A low-temperature preparation process for highly active calcium oxide and its products and applications

Abstract

The present invention discloses a low-temperature preparation process for highly active calcium oxide, its products and applications. Specifically, waste liquid from alkali production by ammonia-alkali method, metallurgical acid-base wastewater, cotton textile wastewater, papermaking wastewater and the like are sprayed on the surface of large-particle block limestone, and calcium carbonate is decomposed into calcium oxide under low-temperature calcination conditions. This method can prepare large-particle block calcium oxide with high activity. Among them, large-particle limestone is used as raw material, which reduces the crushing cost; industrial waste liquid is sprayed to form local defects on the hard limestone surface, improve its heat transfer and mass transfer process, thereby reducing the calcination temperature and insulation time; the obtained calcium oxide is block-shaped with large particle size, has high activity, high stability and durability, and is easy to transport and store. The preparation method of the present invention overcomes the shortcomings of lime powdering and easy overburning caused by current low-temperature calcination. The preparation method of the present invention utilizes industrial waste liquid, can be insulated at a lower temperature for a shorter time to form the target product, and is suitable for industrial application.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection and metallurgy, and in particular to a low-temperature preparation process of highly active calcium oxide and a product and application thereof. Background Art

[0002] Calcium oxide (CaO), also known as quicklime, is an important chemical raw material, widely used in steel smelting, building materials, environmental governance, desulfurization and denitrification, etc. Its main applications include clinker raw materials in cement production, desulfurizers in the steel industry, soil conditioners in agriculture, and gas purification in the field of environmental protection.

[0003] The activity of calcium oxide is closely related to the surface area of ​​its particles. A higher surface area can increase its reaction rate with other substances. Traditional calcium oxide preparation processes usually rely on high-temperature calcination processes, which usually need to be carried out at temperatures above 1000°C. Although these traditional processes can effectively produce calcium oxide, their high-temperature calcination processes are energy-intensive and polluting, and the carbon emissions during the production process have a significant impact on the environment. In addition, the activity of calcium oxide in traditional high-temperature preparation processes is often limited by higher calcination temperatures and calcination times, making it difficult to achieve low-temperature, high-efficiency, and highly active calcium oxide production.

[0004] In recent years, with the increasing requirements for environmental protection and energy conservation and emission reduction, low-temperature preparation technology has become an emerging research direction for the preparation of highly active calcium oxide. By optimizing the preparation process and reducing the preparation temperature of calcium oxide, it can not only reduce energy consumption and carbon dioxide emissions, but also effectively improve the activity of calcium oxide and broaden its application potential in various fields. However, the process of preparing calcium oxide at low temperature still faces many challenges, including the control of calcium oxide activity at low temperatures, the improvement of reaction rate and the stability of product quality.

[0005] In the current low-temperature preparation technology, although there are studies on improving the activity of calcium oxide through different physical methods, such as using different particle size control methods or optimizing calcination time, these methods are relatively limited in their effect on reducing the firing temperature and mostly rely on more traditional sintering mechanisms. How to further reduce the preparation temperature and at the same time improve the activity of calcium oxide has become a bottleneck restricting the further development of this technology. It is necessary to develop a new low-temperature preparation process to solve the shortcomings of the above-mentioned preparation method, such as high calcination temperature, high calcium oxide pulverization rate, poor ventilation in the kiln, and inconsistent calcium oxide activity, and to further improve the activity of calcium oxide. Summary of the invention

[0006] In order to solve the deficiencies in the prior art, the present invention aims to provide a low-temperature preparation process for highly active calcium oxide, its products and applications, pre-treating large-particle limestone with industrial waste liquid, forming local defects on the hard limestone surface, improving its heat and mass transfer process, and preparing active calcium oxide by low-temperature calcination, thereby preparing highly active and large-particle-size (20-60mm) blocky calcium oxide.

[0007] The present invention provides the following technical solution: a low-temperature preparation process of highly active calcium oxide, comprising the following steps: 1) Crushing limestone to obtain large-size block limestone as calcination raw material; 2) Pre-treating the calcined raw materials with industrial waste liquid, specifically using industrial waste liquid to spray on the surface of large-particle block limestone to obtain locally eroded block limestone; using industrial waste liquid spraying to form local defects on the hard limestone surface, improve its heat and mass transfer process, thereby reducing the calcination temperature and insulation time; 3) Place the locally eroded limestone blocks (which can be dried) into a high-temperature furnace and calcine at low temperature to obtain block-shaped active calcium oxide.

[0008] Preferably, in step 1), the limestone mineral is crushed into large particles, the particle size of which ranges from 20 to 60 mm.

[0009] As a preferred embodiment, the limestone mineral is crushed into large particles, and the particle size range is: 50-60mm.

[0010] As the most preferred embodiment, the limestone mineral is crushed into large particles, the particle size of which is 50 mm.

[0011] Preferably, in step 2), industrial waste liquid (ammonia-soda alkali waste liquid, metallurgical acid or alkaline waste water, cotton textile waste water, papermaking waste liquid, etc.) is evenly sprayed on the surface of large-particle-size block limestone for a spraying time of 1 min-15 min; Before low-temperature calcination in step (3), the locally corroded limestone block is dried for 0-1 hour.

[0012] In step 3), during low temperature calcination, Place the locally eroded block limestone into a high temperature furnace preheated to 600-800℃ and keep it at 930-980℃ for 0.5-1.5h. Or put it into a high temperature furnace and heat it to 980-1000℃ for 1-5h. After that, it is rapidly cooled in the air to obtain block-shaped active calcium oxide.

[0013] The block active calcium oxide has a content of 92-99%, a particle size of 20-60 mm, and an activity of 380-440 mL.

[0014] The second purpose of the present invention is to provide a high-activity calcium oxide low-temperature preparation process (i.e., pre-treating various industrial waste liquids and calcining raw materials) to prepare high-activity calcium oxide. The industrial waste liquid pretreatment process is simple and only requires the addition of a simple injection device. The rest is the same as the original process, and the economic benefits are significant.

[0015] Another object of the present invention is to provide an application of the aforementioned highly active calcium oxide in metallurgical lime.

[0016] A high-activity metallurgical lime comprises high-activity calcium oxide, so that the metallurgical lime has high activity and is substantially free of pulverization.

[0017] In operation, the present invention pre-treats large-particle limestone with common industrial waste liquid and adopts appropriate calcination conditions to reduce its calcination temperature and insulation time to obtain block-shaped active calcium oxide. The preparation process is simple and has greater industrial production value than the traditional single-temperature high-temperature solid-phase method, overcoming the shortcomings of the high-temperature solid-phase method of too high temperature and too much insulation time.

[0018] The preparation method of the present invention can form the target product after heat preservation at a relatively low temperature (930-1000°C), and is suitable for industrial application. The prepared block active calcium oxide can also be used to obtain metallurgical lime with higher activity and more active calcium oxide content by adjusting the pretreatment time of industrial waste liquid and calcination conditions. Among them, the block active calcium oxide is basically not pulverized, has a very low pulverization rate and very high stability and durability, and is more conducive to calcination operation in the kiln, long-distance transportation and long-term storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the XRD pattern of the sample obtained by low temperature calcination in Example 1 of the present invention; Figure 2 This is the XRD diagram of the active calcium oxide prepared by the method of Comparative Example 1 of the present invention after being placed for 15 days. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with specific embodiments and drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0021] Example 1 A low-temperature preparation process of highly active calcium oxide comprises the following steps: 1) The limestone mineral is initially crushed to obtain large-sized block limestone with a particle size range of 50-60mm; 2) Spray the waste liquid from the ammonia-soda process evenly on the surface of the large-particle limestone blocks in step 1) for 12 minutes.

[0022] 3) Dry the limestone blocks pretreated in step 2) for 0.6h. 4) The dried limestone block in step 3) is added into a high-temperature furnace preheated to 750°C and kept at 980°C for 1 hour, and then rapidly cooled in air to obtain block active calcium oxide.

[0023] Example 2 A low-temperature preparation process of highly active calcium oxide comprises the following steps: 1) The limestone mineral is initially crushed to obtain large-sized block limestone with a particle size of 50 mm; 2) Evenly spray the metallurgical alkaline wastewater (i.e., alkaline wastewater discharged during the metallurgical process) on the surface of the large-particle limestone blocks in step 1) for 15 minutes.

[0024] 3) Dry the limestone blocks pretreated in step 2) for 1 hour. 4) The dried limestone blocks in step 3) are added into a high-temperature furnace preheated to 600°C and kept at 970°C for 1.5 hours, and then rapidly cooled in air to obtain block active calcium oxide.

[0025] Example 3 A low-temperature preparation process of highly active calcium oxide comprises the following steps: 1) The limestone mineral is initially crushed to obtain large-sized block limestone with a particle size range of 20-40mm; 2) Spray the metallurgical acid wastewater evenly on the surface of the large-particle limestone blocks in step 1) for 1 minute.

[0026] 3) Dry the limestone blocks pretreated in step 2) for 0.7h. 4) The dried limestone blocks in step 3) are added into a high-temperature furnace preheated to 750°C and kept at 930°C for 1.5 hours, and rapidly cooled in air to obtain block active calcium oxide.

[0027] Example 4 A low-temperature preparation process of highly active calcium oxide comprises the following steps: 1) The limestone mineral is initially crushed to obtain large-sized block limestone with a particle size range of 50-60mm; 2) Spray the cotton textile wastewater (i.e., wastewater discharged during the preparation of cotton textiles) evenly on the surface of the large-particle block limestone in step 1) for 8 minutes; 3) Dry the limestone blocks pretreated in step 2) for 0.1 h; 4) The dried limestone blocks in step 3) are placed in a high temperature furnace and kept at 1000° C. for 4 hours, and then rapidly cooled in air to obtain block active calcium oxide.

[0028] Example 5 A low-temperature preparation process of highly active calcium oxide comprises the following steps: 1) The limestone mineral is initially crushed to obtain large-sized block limestone with a particle size range of 50-60mm; 2) Spray the papermaking waste liquid evenly on the surface of the large-sized limestone blocks in step 1) for 14 minutes; 3) The limestone block in step 2) is kept at 1000°C for 5 hours, and then rapidly cooled in air to obtain block active calcium oxide.

[0029] Performance and testing are as follows: Taking Example 1 as an example, the pretreatment low temperature calcination method in Example 1 prepared the active calcium oxide with large particle size, and the obtained XRD pattern is as follows: Figure 1 The sample in the figure is the sample prepared in Example 1, and the standard is the CaO standard spectrum. By comparing with the standard spectrum card PDF 48-1467, it can be found that the peak shape of the sample is completely consistent with the standard spectrum, and there is no stray peak, indicating that the pre-etching low-temperature calcination method successfully prepared the calcium oxide sample, and no stray images were generated, with a high degree of crystallinity.

[0030] The chemical titration method with sucrose was used to test the active calcium oxide content and the activity of samples 1 to 5 corresponding to Examples 1 to 5, respectively. In order to test the durability of the sample performance, the performance of the samples after being placed for a certain period of time was also tested. The specific parameter values ​​are shown in Table 1.

[0031] Table 1: As can be seen from the figure, the active calcium oxide content of the several samples shown in the embodiment is relatively high (greater than 92%), and the activity determined by the hydrochloric acid titration when using hydrochloric acid titration is also greater than 400mL; and after being placed for 15 days, the active calcium oxide content and activity are basically unchanged, indicating that the method described in the present invention can obtain high-quality active calcium oxide. In summary, using limestone as raw material, after pre-spraying with industrial waste liquid, low-temperature calcination method is used to prepare large-particle active calcium oxide, which can be used as an active lime in construction, metallurgy, environmental protection and other industries.

[0032] The invention obtains active calcium oxide with large particle size, low pulverization rate and high activity at a relatively low temperature. Compared with the previous production experience, the limestone raw material with large particle size is obtained through preliminary crushing, is easy to obtain and easy to transport over long distances. The surface of the calcined raw material is pretreated with industrial waste liquid such as ammonia-alkali process alkali waste liquid, metallurgical acid or alkaline waste water, cotton textile waste water, papermaking waste liquid, etc., so as to form a porous limestone structure at the microscopic level, improve the heat transfer efficiency, provide a channel for CO2 mass transfer during limestone decomposition, and avoid lime pulverization. The potassium, sodium, magnesium and other ions in the industrial waste liquid can be used as auxiliary solvents to reduce the decomposition temperature of the limestone. At the same time, the potassium, sodium, and magnesium ions can be used as doping elements to change the crystal structure of the calcium oxide, reduce its lattice energy, thereby improving its activity, and decompose calcium carbonate into highly active calcium oxide under low-temperature calcination conditions.

[0033] Comparative Example 1 A method for preparing active calcium oxide by low-temperature calcination comprises the following steps: 1) Preliminary crushing of limestone minerals to obtain large-sized block limestone with a particle size range of 50-60 mm as the reaction raw material; 2) Put the lump limestone raw material obtained in step 1) into a high-temperature furnace, calcine at low temperature, heat it to 1000°C and keep it for 5 hours, and rapidly cool it in the air to obtain lump active calcium oxide.

[0034] The performance and tests are as follows: In comparative example 1, steps 2)-4 in example 1 are missing. The bulk limestone raw material is not pretreated with industrial waste liquid, and no erosion occurs. In step 2), the low-temperature calcination process of active calcium oxide is not a preheating low-temperature method, but directly heated to 1000°C and kept warm for 4 hours, which is different from example 1. When the sample was taken out of the high-temperature furnace, it was found that there were a lot of fine powders in it, indicating that the sample was pulverized. The performance of the comparative sample was measured by chemical titration. The active calcium content was 89.1% in 1 day and 80.4% in 15 days, indicating that after being placed for a period of time, the performance of the sample was unstable and the durability was low. Figure 2 This is the XRD pattern of the active calcium oxide prepared by the method of comparative example 1 of the present invention after being placed for 15 days. In the figure, the reference substance is the powder obtained after calcination in comparative example 1, and the standard substance is the standard spectrum of calcium oxide. By comparing with the standard spectrum card PDF 48-1467, it can be found that the peak shape of the reference substance has many more peaks than the standard spectrum. After analysis, it can be known that in addition to calcium oxide, another substance formed in comparative example 1 is calcium hydroxide (Ca(OH)2), which means that the sample has undergone hydration reaction after being placed for 1 day, which is not conducive to long-distance transportation and long-term storage.

[0035] The low-temperature calcination method of pre-eroded limestone of the present invention is used to prepare large-particle active calcium oxide, and the method can successfully prepare high-quality active calcium oxide without impurities. The preparation method of the present invention overcomes the disadvantages of the high-temperature solid phase method that the decomposition temperature is too high and the time is too long. The preparation method of the present invention can form the target product at a lower temperature (for example, 960°C) and a shorter insulation time (0.5h), and has high durability, and is suitable for industrial application.

[0036] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A low-temperature preparation process for highly active calcium oxide, characterized in that: The following steps are involved: 1) After crushing limestone, large-sized block limestone is obtained as calcination raw material; 2) Pre-treating the raw materials with industrial waste liquid to obtain locally eroded block limestone; 3) Place the locally eroded limestone blocks into a high-temperature furnace and calcine at low temperature to obtain block-shaped active calcium oxide.

2. The low-temperature preparation process of highly active calcium oxide according to claim 1, characterized in that: In step 1), the large-sized block limestone has a particle size range of 20-60 mm.

3. The low-temperature preparation process of highly active calcium oxide according to claim 1, characterized in that: In step 2), the industrial waste liquid is evenly sprayed on the surface of large-size block limestone, and the spraying time is 1 min-15 min.

4. The low-temperature preparation process of highly active calcium oxide according to claim 2, characterized in that: The industrial waste liquid is ammonia-alkali process alkali waste liquid, metallurgical acid or alkaline waste water, cotton textile waste water or papermaking waste liquid.

5. The low-temperature preparation process of highly active calcium oxide according to claim 1, characterized in that: In step 3), the locally corroded limestone block is dried for 0-1h before low-temperature calcination.

6. The low-temperature preparation process of highly active calcium oxide according to claim 1, characterized in that: In step 3), during low-temperature calcination, the partially corroded block limestone is added to a high-temperature furnace preheated to 600-800°C and kept at 930-980°C for 0.5-1.5h, or directly added to a high-temperature furnace and heated to 980-1000°C and kept for 1-5h, and then rapidly cooled in air to obtain block active calcium oxide.

7. The low-temperature preparation process of highly active calcium oxide according to claim 1, characterized in that: The content of the block active calcium oxide: 92-99%; Particle size: 20-60mm; activity: 380-440mL.

8. A highly active calcium oxide prepared by the low-temperature preparation process for highly active calcium oxide according to any one of claims 1 to 7.

9. Use of the highly active calcium oxide according to claim 8 in highly active metallurgical lime.

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