Metallurgical and Materials Transactions B

, Volume 26, Issue 4, pp 677–685 | Cite as

Kinetics of pyrite oxidation in sodium hydroxide solutions

  • V. S. T. Ciminelli
  • K. Osseo-Asare


The kinetics of pyrite oxidation in sodium hydroxide solution were investigated in a stirred reactor, under temperatures ranging from 50 °C to 85 °C, oxygen partial pressures of up to 1 atm, particle size fractions from -150 + 106 to -38 + 10µm (-100 + 150 mesh to -400 mesh + 10 µ), and pH values of up to 12.5. The surface reaction is represented by the rate equation:-dN/dt = Sbk″pO0.5 2[oH- 0.25/(1 +k‴ pO2 0.5) where N represents moles of pyrite, S is the surface area of the solid particles,k″ andk″ are constants,b is a stoichiometric factor, pO2 is the oxygen partial pressure, and [OH-] is the hydroxyl ion concentration. The corresponding fractional conversion (X) vs time behavior follows the shrinking particle model for chemical reaction control: 1 - (1 -X)1/3 =k ct The rate increases with the reciprocal of particle size and has an activation energy of 55.6 kJ/mol (13.6 kcal/mol). The relationship between reaction rate and oxygen partial pressure resembles a Langmuir-type equation and thus suggests that the reaction involves adsorption or desorption of oxygen at the interface. The square-root rate law may be due to the adsorption of a dissociated oxygen molecule. The observed apparent reaction order with respect to the hydroxyl ion concentration is a result of a complex combination of processes involving the oxidation and nydrolysis of iron, oxidation and hydrolysis of sulfur, and the oxygen reduction.


Pyrite Material Transaction Oxygen Partial Pressure Sodium Hydroxide Solution Sulfur Species 
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Copyright information

© The Minerals, Metals & Material Society 1995

Authors and Affiliations

  • V. S. T. Ciminelli
    • 1
  • K. Osseo-Asare
    • 2
  1. 1.Department of Metallurgical EngineeringUniversidade Federal de Minas GeraisBelo HorizonteBrazil
  2. 2.Metals Science and Engineering Program, Department of Materials Science and EngineeringPennsylvania State UniversityUniversity Park

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