Mineral evolution and separation of rare-earth phases from Bayan Obo rare-earth concentrate in a super-gravity field

Accepted Manuscript Mineral evolution and separation of rare-earth phases from Bayan Obo rare-earth concentrate in a super-gravity field Xi Lan, Jintao Gao, Yu Du, Zhancheng Guo PII:

S0925-8388(17)33534-X

DOI:

10.1016/j.jallcom.2017.10.100

Reference:

JALCOM 43497

To appear in:

Journal of Alloys and Compounds

Received Date: 16 May 2017 Revised Date:

12 October 2017

Accepted Date: 13 October 2017

Please cite this article as: X. Lan, J. Gao, Y. Du, Z. Guo, Mineral evolution and separation of rareearth phases from Bayan Obo rare-earth concentrate in a super-gravity field, Journal of Alloys and Compounds (2017), doi: 10.1016/j.jallcom.2017.10.100. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Mineral Evolution and Separation of Rare-Earth Phases from Bayan Obo Rare-Earth Concentrate in a Super-Gravity Field Xi Lan, Jintao Gao*, Yu Du and Zhancheng Guo

State Key Laboratory of Advanced Metallurgy, University of Science and

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Technology Beijing, Beijing 100083, P. R. China.

Jintao GAO: Corresponding author, [email protected] Tel.: +86 010 82377750

Fax.: +86 010 82375042

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Xi Lan: [email protected] Yu Du: [email protected]

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Zhancheng Guo: [email protected]

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*[email protected]

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ACCEPTED MANUSCRIPT ABSTRACT Rare-earth concentrate obtained through mineral processing of rare-earth ore was characterized by a high rare-earth content and various rare-earth minerals. To

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effectively recover rare earth from the rare-earth concentrate, a novel method of enriching rare-earth elements and separating the RE-rich phases from Bayan Obo rare-earth concentrate by super gravity was proposed in current study. The mineral

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evolutions of rare-earth phases and the migrations of rare earth in various phases

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with temperature rising were investigated. The variations of mineralogical compositions and microstructures indicated the rare-earth phases transformed into fine britholite, cerium oxyfluoride, rare-earth ferrate and monazite particles at a low temperature range of 1423 K - 1523 K, which transformed further into lager

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equiaxed cerium oxyfluoride crystals and most rare-earth elements enriched into the cerium oxyfluoride phase significantly at a higher temperature range of 1573 K 1773 K. Consequently, separation of the RE-rich phases was carried out at the high

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temperature range in a super-gravity filed, and the cerium oxyfluoride phase and the

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britholite containing slag phase were effectively separated by super gravity.

Keywords: rare-earth phases; mineral evolution; separation; cerium oxyfluoride; rare-earth concentrate; super-gravity field

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ACCEPTED MANUSCRIPT 1. Introduction Rare-earth elements (RE) are known as the industrial vitamin, which have wide application in all walks of life [1]. It is well known that the Bayan Obo REEs-Nb-Fe

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deposit located in Inner Mongolia of China is the world’s largest REE deposit, which accounts for 35 % of rare-earth reserves around the world [2, 3]. Nevertheless, the rare-earth reserves in China decreased gradually with the rapid increase of rare-earth

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consumption. Considering that the designed capacity of Bayan Obo ore was 12

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million ton per year, only 230 million ton raw ores were left in the Bayan Obo ore body [4]. Therefore, it was urgent to propose some practical techniques to effectively extract rare-earth resources from the raw ores and recover them from the byproducts, especially for the Bayan Obo deposit which has been limitedly mined as an iron ore

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in China since its first discovery [5].

Generally speaking, the iron concentrate and the rare-earth concentrate were obtained respectively through the multistage fine-grinding and mineral processing of

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rare-earth ore, and the iron concentrate with a high iron content was used further as a

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raw material of Blast Furnace process for extracting iron [6]. However, due to the complex mineral compositions and the ultrafine dissemination of rare-earth minerals, it was difficult to effectively separate the rare-earth minerals from other minerals by the conventional beneficiation methods [7]. Thus some hydrometallurgy methods were adopted for recovering rare earth from the rare-earth concentrate, including acid leaching process [8, 9], alkali decomposition process [10, 11], and chlorination process [12, 13]. 3

ACCEPTED MANUSCRIPT In view of the similar ionic radii of various rare-earth elements and the diversity between the rare earth and other elements [14], it would be beneficial to effectively separate rare earth from the rare-earth concentrate if the rare-earth elements could be

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enriched into a single mineral phase. As for the precipitation and crystallization behaviors of rare-earth minerals, most investigations were focused on the rare-earth bearing blast furnace slag [15] and the direct reduced rare-earth ore [3, 16, 17]. Li

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[15] proposed that rare-earth elements precipitated as the calcium cerite phase from

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the rare-earth bearing blast furnace slag with a lower CaF2 content during slow cooling process. Ding [16] proposed that rare-earth elements precipitated as the strip-shape cefluosil phase from the carbon reduced rare-earth ore during furnace cooling process, while Li [3] reported the britholite-Ce phase precipitated from

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which during slow cooling process, respectively. Gao [17] found the britholite phase with a theoretical hexagonal structure precipitated from the gaseous reduced rare-earth ore. However, few investigations on rare-earth concentrate, which was

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characterized by a higher rare-earth content and various rare-earth minerals, were

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proposed due to the lack of thermodynamic data of rare earth. Hence, the mineral evolutions of rare-earth phases and the migrations of rare earth in various phases of rare-earth concentrate at different temperature ranges were investigated first in current study.

Moreover, if the RE-rich phases could be separated directly from other minerals at a specific high temperature, at which the rare-earth elements enriched into a solid phase while other minerals form into molten slag, it would be beneficial for 4

ACCEPTED MANUSCRIPT effectively separating the two different phases, whereas it was infeasible to accomplish this task under the conventional conditions. Ramshaw [18] found that the mass transfer and mass migration of heterogeneous phases were improved

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immensely in a super-gravity field, and thus the super-gravity technology has been successfully applied to the preparation of functionally graded materials and removing impurities from alloy melts. Rajan [19] prepared functionally graded Al

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matrix composite components with the centrifugal casting method, and he found the

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primary Si particles were dispersed toward inner periphery of the casting. Zhao [20] reported that the refined grains of pure aluminum could be effectively removed in a super-gravity field, and the grain size of aluminum decreased rapidly with gravity coefficient increasing. Inspired by previous investigations on separating various

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value phases from various slag melts by super gravity, the perovskite crystals [21], the anosovite crystals [22], the olivine crystals [23] and the phosphorous mineral [24] were selectively precipitated and separated from the slag melts, these indicated

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super-gravity field could enhance the directional migration and concentration of

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heterogeneous phases. Consequently, the solid-liquid separation of RE-rich phases and other minerals was carried out further in a super-gravity field in current study. The aim of the current study was improving our understanding on the mineral evolutions of rare-earth phases and the migrations of rare earth in various phases, and initially proposed a novel method to effectively separate the RE-rich phases from rare-earth concentrate by super gravity.

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ACCEPTED MANUSCRIPT 2. Experimental section 2.1 Apparatus The super-gravity field used in current study was generated by a centrifugal

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apparatus as illustrated in Fig.1. For generating a stable and adjustable super-gravity field, a heating furnace and a counterweight were fixed symmetrically onto a centrifugal rotor, which rotated from vertical to horizontal when the centrifugal rotor

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started running. Moreover, the heating furnace was heated by the resistance wire,

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with an isothermal zone of 80 mm long, and the temperature was controlled by a program controller with an R-type thermocouple, within the observed precision range of ±3K.

The

rare-earth

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2.2 Materials concentrate

obtained

by

multistage

magnetic-flotation

separations process of Bayan Obo ore was employed as the raw material in current

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study. The chemical compositions of the raw material were measured by the XRF

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method and calculated further through weighted mean method as listed in Table 1, in which the mass fraction of ∑ReO (Re= Ce, La, Nd, Pr) was 48.09 wt%. Combined with the XRD pattern and the SEM-EDS photographs of the raw material as shown in Fig.2 and Fig.3, the mineral phases of which mainly included bastnaesite, monazite and fluorite, while the rare-earth elements distributed among the various minerals.

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ACCEPTED MANUSCRIPT 2.3 Methods (1) Mineral evolutions of rare-earth phases with temperature rising The mineral evolutions of rare-earth phases and the migrations of rare earth in

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various phases with temperature rising were investigated by hot-quenching method at different temperature ranges combined with various off-line analysis methods. 200 grams rare-earth concentrate powder were filled in 10 magnesia crucibles with an

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inner diameter of 18 mm and a high of 60 mm evenly, which were sequentially

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heated to 1323K, 1373K, 1423K, 1473K, 1523K, 1573K, 1623K, 1673K, 1723K and 1773K under argon atmosphere in a muffle furnace at a heating rate of 1 K/min, respectively. After heating at each targeted temperature for 30 min, the magnesia crucibles were taken out and water-quenched immediately.

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Thereafter, the samples were measured by the X-ray diffraction method (XRD, monochromatized CuKα radiation (λ=1.5418Å) from 15 to 65°) from a macroscopic view, combined with the scanning electron micrograph and energy-dispersive

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spectrum (SEM-EDS) and the electron probe microanalyzer (EPMA) methods from

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a microscopic view, to determine the variations in mineral compositions and microstructures of various rare-earth phases at different temperature ranges. Moreover, average of 10 fields of scanning electron micrograph in each sample were characterized further on image analyzer (LEICA Qwin 500), and average of 10 sets of energy-dispersive spectrum data of each rare-earth phase were measured to conduct the statistical analysis on variations in the volume fractions of rare-earth phases and the Re contents in various rare-earth phases with temperature rising, 7

ACCEPTED MANUSCRIPT respectively. (2) Separation of RE-rich phases in a super gravity field Based on the mineral evolutions of rare-earth phases and the migrations of rare

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earth in various phases, the separation experiments of the RE-rich phases were carried out further in a super-gravity field generated by the centrifugal apparatus. 20 grams rare-earth concentrate powder were placed into a same magnesia crucible and

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heated to 1623 K in the heating furnace of centrifugal apparatus for 10 min to make

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other minerals forming molten slag while keep RE-rich phases in a solid state, and then the centrifugal apparatus was started and adjusted to an angular velocity of 1625 r/min to achieve gravity coefficient of G=600 as calculated via equation (1). After centrifugal rotating at the constant temperature for 5 min, the apparatus was shut off

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and the crucible was water-quenched, and then the sample was sectioned longitudinally along the center axis to gain a macrograph, and the layered samples were analyzed further by SEM-EDS, XRD and XRF methods for accurately

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characterizing the mineralogical constitutions and the chemical compositions of the

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separated samples obtained by super gravity.

G=

g + (ω R ) = g 2

2

2

g2 + (

N 2π 2 R 2 ) 900 g

(1)

where G is gravity coefficient, g is the normal-gravitational acceleration (g=9.8m/s2), ω is the angular velocity (rad/s-1), N is the rotating speed (r/min), and R is the distance between centrifugal axis and sample center (R=0.25m).

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ACCEPTED MANUSCRIPT 3. Results and discussion 3.1 Mineral evolutions of rare-earth phases and migrations of rare earth (1) Mineral evolutions of rare-earth phases

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The variations in the mineral compositions and microstructures of various rare-earth phases in Bayan Obo concentrate with temperature rising are shown in Fig.4 and Fig.5, respectively. Combined with the EDS data of various rare-earth

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phases obtained at different temperatures given in Table 2, it was obvious that the

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primary rare-earth mineral - bastnaesite ([Ce,La,Nb,Pr]CO3F) decomposed with temperature increasing, and the rare-earth phases transformed from the original dispersed bastnaesite and monazite ([Ce,La,Nd,Pr]PO4) minerals into the acicular britholite (Ca3[Ce,La,Nd,Pr]2[(Si,P)O4]3F), the fine granular cerium oxyfluoride

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([Ce,La,Pr,Nd]3O4F3), the rare-earth ferrate ([Ce,La,Pr,Nd]FeO3) and the monazite particles at a low temperature range of 1423K - 1523 K as shown in Fig.5 (a) - (c). With temperature increasing further to a higher temperature range of 1573 K -

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1773 K as shown in Fig.5 (d) - (h), the monazite disappeared completely, and the

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britholite and rare-earth ferrate decreased significantly instead of forming the slag melt, whereas the fine cerium oxyfluoride particles gradually aggregated and grew into the larger equiaxed crystals. As the variations in volume fractions of various rare-earth phases shown in Fig.6 (a), with temperature increasing from 1423 K 1523 K to 1573 K - 1773 K, the volume fraction of monazite decreased from 6.20 % to zero, the volume fraction of britholite decreased from 58.10 % to 25.86 %, and the volume fraction of rare-earth ferrate decreased from 15.80 % to 8.26 %. In contrast, 9

ACCEPTED MANUSCRIPT the volume fraction of cerium oxyfluoride increased significantly from 20.23 % to 65.88 %. These indicated that the rare-earth phases transformed further into lager equiaxed cerium oxyfluoride crystals at the high temperature range.

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(2) Migrations of rare earth in various phases Moreover, Fig.6 (b) presents further the variations of Re contents in various rare-earth phases with temperature rising. Obviously, with temperature increasing

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from 1423 K - 1523 K to 1573 K - 1773 K, the mass fraction of Re in cerium

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oxyfluoride phase increased from 69.09 wt% to 87.56 wt%, in which the mass fraction of cerium (Ce) increased significantly from 34.13 wt% to 80.16 wt%, whereas the mass fraction of Re in britholite phase decreased from 46.00 wt% to 18.23 wt%. It was evidenced that most rare-earth elements, especially the cerium,

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enriched into the cerium oxyfluoride phase at the high temperature range, which was further verified by the EPMA results of the cerium content in various rare-earth

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phases obtained at different temperature ranges as shown in Fig.7.

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3.2 Separation of RE-rich phases by super gravity (1) Characterization of macro and micro structures To further separate the RE-rich phases from rare-earth concentrate, isothermal

separation experiments were carried out at the high temperature range of 1573 K 1773 K in a super-gravity field. As the macrograph and micrograph of the samples obtained by super gravity with gravity coefficient of G=600 at 1623 K shown in Fig.8 (a) and (b), two different layers with an explicit interface appeared 10

ACCEPTED MANUSCRIPT significantly in the sample. Combined with the SEM-EDS analysis of different areas in the layered sample, it was obvious that all the equiaxed cerium oxyfluoride crystals migrated along the super-gravity direction due to its density was greater than

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that of the slag, thus the cerium oxyfluoride crystals concentrated as the cerium oxyfluoride phase at the bottom area as shown in Fig.9 (b) and (d). Conversely, the slag melt containing britholite crystals with a hollow hexagonal prism structure

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migrated to the upper area against the super-gravity direction and separated from the

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cerium oxyfluoride phase as shown in Fig.9 (a) and (c).

(2) Components of the separated samples by super gravity

Furthermore, the chemical compositions of the separated samples obtained by super gravity are given in Table 3. After separating in a super-gravity field with

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gravity coefficient of G=600 at 1623 K for 5 min, the mass fraction of ∑ReO in the cerium oxyfluoride phase was up to 57.37 wt%, and that of CeO2 was up to 32.76 wt%. In contrast, the mass fractions of ∑ReO and CeO2 in the britholite containing

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(3) Discussion

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slag phase were decreased to 34.44 wt% and 17.07 wt%, respectively.

With respect to the Stokes’ law [25] via equation (2), the effect of super-gravity

field on the concentration and growth behaviors of cerium oxyfluoride crystals in the slag melt can be explained as follows.

Vr =

dr d 2 ∆ρ 2 = w R (2) dt 18η

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ACCEPTED MANUSCRIPT where Vr is the migration velocity of cerium oxyfluoride crystals (m/s), d is the diameter of cerium oxyfluoride crystals (m), ∆ρ is the density difference between cerium oxyfluoride crystals and slag melt (kg/m3), and η is the viscosity of slag

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melt (N·s/m2). As described in Fig.10, most rare-earth elements enriched and transformed into the cerium oxyfluoride crystals while other minerals formed the slag melt at the high

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temperature range of 1573 K - 1773 K. However, the viscosity of slag melt increased

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with the existence of cerium oxyfluoride crystals, and so the crystals were difficult to move or aggregate thereby dispersing among the slag melt in the normal gravity field. In case of a super-gravity field, the diffusion rate of cerium oxyfluoride crystals enhanced significantly, all of which migrated along the super-gravity direction as a

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result of the density difference with slag melt, which concentrated as the cerium oxyfluoride phase at the bottom area and effectively separated from the slag melt. Moreover, the interfacial free energy between the crystals and slag melt increased in

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a super-gravity field, thus the super gravity forced the fine crystals aggregated and

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grown further into the larger crystals. Subsequently, some works on adequately enriching rare-earth elements into the

specified RE-rich phase with a simple composition, efficiently separating the RE-rich phase enhanced by super gravity, and effectively extracting rare earth from the RE-rich phase are needed to improve further the extraction efficiency of rare earth.

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ACCEPTED MANUSCRIPT 4. Conclusions In this paper, a novel method of enriching rare-earth elements and separating the RE-rich phases from rare-earth concentrate by super gravity was proposed. The

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Bayan Obo rare-earth concentrate was employed as the raw material, the mineral evolutions of rare-earth phases and the migrations of rare earth in various phases with temperature rising, and separation of the RE-rich phases in a super-gravity field

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were investigated. The following conclusions can be drawn:

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(1) It was indicated by the mineral evolutions results that the rare-earth phases transformed from original bastnaesite and monazite minerals into fine britholite, cerium oxyfluoride, rare-earth ferrate and monazite particles at 1423 K - 1523 K, which transformed further into lager equiaxed cerium oxyfluoride crystals at 1573 K

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- 1773 K, and most rare-earth elements enriched into the cerium oxyfluoride phase significantly.

(2) In a super-gravity field, all the cerium oxyfluoride crystals concentrated as

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the cerium oxyfluoride phase along the super-gravity direction and effectively

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separated from the britholite containing slag phase, and the mass fractions of ∑ReO and CeO2 in the separated cerium oxyfluoride phase were up to 57.37 wt% and 32.76 wt%, respectively.

Acknowledgements This study is supported by the National Natural Science Foundations of China (No.51404025 and No.51774037). 13

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Table captions Table 1 Chemical compositions (wt %) of the rare-earth concentrate

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Table 2 Energy-dispersive spectrum data (wt %) of various rare-earth phases at different temperature ranges

Table 3 Chemical compositions (wt %) of the separated samples obtained by super

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ACCEPTED MANUSCRIPT Table 1 Chemical compositions (wt %) of the rare-earth concentrate

CaO

P2O5

Fe2O3

SO3

F

SiO2

MgO

BaO

MnO

Ce2O3

La2O3

Nd2O3

Pr6O11

#1

14.54

9.67

8.08

4.83

8.45

1.07

3.54

1.60

0.42

26.27

11.49

8.95

1.09

#2

14.33

9.88

7.88

4.92

8.54

1.15

3.41

1.42

0.65

26.41

11.88

8.59

0.94

#3

14.14

9.63

8.01

5.08

8.96

1.08

3.42

1.39

0.35

#4

14.22

9.51

8.52

4.86

8.87

0.97

3.44

1.61

0.20

#5

14.47

9.46

7.96

4.96

8.65

1.18

3.49

1.93

0.23

Weighted average

14.34

9.63

8.09

4.93

8.41

1.09

3.46

1.59

0.37

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Composition

11.81

8.82

0.99

26.08

12.05

8.93

0.74

27.02

11.97

8.91

1.19

26.42

11.84

8.84

0.99

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26.32

ACCEPTED MANUSCRIPT Table 2 Energy-dispersive spectrum data (wt %) of various rare-earth phases at different temperature ranges Positions

O

P

C

F

Ca

Si

Fe

Ce

La

Pr

Nd

Pt.1

Fig.5 (b)

26.64

--

--

4.27

--

--

--

34.13

23.49

4.41

7.06

Pt.2

Fig.5 (b)

10.17

--

--

--

--

--

28.64

22.80

24.06

3.16

11.17

Pt.3

Fig.5 (b)

16.34

8.48

--

11.23

16.40

1.55

--

12.25

20.33

3.30

10.12

Pt.4

Fig.5 (b)

17.56

16.34

--

--

--

--

--

25.15

24.65

4.21

12.09

Pt.5

Fig.5 (g)

10.29

--

2.15

--

--

--

80.16

7.4

0

0

Pt.6

Fig.5 (g)

10.09

--

--

--

--

--

24.93

28.16

21.61

3.60

11.61

Pt.7

Fig.5 (g)

28.67

12.74

--

4.92

33.94

1.50

--

7.19

8.99

0

2.05

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ACCEPTED MANUSCRIPT Table 3 Chemical compositions (wt %) of the separated samples obtained by super gravity Samples

CaO

P2O5

Fe2O3

SO3

F

SiO2

MgO

BaO

MnO

Ce2O3

La2O3

Nd2O3

Pr6O11

9.66

9.05

7.84

0.25

11.38

0.96

2.23

1.01

0.25

32.76

13.54

9.94

1.13

15.34

14.98

8.38

0.38

18.05

1.22

4.91

1.81

0.49

Cerium

Britholite

17.07

10.36

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containing slag

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oxyfluoride 6.32

0.69

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Figure captions Fig.1 Sketch of the centrifugal apparatus: (1) counterweight, (2) centrifugal axis, (3) conductive sliping, (4) thermocouple, (5) insulating layer, (6) temperature controller,

Fig.2 XRD pattern of the rare-earth concentrate Fig.3 SEM-EDS photographs of the rare-earth concentrate

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(7) magnesia crucible

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Fig.4 Variations in XRD patterns of the rare-earth concentrate with temperature

Fig.5 Variations in SEM photographs of the rare-earth concentrate with temperature:

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(a) 1423 K, (b) 1473 K, (c) 1523 K, (d) 1573 K, (e) 1623 K, (f) 1673 K, (g) 1723 K, (h) 1773 K

Fig.6 Variations in volume fractions of rare-earth phases and the Re contents in various rare-earth phases with temperature: (a) volume fractions of rare-earth phases, (b) mass fractions of Re in rare-earth phases

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Fig.7 EPMA results of the cerium content in various rare-earth phases at different temperature ranges: (a) 1423 K - 1523 K, (b) 1573 K - 1773 K Fig.8 Macrograph and micrograph of the layered samples obtained by super gravity:

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(a) vertical profile, (b) SEM photograph of layered interface

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Fig.9 SEM-EDS photographs of the separated samples obtained by super gravity: (a) and (c) SEM-EDS photographs of britholite phase, (b) and (d) SEM-EDS photographs of cerium oxyfluoride phase

Fig.10 Systematic diagram of concentration and growth process of cerium oxyfluoride crystals in a super-gravity field.

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Fig.1 Sketch of the centrifugal apparatus: (1) counterweight, (2) centrifugal axis, (3) conductive sliping, (4) thermocouple, (5) insulating layer, (6) temperature controller,

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EP

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(7) magnesia crucible

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1 2

1

2 3

30

3

CaF2

1

1 3

2

20

[Ce,La,Nd,Pr]CO3F [Ce,La,Nd,Pr]PO4

40

2-Theta-Scale (degree)

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Intensity (counts)

1

1 2

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2 1

50

60

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EP

TE D

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Fig.2 XRD pattern of the rare-earth concentrate

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SC

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AC C

EP

TE D

Fig.3 SEM-EDS photographs of the rare-earth concentrate

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1 [Ce,La,Nd,Pr]3O4F3

2 [Ce,La,Nd,Pr]FeO3

3 Ca3[Ce,La,Nd,Pr]2[(Si,P)O4]3F

4 [Ce,La,Nd,Pr]PO4

13 2

12

3

1 2

3

1773K

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Intensity (counts)

1723K

1673K

1623K 1573K

2 2 1

3

1523K

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1

3 4 31

4

1473K

20

30

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1423K

40

50

60

2-Theta-Scale (degree)

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EP

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Fig.4 Variations in XRD patterns of the rare-earth concentrate with temperature

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(a)

+4

(b)

(c)

(d)

+2

+3

200µm

200µm

200µm

(f)

(e)

(g) +5

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+7 200µm

200µm

(h)

+6

200µm

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+1

200µm

200µm

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Fig.5 Variations in SEM photographs of the rare-earth concentrate with temperature: (a) 1423 K, (b) 1473 K, (c) 1523 K, (d) 1573 K, (e) 1623 K, (f) 1673 K, (g) 1723 K,

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EP

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(h) 1773 K

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Fig.6 Variations in volume fractions of rare-earth phases and the Re contents in

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various rare-earth phases with temperature: (a) volume fractions of rare-earth phases,

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(b) mass fractions of Re in rare-earth phases

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(a) + britholite

(b)

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+ cerium oxyfluoride

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+ rare earth ferrate

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+ monazite

Fig.7 EPMA results of the cerium content in various rare-earth phases at different

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EP

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temperature ranges: (a) 1423 K - 1523 K, (b) 1573 K - 1773 K

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(b)

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(a)

Fig.8 Macrograph and micrograph of the layered samples obtained by super gravity:

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EP

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(a) vertical profile, (b) SEM photograph of layered interface

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(a)

(c)

(b)

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+c

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SC

(d)

+d

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Fig.9 SEM-EDS photographs of the separated samples obtained by super gravity: (a) and (c) SEM-EDS photographs of britholite phase, (b) and (d) SEM-EDS photographs

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EP

of cerium oxyfluoride phase

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SC

Fig.10 Systematic diagram of concentration and growth process of cerium

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oxyfluoride crystals in a super-gravity field.

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A novel method was proposed to separate REEs from REEs concentrate by super gravity Rare-earth phases transformed into cerium oxyfluoride crystals at 1573K - 1773K




Most rare-earth elements enriched into cerium oxyfluoride phase at 1573K -

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1773K

Cerium oxyfluoride phase and slag phase were effectively separated by super

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gravity

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