Viscosity and structural transformation of slags from the co-smelting process of lead concentrate and zinc hydrometallurgical residues

Co-treating zinc hydrometallurgical residues with high Fe, Zn, and Al contents in lead smelting systems poses significant challenges for slag property control, thereby adversely affecting process efficiency and industrial sustainability. In this study, the effects of CaO/SiO 2 mass ratio of 0.2–0.6, ZnO content of 10–30 wt%, and Al 2 O 3 content of 2–10 wt% on viscosity ( η ), activation energy for viscous flow ( E η ), and slag structure for “Fe x O”-SiO 2 -CaO-ZnO-5.5 wt%PbO-Al 2 O 3 system were systematically investigated. Increasing the CaO/SiO 2 mass ratio reduced η and E η at high temperatures because of silicate network depolymerization. At 1573 K, the proportion of monomeric [SiO 4 ] 4- units increased, leading to an increase in the NBO/Si value from 2.22 to 2.91. The slag with a CaO/SiO 2 mass ratio of 0.4 showed the most stable viscous-flow behavior at low temperatures and had the lowest T c (temperature at η = 0.5 Pa·s) of 1426 K. Increasing the ZnO content also reduced η and E η at high temperatures, and the NBO/Si value increased from 2.87 to 3.03 at 1573 K. Opposite trends exhibited at low temperatures due to the enhanced crystallization ability. The T c increased from 1413 K to 1475 K, always meeting the slag temperature range for lead smelting (＜1523 K). Al 2 O 3 acted as a network former in the studied slag, without showing amphoteric transition behavior. The NBO/Si value decreased from 3.07 to 2.50 as the Al 2 O 3 content increased. The T c of the slag containing 10 wt% Al 2 O 3 was 1573 K, exceeding the normal slag temperature range for lead smelting.