Valorization of citrus waste for circular economy: A case study on bergamot pomace as sorbent for Cd2+ removal and source of added value compounds

The potential of bergamot pomace for the development of materials able to efficiently remove cadmium(II) from water and for the recovery of bioactive compounds has been explored. To this purpose, raw bergamot waste resulting after industrial essential oil and juice extraction was mechanically ground, desiccated, pretreated with various chemicals (e.g. NaOH, HNO3, H2O2, H2O, 2-propanol) and dried up to constant weight thus affording solid samples that were characterized by ATR FT-IR spectroscopy. The solutions recovered after the pomace pretreatments were investigated by means of HPLC in combination with PDA and MS detectors to assess the residual content of bioactive components, e.g., phenolic and oxygenated heterocyclic compounds (OHCs). Potentiometric studies were performed on suspensions at t = 25 °C, I = 0.10 mol dm−3 in NaNO3(aq) to investigate pomace acid-base properties and binding ability towards Cd2+ ions. Sorption efficiency was investigated by means of kinetic and isotherm batch experiments and resulted to be 92 ± 7 mg g−1. Once loaded, sorbent reusability was tested by performing metal stripping cycles using various desorbents (HCl, HNO3, L-GLDA, S,S-EDDS, EDTA) with an efficiency of ∼ 60% after one cycle. The equilibrium Cd2+ concentration in solution was determined by differential pulse voltammetry and ICP-OES.