Abstract
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•Removal of heavy metals such as Pb(II) and Zn(II) from environment is very important.•Adsorption of Pb(II) and Zn(II) using low cost coal fly ash (CFA) has been studied.•Modified CFA showed good performance for adsorption of Pb(II) and Zn(II).•Effect of pH and contact time in the adsorption process was also studied.•MEL and CALL isotherm models was proposed to study the adsorption mechanism.
Coal fly ash (CFA) is composed of minerals containing some oxides in crystalline phase (i.e., quartz and mullite), as well as unburned carbon as mesoporous material, thus enabling CFA to act as a dual-sites adsorbent with unique properties. This work focused on the adsorption of Pb(II) and Zn(II) from binary system, a mixture containing two metal ion solutions present simultaneously, onto NaOH-modified CFA (MCFA). Several adsorption tests were conducted to evaluate the effect of several parameters, including pH and contact times. The experiment results indicated that chemical treatment of CFA with NaOH increased pore volume from 0.021 to 0.223 cm3·g−1. In addition, it could also enhance the availability of functional groups on both minerals and unburned carbon, resulting in almost 100% Pb(II) and 97% Zn(II) adsorbed. The optimum pH for adsorption system was pH = 3 and quasi-equilibrium occurred in 240 minutes. Equilibrium data from the experimental results were analyzed using Modified Extended Langmuir (MEL) and Competitive Adsorption Langmuir-Langmuir (CALL) isotherm models. The analysis results showed that the CALL isotherm model could better describe the Pb(II) and Zn(II) adsorption process onto MCFA in binary system compared with MEL isotherm model.