Adsorption of arsenate on alginate encapsulated magnetic sorbent with the presence of humic substances: A spectroscopy analysis

Abstract

The adsorption of arsenate onto alginate encapsulated magnetic sorbent with the presence of humic substances is studied in this paper. The purpose of this investigation is to explore the adsorption chemistry of arsenate with the presence of humic substances through the surface morphology, microstructure, and element constitution of the sorbent, as well as the binding characteristics between arsenate and magnetic sorbent. The scanning electron microscopy (SEM) analysis for elemental compositions was used to study the morphology of the sorbent. X-ray Photoelectron Spectroscopy (XPS) was employed to investigate the interactions between the sorbent and arsenate. Batch kinetic experiments of arsenate using the magnetic sorbent with the presence of humic substances show that equilibrium sorption capacity is reduced. This finding is in parallel with the XPS analysis results where the metal oxide bond decreases with the presence of humic substances. The arsenate adsorption equilibrium time is not affected by the presence of humic substances. The SEM analysis indicates that the precipitates of humic substances create irregular homogeneous structure on the sorbent surface which consequently reduces the sorbent pores. The XPS analysis reveals that humic substances and arsenate simultaneously adsorb onto the magnetic sorbent which creates a competition phenomenon. The XPS results also show that the solid state reduction of arsenate to arsenite is promoted by the presence of humic substances.