Adsorption mechanism modeling using lead (Pb) sorption data on modified rice bran-insoluble fiber as universal approach to assess other metals toxicity

Abstract

The binding capacity of Pb on modified rice bran-insoluble fibers RBIF-0.2, RBIF-1.25, and RBIF-2.0 (0.2%, 1.25%, and 2.0% H2SO4 with 1.25% KOH) having the variable specific surface area and cation-exchange capacity was evaluated. The Pb binding in terms of maximum binding capacity (BCmax) with RBIF increased with pH (2–7). However, the presence of sodium and calcium reduced the binding of Pb to RBIFs. Further, adsorption kinetics followed pseudo-second-order kinetic model when fitted to real Pb sorption data. However, sorption mechanism data (scanning electron microscopy images) were well fitted to Langmuir model instead of Freundlich and Dubinin–Radushkevich that suggests monomolecular adsorption of Pb to RBIF (<8 kJ/mol). Moreover, negative ΔG and positive ΔH of Pb2+ sorption confirmed the occurrence of spontaneous and endothermic process. The modeling of single-metal (Pb) data will be advantageous to use as a universal model for other heavy metals that will save the experimental costs. The data on all other heavy metals could be used with chosen models to elucidate their sorption mechanism to control the metallic-induced toxicity.