High-temperature chlorination of gold with transformation of iron phase

Gold in cyanide tailings from Shandong Province is mainly encapsulated by hematite and magnetite at distribution rates of 76.49 % and 10.88 %, respectively. Chlorination–reduction one-step roasting of cyanide tailings was conducted under the following conditions: calcium chloride dosage of 6 %, bituminous coal dosage of 30 %, calcium oxide dosage of 10 % (all dosages are vs. the mass of cyanide tailings) at 1000 °C of roasting temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM), and chemical-phase analysis were performed to investigate the effects of iron phase transformation on the high-temperature chlorination of gold. Results indicate that the lattice structure of hematite undergoes expansion, pulverization, and reorganization when hematite is reduced to magnetite, which leads to 42.03 % gold exposure, and the high-temperature chlorination rate of gold is 41.17 % at the same time. The structure of wustite formed by the reduction in magnetite is porous and loose, and thus 44.02 % of gold is exposed. The high-temperature chlorination rate of gold is increased by 41.98 percentage points. When wustite is reduced to metallic iron, 4.42 % of gold is exposed, and the high-temperature chlorination rate of gold is increased by 3.38 percentage points. Accordingly, the high-temperature chlorination of gold mainly occurs in two stages, in which Fe₂O₃ is reduced to Fe₃O₄, and Fe₃O₄ is reduced to Fe _x O finally.