RU2617398C1 - Method of processing waste potassium bifluoride - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: exhaust potassium bifluoride (EBFP) is crushed, mixed with aqueous potassium hydroxide or potassium carbonate, or potassium bicarbonate, taken in stoichiometric ratio to the content of potassium bifluoride in EBFP. The resulting slurry is hold with stirring at 80-90°C for 20-24 hours, then it is filtered. A portion of the filtrate is directed to evaporation at a temperature of 120-135°C to get potassium fluoride dihydrate. Another portion of the filtrate is directed to a hydrofluorination stage where it is passed through the hydrogen fluoride to achieve pH 2. The resulting solution is stirred for another 2-3 hours, then cooled from 10 to 0°C. Potassium bifluoride precipitated crystals are filtered and dried at 130°C.

EFFECT: invention allows to recycle the spent potassium bifluoride to products having a demand in the industry, to obtain potassium hydrogen bifluoride and potassium fluoride dihydrate with qualifications not lower than pure.

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Description

The invention relates to inorganic chemistry, namely to the processing of spent potassium bifluoride to produce acid potassium bifluoride and / or potassium fluoride dichloride.

Spent potassium bifluoride (OBFK) after use is a solid, marble-like mass, slowly soluble in water.

Potassium bifluoride (BFC) is used to produce elemental fluorine, as a soft fluorinating agent, as a catalyst in organofluorine synthesis and in the conservation of wood.

Potassium fluoride is used as a salt additive in cryolite, in the electrolytic production of fluorine and potassium; it is used in the manufacture of acid-resistant putties and fluxes for soldering and welding, for introducing fluorine into organic compounds.

OBFK consists of 80% KF⋅nHF compound, where n = 0.6-0.9, the rest are impurities, including fluorides and oxyfluorides of copper, iron and other metals, as well as fluorine and oxyfluorosilicates. Due to the high acidity and toxicity, as well as due to solubility in water, the destruction of OBFK is a complex and expensive task.

A known method of regeneration of the spent product, based on obtaining potassium bifluoride by the interaction of potassium hydroxide (or carbonate) with hydrogen fluoride (see NP Galkin, A.B. Krutikov. Fluorine technology. - M .: Atomizdat, 1968) . In this method, the acidic potassium fluoride melt is neutralized with an aqueous potassium hydroxide solution, then filtered, the filtrate is saturated with hydrogen fluoride (HF) until crystals of potassium bifluoride precipitate, which are separated, dried and sent to prepare an acidic melt of potassium fluoride with the required content of hydrogen fluoride.

The filtered precipitate (cake) from the suction filter, consisting mainly of compound K ₃ FeF ₆ , is immersed in the same reactor with a stirrer and treated with a 26% aqueous KOH solution at a temperature of 70-80 ° C. The disadvantage of this method is the formation of a difficult to filter gelatinous precipitate and a low degree of extraction of fluorine ion from cake. At the same time, a significant amount of iron remains in the filtrate, to reduce its content to the level of 0.05 mass. % have to enter an additional amount of potassium hydroxide and anhydrous hydrogen fluoride.

The closest technical solution is a method for purifying spent acidic melt of potassium fluoride (RF patent 2296710, IPC C01D 3/02; C01B 7/24, publ. 10.04.2007). This method consists in the fact that the spent acid potassium fluoride is treated with an aqueous solution of potassium hydroxide, followed by filtration of the resulting mixture. After that, the filtrate is saturated with anhydrous hydrogen fluoride until potassium bifluoride precipitates. The filter cake (cake) is mixed with dry potassium hydroxide in a mass ratio of sediment: potassium hydroxide 1: (1.8-2.2) and the resulting mixture is either treated with water at a temperature of 80-90 ° C, or subjected to heat treatment at a temperature of 150 -200 ° C with further processing of the obtained melt with water, followed by filtration, returning the filtrate to the preparation of potassium bifluoride. The filtered sediment is sent for disposal. However, the prototype method is characterized by a large amount of non-recyclable waste.

The inventors were faced with the task of creating a method that allows processing OBFK into products that are in demand in industry, namely, potassium acid bifluoride (BFK) and / or two-water potassium fluoride (DFK). It is desirable that these products have a qualification no lower than “pure” (“H”).

The essence of the invention lies in the fact that a method for processing spent potassium bifluoride (OBFK) has been developed, which consists in the fact that OBFK is ground, then mixed with aqueous potassium hydroxide or potassium carbonate, taken in a stoichiometric ratio to the potassium bifluoride content in the spent potassium bifluoride obtained the suspension with stirring is kept at 80-90 ° C for 20-24 hours, filtered, and then part of the filtrate is directed to evaporation at a temperature of 120-135 ° C, as a result of which potassium fluoride, two-water, and others The coarse part of the filtrate is sent to the hydrofluorination stage, where hydrogen fluoride is passed through it until pH 2 is reached, the resulting solution is stirred for another 2-3 hours, then cooled to 10-0 ° С, the precipitated potassium bifluoride crystals are filtered off and dried at 130 ° С.

As potassium carbonate, potassium hydrogen carbonate KHCO ₃ can be used, which is also taken in a stoichiometric ratio.

To implement the method, a solid marble-like mass, slowly soluble in water and representing 80% KF⋅nHF, where n = 0.6-0.9, the rest are impurities, including fluorides and oxyfluorides of copper, iron and other metals, and also potassium fluorine and oxyfluorosilicates are subjected to grinding. The ground OPFK is sent to the alkaline hydrolysis stage, for which water and the calculated (stoichiometric) amount of potassium hydroxide or potassium carbonate (potash) are added to the crushed substrate. The mixture is heated to 85-90 ° C, incubated for 20-24 hours at this temperature with continued stirring. The resulting reaction mass has a pH of 7.5-8. After that, the solution of the resulting potassium fluoride is filtered, with up to 0.2 kg of metal oxides and oxyfluorides remaining on the filter, as well as potassium fluorine and hydroxypolyfluorosilicates.

Part of the filtrate was evaporated at 120-135 ° C and potassium fluoride dihydrate was obtained. Another part of the filtrate can be processed into potassium bifluoride (BFC) by passing hydrogen fluoride through it at a temperature of 60-85 ° C until a solution with pH 2 is obtained. After this, the flow of hydrogen fluoride is stopped, the mixture is stirred for another 2-3 hours, then cooled to 10 -0 ° C. The precipitated crystals of BFK are filtered off and dried at 130 ° C, whereby BFC is obtained.

The solution after filtration can be reused for subsequent production of BFK from OBFK at least 10 times.

The analysis showed that the products obtained correspond to the qualification “pure”.

Interaction with potassium fluoride:

Interaction with potassium fluorosilicates takes place according to the scheme

EXAMPLE 1

A sample of spent potassium bifluoride weighing 46.2 g, contains 80.1 mass. %, KF⋅0.5HF. The total content of impurities - fluorides, oxyfluorides of iron (Fe), copper (Cu), fluorosilicates and potassium polyfluorosilicates - 19.9 mass. %

The sample is ground to a particle size of 0.5-5 mm and loaded into a 0.25 L polypropylene reactor equipped with a stirrer and heating.

61.6 ml (g) of distilled water and 15.5 g KOH qualification “H” are added.

The reactor is heated to 85 ° C, the mass is stirred for 18 hours, after which the reactor is cooled to 20 ° C and the contents are transferred to a filter. The obtained filtrate (120 g) has a pH of 8, it is evaporated to 98 g at 130 ° C and crystallized by cooling to ambient temperature. The result is a crystalline mass of 72.6 g, the analysis of which showed that it is a potassium fluoride dihydrate composition (wt.%):

KF⋅2H ₂ O 98.89 Water insoluble matter less than 0.005 Acids in terms of HF 0.01 Alkali in terms of KOH 0.08 Chlorides 0.002 Sulphates 0.005 Iron 0.0001 The total mass of compounds of lead, copper, manganese 0,0009 Silicon 0.004

This composition corresponds to the qualification "Clean".

Example 2

A sample of OBFK weighing 46.2 g, containing 80.1 mass. % KF⋅1.5HF, containing impurities similar to the composition of example 1, was treated with KOH technical grade.

The treatment was carried out similarly to the procedure described in example 1, the pH of the solution was 7.5.

Received potassium fluoride dihydrate 72.7 g of the composition (wt.%):

KF⋅2H ₂ O 99.02 Water insoluble matter less than 0.005 Acids in terms of HF 0.01 Alkali in terms of KOH 0,07 Chlorides 0.002 Sulphates 0.005 Iron 0.0001 The total mass of compounds of lead, copper, manganese 0,0005 Silicon 0.004

This composition also meets the qualifications "Clean".

Example 3

A sample of spent potassium bifluoride weighing 46.2 g, composition:

KF⋅0.5HF - 80.1 mass. % The total content of impurities - fluorides, oxyfluorides of iron (Fe), copper (Cu), fluorosilicates and potassium polyfluorosilicates is similar to example 1. The composition is treated with KOH and heated to 80-85 ° C, the mass is stirred for 18 hours, after which the reactor is cooled to 20 ° C and the contents are transferred to a filter. The obtained filtrate (120 g) was crystallized by cooling to minus 12 ° C and maintained at this temperature for 6 hours.

The precipitate is filtered off, dried at a temperature of 100 ° C.

The result is 58.0 g of crystalline mass.

The analysis showed that it is a potassium fluoride dihydrate composition (wt.%):

KF⋅2H ₂ O 99.6 Water insoluble matter less than 0,002 Acids in terms of HF 0.005 Alkali in terms of KOH 0.05 Chlorides 0.002 Sulphates 0.004 Iron 0,0004 The total mass of compounds of lead, copper, manganese 0.001 Silicon 0.004

This composition corresponds to the qualification “Clean for analysis”.

Example 4

A sample of OBFK containing 79.2% KF⋅0.4HF weighing 47.5 g was treated with a technical grade KOH solution under the conditions of Example 2. 74.9 g of pure KF⋅2H ₂ O qualification was obtained.

Example 5

In a reactor of fluoroplastic 4 with a volume of 200 l, equipped with a stirrer of the same material, load 48.0 kg pre-crushed to particles with a size of 0.5-10 mm OBFK, which contains 81.0 mass. % KF⋅0.58HF. 52 l of water and 18.2 kg of KOH are charged there.

The reactor is heated to 85 ° C, stirred for 20 hours, and then cooled to 20 ° C. The resulting mass is filtered through a double layer of beltig fabric and get 109.1 kg of filtrate, which is cooled to minus 12 ° C for 12 hours. The precipitated KF⋅2H ₂ O crystals are dried at 100 ° C to constant weight. Obtain 66.3 kg of the product of potassium fluoride dihydrate (KF⋅2H ₂ O), corresponding to the qualification "Clean for analysis". The filtrate is used for subsequent processing cycles OBFK.

Example 6

A sample of OBFK weighing 48.1 g and containing 80.1 mass. % KF⋅0.5HF, loaded into the reactor, as described in example 1. There are served 65 g of distilled water and 20.0 g of K ₂ CO ₃ brand "H". The mixture is gradually heated with stirring to 90 ° C and kept under stirring for 16 hours. After cooling to 20 ° C, the reaction mass is filtered, evaporated with distillation of 20 g of water, and then cooled to minus 12 ° C for 12 hours. The precipitated KF⋅2H ₂ O crystals are filtered off and dried at 110 ° C to constant weight. Obtain 63.5 g of KF⋅2H ₂ O qualification "PSA".

Example 7

A sample of OBFK weighing 48.1 g and a content of 80.1% KF⋅0.5HF is loaded into the reactor, as described in examples 1 and 6. 65 ml of distilled water and 28.5 g _of grade “KHCO ₃ ” are fed there. The mixture was stirred at 90 ° C. for 24 hours. The reaction mass is processed analogously to example 6 and get 63.5 g of KF⋅2H ₂ O qualification "PSA".

Example 8

In the reactor described in example 5, load 49.2 kg OBFK containing 81.5 mass. % KF⋅0.63HF, and 70 kg of water are poured. The mixture is heated to 80 ° C and 25.0 kg of K ₂ CO ₃ brand “technical” are metered into it for 3 hours. The contents are stirred for 16 hours, then cooled to 20 ° C, filtered through a belting cloth. 124.5 kg of solution are obtained. Then, in a 200 l polypropylene reactor, the filtrate is cooled to a temperature of minus 12 ° С, stirred for 16 hours, after which it is filtered and dried at 100 ° С. Receive 69.6 kg of KF⋅2H ₂ O qualification "PSA". The filtrate (mother liquor) is used in subsequent processing trials of OBFK.

Example 9

0.55 kg of a KF solution prepared as described in Example 5 and containing 0.26 kg of KF was loaded into a 0.8 L polypropylene reactor equipped with a fluoroplastic bubbler, a fluoroplastic propeller stirrer 4, and a heating and cooling jacket . The solution is heated to 40 ° C and HF is fed through a bubbler, preventing the reaction mass from heating above 65 ° C. After supplying 0.11 kg and reaching a pH of solution 2, the supply of HF is stopped and the solution is stirred for 3 hours at 65 ° C, then cooled to minus 10 ° C, the precipitated crystals of BFK are filtered off, dried at 110 ° C and 0.31 kg is obtained BFK of the following composition:

KF⋅HF 99.3 Chlorides 0.003 Sulphates 0.004 Iron 0.0001 Total content lead, copper, manganese 0,0006 Silicon 0.01

The product meets the qualification of "ChDA".

Example 10

109.1 kg of the KF solution in water obtained in Example 5 and containing 51.2 kg of KF is loaded into a 200 L reactor of fluoroplastic 4, equipped with a fluoroplastic agitator 4, a bubbler, also of fluoroplastic, a bottom drain, a heating jacket and cooling.

The reactor is heated to 40 ° C and sparged with HF, preventing the solution from heating above 95 ° C. After the solution reaches pH 2, the HF supply is stopped (17.8 kg fed), the solution is stirred for 3 hours, then cooled to 0 ° C by feeding chilled water into the jacket. The precipitated crystals of BFK are filtered on a belting cloth, dried at 110 ° C, and 62.7 kg of potassium bifluoride are obtained.

Salt has the following composition (wt.%):

KF⋅HF 99,2 Chlorides 0.003 Sulphates 0.004 Iron 0.0001 Total content lead, copper, manganese 0,0006 Silicon 0.01

The product meets the qualification of "ChDA".

Example 11

124.5 kg of the KF solution obtained in example 7 and containing 54.9 kg of KF is loaded into the reactor described in example 8 and hydrogen fluoride is dosed, without allowing the reaction mass to warm up above 95 ° C. After supplying 19.1 kg of hydrogen fluoride HF and reaching a solution of pH 2, the solution was stirred for 3 hours, then cooled to + 5 ° C and the precipitated potassium bifluoride was filtered off. After drying at 110 ° C., 67.2 kg of potassium bifluoride were obtained.

The product has a composition (wt.%):

KF⋅HF 99.1 Chlorides 0.004 Sulphates 0.005 Iron 0.0001 Total content lead, copper, manganese 0,0008 Silicon 0.015

The product meets the qualification of "ChDA".

Thus, the problem faced by the inventors has been solved - a method has been developed that allows to process spent potassium bifluoride into products that are in demand in the industry, namely, to obtain acid potassium bifluoride (BFC) and potassium fluoride two-water (DPC), which qualify as “pure” ”(“ H ”) and“ pure for analysis ”(“ CHDA ”).

Claims (1)

A method of processing spent potassium bifluoride, which consists in the fact that OBFK is ground, then mixed with aqueous potassium hydroxide, or potassium carbonate, or potassium bicarbonate, taken in a stoichiometric ratio to the content of potassium bifluoride in the spent potassium bifluoride, the resulting suspension is kept at 80- under stirring 90 ° C for 20-24 hours, filtered, and then part of the filtrate is directed to evaporation at a temperature of 120-135 ° C, as a result of which two-water potassium fluoride is obtained, and the other part of the filtrate is sent to the hydrofluorination stage, where hydrogen fluoride is passed through it until a pH of 2 is reached, the resulting solution is stirred for another 2-3 hours, then cooled to 10-0 ° C, the precipitated potassium bifluoride crystals are filtered off and dried at 130 ° C.