micro-XANES evidence for the reduction of Sb(V) to Sb(III) in soil from Sb mine tailing.

ABSTRACT

The aim of this study was to determine the mechanism of Sb immobilization occurring under reductive soil conditions. In this work, we investigated the distribution and speciation of Sb in reductive soil formed in Sb mine tailing by micro-X-ray absorption near edge structure spectroscopy (micro-XANES) and electron probe microanalyzer (EPMA). EPMA and Fe K-edge micro-XANES analyses of the soil grains indicated that Sb in soil was strongly associated with Fe(III) hydroxides secondarily formed during sedimentation. The Sb concentrations in Sb hot-spot were found to be as high as 10-30 wt % (as Sb(2)O(5)). We also found quartz particles coated by secondary rims bearing Fe(III) hydroxides and Sb. The Sb K-edge micro-XANES analyses of the rims showed that a significant amount of Sb(III) was present only at the surfaces of the rims (thickness <10 microm), indicating that Sb reduction occurred in the reducing soil. The facts suggest that the reduction to Sb(III) in the system can be an important factor for Sb immobilization under reducing conditions, since the Sb(III) sorbs more strongly on Fe(III) hydroxides than Sb(V) and its solubility is also much lower than that of Sb(V) species.