Method for regulating phosphorus phase in sludge calcined product by utilizing kaolinite

Abstract

The invention relates to the technical field of sludge calcination, in particular to a method for regulating and controlling a phosphorus phase in a sludge calcination product by utilizing kaolinite. The invention discloses a method for regulating and controlling a phosphorus phase in a sludge calcined product by utilizing kaolinite. The method comprises the following steps: calcining a mixture of kaolinite and sludge in a certain proportion at 600-700 DEG C for 2-4 hours; in the mixture, the mass ratio of kaolinite is 8-10%. The kaolinite is added to be pyrolyzed and calcined with the sludge, under the synergistic effect of proportion, temperature and the like, phosphorus phase reconstruction in the calcined sludge product is regulated and controlled, the total phosphorus (TP) preservation amount is increased, and phosphorus in the sludge is converted into a form which has higher recovery value, higher bioavailability and is easier to extract subsequently, especially apatite-state phosphorus (AP); the phosphate fertilizer is stable in chemical property and moderate in solubility, and is a source of high-quality phosphate fertilizer or phosphorus chemical raw materials.

Description

Technical Field

[0001] This invention relates to the field of sludge calcination technology, and in particular to a method for controlling the phosphorus phase in sludge calcination products using kaolinite. Background Technology

[0002] Traditional sludge treatment methods (landfill, incineration, agricultural use) suffer from resource waste, environmental pollution (such as heavy metals and pathogens), and phosphorus loss, and are difficult to efficiently recover phosphorus. In traditional activated sludge systems, phosphorus is usually stored in the form of microbial cells, resulting in low phosphorus recovery rates and requiring additional treatment processes. Existing phosphorus recovery technologies include chemical precipitation, biological treatment, and adsorption, but these methods suffer from drawbacks such as high cost, complex processes, long processing times, and limited adsorption capacity, making large-scale application difficult. In chemically dephosphorized sludge (especially sludge from aluminum and iron salt dephosphorization), phosphorus mainly exists in the form of metal phosphates (Al-P, Fe-P), which are difficult to release or recover effectively in conventional treatments, and have low bioavailability. Thermochemical treatment (such as calcination, pyrolysis, and gasification) can effectively reduce sludge volume, kill pathogens, and decompose organic pollutants, making it an effective technology for achieving sludge stabilization, harmlessness, and resource recovery. In the calcination products obtained from thermochemical treatment of sludge, phosphorus is mainly present in organic phosphorus (OP) and inorganic phosphorus (IP). Inorganic phosphorus includes apatite-form inorganic phosphorus (AP) and non-apatite-form inorganic phosphorus (NAIP). In the calcination products of existing sludge technologies, the total phosphorus content is relatively low, and phosphorus usually accounts for a large proportion in the form of non-apatite-form inorganic phosphorus, which is not conducive to subsequent utilization and extraction. Summary of the Invention

[0003] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing a method for controlling the phosphorus phase in sludge calcination products using kaolinite.

[0004] The present invention discloses a method for controlling the phosphorus phase in sludge calcination products using kaolinite, wherein a mixture of a certain proportion of kaolinite and sludge is calcined at 600-700℃ for 2-4 hours; the mass percentage of kaolinite in the mixture is 8%-10%.

[0005] Furthermore, the heating rate is 10℃ / min.

[0006] Furthermore, the calcination time is 4 hours.

[0007] Furthermore, the calcination temperature is 700℃.

[0008] Furthermore, kaolinite accounts for 10% of the total mass.

[0009] Furthermore, the sludge is dried, pulverized, and passed through a 60-mesh sieve as powdered activated sludge.

[0010] Furthermore, in the calcined product, the proportion of apatite-state inorganic phosphorus to total phosphorus is 40.5%-41.05%.

[0011] Furthermore, the calcined product contains 11.65-11.66 mg / g of inorganic phosphorus in apatite form.

[0012] This invention regulates the phosphorus phase reconstruction in the calcined sludge products by adding kaolinite and pyrolyzing sludge, under the synergistic effect of proportion and temperature, thereby increasing the total phosphorus (TP) retention. It also transforms the phosphorus in the sludge into a form with higher recycling value, greater bioavailability, and easier subsequent extraction, especially apatite phosphorus (AP), which has stable chemical properties and moderate solubility, making it a source of high-quality phosphate fertilizer or phosphate chemical raw materials. Attached Figure Description

[0013] Figure 1 TG analysis of sludge and kaolin at different mass ratios in air atmosphere (10℃ / min) (K0---K10 corresponds to Kaolin, 0%---Kaolin, 10%); Figure 2 Loss on ignition (K0-K10 corresponds to Kaolin, 0%---Kaolin, 10%) was obtained by weighing sludge and kaolin with different mass ratios before and after ignition in air atmosphere (10℃ / min). Figure 3 Total phosphorus content in sludge kaolinite calcination residue; Figure 4 Distribution of various forms of phosphorus in sludge kaolinite pyrolysis calcination residue; Figure 5 Retention of NAIP and AP in calcined kaolinite pyrolysis residue from sludge; Figure 6a Recovery rates of total phosphorus and non-apatite phosphorus from sludge kaolinite pyrolysis calcination residue; Figure 6b Recovery rates of total phosphorus and non-apatite phosphorus from sludge kaolinite pyrolysis calcination residue; Figure 7 Increase in the recovery of phosphorus (AP) from kaolinite pyrolysis calcination residue in sludge; Figure 8a The percentage of AP and NAIP in the sample relative to IP; Figure 8b The solubility of the sample in 2% citric acid (CA) and neutral ammonium citrate (NAC). Detailed Implementation

[0014] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0015] Example 1: Step S1001: Place 10g of powdered activated sludge that has passed through a 60-mesh sieve into a crucible and calcine it in a muffle furnace at a heating rate of 10℃ / min. Repeat this process for 6 identical samples, calcining them at 400℃, 500℃, 600℃, 700℃, 800℃, and 900℃ for 4 hours respectively.

[0016] Step S1002: The total phosphorus (TP), organic phosphorus (OP), inorganic phosphorus (IP), apatite-based inorganic phosphorus (AP), and non-apatite-based inorganic phosphorus (NAIP) content of the calcined product are determined by SMT method.

[0017] Example 2: Step S2001: After thoroughly mixing 9.8g of powdered activated sludge that has passed through a 60-mesh sieve and 0.2g of pharmaceutical-grade powdered kaolinite, place the mixture in a crucible and calcine it in a muffle furnace at a heating rate of 10℃ / min. Repeat this process for 6 identical samples, calcining them at 400℃, 500℃, 600℃, 700℃, 800℃, and 900℃ for 4 hours respectively.

[0018] Step S2002: The total phosphorus (TP), organic phosphorus (OP), inorganic phosphorus (IP), apatite-based inorganic phosphorus (AP), and non-apatite-based inorganic phosphorus (NAIP) content of the calcined product are determined by SMT method.

[0019] Example 3: Step S3001: After thoroughly mixing 9.2g of powdered activated sludge that has passed through a 60-mesh sieve and 0.8g of pharmaceutical-grade powdered kaolinite, place the mixture in a crucible and calcine it in a muffle furnace at a heating rate of 10℃ / min. Repeat this process for 6 identical samples, calcining them at 400℃, 500℃, 600℃, 700℃, 800℃, and 900℃ for 4 hours respectively.

[0020] Step S3002: The total phosphorus (TP), organic phosphorus (OP), inorganic phosphorus (IP), apatite-based inorganic phosphorus (AP), and non-apatite-based inorganic phosphorus (NAIP) content of the calcined product are determined by SMT method.

[0021] Example 4: Step S4001: After thoroughly mixing 9.0g of powdered activated sludge that has passed through a 60-mesh sieve and 1.0g of pharmaceutical-grade powdered kaolinite, place the mixture in a crucible and calcine it in a muffle furnace at a heating rate of 10℃ / min. Repeat this process for 6 identical samples, calcining them at 400℃, 500℃, 600℃, 700℃, 800℃, and 900℃ for 4 hours respectively.

[0022] Step S4002: Determine the content of total phosphorus (TP), organic phosphorus (OP), inorganic phosphorus (IP), apatite-based inorganic phosphorus (AP), and non-apatite-based inorganic phosphorus (NAIP) in the calcined product using the SMT method.

[0023] In the above examples, the phosphorus determination method was the molybdenum blue colorimetric method, and the ultraviolet-visible spectrophotometer was set at a wavelength of 700 nm.

[0024] The specific steps for SMT testing are as follows: (1) Weigh 0.2 g of calcined sample using weighing paper, transfer it to a porcelain boat and spread it evenly. Place the porcelain boat in a muffle furnace at 450℃ and calcine for 3 h. After calcination, place the porcelain boat in a desiccator and cool it to room temperature.

[0025] (2) The ignited sample was then transferred to a centrifuge tube, and 20 ml of 3.5 mol / L hydrochloric acid solution was added. The tube was shaken at room temperature for 16 h. After shaking, the sample was centrifuged at 4500 r / min for 40 s. Then, an appropriate amount of the supernatant was drawn up using a disposable syringe and filtered through a 0.45 μm inorganic aqueous filter membrane to obtain the filtrate to be tested. The result was the total phosphorus (TP) content.

[0026] (3) Add 0.2 g of sample to a 50 ml centrifuge tube and add 20 ml of 1 mol / L HCl solution; shake at room temperature for 16 h, separate by centrifuge, take the supernatant and filter it through a 0.45 μm inorganic aqueous filter membrane to obtain the test filtrate, and determine the inorganic phosphorus (IP) content.

[0027] (4) Collect the solid residue after centrifugation in step (3), and rinse the solid residue with deionized water several times. Then dry it in an oven at 105 ℃ for 24 h. Put the remaining solid after washing into a crucible and incinerate it in a muffle furnace at 450 ℃ for 3 hours. Put the remaining solid after incineration into a 50 ml centrifuge tube and add 20 ml of 1 mol / L HCl solution. Shake at room temperature for 16 h, separate it with a centrifuge, and take the supernatant and filter it through a 0.45 μm inorganic aqueous filter membrane to obtain the filtrate to be tested. The result is the content of organic phosphorus (OP).

[0028] (5) Add 0.2 g of sample to a 50 ml centrifuge tube and add 20 ml of 1 mol / L NaOH solution. Shake at room temperature for 16 h. After separation by centrifugation, take the supernatant and filter it through a 0.45 μm inorganic aqueous filter membrane. Extract 10 ml of the filtered supernatant and transfer it to a 50 ml centrifuge tube. Add 4 ml of 3.5 mol / L HCl solution to it and mix well. Let it stand at room temperature for 16 h. Take the supernatant and filter it through a 0.45 μm inorganic aqueous filter membrane to obtain the filtrate to be tested. The result is the nonapatite inorganic phosphorus (NAIP) content.

[0029] (6) Collect the solid residue obtained after the first centrifugation following the shaking in step (5), rinse it several times with deionized water, and then dry it in a 105 ℃ oven. After drying, transfer the solid residue to a 50 ml centrifuge tube, add 20 ml of 1.0 mol / L HCl solution, and shake at room temperature for 16 h. After shaking, centrifuge at 4500 r / min for 40 s, and then use a disposable syringe to draw an appropriate amount of supernatant and filter it through a 0.45 μm inorganic aqueous filter membrane to obtain the filtrate to be tested. The result is the content of apatite-state inorganic phosphorus (AP).

[0030] Appendix Table 1 shows the industrial analysis of the dried sludge. Its high volatile matter content suggests a decrease in mass during high-temperature calcination. The addition of kaolinite provides physical support to the sludge system under high-temperature calcination conditions, improving the sludge's pore structure and promoting the fusion and reaction of various components, thus accelerating solidification and stabilization. Under high-temperature calcination, kaolinite can inhibit phosphorus volatilization and increase the retention rate of phosphorus in the treated sludge product, achieving a phosphorus phase reconstruction effect. Table 2 shows the organic elemental analysis of the dried sludge, with an organic sulfur content of 0.

[0031] Appendix Table 3 shows the total phosphorus concentration in the calcined kaolinite residue from the sludge. It can be seen that the total phosphorus content increases with increasing temperature, but decreases with the addition of kaolinite. Since the loss on ignition rate varies at each temperature, the proportion of kaolinite added also varies. The phosphorus content is defined as phosphorus retention (PS, mg P / g SS): PS = PC * Y char / WR sludge PC represents the concentration of phosphorus (mgP / g char), Y char WR represents the coke yield after sludge pyrolysis at the corresponding pyrolysis temperature. sludge This indicates the weight percentage of sludge in the pyrolysis feedstock. The total phosphorus content in the sludge-kaolinite calcination residue is... Figure 3 .

[0032] Table 1 Industrial Analysis of Dried Sludge

[0033] Table 2 Organic element analysis of dried sludge

[0034] Table 3 Total phosphorus concentration in sludge kaolinite calcination residue

[0035] Appendix Figure 1 and Figure 2The data includes TG analysis of sludge and kaolin at different mass ratios in air (10℃ / min) and loss on ignition obtained by weighing before and after calcination. The mass decreased significantly under high-temperature calcination.

[0036] Appendix Figure 3 The total phosphorus retention of sludge and kaolin at different mass ratios and temperatures is shown. It can be seen that the addition of kaolinite alters the effective total phosphorus content, i.e., the total phosphorus retention. The total phosphorus concentration of the kaolinite-sludge co-pyrolysis products decreases, but the total phosphorus retention changes significantly. At 800℃ with an added kaolinite content of 8% or at 700℃ with an added kaolinite content of 10%, the total phosphorus retention reaches a certain maximum. At 900℃, the total phosphorus retention decreases, as a small portion of the phosphorus volatilizes at high temperatures. Kaolinite plays a certain role in phosphorus fixation under high-temperature calcination conditions, and due to its unique structure and composition, it retains the total phosphorus to the maximum extent.

[0037] Appendix Figure 4 The distribution of various forms of phosphorus in the pyrolysis and calcination residue of sludge and kaolinite was investigated. The addition of kaolinite altered the content of phosphorus by form. As the temperature increased, the content of organic phosphorus gradually decreased, while the content of inorganic phosphorus increased. Simultaneously with the increase in temperature, the content of non-apatite inorganic phosphorus (NAIP) decreased, while the content of apatite inorganic phosphorus (AP) increased. This demonstrates that increasing the temperature can promote the conversion of phosphorus from NAIP to AP in sludge. Furthermore, the addition of kaolinite, through a synergistic effect, further promotes the NAIP-AP conversion, increases the relative content of AP, and achieves a phase reconstruction of phosphorus.

[0038] Appendix Table 4 shows the content of apatite-based inorganic phosphorus (AP) in the pyrolysis and calcination residue of sludge kaolinite. Figure 5 The NAIP and AP content in the pyrolysis calcination residue of sludge kaolinite was analyzed. Below 600℃, AP content decreased with increasing kaolinite content; above 600℃, AP content increased with increasing kaolinite content. The increase in temperature and the addition of kaolinite synergistically promoted the NAIP-AP conversion. Before 600℃, a small amount of Al... 3+ With PO4 3- AlPO4 is formed by combination, while Ca in the sludge... 2+ It may preferentially combine with SiO2 released from kaolinite to form calcium silicates (such as CaSiO3), reducing the amount of Ca reacting with PO4. 3- The combination of opportunities for apatite (AP) formation leads to a decrease in the AP content. Kaolinite decomposes above 600℃, generating active aluminum oxide (Al2O3) and silicon oxide (SiO2). The fixation and structural reorganization of phosphorus by aluminum and silicon oxides are the main reasons for the phosphorus phase reconstruction by kaolinite. Under high-temperature calcination, Ca... 2+ Release and preferentially bind to PO4 3-At the same time, kaolinite and ash co-melt at high temperature to form a glassy phase, which encapsulates phosphate particles, reduces phosphorus volatilization, and increases the total phosphorus (TP) retention, resulting in an increase in the absolute amounts of NAIP and AP. However, the increase in the proportion of AP demonstrates the success of phosphorus phase reconstruction.

[0039] Table 4. Phosphorus content of kaolinite and apatite in sludge

[0040] Figure 6 shows the recovery rates of total phosphorus and non-apatite phosphorus in the pyrolysis and calcination residue of sludge kaolinite.

[0041] The phosphorus recovery rate (RR) is defined as the ratio of phosphorus content in the pyrolysis coke to the phosphorus content in the original sludge. char *W char / PS sludge *Ws ludge ) * 100%. PS char and PS sludge The values ​​represent the phosphorus content (mg P / g SS) in the pyrolysis calcined sludge of sludge and the unpyrolyzed raw sludge, respectively. char and W sludg e represents the weight (g) of the corresponding pyrolysis calcination residue and raw sludge, respectively.

[0042] The recovery rate of phosphorus after the pyrolysis of sludge with different amounts of kaolinite is defined as the recovery rate (IRR).

[0043] IRR = (RR) mix / RR Char -1)∗100%, RR mix The phosphorus recovery rate (RR) is the phosphorus recovery rate in the coke after the pyrolysis of sludge and kaolinite. char This indicates the phosphorus recovery rate in sludge pyrolysis coke without kaolinite additives.

[0044] When the temperature is between 400-900℃, the addition of an appropriate amount of kaolin promotes the increase and recovery of TP and NAIP. With increasing temperature, it also promotes the NAIP-AP conversion, leading to an increase in AP content. Furthermore, with the increase in kaolinite content, the proportion of AP increases. At 900℃, the addition of kaolin reduces the ratio of TP and AP, while NAIP remains almost unaffected.

[0045] Appendix Figure 7 The recovery of NAIP (phosphorus) from kaolinite pyrolysis calcination residue in sludge is increasing. After 600-700℃, kaolinite undergoes dehydroxylation, releasing Al sources. The recovery rate of NAIP gradually increases rapidly, while the recovery rate of AP also increases, but the trend gradually slows down and decreases. The addition of kaolinite, accompanied by an increase in temperature, synergistically promotes the conversion of NAIP to AP, forming a more stable form.

[0046] The synergistic effect of kaolinite with different additive ratios at different temperatures demonstrated its role in the reconstructing of phosphorus phases in sludge. This was reflected in the increase in total phosphorus content and the relative content of apatite-form phosphorus. With increasing kaolinite content, the conversion of NAIP-AP was further promoted simultaneously with rising temperature, achieving the goal of phase reconstruction. Maximizing total phosphorus content was achieved at 800℃ with 8% kaolinite addition and at 700℃ with 10% kaolinite addition. Simultaneous temperature increase and the promotion of apatite-form phosphorus recovery further validated the NAIP-AP conversion, reflecting that kaolinite alters the reaction pathway and final fate of phosphorus at high temperatures, successfully reconstructing phosphorus in sludge and increasing the relative proportion of high-value, easily recoverable apatite-form phosphorus.

[0047] Figure 8 shows the percentages of AP and NAIP in the total IP of the calcined kaolinite product from sludge, and their solubility in 2% citric acid (CA) and neutral ammonium citrate (NAC). During pyrolysis, the addition of an appropriate amount of kaolinite effectively further promoted the NAIP-AP transition, increasing the AP percentage. In the 2% CA solution, the reaction involves the dissolution of soluble phosphorus in the sample; in the neutral ammonium citrate solution, the reaction involves specific citrate-soluble phosphorus. As shown in the figure, the soluble phosphorus in the pyrolysis residue increased from 19.95 mg / g ss in the original sludge to 27.01 mg / g ss in the 700-8% sludge kaolinite pyrolysis product, significantly improving phosphorus bioavailability. At 700℃, with the increase of kaolinite, the solubility of Fe-P and Al-P compounds (NAIP) in NAC decreased from 21.5 mg / g ss to 21.39 mg / g ss, since the solubility of Fe-P and Al-P compounds (NAIP) in NAC is higher than that of inorganic phosphorus in apatite. This indicates that the addition of kaolinite promotes the conversion of NAIP to AP. That is, the increase in the solubility of soluble phosphorus in pyrolysis slag at 2% in CA and the relative content of AP can show that kaolinite can improve the bioavailability of phosphorus to a certain extent.

[0048] Data show that kaolinite affects the migration and transformation of phosphorus in sludge. By utilizing the unique structural composition advantages of kaolinite and the synergistic effect of ratio-temperature optimization in experimental conditions, the phosphorus phase reconstruction effect can be achieved.

[0049] For any points not covered above, existing technologies shall apply.

[0050] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for regulating phosphorus phase in sludge calcination product using kaolinite, characterized by, A mixture of kaolinite and sludge in a certain proportion is calcined at 600-700 DEG C for 2-4 h; the mass proportion of kaolinite in the mixture is 8-10%.

2. A method for controlling the phosphorus phase in the calcined product of sludge according to claim 1, characterized in that, The heating rate is 10 DEG C / min.

3. The method for controlling the phosphorus phase in the sludge calcination product using kaolinite according to claim 1, characterized by, The calcination time is 4 h.

4. The method for controlling the phosphorus phase in the sludge calcination product using kaolinite according to claim 1, characterized by, The calcination temperature is 700 DEG C.

5. The method for controlling the phosphorus phase in the sludge calcination product using kaolinite according to claim 1, characterized by, The mass proportion of kaolinite is 10%.

6. The method for controlling the phosphorus phase in the sludge calcination product using kaolinite according to claim 1, characterized by, The sludge is dry-pulverized and screened to a powder of 60 mesh.

7. The method for controlling the phosphorus phase in the sludge calcination product using kaolinite according to claim 1, characterized by, In the calcination product, the proportion of apatite-state inorganic phosphorus in total phosphorus is 40.5-41.05%.

8. The method for controlling the phosphorus phase in the sludge calcination product using kaolinite according to claim 1, characterized by, In the calcination product, the content of apatite-state inorganic phosphorus is 11.65-11.66 mg / g.

Images