Comparative Sb(V) removal efficacy of different iron oxides from textile wastewater: effects of co-existing anions and dye compounds

Elevated Sb(V) concentration in textile wastewater is a growing environmental concern worldwide and has received wider attention in recent years. Iron oxides possess appealing characteristics as efficient and cost-effective adsorbents in large-scale applications. In the present study, Sb(V) adsorption capacity of α-Fe 2 O 3 , γ-Fe 2 O 3 , and Fe 3 O 4 was compared under experimental conditions close to the practical textile wastewater treatment. Results demonstrated that α-Fe 2 O 3 performed better under different pH values, reaction times, dye compounds, and co-existing ions as compared to γ-Fe 2 O 3 and Fe 3 O 4 , and the adsorption equilibrium was achieved within 8 h. Sb(V) adsorption is found to be highly pH dependent, and higher removal was achieved in lower pH, indicating the involvement of electrostatic interactions. The pH pzc value of α-Fe 2 O 3 was 7.15, which favored Sb(V) adsorption in practical wastewater having neutral pH value (pH ~ 7). Pseudo-first- and pseudo-second-order described the data and the simulated values of q e fitted well with the experimental values, indicating that pseudo-second-order model described the adsorption kinetics better with R 2 (> 0.95) higher than of pseudo-first-order plots. The Langmuir and Freundlich models both described well the sorption data of all the adsorbents, where the R 2 values were > 0.90 with a better fit in the Freundlich model for α-Fe 2 O 3 , suggesting that the adsorbent has heterogeneous surface characteristics. Similarly, characterizations revealed that the specific surface area, pore volume, and hydroxyl group content in α-Fe 2 O 3 were higher than others, making it easier for contaminants to bind on to the active sites. Furthermore, the effect of dyes and co-existing anions on Sb(V) adsorption was negligible, except for SO 4 2− , CO 3 2− , and PO 4 3− by the formation of inner-sphere complexes with iron oxides through competitive adsorption with [Sb(OH) 6 ] − . Findings from the present study suggested that α-Fe 2 O 3 effectively reduced Sb(V) in textile wastewater and could be a promising alternative for practical textile wastewater treatment. Graphical Abstract