Geology Reference
In-Depth Information
Europium Oxide
Gadolinium Oxide
Precipitation
Filtering
Calcining
Precipitation
Filtering
Calcining
Samarium Oxide
Sm-Eu-Gd
Solution
RECl 3
Precipitation
Filtering
Calcining
Calcination
(620°C)
Dissolution
HCI (30%)
SX Loading
Mixed -Settlers
Eu Redox
Separation
SX Gd-Sm
Separation
Bastnasite (60% REO)
La-Nd-Pr
Solution
CeO 2 (50-60%)
CO 2 Removal
Dissolution
HNO 3
SX La-Nd-Pr
Separation
Dissolution
HNO 3
Lantanum Nitrate
Precipitation
Filtering
Calcining
SX Nd-Pr
Separation
SX with TBP
Neodymium Oxide
Cerium Nitrate
Precipitation
Filtering
Calcining
Praseodymium Oxide
Fig. 8.13 Representative separation of REO using solvent extraction (SX)
8.13.7 FromREOtoREmetals
RE metals are obtained from REO through reduction. Owing to the basicity of
RE 2 O 3 , the reducing agent must be quite strong since its stability is greater than
that of magnesium, aluminium or silicon oxides and only slightly less than calcium
oxide. Similarly, the stability of RE-fluorides and anhydrous RE-chlorides is only
superseded by CaF 2 of the fluorides and KCl;NaCl;LiCl and CaCl 2 of the chlo-
rides. Given this fact, the alternative consisting of a metallothermic reduction with
alkaline or alkaline earth metals is a di cult one. This reduction can be achieved
in a vacuum or inert atmosphere (to avoid reactions with oxygen) with calcium
metal in the case of REO and RE-fluorides and with K;Na;Li and Ca metals
with respect to the chlorides. This fact also explains the need for special crucibles
made from refractory metals such as of niobium, molybdenum, tantalum or tung-
sten. In addition, the feed must be free of carbon, nitrogen and silicon impurities
since REE form interstitial dicarbides, mononitrides and disilicides which alter the
composition and properties of pure metals (Gupta and Krishnamurthy, 2005)
Specifically, there are several commonly used routes for obtaining the pure rare
earth metals: a) via the reduction of anhydrous chlorides or fluorides; b) via a
carbothermic reduction of the oxides; and c) via the electrolysis of fused chlorides
salts or oxide-fluoride mixtures.
The first option, direct reduction-distillation, is used for obtaining volatile lan-
thanides like Sm;Eu;Tm and Y b. The reducing agent is commonly lanthanum but
can also be Ce, mischmetal (a commercial mixture of lantanides), Zr and even Th
(Gupta and Krishnamurthy, 2005). Essentially the process consists of mixing La
 
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