Mathematical modeling of the zinc pressure leach process
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I.
INTRODUCTION
OXIDATIVE leaching of zinc sulfide concentrates in horizontal, pressure autoclaves is becoming a preferred technology in the zinc industry. The Sherritt zinc pressure leach process has been developed by Sherritt Inc. (Fort Saskatchewan, AB) as an environmentally and economically more sound alternative to the traditional pyrometallurgical route. In the latter, levels of sulfur dioxide emissions unacceptable for release to the environment have necessitated expensive gas cleaning equipment and production of sulfuric acid. However, in the zinc pressure leach process, the sulfides are oxidized to elemental sulfur, which is recovered and stockpiled. The first zinc pressure leach facility was built by Cominco Ltd. (Trail, BC) in 1980. tl,z~ Two other plants exist: at Kidd Creek Mines (Tirnmins, ON) and at Ruhr-Zink refinery (Datteln, Germany). Recently, the first two-stage facility was built by Hudson Bay Mining and Smelting Company (Flin Flon, Northern MB), where pressure leaching has completely replaced the roast-leach section.t31 There, leaching is carried out, countercurrently, in two stages. These autoclaves are complex, three-phase reactors, the understanding of which, from a mathematical modeling stand, is still in its early stages. Several models have been proposed for the zinc pressure leach system.[4,5,6] However, these are either limited to a specific concentrate composition or have used major assumptions. They have provided information on the general trends for the specific conditions modeled, but are not broadly applicable. In this article, we describe the development of a comprehensive model for the zinc pressure leach reactor, which considers rate processes in all three phases. Kinetic information for each reaction is gleaned from experimental data published in the literature. Using the rate expressions thus obtained, material balance
SUSAN A. BALDWIN, Research Associate, and GEORGE P. DEMOPOULOS, Associate Professor, are with the Department of Mining and Metallurgical Engineering, McGill University, Montreal, PQ, H3A 2A7, Canada. VLADIMIROS G. PAPANGELAKIS, Assistant Professor, is with the Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON, M5S 1A1 Canada. Manuscript submitted August 16, 1994. METALLURGICAL AND MATERIALS TRANSACTIONS B
equations for the gas, aqueous, and solid components are solved, together with an energy balance, to predict the steady-state performance of the reactor. Model predictions are shown to compare very favorably with the performance of an industrial process. 1I.
BACKGROUND
A. Comparison with the Gold Pressure Oxidation Process and Model
Elsewhere, the development of a comprehensive model for the gold pressure oxidation process has been described, tTm There, oxidative decomposition of refractory minerals* in a sulfuric acid medium, at high temperatures * Namely, the following sulfide minerals: pyrite, pyrrhotite, marcasite, and arsenopyrite.
(180 ~ to 250 ~ and pressures (2 to 3 MPa), was modeled using the reaction
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