Thesis (Ph.D.) - Cairo University - Faculty of Science - Department of Inorganic Chemistry

In this study the recovery of zinc from its dross using hydrometallurgical, pyrometallurgical and electrochemical methods was investigated. In hydrometallurgical method sulfuric acid is used as a leaching reagent and the different factors affecting the leaching process were thoroughly investigated, these factors include: concentration of leaching reagent, solid/liquid ratio, temperature at which the leaching was carried out and time of leaching. The leached zinc solution was taken and used in the experiments of electrowinning of zinc. Two lead sheets were used as anodes whereas copper sheet was used as the cathode. Different current densities (30-80 mA/cm2) were tested. Fortunately, the deposit was almost 100% zinc with minute traces of Fe and Al. A small bench scale system for investigating the recovery of zinc using pyrometallurgical method was developed. The system based on the evaporation of zinc (in the dross) at 1050oC and condensing zinc vapors into pure zinc in a separate crucible. Almost pure Zn (99.95%) is obtained using this method. A pilot scale pyrometallurgical system (300 Kg) was fabricated and used for zinc recovery. The cost of this system is almost one tenth of the imported one. In the electrorefining experiments anodes were made from zinc dross whereas the cathode was aluminium. The electrolyte used was 4 M NH4Cl, 4MNH3, zinc sulfate (1.2 g.L{u2212}1 Zn ions) and gelatin at 0.1 g.L{u2212}1. At sufficiently high current (6 A) the efficiency of zinc electrorefining is largely increased. Efficiency is slightly decreased with time (2%) till 8 h and then markedly decreased at 10 h. Preparation of inorganic glasses that can be used as Þ-ray shielding materials and also preparation of pure zinc sulfate salt were achieved

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