Removal of aluminium, arsenic, and zinc using rice husk ash geopolymer

This study investigated the potential of rice husk ash (RHA)-derived geopolymer as an adsorbent for removing heavy metals aluminium (Al), arsenic (As), and zinc (Zn) from wastewater. The Response Surface Methodology (RSM) and Random Forest (RF) modelling were used for modelling the adsorption process. The RHA gepolymer was characterized using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Brunauer-Emmett-Teller (BET) analysis. The adsorption could be modelled using Langmuir isotherm and pseudo first order kinetic equation. The geopolymer achieved a 96–99%, 85–92% and (94–98%) removal Al, As and Zn respectively. The BET analysis showed the geopolymer was a mesoporous adsorbent with capillary condensation favouring type IV isotherm adsorption. The desirability studies showed that temperatures below 30 0 C and adsorbent loading around 5% m/v were ideal for the removal of As and Al whilst Zn demonstrated an increase in removal efficiency with an increase in temperature. Extended adsorption time above 8 hrs led to desorption of heavy metals. The adsorption was endothermic and the mechanism of sorption was physisorption.