Removal of Cadmium (II) using water hyacinth (Eichhornia crassipes) biochar alginate beads in aqueous solutions

Abstract

Biochar produced from water hyacinths (Eichhornia crassipes) has been demonstrated to be an effective adsorbent for the removal of certain heavy metals and as a means of control for this highly invasive species. This study involved examined the Cd2+ sorption dynamics of an alginate encapsulated water hyacinth biochar (BAC) generated at different temperatures and modified using ferric/ferrous sulfate (MBAC). The maximum Cd2+ sorption occurred at a pH of 6 and at a solution temperature of 37 °C. Sorption equilibria for the biochar-alginate capsule (BAC) and modified biochar-alginate capsule (MBAC) treatments fit both the Langmuir (R2 = 0.876 to 0.99) and Freundlich (R2 = 0.849 to 0.971) equations. Langmuir isotherms had a better fit than the Freundlich isotherms, with maximum sorption capacities ranging from 24.2 to 45.8 mg Cd2+ g−1. Larger KL values in Freundlich modeling suggest strong bonding of the BAC and MBAC sorbents to Cd2+, with values of KL in the MBAC treatments ranging between 31 and 178% greater than the BAC treatments. Cd2+ sorption followed pseudo first-order kinetics (R2 = 0.926 to 0.991) with greater efficiency of removal using treatments with biochar generated at temperatures >500 °C. Results from this study highlight the potential for biochar-alginate capsules derived from water hyacinth to be effective for the removal of Cd2+ from wastewaters.