Adsorption of indigo carmine from aqueous solution using coal fly ash and zeolite from fly ash

Abstract

Coal fly ash, a waste generated at the Figueira coal-fired electric power plant located in Brazil, was used to synthesize zeolite by hydrothermal treatment with NaOH solution at 100 C for 24 h. The fly ash (FA) and this synthesized zeolite (ZM) that was characterized pre- dominantly as hydroxy-sodalite were used as adsorbents for anionic dye indigo carmine from aqueous solutions. The samples were analyzed by instrumental neutron acti- vation analysis (INAA) for the determination of As, Co, Fe, La, Mo, Na, Sb, Sc, Sm, Th, U and Zn. Effects of contact time and initial dye concentration were evaluated in the adsorption processes. The kinetics studies indicated that the adsorption followed the pseudo-second order kinetics and that surface adsorption and intraparticle diffusion were involved in the adsorption mechanism for both the adsor- bents. The Langmuir isotherm model provided the best correlation of the experimental data. The maximum adsorption capacity was found to be 1.48 mg L -1 for FA and 1.23 mg L -1 for ZM. Laboratory leaching and solu- bilization tests conducted to classify this ZM as if was a waste residue according to the Brazilian regulation classi- fied it as a residue non-hazardous and non-inert.