Ion-chromatographic determination of fluorine in texas lignite

Abstract

Samples of approximately 1.0 g were taken from three Texas lignite cores and mineralized in oxygen bombs. The residue was dissolved in distilled water to a total volume of 50 ml. The resulting solutions were analyzed for fluoride by ion chromatography and with a fluoride-sensitive electrode. The results obtained with these two methods were in good agreement. The pH of solutions prepared from mineralized lignite samples must be adjusted to fall into the range 4 to 12 before fluoride is determined by ion chromatography. The calibration curve is linear to 10 mg/l F− (in solution). Twenty μg/l of F− (in solution) corresponding to 1 mg/kg of dry lignite can still be determined. Ion chromatography has higher sensitivity for fluoride than fluoride-sensitive electrodes and provides at the same time information about other anionic species. The fluorine concentrations in the three cores varied from 10 to 140 mg/kg (dry lignite). Layers of clay interspersed between the lignite seams had higher fluorine concentrations than the lignite.