RU2330811C2 - Method of obtaining high-purity lithium fluoride - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of obtaining high-purity lithium fluoride from processing lithium compounds, such as lithium carbonate or hydroxide, involves transition of the compounds to lithium hydrocarbonate solution by processing of their water solutions by carbon dioxide, sorption purification of the lithium hydrocarbonate solution by cation exchange resin, obtaining of purified lithium carbonate, its washing, preparation of water slurry of purified lithium carbonate, repeated bicarbonisation of water lithium carbonate slurry by carbon dioxide, obtaining of lithium hydrocarbonate solution, followed by fluorination, washing and drying of obtained lithium fluoride. Fluorination is implemented by slow addition and continuous stirring of lithium hydrocarbonate solution in a reactor filled with fluorine hydride with 10-30% stoichiometry excess. Lithium fluoride is washed by distilled water without CO₂ or by 1% solution of fluorine hydride. Lithium fluoride is dried in two stages in vacuum furnace, first stage drying temperature is under 100°C, and second stage drying temperature is under 150°C.

EFFECT: obtaining lithium fluoride with high content of the main substance.

3 ex, 2 tbl, 3 dwg

Description

The development of many modern "subtle technologies" is determined by the purity of the materials used. In industries such as microelectronics, radio engineering, nuclear power, there is a need for high-purity materials.

One of the sought-after lithium compounds is lithium fluoride (LiF). Lithium fluoride with a basic substance content of 99.5% and higher is used as a solvent for nuclear fuel (in the form of molten LiF), ionizing radiation detectors are made on the basis of lithium fluoride in thermoluminescent dosimetry. Lithium fluoride is also used to produce lithium hexafluorophosphate (GFFL) and lithium tetrafluoroborate (additives in non-aqueous electrolyte), which are used in the production of lithium-ion batteries.

Lithium fluoride single crystals are used in the manufacture of optical instruments used in the infrared and ultraviolet regions, as well as within the entire visible spectrum, where they are practically transparent for rays with a wavelength of up to 1000 Å, and have a constant dispersion throughout the entire visible spectrum.

LiF is used as a component of many fluxes in the smelting and welding of magnesium, aluminum and light alloys, in the production of aluminum in bauxite-cryolite baths; widely used in the production of lead-free glazes of glasses with high acid resistance and special optical properties.

Lithium fluoride can be obtained in various ways (Yu.I. Ostroushko and others. Lithium, its chemistry and technology. M., 1960), for example:

- by the method of neutralizing lithium hydroxide with hydrofluoric acid

- the method of neutralization of Li ₂ CO ₃ hydrofluoric acid

- NH ₄ F can be used as a fluorinating agent

Using these technologies, LiF of the “chda” grade TU 6-09-3529-84 was obtained, which has the following impurity analysis:

OM>99.0%; SO ₄ <1 · 10 ^-2 %; PO ₄ <5 · 10 ^-3 %; NO ₃ <5 · 10 ^-3 %; Cl <2 · 10 ^-3 %; K <1 · 10 ^-2 %; Na <1 · 10 ^-2 %; Ba <5 · 10 ^-2 %; Fe <1 · 10 ^-2 %; Si <2 · 10 ^-2 %; Pb <5 · 10 ^-3 %.

There is a patent RU 2104932, С01D 3/02, 1998 - a method for producing high-purity fluoride, where fluorination is carried out with gaseous hydrogen fluoride. The method of producing lithium fluoride according to patent RU 2104932 consists in treating oxygen-containing lithium compounds with hydrogen fluoride in an amount of 110-115% of stoichiometry for 3-4 hours at 300-350 ° C. As oxygen-containing lithium compounds, lithium oxide, hydroxide and carbonate are used.

The process of producing lithium fluoride is carried out in a 2-tubular horizontal apparatus having two screws for forced mixing and transportation of the solid product. The residence time of the product in the reaction zone of the apparatus can be changed depending on the speed of rotation of the screws from 1.2-3.8 rpm The productivity of such an apparatus for loading was 1 kg / h. Gaseous hydrogen fluoride is supplied countercurrent to the movement of the product and hydrogen fluoride is supplied at that time when the screws do not rotate, and therefore the product does not move in the reactor. After 15-20 minutes, the flow of hydrogen fluoride gas is stopped and stirring is carried out for 5-10 minutes and the product is moved by rotating the screws.

The need to choose this type of fluorination is explained by the fact that with the simultaneous supply of hydrogen fluoride and the movement of the product in the reactor, dust removal occurs. In the proposed method, it is almost absent, i.e. does not exceed 0.1%.

According to chemical and x-ray phase analysis, the reaction products are almost 100% lithium fluoride. Analyzes of spectral impurities and other measurements of lithium fluoride samples obtained by the gas method did not reveal deviations from the TU for these compounds. The resulting lithium fluoride has the following impurities:

Mo - 1.5 · 10 ^-3 %; Zr - 3.4 · 10 ^-3 %; Cu - 2 · 10 ^-4 ; Cr - 6.5 · 10 ^-4 %; Fe - 3 · 10 ^-3 %; N - 2.5 · 10 ^-3 %; Na - 8 · 10 ^-3 ; and has a 100% degree of fluorination. Product loss is 0.1%.

The disadvantage of this method is that it is difficult to find structural materials that are stable in the environment of hydrogen fluoride in the presence of released water during synthesis at a temperature of 300-350 ° C. The data of the analysis of the basic substance and the presence of impurities of lithium carbonate, which is formed in the presence of traces of water and temperatures indicated in the patent, are not given. For large-tonnage production, the proposed technology will be costly and “dirty” from an environmental point of view.

The closest method for producing high-purity lithium fluoride from industrial lithium carbonate, prototype, is US patent No. 6592832, class. C01D 015/00; С01D 003/00, 2003. The essence of the invention lies in the process of treating a solution of lithium carbonate with carbon dioxide using high pressure, purification, the resulting solution of lithium hydrogen carbonate on an ion exchange resin, de-carbonization, separation, a clean precipitate of lithium carbonate, washing, drying, repeated bicarbonization and obtaining lithium fluoride by the interaction of the obtained solution of lithium hydrogen carbonate with a solution of hydrogen fluoride with the addition of ammonia, washing and drying the obtained precipitate of lithium fluoride.

LiHCO ₃ + HF = LiF + H ₂ O + CO ₂

The resulting product has the following impurities: Al, Ca, Fe, K, Mg, Na less than or close to 1 mg / kg, Cl less than 5 mg / kg.

The disadvantage of the above invention is the addition of ammonia, which leads to contamination of the resulting product with ammonium cations. Also, the patent does not show the content of the basic substance, ammonium cations, carbon and moisture, which is often crucial for obtaining compounds such as hexafluorophosphate or lithium tetrafluoroborate from lithium fluoride.

The objective of the invention is to develop a highly efficient technology for the production of high-purity lithium fluoride with a basic substance content of at least 99.5% and a reduced amount of element-impurities determined.

The problem is solved due to the fact that the method of producing high-purity lithium fluoride from technical lithium compounds, including the conversion of technical lithium salts into a solution of lithium hydrogen carbonate by treating their aqueous solutions with carbon dioxide, sorption cleaning them on a cation exchange resin, obtaining purified lithium carbonate, washing it, preparing it water pulp of lithium carbonate, the repeated process of bicarbonization of water pulp of purified lithium carbonate with carbon dioxide and obtaining a solution of bicarbonate from it lithium, subsequent fluorination, washing and drying of the obtained lithium fluoride, according to the claims, technical lithium carbonates or lithium hydroxide are used as technical lithium compounds, fluorination is carried out by slow addition with constant stirring of a solution of lithium hydrogen carbonate in a reactor filled with a solution of hydrogen fluoride with 10-30% excess from stoichiometry, washing lithium fluoride is carried out with distilled water without CO ₂ or 1% solution of hydrogen fluoride, and its drying is carried out in two stages in a vacuum oven, n and that the drying temperature of the 1st stage is not higher than 100 ° C, and the drying temperature 2nd step - not higher than 150 ° C.

The indicated set of features according to the method for producing high-purity lithium fluoride is new and has an inventive step, since the use of technical carbonate or lithium hydroxide as a raw material makes it possible to clean them in a bicarbonate method using carbon dioxide in one technological scheme, obtain a solution of lithium hydrogen carbonate, and clean it with cation exchange resin, after which to obtain purified lithium carbonate, from which to obtain high-purity lithium fluoride. Adding a solution of lithium hydrogen carbonate to a solution of hydrogen fluoride allows you to get a precipitate of lithium fluoride with a high content of the main substance. This is explained by the fact that during the deposition of lithium fluoride, the precipitator - fluorine ion is in excess, and a limited amount of lithium cations enters the solution. In view of the fact that the solubility of lithium fluoride is 1.3 g / l, and lithium carbonate is 13 g / l, a lithium fluoride crystal is primarily formed without capturing the carbonate ion. This method of adding solutions allows the excess precipitant to be reduced to a minimum value.

The proposed method of optimal drying modes in two stages allows avoiding the carbonization process and obtaining lithium fluoride of the required quality with a low content of elemental impurities, since the first stage is the removal of the main moisture, and the second stage is the destruction of LiF · HF and removal of HF.

With other methods of drying a wet precipitate of lithium fluoride, the processes of reaction 8 and 9 can take place simultaneously during the first minutes. Upon receipt of the LiF precipitate after filtration and extraction, we actually have a number of the following compounds: LiF, LiF · HF, water, free HF, t .to. it is given in excess, LiOH - according to reaction (8), Li ₂ CO ₃ - according to reaction (9), because as a result of hydrolysis in micro quantities, the following processes are possible:

This explains the increased content of lithium carbonate, traces of lithium hydroxide, the unstable content of the basic substance and the inability to obtain a moisture content in lithium fluoride below 0.01%.

The use of distilled water without CO ₂ avoids an increase in the carbonate ion content in the resulting lithium fluoride. Since distilled water cannot be stored without CO _{2 for a} long time, it quickly absorbs carbon dioxide from the air, then a 1% hydrogen fluoride solution avoids this drawback.

Figure 1 presents the results of x-ray phase analysis obtained in example 1, lithium fluoride. The amount of impurities does not exceed 0.1%.

Figure 2 shows the data of fractional analysis obtained in example 1, lithium fluoride. Fractional analysis showed the uniformity of the obtained crystals.

Figure 3 presents the electron microscopic studies obtained in example 1, lithium fluoride. A micrograph of a sample of lithium fluoride showed the correct cubic shape of the obtained crystals.

Example 1

The method of obtaining high-purity lithium fluoride is as follows. The aqueous pulp of industrial lithium carbonate (or a solution of technical lithium hydroxide) is bicarbonized using carbon dioxide. After receiving a solution of lithium bicarbonate with a concentration of 42-43 g / l (lithium carbonate), it is filtered off and passed through a column with a cation exchange resin, where alkaline earth and non-ferrous metal cations are purified from impurities. After purification from impurities, the hydrocarbonate solution is de-carbonized at a temperature of 95-100 ° C, while the removed carbon dioxide is returned to the reactor to bicarbonize the next batch of lithium carbonate pulp or lithium hydroxide solution.

The resulting purified precipitate of lithium carbonate is filtered off, washed with distilled hot water T = 90-95 ° C, the aqueous pulp of purified lithium carbonate is prepared, the aqueous pulp of lithium carbonate is bicarbonated again with carbon dioxide and a lithium hydrogen carbonate solution is obtained. The resulting solution of lithium bicarbonate with constant stirring is slowly poured into a polymer reactor, which previously poured a solution of hydrogen fluoride with a 10-30% excess relative to stoichiometry. The precipitate of lithium fluoride is washed with distilled water without CO ₂ . Then dried in a vacuum oven in two stages. In the first stage, the main moisture is distilled off at a temperature not exceeding 100 ° С, in the second stage, the destruction of LiF · HF and the removal of HF at a temperature not higher than 150 ° С. Using this technology, lithium fluoride was obtained, which has the following composition (see table 1): OM - 99.8%; H ₂ O <0.01%;

Example 2. Shows the reverse order of addition of reagents, which affects the quality of the resulting lithium fluoride.

Technical lithium carbonate (or technical lithium hydroxide) is bicarbonized using carbon dioxide. After receiving a solution of lithium bicarbonate with a concentration of 42-43 g / l (lithium carbonate), it is filtered off and passed through a column with a cation exchange resin, where alkaline earth and non-ferrous metal cations are purified from impurities. After purification from impurities, the bicarbonate solution is de-carbonized at a temperature of 95-100 ° C, while the carbon dioxide removed is returned to the reactor to bicarbonize the next batch of lithium carbonate or hydroxide.

The resulting purified precipitate of lithium carbonate is filtered off, washed with distilled hot water T = 90-95 ° C, the aqueous pulp of purified lithium carbonate is prepared, the aqueous pulp of lithium carbonate is bicarbonated again with carbon dioxide and poured into a polymer reactor, after which a solution of hydrogen fluoride is fed into the reactor with constant stirring. with 10-30% excess of stoichiometry. The resulting lithium fluoride precipitate is filtered off and washed with distilled water without CO ₂ . Then dried in a vacuum oven in two stages. In the first stage, the main moisture is distilled off at a temperature not exceeding 100 ° С, in the second stage, LiF · HF is destroyed and HF is removed at a temperature not higher than 150 ° С. The resulting product had the following composition (see table 1. p. 2): OM - 99.5%; H ₂ O - 0.02%.

Table 1. Impurity content, ppm FROM Na TO Sa Mg Fe Pb Zn Si Cl ^- RO ₄ ^2- SO ₄ ^2- one <0.005% <3 <4 <2 <3 <3 <2 <10 <5 <10 <40 <30 2 0.1% 6 6 5 3 3 2 10 5 25 40 thirty

Example 3

The method of obtaining high-purity lithium fluoride is as follows. The aqueous pulp of industrial lithium carbonate (or a solution of technical lithium hydroxide) is bicarbonized using carbon dioxide. After receiving a solution of lithium bicarbonate with a concentration of 42-43 g / l (lithium carbonate), it is filtered off and passed through a column with a cation exchange resin, where alkaline earth and non-ferrous metal cations are purified from impurities. After purification from impurities, the hydrocarbonate solution is de-carbonized at a temperature of 95-100 ° C, while the removed carbon dioxide is returned to the reactor to bicarbonize the next batch of lithium carbonate pulp or lithium hydroxide solution.

The resulting purified precipitate of lithium carbonate is filtered off, washed with distilled hot water T = 90-95 ° C, the aqueous pulp of purified lithium carbonate is prepared, the aqueous pulp of lithium carbonate is bicarbonated again with carbon dioxide and a lithium hydrogen carbonate solution is obtained. The resulting solution of lithium bicarbonate with constant stirring is slowly poured into a polymer reactor, which previously poured a solution of hydrogen fluoride with a 10-30% excess relative to stoichiometry. The resulting lithium fluoride precipitate is filtered off and washed with a 1% hydrogen fluoride solution. Then dried in a vacuum oven in two stages. In the first stage, the main moisture is distilled off at a temperature not exceeding 100 ° С, in the second stage, the destruction of LiF · HF and the removal of HF at a temperature not higher than 150 ° С. Using this technology, lithium fluoride was obtained, which has the following composition (see table 1): OM - 99.8%; H ₂ O <0.01%;

Table 2. Impurity content, ppm FROM Na TO Sa Mg Fe Pb Zn Si Cl ^- RO ₄ ^2- SO ₄ ^2- <0.005% <3 <4 <2 <3 <3 <2 <10 <5 <10 <40 <30

Claims (1)

A method for producing high-purity lithium fluoride from technical lithium compounds, including the conversion of lithium technical compounds to a solution of lithium hydrogen carbonate by treating aqueous solutions of technical lithium compounds with carbon dioxide, their sorption purification on a cation exchange resin, obtaining purified lithium carbonate, washing it, preparing an aqueous pulp of purified lithium carbonate , the repeated process of bicarbonization of aqueous pulp of lithium carbonate with carbon dioxide and obtaining from it a solution of lithium hydrogen carbonate, followed by its fluorination, washing and drying of the obtained lithium fluoride, characterized in that technical lithium carbonate or lithium hydroxide is used as technical lithium compounds, fluorination is carried out by slow addition with constant stirring of a solution of lithium hydrogen carbonate in a reactor filled with a solution of hydrogen fluoride with 10-30% excess of stoichiometry, washing lithium fluoride is carried out with distilled water without CO ₂ or 1% hydrogen fluoride solution, and it is dried in two stages in a vacuum oven, while the drying temperature and the 1st stage is not higher than 100 ° C, and the drying temperature of the 2nd stage is not higher than 150 ° C.

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