Thermodynamic modeling of metal reduction in copper-smelting slags and experimental verification of its results

Over 110 million tons of slag were accumulated in the dumps of the Russian copper-smelting enterprises, and their number is increasing. Environmental taxes and dumps maintenance costs are burdensome, which makes it necessary to make the most complete disposal of these production wastes. At the same time, these slags contain valuable elements, in particular, iron, copper, zinc, selenium, arsenic and some others, the extraction of which can make recycling profitable. The paper presents the results of a thermodynamic calculation of the behavior of copper-smelting slag elements in the mixture with carbon during heating. Modeling was performed using the TERRA software package. The influence of the process temperature in the range of 600 – 1750 °C on reduction of iron, zinc and silicon was analyzed at the amount of carbon in the system corresponding to the stoichiometry of iron reduction reactions and exceeding the stoichiometric one. It was established that when heated above 650 °C, metallic iron appears in the system, and its full reduction is completed at 1250 °C. The appearance of metallic zinc is observed in two temperature ranges: in the first, appearance of zinc is observed with a simultaneous decrease in concentration of zinc oxide; in the second, an increase in concentration of metallic zinc with a simultaneous decrease in concentration of zinc sulfide. At temperatures above 1650 °C, silicon appears in the system. Under laboratory conditions, the processes of solid-phase reduction of iron with the capture of zinc oxide and separation of the reduction products were tested. It was established that as a result of pyrometallurgical separation by melting reduction products, iron-carbon alloys (steel and cast iron) and alloys with high silicon content can be obtained. The results of the work can be used in development of theoretical and technological foundations for the processing of copper smelting slags, which are not processed by existing technologies.