USE OF X-RAY-DIFFRACTION IN A STUDY OF AMMONIA LEACHING OF MULTIMETALSULFIDES

X-ray diffraction has been used to study the changes in mineralogy tha t occur during ammonia leaching of sulfide minerals and complex bulk s ulfide concentrates. Leaching results in high extraction rates (>90 pc t) of copper from chalcopyrite, zinc from sphalerite, and lead from ga lena. However, under experimental leaching conditions (temperature, 11 5-degrees-C to 135-degrees-C; partial pressure of oxygen, 1.5 kg/cm2; pH approximately 10.0), the pyrite grains are practically inert. Appar ently, the amount of pyrite in leach residue is constant in absolute t erms. However, its relative percentage changes because the amount of c opper and zinc minerals is reduced in the leach residue during progres sive leaching. The products formed during the leaching reaction, such as goethite and lead sulfate, tend to increase the weight of the leach residue, and thus the relative weight of pyrite remains nearly unchan ged. The ratios of selected line pair intensities of pyrite lines and characteristic (selected) lines of chalcopyrite, sphalerite, and galen a are used to establish the oxidative ammonia leaching kinetics of Cu- Zn-Pb bulk concentrates. That is, the variation in the line pair inten sity ratios, with time, correlates with the changes in the elemental c oncentrations in the leach liquor.