Abstract:Uranium leaching is realized by a series of hydrogeochemical interactions between leaching solution and uranium minerals. In Bayanwula uranium mine, blockage of ore-bearing strata occurred in acid in-situ leaching. Based on mineral characteristics of ore-bearing bed and chemical components of leachate, leachate - mineral balance was simulated by model of geochemical process PHREEQCI, saturation index of mineral and reaction condition index (RCI) were calculated, mineral dissolution precipitation stat was determined, and hydrogeochemical mechanism of blockage of ore-bearing bed was revealed. The results show that hydrogeochemical reason for blockage of ore-bearing strata is that Ca2+, SO42- and Fe3+ in leaching solution are in supersaturated state, resulting in precipitation of gypsum, goethite and hematite, with saturation index of 0.06—0.20, 0.01—0.83 and 0.94—2.58, respectively. RCICa of gypsum is 0.34—0.42, and RCIS is 1.17—1.35. Ca2+ concentration is main factor affecting solution-precipitation of gypsum. RCIpH (-3.47—-3.27), RCIEh (-599.44—-474.72 mV) and RCIFe (0.96—1.37) of hematite and goethite are all in precipitated state. Precipitation of gypsum and iron minerals is the result that ionic activity product of leaching solution exceeds its solution product constant after interaction between leaching solution and minerals in ore bearing layer.