Huhmann Brittany L, Neumann Anke, Boyanov Maxim I, Kemner Kenneth M, Scherer Michelle M
Department of Civil and Environmental Engineering, University of Iowa, Iowa City, IA 52242, USA.
Environ Sci Process Impacts. 2017 Oct 18;19(10):1208-1219. doi: 10.1039/c7em00237h.
Exposure to As in groundwater negatively impacts millions of people around the globe, and As mobility in groundwater is often controlled by Fe mineral dissolution and precipitation. Additionally, trace elements can be released from and incorporated into the structure of Fe oxides in the presence of dissolved Fe(ii). The potential for As to redistribute between sorbed on the magnetite surface and incorporated in the magnetite structure, however, remains unclear. In this study, we use selective chemical extraction and X-ray absorption spectroscopy (XAS) to distinguish magnetite-sorbed and incorporated As(v) and to provide evidence for As(v) incorporation during magnetite precipitation. While As in the As-magnetite coprecipitates did not redistribute between sorbed and incorporated over a 4 month period, a small, but measurable increase in incorporated As(v) of up to 13% was observed for sorbed As(v). We suggest that Fe(ii)-catalyzed recrystallization of magnetite did not significantly influence the redistribution of sorbed As(v) because the extent of Fe atom exchange was small (∼10%). In addition, the extent of As redistribution was the same in the absence and presence of added aqueous Fe(ii), suggesting that aqueous Fe(ii) had, overall, a minor effect on As redistribution for both coprecipitated and sorbed As(v). Our results suggest that coprecipitation of As(v) with magnetite and redistribution of As(v) sorbed on magnetite are potential pathways for irreversible As(v) uptake and sequestration. These pathways are likely to play a significant role in controlling As mobility in natural systems, during human-induced redox cycling of groundwater such as aquifer storage and recovery, as well as in iron oxide-based As removal systems.
地下水中的砷暴露对全球数百万人产生负面影响，并且地下水中砷的迁移性通常受铁矿物溶解和沉淀控制。此外，在溶解的Fe(ii)存在下，微量元素可从铁氧化物结构中释放出来并掺入其中。然而，砷在磁铁矿表面吸附态与掺入磁铁矿结构之间重新分布的可能性仍不清楚。在本研究中，我们使用选择性化学萃取和X射线吸收光谱(XAS)来区分磁铁矿吸附态和掺入态的As(v)，并为磁铁矿沉淀过程中As(v)的掺入提供证据。虽然As-磁铁矿共沉淀物中的As在4个月内未在吸附态和掺入态之间重新分布，但观察到吸附态As(v)中掺入态As(v)有小幅但可测量的增加，最高可达13%。我们认为，磁铁矿的Fe(ii)催化重结晶对吸附态As(v)的重新分布没有显著影响，因为Fe原子交换程度较小(约10%)。此外，在添加和不添加水溶Fe(ii)的情况下，As的重新分布程度相同，这表明水溶Fe(ii)总体上对共沉淀态和吸附态As(v)的As重新分布影响较小。我们的结果表明，As(v)与磁铁矿的共沉淀以及吸附在磁铁矿上的As(v)的重新分布是As(v)不可逆吸收和固存的潜在途径。这些途径可能在控制自然系统中砷的迁移性、在人类诱导的地下水氧化还原循环(如含水层储存和回灌)过程中以及在基于铁氧化物的砷去除系统中发挥重要作用。
