Synthesis and characterization of lignin-modified geopolymer composites for aqueous phase sequestration of methyl orange dye in a fixed-bed column

Abstract

The present work evaluated the performance of pozzolan and sawdust derived geopolymer–lignin composites in the sequestration of methyl orange (MO) in a fixed bed as an auspicious strategy for valorization of waste sawdust. GP0, GP-CL5 and GP-CL10 composites were prepared via alkalination, replacing pozzolan with 0, 5 and 10% lignin (CL) extracted from sawdust, respectively. The composites were characterized using standard methods, namely X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) surface analysis and scanning electron microscopy (SEM). The specific surface areas were decreased by the addition and increase in CL fraction from 53.4 to 24.9 m² g⁻¹ for GP0 and GP-CL10, respectively. Incorporation of CL resulted into a poly(ferro-lignino-sialate) single-network. Addition of CL increased the breakthrough time and the operating time of the column. The Thomas model best described the breakthrough curves. MO sequestration performance (Q₀) was three times better on GP-CL10 than GP0 when the feed rate was increased. The MO fixation mechanism mainly includes external and internal diffusion and electrostatic interactions. The adsorption is driven by the surface chemistry rather than textural characteristics of the adsorbent. These results indicate that geopolymer–lignin composites are potential eco-adsorbents for the removal of azo dyes in a continuous adsorption system and presents a plausible way for recycling sawdust.