Method for producing modified calcium fluoride-containing solid material

Abstract

Provided is a method for producing a modified calcium fluoride-containing solid material in which the lime component is reduced, by separating at least one lime component selected from the group consisting of calcium carbonate, calcium hydroxide, and calcium oxide from a calcium fluoride-containing solid material that contains calcium fluoride and the lime component, wherein the lime component is eluted by supplying a carbon dioxide-containing gas to a slurry containing the calcium fluoride-containing solid material and water while keeping the pH value of the slurry at 6.0 or less.

Description

Method for producing modified calcium fluoride-containing solids 【0001】 The present invention relates to a method for separating the lime component from a calcium fluoride-containing solid that contains calcium fluoride and lime components, thereby reducing the amount of lime component in the calcium fluoride-containing solid. 【0002】 Traditionally, hydrofluoric acid has been produced by reacting fluorite (calcium fluoride) with concentrated sulfuric acid, and much of it is used in semiconductor manufacturing and glass processing. Used hydrofluoric acid from semiconductor manufacturing and other processes is precipitated as calcium fluoride along with wastewater generated from other production lines using lime-based additives. After solid-liquid separation and dewatering, it becomes calcium fluoride sludge. At this time, calcium carbonate and calcium hydroxide contained in the lime-based additives also precipitate together with the calcium fluoride, and these are included as impurities in the calcium fluoride sludge (calcium fluoride-containing solid matter). 【0003】 On the other hand, fluorite is a mineral resource, and its depletion is a concern, leading to worries about price increases. Therefore, the use of calcium fluoride sludge as a raw material in hydrofluoric acid production is being considered. However, when using calcium fluoride sludge as a substitute for fluorite, there are problems. For example, if the calcium fluoride sludge contains calcium carbonate, carbon dioxide gas will be generated during hydrofluoric acid production. Also, if the calcium fluoride sludge contains calcium hydroxide, water will be generated, leading to a decrease in the quality of hydrofluoric acid. 【0004】 Therefore, methods using acids or alkalis such as hydrochloric acid or hydrofluoric acid have been proposed to recover high-purity calcium fluoride from calcium fluoride sludge (see, for example, Patent Documents 1 and 2). 【0005】 Japanese Patent Publication No. 2010-202433 Japanese Patent Publication No. 2021-11418 【0006】 However, strong acids such as hydrochloric acid and nitric acid react with calcium fluoride in calcium fluoride sludge to produce hydrofluoric acid, resulting in the loss of calcium fluoride. Furthermore, acids and alkalis are highly dangerous to handle, and particular care must be taken when handling hydrofluoric acid. 【0007】The object of the present invention is to provide a method for safely separating the lime component from a calcium fluoride-containing solid while suppressing the loss of calcium fluoride, without using acids or alkalis, and for producing a modified calcium fluoride-containing solid with reduced lime content. 【0008】 The inventors have discovered that by supplying a carbon dioxide-containing gas to a slurry containing calcium fluoride-containing solids and water, and maintaining the pH of the slurry at 6.0 or lower, the lime component in the calcium fluoride-containing solids can be bicarbonated and eluted, thereby reducing the lime component in the calcium fluoride-containing solids, and have completed the present invention. 【0009】 In other words, the present invention is as follows: [1] A method for producing a modified calcium fluoride-containing solid in which the lime component is reduced, by separating the lime component from a calcium fluoride-containing solid containing calcium fluoride and at least one lime component selected from calcium carbonate, calcium hydroxide and calcium oxide, characterized in that a carbon dioxide-containing gas is supplied to a slurry containing the calcium fluoride-containing solid and water, and the pH of the slurry is maintained at 6.0 or less to dissolve the lime component. 【0010】 [2] A method for producing a modified calcium fluoride-containing solid according to [1], characterized in that the content ratio of the lime component in the modified calcium fluoride-containing solid is 0.5% by mass or less. 【0011】 [3] A method for producing a modified calcium fluoride-containing solid according to [1] or [2] above, characterized in that the pH of the slurry is maintained at 5.0 or higher and 6.0 or lower. [4] A method for producing a modified calcium fluoride-containing solid according to any one of [1] to [3] above, characterized in that the pH of the slurry is maintained at 6.0 or lower for 15 minutes or more. 【0012】[5] A method for producing a modified calcium fluoride-containing solid according to any one of [1] to [4] above, characterized in that the calcium fluoride-containing solid contains 60% by mass or more of calcium fluoride on a dry matter basis. [6] A method for producing a modified calcium fluoride-containing solid according to any one of [1] to [5] above, characterized in that the carbon dioxide-containing gas is exhaust gas generated from a thermal power plant or exhaust gas generated from a cement manufacturing facility. 【0013】 According to the present invention, it is possible to safely separate the lime component from a calcium fluoride-containing solid while suppressing the loss of calcium fluoride, without using acids or alkalis, and to produce a modified calcium fluoride-containing solid with reduced lime content. 【0014】 The present invention provides a method for producing a modified calcium fluoride-containing solid, comprising separating the lime component from a calcium fluoride-containing solid containing calcium fluoride and at least one lime component selected from calcium carbonate, calcium hydroxide, and calcium oxide, to produce a modified calcium fluoride-containing solid with reduced lime component, characterized by supplying a carbon dioxide-containing gas to a slurry containing the calcium fluoride-containing solid and water, maintaining the pH of the slurry at 6.0 or lower, and eluting the lime component. 【0015】 Here, calcium fluoride-containing solids refer to calcium fluoride (CaF ２ ) and calcium carbonate (CaCO3) ３ ), calcium hydroxide (Ca(OH) ２ A solid containing at least one lime component selected from fluorine and calcium oxide (CaO), for example, calcium fluoride sludge obtained by treating fluorine-based wastewater generated in semiconductor manufacturing, liquid crystal manufacturing, glass processing, etc. Specifically, calcium fluoride sludge produced by adding lime-based additives such as calcium carbonate and calcium hydroxide to fluorine-based wastewater can be an example. This calcium fluoride sludge may be sludge that has undergone dewatering treatment after solid-liquid separation, or it may be sludge that contains moisture. 【0016】The calcium fluoride-containing solid preferably contains 60% by mass or more of calcium fluoride on a dry matter basis (the total value of components excluding water is taken as 100% by mass), more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more. On the other hand, there is no particular upper limit, but for example it is about 90% by mass. 【0017】 This calcium fluoride-containing solid may contain other components in addition to calcium fluoride and lime components. These other components vary depending on the production route of the calcium fluoride-containing solid. For example, in the case of calcium fluoride sludge, examples include aluminum compounds (including metallic aluminum) and silicon compounds (including silicon). 【0018】 In this invention, by supplying a carbon dioxide-containing gas to a slurry containing calcium fluoride-containing solid and water, and maintaining the pH of the slurry at 6.0 or lower, the lime component in the calcium fluoride-containing solid can be bicarbonated and eluted. Therefore, without using acids or alkalis, the lime component can be separated from the calcium fluoride-containing solid, and a calcium fluoride-containing solid with reduced lime content can be obtained. 【0019】 In other words, in the present invention, as shown in the following formula, calcium carbonate contained in the calcium fluoride-containing solid is bicarbonated and elutes into the slurry. 【0020】 CaCO ３ (s) + H ２ O(l) + CO ２ (g) → Ca(HCO ３ ) ２ (ax) 【0021】 Furthermore, calcium hydroxide and calcium oxide, which are lime components in calcium fluoride-containing solids, are converted to calcium carbonate and then to bicarbonate upon the supply of carbon dioxide-containing gas. 【0022】Furthermore, in this invention, by not using acids or alkalis, the loss of calcium fluoride can be suppressed or prevented, and the lime component in the calcium fluoride-containing solid can be safely separated and reduced. In addition, the amount of waste of calcium fluoride-containing solid can be reduced, thereby suppressing environmental pollution, and the reuse of calcium fluoride-containing solid promotes the effective use of resources and reduces the use of fluorite, a mineral resource. 【0023】 The method for producing the modified calcium fluoride-containing solid of the present invention will be described in detail below. 【0024】 First, a slurry is prepared by adding calcium fluoride-containing solids and water to a container (slurry preparation step). 【0025】 The proportion of calcium fluoride-containing solids (dried material) in the slurry can be appropriately adjusted, for example, depending on the type of calcium fluoride-containing solids, and is preferably 0.1 to 20% by mass, more preferably 0.2 to 15% by mass, even more preferably 0.5 to 10% by mass, and particularly preferably 0.5 to 5% by mass. This allows the calcium fluoride-containing solids to be sufficiently dispersed in the liquid and to be effectively brought into contact with carbon dioxide-containing gas, thereby increasing the production efficiency of modified calcium fluoride-containing solids. 【0026】 Next, carbon dioxide-containing gas is supplied to the slurry containing calcium fluoride-containing solids and water to maintain the slurry's pH at 6.0 or below (carbon dioxide supply step). This allows the lime components in the calcium fluoride-containing solids to be bicarbonated and dissolved into the liquid. 【0027】The treatment in this carbon dioxide supply process can be carried out in a continuous or batch manner. As a continuous method, for example, a mode can be cited where a predetermined amount of calcium fluoride-containing solid and water are continuously supplied to and discharged from a stirring vessel, while carbon dioxide gas is supplied to the stirring vessel to maintain the pH of the slurry at 6.0 or less. The supply rate of the calcium fluoride-containing solid and water into this stirring vessel, that is, the treatment time (residence time) in the stirring vessel, is preferably adjusted appropriately according to the content of the lime component in the calcium fluoride-containing solid, the supply amount of carbon dioxide, etc. In actual operation, the content of the lime component in the reformed calcium fluoride-containing solid discharged from the stirring vessel can be measured, and various conditions can be adjusted. 【0028】 As a batch method, for example, a mode can be cited where carbon dioxide gas is supplied while stirring the slurry in the stirring vessel so that the pH of this slurry is maintained at 6.0 or less, and it is maintained for a predetermined time. The treatment time in the stirring vessel is preferably adjusted appropriately according to the content of the lime component in the calcium fluoride-containing solid, the supply amount of carbon dioxide, etc. After the treatment, the reformed calcium fluoride-containing solid and the water in which the lime component has been eluted are taken out from the stirring vessel, and the above-described procedure is continuously repeated. 【0029】 The carbon dioxide-containing gas supplied to the slurry is not particularly limited as long as it is a gas containing carbon dioxide (CO ２ )), but for example, exhaust gas generated from a thermal power plant or exhaust gas generated from a cement manufacturing facility can be preferably exemplified. Thereby, since the carbon dioxide generated from a thermal power plant or a cement manufacturing facility can be utilized as a resource without being released into the atmosphere, effective utilization of resources can be achieved. 【0030】 This carbon dioxide-containing gas is carbon dioxide (CO ２The gas is not particularly limited as long as it contains ), but it is preferable that it contains 10% or more by volume of carbon dioxide, more preferably 30% or more by volume, even more preferably 50% or more by volume, particularly preferably 80% or more by volume, and most preferably carbon dioxide alone (100% by volume). This makes it possible to improve the production efficiency of the modified calcium fluoride-containing solid. 【0031】 The pH of the slurry is usually around 7.0 (neutral) before the supply of carbon dioxide-containing gas, and can decrease to 6.0 or below with the supply of carbon dioxide-containing gas. However, from the viewpoint of efficiently dissolving the lime components, it is preferable to maintain it between 4.0 and 6.0, more preferably between 4.5 and 6.0, and even more preferably between 5.0 and 6.0. 【0032】 Here, the retention time of the slurry at a pH of 6.0 or lower is preferably 15 minutes or more, more preferably 20 minutes or more, and even more preferably 30 minutes or more, from the viewpoint of ensuring the reaction time necessary for the bicarbonation treatment (elution) of the lime components. On the other hand, there is no particular upper limit, but considering the production efficiency of the modified calcium fluoride-containing solid, it is about 120 minutes. 【0033】 After dissolving the lime components in water, the slurry can be subjected to solid-liquid separation to obtain a modified calcium fluoride-containing solid, after removing other components (impurities) as needed. It is preferable to wash the solid-liquid separated modified calcium fluoride-containing solid with water to remove any attached substances. Examples of equipment used for solid-liquid separation include atmospheric pressure filtration, vacuum filtration, filter press, screw press, centrifuge (screw decanter), and thickener. 【0034】The content ratio of the lime component in the produced solid containing modified calcium fluoride is preferably 0.5% by mass or less, more preferably 0.4% by mass or less, still more preferably 0.3% by mass or less, and particularly preferably 0.25% by mass or less in order to maintain high quality of hydrofluoric acid produced using this solid containing modified calcium fluoride. On the other hand, regarding the lower limit, although a smaller content is preferable, it is about 0.1% by mass in consideration of production efficiency and the like. 【0035】 Here, the amount of the lime component in the solid containing modified calcium fluoride refers to a value (amount of calcium carbonate) obtained from the weight loss due to thermal decomposition at 680 to 755°C by raising the temperature from room temperature to 1000°C at 10°C / min in a nitrogen atmosphere using a TG-DTA (thermogravimetry-differential thermal analysis) apparatus. 【0036】 Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. 【0037】 (Sample) As the sample, dried calcium fluoride sludge (solid containing calcium fluoride) having the component composition shown in Table 1 was used. 【0038】 【0039】 (Test method) 100 mL of water was mixed with 1 g of the above sample, the sample was dispersed in water to form a slurry, and a carbon dioxide-containing gas was supplied to this slurry. As this carbon dioxide-containing gas, industrial exhaust gas with a carbon dioxide content of 100% by volume (Examples 1 and 2) and simulated exhaust gas composed of nitrogen and carbon dioxide with a carbon dioxide content of 15% by volume (Example 3) were used. Also, the supply amount of industrial exhaust gas (carbon dioxide) to the slurry was 0.5 L / min, and the supply amount of the simulated exhaust gas was 1.18 L / min (carbon dioxide supply amount 0.18 L / min). 【0040】 The test conditions and test results are shown in Table 2. Note that the reaction time in Table 2 indicates the treatment time after supplying carbon dioxide until the pH becomes 6.0 or less. 【0041】In addition, the lime component in the sample before and after the treatment was calculated from the weight loss due to thermal decomposition at 680 to 755°C by raising the temperature from room temperature to 1000°C at 10°C / min under a nitrogen atmosphere using a TG-DTA (thermogravimetry-differential thermal analysis) apparatus. Also, the bicarbonation rate in Table 2 was calculated by the following formula. 【0042】 Bicarbonation rate (%) = [{{(CaCO concentration before reaction) × (weight of the whole sample before reaction)} - {(CaCO concentration after reaction) × (weight of the whole sample after reaction)}} / {{(CaCO concentration before reaction) × (weight of the whole sample before reaction)}}] × 100 ３ concentration) × (weight of the whole sample before reaction)} - {(CaCO ３ concentration) × (weight of the whole sample after reaction)}} / {{(CaCO ３ concentration) × (weight of the whole sample before reaction)}}] × 100 【0043】 【0044】 As shown in Examples 1 to 3 of Table 2, by supplying carbon dioxide and maintaining the pH of the slurry at 6.0 or less, the lime component (calcium carbonate) in the modified calcium fluoride-containing solid could be reduced from before the treatment. In particular, as in Examples 2 and 3, by extending the time for maintaining the pH of the slurry at 6.0 or less to 15 minutes, the bicarbonation rate was increased compared to Example 1, and the lime component in the modified calcium fluoride-containing solid could be reduced to 0.5% by mass or less. 【0045】 As described above, it was confirmed that according to the present invention, the lime component in the calcium fluoride-containing solid can be effectively reduced without using an acid or an alkali. 【0046】 The method for producing the modified calcium fluoride-containing solid of the present invention is industrially useful because a high-quality calcium fluoride-containing solid that can be used as a raw material for hydrofluoric acid can be obtained.

Claims

1. A method for producing a modified calcium fluoride-containing solid in which the lime component is reduced, by separating the lime component from a calcium fluoride-containing solid containing calcium fluoride and at least one lime component selected from calcium carbonate, calcium hydroxide, and calcium oxide, characterized in that a carbon dioxide-containing gas is supplied to a slurry containing the calcium fluoride-containing solid and water, and the pH of the slurry is maintained at 6.0 or below to dissolve the lime component.

2. The method for producing a modified calcium fluoride-containing solid according to claim 1, characterized in that the content ratio of the lime component in the modified calcium fluoride-containing solid is 0.5% by mass or less.

3. The method for producing a modified calcium fluoride-containing solid according to claim 1, characterized in that the pH of the slurry is maintained at 5.0 or higher and 6.0 or lower.

4. The method for producing a modified calcium fluoride-containing solid according to claim 1, characterized in that the pH of the slurry is maintained at 6.0 or lower for 15 minutes or more.

5. The method for producing a modified calcium fluoride-containing solid according to claim 1, characterized in that the calcium fluoride-containing solid contains 60% by mass or more of calcium fluoride on a dry matter basis.

6. The method for producing a modified calcium fluoride-containing solid according to claim 1, characterized in that the carbon dioxide-containing gas is exhaust gas generated from a thermal power plant or exhaust gas generated from a cement manufacturing facility.

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