A method for preparing high-strength unburned ceramsite using phosphogypsum and coal gangue

Abstract

The present invention discloses a method for preparing high-strength unfired ceramsite using phosphogypsum and coal gangue. The preparation method of the present invention comprises: drying, grinding, and screening phosphogypsum cementitious material powder and coal gangue, and then uniformly mixing them, adding distilled water while stirring until a sticky mud mass is formed to obtain a mixture containing a ball core; transferring the mixture into a ball-forming device, adjusting and preparing the amount of water for ball-forming, and screening after ball-forming to obtain wet raw material balls; aging and drying the wet raw material balls in sequence to obtain dry raw material balls, and evenly laying the dry raw material balls and naturally curing them to obtain a formed ceramsite product. The present invention creates an alkaline hydration environment by adding phosphogypsum-based all-solid waste cementitious material and coal gangue to promote the volcanic ash reaction of mineral powder, silicon-rich material and coal gangue to generate gel substances such as hydrated calcium silicate, thereby forming a denser structure, promoting the growth of ceramsite strength, and obtaining unfired ceramics with good performance.

Description

Technical Field

[0001] The invention relates to a method for preparing high-strength unburned ceramsite by utilizing phosphogypsum and coal gangue, and belongs to the technical field of resource recycling. Background Art

[0002] Phosphogypsum is a solid waste emitted during the production of phosphate fertilizers from the phosphoric acid industry. It is a fine-grained powder with a yellowish-white, off-white, or blackish-gray color. Its primary component is dihydrate gypsum, along with small amounts of harmful substances such as phosphorus and fluorine. Its low overall utilization rate has led to large quantities of phosphogypsum being stored in open-air dumps. According to statistics, my country produces nearly 80 million tons of phosphogypsum annually, with a national stockpile exceeding 600 million tons. Most of this is handled in open-air dumps, failing to effectively utilize the resource. Phosphogypsum is rich in dihydrate gypsum and possesses certain gelling properties, making it suitable for use in cement, building materials, and other fields. However, its fine particle size and the presence of impurities such as soluble phosphorus, fluorine, organic matter, and heavy metals pose challenges to its comprehensive utilization.

[0003] Gangue is solid waste separated from the coal mining industry. As of now, large-scale accumulations of gangue have occurred in over 1,200 counties and districts in my country, with over 7 billion tons of unused gangue covering over 20,000 hectares. This not only pollutes the surrounding soil and groundwater but also severely damages the environment and ecology. In most coal mining areas in my country, gangue is simply accumulated, forming numerous large and small gangue mountains around the areas. Years of weathering and oxidation have caused some of the gangue to spontaneously combust, posing serious hazards or hidden dangers to mine production and safety. Gangue, containing SiO₂, Al₂O₃, and Fe₂O₃, is a potential volcanic ash material with potential utilization as a building material. Currently, it is primarily used in the production of sintered bricks and cement, consuming large quantities of gangue, but energy efficiency is low due to the widespread use of calcination processes, which result in high energy consumption and emissions. Therefore, efforts should be made to explore new approaches for its safe disposal and large-scale utilization in various civil engineering applications.

[0004] The ceramsite preparation processes in the currently disclosed patents and methods mostly use cement, lime, and gypsum as gelling agents and calcinate them. Although they can meet certain performance requirements, they consume a large amount of gelling agents and energy, and are economical and environmentally friendly. The ceramsite prepared at the same time has problems such as low forming rate, many cracks, high water absorption, and difficulty in balancing lightness and high strength, which limits its further application. For example, CN202110243048.5 is a process for preparing new sludge ceramsite. Although municipal sludge, industrial sludge, construction waste, etc. are used as raw materials, a calcination process is still used. The firing temperature is as high as 800-1150°C, which consumes a lot of energy. CN 114751766 A uses light ceramsite and its method for firing solid waste, using gold tailings and fly ash, with a firing temperature of 1100-1200°C, high energy consumption, and is not conducive to large-scale utilization. CN 115073072 A discloses a method for producing high-strength unburned ceramsite using iron tailings and subway slag. Although the method consumes the iron tailings and subway slag and realizes the unburned process, cement and lime are still used as gelling agents, which increases production costs and fails to achieve comprehensive utilization of solid waste. Summary of the Invention

[0005] The purpose of the present invention is to address the problems of low molding rate, numerous cracks, high water absorption, difficulty in achieving both lightness and high strength in ceramsite prepared in the prior art, as well as the inability to achieve comprehensive utilization of all solid waste. The present invention proposes a method for preparing high-strength, unfired ceramsite using phosphogypsum and coal gangue. This method not only eliminates the need for calcination of ceramsite, reduces energy consumption, and improves production efficiency, but also reduces the raw material cost of ceramsite production, while simultaneously achieving resource utilization of industrial solid waste. The method uses coal gangue as the main raw material and phosphogypsum as a binder and gelling agent. Through mixing, granulation, drying, and other processes, the prepared lightweight ceramsite has excellent performance, high production efficiency, low energy consumption, and low cost, achieving comprehensive resource utilization of phosphogypsum and coal gangue.

[0006] In order to achieve the above object, the present invention provides a method for preparing high-strength unburned ceramsite using phosphogypsum and coal gangue, comprising the following steps:

[0007] Step 1: preparing phosphogypsum cementitious material powder using phosphogypsum, mineral powder, silicon-rich material with SiO2 content greater than 80wt% and alkali-activated material as raw materials, drying and grinding the phosphogypsum cementitious material powder and coal gangue, and sieving the sieved powder;

[0008] Step 2: Evenly mix 20-30 parts of the phosphogypsum cementitious material powder obtained by sieving in step 1 and 70-80 parts of coal gangue powder, and add distilled water while stirring until a sticky mud mass is formed to obtain a mixture containing a spherical core;

[0009] Step 3: Transfer the mixture obtained in step 2 to a pelletizing device, adjust and prepare the amount of water for pelletizing, and screen the pellets to select wet raw pellets with a diameter of 10 to 20 mm;

[0010] Step 4: The wet raw material balls obtained in step 3 are sequentially aged and dried to obtain dry raw material balls, which are evenly laid and naturally cured to obtain a formed unfired ceramsite product. The purpose of aging is to ensure that the phosphogypsum cementitious material in the ceramsite is fully hydrated with the coal gangue to form a bonded and high-strength ettringite and CSH (calcium silicate hydrate) structure to enhance the strength of the ceramsite, while preventing the wet ceramsite from losing water too quickly and breaking up the ceramsite in large quantities; the natural curing step can significantly solidify the phosphorus and fluorine in the phosphogypsum.

[0011] Preferably, the alkali-activated material in step 1 is steel slag, the CaSO4 content in the phosphogypsum is greater than 70wt%, and the CaO content in the steel slag is greater than 40wt%.

[0012] Preferably, the mass ratio of the phosphogypsum, ground mineral powder, silicon-rich material with SiO2 content greater than 80wt% and steel slag is 2.5-4.5:2.5:2:1; the water-cement ratio of the phosphogypsum cementitious material powder is 0.3-0.8.

[0013] Preferably, the grinding time in step 1 is 20 to 40 minutes; the drying temperature is 100 to 110° C. and the drying time is 1 to 2 hours; and the sieving is through a 100 to 150 mesh sieve.

[0014] Preferably, the water content of the pellets in step 3 is 10-20 wt%.

[0015] Preferably, the drying and dehydration temperature in step 5 is below 70° C. and the drying time is 3 to 5 hours. The control of temperature and time can prevent the decomposition of the hydration product ettringite mineral in the obtained dry raw material balls.

[0016] Preferably, the natural curing time in step 4 is 6 to 8 days.

[0017] Preferably, the unfired ceramsite product obtained in step 4 has a cylinder compressive strength of 1-6 MPa and a density of 800-1200 kg / m 3 , 1h water absorption rate is less than 10wt%. The test methods of the above parameters meet the standard GB / T17431.1-2010 "Lightweight aggregate and its test methods".

[0018] The present invention also provides a phosphogypsum cementitious material powder, comprising phosphogypsum, ground mineral powder, a silicon-rich material having an SiO2 content greater than 80 wt%, and steel slag in a mass ratio of 2.5 to 4.5:2.5:2:1; the water-cement ratio of the phosphogypsum cementitious material powder is 0.3 to 0.8. Compared with the prior art, the present invention has the following advantages:

[0019] (1) The strength of traditional ceramsite is mainly provided by the hydration of cement and other gelling agents and high-temperature firing, while the strength of the ceramsite of the present invention is provided by the sulfate excitation of phosphogypsum and the pozzolanic reaction of coal gangue. The present invention creates an alkaline hydration environment by adding phosphogypsum-based all-solid waste gelling materials and coal gangue to promote the pozzolanic reaction of mineral powder, silicon-rich materials (SiO2 content greater than 80wt%) and coal gangue to generate gel substances such as hydrated calcium silicate, thereby forming a denser structure and promoting the growth of ceramsite strength;

[0020] (2) The present invention uses phosphogypsum as a gelling agent and adds coal gangue to prepare ceramsite, which can not only reduce the use of gelling agent and reduce costs, but also consume a large amount of solid waste such as phosphogypsum and coal gangue, and at the same time, can solidify harmful substances in the phosphogypsum;

[0021] (3) The raw materials used in the preparation method of the present invention are all solid waste, which is low in cost, does not contain any additives, and does not require high-temperature firing. The generated ceramsite can effectively solidify the phosphorus and fluorine in phosphogypsum, does not pollute the environment, and has a simple production process and is easy to mass produce. In addition, the ceramsite obtained by the method of the present invention has high particle strength and low bulk density, and has high market promotion value when used as building aggregate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The process flow chart of the present invention for preparing unfired ceramsite;

[0023] Figure 2 This is a photo of the unfired ceramsite product prepared by the present invention. DETAILED DESCRIPTION

[0024] To make the present invention more clearly understood, preferred embodiments are described in detail below with reference to the accompanying drawings.

[0025] The phosphogypsum in each example was sourced from the phosphogypsum storage yard of Hubei Zhongfu Chemical Group Co., Ltd., and its specific composition is shown in Table 1:

[0026] Table 1 Composition of phosphogypsum

[0027]

[0028]

[0029] The mineral powder in each embodiment is S95 type mineral powder purchased from Hubei Xinyegang Special Materials Co., Ltd.; the silicon-rich material is purchased from waste glass bottles and recycled and ground in-house, and its main component is SiO2; the alkali-activated material is steel slag from Hebei Yanshan Iron and Steel Group, and its specific composition is shown in Table 2.

[0030] Table 2 Steel slag composition

[0031] Steel slag composition CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> <![CDATA[TiO2]]> <![CDATA[SO3]]> Content / wt% 41.29 11.44 4.85 28.16 1.0 0.84

[0032] Example 1

[0033] A method for preparing high-strength unburned ceramsite using phosphogypsum and coal gangue comprises the following steps:

[0034] Step 1: Select phosphogypsum cementitious materials (phosphogypsum, ground mineral powder, silicon-rich materials (SiO2 content greater than 80wt%), steel slag, and coal gangue raw materials, dry and grind them, and then pass them through a 120-mesh sieve. The sieve residue is used as the main raw material for standby use;

[0035] Step 2: 30 parts of phosphogypsum raw materials (phosphogypsum, ground mineral powder, silicon-rich material (SiO2 content greater than 80wt%), and steel slag in a mass ratio of 4.5:2.5:2:1) and 70 parts of coal gangue powder are mixed evenly, and an appropriate amount of distilled water is added while stirring until a viscous mud mass is formed to obtain a mixture containing a spherical core;

[0036] Step 3: Transfer the mixture in step 2 to a pelletizing device, adjust and prepare the amount of water for pelletizing, and screen the pellets to select wet raw pellets with a diameter of 10 to 20 mm;

[0037] Step 4: aging the wet raw balls in step 3;

[0038] Step 5: Dry and dehydrate the aged balls in step 4 to obtain dry raw balls.

[0039] Step 6: Spread the raw and dry ceramsite evenly and naturally cure it for 7 days to obtain the formed unfired ceramsite product.

[0040] The bulk density and cylinder pressure strength tests of the ceramsite prepared in this embodiment were carried out. According to the relevant regulations of GB / T17431.1-2010 "Lightweight aggregates and their test methods", the density of the ceramsite was measured to be 932.5 kg / m 3 The average cylinder pressure strength is 2.9MPa and the 1h water absorption rate is 1.7%.

[0041] Example 2

[0042] The preparation method of Example 2 is the same as that of Example 1, except that the ratio of the phosphogypsum raw material (phosphogypsum, ground mineral powder, silicon-rich material (SiO2 content greater than 80wt%), and steel slag mass ratio = 4.5:2.5:2:1) and the coal gangue powder is different. In Example 2, the phosphogypsum raw material is 20 parts and the coal gangue powder is 80 parts.

[0043] The bulk density and cylinder pressure strength tests of the ceramsite prepared in this embodiment were performed. According to the relevant regulations of GB / T17431.1-2010 "Light Aggregates and Their Test Methods", the density of the ceramsite was measured to be 825.6 kg / m3, the average cylinder pressure strength was 2.5 MPa, and the 1h water absorption rate was 3.1%.

[0044] Example 3

[0045] The raw material ratio of Example 3 is consistent with that of Example 2, except that steam curing is added during the aging treatment in step 4.

[0046] The bulk density and cylinder pressure strength tests of the ceramsite prepared in this embodiment were carried out. According to the relevant regulations of GB / T17431.1-2010 "Lightweight aggregates and their test methods", the density of the ceramsite was measured to be 1100.2 kg / m 3 The average cylinder pressure strength is 3.2MPa and the 1h water absorption rate is 1.5%.

[0047] Table 3 shows the performance parameters of the ceramsite obtained in various embodiments and comparative examples of the present invention. Some performance parameters of the ceramsite were measured with reference to GB / T1731.2-2010 "Lightweight Aggregates and Their Test Methods", Part II: Lightweight Aggregate Test Methods, and the results are shown in Table 3.

[0048] Table 3 Performance comparison of unfired ceramsite

[0049]

[0050] In Table 3, Comparative Example 1 is the patent "A kind of unburned ceramsite and its preparation method" (CN 115321931 A), and Comparative Example 2 is the patent "A kind of unburned ceramsite based on solidified sludge from steel slag desulfurization byproduct and its preparation method" (CN113173748A). As shown in Table 3, the cylinder pressure strength of Examples 1, 2, and 3 is all above 3.0 MPa, the 24h water absorption rate is all above 15%, and the average bulk density is between 800-1200 kg / m 3 It meets the performance requirements of unfired ceramsite in GB / T17321.2.

[0051] The above descriptions are only some embodiments of the present invention and are not intended to limit the present invention in any form or substance. It should be noted that a person skilled in the art may make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be considered as within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength unburned ceramsite using phosphogypsum and coal gangue, characterized in that: The following steps are involved: Step 1: preparing phosphogypsum cementitious material powder using phosphogypsum, mineral powder, silicon-rich material with SiO2 content greater than 80wt% and alkali-activated material as raw materials, drying and grinding the phosphogypsum cementitious material powder and coal gangue, and sieving the sieved powder; Step 2: Evenly mix 20-30 parts of the phosphogypsum gel material powder obtained by sieving in step 1 and 70-80 parts of coal gangue powder, and add distilled water while stirring until a sticky mud mass is formed to obtain a mixture containing a spherical core; Step 3: Transfer the mixture obtained in step 2 to a pelletizing device, adjust and prepare the amount of water for pelletizing, and screen the pellets to select wet raw pellets with a diameter of 10 to 20 mm; Step 4: The wet raw material balls obtained in step 3 are aged and dried in sequence to obtain dry raw material balls, and the dry raw material balls are evenly laid and naturally cured to obtain a formed unfired ceramsite product; The alkali-activated material in step 1 is steel slag, the CaSO4 content in the phosphogypsum is greater than 70wt%, and the CaO content in the steel slag is greater than 85wt%; The mass ratio of the phosphogypsum, ground mineral powder, silicon-rich material with SiO2 content greater than 80wt% and steel slag is 2.5-4.5:2.5:2:1; the water-cement ratio of the phosphogypsum cementitious material powder is 0.3-0.

8.

2. The method for preparing high-strength unburned ceramsite using phosphogypsum and coal gangue as claimed in claim 1, wherein: The grinding time in step 1 is 20 to 40 minutes; the drying temperature is 100 to 110° C. and the drying time is 1 to 2 hours; and the screening is performed through a 100 to 150 mesh sieve.

3. The method for preparing high-strength unburned ceramsite using phosphogypsum and coal gangue as claimed in claim 1, characterized in that: The water content of the pellets in step 3 is 10-20 wt%.

4. The method for preparing high-strength unburned ceramsite using phosphogypsum and coal gangue as claimed in claim 1, wherein: The drying and dehydration temperature in step 4 is below 70° C. and the drying and dehydration time is 3 to 5 hours.

5. The method for preparing high-strength unburned ceramsite using phosphogypsum and coal gangue as claimed in claim 1, characterized in that: The natural curing time in step 4 is 6 to 8 days.

6. The method for preparing high-strength unburned ceramsite using phosphogypsum and coal gangue as claimed in claim 1, characterized in that: The unfired ceramsite product obtained in step 4 has a cylinder pressure strength of 1-6 MPa and a density of 800-1200 kg / m 3 , water absorption rate is less than 10wt%.

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