The Release/Enrichment Mechanism Of Ursnium During Chemical Weathring In Rock-soil Interface In Weathering Profile Derived From Carbonate Rocks

In the weathering of uranium(U)-poor carbonate rocks, on the one hand, uranium(U) is significantly enriched and even form radon anomalies in weathering profile; on the other hand, Large amounts of U are leached from bedrock and being main contributor of dissolved U of drainage basin.Rock-soil interface in weathering profile derived from carbonate rocks is an important place for the release and enrichment of uranium. The research on its mechanism is weak at present. 9 weathering crust derived from carbonate rocks with different geological ages have been investigated in Guizhou. Based on analysis of major and trace element, the physical and chemical conditions of environment and occurrence states of U, this reasearth revealed the geochemical behavior and the release/enrichment mechanism of U during chemical weathering in rock-soil interface. Some important conclusions have been summarized as follows.U mainly occurs in carbonate minerals of carbonate rocks, with a small amount in acid insoluble matter. As carbonate minerals completely dissolutionduring weathering, the acid soluble U of carbonate minerals is activation and release. Acid soluble U is the main source of U leaching in the chemical weathering process in rock-soil interface.The main reason for enrichment of U in soil is residual and enrichment of U of acid insoluble matter. The U content of acid insoluble matter is much larger than its bedrock. Most U of acid insoluble matter is residued as hard to be activated, and become the main source of U in the soil. The adsorption of U on the soil substrate promoted the further enrichment of U in soil.Acid insoluble matter of bedrock was decomposed during chemical weathering in rock-soil interface of carbonate rocks. Some U of mineral crystal lattice is released and leached out. Organic matter and clay minerals release U in the rock-soil interface, and reabsorb U in the soil. These may be the reasons that U content of bedrock acid insoluble matter is not a decisive factor of U content of soil.Main influence factors Transporting and evolving of U of acid insoluble matter are silicate hydrolysis,decomposition and adsorption U of oxides and hydroxides of iron and manganese in the rock-soil interface.Weathered bedrock of carbonate rocks is an alkaline environment, which is conducive to the migration of U in the weathering process. The soil in rock-soil interface is a partial neutral environment, which is beneficial to keep U in the weathering process.