A modified phosphogypsum artificial aggregate production process

Abstract

This invention provides a process for producing modified phosphogypsum artificial aggregate. Quicklime is hydrated and then phosphogypsum is added, followed by a modifier. After thorough mixing, the mixture is allowed to air dry naturally. Once dried, it is ground in a ball mill to obtain modified phosphogypsum. The modified phosphogypsum and mineral cement are then used as raw materials to granulate phosphogypsum balls. These balls are cured in water for 14-28 days and then crushed to obtain artificial aggregate. Finally, the artificial aggregate is sieved to obtain artificial aggregates of different particle sizes. The modifier in this invention includes a phosphate chelating agent and a phosphate precipitant. This not only does not affect the formation of gel and ettringite by calcium ions during the subsequent phosphogypsum hydration process but also better solidifies phosphate ions, avoiding the slow dissolution of calcium phosphate and pollution during use, thus achieving a better green and environmentally friendly effect.

Description

Technical Field

[0001] This invention relates to the field of phosphogypsum artificial aggregate technology, and in particular to a production process for modified phosphogypsum artificial aggregate. Background Technology

[0002] Phosphogypsum is a solid waste generated in the wet-process phosphoric acid production process. Producing one ton of phosphoric acid yields approximately five tons of phosphogypsum, whose main component is calcium sulfate dihydrate. The composition of phosphogypsum is complex, containing not only calcium sulfate but also incompletely decomposed phosphate rock, residual phosphoric acid, fluorides, acid-insoluble substances, and organic matter. It typically appears as a white or dark gray, moist, fine powder. The presence of fluorine and organic matter has the greatest impact on the resource utilization of phosphogypsum. The indiscriminate dumping and accumulation of phosphogypsum severely damages the ecological environment, polluting groundwater resources and wasting land resources.

[0003] Currently, my country's historical stockpile of phosphogypsum exceeds 500 million tons, with an annual increase of approximately 7,000 tons, and a comprehensive utilization rate of less than 40%. The indiscriminate dumping of phosphogypsum in China restricts the sustainable development of industries such as wet-process phosphoric acid and phosphate fertilizers; therefore, the treatment and recycling of phosphogypsum has become an urgent issue. Phosphogypsum is mainly used in agriculture, industry, and construction. Due to its complex composition and structure, which differs from natural gypsum, appropriate utilization methods must be selected based on its characteristics.

[0004] Making phosphogypsum into phosphogypsum-based artificial aggregate is a new method for the comprehensive utilization of phosphogypsum. The pelletized artificial aggregate can be widely used in highway subgrade materials, C30-C60 grade concrete, and other products. However, current methods of using phosphogypsum as a raw material to manufacture artificial aggregate still have certain problems. Current technologies generally use neutralization and precipitation to remove residual phosphoric acid or other soluble phosphates from the phosphogypsum. For example, quicklime is added to form calcium phosphate precipitate. However, during subsequent use, the prepared phosphogypsum artificial aggregate, when exposed to open air and soaked in water, creates a weakly acidic environment, causing the calcium phosphate to slowly dissolve and continue to release phosphate ions, still polluting the surrounding land. Therefore, a more environmentally friendly phosphogypsum-based artificial aggregate is needed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a modified phosphogypsum artificial aggregate production process, which solves the problem that existing phosphogypsum artificial aggregates, when immersed in water in open-air environments, form a weakly acidic environment, causing calcium phosphate to slowly dissolve and release phosphate ions, resulting in pollution of nearby land.

[0006] According to an embodiment of the present invention, a process for producing modified phosphogypsum artificial aggregate includes the following steps:

[0007] (1) Hydrate quicklime and add it to phosphogypsum, then add 1-2% modifier by weight of phosphogypsum, stir thoroughly and let it air dry naturally. After air drying, put it into a ball mill and grind for 2-4 hours to obtain modified phosphogypsum. The amount of quicklime added is 5-8% of the weight of phosphogypsum.

[0008] (2) Using 80-85% by weight of modified phosphogypsum, 8-12% by weight of mineral powder and 6-9% by weight of cement as raw materials, feed them into a granulator for granulation. During the granulation process, add 15-25% by weight of water of the total mass of the raw materials to prepare phosphogypsum balls.

[0009] (3) Soak the phosphogypsum balls in water for 14-28 days. After curing, let them dry naturally. Then put them into a crushing machine to obtain artificial aggregates. Finally, obtain artificial aggregates of different particle sizes by screening.

[0010] Preferably, the phosphogypsum has been stored for more than one year and has a pH value greater than 3.0, and the moisture content of the phosphogypsum is ≤15%.

[0011] Preferably, the mineral powder is S95 grade mineral powder.

[0012] Preferably, the cement is PO42.5 silicate cement.

[0013] Preferably, the modifier includes a phosphate chelating agent and a phosphate precipitating agent.

[0014] Preferably, the phosphate chelating agent includes one of EDTA, BAPTA, or carboxymethyl chitosan.

[0015] Preferably, the phosphoric acid precipitant includes ammonium permolybdate or ferric sulfate.

[0016] Preferably, the artificial aggregate obtained after screening includes four grades with particle sizes of 0-4.75mm, 4.75-9.5mm, 9.5-19mm, and 19-31.5mm.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] This invention optimizes traditional phosphogypsum modification methods. After neutralization and precipitation with quicklime, a modifier is added, including a phosphate chelating agent and a phosphate precipitant. The chelating agent has a stronger ability to bind calcium ions than phosphate, thus forming a chelate with the calcium ions and releasing the phosphate ions into the solution. The phosphate precipitant then reacts with the phosphate ions to form an acid-insoluble precipitate. This method does not affect the formation of gel and ettringite by calcium ions during the subsequent phosphogypsum hydration process, while better solidifying the phosphate ions and avoiding pollution caused by the slow dissolution of calcium phosphate during use, resulting in better environmental protection. Simultaneously, the formed calcium ion chelate also acts as a microsphere. During hydration, the pre-formed spheres better encapsulate the gel and ettringite, forming a hydraulic material, thereby improving the efficiency of the hydration process and reducing the time required for immersion curing. Detailed Implementation

[0019] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Example 1:

[0021] In this embodiment, the phosphogypsum was stored for 1.5 years, with a pH of 4.0 and a moisture content of 13%. The mineral powder was S95 grade. The cement was PO42.5 silicate cement. The modifiers included phosphate chelating agents and phosphate precipitants. The phosphate chelating agent included one of EDTA, BAPTA, or carboxymethyl chitosan; the phosphate precipitant included ammonium permolybdate or ferric sulfate.

[0022] This embodiment describes a process for producing modified phosphogypsum artificial aggregate, which includes the following steps:

[0023] (1) Hydrate quicklime and add it to phosphogypsum, then add 1% of the modifier by weight of phosphogypsum, stir thoroughly and let it air dry naturally. After air drying, put it into a ball mill and grind for 2 hours to obtain modified phosphogypsum. The amount of quicklime added is 5% of the weight of phosphogypsum.

[0024] (2) Using 80% by weight of modified phosphogypsum, 11% by weight of mineral powder and 9% by weight of cement as raw materials, granulation is carried out in a granulator. During the granulation process, 15% by weight of water is added to the total mass of the raw materials to prepare phosphogypsum balls.

[0025] (3) Soak the phosphogypsum balls in water for 14 days. After curing, let them dry naturally. Then put them into a crushing machine to obtain artificial aggregate. Finally, obtain artificial aggregates of different particle sizes by screening. The artificial aggregates obtained after screening include four grades with particle sizes of 0-4.75mm, 4.75-9.5mm, 9.5-19mm and 19-31.5mm respectively.

[0026] Example 2:

[0027] In this embodiment, the phosphogypsum was stored for 1.5 years, with a pH of 4.0 and a moisture content of 13%. The mineral powder was S95 grade. The cement was PO42.5 silicate cement. The modifiers included phosphate chelating agents and phosphate precipitants. The phosphate chelating agent included one of EDTA, BAPTA, or carboxymethyl chitosan; the phosphate precipitant included ammonium permolybdate or ferric sulfate.

[0028] This embodiment describes a process for producing modified phosphogypsum artificial aggregate, which includes the following steps:

[0029] (1) After hydrating quicklime, add phosphogypsum, then add 1.5% modifier by weight of phosphogypsum, stir thoroughly and let it air dry naturally. After air drying, put it into a ball mill and grind for 3 hours to obtain modified phosphogypsum. The amount of quicklime added is 6.5% of the weight of phosphogypsum.

[0030] (2) Using 82% by weight of modified phosphogypsum, 12% by weight of mineral powder and 6% by weight of cement as raw materials, the raw materials are fed into a granulator for granulation. During the granulation process, water of 20% by weight of the total mass of the raw materials is added to prepare phosphogypsum balls.

[0031] (3) Soak the phosphogypsum balls in water for 21 days. After curing, let them dry naturally. Then put them into a crushing machine to obtain artificial aggregate. Finally, obtain artificial aggregates of different particle sizes by screening. The artificial aggregates obtained after screening include four grades with particle sizes of 0-4.75mm, 4.75-9.5mm, 9.5-19mm and 19-31.5mm respectively.

[0032] Example 3:

[0033] In this embodiment, the phosphogypsum was stored for 1.5 years, with a pH of 4.0 and a moisture content of 13%. The mineral powder was S95 grade. The cement was PO42.5 silicate cement. The modifiers included phosphate chelating agents and phosphate precipitants. The phosphate chelating agent included one of EDTA, BAPTA, or carboxymethyl chitosan; the phosphate precipitant included ammonium permolybdate or ferric sulfate.

[0034] This embodiment describes a process for producing modified phosphogypsum artificial aggregate, which includes the following steps:

[0035] (1) After hydrating quicklime, add phosphogypsum, then add 2% of the modifier by weight of phosphogypsum, stir thoroughly and let it air dry naturally. After air drying, put it into a ball mill and grind for 4 hours to obtain modified phosphogypsum. The amount of quicklime added is 8% of the weight of phosphogypsum.

[0036] (2) Using 85% by weight of modified phosphogypsum, 8% mineral powder and 7% cement as raw materials, they are fed into a granulator for granulation. During the granulation process, 25% by weight of water is added to the total mass of the raw materials to prepare phosphogypsum balls.

[0037] (3) Soak the phosphogypsum balls in water for 28 days. After curing, let them dry naturally. Then put them into a crushing machine to obtain artificial aggregate. Finally, obtain artificial aggregates of different particle sizes by screening. The artificial aggregates obtained after screening include four grades with particle sizes of 0-4.75mm, 4.75-9.5mm, 9.5-19mm and 19-31.5mm respectively.

[0038] Example 4:

[0039] In this embodiment, the phosphogypsum was stored for 1.5 years, with a pH of 4.0 and a moisture content of 13%. The mineral powder was S95 grade. The cement was PO42.5 silicate cement. The modifiers included phosphate chelating agents and phosphate precipitants. The phosphate chelating agent included one of EDTA, BAPTA, or carboxymethyl chitosan; the phosphate precipitant included ammonium permolybdate or ferric sulfate.

[0040] This embodiment describes a process for producing modified phosphogypsum artificial aggregate, which includes the following steps:

[0041] (1) After hydrating quicklime, add phosphogypsum, then add 2% of the modifier by weight of phosphogypsum, stir thoroughly and let it air dry naturally. After air drying, put it into a ball mill and grind for 2 hours to obtain modified phosphogypsum. The amount of quicklime added is 8% of the weight of phosphogypsum.

[0042] (2) Using 84% by weight of modified phosphogypsum, 8% mineral powder and 8% cement as raw materials, they are put into a granulator for granulation. During the granulation process, 25% of the total mass of the raw materials is added to water to prepare phosphogypsum balls.

[0043] (3) Soak the phosphogypsum balls in water for 25 days. After curing, let them dry naturally. Then put them into a crushing machine to obtain artificial aggregate. Finally, obtain artificial aggregates of different particle sizes by screening. The artificial aggregates obtained after screening include four grades with particle sizes of 0-4.75mm, 4.75-9.5mm, 9.5-19mm and 19-31.5mm respectively.

[0044] Example 5:

[0045] In this embodiment, the phosphogypsum was stored for 1.5 years, with a pH of 4.0 and a moisture content of 13%. The mineral powder was S95 grade. The cement was PO42.5 silicate cement. The modifiers included phosphate chelating agents and phosphate precipitants. The phosphate chelating agent included one of EDTA, BAPTA, or carboxymethyl chitosan; the phosphate precipitant included ammonium permolybdate or ferric sulfate.

[0046] This embodiment describes a process for producing modified phosphogypsum artificial aggregate, which includes the following steps:

[0047] (1) After hydrating quicklime, add phosphogypsum, then add 1% of the modifier by weight of phosphogypsum, stir thoroughly and let it air dry naturally. After air drying, put it into a ball mill and grind for 4 hours to obtain modified phosphogypsum. The amount of quicklime added is 5% of the weight of phosphogypsum.

[0048] (2) Using 81% by weight of modified phosphogypsum, 11% by weight of mineral powder and 8% by weight of cement as raw materials, the raw materials are fed into a granulator for granulation. During the granulation process, 22% by weight of water is added to the total mass of the raw materials to prepare phosphogypsum balls.

[0049] (3) Soak the phosphogypsum balls in water for 18 days. After curing, let them dry naturally. Then put them into a crushing machine to obtain artificial aggregate. Finally, obtain artificial aggregates of different particle sizes by screening. The artificial aggregates obtained after screening include four grades with particle sizes of 0-4.75mm, 4.75-9.5mm, 9.5-19mm and 19-31.5mm respectively.

[0050] Example 6:

[0051] In this embodiment, the phosphogypsum was stored for 1.5 years, with a pH of 4.0 and a moisture content of 13%. The mineral powder was S95 grade. The cement was PO42.5 silicate cement. The modifiers included phosphate chelating agents and phosphate precipitants. The phosphate chelating agent included one of EDTA, BAPTA, or carboxymethyl chitosan; the phosphate precipitant included ammonium permolybdate or ferric sulfate.

[0052] This embodiment describes a process for producing modified phosphogypsum artificial aggregate, which includes the following steps:

[0053] (1) After hydrating quicklime, add phosphogypsum, then add 1.8% modifier by weight of phosphogypsum, stir thoroughly and let it air dry naturally. After air drying, put it into a ball mill and grind for 3 hours to obtain modified phosphogypsum. The amount of quicklime added is 7% of the weight of phosphogypsum.

[0054] (2) Using 83% by weight of modified phosphogypsum, 10% mineral powder and 7% cement as raw materials, they are put into a granulator for granulation. During the granulation process, 20% of the total mass of the raw materials is added to water to prepare phosphogypsum balls.

[0055] (3) Soak the phosphogypsum balls in water for 27 days. After curing, let them dry naturally. Then put them into a crushing machine to obtain artificial aggregate. Finally, obtain artificial aggregates of different particle sizes by screening. The artificial aggregates obtained after screening include four grades with particle sizes of 0-4.75mm, 4.75-9.5mm, 9.5-19mm and 19-31.5mm respectively.

[0056] Comparative example:

[0057] In this comparative example, the phosphogypsum was stored for 1.5 years, with a pH of 4.0 and a moisture content of 13%. The mineral powder was S95 grade mineral powder. The cement was PO42.5 silicate cement.

[0058] This embodiment describes a process for producing modified phosphogypsum artificial aggregate, which includes the following steps:

[0059] (1) Hydrate quicklime and add it to phosphogypsum. Stir thoroughly and let it air dry naturally. After air drying, put it into a ball mill and grind for 4 hours to obtain modified phosphogypsum. The amount of quicklime added is 8% of the weight of phosphogypsum.

[0060] (2) Using 85% by weight of modified phosphogypsum, 8% mineral powder and 7% cement as raw materials, they are fed into a granulator for granulation. During the granulation process, 25% by weight of water is added to the total mass of the raw materials to prepare phosphogypsum balls.

[0061] (3) Soak the phosphogypsum balls in water for 28 days. After curing, let them dry naturally. Then put them into a crushing machine to obtain artificial aggregate. Finally, obtain artificial aggregates of different particle sizes by screening. The artificial aggregates obtained after screening include four grades with particle sizes of 0-4.75mm, 4.75-9.5mm, 9.5-19mm and 19-31.5mm respectively.

[0062] 10 kg of each of the products obtained in Examples 1-6 and the comparative example were taken and spread out in a natural environment. After 4 months, samples were taken from each sample. 28 days later, leachate was prepared from the artificial aggregate according to the "Horizontal Oscillation Method for Leaching Toxicity of Solid Waste" (HJ557-2010). The total phosphorus content in the leachate was determined according to the "Determination of Total Phosphorus in Solid Waste - Ammonium Metamolybdate Spectrophotometric Method" (HJ712-2014). The test results are shown in Table 1.

[0063]

[0064] Table 1

[0065] As shown in Table 1, the phosphogypsum artificial aggregate product prepared in this embodiment has a significantly lower phosphate content after long-term storage in a natural environment compared to existing products.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A modified phosphogypsum artificial aggregate production process, characterized by, The method comprises the following steps: (1) adding phosphogypsum after hydration of quicklime, then adding a modifier with a mass of 1-2% of the phosphogypsum, fully stirring and then placing for natural air drying, grinding in a ball mill for 2-4 hours after air drying, and obtaining modified phosphogypsum, wherein the quicklime is added in an amount of 5-8% of the weight of the phosphogypsum; (2) taking 80-85% of the modified phosphogypsum, 8-12% of the mineral powder and 6-9% of the cement by weight as raw materials, feeding into a granulator for granulation, adding 15-25% of the total mass of the raw materials in water during the granulation process, and preparing phosphogypsum balls; (3) soaking the phosphogypsum balls for 14-28 days, placing for natural drying after the soaking, feeding into a crusher to obtain artificial aggregates, and finally screening to obtain artificial aggregates of different particle sizes; the modifier comprises a phosphoric acid chelating agent and a phosphoric acid precipitant; the phosphoric acid chelating agent comprises one of EDTA, BAPTA or carboxymethyl chitosan; the phosphoric acid precipitant comprises ammonium molybdate or iron sulfate.

2. A process for producing modified ardealite artificial aggregates according to claim 1, characterized in that: The phosphogypsum has a storage time of more than 1 year and a pH value greater than 3.0, and the water content of the phosphogypsum is ≤15%.

3. A process for producing modified ardealite artificial aggregates according to claim 1, characterized in that: The mineral powder is S95 grade mineral powder.

4. A process for manufacturing modified ardealite artificial aggregates according to claim 1, characterized in that: The cement is Portland cement of PO42.

5.

5. A process for manufacturing modified ardealite artificial aggregates according to claim 1, characterized in that: The artificial aggregates obtained after the screening comprise four grades with particle sizes of 0-4.75 mm, 4.75-9.5 mm, 9.5-19 mm and 19-31.5 mm, respectively.

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