Influence of reducing conditions on the release of antimony and arsenic from a tailings sediment

Purpose

Burial treatment is a frequently used technology for contaminated solid materials, but little is known about the effect of redox changes on the mobility of metals and metalloids. Here, sediment contaminated by historical tailing slurry from an antimony (Sb) mine was incubated with sodium ascorbate solution (SAS), so as to gain insights into the remobilization of Sb and arsenic (As) under reducing conditions.

Materials and methods

Anaerobic incubation of a tailing sediment was incubated with SAS and high-purity water (HPW) as a comparison for 20 day. Metals and metalloids in various chemical fractions of the sediment were quantified by sequential extraction. Dissolved Sb and As species in the HPW and SAS over the incubation period were quantified by hydride generation atomic fluorescence spectrometry.

Results and discussion

In the tailing sediment, 30.8 % of iron (Fe) was found in Fe(III) oxyhydroxides, which hosted 26.7 % of Sb and 32.8 % of As. The water-soluble and exchangeable fractions of Sb (0.09 and 2.0 %) were approximately 10-fold that of As (0.01 and 0.2 %). When the sediment was incubated with the HPW, the behavior of manganese (Mn) was active and Sb was found to be concomitant with Mn. In the SAS, As was first released more weakly than Sb, but later released more strongly than Sb. The release of Sb before 72 h was approximately 2.6-fold that of As, and after 72 h the release of As was approximately 8.8-fold that of Sb. It was deduced that Sb and As were bound differently to Fe phases, with Sb mainly bound to the early dissolved Fe phases whereas As was mainly bound to the later-dissolved Fe phases.

Conclusions

This work indicated that both Mn and Fe phases played an important role on the behavior of Sb, and Fe phases played an important role on the behavior of As. Under reducing conditions, the reductive dissolution of Mn and Fe phases resulted in a strong release of Sb in the early stage and a strong release of As in the later stage, because Sb and As exhibited different chemical associations in the tailing sediment.