Recovery and separation of cobalt and manganese from one of zinc plant residues (ZPR), namely hot filter cake (HFC) using a hydrometallurgical process was studied. The process is carried out in four steps as follows: (1) washing zinc, (2) reductive leaching with hydrogen peroxide, (3) cadmium cementation with zinc powder and (4) separation of cobalt from manganese with beta naphthol. In this research, the separation between manganese and cobalt from the HFC using N-N reagent was investigated. The influence of several parameters on the course of the reaction such as N-N quantity, pH, temperature and reaction time was also examined. The optimum separation conditions were found to be N-N quantity: 8 times of stoichiometric value, time: 30 min, temperature: 25 °C and pH = 1.5. Using the optimized conditions, the cobalt and manganese precipitation was nearly 99% and 0%, respectively. A kinetic study of manganese precipitation through N-N reagent has been carried out to assess the effect of kinetics parameters. The data obtained for the leaching kinetics indicated that the precipitation of manganese is an ash diffusion controlled reaction and the reaction activation energy is equal to 1.4kJ/mol.
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In the present paper cadmium leaching from zinc plant residue using sulphuric acid was examined. The zinc plant residue is a hazardous waste which is produced in the hydrometallurgical zinc plant and it contains considerable amounts of metals such as zinc, cadmium and nickel. The effects of sulphuric acid and other important factors such as reaction time, solid-to-liquid ratio, particle size, stirring speed and temperature on cadmium recovery were investigated. The concentration of cadmium in solution was observed to increase with the increase of the reaction time, acid concentration, stirring speed and temperature. Decreasing of solid/liquid ratio and particle size were also beneficial for cadmium recovery. The largest cadmium leaching recovery (97%) was obtained after 30 minutes of treatment at 25°C using H2SO4 (8% (v/v)) at solid-to-liquid ratio of 0.10. XRD and SEM analyses of the residues obtained after leaching showed that the cadmium containing phase had been decomposed in the leaching residues. The results indicated that it is possible to use this waste as a secondary resource for cadmium recovery.
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