Rapid removal of Hg (II) from aqueous solution by rice straw activated carbon prepared by microwave-assisted H2SO4 activation: Kinetic, isotherm and thermodynamic studies

Rapid adsorption process of noxious Hg (II) from the liquid phase on to the developed natural agricultural wastes (rice straw (RS)) activated carbon (RSAC) synthesized using the microwave-assisted H2SO4 activation was well investigated and elucidated. The effect of the essential parameters such as solution pH, adsorbent dose, contact time, initial adsorbate concentration and temperature was well studied and optimized. The optimized parameters for metal ions are pH value of 5, the equilibrium time was attained after 6 min, and the maximum removal percentage was achieved at an adsorbent loading weight of 0.01 g. It was found that the adsorption capacity of RSAC increased with increase in the initial mercury concentration and also the percentage adsorption decreased with the increase in initial mercury concentration. Thermodynamic parameters such as Δ G, Δ H and Δ S were well investigated and studied negative value of ΔG°reveals the spontaneity and feasibility of adsorption process, additionally the adsorption of Hg (II) increases with increase in temperature, which reveals the endothermic nature of the adsorption process. The equilibrium data and kinetic data were well fitted and found to be in good agreement with Freundlich isotherm model and pseudo-second-order kinetics model respectively.