Iron-oxide modified sericite alginate beads: A sustainable adsorbent for the removal of As(V) and Pb(II) from aqueous solutions

Sericite powder was used as a substrate to immobilize the iron-oxide particles and it was encapsulated into beads using Na-alginate and Fe(III) ions by a simple cross-linking method to obtain iron-oxide modified sericite alginate beads (IMSA). The presence of iron oxide particle and other functional groups of alginate allows interaction of anionic arsenic species as well as the cationic Pb(II) ions with the IMSA beads; therefore, the material possess enhanced affinity towards these two highly toxic pollutants. The surface morphology and chemical composition of the beads were characterized by SEM-EDX analysis. Various functional groups present in the beads were identified by FT-IR analysis. Moreover, the iron content in the beads was obtained by US EPA 3050B method and the stability of immobilized iron was evaluated as a function of pH. The batch experiment showed that an increase in solution pH facilitate the uptake of Pb(II) whereas the As(V) removal found to decrease at higher pH. The simultaneous adsorption study showed that the As(V) removal was significantly high even at basic solution, which is perhaps, due to the presence of Pb(OH)2 precipitates. The adsorption capacity of IMSA beads is evaluated using Langmuir adsorption isotherm and found to be 21.61 mg/g and 133.73 for As(V) and Pb(II), respectively. The adsorption kinetic data of As(V) fit well to pseudo second order kinetic model whereas Pb(II) showed a better fit to the pseudo first order kinetic model. Moreover, 100 times increase in the ionic strength of the solution did not show significant effect in the uptake of As(V) whereas Pb(II) removal was slightly suppressed. This study demonstrates that IMSA beads obtained by exploiting natural sericite, iron oxide and alginate are efficient and sustainable adsorbent for the removal of arsenic and lead from the aquatic environment.