Effect of Temperature and Graphite Immersion Method on Carbothermic Reduction of Fayalite Slag

Abstract

In this work, graphite flakes were used to reduce fayalite slag originated from the pyrometallurgical copper extraction process. Experiments were conducted with a significantly different contact area between graphite and slag at two temperatures, 1300°C and 1400°C. The process was continuously monitored via the concentration change of CO and CO₂ in off-gas. Reduction rate values in experiments where 150-micron-diameter graphite flakes were submerged into the slag and left to float slowly to the top are about four times higher compared with when graphite flakes were dispersed at the top surface of liquid slag. The activation energy for instigating reduction was 302.61 kJ mol⁻¹ and 306.67 kJ mol⁻¹ in the case where graphite flakes were submerged into the slag and dispersed at the surface, respectively. The reduction process is characterized by two distinctive periods: an initial steep increase in the concentration of CO and CO₂ controlled by the Boudouard reaction and a subsequent slow decrease of CO and CO₂ concentrations in the off-gas controlled by mass transfer of reducible oxides from bulk to the gas–slag interface.