Kinetic equilibrium and thermodynamic analyses of As (V) removal from aqueous solution using iron-impregnated Azadirachta indica carbon

Arsenic emerges out as a potential threat to human health and vegetation in recent past. Therefore, the present study aimed at adsorption of As (V) from the aqueous solution using Fe-AIB and Fe-AIL (iron-impregnated activated carbon synthesized from the powder of bark and leaves of Azadirachta indica tree). The removal of As (V) by Fe-AIB and Fe-AIL was examined under different experimental conditions. The Fe-AIB showed up to 96% As (V) removal at pH of 6.0, and up to 90% removal was observed with Fe-AIL at pH 4.0. Although the kinetic data fit best in the pseudo-second-order model, there are various other processes like intraparticle diffusion, pore diffusion and film diffusion that controls the overall rate. Mechanistic frameworks related to the adsorption process were analysed using various isotherm models. Langmuir and Freundlich models clearly explain As (V) adsorption by Fe-AIB and Fe-AIL. Thermodynamic analysis reveals the spontaneous adsorption on Fe-AIB. Moreover, it also confers the endothermic nature of the adsorption process for both the adsorbents. The presence of co-existing ions like PO43- and SiO32 negatively interfered the removal or arsenate uptake, whereas ions like SO42- and NO3- do not significantly affect the adsorption process. Consistently greater than 90% As (V) removal up to few cycles for both the adsorbents was observed in regeneration studies. Significant reusability characteristics was possessed by both the spent adsorbents, which makes them potentially efficient for large-scale practical application with enhanced performance.