Description

The most common method for minimizing the copper content of residual slag in the process of autogenous smelting of sulfide raw materials is treatment of molten slag in an electric furnace, with optional addition of solid reducing agents, such as coke, and/or sulfiding agents such as pyrite. A drawback of this technique is the fact that the fmal slag produced still contains 0.5% or more Cu. We have tested a method for treating molten slag obtained as a result of autogenous smelting by a gaseous mixture of sulfur dioxide and methane at a ratio of SC:S0₂ = 0.75 :1.0 in the presence of oxygen. Interaction reaction within the S0₂-0₂-CH₄ system proceeded at a high rate at 1373 to 1573 K to form reducing and sulfiding agents: H₂S, S, COS, CO, C0₂, H₂, H₂0. The gas mixture requirement was about 100 to 150 Nm³ per 1tonne of slag. A decrease in the ferric iron concentration (Fe³⁺) fiom 10-15% down to 2-3% resulted in lower solubility of copper in slag, and agitation of the melt with gas stream accelerated the separation of the sulfide phase and slag. Removal of copper from slag was performed in a pilot unit within the second Vanyukov furnace zone where slag arrived with a copper content of 0.8-1.3%. The temperature of molten slag was maintained within 1523 to 1573 K. The copper content of the final slag was at a level of 0.12 to 0.14%. The matte sent to converting was a mixture of bottom matte from the smelting zone and the slag treatment zone. It had a copper content of about 50 to 55%. Process gases from both furnace zones were combined and sent to the acid plant for sulfur recovery. This process was offered forcommercial use at two copper smelters in Russia and CIS.