Valuation of unmodified rice husk waste as an eco-friendly sorbent to remove mercury: a study using environmental realistic concentrations

Abstract

The present work explores the sorption capacity of an inexpensive and highly available agricultural waste, rice husk, to remove mercury using realistic concentrations of this metal. The efficiency of the process was evaluated for two initial Hg(II) concentrations, one representing the maximum value for Hg discharges from industrial sectors (0.05 mg L-1), and the other ten times higher. A very small amount of rice husk (0.25 and 0.50 g L-1) was able to reduce the Hg(II) levels in more than 80 % for an initial concentration of 0.05 mg L-1 and in more than 90 % for 0.50 mg L-1, corresponding to residual concentrations of Hg(II) of 0.048 and 0.009 mg L-1, respectively. The biosorvent was reused in further cleaning treatments, maintaining the efficiency and high performance. The sorption kinetics of the Hg-rice husk system is well fitted by the Elovich model and the diffusion models suggested that, depending on the initial Hg(II) concentrations, the sorption process can be controlled by intraparticle diffusion or by both film and intraparticle diffusion. The equilibrium data are well described by the linear isotherm and the distribution coefficient found was 36.1 L g-1.