Silicate-modified oiltea camellia shell-derived biochar: A novel and cost-effective sorbent for cadmium removal

Oiltea camellia shells are a substantial agricultural waste in southern China, but their resource utilization has not been given due attention. In this study, we prepared oiltea camellia shell biochar by pyrolysis (500 degrees C) in the presence of sodium silicate, and investigated its adsorption capacity for Cd removal. The SEM characterization shows that silicon (Si) is loaded on biochar surfaces as fine particles, and are identified as quartz (SiO2), silicate and C-Si mixture according to X-ray diffraction. Silicate-modification significantly increases (similar to 45-112%) specific surface area (SSA) and slightly increases (similar to 5-12%) porosity of biochar. Batch results reveal that Si-modification significantly enhances Cd adsorption, and this increment is more pronounced at pH > 5. Furthermore, silicate-modification promotes the internal diffusion of Cd on biochar. FTIR and XPS analyses suggest that ion exchange with Na+, surface precipitation (CdCO3, CdSiO3 or Cd2SiO4), coordination with pi electrons (C=C) and complexation with carboxyl and C -Si-O groups are the predominant sorption mechanisms. This study puts a new perspective on the waste utilization of oiltea camellia shells for heavy metal removal from wastewaters or stabilization in contaminated soils. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Oiltea camellia shell biochar was prepared by pyrolysis in the presence of sodium silicate, which significantly enhanced its adsorption capacity for Cd removal. Silicate-modification increased the specific surface area of biochar and promoted the internal diffusion of Cd on biochar.