Precursor pretreatment method for phosphogypsum-red mud-based cementing material

Abstract

The invention discloses a precursor pretreatment method for an ardealite-red mud based cementing material, which comprises the following steps: mixing red mud and water, and adding an acid leaching solution to obtain acidified red mud; adding a complexing agent into the acidified red mud to obtain acidified complexed red mud; the preparation method comprises the following steps: mixing ardealite and acidified complexed red mud, adding water, and stirring to complete a precursor pretreatment step; alkali metal cations in the red mud are dissolved out through acid leaching, and reaction active sites of the red mud are improved. The utilization rate of alkali metal cations, especially iron, in the red mud can be increased through a complexing process. As the content of sodium in the red mud is extremely high, the red mud is easy to soften when encountering water and the strength of the red mud is reduced, in order to improve the strength of the red mud, the red mud is subjected to calcification treatment by utilizing phosphogypsum at a certain temperature, and the main purpose is to accelerate conversion from sodium aluminosilicate to calcium aluminosilicate and dissolution of the phosphogypsum. The materials used in the method are common chemical products, so that the cost is low, and the reaction activity of the phosphogypsum and the red mud can be fully excited.

Description

Technical Field

[0001] The present invention belongs to the technical field of cement, and particularly relates to a method for pretreating a precursor of a phosphogypsum - red mud based cementitious material. Background Art

[0002] In addition to the main component calcium sulfate, phosphogypsum usually contains a large amount of impurity components, such as fluorine, heavy metals, organic substances, etc. These impurities may not only have an adverse impact on the performance of products such as cement and cementitious materials, but also cause environmental pollution. For example, the fluorine content in phosphogypsum is relatively high, which may cause fluoride pollution during the production process, posing a threat to human health and the ecological environment. When phosphogypsum is used as part of a cementitious material, the hydration reaction is relatively slow and the early strength is insufficient, resulting in its limited application in actual engineering. In cement production, phosphogypsum is used as a component to adjust the setting time of cement, mainly to delay the setting of cement. However, when used as the main material of a cementitious material, the hydration reaction of phosphogypsum is relatively slow, resulting in its inability to provide sufficient strength in a short time and affecting the progress of engineering construction.

[0003] Red mud is a solid waste generated during the extraction of bauxite from bauxite ore. It has extremely high alkalinity, fine particles and complex mineral composition, and is usually rich in elements such as iron, calcium, aluminum, silicon, sodium, etc. Due to its complex composition, strong alkalinity and poor chemical stability, it is difficult to be directly applied in the construction field. Especially when used in phosphogypsum - red mud based cementitious materials, the high alkalinity and low reactivity of red mud will affect the early strength and setting performance of the cementitious material. Therefore, improving the activity of red mud and its reactivity with phosphogypsum has become the key to improving the early strength and optimizing the setting time.

[0004] Existing red mud pretreatment methods include roasting method, alkali activation method, biological method, etc. The roasting method treats red mud at high temperature to change its mineral composition and stimulate its reactivity. However, a large amount of energy is consumed during the roasting process, and important elements such as calcium and iron in red mud may be lost during the treatment process, affecting its comprehensive utilization value. In addition, high - temperature roasting may cause the emission of greenhouse gases such as carbon dioxide, posing environmental protection problems. The alkali activation method adds a certain amount of alkaline substances to make the aluminum and silicon minerals in red mud undergo dissolution reactions in an alkaline environment, thereby improving its hydration activity. The alkali activation method requires the use of a large amount of alkali activators, and the activation effect is affected by factors such as the dosage of alkali and temperature, and is easily affected by the environment. The biological activation method is a green technology that has gradually emerged in recent years. It activates red mud by using microorganisms or enzyme substances. However, the research on the biological activation method is still in its infancy, and its actual effect and industrial application have not been fully verified. At the same time, the treatment process of the biological activation method is relatively complex, and it is necessary to control the types, concentrations of microorganisms and reaction conditions, and the operation difficulty is relatively large.

[0005] In summary, when a high dosage of phosphogypsum and red mud are simultaneously used as the cementitious materials, the setting time is too long and the early strength is low. The main reason is that both the activities of phosphogypsum and red mud are very low, the dissolution rate of phosphogypsum is slow, and it cannot provide Ca to the system in time. 2+ , the precursors inside the red mud cannot be hydrated to produce cementitious products in time, resulting in too long setting time and too low early strength of the system. Most of the existing red mud activation methods waste resources or are not applicable to large-scale production. Therefore, it is urgent to find a more suitable precursor activation method.

[0006] The patent document with the publication number of CN108203290A discloses a red mud modified material and its application in road subgrade. The red mud modified material described in this patent is composed of red mud powder, modified phosphogypsum powder, cement, curing agent, latex powder, stabilizer and regulator. This patent uses the treated red mud in road subgrade, but does not involve the technical method of reducing the setting time of the base cementitious material. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a method for pretreating precursors for phosphogypsum-red mud based cementitious materials.

[0008] The present invention is achieved through the following technical solutions.

[0009] A method for pretreating precursors for phosphogypsum-red mud based cementitious materials provided by the present invention includes the following steps:

[0010] S1: Mix red mud and water, and then add an acid leaching solution to obtain acidified red mud;

[0011] S2: Add a complexing agent to the acidified red mud to obtain acidified complexed red mud;

[0012] S3: Mix phosphogypsum and acidified complexed red mud and then add water and stir to complete the precursor pretreatment step.

[0013] Preferably, the cementitious material includes, by mass percentage, 40-50% phosphogypsum, 30-35% slag, 17-24% red mud, 1-4% lime, 0.01-0.08% polycarboxylate water reducer, and the water-cement ratio is 0.25-0.45.

[0014] Preferably, the phosphogypsum is the original state phosphogypsum after drying, with a CaSO 4 content ≥ 85%; the red mud needs to be crushed, with SiO 2 +Al 2 O 3 ≥ 45%, Fe 2 O 1 ≥ 20%; the calcium oxide content of the slag lime > 95%.

[0015] Preferably, in the step S1, the red mud and water are mixed at a liquid-solid ratio of 2-3, and an acid leaching solution of 0.5-1 mol / L is added.

[0016] Preferably, the complexing agent is ethylenediaminetetraacetic acid, and the addition amount is 5-8% of the mass of the red mud.

[0017] Preferably, after the acidified red mud is obtained in the step S1, it is allowed to stand for not less than 1 h.

[0018] Preferably, in the step S3, aged phosphogypsum is used. After the aged phosphogypsum and the acidified complexed red mud are mixed, water is added and stirred at a liquid-solid ratio of 1-7:1, and the reaction is carried out at a reaction temperature of 60-100 °C for not less than 3 h.

[0019] Preferably, the preparation steps of the aged phosphogypsum include: under normal temperature and pressure, aging for 18-36 h with a mass ratio of phosphogypsum to lime = 80-100 and a water-binder ratio of 0.40-0.65.

[0020] Preferably, in the step S3, the mass ratio of the aged phosphogypsum to the acidified complexed red mud = 2-3.

[0021] The beneficial effects of the present invention are as follows:

[0022] The acid leaching process of the present invention can leach out the alkali metal cations with relatively low activity in the red mud from nepheline, albite and various oxides, especially the iron compounds with high content and stability, and can improve the participation degree of the alkali metal cations in the red mud in the gelling reaction. In addition, it can also reduce the high alkalinity of the red mud, increase the reactive sites on the surface of the red mud, and accelerate the synergistic reaction between the red mud and the phosphogypsum.

[0023] The complexing process of the present invention can complex the alkali metal cations leached by acid leaching in time to form metal-EDTA complexes with a certain strength. It improves the utilization rate of the alkali metal cations in the gelling system, gives full play to the activity of the red mud, and EDTA has an excellent complexing effect on iron ions in particular, and can make full use of the iron ions with a content of up to 20% but stable in the red mud, and improve the reaction activity of the red mud.

[0024] The calcification process of the present invention can calcify the sodium-containing compounds such as albite and nepheline in the red mud. Because the albite and nepheline compounds are unstable in water and have low strength, calcification can promote the conversion of sodium aluminosilicate to calcium aluminosilicate, solidify the red mud to improve the strength. Assisted by a temperature of 60 °C to 100 °C, it can accelerate the dissolution of the phosphogypsum, greatly shorten the calcification time, and in addition, it can also accelerate the reaction of the uncomplexed alkali metal cations with calcium ions to form a gelling substance with strength, and finally accelerate the setting and improve the early strength. Description of the Drawings

[0025] Figure 1This is the process flow chart of the present invention. Detailed implementation manners

[0026] The technical solutions of the present invention will be further described below, but the scope of protection is not limited thereto.

[0027] A precursor pretreatment method for phosphogypsum-red mud based cementitious material, characterized by comprising the following steps:

[0028] S1: Mix red mud and water, and then add an acid leaching solution to obtain acidified red mud. This step is the acid leaching process;

[0029] S2: Add a complexing agent to the acidified red mud to complex alkali metal cations and improve the reaction activity of the red mud to obtain acidified complexed red mud. This step is the complexing process;

[0030] S3: Mix phosphogypsum and acidified complexed red mud and then add water and stir. It is mainly to solidify the red mud and improve its activity and strength. This step is the calcification process, and the precursor pretreatment step is completed.

[0031] The cementitious material is in mass percentage and includes 40-50% phosphogypsum, 30-35% slag, 17-24% red mud, 1-4% lime, 0.01-0.08% polycarboxylate water reducer, and the water-binder ratio is 0.25-0.45.

[0032] The phosphogypsum is the original dried phosphogypsum, with a CaSO 4 content ≥ 85%, and the content of harmful impurities such as P 2 O 5 , F - ≤ 1%; the red mud needs to be crushed, with SiO 2 +Al 2 O 3 ≥ 45%, Fe 2 O 1 ≥ 20%; the slag is S95 grade slag, and the calcium oxide content of the lime > 95%.

[0033] In step S1, the red mud and water are mixed at a liquid-solid ratio of 2-3, and 0.5-1 mol / L of acid leaching solution is added by volume.

[0034] When the liquid-solid ratio of red mud and water is lower than 2, the red mud slurry does not have excellent fluidity, which will cause agglomeration of other added substances and affect the pretreatment result; when the liquid-solid ratio is greater than 3, the water will be excessive, and at this time, too much sulfuric acid is added, resulting in a certain degree of waste of resources. Therefore, the liquid-solid ratio is controlled at 2-3. When the sulfuric acid concentration is lower than 0.5 mol / L, the alkali metal cations cannot be leached out, and when it is higher than 1 mol / L, the supernatant will be strongly acidic and difficult to handle properly. Therefore, the sulfuric acid concentration is controlled at 0.5 mol / L - 1 mol / L.

[0035] The complexing agent is ethylenediaminetetraacetic acid (EDTA), and the addition amount is 5-8% of the mass of red mud. When the EDTA content is lower than 5% of the red mud, the complexing effect will be poor and cannot meet the performance requirements. When its content is higher than 8% of the red mud, the EDTA will be in excess, and the excess EDTA no longer has a complexing effect, resulting in material waste. Therefore, the EDTA content is controlled at 5%-8%.

[0036] After obtaining the acidified red mud in step S1, it is allowed to stand for not less than 1 h.

[0037] In step S3, aged phosphogypsum is used. After the aged phosphogypsum is mixed with the acidified complexed red mud, water is added and stirred at a liquid-solid ratio of 1-7:1, and the reaction is carried out at a reaction temperature of 60-100 °C for not less than 3 h.

[0038] The preparation steps of the aged phosphogypsum include: under normal temperature and pressure, aging for 18-36 h at a mass ratio of phosphogypsum to lime = 80-100 and a water-binder ratio of 0.40-65.

[0039] In step S3, the mass ratio of the aged phosphogypsum to the acidified complexed red mud = 2-3.

[0040] When the phosphogypsum / red mud is less than 2, the relatively low solubility of phosphogypsum is not sufficient to provide the calcium ions required for the calcification of red mud. When it is greater than 3, the content of phosphogypsum in the system is too high and the red mud is too low. At this time, the strength improved by the calcification of red mud contributes less to the overall strength. Therefore, the phosphogypsum / red mud is controlled at 2-3. When the liquid-solid ratio is less than 2, the slurry does not have excellent fluidity, and the high content of powder materials and strong water absorption will affect the pretreatment results. When the liquid-solid ratio is greater than 3, the water will be in excess. At this time, part of the phosphogypsum will undergo hydration, and the calcium ions provided by it for the calcification of red mud will be less, resulting in a poor calcification effect. Therefore, the liquid-solid ratio is controlled at 2-3. When the calcification treatment temperature is lower than 60 °C, the time required for calcification is longer, affecting the pretreatment process. When the temperature is higher than 100 °C, the influence of temperature on the calcification time becomes smaller. To save resources, the upper limit of the temperature is set at 100 °C. Therefore, the calcification experiment temperature is controlled at 60 °C-100 °C.

[0041] Since the compounds formed by various alkali metal cations in red mud are relatively stable and are not easily utilized, this is one of the main reasons for its low activity. Therefore, the present invention proposes to first perform acid leaching on red mud. The purpose of acid leaching is to dissolve the alkali metal cations in red mud, increase the reactive active sites of red mud, and at the same time reduce the high alkalinity of red mud, and adjust the pH value of the slurry to 8-9 for the treatment of the supernatant after standing.

[0042] Since the hydration products of the alkali metal cations after dissolution and their utilization rates in subsequent hydration are not clear enough, the present invention needs to complex the acidified red mud. The main purpose is to make full use of the alkali metal cations, especially the complexation of iron which is relatively stable in red mud. This process can improve the utilization rate of alkali metal cations, especially iron, in red mud. Due to the extremely high sodium content in red mud, it also causes the red mud to be easily softened and its strength to decrease when it meets water. To improve the strength of red mud, the present invention proposes to calcify the red mud with phosphogypsum at a certain temperature. The main purpose is to accelerate the conversion of sodium aluminosilicate to calcium aluminosilicate and the dissolution of phosphogypsum. Assisted by a temperature of about 60 - 100 °C, it can reduce the calcification time, increase the dissolution rate of phosphogypsum, and also accelerate the conversion of iron compounds to iron garnet. The products used in the precursor pretreatment method are all common chemical products, which can not only reduce the cost but also fully stimulate the reaction activity of phosphogypsum and red mud.

[0043] Example 1:

[0044] As Figure 1 shown, a precursor pretreatment method for promoting coagulation and early strength of phosphogypsum - red mud - based cementitious materials includes the acid leaching process, complexation process, and calcification process of red mud. First, mix water and red mud at a liquid - solid ratio of 3:1, add 0.5 mol / L sulfuric acid by volume and soak for 4 h to leach out alkali metal cations, then add 5% of the mass of red mud of ethylenediaminetetraacetic acid to complex the alkali metal cations, and let the obtained slurry stand for 1 h to make it react fully.

[0045] Under the action of inorganic acid, the supernatant is acidic at this time, with a pH value of 4 - 5, and record the required data.

[0046] Then carry out calcification treatment. Mix the aged phosphogypsum and the acid - leached red mud at a mass ratio of 2.25:1, add water and stir at a liquid - solid ratio of 3:1, and finally let the slurry stand at 60 °C for 3 h. Since the aged phosphogypsum is alkaline, the pH value of the supernatant is between 7 - 9 at this time, and the interaction between phosphogypsum, lime, and red mud can well solidify heavy metals. The supernatant at this time can meet the Comprehensive Wastewater Discharge Standard (GB 8978 - 1996).

[0047] Example 2:

[0048] As Figure 1 shown, as Figure 1 shown, a precursor pretreatment method for promoting coagulation and early strength of phosphogypsum - red mud - based cementitious materials includes the acid leaching process, complexation process, and calcification process of red mud. First, mix water and red mud at a liquid - solid ratio of 3:1, add 1 mol / L sulfuric acid by volume and soak for 4 h to leach out alkali metal cations, then add 5% of the mass of red mud of ethylenediaminetetraacetic acid to complex the alkali metal cations, and let the obtained slurry stand for 1 h to make it react fully.

[0049] Under the action of inorganic acid, the supernatant is acidic at this time, with a pH value of 4-5, and the required data is recorded.

[0050] Then, calcification treatment is carried out. The aged phosphogypsum and the red mud after acid leaching are mixed at a mass ratio of 2.25:1, and water is added and stirred at a liquid-solid ratio of 3:1. Finally, the slurry is left standing for 3 h at a temperature of 60 °C, and the others are the same as in Example 1. Since the aged phosphogypsum is alkaline, the pH value of the supernatant at this time is between 7 and 9, and the interaction among phosphogypsum, lime and red mud can solidify heavy metals well. The supernatant at this time can meet the Comprehensive Wastewater Discharge Standard (GB 8978-1996).

[0051] Example 3:

[0052] As Figure 1 shown, as Figure 1 shown, a precursor pretreatment method for promoting coagulation and early strength of phosphogypsum-red mud based cementitious materials includes the acid leaching process, complexation process and calcification process of red mud. First, water and red mud are mixed at a liquid-solid ratio of 3:1, and 1 mol / L sulfuric acid is added by volume and soaked for 4 h to leach out alkali metal cations. Then, 8% of the mass of ethylenediaminetetraacetic acid of the red mud is added to complex the alkali metal cations, and the obtained slurry is left standing for 1 h to make it react fully.

[0053] Under the action of inorganic acid, the supernatant is acidic at this time, with a pH value of 4-5, and the required data is recorded.

[0054] Then, calcification treatment is carried out. The aged phosphogypsum and the red mud after acid leaching are mixed at a mass ratio of 2.25:1, and water is added and stirred at a liquid-solid ratio of 3:1. Finally, the slurry is left standing for 3 h at a temperature of 60 °C, and the others are the same as in Example 1. Since the aged phosphogypsum is alkaline, the pH value of the supernatant at this time is between 7 and 9, and the interaction among phosphogypsum, lime and red mud can solidify heavy metals well. The supernatant at this time can reach the direct discharge standard.

[0055] Example 4:

[0056] As Figure 1 shown, as Figure 1 shown, a precursor pretreatment method for promoting coagulation and early strength of phosphogypsum-red mud based cementitious materials includes the acid leaching process, complexation process and calcification process of red mud. First, water and red mud are mixed at a liquid-solid ratio of 3:1, and 1 mol / L sulfuric acid is added by volume and soaked for 4 h to leach out alkali metal cations. Then, 8% of the mass of ethylenediaminetetraacetic acid of the red mud is added to complex the alkali metal cations, and the obtained slurry is left standing for 1 h to make it react fully.

[0057] Under the action of inorganic acid, the supernatant is acidic at this time, with a pH value of 4-5, and the required data is recorded.

[0058] Then, calcification treatment is carried out. The aged phosphogypsum and the red mud after acid leaching are mixed at a mass ratio of 2.25:1, and water is added and stirred at a liquid-solid ratio of 3:1. Finally, the slurry is left standing for 3 h at a temperature of 100 °C, and the rest is the same as in Example 1. Since the aged phosphogypsum is alkaline, the pH value of the supernatant at this time is between 7 and 9, and the interaction among phosphogypsum, lime, and red mud can solidify heavy metals well. The supernatant at this time can meet the Comprehensive Wastewater Discharge Standard (GB 8978-1996).

[0059] Example 5:

[0060] As Figure 1 shown, a precursor pretreatment method for accelerating setting and early strength of phosphogypsum-red mud based cementitious materials includes the acid leaching process, complexation process, and calcification process of red mud. The steps are basically the same as those in Example 1, except that the cementitious materials used, in mass percentage, include 40% phosphogypsum, 35% slag, 24% red mud, and 4% lime, and the water-binder ratio is 0.25.

[0061] After the aged phosphogypsum and the acidified and complexed red mud are mixed, water is added and stirred at a liquid-solid ratio of 1:1, and the reaction is carried out at a reaction temperature of 60 °C for 3 h.

[0062] The preparation steps of the aged phosphogypsum include: under normal temperature and pressure, aging for 18 h with a mass ratio of phosphogypsum to lime = 80 and a water-binder ratio of 0.40.

[0063] The mass ratio of the aged phosphogypsum to the acidified and complexed red mud = 2 - 3.

[0064] Example 6:

[0065] As Figure 1 shown, a precursor pretreatment method for accelerating setting and early strength of phosphogypsum-red mud based cementitious materials includes the acid leaching process, complexation process, and calcification process of red mud. The steps are basically the same as those in Example 1, except that the cementitious materials used, in mass percentage, include 50% phosphogypsum, 30% slag, 17% red mud, and 1% lime, and the water-binder ratio is 0.45.

[0066] After the aged phosphogypsum and the acidified and complexed red mud are mixed, water is added and stirred at a liquid-solid ratio of 7:1, and the reaction is carried out at a reaction temperature of 100 °C for 3 h.

[0067] The preparation steps of the aged phosphogypsum include: under normal temperature and pressure, aging for 36 h with a mass ratio of phosphogypsum to lime = 100 and a water-binder ratio of 0.65.

[0068] The mass ratio of the aged phosphogypsum to the acidified and complexed red mud = 2 - 3.

[0069] The phosphogypsum used in Examples 1 - 6 is the original dried phosphogypsum, CaSO4 Content ≥ 85%, P 2 O 5 、F - and other harmful impurity contents ≤ 1%; the red mud needs to be crushed, SiO 2 +Al 2 O 3 ≥ 45%, Fe 2 O 1 ≥ 20%; the slag is S95 grade slag, and the calcium oxide content of lime > 95%.

[0070] The cementitious materials used in Examples 1-4 are in mass percentage, including 45% phosphogypsum, 33% slag, 20% red mud, 2% lime, and the water-binder ratio is 0.35.

[0071] Under normal temperature and pressure, phosphogypsum is aged for 24 h with the mass ratio of phosphogypsum to / lime = 90 and the water-binder ratio of 0.55.

[0072] After the pretreatment of Examples 1-6, pour out the supernatant of the pretreated red mud, mix the solid part with the slag and the remaining lime, and mix 0.05% polycarboxylate water reducer by the two-component mixing method, supplement the water required by the water-cement ratio, and finally stir slowly together for 120 s, stop stirring for 15 s, and quickly stir for 120 s and then mold. The experimental results of the neat paste performance are shown in the following table. The reference group uses untreated red mud.

[0073] Performance test results

[0074]

[0075] As can be seen from the above table, after the pretreatment of the present invention, the setting time of the phosphogypsum-red mud based cementitious material is accelerated, and at the same time, the strength is also improved. The supernatant reaches the discharge standard, and the treatment effect is good.

Claims

1. A precursor pretreatment method for phosphogypsum-red mud-based cementitious materials, characterized in that: The following steps are involved: S1: mixing red mud and water, and then adding acid leaching solution to obtain acidified red mud; S2: adding a complexing agent to the acidified red mud to obtain acidified complexed red mud; S3: Mix the phosphogypsum and the acidified complexed red mud, add water and stir to complete the precursor pretreatment step.

2. A precursor pretreatment method for phosphogypsum-red mud-based cementitious materials according to claim 1, characterized in that: The cementitious material includes, in units of mass percentage, 40-50% phosphogypsum, 30-35% slag, 17-24% red mud, 1-4% lime, 0.01-0.08% polycarboxylate water reducer, and a water-cement ratio of 0.25-0.

45.

3. A precursor pretreatment method for phosphogypsum-red mud-based cementitious materials according to claim 2, characterized in that: The phosphogypsum is the original phosphogypsum after drying, and the CaSO4 content is ≥85%; the red mud needs to be crushed, SiO2+Al2O3 is ≥45%, Fe2O1 is ≥20%; the slag lime calcium oxide content is >95%.

4. A precursor pretreatment method for phosphogypsum-red mud-based cementitious materials according to claim 1, characterized in that: In step S1, red mud and water are mixed at a liquid-to-solid ratio of 2 to 3, and 0.5 to 1 mol / L of acid leaching solution is added.

5. A method for pretreating a precursor of phosphogypsum-red mud-based cementitious materials according to claim 1, characterized in that: The complexing agent is ethylenediaminetetraacetic acid, and the added amount is 5-8% of the mass of the red mud.

6. A precursor pretreatment method for phosphogypsum-red mud-based cementitious materials according to claim 1, characterized in that: After the acidified red mud is obtained in step S1, it is allowed to stand for no less than 1 hour.

7. A method for pretreating a precursor of phosphogypsum-red mud-based cementitious materials according to claim 1, characterized in that: In the step S3, aged phosphogypsum is used. After the aged phosphogypsum is mixed with the acidified complexed red mud, water is added and stirred at a liquid-to-solid ratio of 1 to 7:1, and the reaction is carried out at a reaction temperature of 60 to 100° C. for not less than 3 hours.

8. A method for pretreating a precursor of phosphogypsum-red mud-based cementitious materials according to claim 7, characterized in that: The preparation step of the aged phosphogypsum comprises: aging for 18 to 36 hours at a mass ratio of phosphogypsum to lime of 80 to 100 and a water-binder ratio of 0.40 to 0.65 at room temperature and pressure.

9. A method for pretreating a precursor of phosphogypsum-red mud-based cementitious materials according to claim 7, characterized in that: In the step S3, the mass ratio of aged phosphogypsum to acidified complexed red mud is 2-3.

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