Mixed-control kinetics of oxygen leaching of chalcopyrite and pyrite from porous primary ore fragments
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I.
INTRODUCTION
THE increasing
demand for metals and the progressive depletion of high-grade ores make it necessary to develop new techniques for extracting metals from low-grade and deeply buried ores. Solution mining is receiving increasing attention as a method for recovery of metal values from these ores. 1-5 It provides a means for recovery of metals from mineral resources inaccessible by conventional mining. The process description and the advantages of solution mining have been well documented. 4-7 Braun et al. 2 carried out experimental work and mathematical modeling of the pressure leaching of chatcopyritebearing ore. A first-order intrinsic kinetics with respect to dissolved oxygen and the diffusion in the pores of ore fragment were included in the reaction zone model to explain the overall leaching kinetics. The consumption of oxygen by reaction with pyrite which also occurs in the ore was not taken into consideration. In this paper we will present experimental data of copper leaching under relatively high oxygen pressures and different temperatures. The experiments were conducted in a batch reactor in which the dissolved oxygen concentration in the bulk was maintained constant. A mathematical model for the process incorporating the kinetics of dissolution of chalcopyrite and pyrite grains, and the diffusion of dissolved oxygen within the ore fragment, was formulated to describe the overall leaching kinetics from ore fragments. II.
EXPERIMENTAL WORK
A. Material
The chalcopyrite-bearing ore used in this study was a porphyry copper ore obtained from Kennecott's Bingham Mine in Utah. The mineral phases, determined by X-ray diffraction, were principally quartz with small amounts of feldspar, biotite, chalcopyrite, and pyrite. The chalcopyrite H, K. LIN, formerly Graduate Student in the Department of Metallurgy and Metallurgical Engineering, University of Utah, is with the University of Alaska, 210 O'Neille Resource Building, Fairbanks, AK 99775-1180. H.Y. SOHN is Professor in the Department of Metallurgy and Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112-1183. Manuscript submitted July 24, 1986.
METALLURGICALTRANSACTIONS B
and pyrite contents were, respectively, 2.1 and 2.0 pct by weight. The porosity and density of the ore samples were determined to be 6.4 pct and 2.6 x 103 kg/m 3, respectively, by the standard ASTM boiling-water test (ASTM designation C20-70).
B. Chemical Analysis
The chemical analysis for chalcopyrite and pyrite contents in the ore consisted of the following steps: (1) A known amount of ground sample was boiled for one hour in 150 ml of aqua regia and then cooled, (2) about 5 ml of bromine were added, (3) more aqua regia was added to bring the total volume back to 150 ml, (4) the mixture was again boiled for one hour, (5) the solution was filtered and the filtration residue was rinsed with dilute HC1, and (6) the resulting solution was used for analysis of both copper and sulfate ions by using an atomic absorption spectrophotometer and by precipitation a
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