Nanostructured α-Fe2O3 derived from siderite as an effective Hg(II) adsorbent: Performance and mechanism

Nanoparticle α-Fe2O3 was prepared by thermal treatment of siderite and utilized to adsorb Hg(II) from an aqueous solution. The physicochemical properties and Hg(II) adsorption capacities of this α-Fe2O3 phase were investigated by various characterization techniques and batch equilibrium experiments. The nanostructured α-Fe2O3 of charge S-500 revealed the best adsorption capacity due to its larger specific surface area (50 m2 g−1) and smaller average pore size (7.3 nm). The maximum Hg(II) sorption capacity of S-500 was calculated from the Langmuir model to be 11.2 mg/g at pH = 6 and T = 303 K. The sorption of Hg(II) at pH < 6.0 could be attributed to the outer-sphere surface complexation, whereas the formation of inner-sphere surface complexation dominated the Hg(II) sorption at higher pH. For the latter, FT-IR and XPS analysis demonstrated that hydroxyl groups on the surface of S-500 are involved in the efficient removal of Hg(II) from aqueous solutions. These results provide an cost-effective method for the comprehensive utilization of siderite rock resources in environmental remediation.