The overlooked potential of raspberry canes: from waste to an efficient low-cost biosorbent for Cr(VI) ions

Screening of various potential biosorbents originated from locally available lignocellulosic biomass has led to the investigation of so far uninvestigated raspberry cane for removal of Cr(VI) ions from aqueous solutions. To estimate its adsorption properties, its structure and textural properties were investigated, as well as kinetic and equilibrium studies. Results showed that adsorption occurs fast manifesting the high removal efficiency over a wide range of chromium concentrations with a maximum over 95%, at an initial concentration of about 50 mg/l. The pseudo-second-order model appeared to be the best for fitting kinetic data, while experimental isotherms were the best described by the Langmuir model. The adsorption mechanism is mainly governed by electrostatic attraction of the positively charged surface and the negatively charged chromium species at pH 2, coupled by the reduction of Cr(VI) ions to cationic Cr(III) that occurs concurrently with the oxidation of the RC lignin. The Cr(III) ions are retained through different mechanisms such as surface complexation, ion exchange, and cation-pi interactions. The results of this research open up new possibilities for the usage and management of solid waste from raspberry cultivation.