Arsenite and Arsenate Adsorption on Ferr

Arsenite [As(III)] and arsenate [As(V)] are highly toxic inorganic arsenic species that pose significant risks to the environment and human health. This study aimed to investigate the released stoichiometry of H+/OH- and the alterations in surface charge properties of ferrihydrite during the adsorption of arsenite and arsenate across a pH range of 4-10. We conducted adsorption experiments to analyze the interactions between arsenic species and the ferrihydrite surface, particularly focusing on the ligand exchange mechanism. Results revealed that arsenate adsorption caused a net release of OH- at specific pH levels, while arsenite exhibited a dual release pattern of net OH- and H+ depending on the pH. The amount of charge species released varied with the surface coverage of arsenic, suggesting distinct adsorption mechanisms for low versus high coverage scenarios. Our findings indicate that at low pH, the interaction between Fe and As may retain a partially protonated form, whereas at elevated pH, a monodentate bonding mechanism appears to gain prominence during arsenate adsorption. This research provides valuable insights into the adsorption behavior of arsenic on ferrihydrite, enhancing our understanding of its environmental impact.