A sulphate-resistant composite cementitious material for full tailings paste filling and a preparation method thereof

Abstract

The application discloses a kind of sulphate-erosion-resistant full tailings paste filling composite cementitious materials and preparation method thereof, and relates to the technical field of building materials.The method is to wet the steel slag powder by water glass-wet shallow carbonization treatment, to stabilize free calcium oxide while retaining late activity;To make magnesium-aluminum precursor by calcining magnesite and kaolin together, and then grind together with slag powder, so that active magnesium and aluminum components are evenly distributed and the pore structure is optimized;Then dry mix the two with medium sulfate-resistant portland cement, fly ash, quicklime and silica fume in proportion.Quicklime provides sustained early alkali reserve, silica fume gradually reduces calcium and densifies, and the two work together to regulate the timing of alkalinity through the difference in action rate, reducing the survival time of early connected pores while reducing the content of residual free calcium in the later stage, significantly improving the sulphate-erosion-resistant ability of the filling body from reducing erosion channels and limiting gypsum formation.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a sulfate-resistant composite cementitious material for filling tailings paste and its preparation method. Background Technology

[0002] The mine uses full tailings paste backfill, which can transport all the tailings of different particle sizes generated from mineral processing to the goaf, taking into account solid waste utilization, goaf support, and surface subsidence control. The backfill body is in a humid underground environment for a long time, and some mine water and tailings pore water contain a lot of sulfate ions. Therefore, in addition to meeting the requirements for transportation, setting, and load-bearing, the cementing material also needs to have long-term resistance to sulfate erosion.

[0003] Once sulfate ions enter the filler, they migrate inward along interconnected pores and microcracks. When there is a significant amount of free calcium hydroxide or active aluminum-containing hydrated phases in the hardened body, gypsum and secondary ettringite are easily formed locally. The concentrated formation of these products within confined pores generates volumetric stress and gradually leads to cracking. Magnesium sulfates can also cause decalcification of calcium silicate hydrates, gradually transforming the cementitious structure from a dense state to a porous state. Therefore, sulfate resistance depends not only on whether the material contains a specific corrosion-resistant component, but also on whether the pores are interconnected, whether the free calcium content is controlled, and the state of aluminum-containing species within the hardened body.

[0004] Tailings particles have a wide particle size distribution and a high content of fine particles, making it easy for water films to form on the particle surface. After hardening, they may retain pores and structurally weak areas. To control backfilling costs, the amount of cementitious material used cannot be too high. Simply increasing the amount of cement can accelerate early hardening, but it will increase costs and increase calcium hydration products in the system. If a large amount of industrial solid raw materials with slow reaction rates are used, the early cementitious skeleton may not form sufficiently, allowing sulfate intrusion channels to remain connected for a longer period of time.

[0005] Steel slag possesses certain potential hydraulic properties, but the free calcium oxide and magnesium oxide within it may undergo delayed hydration, causing localized volume changes. Granulated blast furnace slag can form a relatively dense cementitious structure, but its reaction requires a suitable alkaline environment, and the aluminum released from the slag, if not stably dispersed or confined, may still become a sensitive site for sulfate action. After stabilization treatment, the early release of alkaline calcium from steel slag will be correspondingly reduced; while the slag components containing magnesium and aluminum precursors require a certain early alkalinity to participate in hardening in a timely manner. If the alkalinity is directly supplemented by increasing the amount of lime or cement, a large amount of calcium hydroxide may remain in the later stages, thus increasing the calcium source for gypsum formation.

[0006] Therefore, the technical problem to be solved by this invention is: under the conditions of controlling raw material and production costs and not relying on high doses of strong alkali and large amounts of sulfate components, how to simultaneously reduce the risk of delayed expansion caused by free calcium and magnesium in steel slag, adjust the distribution of calcium, magnesium and aluminum species in the slag system, reduce the interconnected pores in the whole tailings backfill, and solve the problem of the mismatch in the timing of alkalinity supply when the two types of modified components are used together, which requires alkalinity in the early stage and needs to reduce free calcium hydroxide in the later stage, so as to obtain a whole tailings paste backfill composite cementitious material that can resist sulfate migration, expansion and decalcification damage for a long time. Summary of the Invention

[0007] The purpose of this invention is to provide a sulfate-resistant composite cementitious material for filling tailings paste and its preparation method, so as to solve the technical problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing a sulfate-resistant, full-tailings paste-filling composite cementitious material includes the following steps:

[0010] S1. Based on 100 parts by weight of dry steel slag powder, add 2.5 to 3.5 parts by weight of liquid sodium silicate with a solid mass fraction of 28% to 32%, and add water to make the total amount of process water, including the water contained in the liquid sodium silicate, 8 to 10 parts by weight; after mixing and sealing for wetting and aging, perform carbonization treatment in a carbon dioxide atmosphere until the free CaO content in the steel slag powder is 0.5% to 1.0% and the net CO2 absorption is 1.0% to 2.5% of the dry weight of the steel slag powder; after drying and grinding, obtain water glass-wetted—shallow carbonized steel slag powder.

[0011] S2. Based on the dry weight of the material before calcination, mix 58-62 parts of magnesite powder with 38-42 parts of kaolin powder, totaling 100 parts, and co-calcine at 710-730℃; take 5-7 parts of the co-calcined material after calcination weight loss and cooling and grind it together with 93-95 parts of granulated blast furnace slag powder, totaling 100 parts, to obtain magnesium-aluminum precursor activated slag powder;

[0012] S3. 12-18 parts by weight of the water glass-wetted—shallow carbonized steel slag powder, 52-60 parts by weight of magnesium-aluminum precursor activated slag powder, 14-18 parts by weight of medium sulfate-resistant silicate cement, 6-10 parts by weight of Class F low-calcium fly ash, 1.0-2.0 parts by weight of hydrated lime powder, and 2.5-4.0 parts by weight of silica fume are dry-mixed, with a total of 100 parts by weight of each component, and the mass ratio of silica fume to hydrated lime powder is 1.5:1 to 2.5:1, to obtain the composite cementitious material.

[0013] Preferably, in step S1, the steel slag powder is converter steel slag powder that has undergone iron removal and aging, with an initial free CaO content of 2.0% to 4.0%, a free MgO content of no more than 2.0%, and a D90 of no more than 75 μm.

[0014] The modulus of the liquid sodium silicate is 2.6 to 2.8; after mixing steel slag powder, liquid sodium silicate and water for 8 to 15 minutes, it is sealed and moistened for 20 to 40 minutes at 25 to 35°C.

[0015] Preferably, in step S1, the volume fraction of CO2 in the carbon dioxide atmosphere is 15%–20%, the relative humidity of the gas is not less than 75%, the carbonization temperature is 40–50℃, the cumulative amount of mixed gas is 0.05–0.15 Nm³ / kg dry steel slag powder, and the carbonization time is 60–150 min; the material is kept in a turning state during carbonization, and after carbonization, it is dried to a moisture content of not more than 1.0% under the condition that the material temperature does not exceed 60℃, and then ground to a D50 of 10–15 μm.

[0016] Preferably, in step S2, the magnesite powder contains MgCO3 with a mass fraction of not less than 90%, the kaolin powder contains kaolinite with a mass fraction of not less than 80%, and the D90 of both raw materials is not greater than 75μm.

[0017] The mixed raw materials are heated to 710-730℃ at a rate of 5-10℃ / min under air circulation conditions, held at that temperature for 60-90min, and then cooled to below 100℃ with dry air. The residual MgCO3 content in the resulting co-calcined product is controlled to be no higher than 5%.

[0018] Preferably, in step S2, the co-calcined material after calcination loss and cooling is first pre-ground for 5-10 minutes, and then the granulated blast furnace slag powder is added and co-ground for 25-35 minutes. During the co-grinding process, the material temperature does not exceed 65°C. The resulting activated slag powder of magnesium-aluminum precursor has a D50 of 7-12 μm and a specific surface area of ​​450-550 m². 2 / kg.

[0019] Preferably, in step S3, the composite cementitious material, by dry basis mass, consists of 15 parts of water glass-wetted—lightly carbonized steel slag powder, 56 parts of magnesium-aluminum precursor activated slag powder, 16 parts of medium sulfate-resistant silicate cement, 8.5 parts of Class F low-calcium fly ash, 1.5 parts of quicklime powder, and 3 parts of silica fume.

[0020] Preferably, the clinker of the medium-sulfate resistant silicate cement contains no more than 5% C3A; the F-type low-calcium fly ash contains no more than 10% CaO and no more than 5% loss on ignition; the slaked lime powder contains no less than 90% Ca(OH)2 and has a D50 of no more than 20 μm; and the silica fume contains no less than 90% amorphous SiO2 and has a specific surface area of ​​15–25 m². 2 / g.

[0021] Preferably, in step S3, the silica fume and F-type low-calcium fly ash are first premixed in a sealed manner for 3-5 minutes, and the quicklime powder and magnesium-aluminum precursor activated slag powder are premixed in a sealed manner for 3-5 minutes; then the two premixes are dry-mixed together with water glass-wetted shallow carbonized steel slag powder and medium sulfate-resistant silicate cement for 6-10 minutes, and the powder temperature during the dry mixing process does not exceed 45℃.

[0022] Preferably, the method further includes the step of preparing the obtained composite cementitious material into a whole tailings paste filling slurry: ungraded whole tailings and the composite cementitious material are mixed at a dry basis mass ratio of 4.5 to 8:1, and water is added to make the total solid mass fraction of the slurry 76% to 80%; first, the whole tailings are mixed with 65% to 75% of the total mixing water for 1 to 2 minutes, then the composite cementitious material is added in batches and mixed for 2 to 3 minutes, and finally the remaining mixing water is added and mixed for 3 to 5 minutes, wherein the water content of the whole tailings and the residual water of the composite cementitious material are both included in the total mixing water.

[0023] A sulfate-resistant composite cementitious material for filling tailings paste is prepared by the method described above.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. After water glass wetting and controlled shallow carbonization treatment, the free calcium oxide on the surface of steel slag particles changes from a highly active state prone to delayed hydration to a more stable shallow mineralized structure, reducing the possibility of micro-cracks around the steel slag particles caused by volume changes from the source. The degree of carbonization is limited by both the free CaO content and the net CO2 absorption, thus preventing the formation of an excessively thick carbonate layer, and allowing the steel slag to retain a certain degree of late-stage hydraulic activity. The formed fine-grained calcium carbonate and silica-rich amorphous phase can also fill defects on the surface of the steel slag, making the transition zone between the steel slag and the surrounding cementitious matrix more continuous. After sulfate enters the backfill, it is less likely to migrate rapidly along the steel slag interface, nor is it likely to concentrate and form gypsum at the original free calcium enrichment sites, thereby reducing local expansion stress and the risk of crack propagation. The purpose of this treatment is to stabilize the steel slag, reduce erosion channels, and reduce local calcium enrichment, rather than completely isolating sulfate ions using the carbonized layer.

[0026] 2. The magnesium-aluminum precursor activated slag powder ensures that the active magnesium phase and aluminum-silicon phase are evenly distributed around the slag particles at a low dosage, preventing the magnesium and aluminum components from concentrating in a few locations. After hardening, the system has a denser aluminum replacing silicate gel as the main cementing structure, which is conducive to the formation of a small amount of magnesium-aluminum layered hydrated phase, thus relatively reducing the effective aluminum content that is easily readjusted by external sulfate ions. Co-milling also shortens the reaction distance of slag particles, increases the formation sites of cementitious products, and gradually transforms the originally interconnected capillaries into smaller pores with more tortuous paths. As a result, the migration rate of sulfate ions into the interior of the filling body is limited, and secondary ettringite and gypsum are less likely to concentrate in a few weak areas. At the same time, the actual amount of active magnesium oxide introduced is strictly controlled, which can avoid delayed hydration expansion caused by excessive magnesium oxide dosage or insufficient activity.

[0027] 3. Water glass wetting—When using both shallowly carbonized steel slag powder and magnesium-aluminum precursor activated slag powder, the key issue limiting further improvement in sulfate resistance is the mismatch in the timing of alkalinity supply. Although the volume stability of steel slag improves after shallow carbonization, its ability to release alkaline calcium in the early stages decreases. Magnesium-aluminum precursor activated slag, on the other hand, requires appropriate early alkalinity to form a gelled structure in a timely manner. Insufficient early alkalinity slows down the slag reaction initiation, preventing the timely formation of a continuous framework between particles and thus retaining interconnected pores for a longer period. However, if the amount of quicklime is increased alone, the unused Ca(OH)2 from the early hydration process may remain in the later stages and become a calcium source for sulfate formation of gypsum. To address this issue, quicklime and silica fume are added together in a defined ratio. Quicklime, a slightly soluble mineral component, maintains early pore fluid alkalinity through limited but continuous dissolution, promoting the timely activation of slag and magnesium-aluminum precursors, and enabling the cementitious products to connect and seal large pores between particles earlier. Silica fume plays a role in micro-filling and nucleation from the initial stage of water addition. Its active surface gradually reduces the content of unused Ca(OH)2 as curing time increases, forming additional calcium silicate-based cementitious structures. Quicklime provides an early alkali reserve in a "limited quantity and continuous release," while silica fume plays a regulatory role in "gradual accumulation and subsequent calcium reduction." The two do not react sequentially but complement each other in terms of reaction rate. Adding quicklime alone can easily increase free calcium in the later stages, while adding silica fume alone may not fully utilize its reactivity due to insufficient initial alkalinity. The combination of the two shortens the existence time of early interconnected pores and reduces the content of free calcium available for sulfate gypsum formation in the later stages, thus improving the sulfate resistance of the infill from both the erosion channel and reactant source aspects. Attached Figure Description

[0028] Figure 1 This is a SEM image of the composite cementitious material prepared in Example 1 of the present invention. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Except for CO2 concentration, which is a volume fraction, all other percentages are mass percentages; all raw material quantities are calculated on a dry basis. The quantities of intermediate modified powder refer to the mass of the dried finished product.

[0031] Example 1

[0032] A method for preparing a sulfate-resistant, full-tailings paste-filling composite cementitious material includes the following steps:

[0033] (1) Preparation of water glass wetting-shallow carburized steel slag powder

[0034] 100.00 kg of converter steel slag powder that has undergone iron removal and aging has an initial free CaO content of 2.0%, a free MgO content of 0.8%, and a D90 of 75 μm. 2.50 kg of liquid sodium silicate with a modulus of 2.6 and a solid mass fraction of 28% is added, including 0.70 kg of sodium silicate solid and 1.80 kg of its own water content; an additional 6.20 kg of water is added, bringing the total process water volume to 8.00 kg.

[0035] The mixture was mixed in a sealed container for 8 minutes, and then conditioned at 25°C for 20 minutes. The material was placed in a rotary drum reactor, and a mixed gas with a CO2 volume fraction of 15% and a relative humidity of 75% (the remainder being air) was introduced while the material was continuously agitated. The material temperature was 40°C. The cumulative amount of mixed gas used under standard conditions was 0.05 Nm³. 3 / kg dry steel slag, that is, 100kg steel slag with a cumulative aeration of 5.00Nm. 3 Aeration was carried out uniformly over 150 minutes at an average flow rate of 33.3 L / min. Aeration was stopped when the free CaO content reached 1.0% and the net CO2 absorption was 1.0% of the dry weight of the steel slag. Net CO2 absorption was calculated based on the increase in inorganic carbon on a dry basis before and after carbonization.

[0036] The carbonized material was dried at 50°C until the moisture content was no more than 1.0%, and then ground to a D50 of 15μm to obtain water glass-wetted, shallowly carbonized steel slag powder.

[0037] (2) Preparation of magnesium-aluminum precursor activated slag powder

[0038] Take 58.00 kg of magnesite powder with a MgCO3 content of 90% and a D90 of 75 μm, and 42.00 kg of kaolin powder with a kaolinite content of 80% and a D90 of 75 μm, and mix them evenly. Heat the mixture to 710℃ at a rate of 5℃ / min, hold it at that temperature for 90 min under air circulation, and then cool it to below 100℃ with dry air. The residual MgCO3 content in the co-calcined product is no higher than 5% as the criterion for acceptance.

[0039] Based on the actual product after calcination weight loss and cooling, 5.00 kg of the co-calcined material was weighed and pre-ground for 5 min; 95.00 kg of S95 grade granulated blast furnace slag powder was added and ground together for 25 min, controlling the outlet material temperature not to exceed 55℃, to obtain a D50 of 12 μm and a specific surface area of ​​450 m². 2 / kg of magnesium-aluminum precursor activated slag powder.

[0040] (3) Preparation of composite cementitious materials

[0041] Weigh according to the dry basis of the finished product:

[0042] 120 kg of shallow carbide steel slag powder was wetted with water glass.

[0043] 600 kg of activated slag powder containing magnesium-aluminum precursor;

[0044] 145 kg of medium-strength sulfate silicate cement has a C3A content of 5.0% in its clinker;

[0045] 100 kg of Class F low-calcium fly ash, with a CaO content of 10% and a loss on ignition of 5%;

[0046] 10 kg of quicklime powder has a Ca(OH)2 content of 90% and a D50 of 20 μm.

[0047] 25 kg of silica ash, with an amorphous SiO2 content of 90% and a specific surface area of ​​15 m². 2 / g.

[0048] The total weight of the above components is 1000 kg, with a mass ratio of silica fume to hydrated lime powder of 2.5:1. First, silica fume and fly ash are premixed in a sealed container for 3 minutes. Then, hydrated lime powder and magnesium-aluminum precursor activated slag powder are premixed for 3 minutes. Next, lightly carbonized steel slag powder and medium-sulfate resistant silicate cement are added and dry-mixed for 6 minutes. The powder temperature is controlled below 35℃ to obtain a composite cementitious material.

[0049] (4) Preparation of whole tailings paste

[0050] Take 800 kg of ungraded dry tailings and 100 kg of the above-mentioned composite cementitious material, with a dry weight ratio of 8:1. Based on a total solids mass fraction of 76%, the total mixing water is:

[0051] 900×(1-0.76)÷0.76=284.21kg.

[0052] First, add 184.74 kg of water and mix with the tailings for 1 minute. Then, add the composite cementitious material in batches and mix for 2 minutes. Finally, add the remaining 99.47 kg of water and mix for 3 minutes to obtain the tailings paste filling slurry. When using tailings with water, deduct the water content of the tailings and the residual moisture of the cementitious material from the 284.21 kg mixture.

[0053] Example 2

[0054] A method for preparing a sulfate-resistant, full-tailings paste-filling composite cementitious material includes the following steps:

[0055] (1) Preparation of water glass wetting-shallow carburized steel slag powder

[0056] 100.00 kg of converter steel slag powder that has undergone iron removal and aging has an initial free CaO content of 3.0%, a free MgO content of 1.4%, and a D90 of 60 μm. 3.00 kg of liquid sodium silicate with a modulus of 2.7 and a solid mass fraction of 30% is added, including 0.90 kg of sodium silicate solid and 2.10 kg of its own water content; an additional 6.90 kg of water is added, bringing the total process water volume to 9.00 kg.

[0057] The mixture was mixed in a closed system for 12 minutes, and then conditioned at 30°C for 30 minutes. The material was then fed into a rotary drum reactor, through which a mixed gas with a CO2 volume fraction of 18% and a relative humidity of 80% (the remainder being air) was introduced, and the material temperature was controlled at 45°C. Under standard conditions, the cumulative amount of mixed gas used was 0.10 Nm³. 3 / kg dry steel slag, i.e., a cumulative aeration of 10.00 Nm³. 3 Aeration should be uniformly introduced over 100 minutes at an average flow rate of 100 L / min. Aeration should be stopped when the free CaO content reaches 0.5% and the net CO2 absorption is 2.2% of the dry weight of the steel slag.

[0058] The material was dried at 55℃ until the moisture content was no higher than 0.7%, and then ground to a D50 of 12μm to obtain water glass-wetted, shallowly carburized steel slag powder.

[0059] (2) Preparation of magnesium-aluminum precursor activated slag powder

[0060] Take 60.00 kg of magnesite powder with a MgCO3 content of 95% and a D90 of 60 μm, and 40.00 kg of kaolin powder with a kaolinite content of 85% and a D90 of 60 μm. Mix them and heat to 720℃ at a rate of 8℃ / min. Hold at this temperature for 75 min under air circulation, and then cool to below 80℃ with dry air, controlling the residual MgCO3 content in the co-calcined product to be no higher than 3%.

[0061] 6.00 kg of the actual co-calcined product after calcination loss and cooling was weighed and pre-ground for 8 min; 94.00 kg of S95 grade granulated blast furnace slag powder was added, and the mixture was ground together for 30 min. The outlet material temperature was not higher than 60℃, resulting in a D50 of 9.5 μm and a specific surface area of ​​500 m². 2 / kg of magnesium-aluminum precursor activated slag powder.

[0062] (3) Preparation of composite cementitious materials

[0063] Weigh according to the dry basis of the finished product:

[0064] 150 kg of shallow carbide steel slag powder was wetted with water glass.

[0065] 560 kg of activated slag powder containing magnesium-aluminum precursors;

[0066] 160 kg of medium-strength sulfate silicate cement has a C3A content of 4.0% in its clinker;

[0067] 85 kg of Class F low-calcium fly ash, with a CaO content of 7% and a loss on ignition of 3%;

[0068] 15 kg of quicklime powder has a Ca(OH)2 content of 93% and a D50 of 15 μm;

[0069] 30 kg of silica ash has an amorphous SiO2 content of 93% and a specific surface area of ​​20 m². 2 / g.

[0070] The total weight of the above components is 1000 kg, with a mass ratio of silica fume to slaked lime powder of 2:1. First, silica fume and fly ash are premixed for 4 min, and slaked lime powder and magnesium-aluminum precursor activated slag powder are premixed for 4 min. Then, lightly carbonized steel slag powder and medium sulfate-resistant silicate cement are added and dry-mixed for 8 min. The powder temperature should not exceed 40℃ to obtain a composite cementitious material.

[0071] (4) Preparation of whole tailings paste

[0072] Take 500 kg of ungraded dry tailings and 100 kg of composite cementitious material, with a dry mass ratio of 5:1. Based on a total solids mass fraction of 78%, the total mixing water is:

[0073] 600×(1-0.78)÷0.78=169.23kg.

[0074] First, add 118.46 kg of water and mix with the tailings for 2 minutes. Then, add the composite cementitious material in batches and mix for 2.5 minutes. Finally, add the remaining 50.77 kg of water and mix for 4 minutes to obtain the tailings paste filling slurry.

[0075] Example 3

[0076] A method for preparing a sulfate-resistant, full-tailings paste-filling composite cementitious material includes the following steps:

[0077] (1) Preparation of water glass wetting-shallow carburized steel slag powder

[0078] 100.00 kg of converter steel slag powder that has undergone iron removal and aging has an initial free CaO content of 4.0%, a free MgO content of 2.0%, and a D90 of 50 μm. 3.50 kg of liquid sodium silicate with a modulus of 2.8 and a solid mass fraction of 32% is added, including 1.12 kg of solid sodium silicate and 2.38 kg of its own water content; an additional 7.62 kg of water is added, bringing the total process water volume to 10.00 kg.

[0079] Mix in a sealed environment for 15 minutes, then wet and age at 35°C for 40 minutes. Place the material in a rotary drum reactor and introduce a mixed gas with a CO2 volume fraction of 20% and a relative humidity of 85% (the remainder being air), controlling the material temperature at 50°C. The cumulative amount of mixed gas used under standard conditions is 0.15 Nm³. 3 / kg dry steel slag, i.e., a cumulative aeration of 15.00 Nm³. 3 Aeration should be uniformly introduced over 60 minutes at an average flow rate of 250 L / min. Aeration should be stopped when the free CaO content reaches 1.0% and the net CO2 absorption is 2.5% of the dry weight of the steel slag.

[0080] The material was dried at 60℃ until the moisture content was no more than 0.5%, and then ground until the D50 was 10μm to obtain water glass wetting-shallow carburized steel slag powder.

[0081] (2) Preparation of magnesium-aluminum precursor activated slag powder

[0082] Take 62.00 kg of magnesite powder with a MgCO3 content of 95% and a D90 of 45 μm, and 38.00 kg of kaolin powder with a kaolinite content of 85% and a D90 of 45 μm. Mix them and heat to 730℃ at a rate of 10℃ / min. Hold at this temperature for 60 min under air circulation, and then cool to below 60℃ with dry air, controlling the residual MgCO3 content in the co-calcined product to be no higher than 2%.

[0083] Weigh 7.00 kg from the actual co-calcined product after calcination weight loss and cooling, and pre-grind for 10 min; add 93.00 kg of S95 grade granulated blast furnace slag powder, and grind together for 35 min, controlling the outlet material temperature not to exceed 65℃, to obtain a D50 of 7 μm and a specific surface area of ​​550 m². 2 / kg of magnesium-aluminum precursor activated slag powder.

[0084] (3) Preparation of composite cementitious materials

[0085] Weigh according to the dry basis of the finished product:

[0086] 180 kg of shallow carbide steel slag powder was wetted with water glass.

[0087] 520 kg of activated slag powder containing magnesium-aluminum precursors;

[0088] 180 kg of medium-strength sulfate silicate cement has a C3A content of 3.0% in its clinker;

[0089] 60 kg of Class F low-calcium fly ash, with a CaO content of 5% and a loss on ignition of 2%;

[0090] 20 kg of quicklime powder has a Ca(OH)2 content of 95% and a D50 of 10 μm.

[0091] 40 kg of silica ash, with an amorphous SiO2 content of 95% and a specific surface area of ​​25 m². 2 / g.

[0092] The total weight of the above components is 1000 kg, with a mass ratio of silica fume to hydrated lime powder of 2:1. First, silica fume and fly ash are premixed in a sealed container for 5 min. Then, hydrated lime powder and magnesium-aluminum precursor activated slag powder are premixed for 5 min. Next, lightly carbonized steel slag powder and medium sulfate-resistant silicate cement are added and dry-mixed for 10 min. The powder temperature should not exceed 45℃ to obtain a composite cementitious material.

[0093] (4) Preparation of whole tailings paste

[0094] Take 450 kg of ungraded dry tailings and 100 kg of composite cementitious material, with a dry weight ratio of 4.5:1. Based on a total solids content of 80%, the total mixing water is:

[0095] 550×(1-0.80)÷0.80=137.50kg.

[0096] First, add 103.13 kg of water and mix with the tailings for 2 minutes. Then, add the composite cementitious material in batches and mix for 3 minutes. Finally, add the remaining 34.37 kg of water and mix for 5 minutes to obtain the tailings paste filling slurry.

[0097] Comparative Example 1: 120 kg of untreated steel slag powder that has not been wetted with water glass and carbonized with CO2 was used to replace the 120 kg of water glass-wetted and lightly carbonized steel slag powder in Example 1. The proportions of other cementitious materials, the amount of tailings, the amount of water, and the mixing process were the same as in Example 1.

[0098] Comparative Example 2: Steel slag powder was treated according to the amount of water glass, the amount of water replenishment, and the wetting and aging conditions of Example 1, but CO2 was not introduced after wetting and aging. Instead, it was directly dried and ground at 50°C, and the resulting powder was used to replace the lightly carbonized steel slag powder in Example 1 by the same mass. All other aspects were the same as in Example 1.

[0099] Comparative Example 3: No liquid sodium silicate was added to the steel slag powder. Only 8.00 kg of water was added and the powder was wetted, aged and carbonized with CO2 according to the conditions of Example 1. The resulting carbonized steel slag powder was then used to replace the water glass wetted-shallow carbonized steel slag powder in Example 1 by the same mass. All other aspects were the same as in Example 1.

[0100] Comparative Example 4: 600 kg of S95 grade granulated blast furnace slag powder that has not been modified by magnesite-kaolin co-calcination was used to replace the 600 kg of magnesium-aluminum precursor activated slag powder in Example 1. All other aspects were the same as in Example 1.

[0101] Comparative Example 5: 58 kg of magnesite powder and 42 kg of kaolin powder were treated according to the heating, calcination and cooling conditions of Example 1. After cooling, they were remixed according to their actual product mass. Then, 5 kg of the mixture was dry-mixed with 95 kg of slag at low intensity without grinding together. The resulting powder was used to replace the magnesium-aluminum precursor activated slag powder in Example 1 by the same mass. Everything else was the same as in Example 1.

[0102] Comparative Example 6: The 10 kg of quicklime powder and 25 kg of silica fume in Example 1 were removed, and 35 kg of Class F low-calcium fly ash was used to make up the difference, so that the total amount of fly ash was adjusted to 135 kg. The amount of other raw materials and preparation conditions were the same as in Example 1.

[0103] Comparative Example 7: The 10 kg of quicklime powder from Example 1 was retained, but 25 kg of silica fume was removed and replaced with 25 kg of Class F low-calcium fly ash, so that the total amount of fly ash was adjusted to 125 kg. Everything else was the same as in Example 1.

[0104] Comparative Example 8: The 25 kg silica fume from Example 1 was retained, but 10 kg of quicklime powder was removed and replaced with 10 kg of Class F low-calcium fly ash, so that the total fly ash was adjusted to 110 kg. All other aspects were the same as in Example 1.

[0105] Comparative Example 9: Keeping the total amount of quicklime powder and silica fume unchanged at 35 kg, the amounts of the two were adjusted to 17.5 kg and 17.5 kg respectively, so that the mass ratio of silica fume to quicklime powder was reduced to 1:1. The amounts of other raw materials and preparation conditions were the same as in Example 1.

[0106] Comparative Example 10: Keeping the total amount of quicklime powder and silica fume unchanged at 35 kg, the amounts of the two were adjusted to 8.75 kg and 26.25 kg respectively, so that the mass ratio of silica fume to quicklime powder was increased to 3:1. The amounts of other raw materials and preparation conditions were the same as in Example 1.

[0107] Performance testing

[0108] The tailings paste was prepared according to the raw material dosage, feeding sequence, and mixing conditions specified in each embodiment and comparative example. In Example 1 and Comparative Examples 1-10, the mass ratio of tailings to cementitious material was 8:1, with a solids mass fraction of 76%. In Example 2, the ratio was 5:1, with a solids mass fraction of 78%. In Example 3, the ratio was 4.5:1, with a solids mass fraction of 80%. The temperature of the test water and the ambient temperature were controlled at 20±2℃. Except for the freshly mixed performance, after molding, the specimens were covered and allowed to stand for 24 hours. After demolding, they were placed in a standard curing environment with a temperature of 20±2℃ and a relative humidity of not less than 95%. Three parallel specimens were prepared for each age and erosion condition. The results in the table are the arithmetic mean.

[0109] 1. Slump test: The test was conducted according to GB / T 50080—2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The paste, within 5 minutes of mixing, was divided into three layers and placed into a standard slump cone with an upper diameter of 100mm, a lower diameter of 200mm, and a height of 300mm. Each layer was tamped evenly 25 times, leveled, and then the cone was lifted vertically within 5–10 seconds. The vertical height difference between the cone height and the highest point of the paste sample was measured, accurate to 1mm. Each sample was tested using three independent batches, and the average value was taken.

[0110] 2. Water Absorption Rate Test: The test was conducted according to the atmospheric pressure water absorption test procedure in GB / T 50080—2016. 5.00 L of freshly mixed paste was weighed and placed into a covered cylinder. The cylinder was allowed to stand at 20±2℃. For the first 60 minutes, surface water was sampled every 10 minutes, then every 30 minutes thereafter, until no new water absorption was observed after three consecutive tests. The sampled water was then weighed. The water absorption rate was calculated as B=m b / m w Calculate by multiplying by 100%, where m b To calculate the cumulative effluent quality, m w This refers to the actual mass of mixing water contained in the paste within the container.

[0111] 3. Setting Time Test: The test was conducted according to the penetration resistance method in GB / T 50080—2016. The freshly mixed paste was placed in a rigid container with a depth of not less than 150 mm and allowed to stand at 20±2℃. A penetration needle with an appropriate cross-sectional area was selected based on the degree of hardening of the paste, and the penetration resistance was measured periodically. Taking the moment water was added as the starting point, the times when the penetration resistance reached 3.5 MPa and 28.0 MPa were determined by interpolation between adjacent measuring points, and these were taken as the initial setting time and the final setting time, respectively.

[0112] 4. Unconfined compressive strength test: The specimen molding and loading principles were followed according to JGJ / T 70—2009 "Standard for Test Methods of Basic Performance of Building Mortar" and GB / T 50081—2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". 70.7mm×70.7mm×70.7mm cube molds were used for specimen preparation, and the specimens were cured for 3 days, 7 days, and 28 days respectively. Before the test, surface moisture was wiped off and the compressive dimensions were measured. The specimens were placed in the center of the press and continuously loaded until failure. The compressive strength was calculated using f=P / A, where P is the maximum failure load and A is the actual compressive area.

[0113] 5. Mercury intrusion porosimetry test: The test was conducted according to GB / T 21650.1—2008, "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Methods—Part 1: Mercury Intrusion Porosimetry". Fragments with a particle size of 5–8 mm were taken from the interior of 28-day specimens and immersed in isopropanol for 24 hours to terminate hydration. The samples were then vacuum dried at 40±2℃ to constant weight. The cumulative mercury intrusion volume was measured using a mercury intrusion porosimetry instrument within a pressure range of approximately 0.003–400 MPa, and the mercury intrusion porosimetry porosimetry was calculated. All samples were taken from the same sampling location, and the same hydration termination and drying procedures were followed.

[0114] 6. Sulfate Attack Strength Retention Rate Test: Following the parallel evaluation principle of the erosion group and control group in GB / T 749—2008 "Test Method for Sulfate Attack Resistance of Cement", and referring to the environmental control requirements of GB / T 50082—2024 "Standard for Test Methods for Long-Term Performance and Durability of Concrete", a continuous immersion test was established. After 28 days of standard curing, 70.7 mm cubes were immersed in 0.35 mol / L Na₂SO₄ solution, 0.35 mol / L MgSO₄ solution, and clean water, respectively. The Na₂SO₄ solution was prepared by dissolving 49.71 g of anhydrous Na₂SO₄ and bringing the volume to 1.000 L, and the MgSO₄ solution was prepared by dissolving 86.26 g of MgSO₄·7H₂O and bringing the volume to 1.000 L. The SO₄ content of the two erosion solutions was adjusted accordingly. 2- The concentration was the same. The solution temperature was 20±2℃, and the solution volume to specimen volume ratio was 5:1, with all solutions replaced every 7 days. After continuous immersion for 180 days, the compressive strength of the eroded group and the water control group of the same age was measured. The strength retention rate was calculated according to K... X,180 =f X,180 / f W,180 Calculated by multiplying by 100%, where f X,180 f represents the strength after immersion in the corresponding sulfate solution for 180 days. W,180 The strength is the result of soaking in water for the same amount of time.

[0115] 7. Test for the rate of change of length due to sulfate erosion:

[0116] Following the length comparison principle of GB / T 50082—2024, 40mm×40mm×160mm prismatic specimens were used, with stainless steel probes pre-embedded at both ends. Three specimens were prepared for each corrosive medium. After 28 days of standard curing, the initial length L0 was measured. Subsequently, the specimens were immersed in the aforementioned 0.35mol / L Na2SO4 and 0.35mol / L MgSO4 solutions, respectively, with the same immersion temperature, liquid-to-solid volume ratio, and solution replacement cycle as in the strength retention test. A length comparator with a resolution of 0.001mm was used to measure the length after immersion for 7, 28, 60, 90, and 180 days. The length change rate was expressed as ε. X,t =(L X,t -L0) / L g Calculated by multiplying by 100%, where L g To ensure accurate measurement of gauge length, positive values ​​indicate expansion; the table shows the results for 180d.

[0117] Table 1

[0118] Example 1 248 1.08 10.5 / 13.9 0.47 1.03 2.17 31.6 92.4 84.7 0.061 0.044 Example 2 219 0.43 8.2 / 11.0 0.92 2.04 4.29 27.8 94.1 87.3 0.049 0.038 Example 3 187 0.15 8.6 / 11.5 1.17 2.57 5.24 25.6 95.3 89.0 0.041 0.033 Comparative Example 1 251 1.36 9.7 / 12.9 0.49 0.94 1.77 35.7 74.8 58.9 0.228 0.236 Comparative Example 2 238 0.93 8.8 / 11.7 0.54 1.08 1.94 33.5 79.2 64.5 0.181 0.167 Comparative Example 3 255 1.29 11.3 / 15.0 0.38 0.82 1.80 34.2 85.6 73.8 0.112 0.086 Comparative Example 4 258 1.51 11.9 / 15.8 0.34 0.74 1.64 36.1 82.3 69.2 0.143 0.151 Comparative Example 5 247 1.22 10.9 / 14.6 0.41 0.89 1.88 33.1 87.4 77.1 0.098 0.075 Comparative Example 6 263 1.75 13.1 / 17.4 0.27 0.61 1.50 37.4 80.8 66.7 0.154 0.139 Comparative Example 7 259 1.48 9.1 / 12.2 0.45 0.88 1.68 35.0 71.5 55.9 0.257 0.244 Comparative Example 8 232 0.72 12.4 / 16.6 0.30 0.70 1.74 32.4 88.5 79.6 0.086 0.064 Comparative Example 9 244 1.00 8.5 / 11.3 0.56 1.12 1.96 33.8 77.0 61.8 0.207 0.194 Comparative Example 10 226 0.57 11.7 / 15.6 0.35 0.77 1.84 31.9 90.1 81.8 0.074 0.056

[0119] Example 1 exhibited a 28-day compressive strength of 2.17 MPa and a compressible mercury porosity of 31.6%, both superior to the comparative examples under the same slurry preparation conditions. Comparative Examples 2 and 9 showed 3-day strengths of 0.54 MPa and 0.56 MPa, respectively, higher than Example 1 in the short term, indicating that a higher proportion of soluble alkali or quicklime can accelerate early hardening. However, their 28-day strength, porosity, and sulfate attack index all showed a reversal, indicating that improved early strength does not equate to improved long-term structural stability.

[0120] Regarding the control of steel slag wetting-shallow carbonization, Example 1 achieved 180-day strength retention rates of 92.4% and 84.7% in Na2SO4 and MgSO4, respectively, significantly higher than Comparative Examples 1-3. Comparative Example 2, with only water glass wetting, exhibited high early strength, but the unstabilized free calcium phase increased the 180-day length change rate to 0.181% and 0.167%. Comparative Example 3, while improving volume stability through only water-based carbonization, showed slower solidification and lower early strength due to the lack of pre-dispersion of particles by water glass and silicate replenishment. Therefore, the process sequence of wetting and dispersion followed by controlled shallow carbonization balances early reactivity and long-term volume stability.

[0121] Regarding the regulation of activated slag in magnesium-aluminum precursor production, Comparative Example 4, using ordinary S95 slag, exhibited higher porosity and lower strength retention. While Comparative Example 5, which involved separate calcination followed by low-strength dry mixing, showed some improvement, its Na2SO4 and MgSO4 strength retention rates were still 5.0 and 7.6 percentage points lower than those of Example 1, respectively. Co-calcination facilitates uniform contact between magnesite decomposition products and metakaolin active components, while co-milling reduces spatial separation between different powders, resulting in a more uniform distribution of magnesium and aluminum active components around the slag particles, thereby reducing the channels for sulfate ions to migrate inward along continuous pores. These results indicate that neither co-calcination nor co-milling can be replaced by simple physical mixing.

[0122] The combination of quicklime and silica fume primarily addresses the contradiction between insufficient early-stage alkalinity and excessive residual calcium phase in slag systems. Comparative Example 7, with only quicklime, exhibits faster setting and acceptable early-stage strength; however, excessive addition can lead to the formation of gypsum and sulfur-containing aluminate expansion products in a sulfate environment, resulting in Na₂SO₄ and MgSO₄ strength retention rates of only 71.5% and 55.9%, respectively, with length changes reaching 0.257% and 0.244%, respectively. Comparative Example 8, with only silica fume, reduces bleeding rate and porosity, but excessive addition of silica fume in the early stages can lead to problems with OH⁻. - and Ca 2+ Insufficient supply delayed initial setting to 12.4 hours and reduced 3-day strength to 0.30 MPa. In Example 1, quicklime first provided the alkaline environment and available calcium source required for slag activation. Silica fume then gradually consumed the readily reactive Ca(OH)2 through microfilling and pozzolanic reaction, generating secondary C-(A)-SH gel. This avoided insufficient early activation and reduced residual calcium phase in the later stages. When the ratio of silica fume to quicklime was 1:1, the calcium source was excessive, resulting in higher early strength but significantly reduced corrosion resistance. Increasing the ratio to 3:1 improved long-term corrosion resistance but resulted in insufficient early strength. The intermediate ratio used in Example 1 achieved a more balanced settling, strength, pore structure, and sulfate resistance.

[0123] The strength retention rate of all samples under MgSO4 erosion was generally lower than that under Na2SO4 erosion. This is because Mg 2+ Besides participating in the formation of magnesium-containing deposits, it also reduces the alkalinity of the pore fluid and promotes the decalcification and softening of C-(A)-SH gel. However, the length change rate of MgSO4 is not necessarily greater than that of Na2SO4. For example, in Example 1, the length change rate in MgSO4 was smaller, but the strength loss was greater, indicating that MgSO4 damage is more inclined towards decalcification and softening, while Na2SO4 damage is more likely to manifest as positive expansion. In Comparative Examples 1 and 4, due to the looser pore structure, the length change rate of MgSO4 was slightly higher than that of Na2SO4. Therefore, the strength retention rate and length change rate should be evaluated together, and the sulfate resistance should not be judged solely by the amount of expansion.

[0124] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the essence and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sulfate-resistant, full-tailings paste-filling composite cementitious material, characterized in that, Includes the following steps: S1. Based on 100 parts by weight of dry steel slag powder, add 2.5 to 3.5 parts by weight of liquid sodium silicate with a solid mass fraction of 28% to 32%, and add water to make the total amount of process water, including the water contained in the liquid sodium silicate, 8 to 10 parts by weight; after mixing and sealing for wetting and aging, perform carbonization treatment in a carbon dioxide atmosphere until the free CaO content in the steel slag powder is 0.5% to 1.0% and the net CO2 absorption is 1.0% to 2.5% of the dry weight of the steel slag powder; after drying and grinding, obtain water glass-wetted—shallow carbonized steel slag powder. S2. Based on the dry weight of the material before calcination, mix 58-62 parts of magnesite powder with 38-42 parts of kaolin powder, totaling 100 parts, and co-calcine at 710-730℃; take 5-7 parts of the co-calcined material after calcination weight loss and cooling and grind it together with 93-95 parts of granulated blast furnace slag powder, totaling 100 parts, to obtain magnesium-aluminum precursor activated slag powder; S3. 12-18 parts by weight of the water glass-wetted—shallow carbonized steel slag powder, 52-60 parts by weight of magnesium-aluminum precursor activated slag powder, 14-18 parts by weight of medium sulfate-resistant silicate cement, 6-10 parts by weight of Class F low-calcium fly ash, 1.0-2.0 parts by weight of hydrated lime powder, and 2.5-4.0 parts by weight of silica fume are dry-mixed, with a total of 100 parts by weight of each component, and the mass ratio of silica fume to hydrated lime powder is 1.5:1 to 2.5:1, to obtain the composite cementitious material.

2. The preparation method according to claim 1, characterized in that, In step S1, the steel slag powder is converter steel slag powder that has undergone iron removal and aging, with an initial free CaO content of 2.0% to 4.0%, a free MgO content of no more than 2.0%, and a D90 of no more than 75μm; The modulus of the liquid sodium silicate is 2.6 to 2.8; after mixing steel slag powder, liquid sodium silicate and water for 8 to 15 minutes, it is sealed and moistened for 20 to 40 minutes at 25 to 35°C.

3. The preparation method according to claim 2, characterized in that, In step S1, the volume fraction of CO2 in the carbon dioxide atmosphere is 15%–20%, the relative humidity of the gas is not less than 75%, the carbonization temperature is 40–50℃, the cumulative amount of mixed gas is 0.05–0.15 Nm³ / kg dry steel slag powder, and the carbonization time is 60–150 min. During carbonization, the material is kept in a turning state. After carbonization, the material is dried to a moisture content of not more than 1.0% under the condition that the material temperature does not exceed 60℃, and then ground to a D50 of 10–15 μm.

4. The preparation method according to claim 1, characterized in that, In step S2, the magnesite powder contains MgCO3 at a mass fraction of not less than 90%, the kaolin powder contains kaolinite at a mass fraction of not less than 80%, and the D90 of both raw materials is not greater than 75μm. The mixed raw materials are heated to 710-730℃ at a rate of 5-10℃ / min under air circulation conditions, held at that temperature for 60-90min, and then cooled to below 100℃ with dry air. The residual MgCO3 content in the resulting co-calcined product is controlled to be no higher than 5%.

5. The preparation method according to claim 4, characterized in that, In step S2, the co-calcined material after calcination loss and cooling is pre-ground for 5-10 minutes, and then the granulated blast furnace slag powder is added and co-ground for 25-35 minutes. During the co-grinding process, the material temperature does not exceed 65℃. The resulting activated slag powder of magnesium-aluminum precursor has a D50 of 7-12 μm and a specific surface area of ​​450-550 m². 2 / kg.

6. The preparation method according to claim 1, characterized in that, In step S3, the composite cementitious material, by dry basis mass, consists of 15 parts of water glass-wetted shallow carbonized steel slag powder, 56 parts of magnesium-aluminum precursor activated slag powder, 16 parts of medium sulfate-resistant silicate cement, 8.5 parts of Class F low calcium fly ash, 1.5 parts of quicklime powder, and 3 parts of silica fume.

7. The preparation method according to claim 6, characterized in that, The clinker of the sulfate-resistant silicate cement contains no more than 5% C3A; the F-type low-calcium fly ash contains no more than 10% CaO and no more than 5% loss on ignition; the slaked lime powder contains no less than 90% Ca(OH)2 and has a D50 of no more than 20μm; the silica fume contains no less than 90% amorphous SiO2 and has a specific surface area of ​​15-25m². 2 / g.

8. The preparation method according to claim 7, characterized in that, In step S3, the silica fume and F-type low-calcium fly ash are first premixed in a sealed manner for 3-5 minutes, and the quicklime powder and magnesium-aluminum precursor activated slag powder are premixed in a sealed manner for 3-5 minutes. Then, the two premixes are dry-mixed together with water glass-wetted shallow carbonized steel slag powder and medium sulfate-resistant silicate cement for 6-10 minutes. During the dry mixing process, the powder temperature does not exceed 45°C.

9. The preparation method according to any one of claims 1 to 8, characterized in that, The method also includes the step of preparing the obtained composite cementitious material into a full tailings paste filling slurry: ungraded full tailings and the composite cementitious material are mixed at a dry basis mass ratio of 4.5 to 8:1, and water is added to make the total solid mass fraction of the slurry 76% to 80%; first, the full tailings are mixed with 65% to 75% of the total mixing water for 1 to 2 minutes, then the composite cementitious material is added in batches and mixed for 2 to 3 minutes, and finally the remaining mixing water is added and mixed for 3 to 5 minutes, wherein the water content of the full tailings itself and the residual water of the composite cementitious material are both included in the total mixing water.

10. A sulfate-resistant composite cementitious material for filling tailings paste, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

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