Utilization of Waste Copper Slag to Produce Directly Reduced Iron for Weathering Resistant Steel

Waste copper slag is a refractory material with high iron content, but it is difficult to recovery iron minerals from the slag because the iron mainly occurs in fayalite. A new technology of coal-based direct reduction-magnetic separation process was developed to recover iron from the slag assaying 39.85% Fe-total and 0.33% Cu. The results show that the final iron concentrate, assaying 90.68% Fe-total, 94.01% metallization degree, 0.66% Cu and 0.058% S with overall iron and copper recoveries of 90.49% and 79.53%, respectively, was manufactured under the optimized conditions as follows: balling the mixture of copper slag with 20% compound additive at 0.3 of basicity, preheating the green pellets at 1 000 degrees C for 9 min, then reducing the preheated pellets at 1 200 degrees C for 70 min with coal to dried pellets mass ratio of 2, grinding the reduced pellets up to 95% passing 0.074 mm, and magnetically separating the ground product in Davi Tube at 0.08 T magnetic field intensity. The observation of the reduced pellets microstructure shows that the additive plays a role of nucleating agent, which enhances metallic iron grains migrating and coarsening during reduction process. The process is probably one of efficient ways to recover iron from copper slag to produce directly reduced iron (DRI), which can be used as the burden to produce weathering resistant steel by electric arc furnace to replace sponge iron or scrap steel. The process reduces the secondary environmental pollution of copper slag and has been applied well in Tong ling Nonferrous Metals Group Holding Co., Ltd in China.