ISO/TC 226/WG 4 - Smelter grade fluorides

This document specifies a wavelength-dispersive X-ray fluorescence spectrometric (XRF) method for the determination of cryolite (Na3AlF6) from the content of fluorine to the content of trace elements. The calibration reference materials are not specified in this method. The method is applicable to cryolite, which is primarily used for the production of aluminium. Annex A provides conversion factors for converting elements to compounds. The validity and precision of test results for concentrations outside these ranges has not been determined. The concentration range of fluorine (given as F) is from 510 g/kg to 560 g/kg. The concentration range of aluminium (given as Al) is from 120 g/kg to 150 g/kg. The concentration range of sodium (given as Na) is from 270 g/kg to 330 g/kg. The concentration range of silicon (given as SiO2) is from the lowest limit of detection (LLD) to 4,0 g/kg. The concentration range of iron (given as Fe2O3) is from LLD to 0,37 g/kg. The concentration range of sulfur (given as SO4) is from LLD to 5,0 g/kg. The concentration range of phosphorus (given as P2O5) is from LLD to 0,40 g/kg. The concentration range of calcium (given as CaO) is from LLD to 0,80 g/kg.

ISO 12926: 2012 describes an X-ray fluorescence spectrometric (XRF) method for the determination of aluminium fluoride (AlF3) from the content of fluorine and the content of trace elements in the test specimen. The method does not determine the oxygen content. The calibration reference materials are not specified in this method.

Specifies a method based on the fusion of a test portion with sodium carbonate and boric acid and dissolution in perchloric acid solution, followed by formation of the ammonium molybdophosphate complex and extraction of the complex with isobutyl acetate. The solution is absorbed into an acetylene/dinitrogen monoxide flame and the molybdenum, and hence the phosphorus, is determined by measuring the absorbance of the 379,8 nm line emitted by a molybdenum hollow-cathode lamp.

Covers a method, the orinciple of which consists in preparing tablets from a mixture of the test portion and a binder and measuring the intensity of the K line emitted by the sulphur. The measured intensity is then compared with the intensity of emission of standard tablets of known sulphur content. The method is applicable to products having sulphur contents between 0,01 and 2 % (m/m).

Specifies the procedure for the preparation of crude samples and dried samples and of natural and synthetic materials having a molar ratio sodium fluoride/aluminium trifluoride between 3 and 1,7 approximately. The crude sample is intended for the determination of geometric characteristics, for certain physical and physico-chemical tests and for moisture determination. The dried sample serves especially for chemical tests. The principle of the procedure consists in grinding followed by sieving of the sample until the whole passes through a sieve of mesh aperture 0,125 mm. Thorough mixing and drying at approximately 110 °C.

Applicable to products having a water content between 0.01 % (m/m) and 0.5 % (m/m). Is supplemented by ISO 3700 and intended for reference purposes. Bases on addition of a cooled test portion to cooled dry pyridine containing 5 % of anhydous hydrogen fluoride. The apparatus for measuring the test portion and titration and the measuring vessel are shon in figures. Subsequent electrometric titration of the water with the Karl Fischer reagent.

Applicable to products having a chlorides content, expressed as chlorine, of equal to or more than 0.005 % (m/m). The principle consists in precipitation, in the presence of boric acid, of chloride ions with silver nitrate. Comparison of the opalescence of the test solution with that of standard matching solutions using Nessler tubes against a black background. Turbidimetric evaluation of the mass of precipitate.

The methods are applicable as alternatives to products for which the molar ratio NaF/AlF3 is equal to about 3. The principle of the flame emission method consists in atomization of the test solution in a flame of oxygen/hydrogen and determination by measurement of the intensity of the radiation at 589 nm. The principle of the flame atomic absorption method is based on atomization in an air/acetylene flame and measuremnt of the absorption of the 589 nm line emitted by a sodium hollow-cathode lamp. The preparation of the test solution is carried out by dissolution of a test portion in hydrochloric acid and water after attack by concentreted sulphuric acid.

The method can be applied provided the Fe203 content does not exceed 0,15 . It can also be applied to products with molar ratio of NaF to AlF3 between approximately 3 and 1,7. The principle consists in dissolution of a test portion by acid fusion using potassium pyrosulphate and recovery by hydrochloric acid. Separation of the mixture by precipitation of aluminium, with ammonium benzoate , in an acetic reducing medium. Dissolution of the precipitate and reprecipitation as aluminium tri(quinolin-8-oxide) in an acetic buffer medium. Filtration, washing, drying of the precipitate at a temperature of 130 °C and weighing.

Specifies a method applicable to products having phosphorus contents equal to or greater than 0,002 % (m/m). The principle is based on alkaline fusion of a test portion with a mixture of sodium carbonate and boric acid, dissolution of the fused mass in nitric acid, neutralization of suitable aliquot portion with sodium hydroxide solution, reaction with acid ammonium molybdate solution to form a molybdophosphate complex, reduction by a mixture of sodium disulphite and 4-amino-3-hydroxynaphtalene-1-sulphonic acid, and photometric measurement of the reduced complex.