Study of zinc biosorption on natural and chemically modified rice husks

Abstract

Heavy metal contamination is one of the greatest risks to water courses because these pollutants are difficult to eliminate due to their non-biodegradable and persistent nature. Numerous technologies have been developed to solve this environmental problem, being biosorption one of the most widely used alternatives due to its efficiency, low cost and the possibility of using natural materials as biosorbents. Agricultural residues are an important source of biomass that can be used in this type of process. Therefore, the objective of this study was to analyze the physicochemical factors that affect the sorption of zinc in solution using rice husk as biosorbent, either natural or chemically modified with potassium hydroxide or phosphoric acid. This is a highly available residue in the province of Entre Ríos, Argentina. Sorbents were characterized by infrared spectroscopy and by determining the pH at the point zero charge. The chemical treatment with potassium hydroxide improved significantly the removal of the pollutant, while the acid activation did not show improvements regarding to the use of the natural husk. The removal levels were favoured by the increase in pH up to 5 and biosorbent dosage, while they decreased by the rise in zinc concentration. For the systems being evaluated it was found that the equilibrium of the process was reached quickly and adjusted to pseudo-second order kinetics. For the adsorbents used, a monolayer sorption with homogeneous binding sites would be presented.