Mathematical modeling of an exothermic leaching reaction system: pressure oxidation of wide size arsenopyrite participat
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I.
INTRODUCTION
O N E of the principal goals of a kinetic study is the determination of the governing rate law so the latter can be used as the basis of developing a model suitable for design and performance optimization of large-scale industrial process reactors. Although during the past two decades numerous laboratory kinetic studies of mineral leaching systems have been reported, very limited application of these results in designing and optimizing hydrometallurgical process reactors has been undertaken. Laboratory determination of the intrinsic heterogeneous kinetics involves the execution of a series of batch tests using very dilute and monosize particle slurries under isothermal and isoconcentration conditions. However, industrial operation of hydrometallurgical processes calls almost invariably for the use of concentrated slurries of wide size distribution mineral feeds. Under these conditions, secondary reactions (homogeneous and/or heterogeneous), such as hydrolytic precipitation, are very likely to occur, the extent of which will have to be taken into account. Moreover, the flow pattern of the reactor has to be coupled with the rate equations of the principal and secondary reactions to allow for the development of a mathematical model for the process. An additional complication in coupling the heterogeneous reaction kinetics with the industrial reactor performance arises when the process is exothermic, as is the case for oxidative leaching of sulfidic concentrates. In such a system, which is very common in hydrometallurgy, the heat released by the leaching reaction must
be accounted for since it would affect the design and operation of the reactor. Among the few publications describing modeling efforts in the area of sulfide mineral leaching, tl-6j none seem to have considered heat effects. This paper develops a mathematical model that couples leaching kinetics and reactor performance under both isothermal and adiabatic regimes for a strongly exothermic surface reaction-controlled system. The system being investigated is the aqueous pressure oxidation of arsenopyrite. Pressure oxidation is currently considered as the most effective process for the treatment of refractory gold concentrates, i7~ Arsenopyrite, along with pyrite, is the most important mineral carrier of refractory gold. Pressure oxidation is a highly exothermic and complex reaction system. The present paper constitutes part of an ongoing research program t8,9] which focuses on the analysis and optimization of the pressure oxidation process. A preliminary version of the model described here was previously published in a TMS-sponsored topical symposium. [10] II.
THE CHEMICAL REACTION SYSTEM
When arsenopyrite is subjected to high-temperature (160 ~ to 200 ~ pressure oxidation in a H2SO 4 medium, the following reactions occur: t8] 4FeAsS (s) + 1302 (aq) + 6H/O (1) 4H3AsO4 (aq) + 4Fe 2§ (aq) + 4SO 2" (aq)
[1]
1
2Fe 2§ (aq) + ~ 02 (aq) + 2H § (aq) V.G. PAPANGELAKIS, Research Associate, formerly Doctoral Student, and G.P. DEMOPOULOS, Associa
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