RU2424189C1 - Method of producing high-purity strontium fluoride - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: invention relates to production of strontium fluoride used in production of ceramics, fluoride glass and fibre-optic materials. Before fluorination, aqueous strontium nitrate solution is purified from metal impurities by mixing with aluminium nitrate nano-hydrate at a rate of 50-80 rpm, where the said aluminium nitrate nano-hydrate is taken in amount of 2% of the weight of anhydrous strontium nitrate. The formed solution is leached to pH 8.0-8.2, heated to 60-70C and the aqueous solution is then separated from the precipitate on a vacuum filter. The purified aqueous strontium nitrate solution is fed into a reactor for the fluorination step together with 5-25% hydrofluoric acid and with 10% stoichiometric excess. The process is carried out at temperature 50-60C while stirring at a rate of 700-900 rpm. The filtered product is washed with water and then dried at temperature 120-150C. ^ EFFECT: invention enables to obtain high-purity strontium fluoride containing over 99,9 wt % basic substance, which meets requirements for fibre-optic products. ^ 4 cl, 2 ex

Description

The invention relates to a technology for the production of alkaline earth metal fluorides, in particular high purity strontium fluoride, which is used as a feedstock for optical ceramics, optical glass melting, and the production of laser materials.

Three basic methods are known for the synthesis of alkaline earth metal fluorides, including strontium fluoride. These are the so-called liquid-phase, gas-phase and solid-phase methods. The liquid phase method is carried out using liquid phase fluorinating agents, for example, hydrofluoric, fluorosulfonic, hydrofluoric acids, aqueous solutions of ammonium fluoride, alkali metal fluorides. The gas-phase method is carried out using gas-phase fluorinating agents, for example gaseous fluorine, hydrogen fluoride. The solid-phase method, proceeding on the basis of the solid-phase synthesis reaction from solid fluorine-containing compounds, is carried out, for example, from alkali metal fluorides and solid metal-containing compounds, for example, alkaline earth metal chlorides. A common drawback of gas-phase and solid-phase methods is the high energy intensity of the processes, explained by high synthesis temperatures (of the order of 600-1000 ° C and above). For example, it is known to obtain strontium fluoride by heating a mixture of strontium chloride and potassium fluoride to a temperature of about 600-750 ° C in the presence of 5-10 wt.% Hydrofluoric acid, followed by cooling the melt at a certain speed (300-500 ° C per hour) to obtain homogeneous powder with a grain size of the order of 20 microns [SU 632653, C01F 11/22, 1978). As a prototype method, another known method of producing strontium fluoride is selected, which according to the technology differs significantly from the new method, but concerns the production of a high-purity product. Strontium fluoride by a known method is obtained from alkali metal fluoride, for example sodium fluoride dihydrate, and strontium chloride. This process is carried out in a pyrographic reactor, which is calcined before vacuum in a vacuum at a temperature of about 1300 ° C, and then the cooled reactor is washed with hydrofluoric acid, a thin layer of which is deposited on the surface of the reactor. The main fluorination stage is carried out at a temperature of 750 ° C for 3 hours (SU 802178, СВВ 9/08, 1981). Obtained by this method, strontium fluoride contains a basic substance of more than 99.5 wt.% And limited impurities (Si, Pb, Mn, Cu, Fe, Cr, Ni, Na, K) at the level of 0.05-0.001 wt.% (Of each element )

The main disadvantages of the prototype method are the high synthesis temperature, which leads to contamination of the resulting product with structural materials, and the insufficient purity of the final product, which does not meet modern requirements for high purity products.

The purpose of the new method was to develop a low-energy, efficient process for producing high-purity strontium fluoride, which in its purity meets the requirements of modern branches of technology.

A new method for producing high-purity strontium fluoride is carried out by reacting 5-25% hydrofluoric acid with a pre-purified aqueous solution of strontium nitrate, which is purified by contacting with aluminum nitrate nanohydrate, taken in an amount of 2 wt.% Calculated on dry strontium nitrate, and with stirring at a speed of 50-80 rpm, followed by alkalization to pH 8.0-8.2 and filtration on a vacuum filter, the purified solution of strontium nitrate and hydrofluoric acid taken with 10% and to the stoichiometry, it is fed simultaneously in parallel flows to the reactor and stirred at a temperature of 50-60 ° C at a speed of 700-900 rpm, after which the precipitated strontium fluoride precipitate is separated, washed with high-purity water, dried at a temperature of 120-150 ° C.

At the stage of purification of strontium nitrate, filtration is carried out on a vacuum filter with a filter cloth and a membrane of grade PVC-0.25 or SPA-0.25.

The synthesized strontium fluoride is dried at 120-150 ° C, preferably for 5-6 hours.

All stages of obtaining high-purity strontium fluoride are carried out in a multi-section device equipped with a filter for air purification.

An essential feature of the new method is the use as a starting strontium-containing compound of highly soluble strontium nitrate, previously purified in a reactor located in a single multi-section device, placed in a box equipped with a filter for air purification.

The modes of the stage of purification of strontium nitrate, namely the amount of aluminum nitrate nanohydrate used (2 wt.% Of the mass of anhydrous strontium nitrate), mixing speed (50-80 rpm), pH of the stage of coprecipitation of impurities (pH 8.0-8.2) , the temperature at the final stage of processing (60-70 ° C), as well as the type of vacuum filter (with a filter cloth and a membrane of the PVC-0.25 or SPA-0.25 brand), all together provide optimal cleaning of the starting strontium nitrate from impurities of metals.

As a cleaning product, pure crystalline aluminum nitrate nanohydrate is used, for example, chemically pure grade or chda, which is mixed with a solution of starting strontium nitrate of reactive purity, optimally with a 20% solution. After alkalizing this mixture with, for example, high-purity 10% sodium hydroxide, a precipitate of hydrated alumina forms, which acts as a collector on which metal impurities present in the starting strontium nitrate are deposited. After the last stage of filtration, high-purity strontium nitrate is released, which according to the results of chemical spectral analysis contains the following impurities (wt.%): Fe 0.00001-0.000005, Mn, Cr, Ni, Cu <0.000001 (each), Co 0.0000005.

The main stage of fluorination is carried out in a reactor made of fluoroplastic, with optimally selected modes: at a temperature of 50-60 ° C, a stirring speed of 700-900 rpm and when using 10% of stoichiometry the amount of high purity hydrofluoric acid, as well as temperature drying, washed previously with high purity water, obtained strontium fluoride. Carrying out the fluorination process under these conditions ensures high efficiency of the fluorination process itself, and also provides the preparation of finely dispersed high-purity strontium fluoride containing 99.9 wt.% Of the basic substance and limited impurities (wt.%): Fe 0.00005, Mn, Cu, Cr , Ni <0.000005 (each), Co 0.000001 with a particle size distribution of 3-30 μm.

Below the invention is illustrated by the following examples.

Example 1

An initial 20% aqueous solution of strontium nitrate, in an amount of 500 ml, prepared by dissolving reactive purity strontium nitrate in distilled water, is poured into a reactor made of organic glass and equipped with a stirrer. Then, 2 g of crystalline grade aluminum crystalline nanohydrate of chemically pure grade are introduced into the reactor, stirred at a speed of 50 revolutions per minute until the crystals are completely dissolved and a 10% solution of sodium hydroxide os. 18-3 to a pH of 8.0, mix the contents until a precipitate of hydrated alumina is formed, after which the reaction mixture is heated to 60 ° C, kept at this temperature and cooled to room temperature. The resulting suspension is separated on a vacuum filter with a filter cloth and a PVC-0.25 membrane. A purified solution of strontium nitrate is obtained, which according to the results of chemical spectral analysis contains impurities (wt.%): Fe 0.00001, Mn, Cu, Cr, Ni <0.000001 (each), Co 0.0000005.

Next, the fluorination process is carried out in a fluoroplastic reactor equipped with a stirrer, into which at the same time 20% solution of purified strontium nitrate (500 ml) and a solution of 5% hydrofluoric acid are fed in parallel flows. 27-5 (570 g). Fluorination is carried out at 50 ° C and a stirring speed of 700 rpm. After the stirrer is turned off and the reaction mixture is cooled to room temperature, the crystals of strontium fluoride formed are separated on the filter from the porous fluoroplastic, washed with high-purity water until nitrate ions are completely removed (by reaction with diphenylamine) and dried in a platinum cup at 120 ° C for 5 hours . Strontium fluoride (58 g) is obtained containing 99.9 wt.% Of the basic substance and impurities (wt.%): Fe 0.00005, Mn, Cu, Cr, Ni <0.000005 (each) and Co 0.000001. Granular composition of 3-30 microns.

Example 2

The process is carried out analogously to example 1, changing only some of the parameters listed below.

The process of purification of a solution of strontium nitrate is carried out with stirring with aluminum nitrate nanohydrate at a speed of 80 revolutions per minute, and the stage of alkalization with sodium hydroxide is carried out to pH 8.0. After the formation of a precipitate of hydrated alumina, the reaction mass is heated to 70 ° C, maintained and cooled, after which the suspension is separated on a vacuum filter with a filter cloth and a SPA-0.25 membrane.

The process of fluorination of purified strontium nitrate with 25% hydrofluoric acid (115 g) is carried out at a temperature of 60 ° C and at a stirring speed of 900 rpm. The drying process of the final strontium fluoride is carried out in a platinum cup at a temperature of 150 ° C for 6 hours.

Strontium fluoride (58 g) is obtained with a basic substance content of 99.9 and limited impurities (wt.%): Fe 0.00005, Mn, Cu, Cr, Ni <0.000005 (each), Co <0.000001. Granular composition of 3-30 microns.

Claims (4)

1. A method of obtaining high-purity strontium fluoride, including fluorination of an inorganic strontium salt with a fluorinating agent, washing the resulting product with pure water and drying, characterized in that a high-purity 5-25% hydrofluoric acid is used as a fluorinating agent, used with a 10% excess of stoichiometry, and as a strontium-containing salt an aqueous solution of strontium nitrate is used, which is preliminarily purified by contacting with stirring at a speed of 50-80 rpm with pure m of aluminum nitrate nanohydrate, taken in an amount of 2 wt.% by weight of dry strontium nitrate, subsequent alkalization to pH 8.0-8.2, heating the resulting reaction mass at 60-70 ° C and filtering the precipitated precipitate on a vacuum filter moreover, during the fluorination process, both reactants are fed into the reactor simultaneously in parallel streams and stirred at a temperature of 50-60 ° C at a speed of 700-900 rpm, after which the strontium fluoride obtained is washed with high-purity water and dried at a temperature of 120-150 ° C. 2. The method according to claim 1, characterized in that the filtration at the stage of purification of strontium nitrate is carried out on a vacuum filter with a filter cloth and a membrane brand PVC-0.25 or SPA-0.25. 3. The method according to claim 1, characterized in that the drying process of strontium fluoride is carried out at a temperature of 120-150 ° C for 5-6 hours 4. The method according to claim 1, characterized in that the process is carried out in a multi-sectional device placed in a box equipped with a filter for air purification.