Eco-friendly immobilization of dithizone on coal bottom ash for the adsorption of lead(II) ion from water

Abstract

Coal bottom ash is one of coal combustion wastes which mainly contains metal oxides of alumina and silica, thus it can be potentially used as adsorbent for heavy metal removal in aquatic environment. We have developed a new approach of eco-friendy immobilization of dithizone on activated coal bottom ash (CBA-Act) in water medium to yield dithizone-immobilized coal bottom ash (CBA-Dtz). The immobilization process in water medium is intended to replace previous method that uses more toxic organic solvents of toluene or carbon tetrachloride. Dithizone immobilization on CBA-Act is aimed to increase the selectivity and capacity of the adsorbent towards heavy metal ions. Characterization of the materials by FTIR (Fourier Transform Infra-Red), SEM-EDX (Scanning Electron Microscopy-Energy Dispersive X-Ray), TEM (Transmission Electron Microscope), XRD (X-Ray Diffraction) and DSC/TGA (Differential Scanning Calorimetry/Thermogravimetric Analysis) confirms that dithizone immobilization on CBA-Act in water medium has successfully accomplished and the new approach has proved to be twice more effective than that done in toxic organic media. Application of the original and modified CBA-Act in the adsorption of lead(II) ion from water suggests that the adsorption capacity of CBA-Dtz increases approximately three times as much as that of CBA-Act. The adsorption on both adsorbents follows pseudo-2nd order kinetic and can be best described by either Langmuir or BET isotherm adsorption models. Sequential desorption experiments reveal that lead(II) adsorption on CBA-Act is mostly governed by electrostatic and hydrogen bond interactions. However, upon immobilization of dithizone as found in CBA-Dtz, electrostatic interaction decreases while hydrogen bond interaction increases significantly.