Reactors aluminothermic reduction

The reactor used for the aluminothermic reduction of niobium pentoxide is shown schematically in Figure 4.17 (A). It is a steel pipe, lined on the inside with alumina and provided with a pipe cap. The charge, consisting of stoichiometric amounts of niobium pentoxide and aluminum powder, is blended and loaded in the lined pipe, and covered with alumina. The cap is closed and the reaction initiated by placing the loaded bomb in a gas-fired furnace, preheated to 800 °C, and by raising the temperature of the furnace to 1100 °C. 

Instead of a closed-bomb reactor, an open reactor (shown in Figure 4.17 B) has also been used for this aluminothermic reduction. The mild steel reactor is lined on the inside with calcined magnesia. An arrangement is made to initiate the reaction in the center of the... 

Figure 4.17 B Schematic of the reactor for open aluminothermic reduction of niobium pentoxide.

Figure 4.17 C Schematic of the closed-bomb reactor for aluminothermic reduction of vanadium pentoxide.

Vanadium metal can be prepared either by the reduction of vanadium chloride with hydrogen or magnesium or by the reduction of vanadium oxide with calcium, aluminum, or carbon. The oldest and most commonly used method for producing vanadium metal on a commercial scale is the reduction of V2Os with calcium. Recently, a two-step process involving the aluminothermic reduction of vanadium oxide combined with electron-beam melting has been developed. This method makes possible the production of a purer grade of vanadium metal, ie, of the quality required for nuclear reactors (qv). 

Preparation of uranium metal. As discussed previously, some nuclear power plant reactors such as the UNGG type have required in the past a nonenriched uranium metal as nuclear fuel. Hence, such reactors were the major consumer of pure uranium metal. Uranium metal can be prepared using several reduction processes. First, it can be obtained by direct reduction of uranium halides (e.g., uranium tetrafluoride) by molten alkali metals (e.g., Na, K) or alkali-earth metals (e.g.. Mg, Ca). For instance, in the Ames process, uranium tetrafluoride, UF, is directly reduced by molten calcium or magnesium at yoO C in a steel bomb. Another process consists in reducing uranium oxides with calcium, aluminum (i.e., thermite or aluminothermic process), or carbon. Third, the pure metal can also be recovered by molten-salt electrolysis of a fused bath made of a molten mixture of CaCl and NaCl, with a solute of KUFj or UF. However, like hafnium or zirconium, high-purity uranium can be prepared according to the Van Arkel-deBoer process, i.e., by the hot-wire process, which consists of thermal decomposition of uranium halides on a hot tungsten filament (similar in that way to chemical vapor deposition, CVD). 

---