OPTIMIZATION OF LOW-GRADE URANIUM IN-SITU LEACHING IN A ROLL-FRONT DEPOSIT, KAZAKHSTAN

摘要

Katco, a joint-venture between the French Company Orano Mining and the Kazakhstani Company KazAtomProm, operates a mine in Kazakhstan, using the in situ recovery (ISR) method, to extract low-grade uranium from a sandy confined reservoir, located 300 to 500 meters deep, hosting a roll-front type mineralization. Leaching solution (dilute sulfuric acid in this case) is injected into the deposit through injector wells. Pregnant solution is then pumped out and sent through a pipeline network to the processing plant where uranium is extracted for the targeted ammonium diuranate production. The wellfield is organized in technological blocks constituted by 10 to 15 hexagonal cells (injector wells at the vertex and production well at the center). The uranium concentration curve for each technological block is a bell function with a concentration peak generally exceeding the 100 mg/L after 2 to 6 month of production and an operation interval of 3 to 5 years. The overall production is obtained by sequencing the operation of technological blocs over the entire deposit. After more than 10 years of production, engineers from Katco and Orano Mining have developed a strong expertise to predict chemical reaction between leached solution and host rock and to assess dissolved elements transport in the reservoir. A 3D geological model of the deposit, including mineralization, reservoir lithological facies and penalizing components, allowed for a better position of injector and production well screens. Fast processing hydrodynamic streamline simulator, using the FrontSim code, was applied to optimize acid invasion in the reservoir and acid-ore contact. Reservoir characterization and metallogenic studies provided a better understanding of uranium release mechanism in aqueous phase and specific reactive transport models were developed using the HYTEC code (MINES ParisTech). This knowledge was then applied at operational level to highlight levers for uranium recovery optimization, reduction in acid consumption, flow rate enhancement (wells cleaning technics), and enhance reliability of long term planning sequences.This paper outlines the successful operation of the deposit, while providing the main operating parameters and the resulting recovery performance.