RU2715225C1 - Method of quantitative determination of lithium halides in lithium electrolyte for thermal chemical sources of current - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to analytical chemistry, specifically to methods of determining concentration of electrolyte components for thermal chemical current sources (TCCS), and can be used for determination of halogenides of alkali metals at their joint presence in solid lithium electrolytes. For this purpose grinding of solid sample of electrolyte is preliminary grinding, then taken and ground samples of solid lithium electrolyte are directed to separate stages of consecutive determination of fluorides, bromides and chlorides. To determine mass fraction of fluorides gravimetric method is used after preliminary fusion of ground sample with complex reagent from carbonate salts of potassium and sodium and further leaching mixture with hot distilled water. Precipitate of aluminum and silicon impurities is separated and neutralized with hydrochloric acid (HCl), then with nitric acid (HNO₃) at temperature not exceeding 40 °C. Fluorides are concentrated by precipitation with lead acetate solution, lead fluorochloride is washed at pH 3.5–4.6, then dried and weight fraction of fluorides is determined by formula:

,

where C_F is mass fraction of fluorides, %; m_F is weight of produced lead fluorochloride precipitate, g; m_nF is weight of sample of electrolyte taken during analysis for fluoride content, g; 0.0726 is conversion factor of lead fluorochloride weight per weight of fluoride; 200 – capacity of volumetric flask with electrolyte solution, cm³; 100 is volume of aliquot of electrolyte solution, cm³. In the absence of an aluminum-containing thickener in the electrolyte, the mass fraction of fluorides is determined by potentiometric titration with a fluoride-selective electrode. For this purpose, a portion of the ground sample is dissolved in a diluted HCl solution, into which a fluoride-selective and auxiliary electrodes are placed, and while continuously stirring on a magnetic mixer, titration of fluorides from the glass buret is carried out with a solution of lanthanum nitrate to an equivalence point according to a pH meter-ionomer; mass fraction of fluorides is calculated by formula:

,

where C_F is weight fraction of fluorides, %; V_La is volume of nitrate lanthanum solution, consumed for titration, cm³; m_nF is weight of sample of electrolyte taken during analysis for content of fluorides in absence of aluminum, g; T_La-F is mass concentration of lanthanum nitrate solution by fluoride, mg/cm³. To determine weight fraction of bromides in electrolyte water solution of ground sample of solid lithium electrolyte is prepared with addition of concentrated sulfuric acid (H₂SO₄) with subsequent addition of solution with mixture of potassium iodate and sodium thiosulphate. Reaction of lithium bromide with potassium iodide results in production of bromine, its removal by boiling and titration of excess potassium iodide to determine mass fraction of bromides by iodometric method by formula:

,

where C_Br is mass fraction of bromides in electrolyte, %; 10 is volume of iodine nitrate solution added in excess of potassium iodate, cm³; m_nBr is weight of sample of electrolyte, taken during analysis for content of bromides, g; C_K-Br is mass concentration of potassium iodate solution in terms of bromide, mg/cm³. To determine weight ratio of chlorides in electrolyte, difference is determined between total value of weight fractions of bromides and chlorides determined by mercurimetric titration in acid medium with indicator diphenylcarbazone, and preset mass fraction of bromides in sample, which is installed during titration of mercury (I) with nitric-acid. Then, volume difference of mercury (I) nitric-acid for titration of chlorides is calculated from difference of volumes and mass fraction of chlorides in lithium electrolyte corresponding to this value is calculated by formula:

,

where C_Cl is weight fraction of chlorides in electrolyte, %;

is volume of solution of mercury (I) nitric-acid, consumed for titration of sum of chlorides and bromides, cm³;

– volume of mercury (I) nitric-acid solution, consumed for bromides titration, cm³:

– mass concentration of nitric acid solution of mercury chloride and bromide, mg/cm³;

is mass fraction of bromides in electrolyte, %; m_nCl is a charge of electrolyte taken during determination of chlorides, g.

EFFECT: invention provides high accuracy of determining individual concentrations of lithium halides in the presence of aluminum salts in solid lithium electrolyte.

1 cl, 7 tbl, 2 ex

Description

The present invention relates to the field of analytical chemistry, and in particular to methods for determining the concentration of electrolyte components for thermal chemical current sources (TCIT) and can be used to determine alkali metal halides when they are present in solid lithium electrolytes.

The urgency of the problem to be solved is based on the need to determine individual concentrations of lithium halides in the development and study of lithium electrolyte compositions for TCIT in electrolyte masses, in which there are simultaneously chlorides, bromides, lithium fluorides and thickeners based on complex aluminum salts. The difficulties of this definition are that these elements are representatives of one group of elements - a group of halogens and have similar chemical properties. By traditional analytical methods, the determination of impurity concentrations of halogens, both in the joint presence and separately, was realized using a combination of physicochemical methods: neutron activation, X-ray spectral, or mass spectrometric methods of analysis, atomic emission spectrometry with induction-coupled plasma. Such methods are complex and quite long in time (labor-intensive), and are not always available for implementation.

An analysis of the selected patent information showed that the problem of the selective determination of the content of the individual components of complex mixtures is solved by a combination of polysyllabic extraction steps, potentiometric titration using a combination of indicator ion-selective and comparative electrodes.

From the prior art, a method is known for separately determining anionic, cationic and nonionic surface-active substances (SAWs) by potentiometric titration of test samples using an ion-selective solid-state indicator electrode and a comparative silver chloride electrode and using different titrants for anionic, cationic and nonionic compounds, respectively (RF patent No. 2111110 IPC G01N 27/42, published on November 10, 1999)

A known method for determining the concentration of fluoride ions in water (RF patent No. 2331873, IPC G01N 27/42, publ. 08/20/08) using for measuring the background electrolyte, which was selected as an aqueous solution of reactive nitric acid, a fluoride selective electrode .

Known as a prototype of the proposed method for the separate determination of chloride-containing compounds in their joint presence (RF patent No. 2210767, IPC G01N 31/16, publ. 08/20/03), according to which the concentration of chloride-containing compounds is carried out by liquid extraction using dimethylformamide as a differentiating solvent in various volume ratios to the extract, followed by potentiometric titration of the extract with a solution of KOH in ethyl alcohol.

The disadvantages of analogues include the lack of the possibility of separate determination of lithium halides similar in chemical properties when they are combined in solid samples of lithium electrolyte for TCIT containing additional aluminum compounds.

The objective of the authors of the invention is to develop a method for the selective determination of lithium halides in a solid electrolyte with their joint presence and in the presence of aluminum compounds.

The technical result provided by using the present invention is to enable the determination of individual concentrations of alkali metal halides and aluminum salts when they are present together in a solid lithium electrolyte, to increase the accuracy of their determination, to reduce the duration of the process and simplify.

The technical result is achieved by the fact that, in contrast to the known method for determining halogen-containing compounds, including sample preparation, the determination of individual concentrations of halogen ions according to the invention is carried out by preliminary grinding by grinding a solid electrolyte sample, then the selected and crushed samples of solid lithium electrolyte are sent to separate stages of sequential determination of fluorides, bromides and chlorides, at each of which cycles of specific operas tions:

- to determine the mass fraction of fluorides in the electrolyte, the gravimetric method is used after fusion of a sample of solid lithium electrolyte ground by grinding by grinding with a complex reagent from quartz sand and carbonic salts of potassium and sodium, leaching of the melt with hot distilled water, neutralization of the solution with mineral acids, sequentially with hydrochloric, then nitric acid, heating the solution to not more than 40 ° C; separating aluminum hydroxides by filtration; precipitating fluorides by contacting the solution lead acetic acid and washing the precipitate of lead fluorochloride at a pH in the range of 3.5-4.6, the day of the obtained precipitate and the final determination of the mass fraction of fluorides by the mathematical formula (1)

where C _F is the mass fraction of fluorides,%;

m _F - mass of the obtained precipitate of lead fluorochloride, g;

m _{n F} is the mass of a sample of the electrolyte taken in the analysis for fluoride content, g;

0,0726 - conversion factor of the mass of lead fluoride chloride to the mass of fluoride;

200 - capacity of a volumetric flask with an electrolyte solution, cm ³ ;

100 - the volume of an aliquot of the electrolyte solution, cm ³ .

In the absence of aluminum, a potentiometric titration method with a fluoride-selective electrode is used to determine fluorides. For this, a weighed sample of a solid lithium electrolyte sample is dissolved in a dilute hydrochloric acid solution, fluoride-selective and auxiliary electrodes are placed in the solution, and fluoride titration is carried out on a magnetic stirrer with constant stirring. from a glass burette with a solution of lanthanum nitrate with an indication of the equivalence point by the pH meter ionomer.

The calculation of the mass fraction of fluorides is carried out according to the formula (2)

where C _F is the mass fraction of fluorides,%;

V _{L a} - the volume of the solution of lanthanum nitrate used for titration, cm ³ ;

m _{n F} is the mass of a sample of the electrolyte taken in the analysis for the fluoride content in the absence of aluminum, g;

T _{L a -F} - mass concentration of a solution of lanthanum nitrate on fluoride, mg / cm ³ ;

- to determine the mass fraction of bromides in the electrolyte, an aqueous solution is prepared from a crushed sample of solid lithium electrolyte with the addition of concentrated sulfuric acid, followed by contacting the neutralized solution with a solution of potassium iodate (with a pre-determined volume ratio between solutions of potassium iodide and sodium sulfate), boiling for tile for 2 hours to remove the bromine formed, cooling, transferring to a flask, potassium iodine grained, allowing to stand in a dark place for the formation of iodine and titrating with a solution of sodium sernovatistokislogo to transition brown staining solution, straw-yellow, with the addition of a solution of starch and continuation titration until complete bleaching of the solution. The calculation of the mass fraction of bromides in the electrolyte was carried out according to the mathematical formula (3)

where C _Br ) is the mass fraction of bromides in the electrolyte,%;

10 - the amount of added in excess potassium iodate solution, cm ³ ;

m _{n Br} is the mass of a sample of the electrolyte taken in the analysis for the content of bromides, g;

C _K-Br - mass concentration of potassium iodate solution for bromide, mg / cm ³ ;

- to determine the mass fraction of chlorides in the electrolyte, the difference between the total mass fraction of bromides and chlorides determined by mercury titration in an acidic medium with a diphenylcarbazone indicator and the pre-determined mass fraction of bromides in the sample is determined, and the consumed volume of the titration reagent solution - mercury (I) is determined nitric acid for titration of the sum of chlorides and bromides, determine the consumed volume of mercury (I) nitric acid for titration of bromides, after which the difference in volumes asschityvayut consumed amount of mercury (I) nitrate titration for chloride, and determine the corresponding value of the mass fraction of lithium chloride in the electrolyte by the formula (4)

where C _Cl is the mass fraction of chlorides in the electrolyte,%;

- объем раствора ртути (I) азотнокислой, израсходованный на титрование суммы хлоридов и бромидов, см³;

- the volume of a solution of mercury (I) nitric acid spent on titration of the sum of chlorides and bromides, cm ³ ;

- объем раствора ртути (I) азотнокислой, израсходованный на титрование бромидов, см³:

- the volume of a solution of mercury (I) nitrate used for titration of bromides, cm ³ :

- массовые концентрации раствора ртути азотнокислой по хлориду и по бромиду, мг/см³;

- mass concentration of a solution of mercury nitric acid in chloride and bromide, mg / cm ³ ;

- массовая доля бромидов в электролите, %;

- mass fraction of bromides in the electrolyte,%;

m _{n Cl} - electrolyte sample taken in the determination of chlorides, g.

The inventive method for determining lithium halides in lithium electrolyte for thermal chemical current sources is illustrated as follows.

Initially, a sample of the analyzed solid lithium electrolyte is analyzed for TCIT, for which it is ground by grinding a solid electrolyte sample to a powder state, i.e. carry out the so-called "sample averaging". Then, the selected and ground samples of solid lithium electrolyte, in which both bromides, and fluorides and lithium chlorides are present, as well as a thickener substance based on aluminum salts, are sent to separate stages for sequential determination of fluorides, bromides and chlorides. Then, the mass fraction of fluorides is determined by the gravimetric method (in the presence of aluminum).

To determine the mass fraction of fluorides in the electrolyte, the gravimetric method is used after preliminary fusion of the crushed sample of solid lithium electrolyte together with a complex reagent from quartz sand and carbonic salts of potassium and sodium, leaching of the melt with hot distilled water, neutralization of the solution with mineral acids, successively hydrochloric, then nitric acid, heating solution to not more than 40 ° С, separation of aluminum hydroxides by filtration, precipitation of fluorides by contact with the solution ohm lead acetate and lead ftorhlorida washing the precipitate at a pH in the range 3.5-4.6, and the final determination of the mass fraction of fluorides on the mathematical formula (1)

where C _F is the mass fraction of fluorides,%;

m _F - mass of the obtained precipitate of lead fluorochloride, g;

m _{n F} is the mass of a sample of the electrolyte taken in the analysis for fluoride content, g;

0.0726 is the conversion factor for the mass of lead fluoride chloride per mass of fluoride;

200 - capacity of a volumetric flask with an electrolyte solution, cm ³ ;

100 - the volume of an aliquot of the electrolyte solution, cm ³ .

Thus, in the implementation of the above operations, aluminum compounds are removed from the medium of the reaction volume, in the presence of which the determination of fluorides is impossible. The selectivity of the proposed method is based on the fact that conduct fractional sequential analysis for each of the components of the lithium electrolyte. This order of operations is provided in the claimed method as optimal for eliminating the competitive interaction of the selected reagents with aluminum, bromides and chlorides. In the absence of aluminum compounds, fluorides are determined by potentiometric titration with a fluoride ion-selective electrode with a solution of lanthanum nitrate.

To determine the mass fraction of bromides in the electrolyte, an aqueous solution is prepared from a crushed sample of solid lithium electrolyte with the addition of concentrated sulfuric acid, followed by contacting the neutralized solution with a solution of potassium iodate (with a pre-determined volume ratio between solutions of potassium iodide and sodium sulfate), boiling on a tile within 2 hours to remove the bromine formed by cooling, transferring to a flask, potassium iodine supplement of allowing to stand in a dark place for the formation of iodine and titrating with sodium sernovatistokislogo to transition brown staining solution, straw-yellow, with the addition of a solution of starch and continuation titration until complete bleaching of the solution. The calculation of the mass fraction of bromides in the electrolyte was carried out according to the formula (3)

where C _Br ) is the mass fraction of bromides in the electrolyte,%;

10 - the amount of added in excess potassium iodate solution, cm ³ ;

m _{n Br} is the mass of a sample of the electrolyte taken in the analysis for the content of bromides, g;

C _K-Br is the mass concentration of potassium iodate solution for bromide, mg / cm ³ .

To determine the mass fraction of chlorides in the electrolyte, the difference between the total mass fraction of bromides and chlorides determined by mercury titration in an acidic medium with a diphenylcarbazone indicator and the pre-determined mass fraction of bromides in the sample is determined, and the consumed volume of the titration reagent solution - mercury (I) nitric acid is determined for titration of the sum of chlorides and bromides, the consumed volume of mercury (I) nitrate is determined for titration of bromides, after which the difference in the volume of read the volume consumed mercury (I) nitrate titration for chloride, and determine the corresponding value of the mass fraction of lithium chloride in the electrolyte by the formula (4)

where C _Cl is the mass fraction of chlorides in the electrolyte,%;

- объем раствора ртути (I) азотнокислой, израсходованный на титрование суммы хлоридов и бромидов, см³;

- the volume of a solution of mercury (I) nitric acid spent on titration of the sum of chlorides and bromides, cm ³ ;

- объем раствора ртути (I) азотнокислой, израсходованный на титрование бромидов, см³:

- the volume of a solution of mercury (I) nitrate used for titration of bromides, cm ³ :

- массовые концентрации раствора ртути азотнокислой по хлориду и по бромиду, мг/см³;

- mass concentration of a solution of mercury nitric acid in chloride and bromide, mg / cm ³ ;

- массовая доля бромидов в электролите, %;

- mass fraction of bromides in the electrolyte,%;

m _{n Cl} - electrolyte sample taken in the determination of chlorides, g.

Experimentally, the entire proposed sequence of operations for the separate determination of the content of lithium bromides, fluorides, and chlorides was tested in the above sequence, which ensured the possibility of their separate determination with acceptable accuracy of determination.

In the prototype method, there is an extraction step for the concentration of halogen, which is lengthy in relation to the analysis of mixtures containing bromides, chlorides and fluorides with their joint presence in the analyzed mixture, which would ultimately complicate the whole method.

Thus, as shown by experiments, when using the proposed method for the selective determination of lithium halides in an electrolyte, a new, higher, as compared with the prototype, result is provided, namely, the possibility of determining individual concentrations of alkali metal halides when they are combined in a lithium electrolyte, increasing the accuracy of their determination, reducing the duration of the process and simplifying the determination process.

The possibility of industrial implementation of the proposed method is confirmed by the following examples.

Example 1. In laboratory conditions, the proposed method was tested on the example of analysis of solid lithium electrolyte containing lithium halides and a thickener substance based on lithium aluminate. For this, a solid sample of electrolyte was taken, it was ground in an agate mortar using a pestle.

Determination of fluorides. To transfer a sample of a sample weighing approximately 0.500 g, they were fused with 6 g of the reagent potassium carbonate-sodium carbonate in the presence of quartz sand in a muffle furnace at a temperature of 850 ° C for 10 min. The resulting melt was leached with hot distilled water with additional heating. The solution was quantitatively transferred into a volumetric flask with a capacity of 200 cm ³ , the volume of the solution was adjusted to the mark with distilled water. To separate the precipitate of aluminum and silicon compounds, the resulting solution was filtered through a blue ribbon anesthetized filter. In the filtrate, fluorides were determined. An aliquot of the filtrate with a volume of 100 cm ^{3 was} placed in a glass, 1.1 cm ^{3 of a} solution of hydrochloric acid of a concentration of 4 mol / dm ³ , 3 drops of a solution of a methyl orange indicator were added, the sample solution was neutralized with a solution of nitric acid of a concentration of 4 mol / dm ³ until an orange-pink color appeared , then an excess of this acid with a volume of 1 cm ^{3 was} added. 0.5 cm ^{3 of} concentrated acetic acid was added, the beaker with the solution was heated to 40 ° C. Fluoride precipitation was carried out with a solution of lead acetic acid, adding it with stirring until the color changed from pink to orange. After a few minutes, a white precipitate of lead fluorochloride precipitated, which was kept at room temperature for at least 10 hours. Then, the precipitate was filtered off, washed with a saturated solution of lead fluorochloride, distilled water, and dried at 120 ° C to constant weight. Calculated the result of determining the mass fraction of fluorides (C _F ) in the sample as a percentage according to the formula

where C _F is the mass fraction of fluorides,%;

m _F - mass of the obtained precipitate of lead fluorochloride, g;

m _{n F} is the mass of a sample of the electrolyte taken in the analysis for fluoride content, g;

0,0726 - conversion factor of the mass of lead fluoride chloride to the mass of fluoride;

200 - capacity of a volumetric flask with an electrolyte solution, cm ³ ;

100 - the volume of an aliquot of the electrolyte solution, cm ³ .

The obtained values of m _{n F} , m _F and the results of unit determinations are shown in table 1.

.Mass fraction of fluorides in the electrolyte, defined as the average of the three results of parallel determinations was

.

Determination of the mass fraction of bromides. To transfer into the solution a sample of an electrolyte weighing from 0.040 to 0.080 g was placed in a glass and dissolved in 40 cm ^{3 of} distilled water with the addition of 1 cm ^{3 of} concentrated sulfuric acid. Then, 10 cm ³ of potassium iodate solution with a molar concentration of 0.0166 mol / dm ³ with a pre-determined volumetric ratio between potassium iodide solution and sodium sulfate solution (C) was added. The solution in a glass was boiled on a stove for 2 hours to remove the resulting bromine. After cooling, the solution was transferred to a titration flask, 2 g of potassium iodide was added, the flask was closed with a stopper and placed in a dark place to form iodine. After five minutes, the iodine in the flask was titrated with a solution of sodium sulfate until the solution turned brown to straw yellow, then 1 cm ³ of starch solution was added and titration was continued until the solution was completely discolored. The volume of sodium sulfate solution consumed for titration of an excess of potassium iodate, V _{N a} , cm ^{3 was} fixed. The calculation of the results of determining the mass fraction of bromides in the electrolyte (C _Br ),%, was carried out according to the formula

where 10 is the volume of added in excess potassium iodate solution, cm ³ ;

m _{n Br} is the mass of a sample of the electrolyte taken in the analysis for the content of bromides, g;

C _K-Br - pre-determined mass concentration of potassium iodate solution for bromide, mg / cm ³ .

The obtained values of m _{n Br} , V _{N a} , C _K-Br and the results of single determinations of C _Br are shown in table 2.

.Mass fraction of bromide in the electrolyte, defined as the average of three parallel determinations was

.

и по бромиду -

. Затем устанавливали объем раствора ртути (I) азотнокислой, израсходованный на титрование суммы хлоридов и бромидов,

см³. Для этого навеску массой от 0,120 до 0,160 г помещали в стакан, растворяли в 45 см³ дистиллированной воды с добавлением 5 см³ раствора азотной кислоты с массовой долей 25%, не содержащей оксидов азота и титровали раствором ртути (I) азотнокислой молярной концентрации 0,05 моль/дм³ в присутствии раствора дифенилкарбазона в качестве индикатора до перехода окраски из голубоватой в сине-фиолетовую. Фиксировали объем раствора ртути (I) азотнокислой, израсходованный на титрование суммы хлоридов и бромидов,

см³. Используя определенное значение массовой доли бромидов в электролите

вычисляли объем раствора ртути (I) азотнокислой, израсходованный на титрование бромидов,

см³:Determination of the mass fraction of chlorides. Pre-determined mass concentration of a solution of mercury nitrate in mg / cm ³ on chloride

and for bromide -

. Then, the volume of the mercury (I) solution of nitric acid, used for titration of the sum of chlorides and bromides, was determined.

cm ³ . For this, a sample weighing from 0.120 to 0.160 g was placed in a glass, dissolved in 45 cm ^{3 of} distilled water with the addition of 5 cm ³ of a nitric acid solution with a mass fraction of 25% not containing nitrogen oxides, and titrated with a mercury (I) solution of nitric acid with a molar concentration of 0, 05 mol / dm ³ in the presence of a diphenylcarbazone solution as an indicator until the color changes from bluish to blue-violet. The volume of a solution of mercury (I) nitric acid, used for titration of the sum of chlorides and bromides, was recorded.

cm ³ . Using a certain value of the mass fraction of bromides in the electrolyte

calculated the volume of a solution of mercury (I) nitrate consumed in the titration of bromides,

cm ³ :

where m _{n Cl} is the sample of electrolyte taken in the determination of chlorides, g.

The mass fraction of chlorides with electrolyte (C _Cl ,%) was determined by calculation by the difference after determining the mass fraction of the sum of chlorides and bromides and the mass fraction of bromides:

и результаты единичных определений C_Cl приведены в таблице 3.Values obtained

and the results of single determinations of C _Cl are shown in table 3.

Mass fraction of chloride in the electrolyte, defined as the average of three parallel determinations was

Thus, the use of the developed method for the analysis of a lithium electrolyte sample in the presence of a thickener — aluminum containing compounds, made it possible to establish the mass fractions of chlorides — 9.63%, bromides — 30.96% and fluorides — 3.803%, when they are present together.

Example 2 - determination of chlorides, bromides and fluorides in a lithium electrolyte not containing a thickener - aluminum-containing compounds.

Determination of fluorides. To transfer to a solution, 20 cm ^{3 of} distilled water, 4 drops of concentrated hydrochloric acid were added to a sample of sample weighing approximately 0.070-0.080 g. Then, according to the pH meter-ionomer, the pH of the solution was adjusted to a pH value of 6.5-7.0 by adding a solution of sodium hydroxide. Fluoride selective and auxiliary electrodes were placed in the solution and titrated from the burette with a solution of lanthanum nitrate to the potential of the titration endpoint, which was determined in advance. The volume of the lanthanum nitrate solution consumed for titration was recorded. The calculation of the results of measurements of the mass fraction of fluorides (C _F ),%, was carried out according to the formula

where V _{L a} - the volume of the solution of lanthanum nitrate used for titration, cm ³ ;

m _{n F} is the mass of the sample electrolyte, g;

T _{L a -F} - mass concentration of a solution of lanthanum nitrate on fluoride, mg / cm ³ .

The obtained values of m _{n F} , V _{L a} , T _{L a -F} and the results of unit determinations are shown in table 4.

Mass fraction of fluorides in an electrolyte not containing thickener-aluminum containing compounds, defined as the average of three parallel determinations was

Determination of the mass fraction of bromides. The determination of bromides in an electrolyte not containing a thickener — aluminum containing compounds was carried out in accordance with the procedures described in Example 1 for the determination of bromides.

The obtained values of m _{n Br} , V _{N a} , C _K-Br and the results of single determinations of C _Br are shown in table 5.

Mass fraction of bromide in an electrolyte not containing a thickener - aluminum-containing compounds, defined as the average of three parallel determinations was

Determination of the mass fraction of chlorides. The determination of chlorides in an electrolyte not containing a thickener — aluminum containing compounds was carried out in accordance with the procedures described in Example 1 for the determination of bromides.

и результаты единичных определений C_Cl приведены в таблице 6.Values obtained

and the results of single determinations of C _Cl are shown in table 6.

Mass fraction of chloride in the electrolyte, defined as the average of three parallel determinations was

Thus, the use of the developed method for the analysis of a lithium electrolyte sample that does not contain a thickener — aluminum containing compounds allowed us to establish the mass fractions of chlorides - 18.81%, bromides - 61.67% and fluorides - 7.82%,

The results of the control tests are summarized in table 7.

As examples of the implementation of the proposed method showed, it was confirmed that it is possible to achieve a technical result consisting in the possibility of determining individual concentrations of alkali metal halides and aluminum salts with their combined presence in a lithium electrolyte, achieving the required accuracy of their determination, necessary for certification of electrolyte quality, reducing the overall process time and simplification of the determination process.

Claims (30)

A method for determining lithium halides in lithium electrolyte for thermal chemical current sources, including sample preparation, determination of individual concentrations of halide ions, characterized in that, in order to enable the determination of individual concentrations of alkali metal halides and aluminum salts when they are combined in lithium electrolyte , increasing the accuracy of their determination, carry out preliminary grinding by grinding a solid electrolyte sample, then selected and ground Solid samples of solid lithium electrolyte are sent to separate stages for the sequential determination of fluorides, bromides and chlorides, each of which carries out cycles of specific operations: - to determine the mass fraction of fluorides in the electrolyte - gravimetric method after preliminary fusion of the crushed sample of solid lithium electrolyte together with a complex reagent from carbonic salts of potassium and sodium, followed by leaching of the melt with hot distilled water, separation of the precipitate of impurity compounds of aluminum and silicon, neutralization of the solution with mineral acids sequentially hydrochloric, then nitric acid, heating the solution to not more than 40 ° C, precipitating fluorides by contacting with thief lead acetate and lead ftorhlorida washing the precipitate at a pH in the range 3.5-4.6, drying the resulting precipitate and the final determination of the mass fraction of fluorides gravimetrically by mathematical formula:

where C _F is the mass fraction of fluorides,%; m _F - mass of the obtained precipitate of lead fluorochloride, g; m _{n F} is the mass of a sample of the electrolyte taken in the analysis for fluoride content, g; 0,0726 - conversion factor of the mass of lead fluoride chloride to the mass of fluoride; 200 - capacity of a volumetric flask with an electrolyte solution, cm ³ ; 100 - the volume of an aliquot of the electrolyte solution, cm ³ ; - to determine the mass fraction of fluorides in the electrolyte in the absence of an aluminum-containing thickener, the method of potentiometric titration with a fluoride-selective electrode is used, for this a sample of the crushed sample of solid lithium electrolyte is dissolved in a dilute hydrochloric acid solution, the fluoride-selective and auxiliary electrodes are placed in the solution and with constant stirring on magnetic The stirrer is used for titration of fluorides from a glass burette with a solution of lanthanum nitrate with indication of the equivalent point. spine on a pH meter ionomers, calculating a mass fraction of fluorides is carried by the formula (2)

where C _F is the mass fraction of fluorides,%; V _La - the volume of the solution of lanthanum nitrate used for titration, cm ³ ; m _{n F} is the mass of a sample of the electrolyte taken in the analysis for the fluoride content in the absence of aluminum, g; T _La-F - mass concentration of a solution of lanthanum nitrate on fluoride, mg / cm ³ ; - to determine the mass fraction of bromides in the electrolyte, an aqueous solution is prepared from a crushed sample of solid lithium electrolyte with the addition of concentrated sulfuric acid, followed by contacting the neutralized solution with a solution of potassium iodate (with a pre-determined volume ratio between solutions of potassium iodide and sodium sulfate), boiling for tile for 2 hours to remove the bromine formed, cooling, transferring to a flask, potassium iodine of allowing to stand in a dark place for the formation of iodine and titrating with sodium sernovatistokislogo to transition brown staining solution, straw-yellow, with the addition of starch solution and the continuation of the titration until complete bleaching of the solution, the calculation of the mass fraction of bromide in an electrolyte was conducted using the formula (3)

where C _Br is the mass fraction of bromides in the electrolyte,%; 10 - the amount of added in excess potassium iodate solution, cm ³ ; m _{n Br} is the mass of a sample of the electrolyte taken in the analysis for the content of bromides, g; C _K-Br - mass concentration of potassium iodate solution for bromide, mg / cm ³ ; - to determine the mass fraction of chlorides in the electrolyte, the difference between the total mass fraction of bromides and chlorides determined by mercury titration in an acidic medium with a diphenylcarbazone indicator and the pre-determined mass fraction of bromides in the sample is determined, and the consumed volume of the titration reagent solution - mercury (I) is determined nitric acid for titration of the sum of chlorides and bromides, determine the consumed volume of mercury (I) nitric acid for titration of bromides, after which the difference in volumes asschityvayut consumed amount of mercury (I) nitrate titration for chloride, and determine the corresponding value of the mass fraction of lithium chloride in the electrolyte by the formula (4)

where C _Cl is the mass fraction of chlorides in the electrolyte,%;

- the volume of a solution of mercury (I) nitric acid spent on titration of the sum of chlorides and bromides, cm ³ ;

- the volume of a solution of mercury (I) nitrate used for titration of bromides, cm ³ :

- mass concentration of a solution of mercury nitric acid in chloride and bromide, mg / cm ³ ;

- mass fraction of bromides in the electrolyte,%; m _{n Cl} - electrolyte sample taken in the determination of chlorides, g.