Production of low-cost adsorbents by torrefaction of biomass wastes from Arundo donax L. and Phoenix canariensis

The valorization of torrefied biomass wastes of Arundo donax L. and Phoenix canariensis as adsorbents of the methylene blue dye (MB) was investigated. Removal percentages between ca. 90% and 99% were attained for initial MB concentrations up to 200 mg/L, with equilibrium being reached within the first 30 min. Adsorption kinetics followed the pseudo-second order model and the equilibrium data were best described by the Langmuir isotherm model, with adsorption capacities following the order: torrefied palm leaf sheaths (92.68 mg/g) > torrefied Arundo donax L. (89.77 mg/g) > torrefied palm trunk (59.92 mg/g). All adsorbents evidenced other important features, such as selectivity towards a given dye from a mixture and also allowed recovery of adsorbed dye, as opposed to a commercial activated carbon (AC). Results suggest that these abundant wastes have potential as low-cost adsorbents for dye removal from industrial wastewaters, a more sustainable option than the usual landfilling.