Preparation method of high-efficiency phosphorus removal red mud-steel slag-based unburned ceramsite

Abstract

The present application relates to the technical field of resource utilization of bulk solid waste and water treatment, and discloses a preparation method of high-efficiency phosphorus-removing red mud-steel slag-based baking-free ceramsite, which comprises the following steps: stirring preprocessed sintered red mud, steel slag and rice husk ash together with gypsum and cement until uniform to obtain mixed dry materials; continuously spraying Na2SiO3 solution during the stirring of the mixed dry materials to obtain mud balls; placing the mud balls into a rolling cake area to obtain mud cakes; placing the mud cakes into a rolling strip area to obtain mud strips; placing the mud strips into a rolling ball area to obtain ceramsite raw materials; attaching wet gauze to the ceramsite raw materials and aging them in a cool place; steam curing the ceramsite raw materials to obtain semi-finished ceramsite; and placing the semi-finished ceramsite in a sealed cool place at room temperature, spraying water on the surface of the semi-finished ceramsite every day, and naturally curing the semi-finished ceramsite to obtain finished ceramsite. The preparation method is simple, the phosphorus removal rate of the ceramsite is high, the solid waste is recycled, and the problem of high energy consumption in the preparation of traditional water treatment ceramsite is solved.

Description

Technical Field

[0001] This invention relates to the fields of resource utilization of bulk solid waste and water treatment technology, and in particular to a method for preparing highly efficient phosphorus removal red mud-steel slag-based non-fired ceramsite. Background Technology

[0002] As a major aluminum and steel producer, my country generates over 100 million tons of red mud and steel slag annually. Currently, the utilization rate of red mud and steel slag in China is low, with open-air dumping being the primary method. This not only occupies large amounts of land but also poses a risk of soil and groundwater pollution. Furthermore, the calcium, iron, aluminum, and silicon contained within these materials are not effectively utilized, resulting in resource waste. With rapid urbanization and increasingly frequent human activities, domestic sewage contains high levels of phosphorus. If not effectively treated, this phosphorus will accumulate in natural water bodies after being discharged into rivers, leading to eutrophication. Therefore, addressing the problem of excessive phosphorus concentration in sewage is crucial to solving eutrophication.

[0003] Red mud and steel slag possess large specific surface areas and high porosity, making them suitable for producing ceramsite for phosphorus removal in water treatment. While traditional ceramsite for phosphorus removal exhibits excellent adsorption performance, the energy consumption and carbon emissions generated during its high-temperature preparation process cannot be ignored. Therefore, under the current environmental protection context of "carbon emission reduction," a new approach to ceramsite preparation is to utilize the inherent volcanic ash activity of the raw materials, add binders such as cement to assist in pellet formation, and complete granulation through natural or steam curing. Thus, a feasible non-fired granulation process is urgently needed to produce ceramsite that possesses both excellent mechanical properties and phosphorus adsorption performance, achieving the goals of "energy saving and emission reduction, and waste treatment." Summary of the Invention

[0004] This invention provides a method for preparing red mud-steel slag-based non-fired ceramsite with high efficiency in phosphorus removal. The prepared red mud-steel slag-based non-fired ceramsite has good mechanical properties and phosphorus adsorption performance, overcoming the disadvantages of high energy consumption and high cost in the traditional water treatment ceramsite granulation process, and realizing the resource utilization of sintered red mud and steel slag.

[0005] This invention provides a method for preparing highly efficient phosphorus removal red mud-steel slag-based non-fired ceramsite, comprising:

[0006] S1. Mix the pretreated sintered red mud, steel slag and rice husk ash with gypsum and cement until uniform to obtain a mixed dry material.

[0007] S2. During the stirring of the mixed dry materials in step S1, Na2SiO3 solution is continuously sprayed and kneaded to make them stick together into a smooth, compact, and plastic mud.

[0008] S3. First, the clay lumps from step S2 are placed into the rolling and forming area to obtain clay cakes with a thickness of 5-8 mm; then, the clay cakes are placed into the rolling and forming strip area to obtain cylindrical clay strips; finally, the clay strips are placed into the rolling and forming sphere area to obtain ceramsite raw materials with a diameter of 6-8 mm.

[0009] S4. Cover the raw ceramsite from step S3 with a damp gauze and place it in a cool place to age.

[0010] S5. Steam curing the ceramsite raw material from step S4 to obtain semi-finished ceramsite.

[0011] S6. At room temperature, place the semi-finished ceramsite from step S5 in a sealed, cool place, spray water on its surface every day, and naturally cure it to obtain the finished ceramsite.

[0012] Furthermore, in step S1, the pretreatment method for sintering red mud, steel slag, and rice husk ash is to remove impurities, grind them through a 100-mesh sieve, and dry them to constant weight.

[0013] Further, in step S1, the mass of the mixed dry materials is 100%; wherein, 40-45% is sintered red mud, 30-35% is steel slag, 10% is rice husk ash, 10% is cement, and 4% is gypsum, and the mass ratio of sintered red mud to steel slag is 4:3.

[0014] Furthermore, in step S2, the mass of Na2SiO3 is 3% of the sum of the masses of the sintering red mud and steel slag.

[0015] Furthermore, in step S4, the aging time is 2 hours.

[0016] Furthermore, in step S5, the steam curing is carried out in a water bath, with a curing time of 10-12 hours and a curing temperature of 80°C.

[0017] Furthermore, in step S6, the natural curing time is 14 days.

[0018] Furthermore, the prepared red mud-steel slag-based non-fired ceramsite was applied to the treatment of phosphorus-containing wastewater.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. The high content of amorphous aluminosilicate minerals in sintered red mud and steel slag gives them certain hydraulic properties, while their high calcium oxide content provides potential phosphorus removal capabilities. This invention makes extensive and full use of sintered red mud and steel slag and their potential properties. Sintered red mud and steel slag account for 76% of the total mass. The muscovite and CSH gel generated by the hydration reaction fill the internal pores, resulting in a dense structure, which guarantees its strength.

[0021] 2. By creatively incorporating rice husk ash as a pore-forming agent, the surface of the produced ceramsite exhibits numerous mesopores, promoting the adsorption of phosphorus from water. This invention achieves the treatment of phosphorus-containing wastewater while simultaneously recycling red mud and steel slag with low energy consumption and low cost. Furthermore, it provides a new approach to the disposal of rice husk ash. Finally, the granulation process provided by this invention is systematic and convenient, enabling the production of ceramsite with uniform particle size and improving granulation efficiency.

[0022] 3. The red mud-steel slag-based non-fired ceramsite prepared by this invention has a total breakage rate and wear rate of 4.6%; a disintegration rate of 3.9%; and a bulk density of 786 kg / m³. 3 The average pore size is 26.14 nm; the unit adsorption capacity is 0.48–0.91 mg / g; the phosphorus removal rate is 36.2–95.2%; the heavy metal leaching concentration meets the regulations and can be used as an environmentally friendly material. Attached Figure Description

[0023] Figure 1 This is a diagram showing the main components of red mud, steel slag, and rice husk ash in the sintering process of this invention.

[0024] Figure 2 The graph shows the relationship between the mass ratio of red mud to steel slag in the sintering process and the phosphorus removal performance and disintegration rate of ceramsite.

[0025] Figure 3 This is a graph showing the relationship between the disintegration rate of the non-fired ceramsite product prepared by the method of the present invention and the curing time and curing temperature.

[0026] Figure 4 This is an internal SEM image of the non-fired ceramsite product obtained by the method of this invention.

[0027] Figure 5 This is a graph showing the relationship between the phosphorus removal performance of the non-fired ceramsite prepared by the method of this invention and the initial phosphorus concentration in the solution.

[0028] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0029] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0030] Unless otherwise specified, all raw materials used in this invention are commercially available products; and all methods used in this invention are conventional methods in the field unless otherwise specified.

[0031] The sintering red mud used in this invention is taken from an alumina production enterprise, the steel slag is taken from a steel plant, the gypsum is anhydrous calcium sulfate, and the sodium silicate is sodium silicate nonahydrate, all of which are analytical grade reagents; the cement is type 42.5 Polish cement; the method of adsorbing phosphorus in water by ceramsite in this invention is as follows: 2g of non-fired ceramsite is added to 100mL of potassium dihydrogen phosphate solution with a concentration of 10-50mg / L (calculated as P, unless otherwise specified, the phosphorus concentration mentioned below is all calculated as P), and the solution is kept at a constant temperature and shaken at 25℃ and 140r / min for 48h. Subsequently, the phosphorus concentration in the solution was determined using the molybdenum-antimony UV spectrophotometric method; the phosphorus removal rate = (phosphorus concentration in the solution before adsorption - phosphorus concentration in the solution after adsorption) / phosphorus concentration in the solution before adsorption × 100%; the unit adsorption capacity of the ceramsite = (phosphorus concentration in the solution before adsorption - phosphorus concentration in the solution after adsorption) × solution volume / ceramsite mass × 100%; the heavy metals in the ceramsite were extracted according to the "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid-Nitric Acid Method" (HJ 299-2007), and the concentration of heavy metals in the leachate was determined by ICP-OES. The concentration of heavy metals in the leachate was evaluated according to the range specified in the "Technical Guidelines for Pollution Prevention and Control of Solid Waste Recycling" (HJ 1090-2020), as shown in the table below.

[0032] A list of heavy metal leaching indicators for red mud-steel slag-based non-fired ceramsite

[0033]

[0034] Note: The unit is mg / LND, indicating undetectable.

[0035] This invention takes the resource utilization of red mud and steel slag as its starting point, and leverages the phosphorus removal characteristics of red mud and steel slag. It aims to explore a type of ceramsite filter media with excellent mechanical properties and phosphorus removal capabilities that can be applied to the field of water treatment through a non-fired granulation process, thereby solving the problems of low resource utilization rate of red mud and steel slag and high energy consumption and high cost in the traditional water treatment ceramsite preparation process.

[0036] This invention uses sintered red mud and steel slag as main raw materials, and first explored the feasibility of preparing non-fired ceramsite. The study investigated three aspects: material addition amount, ceramsite preparation process, and ceramsite curing process, determining the optimal material mass ratio and relevant parameters for ceramsite preparation and curing. The optimal material ratio and preparation process for red mud-steel slag-based non-fired ceramsite are as follows: red mud and steel slag mass fraction is 76% (red mud to steel slag mass ratio 4:3), and rice husk ash, cement, and gypsum mass fractions are 10%, 10%, and 4%, respectively; 3g of sodium silicate is added per 100g of raw material during preparation; steam curing at 80℃ for 10h. The preferred non-fired ceramsite has a disintegration rate of 3.9%, a combined breakage rate and wear rate of 4.6%, an average pore size of 26.14nm, and a specific surface area of ​​26.7m². 2The various indicators and heavy metal leaching concentrations of the expanded clay aggregate all meet the relevant usage specifications. Characterization results show that the crystalline phase of the expanded clay aggregate mainly consists of calcite, muscovite, Mayeite, and CSH gel, with a loose and porous surface and a dense interior. Calcite and muscovite form the main components, while the interior is filled with a large number of clustered, flocculent, and network-like CSH gels. The interior of the expanded clay aggregate is mainly composed of mesopores ranging from 10 to 50 nm, classifying it as a mesoporous material.

[0037] This invention provides a method for preparing highly efficient phosphorus removal red mud-steel slag-based non-fired ceramsite, comprising:

[0038] S1. The pretreated sintered red mud, steel slag, and rice husk ash are mixed with gypsum and cement until homogeneous to obtain a mixed dry material. The pretreatment method for sintered red mud, steel slag, and rice husk ash is to remove impurities, grind them through a 100-mesh sieve, and dry them to constant weight. The mass of the mixed dry material is 100%. Among them, 40-45% is sintered red mud, 30-35% is steel slag, 10% is rice husk ash, 10% is cement, and 4% is gypsum. The mass ratio of sintered red mud to steel slag is 4:3.

[0039] like Figure 1 As shown, in this example, the sintered red mud is mainly composed of CaO, SiO2, and Al2O3, while the steel slag is mainly composed of CaO and Fe2O3; rice husk ash is mainly composed of SiO2. Rice husk ash can provide amorphous SiO2 to the hydration system, promoting the formation of hydrated calcium silicate; furthermore, its loose and porous structure can adjust the pore size ratio in the unfired ceramsite. Cement is added to improve the strength of the unfired ceramsite, and gypsum is added to utilize its retarding properties to extend the hydration reaction time in the system.

[0040] like Figure 2 As shown in this example, different mass ratios of sintered red mud and steel slag have little effect on the phosphorus removal rate in the solution, with removal rates all above 95%. However, excessively high or low mass ratios of sintered red mud to steel slag both lead to an increase in the disintegration rate of the ceramsite. When the mass ratios of sintered red mud to steel slag are 2:5 and 5:2, obvious cracks appear on the surface of the ceramsite, and the disintegration rates are relatively high, at 14.3% and 12.6%, respectively. When the mass ratio of sintered red mud to steel slag is 4:3, the disintegration rate is the lowest, at only 5.9%. Therefore, mixing sintered red mud and steel slag at a mass ratio of 4:3 allows particles of different fineness to form a continuous particle size distribution within the ceramsite. On the other hand, it can achieve complementary advantages and disadvantages in the oxide content of the raw materials, thereby improving the mechanical properties of the non-fired ceramsite.

[0041] S2. During the stirring of the mixed dry material in step S1, Na2SiO3 solution is continuously sprayed and kneaded to form a smooth, compact, and plastic mud ball. The mass of Na2SiO3 is 3% of the sum of the masses of the sintering red mud and steel slag.

[0042] In this example, the addition of sodium silicate aqueous solution has two main benefits. First, its own cementing effect can directly generate chemical activation, providing binding force to the dry material and promoting the formation of ceramsite. Second, sodium silicate can dissolve the glassy components in red mud and steel slag, thereby releasing the active ingredients and promoting the formation of hydration cementitious products.

[0043] When the amount of sodium silicate added is small, its alkali activation effect is insufficient, and it cannot fully dissolve the glassy structure in red mud and steel slag, thus failing to release active components such as Al and Si. Furthermore, the [HO-Si-OH]O it provides... - The amount added is relatively small. Therefore, during steam curing, hydration is insufficient, failing to form a skeletal structure with high polymerization effect, resulting in a loose ceramsite structure and surface cracks. Excessive addition leads to excessively sticky clumps that can clog the machine as they pass through the roller grooves. It should be noted that, to adapt to the machine's granulation method, the quality of Na2SiO3 used in this invention should not be too high; the quality of Na2SiO3 should not vary depending on the granulation method.

[0044] Preliminary experiments on water usage during granulation revealed that both excessive and insufficient water are detrimental to the formation of expanded clay aggregates. Insufficient water weakens the physical interlocking of materials during granulation, while excessive water increases the fluidity and reduces the plasticity of the clay. Through repeated experiments, the optimal water usage was determined to be 30–35 mL of water per 100 g of mixed dry materials.

[0045] S3. First, the mud lumps from step S2 are placed into the rolling and forming area to obtain mud cakes with a thickness of 5-8mm; then, the mud cakes are placed into the rolling and forming strip area to obtain cylindrical mud strips; finally, the mud strips are placed into the rolling and forming sphere area to obtain ceramsite raw materials with a diameter of 6-8mm.

[0046] Step S3 in this example is only to adapt to the working process of the granulator to prepare non-fired ceramsite with uniform particle size. It should be noted that the technical solution described in this invention is not limited to this granulation method, as long as it can produce standard spheres.

[0047] The plastic clay is processed sequentially through the "cake-strip-sphere" process of the extrusion granulator, and then the clay cake is prepared by rolling in the rolling zone. The clay cake is then passed through the grooves of two rollers rotating in different directions to complete the granulation. The prepared ceramic granule blank is placed in a rolling pan and rolled into an ellipsoid shape.

[0048] S4. Cover the raw ceramsite from step S3 with a damp gauze and place it in a cool place to age for 2 hours.

[0049] In this example, an aging step is incorporated to achieve pre-curing of the non-fired ceramsite. Na₂SiO₃ and cement provide adhesive properties to the material, giving the ceramsite early-stage strength. Simultaneously, an alkaline environment is created within the ceramsite, providing OH-. - The Si-O and Al-O glassy structures in sintered red mud and steel slag are dissolved, allowing them to better participate in the hydration reaction during steam curing.

[0050] S5. The ceramsite raw material from step S4 is steam-cured to obtain semi-finished ceramsite. The steam curing is carried out in a water bath for 10-12 hours, preferably 10 hours, at a curing temperature of 80°C.

[0051] In this example, steam curing is used to provide a high-heat, high-humidity environment to accelerate the hydration reaction of the expanded clay aggregate, enabling it to rapidly increase its strength in a short period and effectively shortening the subsequent natural curing time. Figure 3 As shown, the disintegration rate of ceramsite is affected by the temperature and time of steam curing. Considering the mechanical properties and production cost of ceramsite, the curing time is set to 10 hours and the curing temperature to 80℃.

[0052] S6. At room temperature, place the semi-finished ceramsite from step S5 in a sealed, cool place, spray water on its surface every day, and naturally cure it to obtain the finished ceramsite. The natural curing time is 14 days.

[0053] In this example, the strength of the unfired ceramsite continues to increase over time after steam curing. To maintain the ceramsite in a consistently high-humidity environment, water is sprayed onto its surface daily, allowing moisture to penetrate into the interior of the ceramsite and ensuring the full occurrence of the hydration reaction, thereby improving the mechanical properties of the ceramsite.

[0054] like Figure 4 As shown, after natural curing, the interior of the expanded clay contains columnar calcite and lamellar muscovite. The highly crystalline calcite and muscovite act as crystal nuclei, forming the skeleton of the expanded clay. A large number of clustered CSH gels are attached to the skeleton and connected by network and flocculent CSH gels, filling the pores inside the expanded clay and making the expanded clay structure compact.

[0055] The red mud-steel slag-based non-fired ceramsite prepared by this invention is applied to the treatment of phosphorus-containing wastewater; phosphorus adsorption experiments were conducted on the non-fired ceramsite prepared by the method for preparing highly efficient phosphorus removal red mud-steel slag-based non-fired ceramsite provided by this invention. Figure 5 As shown, a dosage of 20 g / L of ceramsite can achieve a phosphorus removal rate of 95.2% in phosphorus-containing wastewater with a phosphorus concentration of 10 mg / L, with a unit adsorption capacity of 0.48 mg / g; for phosphorus-containing wastewater with a phosphorus concentration of 50 mg / L, the phosphorus removal rate in the solution is 36.2%, with a unit adsorption capacity of 0.91 mg / g.

[0056] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0057] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing highly efficient phosphorus removal red mud-steel slag-based non-fired ceramsite, characterized in that, include: S1. The pretreated sintered red mud, steel slag and rice husk ash are mixed with gypsum and cement until uniform to obtain a mixed dry material; wherein, the mass of the mixed dry material is 100%; 40-45% sintered red mud, 30-35% steel slag, 10% rice husk ash, 10% cement, 4% gypsum, and the mass ratio of sintered red mud to steel slag is 4:3; S2. During the stirring of the mixed dry materials in step S1, Na2SiO3 solution is continuously sprayed and kneaded to make them stick together into a smooth, compact, and plastic mud. S3. First, the mud lumps from step S2 are placed into the rolling and forming area to obtain mud lumps with a thickness of 5-8mm; then the mud lumps are placed into the rolling and forming strip area to obtain cylindrical mud strips; finally, the mud strips are placed into the rolling and forming sphere area to obtain ceramsite raw material with a diameter of 6-8mm. S4. Cover the raw ceramsite from step S3 with a damp gauze and place it in a cool place to age. S5. Steam curing is performed on the raw ceramsite from step S4 to obtain semi-finished ceramsite. S6. At room temperature, place the semi-finished ceramsite from step S5 in a sealed, cool place, spray water on its surface every day, and naturally cure it to obtain the finished ceramsite.

2. The method for preparing highly efficient phosphorus removal red mud-steel slag-based non-fired ceramsite according to claim 1, characterized in that, In step S1, the pretreatment method for sintering red mud, steel slag, and rice husk ash is to remove impurities, grind them through a 100-mesh sieve, and dry them to constant weight.

3. The method for preparing highly efficient phosphorus removal red mud-steel slag-based non-fired ceramsite according to claim 1, characterized in that, In step S2, the mass of Na2SiO3 is 3% of the sum of the masses of the sintering red mud and steel slag.

4. The method for preparing high-efficiency phosphorus removal red mud-steel slag-based non-fired ceramsite according to claim 1, characterized in that, In step S4, the aging time is 2 hours.

5. The method for preparing highly efficient phosphorus removal red mud-steel slag-based non-fired ceramsite according to claim 1, characterized in that, In step S5, the steam curing is carried out in a water bath with a curing time of 10-12 hours and a curing temperature of 80°C.

6. The method for preparing highly efficient phosphorus removal red mud-steel slag-based non-fired ceramsite according to claim 1, characterized in that, In step S6, the natural curing time is 14 days.

7. The method for preparing highly efficient phosphorus removal red mud-steel slag-based non-fired ceramsite according to claim 1, characterized in that, The prepared red mud-steel slag-based non-fired ceramsite was applied to the treatment of phosphorus-containing wastewater.

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