Cesium extraction from the Taron deposit

Abstract

Cascadero Copper Corp. has developed a hydrometallurgical process to recover cesium from mineral samples of the Taron deposit in Argentina. Cesium was extracted by sulfuric acid leaching both without and with SO2 addition, and then precipitated from the leachate as cesium alum for potential refining to cesium hydroxide. Due to a relatively low cesium content in the deposit (< 1 wt%), the cost of sulfuric acid dominates the economics of cesium recovery. The objective of this investigation was to optimize cesium extraction at an acceptable acid consumption within the constraints of hydrometallurgical processing. In sulfuric acid leaching of mineral samples under the condition of 93 °C, a solids concentration of 265 g/L and 4 h of leaching time, the cesium extraction increased with increasing initial acid concentration, reaching 96% at 200 g/L H2SO4. Higher acid concentration gave only marginal increases in cesium extraction. In two-stage countercurrent leaching with 150 g/L H2SO4, the cesium extraction was improved from 83% (in a single stage leaching) to 95%. Reductive leaching with SO2 addition was used to reduce the acid consumption. More cesium was extracted at a higher SO2 addition and a higher temperature. The SO2 leaching process was also improved with increasing sulfuric acid concentration, indicating that a high acid concentration is needed to release some portion of cesium into the solution. At a solids fraction of 30 to 50 vol%, the cesium extraction decreased with increasing solids content as the slurry became too viscous and difficult to agitate, resulting in a lower leaching rate and lower final extraction. Cesium was precipitated from the leachates as cesium alum at 4 °C and the precipitation was enhanced by increased aluminum concentration.