Ilmenite Reduction

Introduction

Reducing ilmenite (FeTiO₃) to produce oxygen, iron, and titanium in a lunar context has produced a number of proposals, many of them specifically aimed at oxygen production. Ilmenite is attractive for this purpose as the iron oxides it contains require less energy to reduce than any other oxide on the lunar surface. For this reason, proposals which have oxygen production as the primary goal usually focus on reduction of the iron content of ilmenite.

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Carbothermal Reduction

Oxygen can be retrieved from Ilmenite (FeTiO₃) and Rutile (TiO₂) by means of carbothermal reduction. In experiments, powdered carbon and powdered ilmenite/rutile were evenly mixed and then heated to 1500 degrees Celsius. The end products of this reaction are Oxygen and a high strength Ceramic-metal composite (Cermet) of Iron (Fe) and Titanium Carbide (TiC) which has high chemical stability. The amount of reinforcing TiC ceramic in the matrix can be controlled via the amount of rutile and carbon used^[1]. While this method provides a means of retrieving all of the oxygen from ilmenite/rutile and a potential for producing reinforced, high performance and wear components and cutting tools from lunar regolith, it is at the cost of highly valuable carbon needed for biological processes.

Stoichiometry for this reaction:

Ilmenite:
FeTiO₃ + 4C ---->Fe + TiC + 3CO

Ilmenite and Rutile:
FeTiO₃ + nTiO₂ + (4+3n)C ---->Fe + (1+n)TiC + (3+2n)CO
Where n represents the number of TiO₂ molecules

Reduction with CO

This reaction is based on a fluidized bed scheme which is similar to large scale proposals for Hydrogen Reduction. The product of CO reduction of Ilmenite is Carbon Dioxide (CO₂), which is reduced to CO and oxygen. The CO is recirculated, and the oxygen stored.^[2]. The presence of solar wind implanted carbon in the regolith will allow the recovery of additional carbon if recycling efficiency is sufficiently great, though a method for dealing with evolved methane (CH₄, from hydrogen present in the regolith) would be required. The CO reduction of ilmenite is slower than the H₂ process, but by less than an order of magnitude for any given temperature.

The reaction sequence is:

Reduction:
FeTiO₃ + CO ---->Fe + TiO₂ + CO₂
Endothermic cracking:
2CO₂ ----> 2CO + O₂
Net Reaction:
2FeTiO₃ + 2CO ---->2Fe + 2TiO₂ + 2CO + O₂