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Abstract
As(V) and Cr(VI) are both highly toxic anionic pollutants and commonly co-exist in
some industrial effluents and contaminated waters. In this study, simultaneous removal
of them was efficiently achieved by employing a composite adsorbent (HFO-201) fabricated
by immobilizing nanoscale hydrous ferric oxide (HFO) within a macroporous anion exchanger
D201. The HFO-201 composite possesses two types of adsorption sites, i.e. the quaternary
ammonium groups fixed on the D201 matrix and the embedded HFO nanoparticles. In the
binary solution, the adsorption kinetic processes of both As(V) and Cr(VI) by HFO-201
were well fitted with the pseudo-first order kinetic model. Furthermore, HFO-201 exhibited
a significantly higher adsorption capacity toward As(V) than D201 and an identical
adsorption capacity toward Cr(VI) to D201. During the removal process, As(V) was captured
by both the electrostatic attraction from the fixed quaternary ammonium groups and
the formation of inner-sphere complex with the embedded HFO nanoparticles. Whereas,
Cr(VI) was primarily adsorbed by the fixed ammonium groups. Fixed-bed treatment of
As(V)/Cr(VI) binary synthetic water by HFO-201 resulted in elimination of As (from
1.0 to below 0.01 mg/L) and Cr (from 5.0 to below 0.05 mg/L), with the treatment capacity
of 1700 bed volume (BV). Moreover, the exhausted HFO-201 was amenable to efficient
in situ regeneration with a binary NaOH-NaCl solution for repeated use without any
significant capacity loss.