Arsenic Migration and Transformation in Aquifer Sediments under Successive Redox Oscillations

Abstract

Sediments were taken from the Hetao basin to investigate effects of different lithologies and grain size distribution on As behaviors during oscillation of redox conditions. Total digestion and sequential extraction procedures showed that Fe and Mn oxide minerals played important roles for As accumulation. The co-variation of As, CIA (Chemical Index of Alteration), ICV (Index of Compositional Variability) and Al₂O₃/SiO₂ indicated that As were enriched in strongly chemical weathering sediments weathered from mature mudrocks. Two sediments samples with the same As contents (21.9 μg/g) but different lithologies (fine sand versus clay) were chosen for redox oscillation experiments. As released from clayey (C-1) suspension was lower than those in C-2 (grounded sand) and C-3 (sand). Under reducing conditions, the maximum As concentration in C-1 was 9.99 μg/L, however, it was 149 μg/L in C-2 and 120 μg/L in C-3. It inferred that the lithology and mineralogy play an important role in As fixation and mobilization. The grounded sands released more As in reducing conditions and sequestrated more As in oxic conditions relative to the pristine sands.