Kinetics of the Oxidation of Bismuthinite in Oxygen–Nitrogen Atmospheres

Abstract

Bismuth is present in copper concentrates mainly as the mineral bismuthinite (Bi₂S₃). In some cases of smelting of concentrates, a substantial amount of bismuth can lead to contaminated copper cathodes. Thus, understanding the behavior of Bi₂S₃ at high temperatures is crucial to assessing the potential of bismuth removal in the pyrometallurgical process. Therefore, the oxidation of bismuthinite in mixtures of oxygen–nitrogen atmospheres was investigated using a thermogravimetric analysis technique. The results indicate that the oxidation process occurs through the following consecutive reactions:

$$ \begin{gathered} {\text{First stage: }}{\text{Bi}}_{ 2} {\text{S}}_{ 3} \left( {\text{s,l}} \right) + 3{\text{O}}_{2} \left( {\text{g}} \right) = 2{\text{Bi}}\left( {\text{l}} \right) + 3{\text{SO}}_{ 2} \left( {\text{g}} \right) \hfill \\ {\text{Second stage: }}2{\text{Bi}}\left( {\text{l}} \right) + 3/2{\text{O}}_{2} \left( {\text{g}} \right) = {\text{Bi}}_{2} {\text{O}}_{3} \left( {\text{s,l}} \right) \hfill \\ \end{gathered} $$

The kinetics of the oxidation of bismuthinite (first stage) was studied, and the model ln(1 – X) = –k_app t describes the kinetics of this reaction well. The bismuthinite oxidation dependence on oxygen partial pressure was of 0.9 order, and the intrinsic kinetic constants were obtained in the temperature range of 873 K to 1273 K (600 °C to 1000 °C), which were used to determine the activation energy of 91 kJ/mol. The results indicate that the oxidation of bismuthinite is a process controlled by chemical reactions. From this study, it can be concluded that the removal of bismuth from the Bi₂S₃-containing concentrates through a mechanism involving gaseous bismuth compounds is not feasible during an oxidizing roasting and/or smelting of concentrates containing Bi₂S₃.