On the prevailing reaction pathways during magnesium production via carbothermic reduction of magnesium oxide under low pressures

摘要

In this work we identify the prevailing reaction pathways of carbothermic reduction of MgO for the tem- perature and pressure ranges of 1375-1450 °Cand1-2 kPa, respectively, and normalized reduction extents of up to 0.4. It has been previously suggested that Mg(g) is produced by either (i) MgO dissociation forming O2 as the reaction intermediate or (ii) MgO(s)-C(s) boundary reaction producing CO that then reduces MgO while forming CO2 as the reaction intermediate. Either of the intermediates (O2 or CO2) are then con- sumed by C, which is necessary to sustain further Mg(g) production. To identify the prevailing pathways, O2 or CO2 was co-fed with Ar to sweep reacting MgO-C blends with the intent to shift the equilibrium of one of the suspected Mg(g)-producing reactions. After accounting for envisaged effects of both the C/MgO ra- tio in the reacting blends and the CO concentration in the reaction atmosphere, it is demonstrated that Mg(g) is produced (1) MgO thermal dissociation and (2) MgO reduction with CO that take place in paral- lel. At 1375 °C and 1400 °C, roughly twice as much Mg(g) was produced pathway (1) as compared to pathway (2). There is no evidence supporting the relevance of a direct MgO(s)-C(s) boundary reaction.