A method for preparing quicklime by using monocyamide slag as main raw material

Abstract

The application discloses a method for preparing quicklime by using monocyamide slag as a main raw material. The method comprises the following steps: uniformly mixing the monocyamide slag, building material crushing material, fly ash and an activator to obtain a mixture; and calcining the mixture at 600-900 DEG C to obtain the quicklime. The application uses the monocyamide slag as the main raw material, cooperates with other solid waste materials, and adds the activator for mixing, and then prepares the quicklime meeting the performance requirements of the building material industry standard JC / T 621-2021 "Quicklime for Silicate Building Products" II level through a specific calcining process. Meanwhile, the application significantly improves the product qualification rate and yield, and improves the product performance stability. The method can utilize the monocyamide slag at high added value, changes the waste into treasure, provides an economic and effective way for the reuse of the monocyamide slag and the preparation of the quicklime, and solves the environmental protection problems caused by the solid waste accumulation and excessive exploitation of natural resources.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial solid waste recycling, and particularly relates to a method for preparing quicklime by using monocyannamide slag as a main raw material. BACKGROUND

[0002] The monocyannamide slag is a waste slag generated in the production of monocyannamide products and is obtained by vacuum filtration. At present, there is no higher value utilization way, and the basic disposal measures are landfill, incineration and the like, but the above ways all bring certain pollution to the soil and the environment. According to statistics, the annual production amount of the monocyannamide slag is about 160,000 tons or so, and if not handled in time, it will seriously affect the ecological environment. At present, the research on the recycling of the monocyannamide slag is mainly concentrated in the aspect of being used as a raw material for preparing ceramics.

[0003] The quicklime, also called burned lime, is mainly composed of calcium oxide (CaO) and generally has a block shape. The pure quicklime is white, and the quicklime containing impurities is light gray or light yellow. The quicklime is widely used as a building material and is also an important raw material for many industries. The quicklime can be used to manufacture calcium carbide, soda ash, bleaching powder and the like, and can also be used as a filler, an analytical reagent, a metallurgical fluxing agent, a cement accelerator, a fluxing agent for fluorescent powder, a refractory material, a drying agent and the like. The preparation method of the quicklime is generally to calcine the natural rock mainly composed of calcium carbonate at high temperature, so that the calcium carbonate is decomposed to generate carbon dioxide and calcium oxide. However, this way can cause the problem of overexploitation of natural resources (natural rock).

[0004] There are also related researches on the method of preparing calcium oxide from solid waste materials, but there is no in-depth research on the application of lime for silicate products in aerated concrete. For example, Chinese patent CN 102795651 A discloses a method for directly producing powder calcium oxide by using dicyandiamide waste residue. The calcium oxide generated by the method has a content of 86%, but it is only one of the indicators of industrial calcium oxide, and the calcium oxide content has no certain relationship with the digestion index, water absorption and other indicators. The patent does not detect the digestion index, water absorption and other indicators, so it cannot be determined whether the prepared product meets the performance requirements of grade II lime for silicate building products. In the production process of silicate building products, a large amount of heat is needed in the lime powder digestion process. The higher the purity, the more heat generated, so there is a certain requirement for the purity of the lime. Under the premise of meeting the production demand and product quality, the higher the purity, the higher the effective ingredient of the raw material, and the less the amount of addition, which can reduce the proportioning cost to a certain extent. In the production of autoclaved aerated concrete products, the gas evolution speed and the thickening hardening speed are required to be consistent, the pore structure formed is more full and uniform, so that the thermal conductivity of the product is lower, and the dry density is lower, so there is a certain requirement for the digestion speed and digestion temperature index of the lime. If the digestion rate is too slow, the thickening speed cannot keep up with the gas evolution speed, the pore structure is damaged, and the product appears to be collapsed. The high content of magnesium oxide in the lime is easy to cause the product to swell in the later period, so that the product appears to be swollen and cracked. The water absorption of the lime directly affects the thickening speed and the internal pore structure of the product. The high content of silicon dioxide in the lime directly affects the generation of the final product hydrated calcium silicate in the product and affects the compressive strength index of the product, so the content of silicon dioxide needs to be controlled.

[0005] From the above index requirements and effects, the lime obtained by the existing technology only detects the calcium oxide index, which is far from enough for the application requirements of downstream silicate building products. On the one hand, the present application prepares lime with high conversion rate and stable performance, and on the other hand, it ensures the performance requirements of grade II lime for silicate building products and meets the index requirements of downstream products. SUMMARY

[0006] The present application aims to overcome the above technical deficiencies and provides a method for preparing lime by using single cyanamide residue as the main raw material, which solves the technical problems of low digestion index, slow and little heat release, and poor water absorption of calcium oxide prepared from solid waste materials in the prior art, and cannot meet the performance requirements of grade II lime for silicate building products.

[0007] The present application provides a method for preparing lime by using single cyanamide residue as the main raw material, which includes the following steps:

[0008] Mixing monocyamide slag, building material crushed material, fly ash and activator uniformly to obtain a mixture;

[0009] Calcining the mixture at 600-900 DEG C to obtain raw lime.

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

[0011] The present application uses monocyamide slag as the main raw material, cooperates with other solid waste materials, and adds activator for mixing, and then prepares raw lime meeting the performance requirements of building material industry standard JC / T 621-2021 "Raw Lime for Silicate Building Products" grade II through a specific calcination process; at the same time, the present application prepares raw lime by blending modification of monocyamide slag, significantly improves the product pass rate and yield, and improves the product performance stability. The method of the present application can utilize monocyamide slag at high added value, turns waste into treasure, provides an economic and effective way for the reuse of monocyamide slag waste and the preparation of raw lime (reduces natural rock mining), and solves the environmental problems caused by solid waste accumulation and overexploitation of natural resources. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0013] The present application provides a method for preparing raw lime using monocyamide slag as the main raw material, comprising the following steps:

[0014] S1, mixing monocyamide slag, building material crushed material, fly ash and activator uniformly to obtain a mixture;

[0015] S2, calcining the mixture at 600-900 DEG C to obtain raw lime.

[0016] Raw lime is prepared from calcium carbonate by calcination, but the calcium carbonate content in monocyamide slag is only below 60%, and the raw lime prepared from monocyamide slag alone is difficult to meet the requirements of calcium oxide content, digestion rate, water absorption and other indicators in the standard of raw lime for silicate building products. In order to stabilize the quality of raw lime, improve the pass rate and yield, the present application mixes monocyamide slag with building material crushed material, fly ash, and adds activator, and then goes through a calcination process at 600-900 DEG C to improve the decomposition conversion rate, adjust the digestion rate, reduce the proportion of undigested residue, improve the calcium oxide product rate, reduce the influence of low calcium in monocyamide slag on the quality stability of the final product, solve the technical problems of low product yield and poor quality caused by low effective calcium content in raw materials, and effectively stabilize the product quality and meet the downstream application requirements.

[0017] In the embodiment, the monocyannamide slag accounts for 30-85% of the total mass of the monocyannamide slag, the building material crushing material and the fly ash, including but not limited to 30%, 40%, 45%, 50%, 60%, 70%, 80%, 85% and the like; the building material crushing material accounts for 10-50% of the total mass of the monocyannamide slag, the building material crushing material and the fly ash, including but not limited to 10%, 20%, 30%, 40%, 50% and the like; the fly ash accounts for 5-20% of the total mass of the monocyannamide slag, the building material crushing material and the fly ash, including but not limited to 5%, 10%, 15%, 20% and the like; the activator accounts for 0.2-1% of the total mass of the monocyannamide slag, the building material crushing material and the fly ash, including but not limited to 0.2%, 0.3%, 0.5%, 0.8%, 1% and the like.

[0018] The application can greatly improve the content of calcium oxide in the product and the yield by mixing the building material crushing material and the monocyannamide slag in a certain proportion and then performing a specific calcination process to make calcium hydroxide dehydrate to form calcium oxide, calcium silicate decompose into calcium oxide and silicon dioxide and calcium carbonate decompose into calcium oxide and carbon dioxide, and the related reactions are as follows:

[0019] CaSiO3===CaO+SiO2;

[0020] CaCO3===CaO+CO2.

[0021] Meanwhile, the content of silicon dioxide is required for the performance index of the Portland cement building product, so the component proportion and the ratio of the raw materials are deeply researched and the data are controlled to meet the requirement of the content of silicon dioxide in the product standard.

[0022] In addition, the dispersion effect of the mixture in the calcination process is improved by adding a certain proportion of fly ash, the flowability and dispersion effect of the microstructure of the fly ash composed of a large number of glass microsphere spheres are excellent, the mixture after adding the fly ash is more fully calcined and decomposed, the conversion rate of the raw materials is higher, the content of calcium oxide in the product is higher and more stable, and then the product yield and the yield are improved. The best adding proportion of the fly ash is 5-20%, if the adding amount is too low, the dispersion effect of the fly ash cannot be achieved, and if the adding amount is too high, the total calcium content in the whole raw material is reduced, and the product quality after calcination is affected.

[0023] In the embodiment, the main components of the building material crushing material include cement hydration product calcium silicate, calcium hydroxide, calcium carbonate small particles and the like. For example, the building material crushing material can be one or more mixtures of building crushing waste, stone crushing waste and artificial stone crushing material, and the application does not limit this.

[0024] In the embodiment, the monocyamine slag has the following main chemical components: calcium carbonate 50-60%, carbon 5-10%, and nitrogen 1% or less; the building material crushing material has the following main chemical components: calcium 50-90%, silicon 20-30%, aluminum 10-20%, and iron 2-5%; and the fly ash has the following main chemical components: calcium 40-50%, silicon 10-20%, aluminum 30-40%, and iron 2-5%.

[0025] In some specific embodiments of the present application, the monocyamine slag has the following main chemical components: calcium carbonate 55-60%, carbon 8-10%, and nitrogen 0.5% or less; the building material crushing material has the following main chemical components: calcium 50-70%, silicon 20-25%, aluminum 10-15%, and iron 2-3%; and the fly ash has the following main chemical components: calcium 45-50%, silicon 15-20%, aluminum 35-40%, and iron 2-3%.

[0026] In the embodiment, the activator is one or a mixture of more than one of stearic acid and lignin. The monocyamine slag itself has a high water content, and thus requires a high calcination process and high energy consumption. After modification by the activator, the hydrophobicity of the calcium carbonate is improved, and thus the energy consumption is effectively reduced and the calcination conversion rate of the calcium carbonate is improved.

[0027] In the embodiment, the calcination conditions are as follows: calcination under normal pressure, an average heating rate of 5-10°C / min, including but not limited to 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, and 10°C / min; a maximum calcination temperature of 600-900°C, including but not limited to 600°C, 700°C, 800°C, and 900°C; and a holding time of 0-10 min, including but not limited to 0 min, 2 min, 4 min, 6 min, 8 min, and 10 min.

[0028] To avoid redundancy, in the following examples and comparative examples of the present application, some raw materials are summarized as follows:

[0029] The monocyamine slag has the following main chemical components: calcium carbonate 57%, carbon 9%, and nitrogen 0.4%; the building material crushing material has the following main chemical components: calcium 60%, silicon 25%, aluminum 10%, and iron 2.0%; and the fly ash has the following main chemical components: calcium 47%, silicon 15%, aluminum 35%, and iron 2.1%.

[0030] Examples 1-4 and Comparative Examples 1-3

[0031] A method for preparing quicklime by using monocyamine slag as a main raw material, comprising the following steps:

[0032] (1) cyanamide slag, building material crushing material, fly ash and activator are mixed in a proportioning mixer to obtain a mixture;

[0033] (2) the mixture is transported to a rotary kiln for calcination under normal pressure to obtain raw lime; wherein the raw material proportions and calcination conditions of different examples and comparative examples are shown in Table 1.

[0034] Table 1 Raw material proportions and calcination conditions of different examples and comparative examples

[0035]

[0036] Test group 1

[0037] The different raw limes obtained in the above examples and comparative examples are subjected to performance tests, and the test results are shown in Table 2. Among them, the digestion speed and digestion temperature are tested according to Appendix A in JC / T 621-2021 standard; A(CaO+MgO), MgO and SiO2 are tested according to GB / T 5762 standard; and the undigested residue is tested according to Chapter 8 of JC / T 478.1-2013.

[0038] Table 2 Performance test results of different raw limes

[0039]

[0040] As can be seen from Table 2, by adjusting the proportions of cyanamide slag, building material crushing material and fly ash, raw lime with high conversion rate and stable performance is successfully prepared, which can also meet the performance requirements of grade II lime for silicate building products and meet the downstream product index requirements.

[0041] Test group 2

[0042] According to the following preparation process of autoclaved aerated concrete block and the proportions in Table 3, the lime powder of the above different examples and comparative examples is used to prepare autoclaved aerated concrete blocks, and the performance of the above different autoclaved aerated concrete blocks is tested according to GB / T11968-2020 "Autoclaved Aerated Concrete Block" standard, and the test results are shown in Table 4.

[0043] Among them, the preparation process of autoclaved aerated concrete block is as follows:

[0044] (1) raw material preparation: fly ash is prepared for slurry, lime block is prepared for grinding, cement is prepared for tank, aluminum powder paste is prepared for water solution, and gypsum is prepared for slurry;

[0045] (2) batching and pouring: after weighing each raw material according to the proportioning ratio in Table 3, the raw materials are added to the stirrer for stirring, the stirring time is 1.5-2 min, the pouring temperature is controlled at 40±2℃, and then the mixture is arranged by a bubble arrangement machine and then enters a pre-curing room;

[0046] (3) Static pre-culture: control the temperature in the pre-culture room to be 50℃, and the pre-culture time is 150 min, to complete the gas generation, thickening and hardening process of the blank;

[0047] (4) Cutting and static standing: after the pre-curing is completed (i.e. the blank reaches a certain strength), the blank with a certain specification is obtained after demolding, cutting and peeling, and then the blank is grouped by a transfer car and enters a pre-pot static standing room; the cut blank enters the pre-pot static standing room to wait for entering the pot, the indoor temperature is 50℃, and water is sprayed regularly, and the pre-pot curing is performed for 150 min;

[0048] (5) Autoclave curing:

[0049] A, vacuum extraction stage: after entering the autoclave from the static standing room, the autoclave door and the valves are closed, the vacuum pump is started, the vacuum extraction is performed for 30 min to be below-0.050 MPa, and the vacuum pump is closed to start the steam heating;

[0050] B, temperature and pressure rising stage: the temperature in the autoclave is uniformly and evenly raised to 185-190℃ at a speed of 20-25℃ / h; at this time, the pressure is gradually raised to 1.10-1.20 MPa along with the temperature;

[0051] C, constant temperature and pressure stage: the temperature and pressure in step B are maintained for 6 hours;

[0052] D, temperature and pressure lowering stage: after the pressure maintaining time is over, the steam valve is closed, the temperature is lowered to below 100℃ at a speed of 30-40℃ / h, the autoclave door is opened when the pressure in the autoclave is 0 MPa, and the product is pulled out from the autoclave, and at this time, the high temperature and high pressure steam curing process is completed.

[0053] (6) Board breaking detection: after the high temperature and high pressure steam curing, the sample is taken out for detection, the board is broken and packed for storage, and the finished product is obtained after 10 days of natural curing.

[0054] Table 3 Preparation ratio and process of autoclaved aerated concrete block B05 A3.5 grade

[0055]

[0056] Table 4 Test results of different autoclaved aerated concrete blocks B05 A3.5 grade

[0057]

[0058]

[0059] As shown in Table 4, the quicklime prepared by examples 1-4 of the present application can meet the demand of quicklime for steam pressure concrete products.

[0060] To sum up, the present application is prepared by using monocyannide slag as the main raw material and other solid waste materials through surface activation and high temperature calcination, so that the product performance index is more stable, the qualified rate of quicklime is significantly improved, the yield is more than doubled, and the energy consumption is reduced. The prepared quicklime meets the performance requirements of building material industry standard JC / T 621-2021 "Quicklime for Silicate Building Products" grade II, and the performance index is stable, which can meet the demand of downstream products, and has been verified by application experiment.

[0061] The specific embodiments of the application described above do not constitute a limitation on the scope of protection of the application. Any various other corresponding changes and modifications made according to the technical concept of the application shall be included in the scope of protection of the claims of the application.

Claims

1. A method for preparing quicklime using cyanamide slag as the main raw material, characterized in that, Includes the following steps: The cyanamide residue, crushed building materials, fly ash, and activator are mixed evenly to obtain a mixture. The mixture is calcined at 600–900°C to obtain quicklime; wherein... The cyanamide residue accounts for 30% to 85% of the total mass of cyanamide residue, crushed building materials, and fly ash; The crushed building materials constitute 10% to 50% of the total mass of cyanamide slag, crushed building materials, and fly ash. The fly ash accounts for 5% to 20% of the total mass of cyanamide slag, crushed building materials, and fly ash. The activator is one or a mixture of stearic acid and lignin; The quicklime in question is quicklime that meets the Grade II performance requirements of the building materials industry standard JC / T 621-2021 "Quicklime for Silicate Building Products".

2. The method for preparing quicklime using cyanamide slag as the main raw material according to claim 1, characterized in that, The crushed building material is one or more of the following: construction waste, stone waste, and artificial stone crushed material.

3. The method for preparing quicklime using cyanamide slag as the main raw material according to claim 1, characterized in that, The main chemical components of the cyanamide slag are as follows (by mass percentage): calcium carbonate 50%–60%, carbon 5%–10%, and nitrogen less than 1%; the main chemical components of the crushed building material are as follows (by mass percentage): calcium 50%–90%, silicon 20%–30%, aluminum 10%–20%, and iron 2%–5%; the main chemical components of the fly ash are as follows (by mass percentage): calcium 40%–50%, silicon 10%–20%, aluminum 30%–40%, and iron 2%–5%.

4. The method for preparing quicklime using cyanamide slag as the main raw material according to claim 3, characterized in that, The main chemical components of the cyanamide slag are as follows (by mass percentage): calcium carbonate 55%–60%, carbon 8%–10%, and nitrogen less than 0.5%; the main chemical components of the crushed building material are as follows (by mass percentage): calcium 50%–70%, silicon 20%–25%, aluminum 10%–15%, and iron 2%–3%; and the main chemical components of the fly ash are as follows (by mass percentage): calcium 45%–50%, silicon 15%–20%, aluminum 35%–40%, and iron 2%–3%.

5. The method for preparing quicklime using cyanamide slag as the main raw material according to claim 1, characterized in that, The activator accounts for 0.2% to 1% of the total mass of cyanamide slag, crushed building materials, and fly ash.

6. The method for preparing quicklime using cyanamide slag as the main raw material according to claim 1, characterized in that, The calcination conditions are as follows: calcination under normal pressure, average heating rate of 5-10℃ / min, maximum calcination temperature of 600℃-900℃, and holding time of 0-10min.

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