METHOD OF QUANTITATIVE DETERMINATION OF LITHIUM HALIDES IN LITHIUM ELECTROLYTE FOR THERMAL CHEMICAL SOURCES OF CURRENT Russian patent published in 2020 - IPC G01N31/16 G01N31/22 

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