RU2494964C1 - Method of obtaining beryllium fluoride - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in chemical industry. Beryllium fluoride is obtained by dissolution of beryllium-containing materials in hydrofluoric acid. Ammonium fluoride is introduced into initial solution before evaporation in amount, providing molar ratio of fluorine to beryllium within 2.06-2.18. After that, solution is evaporated in vacuum with rarefication 300-400 mm Hg and temperature 220 - 400 °C for 1-3 h. Obtained powder is melted at temperature 850 - 900°C until mented glass-like beryllium fluoride with density 1.9-2 g/cm³ is formed.

EFFECT: invention makes it possible to obtain glass-like melted beryllium fluoride with high density, which almost does not contain beryllium oxyfluoride.

3 cl, 2 tbl

Description

The invention can be used to obtain raw materials for reduction and refining melting of beryllium, inorganic chemistry, in particular, the production of beryllium fluoride.

Several methods are known for producing beryllium fluoride:

1. Hydrofluorination of calcined beryllium oxide with hydrogen fluoride at a temperature of 300-340 ° C in a batch mode [RU, Pat. 2104934, IPC ⁶ C01F 3/00]

2. Fluorination of beryllium oxyfluoride or beryllium carbide in a stream of elemental fluorine or hydrogen fluoride by thermal dissociation of ammonium fluoroberylate [Bleshinsky SV, Abramova VF, Druzhinin IG, Viner LR, Surgay VT Chemistry of beryllium. Frunze: Publishing House of the Academy of Sciences of the Kyrgyz SSR, 1955. P.41];

3. Calcination of magnesium fluoride with beryllium sulfate [Kolenkova MA, Crane O.E. Metallurgy of dispersed and light rare metals. M: Metallurgy, 1977. S.315.];

4. Dissolution of beryllium hydroxide in hydrofluoric acid, followed by evaporation of the solution [Everest D. Chemistry of beryllium. M .: Chemistry, 1968. P.49.].

The methods described in the literature did not find application in the production of beryllium due to the complexity of their hardware design, low technological parameters that do not guarantee the receipt of beryllium fluoride of the required quality.

On an industrial scale, a method for producing beryllium fluoride by decomposition of ammonium fluoroberylate at a temperature of 900-950 ° C according to method 2 is implemented.

$${{\text{(NH}}_{\text{four}}\text{)}}_{\text{2}}{\text{Bef}}_{\text{four}}\to {\text{Bef}}_{\text{2}}+{\text{2NH}}_{\text{3}}\uparrow +\text{2HF}\uparrow \text{(one)}$$

The decomposition process proceeds rapidly, accompanied by emissions of the melt, intensive release of aerosols of reaction products, which complicates the operation of the system for the technological capture of gases.

The closest analogue to the proposed method is the process of producing beryllium fluoride by dissolving beryllium hydroxide in hydrofluoric acid by the reaction:

$${\text{Be (OH)}}_{\text{2}}+\text{2HF}={\text{Bef}}_{\text{2}}+{\text{2H}}_{\text{2}}\text{O}\uparrow \text{(2)}$$

followed by evaporation of the solution. The method is described in the monograph: Everest D. Chemistry of beryllium. M .: Chemistry. S.49.

The disadvantage of this method of producing beryllium fluoride is the high content of beryllium oxyfluoride in the final product. It is practically impossible to obtain high-quality beryllium fluoride without an admixture of oxyfluoride by simple evaporation of fluoride solutions. An attempt to use an excess of hydrogen fluoride or hydrofluoric acid in the process of evaporation of solutions to reduce the content of oxyfluoride in the final product (BeF ₂ ) does not lead to positive results.

It is known that beryllium fluoride in aqueous solutions is partially hydrolyzed, the presence of water in the reaction products leads to the formation of beryllium oxyfluoride by the reaction:

$$Be{F}_2+H_{2}O=BeOHF+HF\uparrow \left(3\right)$$

Therefore, in the process of evaporation of the BeF ₂ solution, due to a shift in the equilibrium of reaction (3), a powder is obtained to the right with a beryllium oxyfluoride content of up to 10% (to beryllium). In this case, the density of beryllium fluoride decreases from 2.0 g / cm ³ to 0.02 g / cm ³ - the result of the polymorphic conversion of BeF ₂ [Novoselova A.V., Batsanova L.R. Analytical chemistry of elements. Beryllium. M .: Nauka, 1966. P.23], which is accompanied by a sharp increase in volume (volumetric effect with a “+” sign), the so-called phenomenon of “swelling”. When using beryllium fluoride with a low density, the fill factor of the furnace decreases and its transfer to the gas treatment system increases.

In addition, the use of beryllium fluoride containing oxyfluoride in the process of reductive melting of beryllium causes side reactions, reduces the amount of heat generated, increases the viscosity of the melt, which prevents a high-quality phase separation. This, in turn, reduces the yield of beryllium, increasing its turnover, worsens the technical and economic indicators of production by increasing the consumption of reagents, energy, watering, etc.

The technical result is to obtain glassy fused beryllium fluoride with a high density, practically free of beryllium oxyfluoride, and meeting the requirements of modern beryllium production.

The technical result is achieved by dissolving the materials containing beryllium in hydrofluoric acid, followed by evaporation of the solution. Ammonium fluoride is added to the initial solution of beryllium fluoride before evaporation in an amount providing a molar ratio of fluorine to beryllium in the range 2.06-2.18, after which the solution is evaporated under vacuum at a pressure of 300-400 mm Hg. (0.04-0.06 MPa), at a temperature of 220-400 ° C for 1-3 hours to obtain beryllium fluoride powder with a density of 0.75-0.9 g / cm ³ and an oxyfluoride content of not more than 0.3% to beryllium. The beryllium fluoride powder is melted at a temperature of 850-900 ° C to obtain a fused glassy beryllium fluoride with a density of 1.9-2 g / cm ³ .

The essence of the process is that in the presence of hydrofluoric acid used to dissolve the starting material, ammonium fluoride passes into a more stable compound - ammonium bifluoride (NH ₄ HF ₂ ). In the process of evaporation of the solution, it plays the role of an HF accumulator, inhibits the hydrolysis of beryllium fluoride, shifts the equilibrium of reaction (3) to the left, and thereby contributes to a decrease in the content of beryllium oxyfluoride in the finished product and an increase in its density. Carrying out the evaporation process in the optimal mode: temperature 360-375 ° C, residual pressure 0.04-0.06 MPa, (300-400 mm Hg) time 1-2 hours, followed by melting of the powder at a temperature of 900 ° C leads to fused beryllium fluoride with a content of oxyfluoride to beryllium in the range of 0.18-0.25% and a density of 1.9-2 g / cm ³ .

An example implementation of the method.

The initial solution of beryllium fluoride is obtained by dissolving metallic beryllium (99.0%) in hydrofluoric acid (conc. 40%) by the reaction:

$$\text{Be}+\text{2 hf}={\text{Bef}}_{\text{2}}+{\text{H}}_{\text{2}}\uparrow \text{(four)}$$

The characteristics of the resulting solution are given in table 1.

Table 1 Characterization of the beryllium fluoride stock solution Be content, g / dm ³ F / Be molar ratio The content of beryllium oxyfluoride,% of the original Be 78.5 2.0 0,0

In each experiment, 50 ml of the solution is taken and a different amount (0.06-0.18 mol F per mole of Be) of ammonium fluoride (analytical grade) is added in the form of dry salt. To assess the effect of the molar ratio of fluorine to beryllium on the quality of the obtained beryllium fluoride, part of the experiments is carried out without adding ammonium fluoride. The resulting solutions are evaporated in an oven at a temperature in the range of 220-400 ° C. Moisture and gases are removed by evacuation at a vacuum of 300-400 mm Hg. After a certain exposure time at a given temperature (0.67-7 h), the obtained powders are cooled (to room temperature), analyzed for the content of beryllium, beryllium oxyfluoride (BeOHF) and their bulk density is determined. Then, the obtained powders are heated to a temperature of 900 ° C (5-7 min). Upon completion of the heating and cooling operation, the volumetric effect of the conversion of the powder into the finished product is evaluated. The experimental results are shown in table 2.

From an analysis of the data given in Table 2, it follows that during the evaporation of the initial solution of beryllium fluoride without adding ammonium fluoride (molar ratio F / Be = 2) in the temperature range from 220 to 400 ° C and the duration of the process from 7 h to 40 min (respectively) obtained powders containing 5.5-5.8% beryllium oxyfluoride (% to Be), with a bulk density of 0.3-0.5 g / cm ³ . Subsequent heating of these powders to 900 ° C led to an increase in their volume by about 7–8 times.

When ammonium fluoride is added to the initial solution in an amount of 0.06-0.18 mol F / mol Be (total molar ratio F / Be = 2.06-2.18) in the temperature range 360-375 ° C and the duration of evaporation 2 and For 1 h (respectively), powders with a rather low content of beryllium oxyfluoride (<0.3% to beryllium) and the highest density (0.75-0.9 g / cm ³ ) were obtained. The indicated parameters of the evaporation process also ensured effective removal of the reaction products (the residual NH ₄ F content in the powder is less than 3.5% of beryllium). During the subsequent melting of these powders at a temperature of 900 ° C, “swelling” did not occur. The density of glassy fused beryllium fluoride was 2 g / cm ³ .

The introduction of more ammonium fluoride (> 0.18 mol F / mol Be), as well as an increase in temperature of more than 400 ° C during the evaporation of the solution does not contribute to a better powder.

As initial products for producing beryllium fluoride can be used: metallic beryllium, various inorganic compounds of beryllium, as well as waste containing beryllium.

Claims (3)

1. A method of producing beryllium fluoride by dissolving beryllium-containing materials in hydrofluoric acid, followed by evaporation of the solution, characterized in that ammonium fluoride in an amount providing a molar ratio of fluorine to beryllium in the range of 2.06- is added to the initial solution of beryllium fluoride 2.18, after which the solution is evaporated under vacuum at a pressure of 300-400 mm Hg, temperature 220-400 ° C for 1-3 hours to obtain beryllium fluoride powder, which is subjected to melting at a temperature of 850-900 ° C for getting melt glassy beryllium fluoride with a density of 1.9-2 g / cm ³ . 2. The method according to claim 1, characterized in that when the solution is evaporated, beryllium fluoride powder is obtained with a density of 0.75-0.9 g / cm ³ and an oxyfluoride content of not more than 0.3% to beryllium. 3. The method according to claim 1, characterized in that as the materials containing beryllium, to obtain beryllium fluoride can be used metallic beryllium.