Thermoelectric power measurements of sulfide ores from the Matsumine

Abstract

The thermoelectric power (α) and semiconducting properties are closely related. For a particulate sample of sulfide minerals and ores the former can easily be obtained by measuring the thermo-emf (which does not invole the passage of current) of a packed bed which is subjected to a temperature gradient. In this study an improved apparatus was designed and used to measure α, activation energy for α (Eα) and that for conductivity (Eσ) in the temperature range of 55°-85°(328-358 K).
Sulfide ores involving yellow ores and black ores were supplied from the Matsumine, Ezuri, and Fakazawa mines. Samples for the measurements were prepared by proper methods involving crushing and/or washing to pick up small crystals, crushing and sieving for massive lumps. The composition of the samples was determined by chemical analysis and the mineralogical composition was calculated.
The results obtained are as follows:
(1) The α vs.±E_α plot (Fig. 1) reveals that most of yellow ores are n-type semiconductors and they are distributed differently with each mine. Galena and sphalerite samples are both p-type semiconductors, whereas black ores (mixture of chalcopyrite, pyrite, galena, and sphalerite) are n-type.
(2) α of yellow ores containing pyrite and chalcopyrite is strongly dependent on the chalcopyrite content. A critical value of 1.5 mol% chalcopyrite is found, below which α (-108μV/deg), E_α(0.046 eV) and E_σ (0.20 eV) are irrelevant to the chalcopyrite content. In the range from 1.5 to 20 mol% chalcopyrite, α varies from about 100 to -200 μV/deg and following correlations are obtained (Cp: mol% chalcopyrite).
α=160-300 log(Cp)
-E_α=0.04-0.116 log(Cp)
Correlations are also obtained between α and E_α and between E_α and E_σ.
(3) Galena samples contaminated with 4 mol% chalcopyrite are p-type semiconductors with α: 300-400 μV/deg, E_α:0.40-0.50 eV, and E_σ: 0.28-0.38 eV. Sphalerite samples contaminated with 1-2 mol% chalcopyrite are also p-type semiconductors with α: 200 μV/deg, whereas that contaminated with 6 mol% chalcopyrite is n-type.
(4) The average composition of black ores in mol ratio is chalcopyrite: galena: sphalerite: pyrite=1:0.2:1:1.5. Values of α, E_α, and E_σ of black ores are 0--350 μV/deg, 0-0.45 eV, and 0.11-0.28 eV, respectively.
For the samples from Matsumine ore deposit, α and E_σ tend to decrease with an increase in galena content.
(5) The correlations for yellow ores were discussed. It is shown that α is represented by, α(V/deg)=98×10^-6+0.095/(2eT)-3.9k/(2e)⋅In(Cp)
where e is the charge of an electron, T is the absolute temperature, and k is Boltzmann′s constant.