Mineralogical Associations of Sedimentary Arsenic within a Contaminated Aquifer Determined through Thermal Treatment and Spectroscopy
Mineralogical Associations of Sedimentary Arsenic within a Contaminated Aquifer Determined through Thermal Treatment and Spectroscopy
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DOI：
10.3390/min13070889
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发表时间：
2023-06
期刊：
影响因子：
2.5
通讯作者：
Thomas S. Varner;H. Kulkarni;M. U. Bhuiyan;M. Cardenas;P. Knappett;S. Datta
中科院分区：
文献类型：
--
作者：
Thomas S. Varner;H. Kulkarni;M. U. Bhuiyan;M. Cardenas;P. Knappett;S. Datta
孟加拉国浅层含水层中的沉积砷（As）富集于富含有机质（OM）、粘土和氧化铁（Fe）的细粒沉积物中。在孟加拉国，沉积物颜色是孔隙水As浓度的有用指标。橙色沉积物的孔隙水通常具有较低的砷浓度（<50µg/L），因为其含有丰富的铁氧化物，可以吸附砷。利用这种颜色信号作为指导，光谱测量和热处理被广泛用于分析铁氧化物和粘土矿物的性质。本研究使用傅里叶变换红外（FTIR）和漫反射（DR）测量以及热处理来评估孟加拉国梅克纳河沿岸沉积物中As的固相关联。本研究中分析的样品代表了研究地点存在的各种岩性，包括河岸砂（1米深）、淤泥砂（6米深）、含水层砂（23米深）和粘土含水层砂（37米深）。采用x射线荧光法测定了沉积As和Fe的浓度，并在热处理前对样品进行了光谱测量。对于热处理，将沉积物样品置于600℃的预热炉中3小时。热处理导致所有样品的红棕色色调加深，并且在细粒样品中观察到最大的颜色变化。红外光谱分析表明，黏土矿物主要由伊利石、蒙脱石和高岭石组成。DR结果表明，砂中铁主要以针铁矿形式存在；而在粘土和粉土样品中，Fe以Fe（II）的形式掺入粘土矿物结构中。结构Fe（II）含量与沉积As浓度呈极显著正相关，在细粒样品中最高。热处理后，细粒试样中As的浓度平均下降40%，而砂样中As的浓度变化可以忽略不计。这些结果表明，含OM和含Fe（II）的粘土矿物可能保留了相当比例的固相As。
Sedimentary arsenic (As) in the shallow aquifers of Bangladesh is enriched in finer-grained deposits that are rich in organic matter (OM), clays, and iron (Fe)-oxides. In Bangladesh, sediment color is a useful indicator of pore water As concentrations. The pore waters of orange sediments are usually associated with lower As concentrations (<50 µg/L) owing to abundant Fe-oxides which sorb As. Using this color signal as a guide, spectroscopic measurements alongside thermal treatment were extensively utilized for analyzing the properties of both Fe-oxides and clay minerals. This study uses Fourier transform infrared (FTIR) and diffuse reflectance (DR) measurements along with thermal treatment to evaluate the solid-phase associations of As from sediment collected along the Meghna River in Bangladesh. The samples analyzed in this study were chosen to represent the various lithologies present at the study site and included riverbank sands (1 m depth), silt (6 m depth), aquifer sand (23 m depth), and a clay aquitard (37 m depth). The concentrations of sedimentary As and Fe were measured by X-ray fluorescence, and the spectroscopic measurements were taken on the samples prior to the thermal treatment. For the thermal treatment, sediment samples were placed in a preheated furnace at 600 °C for 3 h. The thermal treatment caused a deepening of reddish-brown hues in all samples, and the greatest change in color was observed in the finer-grained samples. The FTIR spectral analysis revealed that the clay minerals were composed primarily of illite, smectite, and kaolinite. The DR results indicate that the majority of Fe in sands was present as goethite; however, in the clay and silt samples, Fe was incorporated into the structure of clay minerals as Fe(II). The amount of structural Fe(II) was strongly positively correlated with the sedimentary As concentrations, which were highest in the finer-grained samples. After thermal treatment, the concentrations of As in the finer-grained samples decreased by an average of 40%, whereas the change in the As concentrations of the sand samples was negligible. These findings indicate that significant proportions of solid-phase As may be retained by OM and Fe(II)-bearing clay minerals.