In this study, the adsorption of Cu(II) from aqueous solutions by agricultural by-products, such as rice
husks, olive pomace and orange waste, as well as compost, was evaluated. The aim was to obtain sorbent
materials (biochars) through hydrothermal treatment (300 _C) and pyrolysis (300 _C and 600 _C). The
effect of adsorbent dose, pH, contact time and initial Cu(II) concentration in batch-mode experiments
was investigated. The optimum Cu(II) adsorption conditions was found to occur at 5e12 g/L adsorbent
dose, initial pH 5e6, and reaction time 2e4 h. Furthermore, the adsorption kinetics were best described
by the pseudo-second order model for all the tested materials, while the adsorption equilibrium best
fitted by the linear and Freundlich isotherms. Comparing rice husks and olive pomace, the higher
adsorption capacity resulted after pyrolysis at 300 _C. With respect to the orange waste and compost, the
highest adsorption capacity was observed using biochars obtained after hydrothermal treatment and
pyrolysis at 300 _C.