Iron-rich belite sulphoaluminate cement prepared from iron tailings and fluorgypsum and method

Abstract

The invention relates to iron-rich-belite sulphoaluminate cement prepared from iron tailings and fluorgypsum and a method. The iron-rich-belite sulphoaluminate cement is prepared from iron-rich-belite sulphoaluminate cement clinker and natural gypsum in a mass ratio of 100: (6-18), the iron-rich type-belite sulphoaluminate cement clinker is prepared from the following raw materials in percentage by mass: 15 to 18 percent of iron tailings, 6 to 10 percent of fluorgypsum, 20 to 23 percent of steel slag, 12 to 14 percent of aluminum ash and 39 to 43 percent of limestone. The iron tailings, the fluorgypsum, the steel slag, the aluminum ash and the limestone synergistically provide required calcium, silicon, aluminum, iron and sulfur, hydration of the iron-rich belite sulphoaluminate cement clinker is facilitated to generate a target hydration product by supplementing a certain amount of natural gypsum, and the ratio of the raw materials is controlled, so that the mechanical property of the obtained cement is excellent; the consumption of natural raw materials is reduced, the cost of the raw materials is reduced, and the preparation method is simple and beneficial to industrialization.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste construction materials, and specifically relates to an iron-rich type-belite sulphoaluminate cement prepared from iron tailings and fluorgypsum and a method thereof. Background Art

[0002] Portland cement production is the third largest source of industrial CO2 emissions, and 26% of industrial CO2 emissions each year come from the Portland cement production industry. Today, the Portland cement production industry has been listed as a high-energy consumption industry. Therefore, in order to alleviate the high carbon emission problem of the cement production industry, the development and promotion of low-carbon cement varieties has become an important task that the cement industry urgently needs to promote. Iron-rich Belite sulphoaluminate cement is a new type of low-carbon cement with an iron-aluminate content of more than 15% and a dicalcium silicate content of more than 50% in the clinker. Compared with Portland cement, iron-rich Belite sulphoaluminate cement not only has the low-carbon advantages of significantly reduced limestone consumption, sintering, and grinding clinker energy consumption (CO2 emissions are reduced by about 30% during the production process), but also has the advantages of rapid setting, shrinkage compensation, low alkalinity, frost resistance, corrosion resistance, and low requirements for the grade of raw materials. Among them, the advantage of low requirements for the grade of raw materials makes iron-rich Belite sulphoaluminate cement able to better recycle many industrial wastes as raw materials for preparation, which also has far-reaching significance for alleviating the increasing depletion of natural resources and the increasingly serious waste pollution. Therefore, in order 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 the production of iron-rich Belite sulphoaluminate cement.

[0003] Iron tailings are industrial waste produced as a byproduct of the process of extracting iron from iron ore. Fluorogypsum is an industrial waste produced as a byproduct of the process of producing hydrofluoric acid using fluorite. At present, the annual discharge of iron tailings and fluorogypsum is as high as 600 million tons and 1 million tons, but their recycling rate is less than 7% and 25%. This makes the main treatment method for iron tailings and fluorogypsum in industry open-air storage. This not only causes a waste of land resources and disposal funds, but also causes environmental pollution and safety hazards. Therefore, in order to alleviate the series of problems caused by the storage of iron tailings and fluorogypsum, it is urgent to recycle iron tailings and fluorogypsum. The main components of iron tailings and fluorogypsum, calcium, silicon, aluminum, iron, and sulfur, are the raw materials required for the preparation of iron-rich-belite sulphoaluminate cement. The impurity components of iron tailings and fluorogypsum, magnesium and fluorine, have fluxing and mineralization effects during the sintering process, which can reduce the difficulty of burning iron-rich-belite sulphoaluminate cement clinker. Therefore, iron tailings and fluorgypsum are theoretically extremely suitable for recycling and use in the preparation of iron-rich belite sulphoaluminate cement.

[0004] However, there are few relevant documents on the preparation of sulphoaluminate cement using iron tailings and fluorgypsum. Patent CN105645795A provides a method for preparing sulphoaluminate cement using iron tailings. The method mixes iron tailings, bauxite, limestone and desulfurized gypsum into cement raw material and burns out sulphoaluminate cement. Patent CN101857389A provides a method for preparing sulphoaluminate cement using fluorgypsum. The method mixes fluorgypsum, limestone, bauxite, phosphogypsum and copper tailings into cement raw material and burns out sulphoaluminate cement. Patent CN102765893B provides a method for preparing sulphoaluminate cement using fluorgypsum. The method mixes fluorgypsum, red mud, limestone and bauxite into cement raw material and burns out sulphoaluminate cement.

[0005] Although the above patents have made important contributions to the application of iron tailings and fluorgypsum in the preparation of sulphoaluminate cement, they have the following shortcomings: (1) Only the separate utilization of iron tailings or fluorgypsum is realized, and the simultaneous utilization of iron tailings and fluorgypsum is not realized. (2) A large amount of high-cost or natural materials are consumed, such as the use of 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 sulphoaluminate cement in which calcium sulphoaluminate accounts for more than 60% of the clinker, dicalcium silicate accounts for less than 30%, and ferroaluminate accounts for less than 10%, the produced cement has the disadvantages of poor strength development and low strength in the later stage. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned technical deficiencies and provide an iron-rich type-belite sulphoaluminate cement prepared from iron tailings and fluorgypsum and a method, so as to solve the technical problems in the prior art that iron tailings and fluorgypsum are difficult to utilize simultaneously and the utilization rate of solid waste is low, and the cost of preparing sulphoaluminate cement is high and the later strength is low.

[0007] In order to achieve the above technical purpose, the technical solution provided by the present invention is: In a first aspect, the present invention provides an iron-rich-belite sulphoaluminate cement prepared from iron tailings and fluorgypsum, comprising iron-rich-belite sulphoaluminate cement clinker and natural gypsum in a mass ratio of 100:(6-18); wherein, in terms of mass percentage, the raw materials of the iron-rich-belite sulphoaluminate cement clinker comprise 15-18% of iron tailings, 6-10% of fluorgypsum, 20-23% of steel slag, 12-14% of aluminum ash, and 39-43% of limestone.

[0008] In a second aspect, the present invention provides a method for preparing iron-rich Belite sulphoaluminate cement from iron tailings and fluorgypsum, comprising the following steps: (1) drying the iron tailings, fluorgypsum, steel slag, aluminum ash and limestone respectively and grinding them into powder to obtain powder; (2) mixing the powder in proportion to obtain cement raw material powder; (3) adding water to the cement raw material powder to moisten and mix well, pressing and forming to obtain raw material cake; (4) calcining the raw material cake, and cooling after calcination to obtain clinker cake; (5) mixing the clinker cake with natural gypsum and grinding to obtain iron-rich Belite sulphoaluminate cement.

[0009] Compared with the prior art, the beneficial effects of the present invention include: The present invention uses five raw materials, namely, iron tailings, fluorgypsum, steel slag, aluminum ash and limestone, to synergistically provide calcium, silicon, aluminum, iron and sulfur required for preparing iron-rich Belite sulphoaluminate cement. By adding a certain amount of natural gypsum, the iron-rich Belite sulphoaluminate cement clinker is promoted to be hydrated to generate a target hydration product (ettringite). By controlling the ratio of each raw material, the solid waste-based iron-rich Belite sulphoaluminate cement obtained by the present invention has excellent mechanical properties and good strength development of the cement slurry. The present invention realizes the simultaneous utilization of iron tailings and fluorgypsum, alleviates the pollution status of the storage of iron tailings and fluorgypsum, and simultaneously utilizes a variety of solid wastes as raw materials, significantly reduces the consumption of natural raw materials, reduces the cost of raw materials, and has a simple preparation method, which is conducive to industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a flow chart of a method for preparing iron-rich-belite sulphoaluminate cement from iron tailings and fluorgypsum according to the present invention; Figure 2 The X-ray diffraction pattern of cement clinker of Example 1 of the present invention; Figure 3 This is the X-ray diffraction pattern of cement clinker of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0012] At present, in the preparation of sulphoaluminate cement, usually only one of iron tailings or fluorgypsum is used, and a large amount of high-cost materials are consumed, and the overall solid waste utilization rate is not high; the prepared sulphoaluminate cement contains more than 60% calcium sulphoaluminate, less than 30% dicalcium silicate, and less than 10% aluminafer. Usually, the clinker grinding is difficult, the slurry durability, frost resistance and impermeability are weak, and the prepared cement has the disadvantages of poor strength development and low late strength.

[0013] In view of the defects existing in the prior art, the present invention provides a method for preparing iron-rich Belite sulphoaluminate cement by using iron tailings and fluorgypsum, which realizes the first application of iron tailings and fluorgypsum in the preparation of iron-rich Belite sulphoaluminate cement, alleviates the pollution status of iron tailings and fluorgypsum storage, and promotes the development and promotion of iron-rich Belite sulphoaluminate low-carbon cement.

[0014] In a first aspect, the present invention provides an iron-rich-belite sulphoaluminate cement prepared from iron tailings and fluorgypsum, comprising iron-rich-belite sulphoaluminate cement clinker and natural gypsum in a mass ratio of 100:(6-18); wherein, in terms of mass percentage, the raw materials of the iron-rich-belite sulphoaluminate cement clinker comprise 15-18% of iron tailings, 6-10% of fluorgypsum, 20-23% of steel slag, 12-14% of aluminum ash, and 39-43% of limestone.

[0015] Preferably, the raw materials of the iron-rich-belite sulphoaluminate cement clinker include, by mass percentage, 15.5-17.5% of iron tailings, 6-10% of fluorgypsum, 21-23% of steel slag, 12-13.5% of aluminum ash, and 39.5-42% of limestone.

[0016] Preferably, the mineral composition of the iron-rich-belite sulphoaluminate cement clinker includes, by mass percentage, 26-29% calcium sulphoaluminate, 50-53% dicalcium silicate, 15-18% aluminaferrite, and 2-4% magnesium oxide.

[0017] The present invention provides five resources of calcium, silicon, aluminum, iron and sulfur required for preparing iron-rich Belite sulphoaluminate cement by synergistically providing five raw materials; and by adding a certain amount of natural gypsum, it is convenient to promote the hydration of iron-rich Belite sulphoaluminate cement clinker to generate the target hydration product ettringite.

[0018] Second, see Figure 1 The present invention provides a method for preparing iron-rich belite sulphoaluminate cement from iron tailings and fluorgypsum, comprising the following steps: (1) Drying iron tailings, fluorinated gypsum, steel slag, aluminum ash and limestone respectively and grinding them into powder to obtain powder; (2) Mixing the powder materials in proportion to obtain cement raw material powder; (3) Add water to the cement raw material powder to moisten and mix well, and press into shape to obtain raw material cake; (4) calcining the raw material cake and cooling it to obtain a cooked material cake; (5) The clinker cake is mixed with natural gypsum and ground to obtain iron-rich belite sulphoaluminate cement.

[0019] Preferably, in step (1), the fineness of the powder is -200 mesh.

[0020] Preferably, in step (3), the mass ratio of cement raw material powder to water is 100:(8-12).

[0021] Preferably, in step (3), the pressure during the pressing process is above 15 MPa.

[0022] Preferably, in step (4), the heating rate during the calcination process is 4 to 6 °C / min.

[0023] Preferably, in step (4), the calcination temperature is 1220°C to 1270°C, and the calcination time is 50 min to 110 min. In the present invention, too high a calcination temperature and too long a sintering time will result in too much energy being input into the system, which will lead to overburning of the clinker and a decrease in the content of the main mineral phase of the clinker; conversely, too low a calcination temperature and too short a sintering time will result in insufficient energy input into the system and the main mineral phase cannot be fully formed.

[0024] Preferably, in step (4), cooling is performed by air cooling to room temperature.

[0025] Preferably, in step (5), the grinding fineness is -200 mesh.

[0026] The mechanism of action and advantages of the present invention are: (1) The present invention realizes the simultaneous utilization of iron tailings and fluorgypsum, alleviates the pollution status of iron tailings and fluorgypsum storage, and brings high value-added product cement; (2) The present invention also utilizes solid waste raw materials such as fluorgypsum, steel slag and aluminum ash to prepare iron-rich belite sulphoaluminate cement, which significantly reduces the consumption of natural raw materials and reduces the input of raw material costs; (3) The mechanical properties of the solid waste-based iron-rich belite sulphoaluminate cement prepared by the present invention are superior to those of ordinary Portland cement and ordinary sulphoaluminate cement of level 42.5 in Chinese standards GB175-2007 and GB 20472-2006; (4) The iron-rich Belite sulphoaluminate cement prepared by the present invention has better durability, frost resistance and impermeability than ordinary sulphoaluminate cement because dicalcium silicate accounts for more than 50% and aluminaferrite accounts for more than 15%.

[0027] The present invention is further described in detail below with reference to specific embodiments and comparative examples.

[0028] The chemical compositions of the raw materials in the embodiments and comparative examples of the present invention are shown in Table 1.

[0029]

[0030] Example 1 A method for preparing iron-rich belite sulphoaluminate cement from iron tailings and fluorgypsum, comprising the following steps: (1) Grinding raw materials: Dry iron tailings, fluorgypsum, steel slag, aluminum ash and limestone and grind them into fine powder with a fineness of -200 mesh.

[0031] (2) Preparation of cement raw material: The raw material fine powder obtained in (1) was uniformly mixed with iron tailings 16.58 wt%, fluorgypsum 8.42 wt%, steel slag 21.21 wt%, aluminum ash 12.90 wt%, and limestone 40.89 wt% in mass fraction to obtain cement raw material powder.

[0032] (3) Pressing cement raw material cake: adding 10 wt% of water to the raw material powder to moisten and mix the raw material powder obtained in (2), and then pressing it into a cake at 20 MPa using a tableting mold and a tablet press.

[0033] (4) Calcination of cement clinker: The raw material cake obtained in (3) was placed in a high-temperature furnace for calcination. The calcination conditions were as follows: a heating rate of 5 °C / min, a calcination temperature of 1250 °C, and a holding time of 80 min. After the calcination, the sample was taken out at high temperature and quickly cooled to room temperature by air to obtain a cement clinker cake.

[0034] (5) Grinding cement clinker: The clinker cake obtained in (4) is mixed with natural gypsum accounting for 10 wt% of the clinker cake, and then ground into fine powder with a fineness of -200 mesh to obtain a cement product.

[0035] In Example 1, the three ratio values ​​of the cement raw material ratio are basicity coefficient Cm = 0.99, aluminum-sulfur ratio P = 1.51 and aluminum-silicon ratio N = 0.86.

[0036] The phase composition of the cement clinker prepared in Example 1 is as follows Figure 2 As shown in the figure, the phase composition of cement clinker is calcium sulfoaluminate, dicalcium silicate, aluminoferrite and magnesium oxide. The results of XRD refinement and quantitative analysis show that the proportion of each mineral phase is: calcium sulfoaluminate 28%, dicalcium silicate 52%, aluminoferrite 17%, and magnesium oxide 3%.

[0037] Example 2 A method for preparing iron-rich belite sulphoaluminate cement from iron tailings and fluorgypsum, comprising the following steps: (1) Grinding raw materials: Dry iron tailings, fluorgypsum, steel slag, aluminum ash and limestone and grind them into fine powder with a fineness of -200 mesh.

[0038] (2) Preparation of cement raw material: The raw material fine powder obtained in (1) is uniformly mixed with iron tailings 15.71 wt%, fluorgypsum 9.82 wt%, steel slag 22.53 wt%, aluminum ash 12.19 wt%, and limestone 39.75 wt% in mass fraction to obtain cement raw material powder.

[0039] (3) Pressing cement raw material cake: adding 10 wt% of water to the raw material powder to moisten and mix the raw material powder obtained in (2), and then pressing it into a cake at 20 MPa using a tableting mold and a tablet press.

[0040] (4) Calcination of cement clinker: The raw material cake obtained in (3) was placed in a high-temperature furnace for calcination. The calcination conditions were as follows: a heating rate of 5 °C / min, a calcination temperature of 1230 °C, and a holding time of 60 min. After the calcination, the sample was taken out at high temperature and quickly cooled to room temperature by air to obtain a cement clinker cake.

[0041] (5) Grinding cement clinker: The clinker cake obtained in (4) is mixed with natural gypsum accounting for 10 wt% of the clinker cake, and then ground into fine powder with a fineness of -200 mesh to obtain a cement product.

[0042] Example 3 A method for preparing iron-rich belite sulphoaluminate cement from iron tailings and fluorgypsum, comprising the following steps: (1) Grinding raw materials: Dry iron tailings, fluorgypsum, steel slag, aluminum ash and limestone and grind them into fine powder with a fineness of -200 mesh.

[0043] (2) Preparation of cement raw material: The raw material fine powder obtained in (1) was uniformly mixed with iron tailings 17.02 wt%, fluorgypsum 6.02 wt%, steel slag 22.14 wt%, aluminum ash 13.01 wt%, and limestone 41.81 wt% in mass fraction to obtain cement raw material powder.

[0044] (3) Pressing cement raw material cake: adding 10 wt% of water to the raw material powder to moisten and mix the raw material powder obtained in (2), and then pressing it into a cake at 20 MPa using a tableting mold and a tablet press.

[0045] (4) Calcination of cement clinker: The raw material cake obtained in (3) was placed in a high-temperature furnace for calcination. The calcination conditions were as follows: a heating rate of 5 °C / min, a calcination temperature of 1260 °C, and a holding time of 100 min. After the calcination, the sample was taken out at high temperature and quickly cooled to room temperature by air to obtain a cement clinker cake.

[0046] (5) Grinding cement clinker: The clinker cake obtained in (4) is mixed with natural gypsum accounting for 10 wt% of the clinker cake, and then ground into fine powder with a fineness of -200 mesh to obtain a cement product.

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that the raw material ratio is 14.81 wt % of iron tailings, 1.13 wt % of fluorgypsum, 25.01 wt % of steel slag, 11.93 wt % of aluminum ash, and 47.12 wt % of limestone. The other steps and conditions are the same as those in Example 1.

[0048] The finished cement product obtained in this comparative example has a phase composition of clinker as follows Figure 3 shown.

[0049] Depend on Figure 3 It can be seen that the phase composition of the cement clinker prepared in Comparative Example 1 is calcium sulfoaluminate, dicalcium silicate, aluminoferrite, magnesium oxide, calcite and aluminate. The results of XRD refinement and quantitative analysis show that the proportion of each mineral phase is: 13% calcium sulfoaluminate, 36% dicalcium silicate, 14% aluminoferrite, 4% magnesium oxide, 27% calcite and 6% aluminate. Obviously, the clinker mineral composition of Comparative Example 1 does not meet the corresponding restriction requirements (the content of dicalcium silicate is higher than 50%, and the content of aluminoferrite is higher than 15%). This is because the addition of fluorgypsum is too low, resulting in the inability of the intermediate mineral phases calcite and aluminate to be fully converted into the main mineral phase of the clinker.

[0050] Comparative Example 2 The difference between this comparative example and Example 1 is that the calcination temperature is 1100° C. and the holding time is 30 min.

[0051] Comparative Example 3 The difference between this comparative example and Example 1 is that the calcination temperature is 1300° C. and the holding time is 120 min.

[0052] The cement paste strength test was performed on the finished cement products obtained in the above embodiments and comparative examples, and conventional ordinary Portland cement and ordinary sulphoaluminate cement were added for comparison; the mass ratio of cement to water was 2:1, and the specific test conditions and steps were referred to GB / T17671-1999.

[0053]

[0054] As can be seen from Table 2, the strength development of the cement pastes prepared in Examples 1-3 is good, better than ordinary Portland cement and ordinary sulphoaluminate cement of 42.5 level. However, the strength development of the cement pastes prepared in Comparative Examples 1-3 is poor, inferior to ordinary Portland cement and ordinary sulphoaluminate cement of 42.5 level. This is because the main mineral phase in the clinker that is beneficial to the strength development of the paste cannot be fully formed due to inappropriate raw material ratio, too low or too high calcination temperature, too short or too long insulation time.

[0055] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. An iron-rich type-belite sulphoaluminate cement prepared from iron tailings and fluorgypsum, characterized in that: It comprises iron-rich-belite sulphoaluminate cement clinker and natural gypsum in a mass ratio of 100:(6-18); wherein, in terms of mass percentage, the raw materials of the iron-rich-belite sulphoaluminate cement clinker comprise 15-18% of iron tailings, 6-10% of fluorgypsum, 20-23% of steel slag, 12-14% of aluminum ash, and 39-43% of limestone.

2. The iron-rich belite sulphoaluminate cement prepared from iron tailings and fluorgypsum according to claim 1, characterized in that: Calculated by mass percentage, the raw materials of the iron-rich-belite sulphoaluminate cement clinker include 15.5-17.5% of iron tailings, 6-10% of fluorgypsum, 21-23% of steel slag, 12-13.5% of aluminum ash, and 39.5-42% of limestone.

3. The iron-rich-belite sulphoaluminate cement prepared from iron tailings and fluorgypsum according to claim 1, characterized in that: Calculated by mass percentage, the mineral composition of the iron-rich-belite sulphoaluminate cement clinker includes: 26-29% calcium sulphoaluminate, 50-53% dicalcium silicate, 15-18% aluminaferrite, and 2-4% magnesium oxide.

4. The method for preparing iron-rich belite sulphoaluminate cement from the iron tailings and fluorgypsum as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Drying iron tailings, fluorinated gypsum, steel slag, aluminum ash and limestone respectively and grinding them into powder to obtain powder; (2) mixing the powder materials in proportion to obtain cement raw material powder; (3) adding water to the cement raw material powder to moisten and mix well, and pressing and molding to obtain a raw material cake; (4) calcining the raw material cake, and cooling the raw material cake after calcination to obtain a cooked material cake; (5) The clinker cake is mixed with natural gypsum and ground to obtain iron-rich belite sulphoaluminate cement.

5. The method for preparing iron-rich belite sulphoaluminate cement from iron tailings and fluorgypsum according to claim 4, characterized in that: In step (1), the fineness of the powder is -200 mesh.

6. The method for preparing iron-rich belite sulphoaluminate cement from iron tailings and fluorgypsum according to claim 4, characterized in that: In step (3), the mass ratio of the cement raw material powder to water is 100:(8-12).

7. The method for preparing iron-rich belite sulphoaluminate cement from iron tailings and fluorgypsum according to claim 4, characterized in that: In step (3), the pressure during the pressing process is above 15 MPa.

8. The method for preparing iron-rich belite sulphoaluminate cement from iron tailings and fluorgypsum according to claim 4, characterized in that: In step (4), the heating rate during the calcination process is 4 to 6 °C / min.

9. The method for preparing iron-rich belite sulphoaluminate cement from iron tailings and fluorgypsum according to claim 4, characterized in that: In step (4), the calcination temperature is 1220°C to 1270°C, and the calcination time is 50 min to 110 min.

10. The method for preparing iron-rich belite sulphoaluminate cement from iron tailings and fluorgypsum according to claim 4, 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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