Abstract
Recovery of a Copper-rich Alloy through Hydrogen Reduction of a Combined Converter-Anode Furnace Slag from Secondary Copper Production
Felkl, L.1; Stelter, M.1 & Charitos, A.1
1 Institute of Nonferrous Metallurgy and Purest Materials, TU Bergakademie Freiberg, Leipziger Straße 34, 09599 Freiberg
In secondary copper production within the black copper smelting route, slags produced from the converter and the anode furnace contain high amounts of copper and other valuable elements
(16.3 – 41.7 wt.% Cu2O) as well as volatiles like zinc (3.9 – 7.0 wt.% Zn), tin (up to 15wt.% Sn) and lead (1.8 – 7.5 wt.% Pb). Besides this aspect, the composition of the slags differ from typical fayalitic ones. The slag from the converter is quite similar to these used in primary production (Cu2O-FeO-SiO2-Fe2O3) while in the anode furnace a Cu2O-SiO2-CaO-Fe2O3 slag is produced. Both slags are promising for the direct recovery of a copper-rich alloy, at black copper quality (> 80 wt.-% Cu), as well as a high volatilization yield of lead and zinc, as shown in previous studies. This could be advantageous in comparison to the practice of internal slag recycling which leads to impurity accumulation and capacity decrease.
The secondary slag resulting from the reduction of the anode furnace slag shows high viscosity at 1300°C. This hinders further reduction as gas movement in the highly viscous melt is impeded. Trials have shown that the phase separation is to be more difficult. To compensate with regard to the above, the co-reduction of the converter slag together with the anode furnace slag is studied using industrial slag samples. The intent is to use the converter slag as iron oxide source for the anode furnace and the anode furnace slag as calcia source as flux in the reduction process.
The achieved secondary slag from this combined reduction is located in the classical ferro-calcium-silicate (FeO-CaO-SiO2) system but with elevated content of Al2O3. For the reduction a hydrogen-argon stream with pH2=0.33 atm at 500 ml/min is used to achieve a good mixing within the molten phase while maintaining a high hydrogen utilisation and to prevent secondary reactions. The dependence of the reduction grade from the hydrogen input is modelled in an open system approach in the thermodynamical modelling program FactSage™ and used to predict the experimental outcome. The usage of hydrogen, injected by a submerged alumina lance, for the combined reduction of both slags is recommended for higher selectivity when compared to carbon-based reducing agents.
Keywords: slag reduction, copper, hydrogen, open system modelling, slag treatment