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Oxidation kinetics of lead sulfide Constantineau, Jean Pierre

Abstract

This project is a theoretical and experimental study of the oxidation kinetics of lead sulfide. Experimental intrinsic kinetic data applicable to the pre-ignition oxidation of lead sulfide particles has been undertaken to enable a better understanding of flash smelting processes through modelling. A thorough literature review has shown that the knowledge needed for modelling the oxidation of lead sulfide is limited even though numerous studies have already been done on the subject. The main objectives of this project were to obtain the activation energy of the oxidation of lead sulfide in the presence of sulfur dioxide as well as the reaction order with respect to the oxygen and sulfur dioxide concentrations. Experiments were performed to verify the effect of temperature, oxygen and sulfur dioxide concentrations on the reaction rates of lead sulfide oxidation. Between 250 and 450°C, under an atmosphere of 20.4% O2 and 2.7% SO2, the observed activation energy is 36.8 +/- 5.6 kJ/mol. The reaction order with respect to the oxygen concentration is fractional. Sulfur dioxide does not seem to have an effect on the initial oxidation rates. In all cases, lead sulfate was the oxidation product. The observations can be explained by a reaction mechanism that includes adsorption and ionic diffusion through the sulfate layer. A new type of diagram describing gas-solid reactions has been created. These diagrams unite thermodynamics and kinetics into a new tool that should be useful for many metallurgical and chemical systems. These diagrams are created from predominance diagrams by applying a mathematical transformation derived from kinetic equations. The diagrams, called modified predominance diagrams, predict the reaction product for given kinetics conditions and atmospheric compositions. The approach presented to modify the predominance diagrams can also be used for hydrometallurgical systems to modify Eh-pH diagrams. Their applicability for this purpose, has, however, not been verified. [Scientific formulae used in this abstract could not be reproduced.]

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