The kinetics of leaching galena with ferric nitrate
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I.
INTRODUCTION
THErecovery of lead from galena v i a
a hydrometallurgical route has been studied by several investigators under various chemical environments. 1-~7A hydrometallurgical alternative has been sought because of the growing concern about the adverse environmental impact of high-temperature processing of galena. Anderson e t al. ~ have observed complete dissolution of finely-ground galena particles (325 • 400 mesh) in 1.2 hours at a reaction temperature of 150 ~ and an oxygen pressure of 5.7 atm. Seraphim and Samis ~ have demonstrated that galena can be leached with oxygen at neutral pH by forming acetate complexes and elemental sulfur at temperatures and oxygen pressures in the vicinity of 120 ~ and 3 atm, respectively. Awakura e t a l . H studied the kinetics of galena dissolution in hydrochloric acid and in perchloric acid solutions. They reported that the dissolution rates under such chemical environments were controlled by chemical reactions on the surface of galena. Haver e t al. lo investigated the recovery of lead and sulfur from galena using ferric sulfate as oxidant. The leach residue was treated with an ammonium carbonate solution to alter the lead to an acid soluble form and to produce ammonium sulfate. The leaching of galena in chloride bearing lixiviants has been investigated by various researchers. 3'6'7'~2-J7 Ferric chloride leaching in the presence of hydrochloric acid and sodium chloride has proven to be a possible means of extracting lead v i a the hydrometallurgical route, since soluble lead-bearing species and elemental sulfur are formed. Various researchers have noted these important attributes of the chloride-beating lixiviants containing ferric ion. Economics appears to be a problem with this technique, however. Lead nitrate does not exhibit the solubility problems that contribute to the poor economics of the lead chloride system. As such, ferric nitrate would seem to offer attractive possibilities as an oxidant for galena. It was the objective of this investigation to establish the kinetics of leaching galena with this oxidant and develop a model for this system. M.C. FUERSTENAU, Professor and Head, C.O. NEBO, Research Assistant, B.V. ELANGO, former Research Assistant, and K.N. HAN, Professor, are with the Department of Metallurgical Engineering, South Dakota School of Mines and Technology, Rapid City, SD 57701. Manuscript submitted June 2, 1986.
METALLURGICALTRANSACTIONS B
II. EXPERIMENTAL MATERIALS AND PROCEDURES All of the galena samples used in this study were obtained from the Galena Mine, Kansas. The lead and sulfur contents were 85.6 pct and 13.0 pct, respectively. X-ray diffraction analysis of the galena sample and leached solid product showed that the galena d-spacings are almost identical to those of the ASTM values and also that the solid product after leaching is pure elemental sulfur. Only reagentgrade materials and distilled water were used in preparation of the lixiviants. Galena leaching was conducted in a covered two-liter glass reaction vessel. Openings wer
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