This study investigated the efficiency and mechanisms of Cd removal by biochar pyrolyzed from water
hyacinth (BC) at 250e550 C. BC450 out-performed the other BCs at varying Cd concentrations and can
remove nearly 100% Cd from aqueous solution within 1 h at initial Cd 50 mg l1
. The process of Cd
sorption by BC450 followed the pseudo-second order kinetics with the equilibrium being achieved after
24 h with initial Cd ranging from 100 to 500 mg l1
. The maximum Cd sorption capacity of BC450 was
estimated to be 70.3 mg g1 based on Langmuir model, which is prominent among a range of low-cost
sorbents. Based on the balance analysis between cations released and Cd sorbed onto BC450 in combination
with SEM-EDX and XPS data, ion-exchange followed by surface complexation is proposed as the
dominant mechanism responsible for Cd immobilization by BC450. In parallel, XRD analysis also suggested
the formation of insoluble Cd minerals (CdCO3, Cd3P2, Cd3(PO4)2 and K4CdCl6) from either (co)-
precipitation or ion exchange. Results from this study highlighted that the conversion of water hyacinth
into biochar is a promising method to achieve effective Cd immobilization and improved management of
this highly problematic invasive species.