Galvanic interaction between chalcopyrite and manganese dioxide in sulfuric acid medium
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I. INTRODUCTION
GALVANIC interaction is known to occur between different conducting minerals and plays a significant role in wet grinding,[1,2] flotation,[3,4] and leaching,[5,6,7] of sulfide minerals. Many base-metal sulfides such as galena, sphalerite, chalcopyrite, and pyrite, are semiconductors, and when any two of such minerals in contact with one another are placed in an electrolyte, a galvanic couple is formed in which the mineral of lower rest potential corrodes at an enhanced rate as the anode of the couple, and the one with higher rest potential corrodes at a slower rate as the cathode. Manganese dioxide is also a semiconductor having rest potential much higher than the aforementioned sulfide minerals so that, in contact with any of them, it can form a galvanic corrosion couple in which both the minerals would dissolve at enhanced rates simultaneously. In a recent study, Rath and Paramguru[8] have examined the galvanic interaction between sphalerite and MnO2 and observed that under galvanic contact, the rate of corrosion of the two minerals was much higher than their individual self-corrosion rates. Through polarization measurements, they obtained a quantitative measure of the galvanic interaction taking place between the two minerals and observed a galvanic current of ,2 mA/cm2 between the minerals in 0.1 M sulfuric acid solution, which suggests a considerably high dissolution rate for both the minerals under mild conditions. Similar interaction between MnO2 and FeS2 has been reported[9,10] with observed galvanic current as high as 1.7 mA/cm2. In these studies the anodic half-reactions were the oxidation of the sulfide minerals, whereas the cathodic half-cell reaction was MnO2 1 4H+ 1 2e2 → Mn11 1 2H2O
[1]
Chalcopyrite and MnO2 have rest potentials 10.46 V (SHE)[11] and 11.20 V (SHE), respectively,[12] and are expected to form a galvanic couple in an electrolyte where
B.P. GANTAYAT, Lecturer, Senior Scale, is with BJB College, Bhubaneswar- 751-013, India. P.C. RATH, Scientist, and R.K. PARAMGURU and S.B. RAO, Scientists-F, are with the Regional Research Laboratory, Bhubaneswar - 751 013, India. Manuscript submitted March 5, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS B
both the minerals would corrode; CuFeS2 as anode because of its lower rest potential and MnO2 as cathode. Considering the environmental impact of the conventional smelting process of copper production, the reaction between chalcopyrite and manganese dioxide is quite significant as it offers a relatively pollution-free method of leaching copper. In this context, evaluation of the galvanic interaction between the two minerals is quite necessary, as it would be useful in understanding the leaching process. Galvanic interactions between chalcopyrite and other minerals are reported in the literature,[13,14,15] but so far, no study is reported on the galvanic interaction between chalcopyrite and manganese dioxide. This article discusses the galvanic interaction between these two minerals in sulfuric acid medium.
II. EXPERIMENTAL A. Minera
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