Preparation method of ardealite cement retarder

Abstract

The invention relates to the technical field of ardealite cement, and particularly discloses a preparation method of an ardealite cement retarder, which comprises the following steps: S1, carrying out gradient activation pretreatment on an ardealite raw material, sequentially comprising acid activation, ultrasonic dispersion and low-temperature calcination, to obtain modified ardealite; s2, carrying out a grafting reaction on the obtained modified ardealite and carboxymethyl cellulose or lignosulfonate through a mechanochemical method to form an organic-inorganic hybrid retarder matrix; and S3, mixing the obtained hybrid retarder matrix with a sodium gluconate solution, and freeze-drying to form the phosphogypsum cement retarder with a porous structure, through setting of gradient activation pretreatment and multi-stage cooperative treatment of acid activation, ultrasonic dispersion and low-temperature calcination, soluble phosphorus and fluorine impurities in ardealite are directionally removed, and meanwhile, the crystal proportion of beta-semi-hydrated gypsum and dihydrate gypsum is precisely regulated and controlled, so that the chemical purity and physical activity of ardealite are improved; and the cement retarder is more suitable for cement retarding requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of phosphogypsum cement, and particularly relates to a preparation method of a phosphogypsum cement retarder. Background Art

[0002] In the cement industry, as an important admixture, retarders are widely used to adjust the setting time of cement to meet the performance requirements of different projects. With the rapid development of the construction industry, the requirements for cement performance are increasing day by day. The research and development of retarders have become an important topic in the field of cement admixtures. Phosphogypsum, as an industrial by-product, is regarded as a potential retarder raw material because it is rich in calcium sulfate components. However, phosphogypsum often contains impurities such as soluble phosphorus and fluorine. The presence of these impurities not only affects the chemical purity of phosphogypsum, but may also have an adverse impact on the setting performance and later strength of cement.

[0003] In recent years, certain progress has been made in the research on phosphogypsum cement retarders. There are already various methods in the prior art to attempt to prepare retarders using phosphogypsum. However, when dealing with phosphogypsum raw materials, these methods often have problems such as a single treatment process and incomplete impurity removal. Specifically, although the traditional pickling method can remove some soluble impurities, it is difficult to achieve deep purification, resulting in a certain amount of harmful substances remaining in phosphogypsum; while the high-temperature calcination method can change the crystal structure of phosphogypsum and improve its activity, but high-temperature treatment is often accompanied by an increase in energy consumption and partial loss of gypsum activity, and it is unable to effectively remove impurities such as fluorine; in addition, the simple physical mixing method is easy to operate, but it is difficult to effectively compound phosphogypsum with organic retarder components, resulting in unstable retardation effects and being difficult to meet the high requirements for cement performance in modern projects. Therefore, it is necessary for workers to improve it. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a phosphogypsum cement retarder to solve the problems mentioned in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A preparation method of a phosphogypsum cement retarder includes the following steps:

[0007] S1. Gradient activation pretreatment is carried out on the phosphogypsum raw material, including acid activation, ultrasonic dispersion, and low-temperature calcination in sequence to obtain modified phosphogypsum;

[0008] S2. The modified phosphogypsum obtained in step S1 is grafted with carboxymethyl cellulose or lignosulfonate by mechanochemical reaction to form an organic-inorganic hybrid retarder matrix;

[0009] S3. Mix the hybrid retarder matrix obtained in step S2 with the sodium gluconate solution, and form a porous-structured phosphogypsum cement retarder after freeze-drying.

[0010] Preferably, in step S1, the acid activation is carried out using a sulfuric acid solution with a concentration of 5% to 10%, the solid-liquid ratio is 1:3 to 1:5, and the reaction time is 30 to 60 minutes.

[0011] Preferably, in step S1, the frequency of the ultrasonic dispersion is 20 to 40 kHz, and the treatment time is 15 to 30 minutes.

[0012] Preferably, in step S1, the temperature of the low-temperature calcination is 150 to 250 °C, and the calcination time is 1 to 2 hours.

[0013] Preferably, in step S2, the process conditions for the mechanochemical grafting reaction are: the ball-to-material ratio is 10:1 to 20:1, the rotation speed is 300 to 500 rpm, and the reaction time is 1 to 3 hours.

[0014] Preferably, in step S2, the addition amount of the carboxymethyl cellulose or lignosulfonate is 5% to 15% of the mass of the modified phosphogypsum.

[0015] Preferably, in step S3, the concentration of the sodium gluconate solution is 10% to 20%, and the mass ratio of the hybrid retarder matrix to the sodium gluconate solution is 1:1 to 1:2.

[0016] Preferably, in step S3, the conditions for freeze-drying are: the pre-freezing temperature is -40 to -30 °C, the vacuum degree is 10 to 30 Pa, and the drying time is 24 to 48 hours.

[0017] Preferably, in step S1, the mass ratio of β-hemihydrate gypsum to dihydrate gypsum in the obtained modified phosphogypsum is 3:7 to 7:3.

[0018] Preferably, in step S3, the porosity of the obtained porous-structured phosphogypsum cement retarder is 40% to 60%, and the pore size distribution is 10 to 100 μm.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) Through the setting of gradient activation pretreatment, multi-stage cooperative treatment of acid activation, ultrasonic dispersion and low-temperature calcination is adopted to directionally remove soluble phosphorus and fluorine impurities in phosphogypsum, and at the same time accurately control the crystal ratio of β-hemihydrate gypsum and dihydrate gypsum, thereby significantly improving the chemical purity and physical activity of phosphogypsum and making it more suitable for the cement retardation requirements.

[0021] (2) By setting up an organic-inorganic hybrid structure, carboxymethyl cellulose or lignosulfonate is grafted onto the surface of modified phosphogypsum by mechanochemistry to form a hybrid retarder matrix with a core-shell structure. The inorganic phase delays the early hydration, and the organic phase inhibits the rapid reaction of C3A through steric hindrance, thus achieving the synergistic enhancement of the retardation effect and the improvement of stability.

[0022] (3) By setting up a porous structure loading technology, the hybrid retarder matrix is combined with a sodium gluconate solution and freeze-dried to form a porous carrier with a controllable pore distribution, realizing the uniform loading and intelligent release of the organic retardation components, and thus achieving the dual effects of precise control of the retardation time and synchronous optimization of the cement strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a preparation flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0025] Example 1:

[0026] Preparation method of phosphogypsum cement retarder

[0027] Raw materials and equipment:

[0028] Phosphogypsum raw material: calcium sulfate dihydrate (CaSO4·2H2O), containing 1.2% soluble phosphorus (calculated as P2O5) and 0.5% fluorine (calculated as F).

[0029] Chemical reagents: sulfuric acid (industrial grade, concentration 98%), carboxymethyl cellulose (CMC, viscosity 800 to 1200 mPa·s), sodium gluconate (analytical pure).

[0030] Equipment: pickling reactor, ultrasonic disperser (frequency 20 to 40 kHz), box-type resistance furnace, planetary ball mill, freeze dryer.

[0031] Preparation steps

[0032] Gradient activation pretreatment of phosphogypsum:

[0033] Acid activation: The phosphogypsum raw material is mixed with a 5% sulfuric acid solution at a solid-liquid ratio of 1:4 and stirred and reacted at 60°C for 45 minutes.

[0034] After the reaction, filter and wash with deionized water until the pH of the filtrate is 6.5 to remove soluble phosphorus and fluorine impurities.

[0035] Ultrasonic dispersion: Place the pickled phosphogypsum slurry in an ultrasonic disperser and process it at a frequency of 30 kHz for 20 minutes to break up the aggregates.

[0036] Low-temperature calcination: Calcinate the dispersed wet phosphogypsum at 200 °C for 1.5 hours to obtain modified phosphogypsum.

[0037] Product analysis: XRD shows that the mass ratio of β-hemihydrate gypsum (CaSO4·0.5H2O) to dihydrate gypsum is 5:5, and the specific surface area increases from 2.1 m 2 / g of the original sample to 8.7 m 2 / g.

[0038] Preparation of organic-inorganic hybrid retarder matrix:

[0039] Add the modified phosphogypsum and carboxymethyl cellulose (CMC, addition amount 10 wt%) to a planetary ball mill.

[0040] Set the ball-to-material ratio to 15:1, the rotation speed to 400 rpm, and react for 2 hours to form a core-shell structure through mechanochemical action (SEM shows that CMC uniformly coats the phosphogypsum particles).

[0041] Freeze-drying forming of porous retarder:

[0042] Mix the hybrid retarder matrix and 15% sodium gluconate solution at a mass ratio of 1:1.5 and stir until completely wetted.

[0043] Pre-freezing: Place the mixture at -35 °C and freeze for 12 hours to form a solid precursor.

[0044] Freeze-drying: Dry at a vacuum degree of 20 Pa for 36 hours to obtain a porous phosphogypsum retarder.

[0045] Structure characterization: BET test shows that the porosity is 52%, and the pore diameter is mainly distributed between 20 and 80 μm; FTIR confirms that sodium gluconate is successfully loaded into the pores.

[0046] Example 2:

[0047] Preparation method of phosphogypsum cement retarder

[0048] Raw materials and equipment:

[0049] Phosphogypsum raw material: Industrial by-product phosphogypsum (CaSO4·2H2O), containing 1.5% P2O5, 0.6% F, and 15% moisture.

[0050] Chemical reagents: sulfuric acid (analytical grade, concentration 98%), sodium lignosulfonate (industrial grade, purity ≥90%), sodium gluconate (food grade).

[0051] Equipment: acid leaching reactor, high-pressure homogenizer (replacing ultrasonic wave), rotary calciner, high-speed mixer, vacuum freeze dryer.

[0052] Preparation steps

[0053] Gradient activation pretreatment of phosphogypsum:

[0054] Acid activation: Mix phosphogypsum with 8% sulfuric acid solution at a solid-liquid ratio of 1:3, and mechanically stir at 70°C for 60 minutes.

[0055] After the reaction, centrifuge and separate, wash with water until neutral (pH = 7.0), and dry until the moisture content ≤5%.

[0056] High-pressure homogenization dispersion (replacing ultrasonic wave): Prepare the pickled phosphogypsum into a slurry with a solid content of 20%, and circulate it through a high-pressure homogenizer at 50 MPa for 3 times, and the particle size D50 is reduced from 45 μm to 12 μm.

[0057] Low-temperature calcination: Use a rotary calciner to calcine at 180°C for 2 hours to obtain modified phosphogypsum.

[0058] Product analysis: XRD shows that the mass ratio of β-hemihydrate gypsum to dihydrate gypsum is 6:4, and thermogravimetric analysis (TGA) shows that the crystal water content is 5.8%.

[0059] Preparation of organic-inorganic hybrid retarder matrix:

[0060] Add the modified phosphogypsum and sodium lignosulfonate (addition amount 12wt%) to a high-speed mixer.

[0061] Mix at 80°C and a rotation speed of 800 rpm for 90 minutes, and use thermomechanical force to promote the grafting of sodium lignosulfonate onto the surface of phosphogypsum (the displacement of the characteristic peak of sulfonic acid group shown by FTIR confirms the successful grafting).

[0062] Freeze-drying molding of porous retarder: Mix the hybrid matrix with 18% sodium gluconate solution at a mass ratio of 1:1.2, and impregnate with ultrasonic assistance for 30 minutes.

[0063] Pre-freezing: Rapidly freeze at -40°C for 6 hours, and then maintain at -25°C for 10 hours to form a gradient freezing structure.

[0064] Freeze-drying: Dry at a vacuum degree of 15 Pa for 40 hours to obtain a porous retarder.

[0065] Structure characterization: Mercury intrusion porosimetry test shows that the porosity is 58%, the proportion of macropores (>50 μm) is 35%, and the proportion of mesopores (10-50 μm) is 55%.

[0066] Example 3:

[0067] Preparation method of phosphogypsum cement retarder

[0068] Raw materials and equipment:

[0069] Phosphogypsum raw material: industrial by - product phosphogypsum (CaSO4·2H2O), containing 1.8% P2O5, 0.7% F, and 18% moisture.

[0070] Chemical reagents: industrial - grade sulfuric acid (concentration 93%), modified calcium lignosulfonate (CLS, molecular weight 5000 - 10000), and sodium gluconate (industrial - grade).

[0071] Equipment: continuous pickling reactor (with automatic pH control), air - flow crushing and classification system (replacing ultrasonic / high - pressure homogenization), swirl - flow dynamic calcination furnace (processing capacity 500 kg / h), twin - screw extruder (for organic - inorganic compounding), and continuous vacuum freeze - drying production line.

[0072] Preparation steps

[0073] Continuous gradient activation pretreatment of phosphogypsum

[0074] Continuous acid activation:

[0075] Continuously feed the phosphogypsum raw material and 7% sulfuric acid solution at a ratio of 1:3.5;

[0076] React at 65 °C for a residence time of 50 minutes;

[0077] Adopt three - stage counter - current washing, and the final pH = 6.8.

[0078] Air - flow crushing treatment:

[0079] Process with an air - flow mill at a pressure of 0.8 MPa;

[0080] The product D97 ≤ 15 μm, and the specific surface area reaches 11.3 m 2 / g.

[0081] Dynamic calcination:

[0082] Treat at 190 °C for 100 minutes in a swirl - flow calcination furnace;

[0083] The thermal efficiency is increased by 40% compared with the box - type furnace;

[0084] The proportion of the product β - hemihydrate gypsum is 55 ± 2%.

[0085] Continuous organic - inorganic compounding: Adopt the twin - screw extrusion process:

[0086] The temperature of Zone 1 is 80°C, and the temperature of Zone 2 is 110°C;

[0087] The screw rotation speed is 120 rpm;

[0088] The addition amount of modified calcium lignosulfonate is 8%;

[0089] The residence time is 8 minutes;

[0090] Online infrared monitoring shows that the grafting rate ≥ 92%.

[0091] Industrial freeze-drying:

[0092] The composite material is mixed with 20% sodium gluconate solution at a ratio of 1:1;

[0093] 3-5 mm particles are prepared by spray granulation;

[0094] Continuous freeze-drying process:

[0095] Pre-freezing zone: -38°C / 2 h;

[0096] Sublimation zone: Gradual temperature rise from -25°C to 20°C, vacuum degree 10 Pa;

[0097] The total drying time is 28 hours;

[0098] The moisture content of the final product ≤ 1.5%.

[0099] Control example:

[0100] Preparation method of traditional single pickling method (existing technology):

[0101] The phosphogypsum raw material is pickled with 5% sulfuric acid solution (solid-liquid ratio 1:4) at 60°C for 45 minutes, and washed with water until neutral.

[0102] It is directly dried and used as a retarder without ultrasonic dispersion, calcination or organic modification.

[0103] Performance comparison:

[0104] Index Prior art Example 1 Residual amount of soluble phosphorus 0.5％ ≤0.1％ Initial setting time (minutes) 150 245 Retention rate of 28-day compressive strength 92％ 108％ <![CDATA[Specific surface area (m 2 / g)]]> 3.2 8.7

[0105] Defect analysis: The impurity removal is not complete, resulting in the reverse shrinkage of the later strength of the cement, no porous structure and organic components, and poor retardation effect.

[0106] Preparation method of conventional calcination method (existing technology):

[0107] Phosphogypsum is calcined at 300°C for 2 hours, directly ground and used without gradient activation or hybridization modification.

[0108] Performance comparison:

[0109] Index Prior art Example 2 Proportion of β-hemihydrate gypsum 85% (too high) 60% (optimization range) Initial setting time (minutes) 190 268 Porosity No porosity 58％ Energy consumption (kWh / t) 180 120 (high-pressure homogenization process)

[0110] Defect analysis: High-temperature calcination destroys the activity of gypsum, resulting in unstable setting time, no pore structure, and inability to load organic retarder components.

[0111] Preparation method by simple physical mixing method (prior art):

[0112] Phosphogypsum and sodium lignosulfonate (10wt%) are physically mixed without mechanochemical grafting.

[0113] Directly dry-mixed with sodium gluconate without freeze-drying.

[0114] Performance comparison:

[0115]

[0116]

[0117] Defect analysis: Physical mixing leads to component separation, the retardation effect is uncontrollable, and industrial continuous production cannot be achieved.

[0118] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a phosphogypsum cement retarder, characterized in that, It includes the following steps: S1. Gradiently activate and pretreat the phosphogypsum raw material, successively including acid activation, ultrasonic dispersion, and low-temperature calcination to obtain modified phosphogypsum; S2. Graft react the modified phosphogypsum obtained in step S1 with carboxymethyl cellulose or lignosulfonate by mechanochemical method to form an organic-inorganic hybrid retarder matrix; S3. Mix the hybrid retarder matrix obtained in step S2 with a sodium gluconate solution, and form a phosphogypsum cement retarder with a porous structure after freeze-drying.

2. The preparation method of a phosphogypsum cement retarder according to claim 1, characterized in that: In step S1, the acid activation uses a sulfuric acid solution with a concentration of 5% to 10%, the solid-liquid ratio is 1:3 to 1:5, and the reaction time is 30 to 60 minutes.

3. The preparation method of a phosphogypsum cement retarder according to claim 1, characterized in that: In step S1, the frequency of the ultrasonic dispersion is 20 to 40 kHz, and the treatment time is 15 to 30 minutes.

4. The preparation method of a phosphogypsum cement retarder according to claim 1, characterized in that: In step S1, the temperature of the low-temperature calcination is 150 to 250 °C, and the calcination time is 1 to 2 hours.

5. The preparation method of a phosphogypsum cement retarder according to claim 1, characterized in that: In step S2, the process conditions of the mechanochemical graft reaction are: the ball-to-material ratio is 10:1 to 20:1, the rotation speed is 300 to 500 rpm, and the reaction time is 1 to 3 hours.

6. The preparation method of a phosphogypsum cement retarder according to claim 1, characterized in that: In step S2, the addition amount of the carboxymethyl cellulose or lignosulfonate is 5% to 15% of the mass of the modified phosphogypsum.

7. The preparation method of a phosphogypsum cement retarder according to claim 1, characterized in that: In step S3, the concentration of the sodium gluconate solution is 10% to 20%, and the mass ratio of the hybrid retarder matrix to the sodium gluconate solution is 1:1 to 1:

2.

8. The preparation method of a phosphogypsum cement retarder according to claim 1, characterized in that: In step S3, the conditions of the freeze-drying are: the pre-freezing temperature is -40 to -30 °C, the vacuum degree is 10 to 30 Pa, and the drying time is 24 to 48 hours.

9. The preparation method of a phosphogypsum cement retarder according to claim 1, characterized in that: In step S1, the mass ratio of β-hemihydrate gypsum to dihydrate gypsum in the obtained modified phosphogypsum is 3:7 to 7:

3.

10. The preparation method of a phosphogypsum cement retarder according to claim 1, characterized in that: In step S3, the porosity of the obtained phosphogypsum cement retarder with a porous structure is 40% to 60%, and the pore size distribution is 10 to 100 μm.

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