Enrichment characteristics and mechanisms of particulate organic matter in mine wastes containing mercury and thallium

The decomposition of plant litter in the soil affects the formation of particulate organic matter (POM) and nutrient contents, and has an important influence on the regulation of heavy metal migration and transformation. However, research on the migration and transformation of heavy metals in the ecological restoration of polymetallic slag yards as affected by POM is limited. In this paper, four types of plant litter were left to degrade in mercury (Hg)-thallium (Tl) mine waste to study the effect of the formed POM on the enrichment of the heavy metals Hg and Tl. The results showed that the total amount of POM produced by the degradation of the four litters increased in the order Perennial ryegrass > Robinia pseudoacacia > Trifolium repens > Broussonetia papyrifera . Fine POM (0.05–0.25 mm) had the highest mass percentage for all litters. As the particle size of POM decreased, the content of Hg and Tl increased, mainly because fine POM has a larger specific surface area , pore volume , and surface charge density, which provides greater adsorption capacity and sites for Hg and Tl adsorption. Moreover, fine POM has more active functional groups such as -OH and C O with high affinity for heavy metals, which increase its adsorption and binding capacity for Hg and Tl. The results provide a scientific basis for understanding the migration behavior and environmental fate of Hg and Tl in the context of ecological restoration of waste dumps .