Browsing by Author "Steyl, Johann Du T."

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    Simulating the medium temperature chalcopyrite oxidation system in batch and continuous autoclaves
    (Stellenbosch : Stellenbosch University, 2012-12) Steyl, Johann Du T.; Bradshaw, S. M.; Akdogan, G.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: A detailed mathematical description of the pressure oxidation of chalcopyrite concentrates in acidic sulfate solutions is presented in this dissertation, including descriptions of the most important accompanying reactions under typical medium operating temperatures (140-155ºC) in batch and steady-state continuous stirred tank reactors. The mathematical framework consists of various modules, each addressing particular thermodynamic and kinetic aspects of the primary processes occurring in a pressure oxidation reactor. Comprehensive literature investigations are presented which constituted the departure point of this study, supplemented by phenomenological data obtained from controlled batch and continuous experimentation. The different modules are each covered in a chapter of this dissertation, and include the following: i) the solution thermodynamic framework, ii) the interfacial oxygen mass transfer rate, iii) the iron(II) oxidation rate, iv) the iron(III) precipitation rate, (v) the intrinsic oxidation kinetics of the sulfide minerals, and vi) the particulate batch and continuous reactor frameworks. These modules are imbedded within a continuous mass and energy balance platform of a primary leaching – solvent extraction circuit, while the batch reactor analogy describes the conservation of mass, and its movement between phases, in a stand-alone configuration. Literature information proved particularly important in deriving the generic functional forms of the most important reaction rate expressions, while the phenomenological expressions were refined, and the associated constants obtained, from low pulp density batch experimentation. Higher pulp density batch reactor and continuous (pilot plant) data were then used to confirm the successful integration of these expressions in the overall simulation. This is the first truly comprehensive study of chalcopyrite concentrate pressure oxidation, the kinetics of the accompanying reactions and each of the underlying thermodynamic aspects. Consistent theoretical arguments and insights are presented, while conceptual proposals are tabled in cases where the fundamental information is lacking. This dissertation presents an internally consistent simulation, with each of the modules contributing to an overall mathematical description of the pressure oxidation of chalcopyrite concentrates. It provides a powerful research and process engineering tool, and may be used to simulate the performance of a primary leaching circuit on a full-scale plant. As an example, the simulation was used to study the impact of selected intrinsic properties and control parameters on the autoclave and primary leach circuit performance. Various recommendations on improving the simulation are highlighted, as well as the aspects to explore in follow-up studies.