Simultaneous removal of multiple heavy metals from wastewater by novel plateau laterite ceramic in batch and fixed-bed studies

Abstract

The wastewater in mining is usually contaminated by multi-heavy metals, and the removal of heavy metals in aqueous solutions by adsorption is a hot topic nowadays. Low-cost, multi-target, sufficient capability, and good reusability are always the first considerations for adsorbents. In this study, a unique plateau laterite ceramic (PLC) made from a characteristic clay soil that naturally contained rich Fe and Al ions was used to simultaneously adsorb six heavy metals from wastewater in batch and fixed-bed experiments. The adsorption isotherms, kinetics, and pH effects were investigated thoroughly. The Langmuir model, pseudo-first-order, and pseudo-second-order kinetic models fitted the experimental data, indicating that the adsorption process was monolayer adsorption, and both physisorption and chemisorption occurred. The pH of the zero-point charge (pHzpc) of the prepared PLC was 6.8, and the best adsorption efficiencies were 97.38% (As), 96.55% (Cr), 95.62% (Pb), 89.85% (Cu), 87.14% (Cd), and 81.08% (Hg). The crystalline morphology observed by scanning electron microscopy (SEM) along with new and enhanced X-ray diffraction (XRD) peaks revealed that heavy metals were successfully adsorbed onto the PLC. In the fixed-bed study, breakthrough occurred at 270 bed volume (12.72 L). The regeneration ability of the PLC could meet at least three cycles. The adsorption capacity was ranked as As > Cr > Pb > Cu > Cd > Hg in both the batch and fixed-bed experiments. The removal efficiency of As was the best because, except for the dominant complexation and precipitation reaction, As ions had a wider reaction pH range, underwent ligand exchange, and were involved in the formation of an As–Fe shell. Hence, plateau laterite was used for the first time in this study as a ceramic adsorbent to simultaneously adsorb six heavy metals from wastewater. The PLC exhibited a solid structure and easy separation qualities in all experiments, thus having significant implications for removing multiple heavy metals from wastewater in practice.