Fluorine in Coal: The Modes of Occurrence and its Removability by Froth Flotation

Fluorine is one of the trace elements in coal that is harmful to the ecological environment and human's health. Flotation, a method of fine-coal processing, may be useful in reducing the fluorine content in coal before coal combustion. For this purpose, a coal sample with high fluorine content (357 g/g) was selected for the present work. The modes of occurrence of fluorine were examined by sequential chemical extraction, screening tests, and float-and-sink tests; the removability of fluorine in coal was investigated by bench-scale flotation tests. Results indicated that fluorine tends to enrich in large-density fractions and fine-size fractions; fluorine mainly occurred in residual-associated form and carbonate- and Fe/Mn-associated form. Flotation can play an important role in the removal of fluorine from coal. In this study, the optimal amount of flotation reagents was determined by statically designed experiments. Under the optimum condition of 100 g/t diesel oil, 150 g/t 2-octanol, and 200 g/t sodium hexametaphosphate and a 5-minute flotation time provided a 56.81% yield of clean coal. The relative fluorine removal rate was 57.84%, and a total of 76.05% of the total fluorine was removed.