DEVELOPMENT OF AMMONIACAL LIXIVIANTS FOR THE IN-SITU LEACHING OF CHALCOPYRITE

Researchers at the U.S. Bureau of Mines are investigating the ammonia- oxygen leaching of chalcopyrite at conditions anticipated in an in-sit u environment. Two major problems were identified in a review of the l iterature: (1) providing sufficient oxidant to drive the leaching reac tion, and (2) decreased leaching kinetics due to the build-up of a fer ric oxide reaction product layer at the mineral surface. Preliminary c haracterization studies were performed in a 2-1, well-mixed autoclave system incorporating automated sampling and data acquisition. A statis tical experimental design was utilized to determine which parameters w ere most influential in the dissolution of copper from relatively pure chalcopyrite specimens. The most significant leaching parameters for the ammoniacal leaching of copper from chalcopyrite were determined to be temperature, oxidant concentration, ammonium hydroxide concentrati on, and an interaction between temperature and the ammonium hydroxide concentration. Preliminary leaching studies indicate that further rese arch must be undertaken to evaluate oxidant delivery to an in-situ ore body and that the addition of organic compounds, such as simple sugars or polyvinyl alcohols, stabilize at least some of the reacted iron in solution, which could result in decreased passivation due to the form ation of an iron oxide coating. In order to determine the practicality and effectiveness of this approach, researchers have been investigati ng several types of organic additives, the extent to which iron is seq uestered, and methods to control the sequestered iron.