The Potential Use of Pressmud as Reactive Material for Cd2+ Removal: Adsorption Equilibrium, Kinetics, Desorption, and Bioaccessibility

Pressmud is one of the most abundant wastes produced in the sugarcane industry; however, far too little attention has been paid to it as a reactive material for pollutant removal. This paper investigates the potential use of the composted pressmud for Cd2+ removal and considers the possible remobilization of the ion after the use and subsequent disposal of this material. Characterization and adsorption analyses (batch equilibrium and kinetic) were carried out in addition to desorption and bioaccessibility assays. The pressmud revealed promising adsorption characteristics, including a high specific surface area (SSA) (236.1 m2 g−1) and the presence of oxygen surface functional groups. The batch equilibrium data exhibit a better fit with the Langmuir isotherm model, assuming a monolayer adsorption capacity of 12.063 mg g−1, and for kinetic data, the pseudosecond-order model satisfactorily suited the adsorption. The equilibrium time was attained rapidly at lower concentrations (within 30 min), increasing to 180 min at 500 mg L−1, due to the contribution of the intraparticle diffusion process. According to the desorption and bioaccessibility tests, pressmud is capable of maintaining the element at the binding sites, although the Cd2+ adsorbed by the material is almost in its bioaccessible form, which supports the need of the correct handling after use. The results indicate that pressmud may be a promising reactive material for Cd2+ adsorption, identifying upcycling opportunities for this low-cost and renewable waste.