Pb2+ adsorption onto collagen/cellulose hydrogel beads from aqueous solution: kinetic, isothermal, and thermodynamic analyses

The removal of Pb2+ ions from aqueous solutions using collagen/cellulose hydrogel beads (CCHBs) was investigated using batch adsorption experiments. The results indicate that Pb2+ adsorption capacity for the CCHBs is obviously higher than that for the cellulose hydrogel beads (CHBs). The maximum adsorption capacity of Pb2+ is at pH 4.2 for the prepared biosorbents. The co-anions slightly influence Pb2+ adsorption, whereas the adsorption capacity of Pb2+ remains at a high level during the competitive adsorption of heavy metal ions. The behaviors of Pb2+ adsorption onto the prepared biosorbents were further analyzed using kinetics, isotherm, and thermodynamics. The overall kinetic data can be adequately explained by a pseudo-second-order model, and Pb2+ adsorption is controlled by multiple diffusion mechanism. Pb2+ adsorption is described well using the Langmuir model. Thermodynamic evaluations show a spontaneous and endothermic Pb2+ adsorption. The entropy for the CCHBs is higher than that for the CHBs and decreases with increasing collagen/cellulose mass ratio from 1:1 to 3:1. This phenomenon indicates that blending collagen in hydrogels changes the interaction or distribution of biopolymers, thereby greatly influencing Pb2+ adsorption.