CN112897562B - Method for purifying calcium fluoride from calcium fluoride sludge - Google Patents
Method for purifying calcium fluoride from calcium fluoride sludge Download PDFInfo
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Abstract
The invention discloses a method for purifying calcium fluoride from calcium fluoride sludge, which comprises the steps of mixing, stirring and leaching acid and calcium fluoride sludge at high temperature and high pressure, filtering, washing a filter cake to be neutral, reacting the filter cake with alkali liquor, filtering to obtain a filter cake, calcining, or washing the filter cake with an organic solvent to remove organic matters, thus obtaining high-purity calcium fluoride. In addition, the calcium fluoride sludge can be leached under the alkaline supercritical condition, then is filtered, and the filter cake is washed to be neutral, thus obtaining the high-purity calcium fluoride. Wherein, the acid leaching filtrate can be used for circularly leaching calcium fluoride sludge by adding acid; alkali liquor can circularly leach calcium fluoride sludge through adding alkali; and after the impurities in the acid leaching filtrate and the alkali leaching filtrate are accumulated to a certain amount, the impurities are removed by precipitation. The method has simple process, can solve the problem of the increasing shortage of fluorite resources, can reduce a large amount of calcium fluoride sludge generated every year, and reduces the pollution of the calcium fluoride sludge to the environment.
Description
Technical Field
The invention relates to a method for purifying calcium fluoride sludge, belonging to the technical fields of inorganic, chemical and environmental technologies. The method uses acid leaching, alkali leaching, calcining and other methods to purify the calcium fluoride sludge, and aims to improve the purity of calcium fluoride as much as possible under the conditions of economy and no pollution.
Background
The fluorine pollution source mainly comes from two aspects of natural fluorine-containing minerals and industrial fluorine pollution. The natural fluorine-containing minerals mainly comprise fluorite, magnesium fluoride, cryolite, fluorophosphate and the like; the industrial fluorine pollution is mainly fluorine-containing waste gas, waste water, fluorine-containing sludge and the like generated in the metallurgical industry, the fluorine organic chemical industry, the integrated circuit industry and the like. These fluorine sources have a great influence on various aspects of the ecosystem, and since fluorine cannot be biodegraded but can be biologically enriched to enter the human body from the food chain, effective measures must be taken to control the spread of excess fluorine in the ecosystem.
The Integrated Circuit (IC) industry in China has been rapidly developed in recent years, and calcium fluoride sludge generated by the IC industry mainly for manufacturing chips is a new fluorine pollution source in nearly ten years in China. In the process of treating monocrystalline silicon wafer products in the IC industry, a large amount of hydrofluoric acid is used for corroding the silicon wafers, so that fluorine-containing wastewater is discharged, and a large amount of calcium fluoride sludge is generated after treatment. The chemical/coagulating sedimentation treatment process is the mainstream treatment process of the fluorine-containing wastewater at present, and is shown in figure 1. The process firstly adjusts the pH value of the wastewater and then precipitatesAdding CaCl into the pool 2 Or CaF formation from CaO 2 Precipitating, adding Polyacrylamide (PAM) or polyaluminium chloride (PAC) for flocculation to obtain CaF as main component of sludge 2 And SiO 2 And is therefore commonly referred to as calcium fluoride sludge.
At present, the main disposal mode of calcium fluoride sludge is a landfill method. The method is simple and convenient, but simultaneously causes resource waste, higher treatment cost and land occupation, and if the treatment is not proper, the fluorine ions contained in the method can pollute the surrounding soil, further pollute underground water and drinking water for human and influence the health of human. Although calcium fluoride has very low solubility in water, it is only 0.0016g, i.e., 16mg/L, in terms of fluoride ion, which is 7.9mg/L in 100g of water at 18 ℃, but this value far exceeds the limit of 1.0mg/L of fluoride in drinking water specified in sanitary Standard for Drinking Water (GB 5749-2006). Therefore, how to utilize calcium fluoride sludge as a resource is the focus of attention at present.
Calcium fluoride sludge in comprehensive utilization, to CaF 2 The purity of the product has different requirements, and the main purification methods and optimization ideas at present comprise a flotation enrichment method, an atmospheric distillation method, a water washing purification method, a hydrochloric acid pickling purification method, a hydrofluoric acid pickling purification method and the like. The flotation enrichment method is that in CaF 2 The trapping agent is added into the suspension formed by the water, and the purpose of air floatation separation is achieved by utilizing the surface property difference of the materials. The atmospheric distillation method is to distill hydrofluoric acid by atmospheric distillation of sulfuric acid containing fluorine. Firstly, filtrate with diluted HF acid as main component for secondary acidification is used for primary acidification, and then filter cake obtained by primary acidification is subjected to precipitation conversion step, namely, sodium carbonate is used for removing CaSO in the filter cake 4 And reacting the filter cake obtained in the precipitation conversion step with the distilled HF acid in a secondary acidification reaction kettle, and drying the finally obtained filter cake to achieve the aim of purifying the calcium fluoride sludge. The acid used in the acid cleaning purification method is mainly divided into two types, namely HCl acid cleaning and HF acid cleaning. The HCl pickling method is a method for purifying calcium fluoride sludge by using hydrochloric acid, soda ash and caustic soda as main raw materials.
These purification methods have their own advantages and disadvantages, and are produced by semiconductor integrated circuit enterprisesCalcium fluoride sludge is different and needs to be adjusted according to local conditions. As the enterprises can use the flocculating agent when treating the fluorine-containing wastewater, organic matters exist in the generated calcium fluoride sludge, and the CaF in the calcium fluoride sludge can be reduced due to the existence of the organic matters 2 The purity of (2). Although the content of the organic matter in the calcium fluoride sludge is low, the calcium fluoride sludge may be wrapped by the organic matter, so that the chemical agent used in the purification process cannot fully contact the calcium fluoride sludge, the removal effect on impurities is reduced, and the purification effect is influenced. At present, the common purification methods can not effectively remove organic matters, and become a technical problem to be solved urgently.
Disclosure of Invention
In order to solve the problems of the prior art, the invention aims to overcome the defects in the prior art and provide a method for purifying calcium fluoride from calcium fluoride sludge.
In order to achieve the purpose of the invention, the invention adopts the following inventive concept:
the invention adopts high-temperature high-pressure acid leaching- (alkaline leaching) -calcining process or organic solvent or supercritical dissolved organic matter to purify calcium fluoride sludge, and finally calcium fluoride products with the purity not lower than 85 percent, even calcium fluoride products with the purity not lower than 90 percent can be obtained, and fluorite is replaced for other industrial production needs.
1. Acid leaching: because the calcium fluoride sludge contains CaF with high content 2 In addition, it contains excessive Ca, and small amounts of other metals and impurities such as Al, K, na, etc. The other metal salts of calcium fluoride can be dissolved away using mineral acids such as HCl, or excess Ca can be converted to CaF using fluorides such as HF 2 。
CaCO 3 +2HCl→CaCl 2 +CO 2 ↑+H 2 O (1)
Ca(OH) 2 +2HCl→CaCl 2 +2H 2 O (2)
NaF+HCl→NaCl+HF↑ (3)
CaCO 3 +2HF→CaF 2 +CO 2 ↑+H 2 O (4)
Ca(OH) 2 +2HF→CaF 2 +2H 2 O (5)
2. Alkaline leaching: certain substances in calcium fluoride sludge need to be removed under alkaline conditions. And because the flow of treating the fluorine-containing wastewater in semiconductor enterprises is different, certain enterprises can contain a certain amount of SiO in calcium fluoride sludge 2 Therefore, it is necessary to remove it to increase the purity of calcium fluoride. Then the calcium fluoride sludge after the inorganic acid leaching is further subjected to alkali leaching by alkali containing NaOH and SiO 2 The sodium silicate generated by the reaction is removed.
2NaOH+SiO 2 →Na 2 SiO 3 +H 2 O (6)
3. Calcination or organic solvent washing: in order to make the generated calcium fluoride rapidly settle, the enterprises in the prior art usually add an organic flocculant Polyacrylamide (PAM) or polyaluminium chloride (PAC) for precipitation and flocculation. Although the content of the calcium fluoride is low, the calcium fluoride sludge can be wrapped by organic matters, so that the purification effect is influenced. In the invention, the calcium fluoride sludge is calcined by adopting a muffle furnace, or the used organic solvent comprises dimethylformamide, dimethyl sulfoxide, dimethylacetamide and the like, but is not limited by the organic solvent for washing the calcium fluoride sludge, so that the organic matters in the calcium fluoride product prepared by the calcium fluoride sludge are effectively removed.
According to the inventive concept, the invention adopts the following technical scheme:
a method for purifying calcium fluoride from calcium fluoride sludge comprises the following steps:
a. acid leaching:
putting acid and calcium fluoride sludge to be treated into a high-temperature high-pressure reaction kettle; or crushing the filter cake prepared in the step b to obtain calcium fluoride sludge granules, and putting the calcium fluoride sludge granules and acid into a high-temperature high-pressure reaction kettle;
stirring and mixing at high temperature and high pressure to obtain acid leaching mixed liquor, performing acid leaching reaction, filtering the product mixed liquor obtained after leaching, separating the filtrate from solid matters, collecting the solid matters, washing the solid matters to be neutral, and drying to prepare a filter cake;
b. alkaline leaching:
mixing calcium fluoride sludge to be treated with alkali liquor, or mixing calcium fluoride sludge granules obtained by crushing the filter cake prepared in the step a with alkali liquor;
stirring to obtain alkaline leaching mixed liquor, performing alkaline leaching reaction, filtering the product mixed liquor obtained after leaching, separating the filtrate from solid matter, collecting the solid matter, washing the solid matter to be neutral, and drying to obtain a filter cake;
c. and (3) post-treatment:
crushing the filter cake obtained in the step a or the step b, and then calcining to obtain a high-purity calcium fluoride product;
or crushing the filter cake obtained in the step a or the step b, and washing the crushed filter cake with an organic solvent to remove organic matters, thereby obtaining a high-purity calcium fluoride product.
Preferably, the impurities in the acid leach solution collected in the step a and the alkali leach solution collected in the step b are removed by precipitation after accumulated to a set amount.
Preferably, in the step a, when acid leaching is carried out, the solid-liquid ratio of the mixture of acid and calcium fluoride sludge is 1:5-1, 20, the stirring speed is 1000-2000 r/min, the acid leaching reaction temperature is 25-90 ℃, the pressure is 0.1-50 MPa, and the acid leaching reaction time is 1-3 hours.
Preferably, in the step a, at least one inorganic acid of hydrochloric acid and nitric acid is used as the acid, and the molar concentration is 1-12 mol/L.
Preferably, in the step a, the acid is concentrated fluorine wastewater or a fluorine-containing solution, and the fluorine-containing solution contains one or a mixture of hydrofluoric acid, ammonium fluoride, sodium fluoride and ammonium bifluoride solution, and the mass percentage concentration is 20-40%.
Preferably, in the step a, when acid leaching is performed, performing a second acid leaching reaction on a primary acidified filtrate obtained by performing the first acid leaching reaction and filtering and a supplemented acid, filtering again to obtain a secondary acidified filtrate, performing a secondary acid leaching process, performing at least two times of multiple acid leaching processes by adding the acid, filtering the acidified filtrate obtained at the last time, separating the acidified filtrate from solid matters, collecting the solid matters, washing the solid matters to be neutral, and drying to prepare a filter cake; and controlling the amount of the added acid to make the solid-liquid mass ratio of the calcium fluoride sludge to the solution be 1:5-1.
Preferably, in the step b, when alkaline leaching is performed, the mass ratio of the alkali liquor to the sludge is 2:1-8:1, the reaction temperature is 20-70 ℃, and the alkaline leaching time is 1-3 hours.
Preferably, in the step b, the alkali in the alkali liquor is at least one of sodium hydroxide and potassium hydroxide or is any one or a mixture of sodium carbonate, ammonium bicarbonate and ammonia water, and the mass percentage concentration is 20-50%.
Preferably, in the step b, the filter cake obtained in the step a is reacted with alkali liquor, alkali leaching treatment is carried out under supercritical condition, supercritical extraction is carried out, then the filtrate is separated from solid matters, the solid matters are collected, the solid matters are washed to be neutral, and then the filter cake is prepared.
Preferably, in the step b, the supercritical extraction of calcium fluoride is carried out at the temperature of 400-600 ℃, the pressure of 22-50 MPa and the reaction time of 0.5-2 hours.
Preferably, in the step c, the calcining temperature of the muffle furnace adopted for calcining is 500-800 ℃, and the calcining time is 1-3 hours.
Preferably, in the step c, when the organic matter in the filter cake is washed by the organic solvent, the organic solvent is at least one of dimethylformamide, dimethyl sulfoxide and dimethylacetamide; the mixing mass ratio of the organic solvent to the calcium fluoride sludge is 2:1-10, the washing temperature is 30-90 ℃, and the washing time is 1-2 hours.
Preferably, in the step c, the purity of the calcium fluoride in the high-purity calcium fluoride product is not less than 85% by mass.
Preferably, when acid leaching and alkali leaching are carried out, the calcium fluoride sludge or filter cake is treated by adopting a weak acid leaching-alkali leaching-strong acid leaching-alkali leaching method, wherein the mass percentage concentration of acid in the weak acid leaching is not more than 10%.
The invention can adjust different processes according to different sources and different components of calcium fluoride sludge. The invention adopts the following different leaching methods and auxiliary means for purifying calcium fluoride sludge:
(1) Acid leaching;
(2) Alkaline leaching;
(3) Weak acid leaching-alkali leaching-strong acid leaching-alkali leaching;
(4) Calcining;
(5) Extracting with an organic solvent;
(6) Acid circulation;
(7) High temperature and high pressure;
(8) Alkaline supercritical leaching;
(1) The leaching method and the auxiliary means for purifying calcium fluoride sludge of (1) to (8) may be any combination of methods, means and sequences according to actual needs. For example, when some enterprises treat the fluorine-containing wastewater, the silicon-containing wastewater is not combined with the fluorine-containing wastewater for treatment, so the calcium fluoride sludge does not contain SiO 2 Under the condition, the treatment step of alkaline leaching can be omitted on the premise of meeting the requirement of calcium fluoride purity of downstream enterprises according to the requirements of the downstream enterprises. Namely, different combinations without an alkaline leaching step, such as (1) acid leaching + (4) calcining, or (1) acid leaching + (5) organic solvent extraction, are adopted. In addition, the process can be adjusted according to the requirements of downstream enterprises on the purity of the calcium fluoride sludge and other impurity components. If the requirement on purity is not high, only the acid leaching method (1) can be adopted to judge whether the purity meets the requirement. If the calcium fluoride purity requirement is high, multiple leaching methods and means can be adopted, such as (1) acid leaching + (2) alkaline leaching + (4) calcining.
In addition, the method can adopt the steps of firstly leaching calcium fluoride sludge by acid, then treating the calcium fluoride sludge by strong alkali, then treating the calcium fluoride sludge by weak alkali, and then treating the calcium fluoride sludge by weak acid, wherein the purity of the calcium fluoride after treating the calcium fluoride sludge is more than 85%. Wherein, the high-temperature high-pressure process is applied in any one or the whole four steps of the acid leaching process, the strong alkali treatment, the weak alkali treatment and the weak acid treatment, and the purity of the calcium fluoride after the calcium fluoride sludge is treated is more than 92 percent.
Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:
1. the calcium fluoride obtained by the method has high purity, can replace fluorite to be applied in most industries, not only can solve the problem of the gradual shortage of fluorite resources, but also can reduce a large amount of calcium fluoride sludge generated every year and reduce the pollution of the calcium fluoride sludge to the environment;
2. the method is simple and easy to implement, low in cost and suitable for popularization and application.
Drawings
FIG. 1 is a schematic flow diagram of a prior art chemical/coagulative precipitation treatment process.
FIG. 2 is a schematic flow diagram of the method for purifying calcium fluoride from calcium fluoride sludge according to the present invention.
Detailed Description
The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below:
example 1
The used calcium fluoride mud of this embodiment is got from a certain semiconductor manufacturing limited company in Shanghai, produces for the fluoride waste water treatment process, and mud passes through plate and frame filter pressing in the processing procedure, and most interstitial water in the mud has been separated from mud to because place for a long time and take out again, the calcium fluoride mud has air-dried the breakage, and the shape is irregular granule. It is not treated any more since it has been dried, crushed and sieved in the factory.
50g of calcium fluoride sludge is weighed and placed into a 500ml high-temperature high-pressure reaction kettle, hydrofluoric acid with the concentration of 40% is added according to the solid-to-liquid ratio of 1. Then filtering the solution to obtain a filter cake, and recycling the filtrate. Washing the filter cake to neutrality, drying and grinding. And (3) putting the ground calcium fluoride sludge into a muffle furnace, and calcining at 600 ℃ to remove organic matters. Finally, the calcium fluoride sludge after calcination is ground by a grinderThen high-purity calcium fluoride, caF is obtained 2 Purity was 96% wt.
Example 2
This embodiment is substantially the same as embodiment 1, and is characterized in that:
this example uses the same sludge source as example 1.
50g of calcium fluoride sludge is weighed and put into a 500ml high-temperature high-pressure reaction kettle, hydrochloric acid with the concentration of 12mol/L is added according to the solid-to-liquid ratio of 1:8, and the mixture is heated and stirred for 90min at the temperature of 90 ℃ at 1000 r/min. Then filtering the solution to obtain a filter cake, and recycling the filtrate. Washing the filter cake to be neutral, drying and grinding. Putting the ground calcium fluoride sludge into a 500ml high-temperature high-pressure reaction kettle, adding 30 percent NaOH solution according to the 1:3 solid-to-liquid ratio, stirring and reacting at 70 ℃ for 1 hour, filtering, washing a filter cake to be neutral, drying and grinding. The ground calcium fluoride sludge is placed into a muffle furnace and calcined at 565 ℃ to remove organic matters. Finally, crushing by a crusher, and grinding the calcined calcium fluoride sludge to obtain high-purity calcium fluoride, caF 2 Purity 93% by weight.
Example 3
This embodiment is substantially the same as the above embodiment, and is characterized in that:
this example uses the same sludge source as example 1.
50g of calcium fluoride sludge is weighed and put into a 500ml high-temperature high-pressure reaction kettle, hydrofluoric acid with the concentration of 20 percent is added according to the solid-to-liquid ratio of 1:5, and the mixture is heated and stirred for 60min at the temperature of 90 ℃ at the speed of 1000 r/min. Then filtering the solution to obtain a filter cake, and recycling the filtrate. Washing the filter cake to be neutral, drying and grinding. And (3) putting the ground calcium fluoride sludge into a 500ml high-temperature high-pressure reaction kettle, and adding Dimethylformamide (DMF) at 50 ℃ in a 1:5 solid-liquid ratio to wash the calcium fluoride sludge to remove organic matters. Reacting for 1 hour, filtering, washing the filter cake to remove the organic solvent, drying and grinding. Obtaining high-purity calcium fluoride, caF 2 Purity 92% by weight.
Example 4
This embodiment is substantially the same as the above embodiment, and is characterized in that:
this example uses the same sludge source as example 1.
50g of calcium fluoride sludge was weighed into a 500ml high-temperature high-pressure reaction vessel, and the concentration of 63% NH was calculated from 1 4 F +40% of HF (90% in one portion) 4 F and 10% of HF), and stirring by heating at 90 ℃ for 120min at a rate of 1000 r/min. Then filtering the solution to obtain a filter cake, and recycling the filtrate. Washing the filter cake to neutrality, drying and grinding. And (3) putting the ground calcium fluoride sludge into a muffle furnace, and calcining at 700 ℃ to remove organic matters. Finally, crushing by a crusher, and grinding the calcined calcium fluoride sludge to obtain high-purity calcium fluoride, caF 2 Purity was 97% by weight.
Example 5
This embodiment is substantially the same as the above embodiment, and is characterized in that:
this example uses the same sludge source as example 1.
50g of calcium fluoride sludge is weighed and put into a 500ml high-temperature high-pressure reaction kettle, nitric acid with the concentration of 6mol/L is added according to the solid-to-liquid ratio of 1:5, and the mixture is heated and stirred for 100min at the temperature of 60 ℃ at the speed of 1500 r/min. Then filtering the solution to obtain a filter cake, and recycling the filtrate. Washing the filter cake to be neutral, drying and grinding. Putting the ground calcium fluoride sludge into a 500ml high-temperature high-pressure reaction kettle, adding 40% of KOH + Na according to the solid-to-liquid ratio of 1:8 2 CO 3 Stirring the mixed solution at 60 ℃ for reaction for 2 hours, filtering, washing a filter cake to be neutral, drying and grinding. The ground calcium fluoride sludge is put into a 500ml high-temperature high-pressure reaction kettle, and dimethyl sulfoxide (DMSO) is added into the calcium fluoride sludge at the solid-liquid ratio of 1:5 at 50 ℃ to wash the calcium fluoride sludge to remove organic matters. Reacting for 1 hour, filtering, washing the filter cake to remove the organic solvent, drying and grinding. Obtaining high-purity calcium fluoride, caF 2 Purity 92% by weight.
Example 6
This embodiment is substantially the same as the above embodiment, and is characterized in that:
this example used the same sludge source as example 1.
50g of calcium fluoride sludge is weighed and placed into a 500ml high-temperature high-pressure reaction kettle, hydrofluoric acid with the concentration of 40% is added according to the solid-to-liquid ratio of 1. Then filtering the solution to obtain a filter cake, and recycling the filtrate. Washing the filter cake to be neutral, drying,and (4) grinding. And (3) putting the ground calcium fluoride sludge into a muffle furnace, and calcining at 600 ℃ to remove organic matters. Finally, crushing by a crusher, and grinding the calcined calcium fluoride sludge to obtain high-purity calcium fluoride, caF 2 Purity up to 96 wt%.
And mixing the primary acidification filtrate and the supplemented hydrofluoric acid with the concentration of 40% with new calcium fluoride according to the solid-liquid ratio of 1. And mixing the secondary acidification filtrate and the supplemented hydrofluoric acid with the concentration of 40% with new calcium fluoride according to the solid-liquid ratio of 1. And the process is circulated until the waste water is not used again.
Example 7
This embodiment is substantially the same as the above embodiment, and is characterized in that:
this example uses the same sludge source as example 1.
50g of calcium fluoride sludge is weighed and placed into a 500ml high-temperature high-pressure reaction kettle, hydrofluoric acid with the concentration of 20 percent is added according to the solid-to-liquid ratio of 1. Then filtering the solution to obtain a filter cake, and recycling the filtrate. Washing the filter cake to be neutral, drying and grinding. And (3) putting the ground calcium fluoride sludge into a muffle furnace, and calcining at 600 ℃ to remove organic matters. Finally, crushing by a crusher, and grinding the calcined calcium fluoride sludge to obtain high-purity calcium fluoride, caF 2 Purity 92% by weight.
Example 8
This embodiment is substantially the same as the above embodiment, and is characterized in that:
the same sludge source was used as in example 1.
Weighing 50g calcium fluoride sludge, adding 30% NaOH solution at 1:5 solid-to-liquid ratio, and reacting at 500 deg.C and 35MPa in supercritical state for 1.5 hr. Filtering, washing the filter cake to be neutral, drying and grinding. Obtaining high-purity calcium fluoride, caF 2 Purity of 90% by weight.
Example 9
This embodiment is substantially the same as the above embodiment, and is characterized in that:
the same sludge source as in example 1 was used.
When acid leaching is carried out, carrying out secondary acid leaching on primary acidified filtrate obtained by completing primary acid leaching reaction and filtering and supplemented acid, filtering again to obtain secondary acidified filtrate, completing secondary acid leaching process, carrying out multiple acid leaching processes for 3 times by adding acid, filtering the acidified filtrate obtained at last, separating the acidified filtrate from solid matters, collecting the solid matters, washing the solid matters to be neutral, and then drying to prepare a filter cake; the amount of the added acid is controlled to ensure that the solid-liquid mass ratio of the calcium fluoride sludge to the solution is 1:5. Obtaining high-purity calcium fluoride, caF 2 Purity 90% by weight.
To sum up, in the method for purifying calcium fluoride from calcium fluoride sludge in the above embodiment, acid and calcium fluoride sludge are mixed, stirred and leached at high temperature and high pressure, and then filtered, the filter cake is washed to be neutral, the filter cake is reacted with alkali liquor, and the filter cake obtained by filtering is calcined, or the filter cake is washed with an organic solvent to remove organic matters, so that high-purity calcium fluoride can be obtained. In addition, the calcium fluoride sludge can be leached under the alkaline supercritical condition, then is filtered, and the filter cake is washed to be neutral, thus obtaining the high-purity calcium fluoride. Wherein, the acid leaching filtrate can be used for leaching calcium fluoride sludge by adding acid circularly; alkali liquor can circularly leach calcium fluoride sludge through adding alkali; the impurities in the acid leaching filtrate and the alkali leaching filtrate are removed by precipitation after accumulating to a certain amount. The method provided by the embodiment of the invention has a simple process, can solve the problem of the increasing shortage of fluorite resources, can reduce a large amount of calcium fluoride sludge generated every year, and reduces the pollution of the calcium fluoride sludge to the environment.
The embodiments of the present invention have been described with reference to the accompanying drawings, but the present invention is not limited to the embodiments, and various changes and modifications can be made according to the purpose of the invention, and any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention shall be equivalent substitutions, as long as the purpose of the present invention is met, and the present invention shall fall within the protection scope of the present invention without departing from the technical principle and inventive concept of the present invention.
Claims (7)
1. A method for purifying calcium fluoride from calcium fluoride sludge generated by semiconductor integrated circuit enterprises is characterized by comprising the following steps: the method comprises the following steps:
a. acid leaching:
putting nitric acid and calcium fluoride sludge to be treated into a high-temperature high-pressure reaction kettle; or crushing the filter cake prepared in the step b to obtain calcium fluoride sludge granules, and putting the calcium fluoride sludge granules and nitric acid into a high-temperature high-pressure reaction kettle;
stirring and mixing at high temperature and high pressure, carrying out acid leaching reaction to obtain acid leaching mixed liquor, filtering the product mixed liquor obtained after leaching, separating the filtrate from solid matters, collecting the solid matters, washing the solid matters to be neutral, and then drying to prepare a filter cake;
b. alkaline leaching:
mixing calcium fluoride sludge to be treated with alkali liquor, or mixing calcium fluoride sludge granules obtained by crushing the filter cake prepared in the step a with alkali liquor;
stirring, carrying out supercritical alkaline leaching reaction to obtain alkaline leaching mixed liquor, after supercritical alkaline leaching, adopting at least one organic solvent of dimethylformamide, dimethyl sulfoxide and dimethylacetamide to remove residual organic matters in calcium fluoride sludge, then filtering the product mixed liquor obtained after leaching, separating filtrate from solid matters, collecting the solid matters, washing the solid matters to be neutral, and then drying to prepare a filter cake; when alkaline leaching is carried out, the mass ratio of the alkali liquor to the sludge is 2 to 1; performing supercritical extraction on calcium fluoride at the temperature of 400-600 ℃, the pressure of 22-50MPa and the reaction time of 0.5-2 hours;
c. and (3) post-treatment:
crushing the filter cake obtained in the step a or the step b, and then calcining to obtain a high-purity calcium fluoride product;
or crushing the filter cake obtained in the step a or the step b, and washing the crushed filter cake with an organic solvent to remove organic matters, thereby obtaining a high-purity calcium fluoride product.
2. The method of claim 1, wherein the method comprises the steps of: and (c) removing impurities in the acid leaching filtrate collected in the step a and the alkali leaching filtrate collected in the step b by a precipitation method after the impurities are accumulated to a set amount.
3. The method for purifying calcium fluoride from calcium fluoride sludge produced by semiconductor integrated circuit enterprises according to claim 1, wherein: in the step a, when acid leaching is carried out, the solid-to-liquid ratio of the mixture of nitric acid and calcium fluoride sludge is 1 to 5 to 1, the stirring speed is 1000 to 2000r/min, the acid leaching reaction temperature is 25 to 90 ℃, the pressure is 0.1 to 50MPa, and the acid leaching reaction time is 1~3 hours; the molar concentration of the nitric acid is 1 to 12mol/L.
4. The method for purifying calcium fluoride from calcium fluoride sludge produced by semiconductor integrated circuit enterprises according to claim 1, wherein: in the step a, when acid leaching is carried out, carrying out secondary acid leaching on primary acidified filtrate obtained by completing primary acid leaching reaction and filtering and supplemented acid, filtering again to obtain secondary acidified filtrate, completing secondary acid leaching process, carrying out multiple acid leaching process for at least two times by adding acid, filtering the acidified filtrate obtained at the last time, separating the acidified filtrate from solid matters, collecting the solid matters, washing the solid matters to be neutral, and then drying to prepare a filter cake; controlling the amount of the added acid so that the solid-liquid mass ratio of the calcium fluoride sludge to the solution is 1 to 5 to 1.
5. The method for purifying calcium fluoride from calcium fluoride sludge produced by semiconductor integrated circuit enterprises according to claim 1, wherein: in the step b, the alkali in the alkali liquor is at least one of alkali metal hydroxide of sodium hydroxide and potassium hydroxide or one or a mixture of sodium carbonate, ammonium bicarbonate and ammonia water, and the mass percentage concentration is 20-50%.
6. The method for purifying calcium fluoride from calcium fluoride sludge produced by semiconductor integrated circuit enterprises according to claim 1, wherein: in the step c, the muffle furnace adopted for calcination has the calcination temperature of 500-800 ℃ and the calcination time of 1-3 hours;
or when the organic solvent is used for washing the organic matters in the filter cake, the organic solvent is at least one of dimethylformamide, dimethyl sulfoxide and dimethylacetamide; the mixing mass ratio of the organic solvent to the calcium fluoride sludge is 2 to 1, the washing temperature is 30 to 90 ℃, and the washing time is 1~2 hours.
7. The method for purifying calcium fluoride from calcium fluoride sludge produced by semiconductor integrated circuit enterprises according to claim 1, wherein: in the step c, the purity of the calcium fluoride in the high-purity calcium fluoride product is more than or equal to 85 percent according to the mass percentage.
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