Synthesis of composites from coal gasification slag by acid leaching and NaOH activation for efficient adsorption of methylene blue

Abstract

This study successfully developed a carbon-silicon composite material (C-Si@GS) by acid leaching (HCl) and alkali activation (NaOH) treatments from solid waste CGS and applied to the adsorption of methylene blue (MB). The effects of material dosage, pH, contact time, initial concentration and co-existing ions on the removal of MB were investigated. The results revealed C-Si@GS had good adsorption performance at different pH and cations, suggesting that the material had stable properties. The adsorption of MB by C-Si@GS reached the equilibrium within 12 h, and the removal rate was up to 99 %. The maximum adsorption capacity of C-Si@GS was 456.8 mg/g calculated by Langmuir model (C0 (MB) = 120 mg/L, pH=7 ± 0.2, dosage = 0.6 g/L, and T=298 K). The adsorption process is consistent with Pseudo-secondary and Freundlich models, suggesting that both physical and chemical adsorption processes coexist. Adsorption mechanisms are mainly van der Waals forces, hydrogen bonding, electrostatic attraction and π-π bond interaction, as analyzed by XPS and FT-IR. The composites were regenerated using HCl as desorption agent and the removal rate was about 50 % after 3 cycles. The results illustrated that C-Si@GS can serve as an effective adsorbent for removing MB.