Hemp Shives: A Sustainable Biosorbent for Water Purification by Dye Removal

This study evaluates the potential of hemp shives (HS) as candidate for two basic dyes removal, namely Azure B (AB) and Malachite Green (MG), from aqueous solutions. The biosorption tests were conducted in batch mode. The influence of experimental variables, including pH, dye concentration, adsorbent dosage, and contact time, was evaluated. Under optimal biosorption conditions, equilibrium and kinetic studies were conducted in order to gain further insight into the process. Hemp shives, without any additional treatment, exhibited the highest value of the maximum Langmuir adsorption capacity reported in the literature for AB ( q max = 364.4 mg/g). Furthermore, HS has demonstrated superior MG removal efficiency compared to other biosorbents previously reported, reaching a value of q max = 91.0 mg/g. The biosorption of both dyes can be described by a pseudo-second-order kinetic model. The formation of chemical bonds between the dye molecules and the active sites of the biosorbent represents the rate-limiting step in the process. Moreover, it has been demonstrated that the spent hemp shives can be partially regenerated. The AB biosorption capacity of the recycled material ( q 2 = 23.60 mg/g), which had been washed with HCl, was approximately half that of the adsorption capacity of the fresh HS ( q 1 = 44.80 mg/g). Following the washing of spent hemp shives with acetic acid, it was observed that the recycled material retained in excess of 40% of its original biosorption capacity for AB ( q 2 = 18.72 mg/g). The desorption of MG from HS is a more challenging process than that of AB.