Pressure Oxidative Leaching of Molybdenite in Alkaline Media. Autoclave processing of low-grade molybdenite concentrates. (2nd Report)
Shigen-to-Sozai 01/2001; 117(1):72-76. DOI: 10.2473/shigentosozai.117.72
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ABSTRACT: The leaching results of bismuth sulfide concentrate containing molybdenum and tungsten in air-H2O2-NaOH system, pressure-O2-Na2CO3 system and pressure-O2-NaOH system were investigated. The results show that the extraction of molybdenum, tungsten and sulfur goes up with the increase of NaOH concentration, oxygen partial pressure and reaction time. The extraction of molybdenum and tungsten also rises up with temperature, but the leaching ratio of sulfur increases initially to a peak of 98% at 150°C and then decreases with the increase of temperature. Under the optimal conditions, the extraction of molybdenum, tungsten and sulfur is more than 95.6%, 93.8% and 96.0%, respectively, and the main phases of residue are Bi2O3 and Fe2O3. Therefore, the method of pressure leaching in alkaline solution is provided as an effective separation of molybdenum, tungsten and sulfur from bismuth and a beneficial pretreatment for consequent process.
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ABSTRACT: Annually, a great amount of Cold Filter Cake (CFC) residue is produced in lead and zinc plants in Iran. CFC, the Ni–Cd purification step residue, with elemental analysis of 45–55% Zn, 11–16% Cd, 2.5–4% Ni and 0.2–1.5% Cu can be used as a secondary source of zinc, nickel and cadmium. Unfortunately, despite its hazardous content, the waste is treated in such a way that most of the hazardous constituents get easily exposed to the environment. In the present study, treatment of CFC for separation of zinc and recovery of cadmium has been conducted employing alkaline leaching and electowinning processes respectively. Affecting factors, such as alkaline concentration, leaching temperature, holding time, and liquid:solid ratio (volume/weight, L/S), and stirring rate were studied on zinc leaching from CFC with NaOH solution. Results showed that under two-stage alkaline leaching, when CFC was leached for 1 h at 75 °C in the presence of 8 mol/l sodium hydroxide and liquid:solid ratio of 10:1, the leaching rate of Zn was 98% while Ni and Cd remained intact in residue. Thus, zinc was separated from Ni and Cd selectively. In the next step, sulfuric acid leaching of alkaline leach residue, with 1 mol/l H2SO4 at 70 °C and liquid/solid ratio of 10:1, provided a stock sulfate solution containing 49.92 g/l Cd, 2.77 g/l Zn, 12.76 g/l Ni, and 1.18 g/l Cu. The Cd electrowinning experiments and the effects of current density (A/m2) and electrolysis time (h) were studied on stock sulfate solution in the presence of Ni and Zn. The electrowinning was carried out at various current density (100, 180, 250 and 400 A/m2) and electrolysis time (5, 8, and 18 h). Concentrations of Cd2 +, Ni2 + and Zn2 + were determined every hour. Cadmium recovery of 9.8% at 100 A/m2 increased sharply to 87% at 400 A/m2 in 5 h. Maximum total recovery of cadmium from solution was 99.9% achieved at 25 °C and 400 A/m2 in 18 h. Final product was cadmium sponge of high purity 98% and copper was considered the main impurity in cadmium sponge deposit (1.7%). A complete flow sheet of process for the selective separation of zinc and cadmium recovery is presented.
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