Decolorization of multicomponent dye-laden wastewater by modified waste fly ash: A parametric analysis for an anionic and cationic combination of dyes

Abstract WFA modification was done by its reaction with the mixture of ammonia solution and phosphoric acid. BET analysis of modified WFA elucidate pore volume and surface area of 0.017cm 3 /g, 11.1m 2 /g respectively. Thermo-Gravimetric Analysis (TGA) confirmed the 45% loss in weight for the WFA whereas, for modified WFA, the loss was about 12%. XRD results proposed the improved crystallinity of the modified WFA. Moreover, the zeta-potential of -40mV indicates the favorable removal efficiency, against the pH value of 6.41. Regression results from the comparison of order-based kinetic models suggest that nth model parameters justify the complex nature of the adsorption mechanism with its feasible correlation coefficient (R 2 > 0.95) and its lower error values for both single and binary solutions. Monolayer coverage capacities for a single solution system of Methylene Blue (MB), Rhodamine-6G (Rh) and Methyl Orange (MO) were 24.93mg/g, 24.83mg/g and 14.95mg/g respectively. Further, the isothermal model’s results suggest that the “Extended Sips” model gives relatively higher R 2 = 0.99 values and deals with the failed assumptions of both the Langmuir and Freundlich models. The thermodynamic model generated results conclude that involved single and binary physisorption processes were spontaneous and endothermic in the case of cation dyes solution and for MB/MO mixture it was exothermic.