Data for "Mineralogical Associations of Sedimentary Arsenic within a Contaminated Aquifer Determined through Thermal Treatment and Spectroscopy"

This repository contains all the sediment and experimental data used in this study. Study Abstract 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.本数据集存储库收录了本研究使用的全部沉积物与实验数据。 研究摘要 孟加拉国浅层含水层中的沉积态砷（As）富集于富含有机质（OM）、黏土与铁（Fe）氧化物的细粒沉积物中。在孟加拉国，沉积物颜色可作为孔隙水砷浓度的有效指示指标。橙色沉积物的孔隙水通常砷浓度较低（<50 μg/L），这是因为其富含可吸附砷的铁氧化物。以此颜色特征为指引，本研究广泛采用光谱测量与热处理手段，分析铁氧化物与黏土矿物的特性。本研究借助傅里叶变换红外光谱（FTIR）、漫反射光谱（DR）测量结合热处理方法，对孟加拉国梅格纳河沿岸采集的沉积物中砷的固相赋存状态进行评估。本研究选取的样品覆盖了研究点位的各类岩性，包括河岸砂（深度1 m）、粉砂（深度6 m）、含水层砂（深度23 m）以及黏土隔水层（深度37 m）。采用X射线荧光光谱法测定沉积物中砷与铁的含量，并在热处理前对样品进行光谱测量。热处理环节为将沉积物样品置于600 ℃的预热炉中保温3 h。热处理使所有样品的红棕色调加深，其中细粒样品的颜色变化最为显著。傅里叶变换红外光谱分析显示，黏土矿物主要由伊利石、蒙脱石与高岭石组成。漫反射光谱结果表明，砂样中的铁多以针铁矿形式存在；而黏土与粉砂样品中的铁则以Fe(II)的形式嵌入黏土矿物结构中。结构态Fe(II)的含量与沉积态砷浓度呈显著正相关，且细粒样品中的砷浓度最高。热处理后，细粒样品中的砷浓度平均下降40%，而砂样的砷浓度变化可忽略不计。上述结果表明，固相砷的很大一部分可能由有机质与含Fe(II)的黏土矿物所固持。