Activated Carbon Production from Coffee Waste Employing Soil, Mining Waste, and Hematite as Activating Agents

Abstract Coffee bean cake (CC) is the waste generated after the extraction of syrup from coffee beans. In this study, CC was used as a precursor to prepare activated carbons (AC) using novel Fe-rich activating agents. Initially, the biomass (CC) was pyrolyzed at 450 °C for 90 min to obtain biochar (pyrolyzed coffee cake─PCC). Then, PCC was subjected to activation using three different iron-rich materials: commercial hematite (AC_Fe2O3), mining waste (AC_waste), and a soil sample (AC_soil). The materials were characterized and used to adsorb paracetamol (acetaminophen). The activated carbons AC_Fe2O3, AC_soil, and AC_waste showed specific surface areas of 614, 578, and 458 m2 g–1, respectively, which were nearly 22 times higher when compared with their precursor CC (21 m2 g–1). In the adsorption experiments of paracetamol, equilibrium was reached in approximately 180 min of reaction with high removal by the prepared activated carbons (AC_Fe2O3 = 82.5%, AC_soil = 67.1%, and AC_waste = 51.4%) when compared with CC and PCC (4.2% and 3.7%, respectively). The kinetic and adsorption isotherm models suggest that the adsorption of paracetamol by AC_Fe2O3 may be described by a process predominantly associated with chemisorption, while AC_soil and AC_waste show a better fit to the Freundlich model, which may indicate the occurrence of a multilayer removal mechanism.