3.6.2. Interactive Effects on Other Parameters of the SKS Process

In order to ensure normal production and avoid big changes in other major process parameters (smelting temperature, copper loss to slag, matte grade, etc.), the impact of major elements (Cu, Fe and S) in sulfide concentrate on other parameters (matte grade, slag type Fe/SiO2, smelting temperature, copper loss to slag, Fe3O4 content in slag, S content in slag) was evaluated.

Matte grade, smelting temperature and slag type are the main factors considered in the copper smelting process. Matte grade with the change in the initial content of Cu and S in concentrate is given in Figure 8a. As the S content in concentrate decreases and Cu increases, matte grade increases. With Cu 24% and S 28% in concentrate, the matte grade increases to about 70%. With Cu 18% and S 34% in concentrate, the matte grade drops to around 50%. Therefore, as the total oxygen blown into the SKS furnace is fixed, to produce high grade matte, the initial content of Cu in concentrate should be increased, and the initial content of S in concentrate should be reduced. However, in the Hengbang copper smelter (Yantai, China), low grade matte (around 50% [13]) was chosen, and more arsenic was removed to the gas phase.

**Figure 8.** Interactive effects on other parameters of the SKS process: (**a**) matte grade; (**b**) slag type Fe/SiO2; (**c**) smelting temperature; (**d**) copper loss to slag; (**e**) Fe3O4 content in slag; (**f**) S content in slag.

Slag type could affect the copper loss to slag and the capacity to remove impurities. Slag type Fe/SiO2 with the change in the initial content of Cu and S in concentrate is given in Figure 8b. As the Cu and S content in concentrate both increase, slag type Fe/SiO2 decreases. With Cu 18% and S 28%, Fe/SiO2 is about 1.9. However, as Cu and S content in concentrate increase to 24% and 34%, respectively, Fe/SiO2 is nearly 1.2. In the SKS process, Fe/SiO2 should be around 1.7.

Smelting temperature with the change in the initial content of Cu and S in concentrate is given in Figure 8c. As both the Cu and S content in concentrate increase, the smelting temperature decreases. With Cu 18% and S 28%, Fe/SiO2 is about 1200 ◦C. However, as Cu and S content in concentrate increases to 24% and 34%, respectively, Fe/SiO2 is nearly 1050 ◦C. In the actual industrial production of the SKS copper smelting process, the smelting temperature should be above 1170 ◦C.

Copper loss to slag is an important factor in production. The mass fraction of copper in slag with the change in the initial content of Cu and S in concentrate is given in Figure 8d. As S content in concentrate decreases and Cu increases, the copper loss to slag increases. With Cu 24% and S 28% in concentrate, the mass fraction of copper in slag increases to about 2.9%. However, with Cu 18% and S 34% in concentrate, the mass fraction of copper in slag drops to around 1.5%. In industrial production, the mass fraction of copper in slag should be controlled below 2.5% for the high direct recovery rate of copper.

In slag, Fe3O4 can increase the viscosity of slag and further increase the copper loss to slag, thus Fe3O4 content in slag is a very important indicator. In Figure 8e, Fe3O4 content in slag with the change in the initial content of Cu and S in concentrate is given. As both the Cu and S content in concentrate increase, the Fe3O4 content in slag decreases. With Cu 18% and S 28%, the Fe3O4 content in slag is about 27%. However, when the Cu and S contents in concentrate increase to 24% and 34%, respectively, the Fe3O4 content in slag is nearly 24.5%.

The mass fraction of sulfur in slag with the change in the initial content of Cu and S in concentrate is given in Figure 8f. As S content in concentrate decreases and Cu increases, the S content in slag increases. With Cu 24% and S 28% in concentrate, the S content in slag increases to about 0.74%. However, with Cu 18% and S 34% in concentrate, the S content in slag drops to around 0.63%. The S element exists in slag mainly in the form of Cu2S and FeS by the mechanical entrainment of matte.

In short, under normal production or little change of other major process parameters (smelting temperature, copper loss to slag, matte grade, copper loss to slag, slag type Fe/SiO2, Fe3O4 content in slag, etc.), the proportions of ore should be optimized to remove more arsenic from the matte to the gas or slag phase in the actual industrial production.
