Method for producing modified calcium fluoride-containing solid matter

Abstract

A method for producing a modified calcium fluoride-containing solid matter which is obtained by separating, from a calcium fluoride-containing solid matter containing calcium fluoride, a silicon compound, and an aluminum compound, the silicon compound and the aluminum compound to reduce the same, the method comprising eluting the silicon compound and the aluminum compound by performing an alkali treatment on a slurry containing the calcium fluoride-containing solid matter and water at a temperature of 50°C or higher.

Description

Method for producing modified calcium fluoride-containing solids 【0001】 The present invention relates to a method for separating silicon compounds and aluminum compounds from calcium fluoride-containing solids and reducing the amount of silicon compounds and aluminum compounds in the calcium fluoride-containing solids. 【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 and inorganic coagulants such as aluminum sulfate and polyaluminum chloride. After solid-liquid separation and dewatering, it becomes calcium fluoride sludge. At this time, silicon such as product silicon, organic matter, and inorganic coagulants 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, if it contains, for example, silicon or aluminum, unintended chemical reactions may occur during hydrofluoric acid production, potentially leading to hydrofluoric acid loss. 【0004】 To solve this problem, a method has been proposed in which calcium fluoride sludge is washed with hydrofluoric acid to convert calcium carbonate to calcium fluoride, dissolve silicon compounds to reduce their concentration, and then an alkaline component is added and washed to dissolve aluminum compounds, thereby reducing impurities contained in the calcium fluoride sludge (see, for example, Patent Document 1). 【0005】 Japanese Patent Publication No. 2021-11418 【0006】 However, hydrofluoric acid is highly hazardous to handle and requires careful handling. Furthermore, simply performing alkaline treatment is not sufficient to adequately reduce impurities such as aluminum compounds. 【0007】 The object of the present invention is to provide a method for safely and effectively separating silicon compounds and aluminum compounds from calcium fluoride-containing solids without using hydrofluoric acid, and for producing modified calcium fluoride-containing solids with reduced silicon and aluminum compounds. 【0008】 The inventors of the present invention have discovered that by alkaline treatment of a slurry containing calcium fluoride-containing solid and water at 50°C or higher, silicon compounds and aluminum compounds can be eluted, thereby reducing the amount of silicon compounds and aluminum compounds in the calcium fluoride-containing solid, 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 silicon compound and aluminum compound are reduced, by separating the silicon compound and aluminum compound from a calcium fluoride-containing solid containing calcium fluoride, a silicon compound (containing silicon), and an aluminum compound (containing metallic aluminum), characterized in that a slurry containing the calcium fluoride-containing solid and water is subjected to alkali treatment at 50°C or higher to elute the silicon compound and aluminum compound. 【0010】 [2] The silicon content (in Si equivalent) in the modified calcium fluoride-containing solid is 4.0% by mass or less, and the aluminum content (Al ２ O ３ A method for producing a modified calcium fluoride-containing solid according to [1] above, characterized in that the converted amount is 6.0% by mass or less. 【0011】 [3] The method for producing a modified calcium fluoride-containing solid according to [1] or [2] above, characterized in that, before the alkali treatment, the calcium fluoride-containing solid is heat-treated to decompose and remove organic matter contained in the calcium fluoride-containing solid. [4] The method for producing a modified calcium fluoride-containing solid according to [3] above, characterized in that the heating temperature in the heat treatment is 250°C or higher. 【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 alkali treatment is carried out for one hour or more. [6] A method for producing a modified calcium fluoride-containing solid according to [3] or [4] above, characterized in that the heat treatment is carried out for one hour or more. 【0013】 [7] A method for producing a modified calcium fluoride-containing solid according to any one of [1] to [6] above, characterized in that the calcium fluoride-containing solid contains 60% by mass or more of calcium fluoride on a dry matter basis. [8] A method for producing a modified calcium fluoride-containing solid according to any one of [1] to [7] above, characterized in that the alkali source used in the alkali treatment is sodium hydroxide and / or potassium hydroxide. 【0014】 According to the present invention, silicon compounds and aluminum compounds can be safely and effectively separated from calcium fluoride-containing solids without using hydrofluoric acid, thereby producing modified calcium fluoride-containing solids with reduced levels of these compounds. 【0015】 The present invention provides a method for producing a modified calcium fluoride-containing solid, comprising separating the silicon compound and the aluminum compound from a calcium fluoride-containing solid containing calcium fluoride, a silicon compound, and an aluminum compound, thereby producing a modified calcium fluoride-containing solid with reduced silicon and aluminum compounds, characterized in that a slurry containing the calcium fluoride-containing solid and water is subjected to alkali treatment at 50°C or higher to elute the silicon compound and the aluminum compound. 【0016】 Here, calcium fluoride-containing solids refer to calcium fluoride (CaF ２), a solid containing silicon compounds and aluminum compounds, wherein the silicon compounds contain silicon (Si) and the aluminum compounds contain metallic aluminum (Al). Specific examples of calcium fluoride-containing solids include calcium fluoride sludge obtained by treating fluorinated wastewater generated in semiconductor manufacturing, liquid crystal manufacturing, glass processing, etc. More specifically, calcium fluoride sludge produced by adding lime-based additives such as calcium carbonate and calcium hydroxide to fluorinated wastewater, along with inorganic flocculants such as aluminum sulfate and polyaluminum chloride. This calcium fluoride sludge may be sludge that has undergone dewatering treatment after solid-liquid separation, or sludge that contains moisture. 【0017】 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. 【0018】 This calcium fluoride-containing solid may contain other components in addition to calcium fluoride, silicon compounds, and aluminum compounds. These other components vary depending on the production route of the calcium fluoride-containing solid. For example, in the case of calcium fluoride sludge, these may include organic matter and inorganic flocculants. 【0019】 In this invention, by not using hydrofluoric acid, silicon and aluminum compounds in calcium fluoride-containing solids can be safely reduced, and by alkaline treatment at 50°C or higher, the purity of calcium fluoride can be increased. Furthermore, since the amount of calcium fluoride-containing solids to be discarded can be reduced, environmental pollution can be suppressed, and the reuse of calcium fluoride-containing solids can be made more efficient in terms of resource utilization, while the use of fluorite, a mineral resource, can be reduced. 【0020】In the present invention, it is preferable to heat-treat the calcium fluoride-containing solid before alkali treatment. This allows for the decomposition and removal of organic matter contained in the calcium fluoride-containing solid. When the calcium fluoride-containing solid is calcium fluoride sludge, the organic matter includes, for example, various organic solvents such as alcohol and acetone, surfactants, microbial decomposition products, and microbial residues. 【0021】 Thus, by heat-treating the calcium fluoride-containing solid before alkali treatment, organic matter can be decomposed and removed. This suppresses or prevents foaming caused by organic matter during alkali treatment, allowing for safe and easy handling of the alkali treatment. In particular, in this invention, alkali treatment is performed at high temperatures, which tends to cause vigorous foaming due to organic matter, but this can be effectively prevented. 【0022】 The method for producing the modified calcium fluoride-containing solid of the present invention will be described in detail below. 【0023】 First, depending on the type of calcium fluoride-containing solid, the calcium fluoride-containing solid is heat-treated (heat treatment step) before alkaline treatment. This allows for the decomposition and removal of organic matter contained in the calcium fluoride-containing solid. 【0024】The heating temperature in this heat treatment varies depending on, for example, the type of organic matter in the calcium fluoride-containing solid, i.e., the formation pathway of the calcium fluoride-containing solid. It is not particularly limited as long as it is a temperature that can decompose and remove the organic matter. For example, it is about 100 to 800°C, preferably 200°C or higher, more preferably 250°C or higher, and even more preferably 650°C or higher, considering the reduction of calcium carbonate in the calcium fluoride-containing solid. If calcium carbonate is present in the calcium fluoride-containing solid, carbon dioxide gas is generated during hydrofluoric acid production, leading to a decrease in the quality of hydrofluoric acid. However, by reducing the calcium carbonate content, the generation of carbon dioxide gas caused by calcium carbonate can be suppressed or prevented, thereby improving the quality of the hydrofluoric acid produced. 【0025】 Examples of heating equipment include electric furnaces that use electrical energy as a heat source, combustion furnaces that use oil or gas as a heat source, and heating furnaces that utilize factory exhaust gas, etc. Heating treatment using these devices can be carried out in batch or continuous manner. 【0026】 Here, the time for the heat treatment is not particularly limited as long as it can decompose and remove organic matter. For example, it is preferably 1 hour or more, more preferably 2 hours or more, and even more preferably 3 hours or more. 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 5 hours. 【0027】 Next, the heat-treated calcium fluoride-containing solid is added to a container along with water to prepare a slurry (slurry preparation step). 【0028】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 solid, 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 effectively brought into contact with the alkali source used for alkali treatment, thereby increasing the production efficiency of the modified calcium fluoride-containing solids. 【0029】 Next, the slurry containing calcium fluoride-containing solids and water is subjected to alkaline treatment at 50°C or higher (alkaline treatment step). This effectively dissolves silicon and aluminum compounds from the calcium fluoride-containing solids into the liquid, allowing them to be separated from the calcium fluoride-containing solids. 【0030】 This alkali treatment can be carried out in a continuous or batch manner. A continuous method, for example, involves continuously supplying and discharging a predetermined amount of calcium fluoride-containing solid, an alkali source, and water into a stirring vessel, while simultaneously heating the slurry in the stirring vessel to maintain its temperature at 50°C or higher. Here, the alkali source can be supplied to the stirring vessel either pre-added to water or separately. Furthermore, it is preferable to pre-heat the water supplied to the stirring vessel, for example, to a temperature equivalent to the slurry temperature before supplying it to the stirring vessel. 【0031】 The rate at which calcium fluoride-containing solids, an alkali source, and water are supplied into this stirring vessel, i.e., the processing time (residence time) in the stirring vessel, is determined by the silicon content in the calcium fluoride-containing solids and the alumina equivalent (Al ２ O ３It is preferably adjusted as appropriate according to the converted aluminum content ratio (hereinafter, also simply referred to as the aluminum content ratio), etc. In actual operation, the silicon content ratio and aluminum content ratio in the modified calcium fluoride-containing solid discharged from the stirring vessel can be measured, and various conditions can be adjusted. 【0032】 As a batch method, for example, a mode can be cited in which the slurry in the stirring vessel is heated while stirring so that the temperature of this slurry is maintained at 50 °C or higher and held for a predetermined time. Here, the slurry can be prepared, for example, by adding an alkali source to the water stored in the stirring vessel, stirring, and then adding the calcium fluoride-containing solid to the stirring vessel and stirring. Further, the slurry (mainly water) supplied into the stirring vessel may be supplied into the stirring vessel in a pre-heated state, for example, in a state heated to 50 °C or higher. 【0033】 The treatment time in the stirring vessel is preferably adjusted as appropriate according to the silicon content ratio and aluminum content ratio in the calcium fluoride-containing solid, etc. After the treatment, the modified calcium fluoride-containing solid and the liquid in which silicon, aluminum, etc. are eluted are taken out from the stirring vessel, and the above-described procedure is continuously repeated. 【0034】 As the alkali source used for the alkali treatment, a strong base is preferable. Specifically, it is preferable to use sodium hydroxide (NaOH) and potassium hydroxide (KOH). Here, the concentration of the alkali source with respect to water and the alkali source (= (mass of the alkali source) / {(mass of water) + (mass of the alkali source)} × 100%) is preferably, for example, 1 to 30% by mass, more preferably 5 to 30% by mass, further preferably 5 to 25% by mass, particularly preferably 10 to 25% by mass, and most preferably 10 to 20% by mass. 【0035】In the present invention, the alkali treatment temperature is 50°C or higher as described above. From the viewpoint of more effectively eluting silicon compounds, aluminum compounds, etc., it is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 75°C or higher. On the other hand, the upper limit is not particularly limited, but considering the production efficiency of the modified calcium fluoride-containing solid and the heat energy cost associated with heating, it is about 95°C. 【0036】 Here, the alkali treatment time at 50°C or higher is preferably 1 hour or longer, more preferably 1.5 hours or longer, from the viewpoint of ensuring the reaction time required for the alkali treatment (elution). On the other hand, the upper limit is not particularly limited, but considering the production efficiency of the modified calcium fluoride-containing solid, etc., it is about 3 hours. 【0037】 After eluting silicon, metallic aluminum, etc. in water, the slurry is, if necessary, subjected to removal of other components (impurities) and then solid-liquid separated to obtain a modified calcium fluoride-containing solid. The separated modified calcium fluoride-containing solid is preferably washed with water to remove the adhering substances. Here, examples of the equipment for performing solid-liquid separation include normal pressure filtration, reduced pressure filtration, filter press, screw press, centrifuge (screw decanter), thickener, etc. 【0038】 The silicon content ratio and aluminum content ratio in the produced modified calcium fluoride-containing solid are such that, in order to reduce the loss of hydrofluoric acid produced using this modified calcium fluoride-containing solid, etc., the silicon content ratio (in terms of Si) is preferably 4.0% by mass or less, more preferably 3.5% by mass or less, and even more preferably 3.0% by mass or less. Also, the aluminum content ratio (Al ２ O ３The (conversion) is preferably 6.0% by mass or less, more preferably 4.0% by mass or less, still more preferably 3.5% by mass or less, even more preferably 3.0% by mass or less, particularly preferably 2.5% by mass or less, and most preferably 2.0% by mass or less. On the other hand, regarding the lower limit, although a smaller content ratio is preferable, considering production efficiency and the like, the silicon content ratio is about 1.0% by mass, and the aluminum content ratio is about 0.5% by mass. 【0039】 Further, the produced calcium fluoride-containing solid substance preferably contains 80% by mass or more of calcium fluoride, more preferably 85% by mass or more, and still more preferably 90% by mass or more in terms of dry matter. 【0040】 Here, the calcium fluoride, silicon content ratio, and aluminum content ratio in the calcium fluoride-containing solid substance are measured and calculated using a scanning fluorescent X-ray analyzer. Specifically, it is as shown in the examples. 【0041】 Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. 【0042】 (Test method) Calcium fluoride sludge was held in an electric furnace maintained at the heat treatment temperature shown in Table 1 for 3 hours. Next, 15 g of an alkali source (potassium hydroxide or sodium hydroxide) and 85 mL of water were placed in a beaker and dissolved, and then 2 g of the above calcium fluoride sludge was dispersed in water to form a slurry, and alkali treatment was performed at the alkali treatment temperature shown in Table 1 for 1 hour. Then, the slurry was filtered and dried at 100°C to measure the content ratios (mass %) of calcium fluoride (CaF ２ ), calcium carbonate (CaCO ３ ), calcium sulfate (CaSO ４ ), silicon (Si), and aluminum (Al ２ O ３ ). 【0043】 The measurement and calculation methods for the content ratios of each component are shown below. Calcium fluoride (CaF ２ ) and calcium sulfate (CaSO ４The following methods were used to measure and calculate the total sulfur and calcium concentrations (S) and the oxide equivalent (SO₂) using a Rigaku scanning X-ray fluorescence analyzer (ZSX Primus IV). ３ The CaO concentration was measured. From the total S concentration, CaSO2 was calculated. ４ The concentration was calculated from the total amount of Ca in moles. ４ The amount of Ca derived from the source and the separately measured CaCO2 ３ From the mol of Ca remaining after subtracting the mol of Ca from the source, CaF ２ The concentration was calculated. 【0044】 Calcium carbonate (CaCO3) ３ The concentrations were calculated using a TG-DTA (thermogravimetric differential thermal analysis) instrument, heating from room temperature to 1000°C at a rate of 10°C / min under a nitrogen atmosphere, and then measuring the weight loss due to thermal decomposition at 680-755°C. Silicon (Si), Aluminum (Al ２ O ３ The analysis was performed using a Rigaku scanning X-ray fluorescence analyzer (ZSX Primus IV). The sum of all these compositions was set to 100. 【0045】 【0046】 As shown in Examples 1 to 10 of Table 1, alkaline treatment of the slurry at 50°C or higher significantly reduced the silicon and aluminum content in the calcium fluoride sludge. In particular, as in Examples 7 to 10, heat treatment at 700°C or higher reduced the calcium carbonate content in the calcium fluoride sludge to approximately 0.1% by mass. Furthermore, as in Examples 4 to 10, heat treatment at 300°C or higher before alkaline treatment decomposed and removed organic matter in the calcium fluoride-containing solids, suppressing or preventing foaming of the slurry during alkaline treatment. 【0047】 In summary, the present invention has confirmed that silicon compounds and aluminum compounds in calcium fluoride-containing solids can be effectively reduced without the use of hydrofluoric acid. 【0048】The present invention's method for producing a modified calcium fluoride-containing solid is industrially useful because it can produce a modified calcium fluoride-containing solid that can reduce or prevent the loss of hydrofluoric acid during hydrofluoric acid production.

Claims

1. A method for producing a modified calcium fluoride-containing solid in which the silicon compound and aluminum compound are reduced, by separating the silicon compound and aluminum compound from a calcium fluoride-containing solid containing calcium fluoride, a silicon compound and an aluminum compound, characterized in that a slurry containing the calcium fluoride-containing solid and water is subjected to alkali treatment at 50°C or higher to elute the silicon compound and aluminum compound.

2. The silicon content (in Si equivalent) in the modified calcium fluoride-containing solid is 4.0% by mass or less, and the aluminum content (Al ２ O ３ A method for producing a modified calcium fluoride-containing solid according to claim 1, characterized in that the converted amount is 6.0% by mass or less.

3. The method for producing a modified calcium fluoride-containing solid according to claim 1, characterized in that, before the alkali treatment, the calcium fluoride-containing solid is heat-treated to decompose and remove organic matter contained in the calcium fluoride-containing solid.

4. The method for producing a modified calcium fluoride-containing solid according to claim 3, characterized in that the heating temperature in the heat treatment is 250°C or higher.

5. The method for producing a modified calcium fluoride-containing solid according to claim 1, characterized in that the alkaline treatment is performed for one hour or more.

6. The method for producing a modified calcium fluoride-containing solid according to claim 3, characterized in that the heat treatment is performed for one hour or more.

7. 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.

8. The method for producing a modified calcium fluoride-containing solid according to claim 1, characterized in that the alkali source used in the alkali treatment is sodium hydroxide and / or potassium hydroxide.

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