Geochemical research on enrichment behavior of thorium in limestone soil profiles

Selecting four limestone soil profiles as the subject investigated from karst area of central Guizhou Province. and based on careful sampling and analysis, this work discusses geochemical characteristics and behavior of Th enrichment during the formation of limestone soils. The results show that: 1) the rock-soil interface is an important geochemical reaction place for significant enrichment of Th, and this mainly stems from residual enrichment of Th through huge changes in volume reduction of weathered residua accompanied by rapid dissolution of carbonates in the interaction of rock-soil interface. In this process, Th appears obviously inert. 2) During the formation and evolution of limestone soil profiles, different geo- chemical behavior of Th exists between profiles possibly owing to micro-environmental diversities. For shallowly developed profiles, Th shows evident inertia by adsorption of iron oxide/ hydroxide and clay minerals; for relatively profoundly developed profiles, Th exhibits some activity, and its behavior is not susceptible to iron oxide/hydroxide and clay minerals. (authors)