Evaluation of Oxidation Reaction of Copper Concentrate Mixed with Silica Sand by Hot-Thermocouple Method

Abstract

The hot-thermocouple method was applied to observe the oxidation reaction of a copper concentrate/silica sand mixture and the separation process of sulfide matte/oxide slag melts. The powder sample (0.3–0.4 mg), attached to a Pt–13%Rh/Pt thermocouple, was heated rapidly up to ≥ 1250 °C in Ar gas with the aid of an exothermic reaction of the chalcopyrite due to the introduction of oxidizing gas flow via a needle located near the sample. The sample was a mixture of Cu concentrate/silica sand with an initial Fe/SiO2 mass ratio of 2.0. The reaction processes were monitored by a charge-coupled device through the microscope and recorded by a personal computer. The hot-thermocouple method revealed chalcopyrite ignition with oxygen flow for optimized conditions (temperature of the sample raised rapidly within 1 s up to ≥ 1300 °C). Then, sulfide matte melt spread along the Pt–13%Rh/Pt thermocouple wire and sulfide droplets were isolated inside the oxide slag melt held between the thermocouple wires. The rapid temperature change of the sample within 2 s was evaluated using a previously obtained relation between the temperature and sample color for fayalite slag melt with a composition of 2FeO·SiO2. The quenched samples were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy to observe microstructures of the compositions of the matte and slag, unreacted mineral particles, and the presence of magnetite precipitates. The conditions to form magnetite under the hot-thermocouple experiments were qualitatively discussed in terms of the Cu–Fe–S–O–SiO2 phase diagram.