Influence of Minor Elements on Liquidus Temperature in the Cu–As–Sb–S System and Its Implications on the Degradation of a Sole in a Copper Flash Smelting Furnace

The unexpected and undesirable formation of speiss—a metallic phase rich in copper and arsenic—represents an operational challenge in flash smelting furnaces due to its contribution to the complex degradation process of the refractory lining. This study combines a thermodynamic and operational analysis to propose a mechanism of speiss formation considering as main variables the presence of minor elements such as sulfur, antimony, and lead affecting the phase equilibria decreasing liquidus and solidus temperatures of the Cu–As rich system and the operational conditions such matte grade objective and enrichment of the blast, that finally impacts on the operational oxygen potential. Using the software FactSage 8.3, specific phase diagrams (isopleths) were constructed for different contents of these elements, showing that even small concentrations can significantly decrease liquidus and solidus temperatures. The very low solidus temperature facilitates infiltration into the refractory materials. The findings highlight the importance of strictly controlling the chemical composition of the feed and operational conditions to minimize speiss formation and mitigate its adverse effects on the integrity of the flash furnace sole.