Antimony sorption to schwertmannite in acid sulfate environments
Mohammad Rastegari, N. Karimian, Scott G. Johnston, Girish Choppala, Mona Hosseinpour Moghaddam, Edward D. Burton
Abstract
Schwertmannite is a poorly-crystalline Fe(III) oxyhydroxysulfate mineral that may control Sb(V) mobility in acid sulfate environments, including acid mine drainage and acid sulfate soils. However, the mechanisms that govern uptake of aqueous Sb(V) by schwertmannite in such environments are poorly understood. To address this issue, we examined Sb(V) sorption to schwertmannite across a range of environmentally-relevant Sb(V) loadings at pH 3 in sulfate-rich solutions. Antimony K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that Sb(V) sorption (at all loadings) involved edge and double-corner sharing linkages between Sb V O 6 and Fe III O 6 octahedra. The coordination numbers for these linkages indicate that sorption occurred by Sb(V) incorporation into the schwertmannite structure via heterovalent Sb(V)-for-Fe(III) substitution. As such, Sb(V) sorption to schwertmannite was not limited by the abundance of surface complexation sites and was strongly resistant to desorption when exposed to 0.1 M PO 4 3- . Sorption of Sb(V) also conferred increased stability to schwertmannite, based on changes in the schwertmannite dissolution rate during extraction with an acidic ammonium oxalate solution. This study provides new insights into Sb(V) sorption to schwertmannite in acid sulfate environments, and highlights the role that schwertmannite can play in immobilizing Sb(V) within its crystal structure. • Sb(V) sorption by schwertmannite was investigated under acid sulfate conditions. • Sorption involved incorporation of Sb(V) into the schwertmannite structure. • Sb(V)-sorbed schwertmannite showed resistance to desorption and dissolution. • Schwertmannite may be a secure host-phase for Sb(V) in acid sulfate environments.