A Study on Reduction of Copper Smelting Slag by Carbon for Recycling into Metal Values and Cement Raw Material

Copper smelting slag is a solution of molten oxides created during the copper smelting and refining process, and about 1.5 million tons of copper slag are generated annually in Korea. The oxides in copper smelting slag include ferrous (FeO), ferric oxide (Fe2O3), silica (SiO2 from flux), alumina (AI2O3), calcia (CaO) and magnesia (MgO). The main oxides in copper slag, which are iron oxide and silica, exist in the form of fayalite (2FeO·SiO2). Since copper smelting slag contains high content of iron, and copper and zinc, common applications of copper smelting slag can be used in value-added products such as abrasive tools, roofing granules, road-base construction, railroad ballast, fine aggregate in concrete, etc. Some studies have attempted to recover metal values from copper slag. This research was intended to recover ferrous alloy contained Cu, a raw material of zinc, from copper slag, and produce reformed slag such as blast furnace slag for Portland cement. As a result, it was confirmed that with reduction smelting by carbon at temperatures above 1400 °C, it is possible to recover pig iron containing copper from copper smelting slag, and the addition of CaO in reduction smelting helped to reduce iron oxide in the fayalite and change the chemical and mineralogical composition of the slag. The copper oxide in the slag can be easily reduced and dissolved in the molten pig iron, and zinc oxide is also reduced to a volatile zinc, which is removed from the furnace as fumes, by carbon during the reduction process. When CaO addition is above 5%, acid slag is completely transformed into calcium silicate slag and is observed to be like blast furnace slag.