Simultaneous removal of As(V) and Cr(VI) from water by macroporous anion exchanger supported nanoscale hydrous ferric oxide composite

- The HFO-201 is obtained by impregnating HFO into the pores of anion exchanger D201.
- HFO-201 could simultaneously adsorb As(V) and Cr(VI) in aquatic solution.
- Cr(VI) was adsorbed by quaternary ammonium groups, As(V) was captured by HFO.
- When competing anions coexisted, HFO-201 revealed superior adsorption than D201.
- The saturated HFO-201 could be regenerated by NaOH-NaCl binary solution.

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.

In As-Cr binary solution, Cr(VI) was primarily adsorbed by quaternary ammonium groups fixed on the matrix of HFO-201, while As(V) was preferentially captured by the embedded HFO nanoparticles.195