Kinetics of pressure oxidative leaching of molybdenite concentrate by nitric acid

Department of Materials Science and Engineering, Sharif University of Technology, Azadi Ave., Tehran, P.O. Box 11155-9466, Iran
Hydrometallurgy (Impact Factor: 1.93). 01/2011; 111(1). DOI: 10.1016/j.hydromet.2011.10.002


The current study was carried out to investigate the kinetics of reactions for the pressure oxidative leaching of a molybdenite concentrate in less than one hour. The effects of oxygen pressure, stirring speed, pulp density, acid concentration and temperature on the leaching rate of the molybdenum were studied. It was found that about 85% of molybdenite was oxidized to molybdic oxide precipitate with remaining molybdenum dissolved in the leaching liquor. Analysis of experimental data showed that the reaction is chemically controlled with activation energy of 68.8kJ/mol. Furthermore SEM images showed no significant boundary diffusion layer and it was noted that the molybdic oxide precipitates were of fibrous shape.

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Available from: Mahdi Mozammel, Apr 06, 2015
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    • "Leaching Experiments of mechanically activated molybdenite were carried out in nitric acid solution. Nitric acid as a relatively strong oxidizing agent is used in molybdenite leaching, frequently, Khoshnevisan et al. (2012), Vizsolyi and Peters (1980), Zhao et al. (2003). Vizsoly proposed the following reaction in this case, "
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    ABSTRACT: In this research, mechanical activation (MA) was employed for leaching rate improvement of molybdenite concentrate in nitric acid media. These experiments were performed in two groups: with and without aluminum oxide (alumina). A full factorial design was used for each group of experiments. Leaching rate increment up to 5 times was observed only in 2 hours activation procedure. XRD analysis demonstrated structural disordering in activated MoS 2. TEM images showed that particle size has been reduced to nanoscale. The initial powder size was 80% between 2-44 µm and dropped to about 10nm and 140nm in MA experiments with and without alumina, respectively. This size reduction would be the main reason of leaching rate enhancement which is more achievable in MA in presence of alumina. The results demonstrate that alumina has a motivating effect in activation procedure to achieve a nanostructure molybdenite. Analysis of variance revealed milling speed is the main parameter in MA without alumina, while, ball to powder ratio is the most important factor in MA procedure in presence of alumina on leaching rate.
    Full-text · Article · Dec 2015
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    • "Additionally, nitric acid can be readily regenerated in two ways: through the external oxidation of nitrous oxides existing in exhaust gas, followed by water absorption; and through the sulfate ion replacement of nitrate ion existing in liquor, after which the recycling process can be initiated. Since 1959, the study of the nitric acid leaching process has indeed expanded to the treatment of sulfide ores and concentrates, and satisfactory results have been achieved (Droppert and Shang, 1995; Holloway et al., 2004; Khoshnevisan et al., 2012; Mulak, 1985; Pashkov et al., 2002; Posel, 1972, 1974, 1976; Schaufelberger, 1959; Zárate-Gutiérrez et al., 2010). Notably, Australia-based firm Direct Nickel completed the construction of a test plant for processing laterite ores via nitric acid leaching. "
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    ABSTRACT: In 2008, the nitric acid pressure leaching (NAPL) technology was patented and developed to treat laterite ores in China. In the following year, a pilot plant with an annual processing capacity of 330,000 tons of dry ores was assembled and tested. The pilot-scale tests were documented to illustrate the innovative technology. NAPL consists of six process steps: raw ore preparation, selective pressure leaching, pregnant leach liquor purification, Ni/Co intermediate product preparation, Mg precipitation, and HNO3 regeneration/recycle. The results of the treatment of limonitic laterite ores with NAPL are as follows: (i) the recoveries of both Ni and Co were over 82%, (ii) Ni/Co hydroxide with 25.4% Ni and 2.6% Co was obtained, (iii) above 85% of HNO3 could be regenerated/recycled, and (iv) several valuable by-products could be produced. The leach iron residue without sulfur in particular is marketable because of its application in iron making. Meanwhile, fibrous calcium sulfate used in papermaking was produced in the regeneration of HNO3. In the processing of high magnesium-bearing laterite ores, nickel, cobalt, and iron extractions reached over 98%, approximately 99%, and less than 1.5%, respectively. Such advantages make the NAPL technology for laterite processing profitable, as proven by preliminary economic accounting.
    Full-text · Article · Apr 2015 · Hydrometallurgy
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    • "Since 1959, the study of nitric acid leaching process has expanded (Schaufelber ger, 1959 ). The process was developed and utilized in the leaching of sulfide ores and concentrates (Posel, 1972, 1974, 1976; Mulak, 1985; Droppert and Shang, 1995; Pashkov et al., 2002; Holloway et al., 2004; Zárate- Gutiérrez et al., 2010; Khoshnevisan et al., 2012 ). In addition, several nitric acid processes for laterite ores have been developed and patented (Wang et al., 2008; Dong et al., 2009; Drinkard and Woerner, 2010; Drinkard, 2010 ). "
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    ABSTRACT: The selective extraction of nickel and cobalt over iron from an Indonesian limonitic laterite was investigated using nitric acid pressure leaching (NAPL). The mineralogical analysis showed that the major minerals were goethite and magnetite, and the content of the divalent iron was as high as 7.06%. Nickel and cobalt were mainly distributed in these two minerals; however, the distribution was non-uniform. A series experiments were conducted to examine the basic parameters and propose the optimal conditions for the extraction. When the ore was treated via HPAL under the optimal condition, the extracted nickel and cobalt were less than 75%, and the iron concentration in the leach liquor was over 12.5 g/L. By contrast, over 85% of nickel and cobalt were extracted and about 1.8 g/L iron was achieved using NAPL. The loss of nickel and cobalt can be mainly attributed to the undissolved magnetite and manganese minerals. The leaching process of NAPL is a dissolution-oxidation-precipitation mechanism, and in this process nitric acid acts as both a lixiviant and an oxidant. The formation of hematite results in a low iron concentration in the leach liquor without oxygen injected. Meanwhile, the oxidation and the precipitation of dissolved divalent iron results in a calculated savings in acid consumption of about 120 kg nitric acid per ton of ore can be obtained, which is equal to over 93 kg of sulfuric acid per ton of ore. Moreover, lower residual acid (20 g/L nitric acid) is a significant advantage of NAPL. The iron residues had a high iron content (>56 wt%) with no sulfur, making it suitable as raw materials for ironmaking.
    Full-text · Article · May 2013 · Minerals Engineering
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