Method for preparing high-quality calcium fluoride based on secondary calcination treatment of fluorine-containing sludge

Abstract

The invention belongs to the technical field of solid waste treatment and resource recovery, and particularly relates to a method for preparing high-quality calcium fluoride based on secondary calcination treatment of fluorine-containing sludge. The method comprises the following steps: drying fluorine-containing sludge, crushing and mixing the dried fluorine-containing sludge with sodium carbonate, carrying out first-stage dynamic calcination at 850-950 DEG C, feeding the primarily calcined fluorine-containing sludge into a water-quenching acid leaching solution in a high-temperature state of 800-900 DEG C, carrying out stirring acid leaching treatment, and carrying out solid-liquid separation, and washing the obtained solid phase with water, drying, mixing with a calcium chloride fluxing agent and a calcium fluoride seed crystal, carrying out two-stage dynamic calcination at the temperature of 950-1100 DEG C, naturally cooling after calcination, washing and drying to obtain a high-quality calcium fluoride product. According to the method, acid leaching separation of calcium fluoride and impurities and granulation and quality improvement of the calcium fluoride product can be effectively promoted through the two-stage calcination process, so that the particle size and quality of the calcium fluoride product are greatly increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste treatment and resource recovery, and particularly relates to a method for preparing high-quality calcium fluoride by treating fluorine-containing sludge through secondary calcination. Background Art

[0002] Fluorine-containing sludge is a common solid waste in industrial production, widely sourced from industries such as chemical engineering, metallurgy, and electroplating. This type of sludge contains high concentrations of fluorides, which are toxic and corrosive. If not properly treated, it may cause serious harm to the ecological environment and human health. High-fluoride wastewater generated during the production process of enterprises often adopts a calcium salt precipitation + coagulation treatment process to remove fluorine by combining fluoride ions with calcium ions to form calcium fluoride precipitation; to meet the standard of fluoride in the effluent, an excessive amount of calcium salt needs to be added, thus generating a large amount of fluorine-containing sludge. The accumulation of fluorine-containing sludge not only occupies a large amount of land, but also has a high leaching risk of fluoride ions during long-term storage. After storage or landfill, fluoride ions will enter surface water and soil through rain leaching and infiltration, causing fluoride exceeding the standard in the water and soil environment, and even threatening human health through the enrichment and migration of crops. Therefore, the reasonable disposal of fluorine-containing sludge has become an important environmental protection issue.

[0003] At present, the conventional treatment methods for fluorine-containing sludge mainly include solidification / stabilization treatment, heat treatment, flotation method, direct acid leaching method, etc. Solidification / stabilization treatment is to add cement, lime or other solidifying agents to fix the fluorine in the fluorine-containing sludge in the solid matrix, reducing the risk of its migration and release. This method is easy to operate and the treatment effect is relatively stable, especially suitable for the sludge coexisting with heavy metals and fluorine. However, its main disadvantages are the significant increase in volume, occupying a large landfill space, and the potential risk of secondary pollution. Especially when the solidification is insufficient or after long-term degradation, it may lead to the release of fluorine. Heat treatment methods include processes such as incineration and melting. By decomposing the organic matter in the sludge at high temperature, the fluoride is gasified or mineralized at the same time. Incineration is suitable for sludge containing a large amount of organic matter, while melting is more suitable for inorganic sludge with high-concentration fluorides. Its advantages are that it can greatly reduce the sludge volume and completely destroy organic pollutants; the disadvantages are high energy consumption, high equipment requirements, and the need for further capture and treatment of fluoride gases to avoid air pollution. The flotation method is a separation technology based on the differences in the physicochemical properties of the mineral surface. Collector, foaming agent and other agents are added to the fluorine-containing sludge to adjust the flotation environment, enhancing the hydrophilicity difference between the impurity particles and calcium fluoride, and selectively separating calcium fluoride in the fluorine-containing sludge. However, due to the poor crystallization degree of calcium fluoride and impurities, the crystal surface difference is small. At the same time, the nano-particles in the fluorine-containing sludge are lower than the particle lower limit for effective flotation. Therefore, it is difficult to achieve the selective separation of calcium fluoride in the fluorine-containing sludge by the flotation method. In addition, some enterprises have tried to purify calcium fluoride in fluorine-containing sludge using common chemical leaching methods and found that the acid leaching selectivity of calcium fluoride and impurities is poor, and the content of calcium fluoride in the fluorine-containing sludge hardly increases after acid leaching. The reason is that large particles of calcium fluoride with a complete crystal structure are theoretically insoluble in low-concentration acid solutions. However, due to the poor crystallization degree of calcium fluoride in the fluorine-containing sludge, calcium fluoride and impurities are mixed with each other, and the particle size is nanoscale. Under acid leaching conditions, calcium fluoride is easily dissolved in the acid solution together with impurities. Therefore, the direct acid leaching method cannot achieve the selective separation of calcium fluoride in the fluorine-containing sludge. To sum up, the traditional treatment methods cannot effectively separate calcium fluoride from the fluorine-containing sludge, resulting in a very low recovery rate of calcium fluoride. The main reason is that both calcium fluoride and impurities in the fluorine-containing sludge are nano-particles with poor crystallinity, mixed with each other, and they are similar in crystal size, crystal structure, surface properties, acid solubility, etc., with small differences. Therefore, there is an urgent need for a treatment method that can selectively separate calcium fluoride and impurities in the fluorine-containing sludge and recycle calcium fluoride resourcefully. Summary of the Invention

[0004] Aiming at the above-mentioned disadvantages and deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing high-quality calcium fluoride by treating fluorine-containing sludge based on secondary calcination.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A method for preparing high-quality calcium fluoride by treating fluorine-containing sludge through secondary calcination, comprising the following steps:

[0007] (1) After drying the fluorine-containing sludge, it is crushed and mixed with sodium carbonate, and then fed into a dynamic heating device for the first-stage dynamic calcination at a temperature of 850 - 950 °C to obtain the once-calcined fluorine-containing sludge;

[0008] (2) The once-calcined fluorine-containing sludge is fed into a water-quenched acid leaching solution at a high temperature of 800 - 900 °C for stirring acid leaching treatment, and then solid-liquid separation is carried out. The obtained solid phase is washed with water to obtain the fluorine-containing sludge after acid leaching and impurity removal;

[0009] (3) The fluorine-containing sludge after acid leaching and impurity removal is dried and then mixed with calcium chloride flux and calcium fluoride crystal seeds, and then fed into a dynamic heating device for the second-stage dynamic calcination at a temperature of 950 - 1100 °C. After the calcination is completed, it is naturally cooled, washed, and dried to obtain a high-quality calcium fluoride product.

[0010] Furthermore, in step (1), the fluorine-containing sludge is the fluorine-containing sludge generated during the fluorochemical production process, and its main solid-phase components include calcium fluoride, calcium carbonate, and silicon dioxide. The content of calcium fluoride in the solid-phase components is 60 - 80 wt.%.

[0011] Furthermore, in steps (1) and (3), the drying means drying at a temperature of 105 - 120 °C until the moisture content is 4 - 6%.

[0012] Furthermore, in step (1), the mass ratio of the sodium carbonate to the dried fluorine-containing sludge for crushing and mixing is 1:8 - 15.

[0013] Furthermore, in step (1), the rotation speed of the first-stage dynamic calcination is 30 - 50 r / min, and the calcination time is 1 - 2 h.

[0014] Furthermore, in step (2), the water-quenched acid leaching solution uses a dilute hydrochloric acid solution with a mass concentration of 10 - 20%; the solid-liquid ratio of the once-calcined fluorine-containing sludge to the water-quenched acid leaching solution is 1:4 - 6; the rotation speed of the stirring acid leaching treatment is 100 - 200 r / min, and the time is 40 - 80 min.

[0015] Furthermore, in step (2), the solid-liquid separation means carrying out vacuum filtration for solid-liquid separation under a vacuum degree of 0.01 - 0.1 MPa; the obtained liquid phase after solid-liquid separation respectively obtains sodium chloride and calcium chloride through the fractional crystallization method; the obtained calcium chloride is used as the calcium chloride flux in step (3) for resource utilization.

[0016] Furthermore, in step (3), the particle size of the calcium fluoride crystal seeds is 50 - 100 μm.

[0017] Further preferably, the mass ratio of the dried fluorine-containing sludge after acid leaching and impurity removal to calcium chloride flux and calcium fluoride seed crystal is 10:0.4-0.6:0.2-0.4.

[0018] Further, in step (3), the dynamic calcination rotation speed in the second stage is 50-100 r / min, and the calcination time is 1-3 h.

[0019] Further, in step (3), the purity of the high-quality calcium fluoride product is >97%, and the proportion of the product particle size on the 325-mesh sieve is more than 90%.

[0020] The principle of the present invention is as follows: The main components of the fluorine-containing sludge generated in the fluorochemical production process are calcium fluoride (CaF2), silicon dioxide (SiO2), and calcium carbonate (CaCO3). Since the acid leaching process will reduce the particle size of the calcium fluoride product, the present invention adopts a two-stage calcination method. The first-stage calcination mainly promotes the differential growth process of calcium fluoride crystals and impurities. During the high-temperature calcination process, calcium fluoride gradually forms a crystal structure from amorphous, calcium carbonate undergoes a decomposition reaction to generate calcium oxide (CaO), and together with sodium carbonate (Na2CO3), it reacts with silicon dioxide (SiO2) to generate calcium silicate (CaSiO3) and sodium silicate (Na2SiO3). The specific reaction formulas are as follows:

[0021] CaCO3(s) = CaO(s) + CO2(g);

[0022] CaO(s) + SiO2(s) = CaSiO3(s);

[0023] Na2CO3(s) + SiO2(s) = Na2SiO3(s) + CO2(g);

[0024] Subsequently, the first-stage calcination product is separated and purified by quenching the acid leaching solution. Sodium silicate, calcium silicate, and calcium oxide in the solid phase will react and dissolve with heated hydrochloric acid (HCl) to generate sodium chloride (NaCl), calcium chloride (CaCl2), and colloidal silicic acid (H2SiO3) precipitate. After solid-liquid separation, a liquid phase containing sodium chloride and calcium chloride is obtained, and fractional crystallization is carried out on it for resource recovery and utilization. Subsequently, a small amount of colloidal silicic acid and attached dilute hydrochloric acid in the solid phase are washed away with water to obtain purified calcium fluoride. The specific reaction formulas are as follows:

[0025] Na2SiO3(s) + 2HCl(aq) = 2NaCl(aq) + H2SiO3(s);

[0026] CaSiO3(s) + 2HCl(aq) = CaCl2(aq) + H2SiO3(s) + H2O(aq);

[0027] CaO(s) + 2HCl(aq) = CaCl2(aq) + H2O(aq);

[0028] Finally, large-sized calcium fluoride seeds and calcium chloride flux are added to the calcium fluoride after impurity removal and mixed in a certain proportion, and then two-stage calcination is carried out. The flux can reduce the surface energy of calcium fluoride, accelerate grain boundary migration, and will not introduce other impurities. The residual calcium chloride is removed after rinsing. The large-sized seeds provide heterogeneous nucleation sites, reduce random nucleation, promote directional growth, further granulate and improve the quality of calcium fluoride, and finally obtain high-quality calcium fluoride products.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) Since the particle size of calcium fluoride will be reduced during the water quenching and acid leaching process, the present invention adopts a two-stage calcination method to separate the water quenching and acid leaching impurity removal process from the calcination and quality improvement process, so that the particle size and quality of the calcium fluoride product are greatly increased.

[0031] (2) The present invention can effectively remove impurities (calcium carbonate and silicon dioxide) in the fluorine-containing sludge. After treatment, the calcium fluoride content of the product reaches more than 97%, and the particle size reaches more than 90% of the proportion on the 325-mesh sieve. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a process flow chart of a method for preparing high-quality calcium fluoride by treating fluorine-containing sludge based on secondary calcination in an embodiment of the present invention.

[0033] Figure 2 It is an SEM spectrum diagram of the fluorine-containing sludge before treatment and the high-quality calcium fluoride product obtained after treatment in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The present invention will be further described in detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0035] Example 1

[0036] A method for preparing high-quality calcium fluoride by treating fluorine-containing sludge based on secondary calcination, the process flow chart of which is as Figure 1 shown, and includes the following steps:

[0037] (1) One-stage calcination for impurity removal: Put the fluorine-containing sludge into an oven and dry it at 110°C until the water content is 5%. Mix sodium carbonate and the dried sample in a mass ratio of 1:10, add them together into a wall-breaking mill, and carry out crushing and mixing at 3000 r / min. Then send it into a rotary tube muffle furnace and conduct dynamic calcination for 1.5 h at a temperature of 900°C and a rotation speed of 40 r / min to remove impurities such as silicon dioxide and calcium carbonate, and obtain the once-calcined fluorine-containing sludge.

[0038] (2) Water quenching and acid leaching for impurity removal: Send the once-calcined fluorine-containing sludge into a water quenching and acid leaching tank at a high temperature of 800°C (dilute hydrochloric acid with a mass concentration of 15%, solid-liquid ratio 1:5), stir and leach with acid at a rotation speed of 150 r / min for 60 min, and then carry out vacuum filtration for solid-liquid separation under the condition that the vacuum degree is higher than 0.09 MPa. After the solid phase is washed to remove colloidal silicic acid, it is the fluorine-containing sludge after acid leaching and impurity removal; in the liquid phase are dissolved sodium chloride and calcium chloride, and then the solubility difference-based fractional crystallization is used to respectively recycle sodium chloride and calcium chloride for resource utilization.

[0039] (3) Two-stage calcination for purification: Put the fluorine-containing sludge after acid leaching and impurity removal into an oven and dry it at 110°C until the water content is 5%. Then mix it with calcium chloride obtained from the fractional crystallization in step (2) and calcium fluoride seeds with a particle size of 50 - 100 μm in a mass ratio of 10:0.5:0.3. Subsequently, send it into a rotary tube muffle furnace and conduct dynamic calcination at a temperature of 1000°C and a rotation speed of 60 r / min for 2 h. After the calcination is completed, let it cool naturally, and after washing and drying, obtain high-quality calcium fluoride products.

[0040] The SEM spectra of the fluorine-containing sludge before treatment and the high-quality calcium fluoride products obtained after treatment in this example are as Figure 2 shown. The calcium fluoride or calcium carbonate in the fluorine-containing sludge is mainly nanoscale aggregates or dispersed particles, while the calcium fluoride in the treated product grows into large particle crystals with a size of about 50 microns, and the particle size of the calcium fluoride product obtained after treatment increases significantly.

[0041] The main components of the fluorine-containing sludge before treatment and the high-quality calcium fluoride products obtained after treatment in this example are shown in Table 1 below. The calcium fluoride content of the product after treatment in this example is 98.33%, the removal rate of silicon dioxide is 87.71%, and the proportion of the product particle size on the 325-mesh sieve is 94.8%.

[0042] Table 1

[0043] Composition <![CDATA[CaF2]]> <![CDATA[CaCO3]]> CaO <![CDATA[SiO2]]> Fluoride-containing sludge (wt.%) 72.45 17.91 / 8.87 Treated product (wt.%) 98.33 / 0.17 1.09

[0044] Example 2

[0045] A method for preparing high-quality calcium fluoride by treating fluorine-containing sludge through secondary calcination, the process flow chart of which is as Figure 1 shown, and it includes the following steps:

[0046] (1) Impurity removal by one-stage calcination: Put the fluorine-containing sludge into an oven and dry it at 105°C until the moisture content is 6%. Mix sodium carbonate and the dried sample in a mass ratio of 1:8, add them together into a wall-breaking pulverizer, crush and mix them at 3000 r / min, and then send them into a rotary tube muffle furnace. Carry out one-stage dynamic calcination for 2 h at a temperature of 850°C and a rotation speed of 30 r / min to remove silicon dioxide and calcium carbonate impurities, and obtain the once-calcined fluorine-containing sludge.

[0047] (2) Water quenching and acid leaching for impurity removal: Feed the once-calcined fluorine-containing sludge into a water quenching and acid leaching tank at a high temperature of 800°C (10% dilute hydrochloric acid by mass concentration, solid-liquid ratio 1:6), stir and leach with acid at a rotation speed of 100 r / min for 40 min, and then carry out vacuum filtration for solid-liquid separation under the condition that the vacuum degree is higher than 0.09 MPa. After the obtained solid phase is washed to remove colloidal silica, it is the fluorine-containing sludge after acid leaching and impurity removal; in the liquid phase are dissolved sodium chloride and calcium chloride, and then the solubility difference is used for fractional crystallization to respectively recycle sodium chloride and calcium chloride.

[0048] (3) Two-stage calcination for purification: Put the fluorine-containing sludge after acid leaching and impurity removal into an oven and dry it at 105°C until the moisture content is 6%. Then mix it with the calcium chloride obtained by fractional crystallization in step (2) and calcium fluoride crystal seeds with a particle size of 50 - 100 μm in a ratio of 10:0.4:0.2, and then send it into a rotary tube muffle furnace. Carry out dynamic calcination for 1 h at a temperature of 950°C and a rotation speed of 60 r / min. After the calcination is completed, cool it naturally, wash and dry it to obtain a high-quality calcium fluoride product.

[0049] The main components of the fluorine-containing sludge before treatment and the obtained high-quality calcium fluoride product after treatment in this example are shown in Table 2 below. The calcium fluoride content of the product after treatment in this example is 97.54%, the removal rate of silicon dioxide is 86.25%, and the proportion of the product particle size on the 325-mesh sieve is 90.4%.

[0050] Table 2

[0051] Composition <![CDATA[CaF2]]> <![CDATA[CaCO3]]> CaO <![CDATA[SiO2]]> Fluoride-containing sludge (wt.%) 72.45 17.91 / 8.87 Treated product (wt.%) 97.54 / 0.37 1.22

[0052] Example 3

[0053] A method for preparing high-quality calcium fluoride by treating fluorine-containing sludge through secondary calcination, the process flow chart of which is as Figure 1 shown, and it includes the following steps:

[0054] (1) One-stage calcination for impurity removal: Put the fluorine-containing sludge into an oven and dry it at 120 °C until the moisture content is 4%. Mix sodium carbonate and the dried sample in a mass ratio of 1:15, add them together into a wall-breaking mill, and carry out crushing and mixing at 2000 r / min. Then send it into a rotary tube muffle furnace and carry out one-stage dynamic calcination at a temperature of 950 °C and a rotation speed of 50 r / min to remove silicon dioxide and calcium carbonate impurities, obtaining the once-calcined fluorine-containing sludge.

[0055] (2) Water quenching and acid leaching for impurity removal: Feed the once-calcined fluorine-containing sludge into a water quenching and acid leaching tank at a high temperature of 850 °C (20% dilute hydrochloric acid by mass concentration, solid-liquid ratio 1:4), stir and leach for 80 min, then carry out solid-liquid separation. After the obtained solid phase is rinsed to remove colloidal silica, it is the fluorine-containing sludge after acid leaching for impurity removal; in the liquid phase are dissolved sodium chloride and calcium chloride, and then the solubility difference-based fractional crystallization is used to respectively recycle sodium chloride and calcium chloride for resource recovery.

[0056] (3) Two-stage calcination for purification: Put the fluorine-containing sludge after acid leaching for impurity removal into an oven and dry it at 120 °C until the moisture content is 4%. Then mix it with calcium chloride obtained from the fractional crystallization in step (2) and calcium fluoride crystal seeds with a particle size of 50 - 100 μm in a ratio of 10:0.6:0.4. Subsequently, send it into a rotary tube muffle furnace and carry out dynamic calcination at a temperature of 1100 °C and a rotation speed of 60 r / min for 3 h. After the calcination ends, let it cool naturally, and after rinsing and drying, obtain high-quality calcium fluoride products.

[0057] The main components of the fluorine-containing sludge before treatment and the high-quality calcium fluoride products obtained after treatment in this example are shown in Table 3 below. The calcium fluoride content of the product after treatment in this example is 98.85%, the removal rate of silicon dioxide is 91.89%, and the proportion of the product particle size on the 325-mesh sieve is 95.3%.

[0058] Table 3

[0059] Composition <![CDATA[CaF2]]> <![CDATA[CaCO3]]> CaO <![CDATA[SiO2]]> Fluoride-containing sludge (wt.%) 72.45 17.91 / 8.87 Treated product (wt.%) 98.85 / 0.14 0.72

[0060] Comparative Example 1

[0061] Compared with Example 1, in this comparative example, only acid leaching for impurity removal and two-stage quality-improving calcination treatment are carried out on the fluorine-containing sludge (directly carry out the treatments in steps (2) and (3) of Example 1), without the one-stage calcination for impurity removal process, including the following steps:

[0062] (1) Acid leaching for impurity removal: Feed the fluorine-containing sludge into an acid leaching tank (dilute hydrochloric acid with a mass concentration of 15%, solid-liquid ratio 1:5), stir and leach for 60 min at a rotation speed of 150 r / min, then perform vacuum filtration for solid-liquid separation under the condition that the vacuum degree is higher than 0.09 MPa. The obtained solid phase is the fluorine-containing sludge after acid leaching and impurity removal after being washed with water; calcium chloride dissolved out is in the liquid phase, and then calcium chloride is recycled by crystallization using solubility differences.

[0063] (2) Calcination and purification: Put the fluorine-containing sludge after acid leaching and impurity removal into an oven, dry it at 110 °C until the water content is 5%, then mix it with calcium chloride obtained by crystallization in step (2) and calcium fluoride crystal seeds with a particle size of 50 - 100 μm according to a mass ratio of 10:0.5:0.3, and then send it into a rotary tube muffle furnace. Dynamically calcine it for 2 h at a temperature of 1000 °C and a rotation speed of 60 r / min. After the calcination is completed, cool it naturally, and obtain calcium fluoride products after washing and drying.

[0064] The main components of the fluorine-containing sludge before treatment and the obtained calcium fluoride products after treatment in this example are shown in Table 4 below. The calcium fluoride content of the product after treatment in this example is 86.94%. Due to the lack of the first-stage calcination and impurity removal process, the removal rate of silicon dioxide is only 5%, which in turn affects the crystal growth process of the second-stage calcination. The proportion of particles larger than 325 mesh in the product particle size is 59.6%.

[0065] Table 4

[0066] Composition <![CDATA[CaF2]]> <![CDATA[CaCO3]]> CaO <![CDATA[SiO2]]> Fluoride-containing sludge (wt.%) 72.45 17.91 / 8.87 Treated product (wt.%) 86.94 / 2.68 8.44

[0067] Comparative Example 2

[0068] Compared with Example 1, in this comparative example, only the first-stage calcination and impurity removal and water quenching acid leaching and impurity removal treatments are performed on the fluorine-containing sludge (directly perform the steps (1) and (2) of Example 1), and the second-stage calcination and quality improvement process is not carried out, including the following steps:

[0069] (1) First-stage calcination and impurity removal: Put the fluorine-containing sludge into an oven, dry it at 110 °C until the water content is 5%, mix sodium carbonate and the dried sample according to a mass ratio of 1:10, add them together into a wall-breaking mill, crush and mix them at 3000 r / min, and then send them into a rotary tube muffle furnace. Perform the first-stage dynamic calcination for 1.5 h at a temperature of 900 °C and a rotation speed of 40 r / min to remove silicon dioxide and calcium carbonate impurities, and obtain the once-calcined fluorine-containing sludge.

[0070] (2) Quenching in water and acid leaching for impurity removal: Feed the once-calcined fluorine-containing sludge into the water quenching and acid leaching tank at a high temperature of 800 °C (dilute hydrochloric acid with a mass concentration of 15%, solid-liquid ratio 1:5), stir and leach with acid for 60 min at a rotation speed of 150 r / min, and then carry out vacuum filtration for solid-liquid separation under the condition that the vacuum degree is higher than 0.09 MPa. After the obtained solid phase is rinsed to remove colloidal silica, it is the fluorine-containing sludge after acid leaching for impurity removal; the liquid phase contains dissolved sodium chloride and calcium chloride, and then the solubility difference-based fractional crystallization is used to respectively recycle sodium chloride and calcium chloride for resource recovery.

[0071] The main components of the fluorine-containing sludge before treatment and the obtained calcium fluoride product after treatment in this example are shown in Table 5 below. The calcium fluoride content of the product after treatment in this example is 97.74%, and the removal rate of silicon dioxide is 85.79%. Due to the lack of the two-stage calcination and quality improvement process, the proportion of the product particle size on the 325-mesh sieve is only 10.1%.

[0072] Table 5

[0073] Composition <![CDATA[CaF2]]> <![CDATA[CaCO3]]> CaO <![CDATA[SiO2]]> Fluoride-containing sludge (wt.%) 72.45 17.91 / 8.87 Treated product (wt.%) 97.74 / 0.39 1.26

[0074] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing high-quality calcium fluoride based on secondary calcination of fluorine-containing sludge, characterized in that: The steps include: (1) drying the fluorine-containing sludge, crushing and mixing it with sodium carbonate, and then sending it into a dynamic heating device for dynamic calcination at a temperature of 850-950° C. to obtain primary calcined fluorine-containing sludge; (2) sending the once calcined fluorine-containing sludge into a water-quenched acid leaching solution at a high temperature of 800-900°C for stirring and acid leaching treatment, and then separating the solid and liquid, and washing the obtained solid phase with water to obtain the fluorine-containing sludge after acid leaching and impurity removal; (3) The fluorine-containing sludge after acid leaching and impurity removal is dried and mixed with a calcium chloride flux and calcium fluoride seed crystals, and then sent to a dynamic heating device for two-stage dynamic calcination at a temperature of 950-1100°C. After the calcination, it is naturally cooled, rinsed and dried to obtain a high-quality calcium fluoride product.

2. The method for preparing high-quality calcium fluoride based on secondary calcination of fluorine-containing sludge according to claim 1, characterized in that: The fluorine-containing sludge in step (1) is fluorine-containing sludge produced in the fluorine chemical production process, and its main solid phase components include calcium fluoride, calcium carbonate and silicon dioxide, and the content of calcium fluoride in the solid phase components is 60-80wt.%.

3. The method for preparing high-quality calcium fluoride based on secondary calcination of fluorine-containing sludge according to claim 1, characterized in that: The drying in steps (1) and (3) refers to drying at a temperature of 105-120° C. until the moisture content is 4-6%.

4. The method for preparing high-quality calcium fluoride based on secondary calcination of fluorine-containing sludge according to claim 1, characterized in that: In step (1), the mass ratio of the sodium carbonate to the dried fluorine-containing sludge for crushing and mixing is 1:8-15; the dynamic calcination speed of the first stage is 30-50r / min, and the calcination time is 1-2h.

5. The method for preparing high-quality calcium fluoride based on secondary calcination of fluorine-containing sludge according to claim 1, characterized in that: The water-quenching acid leaching solution in step (2) is a dilute hydrochloric acid solution with a mass concentration of 10-20%; the solid-liquid ratio of the primary calcined fluorine-containing sludge to the water-quenching acid leaching solution is 1:4-6; the rotation speed of the stirring acid leaching treatment is 100-200r / min, and the time is 40-80min.

6. The method for preparing high-quality calcium fluoride based on secondary calcination of fluorine-containing sludge according to claim 1, characterized in that: The solid-liquid separation in step (2) refers to vacuum filtration solid-liquid separation under the condition of a vacuum degree of 0.01-0.1 MPa; the liquid phase obtained after solid-liquid separation is used to obtain sodium chloride and calcium chloride respectively by distributed crystallization; the obtained calcium chloride is used as a calcium chloride flux in step (3) for resource utilization.

7. The method for preparing high-quality calcium fluoride based on secondary calcination of fluorine-containing sludge according to claim 1, characterized in that: The particle size of the calcium fluoride seed crystals in step (3) is 50-100 μm.

8. The method for preparing high-quality calcium fluoride based on secondary calcination of fluorine-containing sludge according to claim 7, characterized in that: The fluorine-containing sludge after acid leaching and impurity removal is dried and mixed with calcium chloride flux and calcium fluoride seed crystals in a mass ratio of 10:0.4-0.6:0.2-0.

4.

9. The method for preparing high-quality calcium fluoride based on secondary calcination of fluorine-containing sludge according to claim 1, characterized in that: The dynamic calcination speed of the second stage in step (3) is 50-100 r / min, and the calcination time is 1-3 h.

10. The method for preparing high-quality calcium fluoride based on secondary calcination of fluorine-containing sludge according to claim 1, characterized in that: The purity of the high-quality calcium fluoride product in step (3) is greater than 97%, and the proportion of the product particle size on a 325-mesh sieve is greater than 90%.

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