Analysis of the main technological parameters of CO₂ + O₂ in situ leaching uranium and problems by chemical precipitation blocking

According to the main composition of leached liquor pH, HCO₃^- concentration as well as three grade stability constants of UO₂²⁺ with CO₃^2- and two grade ionization constant of HCO₃^-, the relationship between the yielded mole fraction percentage of three grade uranyl carbonate complex and composition of leached liquor was calculated. The influence rule of both pH and HCO₃^- concentration to UO₂CO₃ precipitation quantity and the mole ratio of UO₂(CO₃)₃^4-/(CO₃)₃^4-/UO₂(CO₃)₂^2- was determined. It is pointed out that when leached liquor pH is about 7, HCO₃ concentration is about 1 g/L, and precipitation percentage rate of UO₂CO₃ is about l% of sexivalent uranium, good leaching rate can be guaranteed. When pH and HCO₃^- concentration is higher in the natural aquifer, and production of chemical precipitation is not easily formed to block leaching liquor circulation, the two components can be properly higher in order to intensify uranium leaching. The chemical precipitation, blocking and other influence factors in in-situ leaching process are also discussed. CO₂ + O₂ in situ leaching uranium is only suitable to high content of carbonate kind of sand stone uranium deposit, otherwise, HCO₃^- has to be added in order to intensify uranium leaching. (author)