Process for the recovery of calcium fluoride from fluorine-containing sludge resulting from the purification of quartz sand by acid washing

Abstract

This invention discloses a method for recovering calcium fluoride from fluoride-containing tailings generated during the acid washing and purification of quartz sand, belonging to the field of industrial solid waste resource utilization technology. This invention obtains calcium fluoride concentrate through pretreatment, medium-temperature calcination, and flotation separation. This invention combines the processes of "calcination conversion and flotation separation" to treat fluoride-containing tailings generated from the acid washing and purification of quartz sand, converting calcium oxalate in the fluoride-containing tailings into calcium carbonate while ensuring that calcium fluoride does not undergo a crystal transformation. This achieves the goal of utilizing existing flotation reagents to amplify the difference in flotationability between impurities in the fluoride-containing tailings and the target product, calcium fluoride, creating decisive conditions for subsequent flotation separation of calcium fluoride and impurities. Furthermore, the final calcium fluoride concentrate has a high grade and high calcium fluoride content, and can be used as a substitute for metallurgical-grade or chemical-grade fluorite, realizing the transformation of hazardous waste into resources, and is also very environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste resource utilization technology, and in particular to a method for recovering calcium fluoride from fluorine-containing tailings produced by acid washing and purification of quartz sand. Background Technology

[0002] Quartz sand is an important raw material for industries such as glass, electronics, and photovoltaics, and its purity requirements are extremely high. In the acid washing and purification process of quartz sand, mixed acids containing hydrofluoric acid, oxalic acid, and hydrochloric acid are often used to remove impurities such as iron and aluminum. Acid washing generates a large amount of acidic wastewater, which is usually neutralized using lime slurry. This process produces precipitated sludge mainly composed of calcium fluoride (CaF2) and calcium oxalate (CaC2O4).

[0003] Currently, such fluoride-containing sludge is typically disposed of as hazardous waste through landfill, which not only occupies land resources and poses environmental risks but also incurs high disposal costs. Calcium fluoride (commonly known as fluorite) is an important strategic mineral resource and a basic raw material for the fluorochemical industry (such as hydrofluoric acid production). If high-purity calcium fluoride can be recovered from this type of sludge, it will not only achieve the harmless treatment and reduction of hazardous waste but also realize resource recycling, resulting in significant economic and environmental benefits.

[0004] For the fluoride-containing sludge generated from the treatment of industrial fluoride-containing wastewater, the following solutions are proposed: Option 1: Processing through chemical purification, the core of which is to dissolve impurities (such as calcium carbonate and silicon dioxide) using chemical means such as acid leaching and alkali leaching. However, this type of method has poor selectivity for mixtures of chemically stable calcium fluoride and calcium oxalate, both of which are poorly soluble in weak acids.

[0005] Option 2: Processing via a secondary calcination method, where impurities are converted into soluble substances at temperatures above 850℃ before separation. Although calcium oxalate can decompose under high-temperature conditions, this process is extremely energy-intensive. Moreover, when the target product is calcium fluoride, excessively high calcination temperatures may cause calcium fluoride to sinter or partially volatilize, thus reducing the recovery rate and resulting in poor economic efficiency.

[0006] Option 3: Processing by dispersion-gradation. This method is effective for mineral systems with good crystallinity and significant particle size differences. However, for quartz sand acid washing tailings, the characteristics are that calcium fluoride and calcium oxalate are both fine particles, and their surface physicochemical properties (such as density and floatability) are very similar, making it difficult for conventional physical separation methods (such as gravity classification and direct flotation) to achieve effective separation.

[0007] Option 4: Using fluorinated sludge in the production of bricks and other building materials. This method fails to recover valuable components, especially fluorine resources. It is merely a solidification and disposal of waste with a low degree of resource utilization. Moreover, there is a potential environmental risk of long-term leaching of fluorides, which is not the optimal resource utilization approach.

[0008] Therefore, while there are many existing methods for solving the problem, there is a lack of efficient and economical methods for separating mixtures of calcium fluoride and calcium oxalate. Thus, developing a new method for recovering calcium fluoride from fluoride-containing sludge that is simple in process, low in energy consumption, and highly efficient in separation has become an urgent problem to be solved in this field. Summary of the Invention

[0009] The main objective of this invention is to provide a method for recovering calcium fluoride from fluorine-containing tailings produced by acid washing and purification of quartz sand, thereby solving the technical problem of difficulty in separating calcium fluoride with high recovery rate and high grade from fluorine-containing tailings.

[0010] To achieve the above objectives, the present invention provides a method for recovering calcium fluoride from fluoride-containing tailings generated during the acid washing and purification of quartz sand, wherein the fluoride-containing tailings comprises calcium fluoride and calcium oxalate, and the method includes the following steps: Pretreatment: The fluorine-containing tailings are dried and ground to obtain powder; Medium-temperature calcination: The powder is calcined to decompose the calcium oxalate in the powder into calcium carbonate, and to prevent the calcium fluoride in the powder from undergoing a crystal transformation, thereby obtaining calcined clinker; Flotation separation: The calcined clinker is slurryed and flotation reagents are added for flotation. Calcium fluoride concentrate is obtained by separating calcium carbonate and calcium fluoride concentrate by utilizing the difference in floatability between the two substances in the calcined clinker.

[0011] In some embodiments of the present invention, the water content of the fluoride-containing tailings is 40% to 50%; And / or, the particle size of the powder is less than or equal to 0.15 mm.

[0012] In some embodiments of the present invention, in the medium-temperature calcination step, the calcination temperature is 400℃~650℃ and the calcination time is 60min~180min.

[0013] In some embodiments of the present invention, the calcined clinker is slurried with a solvent, wherein the mass ratio of the calcined clinker to the solvent is (3~5):1.

[0014] In some embodiments of the present invention, the pH of the slurry is adjusted to above 9.0 before the flotation reagent is added.

[0015] In some embodiments of the present invention, the flotation reagents include inhibitors, collectors, and frothers.

[0016] In some embodiments of the present invention, the inhibitor includes at least one of water glass, starch, tannic acid, sodium humate, sodium hexametaphosphate, sodium tripolyphosphate, hypozoxytriacetic acid, polyepoxysuccinic acid, and lignin sulfonate. And / or, the collector includes at least one of oleic acid, sodium alkyl sulfate, sodium naphthenate, oxidized paraffin soap, and styrene-propenyl hydroxamic acid; And / or, the foaming agent includes at least one of pine oil, methyl isobutyl methanol, and butyl ether oil.

[0017] In some embodiments of the present invention, based on the total mass of the fluorinated tailings, the amount of the inhibitor added is 200g / t to 1000g / t, the amount of the collector added is 200g / t to 1000g / t, and the amount of the foaming agent added is 50g / t to 150g / t.

[0018] In some embodiments of the present invention, the flotation separation includes roughing, sweeping and cleaning, wherein the roughing is performed at least once, the sweeping is performed at least once, and the cleaning is performed at least five times.

[0019] In some embodiments of the present invention, the calcium fluoride concentrate is dehydrated and dried; And / or, the calcium fluoride concentrate contains more than 85% calcium fluoride by mass.

[0020] The beneficial effects that this invention can achieve are: This invention combines calcination conversion and flotation separation to treat fluorine-containing tailings from quartz sand acid washing and purification. It converts calcium oxalate in the fluorine-containing tailings into calcium carbonate while ensuring that the calcium fluoride does not undergo a crystal transformation, maintaining structural stability. This achieves the goal of amplifying the difference in flotationability between impurities in the fluorine-containing tailings and the target recovered product, calcium fluoride, using existing flotation reagents. This creates crucial conditions for subsequent flotation separation of calcium fluoride and impurities. Furthermore, the resulting calcium fluoride concentrate has a high grade and high calcium fluoride content, serving as a substitute for metallurgical or chemical-grade fluorite. This realizes the transformation of hazardous waste into resources with a high degree of resource utilization, aligning with the concept of a circular economy. The entire recycling process of this invention is also environmentally friendly, achieving the harmlessness and resource recovery of sludge and eliminating the environmental risks associated with landfilling. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1 This is a schematic flowchart of a method for recovering calcium fluoride from fluorine-containing tailings produced by acid washing and purification of quartz sand according to an embodiment of the present invention.

[0023] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0024] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] In this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Furthermore, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. If the combination of technical solutions is contradictory or impossible to implement, such a combination should be considered non-existent and not within the scope of protection claimed by this invention.

[0027] This invention provides a method for recovering calcium fluoride from fluoride-containing tailings generated during the acid washing and purification of quartz sand. The fluoride-containing tailings consist of calcium fluoride and calcium oxalate. (Refer to...) Figure 1 The preparation method includes the following steps: S10. Pretreatment: Fluorine-containing tailings are dried and ground to obtain powder. S20, medium-temperature calcination: Calcination of powder materials to decompose calcium oxalate into calcium carbonate and prevent calcium fluoride in powder materials from undergoing crystal transformation, thus obtaining calcined clinker; S30. Flotation separation: The calcined clinker is slurryed and flotation reagents are added for flotation. The calcium fluoride concentrate is obtained by separating the calcium carbonate and calcium fluoride in the calcined clinker by utilizing the difference in floatability between them.

[0028] This invention combines calcination conversion and flotation separation to treat fluorine-containing tailings from quartz sand acid washing and purification. It converts calcium oxalate in the fluorine-containing tailings into calcium carbonate while ensuring that the calcium fluoride does not undergo a crystal transformation, maintaining structural stability. This achieves the goal of amplifying the difference in flotationability between impurities in the fluorine-containing tailings and the target recovered product, calcium fluoride, using existing flotation reagents. This creates crucial conditions for subsequent flotation separation of calcium fluoride and impurities. Furthermore, the resulting calcium fluoride concentrate has a high grade and high calcium fluoride content, serving as a substitute for metallurgical or chemical-grade fluorite. This realizes the transformation of hazardous waste into resources with a high degree of resource utilization, aligning with the concept of a circular economy. The entire recycling process of this invention is also environmentally friendly, achieving the harmlessness and resource recovery of sludge and eliminating the environmental risks associated with landfilling.

[0029] In some embodiments, the moisture content of the fluorinated tailings is 40% to 50%. Controlling the moisture content of the fluorinated tailings helps to reduce the energy consumption of calcination and facilitates the full decomposition of calcium oxalate in the fluorinated tailings into calcium carbonate.

[0030] In some embodiments, the fluorine-containing tailings are dried to constant weight at 105±5°C.

[0031] In some embodiments, fluorine-containing tailings are ground into powder using a crusher and a double-roll mill.

[0032] In some embodiments, the particle size of the powder is less than or equal to 0.15 mm. A particle size of less than 0.15 mm can promote the complete decomposition of calcium oxalate in the powder to obtain calcium carbonate during subsequent calcination.

[0033] In some embodiments, when the particle size of the fluorine-containing tailings is large, it can be crushed before grinding, which is beneficial to obtain uniform powder with a particle size of less than or equal to 0.15 mm in the grinding step.

[0034] In some embodiments, the mass percentage of particles with a diameter of 0.15 mm or less in the powder is above 90%, which can promote the full decomposition of calcium oxalate in the powder to obtain calcium carbonate during the subsequent calcination process.

[0035] In some embodiments, in the medium-temperature calcination step, the calcination temperature is 400℃~650℃, which can be 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, etc., and the calcination time is 60min~180min, which can be 60min, 70min, 80min, 90min, 100min, 120min, 140min, 150min, 170min, 180min, etc.

[0036] In this embodiment, the powder is calcined at a medium temperature of 400℃ to 650℃ for 60 min to 180 min, which can fully decompose the calcium oxalate in the fluorine-containing tailings into calcium carbonate. At the same time, the structure of the target recovered product, calcium fluoride, is kept stable, preventing crystal transformation and decomposition.

[0037] The reaction formula for decomposing calcium oxalate into calcium carbonate through medium-temperature calcination is as follows: CaC2O4·H2O → CaC2O4+ H2O↑; CaC2O4→ CaCO3+ CO↑.

[0038] In some embodiments, the powder is placed in a muffle furnace for calcination.

[0039] In this invention, the weight loss of the calcined clinker mainly comes from the decomposition of calcium oxalate and the volatilization of a small amount of organic matter.

[0040] Therefore, in some embodiments, the decomposition and transformation of calcium oxalate can be determined by detecting the weight loss rate of the calcined clinker.

[0041] In some embodiments, if the weight loss rate of the calcined clinker is above 8.4%, it is determined that the calcium oxalate has basically decomposed into calcium carbonate. The weight loss rate is calculated as follows: weight loss rate = (dry basis mass of powder - dry basis mass of calcined clinker) / dry basis mass of powder × 100%.

[0042] In some embodiments, the calcined clinker is slurried with a solvent to obtain a slurry. The mass ratio of the calcined clinker to the solvent is (3~5):1. The mass ratio can be 3:1, 3.5:1, 4:1, 4.5:1, 5:1, etc., so that the slurry is kept in a liquid state, so that calcium fluoride concentrate can be obtained by flotation separation.

[0043] In some embodiments, the slurry is placed in a flotation cell for flotation separation.

[0044] In some embodiments, the pH of the slurry is adjusted to be greater than or equal to 9.0, such as 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, etc. This can suppress the flotation of impurities such as silicates, while enhancing the collector's selectivity for calcium fluoride and improving the grade of calcium fluoride concentrate.

[0045] In some embodiments, the pH of the slurry is adjusted to 9.0 or above using a pH adjuster, including sodium carbonate.

[0046] In some embodiments, the flotation reagents include inhibitors, collectors, frothers, and pH adjusters. Inhibitors can selectively adsorb onto the surface of calcium carbonate particles, occupying active sites on the surface and preventing or reducing the subsequent adsorption of collectors onto their surface. Collectors can adsorb onto the surface of calcium fluoride particles, enhancing the hydrophobic properties of calcium fluoride and making it easier for calcium fluoride particles to adhere to bubbles and float, thus separating them from calcium carbonate particles. Frothers can reduce the surface tension of water, increase air dispersion in the slurry, and stabilize the bubbles generated during agitation and aeration during flotation. This invention utilizes inhibitors to suppress the flotation of calcium carbonate particles, utilizes frothers to generate stable bubbles, and utilizes collectors to promote the flotation of calcium fluoride-adhered bubbles, thereby achieving the flotation separation of calcium fluoride and calcium carbonate impurities.

[0047] In some embodiments, the inhibitor includes at least one of water glass, starch, tannic acid, sodium humate, sodium hexametaphosphate, sodium tripolyphosphate, hypozoxytriacetic acid, polyepoxysuccinic acid, and lignin sulfonate. The above inhibitors can selectively adsorb onto the surface of calcium carbonate particles, occupying a large number of active sites on the surface of calcium carbonate particles, and preventing the subsequent adsorption of collectors on their surface.

[0048] In some embodiments, the collector includes at least one of oleic acid, sodium alkyl sulfate, sodium naphthenate, oxidized paraffin soap, and styrene-propenyl hydroxamic acid. The above collectors can be adsorbed on the surface of calcium fluoride particles, enhance the hydrophobic properties of calcium fluoride, and make it easier for calcium fluoride particles to adhere to bubbles and float to the surface, thus separating them from calcium carbonate particles.

[0049] In some embodiments, the foaming agent includes at least one of pine oil, methyl isobutyl methanol, and butyl ether oil. The above foaming agents can generate stable bubbles, which is beneficial for the adhesion of calcium fluoride after the action of the collector. The calcium fluoride floats up with the bubbles, achieving the purpose of separation from calcium carbonate.

[0050] In some embodiments, based on the total mass of fluoride-containing tailings, the amount of inhibitor added is 200g / t to 1000g / t, which can be 200g / t, 300g / t, 400g / t, 500g / t, 600g / t, 700g / t, 800g / t, 900g / t, 1000g / t, etc.

[0051] In some embodiments, based on the total mass of fluorinated tailings, the amount of collector added is 200 g / t to 1000 g / t, which can be 200 g / t, 300 g / t, 400 g / t, 500 g / t, 600 g / t, 700 g / t, 800 g / t, 900 g / t, 1000 g / t, etc. In some embodiments, based on the total mass of fluorinated tailings, the amount of foaming agent added is 50g / t to 150g / t, which can be 50g / t, 60g / t, 70g / t, 80g / t, 90g / t, 100g / t, 110g / t, 120g / t, 130g / t, 140g / t, 150g / t, etc.

[0052] In some embodiments, flotation separation includes roughing, scavenging, and cleaning. Roughing can quickly separate most of the tailings and obtain a low-grade rough concentrate. Then, cleaning is used to further separate the low-grade rough concentrate by flotation to increase the calcium fluoride content and obtain a high-grade calcium fluoride concentrate. Scavenging separates the tailings separated by roughing by flotation to recover residual minerals. The recovered residual minerals are then enriched again through roughing and cleaning processes to obtain calcium fluoride concentrate, thereby improving the recovery rate of calcium fluoride.

[0053] In some embodiments, the number of roughing processes is at least one, the number of scavenging processes is at least one, and the number of cleaning processes is at least five. This not only improves the recovery rate of calcium fluoride but also increases the grade of the calcium fluoride concentrate, enabling the recovered calcium fluoride concentrate to meet the requirements of metallurgical-grade fluorite and chemical-grade fluorite, thus serving as a substitute and achieving efficient conversion of hazardous waste into resources.

[0054] In some embodiments, the calcium fluoride concentrate is dehydrated and dried.

[0055] The calcium fluoride concentrate recovered by the recycling method of this invention has a calcium fluoride content of over 85% by mass.

[0056] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following specific embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0057] Example 1 Example 1 describes a method for recovering calcium fluoride from fluoride-containing tailings produced during the acid washing and purification of quartz sand: Fluorine-containing tailings from a quartz sand processing plant were taken, with a controlled moisture content of 45%. After testing, its dry basis composition was approximately: calcium fluoride 65%, calcium oxalate 21%, and other impurities 14%.

[0058] S10. Pretreatment: The fluorine-containing tailings are dried to constant weight at 105℃, and then ground to a particle size of less than 0.15mm using a crusher and a roller mill to obtain powder. The mass ratio of particles with a particle size of less than 0.15mm in the powder is more than 90%.

[0059] S20, Medium-temperature calcination: Take 1000g of the powder from step S10 and place it in a muffle furnace. Calcinate at 550℃ for 90 minutes to decompose the calcium oxalate in the powder into calcium carbonate, while preventing the calcium fluoride in the powder from undergoing a crystal transformation. After cooling, remove the powder to obtain calcined clinker. The weight loss rate of the calcined clinker is approximately 8.4% or higher, indicating that the calcium oxalate has been largely converted into calcium carbonate, while other stable impurities and calcium fluoride do not undergo significant chemical changes.

[0060] S30. Flotation Separation: Calcined clinker is placed in a 1.5L flotation cell, and tap water is added and stirred to prepare a slurry. The pH of the slurry is adjusted to 9.0 by adding sodium carbonate. Then, water glass inhibitor is added at a rate of 800g / t, oleic acid collector at a rate of 450g / t, and pine oil frother at a rate of 70g / t. A closed-circuit flotation test of "one roughing, one scavenging, and five cleaning" is carried out to separate calcium fluoride concentrate and flotation tailings. The main components of the flotation tailings are calcium carbonate and silicon dioxide.

[0061] Example 2 Example 2 describes a method for recovering calcium fluoride from fluoride-containing tailings produced during the acid washing and purification of quartz sand: Another batch of fluoride-containing tailings was taken, with a moisture content of 46%. Its dry basis composition was approximately: calcium fluoride 62%, calcium oxalate 23%, and other impurities 15%.

[0062] S10, Pre-processing: Refer to step S10 of Example 1.

[0063] S20, Medium-temperature calcination: The procedure is the same as step S20 in Example 1, except that the powder is calcined at 580°C for 75 minutes to decompose calcium oxalate into calcium carbonate and prevent calcium fluoride from undergoing a crystal transformation. After cooling, the calcined clinker is obtained. The weight loss rate of the calcined clinker is above 8.4%, indicating that calcium oxalate has been largely converted into calcium carbonate, while other stable impurities do not undergo significant chemical changes with calcium fluoride.

[0064] S30, Flotation Separation: Refer to step S30 of Example 1, except that: sodium carbonate is used to adjust the pH of the pulp to 9.5, 600 g / t of starch and 200 g / t of water glass are added as inhibitors, and 500 g / t of sodium alkyl sulfate is added as a collector.

[0065] Example 3 Example 3 uses the fluorine-containing tailings from Example 1 and recycles them using the same method. The difference is that in step S20, the calcination temperature is 650℃ and the calcination time is 80 minutes. This decomposes the calcium oxalate in the powder into calcium carbonate, while preventing the calcium fluoride in the powder from undergoing a crystal transformation. After cooling, the calcined clinker is obtained. The weight loss rate of the calcined clinker is above 8.4%, indicating that the calcium oxalate has been largely converted into calcium carbonate, while other stable impurities do not undergo significant chemical changes with the calcium fluoride.

[0066] Example 4 Example 4 selects the fluorine-containing tailings from Example 1 and recycles them according to the recycling method of Example 1. The difference is that the flotation reagents in step S30 are as follows: 700 g / t of lignin sulfonate inhibitor is added, 450 g / t of sodium naphthenate collector is added, and 70 g / t of frother methyl isobutyl methanol is added.

[0067] Example 5 Example 5 selects the fluorine-containing tailings from Example 1 and performs recycling treatment according to the recycling method of Example 1. The difference is that the number of scavenging steps in step S30 is 2.

[0068] Comparative Example 1 Comparative Example 1 uses the fluorine-containing tailings from Example 1 and recycles them using the same method as in Example 1. The difference is that Comparative Example 1 does not calcine the powder but directly performs flotation separation.

[0069] Comparative Example 2 Comparative Example 2 uses the fluorine-containing tailings from Example 1 and is recycled using the same method as in Example 1. The difference is that the calcination temperature of Comparative Example 2 is 800℃ and the calcination time is 200min.

[0070] Comparative Example 3 Comparative Example 3 uses the fluorine-containing tailings from Example 1 and is recycled using the same method as in Example 1. The difference is that the calcination temperature of Comparative Example 3 is 250°C and the calcination time is 20 min.

[0071] Performance testing 1. Calculate the yield (%) of calcium fluoride concentrate. The calculation method is: (M1 / M2)×100%, where M2 is the dry basis mass of calcined clinker and M1 is the dry basis mass of calcium fluoride concentrate.

[0072] 2. The quality (%) of calcium fluoride concentrate is determined by the following method: (M3 / M1)×100%, where M1 is the dry basis mass of calcium fluoride concentrate and M3 is the dry basis mass of calcium fluoride in calcium fluoride concentrate.

[0073] 3. Calculate the recovery rate (%) of calcium fluoride. The calculation method is (M3 / M0)×100%, where M0 is the dry basis mass of calcium fluoride in the fluoride tailings and M3 is the dry basis mass of calcium fluoride in the calcium fluoride concentrate.

[0074] Table 1

[0075] As shown in Table 1, Examples 1 to 5 utilize the combined "calcination conversion and flotation separation" process of this invention to treat fluoride-containing tailings generated from the acid washing and purification of quartz sand. This process converts calcium oxalate in the fluoride-containing tailings into calcium carbonate, achieving the goal of amplifying the difference in flotationability between impurities in the fluoride-containing tailings and the target recovered product, calcium fluoride, using existing flotation reagents. The resulting calcium fluoride concentrate has a high grade and can serve as a substitute for metallurgical or chemical-grade fluorite, realizing the transformation of hazardous waste into resources with a high degree of resource utilization, aligning with the concept of a circular economy. Furthermore, the entire recycling process of this invention is environmentally friendly, achieving the harmlessness and resource utilization of sludge and eliminating the environmental risks associated with landfilling.

[0076] Comparative Example 1 was directly separated by flotation without medium-temperature calcination. Calcium oxalate was not decomposed into calcium carbonate. The floatability difference between calcium fluoride and calcium oxalate was minimal, and they floated almost simultaneously. Therefore, although the rough concentrate yield was as high as 86.9%, the concentrate grade was only 70.3%, far lower than the 85% or more in the example, and could not meet the quality requirements of metallurgical or chemical grade fluorite.

[0077] The calcination temperature of Comparative Example 2 was too high. After calcium oxalate was converted into calcium carbonate, it further decomposed into calcium oxide. The difference in flotation properties between calcium oxide and calcium fluoride was not as great as that between calcium carbonate and calcium fluoride, which led to a decrease in the yield, grade and recovery rate of calcium fluoride concentrate.

[0078] The calcination temperature of Comparative Example 3 was too low, and calcium oxalate was not completely decomposed into calcium carbonate, which also led to a decrease in the grade of calcium fluoride concentrate.

[0079] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for recovering calcium fluoride from fluorine-containing tailings produced during the acid washing and purification of quartz sand, characterized in that, The fluoride-containing tailings sludge comprises calcium fluoride and calcium oxalate, and the method includes the following steps: Pretreatment: The fluorine-containing tailings are dried and ground to obtain powder; Medium-temperature calcination: The powder is calcined to decompose the calcium oxalate in the powder into calcium carbonate, and to prevent the calcium fluoride in the powder from undergoing a crystal transformation, thereby obtaining calcined clinker; Flotation separation: The calcined clinker is slurryed and flotation reagents are added for flotation. Calcium fluoride concentrate is obtained by separating calcium carbonate and calcium fluoride concentrate by utilizing the difference in floatability between the two substances in the calcined clinker.

2. The method for recovering calcium fluoride from fluoride-containing tailings produced by acid washing and purification of quartz sand according to claim 1, characterized in that, The moisture content of the fluoride-containing tailings is 40%~50%; And / or, the particle size of the powder is less than or equal to 0.15 mm.

3. The method for recovering calcium fluoride from fluoride-containing tailings produced by acid washing and purification of quartz sand according to claim 1, characterized in that, In the medium-temperature calcination step, the calcination temperature is 400℃~650℃ and the calcination time is 60min~180min.

4. The method for recovering calcium fluoride from fluoride-containing tailings produced by acid washing and purification of quartz sand according to claim 1, characterized in that, The calcined clinker is slurried using a solvent, wherein the mass ratio of the calcined clinker to the solvent is (3~5):

1.

5. The method for recovering calcium fluoride from fluorine-containing tailings produced by acid washing and purification of quartz sand according to claim 1, characterized in that, The pH of the slurry is adjusted to above 9.0 before the flotation reagent is added.

6. The method for recovering calcium fluoride from fluoride-containing tailings produced by acid washing and purification of quartz sand according to claim 1, characterized in that, The flotation reagents include inhibitors, collectors, and frothers.

7. The method for recovering calcium fluoride from fluoride-containing tailings produced by acid washing and purification of quartz sand according to claim 6, characterized in that, The inhibitors include at least one of water glass, starch, tannic acid, sodium humate, sodium hexametaphosphate, sodium tripolyphosphate, hypozinotriacetic acid, polyepoxysuccinic acid, and lignin sulfonate. And / or, the collector includes at least one of oleic acid, sodium alkyl sulfate, sodium naphthenate, oxidized paraffin soap, and styrene-propenyl hydroxamic acid; And / or, the foaming agent includes at least one of pine oil, methyl isobutyl methanol, and butyl ether oil.

8. The method for recovering calcium fluoride from fluoride-containing tailings produced by acid washing and purification of quartz sand according to claim 6, characterized in that, Based on the total mass of the fluoride-containing tailings, the amount of the inhibitor added is 200g / t to 1000g / t, the amount of the collector added is 200g / t to 1000g / t, and the amount of the foaming agent added is 50g / t to 150g / t.

9. The method for recovering calcium fluoride from fluorine-containing tailings produced by acid washing and purification of quartz sand according to claim 1, characterized in that, The flotation separation includes roughing, scavenging, and cleaning, wherein the roughing is performed at least once, the scavenging is performed at least once, and the cleaning is performed at least five times.

10. The method for recovering calcium fluoride from fluorine-containing tailings produced by acid washing and purification of quartz sand according to claim 9, characterized in that, The calcium fluoride concentrate is dehydrated and dried; And / or, the calcium fluoride concentrate contains more than 85% calcium fluoride by mass.

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