Interaction between Iron-Aluminum Oxides and Organic Carbon in Soils with Different Parent Materials and Its Influence on Heavy Metal Migration

Iron-aluminum oxides, as significant mineral components, exhibit a notable influence on the organic carbon content in soil. The interaction between these two elements constitutes a crucial aspect of soil environmental processes, particularly in the migration and transformation of heavy metals. This study focuses on soils developed from aeolian and alluvial-pluvial parent materials in Heilongjiang Province. By analyzing the distribution characteristics of various forms of iron-aluminum oxides and organic carbon content in different soil profiles, correlation analysis and redundancy analysis was employed to investigate the interactions between iron-aluminum oxides and organic carbon, as well as their manifestations in different parent material soils. Furthermore, the correlations with heavy metal elements were analyzed. Through comparative analysis, certain differences in the vertical distribution of iron-aluminum oxides were observed, while the vertical changes in organic carbon content were similar. Correlation analysis revealed that complexed alumina (Al_p) and free alumina (Al_d) exhibited a stronger positive correlation with organic carbon compared to other forms. Complexed iron-aluminum oxides demonstrated a significant correlation with most heavy metal elements. Furthermore, complexed iron oxide (Fe_p), free iron oxide (Fe_d), amorphous iron oxide (Fe_o), and Al_p showed a significant positive correlation with Hg, while amorphous alumina (Al_o) correlated positively with As and Ni. Analysis suggests that in soils derived from alluvial-pluvial parent materials, the low pH environment promotes higher levels of free and complexed iron-aluminum oxides, facilitating stronger binding with organic carbon to form more stable complexes. Conversely, in the soils developed from aeolian parent materials, due to the high pH, the dissolution of iron-aluminum oxides is inhibited, and the concentrations of free and complexed iron-aluminum oxides are low, thereby reducing the binding capacity with organic carbon and resulting in a higher organic carbon content. Further analysis indicates that iron-aluminum oxides and their organic carbon complexes interact with heavy metal elements through complexation, adsorption, and co-precipitation, thereby influencing heavy metal migration and accumulation in soil.