Near-Infrared Spectroscopic Study of Heavy-Metal-Contaminated Loess Soils in Tongguan Gold Area, Central China

Abstract

Loess soil is a kind of widespread soil type in northwest China. Human engineering activities such as mining have caused numerous problems related to heavy metal pollution in soils, which threaten people’s health. The band formation mechanism of the near-infrared (NIR) spectral features in loess soils forms the theoretical basis for the study of the soil environment by hyperspectral remote sensing. Some NIR features of loess soils will shift because of the variations of the soil composition and microstructure after they adsorb heavy metal cations. In this study, we focused on the heavy metal adsorption of the illite, smectite, and illite–smectite (I/S) mixed layer in loess soils; evaluated the pollution by Nemerow indexing; applied X-ray diffraction (XRD), mid-infrared (MIR) spectral analysis, and inductively coupled plasma mass spectrometry (ICP-MS); and carefully observed the shift behavior of the MIR and NIR features. Then, the NIR bands were assigned to MIR bands according to the vibration behavior. Furthermore, the relationships between the NIR band positions and the six heavy metal cations as well as the Nemerow index were investigated via multiregression and simple linear correlation methods. Finally, the relationship obtained from the experiments was analyzed using the physical and chemical mechanisms of the heavy metal cations in the clay minerals. These findings may benefit the application of NIR and remote sensing techniques for detecting heavy-metal-polluted soils.

Remote Sensing Inventory and Geospatial Analysis of Brick Kilns and Clay Quarrying in Kabul, Afghanistan

“…Moreover, the presence of moisture in these surficial sediments of agricultural areas overrides the clay absorption feature in their spectral signature, making the irrigated agricultural fields more prominent in band ratio analysis than the immediately adjacent brick making areas (visible in Figure 13). The band ratio values in this region may also be affected by un-examined factors such as absorption of heavy-metals from nearby industrial and developed areas, which has been shown to cause changes in the absorption of NIR and SWIR wavelengths [25].…”

Detecting cadmium contamination in loessal soils using near-infrared spectroscopy in the Xiaoqinling gold area

“…59 However, the positions of characteristic NIR bands are determined by the composition of the soil, and spectrometry can locate the spectral wavelength with high accuracy 60 ; therefore, a prediction model based on absorption band locations and heavy metals contents according to the mineral properties of loessal soils may be able to solve this problem. 3 Many mineralogical studies on the loess soil covering northwest China have shown that illite is the dominant clay mineral. 61 This study indicated an abundance of quartz, albite, and pyrite, with strong XRD peaks.…”

“…The interlayer domain is typically filled with K but can also capture Ca, Mg, Pb, Cd, Mn, Cu cations (Figure 1). 3 Therefore, the intercalation of cations gives illite minerals the ability to adsorb heavy metal cations. 7 The detection of heavy metals in soil mainly relies on traditional chemical analysis methods, such as atomic fluorescence spectroscopy, atomic absorption spectroscopy, and inductively coupled plasma mass spectroscopy.…”

“…9 This method indicates the overtone and combination absorption of hydrogen groups such as CH, N-H, and O-H, so can be used to analyze the physical and chemical properties of almost all samples involving hydrogen groups. 3 The majority of hyperspectral sensors (space- and air-borne) are equipped with the NIR band. Furthermore, the characteristic absorption peaks of illite minerals in soil are located in the NIR band.…”

“…Moreover, without considering soil physics, chemistry, and mineralogy, prediction models of heavy metal content and reflectance based on the mathematical regression method can only be applied on a limited spatiotemporal scale. 3 Therefore, developing a prediction model between the absorption band position and heavy metal content based on the soil mineral properties could partly solve this problem for particular soil types.…”