Method for converting byproduct hydrogen fluoride and fluorosilicic acid of phosphorite with low energy consumption

Abstract

The present application relates to a kind of low energy consumption conversion phosphorite by-product hydrogen fluoride, fluorosilicic acid method, belong to fine chemical industry technical field.The new low energy consumption conversion phosphorite by-product hydrogen fluoride, fluorosilicic acid method includes: a, extraction;B, inorganic base back extraction;Or inorganic salt back extraction;C, remove water to obtain fluorosilicate solid from the aqueous phase fluorosilicate solution;D, pyrolysis;Or acidolysis.The present application is compared with the process for preparing anhydrous hydrogen fluoride and silicon tetrafluoride using phosphorite by-product dilute fluorosilicic acid currently, with wide application range, the difficulty of fluorosilicic acid preparation process is reduced, and energy consumption is greatly reduced;The economic value of the present application is that high-value fluorination product, high-purity silicon tetrafluoride gas and anhydrous hydrogen fluoride gas can be obtained simultaneously, and the final obtained product is recycled or can be sold as product, without by-product and waste to be treated again.

Description

TECHNICAL FIELD

[0001] The application relates to a method for converting byproduct hydrogen fluoride and fluorosilicic acid of phosphorite, and belongs to the technical field of fine chemical industry. BACKGROUND

[0002] In the phosphate fertilizer industry, fluorine mainly overflows in the form of gas (hydrogen fluoride and silicon tetrafluoride), and is absorbed by water to obtain a fluorosilicic acid solution. The content of fluorine in the phosphorite is about 2% to 4%. In the process of producing phosphoric acid by wet treatment of the phosphorite, SiF4 and HF are produced as byproducts, and if they are not recycled, it means that more than 1 million tons of fluorosilicon resources are wasted every year, and the environment is also polluted.

[0003] At present, the fluorosilicic acid of the phosphorite byproduct is only applied to several industrial productions, important applications of which are fluorination of drinking water and production of fluorine chemical series products: fluorosilicate products, aluminum fluoride or cryolite, etc. In these various applications, a common feature and difficulty is to remove water from the fluorosilicic acid. The concentration process of the fluorosilicic acid has the following problems: a large amount of silica gel is generated in the phosphoric acid concentration system, which blocks the production equipment; heat loss is serious in the heating process, and the low purity in the purification process leads to difficulty in filtration and drying.

[0004] Anhydrous hydrogen fluoride (AHF) is a key raw material and product of fluorine chemical industry, and has a wide range of applications in fluorine-containing polymer materials, chemical industry, medicine, pesticides, refrigerants, cleaning agents and other fields. SiF4 is an important raw material in the electronic industry, which has a large number of applications in polycrystalline silicon solar cells, polycrystalline silicon thin film batteries, new type of electric light source, photoelectric semiconductor, optical fiber communication and other aspects, and is also used as a chemical vapor deposition silicon source, a P-type dopant, an etchant for silicon nitride and tantalum silicide. In addition, SiF4 can also be used for preparing aluminum fluoride, cryolite, fumed silica and the like. Therefore, it is urgent to develop the utilization of AHF and SiF4 from the phosphorite, to recover fluorine and silicon resources from the phosphor chemical industry and to convert the products, to improve the comprehensive utilization rate of fluorine and silicon resources, and to promote the development of clean processing of phosphorite and high-end fluorine material industry.

[0005] A Chinese invention patent with the application number 202011029531.5 discloses a method for preparing anhydrous silicon tetrafluoride and hydrogen fluoride mixed gas from phosphorite associated fluorine. The method reacts water-containing fluorosilicic acid with washed sulfuric acid to obtain fluorine-containing sulfuric acid and water-containing silicon tetrafluoride and hydrogen fluoride mixed gas, and washes the mixed gas with hot concentrated sulfuric acid to obtain anhydrous silicon tetrafluoride and hydrogen fluoride mixed gas. Although the method is simple to operate, a large amount of concentrated sulfuric acid is needed to absorb water, and a large amount of 70-80wt% sulfuric acid is generated.

[0006] A Chinese invention patent with application number 201110446235.X discloses a method for preparing silicon tetrafluoride and hydrogen fluoride from sodium fluorosilicate as raw material. After drying and removing water from sodium fluorosilicate, it is reacted with sulfuric acid at a molar ratio of 1:1 at 160-220℃, then dust removal and pressurization pre-cooling to -30℃, and then sent to the rectifying column to separate the mixed gas, finally, anhydrous hydrogen fluoride and silicon tetrafluoride are obtained respectively. The patent uses a brick kiln reactor with low energy utilization rate, and is only suitable for solid sodium fluorosilicate, and cannot be applied to low-concentration fluorosilicic acid.

[0007] A Chinese invention patent with application number 201510955081.5 discloses a method for preparing ammonium fluoride from tertiary amine-fluorosilicate. a) The tertiary amine-fluorosilicate solution obtained by extracting the dilute fluorosilicic acid and tertiary amine is passed into ammonia gas, stirred, and then filtered to separate ammonium fluoride and silicon dioxide mixture and tertiary amine filtrate; b) The obtained tertiary amine filtrate is returned to extract dilute fluorosilicic acid; c) A saturated aqueous solution of ammonium fluoride is prepared at 0℃, and the obtained ammonium fluoride and silicon dioxide mixture is added to the solution after heating, stirring, washing, and incubation, and then filtered to obtain an ammonium fluoride supersaturated solution and silicon dioxide, respectively; d) The silicon dioxide is washed and dried to obtain white carbon black. However, the generated silicon dioxide, i.e. white carbon black, can absorb a large amount of organic extractant, which can cause difficulty in drying the filter cake and excessive waste of organic amine extractant. In addition, it can only handle dilute fluorosilicic acid with a mass concentration of 5-18%, and cannot handle dilute fluorosilicic acid with a lower concentration.

[0008] A Chinese invention patent with application number 202311418788.3 discloses a process for purifying and concentrating dilute fluorosilicic acid solution by chemical extraction method: (1) using organic base or modified organic base as extractant for chemical extraction of dilute fluorosilicic acid; the organic base is trioctylmethylammonium chloride, triisooctylamine, trioctylamine, and diisooctylamine; (2) adding or not adding an additive to the extractant for chemical extraction of dilute fluorosilicic acid; (3) using inorganic acid as a stripping agent for chemical stripping of fluorosilicic acid in the extract; (4) adding polar or non-polar organic matter as an additive to the stripping agent for chemical stripping of fluorosilicic acid in the extract; (5) using heavy metal soluble salt chemical treatment method to treat the raffinate; (6) using vacuum distillation method to recover the additive; (7) using vacuum heating decomposition method to recover the extractant. However, it only concentrates fluorosilicic acid. In order to recover the acid ion in the extract, a large amount of heavy metal salt saturated solution needs to be added to concentrate the fluorosilicic acid solution. A large amount of heavy metal salt saturated solution is added to synthesize the salt as a precipitate, which can be recovered, but cannot be recycled. It is not only not environmentally friendly, but also has poor economic benefits. The dilute fluorosilicic acid it can handle comes from phosphorus chemical production enterprises, with a concentration range of 2-18%, and cannot handle dilute fluorosilicic acid with a lower concentration. SUMMARY

[0009] The present application aims to provide a new method for converting the by-products of phosphate ore, hydrogen fluoride and fluosilicic acid, with low energy consumption.

[0010] To achieve the aim of the present application, the new method for converting the by-products of phosphate ore, hydrogen fluoride and fluosilicic acid, with low energy consumption, comprises:

[0011] a. Extraction: using an organic amine extractant R x NH 3-x , extracting the fluosilicic acid by-product of phosphate ore, and after extraction, allowing the layers to separate, to obtain an organic phase of fluosilicic acid salt (R x NH 4-x ) + 2SiF6 2- and an aqueous phase, wherein x is at least one of 1, 2, and 3;

[0012] b. Inorganic base stripping: reacting the organic phase of fluosilicic acid salt (R x NH 4-x ) + 2SiF6 2- with an inorganic base solution, allowing the phases to separate, to obtain a solution containing fluosilicic acid salt precipitate in the aqueous phase and an organic ammonium base (R x NH 4-x ) + OH - ; the inorganic base comprises at least one of KOH, NaOH, Ca(OH)2, and liquid ammonia; the phase ratio of the organic phase of inorganic base stripping to the inorganic base stripping agent is 2:1 to 1:5;

[0013] or inorganic salt stripping: reacting the organic phase of fluosilicic acid salt (R x NH 4-x ) + 2SiF6 2- with a salt solution, allowing the phases to separate, to obtain a solution containing fluosilicic acid salt precipitate in the aqueous phase and an organic ammonium salt solution;

[0014] c. Removing water from the solution containing fluosilicic acid salt precipitate in the aqueous phase to obtain fluosilicic acid salt solids;

[0015] d. Pyrolysis: heating and decomposing the fluosilicic acid salt solids in a vacuum or inert atmosphere to obtain anhydrous silicon tetrafluoride gas and a fluorinated salt;

[0016] or acidolysis: using sulfuric acid to decompose the fluosilicic acid salt solids to obtain anhydrous SiF4 gas, HF, and a sulfate salt, and separating to obtain anhydrous hydrogen fluoride and silicon tetrafluoride.

[0017] The pyrolysis in step d can be pyrolysis under vacuum or pyrolysis under inert atmosphere, after pyrolysis under inert atmosphere, the mixed gas of inert atmosphere and SiF4 gas is recovered, and then SiF4 gas is recovered by low-temperature rectification with liquid nitrogen; the pyrolysis under vacuum directly obtains SiF4 gas. The inert atmosphere is a gas that does not react with the system, such as anhydrous and oil-free nitrogen, argon, noble gas, etc.

[0018] In one specific embodiment, the extractant in step a is at least one of quaternary ammonium salt, trioctylamine, trialkylamine, methyl trialkyl ammonium chloride N263;

[0019] The mass concentration of the by-product fluosilicic acid of the phosphate ore in step a is 0.1% to 99.9%, and preferably 0.1% to 1.5%.

[0020] In one specific embodiment, the temperature of the extraction in step a is 10 to 70°C, the extraction time is preferably 10 to 90 minutes, and the volume ratio of the extractant to the by-product fluosilicic acid of the phosphate ore is preferably 0.5 to 8:1; preferably the extraction rate of the extraction is >99%.

[0021] The aqueous phase in step a is preferably recovered for dissolving solid salt or alkali to prepare the inorganic alkali solution or salt solution in step b.

[0022] In one specific embodiment, the temperature of the inorganic alkali back extraction in step b is 10 to 70°C, the back extraction time is preferably 0.25 to 2 hours, and preferably the back extraction rate of the back extraction is >80%.

[0023] In one specific embodiment, the salt solution in step b includes at least one of sulfate solution, chloride salt solution, nitrate salt solution; and preferably at least one of K2SO4, KHSO4, Na2SO4, (NH4)2SO4, KCl, NaCl, NH4Cl, KNO3, NaNO3, NH4NO3.

[0024] The temperature of the inorganic salt back extraction in step b is 10 to 70°C, the back extraction time is preferably 0.25 to 4 hours, the phase ratio of the organic phase to the inorganic salt back extraction agent is preferably 2:1 to 1:5, and preferably the back extraction rate of the back extraction is >80%.

[0025] In one specific embodiment, the method further includes adding the organic ammonium base (R x NH 4-x ) + OH - at 100 to 150°C to recover the organic amine extractant;

[0026] or secondary stripping: mixing the organic ammonium salt solution of step b with liquid ammonia to recover the organic amine extractant and the ammonium salt, the organic amine extractant is recycled to step a for extraction, and the ammonium salt is recycled to step b for stripping;

[0027] Preferably, the temperature of the secondary stripping is room temperature of 10-70℃, the time of the stripping is 0.25-2 hours, and the molar ratio of the organic ammonium salt solution to liquid ammonia is 2:1-1:3, preferably the stripping rate of the stripping is >80%.

[0028] In a specific embodiment, the method for removing water from the solution containing the precipitated fluorosilicate salt of step c includes solid-liquid separation and drying; the solid-liquid separation is preferably filtration, and the water after filtration is recycled to prepare the inorganic base solution of step b, the salt solution or the liquid ammonia for secondary stripping; preferably, the drying temperature is controlled at 100-300℃, and the water content after drying is less than 0.1%.

[0029] In a specific embodiment, the temperature of the pyrolysis of step d is 200-800℃, and the time of the pyrolysis is preferably 1-3h.

[0030] More preferably, the temperature of the pyrolysis of the fluorosilicate salt K2SiF6 is 400-600℃, the temperature of the pyrolysis of Na2SiF6 is 300-800℃, the temperature of the pyrolysis of CaSiF6 is 300-400℃, and the temperature of the pyrolysis of (NH4)2SiF6 is 400℃.

[0031] In a specific embodiment, the acidolysis of step d includes high-temperature acidolysis or low-temperature acidolysis, the fluorosilicate salt for the high-temperature acidolysis is at least one of Na2SiF6, CaSiF6 and K2SiF6, the temperature of the high-temperature acidolysis is 19-450℃, and the reaction time of the high-temperature acidolysis is preferably 30-90 minutes.

[0032] The fluorosilicate salt for the low-temperature acidolysis is at least one of (NH4)2SiF6, K2SiF6 and CaSiF6, the temperature of the low-temperature acidolysis is in the range of -90-19℃, and the reaction time of the low-temperature acidolysis is preferably 30-180 minutes.

[0033] The concentration of the sulfuric acid for the acidolysis is preferably 95-105wt%.

[0034] The sulfuric acid used in the present application is fuming sulfuric acid, and the concentration thereof is determined according to the content of sulfate SO4 2- in the fuming sulfuric acid, which is in gaseous state, and thus the concentration can be greater than 100wt%. 2-

[0035] ​In one specific embodiment, the separation method in step d includes: obtaining a mixed gas of anhydrous hydrogen fluoride and silicon tetrafluoride after high-temperature acid hydrolysis, and then obtaining high-purity anhydrous hydrogen fluoride and silicon tetrafluoride by distillation.

[0036] The low-temperature acid hydrolysis can directly collect anhydrous silicon tetrafluoride gas, and then the liquid after low-temperature acid hydrolysis is heated to 20℃~60℃ and reacted for 20~55 minutes to separate anhydrous hydrogen fluoride gas.

[0037] Preferably, the sulfate separated in step d is returned to step b for recycling and back-extraction.

[0038] Beneficial effects:

[0039] Compared with the currently used process for preparing anhydrous hydrogen fluoride and silicon tetrafluoride from dilute fluorosilicic acid, a byproduct of phosphate rock, the present invention has the following advantages:

[0040] (1) The concentration of fluorosilicic acid in the process of the present invention ranges from 0.1% to 99.9%, which has a wide range of applications, reduces the difficulty of fluorosilicic acid preparation process, and significantly reduces production energy consumption.

[0041] (2) The process of the present invention uses inorganic base and inorganic salt for back-extraction to synthesize fluorosilicates with high value and high subsequent reaction efficiency, avoiding the loss of a large amount of extractant absorbed by the formation of white carbon black. The process of the present invention can recover all extractant and sulfate to form a cycle reaction.

[0042] (3) The process of the present invention uses filtration and drying of fluorosilicate to remove a large amount of water in the remaining solution, avoiding the disadvantage of the sulfuric acid method which requires a large amount of concentrated sulfuric acid to treat the water in fluorosilicic acid. At the same time, a large amount of dilute sulfuric acid will be generated, which needs to be concentrated before it can be reused.

[0043] (4) The process of the present invention can directly obtain silicon tetrafluoride gas with high quality by pyrolysis, which is beneficial to the subsequent further purification to produce high-purity silicon tetrafluoride gas, and can also obtain high-value fluoride products.

[0044] (5) The process of the present invention is divided into two process routes based on the different physicochemical properties of fluorosilicates: high-temperature acid hydrolysis and low-temperature acid hydrolysis. The mixed gas hydrogen fluoride and silicon tetrafluoride obtained by high-temperature acid hydrolysis can be obtained by simple separation to obtain anhydrous hydrogen fluoride and silicon tetrafluoride gas with high purity.

[0045] (6) The low-temperature acid hydrolysis process of the present invention not only has low energy consumption, but also can directly separate high-purity silicon tetrafluoride gas in the first step without generating other gaseous impurities; the second step can separate anhydrous hydrogen fluoride by slight heating, which is also of high purity and without other gaseous impurities; finally, the sulfate generated can be recycled and circulated. The simple operation can completely separate several products without loss or waste, which is a process that can improve the comprehensive utilization efficiency.

[0046] (7) The final products obtained by the process of the present invention are all recycled or can be sold as products, and no by-products or wastes are generated that need to be processed again.

[0047] (8) The economic value of the process of the present invention lies in its ability to simultaneously obtain high-value fluorinated products, high-purity silicon tetrafluoride gas, and anhydrous hydrogen fluoride gas.

[0048] (9) The process of the present invention does not cause any loss of fluorine and silicon resources, and the total yield of fluorine and silicon is high, thus achieving comprehensive and efficient utilization of fluorine and silicon resources.

[0049] (10) The process of the present invention is simple to operate, saves energy, has abundant raw material market and high conversion rate, low production cost and low environmental pollution, which significantly improves resource utilization, saves corresponding mineral resources and is easy to implement in industrialization. Attached Figure Description

[0050] Figure 1 This is a process flow diagram of the method for low-energy conversion of hydrofluoric acid, a byproduct of phosphate rock, according to the present invention. Detailed Implementation

[0051] To achieve the objectives of this invention, the novel low-energy-consumption method for converting hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, comprises:

[0052] a. Extraction: using organic amine extractant R x NH 3-x Fluorosilicic acid, a byproduct of phosphate rock, was extracted and allowed to separate into layers after standing to obtain organofluorosilicates (R). x NH 4-x ) + 2SiF6 2- The organic phase and the aqueous phase, wherein x = 1, 2, 3 or more;

[0053] b. Inorganic base back-extraction: The organic fluorosilicate (R... x NH 4-x ) + 2SiF6 2- The organic phase reacts with an inorganic alkaline solution, and after standing and phase separation, an aqueous phase containing a fluorosilicate precipitate and an organic ammonium base (R) are obtained. x NH4-x ) + OH - The inorganic base includes at least one of KOH, NaOH, Ca(OH)2, and liquid ammonia; the ratio of the organic phase to the inorganic base stripping agent in the inorganic base back-extraction is 2:1 to 1:5.

[0054] The reaction equation for inorganic base back-extraction is as follows:

[0055] (R x NH 4-x ) + 2SiF6 2- +KOH→K2SiF6+(R x NH 4-x ) + OH -

[0056] (R x NH 4-x ) + 2SiF6 2- +NaOH→Na2SiF6+(R x NH 4-x ) + OH -

[0057] (R x NH 4-x ) + 2SiF6 2- +Ca(OH)2→CaSiF6+(R x NH 4-x ) + OH -

[0058] (R x NH 4-x ) + 2SiF6 2- +NH3→(NH4)2SiF6+(R x NH 4-x ) + OH -

[0059] Organic ammonium bases (R x NH 4-x ) + OH - It can be decomposed back into organic amine R upon heating. x NH 3-x After recovery, it can be returned to step a for cyclic extraction. The reaction equation is as follows:

[0060] (R x NH 4-x )+ OH - →R x NH 3-x +H2O

[0061] Or inorganic salt back-extraction: the organofluorosilicate (R) x NH 4-x ) + 2SiF6 2- The organic phase reacts with the salt solution, and after standing, the phases separate to obtain an aqueous solution containing fluorosilicate precipitate and an organic ammonium salt solution.

[0062] c. Remove water from the aqueous solution containing fluorosilicate precipitate to obtain solid fluorosilicate;

[0063] d. Pyrolysis: The fluorosilicate solid is heated and decomposed in a vacuum or inert atmosphere to obtain anhydrous silicon tetrafluoride gas and fluoride salts;

[0064] The pyrolysis reaction equations for the dried fluorosilicate solids K₂SiF₆, Na₂SiF₆, CaSiF₆, and (NH₄)₂SiF₆ are as follows:

[0065] K2SiF6→SiF4↑+KF

[0066] Na₂SiF₆→SiF₄↑+NaF

[0067] CaSiF6→SiF4↑+CaF2

[0068] (NH4)2SiF6→SiF4↑+NH4F

[0069] Alternatively, acid hydrolysis: the fluorosilicate solid is decomposed with sulfuric acid to obtain anhydrous SiF4 gas, HF and sulfate, and anhydrous hydrogen fluoride and silicon tetrafluoride are separated.

[0070] The dried fluorosilicate solids K2SiF6, Na2SiF6, CaSiF6, and (NH4)2SiF6 are decomposed using sulfuric acid. The fluorosilicate solids Na2SiF6, CaSiF6, and K2SiF6 undergo acid hydrolysis at high temperatures of 19℃ to 450℃; while the fluorosilicate solids (NH4)2SiF6, K2SiF6, and CaSiF6 can undergo acid hydrolysis at low temperatures of -90℃ to 19℃.

[0071] Among them, K2SiF6 can be further divided into two cases during high-temperature acid hydrolysis, depending on the acid hydrolysis temperature. The reaction equations are as follows:

[0072] K2SiF6+H2SO4→SiF4↑+HF↑+KHSO4(200~300℃)

[0073] K2SiF6+H2SO4→SiF4↑+HF↑+K2SO4(300~450℃)

[0074] The reaction equations for the high-temperature acid hydrolysis of CaSiF6 and K2SiF6 are as follows:

[0075] Na2SiF6+H2SO4→SiF4↑+HF↑+Na2SO4

[0076] CaSiF6+H2SO4→SiF4↑+HF↑+CaSO4

[0077] During the low-temperature acid hydrolysis of K2SiF6, two sulfates, K2SO4 and KHSO4, are produced due to side reactions. The reaction equations are as follows:

[0078] K2SiF6+H2SO4→SiF4↑+HF+K2SO4+KHSO4

[0079] The reaction equations for the low-temperature acid hydrolysis of CaSiF6 and K2SiF6 are as follows:

[0080] (NH4)2SiF6+H2SO4→SiF4↑+HF+(NH4)2SO4

[0081] CaSiF6+H2SO4→SiF4↑+HF+CaSO4.

[0082] The organic amine extractant used in step a includes primary amines (RNH2), secondary amines (R2N), tertiary amines (R3N), and quaternary ammonium salts (R4N). + X - Organic amines of all carbon chain lengths in ).

[0083] In one specific embodiment, the extractant in step a is a quaternary ammonium salt; preferably at least one of trioctylamine, trialkylamine, and N263.

[0084] The mass concentration of fluorosilicic acid, a byproduct of phosphate rock, in step a is 0.1% to 99.9%, preferably 0.1% to 1.5%.

[0085] In one specific embodiment, the extraction temperature in step a is 10–70°C, the extraction time is preferably 10–90 minutes, and the volume ratio of the extractant to the fluorosilicic acid byproduct of phosphate rock is preferably 0.5–8:1; preferably, the extraction rate is >99%.

[0086] The aqueous phase described in step a is preferably recovered for dissolving solid salts or alkalis, and used to prepare the inorganic alkali solution or salt solution described in step b.

[0087] In one specific embodiment, the temperature of inorganic alkali back-extraction in step b is 10-70°C, the back-extraction time is preferably 0.25-2 hours, and the back-extraction rate is preferably >80%.

[0088] In one specific embodiment, the salt solution in step b includes at least one of sulfate solution, chloride solution, and nitrate solution; preferably at least one of K2SO4, KHSO4, Na2SO4, (NH4)2SO4, KCl, NaCl, NH4Cl, KNO3, NaNO3, and NH4NO3.

[0089] The reaction equation for inorganic salt back-extraction is as follows:

[0090] (R x NH 4-x ) + 2SiF6 2- +K₂SO₄→K₂SiF₆+(R x NH 4-x ) + 2SO4

[0091] (R x NH 4-x ) + 2SiF6 2- +KHSO4→K2SiF6+(R x NH 4-x ) + 2SO4

[0092] (R x NH 4-x ) + 2SiF6 2- +Na₂SO₄→Na₂SiF₆+(R x NH 4-x ) + 2SO4

[0093] (R x NH 4-x ) + 2SiF6 2- +(NH4)2SO4→(NH4)2SiF6+(R x NH 4-x ) + 2SO4

[0094] (R x NH 4-x ) + 2SiF6 2- +KCl→K2SiF6+(R x NH 4-x ) + Cl-

[0095] (R x NH 4-x ) + 2SiF6 2- +NaCl→Na2SiF6+(R x NH 4-x ) + Cl -

[0096] (R x NH 4-x ) + 2SiF6 2- +NH4Cl→(NH4)2SiF6+(R x NH 4-x ) + Cl -

[0097] (R x NH 4-x ) + 2SiF6 2- +KNO3→K2SiF6+(R x NH 4-x ) + NO3 -

[0098] (R x NH 4-x ) + 2SiF6 2- +NaNO3→Na2SiF6+(R x NH 4-x ) + NO3 -

[0099] (R x NH 4-x ) + 2SiF6 2- +NH4NO3→(NH4)2SiF6+(R x NH 4-x ) + NO3 -

[0100] Step b, the temperature for inorganic salt back-extraction is 10–70°C, the back-extraction time is preferably 0.25–4 hours, the ratio of organic phase to inorganic salt back-extraction agent is preferably 2:1–1:5, and the back-extraction rate is preferably >80%.

[0101] In one specific embodiment, the method further includes adding the organic ammonium base (R) from step b. x NH4-x ) + OH - Decompose at 100–150°C to recover the organic amine extractant;

[0102] Alternatively, a second back-extraction: the organic ammonium salt solution described in step b is mixed with liquid ammonia to recover the organic amine extractant and ammonium salt. The organic amine extractant is returned to step a for cyclic extraction, and the ammonium salt is returned to step b for cyclic back-extraction.

[0103] The reaction equation for the second back-extraction is as follows:

[0104] (R x NH 4-x ) + 2SO4 + NH3 → (NH4)2SO4 + R x NH 3-x

[0105] (R x NH 4-x ) + Cl - +NH3→NH4Cl+R x NH 3-x

[0106] (R x NH 4-x ) + NO3 - +NH3→NH4NO3+R x NH 3-x

[0107] Preferably, the secondary back-extraction temperature is room temperature of 10-70°C, the back-extraction time is 0.25-2 hours, the molar ratio of organic ammonium salt solution to liquid ammonia is 2:1-1:3, and preferably the back-extraction rate is >80%.

[0108] In one specific embodiment, the method for removing water from the aqueous solution containing fluorosilicate precipitate in step c includes solid-liquid separation and drying; the solid-liquid separation is preferably filtration, and the filtered water is recycled for preparing the inorganic alkaline solution, salt solution, or liquid ammonia for secondary back-extraction in step b; preferably, the drying temperature is controlled at 100℃ to 300℃, and the moisture content after drying is less than 0.1%.

[0109] In one specific embodiment, the aqueous phase after back-extraction in step b is filtered, and the aqueous ointment containing fluorosilicate solution is dried to remove moisture.

[0110] Filtration can be performed using methods such as plate and frame filter press, belt vacuum filter, and fully automatic vertical filter press. After filtration, the resulting filter cake is a fluorosilicate, such as K2SiF6, Na2SiF6, CaSiF6, or (NH4)2SiF6, depending on the alkali and salt used. The moist cake is dried to remove moisture and other volatile substances. The drying temperature is controlled between 100℃ and 300℃, and the moisture content is less than 0.1%.

[0111] In one specific embodiment, the pyrolysis temperature in step d is 200–800°C, and the pyrolysis time is preferably 1–3 hours.

[0112] More preferably, the pyrolysis temperature of solid fluorosilicate K2SiF6 is 400–600℃, the pyrolysis temperature of Na2SiF6 is 300–800℃, the pyrolysis temperature of CaSiF6 is 300–400℃, and the pyrolysis temperature of (NH4)2SiF6 is 400℃.

[0113] The pyrolysis process involves holding the product at high temperature for a period of time to remove residual organic solvents. The resulting silicon tetrafluoride gas is then separated, purified, and the fluorides NH4F, KF, CaF2, and NaF are recovered and sold.

[0114] In one specific embodiment, the silicon tetrafluoride gas obtained after pyrolysis is further purified. The method for purifying the silicon tetrafluoride gas includes at least one of condensation, dust removal, and purification, and finally the fluoride products NH4F, KF, CaF2 and NaF are separated and recovered.

[0115] In one specific embodiment, the acid hydrolysis in step d includes high-temperature acid hydrolysis or low-temperature acid hydrolysis. The fluorosilicate solid of the high-temperature acid hydrolysis is at least one of Na2SiF6, CaSiF6, and K2SiF6. The temperature of the high-temperature acid hydrolysis is 19°C to 450°C, and the reaction time of the high-temperature acid hydrolysis is preferably 30 to 90 minutes.

[0116] The fluorosilicate solid undergoing low-temperature acid hydrolysis is at least one of (NH4)2SiF6, K2SiF6, and CaSiF6. The low-temperature acid hydrolysis temperature is less than 19°C, and the reaction time for low-temperature acid hydrolysis is preferably 30 to 180 minutes.

[0117] The concentration of sulfuric acid used in the acid hydrolysis is preferably 95–105 wt%.

[0118] The sulfuric acid used in this invention is fuming sulfuric acid, and its concentration is determined according to the sulfate ions (SO4) present in it. 2- The determination was made because fuming sulfuric acid contains gaseous sulfate ions (SO4). 2- Therefore, there are cases where the content is greater than 100wt%.

[0119] In one specific embodiment, the separation method in step d includes: obtaining a mixed gas of anhydrous hydrogen fluoride and silicon tetrafluoride after high-temperature acid hydrolysis, and then obtaining high-purity anhydrous hydrogen fluoride and silicon tetrafluoride by distillation.

[0120] The low-temperature acid hydrolysis can directly collect anhydrous silicon tetrafluoride gas, and then the liquid after low-temperature acid hydrolysis is heated to 20℃~60℃ and reacted for 20~55 minutes to separate anhydrous hydrogen fluoride gas.

[0121] Preferably, the sulfate separated in step d is returned to step b for recycling and back-extraction.

[0122] The methods used for distillation and purification include, but are not limited to, adsorption, freezing, fluorine gas, and fluorinating agent methods.

[0123] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0124] Example 1

[0125] Extraction was performed at room temperature (25°C). Trioctylamine and 8% fluorosilicic acid (2:1 volume ratio) were added to a separatory funnel. After 25 minutes, the aqueous phase was separated and used to dissolve the subsequently added solid salt K₂SO₄. A sulfate solution of K₂SO₄ (1:2.5 volume ratio) was added to the organic phase for back-extraction. After 40 minutes of reaction and separation, the aqueous phase was filtered, and the filtrate (water) was passed through it. 32.5 g of ammonia gas was introduced, and the filter cake was dried at 120°C for 6 hours, resulting in a moisture content of less than 0.1%. Liquid ammonia was added to the oil phase for a second back-extraction. After 40 minutes of separation, the organic phase (trioctylamine N₂35) was recovered and recycled for extraction. The aqueous phase (K₂SO₄ sulfate solution) was recovered and back-extracted again. The dried filter cake was fluorosilicate K2SiF6. After grinding, it was calcined at 500°C for 2 hours under a nitrogen atmosphere. SiF4 gas was collected using a gas bag. After the reaction was complete, the solid KF after pyrolysis was collected as a byproduct for recovery. The SiF4 gas was further recovered after being purified by cryogenic distillation in liquid nitrogen. The final gas purity was >99%. The final total yield of fluorosilicone in this example was 97.3%.

[0126] Example 2

[0127] Extraction was performed at room temperature (25°C). Trioctylamine and 8% fluorosilicic acid (4:1 volume ratio) were added to a separatory funnel. After 10 minutes, the aqueous phase was separated and used to dissolve the subsequently added solid salt K₂SO₄. A sulfate solution of K₂SO₄ (1:1.5 volume ratio) was added to the organic phase for back-extraction. After 40 minutes of reaction and standing, the phases were separated. The aqueous phase was filtered, and the filtrate, consisting of water, was passed through it. 55 g of ammonia gas was then introduced, and the filter cake was dried at 120°C for 6 hours. Liquid ammonia was added to the oil phase for a second back-extraction. After 40 minutes of standing and separation, the organic phase (trioctylamine N₂35) was recovered and recycled for extraction. The aqueous phase (K₂SO₄ sulfate solution) was recovered and back-extracted again. The dried filter cake was fluorosilicate K2SiF6, which underwent low-temperature acid hydrolysis at 10℃. 98% sulfuric acid was added to the K2SiF6 solid, and the reaction was carried out for 1 hour. SiF4 gas was collected using a gas bag, and the final gas purity was >95%. Then, the temperature was raised to 30℃ and held for 30 minutes. HF gas with a purity >95% was collected using a gas bag. After the gas was completely released, the product obtained was a mixture of sulfate K2SO4 and KHSO4. After recovery, it could be directly back-extracted without separation. The final total yield of fluorosilicone in this example was 97.8%.

[0128] Example 3

[0129] Extraction was performed at room temperature (25°C). Trioctylamine and 8% fluorosilicic acid (2:1 volume ratio) were added to a separatory funnel. After 25 minutes, the aqueous phase was separated and used to dissolve the subsequently added solid salt Ca(OH)₂. Sulfate solution Ca(OH)₂ was added to the organic phase for back-extraction (Ca(OH)₂ to organic phase volume ratio 1:2). After reacting for 30 minutes and allowing to stand for separation, the aqueous phase was filtered and dried at 180°C for 6 hours. The organic phase was heated to 100°C to generate trioctylamine N₂₃₅, which was recovered and recycled for extraction. The dried filter cake was fluorosilicate CaSiF₆, which was ground and calcined at 550°C for 2.5 hours under a nitrogen atmosphere. SiF₄ gas was collected using a gas bag. After complete reaction, the pyrolyzed solid CaF₂ was collected as a byproduct for recovery. The SiF₄ gas was further purified by cryogenic distillation in liquid nitrogen, achieving a final gas purity >99%. The final total fluorosilicone yield in this example was 98.3%.

[0130] Example 4

[0131] Extraction was performed at room temperature (15°C). Trioctylamine and 8% fluorosilicic acid (volume ratio 1.5:1) were added to a separatory funnel. After 35 minutes, the aqueous phase was separated and used to dissolve the subsequently added solid salt, Na₂SO₄. A sulfate solution of Na₂SO₄ (volume ratio 1:3) was added to the organic phase for back-extraction. After 65 minutes of reaction and standing, the phases were separated. The aqueous phase was filtered, and the filtrate, consisting of water, was passed through it. 23.7 g of ammonia gas was introduced, and the filter cake was dried at 110°C for 8 hours. Liquid ammonia was added to the oil phase for a second back-extraction. After 65 minutes of standing and separation, the organic phase (trioctylamine N₂SO₄) was recovered and recycled for extraction. The aqueous phase (Na₂SO₄ sulfate solution) was recovered and back-extracted again. The dried filter cake was fluorosilicate Na₂SiF₆, which underwent high-temperature acid hydrolysis at 160℃. 95% sulfuric acid was added to the Na₂SiF₆ solid, and after reacting for 30 minutes, a mixture of SiF₄ and HF was collected using a gas bag. The mixture was first cooled to 10℃ and condensed to recover HF gas with a purity >95%. The remaining gas was further recovered after low-temperature distillation with liquid nitrogen, yielding SiF₄ gas with a purity >99%. After all the gas was released, the resulting sulfate product, Na₂SO₄, was recovered and further back-extracted. In this example, the final total fluorosilicone yield was 97.1%.

[0132] Example 5

[0133] Extraction was performed at room temperature (15°C). Trioctylamine (0.5:1 volume ratio) and fluorosilicic acid (0.2% concentration) were added to a separatory funnel. After 30 minutes, the aqueous phase was separated and used to dissolve the subsequently added solid salt, Na₂SO₄. A sulfate solution of Na₂SO₄ was added to the organic phase for back-extraction, with a Na₂SO₄ to organic phase volume ratio of 1:2.5. After reacting for 50 minutes and allowing the phases to separate, the aqueous phase was filtered, and the filtrate, consisting of water, was passed through it. The filter cake was dried at 110°C for 6 hours, with a moisture content below 0.1%. Liquid ammonia was added to the oil phase for a second back-extraction. After 50 minutes of standing and separation, the organic phase was trioctylamine (N₂SO₄), which was recovered and recycled for extraction. The aqueous phase was a sulfate solution of Na₂SO₄, which was recovered and back-extracted again. The dried filter cake was fluorosilicate Na₂SiF₆. After grinding, it was calcined at 500°C under vacuum for 2 hours. SiF₄ gas was collected using a gas bag. After the reaction was complete, the pyrolyzed solid NaF was collected as a byproduct for recovery. The SiF₄ gas was further recovered after low-temperature distillation, with a purity >99%. The final total fluorosilicone yield in this example was 97.9%.

[0134] Example 6

[0135] Extraction was performed at room temperature (15°C). Trialkylamine and 17% fluorosilicic acid (volume ratio 3:1) were added to a separatory funnel. After 45 minutes, the aqueous phase was separated and used to dissolve the subsequently added solid salt K₂SO₄. A sulfate solution of K₂SO₄ (volume ratio 1:3) was added to the organic phase for back-extraction. After 55 minutes of reaction and separation, the aqueous phase was filtered, and the filtrate (water) was passed through it. 19.3 g of ammonia gas was then introduced. The filter cake was dried at 110°C for 6 hours after filtration. Liquid ammonia was added to the oil phase for a second back-extraction. After 55 minutes of separation, the organic phase (trialkylamine) was recovered and recycled for extraction. The aqueous phase (K₂SO₄ sulfate solution) was recovered and back-extracted again. The dried filter cake was fluorosilicate K2SiF6, which underwent low-temperature acid hydrolysis at 5°C. 98% sulfuric acid was added to the K2SiF6 solid, and the reaction was carried out for 1 hour. SiF4 gas with a purity >95% was collected using a gas bag. Then, the temperature was raised to 50°C and held for 30 minutes. HF gas with a purity >95% was collected using a gas bag. After the gas was completely released, the resulting sulfate product was a mixture of K2SO4 and KHSO4. After recovery, it could be directly back-extracted without separation. The final total yield of fluorosilicone in this example was 97.3%.

[0136] Comparative Example 1

[0137] At room temperature (25°C), trioctylamine (2:1 volume ratio) and 8% fluorosilicic acid were added to a separatory funnel for extraction. After standing for 30 minutes, the aqueous phase was removed by separation, and 35g of ammonia gas was added to form a solution. Liquid ammonia was then added as a back-extraction agent to the organic phase, with a ratio of organic phase to back-extraction agent of 1:10. Liquid ammonia was in excess at this point. The reaction was continued for 40 minutes to obtain the solid product, silica. The reaction that occurred was as follows:

[0138] H2SiF6+6NH4OH→SiO2+6NH4F+2H2O

[0139] The filter cake obtained by filtration has absorbed a large amount of extractant and contains crystalline products of ammonium fluoride, which are difficult to separate.

Claims

1. A method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, characterized in that, The method includes: a. Extraction: using organic amine extractant R x NH 3-x Fluorosilicic acid, a byproduct of phosphate rock, was extracted and allowed to separate into layers after standing to obtain organofluorosilicates (R). x NH 4-x ) + 2SiF6 2- The organic phase and the aqueous phase, wherein x = 1, 2, 3 or more; b. Inorganic base back-extraction: The organic fluorosilicate (R... x NH 4-x ) + 2SiF6 2- The organic phase reacts with an inorganic alkaline solution, and after standing and phase separation, an aqueous phase containing a fluorosilicate precipitate and an organic ammonium base (R) are obtained. x NH 4-x ) + OH - The inorganic base includes at least one of KOH, NaOH, Ca(OH)2, and liquid ammonia; the ratio of the organic phase to the inorganic base stripping agent in the inorganic base back-extraction is 2:1 to 1:

5. Or inorganic salt back-extraction: the organofluorosilicate (R) x NH 4-x ) + 2SiF6 2- The organic phase reacts with the salt solution, and after standing, the phases separate to obtain an aqueous solution containing fluorosilicate precipitate and an organic ammonium salt solution. c. Remove water from the aqueous solution containing fluorosilicate precipitate to obtain solid fluorosilicate; d. Pyrolysis: The fluorosilicate solid is heated and decomposed in a vacuum or inert atmosphere to obtain anhydrous silicon tetrafluoride gas and fluoride salts; Alternatively, acid hydrolysis: the fluorosilicate solid is decomposed with sulfuric acid to obtain anhydrous SiF4 gas, HF and sulfate, and anhydrous hydrogen fluoride and silicon tetrafluoride are separated.

2. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 1, is characterized in that... The extractant used in step a is a quaternary ammonium salt; The mass concentration of fluorosilicic acid, a byproduct of phosphate rock, in step a is 0.1% to 99.9%.

3. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 2, is characterized in that... The extractant in step a is at least one of trioctylamine, trialkylamine, and methyltrialkylammonium chloride.

4. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 2, is characterized in that... The mass concentration of fluorosilicic acid, a byproduct of phosphate rock, in step a is 0.1% to 1.5%.

5. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 1 or 2, is characterized in that... The extraction temperature in step a is 10–70°C.

6. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 5, is characterized in that... The extraction time described in step a is 10 to 90 minutes.

7. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 5, is characterized in that... The volume ratio of the extractant to the fluorosilicic acid byproduct of phosphate rock in step a is 0.5 to 8:

1.

8. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 5, is characterized in that... The extraction rate described in step a is >99%.

9. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 5, is characterized in that... The aqueous phase recovery described in step a is used to dissolve solid salts or alkalis and to prepare the inorganic alkali solution or salt solution described in step b.

10. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 1 or 2, is characterized in that, The temperature for inorganic alkali back-extraction in step b is 10–70°C.

11. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 10, is characterized in that... The back-extraction time for step b is 0.25 to 2 hours.

12. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 10, is characterized in that... The back-extraction rate in step b is >80%.

13. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 1 or 2, is characterized in that... The salt solution mentioned in step b includes at least one of sulfate solution, chloride solution, and nitrate solution; The temperature for inorganic salt back-extraction in step b is 10–70°C.

14. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 13, is characterized in that, The salt solution in step b is at least one of K2SO4, KHSO4, Na2SO4, (NH4)2SO4, KCl, NaCl, NH4Cl, KNO3, NaNO3, and NH4NO3.

15. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 13, is characterized in that... The inorganic salt back-extraction time in step b is 0.25 to 4 hours.

16. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 13, is characterized in that, In step b, the ratio of the organic phase to the inorganic salt stripping agent is 2:1 to 1:

5.

17. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 13, is characterized in that, The back-extraction rate in step b is >80%.

18. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 1 or 2, is characterized in that... The method further includes adding the organic ammonium base (R) from step b. x NH 4-x ) + OH - Decompose at 100–150°C to recover the organic amine extractant; Alternatively, a second back-extraction: the organic ammonium salt solution described in step b is mixed with liquid ammonia to recover the organic amine extractant and ammonium salt. The organic amine extractant is returned to step a for cyclic extraction, and the ammonium salt is returned to step b for cyclic back-extraction.

19. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 18, is characterized in that... The secondary back-extraction is performed at room temperature (10–70°C) for 0.25–2 hours, and the molar ratio of organic ammonium salt to liquid ammonia is 2:1–1:

3.

20. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 18, is characterized in that... The back-extraction rate is >80%.

21. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 18, is characterized in that... Step c describes a method for removing water from a solution containing fluorosilicate precipitates in the aqueous phase, which includes solid-liquid separation and drying.

22. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 21, is characterized in that... The solid-liquid separation in step c is filtration, and the filtered water is recycled to prepare the inorganic alkaline solution, salt solution, or liquid ammonia from secondary back-extraction in step b.

23. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 21, is characterized in that... The drying temperature in step c is controlled between 100℃ and 300℃, and the moisture content after drying is less than 0.1%.

24. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 1 or 2, is characterized in that... The pyrolysis temperature in step d is 200–800℃.

25. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 24, is characterized in that... The pyrolysis time in step d is 1 to 3 hours.

26. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 24, is characterized in that... The pyrolysis temperatures of the fluorosilicate solids K2SiF6 in step d are 400–600℃, Na2SiF6 is 300–800℃, CaSiF6 is 300–400℃, and (NH4)2SiF6 is 400℃.

27. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 1 or 2, is characterized in that... The acid hydrolysis in step d includes high-temperature acid hydrolysis or low-temperature acid hydrolysis. The fluorosilicate solid for high-temperature acid hydrolysis is at least one of Na2SiF6, CaSiF6, and K2SiF6. The temperature for high-temperature acid hydrolysis is 19℃~450℃. The fluorosilicate solid subjected to low-temperature acid hydrolysis is at least one of (NH4)2SiF6, K2SiF6, and CaSiF6, and the temperature range of low-temperature acid hydrolysis is -90℃ to 19℃.

28. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 27, is characterized in that... The reaction time for the high-temperature acid hydrolysis described in step d is 30 to 90 minutes.

29. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 27, is characterized in that... The reaction time for the low-temperature acid hydrolysis described in step d is 30 to 180 minutes.

30. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 27, is characterized in that... The concentration of sulfuric acid used in step d is 95–105 wt%.

31. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 27, is characterized in that, The separation method described in step d includes: obtaining a mixed gas of anhydrous hydrogen fluoride and silicon tetrafluoride after high-temperature acid hydrolysis, and then obtaining high-purity anhydrous hydrogen fluoride and silicon tetrafluoride by distillation. The low-temperature acid hydrolysis can directly collect anhydrous silicon tetrafluoride gas, and then the liquid after low-temperature acid hydrolysis is heated to 20℃~60℃ and reacted for 20~55 minutes to separate anhydrous hydrogen fluoride gas.

32. The method for low-energy conversion of hydrofluoric acid and fluorosilicic acid, byproducts of phosphate rock, according to claim 31, is characterized in that... The sulfate separated in step d is returned to step b for cyclic back-extraction.

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