| Under certain conditions of moisture and oxygen, sulphides can spontaneously heat, known as self-heating or pyrophoric behaviour. In this thesis the hypothesis that galvanic interaction between some sulphides can promote self-heating is tested. Galvanic interaction is controlled by rest-potential difference between the minerals and the surface area of contact (particle size). In order of decreasing rest-potential, four sulphides were tested: pyrite, chalcopyrite, sphalerite and galena. Two series of samples consisting of mixtures of two sulphides each representing a mass fraction of 50 % were run in standard self-heating tests. The first series comprised five mixtures were prepared, two with low rest-potential difference (pyrite-chalcopyrite and chalcopyrite-sphalerite) and three with high rest-potential difference (pyrite-galena, chalcopyrite-galena and pyrite-sphalerite). The second series was performed on a pyrite-sphalerite mixture at four particle sizes (80 % passing 850 mum, 300 mum, 75 mum and 38 mum). The first series showed that the individual sulphides and the mixtures of low rest-potential difference did not self-heat but the mixtures of high rest-potential difference did self-heat. The second series showed that self-heating increased inversely with particle size (increasing specific surface area) and that it was the fineness of the pyrite (the high rest-potential sulphide) that governed the self-heating effect, indicating the rate-limiting reaction is reduction at the more noble pyrite (cathodic mineral). The increase in self-heating with high rest-potential difference and increasing particle fineness supports the hypothesis that galvanic interaction contributes significantly to sulphide self-heating. A possible mechanism based on the H2S hypothesis is proposed. The understanding gained will be of interest to those involved in storage, shipping and disposal of sulphide mineral mixtures. |
