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 GP95-5 (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.

Synthesis of pozzolan and sugarcane bagasse derived geopolymer-biochar composites for methylene blue sequestration from aqueous medium.

In this study, four pozzolan-based geopolymers GP0, GP5, GP10, and GP20 were synthesized by alkaline activation and by substituting 0, 5, 10, and 20% of the precursor with sugarcane bagasse-derived biochar, respectively. The composites were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM/EDX), and Brunauer-Emmett-Teller (BET) surface area analyses, and applied to sequester methylene blue (MB) dye in an aqueous medium in batch mode. The alkaline activation of pozzolan-biochar blends resulted in the formation of poly (Ferro-sialate-siloxo)-biochar chains. The adsorption capacity increased with an increase in biochar content from 24.44 to 455.46 mg/g (18-fold) for GP0 and GP10, respectively. The sorption kinetics of MB onto the composites followed pseudo-second-order kinetics while the equilibrium data were best described by the Sips isotherm model. The adsorption process was thermodynamically spontaneous, endothermic (ΔH = 14.32-32.20 kJ/mol), and physical. The amount of adsorbent required for the removal of 99% of a fixed amount of MB in different volumes of effluent was predicted. Cost-analysis indicates that the composites are efficient and cheaper eco-adsorbents than commercial activated carbon and are suitable alternative candidates for the removal of dyes from water.