Geoscience Reference
In-Depth Information
Sc
2
O
3
/Sb
2
O
3
ratio
1:1, Sc
3
Sb
5
O
12
crystallizes with 100% output. The morphol-
ogy of these crystals is similar to that of indium analogue
[113]
.
Rare earth antimonites with a general formula R
3
Sb
5
O
12
(R
.
La, Pr, Ti, and Yb)
are the important compounds in this group
[114]
. It is interesting to note that the lan-
thanum penta-antimonite crystallization field does not exist and its crystallization in
aqueous solutions of KF with concentrations of 5
5
50 wt% is always accompanied by
the related phases. Stefanovich et al.
[115]
have studied the phase transformations in
these rare earth antimonites in detail. In the presence of an oxidizing agent, trivalent
antimony oxidizes up to the pentavalent state forming antimonates and producing H
[Sb(OH)
6
]
6
acid. They are poorly soluble in water. There are several antimonate
minerals; among the synthetic varieties, only a few compounds have been obtained:
Na[SbO
3
], Na
3
Sb
3
[Sb
2
O
11
], and Sb[SbO
4
]
[116,117]
.
Figure 9.27
shows (a) the field
of crystallization of antimonites in the system Na
2
O
H
2
O and (b)
the field of synthesis of antimonites.
Figure 9.28
shows the field of crystallization of
a
Sb
2
O
3
a
Sb
2
O
5
a
Sb(SbO
4
)
3:1
Sb(SbO
4
)
1:1
Sb
2
O
3
Sb
2
O
3
1:3
10
30
50
70
μ
Na
2
O
μ
Na
2
O
(a)
(b)
Figure 9.27 (a) Field of crystallization of antimonates in the system
Na
2
O
a
Sb
2
O
3
a
Sb
2
O
5
a
H
2
O and (b) field of synthesis of antimonites.
N(Sb
2
O
3
/Sb
2
O
5
)
3:1
Sb
2
O
3
Sb
2
O
3
Sb
2
O
3
+ Sb(SbO
4
)
Sb
2
O
3
1:1
Sb
2
O
3
+ Sb(SbO
4
)
1:3
10
20
30
40
50
60
10
20
30
C
KHF
2
(Mac,%)
C
H
2
O
2
(Mac,%)
(a)
(b)
Figure 9.28 Field of crystallization of antimonates at (a) lower and (b) higher oxygen
potentials
[116]
.
