LU500915A1

LU500915A1 - High-iron and low-calcium silicate cement and preparation method therefor

Info

Publication number: LU500915A1
Application number: LU500915A
Authority: LU
Inventors: Songhui Liu; Mifeng Gou; Xuemao Guan; Haibo Zhang; Jianping Zhu; Yuli Wang; Caijun Shi
Original assignee: Univ Henan Polytechnic
Priority date: 2020-03-27
Filing date: 2020-12-29
Publication date: 2021-12-01
Also published as: CN111393047B; LU500915B1; WO2021190045A1; CN111393047A

Abstract

A high-iron and low-calcium silicate cement and a preparation method therefor. The preparation method comprises: mixing Bayer process red mud and limestone uniformly, grinding, and then sheeting to obtain a green sheet; calcining the green sheet and then quickly cooling to obtain cement clinker; and then, mixing with gypsum uniformly and grinding to prepare a high-iron and low-calcium silicate cement. The early strength of the cement is high, the later strength continuously increases, mechanical properties are good, and the amount of Bayer process red mud in the cement clinker is large, thereby greatly improving the utilization rate of Bayer process red mud solid waste; moreover, the burning temperature of the cement clinker is lower, thereby reducing the production costs of the cement, and reducing the emissions of polluting gases such as CO2, SO2, and NOx in a production process.

Description

BL-5336 HIGH-IRON AND LOW-CALCIUM SILICATE CEMENT AND °°°

PREPARATION METHOD THEREFOR

FIELD OF THE INVENTION The present invention belongs to the technical field of red mud application, and specifically relates to a high-iron and low-calcium silicate cement and preparation method therefor (high-iron and low-calcium portland cement and a preparation method thereof).

BACKGROUND OF THE INVENTION Bayer process red mud is a solid waste discharged from natural bauxite ore after alumina is dissolved in hot alkali. With the annual increase of alumina production capacity in China, the annual discharge of Bayer process red mud in China exceeds 100 million tons. At present, due to the lack of economic and feasible technologies for bulk utilization of red mud, the comprehensive utilization rate of red mud has been at a low level. On the other hand, cement is currently the most widely used building material in the world. The basic reason for the high energy consumption of traditional portland cement clinker calcined lies in its high-calcium mineral design. The design of high-calcium minerals also leads to excessive consumption of high-quality limestone and high-quality coal resources, and a large emissions of greenhouse gas of CO, and harmful gases of SO», NO, etc, which intensifies the consumption of the energy and resource and the environmental load in the cement industry.

Based on the new requirements of the energy saving and emission reduction, as well as the response to climate change, the production of low-calcium portland cement with low-calcium minerals (such as dicalcium silicate and tetracalcium aluminoferrite) as the main minerals can not only reduce the CO; emission and lower the calcination temperature, but also greatly increase the proportion of solid wastes such as red mud in the raw materials of cement production, which is of great significance in many aspects.

Therefore, There is a need to provide an improved technical solution for the above-mentioned shortcomings of the prior art.

SUMMARY OF THE INVENTION 1

BL-5336 The present invention aims to provide a high-iron and low-calcium portland cement anda preparation method thereof (the high-iron and low-calcium portland cement is also called high-iron belite cement), which are used to overcome the problems of serious pollution to the surrounding groundwater, soil, air and ecological environment caused by red mud accumulation in the prior art, and the problems of excessive energy consumption and serious environmental pollution which are caused by high-calcium mineral design in traditional portland cement clinker.

In order to achieve the above objective, the present invention provides the following technical solutions.

A preparation method of high-iron and low-calcium portland cement, comprising the following steps of: Step 1: mixing Bayer process red mud and limestone uniformly, grinding into raw meal powder, and then tableting to obtain raw meal tablets, wherein the Bayer process red mud accounts for 50-60 wt% and the limestone accounts for 40-50 wt%: Step 2: calcining and then cooling the raw meal tablets obtained in Step 1 to obtain cement clinker; Step 3: mixing uniformly the cement clinker obtained in Step 2 with gypsum and then grinding to prepare the high-iron and low-calcium portland cement.

Preferably, the raw meal powder comprises the following components by mass percentage: 50-55 wt% of Bayer process red mud, and 45-50 wt% of the limestone.

Preferably, both the Bayer process red mud and limestone in Step 1 include the following components: SiOz, Al>O3, Fe;O3, CaO, MgO, K,O, Na:O and TiO».

Preferably, the content of SiO, in the Bayer process red mud is 15-30 wt %; the content of ALOs in the Bayer process red mud is 15-25 wt%; the content of Fe;O; in the Bayer process red mud is 15-20 wt%; the content of CaO in the Bayer process red mud is 5-20 wt%; the content of CaO in the limestone is 45-55 wt%; the content of MgO in the Bayer process red mud is less than 5 wt%; the total content of K:O and NaO in the Bayer process red mud is less than 10 wt%; and the content of TiO; in the Bayer process red mud is less than 10 wt%.

Preferably, the raw meal power ground in Step 1 has a fineness of less than 75 um.

The purpose of tabletting in Step 1 is to make the raw meal powder come into close contact and promote the solid-phase reaction of the clinker during the calcination process. In the actual 2

BL-5336 LU500915 industrial production process, a rotary kiln is used for calcination.

The tabletting is that the uniformly mixed raw meal power is pressed down to form a compact raw meal tablets under the action of pressure, which is then calcined in a furnace.

Preferably, the calcination temperature in Step 2 is 1100-1250 °C, and the calcination time is 12h The cooling in Step 2 is rapid cooling, and the rate of the rapid cooling is greater than 100 °C/min.

The rapid cooling is specifically that the cold air is adopted to exchange heat with the cement clinker calcined at a high temperature so as to achieve the purpose of reducing the temperature of the calcined cement clinker and stabilizing its high temperature crystal form.

Preferably, the mass ratio of the gypsum to the high-iron and low-calcium portland cement clinker in Step 3 is 0-20 %. Preferably, the specific surface area of the high-iron and low-calcium portland cement prepared by grinding in Step 3 is 350-450 m°/kg.

The high-iron and low-calcium portland cement prepared by any of the above-mentioned methods for preparing high-iron and low-calcium portland cement.

A high-iron and low-calcium portland cement, wherein the cement clinker in the high-iron and low-calcium portland cement comprises minerals in the following mass percentages: C2S: 45-60 %, C4AF: 25-40 %, and C12A7: 5-20 %. Preferably, the cement clinker comprises minerals in the following mass percentages: C,S: 50-60 %, C4AF: 30-40 %, and C12A7: 5-10 %. Wherein, C,S is dicalcium silicate, the molecular formula is 2CaO-S102, and the content of CaO in CS is 65.1 wt%; C4AF is tetracalcium aluminoferrite, the molecular formula is 4ACaO Al>O3'FezO3, and the content of CaO in C4AF is 46.2 wt%; CizA7 is dodecacalcium heptaaluminate, the molecular formula is 12Ca0O-7AL 0s, and the content of CaO in CizA7 is 48.4 wt%. Compared with the closest prior art, the technical solution provided by the present invention has the following excellent effects.

The cement clinker in the present invention uses Bayer process red mud and limestone as raw materials, and the mixing amount of Bayer process red mud is as high as 60%, which greatly improves the utilization rate of solid waste of Bayer process red mud, and not only reduces the 3

BL-5336 emission reduction pressure of the alumina industry, but also reduces the harm to the environment 090975 Compared with the sintering temperature of the traditional portland cement clinker, the sintering temperature of the cement clinker is reduced by 200-350 °C, so that the production cost of the cement is reduced, and the emission of CO; and the polluting gases such as the harmful gases of SO; and NO, is greatly reduced in the production process.

The CizA7 and C4AF minerals in the cement clinker of the present invention are hydrated to provide the early strength of the cement, and the C:S minerals are hydrated to provide the later strength of the cement, so that the prepared cement has high early strength, continuous growth of late strength, and slightly better mechanical properties than the ordinary portland cement. It can be widely applied to the outdoor building products, emergency repair engineering, underground engineering, etc.

THE DESCRIPTION OF THE DRAWINGS The accompanying drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary examples and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention. Wherein: Fig.1 is a XRD pattern of Bayer process red mud used in various examples and comparative examples of the present invention.

Fig.2 shows XRD patterns of cement clinker prepared in specific Examples 2, 4 and 7 of the present invention.

DETAILED EMBODIMENTS The high-iron and low-calcium portland cement in the present invention is made by mixing cement clinker with a certain proportion of gypsum and then grinding. The cement clinker comprises C:S, C4AF, and CizA7 minerals. The C12A7 and C4AF minerals in the cement clinker are hydrated to provide early strength of the cement, and the C:S minerals are hydrated to provide the later strength of the cement, so that the prepared cement has high early strength, continuous growth of late strength and slightly better mechanical properties than the ordinary portland cement. It can be widely applied to the outdoor building products, emergency repair engineering, underground 4

BL-5336 a LU500915 engineering, etc.

In the raw materials used in the following examples and comparative examples, the Bayer process red mud was obtained from the Zhongzhou subsidiary of Aluminum Corporation of China , and the limestone was obtained from the limestone used in the local (Jiaozuo, China) cement plant.

The chemical composition of the raw materials is shown in Table 1 below. Table 1 Chemical compositions of Bayer process red mud and limestone — EEEEEEEEEE Raw materials (wt%) | (Wt%) | (wt%) | (wt%) | (wt%o) | (wt%) | (Wt%) | (Wit%) | (Wit%) | (wt%) SE eff] [ele] ml ale

14.3 20.38 23.32 16.7 11.41 0.63 7.38 5.15 99.96 red mud As shown in Fig 1, it is the XRD pattern of the Bayer process red mud used in the following examples and comparative examples. The XRD phase analysis results show that the phase of the Bayer process red mud comprises 1-AlLSiOs(OH)s (kaolin), 2-AIO(OH) (diaspore), 3-CasAl(Si04)(OH)s (hydrated garnet), 4-SiO, (quartz), 5-CaCO; (calcite), 6-Nag(SiAlO4)s (Ho 33(CO3)1 44) (H20)2 (cancrinite), 7-Fe2Os3 (hematite). Example 1 The example of the present invention provides a preparation method of high-iron and low-calcium portland cement, which comprises the following steps of: Step 1: Mixing 60 parts of Bayer process red mud and 40 parts of limestone uniformly, grinding them into raw meal powder with a fineness of less than 75 um, and then tabletting to obtain raw meal tablets; Step 2: Calcining the raw meal tablets obtained in Step 1 at the temperature of 1200 °C for 2 hours and then cooling to obtain cement clinker; Step 3: Mixing the cement clinker obtained in Step 2 with gypsum (the mass of gypsum is 10% of the mass of cement clinker) uniformly, and grinding to prepare the high-iron and low-calcium portland cement.

Mineral composition analysis: the mineral composition of high-iron and low-calcium portland 5

BL-5336 LU500915 cement clinker was determined by XRD full spectrum fitting quantitative analysis technique.

In the example of the invention, the cement clinker in the high-iron and low-calcium portland cement prepared by the preparation method of high-iron and low-calcium portland cement comprises the following minerals in percentage by mass: CaS: 51 %, C4AF: 32.7 %, Ci2A7 : 16.3 %, as shown in Table 2.

Performance Testing The specific surface area of the high-iron and low-calcium portland cement prepared in the example of the present invention is tested, and the specific surface area test is determined by using Cement Blaine (Przibram) specific surface area tester with reference to the cement Blaine specific surface area measurement method, namely Testing method for specific surface of cement—Blaine method GB/T 8074-2008. The high-iron and low-calcium portland cement prepared in the example of the present invention is mixed with water, poured and molded to make a 4cm*4cm*4cm test block. The test block is placed in a cement concrete standard curing room for curing (the temperature is 20 °C + 2 °C, humidity >95 %), and cured for 28 days. The compressive strength of the test block after curing for 3 days and 28 days is determined according to GB/T 17671-1999 Cement Mortar Strength Detection Method (ISO method). The specific surface area of the high-iron and low-calcium portland cement prepared in the example of the present invention is 373 m°/kg, as shown in Table 2.

The compressive strength of the high-iron and low-calcium portland cement prepared in the example of the present invention after 3 days is 18.6 MPa, and the compressive strength after 28 days is 44.4 MPa, as shown in Table 2.

Example 2 In the preparation method of high-iron and low-calcium portland cement provided by the example of the present invention, the raw meal tablets are placed at 1100 °C and calcined for 2 hours in Step 2; no gypsum is added in Step 3. Other methods and steps are the same as those described in Example 1, which will not be described in detail herein.

The mineral composition of cement clinker in the high-iron and low-calcium portland cement 6

BL-5336 prepared in the example of the present invention is analyzed, and the specific surface area of the high-iron and low-calcium portland cement and the compressive strength of the high-iron and low-calcium portland cement after 3 days and 28 days is tested, wherein the mineral composition analysis method, the test standard and method for specific surface area and the test standard and method for the compressive strength are the same as those in Example 1, which will not be described in detail herein.

In the example of the present invention, the cement clinker in the high-iron and low-calcium portland cement prepared by the preparation method of high-iron and low-calcium portland cement comprises the following minerals by mass percentage: CS: 50.3%, C4AF: 31.9%, Ci12A7: 17.8%, as shown in Table 2.

The specific surface area of the high-iron and low-calcium portland cement prepared in the example of the present invention is 365 m°/kg, as shown in Table 2.

The compressive strength of the high-iron and low-calcium portland cement prepared in the example of the present invention after 3 days is 19.1 MPa, and the compressive strength after 28 days is 43.9 MPa, as shown in Table 2.

As shown in Fig.2, it shows the XRD pattern of the cement clinker prepared in this example. It can be seen from XRD that the mineral composition of the cement clinker in the high-iron and low-calcium portland cement prepared in this example is C:S, C4AF and C12A7.

Example 3 In the preparation method of high-iron and low-calcium portland cement provided by the example of the present invention, the raw meal tablets are placed at 1200 °C and calcined for 2 hours in Step 2; the addition amount of gypsum in Step 3 is 20 % of the mass of the cement clinker. Other methods and steps are the same as those described in Example 1 which will not be described in detail herein.

The mineral composition of cement clinker in the high-iron and low-calcium portland cement prepared in the example of the present invention is analyzed, and the specific surface area of the high-iron and low-calcium portland cement and the compressive strength of the high-iron and low-calcium portland cement after 3 days and 28 days is tested, wherein the mineral composition analysis method, the test standard and method for specific surface area and the test standard and 7

BL-5336 method for the compressive strength are the same as those in Example 1, which will not De described in detail herein.

In the example of the present invention, the cement clinker in the high-iron and low-calcium portland cement prepared by the preparation method of high-iron and low-calcium portland cement comprises the following minerals by mass percentage: C:S: 51.3 %, C4AF: 33.1 %, C12A7: 15.6 %, as shown in Table 2.

The specific surface area of the high-iron and low-calcium portland cement prepared in the example of the present invention is 369 m°/kg, as shown in Table 2.

The compressive strength of the high-iron and low-calcium portland cement prepared in the example of the present invention after 3 days is 18.4 MPa, and the compressive strength after 28 days is 45.2 MPa, as shown in Table 2.

Example 4 In the preparation method of high-iron and low-calcium portland cement provided by the example of the present invention, 55 parts of Bayer process red mud and 45 parts of limestone are mixed in Step 1. Other methods and steps are the same as those described in Example 1, which will not be described in detail herein.

The mineral composition of cement clinker in the high-iron and low-calcium portland cement prepared in the example of the present invention is analyzed, and the specific surface area of the high-iron and low-calcium portland cement and the compressive strength of the high-iron and low-calcium portland cement after 3 days and 28 days is tested, wherein the mineral composition analysis method, the test standard and method for specific surface area and the test standard and method for the compressive strength are the same as those in Example 1, which will not be described in detail herein.

In the example of the present invention, the cement clinker in the high-iron and low-calcium portland cement prepared by the preparation method of high-iron and low-calcium portland cement comprises the following minerals by mass percentage: CS: 55.4 %, C4AF: 33 %, CizA7: 11.6 %, as shown in Table 2.

The specific surface area of the high-iron and low-calcium portland cement prepared in the example of the present invention is 360 m?*/kg, as shown in Table 2.

8

BL-5336 The compressive strength of the high-iron and low-calcium portland cement prepared in the example of the present invention after 3 days is 26.7 MPa, and the compressive strength after 28 days is 54.7 MPa, as shown in Table 2.

As shown in Fig.2, it shows the XRD pattern of the cement clinker prepared in this example. It is known from XRD, the mineral composition of the cement clinker in the high-iron low-calcium portland cement prepared in this example is C,S, C4AF and C12A-.

Example 5 In the preparation method of high-iron and low-calcium portland cement provided by the example of the present invention, the raw meal tablets are placed at 1100 °C and calcined for 2 hours in Step 2. Other methods and steps are the same as those described in Example 4, which will not be described in detail herein.

In the example of the present invention, the cement clinker in the high-iron and low-calcium portland cement prepared by the preparation method of high-iron and low-calcium portland cement comprises the following minerals by mass percentage: CS: 54.4 %, C4AF: 33.5 %, Ci2A7: 12.1 %, as shown in Table 2.

The specific surface area of the high-iron and low-calcium portland cement prepared in the example of the present invention is 367 m?*/kg, as shown in Table 2.

The compressive strength of the high-iron and low-calcium portland cement prepared in the example of the present invention after 3 days is 27.1 MPa, and the compressive strength after 28 days is 52.8 MPa, as shown in Table 2. Example 6 9

BL-5336 In the preparation method of high-iron and low-calcium portland cement provided by the example of the present invention, the raw meal tablets are placed at 1250 °C and calcined for 2 hours in Step 2; the addition amount of gypsum in the Step 3 is 20 % of the mass of the cement clinker. Other methods and steps are the same as those described in Example 4, which will not be described in detail herein.

In the example of the present invention, the cement clinker in the high-iron and low-calcium portland cement prepared by the preparation method of high-iron and low-calcium portland cement comprises the following minerals by mass percentage: C:S: 56.1 %, C4AF: 32.4 %, Ci2A7: 11.5 %, as shown in Table 2.

The specific surface area of the high-iron and low-calcium portland cement prepared in the example of the present invention is 364 m°/kg, as shown in Table 2.

The compressive strength of the high-iron and low-calcium portland cement prepared in the example of the present invention after 3 days is 26.9 MPa, and the compressive strength after 28 days is 55.2 MPa, as shown in Table 2. Example 7 In the preparation method of high-iron and low-calcium portland cement provided by the example of the present invention, 50 parts of Bayer process red mud and 50 parts of limestone are mixed in Step 1; and the addition amount of gypsum in the Step 3 is 20 % of the mass of the cement clinker. Other methods and steps are the same as those described in Example 1, which will not be described in detail herein.

The mineral composition of cement clinker in the high-iron and low-calcium portland cement prepared in the example of the present invention is analyzed, and the specific surface area of the 10

BL-5336 high-iron and low-calcium portland cement and the compressive strength of the high-iron and low-calcium portland cement after 3 days and 28 days is tested, wherein the mineral composition analysis method, the test standard and method for specific surface area and the test standard and method for the compressive strength are the same as those in Example 1, which will not be described in detail herein.

In the example of the present invention, the cement clinker in the high-iron and low-calcium portland cement prepared by the preparation method of high-iron and low-calcium portland cement comprises the following minerals by mass percentage: CS: 58 %, C4AF: 33.9 %, CizA7: 8.1 %, as shown in Table 2.

The specific surface area of the high-iron and low-calcium portland cement prepared in the example of the present invention is 370 m°/kg, as shown in Table 2.

The compressive strength of the high-iron and low-calcium portland cement prepared in the example of the present invention after 3 days is 28.1 MPa, and the compressive strength after 28 days is 64.4 MPa, as shown in Table 2.

As shown in Fig.2, it shows the XRD pattern of the cement clinker prepared in this example. It can be seen from XRD that the mineral composition of the cement clinker in the high-iron and low-calcium portland cement prepared in this example is C:S, C4AF and C12A7. Compared with the high-iron and low-calcium portland cement prepared in Example 2 and Example 4,the higher the content of limestone in the raw meal powder, the lower the content of Bayer process red mud. At this time, the contents of C:S and C4AF in the mineral components of the cement clinker of the prepared high-iron and low-calcium portland cement increase, while the content of C12A7 decrease. The compressive strength of the prepared high-iron and low-calcium portland cement after curing for 3 days and curing for 28 days has improved.

Example 8 In the preparation method of high-iron and low-calcium portland cement provided by the example of the present invention, the raw meal tablets are placed at 1100 °C and calcined for 2h in Step 2; an addition amount of gypsum is 10 % of the mass of the cement clinker in Step 3. Other methods and steps are the same as those described in Example 7, which will not be described in detail herein.

11

BL-5336 The mineral composition of cement clinker in the high-iron and low-calcium portland cement prepared in the example of the present invention is analyzed, and the specific surface area of the high-iron and low-calcium portland cement and the compressive strength of the high-iron and low-calcium portland cement after 3 days and 28 days is tested, wherein the mineral composition analysis method, the test standard and method for specific surface area and the test standard and method for the compressive strength are the same as those in Example 1, which will not be described in detail herein.

In the example of the present invention, the cement clinker in the high-iron and low-calcium portland cement prepared by the preparation method of high-iron and low-calcium portland cement comprises the following minerals by mass percentage: C:S: 57.2 %, C4AF: 34.0 %, C12A7: 8.8 %, as shown in Table 2. The specific surface area of the high-iron and low-calcium portland cement prepared in the example of the present invention is 367 m°/kg, as shown in Table 2. The compressive strength of the high-iron and low-calcium portland cement prepared in the example of the present invention after 3 days is 27.8 MPa, and the compressive strength after 28 days is 63.9 MPa, as shown in Table 2. Example 9 In the preparation method of high-iron and low-calcium portland cement provided by the example of the present invention, the raw meal tablets are placed at 1250 °C and calcined for 2 hours in Step 2; the addition amount of gypsum is 10 % of the mass of the cement clinker in Step 3. Other methods and steps are the same as those described in Example 7, which will not be described in detail herein.

The mineral composition of cement clinker in the high-iron and low-calcium portland cement prepared in the example of the present invention is analyzed, and the specific surface area of the high-iron and low-calcium portland cement and the compressive strength of the high-iron and low-calcium portland cement after 3 days and 28 days are tested, wherein the mineral composition analysis method, the test standard and method for specific surface area and the test standard and method for the compressive strength are the same as those in Example 1, which will not be described in detail herein. 12

BL-5336 In the example of the present invention, the cement clinker in the high-iron and low-calcium. portland cement prepared by the preparation method of high-iron and low-calcium portland cement comprises the following minerals by mass percentage: C:S: 58.1 %, C4AF: 34.2 %, C12A7: 7.7 %, as shown in Table 2.

The specific surface area of the high-iron and low-calcium portland cement prepared in the example of the present invention is 361 m°/kg, as shown in Table 2.

The compressive strength of the high-iron and low-calcium portland cement prepared in the example of the present invention after 3 days is 27.5 MPa, and the compressive strength after 28 days is 66.2 MPa, as shown in Table 2.

Comparative example 1 In the preparation method of high-iron and low-calcium portland cement provided by this comparative example, 80 parts of Bayer process red mud and 20 parts of limestone are mixed in Step 1. Other methods and steps are the same as those described in Example 1, which will not be described in detail herein.

The mineral composition of cement clinker in the high-iron and low-calcium portland cement prepared in this comparative example is analyzed, and the specific surface area of the high-iron and low-calcium portland cement and the compressive strength of the high-iron and low-calcium portland cement after 3 days and 28 days is tested, wherein the mineral composition analysis method, the test standard and method for specific surface area and the test standard and method for the compressive strength are the same as those in Example 1, which will not be described in detail herein.

In this comparative example, the cement clinker in the high-iron and low-calcium portland cement prepared by the preparation method of high-iron and low-calcium portland cement comprises the following minerals by mass percentage: C2AS: 58.6 %, C2S: 5.6 %, Fe Os: 22.3 %, CaT1O3:13.5 %, wherein CAS is is gehlenite; C,S is dicalcium silicate; Fe,Os is hematite; CaTiO; is perovskite.

The specific surface area of the high-iron and low-calcium portland cement prepared in this comparative example is 350 m°/kg, as shown in Table 2.

The compressive strength of the high-iron and low-calcium portland cement prepared in this 13

BL-5336 comparative example after 3 days is 0.7 MPa, and the compressive strength after 28 days is EX MPa, as shown in Table 2. In this comparative example, only C,S in the mineral components of cement clinker has hydration activity, and other minerals have no hydration activity. Therefore, the high-iron and low-calcium portland cement prepared in this comparative example has poor mechanical properties after curing.

Comparative example 2 In the preparation method of high-iron and low-calcium portland cement provided by this comparative example, 40 parts of Bayer process red mud and 60 parts of limestone are mixed in Step 1. Other methods and steps are the same as those described in Example 1, which will not be described in detail herein.

In this comparative example, the cement clinker in the high-iron and low-calcium portland cement prepared by the preparation method of high-iron and low-calcium portland cement comprises the following minerals by mass percentage: CsA: 50.9 %, CaS: 22.7 %, C4AF: 17.5 %, f-CaO: 9.0 %, wherein C3A is tricalcium aluminate; C,S is dicalcium silicate; C4AF is tetracalcium aluminoferrite; f-CaO is free calcium oxide.

The specific surface area of the high-iron and low-calcium portland cement prepared in this comparative example is 361 m°/kg, as shown in Table 2.

The compressive strength of the high-iron and low-calcium portland cement prepared in this comparative example after 3 days is 10.3 MPa, and the compressive strength after 28 days is 12.5 MPa, as shown in Table 2. Since the minerals CsA and C4AF in cement clinker have high hydration activity but poor cementing performance in the early stage, the cement in this comparative example has rapid hydration and setting, but poor mechanical properties, and slow strength growth in the 14

BL-5336 LU500915 later stage.

Comparative example 3 In the preparation method of high-iron and low-calcium portland cement provided by this comparative example, the raw meal tablets are placed at 900 °C and calcined for 2 hours in Step 2. Other methods and steps are the same as those described in Example 1, which will not be described in detail herein.

In this comparative example, after the raw meal tablets are calcined at 900 °C, the limestone in the raw material is decomposed to produce calcium oxide, which then reacts with the oxides such as alumina and silica in the Bayer process red mud to produce C,S and Ci2A7 minerals, but the yield is so small and C4AF cannot be generated.

The specific surface area of the high-iron and low-calcium portland cement prepared in this comparative example is 372 m*/kg, as shown in Table 2.

The compressive strength of the high-iron and low-calcium portland cement prepared in this comparative example after 3 days is 5.2 MPa, and the compressive strength after 28 days is 7.8 MPa, as shown in Table 2.

Table 2 shows the mineral composition of the cement clinker, the specific surface area of the high-iron and low-calcium portland cement, the compressive strength of the high-iron and low-calcium portland cement after 3 days and 28 days in different examples and the specific surface area of the high-iron and low-calcium portland cement, the compressive strength of the high-iron and low-calcium portland cement after 3 days and 28 days in different comparative examples.

15

BL-5336 Table 2 LU500915 (wt%) surface area | Strength (MPa) (nk) Comparative example 1 | - | - | - | 35 | 07 | 39 Comparative example | = | | = | 361 | 103 | 125 Comparative examples | - | | - | sm | 52 | 78 | In summary, the cement clinker in the present invention mainly uses Bayer process red mud and limestone as raw materials, and the mixing amount of Bayer process red mud is as high as 60 wt%. The utilization rate of solid wastes of the Bayer red mud is greatly improved, the pollution to environment decreases, meanwhile, the emission reduction pressure of the alumina industry is reduced.

In the production process of the cement clinker, the sintering temperature of the cement clinker is reduced by 200-350 °C compared with the sintering temperature of the traditional portland cement clinker, so that the production cost of the cement is reduced, and the emission of the polluting gases, for example, CO, and the harmful gases such as SO; and NOx is greatly reduced, the mechanical property of the finally prepared high-iron and low-calcium portland cement is slightly better than that of ordinary portland cement.

C12A7 and C4AF minerals in cement clinker after hydration provide early strength of cement, and C:S mineral after hydration provides late strength of cement, so that the early strength of the prepared cement is high, and the later strength increases continuously. 16

Claims

BL-5336 LU500915 CLAIMS

1. A preparation method of high-iron and low-calcium portland cement, characterized in that, the preparation method comprises the following steps of: Step 1: mixing Bayer process red mud and limestone uniformly, grinding into raw meal powder, and then tableting to obtain raw meal tablets, wherein the Bayer process red mud accounts for 50-60 wt% and the limestone accounts for 40-50 wt%: both Bayer process red mud and limestone include the following components: SiO), ALOs, FezO;, CaO, MgO, K»0, Na:O and TiO; the content of SiO; in the Bayer process red mud is 15-30 wt%; the content of Al,Os in the Bayer process red mud is 15-25 wt%; the content of Fe:O; in the Bayer process red mud is 15-20 wt%,; the content of CaO in the Bayer process red mud is 5-20 wt%; a content of CaO in the limestone is 45-55 wt%; Step 2: calcining and then cooling the raw meal tablets obtained in Step 1 to obtain cement clinker; the calcination temperature is 1100-1250 °C, and the calcination time is 1-2 h; Step 3: mixing uniformly the cement clinker obtained in Step 2 with gypsum and then grinding to prepare the high-iron and low-calcium portland cement; a mass ratio of the gypsum to the cement clinker is 0-20 %.

2. The preparation method of high-iron and low-calcium portland cement according to claim 1, characterized in that, raw meal power comprises the following components by mass percentage: 50-55 wt% of Bayer process red mud and 45-50 wt% of limestone.

3. The preparation method of high-iron and low-calcium portland cement according to claim 1, characterized in that, the raw meal power ground in Step 1 has a fineness of less than 75 um.

4. The preparation method of high-iron and low-calcium portland cement according to claim 1, characterized in that, the specific surface area of the high-iron and low-calcium portland cement prepared by grinding in Step 3 is 350-450 m°/kg.

5. A high-iron and low-calcium portland cement prepared by the preparation method of high-iron and low-calcium portland cement according to any one of claims 1 to 4.

6. A high-iron and low-calcium portland cement, characterized in that, 17

BL-5336 ; ; a ; ; ; .LU500915 a cement clinker in the high-iron and low-calcium portland cement comprises minerals in the following mass percentages: CS: 45-60 %, C4AF: 25-40 %, and CrzA7: 5-20 %.

7. A high-iron and low-calcium portland cement according to claim 6, characterized in that, the cement clinker comprises minerals in the following mass percentages: C:S: 50-60 %, C4AF: 30-40 %, and C12A7: 5-10 %. 18