Preparation method of cement retarder with controllable retarding time

Abstract

The invention discloses a preparation method of a cement retarder with controllable retarding time, which comprises the following steps: mixing phosphogypsum with an oxalic acid solution, pulping to remove eutectic phosphorus, then removing soluble phosphorus by a washing process, mixing the obtained two-step washed gypsum with a modifier and a binder, granulating, and curing to obtain the cement retarder. The initial setting time and the final setting time of the cement can be obviously reduced. The process is simple, the raw materials are few in variety and wide in source, the influence of phosphorus in phosphogypsum on cement performance is reduced, the requirement for retarding time during cement construction can be met, and wide application prospects are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste recycling, and particularly relates to a method for preparing a cement retarder with controllable retarding time. Background Art

[0002] Phosphogypsum is a solid waste produced in the wet phosphoric acid process, and its main component is calcium sulfate dihydrate. The composition of phosphogypsum is relatively complex. In addition to calcium sulfate, there are also incompletely decomposed phosphate rock, residual phosphoric acid, fluoride, acid insoluble matter, organic matter, etc. At present, 4.5-5 tons of phosphogypsum are produced as a by-product for every ton of phosphoric acid produced. The random discharge and accumulation of phosphogypsum has seriously damaged the ecological environment, not only polluting groundwater resources, but also causing waste of land resources.

[0003] SO4 produced by dissolution of phosphogypsum 2- It reacts with calcium aluminate hydrate produced by cement hydration to form monosulfide calcium sulfoaluminate hydrate. If there is too much gypsum, it will further form polysulfide calcium sulfoaluminate hydrate, commonly known as calcium sulfoaluminate. This precipitate adheres to the surface of clinker particles, reducing the contact area with water, thereby delaying the hydration process of cement clinker. Therefore, phosphogypsum can be used as a cement retarder to slow down the hydration rate of C3A, thereby prolonging the setting time of cement.

[0004] The SO3 content in phosphogypsum is high and stable, but the total amount of harmful impurities such as phosphorus, fluorine, and organic matter it contains is about 3% of phosphogypsum. The content of impurity phosphorus is relatively high, and it can be divided into three types according to its existence form, namely water-soluble phosphorus, insoluble phosphorus, and eutectic phosphorus. Among them, water-based phosphorus is mainly in the form of H3PO4, H2PO4 - or HPO4 2- It exists in the form of , which has the greatest impact on cement performance. It will delay the coagulation and hardening of cement, reduce the strength of the hardened body, and reduce the early strength of cement. Therefore, it is required that the water-soluble phosphorus should be controlled below 1.5%; the eutectic phosphorus in phosphogypsum can also be released in a strong alkaline environment, producing the same harmful effects as soluble phosphorus. The content of eutectic phosphorus should be controlled below 0.2%, otherwise it will have a greater impact on the performance of cement.

[0005] Chinese patent CN101367632A discloses a modified phosphogypsum cement retarder and a preparation method thereof, wherein the industrial waste residue phosphogypsum is compositely modified by industrial waste residue carbide slag and fly ash, and cement activator sodium sulfate powder and / or cement grinding aid triethanolamine scraps are added, and the product is obtained after being fed into a silo, crushed, balled in a drum-type balling machine, and dried; the product has the advantages of accelerating hydration, promoting cement coagulation, improving early strength of cement, and eliminating the influence of soluble trace components on cement hydration.

[0006] Chinese patent CN1279219A discloses a phosphogypsum cement retarder and a preparation method thereof. The new phosphogypsum cement retarder containing activated fly ash and dihydrate gypsum as main components is prepared from industrial by-product phosphogypsum, fly ash, calcium materials and activator as main raw materials through batching, mixing, molding, curing and other processes. The retarder can stabilize and normally adjust the setting of cement, improve the early strength of cement, reduce cement cost and increase cement output.

[0007] At present, when preparing cement retarders with phosphogypsum, a large amount of other ingredients need to be added to modify the phosphogypsum to achieve the retarding effect. The ingredients are relatively complex, and no attention is paid to the removal of phosphorus in the phosphogypsum. Therefore, it is necessary to develop a method that can accurately control the phosphorus content in phosphogypsum and then prepare cement retarders, so as to achieve the ideal setting time and late strength of cement by using simple raw materials. Summary of the invention

[0008] In view of the above technical problems, the present invention provides a method for preparing a cement retarder with controllable retarding time, which utilizes a water washing process to remove eutectic phosphorus and water-soluble phosphorus in phosphogypsum, and then mixes with a modifier and a binder to form granules and cure to obtain the cement retarder, which can effectively adjust the retarding time of cement and realize the comprehensive utilization of phosphogypsum.

[0009] In order to achieve the above object, the present invention provides a method for preparing a cement retarder with controllable retarding time, comprising the following steps: (1) Removing eutectic phosphorus: mixing phosphogypsum with the phosphorus removal liquid, leaching and stirring in the slurry to obtain phosphogypsum slurry; (2) Dehydration: Filter the phosphogypsum slurry to obtain one-step water-washed gypsum; (3) Removal of water-soluble phosphorus: washing the first-step water-washed gypsum twice and filtering to obtain the second-step water-washed gypsum; (4) Granulation: Mix the two-step water-washed gypsum with a modifier and a binder, and granulate to obtain gypsum balls; (5) Curing: Gypsum balls are cured to obtain cement retarder.

[0010] Preferably, the solid content of the phosphogypsum slurry in step (1) is 30-35%.

[0011] Preferably, the immersion time in step (1) is 20-40 minutes.

[0012] Preferably, the phosphorus removal liquid in step (1) is oxalic acid solution.

[0013] Further preferably, the mass concentration of the oxalic acid solution is 0.8-1.5%.

[0014] Preferably, the solid content during the secondary water washing in step (3) is 30-35%, and the secondary water washing time is 30-45 minutes.

[0015] Preferably, the attached water content of the two-step water-washed gypsum in step (3) is 20%-25%.

[0016] Preferably, the gypsum balls in step (4) are composed of 88-98% two-step water-washed gypsum, 5-12% modifier and 0.5-1% binder.

[0017] Further preferably, the modifier is carbide slag and / or quicklime.

[0018] Further preferably, the binder is bentonite and / or starch.

[0019] Preferably, the granulation method in step (4) is disc granulation or cylinder granulation.

[0020] Preferably, the particle size of the gypsum balls in step (4) is 25-40 mm.

[0021] Preferably, the curing method in step (5) is aging or steam curing.

[0022] Further preferably, the steam curing temperature is 150-180° C., the curing time is 120-170 min; and the aging time is 3-7 days.

[0023] The beneficial effects of the present invention are: 1. Use oxalic acid solution to first remove eutectic phosphorus in phosphogypsum, and then use a water washing process to remove soluble phosphorus, which significantly reduces the phosphorus content in phosphogypsum and reduces the amount of water used. At the same time, the water after the water washing process can be recycled to further save water resources.

[0024] 2. Phosphogypsum with significantly reduced phosphorus content is mixed with a modifier and a binder to obtain a cement retarder without the need to compound multiple raw materials. When mixed with cement, it can significantly reduce the initial setting time and final setting time of cement, meeting the setting time requirements during cement construction.

[0025] 3. The process of the present invention is simple, the raw materials are widely available and simple in variety, the cost is low, and it has broad application prospects. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further explained below in conjunction with specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The protection scope of the present invention shall be subject to the contents recorded in the claims. Any modification or replacement made by a person skilled in the art to the technical solution of the present invention without creative work shall fall within the protection scope of the present invention.

[0027] Example 1 (1) mixing phosphogypsum with oxalic acid solution (mass concentration of 1%) and re-slurrying, stirring for 30 minutes and then filtering to obtain one-step water-washed gypsum; wherein the solid content during re-slurrying is 35%; (2) Mixing the first-step water-washed gypsum with clean water for re-slurrying, stirring for 30 minutes and then filtering to obtain the second-step water-washed gypsum; wherein the solid content during re-slurrying is 35%; (3) 90% of the two-step water-washed gypsum, 9% of carbide slag and 1% of bentonite are placed in a disc granulator for granulation to obtain gypsum balls; (4) The gypsum balls are aged at room temperature for 3 days to obtain a cement retarder.

[0028] Example 2 (1) mixing phosphogypsum with oxalic acid solution (mass concentration of 1.2%) and re-slurrying, stirring for 30 minutes and then filtering to obtain one-step water-washed gypsum; wherein the solid content during re-slurrying is 30%; (2) Mixing the first-step water-washed gypsum with clean water for re-slurrying, stirring for 30 minutes and then filtering to obtain the second-step water-washed gypsum; wherein the solid content during re-slurrying is 30%; (3) 90% of the two-step water-washed gypsum, 9% of carbide slag and 1% of bentonite are placed in a disc granulator for granulation to obtain gypsum balls; (4) The gypsum balls are aged at room temperature for 3 days to obtain a cement retarder.

[0029] Example 3 The method and steps are the same as those in Example 1, except that the mass concentration of the oxalic acid solution in step (1) is changed to 0.8%.

[0030] Example 4 The method and steps are the same as those of Example 1, except that the amount of the second-step water-washed gypsum in step (3) is changed to 88%, the amount of carbide slag is changed to 11.5%, and the amount of bentonite is changed to 0.5%, to prepare a cement retarder.

[0031] Example 5 The method and steps are the same as those in Example 1, except that the amount of the second-step water-washed gypsum in step (3) is changed to 94%, the 9% carbide slag is changed to 5.2% quicklime, and the 1% bentonite is changed to 0.8% starch to prepare a cement retarder.

[0032] Comparative Example 1 (1) Take 90% of phosphogypsum raw materials, directly put them into a disc granulator with 9% of carbide slag and 1% of bentonite, and granulate them to obtain gypsum balls; (2) The gypsum balls are aged at room temperature for 3 days to obtain a retarder.

[0033] Comparative Example 2 (1) mixing phosphogypsum with oxalic acid solution (mass concentration of 1%) and re-slurrying, stirring for 30 minutes and then filtering to obtain one-step water-washed gypsum; wherein the solid content during re-slurrying is 30%; (2) 90% of one-step water-washed gypsum, 9% of carbide slag and 1% of bentonite are placed in a disc granulator to granulate to obtain gypsum balls; (2) The gypsum balls are aged at room temperature for 3 days to obtain a retarder.

[0034] Comparative Example 3 (1) mixing phosphogypsum with clean water and re-slurrying, stirring for 30 minutes and then filtering to obtain one-step water-washed gypsum; wherein the solid content during re-slurrying is 30%; (2) 90% of one-step water-washed gypsum, 9% of carbide slag and 1% of bentonite are placed in a disc granulator to granulate to obtain gypsum balls; (3) The gypsum balls are aged at room temperature for 3 days to obtain a retarder.

[0035] Comparative Example 4 The method and steps are the same as those in Example 1, except that the mass concentration of the oxalic acid solution in step (1) is changed to 0.5% to prepare a retarder.

[0036] Comparative Example 5 The method and steps are the same as those in Example 1, except that the mass concentration of the oxalic acid solution in step (1) is changed to 2% to prepare a retarder.

[0037] Comparative Example 6 The method and steps are the same as those in Example 1, except that the solid content in steps (1) and (2) is changed to 25%, thereby preparing a retarder.

[0038] Comparative Example 7 The method and steps are the same as those in Example 1, except that the solid content in steps (1) and (2) is changed to 40%, thereby preparing a retarder.

[0039] Comparative Example 8 (1) mixing phosphogypsum with clean water and re-slurrying, stirring for 30 minutes and then filtering to obtain one-step water-washed gypsum; wherein the solid content during re-slurrying is 30%; (2) Mixing the first-step water-washed gypsum with oxalic acid solution (mass concentration of 1.2%) for re-slurry, stirring for 30 minutes and then filtering to obtain the second-step water-washed gypsum; wherein the solid content during re-slurrying is 30%; (3) 90% of the two-step water-washed gypsum, 9% of carbide slag and 1% of bentonite are placed in a disc granulator for granulation to obtain gypsum balls; (4) The gypsum balls are aged at room temperature for 3 days to obtain a retarder.

[0040] Comparative Example 9 The method and steps are the same as those in Example 1, except that the oxalic acid solution in step (1) is replaced by sodium acetate solution to prepare a retarder.

[0041] Results: The retarders prepared in the above examples and comparative examples were tested for phosphorus content using the quinoline phosphomolybdic acid weight method. The results are shown in Table 1. The retarder prepared in the above embodiments and comparative examples was mixed with cement clinker and other auxiliary materials in a mass ratio of 5:95, and the initial setting time and final setting time were tested according to GB / T 1346-2011 "Test method for water consumption, setting time and stability of cement standard consistency", and the strength of cement on the 7th and 28th days was tested according to GB / T 17671-2021 "Test method for strength of cement mortar", and the results are shown in Table 1.

[0042] Table 1 Performance of retarder

[0043] The results are shown in Table 1: mixing phosphogypsum with oxalic acid can effectively reduce the phosphorus content in phosphogypsum, and as the concentration of oxalic acid increases, the phosphorus content gradually decreases. However, considering the cost and cleaning effect, the optimal concentration of oxalic acid is 0.8-1.5%.

Claims

1. A method for preparing a cement retarder with controllable retarding time, characterized in that: The steps include: (1) Removing eutectic phosphorus: mixing phosphogypsum with the phosphorus removal liquid, leaching and stirring in the slurry to obtain phosphogypsum slurry; (2) Dehydration: Filter the phosphogypsum slurry to obtain one-step water-washed gypsum; (3) Removal of water-soluble phosphorus: washing the first-step water-washed gypsum twice and filtering to obtain the second-step water-washed gypsum; (4) Granulation: Mix the two-step water-washed gypsum with a modifier and a binder, and granulate to obtain gypsum balls; (5) Curing: Gypsum balls are cured to obtain cement retarder.

2. The method for preparing a cement retarder with controllable retarding time according to claim 1, characterized in that: The solid content of the phosphogypsum slurry in step (1) is 30-35%.

3. The method for preparing a cement retarder with controllable retarding time according to claim 1, characterized in that: The immersion time in step (1) is 20-40 minutes.

4. The method for preparing a cement retarder with controllable retarding time according to claim 1, characterized in that: The phosphorus removal liquid in step (1) is an oxalic acid solution; the mass concentration of the oxalic acid solution is 0.8-1.5%.

5. The method for preparing a cement retarder with controllable retarding time according to claim 1, characterized in that: The solid content during the secondary water washing in step (3) is 30-35%, and the secondary water washing time is 30-45 minutes.

6. The method for preparing a cement retarder with controllable retarding time according to claim 1, characterized in that: The attached water content of the two-step water-washed gypsum in step (3) is 20%-25%.

7. The method for preparing a cement retarder with controllable retarding time according to claim 1, characterized in that: The gypsum balls described in step (4) are composed of 88-98% two-step water-washed gypsum, 5-12% modifier and 0.5-1% binder.

8. The method for preparing a cement retarder with controllable retarding time according to claim 7, characterized in that: The modifier is carbide slag and / or quicklime.

9. The method for preparing a cement retarder with controllable retarding time according to claim 7, characterized in that: The binder is bentonite and / or starch.

10. The method for preparing a cement retarder with controllable retarding time according to claim 1, characterized in that: The curing method in step (5) is aging or steam curing; the temperature of the steam curing is 150-180° C., and the curing time is 120-170 min; and the aging time is 3-7 days.

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