Evaluation of Libidibia ferrea (Fabaceae) pod skin as chromium adsorbent applied to a synthetic tanner effluent

Abstract

Two biosorbents for Cr(VI) ions, derived from Libidibia ferrea (LF) pod biomass, were investigated in this study—one in its unmodified state and the other subjected to an alkaline modification. The synthesized biosorbents underwent characterization both before and after the adsorption of Cr(VI) using diverse analytical techniques, such as FTIR, SEM, EDX, surface area analysis, pore volume and diameter determination, and Raman spectroscopy. Additionally, studies on adsorption equilibrium and kinetics were conducted to gain insights into the adsorption process. Furthermore, an adsorption test was performed using synthetic tannery effluent. The unmodified biosorbent exhibited a maximum removal efficiency of approximately 90% for Cr(VI) from the synthetic tannery effluent. Characterization of the unmodified adsorbent revealed a greater surface area and pore volume. Adsorption equilibrium and kinetic studies indicated that the unmodified biosorbent possessed a heterogeneous surface with the potential for multiple adsorption sites. Kinetically, it was demonstrated that both physisorption and chemisorption occurred simultaneously, justifying the rapid adsorption of Cr(VI) onto the biomass. In conclusion, this study underscores that unmodified LF pod biomass can serve as an effective Cr(VI) biosorbent, suggesting a potential application in real tannery effluent treatment. By developing a Cr(VI) adsorbent from an unconventional material—unmodified LF pod biomass—this research provides a sustainable and cost-effective alternative for effluent treatment processes.