Adsorption of Fulvic Acid and Water Extractable Soil Organic Matter on Kaolinite and Muscovite

Abstract

The interaction of organic matter with mineral components of the solid phase of soils is the most important process that regulates the cycle and balance of carbon in the biosphere. The adsorption of humic acids on minerals is accompanied by their fractionation in size, composition, and amphiphilicity, thus decreasing their heterogeneity. Despite a strong interest in studying the regularities and mechanisms of the interaction between natural organic matter and layered aluminosilicates, it is necessary to take into account the natural diversity of soil organic matter, adsorption conditions, and mineral composition. This study was designed to investigate the adsorption regularities of fulvic acid (FA) and water-extractable organic matter (WEOM) isolated from horizon H of peaty-podzolic-gleyic soil on kaolinite and muscovite. Sorbates and sorbents were examined by the following methods: high-pressure size exclusion chromatography (HPSEC), high-performance liquid chromatography (HPLC), and potentiometric titration. The specific surface areas of the sorbents were determined by the sorption of N2 molecules. We found that hydrophobic components of FA and WEOM are mainly adsorbed on mineral surfaces. The adsorption of FA and WEOM on kaolinite and muscovite is followed by decreased hydrophobicity of organic matter and decreased heterogeneity of its amphiphilic properties in an equilibrium solution. At pH levels around 6, sorption of organic matter from FA solution containing 19% and 81% hydrophilic and hydrophobic components, respectively, onto kaolinite and muscovite occurs mainly due to hydrophobic components. Hydrophobic interactions on siloxane surfaces are the main mechanism to fix FA on both minerals. Kaolinite adsorbs slightly more organic carbon per unit area than muscovite. The adsorption of WEOM from a solution with 41% hydrophilic and 59% hydrophobic components results not only from hydrophobic and hydrophilic components but also from hydrophobic and electrostatic interactions and depends on pH. The most hydrophobic fractions of organic matter are adsorbed from the hydrophobic components on the surface of both minerals. Under conditions of the performed experiments at pH < 5, more WEOM is adsorbed on muscovite than on kaolinite.

Thermal Stability and Resistance to Biodegradation of Humic Acid Adsorbed on Clay Minerals

“…The pH of the zero-charge point (pH PZC ) for bentonite clays is about 8 units [34][35][36], and the pKa of the silanol and aluminol groups of montmorillonite vary from 6.7 to 8.2 and from 4.8 to 8.5, respectively [37,38]. The pH PZC of the muscovite used in the experiment is 8.1 [39]. HA sorption was carried out at pH 4.5, which was lower than the pKa for the functional groups of the pH-dependent surfaces of kaolinite, muscovite, and montmorillonite.…”

Effects of Fertilization Mode on the Growth of Lactuca sativa L. and Soil Nutrients in Facilitated Cultivation

“…SAK is the main form of potassium available in the soil for plant uptake and has a significant impact on crop yield and quality. SOM is an important component of the solid phase fraction of the soil and is one of the main sources of plant nutrition, contributing positively to the activity of microorganisms and soil organisms as well as to the decomposition of nutrient elements in the soil [22].…”