Abstract
This paper illustrates a spectroscopic analysis of heavy metal concentration in mine soils with the consideration of mineral assemblages originated by weathering and mineralization processes. The mine soils were classified into two groups based on the mineral composition: silicate clay mineral group (Group A) and silicate–carbonate–skarn–clay mineral group (Group B). Both soil groups are contaminated with Cu, Zn, As, and Pb, while the contamination level was higher for Group A. The two groups exhibit different geochemical behaviors with different heavy metal contamination. The spectral variation associated with heavy metal was highly correlated with absorption features of clay and iron oxide minerals for Group A, and the absorption features of skarn minerals, iron oxides, and clay minerals for Group B. It indicates that the geochemical adsorption of heavy metal elements mainly occurs with clay minerals and iron oxides from weathering, and of skarn minerals, iron oxides, and clay minerals from mineralization. Therefore, soils from different secondary mineral production processes should be analyzed with different spectral models. We constructed spectral models for predicting Cu, Zn, As, and Pb in soil group A and Zn and Pb in soil group B using corresponding absorptions. Both models were statistically significant with sufficient accuracy.
Highlights
Soils play an important role in the earth system as a boundary between lithosphere and atmosphere and the settlement basement for biosphere
The heavy metal concentration of the soil samples was analyzed by a portable X-ray fluorescence spectrometry (PXRF hereafter)
The results revealed that the mineral composition of heavy metal contaminated soil samples showed distinctive differences in mineral composition depending on the geographic distribution and geology
Summary
Soils play an important role in the earth system as a boundary between lithosphere and atmosphere and the settlement basement for biosphere. Spectral signals of heavy metal elements in soils must be studied by considering the geochemical reaction agents, such as clay minerals, organic matters, and iron/manganese oxides [11,13,15,16,17,18]. Previous studies on visible-near infrared-shortwave infrared (VNIR-SWIR hereafter) spectroscopy applied to heavy metal concentration in soils have identified spectral regions associated with chemical compounds participating physicochemical reactions in soils [5,13,14,18,19,20,21]. The association between spectral signals with heavy metal contamination controlled by different combinations of mineralogy, with respect to geological processes in mine soils, has rarely been reported before. The spectral signals of heavy metal concentration controlled by mineral assemblage and associated geochemical agents are discussed
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