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 41wt% 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 1000oC for 1hr. The iron recovery increased to 83.45, 93.39 and 97.8%, respectively, after further 1hr leaching by 2M NaOH, 1M Na2CO3 and 2M NaOH+1M Na2CO3 at 100oC. The leaching results indicated that the increased NaOH concentration from 1 to 2M improved the removal of silica, which in turn led to higher iron recovery. The increase of Na2CO3 concentration from 1 to 2M showed a negative effect on iron recovery. The combination of 2M NaOH and 1M 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 -194.3kJ energy requirement. Mass balance calculations indicated that before the leaching process, 345kg mass was lost, whereas, after the leaching process the amount of discarded waste was only 260.8g. 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.