Single and binary adsorption of heavy metals on fly ash samples from aqueous solution

Abstract

Thousands of toxins are released every day into the environment through numerous industrial operations and this resulted in continuous search for newer adsorbents. Two types of adsorbents, 1:10 fly ash and 1:15 fly ash samples were prepared from coal fired thermal power plant fly ash by treating it with calculated amount of calcium carbonate and phosphoric acid. Adsorbents were characterized on the basis of FTIR, XRF, surface area, pH and particle size studies. Adsorption of Pb(II), Ni(II) and Cr(VI) from single metal solutions on 1:10 fly ash from aqueous solution was carried out as a function of initial metal ion concentration, adsorbent dose, contact time and pH of the solution. Adsorption data obtained was analyzed with Langmuir, Freundlich and Temkin adsorption isotherm equations. Binary adsorption of Pb(II) and Ni(II) was studied on 1:10 and 1:15 fly ash samples as a function of initial metal ion concentration to investigate their efficiencies in removing metal ions from aqueous solution. In the case of 1:10 and 1:15 fly ash samples, Pb(II) and Ni(II) removal was observed to be almost the same. The significant difference observed between single and binary metal adsorption is in the initial metal removal rate. Slightly lower initial metal removal rate observed in the case of binary adsorption is probably due to the presence of competing metal ions in the solution. Fly ash based adsorbents prepared in the laboratory exhibited comparatively more adsorption capacity than that of the parent material, fly ash. Further, used adsorbents can be disposed in the form of concrete blocks as leaching of toxic metals is almost nil both under mild acidic and basic conditions. As cost involved in developing adsorbents from fly ash is comparatively less than other commercial adsorbents, reactivation or regeneration of used adsorbents was not considered.