Aluminum-containing sludge resource treatment method and application thereof

Abstract

The application provides a kind of aluminum-containing sludge resource processing method and application thereof, belongs to environmental protection technical field.The aluminum-containing sludge resource processing method includes the following steps: the aluminum-containing sludge is dewatered;Magnesium source and rare earth compound are added to the dewatered sludge, and mixed;Phosphate-containing substances are used to pre-activate the mixed material;The granulation reaction of the pre-activated material and sodium silicate solution is carried out to obtain granular product;The granular product is aged and dried to obtain a granular phosphorus removal agent.The application realizes the synergistic effect between the components and structures through the steps of phosphoric acid pre-activation, rare earth element addition, suitable sodium silicate granulation and core-shell structure construction, significantly improves the adsorption capacity and adsorption speed of the phosphorus removal agent, and has wide application prospect and practical value in the field of advanced phosphorus removal in wastewater treatment.

Description

Technical Field

[0001] This application relates to the field of environmental protection technology, and in particular to a method for the resource utilization of aluminum-containing sludge and its application. Background Technology

[0002] In aluminum processing, surface treatment is an essential step. Polishing, pickling, oxidation, and coloring processes consume a large amount of cleaning water, approximately 65-180 liters per square meter of aluminum, making it a major source of industrial wastewater in aluminum plants. After neutralization, adjustment, coagulation, and sedimentation, wastewater sludge is obtained. This sludge mainly consists of colloidal aluminum hydroxide and some amorphous substances. Traditional treatment methods involve stockpiling or landfilling, which not only occupies land but also poses environmental risks. Existing resource recovery methods include:

[0003] Preparation of building materials: such as brick making and cement additives, but with low added value and may cause salt accumulation.

[0004] Aluminum salts can be recycled by acid leaching to produce aluminum sulfate or polyaluminum chloride (PAC), but the process is complex, costly, and causes serious acid mist pollution.

[0005] Direct use as a phosphorus removal agent: Some studies have attempted to use dried aluminum sludge directly for phosphorus removal, but its phosphorus removal capacity is low, the rate is slow, and it is prone to caking, so the effect is far inferior to commercial agents.

[0006] Patent CN201610775907.4 discloses a method for preparing wear-resistant and refractory castables using aluminum-containing sludge. The method involves first adding aluminum-containing sludge, lime, and filler sequentially to water glass under stirring to form a suspension; adjusting the pH to 8-10; homogenizing the suspension under microwave radiation; removing it and heating to dry to obtain raw material; calcining the raw material for 4-8 hours; cooling and grinding the discharged material to obtain the wear-resistant and refractory castable, which exhibits good wear resistance and thermal conductivity. Patent CN202010047250.6 discloses a method for resource recovery from aluminum-containing sludge, the steps of which include: ore blending, roasting, leaching, solid-liquid separation, carbon separation, and physical sorting. This invention controls the molar ratio of calcium oxide to aluminum oxide in the raw materials to convert aluminum oxide into calcium sulfoaluminate and calcium aluminate during the clinker roasting process. Subsequently, aluminum and calcium are separated by leaching with sodium carbonate solution. The resulting sodium aluminate solution can be used to prepare aluminum hydroxide using a carbonation process, and the sodium carbonate solution can be returned to the clinker leaching step for recycling. At the same time, the leaching residue is physically sorted to obtain calcium carbonate concentrate, which can be returned to the ore blending step for recycling or used for wastewater treatment.

[0007] The products obtained by these methods cannot be used for phosphorus removal from wastewater because they fail to effectively activate the chemical activity of aluminum in the sludge and reconstruct its physical structure to meet the requirements of efficient phosphorus removal. Summary of the Invention

[0008] This application is made in view of the above-mentioned problems, and its purpose is to provide a method for the resource utilization treatment of aluminum-containing sludge and its application. The present invention has a simple process flow, low cost, high product added value, and environmentally friendly method for the resource utilization of aluminum-containing sludge, which transforms it into a granular high-efficiency phosphorus removal agent with high phosphorus adsorption capacity and rapid kinetic performance, turning waste into treasure.

[0009] Specifically, the first aspect of this application provides a method for the resource utilization of aluminum-containing sludge, including the following steps:

[0010] Dewatering of aluminum-containing sludge;

[0011] Magnesium source and rare earth compound are added to the dewatered sludge and mixed.

[0012] The mixed materials are pre-activated using a substance containing phosphate.

[0013] The pre-activated material is granulated with sodium silicate solution to obtain particulate product;

[0014] The granular product is aged, cured, and dried to obtain a granular phosphorus removal agent.

[0015] Furthermore, the rare earth compound is one or more of nitrates, chlorides or oxides of cerium or lanthanum; and / or the amount of the rare earth compound added is 0.5%-3% of the mass of Al2O3 in the dry basis of the aluminum-containing sludge.

[0016] Further, the magnesium source is lightly calcined magnesium oxide; and / or the amount of magnesium source added satisfies the following molar ratio: n(Al): n(Mg) = (5-10): 1, where n(Al) originates from the aluminum content in the dry basis of aluminum-containing sludge.

[0017] Furthermore, the phosphate-containing substance is one or more of phosphoric acid, dihydrogen phosphate, and hydrogen phosphate.

[0018] Furthermore, the pre-activation treatment involves adding a phosphate-containing substance to the mixture and controlling the pH of the reaction system to 6.0-7.5, reacting at 50-70°C for 0.5-2 hours.

[0019] Furthermore, the granulation reaction is carried out at a temperature of 70-95°C, and the reaction residence time is 30-70 min; and / or the modulus of the sodium silicate solution is 2.0-2.4, and the concentration is 5%-10%.

[0020] Furthermore, the aging and curing conditions are as follows: curing at 50-65℃ and humidity greater than 70% for 12-36 hours; the drying temperature is not higher than 120℃.

[0021] Furthermore, the phosphorus removal agent is a composite particle containing rare earth elements, magnesium, aluminum, silicon, and phosphate.

[0022] Furthermore, the phosphorus removal agent has a particle size of 1-5 mm and a bulk density of 0.8-1.1 g / cm³. 3 The static saturated adsorption capacity for phosphate is not less than 30 mg PO4. 3- -P / g.

[0023] A second aspect of this application provides the application of the phosphorus removal agent in wastewater treatment, wherein the phosphorus removal agent is used for deep removal of phosphates from water bodies.

[0024] The present invention has the following beneficial effects:

[0025] This invention first adds a magnesium source and rare earth compounds to the dewatered sludge. The addition of magnesium source and rare earth compounds plays a key role in improving the performance of aluminum-containing sludge. The magnesium source can change the chemical composition and structure of the sludge, enhancing its binding capacity with phosphorus; while the rare earth compounds have unique electronic structures and chemical properties, accelerating the hydrolysis of MgO and OH through a catalytic effect. - The release of rare earth ions ensures a highly efficient and thorough activation reaction. Simultaneously, rare earth ions act as structure-directing agents, guiding the formation of an ordered and stable mesoporous structure, increasing the specific surface area and active sites. This not only enhances the activity of aluminum in the sludge but also promotes chemical reactions on the sludge surface, significantly improving phosphorus removal efficiency. In the pre-activation treatment step, the mixed material is treated with phosphate-containing substances, enabling the formation of specially active sites on the surface of the sludge particles. These sites can interact more strongly with phosphorus ions, laying the foundation for subsequent efficient phosphorus removal. The trace rare earth elements loaded in the phosphorus removal agent produce a ternary synergistic effect with aluminum and magnesium, significantly improving the adsorption capacity for ultra-low concentrations of phosphorus. In the granulation reaction, the pre-activated material is reacted with a sodium silicate solution. Sodium silicate plays a binding and structural support role during the reaction. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0027] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0028] An embodiment of the first aspect of the present invention provides a method for the resource utilization treatment of aluminum-containing sludge, comprising the following steps:

[0029] Dewatering of aluminum-containing sludge;

[0030] Magnesium source and rare earth compound are added to the dewatered sludge and mixed.

[0031] The mixed materials are pre-activated using a substance containing phosphate.

[0032] The pre-activated material is granulated with sodium silicate solution to obtain particulate product;

[0033] The granular product is aged, cured, and dried to obtain a granular phosphorus removal agent.

[0034] In the above treatment methods, dewatering can reduce the water content of aluminum-containing sludge, facilitating subsequent processing. Adding magnesium sources and rare earth compounds serves two purposes: firstly, the magnesium source alters the chemical composition and structure of the sludge, making it more conducive to phosphorus binding; secondly, the unique electronic structure and chemical properties of rare earth compounds can accelerate the hydrolysis of MgO and OH-. - Release makes the activation reaction more efficient, and can also act as a structure directing agent to guide the formation of an ordered and stable mesoporous structure, increase the specific surface area and active sites, and greatly improve the activity of aluminum in sludge and the chemical reactivity of sludge surface.

[0035] In the pre-activation treatment step, the mixture is treated with phosphate-containing substances, which can form special active sites on the surface of sludge particles. These sites have a stronger interaction with phosphorus ions, ensuring efficient phosphorus removal. Moreover, the trace rare earth elements loaded on the phosphorus removal agent produce a ternary synergistic effect with aluminum and magnesium, which greatly enhances the adsorption capacity for ultra-low concentrations of phosphorus.

[0036] During the granulation reaction, the sodium silicate solution reacts with the pre-activated material. Sodium silicate acts as a binder and structural support, resulting in granular products with excellent physical properties. The aging and drying steps further stabilize the structure and properties of the granular products, ensuring the reliable quality of the final granular descaling agent.

[0037] The granular phosphorus remover prepared by this treatment method has a particle size of 1-5 mm and a bulk density of 0.8-1.1 g / cm³. 3 The static saturated adsorption capacity for phosphate is not less than 30 mg PO4. 3- With a phosphorus adsorption capacity of -P / g and rapid kinetic performance, this method can deeply remove phosphates from water bodies and realize the resource utilization of aluminum-containing sludge. It solves the problem of aluminum-containing sludge treatment and yields high-value-added products, resulting in significant economic and environmental benefits. Furthermore, this method achieves waste-to-waste treatment, co-treating aluminum sludge and high-phosphorus digestate to form a closed-loop waste flow, eliminating the need for purchased phosphoric acid and further enhancing its application value and market competitiveness.

[0038] In this embodiment, the dewatering treatment of the aluminum-containing sludge specifically involves using a high-pressure diaphragm plate and frame filter press and adding 0.3% (by dry sludge mass) of anionic PAM flocculant. The sludge is held at 1.8 MPa for 40 minutes to reduce its moisture content to 60%-65%. This moisture content is within the optimal viscosity range for subsequent mixing reactions.

[0039] In this embodiment, the rare earth compound is one or more of cerium or lanthanum nitrates, chlorides, or oxides, such as cerium nitrate (Ce(NO3)3) or lanthanum chloride (LaCl3), which can be dissolved in a diluted sodium silicate solution and sprayed together; the amount of the rare earth compound added is 0.5%-3% of the mass of Al2O3 in the dry basis of the aluminum-containing sludge. 4+ / Ce 3+ Or La 3+ It has a unique electronic structure and can catalyze the hydrolysis of MgO and OH at low temperatures. - The release process makes the activation reaction faster and more thorough. Rare earth ions can serve as nucleation sites, guiding the magnesium-aluminum-silicon gel to form a more ordered and stable mesoporous structure, greatly increasing the specific surface area and active sites. The trace rare earth elements loaded in the final product are also excellent phosphorus removal agents, producing a ternary synergistic effect with aluminum and magnesium, further significantly improving the adsorption capacity and adsorption rate for ultra-low concentrations of phosphorus.

[0040] Furthermore, the magnesium source is light-burned magnesium oxide; the amount of magnesium source added, in molar ratio, satisfies: n(Al):n(Mg) = (5-10):1, preferably 8:1, where n(Al) originates from the aluminum content in the dry basis of aluminum-containing sludge. The amount of magnesium source added significantly affects the performance of the phosphorus removal agent. When n(Al):n(Mg) is in the range of (5-10):1, the activity of aluminum in the sludge can be fully activated, while ensuring that the phosphorus removal agent has good structural stability and adsorption performance. If the amount of magnesium source added is too small, i.e., n(Al):n(Mg) is greater than 10:1, then the degree of change in the chemical composition and structure of the sludge is limited, the binding capacity with phosphorus is not significantly improved, and the phosphorus removal effect of the phosphorus removal agent is difficult to achieve the ideal state. However, if too much magnesium source is added, resulting in an n(Al):n(Mg) ratio less than 5:1, it will increase costs and may also lead to an overly dense structure in the phosphorus removal agent, reducing the specific surface area and covering the active sites, which is detrimental to phosphorus adsorption. When the n(Al):n(Mg) ratio is 8:1, the various properties of the phosphorus removal agent reach a relatively balanced state, ensuring sufficient active sites to bind with phosphorus while maintaining a good physical structure, thereby achieving high phosphorus adsorption capacity and rapid kinetic performance.

[0041] This invention employs phosphate pre-activation, specifically as follows:

[0042] The dehydrated sludge cake was conveyed to a twin-shaft differential mixer, and lightly calcined magnesium oxide (MgO, active content ≤40s, 200 mesh) powder was added at a molar ratio of n(Al):n(Mg) = 7:1. Simultaneously, cerium nitrate (Ce(NO3)3·6H2O) powder was added at 1.5% of the Al2O3 mass in the dry sludge. During mixing, a 2% phosphoric acid (H3PO4) solution was sprayed at low speed. The amount of phosphoric acid solution sprayed was controlled by an online pH meter, ultimately stabilizing the pH of the mixture at 6.5-7.0 (slightly acidic to neutral), with a total mixing time of 20 minutes. The pre-activated material was then transferred to a sealed aging chamber and aged at 60°C for 1 hour to ensure a thorough and uniform pre-activation reaction.

[0043] Under these conditions, partial hydrolysis of MgO provides OH- - H3PO4 provides PO4 3- Ce 30 As catalysts, the three react rapidly with the active aluminum in the sludge to generate trace amounts of amorphous aluminum phosphate / magnesium phosphate complexes in situ, providing a large number of highly active crystal nuclei for subsequent steps.

[0044] In this embodiment, the phosphate-containing substance is one or more of phosphoric acid, dihydrogen phosphate, and hydrogen phosphate. This invention adds a "pre-reaction" step before the "activation and granulation" step. The sludge material mixed with MgO is aged at 50-70℃ for 0.5-2 hours, during which a dilute phosphoric acid solution (concentration 1-3%) is sprayed to adjust the pH value of the material to 6.0-7.5. These conditions are set to ensure that special active sites can form on the surface of the sludge particles. When the pH value is below 6.0, the reaction system is too acidic, which may damage the sludge structure and hinder the formation of active sites; while when the pH value is above 7.5, the alkalinity may cause some aluminum to precipitate, reducing its activity. Controlling the reaction temperature at 50-70℃ can accelerate the reaction rate and make the formation of active sites more complete. The reaction time is between 0.5-2 hours, which ensures that the reaction proceeds fully without being too long and wasting energy.

[0045] Pre-added PO4 3- It preferentially reacts with the most active aluminum and magnesium sites in the material, pre-forming an extremely thin, insoluble, amorphous primary active layer of aluminum / magnesium phosphate within the particles. This active layer becomes a more powerful "nucleus" during subsequent sodium silicate granulation, attracting more active gel to coat it, ultimately forming a "core-shell structure" of active sites with phosphate as the core and hydroxyl gel as the outer shell. The activity of this structure is far higher than that of randomly formed gels. When the product is placed in phosphorus-containing water, the phosphate ions in its core generate a "common ion effect," more strongly "attracting" phosphate ions from the water to its surface for enrichment and exchange reactions, with extremely rapid kinetics. The product prepared by this method has an extremely fast phosphorus adsorption rate and is particularly suitable for deep-treatment filters with short hydraulic retention times.

[0046] In this embodiment, the granulation reaction is carried out at a temperature of 70-95℃, with a reaction residence time of 30-70 min; the modulus of the sodium silicate solution is 2.0-2.4, and the concentration is 5%-10%. The 30-70 min residence time in the granulation reaction allows the sodium silicate solution to better exert its binding and structural support functions, promoting the formation of granular products. If the temperature is too low, the viscosity and reactivity of the sodium silicate are insufficient, making it difficult to form a good granular structure; if the temperature is too high, it may cause excessively rapid evaporation of moisture, affecting the uniformity of the particles. Controlling the reaction residence time is also crucial; if the time is too short, the reaction is incomplete, resulting in poor particle strength and stability; if the time is too long, it increases energy consumption and cost. The modulus of the sodium silicate solution is 2.0-2.4, and the concentration is 5%-10%. The modulus reflects the molar ratio of silicon dioxide to sodium oxide in sodium silicate; when the modulus is between 2.0 and 2.4, the sodium silicate exhibits better binding performance and stability. A solution concentration of 5%-10% ensures that sodium silicate can effectively bind materials during granulation without making the particles too wet, which would affect subsequent aging, curing, and drying processes.

[0047] Specifically, the low-temperature activation granulation process involves diluting an industrial sodium silicate solution with a modulus of 2.2 to a working concentration of 6%. A rotary drum granulator equipped with a steam heating jacket and a dual-fluid atomizing spray gun is used. The pre-activated material is continuously fed into the granulator. The prepared 6% sodium silicate solution is atomized (atomization pressure 0.4 MPa) and sprayed onto the tumbling material bed through the spray gun, while simultaneously introducing 0.3 MPa steam into the granulator jacket to precisely control the material temperature at 85±2℃. The total residence time of the material in the granulator is 50 minutes. Under the synergistic effect of temperature and sodium silicate, the crystal nuclei generated in the pre-activation stage grow rapidly. Silicate ions crosslink with aluminum, magnesium, and cerium ions to form a "Ce-magnesium-aluminum-silicon" multi-component composite hydrated gel, which encapsulates the pre-generated phosphate core, initially constructing a "phosphate core-hydroxyl gel shell" composite structure.

[0048] In this embodiment, the granulated particles are sent to a curing chamber, where they are cured at 50-65°C and humidity greater than 70% for 12-36 hours; the drying temperature does not exceed 120°C. This allows the gel network to further condense and solidify, forming a stable mesoporous structure and achieving sufficient mechanical strength.

[0049] More specifically, the drying process employs a three-layer belt dryer, with the following zones: Zone 1 (preheating zone): 105℃, 10 minutes; Zone 2 (main drying zone): 118℃ (strictly controlled <120℃), 35 minutes; Zone 3 (cooling zone): ambient air cooling. The final moisture content of the product is ≤ 4%.

[0050] Particles of 1-5mm are selected as qualified products through vibrating sieve screening.

[0051] In this embodiment, the phosphorus removal agent is a composite particle containing rare earth elements, magnesium, aluminum, silicon, and phosphate. The particle size of the phosphorus removal agent is 1-5 mm, and the bulk density is 0.8-1.1 g / cm³. 3 The static saturated adsorption capacity for phosphate is not less than 30 mg PO4. 3- -P / g.

[0052] A second aspect of this application provides the application of the phosphorus removal agent in wastewater treatment, wherein the phosphorus removal agent is used for deep removal of phosphates from water bodies.

[0053] In phosphate removal agents, aluminum and magnesium elements react chemically with phosphate ions to form insoluble phosphate precipitates. Specifically, aluminum ions combine with phosphate ions to form aluminum phosphate precipitate, while magnesium ions react with phosphate ions to form magnesium ammonium phosphate or magnesium phosphate precipitate, thus removing phosphate from the water solution. The presence of rare earth elements further enhances this chemical reaction; their unique electronic structure and chemical properties promote the combination of aluminum and magnesium with phosphate ions, increasing the reaction rate and efficiency.

[0054] The mesoporous structure of phosphorus removal agents also plays a crucial role. Their abundant specific surface area and active sites provide ample space for phosphate adsorption. When phosphorus-containing water comes into contact with the phosphorus removal agent, phosphate ions rapidly diffuse into the pores of the agent and are adsorbed onto the active sites. This physical adsorption, combined with the chemical reaction, significantly enhances the phosphorus removal efficiency.

[0055] The "core-shell structure" of phosphorus removal agents offers unique advantages. The phosphate ions in the core generate a "common ion effect," strongly attracting phosphate ions from the water to their surface for enrichment. This enrichment increases the concentration of phosphate ions on the phosphorus removal agent surface, further promoting chemical reactions and adsorption processes. Moreover, this structure enables the phosphorus removal agent to exhibit excellent adsorption capacity even for ultra-low concentrations of phosphorus, deeply removing phosphates from water and reducing phosphorus content to extremely low levels.

[0056] In practical applications of wastewater treatment, this phosphorus removal agent exhibits rapid response, achieving highly efficient removal of phosphates in a short time. Its rapid kinetic properties make it particularly suitable for scenarios such as advanced treatment filters with short hydraulic retention times. When treating high-phosphorus wastewater, the agent can quickly reduce phosphorus content, ensuring the effluent meets stringent discharge standards. Furthermore, due to its high phosphorus adsorption capacity, the agent has a long service life, reducing replacement frequency and lowering operating costs.

[0057] This phosphorus removal agent also possesses excellent physical properties and stability. Its compact particle structure and moderate bulk density prevent it from easily breaking or being lost under the impact of water flow. Under varying water quality conditions and ambient temperatures, the phosphorus removal agent maintains a stable phosphorus removal effect, demonstrating strong adaptability and reliability.

[0058] Example

[0059] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0060] Example 1

[0061] A method for resource recovery treatment of aluminum-containing sludge includes the following steps:

[0062] A high-pressure diaphragm plate and frame filter press was used, with the addition of 0.3% (dry sludge mass ratio) of anionic PAM flocculant. The sludge was held at 1.8 MPa for 40 minutes to reduce the sludge moisture content to 60%.

[0063] The dewatered sludge was transported to a twin-shaft differential mixer, and lightly calcined magnesium oxide powder was added at a molar ratio of n(Al):n(Mg) = 7:1. At the same time, cerium nitrate (Ce(NO3)3·6H2O) powder was added at 1.5% of the mass of Al2O3 in the dry sludge. During the mixing process, a 2% phosphoric acid (H3PO4) solution was sprayed at low speed to stabilize the pH value of the mixture at 6.5. The total mixing time was 60 minutes, and the pre-activated material was obtained.

[0064] A 6% sodium silicate solution is atomized by a spray gun (atomization pressure 0.4 MPa) and sprayed onto the tumbling material bed. At the same time, 0.3 MPa of steam is introduced into the granulator jacket to precisely control the material temperature at 85℃. The total residence time of the material in the granulator is 50 minutes.

[0065] The granular product was cured at 55°C and 72% humidity for 20 hours and then dried to obtain a granular phosphorus removal agent.

[0066] Example 2

[0067] This embodiment is basically the same as Example 1, except that cerium nitrate (Ce(NO3)3·6H2O) powder is added at 1% of the mass of Al2O3 in the dry sludge.

[0068] Example 3

[0069] This embodiment is basically the same as Example 1, except that cerium nitrate (Ce(NO3)3·6H2O) powder is added at 2% of the mass of Al2O3 in the dry sludge.

[0070] Example 4

[0071] This embodiment is basically the same as Example 1, except that cerium nitrate is replaced with an equimolar amount of lanthanum chloride (LaCl3).

[0072] Comparative Example 1

[0073] Aluminum sludge with 80% water content was dried at 105°C to constant weight, then crushed and ground through a 100-mesh sieve.

[0074] Comparative Example 2

[0075] Aluminum sludge was acid-leached with 20% sulfuric acid at 90°C for 2 hours, and the filtrate was concentrated after filtration to obtain liquid polyaluminum chloride (PAC).

[0076] Comparative Example 3

[0077] This comparative example is basically the same as Example 1, except that MgO is added at a ratio of n(Al):n(Mg)=7:1, and granulation is carried out with 8% sodium silicate solution (85°C, 50 min), followed by curing and drying.

[0078] Comparative Example 4

[0079] Based on Comparative Example 3, 1.5% cerium nitrate was added, but the phosphoric acid pre-activation step was not performed.

[0080] Comparative Example 5

[0081] This comparative example is basically the same as Example 1, except that the pH of the material mixed with MgO was adjusted to 6.5 with 2% H3PO4, pre-activated for 1 hour, and then granulated with 8% sodium silicate. No rare earth elements were added.

[0082] Experimental Case

[0083] Take 100 mL of a 10.0 mg / L potassium dihydrogen phosphate solution (calculated as P) into an Erlenmeyer flask. Accurately weigh 0.100 g (dry weight) of the adsorbent sample to be tested (samples prepared in Examples 1-4 and Comparative Examples 1-5) and add it to the flask. Place the Erlenmeyer flask in a constant temperature shaker (25℃, 150 rpm) and shake for 24 h to ensure adsorption equilibrium is reached. After filtration, determine the residual phosphorus concentration in the filtrate using the ammonium molybdate spectrophotometric method.

[0084] Adsorption capacity Qe (mg / g) calculation formula: Qe = (C o -C e ) * V / m

[0085] Where: C o ,Ce, and V represent the initial and equilibrium phosphorus concentrations (mg / L), respectively; V is the solution volume (L); and m is the adsorbent mass (g). Experimental results are shown in Table 1.

[0086] Table 1. Test results of Examples 1-4 and Comparative Examples 1-5

[0087]

[0088] As shown in Table 1, the adsorption capacity and time required to reach 90% Qe in Examples 1-5 were significantly better than those in Comparative Examples 1-5. In the examples, variations in additives and operating conditions also had a certain impact on the phosphorus removal effect. In Example 3, cerium nitrate was added at 2% of the mass of Al2O3 in the dry sludge, resulting in an adsorption capacity of 40.5 mg / g and a time required to reach 90% Qe of only 10 minutes. This indicates that appropriately increasing the amount of cerium nitrate added can further improve the adsorption performance and adsorption rate of the phosphorus removal agent. Comparing Examples 1 and 4, replacing cerium nitrate with an equimolar amount of lanthanum chloride resulted in a decrease in adsorption capacity and an increase in the time required to reach 90% Qe, indicating that cerium nitrate had a better phosphorus removal effect than lanthanum chloride in this system.

[0089] In the comparative examples, Comparative Example 1, which only involved drying and grinding aluminum sludge, exhibited extremely low adsorption capacity, requiring a very long time to reach 90% Qe. This is likely because no chemical modification or structural adjustment was performed, resulting in few active sites and a small specific surface area for the aluminum sludge, thus limiting its adsorption capacity and rate for phosphate. Comparative Example 2, which used sulfuric acid leaching of aluminum sludge to prepare liquid polyaluminum chloride, improved phosphorus removal to some extent. However, since it primarily removed phosphorus through the hydrolytic polymerization of aluminum ions, lacking the core-shell structure and synergistic effect of rare earth elements found in the examples, its adsorption capacity and rate remained far inferior to those of the examples. Comparative Example 3, which used 8% sodium silicate solution for granulation, formed a certain particle structure, but lacked a phosphoric acid pre-activation step, failing to form effective crystal nuclei and core-shell structures, resulting in inferior adsorption performance compared to the examples. Comparative Example 4, which added cerium nitrate to Comparative Example 3 but did not undergo phosphoric acid pre-activation, prevented the rare earth elements from fully exerting their synergistic effect, resulting in insufficient formation of active crystal nuclei and still poor adsorption performance. Comparative Example 5 did not add rare earth elements, and relied solely on phosphoric acid pre-activation and sodium silicate granulation. Lacking the promoting effect of rare earth elements on the chemical reaction, its adsorption capacity and adsorption rate were significantly lower than those of the Example.

[0090] In summary, the phosphorus removal agent prepared by the aluminum-containing sludge resource utilization treatment method provided by this invention achieves synergistic effects among various components and structures through steps such as phosphoric acid pre-activation, rare earth element addition, appropriate sodium silicate granulation, and core-shell structure construction. This significantly improves the adsorption capacity and adsorption rate of the phosphorus removal agent, and has broad application prospects and practical value in the field of deep phosphorus removal in wastewater treatment.

[0091] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. The application of a phosphorus removal agent in wastewater treatment, characterized in that, The phosphorus removal agent is used to remove phosphates from water, and the preparation method of the phosphorus removal agent includes the following steps: Dewatering of aluminum-containing sludge; Lightly calcined magnesium oxide and rare earth compounds are added to the dewatered sludge and mixed. The rare earth compounds are one or more of nitrates, chlorides or oxides of cerium or lanthanum. The mixed materials are pre-activated by adding a phosphate-containing substance to the mixture, and the pH of the reaction system is controlled at 6.0-7.5, and the reaction is carried out at 50-70℃ for 0.5-2 hours. The pre-activated material is granulated with sodium silicate solution to obtain particulate product; The granular product is aged, cured, and dried to obtain a granular phosphorus removal agent.

2. The application of the phosphorus removal agent according to claim 1 in wastewater treatment, characterized in that, The amount of rare earth compound added is 0.5%-3% of the mass of Al2O3 in the dry basis of the aluminum-containing sludge.

3. The application of the phosphorus removal agent according to claim 1 in wastewater treatment, characterized in that, The amount of lightly calcined magnesium oxide added, expressed as a molar ratio, satisfies: n Al : n Mg =5-10 : 1, where n Al Aluminum content derived from the dry basis of aluminum-containing sludge.

4. The application of the phosphorus removal agent according to claim 1 in wastewater treatment, characterized in that, The phosphate-containing substance is one or more of phosphoric acid, dihydrogen phosphate, and hydrogen phosphate.

5. The application of the phosphorus removal agent according to claim 1 in wastewater treatment, characterized in that, The granulation reaction is carried out at a temperature of 70-95°C, with a reaction residence time of 30-70 min; and / or the sodium silicate solution has a modulus of 2.0-2.4 and a concentration of 5%-10%.

6. The application of the phosphorus removal agent according to claim 1 in wastewater treatment, characterized in that, The aging and curing conditions are as follows: curing at 50-65℃ and humidity greater than 70% for 12-36 hours; the drying temperature is not higher than 120℃.

7. The application of the phosphorus removal agent according to claim 1 in wastewater treatment, characterized in that, The phosphorus removal agent has a particle size of 1-5 mm and a bulk density of 0.8-1.1 g / cm³. 3 The static saturated adsorption capacity for phosphate is not less than 30 mg PO4. 3- -P / g.

Images