Comparison of Arsenic Adsorption and Desorption Performance by Different Microaggregates in Black Soil

The adsorption and desorption behavior of arsenic (As) in agricultural soils is a critical process controlling its migration, transformation, and bioavailability, with direct implications for food safety and environmental risk. Although black soil regions are major grain-producing areas in China, the roles of different soil microaggregate fractions and their components in As retention remain poorly understood. Therefore, batch equilibrium adsorption experiments were performed to study the adsorption and desorption behaviors of As(V) on the different microaggregates and to explore the effects of soil particle size, organic matter and iron oxide on the adsorption performance of As(V). The results show that as the concentration of As(V) increases, the adsorption capacity gradually reaches equilibrium, and the Freundlich equation fits the results well. The order of the As adsorption capacity of microaggregates of different particle sizes in black soil is as follows: ( 0.005–0.05 mm > 0.002–0.005 mm > 0.05–0.25 mm > 0.25–2 mm. The maximum adsorption capacity occurs in the microaggregates of the soil with the smallest particle size. The order of the As desorption capacity of microaggregates of each particle size is opposite to their adsorption capacity and inversely proportional to the content of each component in the soil. Removal of soil organic matter (SOM) and free iron oxide (Fed) significantly reduced the specific adsorption and immobilization capacity of black soil for As(V), while enhancing non-specific adsorption. This study elucidates the differential contributions of soil microaggregates and key components to As(V) retention and provides an experimental foundation for further research on the occurrence and migration mechanisms of As in black soil.