A kind of alkali activated gelling material and preparation method thereof

Abstract

The invention discloses an alkali-activated cementitious material and a preparation method thereof. The raw materials of the alkali-activated cementitious material include lead-zinc slag, coal gangue, fly ash, red mud and an alkali activator aqueous solution; the mass ratio of the lead-zinc slag, coal gangue, fly ash and red mud is 1:0.2-0.3:6-7:0.4-0.5; the mass ratio of the total mass of the lead-zinc slag, coal gangue, fly ash and red mud to the alkali activator aqueous solution is 1:0.3-0.7; the mass percentage of the alkali activator in the alkali activator aqueous solution is 4%-14%; the alkali activator is Na2O·SiO2 with a modulus of 1.5-3.0, and the modulus represents the molar ratio of SiO2 to Na2O. The preparation method comprises: mixing the alkali activator aqueous solution with the mixture of lead-zinc slag, coal gangue, fly ash and red mud, vibrating and demolding, and curing to obtain the alkali-activated cementitious material.

Description

Technical Field

[0001] The invention relates to the technical field of tailings resource utilization, and in particular to an alkali-activated gelling material and a preparation method thereof. Background Art

[0002] Lead-zinc slag is solid waste generated during the mining process of lead-zinc mines. Due to the continuous mining of lead and zinc resources, a large amount of lead-zinc slag is produced. These slags pose potential hazards to the environment. Therefore, unreasonable disposal methods will cause serious heavy metal pollution to the surrounding environment. Research on the heavy metal pollution problem caused by lead-zinc slag and its resource utilization has been a hot topic in recent years.

[0003] Alkali-Activated Materials (AAMs) are a type of cementitious material that has certain cementitious properties after adding water, and solidifies to form a material with a certain strength after a period of time. Alkali-activated materials refer to materials with volcanic ash activity or potential hydraulic properties that are prepared by adding some alkaline reagents as activators. Commonly used alkaline activators include sodium hydroxide, water glass, sodium carbonate and other alkaline reagents.

[0004] Alkali-activated materials are considered to be new materials with great prospects in the construction industry because they have many good properties. Compared with traditional silicate cement, which needs to be calcined during production and produces a lot of carbon dioxide and energy consumption, alkali-activated materials have lower energy consumption in the entire production process, and their raw materials are abundant. A large amount of industrial solid waste can be used as production raw materials, which is in line with the concept of sustainable development. The research and development of alkali-activated cementitious materials is of great significance.

[0005] The patent specification with publication number CN104003632A discloses a method for preparing inorganic mineral polymers using lead-zinc tailings, which comprises activating the lead-zinc tailings by wet alkali calcination, adding kaolin and sand, stirring, and then adding an alkali activator to carry out an inorganic polymerization reaction to form an inorganic mineral polymer with a network structure. The obtained inorganic mineral polymer can be further prepared into a foamed inorganic mineral polymer by adding a foaming agent and a foam stabilizer.

[0006] The patent specification with publication number CN105565691A discloses a lead-zinc smelting slag-based polymer gelling material and its preparation method, which belongs to the field of geopolymer technology. The raw material components and their mass percentages are: lead-zinc smelting slag 65~72wt.%, fly ash 5~10wt.%, composite alkali activator 8~15wt.%, sulfate activator 3~6wt.%, aluminate activator 1~3wt.%, deionized water 10~14wt.%. The preparation method is: lead-zinc smelting slag and fly ash are dried and ground respectively, and then mixed with sulfate activator and aluminate activator and ground together to obtain a ball-milled mixture; then the composite alkali activator solution is added to the ball-milled mixture, stirred evenly, formed, and cured to obtain a lead-zinc smelting slag-based polymer gelling material. Summary of the invention

[0007] In order to realize the resource utilization of lead-zinc slag, the present invention adopts lead-zinc slag and three other solid wastes to prepare alkali-activated cementitious material (or simply referred to as "alkali-activated material"), and uses sodium silicate as an alkali activator, which can make the alkali-activated cementitious material have excellent strength performance and heavy metal solidification stabilization effect.

[0008] The specific technical solutions are as follows:

[0009] In a first aspect, the present invention provides an alkali-activated cementitious material, the raw materials of which include lead-zinc slag, coal gangue, fly ash, red mud and an alkali activator aqueous solution;

[0010] The mass ratio of lead-zinc slag, coal gangue, fly ash and red mud is 1:0.2~0.3:6~7:0.4~0.5;

[0011] The mass ratio of the total mass of lead-zinc slag, coal gangue, fly ash and red mud to the alkaline activator aqueous solution is 1:0.3-0.7, such as 1:0.4, 1:0.5, etc.;

[0012] The mass percentage of the alkaline activator in the alkaline activator aqueous solution is 4% to 14%, such as 10%, 12%, etc.;

[0013] The alkaline activator is Na2O·SiO2 with a modulus of 1.5 to 3.0 (eg, 2.5, etc.), where the modulus represents the molar ratio of SiO2 to Na2O.

[0014] In the present invention, the mass ratio of lead-zinc slag, coal gangue, fly ash and red mud is 1:0.2~0.3:6~7:0.4~0.5, which is a reasonable range determined by calculating the three rate values ​​(lime saturation coefficient (KH), silica rate (SM) and aluminum oxygen rate (IM)) in the cement production process according to the respective components. Specifically, the control target of the lime saturation coefficient (KH) can be between 0.82~0.94 (for example, 0.9, etc.), the control target of the silica rate (SM) can be between 1.5~3.5 (for example, 2.2, etc.), and the control target of the aluminum oxygen rate (IM) can be between 0.9~1.7 (for example, 1.5, etc.). In a preferred example, the mass ratio of lead-zinc slag, coal gangue, fly ash and red mud in the alkali-activated cementitious material described in the first aspect is 1:0.27:6.5:0.44.

[0015] In the alkali-activated cementitious material described in the first aspect, the mass ratio of the total mass of lead-zinc slag, coal gangue, fly ash and red mud to the alkali activator aqueous solution is preferably 1:0.4~0.5.

[0016] In the alkali-activated gelling material described in the first aspect, the mass percentage of the alkali activator in the alkali activator aqueous solution is preferably 10% to 12%.

[0017] In the alkali-activated gelling material described in the first aspect, the alkali activator is preferably Na2O·SiO2 with a modulus of 2.5.

[0018] The alkali-activated cementitious material described in the first aspect contains the following phases: quartz, brucite, orthorhombic zeolite and halite. A large amount of brucite, orthorhombic zeolite and halite are formed in the alkali-activated material of the present invention. Brucite has good strength, so the generation of a large amount of brucite structure helps to improve the strength of the alkali-activated cementitious material. Orthorhombic zeolite has a porous structure and a certain ion exchange capacity, so its presence can effectively adsorb and exchange heavy metals in the material, thereby solidifying and stabilizing the heavy metals in the material, reducing the mobility of the heavy metals and thus reducing the leaching concentration of the heavy metals, and improving the solidification rate of the heavy metals. Halite is a vanadate mineral that has a certain ability to adsorb and fix some heavy metals under alkaline conditions, and the vanadium element in halite may form a complex or precipitate with the heavy metal ions in the material aqueous solution, thereby achieving the solidification and stabilization of the heavy metals.

[0019] In a second aspect, the present invention provides a method for preparing the alkali-activated cementitious material described in the first aspect, comprising: mixing an aqueous solution of an alkali activator with a mixture of lead-zinc slag, coal gangue, fly ash and red mud, compacting and demolding the mixture, and curing the mixture to obtain the alkali-activated cementitious material.

[0020] In the preparation method described in the second aspect, the curing conditions may include: a temperature of 25° C. and a relative humidity of not less than 50%, such as 90%, 95%, etc.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention realizes resource utilization of lead-zinc slag through alkali excitation technology, and simultaneously realizes solidification and stabilization of heavy metals, and can be used in mine backfill engineering.

[0023] The alkali-activated cementitious material of the present invention meets the building strength requirement and can replace part of the cement consumption in the construction project. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 An alkali-activated cementitious material is prepared using a liquid-to-solid mass ratio of 4:10, an alkali activator is a Na2SiO3 solution with a mass fraction of 10% and a modulus of 2.5, and the raw materials are lead-zinc slag, coal gangue, fly ash, and red mud in a mass ratio of 1:0.27:6.5:0.44, as well as the X-ray diffraction (XRD) diagram of the raw materials.

[0025] Figure 2 An alkali-activated cementitious material is prepared using a liquid-to-solid mass ratio of 4:10, an alkali activator is a Na2SiO3 solution with a mass fraction of 10% and a modulus of 2.5, and raw materials are lead-zinc slag, coal gangue, fly ash, and red mud in a mass ratio of 1:0.27:6.5:0.44, as well as heavy metal form analysis diagrams of the raw materials; wherein: Figure (a), Figure (b), Figure (c), and Figure (d) correspond to the heavy metal forms of Mn, Cu, Zn, and Pb in the raw materials and the alkali-activated cementitious material, respectively, F1 represents the weakly acid extractable state, F2 represents the oxidizable state, F3 represents the reducible state, and F4 represents the proportion of the residual state. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0027] Unless otherwise specified, the following experimental processes all use the following method to prepare alkali-activated gelling materials, including:

[0028] The lead-zinc slag, coal gangue, fly ash and red mud are crushed and sieved, and then mixed in a mass ratio of 1:0.27:6.5:0.44 to obtain a solid waste mixture;

[0029] preparing an aqueous solution of an alkaline activator;

[0030] The alkaline activator aqueous solution was added to the solid waste mixture. The sample size was designed to be 40 mm × 40 mm × 160 mm. After being fully stirred, the sample was compacted 60 times with a compaction table to demould, and then cured in a concrete curing box at 25°C and 90% relative humidity. Three groups of each sample were made in parallel.

[0031] The samples were tested for flexural strength, compressive strength, and leaching concentrations of four heavy metals: Mn, Cu, Zn, and Pb. The compressive and flexural strength tests were performed using a fully automatic flexural and compression testing machine from Hebei Zhongke Beigong Experimental Instrument Co., Ltd., model DYE-300S. The pressure rate during the compressive strength test was 1800 N / s, and the pressure rate during the flexural strength test was 40 N / s.

[0032] The present invention tried three alkali activators, namely sodium hydroxide, sodium silicate Na2O·SiO2 (modulus 2.5) and a mixture of sodium hydroxide and sodium silicate Na2O·SiO2 with a modulus of 2.5 in a mass ratio of 1:1. The experimental design is shown in Table 1. Table 2 shows the 28-day curing compressive strength results of the orthogonal experiment according to Table 1. The liquid-to-solid ratio in Tables 1 and 2 refers to the ratio of the mass of the alkali activator aqueous solution to the total mass of lead-zinc slag, coal gangue, fly ash and red mud. The meaning of "liquid-to-solid ratio" will not be repeated below. The 28-day compressive strength results of the orthogonal experiment are shown in Table 2. It can be seen from the table that the range of the alkali activator type among the three factors is the largest, followed by the amount of alkali activator added (i.e., the concentration of alkali activator in the alkali activator aqueous solution), and the factor with the smallest range is the liquid-to-solid ratio. Therefore, the orthogonal experiment can explain that the order of factors affecting the strength of alkali-activated materials is: alkali activator type > alkali activator addition > liquid-to-solid ratio. Combined with the average values ​​in the table, it can be seen that the optimal conditions are: liquid-to-solid ratio is 0.5, the amount of alkali activator added is 10%, and the type of alkali activator is Na2SiO3.

[0033] Table 1

[0034]

[0035] Table 2

[0036]

[0037] Figure 1 The solid waste mixture (or simply referred to as "raw materials") obtained by crushing and sieving lead-zinc slag, coal gangue, fly ash and red mud in a mass ratio of 1:0.27:6.5:0.44 and the XRD diagram of sample No. 6 in Table 1 and Table 2. Figure 1As shown in the figure, there is no treatment in the raw materials, so only some quartz with low crystallinity are tested. However, it can be clearly seen that after the alkali activator catalyzed the reaction, the material of sample No. 6 has undergone tremendous changes, and many sharp peaks have appeared. The new phases are brucite, orthorhombic zeolite, and phillipsite. In addition to quartz, the diffraction peak intensity of brucite is the strongest, indicating that a large amount of hydroxide ions OH are formed in the material after the addition of the alkali activator. - , and the Mg formed by the heavy metals contained in the raw materials dissolving in aqueous solution 2+ Combined to form brucite with a crystal structure, brucite generally has a low density (2.3~2.6g / cm 3 ), but it has good strength, so the formation of a large number of brucite structures helps to improve the strength of alkali-activated cementitious materials. The weaker diffraction peaks near 40°, 60° and 80° in the XRD spectrum correspond to orthorhombic calcium zeolite, which is a hydrated calcium aluminum silicate mineral, indicating that the free Si(OH)4 and Al(OH)4 tetrahedral structures are similar to the Ca(OH)4 in the alkali-activated material. 2+ Combined into orthorhombic calcium zeolite, orthorhombic calcium zeolite has a porous structure and a certain ion exchange capacity, so its presence can effectively adsorb and exchange heavy metals in the material, thereby solidifying and stabilizing the heavy metals in the material, reducing the mobility of heavy metals and thus reducing the leaching concentration of heavy metals, and improving the solidification rate of heavy metals. In addition, vanadium calcium zeolite was also detected in the sample. Catecholite is a vanadate mineral that has a certain ability to adsorb and fix some heavy metals under alkaline conditions, and the vanadium element in vanadium calcium zeolite may form a complex or precipitate with the heavy metal ions in the aqueous solution of the material, thereby achieving the solidification and stabilization of heavy metals.

[0038] The No. 6 test sample cured for 28 days (d) was compared with the raw material. The BCR heavy metal form analysis method was used to analyze the changes in the heavy metal forms in the material before and after. The heavy metal forms were divided into four forms: (F1) weak acid extractable form, (F2) oxidizable form, (F3) reducible form, and (F4) residual form. The specific results are as follows: Figure 2As shown, it can be clearly seen that compared with the raw materials, the weak acid extractable state generally has the highest content. Therefore, the heavy metals in the raw materials have high mobility and are easily introduced into the soil environment with rainwater to cause large-scale pollution. The heavy metal forms in the alkali-activated cementitious materials prepared by alkali activator technology have undergone significant changes. The oxidizable states of the four heavy metals Mn, Cu, Zn, and Pb in the No. 6 28d sample have all increased significantly. Combined with the previous XRD test, it shows that a large amount of heavy metal silicates and aluminates are produced inside the alkali-activated materials, among which the oxidizable states of the three heavy metals Mn, Cu, and Pb are the highest, reaching 35%, 41%, and 45%, respectively, which are 15%, 15%, and 9% higher than the oxidizable states of Mn, Cu, and Pb in the raw materials, which account for 20%, 16%, and 36%, respectively. In addition, the residual state of the four heavy metals has decreased compared with the raw materials, but the amplitude is small. This is because the addition of the alkali activator increases the pH of the material, and a small amount of residual state begins to dissolve in the alkaline environment, resulting in a decrease in the residual state content.

[0039] In addition, the present invention uses sodium silicate (Na2O·SiO2, modulus n is the molar ratio of SiO2 to Na2O) with modulus of 1.5, 2.0, 2.5, and 3.0 as the alkali activator, the mass concentration of the alkali activator in the alkali activator aqueous solution (or simply referred to as "addition amount") is 10%, and the liquid-solid ratio is set to 0.4. During the entire experiment, the strength of the sample was tested on the 3rd, 28th, and 60th day of curing, including compressive strength and flexural strength, and the influence of the sodium silicate modulus on the performance of the alkali-activated material was comprehensively analyzed. Table 3 shows the influence of the sodium silicate modulus on the strength of the alkali-activated material.

[0040] Table 3

[0041]

[0042] It can be seen from Table 3 that the compressive strength and flexural strength of the material are increasing with the extension of time, and when the modulus of sodium silicate increases from 1.5 to 2.5, the strength of the samples in the same period increases, but when the modulus of sodium silicate is 3.0, the compressive strength of the sample decreases significantly, and its 28d and 60d compressive strengths are lower than the samples with modulus of 2.0 and 2.5. The flexural strength of the sample also drops significantly to the lowest, and its 60d flexural strength is only 1.6MPa, which is lower than the levels of the other three groups. It may be due to the influence of the properties of sodium silicate itself. The larger its modulus, the greater the bonding force of sodium silicate, and the more difficult it is to dissolve in water, thus reducing the reaction efficiency of the alkali-activated material, resulting in the phenomenon that the strength of the sample decreases with the increase of the modulus of sodium silicate.

[0043] Overall, the sample with modulus n=2.5 has the highest compressive strength and flexural strength, with the 60d compressive strength and flexural strength reaching 49.1MPa and 4.3MPa respectively.

[0044] The present invention also studies the influence of liquid-to-solid ratio on alkali-activated cementitious materials. The experiment adopts 7 levels of liquid-to-solid ratio, uses sodium silicate with a modulus of 2.5 as an alkali activator, and prepares samples at a 10% addition amount (three parallel samples in each group) to test the compressive strength and flexural strength of the samples when the samples are cured for 3 days, 28 days, and 60 days. The specific results are shown in Table 4. From the data in the table, it can be seen that the compressive strength and flexural strength of all samples are continuously enhanced with the extension of time. Among them, the 60d compressive strength of the sample is the highest when the liquid-to-solid ratio is 0.65, which is 69MPa, which is 10.9% higher than the 60d compressive strength of 62.2MPa of the optimal condition sample screened out in the previous orthogonal experiment. However, from the data in the table, it can be seen that after the liquid-to-solid ratio reaches 0.55, the increase in the flexural strength of the sample decreases significantly. When the liquid-to-solid ratio is 0.5, the flexural strength of the sample reaches a maximum of 6.8MPa. With the increase of the liquid-to-solid ratio, the compressive strength is continuously enhanced, and it is especially reflected in the early strength. However, the enhancement of the flexural strength gradually slows down with the increase of the liquid-to-solid ratio, and even shows a downward trend. For example, the 60d flexural strength of the samples with liquid-to-solid ratios of 0.55, 0.6 and 0.65 is lower than that of the sample with a liquid-to-solid ratio of 0.5. From the data in the analysis table, it can be seen that when the liquid-solid ratio is between 0.35 and 0.65, the compressive strength of the alkali-activated cementitious material will increase with the increase of the liquid-solid ratio, and the increase of the liquid-solid ratio will greatly improve the early compressive and flexural strength of the material, but its 60d flexural strength will increase first and then decrease with the increase of the liquid-solid ratio. At the liquid-solid ratio level of 0.5, the maximum flexural strength reaches 6.8MPa. The study also found that the curing rates of the four heavy metals Mn, Cu, Zn, and Pb in the No. 17 sample cured for 28 days reached 88.35%, 96.04%, 95.27%, and 95.01%, respectively.

[0045] Table 4

[0046]

[0047] The present invention also studies the influence of the amount of alkali activator added on the alkali activated material. When sodium silicate with a modulus of 2.5 is used as an alkali activator and the liquid-solid ratio is 0.5, the results of the influence of the amount of alkali activator added on the strength of the alkali activated cementitious material are shown in Table 5. From the data in the table, it can be seen that whether it is compressive strength or flexural strength, only the 60d compressive strength of the sample with a 14% addition amount is 68MPa, which is 0.7MPa lower than the 60d compressive strength of the sample with a 12% addition amount. Most of them are continuously enhanced with the extension of time and the increase of the amount of alkali activator added. Among them, the 60d compressive strength of the sample with a 12% addition amount in the No. 25 experimental group reaches a maximum of 68.7Ma, and its 28d compressive strength reaches 49.9MPa. According to the standard of ordinary Portland cement, it can meet the requirements of the 42.5 strength level. In addition, it is obvious that the flexural strength of all samples increases with the increase of the amount of alkali activator added and the extension of time. The 60d flexural strength of the sample with 14% alkali activator added reaches a maximum of 7.4MPa, which is 47.3% higher than the 60d flexural strength of the sample with 4% addition. The increase in the amount of alkali activator added mainly affects the early strength of the alkali-activated material sample. Among them, the 3d flexural strength of the sample with 14% addition is 3.7MPa, which is 131.25% higher than the flexural strength of the sample with 4% addition. The flexural strength of the sample is significantly improved.

[0048] Table 5

[0049]

[0050] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. An alkali-activated gelling material, characterized in that: The raw materials include lead-zinc slag, coal gangue, fly ash, red mud and alkaline activator aqueous solution; The mass ratio of lead-zinc slag, coal gangue, fly ash and red mud is 1:0.2~0.3:6~7:0.4~0.5; The mass ratio of the total mass of lead-zinc slag, coal gangue, fly ash and red mud to the alkaline activator aqueous solution is 1:0.3~0.7; The mass percentage of the alkali activator in the alkali activator aqueous solution is 4% to 14%; The alkaline activator is Na2O·SiO2 with a modulus of 1.5 to 3.0, where the modulus represents the molar ratio of SiO2 to Na2O; The alkali-activated gelling material contains the following phases: quartz, brucite, orthorhombic zeolite and phillipsite.

2. The alkali-activated gelling material according to claim 1, characterized in that: The mass ratio of lead-zinc slag, coal gangue, fly ash and red mud is 1:0.27:6.5:0.

44.

3. The alkali-activated gelling material according to claim 1, characterized in that: The mass ratio of the total mass of lead-zinc slag, coal gangue, fly ash and red mud to the alkaline activator aqueous solution is 1:0.4~0.

5.

4. The alkali-activated gelling material according to claim 1, characterized in that: The mass percentage of the alkali activator in the alkali activator aqueous solution is 10% to 12%.

5. The alkali-activated gelling material according to claim 1, characterized in that: The alkaline activator is Na2O·SiO2 with a modulus of 2.

5.

6. The method for preparing an alkali-activated gelling material according to any one of claims 1 to 5, characterized in that: include: The alkali activator aqueous solution is mixed with the mixture of lead-zinc slag, coal gangue, fly ash and red mud, and then compacted, demoulded and cured to obtain an alkali-activated cementitious material.

7. The preparation method according to claim 6, characterized in that: The curing conditions include: temperature 25°C and relative humidity not less than 50%.

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