Potentiometric Determination of Fluoride in Ores of Molybdenum and Tungsten with Fluoride Ion Selective Electrode

Sample of molybdenum ore or tungsten ore was fused with sodium peroxide, and the melt was extracted with solutions of 5-sulfosalicylic acid and EDTA. After standing for 12 h, an aliquot of the supernatant was taken, and mixed solution of EDTA and KNO3 was added as ionic strength buffer. Acidity of the solution was adjusted to pH 5.1. The equilibrium potential value of the solution was measured with the pF-1 fluoride ion selective electrode (using SCE as reference electrode). Content of fluoride in sample was found from the working curve prepared with standard solutions of fluoride. Value of RSD (n=11) was found by analyzing a CRM of molybdenum ore, giving the result of 3.36%. Four CRM′s of molybdenum ores and tungsten ores were analyzed by the present method, giving results of fluoride contents in consistency with the certified values.