The Viscous Behavior of FeOt-Al2O3-SiO2 Copper Smelting Slags

Understanding the viscous behavior of copper smelting slags is essential in increasing the process efficiency and obtaining the discrete separation between the matte and the slag. The viscosity of the FeOt-SiO2-Al2O3 copper smelting slags was measured in the current study using the rotating spindle method. The viscosity at a fixed Al2O3 concentration decreased with increasing Fe/SiO2 ratio because of the depolymerization of the molten slag by the network-modifying free oxygen ions (O2−) supplied by FeO. The Fourier transform infrared (FTIR) analyses of the slag samples with increasing Fe/SiO2 ratio revealed that the amount of large silicate sheets decreased, whereas the amount of simpler silicate structures increased. Al2O3 additions to the ternary FeOt-SiO2-Al2O3 slag system at a fixed Fe/SiO2 ratio showed a characteristic V-shaped pattern, where initial additions decreased the viscosity, reached a minimum, and increased subsequently with higher Al2O3 content. The effect of Al2O3 was considered to be related to the amphoteric behavior of Al2O3, where Al2O3 initially behaves as a basic oxide and changes to an acidic oxide with variation in slag composition. Furthermore, Al2O3 additions also resulted in the high temperature phase change between fayalite/hercynite and the modification of the liquidus temperature with Al2O3 additions affecting the viscosity of the copper smelting slag.