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: 2.17). 01/2011; DOI: 10.1016/j.hydromet.2011.10.002

ABSTRACT 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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    ABSTRACT: The processing of molybdenum-uranium ore in a sulfuric acid solution using hydrogen peroxide as an oxidant has been investigated. The leaching temperature, hydrogen peroxide concentration, sulfuric acid concentration, leaching time, particle size, liquid-to-solid ratio and agitation speed all have significant effects on the process. The optimum process operating parameters were: temperature: 95°C; H2O2 concentration: 0.5 M; sulfuric acid concentration: 2.5 M; time: 2 h; particle size: 74 μm, liquid-to-solid ratio: 14:1 and agitation speed: 600 rpm. Under these experimental conditions, the extraction efficiency of molybdenum was about 98.4%, and the uranium extraction efficiency was about 98.7%. The leaching kinetics of molybdenum showed that the reaction rate of the leaching process is controlled by the chemical reaction at the particle surface. The leaching process follows the kinetic model 1 − (1−X)1/3 = kt with an apparent activation energy of 40.40 kJ/mole. The temperature, concentrations of H2O2 and H2SO4 and the mesh size are the main factors that influence the leaching rate. The reaction order in H2SO4 was 1.0012 and in H2O2 it was 1.2544.
    Frontiers of Chemical Science and Engineering. 7(1).