Measurements of dielectric properties for particulate sphalerite samples and zinc concentrates
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I.
INTRODUCTION
THEREhave been a number of investigations into the oxidative leaching of sphalerite in suspension. ~.2 As reaction rates are low, most experiments have been conducted at high temperatures under pressure. As a result, the effects of temperature, oxygen pressure, Fe > concentration, and other factors on the oxidation rate have been elucidated considerably. Little is known, however, about the effect of the electronic nature of pulverized sphalerite to be oxidized on the reaction rate. Sphalerite has a very high resistance and is almost an insulator at room temperature. The electronic nature of such an insulator can be studied by measuring its dielectric properties including the dielectric constant, the dielectric loss tangent, their relations to the frequency, and the relaxation time. Measurements of these properties are generally made using a plate specimen cut from a crystal free from defects. There have been few measurements of the dielectric properties of pulverized samples. Eyring et al. 3 have shown that the reaction rate of a dielectric substance is proportional to the reciprocal of the dielectric relaxation time, when the reaction is controlled by an activation process of dipoles. Efforts have been made to acertain whether Eyring's theory is applicable to the oxidation of sphalerite in suspension or not. For this purpose, it is first necessary to measure directly the dielectric properties of pulverized samples of sphalerite and zinc flotation concentrates. Because these samples are contaminated with a variety of impurities, and measurement using particulate samples is not sophis-
MIKIHIKO KOBAYASHI, Researcher, is with First Nonferrous Metallurgy Laboratory, Process Metallurgy Division, National Research Institute for Metals, 2-3-12, Nakameguro, Meguro-ku, Tokyo, Japan. HIROSHI KAMETANI, formerly with National Research Institute for Metals, is with Faculty of Science, Science University of Tokyo, 1-3, Kagurazaka, Shinjuku-ku, Tokyo, Japan. Manuscript submitted August 20, 1986. METALLURGICALTRANSACTIONSB
ticated, it is necessary to develop a method for the measurement of pulverized mineral samples. Recently, Yokoyama and Horitsu 4 studied dielectric constants of binary and ternary disperse systems at 500 kHz using silica rock, magnetite and pyrite powders, glass beads, and Rigolac (polyester resin). They recommended Lichtenecker's equation (see Eq. [14]) for calculation of the specific dielectric constant for natural rocks. This study was carried out to assess the dielectric properties of particulate samples of six sphalerites and four zinc flotation concentrates.
II.
DIELECTRIC P R O P E R T I E S
A. Dielectric Properties of Dense Substance 5
The dielectric constant of a dense substance, es, placed between two metal plates is calculated from the equivalent parallel capacitance of the condenser, Cs, as given by, d es = 7 c ,
[11
where A and d are the area and thickness of the specimen, respectively, es is generally compared with the dielectric constant of a vacuum, e0 = 8.855 x 10-12 N
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