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INTRODUCTION

THE dissolution

of cuprite in an oxyacid such as sulfuric acid or perchloric acid, from which oxygen had been stripped, is very interesting, since the reaction is characterized by its disproportionation nature. Sullivan tl] and Sullivan and Oldright [2] measured the rate of dissolution of cuprite in sulfuric acid using samples of crushed natural cuprite. Wadsworth and Wadia t31 studied the kinetics of the dissolution of cuprite in sulfuric acid and perchloric acid using plate samples prepared by oxidizing hot-rolled copper sheets of high purity at 1273 K in an electric furnace. They concluded that the disproportionation dissolution reaction may be described quantitatively by two simultaneous rate reactions involving not only H § but also the hydrolytic adsorption o f H 2 S O 4. Warren and Devuyst t4j proposed a general mechanism for the acid leaching of oxides which accounts for most of the observed results. However, the leaching of cuprite in sulfuric acid is difficult to interpret in terms of the simple mechanism proposed by these authors. Yazawa and Eguchi [51 also pointed out the need for re-examination of cuprite dissolution in oxyacid. A fundamental study of the cuprite dissolution in sulfuric acid or perchloric acid must be conducted in the absence of dissolved molecular oxygen in order to understand the dissolution mechanism which may occur at the surface of cuprite. In this work, the dissolution reactions of three artificial cuprite samples, prepared by different methods, in sulfuric acid or perchloric acid were studied to elucidate the dissolution mechanism.

H. MAJIMA, Professor, Y. AWAKURA, Associate Professor, K. ENAMI, Graduate Student, H. UESHIMA, Graduate Student, and T. HIRATO, Instructor, are with the Department of Metallurgy, Kyoto University, Sakyo-ku, Kyoto 606, Japan. Manuscript submitted July 5, 1988. METALLURGICAL TRANSACTIONS B

II.

EXPERIMENTAL PROCEDURES

A. Materials Three artificial cuprite samples prepared by different methods were used in this study. Sample 1 was an electrolytically produced powder of - 4 0 0 mesh size, which was supplied by Furukawa Mining Co., Ltd., Osaka, Japan. The purity of this material was 96.52 pct, and the main impurity was identified to be alumina by spectrometric and chemical analysis techniques. This material was mainly used as received for the determination o f the stoichiometry of the dissolution reaction. Sample 2 was prepared by melting Furukawa cuprite in an alumina crucible at 1575 K in an argon gas atmosphere for 2 hours, followed by slow cooling. The cylindrical cuprite melt equilibrated with metallic copper. However, the disk of cuprite specimen which was removed from the alumina crucible contained only a small amount of metallic copper in the form of inclusions. The cuprite disk was polished on a grinding wheel using a series of Emery papers, followed by buffing and rinsing. The copper content of the finished disks was analyzed to be 85.86 pct Cu. For comparison purposes, cuprite plates approximately 3 mm in thickness and 20 mm in