Effect of Titanium Dioxide on Aggregation of Reduced Metallic Iron in Molten Slag

Abstract

The reduction process of lunar regolith simulant was designed to obtain metallic iron (Fe) and utilize lunar resources, focusing mainly on the effect of titanium dioxide (TiO2) on the recovery of metallic Fe from molten slag. Thermodynamic calculations were conducted to predict the equilibrium phases existing at high temperature upon heating the regolith simulant to 1600°C under an oxygen partial pressure of 10−15 atm, in which the metallic Fe coexisted with the molten slag. Based on these predictions, two steps were applied in the experimental procedure: a reduction step followed by a melting step. The results showed that metallic Fe droplets were obtained by aggregating fine metallic Fe particles in the melting step. The viscosity of molten slag was found to decrease when TiO2 was added to the regolith simulant, but the recovery ratio—defined as the weight ratio of the metallic Fe obtained from the aggregation of fine metallic Fe particles to the total amount of Fe in the regolith simulant—also decreased. The wettability between liquid Fe and molten slag improved upon increasing the TiO2 content in the latter. These results indicate that wettability exerts a substantially more dominant effect than the viscosity of molten slag does in the recovery of metallic Fe from regolith simulant.