Recovery of Rare Earths

Oil field uses are primarily imidazolines for surfactant and corrosion inhibition (see Petroleum). Besides the lubrication market for metal salts, the miscellaneous market is comprised of free acids used ia concrete additives, motor oil lubricants, and asphalt-paving applications (47) (see Asphalt Lubrication AND lubricants). Naphthenic acid has also been studied ia ore flotation for recovery of rare-earth metals (48) (see Flotation Lanthanides). 

Oxahc acid is used in various industrial areas, such as textile manufacture and processing, metal surface treatments (qv), leather tanning, cobalt production, and separation and recovery of rare-earth elements. Substantial quantities of oxahc acid are also consumed in the production of agrochemicals, pharmaceuticals, and other chemical derivatives. 

Uses of oxalic acid ia each region are summarized in Table 5 (58). The demand for agrochemical/pharmaceutical production and for separation/recovery of rare-earth elements in each region has been increasing. The use for marble polishing in western Europe is unique to the region. 

Separation and Recovery of Rare-Earth Elements. Because rare-earth oxalates have low solubihty in acidic solutions, oxaUc acid is used for the separation and recovery of rare-earth elements (65). For the decomposition of rare-earth phosphate ores, such as mona ite and xenotime, a wet process using sulfuric acid has been widely employed. There is also a calcination process using alkaLine-earth compounds as a decomposition aid (66). In either process, rare-earth elements are recovered by the precipitation of oxalates, which are then converted to the corresponding oxides. 

Other commercial operations known to have used organophosphorus acids for the recovery of rare earths are those of Thorium Ltd. in England,39the Megon Company in Norway,73-95 and Denison Mines in Canada.96,97... 

The second method of recovery of rare earths from monazite involves caustic soda digestion and is illustrated in Fig 1.4. 

Recovery of rare earths as chlorides by hydrochloric acid digestion of bastnasite is illustrated in Fig 1.5. 

Fig. 1.3. Sulphuric acid process for the recovery of rare earths from monazite [2].

The use of various techniques discussed so far is well illustrated by the processing steps adopted in the economic recovery of rare earths from monazite in India [25]. The first step in the processing of monazite is digestion with caustic soda and this is schematically shown in Fig. 1.11. The main reaction that takes place during digestion may be written as ... 

The rare earths and thorium hydroxides are then treated with HC1 (30%) to attain a pH of 3.2 at 70°C. This step in the recovery of rare earths is schematically shown in Fig. 1.12. Rare earths are obtained as soluble chlorides leaving behind insoluble Th(OH>4. Rare earth chlorides are treated with Na2SC>4 and BaCl2 to free the rare earths from Pb, Ra and Th. It is also treated with Na2S to remove Pb, Fe, Th and U. 

Liquid membrane systems were first introduced in 1968 (34), and since then they have been evaluated for various chemical and biochemical applications (35). Some of the applications include the selective extraction of hydrocarbons (36), the recovery of rare earths from process streams (37), the extraction of organic contaminants like phenol from water streams (38), and amino acid recovery (39). 

This list is not all-inclusive but is illustrative. The oxalate is the most insoluble salt and is most often used for recovery of rare earths from solution. The commercial ores mined for extraction of rare earths include ... 

Yang Y (2014) Recovery of rare earth metals fiom end-of-life permanent magnets an overview. In Proceedings of ERES2014—1st European rare earth resources conference, Milos, Greece, 04-07 Sept 2014, pp 429-445... 

For recovery of rare earth elements Needs further development and improvements... 

FIGURE 9 PyrometaUurgical processes suitable for recovery of rare-earth elements from sludge or magnet waste. 

Liang et al. (2009) attempted the application of flotation using sodium dodecylsulfate as a collector. More than 99% recovery was achieved from the model spent powder with the composition of new polishing powder glass containing no rare earths = 1 2. However, when the real sludge obtained by coagulation treatment of spent slurry was treated, the recovery of rare-earth oxides was only 40% with the purity of 44% (35% in feed sample). 

FIGURE 19 Schematic process flow sheet for recovery of rare earths from spent optical glass containing lanthanum, yttrium, and gadolinium. Reproduced from Jiang et al. (2004) after slight modification. M means kmol/m. ... 

Takahashi, T., Tomita, K., Sakuta, Y., Takano, A., Nagano, N., 1996. Separation and recovery of rare earth elements from phosphors in waste fluorescent lamp (part II)—Separation and recovery of rare earth elements by chelate resin. In Reports of the Hokkaido Industrial Research Institute, No. 295, pp. 37-44. 

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