Operating Experience In The Recovery Of Uranium At The Pawnee And Zamzow Sites

Abstract

IEC Corporation is presently recovering uranium by in-situ leaching or solution mining technique at the Zamzow site, and completed as production at the pawnee site An oxidative lixivant with ammonium carbonate and hydrogen peroxide is injected into subsurface ore strata according to a defined wellfield pattern. The resulting uranium-enriched leachate solution is pumped out of pattern. The resulting uranium-enriched leachate solution is pumped out of the ground and brought to the recovery plant. This solution is filtered first and then the uranium is recovered by an ion exchange process. The final product of yellowcake is produced by steam process. The final product of yellowcake is produced by steam precipitation and vacuum drying. The precipitation and vacuum drying. The uranium-free barren solution is re-injected into the orebody after adding the necessary make-up chemicals. Several problems related to ion exchange performance were observed during the initial startup of the Pawnee site. These included fouling with polythionates and oxidative attack on the resin structure. Cooperative studies between IEC Corporation and Sybron Corporation led to the selection of a resin with increased resistance to oxidative attack. Modification of the feed solution chemistry resulted in control of the polythionate fouling and also in reduction in uranium losses. These findings were also applied to the second site operation where acceptable performances have been experienced for the past two years. The Pawnee site, a small orebody, has been worked out and a site restoration program has been under way for over a year. Methods for handling above ground wastes are discussed and approaches to the control of underground ground water contaminants outlined. Lessons learned at Pawnee are discussed in light of restoration of future sites. The Zamzow site has been in full production since July 1978, General plant practices and economics plant practices and economics are outlined and future recommendations on process modifications suggested. Introduction Intercontinental Energy Corporation, doing business as IEC Corporation in Texas, started the valuable of two interesting uranium ore bodies in Texas in 1976, These deposits were located along the South Central Texas uranium belt in an area where several other mining properties were under properties were under development and in actual production. Figure 1 shows I EC's operations along with other in-situ uranium leaching operations in the South Texas area. The Pawnee Site The Pawnee site was known to be a small ore body ideal for a limited pilot plant type operation where pilot plant type operation where valuable process knowledge could be gained for application later at the larger Zamzow site. The Pawnee site is located approximately 2.4 miles east of Pawnee in Bee County. The area involved in mining-related operations is about 20 acres in extent and includes the actual wellfields drilled into 5 ore "pods" which cover about 6.75 acres. Geologically, the ore horizons are within basal channel sands of the Miocene age Oakville formation lying between 200 to 250 feet below the land surface. These mineralized sands (probably uraninite) directly overlie the massive impermeable clays of the Catahoula formation, and are overlain by clays of the Oakville and Fleming formations. There is no aquifer overlying the Oakville sands, and the next deeper aquifer is below the 1000 to 1200 feet thick Catahoula formation clay. Hydrologically, the mineralized horizon can be characterized as a moderately to well sorted, loosely consolidated sandstone or arkosic sandstone. The effective porosity is 30% and the hydraulic gradient is to the south at approximately one to two degrees. The nondirectional transmissibility coefficient of the host sand is 6,430 gallons per day per foot and groundwater flow velocities are about 26 feet per year to the southeast. During the life of the mine, about 400 to 450 million gallons of groundwater was processed by the plant.