Silica derived from rice husk ash and loaded with iron oxide for As(III) adsorption from water: experimental and modelling studies

ABSTRACT

Arsenic in water at low concentration (1–5 mg/L) presents difficulty in its removal by adsorption due to low concentration gradient. In the present study, silica was extracted from rice husk ash via sol–gel method and loaded with iron oxide using co-precipitation method. The maximum removal As(III) percentage (97.5%) was achieved using 0.1 g/L of adsorbent with a contact time of 90 min at pH = 7.0. Modelling of the experimental data with Freundlich isotherm and pseudo-second-order kinetic models showed the highest regression coefficient (R² > 0.95). Adsorption was spontaneous at all temperatures (∆G° value). Film and intraparticle diffusivities followed power-law model with initial concentration. FTIR spectra (at 825 cm⁻¹) indicated the presence of monodentate arsenic complexes. The presence of PO₄^3- ions affected the As(III) removal from water. The synthesised adsorbent exhibited excellent reusability up to three adsorption-desorption cycles.

KEYWORDS:

• Arsenic adsorption
• silica
• iron oxide
• modelling
• monodentate complexes

Acknowledgments

HS and ADG are thankful to Technical Education Quality Improvement Programme (TEQIP-III) for providing the required funding to carry out the experiments and MRC department, IIT Kanpur for SEM analysis.

Disclosure statement

The authors declare that they have no conflict of interest regarding the publication of this paper.