Method for preparing calcium carbonate from carbide slag

Abstract

The invention relates to the technical field of carbide slag recovery, in particular to a method for preparing calcium carbonate from carbide slag. The invention provides a method for preparing calcium carbonate from carbide slag, which comprises the following steps: mixing carbide slag and water, hydrolyzing, carrying out first solid-liquid separation to obtain carbide slag supernatant and undissolved carbide slag precipitate, and recycling the undissolved carbide slag precipitate to the hydrolysis process; carbon dioxide is introduced into the carbide slag supernatant for a mineralization reaction, then second solid-liquid separation is carried out, calcium carbonate and filtrate are obtained, and the filtrate is reused in the hydrolysis process; the gas-liquid volume ratio of the mineralization reaction is (3-4): 1, and the pH value of a system obtained after the mineralization reaction is 6-12. The method disclosed by the invention is low in energy consumption, good in product quality, low in process operation cost and small in influence on the environment.

Description

Technical Field

[0001] The invention relates to the technical field of carbide slag recovery, in particular to a method for preparing calcium carbonate from carbide slag. Background Art

[0002] The production of polyvinyl chloride by hydrolysis of calcium carbide (calcium carbide) produces a large amount of solid waste - carbide slag. According to surveys, the annual output of carbide slag is 34 million tons, but due to its many types of impurities, it is difficult to remove impurities, and the transportation cost is high, so the comprehensive utilization rate is low (only 40%). It is usually landfilled or stored, which often causes surface and groundwater pollution, land salinization and dust pollution, and a large amount of calcium resources in carbide slag are wasted. Therefore, large-scale consumption and resource utilization of carbide slag are imminent.

[0003] The existing processes for preparing calcium carbonate from carbide slag mainly include calcination digestion, acid leaching and ammonium chloride leaching. The calcination digestion method not only has high energy consumption, but also has the problem of low product purity and low product added value. The ammonium chloride leaching method releases ammonia during the leaching process, which poses a risk of secondary pollution. The acid leaching method has high costs and problems such as wastewater discharge. Therefore, it is necessary to seek a process for producing calcium carbonate from carbide slag with low energy consumption, good product quality, low process operation cost and low environmental impact. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a method for preparing calcium carbonate from carbide slag. The method of the present invention has low energy consumption, good product quality, low process operation cost and little impact on the environment.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing calcium carbonate from carbide slag, comprising the following steps:

[0007] After mixing carbide slag and water for hydrolysis, a first solid-liquid separation is performed to obtain a carbide slag supernatant and undissolved carbide slag precipitate, wherein the undissolved carbide slag precipitate is recycled to the hydrolysis process;

[0008] After introducing carbon dioxide into the carbide slag supernatant to carry out a mineralization reaction, a second solid-liquid separation is carried out to obtain calcium carbonate and a filtrate, and the filtrate is recycled to the hydrolysis process;

[0009] The pH of the system obtained after the mineralization reaction is 6-12.

[0010] Preferably, the hydrolysis is carried out under stirring;

[0011] The hydrolysis temperature is 10-70° C. and the time is 5-60 min.

[0012] Preferably, the pH of the carbide slag supernatant is ≥11.

[0013] Preferably, the gas-liquid volume ratio of the mineralization reaction is (3-4):1.

[0014] Preferably, the mineralization reaction is carried out under stirring conditions, and the stirring speed is 1200-1800 rpm.

[0015] Preferably, the temperature of the mineralization reaction is 25-55°C.

[0016] Preferably, after the hydrolysis is completed, clarification is further included, and the clarification is performed under static conditions;

[0017] The clarification time is 30 to 45 minutes.

[0018] Preferably, after the second solid-liquid separation, the obtained solid is further cleaned to obtain a calcium carbonate filter cake and a cleaning liquid;

[0019] The cleaning liquid is subjected to membrane separation and evaporative crystallization in sequence to obtain deionized water and industrial salt, and the deionized water is reused in the hydrolysis process or the cleaning process.

[0020] Preferably, after obtaining the calcium carbonate filter cake, the method further includes drying and breaking up the obtained calcium carbonate filter cake in sequence.

[0021] Preferably, the heat source required for the evaporative crystallization is the waste heat during the drying process.

[0022] The invention provides a method for preparing calcium carbonate from carbide slag, comprising the following steps: mixing carbide slag and water for hydrolysis, performing a first solid-liquid separation to obtain a carbide slag supernatant and undissolved carbide slag precipitate, and recycling the undissolved carbide slag precipitate to the hydrolysis process; introducing carbon dioxide into the carbide slag supernatant for mineralization reaction, performing a second solid-liquid separation to obtain calcium carbonate and a filtrate, and recycling the filtrate to the hydrolysis process; and the pH of the system obtained after the mineralization reaction is 10.5-11.5.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) Water is used as an extractant for hydrolyzing carbide slag to extract pyrolytic calcium. Although the leaching efficiency is relatively low, it does not require the addition of chemical leaching agents and the consideration of subsequent leaching agent recovery and treatment issues, has no secondary pollution, is low in cost, and is easy to promote and apply in industrialization;

[0025] 2) The preparation of calcium carbonate by the mineralization reaction of carbide slag supernatant (calcium hydroxide saturated solution) with carbon dioxide can effectively remove insoluble impurities such as carbon, iron, silicon and aluminum in carbide slag, which is conducive to the preparation of high-purity and high-whiteness calcium carbonate products and the high-value utilization of carbide slag;

[0026] 3) Carbon dioxide is used as a mineralization reagent. It has a wide range of sources and can be provided by flue gas emitted from coal-fired power plants, steel mills, smelters, chemical plants, biomass power plants, etc. This is not only conducive to the conversion and utilization of carbon dioxide to reduce emissions, but also can reduce the production cost of calcium carbonate, which is conducive to achieving corporate economic and social benefits and promoting green and low-carbon development. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a schematic diagram of the process of preparing calcium carbonate from carbide slag as shown in Example 1; wherein 1 is hydrolysis, 2 is clarification, 3 is filtration, 4 is mineralization reaction, 5 is filtration and water washing, 6 is drying and dehydration, 7 is breaking up, 8 is packaging, 9 is membrane separation, and 10 is evaporation crystallization;

[0028] Figure 2 This is a comparison chart of the total amount of calcium carbonate and hydrolysis residue at different mineralization reaction pH endpoints;

[0029] Figure 3 This is a comparison chart of the effects of different hydrolysis temperatures and hydrolysis times on the whiteness of calcium carbonate;

[0030] Figure 4 This is the change chart of calcium carbonate purity and whiteness corresponding to different filtering and washing times;

[0031] Figure 5 is a particle size distribution diagram of the calcium carbonate precipitate described in Examples 19 to 23;

[0032] Figure 6 is a SEM image of the calcium carbonate precipitate described in Example 19;

[0033] Figure 7 This is the XRD pattern of the calcium carbonate precipitate described in Example 19. DETAILED DESCRIPTION

[0034] The present invention provides a method for preparing calcium carbonate from carbide slag, comprising the following steps:

[0035] After mixing carbide slag and water for hydrolysis, a first solid-liquid separation is performed to obtain a carbide slag supernatant and undissolved carbide slag precipitate, wherein the undissolved carbide slag precipitate is recycled to the hydrolysis process;

[0036] After introducing carbon dioxide into the carbide slag supernatant to carry out a mineralization reaction, a second solid-liquid separation is carried out to obtain calcium carbonate and a filtrate, and the filtrate is recycled to the hydrolysis process;

[0037] The pH of the system obtained after the mineralization reaction is 10.5-11.5.

[0038] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0039] The present invention mixes carbide slag and water for hydrolysis, and then performs a first solid-liquid separation to obtain a carbide slag supernatant and undissolved carbide slag precipitate, and the undissolved carbide slag precipitate is recycled to the hydrolysis process.

[0040] In the present invention, the water is preferably deionized water.

[0041] In the present invention, the mass ratio of the carbide slag to water is preferably 1:(100-1000), more preferably 1:(200-300). In an embodiment of the present invention, the mass ratio of the carbide slag to water is 1:220.

[0042] In the present invention, the mixing is preferably carried out under stirring conditions. The present invention does not have any special limitation on the stirring process, and the stirring process may be carried out using a process well known to those skilled in the art.

[0043] In the present invention, the hydrolysis is preferably carried out under stirring; the temperature of the hydrolysis is preferably 10 to 70°C, more preferably 15 to 45°C; the time is preferably 5 to 60 min, more preferably 5 to 30 min. In an embodiment of the present invention, the temperature of the hydrolysis can be 10°C, 20°C, 30°C, 40°C or 50°C; the time of the hydrolysis can be 5 min, 10 min, 20 min, 30 min, 40 min or 60 min.

[0044] In the present invention, the hydrolysis is preferably followed by clarification, and the clarification time is preferably 30 to 45 minutes, more preferably 35 to 40 minutes. In an embodiment of the present invention, the clarification time can be 30 minutes, 35 minutes and 45 minutes.

[0045] In the present invention, the first solid-liquid separation method is preferably filtration. The present invention does not have any special limitation on the filtration process, and the filtration process may be performed using a process well known to those skilled in the art.

[0046] In the present invention, the pH of the carbide slag supernatant is ≥11, and the solid content of the carbide slag supernatant is preferably <0.1%.

[0047] After obtaining the undissolved carbide slag precipitate, the present invention reuses the undissolved carbide slag precipitate and continues to mix it with water for hydrolysis until the undissolved carbide slag precipitate can no longer leach calcium ions in water. In the present invention, the carbide slag supernatant is a solution containing calcium ions.

[0048] After obtaining the carbide slag supernatant, the present invention introduces carbon dioxide into the carbide slag supernatant to carry out a mineralization reaction, and then performs a second solid-liquid separation to obtain calcium carbonate and a filtrate, and the filtrate is recycled to the hydrolysis process; the gas-liquid volume ratio of the mineralization reaction is (3-4):1, and the pH of the system obtained after the mineralization reaction is 10.5-11.5.

[0049] In the present invention, the carbon dioxide is preferably provided by flue gas or tail gas; the volume percentage of carbon dioxide in the flue gas or tail gas is preferably greater than 10%; and the utilization rate of carbon dioxide in the mineralization reaction is preferably greater than 30%.

[0050] In the present invention, the flow rate of the carbon dioxide is preferably 100 to 900 mL / min, more preferably 100 to 150 mL / min. In an embodiment of the present invention, the flow rate of the carbon dioxide may be 100 mL / min.

[0051] In the present invention, the gas-liquid volume ratio of the mineralization reaction is preferably (3-4):1, more preferably (3.2-3.8):1, and most preferably (3.4-3.6):1. The pH value of the system obtained after the mineralization reaction is 6-12, preferably 8-10. In an embodiment of the present invention, the gas-liquid volume ratio of the mineralization reaction may be 3:1, 3.2:1, 3.5:1, 3.8:1; the pH value of the system obtained after the mineralization reaction may be 6, 7, 8, 9, 10, 10.36, 10.60, 11, 11.37, 11.63 or 12. In the present invention, when the pH value of the system obtained after the mineralization reaction reaches the above range, the introduction of carbon dioxide gas can be stopped, that is, the mineralization reaction is stopped.

[0052] In the present invention, the mineralization reaction is preferably carried out under stirring conditions, and the stirring speed is preferably 1200-1800 rpm, more preferably 1500-1700 rpm; the temperature of the mineralization reaction is preferably 15-55° C., more preferably 15-35° C. In an embodiment of the present invention, the stirring speed may be 1600 rpm, and the temperature of the mineralization reaction may be 25° C.

[0053] In the present invention, the second solid-liquid separation method is preferably filtration. The present invention does not have any special limitation on the filtration process, and the filtration process may be performed using a process well known to those skilled in the art.

[0054] After the second solid-liquid separation is completed, the present invention preferably further comprises washing the obtained solid to obtain a calcium carbonate filter cake and a washing liquid; then the washing liquid is subjected to membrane separation and evaporation crystallization in sequence to obtain deionized water and industrial salt; the deionized water is preferably reused in the hydrolysis process or the washing process. The present invention preferably recycles the obtained industrial salt for resource reuse.

[0055] In the present invention, the washing is preferably carried out with deionized water, and the purpose of the washing is to remove soluble impurities in the solid, wherein the soluble impurities include but are not limited to chloride ions, alkali metal ions and sulfate ions, so as to ensure that the purity of calcium carbonate reaches more than 98%.

[0056] The present invention also preferably includes sequentially drying and breaking up the obtained calcium carbonate filter cake; the drying method is preferably drying, and the present invention has no special limitation on the drying and breaking up process, and the process well known to those skilled in the art can be used.

[0057] In the present invention, the heat source required for the evaporation and crystallization is preferably the waste heat in the drying process, so as to realize the recycling of waste heat and achieve the effect of energy saving and emission reduction.

[0058] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0059] Examples 1 to 18

[0060] like Figure 1 The process shown in the figure is to dissolve 10 g of carbide slag in 2200 mL of water, hydrolyze under stirring (the temperature and time of the hydrolysis are shown in Table 1), place for 35 min to clarify, and then filter to obtain 2000 mL of carbide slag supernatant (corresponding to Figure 1 The filtrate in the solution) and the undissolved carbide slag precipitate are recycled to repeat the dissolution and hydrolysis process until calcium in the carbide slag hydrolyzate is no longer leached, and the number of hydrolysis is shown in Table 1;

[0061] The method comprises the following steps: introducing carbon dioxide gas (the flow rate of the carbon dioxide gas is 100 mL / min) into the carbide slag supernatant through an aeration device, and carrying out a mineralization reaction (gas-liquid volume ratio is 3.5:1, temperature is 10-50° C.) under stirring (stirring speed is 1200 rpm) until the pH of the solution reaches a set value (as shown in Table 1), stopping the introduction of carbon dioxide gas, i.e. stopping the mineralization reaction, filtering to obtain a calcium carbonate precipitate and a filtrate, and recycling the filtrate to dissolve and hydrolyze the carbide slag or undissolved carbide slag precipitate in the above-mentioned dissolution and hydrolysis process; washing the calcium carbonate precipitate with deionized water to obtain a calcium carbonate filter cake and a washing liquid, and then subjecting the washing liquid to membrane separation and evaporation crystallization in sequence to obtain deionized water and industrial salt; recycling the deionized water to the hydrolysis process or the washing process, and recycling the industrial salt for resource reuse; drying and dehydrating the calcium carbonate filter cake (specifically, drying), breaking up and packaging in sequence to obtain a calcium carbonate powder;

[0062] Table 1 Conditions and effects of Examples 1 to 18

[0063]

[0064]

[0065] As shown in Table 1, in Embodiment 1~18, 10g carbide slag is under optimal conditions, i.e. at the end point pH=11 of the circulating hydrolysis mineralization reaction, the hydrolysis time is 10min, and the hydrolysis temperature is 30 ℃ (normal temperature). The total amount of calcium carbonate obtained is 10.00g, and the total amount of hydrolysis residue is 1.97g. The transformation efficiency of preparing calcium carbonate by the circulating hydrolysis of carbide slag is 80.3%, and all hydrolysis cycles are 6 times. After testing, the whiteness of described calcium carbonate is 99.7, and the purity is 99.15 before washing. After filtering and washing (calcium carbonate solid content is 5%, and the stirring time is 10min) once, the purity is 99.62, after filtering and washing twice, the purity is 99.70, and after filtering and washing 3 times, the purity is 99.90.

[0066] Examples 19 to 23

[0067] 10 g of carbide slag was dissolved in 2000 mL of water, and hydrolyzed under stirring (the hydrolysis temperature was 25° C. and the time was 10 min), and then allowed to stand for 35 min, and then filtered to obtain a carbide slag supernatant (a clear calcium ion-containing solution);

[0068] Introduce carbon dioxide gas into the carbide slag supernatant through an aeration device (the flow rates of the carbon dioxide gas are 100 mL / min (corresponding to Example 19), 300 mL / min (corresponding to Example 20), 500 mL / min (corresponding to Example 21), 700 mL / min (corresponding to Example 22) and 900 mL / min (corresponding to Example 23)), and carry out mineralization reaction (gas-liquid volume ratio of 3.5:1, temperature of 25°C) under stirring (stirring speed of 1600 rpm) until the pH of the solution reaches 11, stop introducing carbon dioxide gas, i.e. stop the mineralization reaction, filter, and dry the obtained precipitate to obtain calcium carbonate precipitate;

[0069] The calcium carbonate precipitates described in Examples 19 to 23 were subjected to laser particle size analysis, wherein: Figure 5 is the particle size distribution diagram of the calcium carbonate precipitate described in Examples 19 to 23, Figure 5 It can be seen that with the increase of CO2 flow rate, the particle size of the product calcium carbonate increases as a whole. When the CO2 flow rate is 100ml / min, the calcium carbonate particle size is the smallest. 10 , D 50 and D 90 They are approximately 0.72 microns, 1.27 microns, and 2.48 microns respectively;

[0070] The calcium carbonate precipitate described in Example 19 was subjected to SEM test and XRD test, wherein, Figure 6 is a SEM image of the calcium carbonate precipitate described in Example 19 (wherein a is a photo magnified 30,000 times, and b is a photo magnified 60,000 times), Figure 6 It can be seen that the calcium carbonate is a calcium carbonate with a cubic morphology, a calcite crystal form, and an average single crystal particle size of about 70nm; Figure 7 is the XRD pattern of the calcium carbonate precipitate described in Example 19, Figure 7 It can be seen that the mineral composition of the obtained calcium carbonate product is almost all calcite.

[0071] Figure 2 The hydrolysis temperature is 30℃, the hydrolysis stirring time is 5min, the CO2 flow rate during the mineralization reaction is 100mL / min, and the mineralization reaction temperature and stirring rate are consistent with the hydrolysis process. The comparison chart of the total amount of calcium carbonate and hydrolysis residue at different end point pH of the mineralization reaction is shown in the figure. Figure 2 It can be seen that when the pH increases from 6 to 11, the yield of calcium carbonate products increases with the increase of pH, and the corresponding amount of carbide slag hydrolysis residue decreases, but when the pH increases from 11 to 12, the opposite trend occurs. Therefore, the pH of carbide slag cyclic hydrolysis should be controlled at 11 at 30°C to obtain the maximum yield of calcium carbonate products and the minimum amount of hydrolysis residue remaining;

[0072] Figure 3 The CO2 flow rate of the mineralization reaction is 100mL / min, the mineralization reaction temperature and stirring rate are consistent with the hydrolysis process, and at the optimal mineralization reaction endpoint pH, the effect of different hydrolysis temperatures and hydrolysis times on the whiteness of calcium carbonate is compared. Figure 3 It can be seen that the hydrolysis temperature and hydrolysis time of carbide slag have little effect on the whiteness of the product calcium carbonate. Under the conditions of hydrolysis temperature of 10-50℃ and hydrolysis time of 5-60min, the whiteness of the product calcium carbonate can be between 98.5-99.5.

[0073] Figure 4 The following is the change diagram of calcium carbonate purity and whiteness under different filtering and washing times. Figure 4 It can be seen that as the number of water washings increases, the purity of the product calcium carbonate increases, and it can be increased from 99.15 to 99.9 after four water washings; however, the number of water washings has no obvious effect on the whiteness of the product calcium carbonate, and the whiteness basically varies between 99.7 and 100.

[0074] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing calcium carbonate from carbide slag, characterized in that: The following steps are involved: After mixing carbide slag and water for hydrolysis, a first solid-liquid separation is performed to obtain a carbide slag supernatant and undissolved carbide slag precipitate, wherein the undissolved carbide slag precipitate is recycled to the hydrolysis process; After introducing carbon dioxide into the carbide slag supernatant to carry out a mineralization reaction, a second solid-liquid separation is carried out to obtain calcium carbonate and a filtrate, and the filtrate is recycled to the hydrolysis process; The pH of the system obtained after the mineralization reaction is 6-12.

2. The method according to claim 1, characterized in that The hydrolysis is carried out under stirring; The hydrolysis temperature is 10-70° C. and the time is 5-60 min.

3. The method according to claim 1 or 2, characterized in that The pH of the carbide slag supernatant is ≥11.

4. The method according to claim 1, characterized in that The gas-liquid volume ratio of the mineralization reaction is (3-4):

1.

5. The method according to claim 4, characterized in that The mineralization reaction is carried out under stirring conditions, and the stirring speed is 1200-1800 rpm.

6. The method according to claim 1, 4 or 5, characterized in that The temperature of the mineralization reaction is 25-55°C.

7. The method according to claim 1, characterized in that After the hydrolysis is completed, the process further includes clarifying the hydrolysis, wherein the clarification is performed under static conditions; The clarification time is 30 to 45 minutes.

8. The method according to claim 1, characterized in that After the second solid-liquid separation, the obtained solid is washed to obtain a calcium carbonate filter cake and a washing liquid; The cleaning liquid is subjected to membrane separation and evaporative crystallization in sequence to obtain deionized water and industrial salt, and the deionized water is reused in the hydrolysis process or the cleaning process.

9. The method according to claim 8, characterized in that After the calcium carbonate filter cake is obtained, the method further includes drying and breaking up the obtained calcium carbonate filter cake in sequence.

10. The method according to claim 9, characterized in that The heat source required for the evaporative crystallization is the residual heat in the drying process.

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