Settling of Copper Phases in Lime Modified Iron Silicate Slag

Copper in discarded slag decreases the profits and copper recovery during the pyrometallurgical extraction processes. The copper losses to slag can be reduced by using a settling furnace, in which mechanically entrained copper droplets separate from the slag under the action of gravity. The settling rate of entrained droplets can be increased by modifying the slag composition and, thus, the slag properties, which are known to influence the settling rate. The knowledge of industrial CaO slag modification in a reduced iron silicate slag with a Fe/SiO2 ratio close to unity is limited. An industrial trial was thus conducted in an electric settling furnace, where the slag had been pretreated in a fuming furnace, to investigate the effect of CaO slag modification on the final slag copper content. Slag samples were collected from the ingoing and outgoing slag and from within the furnace of batches modified with CaO up to about 16 wt %. The trial was evaluated by comparing the final slag copper content and the copper recovery in the settling furnace. The results indicate that the settling becomes more efficient with the CaO modification as the final slag copper content decreased with increasing CaO content.

Distributions of As, Pb, Sn and Zn as minor elements between iron silicate slag and copper in equilibrium with tridymite in the Cu–Fe–O–Si system

The distributions of arsenic, lead, tin and zinc between iron silicate slag and copper in equilibrium with tridymite in the Cu–Fe–O–Si system have been experimentally determined at selected oxygen partial pressures (P(O2)) at temperatures of 1 523 K and 1 573 K. The experimental technique involved high temperature equilibration in a sealed silica ampoule to minimize the vaporization of minor elements, rapid quenching of the condensed phases, and the direct composition measurements of the condensed phases using microanalysis techniques. The effective P(O2)s of the samples were determined based on the measured Cu2O concentrations in slag. The new experimental data resolve discrepancies found in previous studies and have been used in the development of a new thermodynamic database of the Cu–Fe–O–Si system containing minor elements.