Method for recycling and recycling calcium fluoride sludge

Abstract

The invention is applicable to the technical field of calcium fluoride sludge, and provides a calcium fluoride sludge recycling and recycling method which comprises the following steps: 1) dehydrating and drying calcium fluoride sludge to obtain dried calcium fluoride sludge; 2) crushing and screening the dried calcium fluoride sludge to obtain calcium fluoride sludge powder; (3) carrying out acid leaching treatment on the calcium fluoride sludge powder; 4) calcining the calcium fluoride sludge subjected to acid leaching treatment; (5) carrying out alkaline leaching treatment on the calcium fluoride sludge subjected to calcination treatment; and 6) mixing the calcium fluoride sludge subjected to alkaline leaching treatment with water, adding citric acid, stirring, and carrying out solid-liquid separation to obtain a calcium fluoride product. According to the method, impurities easy to dissolve in acid can be preferentially removed through acid leaching, then organic matter and carbonate left after acid leaching can be decomposed through calcination, meanwhile, the structure of calcium fluoride is more stable, finally, residual acidic substances are neutralized through alkaline leaching, part of metal ions are removed, and the purity of calcium fluoride is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of calcium fluoride sludge, and in particular relates to a method for recycling and resource utilization of calcium fluoride sludge. Background Art

[0002] Fluorine has become the first choice for cleaning and etching processes due to its strong oxidizing properties. In the production process of display screens, integrated circuits, semiconductors, etc., silicon cores and silicon crystals need to be corroded and cleaned, which will form high-concentration fluorine-containing acidic wastewater. After neutralization and precipitation treatment with lime milk, a large amount of calcium fluoride sludge will be formed. According to the detection of calcium fluoride sludge from photovoltaic enterprises, the calcium fluoride content in the calcium fluoride sludge of photovoltaic enterprises can reach 80-95%.

[0003] This type of solid waste belongs to general industrial solid waste. The existing disposal method is mainly landfill, which has the advantages of simplicity and convenience. The disadvantages are waste of resources, high disposal cost, occupation of land, and possible pollution of groundwater. Summary of the invention

[0004] The present invention provides a method for recycling and reusing calcium fluoride sludge, aiming to solve the above-mentioned problems.

[0005] The present invention is achieved by a method for recycling and reusing calcium fluoride sludge, comprising the following steps: 1) Dehydrating and drying the calcium fluoride sludge to obtain dry calcium fluoride sludge; 2) crushing and screening the dried calcium fluoride sludge to obtain calcium fluoride sludge powder; 3) Acid leaching of calcium fluoride sludge powder; 4) Calcination treatment of calcium fluoride sludge after acid leaching; 5) alkaline leaching of the calcined calcium fluoride sludge; 6) After the calcium fluoride sludge after alkali leaching treatment is mixed with water, citric acid is added, and solid-liquid separation is performed after stirring. The obtained solid precipitate is washed 3-5 times, dried and crushed to obtain a calcium fluoride product.

[0006] Acid leaching can first remove acid-soluble impurities such as calcium carbonate and metal oxides, reducing the interference of impurities in the subsequent calcination process. Then, calcination can decompose the organic matter and carbonates remaining after acid leaching, and make the structure of calcium fluoride more stable, which is convenient for further purification by subsequent alkaline leaching. Finally, alkaline leaching is used to neutralize the residual acidic substances and remove some metal ions, further improving the purity of calcium fluoride. Compared with the calcination-acid leaching-alkaline leaching method, calcination first, some impurities (such as carbonates) may react with calcium fluoride at high temperature to generate more difficult to handle compounds, increasing the difficulty of subsequent acid leaching; or acid leaching-alkaline leaching-calcination, alkaline leaching before calcination may introduce new impurities (such as sodium salts), and difficult to handle compounds may be formed again during the calcination process, affecting the final purity.

[0007] Preferably, the dehydration and drying of the calcium fluoride sludge is specifically carried out as follows: 1.1) Use a plate and frame filter press or centrifuge to mechanically dehydrate the calcium fluoride sludge to reduce the moisture content to below 30%; 1.2) Low temperature drying at 80-120℃ removes moisture and prevents calcium fluoride from decomposing.

[0008] Preferably, the crushing and screening of the dried calcium fluoride sludge is specifically carried out as follows: 2.1) Use a crusher to crush the dried calcium fluoride sludge to a particle size of less than 1 mm; 2.2) Remove large particles of impurities such as sand, gravel, metal fragments, etc. through vibration screening.

[0009] Preferably, the acid leaching treatment of the calcium fluoride sludge powder is specifically as follows: 3.1) Mix the calcium fluoride sludge powder with 1-8 times the weight of water and stir evenly; 3.2) adding hydrochloric acid and reacting at 25-50°C for 60-90 minutes, wherein the molar concentration of the hydrochloric acid is 2-6 mol / L, and the molar ratio of the acid equivalent in the hydrochloric acid to the calcium content in the calcium fluoride sludge is 1-3:1; 3.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0010] Preferably, the calcination treatment of the calcium fluoride sludge after acid leaching is specifically: 4.1) Place the acid-leached calcium fluoride sludge into a ball mill at a speed of 500 rpm; 4.2) Heat to 500-600℃ while ball milling, complete calcination after 60-90min, and cool to room temperature.

[0011] Preferably, the alkaline leaching treatment of the calcined calcium fluoride sludge is specifically: 5.1) Mix the calcined calcium fluoride sludge with the sodium hydroxide solution and stir evenly; 5.2) reacting at 60-90°C for 60-120min, wherein the mass fraction of the sodium hydroxide solution is 20-40%, and the mass ratio of the sodium hydroxide solution to the calcined calcium fluoride sludge is 3-6:1.

[0012] 5.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0013] Preferably, the mass ratio of the citric acid to the calcium fluoride sludge after alkaline leaching treatment is 0.02-0.06:1, the pH of the mixed solution obtained after adding citric acid is 2-4, and the sulfur is partially dissolved by adding citrate ions through complexation with calcium ions.

[0014] Preferably, before dehydrating and drying the calcium fluoride sludge, the calcium fluoride sludge is first subjected to fermentation pretreatment, and the fermentation pretreatment method comprises the following steps: The calcium fluoride sludge is initially dehydrated to reduce the moisture content to 80-90%; Adjust the pH value of calcium fluoride sludge to 5.5-6.5; Inoculate Gluconacetobacter into the sludge at a rate of 1-5% of the mass of the calcium fluoride sludge. Add an appropriate amount of carbon source to promote bacterial growth and metabolism. Ferment at 28-30°C for 36-60 hours, stirring at 100-200 rpm for 5-10 minutes every 6 hours during the fermentation process; After fermentation, the bacterial cellulose and the fermentation liquid are separated by filtration or centrifugation; The fermented sludge is washed with water to remove residual organic matter and metabolites.

[0015] Through fermentation pretreatment, Gluconacetobacter can metabolize some organic matter (such as sugars, proteins, etc.) in the sludge and convert them into carbon dioxide, water or other small molecules, thereby reducing the interference of organic matter on the purification of calcium fluoride; Gluconacetobacter will produce a small amount of organic acid (such as acetic acid) during the fermentation process. These acidic substances may help dissolve impurities such as calcium carbonate (CaCO3) in the sludge and improve the purity of calcium fluoride; Gluconacetobacter will produce bacterial cellulose during the fermentation process. This cellulose can absorb impurities in the sludge (such as metal ions, colloidal particles, etc.) and improve the physical properties of the sludge (such as dehydration and filterability).

[0016] Preferably, before the calcium fluoride sludge powder is subjected to acid leaching treatment, the calcium fluoride sludge powder is first treated with bacterial cellulose produced by fermentation pretreatment. The specific method is as follows: the bacterial cellulose produced by fermentation pretreatment is used to prepare a bacterial cellulose suspension, and then the calcium fluoride sludge powder and the bacterial cellulose suspension are mixed at a mass ratio of 1:1-3, and stirred in a stirred reactor for 30-60 minutes at a stirring speed of 200-300 rpm and a temperature of 25-30°C. The mixed slurry is allowed to stand for 2-4 hours to allow the bacterial cellulose to self-assemble on the surface of the calcium fluoride particles to form a protective film, and a filter press or a centrifuge is used to separate the coated solid-liquid mixture to obtain calcium fluoride particles coated with bacterial cellulose, and the coated calcium fluoride particles are dried at 60-80°C to solidify the bacterial cellulose film.

[0017] Organic matter is degraded through fermentation pretreatment, and the generated bacterial cellulose is used to treat calcium fluoride sludge powder to form a complete resource utilization plan. The self-assembly characteristics of bacterial cellulose are used to form a dense protective film on the surface of calcium fluoride particles, reducing its dissolution and loss during the acid washing process, and improving the recovery rate and purity.

[0018] Preferably, the preparation method of the bacterial cellulose suspension is as follows: The bacterial cellulose membrane produced by fermentation pretreatment was repeatedly washed 2-3 times with deionized water; Use 0.1 M NaOH solution at 70-80°C for 60-80 min to remove bacteria and other impurities; The membrane was washed again with deionized water until neutral to obtain a pure bacterial cellulose membrane; The bacterial cellulose membrane was chopped up, added into deionized water, and processed with a high-speed homogenizer for 10-15 minutes to prepare a bacterial cellulose suspension with a concentration of 1-2%.

[0019] Compared with the prior art, the embodiments of the present application have the following beneficial effects: The method for recycling and resource utilization of calcium fluoride sludge provided by the present invention can firstly remove acid-soluble impurities such as calcium carbonate and metal oxides through acid leaching, thereby reducing the interference of impurities in the subsequent calcination process; then, the organic matter and carbonate remaining after acid leaching can be decomposed through calcination, while the structure of calcium fluoride is made more stable, which is convenient for further purification through subsequent alkaline leaching; finally, alkaline leaching is used to neutralize the residual acidic substances and remove some metal ions, thereby further improving the purity of calcium fluoride. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention provides a flow chart of a method for recycling and resource utilization of calcium fluoride sludge.

[0021] Figure 2This is a flow chart of another method for recycling and resource utilization of calcium fluoride sludge provided by the present invention.

[0022] Figure 3 This is a flow chart of another method for recycling and resource utilization of calcium fluoride sludge provided by the present invention. DETAILED DESCRIPTION

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of this application; the terms used in the specification of the application herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, not to describe a specific order.

[0024] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0025] Example 1 The present invention provides a method for recycling and reusing calcium fluoride sludge. Figure 1 As shown, the following steps are included: 1) Dehydrating and drying the calcium fluoride sludge to obtain dry calcium fluoride sludge; 2) crushing and screening the dried calcium fluoride sludge to obtain calcium fluoride sludge powder; 3) Acid leaching of calcium fluoride sludge powder; 4) Calcination treatment of calcium fluoride sludge after acid leaching; 5) alkaline leaching of the calcined calcium fluoride sludge; 6) After the calcium fluoride sludge after alkali leaching is mixed with water, citric acid is added, and the mixture is stirred for solid-liquid separation. The obtained solid precipitate is washed three times, dried and crushed to obtain a calcium fluoride product. The mass ratio of the citric acid to the calcium fluoride sludge after alkali leaching is 0.02:1, and the pH of the mixed solution obtained after adding the citric acid is 2.

[0026] Wherein, the dehydration and drying of calcium fluoride sludge is specifically as follows: 1.1) Use a plate and frame filter press or centrifuge to mechanically dehydrate the calcium fluoride sludge to reduce the moisture content to below 30%; 1.2) Low temperature drying at 80℃ to remove moisture and avoid decomposition of calcium fluoride.

[0027] In this embodiment, the crushing and screening of the dried calcium fluoride sludge is specifically as follows: 2.1) Use a crusher to crush the dried calcium fluoride sludge to a particle size of less than 1 mm; 2.2) Remove large particles of impurities such as sand, gravel, metal fragments, etc. through vibration screening.

[0028] Furthermore, the acid leaching treatment of the calcium fluoride sludge powder is specifically as follows: 3.1) Mix the calcium fluoride sludge powder with 1 times the weight of water and stir evenly; 3.2) adding hydrochloric acid and reacting at 25°C for 60 minutes, wherein the molar concentration of the hydrochloric acid is 2 mol / L, and the molar ratio of the acid equivalent in the hydrochloric acid to the calcium content in the calcium fluoride sludge is 1:1; 3.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0029] Furthermore, the calcination treatment of the calcium fluoride sludge after the acid leaching treatment is specifically as follows: 4.1) Place the acid-leached calcium fluoride sludge into a ball mill at a speed of 500 rpm; 4.2) Heat to 500℃ while ball milling, complete calcination after 60 minutes, and cool to room temperature.

[0030] In a specific implementation, the alkaline leaching treatment of the calcined calcium fluoride sludge is specifically as follows: 5.1) Mix the calcined calcium fluoride sludge with the sodium hydroxide solution and stir evenly; 5.2) reacting at 60° C. for 60 min, wherein the mass fraction of the sodium hydroxide solution is 20%, and the mass ratio of the sodium hydroxide solution to the calcined calcium fluoride sludge is 3:1.

[0031] 5.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0032] Example 2 The present invention provides a method for recycling and reusing calcium fluoride sludge. Figure 1 As shown, the following steps are included: 1) Dehydrating and drying the calcium fluoride sludge to obtain dry calcium fluoride sludge; 2) crushing and screening the dried calcium fluoride sludge to obtain calcium fluoride sludge powder; 3) Acid leaching of calcium fluoride sludge powder; 4) Calcination treatment of calcium fluoride sludge after acid leaching; 5) alkaline leaching of the calcined calcium fluoride sludge; 6) After the calcium fluoride sludge after alkali leaching is mixed with water, citric acid is added, and the mixture is stirred for solid-liquid separation. The obtained solid precipitate is washed three times, dried and crushed to obtain a calcium fluoride product. The mass ratio of the citric acid to the calcium fluoride sludge after alkali leaching is 0.03:1, and the pH of the mixed solution obtained after adding the citric acid is 2.

[0033] Wherein, the dehydration and drying of calcium fluoride sludge is specifically as follows: 1.1) Use a plate and frame filter press or centrifuge to mechanically dehydrate the calcium fluoride sludge to reduce the moisture content to below 30%; 1.2) Low temperature drying at 90°C removes moisture and prevents calcium fluoride from decomposing.

[0034] In this embodiment, the crushing and screening of the dried calcium fluoride sludge is specifically as follows: 2.1) Use a crusher to crush the dried calcium fluoride sludge to a particle size of less than 1 mm; 2.2) Remove large particles of impurities such as sand, gravel, metal fragments, etc. through vibration screening.

[0035] Furthermore, the acid leaching treatment of the calcium fluoride sludge powder is specifically as follows: 3.1) Mix the calcium fluoride sludge powder with 3 times the weight of water and stir evenly; 3.2) adding hydrochloric acid and reacting at 30°C for 65 minutes, wherein the molar concentration of the hydrochloric acid is 3 mol / L, and the molar ratio of the acid equivalent in the hydrochloric acid to the calcium content in the calcium fluoride sludge is 1.5:1; 3.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0036] Furthermore, the calcination treatment of the calcium fluoride sludge after the acid leaching treatment is specifically as follows: 4.1) Place the acid-leached calcium fluoride sludge into a ball mill at a speed of 500 rpm; 4.2) Heat to 525℃ while ball milling, complete calcination after 65min, and cool to room temperature.

[0037] In a specific implementation, the alkaline leaching treatment of the calcined calcium fluoride sludge is specifically as follows: 5.1) Mix the calcined calcium fluoride sludge with the sodium hydroxide solution and stir evenly; 5.2) reacting at 65° C. for 75 min, wherein the mass fraction of the sodium hydroxide solution is 25%, and the mass ratio of the sodium hydroxide solution to the calcined calcium fluoride sludge is 3.5:1.

[0038] 5.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0039] Example 3 The present invention provides a method for recycling and reusing calcium fluoride sludge. Figure 1 As shown, the following steps are included: 1) Dehydrating and drying the calcium fluoride sludge to obtain dry calcium fluoride sludge; 2) crushing and screening the dried calcium fluoride sludge to obtain calcium fluoride sludge powder; 3) Acid leaching of calcium fluoride sludge powder; 4) Calcination treatment of calcium fluoride sludge after acid leaching; 5) alkaline leaching of the calcined calcium fluoride sludge; 6) After the calcium fluoride sludge after alkali leaching is mixed with water, citric acid is added, and the mixture is stirred for solid-liquid separation. The obtained solid precipitate is washed 4 times, dried and crushed to obtain a calcium fluoride product. The mass ratio of the citric acid to the calcium fluoride sludge after alkali leaching is 0.04:1, and the pH of the mixed solution obtained after adding the citric acid is 3.

[0040] Wherein, the dehydration and drying of calcium fluoride sludge is specifically as follows: 1.1) Use a plate and frame filter press or centrifuge to mechanically dehydrate the calcium fluoride sludge to reduce the moisture content to below 30%; 1.2) Low temperature drying at 100°C to remove moisture and avoid decomposition of calcium fluoride.

[0041] In this embodiment, the crushing and screening of the dried calcium fluoride sludge is specifically as follows: 2.1) Use a crusher to crush the dried calcium fluoride sludge to a particle size of less than 1 mm; 2.2) Remove large particles of impurities such as sand, gravel, metal fragments, etc. through vibration screening.

[0042] Furthermore, the acid leaching treatment of the calcium fluoride sludge powder is specifically as follows: 3.1) Mix the calcium fluoride sludge powder with 5 times the weight of water and stir evenly; 3.2) adding hydrochloric acid and reacting at 40°C for 60-90 minutes, wherein the molar concentration of the hydrochloric acid is 4 mol / L, and the molar ratio of the acid equivalent in the hydrochloric acid to the calcium content in the calcium fluoride sludge is 2:1; 3.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0043] Furthermore, the calcination treatment of the calcium fluoride sludge after the acid leaching treatment is specifically as follows: 4.1) Place the acid-leached calcium fluoride sludge into a ball mill at a speed of 500 rpm; 4.2) Heat to 550℃ while ball milling, complete calcination after 75 minutes, and cool to room temperature.

[0044] In a specific implementation, the alkaline leaching treatment of the calcined calcium fluoride sludge is specifically as follows: 5.1) Mix the calcined calcium fluoride sludge with the sodium hydroxide solution and stir evenly; 5.2) reacting at 75° C. for 90 min, wherein the mass fraction of the sodium hydroxide solution is 30%, and the mass ratio of the sodium hydroxide solution to the calcined calcium fluoride sludge is 4.5:1.

[0045] 5.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0046] Example 4 The present invention provides a method for recycling and reusing calcium fluoride sludge. Figure 1 As shown, the following steps are included: 1) Dehydrating and drying the calcium fluoride sludge to obtain dry calcium fluoride sludge; 2) crushing and screening the dried calcium fluoride sludge to obtain calcium fluoride sludge powder; 3) Acid leaching of calcium fluoride sludge powder; 4) Calcination treatment of calcium fluoride sludge after acid leaching; 5) alkaline leaching of the calcined calcium fluoride sludge; 6) After the calcium fluoride sludge after the alkali leaching treatment is mixed with water, citric acid is added, and the mixture is stirred for solid-liquid separation. The obtained solid precipitate is washed 5 times, dried and crushed to obtain a calcium fluoride product. The mass ratio of the citric acid to the calcium fluoride sludge after the alkali leaching treatment is 0.05:1, and the pH of the mixed solution obtained after adding the citric acid is 4.

[0047] Wherein, the dehydration and drying of calcium fluoride sludge is specifically as follows: 1.1) Use a plate and frame filter press or centrifuge to mechanically dehydrate the calcium fluoride sludge to reduce the moisture content to below 30%; 1.2) Low temperature drying at 110℃ to remove moisture and avoid decomposition of calcium fluoride.

[0048] In this embodiment, the crushing and screening of the dried calcium fluoride sludge is specifically as follows: 2.1) Use a crusher to crush the dried calcium fluoride sludge to a particle size of less than 1 mm; 2.2) Remove large particles of impurities such as sand, gravel, metal fragments, etc. through vibration screening.

[0049] Furthermore, the acid leaching treatment of the calcium fluoride sludge powder is specifically as follows: 3.1) Mix the calcium fluoride sludge powder with 6 times the weight of water and stir evenly; 3.2) adding hydrochloric acid and reacting at 45°C for 85 minutes, wherein the molar concentration of the hydrochloric acid is 5 mol / L, and the molar ratio of the acid equivalent in the hydrochloric acid to the calcium content in the calcium fluoride sludge is 2.5:1; 3.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0050] Furthermore, the calcination treatment of the calcium fluoride sludge after the acid leaching treatment is specifically as follows: 4.1) Place the acid-leached calcium fluoride sludge into a ball mill at a speed of 500 rpm; 4.2) Heat to 575℃ while ball milling, complete calcination after 85min, and cool to room temperature.

[0051] In a specific implementation, the alkaline leaching treatment of the calcined calcium fluoride sludge is specifically as follows: 5.1) Mix the calcined calcium fluoride sludge with the sodium hydroxide solution and stir evenly; 5.2) reacting at 85° C. for 105 min, wherein the mass fraction of the sodium hydroxide solution is 35%, and the mass ratio of the sodium hydroxide solution to the calcined calcium fluoride sludge is 5.5:1.

[0052] 5.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0053] Example 5 The present invention provides a method for recycling and reusing calcium fluoride sludge. Figure 1 As shown, the following steps are included: 1) Dehydrating and drying the calcium fluoride sludge to obtain dry calcium fluoride sludge; 2) crushing and screening the dried calcium fluoride sludge to obtain calcium fluoride sludge powder; 3) Acid leaching of calcium fluoride sludge powder; 4) Calcination treatment of calcium fluoride sludge after acid leaching; 5) alkaline leaching of the calcined calcium fluoride sludge; 6) After the calcium fluoride sludge after alkali leaching is mixed with water, citric acid is added, and the mixture is stirred for solid-liquid separation. The obtained solid precipitate is washed 5 times, dried and crushed to obtain a calcium fluoride product. The mass ratio of the citric acid to the calcium fluoride sludge after alkali leaching is 0.0.06:1, and the pH of the mixed solution obtained after adding the citric acid is 4.

[0054] Wherein, the dehydration and drying of calcium fluoride sludge is specifically as follows: 1.1) Use a plate and frame filter press or centrifuge to mechanically dehydrate the calcium fluoride sludge to reduce the moisture content to below 30%; 1.2) Low temperature drying at 120℃ removes moisture and prevents calcium fluoride from decomposing.

[0055] In this embodiment, the crushing and screening of the dried calcium fluoride sludge is specifically as follows: 2.1) Use a crusher to crush the dried calcium fluoride sludge to a particle size of less than 1 mm; 2.2) Remove large particles of impurities such as sand, gravel, metal fragments, etc. through vibration screening.

[0056] Furthermore, the acid leaching treatment of the calcium fluoride sludge powder is specifically as follows: 3.1) Mix the calcium fluoride sludge powder with 8 times the weight of water and stir evenly; 3.2) adding hydrochloric acid and reacting at 50°C for 90 minutes, wherein the molar concentration of the hydrochloric acid is 6 mol / L, and the molar ratio of the acid equivalent in the hydrochloric acid to the calcium content in the calcium fluoride sludge is 3:1; 3.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0057] Furthermore, the calcination treatment of the calcium fluoride sludge after the acid leaching treatment is specifically as follows: 4.1) Place the acid-leached calcium fluoride sludge into a ball mill at a speed of 500 rpm; 4.2) Heat to 600℃ while ball milling, complete calcination after 90 minutes, and cool to room temperature.

[0058] In a specific implementation, the alkaline leaching treatment of the calcined calcium fluoride sludge is specifically as follows: 5.1) Mix the calcined calcium fluoride sludge with the sodium hydroxide solution and stir evenly; 5.2) reacting at 90° C. for 120 min, wherein the mass fraction of the sodium hydroxide solution is 40%, and the mass ratio of the sodium hydroxide solution to the calcined calcium fluoride sludge is 6:1.

[0059] 5.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0060] Example 6 The present invention provides a method for recycling and reusing calcium fluoride sludge. Figure 2 As shown, the following steps are included: 1) Fermentation pretreatment of calcium fluoride sludge; 2) dehydrating and drying the calcium fluoride sludge after fermentation pretreatment to obtain dry calcium fluoride sludge; 3) crushing and screening the dried calcium fluoride sludge to obtain calcium fluoride sludge powder; 4) Acid leaching of calcium fluoride sludge powder; 5) Calcination treatment of calcium fluoride sludge after acid leaching; 6) alkaline leaching of the calcined calcium fluoride sludge; 7) After the calcium fluoride sludge after alkali leaching is mixed with water, citric acid is added, and the mixture is stirred for solid-liquid separation. The obtained solid precipitate is washed 4 times, dried and crushed to obtain a calcium fluoride product. The mass ratio of the citric acid to the calcium fluoride sludge after alkali leaching is 0.04:1, and the pH of the mixed solution obtained after adding the citric acid is 3.

[0061] Wherein, the dehydration and drying of calcium fluoride sludge is specifically as follows: 2.1) Mechanically dewater the calcium fluoride sludge using a plate and frame filter press or centrifuge to reduce the moisture content to below 30%; 2.2) Low temperature drying at 100°C to remove moisture and avoid decomposition of calcium fluoride.

[0062] In this embodiment, the crushing and screening of the dried calcium fluoride sludge is specifically as follows: 3.1) Use a crusher to crush the dried calcium fluoride sludge to a particle size of less than 1 mm; 3.2) Remove large particles of impurities such as sand, gravel, metal fragments, etc. through vibration screening.

[0063] Furthermore, the acid leaching treatment of the calcium fluoride sludge powder is specifically as follows: 4.1) Mix the calcium fluoride sludge powder with 5 times the weight of water and stir evenly; 4.2) adding hydrochloric acid and reacting at 40°C for 60-90 minutes, wherein the molar concentration of the hydrochloric acid is 4 mol / L, and the molar ratio of the acid equivalent in the hydrochloric acid to the calcium content in the calcium fluoride sludge is 2:1; 4.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0064] Furthermore, the calcination treatment of the calcium fluoride sludge after the acid leaching treatment is specifically as follows: 5.1) Place the acid-leached calcium fluoride sludge into a ball mill at a speed of 500 rpm; 5.2) Heat to 550℃ while ball milling, complete calcination after 75 minutes, and cool to room temperature.

[0065] In a specific implementation, the alkaline leaching treatment of the calcined calcium fluoride sludge is specifically as follows: 6.1) Mix the calcined calcium fluoride sludge with the sodium hydroxide solution and stir evenly; 6.2) reacting at 75° C. for 90 min, wherein the mass fraction of the sodium hydroxide solution is 30%, and the mass ratio of the sodium hydroxide solution to the calcined calcium fluoride sludge is 4.5:1.

[0066] 6.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0067] Preferably, the fermentation pretreatment method comprises the following steps: The calcium fluoride sludge is initially dehydrated to reduce the moisture content to 80-90%; Adjust the pH value of calcium fluoride sludge to 5.5-6.5; Inoculate Gluconacetobacter into the sludge at a rate of 1-5% of the mass of the calcium fluoride sludge. Add an appropriate amount of carbon source to promote bacterial growth and metabolism. Ferment at 28-30°C for 36-60 hours, stirring at 100-200 rpm for 5-10 minutes every 6 hours during the fermentation process; After fermentation, bacterial cellulose and fermentation liquid are separated by filtration or centrifugation.

[0068] The fermented sludge is washed with water to remove residual organic matter and metabolites.

[0069] Example 7 The present invention provides a method for recycling and reusing calcium fluoride sludge. Figure 3 As shown, the following steps are included: 1) Fermentation pretreatment of calcium fluoride sludge; 2) dehydrating and drying the calcium fluoride sludge after fermentation pretreatment to obtain dry calcium fluoride sludge; 3) crushing and screening the dried calcium fluoride sludge to obtain calcium fluoride sludge powder; 4) Treating calcium fluoride sludge powder using bacterial cellulose produced by fermentation pretreatment; 5) acid leaching the calcium fluoride sludge after bacterial cellulose treatment; 6) Calcination treatment of calcium fluoride sludge after acid leaching; 7) alkaline leaching of the calcined calcium fluoride sludge; 8) After the calcium fluoride sludge after alkali leaching is mixed with water, citric acid is added, and the mixture is stirred for solid-liquid separation. The obtained solid precipitate is washed 4 times, dried and crushed to obtain a calcium fluoride product, wherein the mass ratio of the citric acid to the calcium fluoride sludge after alkali leaching is 0.04:1, and the pH of the mixed solution obtained after adding the citric acid is 3.

[0070] Wherein, the dehydration and drying of calcium fluoride sludge is specifically as follows: 2.1) Mechanically dewater the calcium fluoride sludge using a plate and frame filter press or centrifuge to reduce the moisture content to below 30%; 2.2) Low temperature drying at 100°C to remove moisture and avoid decomposition of calcium fluoride.

[0071] In this embodiment, the crushing and screening of the dried calcium fluoride sludge is specifically as follows: 3.1) Use a crusher to crush the dried calcium fluoride sludge to a particle size of less than 1 mm; 3.2) Remove large particles of impurities such as sand, gravel, metal fragments, etc. through vibration screening.

[0072] Furthermore, the acid leaching treatment of the calcium fluoride sludge powder is specifically as follows: 5.1) Mix the calcium fluoride sludge powder with 5 times the weight of water and stir evenly; 5.2) adding hydrochloric acid and reacting at 40°C for 60-90 minutes, wherein the molar concentration of the hydrochloric acid is 4 mol / L, and the molar ratio of the acid equivalent in the hydrochloric acid to the calcium content in the calcium fluoride sludge is 2:1; 5.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0073] Furthermore, the calcination treatment of the calcium fluoride sludge after the acid leaching treatment is specifically as follows: 6.1) Place the acid-leached calcium fluoride sludge into a ball mill at a speed of 500 rpm; 6.2) Heat to 550℃ while ball milling, complete calcination after 75 minutes, and cool to room temperature.

[0074] In a specific implementation, the alkaline leaching treatment of the calcined calcium fluoride sludge is specifically as follows: 7.1) Mix the calcined calcium fluoride sludge with the sodium hydroxide solution and stir evenly; 7.2) reacting at 75° C. for 90 min, wherein the mass fraction of the sodium hydroxide solution is 30%, and the mass ratio of the sodium hydroxide solution to the calcined calcium fluoride sludge is 4.5:1.

[0075] 7.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

[0076] Preferably, the fermentation pretreatment method comprises the following steps: The calcium fluoride sludge is initially dehydrated to reduce the moisture content to 80-90%; Adjust the pH value of calcium fluoride sludge to 5.5-6.5; Inoculate Gluconacetobacter into the sludge at a rate of 1-5% of the mass of the calcium fluoride sludge. Add an appropriate amount of carbon source to promote bacterial growth and metabolism. Ferment at 28-30°C for 36-60 hours, stirring at 100-200 rpm for 5-10 minutes every 6 hours during the fermentation process; After fermentation, bacterial cellulose and fermentation liquid are separated by filtration or centrifugation.

[0077] The fermented sludge is washed with water to remove residual organic matter and metabolites.

[0078] Preferably, before the calcium fluoride sludge powder is subjected to acid leaching treatment, the calcium fluoride sludge powder is first treated with bacterial cellulose produced by fermentation. The specific method is as follows: the bacterial cellulose produced by fermentation pretreatment is used to prepare a bacterial cellulose suspension, and then the calcium fluoride sludge powder and the bacterial cellulose suspension are mixed at a mass ratio of 1:1-3, and stirred in a stirred reactor for 30-60 minutes at a stirring speed of 200-300 rpm and a temperature of 25-30°C. The mixed slurry is allowed to stand for 2-4 hours to allow the bacterial cellulose to self-assemble on the surface of the calcium fluoride particles to form a protective film, and a filter press or a centrifuge is used to separate the coated solid-liquid mixture to obtain calcium fluoride particles coated with bacterial cellulose, and the coated calcium fluoride particles are dried at 60-80°C to solidify the bacterial cellulose film.

[0079] Wherein, the preparation method of the bacterial cellulose suspension is as follows: The bacterial cellulose membrane produced by fermentation pretreatment was repeatedly washed 2-3 times with deionized water; Use 0.1 M NaOH solution at 70-80°C for 60-80 min to remove bacteria and other impurities; The membrane was washed again with deionized water until neutral to obtain a pure bacterial cellulose membrane; The bacterial cellulose membrane was chopped up, added into deionized water, and processed with a high-speed homogenizer for 10-15 minutes to prepare a bacterial cellulose suspension with a concentration of 1-2%.

[0080] Comparative Example 1: The difference from Example 3 is that the calcium fluoride sludge is treated in the order of calcination-acid leaching-alkali leaching.

[0081] Comparative Example 2: The difference from Example 3 is that the calcium fluoride sludge is treated in the order of acid leaching-alkali leaching-calcination.

[0082] experiment The purity of the calcium fluoride products obtained in Examples 1-7 and Comparative Examples 1-2 was tested, and the results are shown in Table 1: Table 1 Purity of calcium fluoride products

[0083] It can be seen from the above results that the calcium fluoride product prepared by the present invention has high purity, so the calcium fluoride sludge recycling and resource utilization effect is good.

[0084] It should be noted that, for the above embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should know that the present invention is not limited by the described order of actions, because according to the present invention, some steps may be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present invention.

[0085] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the scope of protection of the invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on these embodiments, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in this field can still combine, add, delete or make other adjustments to the features in the various embodiments of the present invention according to the circumstances without conflict, without making creative work, so as to obtain different other technical solutions that do not deviate from the concept of the present invention in essence, and these technical solutions also belong to the scope of protection of the present invention.

Claims

1. A method for recycling and reusing calcium fluoride sludge, characterized in that: The steps include: 1) Dehydrating and drying the calcium fluoride sludge to obtain dry calcium fluoride sludge; 2) crushing and screening the dried calcium fluoride sludge to obtain calcium fluoride sludge powder; 3) Acid leaching of calcium fluoride sludge powder; 4) Calcination treatment of calcium fluoride sludge after acid leaching; 5) alkaline leaching of the calcined calcium fluoride sludge; 6) After the calcium fluoride sludge after alkali leaching is mixed with water, citric acid is added, and solid-liquid separation is performed after stirring. The obtained solid precipitate is washed 3-5 times, dried and crushed to obtain a calcium fluoride product; Before dehydration and drying, the calcium fluoride sludge is first subjected to fermentation pretreatment, and the fermentation pretreatment method comprises the following steps: The calcium fluoride sludge is initially dewatered; Adjust the pH value of calcium fluoride sludge to 5.5-6.5; Inoculating Gluconacetobacter species into the sludge; Fermentation at 28-30°C; After fermentation, the bacterial cellulose and the fermentation liquid are separated by filtration or centrifugation; The fermented sludge is washed with water.

2. The method for recycling and reusing calcium fluoride sludge according to claim 1, characterized in that: The dehydration and drying of calcium fluoride sludge is specifically as follows: 1.1) Use a plate and frame filter press or centrifuge to mechanically dehydrate the calcium fluoride sludge to reduce the moisture content to below 30%; 1.2) Dry at low temperature of 80-120℃ to remove moisture.

3. The method for recycling and reusing calcium fluoride sludge according to claim 1, characterized in that: The crushing and screening of the dried calcium fluoride sludge is specifically as follows: 2.1) Use a crusher to crush the dried calcium fluoride sludge to a particle size of less than 1 mm; 2.2) Remove large particles of impurities through vibration screening.

4. The method for recycling and reusing calcium fluoride sludge as claimed in claim 1, characterized in that: The acid leaching treatment of the calcium fluoride sludge powder is specifically as follows: 3.1) Mix the calcium fluoride sludge powder with 1-8 times the weight of water and stir evenly; 3.2) adding hydrochloric acid and reacting at 25-50°C for 60-90 minutes, wherein the molar concentration of the hydrochloric acid is 2-6 mol / L, and the molar ratio of the acid equivalent in the hydrochloric acid to the calcium content in the calcium fluoride sludge is 1-3:1; 3.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

5. The method for recycling and reusing calcium fluoride sludge as claimed in claim 1, characterized in that: The calcination treatment of the calcium fluoride sludge after the acid leaching treatment is specifically as follows: 4.1) Place the acid-leached calcium fluoride sludge into a ball mill at a speed of 500 rpm; 4.2) Heat to 500-600℃ while ball milling, complete calcination after 60-90min, and cool to room temperature.

6. The method for recycling and reusing calcium fluoride sludge as claimed in claim 1, characterized in that: The alkali leaching treatment of the calcined calcium fluoride sludge is specifically as follows: 5.1) Mix the calcined calcium fluoride sludge with the sodium hydroxide solution and stir evenly; 5.2) reacting at 60-90°C for 60-120min, wherein the mass fraction of the sodium hydroxide solution is 20-40%, and the mass ratio of the sodium hydroxide solution to the calcined calcium fluoride sludge is 3-6:1; 5.3) The product obtained after leaching is subjected to solid-liquid separation, the solid is collected and washed to neutrality, and then dried and crushed.

7. The method for recycling and reusing calcium fluoride sludge as claimed in claim 1, characterized in that: The mass ratio of the citric acid to the calcium fluoride sludge after alkaline leaching treatment is 0.02-0.06:1, and the pH of the mixed solution obtained after adding citric acid is 2-4.

8. The method for recycling and reusing calcium fluoride sludge as claimed in claim 1, characterized in that: Before the calcium fluoride sludge powder is subjected to acid leaching treatment, the calcium fluoride sludge powder is first treated with bacterial cellulose produced by fermentation pretreatment. The specific method is as follows: the bacterial cellulose produced by fermentation pretreatment is used to prepare a bacterial cellulose suspension, and then the calcium fluoride sludge powder and the bacterial cellulose suspension are mixed at a mass ratio of 1:1-3, and stirred in a stirred reactor for 30-60 minutes at a stirring speed of 200-300 rpm and a temperature of 25-30° C. The mixed slurry is allowed to stand for 2-4 hours to allow the bacterial cellulose to self-assemble on the surface of the calcium fluoride particles to form a protective film, and a filter press or a centrifuge is used to separate the coated solid-liquid mixture to obtain calcium fluoride particles coated with bacterial cellulose, and the coated calcium fluoride particles are dried at 60-80° C. to solidify the bacterial cellulose film.

9. The method for recycling and reusing calcium fluoride sludge as claimed in claim 8, characterized in that: The preparation method of the bacterial cellulose suspension is as follows: The bacterial cellulose membrane produced by fermentation pretreatment was repeatedly washed 2-3 times with deionized water; Use 0.1 M NaOH solution at 70-80°C for 60-80 min to remove bacteria and other impurities; The membrane was washed again with deionized water until neutral to obtain a pure bacterial cellulose membrane; The bacterial cellulose membrane was chopped up, added into deionized water, and processed with a high-speed homogenizer for 10-15 minutes to prepare a bacterial cellulose suspension with a concentration of 1-2%.

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