Adsorption of Natural Organic Matter to Metal (hydr)oxides: Multiple Levels of Heterogeneity
The adsorption of natural organic matter (NOM) onto minerals is a major mechanism protecting carbon from degradation, which also influences distribution of nutrients and pollutants in the environment. However, due to the heterogeneous nature of NOM and the variation of soil conditions, it is so far unclear which mechanisms are regulating the preferential adsorption of NOM to metal (hydr)oxides. With carefully designed laboratory experiments and advanced surface complexation modeling, the results show that adsorbed NOM changes conformation depending on the solution and surface conditions, which is governed by the electrostatic potential gradients. In addition, the heterogeneity of NOM is present at both the ligand and particle levels, which play an essential role in modeling NOM adsorption, especially when competing with oxyanions. Besides, the competitive adsorption of different types of organic matter (e.g., humic and fulvic acids) is strongly governed by space limitations. This study improves our understanding of NOM adsorption to soil metal (hydr)oxides and its influence on competitive adsorption of oxyanion.