Process for recovering calcium fluoride from calcium fluoride sludge

Abstract

The application belongs to the field of sludge recovery, and particularly relates to a method for recovering calcium fluoride from calcium fluoride sludge, wherein the calcium fluoride sludge is pretreated under ultrasonic waves, the power of the ultrasonic waves is above 20 KHz; a flotation reagent is added to the system after ultrasonic treatment for rough selection, and calcium fluoride rough selection material is collected; the flotation reagent comprises an inhibitor and a collector, the collector comprises formula 1 and formula 2 in a weight ratio of 1:1-2, the pH of the slurry in the flotation stage is 3-5.5; the acid for regulating the pH of the slurry is at least one of hydrochloric acid and nitric acid. The application innovatively adopts an ultrasonic process to pretreat the calcium fluoride sludge, and then cooperates with combined collectors in subsequent flotation and joint control of the pH of the flotation process, so that synergy can be achieved, and high-grade calcium fluoride can be efficiently and greenly obtained based on simple processes and means.

Description

Technical Field

[0001] This invention relates to the field of sludge waste resource utilization, specifically to the field of calcium fluoride sludge recycling technology. Background Technology

[0002] Fluorine, as one of the most potent oxidizing agents, is widely used in the photovoltaic and semiconductor industries. In recent years, the rapid development of China's photovoltaic and semiconductor industries has led to the extensive use of hydrofluoric acid, used for etching silicon wafers. Consequently, large amounts of fluoride-containing wastewater from these industries require treatment before discharge. Chemical flocculation is currently the most common process for treating fluoride-containing wastewater. This process first requires the addition of a large amount of lime for neutralization, forming calcium fluoride. Then, flocculants such as polyacrylamide are added to flocculate and precipitate the fluoride, producing sludge containing calcium fluoride and silica, commonly known as calcium fluoride sludge. Currently, the most common method for treating calcium fluoride is landfill. While simple, this method consumes significant land resources and may have adverse environmental impacts, even threatening human health.

[0003] Calcium fluoride in calcium fluoride sludge often exists in an amorphous form, with organic matter encapsulation and complexation, and a high degree of mud-like formation. Recovery of calcium fluoride from this type of sludge via flotation is difficult, and the recovery rate is unsatisfactory. Current solutions primarily involve pretreatment of the calcium fluoride sludge with acids, alkalis, or organic solvents. While this can improve recovery to some extent, it also increases treatment costs and waste generation. Even so, the recovery rate of calcium fluoride remains unsatisfactory. Especially for highly mud-like calcium fluoride sludge, the flotation separation efficiency and selectivity of existing pretreatment-flotation processes still have significant room for improvement. Summary of the Invention

[0004] To address the difficulty of highly selective flotation separation of highly muddy calcium fluoride sludge, the present invention aims to provide a method for recovering calcium fluoride from calcium fluoride sludge, with the goal of improving the recovery rate and grade of calcium fluoride from highly muddy calcium fluoride sludge based on a simple and green process.

[0005] Unlike fluorite minerals, calcium fluoride in calcium fluoride sludge is in an amorphous, non-crystalline form, resulting in poor binding with collectors and difficulty in flotation. Furthermore, calcium fluoride sludge has very small particle sizes and is highly muddy, significantly increasing the difficulty of selectively separating this highly muddy material. This invention addresses the difficulty in separating ultrafine-grained, highly muddy amorphous calcium fluoride sludge by developing the following improved solution:

[0006] A method for recovering calcium fluoride from calcium fluoride sludge involves pretreating the calcium fluoride sludge under ultrasound, wherein the power of the ultrasound is above 20 kHz.

[0007] Flotation reagents were added to the ultrasonically treated system for roughing, and calcium fluoride roughing material was collected.

[0008] The flotation reagents include inhibitors and collectors, wherein the collectors include Formula 1 and Formula 2 in a weight ratio of 1:1 to 2; the pH of the flotation stage is 3 to 5.5; and the acid used to adjust the pH is at least one of hydrochloric acid and nitric acid.

[0009]

[0010] In Equations 1 and 2, M is H, Na, K, or NH4.

[0011] To address the challenges of collecting calcium fluoride sludge due to its organic encapsulation and complexation (e.g., surface complexation with flocculants), amorphous structure, and high degree of mud formation, this invention innovatively employs ultrasonic technology for pretreatment of calcium fluoride sludge. This optimizes the morphology of amorphous calcium fluoride particles and the exposure of active sites. Combined with subsequent flotation collectors and the joint control of flotation processes such as pH, synergistic effects can be achieved. This allows for the efficient and environmentally friendly acquisition of high-grade calcium fluoride based on simple processes and methods.

[0012] In this invention, the calcium fluoride sludge contains amorphous calcium fluoride, with over 90% of the particles being -10μm; the grade of calcium fluoride is 40-60%. The method of this invention is applicable to any calcium fluoride sludge, especially for difficult-to-treat sludge with extremely poor crystallinity, extremely fine particle size, and low CaF2 grade. Thanks to the innovative method of this invention, ideal collection capacity and selectivity can still be achieved.

[0013] The process of this invention can be applied to any calcium fluoride sludge, especially highly muddy calcium fluoride sludge that is difficult to treat effectively in the industry. Using the process of this invention, a better recovery advantage can be obtained.

[0014] In this invention, calcium fluoride sludge is slurried with water to obtain slurry, which is then pretreated under ultrasound.

[0015] Preferably, the solid content in the mud is 30-60%, and more preferably 45-50%.

[0016] In this invention, the pretreatment of calcium fluoride sludge by ultrasound and the subsequent combination of collectors of Formulas 1-2 are key to synergistically solving the problem of difficult recovery of calcium fluoride caused by its organic encapsulation characteristics.

[0017] In this invention, the power of the ultrasound is 20-50 kHz; more specifically, it can be 35-40 kHz.

[0018] Preferably, the ultrasound duration is 5 minutes or more, more preferably 5 to 20 minutes, and further preferably 10 to 15 minutes.

[0019] By utilizing the innovative combined collector and pH settings of this invention, and combining them with industry-known flotation methods, the ultrasonically treated mud system can be subjected to flotation treatment to efficiently and selectively recover calcium fluoride. For example, in this invention, the pH of the ultrasonically treated system (mud) can be pre-adjusted using the aforementioned acid, followed by the addition of flotation reagents, and flotation treatment can be performed using conventional methods to obtain calcium fluoride.

[0020] In this invention, there are no special requirements for the concentration of the acid solution used to control the pH of flotation; for example, it can be 0.3 to 1 M.

[0021] In this invention, the pH of the sludge in the flotation stage can be 3.5–5, and more preferably 3.5–4.5. Studies have shown that under these preferred conditions, it can be further synergistically combined with the process to further solve the problem of difficult recovery of calcium fluoride caused by the special physicochemical characteristics of sludge, and can obtain better recovery grade and yield.

[0022] In this invention, the inhibitor includes at least one selected from water glass, sodium hexametaphosphate, and sodium citrate. Further,

[0023] In this invention, the amount of inhibitor used in the roughing stage is 500-1500 g / t; preferably 750-1100 g / t.

[0024] In this invention, based on ultrasonic pretreatment, the flotation process is further enhanced by the combined use of pH during the flotation stage and a combination of special components and proportions of collectors. This synergistic effect can improve the flotation efficiency and grade of calcium fluoride from highly muddy calcium fluoride sludge.

[0025] Preferably, in the collector, the weight ratio of Formula 1 and Formula 2 is 1:1.4 to 1.6. Research in this invention shows that this preferred composite collector can further synergize with the process to further solve the problem of difficult recovery of calcium fluoride caused by the special physicochemical characteristics of sludge, resulting in better recovery grade and yield.

[0026] In this invention, the amount of collector used in the roughing stage is 1000-6000 g / t; more specifically, it can be 3000-4500 g / t.

[0027] In the roughing stage, conventional frothers can also be added to the system, and their dosage can be adjusted reasonably according to conventional flotation reagents.

[0028] In this invention, the crude calcium fluoride material can be subjected to 1 to 7 stages of fine-tuning treatment as needed to obtain higher quality purified calcium fluoride.

[0029] In this invention, the flotation reagents used in the selection stage include inhibitors.

[0030] Preferably, during the multi-stage refining process, the amount of inhibitor used is reduced to 30-60 wt.% of the amount used in the previous stage of refining.

[0031] In this invention, the amount of inhibitor used in the selection stage can be 1000-6000 g / t; more specifically, it can be 1500-3000 g / t.

[0032] Beneficial effects

[0033] (1) In view of the problems of difficulty in collection caused by organic encapsulation and complexation, amorphous and highly muddy calcium fluoride sludge, this invention innovatively adopts ultrasonic process to pretreat calcium fluoride sludge, and then combines it with the combined collector of subsequent flotation and the joint control of flotation processes such as pH. In this way, synergy can be achieved, and high-grade calcium fluoride can be obtained efficiently and greenly based on simple processes and means.

[0034] (2) The process described in this invention is relatively simple and the parameters are easy to control. In particular, it does not require efficient purification through hydrometallurgical or pyrometallurgical methods, and has great potential for promotion and market application. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the process flow for Example 1;

[0036] Figure 2 This is a flotation flowchart for Example 1. Detailed Implementation

[0037] The photovoltaic sludge targeted in this scheme generally has a low CaF2 content, with 100% of the -10μm particles, making it an extremely fine sludge with severe mudification; the calcium fluoride content is 40-60%, with extremely poor crystallinity, and it exhibits high alkalinity in solution. In addition, it has flocculants such as PAM complexed on its surface, making it a type of photovoltaic CaF2-containing sludge that is extremely difficult to recycle.

[0038] In the following examples, as optional solutions, Equation 1 takes Equation 1A as a typical example, where Equation 1A refers to Equation 1 with M as H. Equation 2 takes Equation 2A as a typical example, where Equation 2A refers to Equation 2 with M as H.

[0039] As an optional option, the water glass is hydrochloric acid-acidified water glass (wherein, the hydrochloric acid / SiO2 molar ratio can be 1:1).

[0040] In this invention, there are no special requirements for the temperature of the system during the ultrasonic pretreatment process. For example, it can be 15 to 50°C; more specifically, it can be 40 ± 5°C.

[0041] In the following cases, there are no special requirements for the temperature during the flotation process. For example, it can be a conventional room temperature process with a temperature of 30±5℃.

[0042] Example 1

[0043] The raw material used in this case was photovoltaic sludge from Henan Province, with a CaF2 content of 58.04%. The specific operation is as follows.

[0044] Step 1: Ultrasonic Pretreatment

[0045] Place the sludge into a beaker, add tap water to ensure the sludge has a solid content of 45%, and keep the sludge temperature at 40±5℃. Place the beaker in an ultrasonic (40KHz) chamber and sonicate for 10 minutes.

[0046] Step 2: Coarse selection:

[0047] according to Figure 2 The schematic diagram illustrates the flotation process, and the steps are as follows:

[0048] First, the ultrasonicated mud was transferred to a 1.5L flotation cell. The flotation machine was started at 2000 rpm, and the pH of the mud was adjusted to 4 using acid (0.5M hydrochloric acid in this case). Then, 1000 g / t of 2.3–2.6 modulus water glass was added and stirred for 3 minutes. 4000 g / t of collector (of which the main components Formula 1A and Formula 2A are in a weight ratio of 1:1.5) was added and stirred for 3 minutes. 20 g / t of pine oil frother was added and stirred for 1 minute. Roughing was carried out for 5 minutes to obtain a rough concentrate and tailings X. The CaF2 grade and recovery rate in the rough concentrate were 77.65% and 33.91%, respectively.

[0049] Step 3: Selection:

[0050] Step 3.1: Transfer the obtained rough concentrate to a 1L flotation machine and start the flotation machine at 2000r / min and stir for 1 minute; adjust the pH of the mud to 4 with hydrochloric acid, then add 1000g / t of water glass with a modulus of 2.3-2.6 and stir for 3 minutes; finally, float for 3 minutes to obtain the first concentrate and middlings M1.

[0051] Step 3.2: Transfer the No. 1 concentrate to a 0.5L flotation machine and repeat step 5, except that the amount of water glass used is 500g / t; to obtain No. 2 concentrate and middlings M2;

[0052] Step 3.3: Transfer the No. 2 concentrate to a 0.25L flotation machine and repeat step 6, except that the water glass dosage is 250g / t; to obtain No. 3 concentrate K and middlings M3;

[0053] Step 3.4: Dry the obtained sample, weigh it, and further analyze the CaF2 content to calculate the recovery rate.

[0054] Finally, after analysis and calculation, a calcium fluoride product with a CaF2 content of 90.27% and a recovery rate of 20.23% was obtained.

[0055] Example 2

[0056] Compared to Example 1, the only difference is the type of acid in step 2, specifically, 0.8M nitric acid. All other operations and parameters remain the same as in Example 1. The CaF2 grade and recovery rate in the crude concentrate are 78.79% and 34.83%, respectively. The final refined product is a calcium fluoride product with a CaF2 grade of 91.53% and a recovery rate of 19.18%.

[0057] Example 3

[0058] Compared with Example 1, the only difference is that in step 1, the solid content is 50%, the ultrasonic power is 35 kHz, the ultrasonic time is 15 minutes, and the CaF2 grade and recovery rate in the rough concentrate are 70.88% and 32.39%, respectively. Finally, a calcium fluoride concentrate product with a CaF2 grade of 89.97% and a recovery rate of 25.21% was obtained.

[0059] Example 4

[0060] Compared with Example 1, the only difference is that in step 2, the modulus of water glass is 3.0-3.2, the amount of water glass used in step 2 is 800 g / t, and the amount of collector is 4500 g / t. Furthermore, in step 3.1, the amount of water glass used is 800 g / t; in step 3.2, the amount of inhibitor used is 50% of the amount used in step 3.1; and in step 3.3, the amount of inhibitor used is 50% of the amount used in step 3.2. All other operations and parameters are the same as in Example 1.

[0061] The CaF2 grade and recovery rate in the rough concentrate were 73.11% and 30.56%, respectively. The final product was a calcium fluoride concentrate with a CaF2 grade of 91.33% and a recovery rate of 18.27%.

[0062] Example 5

[0063] Compared with Example 1, the only difference is that in step 2, the pH of the coarse selection is adjusted to 3.5, and in step 3, only two fine selection steps, 3.1 and 3.2, are performed. In step 3.1, 1500 g / t of water glass is added, and in step 3.2, 1000 g / t of water glass is added. All other operations and parameters are the same as in Example 1.

[0064] The CaF2 grade and recovery rate in the rough concentrate were 76.29% and 34.84%, respectively. The final product was a calcium fluoride concentrate with a CaF2 grade of 91.07% and a recovery rate of 19.94%.

[0065] Example 6

[0066] Compared with Example 1, the only difference is that in step 2, the mud pH is 3.5 during the flotation process, and the CaF2 grade and recovery rate in the rough concentrate are 81.31% and 25.16%, respectively. All other operations and parameters are the same as in Example 1.

[0067] The final product obtained was calcium fluoride concentrate with a CaF2 grade of 92.77% and a recovery rate of 16.59%.

[0068] Example 7

[0069] Compared with Example 1, the only difference is that in step 2, the ratio of Formula 1A and Formula 2A in the collector is 1:1, and all other operations and parameters are the same as in Example 1.

[0070] The CaF2 grade and recovery rate in the rough concentrate were 76.84% and 31.33%, respectively. The final product obtained was calcium fluoride with a CaF2 grade of 87.26% and a recovery rate of 19.03%.

[0071] Example 8

[0072] Compared with Example 1, the only difference is that in step 2, the ratio of Formula 1A and Formula 2A in the collector is 1:2, and all other operations and parameters are the same as in Example 1.

[0073] The CaF2 grade and recovery rate in the rough concentrate were 81.90% and 35.61%, respectively. The final product obtained was calcium fluoride with a CaF2 grade of 89.31% and a recovery rate of 21.47%.

[0074] Comparative Example 1

[0075] Compared with Example 1, the only difference is that the acid solution in step 2 is changed to 0.5M sulfuric acid, while the pH of the mud and other operations and parameters are the same as in Example 1.

[0076] The CaF2 grade and recovery rate in the rough concentrate were 71.19% and 27.27%, respectively. The final beneficiation results were: CaF2 grade 73.25% and 12.27%.

[0077] Comparative Example 2

[0078] Compared with Example 1, the only difference is that step 1 does not involve ultrasonic pretreatment; all other operations and parameters are the same as in Example 1.

[0079] In step 2, the CaF2 grade and recovery rate in the rough concentrate were 63.33% and 42.15%, respectively. The final product was a calcium fluoride concentrate with a CaF2 grade of 72.04% and a recovery rate of 34.84%.

[0080] Comparative Example 3

[0081] Compared with Example 1, the only difference is that in step 1, the ultrasonic power is 10KHz, and all other operations and parameters are the same as in Example 1.

[0082] The CaF2 grade and recovery rate in the rough concentrate were 66.46% and 47.79%, respectively. The final product was a calcium fluoride concentrate with a CaF2 grade of 83.14% and a recovery rate of 32.71%.

[0083] Comparative Example 4

[0084] Compared with Example 1, the only difference is that in step 2, the pH of the mud during the flotation process is 6, while other operations and parameters are the same as in Example 1.

[0085] The CaF2 grade and recovery rate in the rough concentrate were 62.52% and 28.19%, respectively. The final product was a calcium fluoride concentrate with a CaF2 grade of 76.66% and a recovery rate of 22.15%.

[0086] Comparative Example 5

[0087] Compared with Example 1, the only difference is that in step 2, the collector is only Formula 1A, while the total amount of collector and other operating parameters are the same as in Example 1.

[0088] The CaF2 grade and recovery rate in the rough concentrate were 64.23% and 43.26%, respectively. The final product was a calcium fluoride concentrate with a CaF2 grade of 73.19% and a recovery rate of 37.01%.

[0089] Comparative Example 6

[0090] Compared with Example 1, the only difference is that in step 2, the collector is only Formula 2A, while the total amount of collector and other operating parameters are the same as in Example 1.

[0091] The CaF2 grade and recovery rate in the rough concentrate were 65.09% and 42.58%, respectively. The final product obtained was calcium fluoride with a CaF2 grade of 76.01% and a recovery rate of 25.72%.

[0092] Comparative Examples 5 and 6 show that a better calcium fluoride product can only be obtained when the combined collectors are in the appropriate proportions.

[0093] Comparative Example 7

[0094] Compared with Example 1, the only difference is that in step 1, the sludge is not pre-ultrasonicated, but in step 2, pH adjuster, inhibitor and collector are added to the slurry before ultrasonic treatment and flotation test is carried out. All other operations and parameters are the same as in Example 1.

[0095] The CaF2 grade and recovery rate in the rough concentrate were 65.29% and 46.32%, respectively. The final product obtained was calcium fluoride with a CaF2 grade of 82.47% and a recovery rate of 21.59%.

[0096] As can be seen from Example 1 and Comparative Example 7, ultrasonic treatment alone is not sufficient to significantly adapt to the flotation treatment of the calcium fluoride sludge. Pre-modification is expected to work synergistically with the reagents of this invention to improve the recovery rate of calcium fluoride in the sludge.

[0097] Comparative Example 8

[0098] The calcium fluoride sludge from Example 1 was treated using existing conventional treatment processes, as follows:

[0099] Step 1: Acidification treatment

[0100] Place the sludge into a beaker, add tap water to ensure the solid content of the sludge is 50%, and keep the sludge temperature at 60℃. Add 0.9mol / L hydrochloric acid and stir the sludge at 400r / min for 40 minutes.

[0101] Step 2: Coarse selection:

[0102] First, the ultrasonicated mud was transferred to a 1.5L flotation cell. The flotation machine was started at 2000 rpm, and the pH of the mud was adjusted to 7-8 using hydrochloric acid. Then, 250 g / t of water glass was added and stirred for 3 minutes. 450 g / t of collector 1B (M is Na of formula 1) was added and stirred for 3 minutes. 50 g / t of pine oil frother was added and stirred for 1 minute. Roughing was carried out for 5 minutes to obtain a rough concentrate and tailings X. The CaF2 grade and recovery rate in the rough concentrate were 68.32% and 46.51%, respectively.

[0103] Step 3: Selection:

[0104] Step 3.1: Transfer the obtained rough concentrate to a 1L flotation machine and start the flotation machine at 2000 r / min and stir for 1 minute; then add 125 g / t of water glass and stir for 3 minutes; add 225 g / t of type 1B collector and stir for 3 minutes; add 25 g / t of terpineol frother and stir for 1 minute; finally, float for 3 minutes to obtain fine concentrate and middlings M1.

[0105] Step 3.2: Transfer the No. 1 concentrate to a 0.5L flotation machine and repeat step 5, except that the amount of water glass is 62.5 g / t, the amount of Formula 1B is 112.5 g / t, and the amount of terpineol is 12.5 g / t; to obtain No. 2 concentrate and middlings M2.

[0106] Step 3.3: Transfer the No. 2 concentrate to a 0.25L flotation machine and repeat step 6, except that the amount of water glass is 30 g / t, the amount of Formula 1B is 50 g / t, and the amount of terpineol is 6 g / t; to obtain No. 3 concentrate K and middlings M3;

[0107] Step 3.4: Dry the obtained sample, weigh it, and further analyze the CaF2 content to calculate the recovery rate.

[0108] Finally, after analysis and calculation, a calcium fluoride product with a CaF2 grade of 83.27% and a recovery rate of 32.16% was obtained.

[0109] As can be seen from Examples 1 and Comparative Examples 1-8, for the problems of difficulty in collecting calcium fluoride sludge due to its organic encapsulation, amorphous nature, and high degree of mudification, this invention innovatively adopts ultrasonic technology to pretreat the calcium fluoride sludge, and then combines it with the combined collectors of subsequent flotation and the joint control of flotation processes such as pH. In this way, synergy can be achieved, and high-grade calcium fluoride can be obtained efficiently and greenly based on simple processes and methods.

[0110] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recovering calcium fluoride from calcium fluoride sludge, characterized in that, The calcium fluoride sludge is slurried with water to obtain a slurry, which is then pretreated under ultrasound. The power of the ultrasound is above 35 kHz. The calcium fluoride in the sludge is amorphous calcium fluoride, with more than 90% of the -10 μm particles. The grade of calcium fluoride is 40-60%. The ultrasound time is more than 5 minutes. Flotation reagents were added to the ultrasonically treated system for roughing, and calcium fluoride roughing material was collected. The flotation reagents include inhibitors and collectors, wherein the collectors are of formulas 1 and 2 in a weight ratio of 1:1 to 2; the pH of the flotation stage is 3 to 5; and the acid used to adjust the pH is at least one of hydrochloric acid and nitric acid. Formula 1; Formula 2; In Formulas 1 and 2, M is H, Na, K, or NH4; The amount of collector used in the roughing stage is 3000~4500 g / t.

2. The method for recovering calcium fluoride from calcium fluoride sludge as described in claim 1, characterized in that, The solid content in the mud is 30-60%.

3. The method for recovering calcium fluoride from calcium fluoride sludge as described in claim 1, characterized in that, The power of ultrasound is 35~50KHz.

4. The method for recovering calcium fluoride from calcium fluoride sludge as described in claim 1, characterized in that, The ultrasound session lasts 5 to 20 minutes.

5. The method for recovering calcium fluoride from calcium fluoride sludge as described in claim 1, characterized in that, The inhibitors include at least one of water glass, sodium hexametaphosphate, and sodium citrate.

6. The method for recovering calcium fluoride from calcium fluoride sludge as described in claim 1 or 5, characterized in that, The dosage of inhibitor in the roughing stage is 500~1500 g / t.

7. The method for recovering calcium fluoride from calcium fluoride sludge as described in claim 6, characterized in that, The amount of inhibitor used in the roughing stage is 750~1100 g / t.

8. The method for recovering calcium fluoride from calcium fluoride sludge as described in claim 1, characterized in that, In the described collector, the weight ratio of Formula 1 and Formula 2 is 1:1.4~1.

6.

9. The method for recovering calcium fluoride from calcium fluoride sludge as described in claim 1, characterized in that, The crude calcium fluoride feedstock is subjected to a 1-5 stage fine-refining process to obtain purified calcium fluoride; The flotation reagents used in the selection stage include inhibitors; During the selection process of stages 1 to 5, the dosage of inhibitors was reduced to 30 to 60 wt. of the dosage used in the previous stage.

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