Leaching kinetics of copper from natural chalcocite in alkaline Na 4 EDTA solutions
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I.
INTRODUCTION
R E C E N T L Y , a number of reports have appeared on the application of the chelating leachant ethylenediaminetetraacetic acid (EDTA) to various minerals: the leaching of copper from carbonate-silicate ores, m the leaching of nickel from lateritic ores, [2] the leaching of radium from uranium mill railings, 131and the leaching of tungsten from s c h e e l i t e o r e s . [4-7] These previous studies indicated that the alkaline EDTA solutions could rapidly and selectively leach the valuable metals from the minerals even at atmospheric pressure and temperatures up to 373 K, and furthermore, that the EDTA could be regenerated for the purpose of recycling. Although we have more recently reported the leaching kinetics of tungsten from pure scheelite ore and low-grade scheelite ore, I6,71 little work has been done to investigate the kinetics of EDTA leaching processes. This paper considers the kinetics of the dissolution of sized natural chalcocite (Cu2S) in aqueous Na4EDTA solutions. A similar dissolution system was treated by Duda and Bartecki, ~sl who studied experimentally the dissolution of synthetic polydispersive CUES particles in aqueous EDTA solutions. T h e dissolution of synthetic CUES was found to occur in two steps, with the formation of covellite (CuS) as an intermediate product, but their discussion on the reaction kinetics was nevertheless confined to the initial dissolution rate of CuzS. In addition to the copper dissolution, the problem of copper recovery from EDTA leach solutions was addressed by Bauer and Lindstrom. m They found that all of the copper leached YASUHIRO KONISHI, Research Associate, MASAYA KATOH, Graduate Student, and SATORU ASAI, Professor, are with the Department of Chemical Engineering, University of Osaka Prefecture, Sakai, Osaka 591, Japan. Manuscript submitted August 6, 1990. METALLURGICAL TRANSACTIONS B
in EDTA solution could be precipitated as metal powder of high purity (99 pct Cu) by using some reducing agents such as formaldehyde, hydrogen, and carbon monoxide. In order to consider the feasibility of the EDTA leaching process, it is necessary to study quantitatively both problems of the leaching of copper from minerals and the recovery of copper from the EDTA leach solution. The objective of this paper is to examine the kinetics of the leaching of copper from chalcocite ore in aqueous Na4EDTA solutions. An electrochemical leaching mechanism consistent with the experimental data is proposed, and the associated rate equation is formulated in terms of relevant operating variables. The kinetic data are then analyzed to determine the parameters in the rate equation. II.
EXPERIMENTAL PROCEDURE
A. Materials
The chalcocite used in this study was obtained from Arizona. The mineral was ground and then sieved to obtain four different size fractions, 20 to 25 /xm, 25 to 37 gm, 45 to 53 /xm, and 88 to 105 /xm. The X-ray diffraction analysis of the ground particles showed high purity of chalcocite with a small amount of SIO2. The average chalcocite content was 92 pct
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