Microstructure, Mineralogical Characterization and the Metallurgical Process Reconstruction of the Zinc Calcine Relics from the Zinc Smelting Site (Qing Dynasty)

The smelting of zinc is considered as one of the most challenging technologies in ancient civilization. Compared with non-sulfide zinc ores, the smelting of zinc sulfide ores is more complicated since they have to be roasted before smelting. The technological smelting process of the ancient zinc metallurgy technology has been studied and partly reconstructed. However, the roasting technology, including the roasting conditions and involved metallurgical processes, is still unclear. The discovery of the zinc smelting site of Doulingxia dates back to the Qing dynasty (CE 1636–1912), and for the first time provides us with critical archeological evidence to gain an insight into the roasting technology in ancient zinc metallurgy technology. In this paper, the microstructure and mineralogical features of the zinc calcine relics found at the Doulingxia site were characterized by X-ray diffraction (XRD) and scanning electron microscopy coupled with X-ray energy dispersive spectrometer (SEM-EDS). To reconstruct the metallurgical process, the original roasting temperature of the unearthed zinc calcine was estimated by thermogravimetric analysis and differential thermal analysis (TG-DTA), combined with reheating experiments and phase composition analysis as well as microstructural analysis. The simulation experiments were conducted to reconstruct the roasting process. The results indicated that the original roasting temperature of the unearthed zinc calcine should be in a range of 650–850 °C, most probably near 750 °C. As long as the retention time is long enough, all sphalerite can be oxidized when the roasting temperature is above 650 °C. The final roasting products mainly include tiny porous particles of ZnFe2O4, Fe2O3, PbSO4, and ZnO. These findings are helpful to reconstruct the ancient zinc metallurgy technology of zinc sulfide ores.