1. Acid concentration (N)
Chemical Beneficiation of Lateritic Rare Earth Bearing Ores
N. Faris1*, J. Tardio1, R. Ram1, S. Bhargava1, M. I. Pownceby2
1Advanced Materials and Industrial Chemistry Centre: School of Applied Sciences RMIT University GPO Box 2476, Melbourne, Vic, 3001, Australia *
2 CSIRO Mineral Resources, Private Bag 10, Clayton South, Victoria 3169, Australia
1. Introduction
Laterites are an important source of rare metals such as lanthanides and niobium [1] with countries such as Australia, Brazil, Africa and Russia having lateritic rare metal deposits [2, 3]. Rare earths are used in a number of technologies critical to renewable energy such as neodymium magnets and nickel metal hydride batteries whilst niobium is an important alloying additive for high strength steels.
The recovery of rare metals from lateritic ores by physical separation is difficult due to complex mineralogy and fine grain size of mineral values. Leaching of gangue may be an alternative route as rare earth and niobium minerals are refractory to chemical treatment [4]. Aral and Bruckard [4] studied the beneficiation of a niobium ore and found that the Nb and Ta content could not be upgraded by physical separation but chemical treatment using acids and alkalis to dissolve the gangue was successful [4]. The removal of gangue from a REE bearing ore by acid leaching was carried out to determine if concentrates grading over 30 wt% REO could be produced.
2. Materials and Methods
A rare earth ore sourced from a lateritic deposit was used in this study
Leaching with sulfuric and hydrochloric acid was carried out in agitated 2-neck round bottom flasks under identical conditions to Aral and Bruckard [5]; 100°C leach temperature, 2 h leaching time and a solids to liquid ratio of 20 wt%
Chemical analysis was performed using XRF. Mineralogical analysis was carried out by powder XRD.
Table 1: XRF assays of leach residues (wt%) after H2SO4 and HCl leaching for 2 h at 100°C
Acid concentration (N)
wt% loss
Al2O3
CaO
Fe2O3
MgO
Mn3O4
Nb2O5
P2O5
SiO2
REO
TiO2
Feed -
3.65
7.37
45.6
2.12
3.04
0.364
7.43
6.18
7.66
2.43
2.5 N H2SO4
17.6
3.39
5.04
46.1
0.604
3.19
0.425
6.72
6.94
8.54
2.83
5 N H2SO4
37.1
3.38
7.11
34.3
0.533
4.45
0.411
7.91
9.49
10.1
3.26
10 N H2SO4
56.9
3.45
11.1
15.1
0.905
5.38
0.320
10.7
15.4
12.7
4.33
2.5 N HCl
46.9
3.59
0.518
51.7
0.436
3.49
0.524
6.60
8.49
10.3
3.40
5 N HCl
59.1
4.46
0.442
40.8
0.308
1.43
0.811
8.34
13.9
14.2
5.42
conc. HCl (10.17 N)
82.0
4.76
0.415
7.97
0.162
0.261
1.74
14.0
27.0
23.1
11.2
Figure 2: REO grade versus acid concentration
3. Results
3.1 feed characterisation
The rare earth and niobium grade in the ore is 7.66 wt% REO and wt% Nb2O5 respectively
The rare earth bearing minerals identified by XRD (Figure 1) were monazite (CePO4) and florencite [CeAl3(PO4)2(OH)6]
The primary gangue minerals identified in the ore were goethite (FeOOH), dolomite [CaMg(CO3)2] and flourapatite [Ca5(PO4)3F]
3.2 Chemical Treatment
Treatment of the ore using sulfuric and hydrochloric acids was investigated at 100°C for 2 h. XRF assays of leach residues are summarised in Table 1. Grade and recovery curves were plotted in Figures 2 and 3.
Leaching of the gangue rather than the REE/Nb minerals was selected due REE and Nb minerals being refractory [4]
Aggressive leaching conditions were selected due to goethite being refractory to acid dissolution [5]
Figure 3: REO recovery to leach residue versus acid concentration
Figure 4: Residues produced from hydrochloric acid leaching at various concentrations
Figure 1: Powder diffraction pattern of feed material used in this study
4. Findings
REO grade in the leach residues increased with increasing acid concentration however the recovery decreased due to leaching of RE minerals
Residues produced from H2SO4 leaching were of lower REO grade relative to those produced by HCl leaching
REO recoveries to H2SO4 leached residues were higher relative to HCl leached residues
Highest REO grade occurred in the residue produced from leaching with conc. HCl but at a cost of decreased recovery
Leaching with hydrochloric and sulfuric acid failed to produce marketable REO concentrates with a minimum grade of 30 wt% REO
A combination of chemical and physical treatment would be required to produce REO concentrates grading over 30 wt%
References
1. Hoatson, D.M., S. Jaireth, and Y. Miezitis, The major rare-earth-element deposits of Australia: geological setting, exploration, and resources. 2011: Geoscience Australia.
2. Bisaka, K., I. Thobadi, and C. Pawlik. Extraction of Rare-Earth Elements from Iron-Rich Rare-Earth Deposits. in Hydrometallurgy Conference 2016: Sustainable Hydrometallurgical Extraction of Metals Cape Town, South Africa.
3. Faris, N., et al., Application of ferrous pyrometallurgy to the beneficiation of rare earth bearing iron ores–A review. Minerals Engineering, : p
4. Aral, H. and W.J. Bruckard, Characterisation of the Mt Weld (Western Australia) niobium ore. Mineral Processing and Extractive Metallurgy, (4): p
5. Sidhu, P.S., et al., Dissolution of iron oxides and oxyhydroxides in hydrochloric and perchloric acids. Clays and Clay Minerals, (4): p
Acknowledgements
The authors wish to acknowledge the support provided by the Australian Government through an Australian Government Research Training Program scholarship to Nebeal Faris. The authors would like to thank Steve Peacock (CSIRO – XRF) his contribution to this work.