Iron tailings and fluorgypsum for the preparation of iron-rich belite-sulphoaluminate cement and method

Abstract

This invention relates to an iron-rich belite sulfoaluminate cement and its preparation method using iron tailings and fluorogypsum. The method comprises iron-rich belite sulfoaluminate cement clinker and natural gypsum in a mass ratio of 100:(6-18). The raw materials for the iron-rich belite sulfoaluminate cement clinker, by mass percentage, include 15-18% iron tailings, 6-10% fluorogypsum, 20-23% steel slag, 12-14% alumina ash, and 39-43% limestone. This invention utilizes iron tailings, fluorogypsum, steel slag, alumina ash, and limestone to synergistically provide the required calcium, silicon, aluminum, iron, and sulfur. The addition of a certain amount of natural gypsum facilitates the hydration of the iron-rich belite sulfoaluminate cement clinker to generate the target hydration products. By controlling the proportions of each raw material, the resulting cement exhibits excellent mechanical properties. This invention reduces the consumption of natural raw materials, lowers raw material costs, and has a simple preparation method, making it suitable for industrialization.

Description

Technical Field

[0001] This invention belongs to the field of solid waste building materials technology, specifically relating to an iron-rich belite sulfoaluminate cement and its preparation method using iron tailings and fluorogypsum. Background Technology

[0002] Silicate cement production is the third largest source of industrial CO2 emissions, accounting for 26% of annual industrial CO2 emissions. Currently, the silicate cement production industry is classified as a high-energy-consuming industry. Therefore, developing and promoting low-carbon cement varieties has become an urgent and important task for the cement industry to alleviate the high carbon emissions problem. Iron-rich belite sulfoaluminate cement is a new type of low-carbon cement with a clinker content of over 15% ferroaluminate and over 50% dicalcium silicate. Compared to silicate cement, iron-rich belite sulfoaluminate cement not only has the low-carbon advantage of significantly reduced limestone usage, sintering, and clinker grinding energy consumption (reducing CO2 emissions by approximately 30% during production), but also possesses advantages such as rapid setting, shrinkage compensation, low alkalinity, freeze resistance, corrosion resistance, and lower requirements for the grade of raw materials. The low requirements for raw material grades in iron-rich belite sulfoaluminate cement allow for better recycling of numerous industrial wastes as raw materials, which is of profound significance in alleviating the increasing depletion of natural resources and the growing severity of waste pollution. Therefore, to promote the future development and application of this low-carbon cement variety and green production method, it is imperative to develop more types of industrial waste for use in the production of iron-rich belite sulfoaluminate cement.

[0003] Iron tailings are industrial waste generated as a byproduct of iron extraction from iron ore. Fluorogypsum is an industrial waste generated as a byproduct of hydrofluoric acid production from fluorite. Currently, the annual emissions of iron tailings and fluorogypsum reach 600 million tons and 1 million tons respectively, but their recycling rates are less than 7% and 25%. This leads to the primary method of industrial disposal of iron tailings and fluorogypsum being open-air stockpiling. This not only wastes land resources and disposal costs but also causes environmental pollution and safety hazards. Therefore, recycling iron tailings and fluorogypsum is urgently needed to alleviate the series of problems caused by stockpiling. The main components of iron tailings and fluorogypsum—calcium, silicon, aluminum, iron, and sulfur—are raw materials required for the preparation of iron-rich belite sulfoaluminate cement. The impurities magnesium and fluorine in iron tailings and fluorogypsum have fluxing and mineralizing effects during sintering, which can reduce the firing difficulty of iron-rich belite sulfoaluminate cement clinker. Therefore, iron tailings and fluorogypsum are theoretically extremely suitable for recycling and use in the preparation of iron-rich belite sulfoaluminate cement.

[0004] However, there is currently limited literature on the preparation of sulfoaluminate cement using iron tailings and fluorogypsum. Patent CN105645795A provides a method for preparing sulfoaluminate cement using iron tailings. This method involves mixing iron tailings, bauxite, limestone, and desulfurized gypsum into cement raw materials, and then firing the mixture to produce sulfoaluminate cement. Patent CN101857389A provides a method for preparing sulfoaluminate cement using fluorogypsum. This method involves mixing fluorogypsum, limestone, bauxite, phosphogypsum, and copper tailings into cement raw materials, and then firing the mixture to produce sulfoaluminate cement. Patent CN102765893B provides a method for preparing sulfoaluminate cement using fluorogypsum. This method involves mixing fluorogypsum, red mud, limestone, and bauxite into cement raw materials, and then firing the mixture to produce sulfoaluminate cement.

[0005] Although the above-mentioned patents have made significant contributions to the application of iron tailings and fluorinated gypsum in the preparation of sulfoaluminate cement, they have the following shortcomings: (1) They only realize the individual utilization of iron tailings or fluorinated gypsum, and do not realize the simultaneous utilization of iron tailings and fluorinated gypsum. (2) They require the consumption of a large amount of high-cost or natural materials, such as using high-priced aluminum resources as raw materials (bauxite), and the overall solid waste utilization rate is not high. (3) Because the cement produced is ordinary sulfoaluminate cement with a clinker content of more than 60% calcium sulfoaluminate, less than 30% dicalcium silicate, and less than 10% ferroaluminate, the cement produced has the disadvantages of poor strength development and low later strength. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide an iron-rich belite sulfoaluminate cement and method for preparing iron tailings and fluorogypsum, which solves the technical problems in the prior art where iron tailings and fluorogypsum are difficult to utilize simultaneously and the solid waste utilization rate is low, resulting in high cost and low strength in the preparation of sulfoaluminate cement.

[0007] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows:

[0008] In a first aspect, the present invention provides an iron-rich belite sulfoaluminate cement prepared from iron tailings and fluorogypsum, comprising iron-rich belite sulfoaluminate cement clinker and natural gypsum in a mass ratio of 100:(6-18); wherein, by mass percentage, the raw materials of the iron-rich belite sulfoaluminate cement clinker include 15-18% iron tailings, 6-10% fluorogypsum, 20-23% steel slag, 12-14% aluminum ash, and 39-43% limestone.

[0009] In a second aspect, the present invention provides a method for preparing iron-rich belite sulfoaluminate cement from iron tailings and fluorogypsum, comprising the following steps: (1) drying iron tailings, fluorogypsum, steel slag, aluminum ash and limestone separately and grinding them into powder to obtain powder; (2) mixing the powder according to the proportion to obtain cement raw meal powder; (3) adding water to the cement raw meal powder to moisten and mix it, pressing it into shape to obtain raw meal cake; (4) calcining the raw meal cake, and cooling it after calcination to obtain clinker cake; (5) mixing the clinker cake with natural gypsum and grinding it to obtain iron-rich belite sulfoaluminate cement.

[0010] Compared with the prior art, the beneficial effects of the present invention include:

[0011] This invention utilizes five raw materials—iron tailings, fluorogypsum, steel slag, aluminum ash, and limestone—to synergistically provide the calcium, silicon, aluminum, iron, and sulfur required for preparing iron-rich belite sulfoaluminate cement. By adding a certain amount of natural gypsum, it facilitates the hydration of the iron-rich belite sulfoaluminate cement clinker to generate the target hydration product (ettringite). Furthermore, by controlling the proportions of each raw material, the resulting solid waste-based iron-rich belite sulfoaluminate cement exhibits excellent mechanical properties and good strength development of the cement paste. This invention achieves the simultaneous utilization of iron tailings and fluorogypsum, alleviating the pollution caused by the stockpiling of iron tailings and fluorogypsum. Simultaneously, the use of multiple solid wastes as raw materials significantly reduces the consumption of natural raw materials, lowers raw material costs, and the preparation method is simple and conducive to industrialization. Attached Figure Description

[0012] Figure 1 This is a flowchart of the method for preparing iron-rich belite sulfoaluminate cement from iron tailings and fluorogypsum according to the present invention.

[0013] Figure 2 The X-ray diffraction pattern of cement clinker in Example 1 of this invention;

[0014] Figure 3 This is the X-ray diffraction pattern of cement clinker in Comparative Example 1 of the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] Currently, in the preparation of sulfoaluminate cement, only one of iron tailings or fluorogypsum is typically used, which requires a large amount of high-cost materials and the overall solid waste utilization rate is not high. The sulfoaluminate cement produced contains more than 60% calcium sulfoaluminate, less than 30% dicalcium silicate, and less than 10% ferroaluminate. The clinker is usually difficult to grind, and the slurry has weak durability, frost resistance, and impermeability. The cement produced has the disadvantages of poor strength development and low strength in the later stage.

[0017] To address the shortcomings of existing technologies, this invention provides a method for preparing iron-rich belite sulfoaluminate cement from iron tailings and fluorogypsum. This invention represents the first application of iron tailings and fluorogypsum in the preparation of iron-rich belite sulfoaluminate cement, alleviating the pollution caused by the stockpiling of iron tailings and fluorogypsum, while promoting the development and application of iron-rich belite sulfoaluminate low-carbon cement.

[0018] In a first aspect, the present invention provides an iron-rich belite sulfoaluminate cement prepared from iron tailings and fluorogypsum, comprising iron-rich belite sulfoaluminate cement clinker and natural gypsum in a mass ratio of 100:(6-18); wherein, by mass percentage, the raw materials of the iron-rich belite sulfoaluminate cement clinker include 15-18% iron tailings, 6-10% fluorogypsum, 20-23% steel slag, 12-14% aluminum ash, and 39-43% limestone.

[0019] Preferably, the raw materials of iron-rich belite sulfoaluminate cement clinker, by mass percentage, include 15.5-17.5% iron tailings, 6-10% fluorogypsum, 21-23% steel slag, 12-13.5% aluminum ash, and 39.5-42% limestone.

[0020] Preferably, the mineral composition of iron-rich belite sulfoaluminate cement clinker, by mass percentage, includes: 26-29% calcium sulfoaluminate, 50-53% dicalcium silicate, 15-18% ferroaluminate, and 2-4% magnesium oxide.

[0021] This invention provides the five resources required for preparing iron-rich belite sulfoaluminate cement—calcium, silicon, aluminum, iron, and sulfur—through the synergistic use of five raw materials. By adding a certain amount of natural gypsum, it facilitates the hydration of iron-rich belite sulfoaluminate cement clinker to generate the target hydration product, ettringite.

[0022] Secondly, see Figure 1 This invention provides a method for preparing iron-rich belite sulfoaluminate cement from iron tailings and fluorogypsum, comprising the following steps:

[0023] (1) The iron tailings, fluorogypsum, steel slag, aluminum ash and limestone are dried and ground into powder to obtain powder materials;

[0024] (2) Mix the powders according to the proportion to obtain cement raw meal powder;

[0025] (3) Add water to the cement raw meal powder to moisten and mix well, press and shape to obtain raw meal cake;

[0026] (4) The raw material cake is calcined, and after calcination, it is cooled to obtain cooked material cake;

[0027] (5) Mix the clinker cake with natural gypsum and grind it to obtain iron-rich belite sulfoaluminate cement.

[0028] Preferably, in step (1), the fineness of the powder is -200 mesh.

[0029] Preferably, in step (3), the mass ratio of cement raw meal powder to water is 100:(8-12).

[0030] Preferably, in step (3), the pressure during pressing is above 15 MPa.

[0031] Preferably, in step (4), the heating rate during the calcination process is 4 to 6 °C / min.

[0032] Preferably, in step (4), the calcination temperature is 1220 ℃~1270 ℃, and the time is 50 min~110 min. In this invention, excessively high calcination temperature and excessively long sintering time will result in excessive energy input into the system, leading to overburning of the clinker and a decrease in the content of the main mineral phase in the clinker; conversely, excessively low calcination temperature and excessively short sintering time will result in insufficient energy input into the system, and the main mineral phase cannot be fully formed.

[0033] Preferably, in step (4), the cooling is air cooling to room temperature.

[0034] Preferably, in step (5), the grinding fineness is -200 mesh.

[0035] The mechanism of action and advantages of this invention are as follows:

[0036] (1) This invention realizes the simultaneous utilization of iron tailings and fluorogypsum, alleviates the pollution situation of iron tailings and fluorogypsum stockpiling, and brings high value-added cement products.

[0037] (2) The present invention also utilizes solid waste raw materials such as fluorogypsum, steel slag and aluminum ash to prepare iron-rich belite sulfoaluminate cement, which significantly reduces the consumption of natural raw materials and lowers the input of raw material costs;

[0038] (3) The mechanical properties of the solid waste-based iron-rich belite sulfoaluminate cement prepared by the present invention are superior to those of ordinary Portland cement and ordinary sulfoaluminate cement of grade 42.5 in Chinese standards GB175-2007 and GB 20472-2006.

[0039] (4) The iron-rich belite sulfoaluminate cement prepared by the present invention has a dicalcium silicate content of more than 50% and an iron aluminate content of more than 15%, and the slurry has better durability, frost resistance and impermeability than ordinary sulfoaluminate cement.

[0040] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0041] The chemical composition of the raw materials in the various embodiments and comparative examples of the present invention is shown in Table 1.

[0042]

[0043] Example 1

[0044] A method for preparing iron-rich belite sulfoaluminate cement from iron tailings and fluorogypsum includes the following steps:

[0045] (1) Grinding raw materials: Iron tailings, fluorite, steel slag, aluminum ash and limestone are dried and ground into fine powder with a fineness of -200 mesh.

[0046] (2) Cement raw meal preparation: The fine powder of raw materials obtained in (1) is mixed evenly according to the mass fractions of iron tailings 16.58 wt%, fluorite gypsum 8.42 wt%, steel slag 21.21 wt%, aluminum ash 12.90 wt%, and limestone 40.89 wt% to obtain cement raw meal powder.

[0047] (3) Pressing cement raw meal cakes: Add water accounting for 10 wt% of the raw meal powder to wet and mix the raw meal powder obtained in (2), and then use a tableting mold and tableting machine to press it into cakes at 20 MPa.

[0048] (4) Calcination of cement clinker: The raw meal obtained in (3) is placed in a high-temperature furnace for calcination. The calcination conditions are: heating rate 5 ℃ / min, calcination temperature 1250 ℃, and holding time 80 min. After calcination, the sample is taken out at high temperature and quickly cooled to room temperature to obtain cement clinker meal.

[0049] (5) Grinding cement clinker: Mix the clinker cake obtained in (4) with natural gypsum accounting for 10 wt% of the clinker cake, and then grind it into fine powder with a fineness of -200 mesh to obtain cement finished product.

[0050] In Example 1, the three ratios of the cement raw material proportions are: alkalinity coefficient Cm = 0.99, aluminum-sulfur ratio P = 1.51, and aluminum-silicon ratio N = 0.86.

[0051] The phase composition of the cement clinker prepared in Example 1 is as follows: Figure 2As shown in the figure, the phase composition of cement clinker consists of calcium sulfoaluminate, dicalcium silicate, aluminoferrite, and magnesium oxide. XRD refined quantitative analysis results show that the proportions of each mineral phase are: calcium sulfoaluminate 28%, dicalcium silicate 52%, aluminoferrite 17%, and magnesium oxide 3%.

[0052] Example 2

[0053] A method for preparing iron-rich belite sulfoaluminate cement from iron tailings and fluorogypsum includes the following steps:

[0054] (1) Grinding raw materials: Iron tailings, fluorite, steel slag, aluminum ash and limestone are dried and ground into fine powder with a fineness of -200 mesh.

[0055] (2) Cement raw meal preparation: The fine powder of raw materials obtained in (1) is mixed evenly according to the mass fractions of iron tailings 15.71 wt%, fluorite gypsum 9.82 wt%, steel slag 22.53 wt%, aluminum ash 12.19 wt%, and limestone 39.75 wt% to obtain cement raw meal powder.

[0056] (3) Pressing cement raw meal cakes: Add water accounting for 10 wt% of the raw meal powder to wet and mix the raw meal powder obtained in (2), and then use a tableting mold and tableting machine to press it into cakes at 20 MPa.

[0057] (4) Calcination of cement clinker: The raw meal obtained in (3) is placed in a high-temperature furnace for calcination. The calcination conditions are: heating rate 5 ℃ / min, calcination temperature 1230 ℃, and holding time 60 min. After calcination, the sample is taken out at high temperature and quickly cooled to room temperature to obtain cement clinker meal.

[0058] (5) Grinding cement clinker: Mix the clinker cake obtained in (4) with natural gypsum accounting for 10 wt% of the clinker cake, and then grind it into fine powder with a fineness of -200 mesh to obtain cement finished product.

[0059] Example 3

[0060] A method for preparing iron-rich belite sulfoaluminate cement from iron tailings and fluorogypsum includes the following steps:

[0061] (1) Grinding raw materials: Iron tailings, fluorite, steel slag, aluminum ash and limestone are dried and ground into fine powder with a fineness of -200 mesh.

[0062] (2) Cement raw meal preparation: The fine powder of raw materials obtained in (1) is mixed evenly according to the mass fractions of iron tailings 17.02 wt%, fluorite gypsum 6.02 wt%, steel slag 22.14 wt%, aluminum ash 13.01 wt%, and limestone 41.81 wt% to obtain cement raw meal powder.

[0063] (3) Pressing cement raw meal cakes: Add water accounting for 10 wt% of the raw meal powder to wet and mix the raw meal powder obtained in (2), and then use a tableting mold and tableting machine to press it into cakes at 20 MPa.

[0064] (4) Calcination of cement clinker: The raw meal obtained in (3) is placed in a high-temperature furnace for calcination. The calcination conditions are: heating rate 5 ℃ / min, calcination temperature 1260 ℃, and holding time 100 min. After calcination, the sample is taken out at high temperature and quickly cooled to room temperature to obtain cement clinker meal.

[0065] (5) Grinding cement clinker: Mix the clinker cake obtained in (4) with natural gypsum accounting for 10 wt% of the clinker cake, and then grind it into fine powder with a fineness of -200 mesh to obtain cement finished product.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is that the raw material ratio is 14.81 wt% iron tailings, 1.13 wt% fluorogypsum, 25.01 wt% steel slag, 11.93 wt% aluminum ash, and 47.12 wt% limestone. The other steps and conditions are the same as in Example 1.

[0068] The phase composition of the cement clinker obtained in this comparative example is as follows: Figure 3 As shown.

[0069] Depend on Figure 3 As can be seen, the phase composition of the cement clinker prepared in Comparative Example 1 consists of calcium sulfoaluminate, dicalcium silicate, aluminoferrite, magnesium oxide, calcium aluminum feldspar, and aluminates. XRD refined quantitative analysis results show that the proportion of each mineral phase is: calcium sulfoaluminate 13%, dicalcium silicate 36%, aluminoferrite 14%, magnesium oxide 4%, calcium aluminum feldspar 27%, and aluminates 6%. Clearly, the mineral composition of the clinker in Comparative Example 1 does not meet the corresponding limiting requirements (dicalcium silicate content above 50%, aluminoferrite content above 15%). This is because the addition of fluorite is too low, resulting in the intermediate mineral phases calcium aluminum feldspar and aluminates not being fully converted into the main mineral phases of the clinker.

[0070] Comparative Example 2

[0071] The difference between this comparative example and Example 1 is that the calcination temperature is 1100 ℃ and the holding time is 30 min.

[0072] Comparative Example 3

[0073] The difference between this comparative example and Example 1 is that the calcination temperature is 1300 ℃ and the holding time is 120 min.

[0074] The cement paste strength of the cement products obtained in the above embodiments and comparative examples was tested, and ordinary Portland cement and ordinary sulfoaluminate cement were added for comparison; the mass ratio of cement to water was 2:1, and the specific test conditions and steps were in accordance with GB / T17671-1999.

[0075]

[0076] As shown in Table 2, the cement pastes prepared in Examples 1-3 exhibited better strength development than ordinary Portland cement and ordinary sulfoaluminate cement of grade 42.5. In contrast, the cement pastes prepared in Comparative Examples 1-3 showed poorer strength development than ordinary Portland cement and ordinary sulfoaluminate cement of grade 42.5. This is because inappropriate raw material proportions, excessively low or high calcination temperatures, and excessively short or long holding times all prevent the sufficient formation of the main mineral phases in the clinker that are beneficial to paste strength development.

[0077] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing iron-rich belite sulfoaluminate cement from iron tailings and fluorogypsum, characterized in that, It includes iron-rich belite sulfoaluminate cement clinker and natural gypsum in a mass ratio of 100:(6-18); wherein, by mass percentage, the raw materials of the iron-rich belite sulfoaluminate cement clinker include 15.5-17.5% iron tailings, 6-10% fluorogypsum, 21-23% steel slag, 12-13.5% aluminum ash, and 39.5-42% limestone; The mineral composition of the iron-rich belite sulfoaluminate cement clinker, by mass percentage, includes: 26-29% calcium sulfoaluminate, 50-53% dicalcium silicate, 15-18% ferroaluminate, and 2-4% magnesium oxide. The method specifically includes the following steps: (1) The iron tailings, fluorogypsum, steel slag, aluminum ash and limestone are dried and ground into powder to obtain powder materials; (2) Mix the powders according to the specified proportions to obtain cement raw meal powder; (3) Add water to the cement raw meal powder to moisten and mix well, press and shape to obtain raw meal cake; (4) The raw material cake is calcined, and after calcination, it is cooled to obtain cooked material cake; (5) The clinker cake is mixed with natural gypsum and ground to obtain iron-rich belite sulfoaluminate cement; In step (1), the fineness of the powder is -200 mesh; In step (3), the mass ratio of the cement raw material powder to water is 100:(8-12). In step (3), the pressure during the pressing process is above 15 MPa; In step (4), the heating rate during the calcination process is 4–6 °C / min; In step (4), the calcination temperature is 1220 ℃~1270 ℃ and the time is 50 min~110 min.

2. The method for preparing iron-rich belite sulfoaluminate cement from iron tailings and fluorogypsum according to claim 1, characterized in that, In step (4), the cooling is air cooling to room temperature; In step (5), the grinding fineness is -200 mesh.

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