An evaluation of the leaching characteristics of butte leaching ore

The results of leaching experiments in columns simulating 80 and 200 ft deep cores through a leach dump are discussed. By equipping the columns with can precipitation plants, actual plant conditions could be duplicated.The results indicated that the copper grade increased with depth as long as the pH and the availability of oxygen were not limiting. In the sealed 200 ft system lack of oxygen restricted biological activity; activity increased when air was introduced. However the free diffusion of oxygen was restricted by clay formation and fines accumulation at specific levels within the column.Copper grades as high as 2.6 g/l were obtained initially but grade declined steadily as extraction progressed. The decline was most rapid after the extraction had reached 50%. In agreement with field observations, the recirculation of pregnant liquor did not increase the pregnant grade. The reason for this is discussed. The results, which produced a better understanding of physical and chemical limitations of the leaching process, are discussed in the light of commercial practice.