Recovery of locked-up uranium in slag disc by co-melting in magnesio-thermic reduction

Abstract

Magnesio-thermic Reduction (MTR) of Uranium tetra Fluoride (UF4) is one of the main industrial methods for producing commercial pure uranium metal in massive form. Nuclear grade natural Uranium (U) metal ingots are produced regularly in UED, BARC following MTR route for fuelling research reactors in BARC. This is a bomb type reaction and is represented by $$UF_4 + 2Mg = U + 2MgF_{2 - } (\Delta H^ \circ _{298} = - 83.5 Kcal/gm mole)$$ Small excess of magnesium is required to achieve maximum yield. This thermite type reduction is carried out in a closed reaction vessel, popularly known as MTR reactor, lined with magnesium fluoride powder. MTR reactors are made of boiler quality steel. Use of MgF2, a reaction by-product, as lining material completely eliminates the chance of foreign element contamination. This lining of MgF2 not only prevents direct contact of the molten metal and slag with the reaction vessel but also acts as an insulating material immediately after firing and holds the hot molten mass for longer period, thereby facilitating adequate metal-slag separation. This is a batch process and stoichiometric quantity of UF4 and Mg chips are blended and charged inside the lined reactor. Once the charging is over, the surface is covered with fine MgF2 powder and sealed by fixing a lid. This sealed reactor is then heated inside an electric furnace at a predefined heating schedule for the reduction to take place. The initiation of reaction is called ‘Firing”.