The (C(10)H(21))(2) Me(2)NBF(4) was prepd. by reacting the (C(10)H(21))(2)MeNCl with aq. NaBF(4) and used for extn. of Sunset Yellow, Cochineal Red, Allure Red and Brilliant Blue food dyes from their buffered aq. 0.01-1 g/mL solns. at room temp. and pH 3, 7 or 11 for 5 min to study the applicability of the process for purifn. of dye-cong. wastewaters. The distribution coeffs. varied with soln. pH and dye structure. The extn. yield was 99.4-99.9%. The dyes extracted were removed from the ionic liq. by ozonation (98.7-99.8%) and the refined ionic lig. was recycled to the extn.