Synergistic effect of carbothermal reduction and sodium salts leaching in the process of iron recovery from copper slag

Abstract

Copper slag is mostly considered a waste material and around 41 wt% of total iron content present in it is lost. Iron is mostly present in copper slag as fayalite (Fe₂SiO₄). In this study, Iron was recovered by the decomposition of Fe₂SiO₄ using the synergistic effect of carbothermal reduction and sodium salts leaching for the first time. The results showed that 68.39 % of iron was recovered from copper slag by carbothermal reduction at 1000 °C for 1 hr. The iron recovery increased to 83.45, 93.39 and 97.8 %, respectively, after further 1 hr leaching by 2 M NaOH, 1 M Na₂CO₃ and 2 M NaOH+1 M Na₂CO₃ at 100 °C. The leaching results indicated that the increased NaOH concentration from 1 to 2 M improved the removal of silica, which in turn led to higher iron recovery. The increase of Na₂CO₃ concentration from 1 to 2 M showed a negative effect on iron recovery. The combination of 2 M NaOH and 1 M Na₂CO₃, however, led to the highest iron recovery of 97.8 % because NaOH+Na₂CO₃ gives Na₂O that is easier to react with SiO₂ with only −194.3 kJ energy requirement. Mass balance calculations indicated that before the leaching process, 345 kg mass was lost, whereas, after the leaching process the amount of discarded waste was only 260.8 g. Therefore, the present study not only provides 97.8 % iron recovery but also reduces the discharge of secondary solid waste due to no addition of additives.