Published at : 05 Feb 2024
Volume : IJtech
Vol 15, No 2 (2024)
DOI : https://doi.org/10.14716/ijtech.v15i2.6722
Matthew Alexander Tjhia | Department of Metallurgical and Materials Engineering, Faculty of Engineering, University of Indonesia, Kampus Baru UI, Depok, 16424, Indonesia |
Muhammad Nur Fakhriy Yahya | Department of Metallurgical and Materials Engineering, Faculty of Engineering, University of Indonesia, Kampus Baru UI, Depok, 16424, Indonesia |
Reza Miftahul Ulum | Department of Metallurgical and Materials Engineering, Faculty of Engineering, University of Indonesia, Kampus Baru UI, Depok, 16424, Indonesia |
Rare earth metals (REE) constitute one of the most
crucial groups of elements globally.
In Indonesia, deposits of REE have been recognized within
monazite minerals extracted from tin mining operations in Bangka. Nevertheless,
Indonesia has not used these deposits and has instead heavily relied on imports
from other countries. This study aims to recover rare earth metals,
specifically Cerium (Ce), Lanthanum (La), Ytterbium (Yb), and Yttrium (Y), from
monazite sand, a by-product of tin mining. The method employed in this research
is Mechanochemical Decomposition, involving the reaction of monazite samples
with a 33 wt% solid Sodium Hydroxide (NaOH) to convert REE-Phosphate compound
into REE-Hydroxide. The
process begins with sample preparation, involving mechanochemical decomposition
using a ball mill, followed by roasting at 400°C, leaching with distilled
water, and subsequent steps of filtration and drying at 120°C. Various initial
particle sizes, denoted as +65, -65 +100, -100 +140, -140 +170, and -170 mesh,
were used to assess their effect on the recovery and grade of REE. Various
initial particle sizes, denoted as +65, -65 +100, -100 +140, -140 +170, and
-170 mesh, were used to assess their effect on the recovery and grade of REE.
The series of procedures revealed notable improvements in the REE content in
monazite. The highest recovery of Ce, La, Yb, and Y elements reached 46.43%,
70.08%, 22.69%, and 23.31%, while the highest grade of those elements obtained
the values of 4.116%, 1.543%, 0.263%, and 1.681%, respectively. In alignment
with prior research, the recovery of Light Rare Earth Elements (LREEs)
surpasses that of Heavy Rare Earth Elements (HREEs). However, a unique
observation emerges: a diminishing trend in both recovery and grade as particle
sizes become finer. This unexpected phenomenon warrants further investigation
to elucidate the mechanisms governing rare earth metal recovery from monazite
sand under varying particle sizes.
By-product; Monazite; Particle size; REE-Oxide; Roasting
Rare
earth metals (REE) are a mineral group consisting of 17 elements, namely 15
elements of the lanthanide group (La – Lu), Scandium (Sc), and Yttrium (Y)
Trisnawati et al. (2020) reported
that Y, Gd, Er, Dy, and Yb as HREEs2-(SO4)3 products can be recovered
through sulfuric acid leaching, while the result from Prameswara
et al. (2023) showed that Dy and Yb leaching
from solid REE-hydroxide using HCl solution afforded a total of 61.71% Dy and
74.55% Yb recovery.
The processing of REE from monazite can be achieved through chemical
treatment, employing acid and base methods. Two common approaches involve NaOH
digestion or leaching with H2SO4 to extract REE from
monazite
In a few studies, the researcher has used mechanochemical processes,
especially inorganic material. For instance, Bonnaillie et al. used the
mechanochemical method for synthesizing SnO2 nanostructures
2.1. Sample Preparation
Monazite
sand was preliminarily dried at 80°C and subsequently underwent size reduction
through ball milling, with a rotational speed ranging from 67.8 to 71.1 rpm
over a 30-minute duration. The milling process yielded five distinct particle
size fractions, specifically +65 mesh, -65 to +100 mesh, -100 to +140 mesh,
-140 to +170 mesh, and -170 mesh.
2.2. Mechanochemical with NaOH 33wt%
Each
particle size fraction was subjected to a mechanochemical treatment with the
incorporation of 33 wt% sodium hydroxide (NaOH) from Pro Analys Merck 106498.
The purpose of adding NaOH was to react with rare earth element phosphate
(REE-PO4) and produce rare earth element hydroxides (REE-OH). The
mechanochemical process was conducted within a ball mill from NOAH NQM-4,
employing a rotational speed of 650 rpm for a duration of 120 minutes.
2.3. Roasting
Before
the roasting step, the mechanochemically treated samples were subjected to
compaction using a Krisbow Hydraulic Press, thereby increasing the contact
surface area. Subsequently, the roasting procedure was conducted in a Payun
Tech Muffle Furnace within alumina crucibles, sustained at a temperature of
400°C for a duration of 120 minutes. This process served the dual purpose of
finalizing the NaOH and REE-PO4 reaction and facilitating the
oxidation of rare earth elements inherent in the sample.
2.4. Distilled water washing, filtration,
and drying
The roasted product was subjected
to leaching with distilled water at a controlled temperature of 70°C and a
rotational speed of 680 rpm, maintained for a duration of 30 minutes, which was
discussed in the next section as a washing process. The process was conducted
by a Hot Plate Magnetic Stirrer from Thermo Scientific Cimarec SP88857105. The
primary objective of this step was to facilitate the dissolution of the formed
Na3PO4 compound. Following completion of the leaching
process, the mixture was subjected to filtration, yielding a precipitate. This
precipitate was subsequently isolated and subjected to drying at 120°C for 120
minutes using Memmert UN 55 Oven.
2.5.
Characterization
To
identify the REE content in the initial sample, the ICP-OES test was conducted
at Laboratorium Teknologi Bahan Galian Nuklir National Research and Innovation
Agency (BRIN). X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) analyses
were conducted on dried samples as part of a comprehensive characterization
step. The objective of the XRD analysis, undertaken at the Center for Materials
Processing and Failure Analysis (CMPFA) at Universitas Indonesia, and the XRF
is conducted at the Laboratory of the National Research and Innovation Agency
(BRIN), focused on quantifying the concentration increments of key elements,
specifically Cerium (Ce), Lanthanum (La), Ytterbium (Yb), and Yttrium (Y).
These analyses collectively provided essential insights into the composition
and elemental content of the investigated specimens, contributing to a
comprehensive understanding of their properties and potential applications.
3.1. Monazite Raw Sand Characteristics
Following the method outlined by Zhang and Noble,
the initial monazite is characterized using Inductively Coupled Plasma-Optical
Emission Spectroscopy (ICP-OES).
Before the mechanochemical and roasting processes, sample preparation was
carried out on the monazite. Firstly, the monazite was subjected to a drying
process to eliminate any residual moisture present
Table 1 ICP-OES results of initial
monazite samples
Elements |
Ce |
La |
Nd |
Pr |
Sm |
Y |
Gd |
Dy |
Sc |
Tb |
Eu |
Yb |
Concentration (ppm) |
8927 |
4189 |
2860 |
1750 |
737.3 |
436.4 |
161.8 |
158.3 |
23.7 |
6.8 |
2.8 |
0.14 |
Table 2 XRF results of
the initial monazite sample
Particle Size (mesh) |
+65mesh |
-65mesh +100mesh |
-100mesh +140mesh |
-140mesh +170mesh |
-170mesh | |
Concentration (wt%) |
Ce |
0.759 |
1.165 |
0.801 |
0.878 |
0.898 |
La |
0.174 |
0.279 |
0.203 |
0.218 |
0.206 | |
Y |
0.958 |
0.595 |
0.642 |
0.628 |
0.767 | |
Yb |
0.154 |
0.089 |
0.082 |
0.089 |
0.102 |
3.2.
Converting Rare Earth Phosphate to Rare Earth Hydroxide
In order to decompose phosphates in REE, monazite is
milled with the addition of NaOH. The milling process took place in a planetary
ball mill for 120 minutes at 680 rpm, serving two primary purposes: mixing and
milling. Monazite is mixed well with NaOH during milling, while the mechanical
force helps break bonds between REE and phosphates. NaOH will react with
phosphate, producing REE hydroxides and Na3PO4
Besides that, NaOH also reacts with CO2 in the atmosphere,
creating Na2CO3 as a product
3.3. Roasting in
atmospheric condition
This process aims to change hydroxide from mechanochemical to oxide
compound. The method includes heating samples at 400o for 2 hours in the
atmospheric condition. The reaction that occurs during roasting is as shown:
The result shows the change in
morphology and color. The pellets show expansion and shift in color from dark
grey to yellow-greenish. Expansion on +65mesh and -65mesh +100mesh seen are
much more significant than the rest. Lower expansion on -100mesh +140mesh, -140mesh
+170mesh, and -170mesh is caused of
denser pellets. Expansion might occur because of CO2 formation
during the reaction between phosphate and Na2CO3, as
shown in equation 1
The reaction can be validated with XRD,
where REE was found in the oxide form. XRD also shows Na in Na3PO4
and Na2CO3 form, which indicates equations (1) and (2) have
occurred. SnO2, SiO2, Fe3O4, and
FeTiO3 are monazite impurities as a cassiterite by-product, as shown
in Figure 1
Figure 1 XRD results
after the roasting process.
3.4. Leaching
with distilled
water to dissolve Na3PO4
Na (Na2CO3 and Na3PO4)
dissolve in water. Therefore, the by-product will dissolve by agitating the
sample in distilled water, leaving only REE residue
XRD shows that Na is still
present as Na2CO3 and Na3PO4,
indicating insufficient washing time. On the other hand, the REEs and
impurities compound's form doesn't change. The analysis results of the XRD
pattern are shown in Figure 2. Upon completion of the washing and drying
processes, an analysis of the residue revealed an increase in the concentration
levels of elements Ce, La, Y, and Yb. The X-ray Fluorescence (XRF)
characterization results presented in Table 3. demonstrate the observed changes
in element concentrations.
Figure 2 XRD
results after distilled water washing and drying
Table 3 XRF result of the product after distilled water washing and
drying
Particel
Size (mesh) |
+65mesh |
-65mesh +100mesh |
-100mesh +140mesh |
-140mesh +170mesh |
-170mesh | |
Concentration
(wt%) |
Ce |
2.653 |
4.116 |
3.829 |
1.861 |
1.376 |
La |
0.915 |
1.543 |
1.452 |
0.548 |
0.323 | |
Y |
1.681 |
1.006 |
1.171 |
0.972 |
0.960 | |
Yb |
0.263 |
0.159 |
0.148 |
0.117 |
0.108 |
3.5 Product Morphology after roasting and after the
leaching process
SEM results with 1000 x magnification of the sample after the roasting process can be seen in Figure 3. Meanwhile, the SEM results with 1000 x magnification of the sample after the washing and drying process can be seen in Figure 4. According to EDS result, in the samples after the washing process with sizes -100mesh +140mesh and -170mesh, the Ce content was 33.17% and 0.92%, respectively. Meanwhile, other samples did not show any REE content.
Figure 3 SEM results after roasting for particle size (a) +65mesh (b) -65mesh +100mesh (c) -100mesh +140mesh (d) -140mesh +170mesh (e) -170mesh
Figure 4 SEM results after washing for particle size (a) +65mesh (b) -65mesh +100mesh
(c) -100mesh +140mesh (d) -140mesh +170mesh (e) -170mesh
Table 4 EDS result of the product after distilled water washing and
drying
Particle
Size (mesh) |
+65mesh |
-65mesh +100mesh |
-100mesh +140mesh |
-140mesh +170mesh |
-170mesh | |
Concentration
(wt%) |
C |
2.48 |
2.85 |
2.01 |
1.26 |
1.84 |
O |
32.87 |
33.21 |
29.31 |
22.68 |
33.45 | |
Na |
2.04 |
13.99 |
9.88 |
2.30 |
6.24 | |
Mg |
0.19 |
0.11 |
- |
0.52 |
0.78 | |
Al |
0.41 |
2.15 |
1.03 |
0.57 |
1.59 | |
Si |
2.9 |
16.3 |
9.07 |
1.54 |
5.26 | |
S |
0.96 |
2.15 |
1.41 |
0.42 |
1.06 | |
Sn |
51.12 |
6.40 |
3.31 |
67.09 |
39.80 | |
Ca |
0.81 |
0.25 |
0.24 |
1.29 |
0.07 | |
Ti |
0.73 |
2.47 |
1.77 |
0.29 |
0.38 | |
Fe |
4.77 |
19.90 |
8.21 |
1.58 |
7.53 | |
Ni |
0.71 |
0.21 |
0.60 |
0.46 |
0.48 | |
Ba |
- |
- |
- |
- |
0.61 | |
Ce |
- |
- |
33.17 |
- |
0.92 |
%recovery
calculation was done on the final product using REE contents based on equation
(4).
The result of the %recovery calculation from Ce, La, Y, and Yb is present on a graph shown in Figure 5. Based on that picture, the coarser the initial particle size, the higher %recovery will be earned. This phenomenon can be attributed to the fact that samples with finer particle sizes tend to experience greater losses during the processing stages, resulting in higher weight loss percentages.
Figure 5 Effect of initial particle size on (a) %recovery and
(b) %grade of Ce, La, Y, and Yb
Monazite
contains REE, mainly LREE. Sn, Fe, and Ti present as impurities. NaOH is an
effective reagent used for mechanochemical decomposition to remove phosphate
from monazite by reacting and producing Na3PO4. Ce, La,
Yb, and Y had their content increased after the procedure. The highest %grade
of Ce and La achieved at particle size -65mesh +100mesh respectively by 4.116%
and 1.543% each. Yb and Y have the highest %grade at particle size +65mesh,
respectively, by 0.263% and 1.681% each. The highest %recovery of Ce, La, Yb,
and Y was achieved at particle size +65mesh by 46.43%, 70.08%, 22.69%, and
23.31% respectively, which have the final form of CeO2, La2O3,
Yb2O3, and Y2O3.
The authors express their gratitude to the
Center for Materials Processing and Failure Analysis (CMPFA) Department of
Metallurgical and Materials Engineering at Universitas Indonesia for their
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