A method for stabilizing and solidifying phosphogypsum

Abstract

The invention belongs to the technical field of resource utilization of bulk industrial solid wastes, and specifically relates to a method for stabilizing and solidifying phosphogypsum. After adding 5‑10% active binder by dry basis weight, 0.5‑2.0% reinforcing agent, 1‑2% adsorbent and phosphoric acid to the phosphogypsum produced from wet-process phosphoric acid, and adjusting the pH value, the main pollutants dissolved in the mixture meet the Class A emission requirements of the first level standard in GB8978‑1996 Comprehensive Sewage Discharge Standard according to the horizontal oscillation method in HJ557‑2010 Solid Waste Analysis Method, that is, phosphorus content ≤ 0.5 mg / L, fluorine content ≤ 10 mg / L, total arsenic ≤ 0.5 mg / L, and pH 6‑9. The mixture is transported to the site for paving, rolling and coring tests. The 7-day unconfined compressive strength reaches 1.0‑2.0 MPa, and the 28-day unconfined compressive strength reaches 2.5‑6.5 MPa. It can be widely used for mine filling and road base materials, providing technical support for the resource utilization of phosphogypsum, which is of great historical significance.

Description

Technical Field

[0001] The invention belongs to the technical field of resource utilization of bulk industrial solid wastes, and specifically relates to a method for stabilizing and solidifying phosphogypsum. Background Art

[0002] Phosphogypsum is a by-product of the wet process of preparing phosphoric acid. Its main component is CaSO4·2H2O, and it is an important recycled gypsum resource. According to statistics, the global cumulative emission of phosphogypsum is about 6 billion tons, and it is increasing at a rate of 150 million tons / year. At present, the main method of treating phosphogypsum in my country is stacking. The storage of a large amount of phosphogypsum not only occupies a lot of land, but also pollutes groundwater, soil and atmosphere for a long time, and damages the surrounding ecological environment, which hinders the sustainable development of the phosphorus chemical industry. Therefore, how to deal with and dispose of phosphogypsum, how to reduce costs and use phosphogypsum in a high-value way, and how to promote the reduction and resource utilization of phosphogypsum have become urgent problems to be solved.

[0003] Stabilization and solidification is a technology that prevents or reduces the release of harmful chemicals from waste residues. The process of using additives to change the engineering characteristics of waste residues is to change the physical and chemical properties of waste residues, and change the pollutants in the waste residues into a form that is not easy to dissolve, has lower mobility and toxicity. The acidic components and other harmful impurities in phosphogypsum lead to its low utilization rate, so a new method of stabilization and solidification of phosphogypsum is needed to solve the storage problem of phosphogypsum and make it effectively utilized.

[0004] CN201911385406.5 discloses a curing agent for phosphogypsum waste residue and a curing method thereof, which uses cement clinker, fly ash, activator and mineral powder as raw materials, utilizes the synergistic effect between them to improve the consolidation performance of the material, and the cement clinker is easy to form polar ion OH under the action of water medium - , can promote the dissolution and disintegration of phosphogypsum, provide a strong alkaline environment for mineral powder, produce alkaline excitation, accelerate the reaction process, mineral powder can provide hydration active binding sites, and generate a solid body with good mechanical properties and good chemical stability after the activation reaction by the activator. The present invention consumes a large amount of solid waste, realizes the resource utilization of waste slag, achieves the effect of treating waste with waste, and reduces the cost of consolidation of phosphorus slag; has high consolidation strength, effectively solidifies toxic and harmful substances therein, solves the problem of treating pollutants such as phosphorus and arsenic in phosphogypsum, effectively reduces its pollution to the environment, and protects the environment; provides an effective solution for the resource utilization of phosphogypsum.

[0005] CN201910061238.8 discloses a method for the coordinated stabilization and solidification of red mud and phosphogypsum, which comprises grinding the red mud and phosphogypsum, mixing them, adding deionized water and stirring evenly to form a slurry, adjusting the pH value to 7.5-8.5, then adding a conditioner and stirring, and then adding a stabilizer and an anti-seepage agent, stirring evenly to obtain a gel product, and curing for 12-24 hours to solidify the red mud and phosphogypsum to obtain a red mud-phosphogypsum solidified body; the present invention utilizes the acidic ions in the phosphogypsum to react with the alkaline ions in the red mud to produce a neutralization reaction, thereby reducing the pH value of the red mud and the migration ability of pollutants in the waste residue, and synergistically solidifying and treating two solid wastes, red mud generated by the aluminum smelting industry and phosphogypsum generated by the phosphorus chemical industry, and adding a conditioner, a stabilizer and an anti-seepage agent to make the solidified body more stable. The method of the present invention is simple, low-cost, and free of secondary pollution, and solves the environmental problems caused by the storage of red mud and phosphogypsum, thereby achieving sustainable development of the aluminum industry and the phosphating industry.

[0006] CN202111581508.1 discloses a curing agent for curing phosphogypsum roadbed filler, a preparation method and an application thereof. The present invention belongs to the field of highway engineering technology, and specifically relates to a curing agent for curing phosphogypsum roadbed filler, a preparation method and an application thereof. The curing agent for curing phosphogypsum roadbed filler comprises the following raw materials: sodium silicate, silicone waterproof material, auxiliary reinforcing agent, SDS emulsifier, acid catalyst and deionized water. The curing agent prepared by the preparation method of the curing agent for curing phosphogypsum roadbed filler disclosed in the present invention can effectively solidify and stabilize phosphogypsum, and the curing agent stabilized phosphogypsum (CASP) has certain strength and water stability. Under the condition of appropriate weight ratio, the cured phosphogypsum can be used for roadbed filler, which can fully meet the technical requirements for filling highway roadbed.

[0007] CN202111168492.1 discloses a phosphogypsum highway base material and a preparation method thereof, wherein the base material is made of the following raw materials: phosphogypsum, quicklime, fly ash, granular soil, curing agent, crushed stone, phosphorus slag, and silicate cement; the preparation method comprises the following steps: preparing raw materials for use; stirring the quicklime and part of the phosphogypsum at a low speed, and then grinding and sieving them for use, while crushing and sieving the remaining phosphogypsum for use; stirring the sieved phosphogypsum and the curing agent at a low speed, and then adding the sieved quicklime and phosphogypsum mixture and fly ash and stirring at a low speed, and then adding the granular soil, crushed stone, phosphorus slag and silicate cement thereto and stirring evenly; then adding water to the total material after stirring evenly and stirring; simplifying the preparation steps while effectively improving the early strength and other properties of the base material.

[0008] At present, harmful substances in phosphogypsum are stabilized and solidified at home and abroad, so that it can be used as cement retarder or other building materials, roadbed fillers and other fields. "Research on phosphogypsum cement retarder" was published in "Phosphate Fertilizer and Compound Fertilizer" in Volume 20, Issue 5, 2005. By solidifying industrial waste phosphogypsum, the super-retarding effect of soluble phosphorus in phosphogypsum on cement and the high water content of phosphogypsum causing feeding difficulties and easy blockage are solved. Solidified phosphogypsum can replace natural gypsum as a retarder. "High-efficiency coupled fixation / stabilization treatment of phosphogypsum and copper tailings" was published in "Silicon Bulletin" in Volume 40, Issue 5, 2021. CaO is added as an additional calcium source and NaOH as an activator to the mixed slag of phosphogypsum and copper tailings. About 30% (mass fraction) of water is added, stirred evenly, and made into a consolidated body (PG-S) by mechanical compression molding, which has undergone compression resistance test and toxicity leaching test. After coupled fixation / stabilization treatment, the toxic leaching concentration of the main harmful substances in phosphogypsum and copper tailings was significantly reduced. The mobile harmful substances in phosphogypsum and copper tailings were fixed by the formation of sediments and gelling encapsulation adsorption. The 28-day compressive strength of the consolidated body obtained by coupled fixation / stabilization treatment of two industrial solid wastes, phosphogypsum and copper tailings, can reach 14.8MPa. Directly using copper tailings to couple fixation / stabilization treatment of phosphogypsum not only achieves the fixation of harmful substances in the two solid wastes, but also obtains a consolidated body with a certain compressive strength, which provides a new reference for the resource utilization of phosphogypsum and copper tailings.

[0009] In summary, researchers have studied the solidification of phosphogypsum. Alkaline substances are the main means to solve the acidity in phosphogypsum. The formation of hydraulic minerals through chemical reactions such as slag, fly ash, cement, etc. is an important measure to obtain the strength of the solidified body, but it mainly focuses on the physical and mechanical properties, and rarely involves the evaluation of the properties of the solidified body itself. The present invention provides a new method for the stable solidification direction of phosphogypsum. Stability is the main purpose. According to HJ557-2010 Solid Waste Analysis Method-Horizontal Oscillation Method, phosphorus, fluorine, arsenic and pH in the mixture meet the Class A emission requirements of the first level standard in GB8978-1996 Comprehensive Wastewater Discharge Standard; solidification means that the mixture reaches a certain strength after treatment to meet the actual application requirements, which is another purpose of the present invention. Summary of the invention

[0010] The purpose of the invention is to solve the problem of domestic phosphogypsum resource utilization. It is proposed that after stable solidification treatment, the sample is prepared according to the HJ557-2010 solid waste analysis method-horizontal oscillation method, and the main pollutant dissolution of the mixture meets the Class A emission requirements of the first level standard in the GB8978-1996 comprehensive sewage discharge standard. The solidified body can be widely used for mine filling and road base material, providing technical support for the resource utilization of phosphogypsum.

[0011] The present invention is achieved through the following technical solutions:

[0012] A method for stabilizing and solidifying phosphogypsum, which comes from phosphogypsum produced by wet phosphoric acid, stabilizes toxic and harmful substances and increases strength by adding curing binder, reinforcing agent and synergistic adsorbent, neutralizes excess alkaline substances with phosphoric acid, mixes evenly and sends to the construction site, where it becomes a solidified body after paving and rolling.

[0013] The phosphogypsum is filtered and washed phosphogypsum, and the free water content in the phosphogypsum is 22-28%. According to the HJ557-2010 solid waste analysis method-horizontal oscillation method, the phosphorus content in the phosphogypsum is measured to be 60-90 mg / L, the fluorine content is 70-105 mg / L, the arsenic content is 1.0-2.0 mg / L, and the pH is 3.0-3.5.

[0014] The solidified binder material is composed of one or two of steel slag, fly ash and slag. The solidified binder material is ground after drying, and the particle size requirement is that the residue on the 0.38um square hole sieve is less than 10%. The added amount of the solidified binder material is 5-10% of the dry basis mass of the phosphogypsum.

[0015] The reinforcing agent is prepared by mixing one or two of calcium chloride, sodium chloride and sodium sulfate, and the added amount is 0.5-2.0% of the dry basis mass of phosphogypsum.

[0016] The synergistic adsorbent is diatomite that is dried at 200-600°C or low-temperature roasted and ground under reducing atmosphere, and has a particle size of less than 5% on a 0.38um square hole sieve. The amount of the synergistic adsorbent added is 1-2% of the dry basis mass of the phosphogypsum.

[0017] When phosphoric acid neutralizes excess alkaline substances, the pH of the dissolution is adjusted to 6-9. After neutralization, the content of pollutant dissolution in the mixture is tested according to HJ557-2010 Solid Waste Analysis Method-Horizontal Oscillation Method, and the measured phosphorus content is ≤0.5mg / L, fluorine content is ≤10mg / L, and total arsenic is ≤0.5mg / L, which meets the Class A emission requirements of the first level standard in GB8978-1996 Comprehensive Wastewater Discharge Standard.

[0018] After core sampling test, the solidified body has an unconfined compressive strength of 0.5-1.0MPa after 7 days and an unconfined compressive strength of 2.5-6.5MPa after 28 days.

[0019] A method for stabilizing and solidifying phosphogypsum, comprising the following steps:

[0020] Weigh a certain amount of phosphogypsum, add 5-10% of its dry basis weight of active binder, 0.5-2.0% of enhancer and 1-2% of adsorbent, adjust the pH with phosphoric acid, prepare the sample according to HJ557-2010 Solid Waste Analysis Method - Horizontal Oscillation Method, and the main pollutants dissolved in the mixture meet the Class A emission requirements of the first level standard in GB8978-1996 Comprehensive Wastewater Discharge Standard.

[0021] After being evenly mixed, it is transported to the site for paving and rolling, and core samples are taken to test the unconfined compressive strength at 7 days and 28 days.

[0022] The technical principle of the present invention is as follows: by adding solidifying cementing materials, reinforcing agents and adsorbents, the present invention first converts most of the phosphorus, fluorine and arsenic in the phosphogypsum into insoluble substances mainly composed of calcium salts under physical and chemical effects, and cooperates with the adsorbent to jointly reduce the dissolution rate of phosphorus, fluorine and arsenic. The remaining part uses phosphoric acid to adjust the pH value, and generates fluoroapatite through chemical reactions to further reduce the dissolution of phosphorus and fluorine, and ensures that the pH value of the mixture solution is between 6 and 9. At the same time, it creates conditions for the mixture to produce calcium sulfonate and silica, calcium aluminate hydration products in the later stage, which together provide strength for the dense body of the mixture to meet different application requirements.

[0023] Compared with the prior art, the present invention solves the problem of domestic phosphogypsum resource utilization, proposes that after stable solidification treatment, the sample is prepared according to the HJ557-2010 solid waste analysis method-horizontal oscillation method, and the main pollutant dissolution of the mixture meets the Class A emission requirements of the first level standard in the GB8978-1996 comprehensive sewage discharge standard. The solidified body can be widely used for mine filling and road base material, providing technical support for the resource utilization of phosphogypsum. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited by the embodiments. Example 1

[0026] The free water content of the washed and filtered phosphogypsum at the production site is 25wt%. According to the HJ557-2010 solid waste analysis method-horizontal oscillation method, the main environmental pollutants in the phosphogypsum are 60mg / L phosphorus, 70mg / L fluorine, 1.0mg / L arsenic, and pH 3.5. Add 5% of the dry basis weight of the phosphogypsum and steel slag with a particle size of 10% on a 0.38um square hole sieve as a solidifying binder, add 0.5% calcium chloride as a reinforcing agent, and add diatomaceous earth that has been low-temperature roasted under 600℃ reducing gas and a powder particle size of 2% on a 0.38um square hole sieve as a synergistic adsorbent. Use phosphoric acid to adjust the pH, and according to the HJ557-2010 solid waste analysis method-horizontal oscillation method, the main pollutants dissolved in the mixture are ≤0.5mg / L phosphorus, ≤10mg / L fluorine, ≤0.5mg / L total arsenic, and pH 6. The mixture was transported to the site for paving, rolling and core testing. The 7-day unconfined compressive strength reached 1.0 MPa, and the 28-day unconfined compressive strength reached 2.5 MPa. Example 2

[0027] The free water content of the washed and filtered phosphogypsum at the production site is 28wt%. The sample is prepared according to HJ557-2010 Solid Waste Analysis Method - Horizontal Oscillation Method. The main environmental pollutants in the phosphogypsum are phosphorus content of 90mg / L, fluorine content of 105mg / L, arsenic content of 2.0mg / L, and pH of 3.0. Add 3% of the dry mass of phosphogypsum, 10% of steel slag with a particle size of 0.38um square hole sieve residue, and 5% of slag with a particle size of 0.38um square hole sieve residue residue as curing binder, 0.5% of calcium chloride and 1.5% of sodium sulfate as reinforcing agent, 200℃ dried, ground diatomaceous earth with a particle size of 5% of 0.38um square hole sieve residue residue as synergistic adsorbent, adjust the pH with phosphoric acid, and prepare samples according to HJ557-2010 solid waste analysis method-horizontal oscillation method. The main pollutants in the mixture are soluble phosphorus content ≤0.5mg / L, fluorine content ≤10mg / L, total arsenic ≤0.5mg / L, and pH 9. The mixture is transported to the site for paving, rolling, and core testing. The unconfined compressive strength of 7 days strength reaches 2.0MPa, and the unconfined compressive strength of 28 days strength reaches 6.5MPa. Example 3

[0028] The free water content of the washed and filtered phosphogypsum at the production site is 22wt%. The sample is prepared according to HJ557-2010 Solid Waste Analysis Method - Horizontal Oscillation Method. The main environmental pollutants in the phosphogypsum are phosphorus content of 75mg / L, fluorine content of 97mg / L, arsenic content of 1.3mg / L, and pH of 3.2. Add 5% of the dry mass of phosphogypsum, 8% of fly ash with a particle size of 0.38um square hole sieve residue, and 10% of slag with a particle size of 5% of 0.38um square hole sieve residue as curing binder, 0.5% of calcium chloride and 0.5% of chloride as reinforcing agent, 200℃ dried, 5% of diatomaceous earth with a particle size of 0.38um square hole sieve residue as synergistic adsorbent, adjust the pH with phosphoric acid, and prepare samples according to HJ557-2010 solid waste analysis method-horizontal oscillation method. The main pollutants in the mixture are phosphorus content ≤0.5mg / L, fluorine content ≤10mg / L, total arsenic ≤0.5mg / L, and pH 7.5. The mixture is transported to the site for paving, rolling, and core testing. The unconfined compressive strength of 7 days strength reaches 1.2MPa, and the unconfined compressive strength of 28 days strength reaches 4.7MPa.

Claims

1. A method for stabilizing and solidifying phosphogypsum, characterized in that: The phosphogypsum produced from wet phosphoric acid is stabilized by adding curing binder, reinforcing agent and synergistic adsorbent to stabilize the toxic and harmful substances and increase the strength. The excess alkaline substances are neutralized with phosphoric acid. After being mixed evenly, it is sent to the construction site and solidified by paving and rolling. The phosphogypsum is filtered and washed, and the free water content in the phosphogypsum is 22-28%. The sample is prepared according to HJ557-2010 Solid Waste Analysis Method-Horizontal Oscillation Method, and the phosphorus content in the phosphogypsum is measured. The content of phosphogypsum is 60-90mg / L, the content of fluorine is 70-105mg / L, the content of arsenic is 1.0-2.0mg / L, and the pH is 3.0-3.

5. The solidified cementing material is composed of one or two of steel slag, fly ash, and slag. The solidified cementing material is ground after drying, and the particle size requirement is that the residue on the 0.38um square hole sieve is less than 10%. The addition amount of the solidified cementing material is 5-10% of the dry basis mass of the phosphogypsum. The reinforcing agent is composed of calcium chloride, sodium chloride, sulfur The synergistic adsorbent is diatomite dried at 200-600℃ or roasted and ground at low temperature under reducing atmosphere, and the particle size is less than 5% of the residue on the 0.38um square hole sieve. The synergistic adsorbent is added in an amount of 1-2% of the dry mass of the phosphogypsum. When phosphoric acid neutralizes the excess alkaline substances, the pH of the dissolution is adjusted to 6-9. After the neutralization is completed, the solid Waste analysis method - horizontal oscillation method is used to test the content of pollutant dissolution in the mixture, and the phosphorus content is ≤0.5mg / L, the fluorine content is ≤10mg / L, and the total arsenic is ≤0.5mg / L, which meets the Class A emission requirements of the first level standard in GB8978-1996 Comprehensive Sewage Discharge Standard. The solidified body is tested by core sampling, and the 7-day strength is the unconfined compressive strength of 0.5-1.0MPa, and the 28-day strength is the unconfined compressive strength of 2.5-6.5MPa.

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