CN111847956A - A kind of phosphogypsum-based cement retarder and its preparation method and application - Google Patents

Abstract

The invention provides a phosphogypsum-based cement retarder and a preparation method and application thereof. The phosphogypsum-based cement retarder is composed of 90-95% phosphogypsum, 3-6% slag powder or fly ash, After mixing 2-4% calcareous quicklime powder or calcareous slaked lime powder or calcium carbide slag powder, add an appropriate amount of alkali activator to mix and form into pellets; the amount of the alkali activator is converted into the mass of Na2O, which is the slag 6%-15% of the amount of powder or the fly ash. The invention can effectively adsorb and solidify the soluble phosphorus, fluorine, etc. in the phosphogypsum, and neutralize the organic matter, thereby greatly reducing the adverse effects of harmful substances in the phosphogypsum on the setting time and early strength of cement, and the The aging time of the phosphogypsum-based cement retarder is short, which greatly improves the production efficiency of the phosphogypsum-based cement retarder.

Description

A kind of phosphogypsum-based cement retarder and its preparation method and application

technical field

The invention belongs to the technical field of cement retarders, in particular to a phosphogypsum-based cement retarder and a preparation method and application thereof.

Background technique

Phosphogypsum is the waste residue produced during the wet production of phosphoric acid in the phosphate fertilizer industry. About 5 tons of phosphogypsum are emitted for every ton of phosphoric acid produced. Due to the rapid growth and development of the phosphorus chemical industry, the output of phosphogypsum waste also increased rapidly. At present, the annual emission of phosphogypsum in my country is about 84 million tons, and the comprehensive utilization rate is about 30%. Up to now, the cumulative stockpile of phosphogypsum in my country has exceeded 300 million tons. Phosphogypsum is piled up for a long time, which not only occupies a lot of land, but also contains free acid which will pollute the groundwater source, and fluoride will penetrate into the underground polluted soil.

The main component of phosphogypsum is dihydrate gypsum (CaSO ₄ ·2H ₂ O), which is similar to natural gypsum and is an important renewable gypsum resource. At present, cement retarder is the main utilization method of phosphogypsum, and its utilization accounts for more than 60% of the total utilization. However, when phosphogypsum is used as a cement retarder, due to the existence of impurities such as soluble phosphorus, fluorine and organic matter, phosphogypsum will be acidic and corrosive to a certain extent, and will seriously delay the setting time of cement and reduce its early stage. strength, thus limiting the application of phosphogypsum in cement. In addition, the freshly discharged phosphogypsum is wet and coarse granular powder, which generally contains 15-25% of attached water, which is not conducive to transportation and measurement, and is easy to cause agglomeration, blockage, and paste grinding in cement mills. Therefore, before phosphogypsum is used as a cement retarder, it is necessary to modify and preprocess the phosphogypsum for excessive retardation and feeding problems.

The existing phosphogypsum pretreatment methods mainly include: washing method, neutralization method, lime washing method, flotation method, flash burning method, hemi-water-dihydrate phosphogypsum spheronizing method, chemical modification sphering method, etc.

Among them, the washing technology is mature, and the performance of the treated gypsum is relatively stable, but the washing process is complicated, the investment is large, the water consumption and drying energy consumption are high, and the sewage after washing must be treated before it can be discharged. The neutralization method uses cheap lime to neutralize the acid in the phosphogypsum, and forms insoluble matter with soluble P ₂ O ₅ , so that the soluble matter becomes an inert matter. The process is simple, the investment is small, and no pollution is generated. Phosphogypsum is unstable.

The lime water washing method is a combination of the water washing method and the lime neutralization method. It is similar to the water washing method. On the one hand, it can clean the soluble impurities of phosphogypsum, and on the other hand, it can neutralize the residual acid and generate insoluble substances. It is more difficult, and the drying energy consumption is high. The flotation method mainly eliminates the influence of organic impurities on phosphogypsum, but does not fundamentally eliminate the influence of soluble phosphorus and fluorine impurities, and the problem of excessive retardation of phosphogypsum has not been solved.

The flash burning method is to calcine phosphogypsum at 800 °C, decompose and volatilize harmful substances such as fluorine and organic matter at high temperature, and convert soluble phosphorus and eutectic phosphorus into inert pyrophosphate minerals, so as to reduce the harmful impurities in phosphogypsum to cement. However, high temperature calcination needs to consume a large amount of coal, and a small amount of acidic harmful gas is produced during the calcination process, which pollutes the atmosphere.

Hemihydrate-dihydrate phosphogypsum balling method, phosphogypsum is pre-calcined and dehydrated at a certain temperature to form hemihydrate gypsum, and then hemihydrate gypsum is mixed with phosphogypsum, lime and water evenly, and the hemihydrate gypsum is hydrated to form hemihydrate gypsum. It has the characteristics of dihydrate gypsum with a certain strength. The uncalcined phosphogypsum is cemented, formed into balls, dried and put into storage. However, the calcination and dehydration of phosphogypsum in this method needs to use a hammer dryer, which not only consumes high energy but also phosphorus. The organic matter in gypsum enters the atmosphere with the steam and causes environmental pollution.

The chemical modification balling method uses fly ash and lime to chemically modify phosphogypsum and form balls. The pozzolanic reaction under the excitation of phosphogypsum can reduce the content of soluble phosphorus and fluorine in the phosphogypsum and form a sphere with a certain strength. However, due to the slow chemical reaction and low strength, the amount of fly ash should be 30% to 35% and it can be used for at least 7 days after aging at room temperature, which greatly reduces the production efficiency, and because of the large amount of fly ash, the SO ₃ content in the modified phosphogypsum balls is greatly reduced.

SUMMARY OF THE INVENTION

Aiming at the problems existing in the prior art, the present invention aims to propose a phosphogypsum-based cement retarder, so as to solve the problem that the existing phosphogypsum retarder has high production cost, low production efficiency, and SO ₃ in the modified phosphogypsum balls. low content.

The technical scheme adopted by the present invention for solving the problems existing in the prior art is as follows:

A phosphogypsum-based cement retarder, calculated by mass percentage, is composed of 90-95% phosphogypsum, 3-6% slag powder or fly ash, 2-4% calcareous quicklime powder or calcareous slaked lime powder or calcium carbide slag After the powder is mixed, an appropriate amount of alkali activator is added to mix and form into pellets; the amount of the alkali activator is 6%-15% of the amount of the slag powder or the fly ash in terms of the mass of Na ₂ O .

The alkali activator is water glass or sodium hydroxide, and the content of the alkali activator in the cement retarder of the present invention is expressed as a percentage of Na ₂ O equivalent.

The modulus of the water glass is 1.0-1.5.

The CaO content in the calcareous quicklime powder is greater than or equal to 65%, and the balance of the 90 μm sieve is less than or equal to 7%.

The CaO content of the calcareous slaked lime powder or the calcium carbide slag powder after deducting free water and bound water is greater than or equal to 65%, and the balance of the 90 μm sieve is less than or equal to 7%.

The slag powder is S75 grade slag powder.

The fly ash is Class II fly ash.

A method for preparing the above-mentioned phosphogypsum-based cement retarder, comprising the following steps:

Step 1. After uniformly mixing phosphogypsum, slag powder or fly ash, calcareous quicklime powder or calcareous slaked lime powder or calcium carbide slag powder, add an alkali activator, and continue to mix until uniform to obtain mixture A;

Step 2. The mixed material A is formed into wet pellets by a disc pelletizing machine, and then aged for 2 days or more to obtain spherical phosphogypsum-based cement retarder.

The moisture content of the wet material ball when the mixed material A is formed into a ball is 16-18%.

An application of the above-mentioned phosphogypsum-based cement retarder, the phosphogypsum-based cement retarder is used as a raw material to prepare cement, and in terms of mass percentage, the cement comprises the following components: Portland cement clinker 80-85% , 5-8% of electric furnace slag, 5-10% of limestone, and 3-7% of the phosphogypsum-based cement retarder, and the above-mentioned component mixture is ground to a specific surface area of (350±50) m ² /kg.

The present invention has the following advantages:

The phosphogypsum-based cement retarder of the present invention takes phosphogypsum as the main component, and is modified by adding slag powder or fly ash, calcareous quicklime powder or calcareous slaked lime powder or calcium carbide slag powder, and a small amount of alkali activator. On the one hand, lime can effectively solidify soluble phosphorus, fluorine and organic matter in phosphogypsum to form insoluble calcium phosphate and calcium fluoride, thereby greatly reducing the influence of harmful substances in phosphogypsum on cement setting time; On the other hand, the addition of an alkali activator in the phosphogypsum-based cement retarder of the present invention will promote the depolymerization and re-aggregation of the aluminosilicate ore phase in the slag powder or fly ash to form a geopolymer. Phosphorus and fluorine are further adsorbed and solidified, which is beneficial to further reduce the influence of harmful substances in phosphogypsum on the setting time of cement; at the same time, lime and phosphogypsum will also stimulate slag powder or fly ash with alkali and sulfate, so that The chemical activity of slag powder or fly ash is improved, and hydration products with gelling properties such as hydrated calcium silicate gel and ettringite crystals are formed at an early stage, which together improve the early strength of phosphogypsum balls, so that the present invention The raw materials of the phosphogypsum-based cement retarder can be used after being mixed into balls for 2 days, which greatly improves the production efficiency of the phosphogypsum-based cement retarder, and the energy consumption of the whole process is extremely low, which greatly reduces the production cost. In addition, the phosphogypsum-based cement retarder of the present invention can effectively improve the early and late mechanical properties of cement, and the SO ₃ content in the phosphogypsum-based cement retarder of the present invention can be stabilized at more than 35%, and the retarding effect is stable. Different clinkers have good adaptability and can meet the needs of producing high-quality cement performance indicators of grade 42.5 and above.

Detailed ways

Below by embodiment, the technical scheme of the present invention is described in further detail:

Example 1

A phosphogypsum-based cement retarder, calculated by mass percentage, is prepared by mixing 92% phosphogypsum, 5% slag powder, and 3% calcareous quicklime powder, adding water glass to continue mixing until uniform, and forming into a ball; water glass The amount of slag powder, converted into the mass of Na ₂ O, is 6% of the amount of slag powder. Among them, the attached water content of phosphogypsum is 17.2%; the CaO content in calcareous quicklime powder is ≥65%, and the 90 μm sieve balance is ≤7%; the slag powder is S75 grade slag powder; the modulus of water glass is 1.0.

The above-mentioned phosphogypsum-based cement retarder is specifically prepared by the following methods:

1) according to the above-mentioned component distribution ratio, after phosphogypsum, slag powder and calcareous quicklime powder are evenly mixed, water glass is added, and the mixing is continued until uniform to obtain mixture A;

2) Use a disc pelletizing machine to pellet the mixture A, and age it for 2 days to obtain a phosphogypsum-based cement retarder.

Among them, when the disc ball forming machine forms balls, according to the needs of forming balls, the total amount of water of 0.2-2.2% of the total amount of the mixed material A is sprayed on the disc, so that the water content of the material balls is 16-18%, which is convenient for ball formation.

The above-mentioned phosphogypsum-based cement retarder is used to prepare cement, and the cement is prepared from the following components in terms of mass percentage: Portland cement clinker: 82%, electric furnace slag: 6%, limestone: 7%, phosphorus Gypsum-based cement retarder: 5%. The above mixture was ground with a ball mill to a specific surface area of (350±10) m ² /kg.

Example 2

The difference between this example and Example 1 is that: the phosphogypsum-based cement retarder of this example is calculated by mass percentage, after mixing 92% phosphogypsum, 5% slag powder, and 3% calcareous quicklime powder, adding water The glass continues to be mixed until it is uniform, and it is made into balls; the amount of water glass, converted into the mass of Na ₂ O, is 10% of the amount of slag powder; among them, the attached water content of phosphogypsum is 17.2%; The CaO content is greater than or equal to 65%, and the 90μm sieve balance is less than or equal to 7%; the slag powder is S75 grade slag powder; the modulus of water glass is 1.0.

Example 3

The difference between this example and Example 1 is that: the phosphogypsum-based cement retarder of this example is calculated by mass percentage, after mixing 92% phosphogypsum, 5% slag powder, and 3% calcareous quicklime powder, adding water The glass is continued to be mixed until uniform, and is made into balls; the amount of water glass, calculated in terms of the mass of Na ₂ O, is 6% of the amount of slag powder. Among them, the attached water content of phosphogypsum is 17.2%; the CaO content in the calcareous quicklime powder is ≥65%, and the 90 μm sieve balance is ≤7%; the slag powder is S75 grade slag powder; the modulus of water glass is 1.5.

Example 4

The difference between this example and Example 1 is that: the phosphogypsum-based cement retarder of this example is calculated by mass percentage, after mixing 92% phosphogypsum, 5% slag powder, and 3% calcareous quicklime powder, adding water The glass is continued to be mixed until uniform, and is made into a ball; the amount of water glass, calculated in terms of the mass of Na ₂ O, is 10% of the amount of slag powder. Among them, the attached water content of phosphogypsum is 17.2%; the CaO content in the calcareous quicklime powder is ≥65%, and the 90 μm sieve balance is ≤7%; the slag powder is S75 grade slag powder; the modulus of water glass is 1.5.

Example 5

The difference between this example and Example 1 is that: the phosphogypsum-based cement retarder in this example is, in mass percentage, mixed with 92% phosphogypsum, 5% slag powder, and 3% calcareous quicklime powder, and then adds hydrogen The sodium oxide is continuously mixed until it is uniform and spherical, and the amount of sodium hydroxide, calculated in terms of the mass of Na ₂ O, is 6% of the amount of slag powder. Among them, the attached water content of phosphogypsum is 17.2%; the CaO content in the calcareous quicklime powder is ≥65%, and the 90 μm sieve balance is ≤7%; the slag powder is S75 grade slag powder.

Example 6

The difference between this example and Example 1 is that: the phosphogypsum-based cement retarder in this example is, in mass percentage, mixed with 92% phosphogypsum, 5% slag powder, and 3% calcareous quicklime powder, and then adds hydrogen The sodium oxide is continuously mixed until it is uniform and spherical, and the amount of sodium hydroxide, calculated in terms of the mass of Na ₂ O, is 10% of the amount of slag powder. Among them, the attached water content of phosphogypsum is 17.2%; the CaO content in the calcareous quicklime powder is ≥65%, and the 90 μm sieve balance is ≤7%; the slag powder is S75 grade slag powder.

Example 7

The difference between this example and Example 1 is that: the phosphogypsum-based cement retarder in this example is, in mass percentage, mixed with 92% phosphogypsum, 5% slag powder, and 3% calcareous quicklime powder, and then adds hydrogen The sodium oxide is continuously mixed until it is uniform and spherical, and the amount of sodium hydroxide, calculated as the mass of Na ₂ O, is 15% of the amount of the slag powder. Among them, the attached water content of phosphogypsum is 17.2%; the CaO content in the calcareous quicklime powder is ≥65%, and the 90 μm sieve balance is ≤7%; the slag powder is S75 grade slag powder.

The properties of the phosphogypsum-based cement retarders of Examples 1-7 of the present invention were tested, and they were compared with unmodified unmodified phosphogypsum-based cement (Comparative Example 1) and phosphogypsum-based cement retarders without alkali activator. The test results are shown in Table 1 and Table 2. Among them, the compressive strength test of phosphogypsum-based cement retarder in Table 1 is to use a cylindrical test mold of ф50mm × 50mm to press and shape the mixture A, and then cure it under the conditions of 20±1℃ and 60±5%RH 3d measured. The content of water-soluble P ₂ O ₅ and water-soluble fluorine in the phosphogypsum-based cement retarder in Table 2 is determined according to the standard JC/T 2073-2011 "Method for the Determination of Phosphorus and Fluorine in Phosphogypsum", and the pH value is determined according to GB/T 5484-2012 "Chemical Analysis Methods of Gypsum".

As shown in Table 1, Comparative Example 1 is unmodified unmodified phosphogypsum powder, which is also used as a cement retarder, but no strength is obtained after compression molding and curing for 3 days. , it cannot achieve the desired effect, so it needs to be modified. Comparative Example 2 is a phosphogypsum-based cement retarder without alkali activator modification. Calculated by mass percentage, it is mixed with 92% phosphogypsum, 5% slag powder, and 3% calcareous quicklime powder. ball made. Examples 1-7 are based on the comparative example 2, and further use different varieties and dosages of alkali to carry out alkali excitation modification.

The compressive strengths of the phosphogypsum-based cement retarders in Examples 1-7 of the present invention have all exceeded 0.7 MPa after curing for 3 days, which is greatly improved compared with the strength of Comparative Example 2, indicating that the phosphogypsum modified by the alkali activator The base cement retarder has been aged for 3d and has achieved high strength, which can fully meet the requirements of use.

Table 1

The harmful substances in the phosphogypsum-based cement retarders of Example 1 and Example 4 of the present invention were tested, and they were compared with unmodified unmodified phosphogypsum (Comparative Example 1) and phosphorus gypsum modified without alkali activator. The gypsum cement retarder (Comparative Example 2) is compared, and the test results are shown in Table 2. As can be seen from Table 2, the content of water-soluble P ₂ O ₅ and water-soluble F harmful substances in the phosphogypsum-based cement retarders of Examples 1 and 4 of the present invention are relative to the unmodified phosphogypsum of Comparative Example 1. It is greatly reduced, and it is also greatly improved compared with Comparative Example 2, which fully meets the relevant regulations in the national standard "Phosphogypsum" (GB/T 23456-2018), and the obtained phosphogypsum-based cement retarder is relatively alkaline. , which can effectively avoid the corrosion of the mill when it enters the ball mill to grind cement.

Table 2

The phosphogypsum-based cement retarders of Examples 1-7 of the present invention were used in the preparation of cement. The test results of water consumption, setting time and mortar strength for standard consistency of cement are shown in Table 3. As can be seen from Table 3, the setting time of the cement prepared with the phosphogypsum-based cement retarders of Examples 1-7 is relative to the undisturbed phosphogypsum (Comparative Example 1) and the phosphogypsum-based cement retarder modified without alkali activator. The cement prepared by the coagulant (Comparative Example 2) has a relatively large reduction, and the strength properties of the early and late stages are improved to varying degrees.

table 3

The mortar fluidity and compatibility with the water reducing agent of the cement prepared by using the phosphogypsum-based cement retarder of Example 1 and Example 4 of the present invention were tested, and it was compared with the use of unmodified phosphogypsum. The prepared cement (Comparative Example 1) and the cement prepared with natural gypsum (Comparative Example 3) were compared, and the test results are shown in Table 4.

As can be seen from Table 4, the cement prepared by adopting the phosphogypsum-based cement retarder of Example 1 and Example 4 of the present invention is better than Comparative Example 3 in terms of mortar fluidity, compatibility with water reducer, etc. The cement of natural gypsum was slightly inferior to the cement of Comparative Example 1 mixed with unmodified unmodified gypsum, but the difference was not significant.

Table 4

The protection scope of the present invention is not limited to the above-mentioned embodiments. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the scope and spirit of the present invention. If these changes and modifications fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include these changes and modifications.

Claims (10)

1. a phosphogypsum-based cement retarder, is characterized in that: by mass percentage, by 90～95% phosphogypsum, 3～6% slag powder or fly ash, 2～4% calcareous quicklime powder or calcium After mixing slaked lime powder or calcium carbide slag powder, add an appropriate amount of alkali activator to mix and form into pellets; the amount of the alkali activator is converted into the mass of Na ₂ O, which is the amount of the slag powder or the fly ash. 6%-15%. 2. a kind of phosphogypsum-based cement retarder as claimed in claim 1, is characterized in that: described alkali activator is water glass, or sodium hydroxide. 3. The phosphogypsum-based cement retarder according to claim 2, wherein the modulus of the water glass is 1.0-1.5. 4. The phosphogypsum-based cement retarder according to claim 1, characterized in that: the CaO content in the calcareous quicklime powder is greater than or equal to 65%, and the 90 μm sieve balance is less than or equal to 7%. 5. a kind of phosphogypsum-based cement retarder as claimed in claim 1 is characterized in that: the CaO content that deducts free water and bound water in described calcareous slaked lime powder or described calcium carbide slag powder is ≥ 65%, 90 μm The sieve balance is less than or equal to 7%. 6 . The phosphogypsum-based cement retarder according to claim 1 , wherein the slag powder is S75 grade slag powder. 7 . 7 . The phosphogypsum-based cement retarder according to claim 1 , wherein the fly ash is Class II fly ash. 8 . 8. the preparation method of a kind of phosphogypsum-based cement retarder as described in any one of claim 1-7, is characterized in that, comprises the following steps: Step 1. After uniformly mixing phosphogypsum, slag powder or fly ash, calcareous quicklime powder or calcareous slaked lime powder or calcium carbide slag powder, add an alkali activator, and continue to mix until uniform to obtain mixture A; Step 2. The mixed material A is formed into wet pellets by a disc pelletizing machine, and then aged for 2 days or more to obtain spherical phosphogypsum-based cement retarder. 9 . The preparation method of a phosphogypsum-based cement retarder according to claim 8 , wherein the wet pellets have a moisture content of 16-18% when the mixture A is formed into pellets. 10 . 10. the application of a kind of phosphogypsum-based cement retarder according to any one of claims 1-7, it is characterized in that: using phosphogypsum-based cement retarder as raw material to prepare cement, by mass percentage, the The cement consists of the following components: 80-85% of Portland cement clinker, 5-8% of electric furnace slag, 5-10% of limestone, and 3-7% of the phosphogypsum-based cement retarder, the above components are combined The mixture is ground to a specific surface area of (350±50) m ² /kg.