Southern Cross Geoscience, Southern Cross University, Lismore, NSW 2480, Australia.
Environmental Futures Research Institute, Griffith University Gold Coast campus, Southport, QLD 4215, Australia.
Sci Total Environ. 2020 Mar 25;710:136354. doi: 10.1016/j.scitotenv.2019.136354. Epub 2020 Jan 3.
The Macleay River in eastern Australia is severely impacted by historic stibnite- and arsenopyrite-rich mine-tailings. We explore the partitioning, speciation, redox-cycling, mineral associations and mobility of antimony and arsenic along >70 km reach of the upper Macleay River. Elevated Sb/As occur throughout the active channel-zone and in floodplain pockets up to the regolith margin, indicating broad dispersal during floods. Sb concentrations in bulk-sediments decay exponentially downstream more efficiently than As, likely reflecting sediment dilution, hydraulic sorting and comparatively greater leaching of (more mobile) Sb(V) species. However, Sb in bulk-sediments becomes proportionally more bio-available downstream. Sb(V) and As(V) species dominate stream fine-grained (<180 μm) bulk-sediments, reflecting oxidative weathering downstream. Increasing poorly-crystalline Fe(III) [Fe(III)] in bulk-sediments also indicates progressive oxidative weathering of Fe(II)-bearing minerals downstream and significant (P < .05) correlations exist between PO-exchangeable As and Sb fractions and Fe(III). Accumulations of poorly-crystalline Fe(III) precipitates (mainly ferrihydrite/feroxyhyte) occur intermittently in hyporheic-zone seeps and are enriched in As relative to Sb and contain some As(III) and Sb(III) (~30-40%). There is dynamic in-stream redox-cycling of both Sb and As, with localised S-coordinated As and Sb species re-forming in organic-rich, hyporheic sediments subject to contemporary sulfidogenesis. Sb [mainly Sb(V)] is comparatively more mobile in hyporheic and surface waters under oxic conditions, whereas As [mainly As(III)] is more mobile in hyporheic porewaters subject to reducing/sulfidogenic conditions. Repeat water-leaching of bulk-sediments confirms that Sb is proportionally more mobile than As. Mean concentrations of Sb in river water 168 km downstream from the mine are significantly (P < .05) higher than As, while K data indicate Sb is more strongly partitioned to the aqueous phase than As. Although the (mainly) oxic flow path of this river favours aqueous Sb mobility compared to As, localised redox-driven shifts in speciation of both elements strongly influence their respective mobility and partitioning.
澳大利亚东部的麦凯河受到历史上富含辉锑矿和毒砂的尾矿的严重影响。我们探索了沿着麦凯河上游超过 70 公里的河段中锑和砷的分配、形态、氧化还原循环、矿物组合和迁移性。在活动河道带和洪泛区口袋中都发现了升高的 Sb/As，直到表土边缘，表明洪水期间广泛分散。与 As 相比，Sb 在整体沉积物中的衰减效率更高，呈指数下降，这可能反映了沉积物稀释、水力分选以及相对更多的（更易移动的）Sb(V) 物种的浸出。然而，Sb 在整体沉积物中变得更具生物可利用性。Sb(V)和 As(V) 物种在溪流细颗粒（<180μm）整体沉积物中占主导地位，反映出下游的氧化风化。整体沉积物中结晶度较差的 Fe(III)[Fe(III)]的增加也表明下游 Fe(II) 矿物的氧化风化以及 PO 可交换的 As 和 Sb 与 Fe(III)之间存在显著（P<.05）相关性。结晶度较差的 Fe(III)沉淀物（主要是水铁矿/水铁矾）在潜流区渗出物中间歇性地积聚，与 Sb 相比，As 更为丰富，并且含有一些 As(III)和 Sb(III)（~30-40%）。Sb 和 As 都存在动态的河流内氧化还原循环，在受当代硫化作用影响的富含有机质的潜流沉积物中，局部形成 S 配位的 As 和 Sb 物种。在含氧条件下，Sb[主要为 Sb(V)]在潜流和地表水中等更具流动性，而在受还原/硫化作用影响的潜流孔隙水中，As[主要为 As(III)]更具流动性。对整体沉积物的重复水浸提证实 Sb 的移动性比 As 更大。在距离矿山 168 公里的下游河水样本中，Sb 的平均浓度显著（P<.05）高于 As，而 K 数据表明 Sb 比 As 更强烈地分配到水相。尽管这条河流的（主要）有氧流路径有利于 Sb 比 As 更具流动性，但两种元素的局部氧化还原驱动的形态变化强烈影响它们各自的流动性和分配。
