Carbothermal Reduction of Siliceous Minerals in Vacuum.
High Temperature Sci 1970 Jun; 2:95-109
Carbothermal reduction of various quartz- and silicate-graphite mixtures was studied in a batch reactor at a pressure of about 0.01 Torr and a temperature of 1,400 deg c. The extent of reaction was determined by the quantity of carbon consumed in a 5-hour period. Maximum reactivity occurred with particles having diameters of about 0.2 Mm. At this reactant size, the bed porosity was sufficient to permit escape of carbon monoxide from the reaction site while securing maximum interparticle contact. The maximum reactivity occurred with a quartz-to-graphite molar ratio of 1 or weight ratio of 5. Carbo-thermal reducibilities of some 20 silicate minerals were studied at a fixed mineral-to-graphite weight ratio of 5. The millimoles of carbon consumed or carbon monoxide formed in 5 hours increased systematically with the fraction of silicon dioxide in the silicate when the mineral remained in the solid state at the reaction temperature. Silicates that melted at the reaction temperature reduced less readily than those that remained in the solid state. Carbothermal reducibility as well as free energy considerations show that complex silicates behave like weakly associated aggregates of simpler oxide groups. Therefore, the energy to dissociate the complex silicates is small, and the bulk of the energy goes to winning the oxygen from the metal and breaking up the individual oxide groups. Hence the influence of structure on reducibility is insignificant and is easily overrun by the silicate chemical composition.
High Temperature Sci., V. 2, June 1970, PP. 95-109