Pyrochemical separation of lanthanide and actinide metals.

Abstract

A highly efficient group separation of lanthanide and actinide metals can be effected by molten salt extraction of the lanthanide fraction(s) from a solution of actinide and lanthanide metals dissolved in molten copper-magnesium alloy. The extraction salt used for this separation is 50 m/o MgCl 2, 30 m/o NaCl and 20 m/o KCl, and the composition of the solvent metal alloy is approximately 20 to 30 mass-percent magnesium in copper. At 800 °C, the distribution coefficient (K d) for +3 laanthanide chlorides varies from 150 to 70 while the distribution coefficient for the +3 actinide varies from 4.5 to 6.0. At 20 mass percent magnesium, the ratio of K d is about 30 between Cerium (150) and Americium (4.5). With these large differences in K d, a simple batch extraction can be used to separate Cerium from Americium. The lanthanide elements are extracted into molten salt phase as the +3 chloride salt and the equivalent mass of magnesium metal is deposited in the immiscible metal alloy phase. After separation of phases which can be performed mechanically after cooling, or be decantation at elevated temperature, the pure lanthanide metal can be recovered from the salt phase by reduction with calcium metal at 800 °C. The lanthanide metal is formed as a high-density-powder bottom-phase, which can be converted to a molten liquid by the addition of zinc. After retorting, the pure lanthanide metals are recovered as metallic sponge.