Effect of methanol on the dissolution of neodymium oxide in hydrochloric acid solutions

Article abstract of DOI:10.1134/S003602361004025X

The effect of methanol on the solubility of Nd₂O₃ in HCl medium in the temperature range of 25-55°C were studied. HCl-CH ₃OH was observed to be a better solvent than HCl-CH ₃OH-H₂O and hydrochloric acid for the dissolution of Nd₂O₃ mainly due to prevention of neodymium hydroxide and dissolution increased with increase of HCl concentration even at high HCl concentrations. Presence of methanol in the medium was determined to cause corresponding decreases in conductivity, E_SCE, pH values with corresponding increase in E_R values. Neodymium compounds formed in HCl-CH₃OH medium at 25°C were isolated and identified using X-ray diffraction, thermal and chemical analysis methods and their thermal behaviour were investigated between 25-1100°C. NdCl₃ × x ₁CH₃OH and NdCl₃ × x ₂CH ₃OH × 4.14H₂O (x ₁ + x ₂ = 2.8) were formed in non-aqueous medium and these compounds were converted into NdCl₃, NdCl_2.37 and NdCl₃ × 0.47CH ₃OH with complete and partial loss of water and methanol around 240°C respectively. Methanol was completely removed around 390°C with formation of NdCl_2.37 (77.5%) and NdOCl (22.5%) and NdOCl was detected as the major stable phase above 700°C.

Full text of DOI:10.1134/S003602361004025X

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 4, pp. 646–654. © Pleiades Publishing, Ltd., 2010.
·
Original Russian Text © I. Girgin, A. Yörüko
g
lu, 2010, published in Zhurnal Neorganicheskoi Khimii, 2010, Vol. 55, No. 4, pp. 696–704.
PHYSICAL CHEMISTRY
OF SOLUTIONS
Effect of Methanol on the Dissolution of Neodymium Oxide
1
in Hydrochloric Acid Solutions
·
a
b
I. Girgin and A. Yörüko
g
lu
a
Hacettepe University, Mining Engineering Department, 06800 Beytepe, Ankara, Turkey
b
Mineral Research and Exploration General Directorate, 06520 Ankara, Turkey
eꢀmail: girgin@hacettepe.edu.tr
Received July 29, 2008
Abstract
—The effect of methanol on the solubility of Nd O in HCl medium in the temperature range of 25–
2 3
5
5°C were studied. HCl–CH OH was observed to be a better solvent than HCl–CH OH–H O and hydroꢀ
3
3
2
chloric acid for the dissolution of Nd O mainly due to prevention of neodymium hydroxide and dissolution
2
3
increased with increase of HCl concentration even at high HCl concentrations. Presence of methanol in the
medium was determined to cause corresponding decreases in conductivity, ESCE, pH values with correspondꢀ
ing increase in E values. Neodymium compounds formed in HCl–CH OH medium at 25°C were isolated
R
3
and identified using Xꢀray diffraction, thermal and chemical analysis methods and their thermal behaviour
were investigated between 25–1100°C. NdCl3 x1CH OH and NdCl3 x2CH OH 4.14H O (x1 x2 = 2.8)
were formed in nonꢀaqueous medium and these compounds were converted into NdCl , NdCl and
⋅
⋅
⋅
+
3
3
2
3
2.37
NdCl3 0.47CH OH with complete and partial loss of water and methanol around 240°C respectively. Methꢀ
⋅
3
anol was completely removed around 390°C with formation of NdCl2.37 (77.5%) and NdOCl (22.5%) and
NdOCl was detected as the major stable phase above 700°C.
DOI: 10.1134/S003602361004025X
1
A continuous decrease in the solubilities of rareꢀ to be able to point out the differences with that of
earth chlorides in aqueous hydrochloric acid solutions La O3 that might be used in rareꢀearth technology.
2
are observed with increase of HCl concentration [1].
Solubility of rareꢀearth chlorides in alcohols and
aqueous alcohols were studied and it was observed that
EXPERIMENTAL
the solubility increased markedly with temperature
2–4]. Also, complex formation of rareꢀearth eleꢀ described [7] by dissolving Nd(NO3)3
ments with chloride ions in alcohols were investigated 99.9% pure) in Merck grade HNO and by saturating
methanol with HCl gas respectively. For the preparaꢀ
tion of the HCl–CH OH H O solutions, the satuꢀ
Nd O3 and HCl–CH OH solution were prepared as
2 3
⋅
[
6H O (BDH,
2
3
[
2, 5, 6], alcoholates with the general formula MCl3
⋅
−
3
ROH and MCl3 2ROH H O were isolated and some
⋅
⋅
3
2
2
rated HCl–CH OH solution was diluted with water.
physicoꢀchemical properties of the alcoholate derivaꢀ
tives were studied. The precipitation of lanthanum
hydroxide at high HCl concentrations was prevented
by use of mixedꢀaqueous (HCl
preferably nonꢀaqueous (HCl CH OH) solvents, the
solubility of La O was improved, the composition of
the crystal solvates were determined as LaCl3
x1CH OH and LaCl3 x2CH OH 3H O (x1 x2 = 2.35)
and their thermal behaviours were investigated [7].
3
Hydrochloric acid, sulphuric acid and absolute methꢀ
anol were Merck reagents and absolute methanol was
dried before use.
The leaching experiments were carried out in a 200
mL three–necked Pyrex reactor using the same experꢀ
imental procedure, measurements and analyses as
described in the previous work [7].
−
CH OH
−
H O) and
3
2
−
3
2
3
⋅
⋅
⋅
+
3
3
2
ICP and XRF techniques were used for Nd analysis
at low concentrations and gravimetric analysis based
on oxalate precipitation [8, 9] at high concentrations.
This study is a complementary of an earlier investiꢀ
gation on the dissolution behaviour of La O in HCl– The chloride content of the HCl–CH OH solutions
2
3
3
H O, HCl–CH OH H O and HCl–CH OH [7]. It was analyzed by the Volhard method [10]. The prodꢀ
−
2
3
2 3
was aimed to obtain comparative data for determining ucts were identified using Rigaku Model 2ꢀ22E2 therꢀ
the effect of methanol on the solubility of Nd O3 in mal and Leco Model 1000 elemental analyzers. Conꢀ
2
+
HCl medium in the temperature range 25
−
55°C so as ductivity,
H
potential and medium potential meaꢀ
surements were done using Tacusell CD6N Model
conductivity meter with CM02/55 type electrode,
1
The article is published in the original.
646

EFFECT OF METHANOL ON THE DISSOLUTION
647
20
15
10
5
20
25°
40°
55
°
C
C
C
25°
40°
55°
C
C
C
15
10
5
0
60
120 180
Time, min
240 300
360
0
60
120 180
Time, min
240
300
360
Fig. 2. Solubility of Nd O in HCl–CH OH–H O (25%
2
3
3
2
Fig. 1. Solubility of Nd O in HCl–H O.
2
3
2
CH OH).
3
glass electrode and Calomel reference electrode leach solutions are very high compared to pure solvent
against platinum electrode, respectively.
and all decrease with increase of HCl concentration.
ER values for leach solutions are much lower than that
of pure solvent, all increase with HCl concentration
and the most significant change for the leach solutions
is observed at 25°C. Decrease in pH values and
increase in ER values can be related to decrease in solꢀ
ubilities at higher HCl concentrations due to formaꢀ
RESULTS AND DISCUSSION
The dissolution behaviour of Nd O in HCl–H O
,
2
3
2
HCl–CH OH H O and HCl–CH OH solutions at
−
3
2 3
different HCl concentrations between 25–55°C for 6 h
reaction time are given in Figs. 1–5. Dissolution of
Nd O is increased with increase of HCl concentration
tion of NdCl3 6H O as a solid phase [1] and possible
⋅
2
hydroxide precipitation above pH 6.
2
3
and temperature for all the experiments. Although a
Figures 8 to 13 show the change of conductance,
decrease in solubility in HCl–H O system is observed ESCE, pH and ER of HCl–CH OH H O solvent system
−
2
3
2
at increasing reaction times, this tendency is gradually for a reaction time of 6 hours. The conductance and
eliminated with decrease of water in the solvent sysꢀ ESCE values decrease (Figs. 8, 10, 12) in accordance
tems and maximum dissolution values are reached in with the decrease of water contents of the solvent sysꢀ
HCl–CH OH solvent system.
Change of conductance, ESCE, pH and ER with
HCl concentration and temperature for the HCl–
tems. More pronounced decreases in pH and correꢀ
sponding increases in ER (Figs. 9, 11, 13) can be
related to the lowering of conductance of the medium
due to increase of methanol in the solvents and the forꢀ
3
H O solvent system for a reaction time of 6 hours are
2
mation of NdCl3 ·
xH O · yCH OH type compounds.
given in Figs. 6 and 7. The conductance and ESCE valꢀ
2 3
ues of pure HCl–H O solvent increase with HCl conꢀ
Experimental data related with the nonꢀaqueous
2
centration. Similarly, the conductance and ESCE values solvent system and the leach solutions are given in
of the leach solutions are also observed to increase Figs. 14 and 15. Change of conductance and ESCE with
with HCl concentration and temperature. But, for all HCl concentration in nonꢀaqueous medium is comꢀ
temperatures and HCl concentrations, the values pletely different than those of mixedꢀaqueous and
obtained for leach solutions are lower than that of pure aqueous mediums. Due to low conductance value of
solvents. This tendency can be explained by lowering methanol, HCl–CH OH solvent system has the lowest
3
+
of
H
ion concentration in the medium due to basic conductance values for all HCl concentrations. The
property of neodymium and formation of higher conductance values of the leach solutions are lower
valency neodymium complexes. The pH values of the than that of the pure solvent which can be explained by
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 4 2010

648
GIRGIN, YÖRÜKOGLU
20
15
10
5
20
25°
40°
55
°
C
C
C
25°
40°
55
°
C
C
C
15
1
0
5
0
60
120 180 240 300 360
Time, min
0
60
120 180
Time, min
240
300
360
Fig. 3. Solubility of Nd O in HCl–CH OH–H O (50%
Fig. 4. Solubility of Nd O in HCl–CH OH–H O (75%
2 3 3 2
2
3
3
2
CH OH)
.
CH OH).
3
3
formation of neutral neodymium–methanol comꢀ aqueous medium are much lower than those of aqueꢀ
pounds. HCl–CH OH solvent system has the lowest ous and mixedꢀaqueous mediums due to low conducꢀ
3
ESCE value due to low ionization of methanol but the tance of methanol and due to formation of neutral
ESCE values of the leach solutions are higher than those neodymium–methanol compounds. Low pH values
of aqueous and mixedꢀaqueous leach solutions and of the leach solutions prevent neodymium hydroxide
even that of the HCl–CH OH solvent system because precipitation and provide better dissolution.
3
+
of the higher
The conductance values of the leach solutions in nonꢀ
H
ion concentration of the medium.
2
5 g of Nd O3 was reacted with 50 mL of
2
HCl⎯CH OH solvent at 7 M HCl concentration for
3
6
0 minutes and a highly hygroscopic jelly product was
obtained. Reaction products were dried at 75°C for
h, kept in vacuum desiccator and were identified by
Table 1. TGAꢀDTA analysis results for neodymium compounds
2
TGA, DTA, XRD and chemical analyses.
Temperature range, °C
Weight loss, %
15.9
The thermal decomposition curve of the neodyꢀ
mium compounds in HCl–CH OH solvent system
3
showed five endothermic peaks of which the temperaꢀ
ture ranges and the weight losses are given in Table 1.
68.5–126.1
For the determination of the decomposition prodꢀ
ucts, the neodymium compound formed in nonꢀaqueꢀ
ous medium was heated separately considering the
temperature ranges given in Table 1 and compounds
formed were identified by XRD and chemical analyꢀ
ses. The chemical analysis results and the XRD patꢀ
terns are given in Table 2 and Fig. 16, respectively.
126.1–140
140.0–201.6
201.6–250
348.7–505
3.9
4.4
Evaluation of the XRD results together with chemꢀ
ical analysis and weight loss values show the presence
of the neodymium compounds given in Table 3 and
that of lanthanum (Table 4) for comparison purposes.
10.0
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 4 2010

EFFECT OF METHANOL ON THE DISSOLUTION
649
30
25
20
15
10
5
250
700
25°
40°
55
°
C
C
C
solvent
2
4
5
5
0
5
°
°
°
C
C
C
600
500
400
300
200
00
2
00
50
1
100
50
1
0
60
120 180
Time, min
240 300
360
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5
HCl Concentration, mol/L
Fig. 5. Solubility of Nd O in HCl–CH OH
.
2
3
3
Fig. 6. Change of conductance and ESCE in Nd–HCl–
H O system with HCl concentration and temperature.
CONCLUSIONS
HCl–CH OH is a better solvent than HCl–
2
3
CH OH
−
H O and hydrochloric acid for the dissoluꢀ complete removal of methanol from neodymium
3
2
tion of Nd O3. The main advantages of this nonꢀaqueꢀ compounds at 390°C takes place at 200°C for lanthaꢀ
2
ous solvent system is that neodymium hydroxide is not num compounds.
precipitated and dissolution increases with increase of
HCl concentration even at high HCl concentrations.
As can be seen, there are differences in the temperꢀ
atures of water and methanol losses, in the types of
The dissolution behaviour of Nd O in the solvent sysꢀ chloride compound formations (LaCl , NdCl ,
2
3
3
3
tems tested is similar to that of La O but the solubility
2
3
of Nd O is lower. A solubility difference of 1.22 times
2
3
Table 2. Chemical analysis results of the thermal decomposiꢀ
between lanthanum and neodymium in aqueous
medium was observed to increase to 1.40 times in nonꢀ
aqueous medium.
tion products
Temperature,
Although NdCl3
formed in aqueous media at 25 C, NdCl
⋅
n
H O type compounds are
Nd, % Cl, % C, % H, % Weight loss, %
2
°C
o
⋅
x1CH OH
3
3
and NdCl3
⋅
x2CH OH 4.14H O (x1 + x2 = 2.8) are
⋅
3
2
formed in nonꢀaqueous media. Water and methanol
losses are observed up to 165°C and NdCl3 is formed as
25
25
50
65
34.20 28.94 8.12 4.77
38.26 27.20 6.24 3.57
43.80 30.74 5.85 3.14
46.86 32.27 3.98 1.72
56.26 35.47 2.20 0.91
—
12.00
6.00
2.00
4.50
5.00
6.00
a new phase. With increase of temperature to 240°C
water is completely removed and besides NdCl3 as the
major phase, NdCl2.37 and NdCl3 0.47CH OH are
formed. Further increase of temperature to 390°C
leads to decomposition of NdCl3 and NdOCl starts to
,
1
1
1
⋅
3
be formed besides the major phase NdCl2.37. At 700°C
NdOCl becomes the stable phase (96%) with 4% of
NdCl2.37
,
.
240
390
The thermal behaviours of the neodymium and
lanthanum compounds formed in HCl–CH OH solꢀ
vent system are slightly different. For example, comꢀ
plete loss of water in neodymium and lanthanum comꢀ
pounds are at 240 and 165°C, respectively. Similarly,
64.46 32.14
72.29 17.13
–
–
–
–
3
700
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 4 2010

650
GIRGIN, YÖRÜKOGLU
7
6
5
4
3
2
1
0
1
2
solvent
500
200
800
00
600
00
400
00
200
Solvent
25°
°
°
C
C
C
2
4
5
5
0
5
°
°
°
C
C
C
4
0
55
7
400
300
200
100
0
1
50
00
5
1
3
50
100
–
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5
HCl Concentration, mol/L
–
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5
HCl Concentration, mol/L
Fig. 8. Change of conductance and ESCE of Nd–HCl–
CH OH–H O system (25% CH OH) with HCl concenꢀ
tration and temperature.
Fig. 7. Change of pH and ER in Nd–HCl–H O system
2
3
2
3
with HCl concentration and temperature.
7
6
5
4
3
2
1
0
1
2
500
200
solvent
800
00
600
00
2
4
5
5
0
5
°
°
°
C
C
C
solvent
25
°
°
°
C
C
C
7
40
400
300
200
100
0
55
1
50
00
5
1
400
300
200
50
100
–
–
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5
HCl Concentration, mol/L
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5
HCl Concentration, mol/L
Fig. 9. Change of pH and ER of Nd–HCl–CH OH–H O
Fig. 10. Change of conductance and ESCE of Nd–HCl–
CH OH–H O system (50% CH OH) with HCl concenꢀ
tration and temperature.
3
2
system (25% CH OH) with HCl concentration and temꢀ
3
3
2
3
perature.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 4 2010

EFFECT OF METHANOL ON THE DISSOLUTION
651
5
00
200
7
00
7
6
5
4
3
2
1
0
1
2
solvent
25
°
C
C
C
solvent
40
°
2
4
5
5
0
5
°
°
°
C
C
C
5
5
°
600
400
300
200
100
0
1
50
00
500
400
300
1
2
00
00
50
–
–
1
0
0.5 1.0 1.5 2.0 2.5 3.0
HCl Concentration, mol/L
3.5
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5
HCl Concentration, mol/L
Fig. 11. Change of pH and ER of Nd–HCl–CH OH–
Fig. 12. Change of conductance and ESCE of Nd–HCl–
CH OH–H O system (75% CH OH) with HCl concenꢀ
tration and temperature.
3
H O system (50% CH OH) with HCl concentration and
2
3
3
2
3
temperature.
solvent
200
700
6
5
4
3
2
1
0
500
2
4
5
5
0
5
°
°
°
C
C
C
solvent
2
5
0
5
°
°
°
C
C
C
600
500
400
300
200
4
5
400
150
3
00
00
100
2
50
100
–
1
100
0
–2
0
3.5
0
0.5 1.0 1.5 2.0 2.5 3.0
HCl Concentration, mol/L
0
1
2
3
4
HCl Concentration, mol/L
5
Fig. 13. Change of pH and ER of Nd–HCl–CH OH–
3
H O system (75% CH OH) with HCl concentration and
Fig. 14. Change of conductance and ESCE of Nd–HCl–
CH OH system with HCl concentration and temperature.
2
3
temperature.
3
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 4 2010

652
GIRGIN, YÖRÜKO
G
LU
8
7
6
5
4
3
2
1
0
1
600
solvent
25
°
°
°
C
C
C
4
5
0
5
500
400
300
200
–
–
2
3
–
100
0
1
2
HCl Concentration, mol/L
3
4
5
Fig. 15. Change of pH and ER of Nd–HCl–CH OH system with HCl concentration and temperature.
3
Table 3. Neodymium compounds formed in HCl–CH OH Table 4. Lanthanum compounds formed in HCl–CH OH solꢀ
3
3
solvent system and the decomposition products between vent system and the decomposition products between 25–
25–1100°C
1100°C [7]
Temperaꢀ
ture, °C
Chemical Composition
Temperaꢀ
ture, °C
Chemical Composition
2
5
NdCl3
NdCl3
⋅
⋅
x1CH OH
x1
x1
+
+
+
+
x2 = 2.8
x2 = 1.96
x2 = 1.6
x2 = 1.02
3
x2CH OH
⋅
4.14H O
3
2
25
LaCl3
LaCl3
⋅
⋅
x1CH OH
x1
+
+
x2 = 2.35
x2 = 1.90
3
x2CH OH
⋅
3H O
3
2
1
1
1
25
50
65
NdCl3
NdCl3
⋅
⋅
x1CH OH
3
x2CH OH
⋅
2.8H O
3
2
1
20
LaCl3
LaCl3
⋅
⋅
x1CH OH
x1
3
NdCl3
⋅
⋅
x1CH OH
3
x1
x2CH OH
⋅
0.5H O
3
2
NdCl3
x2CH OH
⋅
1.96H O
3
2
NdCl3
NdCl3
NdCl3
x1
165
LaCl3 ⋅ 1.14CH OH
3
⋅
⋅
x1CH OH
3
x2CH OH
⋅
0.6H O
3
2
200
560
700
77.3% LaCl + 22.7% LaOCl
3
2
40
94.2% NdCl + 6.8% NdCl
3 2.37
NdCl3 0.47CH OH
⋅
3
33.14% LaCl + 66.86% LaOCl
3
3
90
00
77.5% NdCl2.37 + 22.5% NdOCl
4.34% NdCl2.37 + 94.36% NdOCl
5.52% LaCl + 94.47% LaOCl
3
7
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 4 2010

EFFECT OF METHANOL ON THE DISSOLUTION
653
NdOCl
Nd 700°C
NdOCl
NdCl2
Nd 390°C
.37
NdCl2
NdCl
.37
3
Nd 240
°
C
?
NdCl · xCH OH
3 3
NdCl · x 1CH OH ·
yH O
2
?
?
3
3
3
Nd 165
°
C
NdCl
NdCl · x2CH OH
3
3
?
?
NdCl3 · x1CH OH ·
3
NdCl3 · x2CH OH
3
yH O
2
Nd 150°C
?
NdCl3 · x1CH OH ·
3
NdCl3 · x2CH OH
yH O
2
?
3
Nd 125°C
?
NdCl3 · x1CH OH ·
3
NdCl3 · x2CH OH
yH O
2
?
3
Nd Jel 1
2.5
10
20
30
40
50
60
70
2
θ
Fig. 16. Comparative XRD patterns of the decomposition products.
NdCl2 37) and in the oxychloride conversion temperaꢀ
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.
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3
2
3.
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(1963).
2
8 (4), 507
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