STUDIES OF THE RATE PHENOMENA IN PARTICULATE FLASH REACTION SYSTEMS: OXIDATION OF METAL SULFIDES

The chemical and physical rate phenomena associated with the flash oxidation of metal sulfides have been examined thoroughly, by means of analysis of the literature, experimental work on single sulfide particles, and examination of the reaction products obtained from the experimental flash reactor at the Henry Krumb School of Mines of Columbia University and the Outokumpu Company pilot plant at Pori, Finland.; On the basis of the above work, the appropriate equations for mass, energy and momentum transfer for gas-solid and gas-liquid reactions were developed, along with the equations of continuity and motion in a mathematical model of the reaction system. A computer program was then developed for solving the simultaneous multi-stage chemical reaction, phase transformation, fragmentation, fluid flow and heat/mass transfer equations involved.; The results of this analysis show that there are three major reaction rate regimes, namely: sulfide decomposition, oxidation of decomposed sulfide and oxidation of molten sulfide. Substantial reduction in the rate of oxygen consumption occurs when particles move from one regime to the next. The initial reaction when particles are still in solid phase was found to proceed topochemically. When particle temperature reaches the melting point, there is some particle fragmentation and mass transfer through the liquid film accompanied by fast chemical reaction is shown to be the rate determining step in the ensuing gas-liquid reaction stage.; The predicted behavior of various process variables was compared with the experimental results obtained in the Pori pilot reactor of Outokumpu Oy. and also the developed model was applied to conditions that simulate those in the reaction shaft of an industrial copper flash smelting reactor. Discussion of results is divided into two sections: (1) Simulation of particle reaction phenomena. (2) Simulation of reactor operation.; The detailed behavior of the particles and gas in the flash reaction shaft is examined in the first section. The temperature and concentration profiles for each size fraction of concentrate and gas, and the average axial velocity profiles for the gas and particles have been provided.; In the second section, the effect of following key process operation and design parameters on the overall performance of a reactor is examined: wall temperature, oxygen enrichment and loading, inlet gas pre-heating, particle size distribution, feed rate of concentrate and inert materials and reactor size.