Enhancement of Rhodamine B removal by low-cost fly ash sorption with Fenton pre-oxidation

The removal of a basic dye, Rhodamine B (RhB), by fly ash adsorption, Fenton oxidation, and combined Fenton oxidation-fly ash adsorption were evaluated. Even though fly ash is a low cost absorbent, a high dose of fly ash was needed to remove RhB. Only 54% of RhB was removed by 80 g L−1 fly ash. Solution pH did not significantly affect the RhB sorption by fly ash after 8 h. Fenton reagents at H2O2 dose of 6 × 10−3 M and pH 3 rapidly decolorized 97% of RhB within 2 min, and 72% of COD removal was obtained at 30 min reaction time. Spectrum analysis result showed that a large area of UV spectrum at 200-400 nm remained after Fenton reaction. The addition of 1 g L−1 fly ash effectively removed COD from Fenton-treated solution, and the UV absorption spectrum at 220-400 nm totally vanished within 2 h. COD removal of RhB by the combined Fenton oxidation and fly ash sorption process was 98%. The COD removal capacity of fly ash for Fenton-treated RhB solution was 41.6 times higher than that for untreated RhB solution. The results indicated that the combined process is a potential technique for RhB removal.