Modified magnesium tailing aggregate, and preparation method and application thereof

Abstract

The application belongs to the field of magnesium tailing resource utilization, and particularly relates to a modified magnesium tailing aggregate, a preparation method and application thereof. The preparation method comprises the following steps: adding sodium silicate and carbonate mineralizing bacteria into the magnesium tailing aggregate, stirring and heating until the sodium silicate is melted and adhered to the surface of the magnesium tailing aggregate; then adding carbon fiber powder, carbon fiber adhesive A microcapsule and carbon fiber adhesive B, uniformly mixing, cooling to room temperature, air drying, and obtaining a mixture; adding a cellulose acetate acetic acid methyl ester solution into the mixture, uniformly mixing, air drying, and obtaining the modified magnesium tailing aggregate. The preparation method of the modified magnesium tailing aggregate effectively controls the adverse effect of expansion of the magnesium tailing as an aggregate on the concrete, realizes the volume application of the magnesium tailing as the concrete aggregate, improves the concrete performance, improves the volume stability of the concrete, and realizes the resource utilization of the magnesium tailing.

Description

Technical Field

[0001] The present invention belongs to the field of magnesium tailings resource utilization, and particularly relates to a modified magnesium tailings aggregate and a preparation method and application thereof. Background Art

[0002] Dolomite magnesia is a common mineral used in industry, often used to smelt magnesium-based products. However, mining this ore produces a significant amount of unusable, low-quality tailings and gravel. This tailings accumulation not only occupies land but also impacts the surrounding environment. The vast stockpile of dolomite tailings, if not fully utilized, will inevitably have lasting adverse environmental impacts. Therefore, resource utilization of dolomite magnesium tailings is urgent.

[0003] The main components of dolomite magnesium tailings are magnesium-calcium carbonate compounds, of which the magnesium compound content accounts for more than 30%. At present, there are a lot of studies on the use of magnesium ore in the field of building materials, but they mainly use magnesium ore to prepare magnesium oxide, and then use magnesium oxide to prepare concrete expansion agents or micro-expansion cement, which can effectively inhibit the volume shrinkage of concrete. The use of magnesium ore to make expansion agents is not only low in quantity and cannot be used on a large scale in concrete, but also mainly uses magnesium ore, and the use of tailings is relatively small, and there is also less research.

[0004] At present, there have been studies on the use of magnesium tailings as admixtures in building products and concrete, mainly using it to generate magnesium hydroxide in cement to produce micro-expansion, thereby inhibiting cracking caused by volume shrinkage. Using magnesium tailings as aggregates is another important way to achieve large-scale application of magnesium tailings. However, due to the frequent occurrence of alkali-carbonate reactions, that is, the alkali in cement reacts with the aggregate dolomite in the presence of water to form magnesium hydroxide crystals, causing the concrete volume to expand and even crack, affecting the concrete volume stability. Therefore, at this stage, magnesium tailings aggregates are rarely used in aggregates, which makes it impossible to achieve large-scale resource utilization and disposal. Summary of the Invention

[0005] In view of the problems and shortcomings in the prior art, the present invention aims to provide a modified magnesium tailings aggregate and a preparation method and application thereof.

[0006] To achieve the purpose of the invention, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention provides a method for preparing modified magnesium tailings aggregate, comprising the following steps:

[0008] (1) Sodium silicate and carbonate mineralizing bacteria are added to the magnesium tailings aggregate, and the mixture is heated while being stirred until the sodium silicate melts and adheres to the surface of the magnesium tailings aggregate; then carbon fiber powder, carbon fiber adhesive A microcapsules and carbon fiber adhesive B are added, mixed well, cooled to room temperature, and air-dried to obtain a mixture;

[0009] (2) Adding a methyl acetate solution of cellulose acetate to the mixture obtained in step (1), mixing well and air-drying to obtain a modified magnesium tailings aggregate.

[0010] According to the above-mentioned preparation method of modified magnesium tailings aggregate, further, the mass ratio of the magnesium tailings aggregate, sodium silicate, and carbonate mineralizing bacteria is 100:5-8:0.1-0.2.

[0011] According to the preparation method of the modified magnesium tailings aggregate, further, the mass ratio of the magnesium tailings aggregate, carbon fiber powder, carbon fiber adhesive A microcapsule and carbon fiber adhesive B is 100:1-2:0.2-0.4:0.02-0.04.

[0012] According to the above-mentioned preparation method of modified magnesium tailings aggregate, further, the mass ratio of the magnesium tailings aggregate, methyl acetate and cellulose acetate is 100:0.5:1-2.

[0013] According to the above-mentioned method for preparing modified magnesium tailings aggregate, further, the carbonate mineralizing bacteria is Bacillus.

[0014] According to the above-mentioned preparation method of modified magnesium tailings aggregate, further, the preparation method of the carbon fiber adhesive A microcapsule includes: adding a water-soluble epoxy resin emulsion and a nano paraffin emulsion to a gelatin solution, dispersing them evenly, then adding 35-40 wt % formaldehyde solution, stirring and reacting for 1 hour, filtering, and drying the filter residue to obtain the carbon fiber adhesive A microcapsule.

[0015] According to the above-mentioned method for preparing modified magnesium tailings aggregate, further, the particle size of the carbon fiber adhesive A microcapsule is not greater than 100 μm.

[0016] According to the above-mentioned preparation method of modified magnesium tailings aggregate, further, the carbon fiber adhesive B is any one of 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, and m-phenylenediamine.

[0017] A second aspect of the present invention provides a modified magnesium tailings aggregate prepared using the above preparation method.

[0018] A third aspect of the present invention provides a use of the modified magnesium tailings aggregate in concrete.

[0019] The present invention first mixes magnesium tailings aggregate with sodium silicate powder and carbonate mineralizing bacteria. The sodium silicate acts as a viscosity enhancer, allowing the subsequently added carbon fiber powder, carbon fiber adhesive A microcapsules, and carbon fiber adhesive B to adhere well to the aggregate surface. Furthermore, when the aggregate later expands in water, the sodium silicate reacts with magnesium hydroxide to form magnesium silicate, increasing the aggregate's crack resistance and toughness while reducing the adverse effects of expansion on the aggregate.

[0020] During the preparation of the modified magnesium tailings aggregate, the added carbon fibers simply adhere to the aggregate surface. However, once the aggregate expands, the capsules of carbon fiber adhesive A are squeezed and ruptured, reacting with carbon fiber adhesive B to form a binder, rapidly enhancing the carbon fiber's performance. Because sodium silicate alone cannot fully offset the expansion stress of the magnesium tailings aggregate, the expansion causes the outer layer structure to lose stability, necessitating the addition of carbon fiber structure.

[0021] Cellulose acetate forms a thin film with a reverse osmosis structure on the outer layer. In the initial stage of concrete mixing, it prevents water from penetrating through the membrane and reaching the aggregate surface. Even under high osmotic pressure conditions, water can penetrate the reverse osmosis membrane and reach the aggregate surface. This reaction between water absorption by sodium silicate and the expansion of the aggregate to form magnesium hydroxide will produce magnesium silicate, which has a toughening and strengthening effect. In the later stage of concrete hardening, after absorbing water, the reverse osmosis membrane also prevents water from penetrating into the aggregate. When water penetrates the aggregate surface under high osmotic pressure conditions, it causes the aggregate to produce magnesium hydroxide, causing volume expansion. The high pressure generated by this volume expansion forces water to penetrate the aggregate to the exterior, thereby reducing further water absorption and expansion reaction. At the same time, the sodium silicate and mineralizing bacteria inside the aggregate begin to slowly participate in the reaction, producing substances such as calcium carbonate and magnesium carbonate, reducing the stress of the magnesium hydroxide. Throughout this process, cellulose acetate effectively controls the expansion volume of the aggregate, preventing overall damage to the concrete structure, maintaining a stable structural equilibrium within the aggregate, and ultimately avoiding adverse effects on the aggregate.

[0022] The capsule is made of gelatin, which can quickly disintegrate under alkaline solution conditions, accelerating the rapid reaction between adhesives A and B, so that the carbon fiber is quickly bonded to the surface of the aggregate to form a mesh-wrapped constraint layer. At the same time, gelatin has viscosity, which constrains the carbon fiber from being dispersed into the slurry.

[0023] Carbon fiber adhesive A is encapsulated in a gelatin capsule. When mixed with carbon fiber adhesive B, this ensures both physical isolation of components A and B and their mutual adhesion. After the gelatin disintegrates in an alkaline solution, components A and B rapidly react to impregnate the carbon fibers, encapsulating them on the aggregate surface and forming a network layer that effectively controls aggregate volume. Furthermore, because components A and B are encapsulated within a reverse osmosis membrane formed by cellulose acetate, water infiltration is controlled, effectively controlling the moisture content on the aggregate surface. This ensures the proper reaction between components A and B and prevents excessive moisture from affecting their curing and bonding to the carbon fibers.

[0024] The preparation method of the modified magnesium tailings aggregate proposed in the present invention effectively controls the adverse effect of the expansion of magnesium tailings on concrete when used as aggregate, realizes the volumetric application of magnesium tailings as concrete aggregate, improves the performance of concrete, increases the volume stability of concrete, and realizes the resource utilization of magnesium tailings. DETAILED DESCRIPTION

[0025] The following examples are intended only to further illustrate the present invention. It should be noted that all technical and scientific terms used herein have the same meanings as in the art to which the present invention pertains, unless otherwise specified. Experimental methods in the following examples, where specific conditions are not specified, were based on conventional techniques in the art or the conditions recommended by the manufacturer. Reagents and instruments used, where the manufacturer is not specified, are commercially available conventional products.

[0026] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0027] The carbon fiber adhesive A microcapsules described in the present invention are prepared by pouring 5 parts of gelatin into 100 parts of water, heating and dissolving to form a gelatin solution; pouring 50 parts of a water-soluble epoxy resin emulsion into the gelatin solution, adding 10 parts of a nano paraffin emulsion, ultrasonically dispersing and continuously stirring to obtain a mixed solution; adding a 37% formaldehyde solution dropwise to the mixed solution, stirring for 60 minutes, centrifuging, filtering, and drying at low temperature to obtain carbon fiber adhesive A capsules.

[0028] In order to explore the influencing factors of modified magnesium tailings aggregate, the present invention conducted experiments of Examples 1 to 3 and Comparative Examples 1 to 10.

[0029] Example 1

[0030] A modified magnesium tailings aggregate, the preparation method of which is as follows:

[0031] (1) The magnesium tailings are crushed and washed with water, and then dried to obtain magnesium tailings aggregate. 100 parts by weight of magnesium tailings aggregate, 5 parts of sodium silicate nonahydrate powder, and 0.2 parts of facultative thermophilic Bacillus (mineralizing Bacillus licheniformis, obtained by culturing Bacillus preserved during the experiment) are taken and stirred evenly in an aggregate mixer to obtain a mixture. The mixture is heated to 50°C and stirred continuously until the sodium silicate nonahydrate melts and evenly adheres to the surface of the magnesium tailings aggregate.

[0032] (2) At 50°C, 2 parts of carbon fiber powder, 0.2 parts of carbon fiber adhesive A microcapsules with a particle size of 50 to 80 μm, and 0.02 parts of carbon fiber adhesive B (4,4′-diaminodiphenylmethane) were added to the magnesium tailings aggregate treated in step (1), and the mixture was stirred evenly so that the above substances were evenly adhered to the surface of the aggregate.

[0033] (3) The aggregate obtained in step (2) is cooled to room temperature, air-dried at room temperature, and then a mixture obtained by mixing 0.5 parts of methyl acetate and 2 parts of cellulose acetate is added thereto. After mixing evenly, the mixture is air-dried at room temperature to obtain a modified magnesium tailings aggregate.

[0034] Example 2

[0035] A modified magnesium tailings aggregate, the preparation method of which is as follows:

[0036] (1) The magnesium tailings are crushed and washed with water, and then dried to obtain magnesium tailings aggregate. 100 parts by weight of magnesium tailings aggregate, 8 parts of sodium silicate nonahydrate powder, and 0.1 parts of facultative thermophilic Bacillus (mineralizing Bacillus licheniformis, obtained by culturing Bacillus preserved during the experiment) are mixed uniformly using an aggregate mixer to obtain a mixture. The mixture is heated to 60°C and stirred continuously until the sodium silicate nonahydrate melts and evenly adheres to the surface of the magnesium tailings aggregate.

[0037] (2) At 50°C, 1 part of carbon fiber powder, 0.4 parts of carbon fiber adhesive A microcapsules with a particle size of 50-80 μm, and 0.04 parts of carbon fiber adhesive B (4,4′-diaminodiphenyl sulfone) were added to the magnesium tailings aggregate treated in step (1), and the mixture was stirred evenly so that the above substances were evenly adhered to the surface of the aggregate.

[0038] (3) The aggregate obtained in step (2) is cooled to room temperature, air-dried at room temperature, and then a mixture obtained by mixing 0.5 parts of methyl acetate and 1 part of cellulose acetate is added thereto. After mixing evenly, the mixture is air-dried at room temperature to obtain a modified magnesium tailings aggregate.

[0039] Example 3

[0040] A modified magnesium tailings aggregate, the preparation method of which is as follows:

[0041] (1) The magnesium tailings are crushed and washed with water, and then dried to obtain magnesium tailings aggregate. 100 parts by weight of magnesium tailings aggregate, 6 parts of sodium silicate nonahydrate powder, and 0.15 parts of facultative thermophilic Bacillus (mineralizing Bacillus licheniformis, obtained by culturing Bacillus preserved during the experiment) are taken and stirred uniformly in an aggregate mixer to obtain a mixture. The mixture is heated to 55°C and stirred continuously until the sodium silicate nonahydrate melts and evenly adheres to the surface of the magnesium tailings aggregate.

[0042] (2) At 50°C, 1.5 parts of carbon fiber powder, 0.3 parts of carbon fiber adhesive A microcapsules with a particle size of 75-90 μm, and 0.03 parts of carbon fiber adhesive B (m-phenylenediamine) were added to the magnesium tailings aggregate treated in step (1), and the mixture was stirred evenly so that the above substances were evenly adhered to the surface of the aggregate.

[0043] (3) The aggregate obtained in step (2) is cooled to room temperature, air-dried at room temperature, and then a mixture obtained by mixing 0.5 parts of methyl acetate and 1.5 parts of cellulose acetate is added thereto. After mixing evenly, the mixture is air-dried at room temperature to obtain a modified magnesium tailings aggregate.

[0044] Comparative Example 1

[0045] A modified magnesium tailings aggregate is prepared by a method substantially the same as that of Example 3, except that sodium silicate nonahydrate powder is not added in step (1).

[0046] Comparative Example 2

[0047] A modified magnesium tailings aggregate is prepared by a method substantially the same as that of Example 3, except that no facultative thermophilic Bacillus is added in step (1).

[0048] Comparative Example 3

[0049] A modified magnesium tailings aggregate is prepared by a method substantially the same as that of Example 3, except that in step (1), the mixture is heated to 40°C.

[0050] Comparative Example 4

[0051] A modified magnesium tailings aggregate is prepared by a method substantially the same as that of Example 3, except that in step (1), the mixture is heated to 80°C.

[0052] Comparative Example 5

[0053] A modified magnesium tailings aggregate is prepared by a method substantially the same as that of Example 3, except that step (2) is not performed, i.e., carbon fiber powder and adhesive are not added.

[0054] Comparative Example 6

[0055] A modified magnesium tailings aggregate is prepared by a method substantially the same as that of Example 3, except that only carbon fiber powder is added in step (2) without adding an adhesive.

[0056] Comparative Example 7

[0057] A modified magnesium tailings aggregate is prepared by a method substantially the same as that of Example 3, except that step (2) is performed. Step (2) comprises the following steps: adding 1.5 parts of carbon fiber powder, 0.3 parts of carbon fiber adhesive A (a commercially available carbon fiber adhesive, the main component of which is epoxy resin emulsion) and 0.03 parts of carbon fiber adhesive B (m-phenylenediamine) to the magnesium tailings aggregate treated in step (1) at 50° C., and stirring the mixture until the above substances are uniformly adhered to the surface of the aggregate.

[0058] Comparative Example 8

[0059] A modified magnesium tailings aggregate is prepared by a method substantially the same as that of Example 3, except that methyl acetate and cellulose acetate are not added in step (3).

[0060] Comparative Example 9

[0061] A modified magnesium tailings aggregate is prepared by a method substantially the same as that of Example 3, except that methyl acetate is not added in step (3).

[0062] Comparative Example 10

[0063] In this comparative example, the magnesium tailings aggregates after crushing, washing and drying were directly taken, that is, the modification of the magnesium tailings aggregates in Examples 1 to 3 was not performed.

[0064] The products prepared in Examples 1 to 3 and Comparative Examples 1 to 10 were tested for 52-week expansion rate of aggregates according to GB / T 50082-2009 “Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete”. The results are shown in Table 1.

[0065]

[0066] As can be seen from the table above, Example 3 and Comparative Example 1 show a significant increase in expansion without the addition of sodium silicate. This is because sodium silicate serves to adhere and secure the carbon fibers to the aggregate surface. Without sodium silicate, the carbon fibers cannot adhere to the aggregate surface, and the aggregate expands significantly upon contact with water due to the formation of magnesium hydroxide. However, the addition of sodium silicate allows it to form magnesium silicate toughening with the generated magnesium hydroxide, thereby controlling aggregate expansion.

[0067] It can be seen from Example 3 and Comparative Example 2 that the expansion rate of the aggregate increases without adding the mineralizing bacteria. This is because the mineralizing bacteria can further convert the magnesium hydroxide generated by the reaction into magnesium carbonate during the reaction process, which has a great optimization effect on the control of alkali aggregate.

[0068] As can be seen from Example 3 and Comparative Example 3, if the temperature is low, the expansion rate of the aggregate increases. This is because sodium silicate does not form a molten state at a relatively low temperature and does not have the effect of adhering to or fixing the carbon fibers, so that the aggregate expansion increases. As can be seen from Comparative Example 1, the sodium silicate material itself has a limited control effect on expansibility. As can be seen from Example 3 and Comparative Example 4, when the temperature is too high, its expansion rate also increases. Because carbonate mineralizing bacteria have an appropriate survival temperature and reaction temperature, too high a temperature causes the bacterial colony to die, and it is impossible to effectively promote the reaction of magnesium hydroxide to be converted into magnesium carbonate, resulting in an increase in volume expansion.

[0069] In summary, the sodium silicate and mineralizing bacteria added to the surface of the magnesium tailings aggregate in the present invention can control the expansion rate of the aggregate by affecting magnesium hydroxide. Therefore, the present invention also has further requirements for the stirring temperature. It is necessary to control the stirring temperature at 50-60°C, which can ensure that the sodium silicate reaches a molten state and does not affect the function of carbonate mineralizing bacteria.

[0070] As can be seen from Example 3 and Comparative Examples 5 and 6, without the addition of carbon fiber and an adhesive, the aggregate cannot effectively restrain expansion in the early stages when forming the expansive substances magnesium hydroxide and calcium hydroxide, causing the expansion rate to increase. Simply using carbon fiber without an adhesive also has limited optimization effects. This also shows that, compared to the restraining force of the concrete structure itself, carbon fiber and an adhesive are more effective in controlling aggregate expansion.

[0071] It can be seen from the examples and comparative example 6 that in comparative example 7, no microcapsules are used, and the adhesive is likely to directly adhere to the aggregate, resulting in the aggregate being destroyed and the expansion rate test being unable to be performed.

[0072] As can be seen from Example 3 and Comparative Examples 8 and 9, not adding methyl acetate or not adding both methyl acetate and cellulose acetate will result in an increase in the expansion rate. This is because cellulose acetate, relying on the dissolution of ethyl acetate, can form a film with a reverse osmosis structure on the outer layer of the aggregate. In the initial stage of mixing the concrete mixture, it will prevent water from penetrating through the film to the aggregate surface. Even under conditions of relatively high osmotic pressure, water penetrates the aggregate surface through the reverse osmosis membrane. The sodium silicate added by the present invention will also convert the magnesium hydroxide formed by the aggregate's water absorption and expansion into magnesium silicate, thereby achieving a toughening and strengthening effect and reducing the expansion rate. After the concrete absorbs water in the later stage of hardening, the reverse osmosis membrane will also prevent water from penetrating into the aggregate. When water penetrates the aggregate surface under conditions of high osmotic pressure, it will cause the aggregate to generate magnesium hydroxide and produce volume expansion. The high pressure generated by volume expansion forces water to penetrate the aggregate to the outside, which can reduce the further water absorption and expansion reaction of the aggregate. At the same time, the sodium silicate and mineralizing bacteria inside begin to slowly participate in the reaction, generating substances such as calcium carbonate and magnesium carbonate, reducing the stress of magnesium hydroxide. Throughout the process, cellulose acetate effectively controls the expansion volume of the aggregate, avoiding overall damage to the concrete structure, maintaining a stable internal structural equilibrium, and ultimately avoiding the adverse effects of the aggregate. If ethyl acetate and cellulose acetate are not added, the reverse osmosis membrane cannot be formed, water penetration and exudation cannot be prevented, and the expansion reaction of the aggregate cannot be controlled. Further expansion will cause damage to the carbon fiber structure and cause structural collapse and damage.

[0073] Compared with Comparative Example 10, it can be seen that the modification measures of the present invention can reduce the expansion rate of the aggregate to a certain extent. When the optimization method of the present invention is used to optimize the aggregate, the results are shown in Examples 1 to 3, and good control of the aggregate expansion rate can be achieved.

[0074] The above embodiments are specific implementation methods of the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any other combination, change, modification, substitution, and simplification that does not exceed the design concept of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing modified magnesium tailings aggregate, characterized in that: The steps include: (1) Sodium silicate and carbonate mineralizing bacteria are added to the magnesium tailings aggregate, and the mixture is heated while being stirred until the sodium silicate melts and adheres to the surface of the magnesium tailings aggregate; then carbon fiber powder, carbon fiber adhesive A microcapsules and carbon fiber adhesive B are added, mixed well, cooled to room temperature, and air-dried to obtain a mixture; (2) Adding a methyl acetate solution of cellulose acetate to the mixture obtained in step (1), mixing well and air-drying to obtain a modified magnesium tailings aggregate.

2. The preparation method of modified magnesium tailings aggregate according to claim 1, wherein The mass ratio of the magnesium tailings aggregate, sodium silicate and carbonate mineralizing bacteria is 100:5-8:0.1-0.

2.

3. The preparation method of modified magnesium tailings aggregate according to claim 1, wherein The mass ratio of the magnesium tailings aggregate, carbon fiber powder, carbon fiber adhesive A microcapsule and carbon fiber adhesive B is 100:1-2:0.2-0.4:0.02-0.

04.

4. The preparation method of modified magnesium tailings aggregate according to claim 1, wherein The mass ratio of the magnesium tailings aggregate, methyl acetate and cellulose acetate is 100:0.5:1-2.

5. The method for preparing modified magnesium tailings aggregate according to any one of claims 1 to 4, characterized in that: The carbonate mineralizing bacteria is Bacillus.

6. The method for preparing modified magnesium tailings aggregate according to claim 5, wherein The preparation method of the carbon fiber adhesive A microcapsule comprises: adding a water-soluble epoxy resin emulsion and a nano paraffin emulsion to a gelatin solution, dispersing them uniformly, then adding a 35-40 wt% formaldehyde solution, stirring and reacting for 1 hour, filtering, and drying the filter residue to obtain the carbon fiber adhesive A microcapsule.

7. The method for preparing a modified magnesium tailings aggregate according to claim 6, wherein: The particle size of the carbon fiber adhesive A microcapsule is no more than 100 μm.

8. The method for preparing a modified magnesium tailings aggregate according to claim 6, wherein: The carbon fiber adhesive B is any one of 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl sulfone, and m-phenylenediamine.

9. Modified magnesium tailings aggregate prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the modified magnesium tailings aggregate according to claim 9 in concrete.

Images