Effect of aging conditions on the leaching of mechanically activated pyrite and sphalerite

The leaching of mechanically activated pyrite and sphalerite exposed to nitrogen (99.999 vol pct) or air at ambient temperature or 573 K was investigated. The results indicate that at the same leaching time, the iron-leaching ratio of mechanically activated pyrite or sphalerite aged in nitrogen at both ambient temperature and 573 K decreases slightly with increasing aging time and remains constant after a certain aging period. The iron-leaching ratio of mechanically activated pyrite exposed to ambient air varies with the exposure period. But, at the same leaching time, the zinc-leaching ratio of mechanically activated sphalerite aged at ambient temperature does not change with the aging atmosphere. The structures of mechanically activated pyrite and sphalerite after being aged were determined. The specific granulometric surface area of mechanically activated pyrite and sphalerite decreases with increasing aging time, but keeps constant after a certain aging period. The X-ray diffraction patterns of mechanically activated pyrites aged in nitrogen do not change with aging time; neither do the X-ray diffraction patterns of mechanically activated sphalerites aged either in air or in nitrogen. For mechanically activated pyrite exposed to ambient air for 3 and 6 months, new phases were found. The lattice distortion and the elemental sulfur content of pyrite and sphalerite mechanically activated in nitrogen were also investigated. The results indicate that the elemental sulfur content of mechanically activated pyrite rises noticeably, and its lattice distortion (ε) rises slightly, with increasing grinding time. The elemental sulfur content of mechanically activated sphalerite remains constant at 0.5 mg elemental sulfur per gram of sphalerite, and its lattice-distortion ratio increases apparently with increasing grinding time. These observations provide further evidence for our opinion that the formation of dangling bonds on the surface of mechanically activated pyrites and the lattice distortion on the surface of mechanically activated sphalerites may mainly result in the enhancement of hydrometallurgical process for corresponding sulfide minerals.