Reactions of [Me3PrN][(CF3SO2)(2)N] and [C(3)mpip][(CF3SO2)(2)N] (C(3)mpip = 1-methyl-1-propylpiperidium) in subcritical water were investigated to develop a technique for recycling fluorine element. By adding KMnO4 to the system, quasi-complete mineralization of the ionic liquids was achieved at 300 degrees C. When [Me3PrN] [(CF3SO2)(2)N] was reacted for 18 h with 158 mM KMnO4, F-,SO42-, andNO(3)(-) yields were 98, 98, and 91%, respectively, and the amount of total organic carbon (TOC) was below the detection limit. [C(3)mpip][(CF3SO2)(2)N] was also almost completely mineralized via the same treatment, affording F-, SO42-, and NO3- yields of 94, 97, and 96%, respectively, with no detectable TOC. The rest of the nitrogen atoms were well accounted for by the formation of NO2-. Compared with a previous reported method using FeO, our approach reduces the reaction temperature for complete mineralization by 76 degrees C and suppresses the formation of environmentally undesirable CHF3.