A comparison of sorptive removal of anthraquinone and azo dyes using fly ash from single and binary solutions

Sorptive removal of an anthraquinone-dye (Acid Blue 127, AB-127) and an azo-dye (Acid Yellow 17, AY-17) from single and binary solutions using fly ash (FA) was compared. The diffuse reflectance infrared Fourier-transform spectra and scanning electron microscopy images were used for analyses of the bare and dye-loaded sorbents. Kinetic results well fit to the McKay equation. Typical two-step isotherms were observed both in single and binary component systems. Solution activity was used instead of concentration in the construction of isotherm plots and various isotherm models were modified for the calculation of two-step isotherm curves. The Liu isotherm shows the best fit to the experimental data of both L-shaped curves of AB-127 and S-shaped curves of AY-17. The Liu sorption capacities of the FA for AB-127 increased from 7.70 × 10^-5 to 3.78 × 10^-4 mol/g with the increasing temperature from 25 to 60 °C whereas it decreased from 2.35 × 10^-4 to 2.10 × 10^-5 mol/g for AY-17 in the same temperature range. Binary sorption was studied at three different molar ratios of AY-17/AB-127 of 1/10, 1/1 and 5/1. The removal capacities of the FA for the dyes were as high as activated carbon and it could be evaluated as an efficient sorbent for in-situ treatments in plants.