Efficient sequestration of malachite green in aqueous solution by laterite-rice husk ash-based alkali-activated materials: parameters and mechanism

In this work, laterite (LA) and rice husk ash (RHA)-based alkali-activated materials (AAMs) with varying %RHA contents (0, 5, 10, 15, and 20%) were prepared for the removal of malachite green (MG) dye from water. The precursors and AAMs were characterized by standard methods (XRF, XRD, TG/DTA SEM, and FTIR). The SEM micrographs and iodine index values showed that the incorporation of RHA improves the microporosity of laterite-based geopolymers. The incorporation of RHA did not result in any new mineral phases after alkalinization. Geopolymerization increased both the adsorption rate and capacity of the geopolymers relative to LA by approximately 5 times. The maximum adsorption capacity was 112.7 mg/g, corresponding to the GP 95−5 (5% RHA) geopolymer. The adsorption capacity was therefore not solely controlled by the RHA fraction. The adsorption kinetics data was best predicted by the pseudo-second-order (PSO) model. The adsorption mechanism entails electrostatic interactions and ion exchange. These results show the suitability of laterite-rice husk ash (LA-RHA)-based alkali-activated materials as adsorbents for the efficient sequestration of malachite green in aqueous solution.