A design method for a composite cement based on red mud and magnesium / calcium carbonate

Abstract

The present application relates to a kind of based on the design method of composite cement of red mud and magnesium / calcium carbonate, composite cement includes red mud, magnesium carbonate and calcium carbonate, cement clinker, design method includes adjusting the amount of red mud, magnesium carbonate and calcium carbonate, cement clinker according to formula a~c: a) m MgO ≤m CO3 ;b)1 / 8m CO3 +7 / 32m MgO ≤m Al2O3 +m Fe2O3 ≤1 / 4m CO3 +3 / 16m MgO ;c)4 / 5m SiO2 +4m CO3 ‑m MgO ≤m CaO ≤3 / 2m SiO2 +8m CO3 ‑2m MgO Compared with the prior art, the present application solves the problem of low red mud pozzolanic activity, reduces the carbon emission of composite cement, and helps the resource utilization of red mud.

Description

Technical Field

[0001] This invention belongs to the field of solid waste material resource utilization and new material technology, and relates to a design method for composite cement based on red mud and magnesium / calcium carbonate, and more particularly to a design method for low-carbon composite cement prepared by combining red mud and magnesium (calcium) carbonate with cement clinker. Background Technology

[0002] Cement is the world's most consumed and widely used inorganic cementitious material, and one of the indispensable basic materials for concrete production. In 2021, my country's cement production reached approximately 1.376 billion tons, exceeding half of the world's total. The production of traditional cement clinker generates enormous energy consumption and carbon emissions, placing a significant burden on the ecological environment. Currently, there is an urgent need for technological reforms in cement production and the development of new cementitious material systems.

[0003] Red mud is a waste product generated during alumina production. my country produces over 70 million tons of red mud annually, but its comprehensive utilization rate is only about 10%. Furthermore, red mud generally contains a certain amount of heavy metals, making its harmless disposal and utilization a pressing problem in my country's environmental and resource sectors. The main components of red mud include glassy alumina and iron oxide, but its silica content is lower than that of high-quality mineral admixtures such as mineral powder. This results in poor pozzolanic activity of red mud, severely affecting the strength development of concrete, making its use as a concrete mineral admixture difficult, and it has yet to achieve engineering and commercial applications.

[0004] Magnesium carbonate and calcium carbonate are widely available materials and are generally considered non-reactive, often used as coarse aggregates and inert fillers in concrete. However, under alkaline conditions, they possess the potential to react with active alumina and iron, which is of great value in stimulating and enhancing the activity of red mud pozzolanics. Therefore, using red mud and magnesium (calcium) carbonate to replace part of the cement clinker holds promise for producing a novel low-carbon composite cement.

[0005] Chinese patent CN113880475B discloses a red mud-based magnesium phosphate cement and its preparation method. The corresponding mineral phase composition is C4AF solid solution, MgO, phosphate, and a small amount of retarding components. The preparation involves two processes: raw meal preparation and cement formulation. The raw meal composition includes 30-50 parts calcium-magnesium components, 30-45 parts red mud, 10-20 parts aluminous raw materials, and 0.5-2 parts boron oxide. The cement formulation consists of 30-50 parts C4AF solid solution, 20-40 parts MgO, 15-25 parts phosphate, and 0-10 parts retarding components. This invention aims to realize the resource utilization of red mud by introducing it into magnesium phosphate cement to form a novel magnesium phosphate cement containing C4AF solid solution. This reduces the demand for magnesium oxide in magnesium phosphate cement, and the introduction of C4AF solid solution improves the cement's hydration hardening performance and enhances its water resistance. However, even with the introduction of red mud reducing the demand for magnesium oxide in magnesium phosphate cement, the production cost of recalcined magnesium oxide remains very high, including the extremely high calcination temperature and the transportation costs associated with raw material origins. Therefore, this patent proposes a strategy that directly utilizes magnesium carbonate (calcium) as the magnesium (calcium) source, supplemented with red mud and a certain amount of silicate cement clinker, to prepare a novel composite cement based on red mud and magnesium carbonate / calcium. This achieves the resource-based and harmless utilization of red mud, demonstrating significant low-carbon implications and technological advantages. Summary of the Invention

[0006] The purpose of this invention is to provide a design method for composite cement based on red mud and magnesium / calcium carbonate. The method involves mixing red mud, magnesium (calcium) carbonate, and cement clinker in a specific ratio. By designing the proportions of aluminum, iron, magnesium, silicon, calcium, and carbonates in the materials, the alumina and ferric oxide components in the red mud react with magnesium (calcium) carbonate during the hydration of the cement clinker to generate products such as hydrotalcite, single-carbon hydrated calcium aluminate (ferric) carbonate, and semi-carbon hydrated calcium aluminate (ferric) carbonate, thereby activating the activity of each material component. When used in concrete preparation, this product accelerates concrete setting and hardening without significantly adversely affecting strength performance. Heavy metal ions in the red mud are effectively solidified, making it a suitable replacement for traditional concrete cement. This invention solves the problem of low activity in red mud volcanic ash, reduces the carbon emissions of composite cement, and contributes to the resource utilization of red mud.

[0007] The objective of this invention can be achieved through the following technical solutions: A design method for composite cement based on red mud and magnesium carbonate / calcium carbonate, wherein the composite cement comprises red mud, magnesium carbonate and calcium carbonate, and cement clinker, the design method being to adjust the proportions of red mud, magnesium carbonate and calcium carbonate, and cement clinker according to the following stoichiometric ratios: a)m MgO ≤m CO3 b) 1 / 8m CO3 +7 / 32mMgO ≤m Al2O3 +m Fe2O3 ≤1 / 4m CO3 +3 / 16m MgO c) 4 / 5m SiO2 +4m CO3 -m MgO ≤m CaO ≤3 / 2m SiO2 +8m CO3 -2m MgO ; Where, m MgO m represents the total molar amount of magnesium oxide in the composite cement. CaO m represents the total molar amount of calcium oxide in the composite cement. CO3 m represents the total molar amount of carbonate in the composite cement. Al2O3 m represents the total molar amount of alumina in the composite cement. Fe2O3 m represents the total molar amount of iron oxide in the composite cement. SiO2 This represents the total molar amount of silica in the composite cement.

[0008] Furthermore, the magnesium carbonate is added in the form of magnesite, and the calcium carbonate is added in the form of at least one of limestone powder, heavy calcium carbonate powder, shell powder, or coral powder.

[0009] Furthermore, the magnesium carbonate and calcium carbonate are added in the form of dolomite.

[0010] Furthermore, the magnesium carbonate and calcium carbonate are added in the form of a mixture of at least one of limestone powder, heavy calcium carbonate powder, shell powder or coral powder and magnesite.

[0011] Furthermore, the magnesium carbonate and calcium carbonate are added in the form of a mixture of at least one of magnesite, limestone powder, heavy calcium carbonate powder, shell powder or coral powder and dolomite.

[0012] Furthermore, 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%.

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

[0014] Furthermore, the red mud is at least one of Bayer process red mud, sintering process red mud, or combined process red mud.

[0015] Furthermore, the total mass content of alumina and iron oxide in the red mud is not less than 30%.

[0016] Furthermore, the cement clinker is at least one of silicate cement, sulfoaluminate cement, or aluminate cement, and its mass content in the composite cement is not less than 10% and not more than 80%.

[0017] This invention mainly utilizes the high content of alumina and iron oxide components in red mud. The optimized formulation design is derived based on the stoichiometry of target products such as hydrotalcite, single-carbon hydrated calcium aluminate (ferrite), and semi-carbon hydrated calcium aluminate (ferrite). When the alumina and ferric oxide components in red mud coexist with magnesium carbonate materials, they can undergo a chemical reaction to generate hydrotalcite-like products (the chemical formula is generally: Mg2(Al, Fe)(OH)6(CO3)). 0.5 (H2O) 1.5 This significantly increases the chemical activity of red mud and magnesium carbonate, greatly improving the reaction efficiency of composite cement. The layered structure of hydrotalcite products can effectively dissolve heavy metal ions within the layers, effectively reducing the leaching and risk of heavy metal ions from red mud.

[0018] When red mud components coexist with calcium carbonate materials, they can undergo a chemical reaction to generate products such as single-carbon hydrated calcium aluminate (ferrite) carbide (chemical formula generally: 4CaO·(Al,Fe)2O3·CO2·11H2O) and semi-carbon hydrated calcium aluminate (ferrite) carbide (chemical formula generally: 4CaO·(Al,Fe)2O3·0.5CO2·11.5H2O). This not only enhances the activity of red mud volcanic ash but also stimulates the chemical activity of calcium carbonate materials, significantly improving the overall reaction efficiency of composite cement.

[0019] In addition to its own hydration, cement clinker also plays a role in supplementing calcium hydroxide in the above reaction process, promoting the continuous generation of the above characteristic reaction products.

[0020] By using formulas a, b, and c to design the proportions, the above chemical reactions can be fully realized.

[0021] Compared with the prior art, the present invention has the following characteristics: Compared to traditional methods that directly combine red mud with cement, the low-carbon composite cement provided by this invention enhances the pozzolanic activity of red mud through a chemical reaction between red mud and calcium carbonate and magnesium, and efficiently activates the potential activity of calcium carbonate and magnesium materials. Based on this principle, the composite cement prepared using red mud, magnesium carbonate (calcium), and cement clinker provided by this invention exhibits high chemical activity. The high alkalinity of red mud effectively shortens the setting time of the composite cement, and even at higher dosages, it has almost no adverse effect on the development of concrete strength, demonstrating good application benefits in formwork construction. Heavy metal ions in red mud can be effectively solidified in concrete products, ensuring the harmlessness of the concrete structure. The incorporation of red mud and magnesium carbonate (calcium) reduces the amount of cement clinker used, thereby reducing the actual carbon emissions from composite cement production. Attached Figure Description

[0022] Figure 1 The X-ray diffraction pattern of the composite cement prepared by red mud, calcium (magnesium) carbonate and silicate cement clinker in Example 3 after hydration is shown; wherein each phase is Ett: Ettringite, Ms: Monosulfate, Hc: Hemicarboaluminate, Mc: Monocarboaluminate, Ht: Hydrotalcite, Gyp: Gypsum, C4AF: Calcium Sulfoaluminate. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments are based on the above-described technical solutions of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. Raw materials not specifically named in the embodiments of the present invention can all be obtained through market purchases. The composition and content of the red mud, dolomite powder, and silicate cement clinker used are shown in Table 1, as determined by X-ray fluorescence spectrometry analysis. CO2 was calculated based on the mass loss of the sample at 550-800℃ during thermogravimetric analysis. Table 1. Chemical composition (mol%) of red mud, dolomite powder and cement clinker Example 1: Using 100g of cement clinker and 25g of dolomite powder as initial raw materials, according to the preferred design method for composite cement proposed in this invention, the sum of the amounts of Al2O3 and Fe2O3 in the composite cement should be within 1 / 8m. CO3 +7 / 32m MgO to 1 / 4m CO3 +3 / 16m MgOBetween (Formula b), the sum of the amounts of CaO in the composite cement should be within 4 / 5m. SiO2 +4m CO3 -m MgO up to 3 / 2m SiO2 +8m CO3 -2m MgO The optimal dosage of red mud is calculated to be between 3.362g and 10.912g (formula c). Within this range, a certain mass of red mud, such as 10g, is selected and mixed with the above-mentioned cement and dolomite powder to produce the composite cement described in this invention.

[0024] Conversely, using 5g of Bayer red mud and 20g of dolomite powder as initial raw materials, according to the preferred design method for composite cement proposed in this invention, the sum of the amounts of Al2O3 and Fe2O3 in the composite cement should be within 1 / 8m. CO3 +7 / 32m MgO to 1 / 4m CO3 +3 / 16m MgO Between (Formula b), the sum of the amounts of CaO in the composite cement should be within 4 / 5m. SiO2 +4m CO3 -m MgO up to 3 / 2m SiO2 +8m CO3 -2m MgO The optimal dosage of cement clinker is calculated to be 91.98-127.15g (formula c). Within this range, a certain mass of cement clinker, such as 100g, is selected and mixed with the aforementioned red mud and dolomite powder to prepare the composite cement described in this invention.

[0025] Example 2: Four raw materials are taken: cement clinker, Bayer red mud, limestone powder, and dolomite powder. They are vacuum dried and ground until the residue on a 45-micron square hole sieve does not exceed 30%.

[0026] Following the method described in Example 1, a series of low-carbon composite cements were designed and prepared, and a control group that did not conform to the method described in this invention was prepared, as shown in Table 2. Among them, formulations 2-4 conform to the proportioning design method described in this invention, while formulations 1 and 5 do not conform to this method.

[0027] Table 2 Examples of composite cement mix proportions prepared using red mud, magnesium (calcium) carbonate, and cement clinker (Unit: kg / 100kg composite cement) Example 3: Using the composite cement of formula 3 above, at a water-cement ratio of 0.4, it was stirred for 5 minutes at 20°C. After 24 hours, it was demolded and cured at 20°C and 95% RH. The hydration yielded the following result: Figure 1 The X-ray diffraction pattern shown.

[0028] from Figure 1 It can be seen that the product produces hydrotalcite-like products, single-carbon hydrated calcium aluminate (ferrite) and semi-carbon hydrated calcium aluminate (ferrite) at different stages, which confirms the chemical reaction between red mud active alumina (ferrite) and calcium carbonate and magnesium materials in the product under the designed ratio.

[0029] Example 4: Concrete was prepared using the series of composite cements prepared above, and the mix proportions are shown in Table 3.

[0030] Table 3 Concrete mix proportions (unit: kg / m³) 3 (concrete) The water-reducing agent used was a polycarboxylate-based water-reducing agent with a water reduction rate of 30%; the yellow sand conformed to the relevant provisions of GB / T 14684-2011 "Sand for Construction"; and the gravel conformed to the relevant provisions of GB / T 14685-2022 "Pebbles and Crushed Stones for Construction". According to GB / T 50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", the 7-day and 28-day compressive strength of the concrete were tested: the mixed concrete was molded in a 10×10×10cm cube mold, demolded after 24 hours, cured under standard conditions to the corresponding age, and the compressive strength of the concrete was tested using a pressure testing machine. The test results are shown in Table 4.

[0031] Table 4. Test results of concrete compressive strength (unit: MPa) As shown in Table 4, the composite cement (formulas 2-4) designed in this invention exhibits significantly better strength performance than the control group (formulas 1 and 5) when used to prepare concrete. This demonstrates that, under the preferred proportions described in this invention, a good chemical reaction can indeed occur between the red mud and calcium carbonate and magnesium materials, stimulating the pozzolanic activity of the red mud and the potential activity of the calcium carbonate and magnesium materials. Since calcium carbonate and magnesium materials such as limestone powder and dolomite powder are widely available and inexpensive, the composite cement prepared using red mud, magnesium carbonate (calcium), and cement clinker proposed in this invention combines good performance with low cost.

[0032] Example 5: Concrete was prepared using the composite cement described in Formulas 3 and 5 of Example 2. The leaching concentrations of heavy metal ions were measured after 1 day and 28 days according to ASTM D3987 "Standard Practice for Shake Extraction of Solid Waste with Water". The test results are shown in Table 5.

[0033] Table 5. Results of heavy metal ion leaching test in concrete (unit: PPM) Note: BDL: less than the detection limit.

[0034] As can be seen from Table 5, the composite cement prepared by red mud, magnesium (calcium) carbonate and cement clinker proposed in this invention can effectively solidify heavy metal ions when used to prepare concrete. This is also due to the full reaction of red mud with magnesium carbonate, calcium materials and cement clinker, forming layered products of hydrotalcite that absorb some ions and reduce the interconnected pores of the concrete matrix, thereby realizing the harmless utilization of red mud.

[0035] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A design method for composite cement based on red mud and magnesium / calcium carbonate, characterized in that, Composite cement comprises red mud, magnesium carbonate and calcium carbonate, and cement clinker. The design method involves adjusting the amounts of red mud, magnesium carbonate and calcium carbonate, and cement clinker to meet the following requirements: a)m MgO ≤m CO3 b)1 / 8m CO3 +7 / 32m MgO ≤m Al2O3 +m Fe2O3 ≤1 / 4m CO3 +3 / 16m MgO c) 4 / 5m SiO2 +4m CO3 -m MgO ≤m CaO ≤3 / 2m SiO2 +8m CO3 -2m MgO ; Where, m MgO m represents the total molar amount of magnesium oxide in the composite cement. CaO m represents the total molar amount of calcium oxide in the composite cement. CO3 m represents the total molar amount of carbonate in composite cement. Al2O3 m represents the total molar amount of alumina in the composite cement. Fe2O3 m represents the total molar amount of iron oxide in the composite cement. SiO2 This represents the total molar amount of silica in the composite cement.

2. The design method for a composite cement based on red mud and magnesium / calcium carbonate according to claim 1, characterized in that, The magnesium carbonate is added in the form of magnesite, and the calcium carbonate is added in the form of at least one of limestone powder, heavy calcium carbonate powder, shell powder or coral powder.

3. The design method for a composite cement based on red mud and magnesium / calcium carbonate according to claim 1, characterized in that, The magnesium carbonate and calcium carbonate are added in the form of dolomite.

4. The design method for a composite cement based on red mud and magnesium / calcium carbonate according to claim 1, characterized in that, The magnesium carbonate and calcium carbonate are added in the form of a mixture of at least one of limestone powder, heavy calcium carbonate powder, shell powder or coral powder and magnesite.

5. The design method for a composite cement based on red mud and magnesium / calcium carbonate according to claim 1, characterized in that, The magnesium carbonate and calcium carbonate are added in the form of a mixture of at least one of magnesite, limestone powder, heavy calcium carbonate powder, shell powder or coral powder and dolomite.

6. The design method for a composite cement based on red mud and magnesium carbonate / calcium 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%.

7. The design method for a composite cement based on red mud and magnesium / calcium carbonate 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%.

8. The design method for a composite cement based on red mud and magnesium / calcium carbonate according to claim 1, characterized in that, The red mud mentioned is at least one of Bayer process red mud, sintering process red mud, or combined process red mud.

9. The design method for a composite cement based on red mud and magnesium / calcium carbonate according to claim 1, characterized in that, The total mass content of alumina and iron oxide in the red mud is not less than 30%.

10. The design method for a composite cement based on red mud and magnesium carbonate / calcium according to claim 1, characterized in that, The cement clinker is silicate cement clinker, and its mass content in the composite cement is not less than 10% and not more than 80%.

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