Development of Ferrous-Calcium Silicate Slag for the Direct to Blister Copper-Making Process and the Equilibria Investigation

To mitigate possible environmental pollutions, the direct to blister (DTB) route is an important process for copper making because a single, SO₂-concentrated stream can be produced. In this study, the ferrous-calcium silicate (FCS) slag system for the DTB process with a CaO content of ~ 15 wt pct was studied, as well as its equilibria with spinel, blister, and gas phases. The investigation was targeted in the spinel primary phase field with accurately controlled P(SO₂) and P(O₂) to be 0.4 and 1 × 10⁻⁵ atm, respectively. The equilibrium chemical compositions of various phases in the samples after high-temperature experiments were quantified using an electron probe X-ray microanalyzer (EPMA). Accordingly, the relationship between the liquidus temperature of slags and Fe/SiO₂ was established, as well as that between the equilibrium “Cu₂O” content and temperature. The solid solubilities in the spinel phase were also identified, including the concentrations of S, CaO, SiO₂, and “Cu₂O.” Last, the present results on FCS slags were compared with those on iron silicate (IRS) slags and the FactSage predictions, which provided more clues for further slag development and thermodynamic modeling.