Wollastonite-ferrosilite crystalline phase microcrystalline ceramic and method for its production

Abstract

The application provides a wollastonite-ferroaugite crystal phase microcrystalline ceramic and a preparation method thereof, which can include the following steps: uniformly mixing copper tailings sulfur extraction iron tailings pretreatment with auxiliary material powder to obtain a green body powder; sieving the granulated powder in a rotary pan granulator to obtain a granular base material; drying the granular base material in a fluidized bed to a water content of 6-8%, sealing and aging to obtain a granular material; loading the granular material into a mold for compression molding to obtain a microcrystalline ceramic body; and coating the microcrystalline ceramic body with glaze, sintering and post-processing to obtain the microcrystalline ceramic. The microcrystalline ceramic comprises a wollastonite-ferroaugite composite crystal phase, has a bulk density of 2.3-2.8 g / cm 3 , a water absorption of 5.2-7.3%, and a compressive strength of 31-62 MPa. The process flow is short and has low environmental hazards. The copper tailings sulfur extraction iron tailings can be completely utilized, and no residual material is generated, which greatly solves the problem of tailings accumulation. The microcrystalline ceramic obtained has a very low iron content and is suitable for many fields such as building decoration, roads and squares.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solid waste treatment and resource utilization, in particular to a wollastonite-ferrohedenbergite crystal phase microcrystalline ceramic prepared from copper tailings sulfur extraction iron tailings and a preparation method thereof. BACKGROUND

[0002] It is estimated that about 400 tons of copper tailings are discharged for every ton of copper produced. Copper tailings sulfur extraction iron tailings are waste residues produced after copper tailings are subjected to oxidation roasting, sulfur release and recovery, magnetic separation and other treatments, and belong to a kind of solid waste. The accumulation of a large amount of waste residues not only occupies land resources, but also can cause harm to the environment, and also causes waste of resources. Using copper tailings sulfur extraction iron tailings as raw materials for preparing microcrystalline ceramic, the obtained microcrystalline ceramic can be used for building decoration, which has important practical significance for the resource utilization of copper tailings sulfur extraction iron tailings and environmental protection.

[0003] Since the early 1960s, Russia has begun to use various methods to produce high-value microcrystalline glass, including melt-sintering and sinter-crystallization. The melt-sintering method refers to melting the ground materials in a furnace, placing them in a mold, and annealing in sequence. The sinter-crystallization method refers to adding various materials to additives, and then going through melting, water quenching, grinding, pressing and heat treatment. Regardless of which method is used, in the process of making mother glass, the raw materials need to be melted at high temperature (above 1300℃), which has high energy consumption. At the same time, the process flow is long and the cost is high. Therefore, how to reduce the process temperature, reduce the production cost and shorten the process route has become the primary consideration for the preparation of microcrystalline glass.

[0004] The microcrystalline glass directly prepared using copper tailings with high iron content as raw materials has problems such as deep color, high brittleness, low application value, and is not suitable for building decoration, etc. At the same time, the iron resources are not recycled, causing waste of resources. Therefore, it is of great significance to develop an environmentally friendly, low-cost and simple process for preparing microcrystalline ceramic. SUMMARY

[0005] The present application aims to solve at least one of the above-mentioned deficiencies in the prior art. For example, one of the purposes of the present application is to provide a resource utilization approach for copper tailings sulfur extraction iron tailings, the second purpose of the present application is to provide a one-step method for directly sintering microcrystalline ceramic, and the third purpose of the present application is to provide a microcrystalline ceramic.

[0006] In order to achieve the above-mentioned purposes, the present application provides a method for preparing microcrystalline ceramic from copper tailings sulfur extraction iron tailings.

[0007] The method can comprise the steps of: uniformly mixing the main material powder and the auxiliary material powder to obtain a blank-making powder; wherein the main material powder is obtained by grinding a copper tailings sulfur extraction iron tailings, and the mass percentage of the main material powder in the blank-making powder is more than 85%; placing the blank-making powder in a rotating round pan granulator, and spraying polyvinyl alcohol aqueous solution at the same time, screening after the granulation process is completed to obtain a granular base material with a qualified particle size; sending the granular base material with a qualified particle size into a fluidized bed dryer, drying to a water content of 6-8%, and sealing and aging for more than 24 hours to obtain a qualified granular material; loading the qualified granular material into a mold for compression molding to obtain a microcrystalline ceramic body; and performing glazing, sintering, cooling and post-processing on the microcrystalline ceramic body to obtain the microcrystalline ceramic.

[0008] Alternatively, the copper tailings sulfur extraction iron tailings can comprise industrial solid waste generated after oxidizing roasting, sulfur release and recovery, and magnetic separation of copper tailings, and contain the following components in terms of mass percentage: 20%-60.12% SiO2, 2.13%-7.82% CaO, 8.09%-12.01% Fe2O3, 3.15%-8.12% MgO, 4.25%-10% Al2O3, 3.56%-5.23% Na2O and 2.48%-5.11% K2O.

[0009] The grinding obtains a powder with a particle size of less than 0.074 mm.

[0010] The uniform mixing refers to placing the main material powder and the auxiliary material powder in a ball mill for 10-30 min to obtain uniformly mixed blank-making powder.

[0011] The screening of the blank-making powder particles can control the particle size of the blank-making particles to be 0.25-0.85 mm.

[0012] The drying of the blank-making powder particles can control the water content of the blank-making particles to be 6-8%.

[0013] The sealing and aging time is controlled to be more than 24 hours.

[0014] Alternatively, the auxiliary material can comprise at least one of quicklime powder, carbide slag powder, quartz powder, feldspar powder, shale powder and clay powder; the mass percentage of each auxiliary material is as follows: 0-10% of quicklime powder, 0-8% of carbide slag, 0-10% of quartz powder, 0-8% of feldspar powder, 0-15% of shale powder and 0-5% of clay powder, and the particle size of the auxiliary material powder is less than 0.074 mm.

[0015] Alternatively, the granulation can adopt a dry granulation method, and polyvinyl alcohol solution is added as a binder during the granulation process; the mass percentage concentration of the polyvinyl alcohol aqueous solution is 3%-8%, and the mass ratio of the polyvinyl alcohol solution to the blank-making powder can be 5-10:90-95.

[0016] Optionally, the pressure of the compression molding can be 22-45 MPa, and the pressure holding time can be 15-20 s.

[0017] Optionally, the sintering uses a tunnel kiln or a roller kiln, the sintering temperature can be 1080-1250℃, and the sintering time can be 30-90 min.

[0018] Optionally, after the cooling, the method can further include polishing and trimming.

[0019] Another aspect of the present application provides a microcrystalline ceramic.

[0020] The microcrystalline ceramic can be prepared by the method described above.

[0021] Optionally, the phases of the microcrystalline glass include wollastonite and ferrosilite.

[0022] Optionally, the microcrystalline ceramic has a bulk density of 2.3-2.8 g / cm 3 , a water absorption of 5.2-7.3%, and a compressive strength of 31-62 MPa.

[0023] Compared with the prior art, the present application can have at least one of the following beneficial effects:

[0024] 1) The process flow of the present application is short, no additional auxiliary agent or volatile chemical additive needs to be added in the preparation process, the cost is low, and the environmental hazard is small.

[0025] 2) The present application can realize the overall resource utilization of the copper tailings sulfur extraction iron tailings, and provides a technical approach to solve the accumulation and resource utilization of copper tailings.

[0026] 3) The microcrystalline ceramic obtained by the present application has no radioactive hazard and is suitable for many fields such as building decoration, road square, etc. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings and the description of the embodiments, similar elements in different embodiments are labeled with similar numerals.

[0028] Figure 1 FIG. 2 shows the X-ray diffraction pattern of the microcrystalline ceramic sample in Example 2;

[0029] Figure 2A FIG. 4 shows the scanning electron microscope image of the microcrystalline ceramic sample in Example 2;

[0030] Figure 2B FIG. 6 shows the EDS spectrum of the microcrystalline ceramic sample in Example 2. DETAILED DESCRIPTION

[0031] Hereinafter, the present application will be described in detail with reference to exemplary embodiments and accompanying drawings, but the following embodiments are only for the purpose of helping to understand the technology of the present application, and should not be further limited to the scope of protection of the present application.

[0032] Example 1

[0033] The present exemplary embodiment provides a preparation method of copper tailings sulfur extraction iron tailings slag microcrystalline ceramic.

[0034] The method can include the following steps:

[0035] S01: uniformly mix the main material powder and the auxiliary material powder to obtain a green body powder.

[0036] In the present embodiment, the main material powder is obtained after the copper tailings sulfur extraction iron tailings slag is pretreated, and the mass percentage of the main material powder and the auxiliary material powder can be 85-100%:0-15%, such as 85:15, 89:11, 90:10, 95:5, etc.

[0037] The copper tailings sulfur extraction iron tailings slag can include industrial solid waste generated after the copper tailings are oxidized and roasted, sulfur is released and recovered, and magnetic separation.

[0038] The copper tailings sulfur extraction iron tailings slag can also contain the following ingredients in terms of mass percentage:

[0039] 20%-60.12% SiO2, such as 20.01%, 26.11%, 30.18%, 41%, 50.12%, 60.11%, etc.

[0040] 2.13%-7.82% CaO, such as 2.14%, 3.64%, 4.68%, 6.12%, 7.81%, etc.

[0041] 8.09%-12.01% Fe2O3, such as 8.10%, 9.09%, 10.68%, 11.09%, 11.36%, 12.00%, etc.

[0042] 3.15%-8.12% MgO, such as 3.16%, 4.35%, 5.95%, 7.15%, 8.11%, etc.

[0043] 4.25%-10% Al2O3, such as 4.26%, 6.28%, 7.01%, 8.26%, 9.99%, etc.

[0044] 3.56%-5.23% Na2O, such as 3.57%, 3.95%, 4.51%, 5.22%, etc.

[0045] 2.48-5.11% K2O, such as 2.49%, 3.29%, 4.16%, 5.10%, etc.

[0046] Further, the particle size of the copper ore dressing tailings sulfur-iron tailings can be 0.075mm-0.15mm.

[0047] Further, the main material powder obtained after grinding the raw material can have a particle size of 0.040-0.074mm, which is conducive to the subsequent powder agglomeration and the increase of sintering driving force; the main material powder obtained by screening is mixed with the auxiliary material powder in a certain proportion to form the green body powder.

[0048] The auxiliary material includes at least one of quicklime powder, carbide slag powder, quartz powder, feldspar powder, shale powder, and clay powder; the particle size range is 0.040-0.074mm, which can be obtained from industrial production; the amount of each auxiliary material added accounts for 0-10% of the total green body powder, 0-8% of the total green body powder, 0-10% of the total green body powder, 0-8% of the total green body powder, 0-15% of the total green body powder, and 0-5% of the total green body powder.

[0049] Further, the mixing uniformly refers to placing the main material powder and the auxiliary material powder in a ball mill for 10-30min to obtain the mixed green body powder. The obtained green body powder has a particle size of 0.040-0.074mm, such as 0.043mm, 0.052mm, 0.055mm, 0.061mm, etc.

[0050] S02: The green body powder is granulated, dried, and sealed to obtain qualified granular material.

[0051] In this embodiment, the granulation is dry granulation, the green body powder is placed in a running granulator, and a polyvinyl alcohol aqueous solution with a mass percentage concentration of 3%-8% is sprayed to perform granulation, such as 4%, 5%, and 6%, etc.; the mass ratio of the polyvinyl alcohol solution to the green body powder is 5-10:90-95, such as 6:94, 8:92, 9:91, etc.; after the granulation process is completed, the granular base material with a particle size of 0.25mm-0.85mm is screened, dried, sealed, and aged to obtain qualified granular material; for example, the particle size of the screened granules can be 0.26mm, 0.45mm, 0.56mm, 0.75mm, 0.84mm, etc.; the purpose of selecting granules with this range of particle sizes is to ensure that the granules are evenly distributed on the mold during the mold pressing process, so as to ensure the internal uniformity of the green body and facilitate subsequent uniform sintering. The screened granules are dried to a water content of 6-8%, such as 6.1%, 7%, 7.9%, etc., to avoid excessive water content causing the green body to be difficult to form or difficult to demold.

[0052] The dry granules are dried by a fluidized bed dryer, and the temperature is controlled at 145-185℃, for example, 146℃, 155℃, 160℃, 172℃, 184℃, etc. The temperature range has the advantage of vaporizing and escaping the moisture in the granules, and the drying heat source is the tail gas of the sintering kiln to reduce the granulation cost. In order to ensure the moisture of the qualified granules more uniform, the granulated granules can be optionally sealed and aged for more than 24h, for example, 25h, 27h, etc.

[0053] S03: The qualified granules are molded to obtain the microcrystalline ceramic body.

[0054] The obtained qualified granules are loaded into a mold for molding to obtain the microcrystalline ceramic body. The molding pressure is 22-45MPa, for example, 23MPa, 28MPa, 30MPa, 38MPa, 44MPa, etc. The pressure range can ensure the normal molding of the ceramic body and save energy consumption and improve production efficiency. The pressure holding time is 15-20s, for example, 16s, 18s, 19s, etc. The pressure holding time range is beneficial to effective molding and demolding and improves work efficiency. At the same time, attention should be paid to ensure that the stress of each part of the body is uniform.

[0055] S04: The microcrystalline ceramic body is glazed, sintered, and cooled and post-processed to obtain the microcrystalline ceramic.

[0056] In the embodiment, the sintering is performed by a tunnel kiln or a roller kiln. The sintering temperature is 1080-1250℃, and the sintering time is 30-90min. If the sintering temperature is too low, the sintering is incomplete, the compactness is poor, the bulk density is small, the porosity is high, and the bending strength is poor. If the sintering temperature is too high, the sample surface will appear pores, internal bubbles, and uneven surface, which will affect the performance of the sample and the actual application of the product. At the same time, the high temperature will increase the energy consumption. If the holding time is too short, the sample sintering is incomplete, and the product performance is poor. If the holding time is too long, although the sintering is promoted, the promoting effect is not obvious. From the green environmental protection point of view, the long holding time will increase the sintering energy consumption, which is not conducive to green environmental protection. From the economic point of view, the long holding time will increase the fuel consumption and reduce the production efficiency, which is not in line with green economy. Further, the sintering temperature is 1080-1250℃, for example, 1081℃, 1120℃, 1180℃, 1201℃, 1030℃, 1249℃, etc. The sintering time is 30-90min, for example, 31min, 48min, 55min, 70min, 89min, etc.

[0057] In the embodiment, the cooling can include air cooling.

[0058] In the embodiment, the post-cooling treatment can further include polishing and trimming.

[0059] Example 2

[0060] The present example embodiment provides a microcrystalline ceramic.

[0061] The microcrystalline ceramic is prepared by the method of the above example embodiment 1. The main crystal phases of the microcrystalline ceramic product include wollastonite and ferrosilite, as shown in Figure 1 The CaO content of the products corresponding to the BZ-0wt.%, BZ-5wt.% and BZ-10wt.% curves is 0%, 5% and 10% respectively, and the main crystal phases of the products are wollastonite and ferrosilite. With the increase of CaO content, the content of wollastonite also gradually increases.

[0062] The microcrystalline ceramic product prepared by the method of the above example embodiment 1 gradually becomes dense inside with the increase of CaO content, which is consistent with the change rule of the porosity in the process of dense sintering.

[0063] Figure 2A The scanning electron microscope image of the ceramic product can be seen from Figure 2A It can be seen that a large number of crystals are produced in the non-porous area at a sintering temperature of 1100°C; Figure 2B The EDS spectrum of the ceramic product can be seen from Figure 2B It can be seen that the crystal phase mainly contains Fe, Al, Mg, Si, O and Ca elements, combined with Figure 1 The X-ray diffraction pattern of the microcrystalline ceramic sample can be seen that the crystal phase of the ceramic product is composed of wollastonite, ferrosilite and other phases.

[0064] The microcrystalline ceramic product prepared by the method of the above example embodiment 1 has excellent performance. The performance indicators include: the bulk density is 2.3-2.8g / cm 3 , such as 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , etc.; the water absorption is 5.2-7.3%, such as 5.3%, 6.1%, 6.8%, 7.0%, 7.2%, etc.; the compressive strength is 31-62Mpa, such as 32Mpa, 42Mpa, 49Mpa, 56Mpa, 61Mpa, etc.

[0065] In order to better understand the above example embodiment 1, the following will further illustrate it with specific examples.

[0066] Example 1

[0067] S01: Mix the main material powder and the auxiliary material uniformly to obtain a green body powder;

[0068] The main chemical components of the copper tailings sulfur extraction iron tailings in mass percent are 55.12% SiO2, 7.37% CaO, 11.95% Fe2O3, 7.23% MgO, 9.32% Al2O3, 4.12% Na2O and 4.68% K2O, etc.

[0069] The main material is ground into a powder of 0.053mm-0.065mm. The auxiliary material, lime powder, has a particle size of 0.052-0.074mm. The mass ratio of the main material powder to the auxiliary material powder is 85:15, and the particle size of the obtained green body powder is 0.043-0.072mm.

[0070] S02: The green body powder is granulated, dried and aged to obtain qualified granular material;

[0071] A dry granulation method is used, and a polyvinyl alcohol solution is added as a binder during the granulation process. The mass ratio of the polyvinyl alcohol solution to the green body powder is 7:93. The particle size of the obtained granular base material can be 0.32mm-0.79mm.

[0072] A fluidized bed dryer with a temperature of 150°C is used to dry the granules, and the heat source is the tail gas of the firing kiln. The sealing aging time is 24h, and the qualified granular material is obtained.

[0073] S03: The qualified granular material is molded into a microcrystalline ceramic body;

[0074] The green body forming pressure is 40MPa, and the pressure holding time is 18s, to ensure that the stress is evenly distributed in all parts of the body.

[0075] S04: The body is glazed, sintered, cooled and post-treated to obtain a microcrystalline ceramic;

[0076] The sintering is carried out in a tunnel kiln or a roller kiln, and the sintering temperature is 1150°C. The sintering time is 65min. Then, the microcrystalline ceramic is obtained by natural cooling to room temperature.

[0077] Through testing, the water absorption rate of the microcrystalline ceramic sample obtained by the method of Example 1 is 7.15%, the linear shrinkage rate is 3.56%, the bulk density is 2.30%, and the bending strength reaches 54MPa.

[0078] Example 2

[0079] S01: The main material powder is mixed with the auxiliary material to obtain a green body powder;

[0080] The main chemical components of the copper tailings sulfur extraction iron tailings in mass percent can be 60.07% SiO, 6.85% CaO, 11.42% Fe2O3, 7.18% MgO, 4.22% Al2O3, 5.18% Na2O and 4.98% K2O, etc.

[0081] The main material is ground into a powder of 0.057mm-0.067mm. The auxiliary material, lime powder, has a particle size of 0.052-0.074mm. The mass percentage of the main material powder to the auxiliary material powder is 90:10. The particle size of the obtained green material powder is 0.049-0.068mm.

[0082] S02: The green material powder is granulated, dried, and aged to obtain qualified granular material;

[0083] The dry granulation method is used, and a polyvinyl alcohol aqueous solution is added as a binder during the granulation process. The mass ratio of the polyvinyl alcohol aqueous solution to the green material powder is 9:91. The particle size of the obtained granular base material can be 0.34mm-0.82mm.

[0084] The granular material is dried using a fluidized bed dryer with a temperature of 175℃, and the heat source is the tail gas of the firing kiln. The sealing aging time is 24h, and the qualified granular material is obtained.

[0085] S03: The qualified granular material is molded to obtain a microcrystalline ceramic body;

[0086] The green body forming pressure is 42MPa, and the pressure holding time is 19s, which ensures that the stress is uniformly distributed in each part of the body.

[0087] S04: The body is glazed, sintered, cooled, and post-processed to obtain a microcrystalline ceramic;

[0088] The sintering is performed using a tunnel kiln or a roller kiln, and the sintering temperature is 1200℃. The sintering time is 80min. Subsequently, the microcrystalline ceramic is obtained by natural cooling to room temperature.

[0089] According to tests, the water absorption rate of the microcrystalline ceramic sample obtained by the method of Example 2 is 5.95%, the linear shrinkage rate is 6.58%, the bulk density is 3.03%, and the bending strength reaches 58MPa.

[0090] Although the present application has been described above by combining the embodiments, it should be clear to those skilled in the art that various modifications and changes can be made to the embodiments of the present application without departing from the spirit and scope defined by the claims.

Claims

1. A method for preparing microcrystalline ceramics from copper tailings sulfur extraction and iron tailings slag, characterized in that, The microcrystalline ceramic mainly comprises wollastonite and pyroxene, and the method includes the following steps: The main powder and auxiliary powder are mixed evenly to obtain the billet powder; wherein, the main powder is obtained by grinding the copper tailings sulfur extraction and iron tailings slag, and the main powder accounts for more than 85% of the mass of the billet powder. The preformed powder is placed in a rotating circular pot granulator, and polyvinyl alcohol aqueous solution is sprayed in at the same time. After the granulation process is completed, it is sieved to obtain granular base material with qualified particle size. The qualified particle size base material is fed into a fluidized bed dryer and dried to a moisture content of 6-8%. It is then sealed and aged to obtain qualified granular material. Qualified granular materials are loaded into a mold and pressed into shape to obtain a microcrystalline ceramic green body; The microcrystalline ceramic preform is glazed, sintered, cooled, and post-treated to obtain the microcrystalline ceramic. The granulation is carried out using a dry granulation method. During the granulation process, a polyvinyl alcohol aqueous solution is added as a binder. The mass ratio of the polyvinyl alcohol aqueous solution to the preform powder is 5-10:95-90. The mass percentage concentration of the polyvinyl alcohol aqueous solution is 3%-8%. The particle size of the obtained qualified particle base material is 0.25mm-0.85mm. The drying and aging process includes: drying the granular base material with a particle size of 0.25 mm to 0.85 mm obtained by granulation in a fluidized bed dryer until the moisture content is 6 to 8%, and aging it in a sealed container for more than 24 hours to obtain qualified granular material; The microcrystalline ceramic has a bulk density of 2.3–2.8 g / cm³. 3 It has a water absorption rate of 5.2-7.3% and a compressive strength of 31-62 MPa.

2. The method for preparing microcrystalline ceramics from copper tailings sulfur extraction and iron tailings slag according to claim 1, characterized in that, The copper tailings sulfur extraction and iron ore beneficiation tailings include: industrial solid waste generated after oxidative roasting, sulfur release and tail gas recovery of copper tailings and magnetic separation of iron concentrate, and contains the following components by mass percentage: 20%–60.12% SiO2, 2.13%–7.82% CaO, 8.09%–12.01% Fe2O3, 3.15%–8.12% MgO, 4.25%–10% Al2O3, 3.56%–5.23% Na2O and 2.48%–5.11% K2O.

3. The method for preparing microcrystalline ceramics from copper tailings sulfur extraction and iron tailings according to claim 1, characterized in that, The process of uniform mixing involves placing the main powder and the auxiliary powder in a ball mill and ball milling for 10 to 30 minutes to obtain the uniformly mixed preform powder.

4. The method for preparing microcrystalline ceramics from copper tailings sulfur extraction and iron tailings slag according to claim 1, characterized in that, The particle size of the blank powder obtained by grinding is less than 0.074 mm.

5. The method for preparing microcrystalline ceramics from copper tailings sulfur extraction and iron tailings slag according to claim 1, characterized in that, The auxiliary materials include at least one of the following: quicklime powder, carbide slag powder, quartz powder, feldspar powder, shale powder, and clay powder; the mass percentage of each auxiliary material is: quicklime powder 0-10%, carbide slag powder 0-8%, quartz powder 0-10%, feldspar powder 0-8%, shale powder 0-15%, and clay powder 0-5%; the particle size of the auxiliary material powder is less than 0.074 mm.

6. The method for preparing microcrystalline ceramics from copper tailings sulfur extraction and iron tailings slag according to claim 1, characterized in that, The pressing pressure is 22-45 MPa, and the holding time is 15-20 s.

7. The method for preparing microcrystalline ceramics from copper tailings sulfur extraction and iron tailings slag according to claim 1, characterized in that, The sintering is carried out in a tunnel kiln or roller kiln, with a sintering temperature of 1080℃~1250℃ and a sintering time of 30min~90min.

8. A microcrystalline ceramic, characterized in that, The microcrystalline ceramic, prepared by the method according to any one of claims 1-7, comprises a wollastonite-calcium iron pyroxene composite crystalline phase and has a bulk density of 2.3–2.8 g / cm³. 3 It has a water absorption rate of 5.2-7.3% and a compressive strength of 31-62 MPa.

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