Phase transformation analysis and process optimisation of low-grade lead–zinc oxysulphide ore carbothermal reduction

Abstract

The continuous exploitation of zinc blende resources leading to primary resources may not be sufficient for future requirements. The abundant low-grade lead–zinc oxysulphide ore will become a crucial source of zinc metal. Thus, methods for utilising low-grade lead–zinc ore resources must be urgently developed; this can contribute to achieving considerable economic value. By studying the mineral technology and thermodynamics of low-grade lead–zinc oxysulphide ore, a Box–Behnken design model of response surface methodology was created to explore the impact of various factors, such as reduction time, temperature, and carbon mass ratio. The outcomes of the study indicated that the aforementioned factors have a significant impact on the zinc volatilisation rate, and it reaches 99.01% under the optimum conditions of 1174 °C, 86 min, and 12% carbon mass ratio. In addition, compared with the carbothermal reduction in air, the carbon mass ratio requirement is reduced by 10–20% in the inert atmosphere. The volatilisation mechanism of zinc, particularly the distribution and migration behaviour, was studied using X-ray diffraction and scanning electron microscopy–energy dispersive X-ray spectroscopy. The results showed that in the high-temperature section of the lead–zinc ore treatment, zinc sulphide and zinc oxide are transformed via the synergistic reduction involving carbon and calcium to zinc, and the presence of iron and calcium in the form of sulphides leads to a decrease in sulphur dioxide formation. This study explores the efficient and green development and utilization of low-grade lead–zinc oxysulphide ore by pyrometallurgical method to provide theoretical support for its large-scale industrial treatment.