This standard specifies the methods for determining the total fluorine content in coal by high temperature combustion hydrolysis - fluoride ion-selective electrode method.
This standard is applicable to the determination of fluorine in brown coal, soft coal and anthracite.
2 Theory
The coal sample is combusted and hydrolyzed in a mixed airflow of oxygen and water vapor, and the fluorine in coal is completely converted into volatile fluoride (SiF4 and HF) and quantitatively dissolved in water. The concentration of fluorine ion in the sample solution is determined by standard addition method by taking the fluorine electrode as the indicator electrode, and the saturated calomel electrode as the reference electrode, so as to work out the total fluorine content in coal.
3 Reagents and materials
3.1 Water: for the purpose of this method, all water shall be the deionized water with a resistivity greater than 3 MΩ/cm.
3.2 Quartz sand: chemically pure, with particle size of (0.5~1) mm.
3.3 Sodium hydroxide solution: 10 g/L.
Dissolve 1g of top-grade pure sodium hydroxide (GB/T 629) in 100mL of water.
3.4 Nitric acid solution: 1+5 (V+V).
