Design, Preparation and Application of Red Mud and Magnesium / Calcium Carbonate Concrete Mineral Admixtures

Abstract

The present invention relates to a design method and application of a concrete mineral admixture based on red mud and magnesium / calcium carbonate, including red mud, magnesium carbonate, and calcium carbonate, and satisfying: a) m MgO ≤m CO3 ; b) 1 / 8m CO3 +7 / 32m MgO ≤m Al2O3 +m Fe2O3 ≤1 / 4m CO3 +3 / 16m MgO . Wherein, m CO3 is the molar amount of carbonate radicals in magnesium carbonate and calcium carbonate, m Al2O3 is the molar amount of alumina in red mud, and m Fe2O3 is the molar amount of iron oxide in red mud. Compared with the prior art, through the chemical reaction between red mud and calcium carbonate and magnesium, the present invention realizes the efficient hydration of red mud, improves the pozzolanic activity of red mud, and efficiently activates the latent activity of calcium carbonate and magnesium-based materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource utilization and harmless disposal of waste materials, and relates to the design, preparation and application of a concrete mineral admixture based on red mud and magnesium / calcium carbonate. Background Art

[0002] Red mud is a waste produced in the production of alumina. For every ton of alumina produced, 1.5 to 2.5 tons of red mud will be generated. More than 70 million tons of red mud are produced in China every year, but the comprehensive utilization rate is only about 10%. The harmless disposal and utilization of red mud have become a major problem in the environmental and resource fields in China. According to different production processes, red mud can be divided into Bayer process red mud, sintering process red mud and combined process red mud. The core components of red mud all include vitreous silica, alumina and iron oxide, which have a certain pozzolanic activity and can be used to prepare concrete mineral admixtures. However, the content of the pozzolanic active component - silica in red mud is lower than that of high-quality mineral admixtures such as mineral powder, but the contents of alumina and iron oxide are higher. This results in poor pozzolanic activity of red mud, seriously affecting the strength development of concrete, and red mud usually contains heavy metal elements and has a certain radioactive hazard. Therefore, the engineering and market applications have not been realized so far. Magnesium and calcium carbonate materials are widely sourced and are generally considered non-reactive under normal conditions and are often used as coarse aggregates and inert fillers in concrete. In fact, magnesium and calcium carbonate have the potential to react with vitreous alumina and iron under alkaline conditions, which has great scientific value for stimulating and improving the pozzolanic activity of red mud.

[0003] Chinese Patent CN113880475B discloses a red mud-based magnesium phosphate cement and its preparation method. Its corresponding mineral phase composition is C 4 AF solid solution, MgO, phosphate and a small amount of setting retarder components. The preparation is divided into two processes: the preparation of raw materials and the preparation of cement. The raw material composition of the raw materials includes 30-50 parts of calcium and magnesium components, 30-45 parts of red mud, 10-20 parts of aluminous raw materials, and 0.5-2 parts of boron oxide; the composition of the cement preparation is 30-50 parts of C 4 AF solid solution, 20-40 parts of MgO, 15-25 parts of phosphate and 0-10 parts of setting retarder components. The purpose of the present invention is to realize the resource utilization of red mud, introduce red mud into magnesium phosphate cement to form a new type of magnesium phosphate cement containing C 4 AF solid solution, reduce the demand of magnesium phosphate cement for magnesium oxide, and at the same time C 4The introduction of AF solid solution can improve the hydration and hardening properties of cement and enhance the water resistance. However, even though the partial requirement of magnesia in magnesium phosphate cement is reduced by introducing red mud, the production cost of dead-burned magnesia remains extremely high, including the extremely high calcination temperature and transportation consumption considering the raw material origin. Therefore, the present invention proposes a strategy of directly using magnesium (calcium) carbonate as the magnesium (calcium) source, supplemented by red mud to prepare a new type of mineral admixture, realizing the resource utilization and harmless treatment of red mud, and having obvious low-carbon significance and technical advantages. Summary of the Invention

[0004] The purpose of the present invention is to provide a design, preparation and application of a concrete mineral admixture based on red mud and magnesium / calcium carbonate. The concrete mineral admixture in the present invention is composed of red mud and magnesium (calcium) carbonate materials. By designing the proportions of components such as aluminum, iron, magnesium, calcium and carbonate in the materials, specific chemical reactions occur between the alumina and iron oxide components in red mud and calcium carbonate and magnesium carbonate, generating target products such as hydrotalcite, monocarbon-type hydrated calcium aluminate (ferrite) and semi-carbon-type hydrated calcium aluminate (ferrite), stimulating the pozzolanic activity of red mud and the potential reaction activity of magnesium carbonate and calcium carbonate. When this product is used to prepare concrete, it has no obvious adverse effect on the strength performance of concrete, and the heavy metal ions commonly present in red mud can be effectively solidified, which can replace traditional concrete mineral admixtures. The invention solves the problem of low pozzolanic activity of red mud, helps the resource utilization and harmless disposal of red mud, and is of great significance for the low-carbon strategy of the building materials industry.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A design method for a concrete mineral composition, the concrete mineral composition includes red mud, magnesium carbonate and calcium carbonate, and the design method includes adjusting the dosages of red mud, magnesium carbonate and calcium carbonate according to the following formula to make them satisfy: m MgO ≤m CO3 and 1 / 8m CO3 +7 / 32m MgO ≤m Al2O3 +m Fe2O3 ≤1 / 4m CO3 +3 / 16m MgO ;

[0007] wherein, m MgO is the molar amount of magnesium oxide in magnesium carbonate, m CO3 is the molar amount of carbonate in magnesium carbonate and calcium carbonate, m Al2O3 is the molar amount of alumina in red mud, m Fe2O3 is the molar amount of iron oxide in red mud.

[0008] A design method for a concrete mineral composition, the concrete mineral composition being composed of red mud and magnesium carbonate, the design method including adjusting the dosages of red mud and magnesium carbonate to satisfy: m MgO ≤m CO3 ,1 / 8m CO3 +7 / 32m MgO ≤m Al2O3 +m Fe2O3 ≤1 / 4m CO3 +3 / 16m MgO ,and 1 ≤ (m Al2O3 +m Fe2O3 ):m MgO ≤ 1.75;

[0009] wherein, m CO3 is the molar amount of carbonate radical in magnesium carbonate, m Al2O3 is the molar amount of aluminum oxide in red mud, m Fe2O3 is the molar amount of iron oxide in red mud, m MgO is the molar amount of magnesium oxide in magnesium carbonate, m CO3 is the molar amount of carbonate radical in magnesium carbonate, m Al2O3 is the molar amount of aluminum oxide in red mud, m Fe2O3 is the molar amount of iron oxide in red mud.

[0010] A design method for a concrete mineral composition, the concrete mineral composition being composed of red mud and calcium carbonate, the design method including adjusting the dosages of red mud and calcium carbonate to satisfy: 1 ≤ (m Al2O3 +m Fe2O3 ):m CaO ≤ 2;

[0011] wherein, m Al2O3 is the molar amount of aluminum oxide in red mud, m Fe2O3 is the molar amount of iron oxide in red mud, m CaO is the molar amount of calcium oxide in calcium carbonate.

[0012] Further, the magnesium carbonate is added in the form of magnesite; the calcium carbonate is added in the form of at least one of limestone powder, heavy calcium powder, shell powder or coral powder; the magnesium carbonate and the calcium carbonate are added in the form of dolomite, or in the form of a mixture composed of at least one of limestone powder, heavy calcium powder, shell powder or coral powder and magnesite, or in the form of a mixture composed of magnesite, at least one of limestone powder, heavy calcium powder, shell powder or coral powder and dolomite.

[0013] Further, in the magnesium carbonate and the calcium carbonate, the mass content of magnesium carbonate is not less than 20%.

[0014] Further, the red mud may be Bayer red mud, sintering red mud or combined-process red mud.

[0015] Further, the red mud, magnesium carbonate and calcium carbonate are in powder form and the residue on a 45-μm square-hole sieve does not exceed 50%.

[0016] A preparation method of a concrete mineral composition includes: weighing two or three raw materials of red mud, calcium carbonate and magnesium mineral powder according to a specific ratio based on the contents of components such as aluminum, iron, magnesium, calcium and carbonate, and mixing them evenly.

[0017] The present invention mainly utilizes the characteristics that the contents of alumina and iron oxide components in the red mud are relatively high. The optimized proportion design scheme is obtained according to the stoichiometry of target products such as hydrotalcite, monocarbon calcium aluminate (ferrite) hydrate and hemicarbon calcium aluminate (ferrite) hydrate:

[0018] When the alumina and iron oxide components in the red mud coexist with the magnesium carbonate material, the two can undergo a chemical reaction to generate hydrotalcite-like products (general chemical formula: Mg 2 (Al,Fe)(OH) 6 (CO 3 ) 0.5 (H 2 O) 1.5 )). This not only significantly increases the chemical activity of the red mud, but also stimulates the chemical activity of inert materials such as magnesium carbonate, greatly improving the reaction efficiency of the admixture. The layered structure of the hydrotalcite-like product can effectively dissolve heavy metal ions in the layer and adsorb anions such as OH- between the layers, effectively reducing the dissolution of heavy metal ions in the red mud and the risk of alkali-aggregate reaction caused by high alkalinity.

[0019] When the red mud component coexists with the calcium carbonate material, the two can undergo a chemical reaction to generate monocarbon calcium aluminate (ferrite) hydrate (general chemical formula: 4CaO·(Al,Fe) 2 O 3 ·CO 2 ·11H 2 O), hemicarbon calcium aluminate (ferrite) hydrate (general chemical formula: 4CaO·(Al,Fe) 2 O 3 ·0.5CO 2 ·11.5H 2 O) and other products. Similarly, while improving the chemical activity of the red mud, it stimulates the chemical activity of calcium carbonate materials, greatly improving the reaction efficiency of the admixture.

[0020] Application of a concrete mineral composition, including using the composition as a mineral admixture in portland cement concrete, and it can also be applied in special cement concretes such as sulfoaluminate cement concrete and aluminate cement concrete. The concrete mineral admixture prepared from red mud, magnesium carbonate, and calcium materials can be used alone as a mineral admixture, or can be used in combination with mineral admixtures such as fly ash, ground granulated blast-furnace slag, volcanic ash, silica fume, and metakaolin.

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

[0022] Compared with the traditional method of directly using red mud as a concrete admixture, the mineral admixture provided by the present invention realizes the efficient hydration of red mud through the chemical reaction between red mud and calcium carbonate and magnesium, improves the pozzolanic activity of red mud, and efficiently activates the latent activity of calcium carbonate and magnesia materials. Under the action of the above principle, the concrete mineral admixture prepared from red mud provided by the present invention has extremely high chemical activity. At a relatively high dosage, it has almost no adverse effect on the development of concrete strength, and the heavy metal ions in red mud are effectively solidified in the concrete product, and the leaching rate tested by experiments is extremely low, ensuring the safety and harmlessness of the prepared concrete. Description of the Drawings

[0023] Figure 1 It is the X-ray diffraction pattern of the hydration of the concrete mineral admixture prepared from red mud, calcium carbonate, and magnesium minerals in Example 2; where Ett: Ettringite, Ms: Monosulfate, Hc: Hemicarboaluminate, Mc: Monocarboaluminate, Ht: Hydrotalcite, Gyp: Gypsum, C4AF: Calcium Sulfoaluminate. Detailed Embodiments

[0024] The present invention will be described in detail below with reference to specific embodiments. The following embodiments are implemented on the premise of the above technical solution of the present invention, and the detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments. The raw materials not specifically indicated as the source in the embodiments of the present invention can be obtained through market purchase channels. Through X-ray fluorescence spectrometer test analysis, the component contents of the red mud, dolomite powder, and limestone powder used in the following embodiments are shown in Table 1:

[0025] Table 1 Chemical composition (mol%) of red mud, dolomite powder, and limestone powder

[0026]

[0027] Example 1:

[0028] The three raw materials, namely Bayer red mud, limestone powder, and dolomite powder, are vacuum-dried and ground to a residue on a 45-μm square-hole sieve of no more than 30%.

[0029] According to the preferred design method of mineral admixtures proposed in the present invention, substitute the chemical composition data of the raw materials shown in Table 1 into the formula 1 / 8m CO3 +7 / 32m MgO ≤m Al2O3 +m Fe2O3 ≤1 / 4m CO3 +3 / 16m MgO , and calculate that the mass ratios of the three raw materials should satisfy: 2w 石灰石 +2.18w 白云石 ≤w 赤泥 ≤3.5w 石灰石 +3.82w 白云石 (where w is the mass of the raw material). According to this relationship, select raw materials in different proportions for mixing to obtain a series of concrete mineral admixtures (Formulas 1-5), as shown in Table 2; select raw materials that do not conform to this relationship for mixing to obtain a control group that does not conform to the design method of the present invention.

[0030] Table 2 Formulas of concrete mineral admixtures prepared from red mud and calcium and magnesium minerals (unit: kg / 100 kg admixture)

[0031]

[0032] Example 2:

[0033] Use the concrete mineral admixture of Formula 3 in Example 1, stir for 5 minutes at a water-cement ratio of 0.4 and a temperature of 20 °C, demold after 24 h, and cure under the conditions of 20 °C and 95% RH. The X-ray diffraction pattern of the obtained hydration product is as Figure 1 shown.

[0034] From Figure 1 it can be seen that hydrotalcite-like products, monocarbon-type hydrated calcium aluminate (ferrite), and semi-carbon-type hydrated calcium aluminate (ferrite) are formed in the neat slurry prepared from the product at different stages, which confirms the chemical reaction between the vitreous alumina (ferrite) in the red mud and the calcium carbonate and magnesium materials in the product under the designed ratio.

[0035] Example 3:

[0036] Use Formulas 1-5 in Example 1 as the mineral admixtures prepared from red mud to prepare concrete, and the mix ratios are shown in Table 3. At the same time, use 2 control groups that do not conform to the method involved in the present invention to prepare concrete for comparison.

[0037] Table 3 Concrete mix ratios (unit: kg / m 3Concrete)

[0038]

[0039]

[0040] The water-reducing agent used is a polycarboxylic acid type water-reducing agent with a water-reducing rate of 30%; the yellow sand complies with the relevant regulations in GB / T 14684-2011 "Sand for Construction"; the stones comply with the relevant regulations in GB / T 14685-2022 "Pebbles and Crushed Stones for Construction". According to GB / T 50081-2002 "Standard Test Method for Mechanical Properties of Ordinary Concrete", the 7-day and 28-day compressive strengths of the concrete are tested: the mixed concrete is molded in a 10-cm cube mold, demolded after 24 hours, cured under standard conditions to the corresponding age, and the compressive strength of the concrete is tested using a compression testing machine. The test results are shown in Table 4.

[0041] Table 4 Test Results of Concrete Compressive Strength (Unit: MPa)

[0042]

[0043] As can be seen from Table 4, the concrete mineral admixture prepared by using red mud and calcium carbonate and magnesium minerals proposed in the present invention, when used to prepare concrete, has significantly higher strength performance than the control group that does not meet the preferred ratio. This shows that under the preferred ratio, a good chemical reaction can indeed occur between the red mud and the calcium carbonate and magnesium materials in the material, activating the pozzolanic activity of the red mud and the latent activity of the calcium carbonate and magnesium materials. Since calcium carbonate and magnesium materials such as limestone powder and dolomite powder are widely sourced and inexpensive, the concrete mineral admixture prepared by using red mud and calcium carbonate and magnesium minerals proposed in the present invention has both good use performance and low cost, and has broad market prospects.

[0044] Example 4:

[0045] Use the concrete mineral admixture of the above formula 3 and the concrete mix ratio in Table 2 to prepare concrete, and measure the heavy metal ion leaching rate according to ASTM D3987 "Standard Practice for Shake Extraction of Solid Waste with Water". Mix 20 g of solid material in 400 ml of deionized water and acetic acid extraction solution (pH < 2), collect the eluate from the leachate after 1 day and 28 days, and detect the heavy metal ion concentration using an atomic absorption spectrometer. At the same time, use the mineral admixture of control group 1 to prepare concrete and test the heavy metal ion leaching rate. The test results are shown in Table 5.

[0046] Table 5 Test Results of Heavy Metal Ion Leaching of Demonstration Concrete (Unit: PPM)

[0047]

[0048]

[0049] Note: BDL: Below the detection limit.

[0050] As can be seen from Table 5, when the concrete mineral admixture prepared by using red mud, calcium carbonate and magnesium minerals proposed in the present invention is used to prepare concrete, it can significantly more effectively solidify harmful ions such as heavy metals than the concrete prepared directly using single red mud. This also benefits from the sufficient reaction between red mud and magnesium carbonate and calcium materials, forming a hydrotalcite-like product with ion adsorption effect, thereby realizing the resource utilization and harmless disposal of red mud.

[0051] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A design method for a concrete mineral composition, characterized in that, When the composition consists of red mud and magnesium carbonate, the design method includes adjusting the dosages of red mud and magnesium carbonate to satisfy: m MgO ≤m CO3 , 1 / 8m CO3 +7 / 32m MgO ≤m Al2O3 +m Fe2O3 ≤1 / 4m CO3 +3 / 16m MgO , and 1≤(m Al2O3 +m Fe2O3 ):m MgO ≤1.75; where m CO3 is the molar amount of carbonate in magnesium carbonate, m Al2O3 is the molar amount of alumina in red mud, m Fe2O3 is the molar amount of iron oxide in red mud, m MgO is the molar amount calculated as magnesium oxide in magnesium carbonate, m CO3 is the molar amount of carbonate in magnesium carbonate, m Al2O3 is the molar amount of alumina in red mud, m Fe2O3 is the molar amount of iron oxide in red mud; When the composition consists of red mud and calcium carbonate, the design method includes adjusting the dosages of red mud and calcium carbonate to satisfy: 1 ≤ (m Al2O3 +m Fe2O3 ):m CaO ≤ 2; where m Al2O3 is the molar amount of alumina in the red mud, m Fe2O3 is the molar amount of iron oxide in the red mud, m CaO is the molar amount of calcium carbonate calculated as calcium oxide; when the composition includes red mud, magnesium carbonate and calcium carbonate, the design method includes adjusting the dosages of red mud, magnesium carbonate and calcium carbonate according to the following formula to make them meet: m MgO ≤m CO3 and 1 / 8m CO3 +7 / 32m MgO ≤m Al2O3 +m Fe2O3 ≤1 / 4m CO3 +3 / 16m MgO ; where m MgO is the molar amount of magnesium oxide in magnesium carbonate, m CO3 is the molar amount of carbonate radicals in magnesium carbonate and calcium carbonate, m Al2O3 is the molar amount of aluminum oxide in red mud, m Fe2O3 is the molar amount of iron oxide in red mud.

2. The design method for a concrete mineral composition according to claim 1, characterized in that, the magnesium carbonate is added in the form of magnesite; the calcium carbonate is added in the form of at least one of limestone powder, heavy calcium powder, shell powder or coral powder; the magnesium carbonate and calcium carbonate are added in the form of dolomite, or in the form of a mixture composed of at least one of limestone powder, heavy calcium powder, shell powder or coral powder and magnesite, or in the form of a mixture composed of magnesite, at least one of limestone powder, heavy calcium powder, shell powder or coral powder and dolomite.

3. The design method for a concrete mineral composition according to claim 1, characterized in that, in the magnesium carbonate and calcium carbonate, the mass content of magnesium carbonate is not less than 20%.

4. The design method for a concrete mineral composition according to claim 1, characterized in that, the red mud, magnesium carbonate and calcium carbonate are in powder form and meet the requirement that the residue on a 45-micron square-hole sieve does not exceed 50%.

5. A preparation method for a concrete mineral composition based on the design method according to any one of claims 1 to 4, characterized in that, it includes: mixing red mud with magnesium carbonate and / or calcium carbonate evenly to obtain a concrete mineral composition.

6. An application of a concrete mineral composition characterized in that, the composition is prepared by the method according to claim 5 and can be used as a mineral admixture in portland cement concrete, sulphoaluminate cement concrete or aluminate cement concrete.

Images