Calcite Control in In-Situ Uranium Leaching Process

Abstract

A method has been developed to control the problem of calcite deposits inthe in-situ uranium leaching process using carbonates as the lixiviant. Achemical inhibitor is added to the calcium-supersaturated lixiviant (andother process streams) at critical locations in sufficient quantity to forma metastable solution of calcite so that the lixiviant can pass throughcritical areas without depositing calcite. Introduction Uranium values can be recovered from undergrounddeposits by open-pit or underground miningfollowed by milling or leaching in a surface mill. Recently, the efficient recovery of uranium fromsedimentary deposits also has been accomplished byin-situ leaching or solution mining. The in-situ leaching process integrates the standard mine/millcomplex by in-place leaching of uranium andprocessing the uranium-rich fluids at the surface. Useof an in-situ leaching process for sedimentaryuranium deposits has proved profitable andcompetitive with the conventional open-pit orunderground mine/mill systems. The advantages ofthe in-situ leaching process have been reviewed. The nature of the lixiviant for successful in-situleaching depends on the nature of the ore bodies.Acid lixiviant, consisting of H2SO4 and NaClO3, has been tested successfully at Shirley basin inWyoming. Sulfuric acid and H2O2 lixiviant has beenused with success at Nine Mile Lake in Wyoming byRocky Mountain Energy Co. For ores with a highcontent of carbonate minerals, such as limestone anddolomite, the acidic lixiviants become uneconomical because of excess acid consumption. For such ores, carbonate lixiviant is preferred. In the carbonate leaching process, the lixiviantsare made up of NaHCO3/Na2CO3 as the complexingagents and NaClO3 or H2O2 as the oxidant.However, in the field a permeability loss often isencountered when NaHCO3/Na2CO3 lixiviant isused. This permeability loss is thought to be due toswelling of clay minerals, such as smectite, in theformation by sodium ion. Use of ammonium ion inplace of sodium ion in the lixiviant can alleviatemuch of the problem of formation permeability loss.Intercontinental Energy Corp. has been successfullyusing (NH4)2CO3 and H2O2 as the lixiviant in southTexas for some time. Mobil Oil Corp. alsosuccessfully pilot tested the use of(NH4)2CO3 andNaClO3 in south Texas. JPT P. 2068＾