Use of X-ray diffraction in a study of ammonia leaching of multimetal sulfides

X-ray diffraction has been used to study the changes in mineralogy that occur during ammonia leaching of sulfide minerals and complex bulk sulfide concentrates. Leaching results in high extraction rates (>90 pct) of copper from chalcopyrite, zinc from sphalerite, and lead from galena. However, under experimental leaching conditions (temperature, 115 °C to 135 °C; par-tial pressure of oxygen, 1.5 kg/cm²; pH ∼ 10.0), the pyrite grains are practically inert. Ap-parently, the amount of pyrite in leach residue is constant in absolute terms. However, its relative percentage changes because the amount of copper and zinc minerals is reduced in the leach residue during progressive 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 unchanged. The ratios of selected line pair intensities of pyrite lines and characteristic (selected) lines of chalcopyrite, sphalerite, and galena are used to establish the oxidative ammonia leaching kinetics of Cu-Zn-Pb bulk concentrates. That is, the variation in the line pair intensity ratios, with time, correlates with the changes in the el-emental concentrations in the leach liquor.