Heavy metal removal from water by adsorption using a low-cost geopolymer

In the present study, a geopolymer from dolochar ash was synthesized and used for the removal of heavy metal ions such as Co(II), Ni(II), Cd(II), and Pb(II) from the aqueous solution through the adsorption process. The geopolymer was characterized by a series of analytical techniques. The XRD pattern revealed the loss of dolochar ash crystallinity on geoploymerization. The peak at 982 cm(-1) observed in the FTIR spectrum due to Si-O-Si and Si-O-Al bonds confirmed the formation of geopolymer. BET surface area analyses indicated the mesoporous nature of the sample. The adsorption experiments revealed the higher removal efficiency of the geopolymer in comparison with the feed dolochar ash. The effects of different experimental factors such as pH, temperature, reaction time, and initial concentration of metal ions on metal uptake efficiency were evaluated to optimize the removal efficiency. The maximum removal of 98-99% was achieved when the pH, temperature, and initial metal ion concentration were 7.8, 343 K, and 10 ppm, respectively. The adsorption process followed the pseudo-second-order rate equation and validated the Langmuir adsorption model. Thermodynamic parameters such as Delta H, Delta S, and Delta G confirmed that the process to be spontaneous and endothermic. This geopolymer was found to compete efficiently with many adsorbents reported in the literature for water treatment.