Thorough understanding of the kinetics and mechanism of heavy metal adsorption onto a pyrophyllite mine waste based geopolymer

Abstract

The present work explored the effectiveness of a geopolymer, synthesized from pyrophyllite mine waste, as an adsorbent for heavy metals such as Co, Cd, Ni, and Pb from aqueous solution. The chemical analysis of mine waste sample revealed the presence of silica (49.38%) and alumina (24.95%) besides Ca and Mg-bearing phases indicating the sample to be a prospective source for the geopolymer formation. The X-ray diffraction studies of the waste sample showed the presence of pyrophyllite, quartz, muscovite with a little amount of anorthite and albite. The presence of these phases was also confirmed by the scanning electron microscopy-energy dispersive X-ray spectroscopy and electron probe microanalysis. The synthesized geopolymerized sample was found to be highly amorphous in nature and did not show any major peaks that were found in the original feed sample. The batch adsorption studies supported the enhanced adsorption capacity of the geopolymer in comparison to the original waste sample. The maximum removal in the range 98-99% of the heavy metals could be accomplished by the geopolymer at pH 7.8, temperature 343 K, and initial metal concentration of 10 ppm. The adsorption data were found to fit pertinently to Langmuir model, Temkin model and pseudosecond order rate kinetics. The mechanism of adsorption was discussed with schematic models. (C) 2018 Elsevier B.V. All rights reserved.