Rate of Slag Reduction in a Laboratory Electric Furnace--Alternating vs Direct Current

The objective of this laboratory investigation was to measure the reduction kinetics of nickel smelting and converting slags using alternating current (AC) and direct current (DC). The two slags tested contained 34 and 51 pct total iron in the form of FeO and Fe3O4. Laboratory experiments were carried out between 1200°C and 1450°C, and the rate of reduction was measured based on the CO and CO2 contents in the off-gas from the furnace. Upon application of power to a pair of electrodes immersed in the molten slag, the reduction rate increased rapidly. This increase is explained by an increase in the electrode tip temperature enhancing the rate of the Boudouard reaction. The rate of reduction of the converter slag containing 29 pct Fe3O4 was 2 to 3 times faster than the smelting slag. With DC, the reduction rates at the anode and cathode were basically identical to each other, while for the smelting slag with only 8 pct Fe3O4, the anode and cathode reduction rates were quite different. With increasing current or power density, the temperatures of the electrodes increase above that of the bulk slag.