Ardealite harmless treatment method and preparation method of harmless ardealite sidewalk brick

Abstract

The invention discloses a phosphogypsum harmless treatment method and a preparation method of a harmless phosphogypsum sidewalk brick, and belongs to the technical field of phosphogypsum treatment. The harmless treatment method for the phosphogypsum comprises the following steps: crushing, grinding and refining the phosphogypsum to obtain phosphogypsum powder; mixing quick lime and a dispersing agent to obtain an auxiliary material; mixing the ardealite powder and auxiliary materials, and carrying out aging reaction to obtain a premix; and adding a fixing agent into the premix, and carrying out an aging reaction to obtain the harmless phosphogypsum. The invention also discloses a preparation method of the harmless phosphogypsum sidewalk brick. According to the method, harmless stockpiling and safe utilization of the phosphogypsum can be achieved, high value-added output of the phosphogypsum is achieved, a solid waste absorption approach is provided for phosphorus chemical enterprises, and sustainable development of the industry is promoted.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of phosphogypsum treatment, and particularly relates to a harmless treatment method of phosphogypsum and a preparation method of a harmless phosphogypsum sidewalk brick. BACKGROUND

[0002] Phosphogypsum is a large industrial solid waste produced in the production process of wet-process phosphoric acid, and its main component is calcium sulfate dihydrate (CaSO4·2H2O), and it also contains harmful substances such as phosphorus, fluorine, organic matter and heavy metals. These harmful substances make phosphogypsum have the physical and chemical characteristics of strong acidity and high salinity, and can continuously release toxic substances through leaching in long-term storage, causing problems such as soil acidification, heavy metal enrichment and excessive fluorine in groundwater around the storage yard, and causing the risk of ecological chain pollution.

[0003] At present, in the field of building materials, the main method for utilizing phosphogypsum is to prepare building gypsum powder by calcination or to use it as a cement retarder. However, in the process of preparing building gypsum powder, there are problems of high energy consumption in high-temperature treatment and easy secondary pollution, and the product is limited to indoor non-load-bearing structures due to low strength and poor water resistance. When used as a cement retarder, excessive phosphorus and fluorine can interfere with the cement hydration process, reduce the 28-day strength by more than 10%, and limit the amount of mixing. In the field of agriculture, although phosphogypsum can supplement calcium and sulfur nutrients for soil improvement, the high fluorine and heavy metal risks make it difficult to pass safety assessment, and there are few practical application cases.

[0004] However, existing outdoor harmless treatment methods mainly use simple water washing or lime neutralization, which can only achieve partial migration of impurities and cannot completely solidify heavy metals. When used for high-value-added applications, there are risks of harmful substance release, insufficient product durability and weak cost competitiveness, and it has not been able to achieve large-scale breakthrough.

[0005] Therefore, developing efficient and low-cost harmless treatment technology and building a high-value-added product system based on phosphogypsum have become the key path to solving the problem of phosphogypsum. SUMMARY

[0006] The problem to be solved by the present application is to provide a harmless treatment method of phosphogypsum and a preparation method of a harmless phosphogypsum sidewalk brick, which can realize harmless storage and safe utilization of phosphogypsum, and realize high-value-added output of phosphogypsum.

[0007] To solve the technical problem, a harmless treatment method of phosphogypsum is provided, which comprises the following steps: (1) crushing and grinding the phosphogypsum to obtain phosphogypsum powder; (2) mixing the quicklime and the dispersant to obtain an auxiliary material; (3) mixing the phosphogypsum powder and the auxiliary material and performing aging reaction to obtain a premix; (4) Add a fixative to the premix and carry out an aging reaction to obtain harmless phosphogypsum.

[0008] The beneficial effects of the above-mentioned technical solution in this invention are as follows: Firstly, this invention reduces the particle size of phosphogypsum and increases its specific surface area, promoting full contact between subsequent chemical reagents and harmful substances, thus improving reaction efficiency. Simultaneously, it disrupts the layered structure of phosphogypsum crystals, releasing the soluble phosphorus, fluorine, and organic matter encapsulated within. Then, by mixing quicklime and a dispersant, the main purpose of adding the dispersant in this invention is to reduce the encapsulation effect of quicklime. In the harmless treatment of phosphogypsum, the role of quicklime is to provide calcium... 2+ With free fluorine (F - ), phosphorus (PO4) 3- The reaction produces stable precipitates such as CaF2 and Ca3(PO4)2. If the coating effect of quicklime is severe, it will lead to a decrease in the utilization rate of quicklime, incomplete removal of fluorine and phosphorus, and the phosphogypsum will still exceed the standard after treatment. If the amount of quicklime added is increased, the treatment cost will increase and the pH will exceed the standard. In this invention, the dispersant is used as an auxiliary material for quicklime. It is added to the quicklime in advance and mixed thoroughly. It can form a colloidal protective film on the surface of quicklime particles, reduce the surface coating caused by the rapid crystallization of Ca(OH)2, and improve the contact efficiency between quicklime and other reactants, such as fluorine and phosphorus in phosphogypsum. The phosphogypsum powder and auxiliary materials are mixed and aged to allow the quicklime to react fully with impurities and form a stable mineral phase. Then, a fixative is added to further stabilize the incompletely fixed heavy metals, fluorine and other harmful substances. After the harmless treatment, the leaching toxicity of harmful substances in the phosphogypsum is significantly reduced, blocking the pollution of soil and groundwater by phosphorus, fluorine and heavy metals through leaching from the source, and solving the ecological damage problem caused by traditional stockpiling methods.

[0009] Preferably, the particle size of the phosphogypsum powder is 200 mesh.

[0010] Preferably, the phosphogypsum powder is further treated as follows before being mixed with the excipients: the chemical oxygen demand, heavy metal, total phosphorus and fluoride content of the phosphogypsum powder are adjusted by water washing and air flotation processes, and the pH is adjusted to 8-9 and / or a heavy metal fixative is added to adjust the heavy metal content of the phosphogypsum powder.

[0011] More preferably, the heavy metal fixative is sodium sulfide.

[0012] Preferably, step (3) further includes the following steps: mixing phosphogypsum powder and activator and aging reaction to obtain a mixture; mixing the mixture and excipients and aging reaction to obtain a premix.

[0013] The beneficial effects of the above technical solution adopted in this invention are as follows: The main purpose of adding the activator in this invention is to better separate and precipitate phosphorus and fluorine in phosphogypsum.

[0014] More preferably, the activator is an inorganic acid or a salt of a strong acid and a weak base; the mass ratio of phosphogypsum powder to activator is 100:0.1~0.5; and the aging reaction time is 1~5 days.

[0015] More preferably, the activator is dilute sulfuric acid, calcium chloride, or calcium nitrate.

[0016] More preferably, the quicklime has a calcium oxide content of ≥80%; the dispersant is sodium silicate or calcium chloride; and the fixative is pickled aluminum mud, polyaluminum chloride, or polyaluminum sulfate.

[0017] The beneficial effects of the above technical solution adopted in this invention are as follows: Acid-washed aluminum sludge is a solid waste generated by the reaction of acid with aluminum / alumina to produce aluminum salts (such as AlCl3, Al2(SO4)3) in the strong acid cleaning process of aluminum materials or aluminum products, and then neutralized and precipitated. Its main components are aluminum hydroxide and unreacted aluminum salts.

[0018] More preferably, the mass ratio of phosphogypsum powder, quicklime, dispersant and fixative is 100:0.8~4:0.01~0.1:0.5~6.

[0019] More preferably, the aging reaction time in step (3) is 2 to 7 days; the aging reaction time in step (4) is 2 to 7 days.

[0020] The present invention also provides a method for harmless phosphogypsum prepared by a method for harmless treatment of phosphogypsum.

[0021] This invention also provides a method for preparing harmless phosphogypsum sidewalk bricks using harmless phosphogypsum, comprising the following steps: S1. Prepare harmless phosphogypsum into a slurry to obtain harmless phosphogypsum slurry; S2. The harmless phosphogypsum slurry is injected into the mold and pre-pressed into shape. After curing, the harmless phosphogypsum sidewalk brick is obtained.

[0022] Preferably, the water content of the harmless phosphogypsum slurry in S1 is 55-70%; the pre-compression molding in S2 includes the following steps: holding pressure at 500-1500t, 50-150MPa and vacuum environment for 5-10min; the curing time is 6-8d.

[0023] The beneficial effects of the above-mentioned technical solution adopted in this invention are as follows: In this invention, the phosphogypsum slurry particles are highly densified by the synergistic effect of high pressure and vacuum, forming a dense mineral network structure, which further improves the mechanical properties of harmless phosphogypsum sidewalk bricks.

[0024] The present invention has the following beneficial effects: (1) The method of the present invention can achieve the harmless treatment of phosphogypsum in a simple and fast manner. The soluble phosphorus / fluorine is initially released by crushing and grinding, and then the pH is adjusted by quicklime to promote the precipitation of heavy metal hydroxides. The fixative is used for secondary aging to form a stable phase, thereby removing harmful substances. The pH value, total phosphorus, fluoride, COD, ammonia nitrogen and heavy metals of the phosphogypsum after harmless treatment meet the national standards. It completely blocks the risk of soil acidification, groundwater fluoride exceeding the standard and ecological chain pollution caused by phosphogypsum storage. The harmless treatment effect is significant.

[0025] (2) The harmless treatment of phosphogypsum in this invention can be directly used to produce sidewalk bricks. The sidewalk bricks produced meet the national product standards after inspection. The sidewalk bricks have high strength and good durability, and can replace traditional concrete bricks, promote the development of the green building materials industry, provide solid waste disposal channels for phosphate chemical enterprises, and promote the sustainable development of the industry. Detailed Implementation

[0026] The principles and features of the present invention are described below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0027] Example 1 A method for harmlessly treating phosphogypsum includes the following steps: (1) The phosphogypsum was crushed and ground into fine powder using a pulverizer to obtain phosphogypsum powder with a particle size of 200 mesh; (2) Mix 0.9g of quicklime and 0.01g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and excipients and age for 2 days to obtain a premix; (4) Add 0.7g of polyaluminum chloride to the premix and allow it to age for 5 days to obtain harmless phosphogypsum.

[0028] Example 2 A method for harmlessly treating phosphogypsum includes the following steps: (1) The phosphogypsum was crushed and ground into fine powder using a pulverizer to obtain phosphogypsum powder with a particle size of 200 mesh; (2) Mix 0.9g of quicklime and 0.01g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and excipients and age for 2 days to obtain a premix; (4) Add 1g of polyaluminum chloride to the premix and allow it to age for 5 days to obtain harmless phosphogypsum.

[0029] Example 3 A method for harmlessly treating phosphogypsum includes the following steps: (1) The phosphogypsum was crushed and ground into fine powder using a pulverizer to obtain phosphogypsum powder with a particle size of 200 mesh; (2) Mix 1.3g of quicklime and 0.01g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and excipients and age for 2 days to obtain a premix; (4) Add 4g of polyaluminum chloride to the premix and allow it to age for 5 days to obtain harmless phosphogypsum.

[0030] Example 4 A method for harmlessly treating phosphogypsum includes the following steps: (1) The phosphogypsum was crushed and ground into fine powder using a pulverizer to obtain phosphogypsum powder with a particle size of 200 mesh; (2) Mix 1.7g of quicklime and 0.02g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and 0.1g of calcium chloride and age for 2 days to obtain a mixture; (4) Mix the mixture and excipients and age them for 2 days to obtain a premix; (5) Add 1.5g of polyaluminum chloride to the premix and allow it to age for 5 days to obtain harmless phosphogypsum.

[0031] Example 5 A method for harmlessly treating phosphogypsum includes the following steps: (1) The phosphogypsum was crushed and ground into fine powder using a pulverizer to obtain phosphogypsum powder with a particle size of 200 mesh; (2) Mix 1.8g of quicklime and 0.02g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and 0.2g of calcium chloride and age for 2 days to obtain a mixture; (4) Mix the mixture and excipients and age them for 2 days to obtain a premix; (5) Add 1.7g of polyaluminum chloride to the premix and allow it to age for 5 days to obtain harmless phosphogypsum.

[0032] Example 6 A method for harmlessly treating phosphogypsum includes the following steps: (1) The phosphogypsum was crushed and ground into fine powder using a pulverizer to obtain phosphogypsum powder with a particle size of 200 mesh; (2) Mix 2g of quicklime and 0.02g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and 0.3g of calcium chloride and age for 2 days to obtain a mixture; (4) Mix the mixture and excipients and age them for 2 days to obtain a premix; (5) Add 4.7g of polyaluminum chloride to the premix and allow it to age for 5 days to obtain harmless phosphogypsum.

[0033] Example 7 A method for harmlessly treating phosphogypsum includes the following steps: (1) The phosphogypsum was crushed and ground into fine powder using a pulverizer to obtain phosphogypsum powder with a particle size of 200 mesh; (2) Mix 2.2g of quicklime and 0.03g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and 0.3g of calcium chloride and age for 2 days to obtain a mixture; (4) Mix the mixture and excipients and age them for 2 days to obtain a premix; (5) Add 2.7g of polyaluminum chloride to the premix and allow it to age for 5 days to obtain harmless phosphogypsum.

[0034] Example 8 A method for harmlessly treating phosphogypsum includes the following steps: (1) The phosphogypsum was crushed and ground into fine powder using a pulverizer to obtain phosphogypsum powder with a particle size of 200 mesh; (2) Mix 3g of quicklime and 0.08g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and 0.5g of calcium chloride and age for 2 days to obtain a mixture; (4) Mix the mixture and excipients and age them for 2 days to obtain a premix; (5) Add 3g of polyaluminum chloride to the premix and allow it to age for 5 days to obtain harmless phosphogypsum.

[0035] Example 9 A method for harmlessly treating phosphogypsum includes the following steps: (1) The phosphogypsum was crushed and ground into fine powder using a pulverizer to obtain phosphogypsum powder with a particle size of 200 mesh; (2) Mix 3.6g of quicklime and 0.1g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and 0.5g of calcium chloride and age for 2 days to obtain a mixture; (4) Mix the mixture and excipients and age them for 2 days to obtain a premix; (5) Add 5g of polyaluminum chloride to the premix and allow it to age for 5 days to obtain harmless phosphogypsum.

[0036] Example 10 A method for harmlessly treating phosphogypsum includes the following steps: (1) Phosphogypsum is crushed and ground into fine powder by a pulverizer, washed with water and the pH is adjusted to 8.5~9, and ammonia nitrogen is removed by air flotation process to obtain phosphogypsum powder with a particle size of 200 mesh. (2) Mix 2g of quicklime and 0.03g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and 0.3g of calcium chloride and age for 2 days to obtain a mixture; (4) Mix the mixture and excipients and age them for 2 days to obtain a premix; (5) Add 1.7g of polyaluminum chloride to the premix and allow it to age for 7 days to obtain harmless phosphogypsum.

[0037] Example 11 A method for harmlessly treating phosphogypsum includes the following steps: (1) Phosphogypsum was crushed and ground into fine powder using a pulverizer, and the chemical oxygen demand was reduced by washing with water to obtain phosphogypsum powder with a particle size of 200 mesh. (2) Mix 1.8g of quicklime and 0.02g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and 0.3g of calcium chloride and age for 2 days to obtain a mixture; (4) Mix the mixture and excipients and age them for 2 days to obtain a premix; (5) Add 1.7g of polyaluminum chloride to the premix and allow it to age for 7 days to obtain harmless phosphogypsum.

[0038] Example 12 A method for harmlessly treating phosphogypsum includes the following steps: (1) Phosphogypsum was crushed and ground into fine powder using a pulverizer, and sodium sulfide was added to adjust the heavy metal content of phosphogypsum to obtain phosphogypsum powder with a particle size of 200 mesh. (2) Mix 1.8g of quicklime and 0.02g of sodium silicate to obtain the auxiliary material; (3) Mix 100g of phosphogypsum powder and 0.3g of calcium chloride and age for 2 days to obtain a mixture; (4) Mix the mixture and excipients and age them for 2 days to obtain a premix; (5) Add 1.7g of polyaluminum chloride to the premix and allow it to age for 7 days to obtain harmless phosphogypsum.

[0039] Example 13 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 1 is prepared into a slurry, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0040] Example 14 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 2 is prepared into a slurry, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0041] Example 15 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 3 is prepared into a slurry, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0042] Example 16 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 4 is prepared into a slurry, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0043] Example 17 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 5 is prepared into a slurry, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0044] Example 18 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 6 is prepared into a slurry, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0045] Example 19 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 7 is slurried, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0046] Example 20 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 8 is prepared into a slurry, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0047] Example 21 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 9 is prepared into a slurry, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0048] Example 22 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 10 is prepared into a slurry, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0049] Example 23 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 11 is prepared into a slurry, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0050] Example 24 The preparation method of harmless phosphogypsum sidewalk bricks includes the following steps: S1. The harmless phosphogypsum treated by the method of Example 12 is prepared into a slurry, and its moisture content is adjusted to 60% to obtain a harmless phosphogypsum slurry. S2. Inject the harmless phosphogypsum slurry into a 28cm*28cm mold, press it in a vacuum negative pressure environment of 500t, 50MPa for 8 minutes to form the inner blank of the sidewalk brick, demold it and put it into storage, and cure it for 7 days to obtain the harmless phosphogypsum sidewalk brick.

[0051] Comparative Example 1 A method for harmlessly treating phosphogypsum includes the following steps: (1) The phosphogypsum was crushed and ground into fine powder using a pulverizer to obtain phosphogypsum powder with a particle size of 200 mesh; (2) Mix 100g of phosphogypsum powder and 0.9g of quicklime and let them age for 2 days to obtain a premix; (3) Add 0.7g of polyaluminum chloride to the premix and allow it to age for 5 days to obtain harmless phosphogypsum.

[0052] Comparative Example 2 A method for harmlessly treating phosphogypsum includes the following steps: (1) The phosphogypsum was crushed and ground into fine powder using a pulverizer to obtain phosphogypsum powder with a particle size of 200 mesh; (2) Mix 100g of phosphogypsum powder and 3.5g of quicklime and let them age for 2 days to obtain a premix; (3) Add 0.7g of polyaluminum chloride to the premix and allow it to age for 5 days to obtain harmless phosphogypsum.

[0053] Experimental Example 1 Sampling and preparation of phosphogypsum leachate were carried out using the method in "Horizontal Oscillation Method for Leaching Toxicity of Solid Waste" (HJ 557-2010). The pH, total phosphorus, fluoride, COD, ammonia nitrogen, and heavy metals of the phosphogypsum before treatment and the harmless phosphogypsum after treatment in Examples 1-12 were tested to see if they met the relevant requirements of "Technical Specification for Pollution Control of Utilization and Harmless Storage of Phosphogypsum" (HJ 1415-2025) and "Integrated Wastewater Discharge Standard" (GB8978-1996). The results are shown in Table 1.

[0054] Table 1. Indicators of phosphogypsum before and after harmless treatment

[0055] As shown in Table 1, this invention achieves the initial release of soluble phosphorus / fluoride through crushing and grinding, followed by pH adjustment with quicklime to promote the precipitation of heavy metal hydroxides, and secondary aging with a fixative to form a stable phase, thus realizing the synergistic and efficient removal of total phosphorus, fluoride, and complex pollutants from phosphogypsum. The pH, total phosphorus, fluoride, COD, ammonia nitrogen, and heavy metal indicators of the harmless phosphogypsum treated by the method of this invention all meet the relevant requirements of the "Technical Specification for Pollution Control of Utilization and Harmless Storage of Phosphogypsum" (HJ 1415-2025) and the "Integrated Wastewater Discharge Standard" (GB8978-1996). Without the addition of a dispersant, the quicklime encapsulation effect is severe, and even without the addition of excessive quicklime, the total phosphorus and fluoride in the treated phosphogypsum both exceed the standard significantly (Comparative Example 1). To achieve the required fluoride level, excessive quicklime needs to be added (Comparative Example 2), but the final phosphogypsum will have a pH exceeding the standard, failing to simultaneously meet the standard requirements.

[0056] Experimental Example 2 The performance of the harmless phosphogypsum sidewalk bricks prepared in Examples 13-24 was tested according to the "Concrete Pavement Bricks" (GB / T 28635-2012), and the results are shown in Table 2.

[0057] Table 2. Test results of mechanical properties of harmless phosphogypsum sidewalk bricks

[0058] As can be seen from Table 2, the harmless phosphogypsum sidewalk bricks prepared by this invention have better compressive strength, flexural strength, wear resistance and anti-slip properties than the standard requirements. The resulting harmless phosphogypsum sidewalk bricks have high strength and good durability, and can replace traditional concrete bricks, realizing the reuse of phosphogypsum.

[0059] The present invention has been described according to the above embodiments. It should be understood that the above embodiments do not limit the present invention in any way. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the scope of the present invention.

Claims

1. A method for harmlessly treating phosphogypsum, characterized in that, Includes the following steps: (1) The phosphogypsum is crushed and ground into fine powder to obtain phosphogypsum powder; (2) Mix quicklime and dispersant to obtain auxiliary material; (3) Mix the phosphogypsum powder and excipients and carry out an aging reaction to obtain a premix; (4) Add a fixative to the premix and carry out an aging reaction to obtain harmless phosphogypsum.

2. The method for harmless treatment of phosphogypsum as described in claim 1, characterized in that, Before being mixed with the excipients, the phosphogypsum powder undergoes the following treatment: the chemical oxygen demand, heavy metal, total phosphorus and fluoride content of the phosphogypsum powder are adjusted by water washing and air flotation processes, and the pH is adjusted to 8-9 and / or a heavy metal fixative is added to adjust the heavy metal content of the phosphogypsum powder.

3. The method for harmless treatment of phosphogypsum as described in claim 1, characterized in that, Step (3) further includes the following steps: mixing phosphogypsum powder and activator and aging reaction to obtain a mixture; mixing the mixture and excipients and aging reaction to obtain a premix.

4. The method for harmless treatment of phosphogypsum as described in claim 3, characterized in that, The activator is an inorganic acid or a salt of a strong acid and a weak base; the mass ratio of the phosphogypsum powder to the activator is 100:0.1~0.5; the aging reaction time is 1~5 days.

5. The method for harmlessly treating phosphogypsum as described in any one of claims 1 to 3, characterized in that, The quicklime has a calcium oxide content of ≥80%; the dispersant is sodium silicate or calcium chloride; and the fixative is acid-washed aluminum sludge, polyaluminum chloride, or polyaluminum sulfate.

6. The method for harmless treatment of phosphogypsum as described in claim 5, characterized in that, The mass ratio of the phosphogypsum powder, quicklime, dispersant, and fixative is 100:0.8~4:0.01~0.1:0.5~6.

7. The method for harmlessly treating phosphogypsum as described in any one of claims 1 to 3, characterized in that, The aging reaction time in step (3) is 2 to 7 days; the aging reaction time in step (4) is 2 to 7 days.

8. Harmless phosphogypsum prepared by the harmless treatment method of phosphogypsum according to any one of claims 1 to 7.

9. The method for preparing harmless phosphogypsum sidewalk bricks according to claim 8, characterized in that, Includes the following steps: S1. Prepare harmless phosphogypsum into a slurry to obtain harmless phosphogypsum slurry; S2. The harmless phosphogypsum slurry is injected into the mold and pre-pressed into shape. After curing, the harmless phosphogypsum sidewalk brick is obtained.

10. The method for preparing sidewalk bricks by harmlessly processing phosphogypsum as described in claim 9, characterized in that, The water content of the harmless phosphogypsum slurry in S1 is 55-70%; the pre-compression molding in S2 includes the following steps: The pressure is maintained at 500~1500t, 50~150MPa and in a vacuum environment for 5~10min; the curing time is 6~8d.

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