Measurements of dielectric properties for particulate sphalerite samples and zinc concentrates

Abstract

Little is known about the electronic nature of pulverized sphalerite which is used for pressure leaching. In order to clarify the relationship between the oxidation rate in suspension and the electronic nature, the dielectric properties of particulate samples of six sphalerites (screen size: 250 to 88 and -88 µm), prepared by crushing and sieving, and four zinc flotation concentrates were measured using a packed bed condenser. A glass plate, particulate samples of it, and pure ZnS powder were used as references. From the capacitance and porosity of the bed, the specific dielectric constant for the dense substance was calculated using Böttcher’s empirical equation. The values obtained at 120 Hz were generally larger than those at 1 kHz, suggesting that dielectric dispersion and absorption occurred. The specific dielectric constant for very low frequency (ε ^*_L ), the maximum value of dielectric loss tangent (tan δ_max), the frequency for the dielectric absorption peak (f_max), and the relaxation time (τ) were calculated according to Debye’s theory, assuming that the specific dielectric constant for very high frequency was constant. The results revealed that ε ^*_L , tan δ_max, and f_max increased with the Fe content of the samples (0.7 to 13.4 wt pct), whereas τ decreased. Particle size (5 to 710 µm) had a slight effect on the dielectric properties. There was an apparent correlation between the dielectric loss tangent measured for the packed bed and that calculated for the dense substance.