Highly selective and efficient lignin-magnesium for removing cationic dyes from wastewater

Lignin-magnesium was manufactured facilely by one-step method to eliminate cationic dyes. Various characterization methods were used for obtained adsorbent, such as FT-IR, XRD, SEM, TEM and XPS. Results indicated lignin-magnesium showed a more coarse surface with many protuberances compared to that of sodium lignin. Methylene blue adsorption by lignin-magnesium conformed to Langmuir isotherm with a maximum adsorption amount of 536.6 mg/g. The homogeneous surface diffusion model (HSDM) was used to predict the kinetic adsorption process. The surface diffusion coefficient was obtained as 2.0 × 10-11 cm2/min, which indicated the intraparticle resistance was the rate-limiting step. Surprisingly, the adsorbent displayed outstanding performance toward methylene blue within pH range of 3-11 with a good regeneration. Removal of MB by lignin-magnesium still achieved 98 % even after 6 cycles. Furthermore, lignin-magnesium possessed a high selectivity for cationic dyes. The adsorption process may be elucidated by electrostatic attraction, hydrogen bonding as well as n-π/π-πinteraction between lignin-magnesium and methylene blue. On the whole, lignin-magnesium shows great potential in selectively and effectively clearing cationic dyes from sewage.