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UBC Theses and Dissertations

The kinetics of the flash converting reaction of MK (chalcocite) concentrate Morgan, Grant John


The chemical kinetics and mechanism of the flash converting reaction of MK concentrate (approximately 93% chalcocite and 7% pentlandite) in oxygen containing atmospheres were determined. The reaction profile of individual particles undergoing flash oxidation in a laminar flow furnace was followed by observing the particle temperature and changes in apparent particle diameter with a fast response two-wavelength pyrometer; and these observations were compared to the predictions of a mathematical model of a single reacting particle. Flash reaction products were examined under a scanning electron microscope to determine chemical composition and particle morphology. A campaign of pilot plant trials was also conducted to further study the flash converting process. The initial oxidation of chalcocite at lower particle temperatures was determined to be chemically rate-controlled, to follow the Arrhenius rate law and to be first order with respect to oxygen partial pressure. It was established, by comparison of experimental particle ignitions results with the predictions of a mathematical model, that the activation energy of the low-temperature chemically rate-controlled reaction was 460 Id mol’. A dust generation mechanism was elucidated whereby preferential evaporation of copper from the surface of the particle leaves a nickel-rich shell encasing the particle. Continued oxidation of sulphides and metallic copper leads to ongoing particle heating and, upon reaching the boiling point of copper, the generation of copper vapour which either vents through a rupture or causes catastrophic fragmentation of the nickel-rich shell. A pilot plant campaign, conducted at the UBC mini pilot plant facility, tested various configurations of the concentrate-oxygen injector, and it was determined that the flash flame could be manipulated to decrease the dust generation rate. A vertical injector design that introduced the oxygen as a high velocity axial jet surrounded by freely falling MK concentrate gave dust generation rates that were as low as one-third of the dust generation rates produced in trials utilizing injector designs that introduced the concentrate and oxygen in a single stream.

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