1. FROTH FLOTATION OF XENOTIME
Mr. Yicheng Zhang and Dr. Corby Anderson
Kroll Institute for Extractive Metallurgy
The George S. Ansell Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden CO
Introduction
Methods & Reagents
Results
The only rare earth element (REE) bearing minerals that have been extracted on a commercial scale are bastnaesite, monazite, and xenotime (Krishnamurthy and Gupta 2004).
Microelectrophoresis and the Mular & Roberts method is used to determine the pzc of xenotime (Pereira and Peres 1997). Further research on the chemical composition, adsorption density, zeta potential and isoelectric point (IEP) of xenotime is also done with current technologies.
BET Stabino UV-Vis Spectrometer
In the USA, sodium oleate and hydroxamate are chosen as collectors, but in China, the biggest rare earth producer uses some advanced collectors on the commercial scale. The most efficient ones are H205 and H316.
H205 has two active basal groups, hdyroxyl base and naphthyl base. Research shows that H205 is chemisorbed onto rare earth ore’s surface, forming surficial chelate complex like O-C=N-RE(III)-O, along with multilayered asymmetric physisorption. Compared to alkyl hydroxamate, H205 can be applied to stronger ore property fluctuations without sodium fluosilicate. However, there are still some disadvantages, when used, it should be prepared with plenty of alcohol and ammonia, and its particles cannot dissolved into solution efficiently.
H316 is the improved version of H205, do not need ammonia to regulate and the stability in solution has been raised. When compared to H205 in the same producing condition, dealing with 50% rare earth preconcentrate, the recovery improved by 10 percentage.
There are also powerful selective depressants such as sodium silicate and a certain aluminum salt named MBF. Research shows that when dealing with monazite, the Al3+
ions from MBF chemisorb with PO43+ ions from surface of monazite, inhibiting monazite lotation. (Jiake, Luo, 2012).
This mechanism suggests that MBF probably cannot be used for xenotime floatation because of the PO43+ ions on the surface of xenotime minerals.
Using sodium oleate or hydroxamate as a collector, the highest recovery of xenotime at 98% is achieved at pH 7 to 8(Cheng, Holtham, and Tran 1993; Pereira and Peres 1997).
Results show that the IEP for yttrium phosphate is measured around pH 7.0 (Cheng et al. 1994).
From 1992 to 1999, the reported points of zero charge of different xenotime samples varied from 2.3 to 5.0 (Cheng 2000).
Unlike the other two, there is little fundamental research on froth flotation of xenotime. Froth flotation, as a fundamental method for processing complex minerals, has been applied to research of surface chemistry of xenotime recently by several research groups.
Conclusions
Anionic collectors such as sodium oleate chemisorb onto xenotime since the point of zero charge of xenotime was found negative with pH greater than 3.
The recovery of xenotime is a function of pH, flotation time, collector concentration and temperature. As the chemical modeling of speciation indicates, the distribution of the first hydroxyl rare earth species, increases the adsorption rate, bubble-particle adhesion strength, and flotation recoveries.
Current Research Status
Few researchers have studied the surface chemistry and beneficiation of xenotime. At present, researchers focus on froth flotation behavior, zeta potential examination, point of zero charge definition, and reagent tests.
Literature findings suggest that there are few problems with reagent adsorption and bubble adhesion during froth flotation of xenotime. The feasibility and efficiency of froth flotation has been proven by several studies (Jordens, Cheng, and Waters 2013).
Chinese researchers, mainly from the Baotou Research Institute of Rare Earths lead the way of Chinese rare earth technology development. Several powerful collectors have been created so far such as;
References
1. Cheng, Ta-Wui, P. N. Holtham, and Tam Tran 'Froth flotation of monazite and xenotime', Minerals Engineering, 6:
2. Cheng, Ta-Wui, AC Partridge, Tam Tran, and PLM Wong 'The surface properties and flotation behavior of xenotime', Minerals Engineering, 7:
3. Cheng, TW 'The point of zero charge of monazite and xenotime', Minerals Engineering, 13:
4. Jordens, Adam, Ying Ping Cheng, and Kristian E Waters 'A review of the beneficiation of rare earth element bearing minerals', Minerals Engineering, 41:
5. Krishnamurthy, Nagaiyar, and Chiranjib Kumar Gupta Extractive metallurgy of rare earths (CRC press).
6. Pereira, Carlos Alberto, and Antônio Eduardo Clark Peres 'Flotation concentration of a xenotime pre-concentrate', Minerals Engineering, 10:
7. HUANG, Wan-fu, Jin-lei WEN, and Yuan-yuan CHEN. "Research status and prospects on flotation reagents and techniques of rare-earth ore." Nonferrous Metals Science and Engineering 6 (2012): 016.
8. Jiake, Luo. "Development on flotation reagents of rare earth minerals in China."JOURNAL-CHINESE RARE EARTH SOCIETY-CHINESE EDITION- 20.5 (2002):
Type
Chemical name
formula
Alkyl collectors
C5-7 alkyl hydroxamic acid
R-C(=O)-NH-OH
C7-9 alkyl hydroxamic acid
Cycloalkyl collector
cycloalkyl alkyl hydroxamic acid
CnC2n-1-R-C(=O)-NH-OH
Aromatic collectors
benzoyl hydroxamic acid
C6H5-C(=O)-NH-OH
salicyl hydroxamic acid
C6H5OH-C(=O)-NH-OH
N-hydroxyethyl phthalimide
C8H5NO3
H205 (2-hydroxyl 3-naphthyl hydroximic acid)
R(-OH)-C(=O)-NH-OH
H316 (improved version of H205)