Optimization of the ferromanganese production from spent primary batteries - Design of the process slag

In order to improve the recycling efficiency and especially the manganese recovery yield in the ferromanganese production from spent primary batteries process, slag-metal equilibrium experiments were conducted in a closed MoSi ₂-resistance furnace above argon atmosphere. Four synthetic slag-series: CaO-SiO₂, CaO-SiO₂-Al₂O ₃, CaO-SiO₂-MgO and CaO-SiO₂-Al ₂O₃-MgO in different compositions were brought into contact with two different Fe-Mn alloys (50 and 90 wt.-%Mn), using alumina crucibles at 1470 °C. The equilibrium computations were carried out with the computer software FactSage using the FACT compound 5.0 databases. The theoretical and experimental results clearly showed the same tendency and an acceptable agreement. Five slag systems were found allowing keeping more than 80 wt.-%Mn in the metallic alloy. The most important factor to increase the manganese fraction in the Fe-Mn-alloy is the CaO-content in the slag, together with the concentration of MgO improving the basicity of the slag. The initial slag basicity must be near to or higher than 1. The best results were obtained using a slag composition of 54 wt.-% CaO, 6 wt.-% SiO₂,37 wt.-% Al₂O₃ and 3 wt.-% MgO.This recovered more than 90 wt.-% of the Mn-input in the alloy.