Method for harmless resource recycling of calcium fluoride from fluorine-containing smoke dust

Abstract

The invention discloses a method for harmless resource recycling of calcium fluoride from fluorine-containing smoke dust, and relates to the technical field of solid waste recycling. The method comprises the following steps: roasting the fluorine-containing smoke dust at 500-750 DEG C for 1-3 hours to obtain roasted slag, and performing desulfurization, dearsenification, decarburization and leaching on the roasted slag; the desulfurization, arsenic removal and decarburization leaching comprises the following steps: roasting slag is firstly subjected to alkaline leaching desulfurization and then subjected to acid leaching arsenic removal and decarburization; or the roasting slag is subjected to acid leaching dearsenification, alkaline leaching desulfurization and acid leaching decarburization. According to the method for harmless resource recycling of the calcium fluoride from the fluorine-containing smoke dust, the fluorine-containing smoke dust is roasted for 1-3 h at the temperature of 500-750 DEG C, carbonaceous materials, adsorbed and coated on the surface of part of arsenic, in the fluorine-containing smoke dust can be damaged in the roasting process, so that the arsenic is fully leached out in the follow-up process, and the calcium fluoride is recycled. And then arsenic removal, desulfurization and decarburization are carried out on the roasting slag in a desulfurization, arsenic removal and decarburization leaching mode, the quality of the final product is guaranteed, and the obtained product calcium fluoride hazardous waste toxic leaching reaches the standard.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste recycling, and in particular to a method for harmlessly recycling fluorine-containing smoke and dust into calcium fluoride. Background Art

[0002] Heavy metal sludge contains a small amount of fluorine. After high-temperature harmlessness treatment, the fluorine is enriched in the flue gas treatment system and produced as fluorine-containing dust. Its main components are calcium salts such as calcium fluoride, calcium oxide, calcium chloride, and calcium sulfate, as well as trace amounts of arsenic, copper, lead, and zinc, making it a hazardous waste. Fluorine-containing dust contains more than 50% calcium fluoride and has a certain recycling value. Arsenic content is a key indicator for the commercialization of fluorine-containing dust. The treated fluorine-containing product must contain less than 0.1% arsenic compounds and meet the leaching toxicity requirements for hazardous waste identification.

[0003] For this type of fluorine-containing dust, arsenic mainly exists in the form of arsenate. Using hydrochloric acid to remove impurities is an ideal method. The main equation is as follows:

[0004] CaO+2HCl=CaCl2+H2O (1)

[0005] CaCO3+2HCl=CaCl2+H2O+CO2 (2)

[0006] CaSO4+2HCl=CaCl2+H2SO4 (3)

[0007] CaF2+2HCl=CaCl2+2HF (4)

[0008] MeO+2HCl=MeCl2+H2O (5)

[0009] M3(AsO4)2+6HCl=3MCl2+2H3AsO4 (6)

[0010] Among them, equations (1) and (2) are common impurity removal reactions that are beneficial to the purification of calcium fluoride products. Equations (3) and (4) will occur when the hydrochloric acid concentration is strong, and a small amount of sulfuric acid and hydrogen fluoride will be generated. Equation (4) will reduce the recovery rate of calcium fluoride products when the hydrochloric acid concentration is high. Equation (5) is the reaction of metal oxides in fluorine-containing smoke being leached by hydrochloric acid. Equation (6) is the leaching reaction of arsenate in a hydrochloric acid system, where M can be elements such as copper, lead, zinc, and calcium.

[0011] However, during actual material processing, it was discovered that arsenic-containing dust contained carbonaceous materials, which encapsulated some arsenic and other impurities. Even in a very strong hydrochloric acid system, these impurities were difficult to leach out, resulting in a high level of arsenic and other impurities in the resulting calcium fluoride product, which failed to meet hazardous waste identification requirements. Furthermore, fluorine has a high solubility in high acid conditions, resulting in fluorine loss and low recovery rates. Therefore, using conventional hydrochloric acid to remove impurities from fluorine-containing dust is difficult to completely remove insoluble impurities such as arsenic.

[0012] In view of this, the present invention is proposed. Summary of the Invention

[0013] The object of the present invention is to provide a method for harmlessly recycling fluorine-containing dust into calcium fluoride.

[0014] The present invention is achieved in that:

[0015] In a first aspect, the present invention provides a method for harmlessly recycling calcium fluoride from fluorine-containing dust, comprising:

[0016] calcining the fluorine-containing dust at 500-750° C. for 1-3 hours to obtain calcined slag, and performing desulfurization, dearsenicization, and decarbonization leaching on the calcined slag;

[0017] The desulfurization, dearsenicization and decarbonization leaching comprises the following steps: the roasted slag is first subjected to alkali leaching for desulfurization and then to acid leaching for dearsenicization and decarbonization; or the roasted slag is first subjected to acid leaching for dearsenicization and then to alkali leaching for desulfurization and acid leaching for decarbonization.

[0018] In an optional embodiment, the roasting slag is first subjected to acid leaching for arsenic removal and then to alkaline leaching for desulfurization and acid leaching for decarbonization, comprising: acid leaching for arsenic removal of the roasting slag to obtain acid leaching for arsenic removal slag and acid leaching for arsenic removal liquid, adding sodium carbonate solution to the acid leaching for alkali leaching for desulfurization to obtain alkaline leaching for desulfurization slag and alkaline leaching for desulfurization, and acid leaching for desulfurization of the alkaline leaching for desulfurization to obtain acid leaching for decarbonization of the alkaline leaching for desulfurization slag and acid leaching for decarbonization, and washing and drying the acid leaching for decarbonization slag to obtain a calcium fluoride product.

[0019] In an optional embodiment, the theoretical amount of acid used for arsenic removal in the acid leaching is: m 脱砷用酸 =1.825×m 氟化钙余钙 , where m 脱砷用酸 is the amount of hydrochloric acid required for the reaction between the calcium-containing substances in the roasted slag and hydrochloric acid, m 氟化钙余钙 The amount of calcium remaining in the fluorine-containing dust except for the calcium composed of CaF2, the actual amount of the acid used for arsenic removal is 1 to 1.3 times the theoretical amount, and the pH of the system is maintained at 1.0 to 1.5 during the acid leaching arsenic removal;

[0020] Preferably, the dearsenicating acid is hydrochloric acid with a concentration of 1 to 3 mol / L;

[0021] Preferably, the hydrochloric acid is low-sulfur waste acid from the flue gas scrubbing process;

[0022] Preferably, the acid leaching temperature is 20-40° C., and the time is 0.5-3 h.

[0023] In an optional embodiment, the theoretical amount of sodium carbonate added to the sodium carbonate solution is calculated based on the sulfur content in the acid leaching arsenic removal slag, and the actual amount of sodium carbonate added is 1 to 2 times the theoretical amount;

[0024] Preferably, the solid-liquid ratio of the acid leaching residue to the sodium carbonate solution is 1t:6-10m 3 .

[0025] In an optional embodiment, the acid leaching decarbonization liquid is returned to the acid leaching arsenic removal step for use.

[0026] In an optional embodiment, sodium sulfate is added to the acid leaching arsenic removal solution for calcium removal to obtain a filtrate and a filter residue, the filtrate is used to recover industrial salt, and the filter residue is sent to metal smelting;

[0027] Preferably, the alkali leaching desulfurization liquid is returned to the alkali leaching step for recycling until the salt concentration in the alkali leaching liquid reaches 70-90% of the saturation concentration, and then is introduced into the decalcification step for use.

[0028] In an optional embodiment, before the calcined slag is subjected to the acid leaching for arsenic removal, the calcined slag is further subjected to slurrying with water and wet grinding;

[0029] Preferably, the water used for slurrying of the roasted slag is the washing water after the acid leaching decarbonization slag washing step.

[0030] In an optional embodiment, the thickness of the fluorine-containing fume during calcination is less than 50 mm, preferably 20 to 30 mm.

[0031] In an optional embodiment, the roasting slag is first subjected to alkaline leaching desulfurization and then to acid leaching for arsenic removal and decarbonization, comprising: adding sodium carbonate solution to the roasting slag for alkaline leaching desulfurization to obtain alkaline leaching desulfurization slag and alkaline leaching desulfurization liquid; the alkaline leaching desulfurization slag is subjected to acid leaching for arsenic removal and decarbonization to obtain acid leaching for arsenic removal and decarbonization slag and acid leaching for arsenic removal and decarbonization liquid; the acid leaching for arsenic removal and decarbonization slag is washed and dried to obtain a calcium fluoride product.

[0032] In an optional embodiment, the mass percentage of CaF2 in the calcium fluoride product is ≥98%, As is <0.04%, Pb is <0.05%, Cl is <0.05%, Si is <0.3%, S is <0.05%, and the fluorine recovery rate is greater than 95%.

[0033] The present invention has the following beneficial effects:

[0034] The present invention provides a method for harmlessly recycling fluorine-containing smoke and recovering calcium fluoride. The method comprises the following steps: firstly roasting the fluorine-containing smoke at 500-750° C. for 1-3 hours. The roasting process can destroy carbonaceous materials adsorbed and coated on the surfaces of some impurities such as arsenic in the fluorine-containing smoke, thereby allowing the arsenic and other impurities to be fully leached out in a subsequent process. Subsequently, the roasting slag is dearsenified, desulfurized and decarbonized by desulfurization, dearsenicization and decarbonization leaching to ensure the quality of the final product. The obtained calcium fluoride has a CaF2 mass percentage of 98% or more, As of 0.04%, Pb of 0.05%, Cl of 0.05%, Si of 0.3% and S of 0.05%, a fluorine recovery rate of greater than 95%, is not classified as hazardous waste after hazardous waste identification, and meets the index requirements of a third-level product in the YB / T 5217-2019 standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 A process flow chart of the method for harmless resource recovery of calcium fluoride from fluorine-containing smoke provided in Example 1 of the present invention;

[0037] Figure 2 This is a process flow chart of the method for harmless resource recovery of calcium fluoride from fluorine-containing smoke provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0038] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0039] The present invention provides a method for harmlessly recycling calcium fluoride from fluorine-containing dust, which comprises:

[0040] S1. calcining the fluorine-containing dust at 500-750° C. for 1-3 hours to obtain calcined slag;

[0041] S2. Desulfurization, dearsenicization and decarbonization are carried out on the roasted slag.

[0042] In the present invention, roasting is performed before leaching. This is because the present invention has found that some arsenic and other impurities in the fluorine-containing smoke are adsorbed and wrapped by the carbonaceous material. Conventional acid and oxidation methods are difficult to leach, and become impurities such as insoluble arsenic. This part of insoluble arsenic and other impurities needs to be roasted at medium temperature to destroy the carbonaceous material before it can be leached. The temperature and time of roasting are crucial in the present invention. The roasting temperature needs to be determined according to the arsenic content of the fluorine-containing smoke. Generally, the arsenic content is low and the temperature can be lower, but the minimum cannot be lower than 500°C. When the temperature is lower than 500°C, the carbonaceous material will not be fully roasted and destroyed, so the arsenic is difficult to be fully leached. A temperature higher than 750°C can also achieve a good effect of destroying the carbonaceous material, but the resulting roasted slag will have a serious agglomeration problem, high energy consumption and difficulty in subsequent treatment. Therefore, the present invention limits the roasting temperature to 500-750°C and the roasting time to 1-3h, preferably 1-2h.

[0043] During the roasting process, sufficient roasting should be ensured. When the fluorine-containing smoke dust is roasted in the reactor, the thickness of the fluorine-containing smoke dust material should be maintained below 50 mm, preferably 20-30 mm. If the material amount is too large, the roasting may be insufficient. It should be understood that to ensure sufficient roasting, stirring or entrained flow operation can be added during the roasting process to improve the roasting effect.

[0044] After roasting, the sulfur, arsenic and carbon in the roasting slag can be effectively removed by desulfurization, dearsenicization and decarbonization leaching treatment.

[0045] Specifically, there are two options for desulfurization, dearsenicization, and decarbonization leaching. The first option is to first desulfurize the roasted slag by alkaline leaching and then dearsenicize and decarbonize it by acid leaching. The first option is to desulfurize the roasted slag by alkaline leaching and then dearsenicize and decarbonize it by acid leaching. The desulfurization process includes: adding sodium carbonate solution to the roasted slag for alkaline leaching to obtain alkaline desulfurization slag and alkaline desulfurization liquid; then dearsenicize and decarbonize the alkaline desulfurization slag by acid leaching to obtain acid dearsenicize and decarbonize slag and acid dearsenicize and decarbonize liquid; and washing and drying the acid dearsenicize and decarbonize slag to obtain the calcium fluoride product. Alternatively, the second option is to first dearsenicize the roasted slag by acid leaching and then desulfurize it by alkaline leaching and then decarbonize it by acid leaching. It can be seen that the order of alkaline desulfurization and acid dearsenicize can be adjusted according to actual conditions.

[0046] The present invention further studies and finds that according to the first scheme, alkaline leaching for desulfurization and then acid leaching for arsenic removal and decarbonization are carried out. The main reaction mechanism is as follows:

[0047] (1) Reactions related to alkaline leaching desulfurization process

[0048] MO+2H2O=M(OH)2↓ (7)

[0049] M(OH)2+M2CO3=MCO3↓+2NaOH (8)

[0050] MSO4+Na2CO3=MCO3↓+Na2SO4 (9)

[0051] M3(AsO4)2+3Na2CO3=3MCO3↓+2Na3AsO4 (10)

[0052] Where M can be elements such as calcium, copper, zinc, lead, and magnesium. The alkaline leaching desulfurization process is mainly based on the desulfurization conversion of calcium sulfate as shown in equation (9).

[0053] (2) Reactions related to acid leaching arsenic removal and decarbonization

[0054] M(OH)2+2HCl=MCl2+H2O (11)

[0055] MCO3+2HCl=MCl2+H2O+CO2 (12)

[0056] CaF2+2HCl=CaCl2+2HF (13)

[0057] M3(AsO4)2+6HCl=3MCl2+2H3AsO4 (14)

[0058] In the above equations, M can be an element such as calcium, copper, zinc, lead, or magnesium. Equations (11) to (14) are all impurity removal reactions, among which equation (12) is a decarburization reaction, equation (14) is a dearsenicization reaction, and equation (13) causes a small amount of fluorine to dissolve, thereby reducing the fluorine recovery rate. Therefore, the acid concentration should not be too high.

[0059] According to the second scheme, acid leaching is first carried out to remove arsenic, and then alkaline leaching desulfurization and acid leaching are carried out to remove arsenic. The main reaction mechanism is as follows:

[0060] (1) Reactions related to acid leaching arsenic removal process

[0061] M(OH)2+2HCl=MCl2+H2O (15)

[0062] MCO3+2HCl=MCl2+H2O+CO2 (16)

[0063] CaF2+2HCl=CaCl2+2HF (17)

[0064] M3(AsO4)2+6HCl=3MCl2+2H3AsO4 (18)

[0065] In the above equation, M can be an element such as calcium, copper, zinc, lead, or magnesium, where M(OH)2 is the form of the oxide in the roasted slag after slurry adjustment, MCO3 is the phase formed during the roasting process, and equation (18) is the reaction of the main dearsenicization process.

[0066] (2) Reactions related to alkaline leaching desulfurization process

[0067] CaSO4+Na2CO3=CaCO3 ↓+Na2SO4 (19)

[0068] M3(AsO4)2+3Na2CO3=3MCO3 ↓+2Na3AsO4 (20)

[0069] The alkaline leaching desulfurization process is mainly based on equation (19), and equation (20) is the reaction of the part of arsenate that is difficult to be leached in the acid leaching process in the alkaline system.

[0070] (3) Reactions related to acid leaching decarbonization process

[0071] CaCO3+2HCl=CaCl2+H2O+CO2 (21)

[0072] Both of the above schemes can purify and produce high-quality calcium fluoride products. The two schemes consume comparable hydrochloric acid, but the first scheme consumes more sodium carbonate than the second. Therefore, in the present invention, it is preferred to first perform acid leaching for arsenic removal, followed by alkaline leaching for desulfurization and acid leaching for decarbonization. This operation can significantly reduce the amount of sodium carbonate used in alkaline leaching for desulfurization.

[0073] Specifically, the roasted slag is first subjected to acid leaching for arsenic removal and then subjected to alkaline leaching for desulfurization and acid leaching for decarbonization, including:

[0074] S201, acid leaching the roasted slag to remove arsenic, thereby obtaining acid leaching arsenic-removed slag and acid leaching arsenic-removed liquid;

[0075] The theoretical amount of acid used for arsenic removal in acid leaching is m 脱砷用酸 =1.825×m 氟化钙余钙 , where m 脱砷用酸 is the amount of hydrochloric acid required for the reaction between calcium-containing substances in the roasted slag and hydrochloric acid, m 氟化钙余钙 The amount of calcium remaining in the roasted slag except for the calcium composed of CaF2, the actual amount of the dearsenicating acid used is 1.0 to 1.3 times the theoretical amount, and the pH of the system is maintained at 1.0 to 1.5 during acid leaching; preferably, the dearsenicating acid is hydrochloric acid with a concentration of 1 to 3 mol / L; preferably, the hydrochloric acid is low-sulfur waste acid in the flue gas scrubbing process; preferably, the acid leaching temperature is 20 to 40° C., and the time is 0.5 to 3 hours.

[0076] When the concentration of the dearsenicating acid is too high, the fluorine recovery rate will be reduced. When the concentration of the dearsenicating acid is too low, the arsenic leaching will not meet the standard. Therefore, it is necessary to strictly control the concentration and addition amount of the dearsenicating acid to ensure that the pH of the system is maintained at 1.0-1.5 during acid leaching. This can ensure that the arsenic is fully leached and that calcium fluoride is not leached by the acid, thereby obtaining a product with a high fluorine recovery rate.

[0077] Before the calcined slag is subjected to acid leaching for arsenic removal, the calcined slag is slurried with water and wet-ground; wherein the water used for slurrying the calcined slag is the washing water after the subsequent acid leaching for decarbonization slag washing step.

[0078] S202, adding sodium carbonate solution to the acid leaching dearsenicization slag for alkaline leaching desulfurization to obtain alkaline leaching desulfurization slag and alkaline leaching desulfurization liquid; the alkaline leaching desulfurization slag is subjected to acid leaching decarbonization to obtain acid leaching decarbonization slag and acid leaching decarbonization liquid, and the acid leaching decarbonization slag is washed and dried to obtain a calcium fluoride product, and the alkaline leaching liquid is returned to the alkaline leaching step for recycling, and the acid leaching decarbonization liquid is returned to the acid leaching dearsenicization step for recycling.

[0079] In the present invention, the theoretical amount of sodium carbonate added to the sodium carbonate solution is calculated according to the sulfur content in the acid leaching arsenic removal residue, and the actual amount of sodium carbonate added is 1 to 2 times the theoretical amount; preferably, the solid-liquid ratio of the acid leaching residue to the sodium carbonate solution is 1t:6 to 10m 3 .

[0080] S203. Sodium sulfate is added to the acid leaching arsenic removal solution for decalcification to obtain a filtrate and a filter residue. The filtrate is used to recover industrial salt, and the filter residue is sent to metal smelting. When the salt concentration in the alkaline leaching desulfurization solution returned to the alkaline leaching step for recycling is close to saturation (i.e., reaches 70-90% of the saturation concentration), it is introduced into the decalcification step for use.

[0081] In an optional embodiment, the mass percentage of CaF2 in the calcium fluoride product is ≥98%, As is <0.04%, Pb is <0.05%, Cl is <0.05%, Si is <0.3%, S is <0.05%, and the fluorine recovery rate is greater than 95%.

[0082] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0083] Example 1

[0084] See also Figure 1 This embodiment provides a method for harmlessly recycling calcium fluoride from fluorine-containing dust, which comprises:

[0085] S1. The composition of fluorine-containing smoke is as follows:

[0086] Table 1 Experimental raw material composition analysis results

[0087] element As Cu Fe Sn Al Mg Zn Ca Pb S F Cl content(%) 0.6 0.088 0.1 0.048 0.32 0.53 0.56 45.85 0.28 2.6 26.88 3.1

[0088] The fluorine-containing dust was calcined at 650° C. for 2 h with a material layer thickness of 40 mm to obtain calcined slag.

[0089] S2. Desulfurization, dearsenicization and decarbonization are carried out on the roasted slag.

[0090] (1) adding water to the roasting slag to prepare a pulp, and wet grinding the slag; after wet grinding, the roasting slag is subjected to acid leaching and arsenic removal treatment with 1.2 mol / L hydrochloric acid, wherein the pH of the system is maintained at 1.0 to 1.5 during the acid leaching and arsenic removal, the leaching time is 1.0 h, the leaching temperature is room temperature, and the stirring rate is 200 r / min, thereby obtaining acid leaching and arsenic removal slag and acid leaching and arsenic removal solution;

[0091] (2) The acid leaching arsenic removal residue is added to sodium carbonate solution for alkaline leaching desulfurization. The theoretical amount of sodium carbonate added to the sodium carbonate solution is calculated according to the sulfur content in the acid leaching arsenic removal residue. The actual amount of sodium carbonate added is twice the theoretical amount. The solid-liquid ratio of the acid leaching arsenic removal residue and the sodium carbonate solution is 1t:8m 3 , the leaching time is 1.0h, the leaching temperature is room temperature, and the stirring rate is 200r / min; alkaline leaching desulfurization slag and alkaline leaching desulfurization liquid are obtained.

[0092] Acid is added to the alkaline leaching desulfurization slag for acid leaching decarbonization, the hydrochloric acid concentration is 1.0 mol / L, the leaching time is 1.0 h, the leaching temperature is room temperature, and the stirring rate is 200 r / min. The acid leaching decarbonization liquid and the acid leaching decarbonization slag are obtained by filtration. The acid leaching decarbonization slag is washed, and the filter residue is dried after washing to obtain a calcium fluoride product. The washing water after the washing step can be used as pulping water for the roasting slag, and the acid leaching decarbonization liquid is returned to the acid leaching dearsenicization step for use.

[0093] The alkaline leaching desulfurization liquid is returned to the alkaline leaching step for recycling.

[0094] (3) Sodium sulfate is added to the acid leaching arsenic removal solution for decalcification to obtain a filtrate and a filter residue. The filtrate is used to recover industrial salt, and the filter residue is sent to metal smelting. When the salt concentration of the alkaline leaching solution returned to the alkaline leaching step for recycling reaches 80% of the saturation concentration, it is introduced into the decalcification step for use.

[0095] Example 2

[0096] See also Figure 2 This embodiment is the same as step S1 of embodiment 1. In step S2, this embodiment first performs alkaline leaching for desulfurization and then performs acid leaching for arsenic removal and decarbonization, specifically comprising:

[0097] (1) Add sodium carbonate solution to the roasting slag for alkaline leaching desulfurization. The theoretical amount of sodium carbonate added to the sodium carbonate solution is calculated according to the sulfur content in the roasting slag. The actual amount of sodium carbonate added is twice the theoretical amount. The solid-liquid ratio of the roasting slag to the sodium carbonate solution is 1t:7m 3 , the leaching time is 1.0h, the leaching temperature is room temperature, and the stirring rate is 200r / min; alkaline leaching desulfurization slag and alkaline leaching desulfurization liquid are obtained.

[0098] (2) The alkaline leaching desulfurization slag was subjected to acid leaching dearsenicization and decarbonization treatment with 1.0 mol / L hydrochloric acid, the pH of the system was maintained at 1.0-1.5, the leaching time was 1.0 h, the leaching temperature was room temperature, and the stirring rate was 200 r / min to obtain acid leaching dearsenicization and decarbonization slag and acid leaching dearsenicization and decarbonization liquid;

[0099] The acid leaching arsenic removal and decarbonization residue is washed, and the filter residue is dried after washing to obtain a calcium fluoride product. The washing water after the washing step can be used as pulping water for the roasting residue.

[0100] The acid leaching dearsenicization and decarbonization liquid is used to recover industrial salt through wastewater.

[0101] (3) The alkaline leaching desulfurization liquid can be used to recover industrial salt through wastewater, or it can be returned to the alkaline leaching step for recycling.

[0102] Comparative Example 1

[0103] This comparative example is substantially the same as Example 1, except that, in this comparative example, the calcination temperature in step S1 is 200°C.

[0104] Comparative Example 2

[0105] This comparative example is substantially the same as Example 1, except that, in this comparative example, the calcination temperature in step S1 is 400°C.

[0106] Comparative Example 3

[0107] This comparative example is substantially the same as Example 1, except that, in this comparative example, the calcination temperature in step S1 is 1000°C.

[0108] Comparative Example 4

[0109] This comparative example is substantially the same as Example 1, with the only difference being that, in this comparative example, step S1 is omitted, i.e., the fluorine-containing fume is directly leached without being roasted.

[0110] Comparative Example 5

[0111] This comparative example is basically the same as Example 1, except that the step (1) of adding water to the roasted slag to make pulp and wet grinding in step S2 is omitted in this comparative example.

[0112] Comparative Example 6

[0113] This comparative example is basically the same as Example 1, except that in this comparative example, the pH of the system during the acid leaching arsenic removal in step S2 (1) is 4.0-4.55.

[0114] Comparative Example 7

[0115] This comparative example is basically the same as Example 1, except that the amount of sodium carbonate added during the alkaline leaching desulfurization in step S2 (2) is 0.8 times.

[0116] Experimental Example 1: Study the treatment effect of fluorine-containing smoke in a hydrochloric acid system.

[0117] The treatment method includes: treating the fluorine-containing smoke according to the treatment process in the following table, and detecting the arsenic content and fluorine recovery rate of the treated product.

[0118] Please refer to Table 2 for the treatment process and test results.

[0119] Table 2. Statistical table of treatment effects on fluorine-containing dust in hydrochloric acid system

[0120]

[0121] As can be seen in the table above, Table 2 tests two different fluorine-containing dusts, one with 0.60% and one with 0.81% arsenic. It was found that even with hydrochloric acid, even under harsh conditions, arsenic removal was difficult. While the arsenic content of the treated product decreased with increasing hydrochloric acid concentration, the arsenic content in the resulting product was still difficult to reduce below 0.04%. Furthermore, excessive acid concentrations significantly reduced fluorine recovery. Furthermore, excessive acid dosages also reduced fluorine recovery. Therefore, the proportion of insoluble arsenic in fluorine-containing dust is relatively high, making it difficult to completely remove arsenic using a hydrochloric acid system.

[0122] Experimental Example 2: Investigating the effects of different roasting conditions on roasted materials

[0123] The calcination was carried out according to the calcination conditions of Example 1 and Comparative Examples 1 to 3. Leaching was carried out according to the same desulfurization, dearsenicization and decarbonization leaching process under different calcination conditions. The final calcium fluoride product index and leaching index were tested. The analysis results are shown in Table 3 below:

[0124] Table 3 Calcium fluoride product analysis results (%)

[0125]

[0126]

[0127] As can be seen from the table above, different roasting conditions have a significant impact on the product. In Comparative Examples 1 and 2, the roasting temperatures were too low, failing to effectively roast and destroy the carbonaceous material on the surface of the fluorine-containing dust. This resulted in difficulty in fully leaching arsenic in subsequent steps, and the arsenic content in the calcium fluoride product was significantly higher than that in Example 1. In Comparative Example 3, however, the roasting temperature was too high. Although the carbonaceous material was effectively destroyed, the arsenic content in the calcium fluoride product remained the same as in Example 1 and did not decrease further. Furthermore, the severe sintering and high hardness of the slag after roasting resulted in high energy consumption and difficulty in subsequent processing.

[0128] Experimental Example 3: Investigating the effects of different leaching processes

[0129] Leaching was carried out according to the leaching process of Examples 1 to 2 and Comparative Examples 4 to 7, and the elements in the filter residue at each stage, the recovery rate of F, and the product were analyzed. Please refer to Tables 4 and 5 for the test results.

[0130] Table 4. Elemental analysis statistics of filter residues under different purification processes

[0131]

[0132] Table 5. Calcium fluoride product indicators and F recovery analysis statistics under different purification processes

[0133]

[0134] As can be seen from the table above, among the calcium fluoride product indicators, the CaF2 content of Examples 1 and 2 is significantly superior to that of Comparative Examples 4-7, and the contents of other elements are significantly lower than those of Comparative Examples 4-7, particularly the As, Pb, and S contents, which are significantly different from those of Comparative Examples 4-7. Since the fluorine recovery rate is primarily related to the acid concentration, the acid concentrations of Examples 1-2 and Comparative Examples 4-7 are the same, so the fluorine recovery rate is not much different. However, the leaching difficulty of the material in Example 1-2 is significantly lower than that of Comparative Examples 4-7, and therefore, the CaF2 content can be significantly superior to that of Comparative Examples 4-7.

[0135] In addition, please refer to Table 6 for the calcium fluoride product requirements in GB / T27804-2011 standard:

[0136] Table 6. Calcium fluoride product requirements in GB / T27804-2011 standard

[0137]

[0138] Table 7. Product requirements for fluorite concentrate in YB / T 5217-2019

[0139]

[0140]

[0141] In the calcium fluoride product obtained in Example 1 of the present invention, the content of As impurity is 0.02%, Zn can be reduced to 0.11%, Pb can be reduced to 0.02%, Si can be reduced to 0.3%, Cl can be reduced to 0.03%, and S can be reduced to 0.04%. The calcium fluoride accounts for 98.5%, and the fluorine recovery rate is 95.1%.

[0142] Tables 6 and 7 above show the indicators of calcium fluoride obtained by purifying fluorite raw materials. The present invention uses fluorine-containing dust as the raw material. Currently, there are no technical indicators for recovering calcium fluoride from fluorine-containing dust. Therefore, referring to Tables 6 and 7 above, the present invention found that the calcium fluoride of the present invention can meet the indicator requirements of the third-grade product in the YB / T 5217-2019 standard by approximately 98%. Furthermore, the fluorine-containing dust raw material of the present invention is a hazardous waste. It can achieve toxicity leaching standards and no longer be treated as a hazardous waste. In particular, meeting the indicator requirements of the third-grade product in the YB / T 5217-2019 standard further enhances its economic value. In addition, during the final acid leaching decarbonization, increasing the amount of acid can further remove iron, so that the iron content meets the minimum iron content requirement of GB / T 27804-2011.

[0143] In summary, the method for harmlessly recycling calcium fluoride from fluorine-containing smoke provided by the present invention is to first roast the fluorine-containing smoke at 500-750°C for 1-3 hours. The roasting process can destroy the carbonaceous material adsorbed and coated on the surface of part of the arsenic in the fluorine-containing smoke, so that the arsenic can be fully leached in the subsequent process. Subsequently, the roasting slag is dearsenized and desulfurized by desulfurization and dearsenicization leaching to ensure the quality of the final product. The obtained calcium fluoride product is not classified as hazardous waste after hazardous waste toxicity identification. At the same time, the content of calcium fluoride in the product obtained by the present invention reaches 98.5%, which meets the index requirements of the third-level product in the YB / T5217-2019 standard.

[0144] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for harmless resource recovery of calcium fluoride from fluorine-containing dust, characterized in that: It includes: The fluorine-containing smoke is roasted at 500-750° C. for 1-3 hours to obtain roasted slag, and the roasted slag is desulfurized, dearsenicized, decarbonized and leached; The desulfurization, dearsenicization and decarbonization leaching comprises that the roasted slag is first subjected to alkaline leaching for desulfurization and then subjected to acid leaching for dearsenicization and decarbonization; or, the roasted slag is first subjected to acid leaching for dearsenicization and then subjected to alkaline leaching for desulfurization and acid leaching for decarbonization.

2. The method for harmless resource recovery of calcium fluoride from fluorine-containing smoke according to claim 1, characterized in that: The roasting slag is first subjected to acid leaching for arsenic removal and then subjected to alkali leaching for desulfurization and acid leaching for decarbonization, comprising: acid leaching for arsenic removal of the roasting slag to obtain acid leaching for arsenic removal slag and acid leaching for arsenic removal liquid; sodium carbonate solution is added to the acid leaching for alkali leaching for desulfurization to obtain alkali leaching for desulfurization slag and alkali leaching for desulfurization; hydrochloric acid is added to the alkali leaching for decarbonization to obtain acid leaching for decarbonization slag and acid leaching for decarbonization; the acid leaching for decarbonization slag is washed and dried to obtain a calcium fluoride product.

3. The method for harmless resource recovery of calcium fluoride from fluorine-containing smoke according to claim 2, characterized in that: The theoretical amount of acid used for arsenic removal in the acid leaching process is: m 脱砷用酸 =1.825×m 氟化钙余钙 , where m 脱砷用酸 is the amount of hydrochloric acid required for the reaction between the calcium-containing substances in the roasted slag and hydrochloric acid, m 氟化钙余钙 The amount of calcium remaining in the fluorine-containing dust except the calcium composed of CaF2, the actual amount of the acid for dearsenication is 1 to 1.3 times the theoretical amount, and the pH of the system is maintained at 1.0 to 1.5 during the acid leaching dearsenication; Preferably, the dearsenicating acid concentration is 1 to 3 mol / L hydrochloric acid; Preferably, the hydrochloric acid is low-sulfur waste acid from the flue gas scrubbing process; Preferably, the acid leaching temperature is 20-40° C. and the time is 0.5-3 h.

4. The method for harmless resource recovery of calcium fluoride from fluorine-containing smoke according to claim 2, characterized in that: The theoretical amount of sodium carbonate added to the sodium carbonate solution is calculated according to the sulfur content in the acid leaching arsenic removal slag, and the actual amount of sodium carbonate added is 1 to 2 times the theoretical amount; Preferably, the solid-to-liquid ratio of the acid leaching arsenic removal slag to the sodium carbonate solution is 1t:6-10m 3 .

5. The method for harmless resource recovery of calcium fluoride from fluorine-containing smoke according to claim 2, characterized in that: The acid leaching decarbonization liquid is returned to the acid leaching dearsenicization step for use.

6. The method for harmless resource recovery of calcium fluoride from fluorine-containing smoke according to claim 2, characterized in that: adding sodium sulfate to the acid leaching arsenic removal solution for calcium removal to obtain a filtrate and a filter residue, wherein the filtrate is used to recover industrial salt and the filter residue is sent to metal smelting; Preferably, the alkali leaching desulfurization liquid is returned to the alkali leaching desulfurization step for recycling until the salt concentration in the alkali leaching desulfurization liquid reaches 70-90% of the saturation concentration, and then introduced into the decalcification step for use.

7. The method for harmless resource recovery of calcium fluoride from fluorine-containing smoke according to claim 2, characterized in that: Before the calcined slag is subjected to the acid leaching for arsenic removal, the calcined slag is slurried by adding water and wet-grinding; Preferably, the water used for pulping the roasted slag is the washing water after the acid leaching decarbonized slag washing step.

8. The method for harmless resource recovery of calcium fluoride from fluorine-containing smoke according to claim 1, characterized in that: The thickness of the fluorine-containing dust during calcination is less than 50 mm, preferably 20 to 30 mm.

9. The method for harmless resource recovery of calcium fluoride from fluorine-containing smoke according to claim 1, characterized in that: The calcined slag is first subjected to alkali leaching desulfurization and then to acid leaching dearsenicization and decarbonization, comprising: adding sodium carbonate solution to the calcined slag for alkali leaching desulfurization to obtain alkali leaching desulfurization slag and alkali leaching desulfurization liquid; the alkali leaching desulfurization slag is subjected to acid leaching dearsenicization and decarbonization to obtain acid leaching dearsenicization and decarbonization slag and acid leaching dearsenicization and decarbonization liquid; the acid leaching dearsenicization and decarbonization slag is washed and dried to obtain a calcium fluoride product.

10. The method for harmless resource recovery of calcium fluoride from fluorine-containing smoke according to claim 2 or 9, characterized in that: The mass percentage of CaF2 in the calcium fluoride product is ≥98%, As is less than 0.04%, Pb is less than 0.05%, Cl is less than 0.05%, Si is less than 0.3%, S is less than 0.05%, and the recovery rate of fluorine is greater than 95%.

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