Page 10 - Academic Press Encyclopedia of Physical Science and Technology 3rd InOrganic Chemistry

P1: FYK Revised Pages
Encyclopedia of Physical Science and Technology EN001F-11 May 7, 2001 12:19

218 Actinide Elements

FIGURE 1

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◦
1000 C barium vapor at 1300 C, followed by increasing the tem-
ThO 2 + 2Ca −−−→ Th + 2CaO. (10) ◦
Ar perature to 1600 C to produce a bead of protactinium
metal. Single-crystal protactinium metal is obtained by
The reaction mass is leached with water and dilute acid, a modified van Arkel process starting from the carbide.
leaving thorium metal powder. Very pure thorium metal More then 150 minerals containing uranium are known.
can be prepared by the van Arkel process involving the Typically, however, uranium ores contain only about 0.1%
thermal decomposition of ThI 4 . uranium. In the commercial production of uranium metal,
To obtain significant quantities of protactinium, a sep- the ore is crushed, concentrated, roasted, and in most cases
aration procedure was developed for extracting protac- leached with sulfuric acid in the presence of an oxidizing
tinium from the sludge that was left after the ether agent such as manganese dioxide or chlorate ions to con-
extraction of uranium at the Springfields refinery. The pro- vert all of the uranium to uranyl sulfato complexes. Car-
cess yielded 127 g of pure 231 Pa from 60 tons of sludge. bonate leaching is used to extract uranium from ores con-
Protactinium metal can be obtained by reducing PaF 4 with taining minerals such as calcite. The recovery of uranium