Carbothermal reduction of copper smelter slag for recycling into pig iron and glass

Slags produced from copper smelting are siliceous and often contain valuable metals such as copper and iron as well as deleterious elements such as arsenic and lead. A copper slag was obtained from the former Anaconda smelter site, USA and characterized by SEM-EDS, XRD, TG-DTA and ICP-OES. A recovery process was developed to separate the valuables from the silicates thereby producing value-added products and simultaneously reducing environmental concerns. Results show that the major phase was an amorphous iron-calcium-aluminosilicate of variable composition with copper sulfide prills. Thermodynamic calculations and carbothermal reduction experiments indicate that most of the copper and iron can be recovered as pig iron from the initial slag using minor amounts of lime and alumina and treating at 1350 °C/1623 K or higher for 30-90 min. The resulting secondary slag can also be recycled as a glass to the glass and ceramic industry. Statistically designed experiments were conducted on the slag to identify the most favored regime to optimize the recovery of pig iron as well as the hardness and density of the secondary slag.