Soh Fong Lim, Taylor's
University College, Malaysia, Chemical and Biomolecular Engineering
Department, National University of Singapore (NUS), Singapore,
Singapore and J. Paul Chen, Environmental Science and Engineering,
National University of Singapore, Singapore, Singapore.
A novel magnetic sorbent,
alginate encapsulated magnetic sorbent has been successfully fabricated
to remove metal contaminants such as arsenic. To better understand the
sorption properties of the sorbent, the sorption studies of both
organic (dimethyl sodium arsenate) and inorganic (sodium hydrogen
arsenate) arsenate were conducted. Further investigations were
performed to elucidate the adsorption behavior with the existence of
humic substances. Using the novel sorbent, adsorption of the metal ion
onto the sorbents is elucidated thoroughly by qualitative and
quantitative methods: experimental studies, instrumental analyses,
mathematical modeling, and simulation. The arsenate adsorption
equilibrium time was not affected by the presence of humic substances;
it can be attained within 25 h. Complete characterizations of the
sorbent were conducted by BET, XRD, ICP, SEM, FT-IR, and XPS. The SEM
analysis indicates that the presence of humic substances created
irregular homogeneous structures on the surface of the sorbent which
consequently reduced the sorbent pores. The XPS analysis also revealed
that humic substances and arsenate simultaneously adsorbed onto the
sorbent; the competitive adsorption between both occurred. The FT-IR
and XPS analyses showed that the –COOH and Fe-O groups in the sorbent
were involved during the arsenate adsorption. Based on both
experimental results and instrumental analyses, the adsorption
mechanisms have been proposed. Arsenate can be partially adsorbed onto
the sorbent and the remaining is further reduced to arsenite. Carbon
and divalent iron could provide electrons to achieve the chemical
reduction of arsenate.