Unraveling the dissociation mechanism of gold in carbonaceous gold ore during vacuum roasting pretreatment: Effect of pyrite

Abstract

Carbonaceous refractory gold ore has been an important gold ore resource for the sustainable development of the gold industry. Solving the harmful effects of mineral-locking is the first step to increase the gold leaching rate. This study employed vacuum roasting technology in the pretreatment of carbonaceous gold ore. The dissociation efficiency and mechanism of gold in carbonaceous gold ore was investigated using a Mineral Liberation Analyser, thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction analysis. The results showed that the effect of gold-locking could be effectively solved through the thermal decomposition of pyrite during vacuum roasting pretreatment. After vacuum roasting, the content of exposed and semi-exposed gold increased from 43.81% to 78.34%, and 72.37% of the gold locked by pyrite was dissociated. Pyrite was continuously desulfurized and converted into low-sulfur pyrrhotite during vacuum roasting, and desulfurization at 400–700 °C was the cause of mass loss and phase transformation of pyrite. The phase transformation of pyrite followed the change pyrite → monoclinic and hexagonal pyrrhotite → hexagonal pyrrhotite → troilite. At 600–700 °C, rapid desulfurization produced a well-developed pore structure of the pyrite particles, which loosened the connection between gold and pyrite. Above 700 °C, the aggregation of pyrrhotite particles by slow desulfurization improved separation of gold and pyrrhotite. Gold locked by pyrite in the carbonaceous gold ore was dissociated effectively under the combined action of the two stages. The high content of exposed and semi-exposed gold provided necessary conditions for the improvement of gold leaching rate in the later leaching process.