Chemical Extractions Affect the Structure and Phenanthrene Sorption of Soil Humin

• Published in: Environmental science & technology Vol. 39; no. 21; pp. 8333 - 8340
• Main Authors: Wang, Kaijun, Xing, Baoshan
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.11.2005
• Subjects: Applied sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Humic Substances; Hydrochloric Acid - chemistry; Hydrofluoric Acid - chemistry; Magnetic Resonance Spectroscopy; Molecular Structure; Phenanthrenes - chemistry; Pollutants; Pollution; Pollution, environment geology; Sodium Hydroxide - chemistry; Soil adsorption; Soil and sediments pollution; Soil contaminants; Organic matter; Phenanthrene; Heat treatment; Hydrocarbon; Adsorption isotherm; Chemical structure; Partition coefficient; Polycyclic aromatic compound; Soil pollution; Sediments; Adsorption; Investigation method; Chemical treatment; Extraction; Phase partition; Property structure relationship; Adsorbent; Conformation
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es050737u

Humin is a major fraction of soil organic matter and strongly affects the sorption behavior and fate of organic contaminants in soils and sediments. This study evaluated four different extraction methods for soil humins in terms of their organic carbon structural changes and the consequent effects on phenanthrene sorption. Solid-state 13C NMR demonstrated that 0.1 M NaOH exhaustively extracted humin and humin extracted with 6 M HF/HCl at 60 °C had a relatively high amount of aliphatic components as compared with 1 M HF-extracted humin. The treatment of 6 M HF/HCl at 60 °C greatly reduced carbohydrate components (50−108 ppm) from humin samples, i.e., more than 50% reduction. In addition, the humin from this 6 M HF/HCl treatment contained relatively more amorphous poly(methylene) domains than the humins extracted by other methods. With the respect to phenanthrene sorption, the linearity of sorption isotherm (N) and sorption affinity (K OC) varied markedly among the humin samples extracted by different methods. The NaOH exhaustively extracted humin had the most nonlinear sorption isotherm and the HF-extracted humin had the lowest K OC. It is concluded that humin samples from different extraction procedures exhibited substantial differences in their organic carbon structure and sorption characteristics, even though they were from the same soil. Therefore, one needs to be cautious when comparing the structural and sorption features of soil humins, especially when they are extracted differently. The 6 M HCl/HF extraction at elevated temperature is not encouraged, due to the modifications of chemical structure and physical conformation of organic matter.