RU2616715C1 - Method of processing waste potassium bifluoride - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of processing waste potassium bifluoride comprises its grinding, treatment with sulfuric acid with concentration of 95-100% in a molar ratio of sulfuric acid: potassium bifluoride as 1:1.02. The resulting mixture is heated to 130-150°C and held for 3-4 hours. The resulting hydrogen fluoride is stripped. Hydrogen fluoride absorption by water to obtain hydrofluoric acid is possible. Neutralisation of mass remaining after stripping of the hydrogen fluoride is carried out using aqueous solution of hydroxide or potassium carbonate to pH 7-7.5.

EFFECT: resulting potassium sulfate is dried The invention enables to process waste potassium bifluoride having high acidity and toxicity into commodity products - hydrogen fluoride and/or hydrofluoric acid and clear potassium sulfate.

5 tbl, 4 ex

Description

The invention relates to inorganic chemistry, and in particular to a method for processing potassium bifluoride waste products to produce hydrogen fluoride HF or hydrofluoric acid (a solution of HF in water) and potassium sulfate.

The spent BFC (hereinafter - OPFC) is potassium fluoride containing 0.7-0.85 mol of HF, as well as fluorides and oxyfluorides of iron, copper, silicon and other elements, in an amount up to 20 wt.%.

The composition of the spent potassium bifluoride has high acidity and toxicity, as well as solubility in water, which makes it dangerous for the environment. In appearance, it is a strong, marble-like mass, slowly soluble in water and acidifying it to pH 2-3. Industries with such waste can pollute the environment, so manufacturers have problems with their disposal.

At the same time, there is a demand in industry for hydrogen fluoride, hydrofluoric acid and potassium sulfate.

Hydrogen fluoride and hydrofluoric acid are widely used in pharmaceutical, metallurgical and chemical technology for the production of chladones, metal fluorides, etc.

Potassium sulfate is used in agriculture as potash chlorine-free fertilizer, in the glass and food industries.

The use of potassium sulfate with nitrogen and phosphate fertilizers enhances the positive effect on productivity. Potassium sulfate is also used in the production of various alum and fluxes in metallurgy.

In the European Union, potassium sulfate is approved for use as a dietary supplement (E515).

The destruction of OBFK is a complex and expensive task. Processing into hydrogen fluoride and potassium sulfate allows not only to reduce the amount of waste polluting the environment, but also to obtain products valuable for industry.

Known [US Pat. RF 2534792, IPC C01B7 / 19, publ. 12/10/2014] A method for producing hydrogen fluoride from aluminum production wastes, including sulfuric acid decomposition of cryolite-containing wastes.

The objective of the invention was to develop a method for producing hydrogen fluoride by sulfuric acid decomposition of fluorine-containing compounds with a large yield of hydrogen fluoride. To do this, the waste is pre-crushed to a particle size of 0.2 mm, placed on pallets with a layer of no more than 0.5 cm high, then it is fired at 800-850 ° C in a hearth furnace to remove the carbon component, dust of electrostatic precipitators is taken as aluminum production waste, sulfuric acid decomposition the concentrate obtained after burning the waste is carried out at a temperature of 240-260 ° C.

The known method [US Pat. RF 2235065, IPC C01D5 / 06, publ. 08/27/2004] processing sodium sulfate containing potash, and obtaining potassium sulfate from raw materials containing potash and sodium sulfate, comprising the following stages:

(a) processing a portion of the raw materials containing potash and sulfate sodium, so that glaserite crystallizes from the solution and the first mother liquor forms;

(b) conversion of glaserite to sedimentary sulfate potassium in the second mother liquor;

(c) returning the second mother liquor to a portion of potash-containing raw materials and sodium sulfate-containing raw materials;

(d) crystallization of the first mother liquor by evaporation to obtain sodium chloride in the third mother liquor; and

(e) returning the third mother liquor to a portion of the feed containing potash and sodium sulfate.

The invention allows to reduce costs, to obtain sulfate potassium free from insoluble substances. However, in this case, a product is obtained mainly containing potash K₂With₃, and, in addition, the method does not allow to obtain hydrogen fluoride.

The challenge facing the authors of the invention is to develop a method for processing spent potassium bifluoride (OBFK), which allows to obtain from potassium sulfate and hydrogen fluoride and / or hydrofluoric acid, i.e. products that are in commercial demand.

The essence of the invention lies in the fact that a method has been developed for processing spent potassium bifluoride to produce hydrogen fluoride and / or hydrofluoric acid and potassium sulfate, including: grinding spent potassium bifluoride, its treatment with sulfuric acid at a concentration of 95-100%, in a molar ratio of sulfuric acid: potassium bifluoride 1: 1.02; heating the resulting mass to 130-150 ° C, keeping the mixture for 3-4 hours with distillation of hydrogen fluoride and possibly absorbing it with water, neutralizing the mass remaining after distillation of hydrogen fluoride with an aqueous solution of potassium hydroxide or carbonate to pH 7-7.5, and drying the resulting potassium sulfate.

When heated and during the aging of the mixture, pure hydrogen fluoride is distilled off, which is collected and, optionally, all or part of it, is sent to absorption by water, passing through an adsorber with water, until the required concentration of hydrofluoric acid is collected, which is collected in a special collection.

After the stage of neutralizing the remainder of the mixture to a pH of 7-7.5 with an aqueous solution of potassium hydroxide or carbonate, pure potassium sulfate is obtained. The resulting potassium sulfate is dried to constant weight and collected in a hopper.

When carrying out the method are the main transformation of potassium salts:

1. KF⋅nHF + H ₂ SO ₄ ^___ KHSO ₄₊ (n + 1) HF

2. (a) KHSO ₄ + KOH → K ₂ SO ₄₊ H ₂ O

(b) 2KHSO ₄ + K ₂ CO ₃ → 2K ₂ SO ₄ + H ₂ O + CO ₂

OBFK is processed into hydrogen fluoride in a plant consisting of a sealed reactor with a capacity of 150 ml, which is equipped with a stirrer, a sulfuric acid dispenser, a droplet separator and a column, which are made of fluoroplastic - 4. The plant is equipped with a direct refrigerator, cooled to a temperature of minus 10 ° С and a container for trapping hydrogen fluoride. KHSO ₄ formed after distillation of hydrogen fluoride is transferred to a 0.5 L reactor made of polyethylene, equipped with a polypropylene stirrer, potassium alkali or potash dispenser.

EXAMPLE 1

1. Obtaining hydrogen fluoride and / or hydrofluoric acid

The spent potassium bifluoride (OBFK) is a composition containing about 90 wt.% Potassium fluoride KF • 0.75 HF, the rest is impurities (about 10 wt.%).

80 g of ground OPFK with a particle size of 0.5-3 mm are loaded into the reactor and 98 g of concentrated sulfuric acid grade XC is metered. The mixture is heated to 130 ° C at a speed that does not allow violent gas evolution at a heating rate of 20 ° C per minute. Then the mixture is heated to 150 ° C and stirred at this temperature for 3-4 hours.

The hydrogen fluoride (34 g) distilled during the experiment was collected in a trap.

To obtain 34 g of hydrogen fluoride (HF) consumes 100 g of sulfuric acid. The resulting hydrogen fluoride is collected in a fluoroplastic trap, cooled to -20 ° C. Then part of the hydrogen fluoride is sent to a container for absorption with distilled water.

Obtained by the absorption of hydrogen fluoride with distilled water, hydrofluoric acid has the parameters shown in table No. 1.

Table number 1

The name of the indicator, the content of residues in wt.% Norm for qual. "Chemically Pure", wt.% Product received
wt.% 1. acid residue, not less 45 45 2. residue after calcination of sulfates, not more than 0.0005 0.0005 3. sulfite, not more 0.0003 0.0003 4. sulfates, no more 0.0002 0.0002 5. phosphates, not more 0.0001 0.0001 6. chlorides, no more 0.0001 0.0001 7. iron, no more 0.00005 0.00005 8. silicon, no more 0.002 0.002 9. heavy metals, no more 0.00005 0.00003 10. substances that restore KMnO ₄ , no more 0.0004 0.0004

The resulting acid corresponds to the grade of qualification "ChP"

2. Neutralization of potassium hydrogen sulfate

From the reactor No. 1, cooled to 60-75 ° C, the resulting potassium hydrogen sulfate is discharged into a 0.5 liter polyethylene reactor, equipped with a jacket, an anchor stirrer made of polyethylene and an alkali dispenser. When the stirrer is on, a 20% KH grade KH solution is dosed to the mass, preventing the reaction mass from heating above 90-95 ° C until a pH of 7.5 is reached. After supplying 290 g of a KOH solution, the mixture was stirred for 2-3 hours at 90-95 ° C, and then filtered. The filtrate is cooled to + 5-0 ° C, the precipitated potassium sulfate is filtered off, dried at 140 ° C to constant weight. Received 80 g of potassium sulfate, the composition of which is presented in table No. 2.

Table number 2

The name of the indicator, the residue content in wt.%: Qualification rate, wt.% Product received
wt.% Pure for analysis, “CHDA” Clean
"H" 1. K ₂ SO ₄ , not less 98.0 97.0 98.0 2. substances insoluble in water, no more 0.005 0.02 0.005 3. ammonium salts, no more 0.002 0.004 0.002 4. nitrates, no more 0.002 0.004 0.002 5. chlorides, no more 0.001 0.002 0.001 6. iron, no more 0.0005 0.001 0.0005 7. arsenic, not more 0.0001 0.0004 0.0001 8. sodium, no more 0.15 0.15 0.15 9. calcium, no more 0.01 0.02 0.01 10. heavy. metals, no more 0.001 0.002 0.001 11. pH of a 5% solution 5.5-8.0 5.5-8.0 5.3-7.5

According to the main indicators, the product corresponds to the qualification "ChDA".

Example No. 2

Prepared OBFK is treated with sulfuric acid in the conditions of example No. 1, however, 107.5 g of industrial sulfuric acid are used (concentration 95.0%). Received 33.5 g of hydrogen fluoride, the composition of which is given in table No. 3.

Table number 3

Name of indicator, residue content, wt.% GOST requirements, wt.% The resulting product, wt.% 1. sulfur dioxide, no more 0.004 0.005 2. sulfuric acid, no more 0.005 0.0055 3. hydrofluoric acid, not more than 0.005 0.0053 4. residue after calcination in the form of sulfates, not more than
0.007
0.0079 5. substances that restore, no more 0.005 0.0061 6. chlorides, no more 0.001 0.002 7. phosphates, not more 0.001 0.0018

Upon absorption of hydrogen fluoride with distilled water (40 g), 73 g of hydrofluoric acid with a concentration of 45.2% are obtained. The composition of the obtained acid corresponds to the qualification of "ChP" and is given in table No. 4.

Table number 4

Name of indicator, residue content, wt.% Norm for qual. "Hc" The resulting product, wt.% 1. acid residue, not less 45 45 2. residue after calcination in the form of sulfates, not more than 0.0005 0.0005 3. sulfites, no more 0.0003 0.0003 4. sulfates, no more 0.0002 0.0002 5. phosphates, no more 0.0001 0.0001 6. chlorides, no more 0.0001 0.0001 7. iron, no more 0.00005 0.00005 8. silicon, no more 0.002 0.002 9. heavy metals, no more 0.00005 0.00003 10. substances that restore KMnO ₄ , no more 0.0004 0.0004

Example No. 3

The neutralization of potassium hydrogen sulfate is carried out in the same manner as in example No. 2, but up to pH 7.0, using a 20% solution of technical potassium hydroxide. After drying to constant weight, 80 g of salt is obtained, which is characterized by the indicators given in table No. 5.

Table number 5

The name of the indicator, the content of residues, wt.% Norm for qualifications Indicators CHDA "H" 1.K ₂ SO ₄ , not less 98 97 97.3 2. substances insoluble in water, no more 0.005 0.02 0.02 3. ammonium salts, no more 0.002 0.004 0.004 4. nitrates, no more 0.002 0.004 0.0037 5. chlorides, no more 0.001 0.002 0.0015 6. iron, no more 0.0005 0.001 0.001 7. arsenic, not more 0.0001 0.0004 0.0004 8. Mass fraction of sodium, no more 0.15 0.15 0.15 9. calcium, no more 0.01 0.02 0.021 10. heavy metals, no more 0.001 0.002 0.002 11. pH of 5% solution 5.5-8.0 5.5-8.0 5.3-7.5

The resulting potassium sulfate meets the qualification "H".

Example No. 4

The decomposition of OBFK is carried out with technical sulfuric acid analogously to example No. 3. The residue, potassium sulfate, is transferred to reactor 2 and neutralized with a 20% solution of technical K ₂ CO ₃ (potash) to pH 7.5, for the preparation of which 74 g of potash are dissolved in 280 ml of water. After drying the residue to constant weight, potassium sulfate (80 g) is obtained, which has the composition shown in table No. 5 and corresponds to qualification “H”.

Claims (1)

A method of processing spent potassium bifluoride, including grinding the spent potassium bifluoride, treating it with sulfuric acid at a concentration of 95-100% in a molar ratio of sulfuric acid: potassium bifluoride 1: 1.02, heating the resulting mass to 130-150 ° C, keeping the mixture for 3 -4 hours with distillation of hydrogen fluoride and, possibly, its absorption with water, neutralization of the remaining mass after distillation of hydrogen fluoride with an aqueous solution of potassium hydroxide or carbonate to pH 7-7.5 and drying of the resulting potassium sulfate.