Adsorption of Pb(II), Zn(II) and Cr(III) on coal fly ash porous pellets

In the present work the application of fly ash porous pellets as adsorbent of lead(II), zinc(II) and chromium(III) ions from aqueous solution was studied. Experiments were carried out using porous pellets developed from fly ash derived from Megalopolis, Greece coal-burning power plant. The material was shaped into spherical agglomerates, after wetting and tumbling in a laboratory scale granulator. The adsorption of heavy metals on fly ash pellets was studied as a function of the initial metal concentration, solution pH and temperature. Kinetic studies indicated that sorption follows a pseudo-second-order model. Adsorption isotherms of lead, zinc and chromium were determined for agglomerated material using the Langmuir equation. The adsorption capacity of fly ash pellets reached at 0.22 mmol Pb/g pellet, 0.27 mmol Zn/g pellet and 0.44 mmol Cr/g pellet. Furthermore adsorption from bimetallic solutions (Cr–Zn, Cr–Pb and Pb–Zn) took place in order to study presumable antagonistic effects on adsorption of heavy metals. Finally, the stabilization of metal saturated pellets was studied. The stabilization procedure took place in structures made of concrete, where 75% of cement was replaced by raw fly ash. The evaluation of the procedure through leaching tests showed excellent heavy metals stabilization in concrete blocks.

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► We developed porous pellets from Class C fly ash as a non-conventional adsorbent for wastewater treatment.
► Pb, Zn and Cr(III) can be efficiently adsorbed on porous pellets following a Langmuirian adsorption isotherm.
► Metals’ adsorption follows a pseudo second order kinetic model.
► Metals’ adsorption process is irreversible in neutral and alkaline solutions and reversible in acidic ones.
► We proved that the encapsulation of metal saturated pellets in concrete blocks is an efficient stabilization method.