Method for preparing a cement retarder using phosphogypsum and cement prepared thereby

Abstract

This invention relates to the field of phosphogypsum treatment technology, specifically disclosing a method for preparing a cement retarder using phosphogypsum and the cement prepared therefrom. The method includes the following steps: S1, washing and filtering the phosphogypsum to remove soluble impurities, then adding an alkaline substance to adjust its pH to 10-11; S2, placing the phosphogypsum obtained in S1 in a sealed container, and purging with CO2 until the pH value drops below 8.5 to stop the reaction, thus obtaining the cement retarder. Using this cement retarder to prepare cement can avoid excessively long retarding times, increase the amount of phosphogypsum used, and ensure the mechanical properties of the cement.

Description

Technical Field

[0001] This invention belongs to the field of phosphogypsum utilization technology, specifically relating to a method for preparing cement retarder using phosphogypsum and the cement prepared therefrom. Background Technology

[0002] Phosphogypsum is an industrial solid waste generated during the sulfuric acid process for producing phosphoric acid. For every ton of phosphoric acid produced, 4-5 tons of phosphogypsum are generated. The main component of phosphogypsum is calcium sulfate dihydrate, followed by silicon dioxide, and it also contains small amounts of phosphorus and fluorine. Due to its large production volume, phosphogypsum is currently primarily disposed of through stockpiling, occupying significant land resources and easily causing water pollution. Using phosphogypsum as a cement retarder instead of natural gypsum not only saves a large amount of valuable gypsum resources but also turns waste into treasure at a low cost, possessing significant environmental and economic value, and becoming one of the main ways to comprehensively reuse phosphogypsum waste. However, because it contains phosphorus and fluorine impurities, when directly applied to industrial cement production, these impurities prolong the cement's setting time and cause surface powdering, affecting the cement's surface smoothness. Therefore, there is an urgent need to develop a method for treating phosphogypsum to avoid excessive addition and to ensure that it undergoes appropriate modification treatment before it can replace natural gypsum in cement production.

[0003] CN101792278A discloses a method for producing cement retarder using phosphogypsum, which involves mixing dihydrate phosphogypsum with carbide slag, granulating, and aging for more than 24 hours. However, this method requires first drying the mixture in a dryer at a temperature of 300℃±10℃ until the moisture content is about 12%, and then using a pneumatic conveyor to transport the mixture and dry the surface water, so that the moisture content of the mixture is about 10%. This method has high requirements for moisture content and high energy consumption. Summary of the Invention

[0004] This invention provides a method for preparing a cement retarder using phosphogypsum and the cement prepared therefrom, which can avoid excessively long retarding time, increase the amount of phosphogypsum, and ensure the mechanical properties of the cement.

[0005] The technical solution of the present invention is to provide a method for preparing a cement retarder using phosphogypsum, comprising the following steps: S1. The phosphogypsum is washed with water and filtered to remove soluble impurities, and then an alkaline substance is added to adjust its pH to 10-12. S2. Place the phosphogypsum obtained in S1 in a sealed container, add aluminum sulfate octadeca and mix well, then introduce CO2 until the pH value is 8.0-8.5, stop the reaction, and store until the moisture content decreases to below 12% to obtain the cement retarder.

[0006] In some embodiments, after phosphogypsum is washed with water, the water-soluble phosphorus content is ensured to be less than 0.2% and the water-soluble fluorine content is less than 0.1%.

[0007] In some embodiments, the alkaline substance in S1 is carbide slag and / or lime.

[0008] In some embodiments, the phosphogypsum is aged for 20-30 hours after the addition of alkaline substances.

[0009] In some embodiments, the amount of aluminum sulfate octadeca added in S2 is 1‰-5‰ of phosphogypsum.

[0010] In some embodiments, when CO2 is introduced, the temperature of the material is controlled at 40-55°C.

[0011] In some embodiments, after CO2 is introduced, the calcium carbonate content in the phosphogypsum is controlled to be 3-8%.

[0012] In some embodiments, the moisture content of the phosphogypsum stored in S2 is 10%-12%.

[0013] The present invention also relates to the preparation of cement with cement retarder obtained by the method, wherein the amount of cement retarder added is 5% of the total raw material mass.

[0014] In some embodiments, the raw materials include clinker, gravel, fly ash, blast furnace slag and cement retarder, in a mass ratio of 71:5:6:13:5.

[0015] The present invention has the following beneficial effects: The method provided by this invention first pre-treats phosphogypsum by washing with water to reduce the content of water-soluble impurities. Then, lime or carbide slag is added to solidify the remaining water-soluble impurities and adjust the pH to alkaline. Aluminum sulfate is added, and then carbon dioxide is introduced to react with excess lime or carbide slag in the phosphogypsum to produce calcium carbonate, thus obtaining phosphogypsum containing a certain amount of calcium carbonate. This material can be used in cement production, which can not only achieve the large-scale addition of phosphogypsum to replace the gypsum raw material in the traditional process, but also avoid the problem of excessively long cement setting time caused by phosphogypsum, and will not affect the performance of cement.

[0016] This invention enables the resource utilization of phosphogypsum and CO2, effectively alleviating the environmental problems caused by phosphogypsum and CO2, and creating economic value. The method is simple, directly mixing pH-modified phosphogypsum with CO2 to form a phosphogypsum containing calcium carbonate, avoiding the problem of excessively long setting time caused by phosphogypsum. The addition of aluminum salts compensates for the influence of calcium carbonate on strength. Attached Figure Description

[0017] Figure 1 A process flow diagram is provided for the method of this invention. Detailed Implementation

[0018] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0019] The phosphogypsum used in the following examples and comparative examples was obtained from a phosphate chemical company, and its composition is shown in Table 1 below.

[0020] Table 1: Main Components of Phosphogypsum

[0021] Example 1 The process flow of the phosphogypsum treatment method provided by this invention is as follows: Figure 1 Specifically, it includes the following steps: (1) Wash the phosphogypsum with water and stir it again. The water-to-sludge ratio is 1:1. The resulting water-washed phosphogypsum has 0.2% water-soluble phosphorus and 0.1% water-soluble fluorine, thus obtaining purified phosphogypsum. (2) Add 10% of the mass of carbide slag to the purified phosphogypsum obtained in step (1), stir and age for 24 hours, the pH value is 11.06, and the modified phosphogypsum is obtained. (3) The modified phosphogypsum was placed in a sealed container, the temperature was controlled at 45-55℃, 1‰ aluminum sulfate octadecyl water was added, stirred, and CO2 was introduced at a flow rate of 25 ml / min. After reacting for 2 hours, phosphogypsum with a pH of 8.45 was obtained. The calcium carbonate content was 5 wt% by detecting the carbonate content in the solid.

[0022] Example 2 The method and steps are the same as in Example 1, except that the reaction in a sealed container is extended to 3 hours, resulting in phosphogypsum with a pH of 8.32 and a calcium carbonate content of 8%.

[0023] Example 3 The method and steps are the same as in Example 1, except that the mass of aluminum sulfate octadeca added is 5‰ of the mass of phosphogypsum, and the reaction in a sealed container is extended to 4 hours to obtain phosphogypsum with a pH of 8.05 and a calcium carbonate content of 9.2%.

[0024] Example 4 The method and steps are the same as in Example 1, except that the amount of carbide slag is adjusted to 8%, the mixture is stirred and aged for 24 hours, the pH value is 10.05, and the reaction is carried out in a sealed container for 2 hours to obtain phosphogypsum with a pH value of 8.47 and a calcium carbonate content of 4.5%.

[0025] Example 5 The method and steps are the same as in Example 1, except that the amount of carbide slag is adjusted to 8%, the mixture is stirred and aged for 24 hours, the pH value is 10.05, and the reaction is carried out in a sealed container for 3 hours to obtain phosphogypsum with a pH value of 8.27 and a calcium carbonate content of 5.2%.

[0026] Example 6 The method and steps are the same as in Example 1, except that the carbide slag is replaced with quicklime at a dosage of 5%, and the mixture is stirred and aged for 24 hours until the pH value is 11.25. The mixture is then reacted in a sealed container for 2 hours to obtain phosphogypsum with a pH value of 8.4 and a calcium carbonate content of 5.5%.

[0027] Comparative Example 1 (1) The phosphogypsum was washed with water and stirred again, with a water-to-sludge ratio of 1:1. The resulting water-washed phosphogypsum contained 0.2% water-soluble phosphorus and 0.1% water-soluble fluorine. (2) Add 10% carbide slag to the purified phosphogypsum obtained in step (1), stir and age for 24 hours, and the pH value is 11.06.

[0028] Comparative Example 2 (1) The phosphogypsum was washed with water and stirred again, with a water-to-sludge ratio of 1:1. The resulting water-washed phosphogypsum contained 0.2% water-soluble phosphorus and 0.1% water-soluble fluorine. (2) Add 10% carbide slag to the purified phosphogypsum obtained in step (1), stir and age for 24 hours, the pH value is 11.06, add 1‰ aluminum sulfate octadeca and 5% industrial calcium carbonate to the phosphogypsum and mix evenly.

[0029] Comparative Example 3 (1) The phosphogypsum was washed with water and stirred again, with a water-to-sludge ratio of 1:1. The resulting water-washed phosphogypsum contained 0.2% water-soluble phosphorus and 0.1% water-soluble fluorine. (2) Add 10% carbide slag to the purified phosphogypsum obtained in step (1), stir and age for 24 hours, and the pH value is 11.06.

[0030] (3) The modified phosphogypsum was placed in a sealed container, the temperature was controlled at 45-55℃, stirred, and CO2 was introduced at a flow rate of 25 ml / min. After reacting for 2 hours, phosphogypsum with a pH of 8.45 and a calcium carbonate content of 5 wt% was obtained.

[0031] Cement was prepared using a cement plant formula with clinker: limestone: fly ash: blast furnace slag: retarder = 76:11:4:6:5 (mass ratio). The retarder was phosphogypsum obtained in Examples 1-6 and Comparative Examples 1-3. The retarding time and strength were tested according to GBT 1346-2011 Cement Standard Consistency Water Requirement, Setting Time and Soundness Test Method and GBT17671-2021 Cement Mortar Strength Test Method. The test results are shown in Table 2.

[0032] Table 2. Results of Examples and Comparative Examples

[0033] As can be seen from Table 2, the setting time of Examples 1-6 is shorter than that of Comparative Example 1, indicating that the modified phosphogypsum solidified carbon dioxide can shorten the setting time of cement. Moreover, the higher the calcium carbonate content, the shorter the setting time. The calcium carbonate content depends on the amount of unreacted alkaline substances in the phosphogypsum and the amount of CO2 introduced. Under the condition that CO2 is not excessive, the amount of calcium carbonate gradually increases. When it is excessive, it will dissolve to form Ca(HCO3)2, and an inflection point will appear at around 8.5.

[0034] Comparative Example 2 has a shorter setting time than Comparative Example 1, indicating that adding calcium carbonate can shorten the setting time. The calcium carbonate content in Example 1 and Comparative Example 2 is similar, and the cement setting time is basically the same, indicating that the effect of calcium carbonate obtained by solidifying CO2 through unreacted alkaline substances is comparable to that of industrial calcium carbonate.

[0035] Comparing Examples 1 and 6, when phosphogypsum was modified with two alkaline materials, carbide slag and lime, and carbon dioxide was solidified, the setting time was similar when the pH value and the calcium carbonate content in the phosphogypsum were similar.

[0036] Comparing Example 3 and Example 1, the calcium carbonate content is similar. The difference is that aluminum sulfate was not added in the comparative example, indicating that calcium carbonate can shorten the setting time and reduce the 28-day compressive strength. Adding aluminum sulfate ensures the strength. The cement setting time in Example 1 and Comparative Example 3 is basically the same, but the 28-day compressive strength is quite different.

[0037] The above embodiments describe preferred embodiments of the present invention, but the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other way. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for preparing a cement retarder using phosphogypsum, characterized in that, Includes the following steps: S1. The phosphogypsum is washed with water and filtered to remove soluble impurities, and then an alkaline substance is added to adjust its pH to 10-12. S2. Place the phosphogypsum obtained in S1 in a sealed container, add aluminum sulfate octadeca and mix well, then introduce CO2 until the pH value is 8.0-8.5, stop the reaction, and store until the moisture content decreases to below 12% to obtain the cement retarder.

2. The method according to claim 1, characterized in that: After washing the phosphogypsum with water, ensure that the water-soluble phosphorus content is less than 0.2% and the water-soluble fluoride content is less than 0.1%.

3. The method according to claim 1, characterized in that: The alkaline substances in S1 are carbide slag and / or lime.

4. The method according to claim 3, characterized in that: After adding alkaline substances, the phosphogypsum is aged for 20-30 hours.

5. The method according to claim 1, characterized in that: The amount of aluminum sulfate octadeca added in S2 is 1‰-5‰ of phosphogypsum.

6. The method according to claim 1, characterized in that: When CO2 is introduced, the temperature of the material should be controlled between 40-55℃.

7. The method according to claim 1, characterized in that: After CO2 is introduced, the calcium carbonate content in phosphogypsum is controlled at 3-8%.

8. The method according to claim 1, characterized in that: The moisture content of S2 stored in phosphogypsum is 10%-12%.

9. Cement is prepared using the cement retarder obtained by the method according to any one of claims 1 to 8, characterized in that, The amount of cement retarder added is 5% of the total raw material mass.

10. The cement according to claim 9, wherein the raw materials include clinker, gravel, fly ash, blast furnace slag and cement retarder, in a mass ratio of 71:5:6:13:5.

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