentration of 1-10 mg/L.

An in-situ calcium carbonate microsphere phosphate fertilizer is obtained by the above method; it can be used as a phosphate fertilizer.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) The in-situ generation of calcium carbonate microsphere phosphate fertilizer provided by the present invention to recover low-concentration phosphate in sewage can effectively recover phosphorus in a phosphate aqueous solution with a concentration as low as 10 mg/L in a short period of time.

(2) The in-situ generation of calcium carbonate microsphere phosphate fertilizer technology can capture phosphate ions very effectively and self-assemble into composite calcium carbonate microspheres. Under optimized conditions, 98% of the phosphate can be recovered within 30 minutes, and the remaining phosphate is 0.2 mg-P/L, which greatly saves time compared with the existing method.

(3) The method can produce a high- _phosphorus fertilizer with a _P2O5 content exceeding 20wt.%, which is 4 times that of using superfine calcium carbonate solid powder.

(4) The high-phosphorus fertilizer has an obvious positive effect on the growth of pakchoi. The fast-growing vegetable pakchoi can increase production by 58.9% by using the method of in-situ generation of calcium carbonate microsphere phosphate fertilizer as phosphate fertilizer, which is beneficial to agricultural growth.

Description of drawings

Fig. 1 is the scanning electron micrograph figure of the product that embodiment 1 prepares; Wherein, a is that in-situ generation calcium carbonate microsphere phosphate fertilizer (calcite/vaterite microsphere), size is 10 μ m; b is in-situ generation calcium carbonate microsphere Phosphate fertilizer (calcite/vaterite microspheres), with a size of 500nm; c is calcium carbonate phosphate fertilizer (calcite) produced by traditional method, with a size of 2 μm; d is calcium carbonate phosphate fertilizer (calcite) produced with traditional method, with a size of 500nm.

Fig. 2 is the X-ray diffraction result diagram of the product prepared in Example 1.

Fig. 3 is the result graph of the Fourier transform infrared absorption spectrum of the product prepared in Example 1.

Fig. 4 is a diagram showing the phosphorus removal effect of different Ca/P molar ratios in the method of changing the in-situ generation of calcium carbonate microsphere phosphate fertilizer in Example 2.

Fig. 5 is a graph showing the phosphorus removal effect of different Ca ²⁺ /CO ₃ ^2- concentration molar ratios in the method of changing the in-situ generation of calcium carbonate microsphere phosphate fertilizer in Example 3.

Fig. 6 is a comparison result graph of the phosphorus removal effect of the two methods under different reaction times in Example 4.

Fig. 7 is a graph showing the effect of coexisting ions on the phosphorus removal process in Example 5.

Fig. 8 is a graph showing the effect of temperature on the phosphorus removal process in Example 6.

Fig. 9 is a graph showing the effect of the final pH of the sewage in Example 7 on the phosphorus removal efficiency.

Fig. 10 is the X-ray photoelectron spectrum analysis result figure of the calcium carbonate phosphate fertilizer that in situ generates calcium carbonate microsphere phosphate fertilizer and traditional method in embodiment 1; Wherein, a is that in situ generates calcium carbonate microsphere phosphate fertilizer, and b is in situ Calcium carbonate microsphere phosphate fertilizer is generated, c is the calcium carbonate phosphate fertilizer made by the traditional method, and d is the calcium carbonate phosphate fertilizer made by the traditional method.

Fig. 11 is a comparison result diagram of the plant height, root length, stem fresh weight and stem dry weight obtained after the in-situ generated calcium carbonate microspheres obtained in Example 1 were applied to the growth of Chinese cabbage in Example 11 and no fertilizer was added.

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example 1

1. In situ generation of calcium carbonate microsphere phosphate fertilizer

The method for preparing in-situ calcium carbonate microsphere phosphate fertilizer by enriching phosphorus from low-concentration simulated sewage (NaH ₂ PO ₄ solution, 10mg-P/L) comprises the following steps:

Prepare a sodium dihydrogen phosphate (NaH ₂ PO ₄ ) solution with a concentration of 38.73mg/L (total phosphorus in terms of P is 10mg/L) to simulate low-concentration phosphorus-containing water (general research focuses on phosphorus concentrations exceeding 10mg-P/ L phosphorus-containing water body, there are few relevant studies on sewage with low phosphorus concentration, so sewage with phosphorus concentration ≤ 10mg-P/L is defined as water body with low concentration of phosphorus). Under regular stirring, first add calcium chloride (CaCl ₂ , 1mol/L) solution until the concentration of CaCl ₂ in the system is 214.8mg/L, then add sodium carbonate (Na ₂ CO ₃ , 1mol/L) solution until the system The concentration of Na ₂ CO ₃ was 205.2 mg/L, and the stirring was stopped after continuing the reaction for 30 minutes. Use fast filter paper to filter the solution. After the filtration is complete, the filtered water sample shall be measured for phosphorus content according to GB11893-89. The solid obtained by filtration was dried in an oven at 80°C. The obtained powder is the calcium carbonate microsphere phosphate fertilizer generated in situ.

2. Calcium carbonate phosphate fertilizer produced by traditional sewage treatment process

As a comparison, we use the traditional calcite crystal form ultrafine calcium carbonate powder (commercially available nano-calcium carbonate, particle size ≤ 100nm) to enrich from low concentration simulated phosphorus-containing water (NaH ₂ PO ₄ solution, 10mg-P/L) Phosphorus, comprising the steps of:

Sodium dihydrogen phosphate (NaH ₂ PO ₄ ) solution with a concentration of 38.73 mg/L (total phosphorus calculated as P is 10 mg/L) was prepared to simulate low-concentration phosphorus-containing water. Add 200mg/L ultrafine calcium carbonate powder and stir for 30 minutes. Filter with fast filter paper, measure the phosphorus content of the filtered water sample according to GB11893-89, and dry the obtained solids to obtain calcium carbonate phosphate fertilizer produced by traditional sewage treatment process.

3. Test results

A and b in Fig. 1 are the scanning electron micrographs (SEM) result figure of generating calcium carbonate microsphere phosphate fertilizer in situ, and c and d are the scanning electron microscope picture of traditional method calcium carbonate phosphate fertilizer; Wherein, a is 2K magnification Measured, b is measured at 50K magnification, c is measured at 10K magnification, d is measured at 50K magnification. SEM shows that the in-situ generation of calcium carbonate microsphere phosphate fertilizer is composed of microspheres with a diameter of 2-10 microns. When enlarged into a single spherical shape, fine nanoparticles can be observed on the surface of the particles, with a particle size of about 50 nanometers, indicating that the in-situ generation Calcium carbonate microsphere phosphate fertilizer is agglomerated by fine vaterite CaCO ₃ nanoparticles, and phosphate ions may be coated between adjacent nanoparticles. Ultrafine calcium carbonate is composed of nanoparticles with small particle size (about 50nm and narrow distribution. Compared with the traditional calcium carbonate fixation composed of nanoparticles with small particle size and narrow distribution, in situ calcium carbonate microparticles The formation of larger microspheres is more conducive to the recovery of phosphate.

Fig. 2 is an X-ray diffraction (XRD) result graph of in-situ generated calcium carbonate microsphere phosphate fertilizer and traditional calcium carbonate phosphate fertilizer. XRD shows that the in situ generation of calcium carbonate microsphere phosphate fertilizer is composed of calcite (JCPDS card number 05-0586) and vaterite (JCPDS card number 33-0268), and the _ultrafine calcium carbonate powder used in traditional water treatment -0586) Mineral fragmentation, very low reactivity.

Fig. 3 is the Fourier transform infrared absorption spectrum (FTIR) result graph of in-situ generated calcium carbonate microsphere phosphate fertilizer and traditional calcium carbonate phosphate fertilizer. There are obvious phosphate absorption peaks in the FTIR spectra at 1048cm ^-1 and 576cm ^-1 of calcium carbonate microsphere phosphate fertilizer produced in situ. Phosphate ions exist in the in-situ generated calcium carbonate microsphere phosphate fertilizer in an amorphous form, and the vaterite crystalline calcium carbonate plays a vital role in the recovery of phosphate. The FTIR absorption peak intensity of traditional calcium carbonate phosphate fertilizer at 1048cm ^-1 and 576cm ^-1 is significantly weaker than that of in situ generated calcium carbonate microsphere phosphate fertilizer, which means that the phosphate content is significantly lower than that of in situ generated calcium carbonate microsphere phosphate fertilizer.

In the same period of time, the recovery rate of phosphorus recovered by the in-situ calcium carbonate microsphere phosphate fertilizer method reached 98%, and the total phosphorus content in the effluent was 0.2mg-P/L, which reached the national sewage discharge level A standard; while the traditional calcium carbonate super The fine powder is used as a phosphorus removal agent, the recovery rate of phosphorus is only 17%, and the total phosphorus content in the effluent is 8.3mg-P/L, which does not meet the national first-class A standard for sewage discharge.

Example 2

The phosphorus removal effect of in-situ generation of calcium carbonate microsphere phosphate fertilizer and traditional synthetic calcium carbonate method under different Ca/P molar ratios includes the following steps:

(1) Phosphorus removal with different Ca/P molar ratios under the method of in-situ generation of calcium carbonate microsphere phosphate fertilizer. In the state of stirring, add CaCl ₂ solution successively to the sodium dihydrogen phosphate (NaH ₂ PO ₄ ) solution (the total phosphorus calculated as P is 10 mg/L) with a volume of 1 L and a concentration of 38.73 mg/L until the system The concentration of CaCl ₂ is 71.6, 143.2, 179, 214.8, 286.4 and 358 mg/L. After reacting for 30 minutes, take a sample to measure the phosphorus content, and then add Na ₂ CO ₃ solution until the Na ₂ CO ₃ concentration in the system is 68.4, 136.8, 171, 205.2, 273.6 and 342mg/L, stop stirring after continuing to react for 30 minutes. Filter the water sample and measure the phosphorus content according to GB11893-89, molybdic acid spectrophotometric determination of total phosphorus.

(2) As a comparison, the phosphorus removal conditions of the traditional method of adding calcium carbonate micropowder at different Ca/P molar ratios are as follows. In a stirring state, add calcium carbonate micropowder 65 _, 129, 161, 194, 258, 323 mg/L, after 30 minutes of reaction, continue to react for 30 minutes. Filter the water sample and determine the phosphorus content according to GB11893-89.

Fig. 4 is a diagram of phosphorus removal effects of different Ca/P molar ratios in the in-situ generation of calcium carbonate microsphere phosphate fertilizer method in Example 2. The results showed that the addition of _CaCl2 could hardly remove any phosphate from wastewater even when the Ca/P molar ratio was increased from 2/1 to 10/1. Traditional calcium carbonate micropowder can remove about 12% of phosphate, because the reaction time is short, even if its dosage is increased, it will not lead to a significant increase in the removal rate of total phosphorus. However, in the process of forming CaCO ₃ microspheres to recover phosphorus in situ, when the Ca/P molar ratio is 2/1, the residual phosphate drops from 10mg-P/L to 4.87mg-P/L, when the Ca/P molar ratio It further decreased to 0.20 mg-P/L when the ratio was increased to 6/1. This concentration not only meets the wastewater discharge standard (0.5mg-P/L), but also meets the Chinese surface water (Ⅲ) standard (0.2mg-P/L).

Example 3

The phosphorus removal effect of different Ca ²⁺ /CO ₃ ^2- molar ratios in the in-situ generation of calcium carbonate microsphere phosphate fertilizer method includes the following steps:

With reference to the operating steps of Example 1, under stirring, to volume is 1L, concentration is 38.73mg/L sodium dihydrogen phosphate (NaH ₂ PO ) solution (total phosphorus in P is 10mg/L) to add CaCl ₂ solution until the concentration of CaCl ₂ in the system is 214.8 mg/L, take a sample to measure the phosphorus content, then add Na ₂ CO ₃ solution respectively until the concentration of Na ₂ CO ₃ in the system is 68.4, 102.6, 136.8, 307.8 and 410.4 mg/L, continue Stirring was stopped after 30 min of reaction. After the reaction, the water sample was filtered to determine the phosphorus content.

Fig. 5 is a graph showing the phosphorus removal effects of different Ca ²⁺ /CO ₃ ^2- molar ratios in the method of in-situ generation of calcium carbonate microsphere phosphate fertilizer in Example 3. The results show that insufficient carbonate leads to a significant decline in phosphorus recovery efficiency, and excessive carbonate content causes a slight decrease in phosphorus recovery rate. The optimal molar ratio of Ca ²⁺ /CO ₃ ^2- is 1/1, that is, the theoretical formation The molar ratio of CaCO ₃ , therefore, the equimolar reaction between calcium ions and carbonate ions to form CaCO ₃ , is important to improve the recovery process.

Example 4

Influence of Reaction Time on Phosphorus Removal Efficiency of In-Situ Generation of Calcium Carbonate Microsphere Phosphate Fertilizer

₍ 1) Add CaCl _{2 solution} (1mol /L) until the concentration of calcium chloride is 214.8mg/L, after reacting for 30min, add _Na2CO3 solution (1mol/L) until the concentration of sodium carbonate is 205.2mg/L, continue to react for 30min, _1h , 2h, 6h, 12h and 24h. At the above reaction time points, the water samples were filtered and the phosphorus content was measured to evaluate the effect of reaction time on phosphorus removal efficiency.

(2) As a control, add traditional calcite to a sodium dihydrogen phosphate (NaH ₂ PO ₄ ) solution with a volume of 1 L and a concentration of 38.73 mg/L (total phosphorus calculated as P is 10 mg/L) under stirring. Crystalline ultrafine calcium carbonate powder (commercially available nano-calcium carbonate, 100nm) to 200mg/L, continue to react for 30min, 1h, 2h, 6h, 12h and 24h. At the above reaction time points, the water samples were filtered to determine the phosphorus content.

Fig. 6 is the dephosphorization effect diagram under different reaction times in two kinds of calcium carbonate methods of embodiment 4. The results showed that the residual phosphate level of the traditional synthetic calcium carbonate method continued to decrease from 10mg-P/L to _2.92mg -P/L. Minutes later, the residual phosphate reached a minimum (0.2mg-P/L), after which the residual phosphate continued to increase slowly, reaching 0.54mg-P/L within 24 hours. Therefore, in situ _CaCO3 should be separated from the treated water as soon as possible to obtain high phosphorus recovery efficiency.

Example 5

Effect of Coexisting Ions on In Situ Formation of Calcium Carbonate Microspheres

Uniformly prepare 2mol/L NaF, NaHCO ₃ , Na ₂ SO ₄ , NaNO ₃ and NaCl solutions, add sodium dihydrogen phosphate (NaH ₂ PO ₄ ) The amount of interfering anion substances added in the solution is respectively 10 times and 60 times that of the phosphate ion (the mixing group is that the aforementioned anion substances are mixed in an equimolar ratio); when the Ca/P molar ratio is 6/1, at Under stirring at 300-500rpm, first add CaCl ₂ solution with a concentration of 214.8mg/L, react for 30 minutes, then add Na ₂ CO ₃ solution with a concentration of 205.2mg/L, react for 30 minutes, filter the water sample, and measure the phosphorus content.

Fig. 7 is a diagram showing the phosphorus removal effect of the calcium carbonate microsphere phosphate fertilizer generated in situ in Example 5 under interfering anions. The results showed that low concentrations of coexisting ions (10 times of P), including Cl ^- , F ^- , HCO ₃ ^- , NO ₃ ^- and SO ₄ ^2- had almost no adverse effects. Even if the amount of chloride ion, nitrate, and sulfate reaches a high concentration of 60 times that of phosphate, there is no obvious adverse effect. Although not often encountered, when the amount of F ^- and HCO ₃ ^- in sewage reaches 60 times that of phosphate, it will have obvious adverse effects. Overall, the method for in situ formation of calcium carbonate microspheres has good resistance to salt interference.

Example 6

Effect of temperature on phosphorus removal process with in situ formation of calcium carbonate microspheres, including the following steps:

Under the four temperature conditions of 15°C, 20°C, 25°C, and 30°C, when the molar ratio of Ca/P is 6/1, under the state of stirring at 300-500 revolutions per minute, to a volume of 1L, calculated as P In the sodium dihydrogen phosphate (NaH ₂ PO ₄ ) solution with a total phosphorus concentration of 10 mg-P/L, add CaCl ₂ solution with a concentration of 214.8 mg/L, then add Na ₂ CO ₃ solution with a concentration of 205.2 mg/L, and react for 30 minutes , filter the water sample, and determine the phosphorus content.

Fig. 8 is the effect diagram of phosphorus removal at different temperatures of the calcium carbonate microsphere phosphate fertilizer generated in situ in Example 6. The results show that the temperature (from 15°C to 30°C) has little effect on the reaction. After treatment, the phosphorus recovery rate is >95%, and the total phosphorus content in the effluent is less than 0.5mg/L, which meets the national sewage discharge level 1 A standard and has good performance. The ability to resist temperature interference.

Example 7

The effect of end point pH on the phosphorus removal process of forming calcium carbonate microspheres in situ, including the following steps:

Prepare a sodium dihydrogen phosphate (NaH ₂ PO ₄ ) solution with a total phosphorus concentration of 10 mg-P/L in terms of P, and adjust the equilibrium pH value of the solution by adding 1.0 mol/L NaOH and HCl solutions to obtain different end point pH values value (from 7.5 to 13), when the Ca/P molar ratio is 6/1, under the state of stirring at 300-500 revolutions per minute, to a volume of 1L, the total phosphorus concentration in terms of P is 10mg-P/L In sodium dihydrogen phosphate (NaH ₂ PO ₄ ) solution, add CaCl ₂ solution until the concentration of calcium chloride is 214.8 mg/L, then add Na ₂ CO ₃ solution to a concentration of 205.2 mg/L, stir at room temperature for 30 min, and measure the final pH, and filtered water samples, determination of phosphorus content.

Fig. 9 is a diagram showing the phosphorus removal effect of the calcium carbonate microsphere phosphate fertilizer generated in situ in Example 7 at different end point pHs. The results show that the impact of the end point pH (from 7.5 to 13) on the reaction is negligible. After treatment, the phosphorus recovery rate is >97%, and the total phosphorus content in the effluent is less than 0.2mg/L, which meets the national sewage discharge level 1 A standard and has good Ability to resist acid and alkali interference.

Example 8

Calcium carbonate microsphere phosphate fertilizer generated in situ and determination of calcium carbonate phosphorus content prepared by traditional method:

Utilize X-ray Photoelectron Spectroscopy (XPS) to further analyze the phosphate ion that in-situ generates calcium carbonate microsphere phosphate fertilizer recovery in the embodiment 1 Existing forms in _CaCO3 . The XPS results showed (as shown in Figure 10) that most of the phosphate ions existed in the form of HPO ₄ ^2- (132.2eV, 64%) and PO ₄ ^3- (133.2eV, 36%) to form calcium carbonate microparticles in situ. in the ball. For calcium carbonate synthesized by traditional methods, phosphate ions exist as HPO ₄ ^2- (54%), PO ₄ ^2- (23%), and H ₂ PO ₄ ¹ (134.6eV, 23%). According to the XPS results, the Ca/P molar ratios of the in-situ formed calcium carbonate microspheres and the traditionally prepared calcium carbonate were 1.82:1 and 4.31:1, respectively. Therefore, _the solid form of calcium carbonate microspheres formed in situ is: CaCO ₃ 0.23Ca ₃ (PO ₄ ) ₂ 1.04CaHPO ₄ 16.48H ₂ O; 0.04Ca(H ₂ PO ₄ ) ₂ .0.16CaHPO ₄ .0.04Ca ₃ (PO ₄ ) ₂ .15.92H ₂ O. After the sample was dissolved in hydrochloric acid and the phosphate concentration in the solution was tested, the P content in the in-situ formed calcium carbonate microspheres was as high as 20.80% (P ₂ O ₅ , weight percent), which was 4 times that of the traditional synthetic calcium carbonate. The phosphorus content of calcium carbonate formed by this in-situ method is much higher than the phosphorus content standards of qualified and high-quality calcium magnesium phosphate fertilizers in China (P ₂ O ₅ is >12% and >18% by weight respectively) (GB20412-2016 , CN).

Example 9

Phosphorus recovery from septic tank sewage by in-situ generation of calcium carbonate:

Collect 1 L of water samples from the effluent of the septic tank, measure the initial total phosphorus concentration to be 80 mg-P/L, and pH=4.3.

Add 5% (w/w) sodium hydroxide solution until the pH of the solution system is 8, add CaCl ₂ solution (1mol/L) until the calcium chloride concentration is 1.2g/L, then add Na ₂ CO ₃ solution (1mol/L L) until the concentration of sodium carbonate is 1.1g/L, react for 30min, filter with fast filter paper, measure the phosphorus content in the effluent with reference to GB11893-89 to be 0.48mg-P/L, and the phosphorus recovery rate is 99.4%.

Example 10

In-situ generation of calcium carbonate method for deep phosphorus removal of aquaculture sewage:

Collect 1L of effluent sewage discharged from the farm after biochemical treatment by activated sludge method, and measure the total phosphorus concentration to be 5.6mg-P/L, pH=6.2.

Add CaCl ₂ solution (1mol/L) until the concentration of calcium chloride is 0.15g/L, then add Na ₂ CO ₃ solution (1mol/L) until the concentration of sodium carbonate is 0.14g/L, react for 30min, filter with fast filter paper, refer to According to GB11893-89, the phosphorus content in the effluent is 0.41mg-P/L, and the phosphorus recovery rate is 92.7%.

Example 11

An application of in-situ generation of calcium carbonate microsphere phosphate fertilizer to the growth of Chinese cabbage, comprising the following steps:

(1) Uniformly prepare multiple 100mL sodium dihydrogen phosphate (NaH ₂ PO ₄ ) solutions with a concentration of 38.73mg/L (total phosphorus in P is 10mg/L), and the total phosphorus concentration in P is 10mg-P/ L of sodium dihydrogen phosphate (NaH ₂ PO ₄ ) solution. Under stirring, first add CaCl ₂ solution until the concentration of CaCl ₂ in the system is 214.8mg/L, after reacting for 30min, then add Na ₂ CO ₃ solution until the concentration of Na ₂ CO ₃ in the system is 205.2mg/L, continue to react for 30min Then stop stirring. Filter the precipitate, dry and collect the powder product to generate calcium carbonate microsphere phosphate fertilizer in situ.

(2) Collect sandy soil from local farmland as planting soil.

(3) Chinese cabbage (Brassica campestris L. ssp.) (purchased from Hebei Xingyun Seed Industry Co., Ltd.) was planted in a flower pot with 1.0 kg of soil. Spray 1g of the prepared calcium carbonate microsphere phosphate fertilizer as phosphate fertilizer (P-CaCO ₃ -insitu) on the soil surface as the phosphate fertilizer group; the control group (CK) does not apply fertilizer; ten seeds are sown in each group.

(4) After germination, keep 5 plants with average germination potential for planting test. The water holding capacity was maintained at about 70% during the planting period, and the flower pots were placed in natural sunlight, and each group had 3 replicates. After 50 days, the plants were harvested, and the stem height, root length, and stem fresh weight were measured.

(5) Measure the dry weight of the stem after oven drying at 105°C for 24 hours.

Fig. 11 is an effect diagram of Example 11 in-situ generation of calcium carbonate microsphere phosphate fertilizer acting on pakchoi growth control without adding phosphate fertilizer. The photos showed that after 50 days of planting, the plants in the fertilized group were significantly taller and had larger leaves. After harvest, the root system of the fertilized group was also longer, indicating that the in situ generation of calcium carbonate microsphere phosphate fertilizer promoted the growth of the root system. After weighing the plants, it was found that the yield of the fertilized group increased by 58.9% (fresh weight) and the dry weight also increased by 60.1%. The significant increase in plant yield indicated that the in situ phosphorus recovery strategy is a potentially useful approach to recover phosphorus from low-concentration water to provide high-quality phosphorus fertilizers.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (8)

1. a kind of in-situ generation calcium carbonate microsphere phosphate fertilizer reclaims the method for phosphate in sewage, it is characterized in that comprising the following steps: (1) Add calcium chloride solution to the phosphorus-containing solution under stirring to obtain mixed solution A; (2) Add sodium carbonate to the mixed solution A under stirring, continue to stir and react to obtain the mixed solution B; (3) Separating the mixed liquid B from solid to liquid, drying the separated solid to obtain calcium carbonate microsphere phosphate fertilizer generated in situ; The amount of calcium chloride added in the step (1) is calculated according to the molar ratio of calcium in calcium chloride: phosphorus in the solution being 2:1 to 10:1; The amount of sodium carbonate added in step (2) is calculated according to the calcium in calcium chloride in step (1): the molar ratio of carbonate in sodium carbonate is 3:1～1:2; The reaction time described in step (2) is 30min-24h. 2. the in-situ generation calcium carbonate microsphere phosphate fertilizer according to claim 1 reclaims the method for phosphate in sewage, it is characterized in that: The amount of calcium chloride added in the step (1) is calculated according to the molar ratio of calcium in calcium chloride: phosphorus in the solution being 4:1 to 10:1; The amount of sodium carbonate added in step (2) is calculated according to the molar ratio of calcium in calcium chloride:carbonate in sodium carbonate in step (1) being 2:1 to 1:2. 3. the in-situ generation calcium carbonate microsphere phosphate fertilizer according to claim 1 reclaims the method for phosphate in sewage, it is characterized in that: The phosphorus-containing solution described in the step (1) is a phosphorus-containing solution with a phosphorus concentration of 1-80 mg/L. 4. the in-situ generation calcium carbonate microsphere phosphate fertilizer according to claim 3 reclaims the method for phosphate in sewage, it is characterized in that: The phosphorus-containing solution is a phosphorus-containing solution with a concentration of 1-10 mg/L in terms of phosphorus. 5. the in-situ generation calcium carbonate microsphere phosphate fertilizer according to claim 1 reclaims the method for phosphate in sewage, it is characterized in that: The method of solid-liquid separation described in step (3) includes filtration, standing or centrifugation; The drying condition described in step (3) is to dry at 50-150°C until completely dry. 6. the in-situ generation calcium carbonate microsphere phosphate fertilizer according to claim 5 reclaims the method for phosphate in sewage, it is characterized in that: The filtration is performed using a 0.22 μm microfiltration membrane. 7. The application of the method for generating calcium carbonate microsphere phosphate fertilizer according to any one of claims 1 to 6 to reclaim phosphate in sewage in reclaiming sewage phosphate. 8. The application according to claim 7, characterized in that: said sewage is sewage with a phosphorus concentration≤10mg/L.

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