Settling separation and reduction cleaning mechanism of slag-matte melt from gold concentrate smelting

To enhance the matte-slag separation effect during matte smelting of complex refractory gold ores and improve the recovery of smelted metals, this study adopted the gold-rich matte-slag mixed melt (Au mass fraction of 0.002 409%) produced from gold concentrate smelting as the raw material. Static matte-slag separation experiments and reduction depletion tests were systematically carried out. The main factors affecting matte-slag separation were analyzed, and the influences of process parameters including temperature, reductant dosage and holding settling time on the recovery of smelted metals were investigated. Meanwhile, the gold capture mechanism of low-grade copper matte was revealed. The results indicate that the matte-slag mixed melt achieves effective separation after heat preservation and settling treatment. Nevertheless, both the matte and slag phases contain a high-melting-point magnetic iron phase with mass fractions of 1.51% and 8.61%, respectively. This phase increases the viscosity of molten slag and weakens the gold capture capacity of the matte phase, which acts as a critical limiting factor restricting matte-slag separation. Reduction depletion was applied to further strengthen the separation efficiency and improve the recovery of smelted metals. The results show that reductant dosage exerts the most significant influence on metal recovery, and the recovery rates of gold and copper increase with the rise in reductant dosage. Under the optimized conditions of temperature 1 300 ℃, coke powder dosage of 1% and holding settling time of 120 min, the recovery rates of gold and copper reach 99.55% and 96.62%, respectively. In terms of the gold capture mechanism of low-grade copper matte, the chemical potential difference of gold between the matte phase and the slag phase was calculated to clarify the thermodynamic principle for the preferential enrichment of gold in the matte phase. Under the optimal experimental conditions, the standard chemical potential difference of gold between the matte and slag phases is about -28 862.97 J/mol.