A laboratory simulation study was carried out to check the possibility of alkaline in-situ leaching of uranium from an arkosic type of sandstone recovered from a specific location at a depth of 300-500 m. The ore body was overlaying impervious clay shale below the water table. Different CO3-2 containing soluble salts were tested as complexing agent of the UO+2 ions along with H2O2 as oxidizing agent. The lixiviant system, comprising NH4HCO3 as complexing agent along with H2O2 as oxidizing agent in concentrations of 5 g/L and 0.5 g/L respectively, was found to be the most efficient for the leaching of uranium among the 25 different compositions employed. Along with uranium, the dissolution behaviour of 15 other metals, non-metals and radicals, including eight transition metals, was also observed in the lixiviant employed. These were Na, K, Ca, Mg, Cl, SO4-2, CO3-2, Ti, V, Cr, Mn, Fe, Cu, Zn and Mo. It was found that the leaching of uranium compared to non-transition metals/radicals followed the trend Cl- > SO4-2 > U > Na+ > K+ > Mg+2 > Ca+2 > CO3-2. The comparison of uranium leaching to the transition metals was in the order U > Cr > Mo > V > Ti > Cu > Zn > Mn > Fe. Physical parameters like pH, oxidation reduction potential (ORP) and conductivity were also measured for the fresh and pregnant lixiviants. It was found that the leaching of uranium is directly related to the concentration of native soluble hexavalent uranium, contact time of the lixiviant and ore and to some extent with the total concentration of uranium as well as the porosity and permeability of the ore.
SYED SAKHAWAT SHAH ,YAHYA KHAN ,MUHAMMAD SIDDIQ ,