Characterization of diatomaceous earth modified by organic ligands for enhanced zinc adsorption

Abstract In order to enhance zinc adsorption, natural diatomaceous earth was modified by a simple batch procedure incorporating ligands with carboxylic and amine functional groups: ethylenediaminetetraacetic acid and 2-N(hydroxyethyl) iminodiacetic acid were used. The supernatants were analysed by square wave anodic stripping voltammetry monitored titrations to quantify ligand incorporation to the diatomaceous earth. The solids were characterized by energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, electrophoretic mobility, Fourier transform infrared spectroscopy and thermogravimetric analyses. Ligands modified the surface of the natural solid and were unable to enter the interlayer space of the smectite, main component of diatomaceous earth. Langmuir model was the most suitable to describe Zn(II) adsorption on diatomaceous earth whereas Freundlich showed better fit to data of the modified solids. The incorporation of organic ligands increased zinc retention by ca. 50%.