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In-Depth Information
A — ZrSiO
4
, Na
2
ZrSi
3
O
9
·H
2
O,
Na
4
Zr
2
Si
5
O
16
·H
2
O
B — Na
2
ZrSi
2
O
7
, Na
4
Zr
2
Si
3
O
12
;
C — ZrSiO
4
, Na
2
ZrSi
3
O
9
·H
2
O,
Na
2
ZrSi
6
O
15
·3H
2
O
D — Na
8
ZrSi
6
O
18
, Na
2
ZrSi
2
O
7
,
Na
2
ZrSi
3
O
9
·2H
2
O
II
— Na
8
ZrSi
6
O
18
III
— Na
3
HZrSi
2
O
8
Na
4
Zr
2
Si
3
O
12
B
A
(
I
)
I + II + III
I +
C
D
II
(trace)
0
10
20
c
NaOH
(wt%)
30
40
50
Figure 7.20 Phase composition of zirconium silicates formed in Na-containing media
[95]
.
ZrO
2
1 — Na
2
ZrSi
6
O
15
·3H
2
O
2 — Na
2
ZrSi
4
O
11
3 — Na
2
ZrSi
3
O
9
·2H
2
O
4 — Na
2
ZrSi
3
O
9
·3H
2
O
5 — Na
4
Zr
2
Si
6
O
18
·4H
2
O
6 — Na
4
Zr
2
Si
5
O
16
7 — Na
2
ZrSi
2
O
7
8 — Na
4
Zr
2
Si
3
O
12
9 — Na
2
ZrSiO
5
10 — Na
3
HZrSi
2
O
8
11 - 12 — Na
8-
x
ZrSiO
4
9
8
7
6
3,4,5
10
2
1
12
11
H
ZrSi
6
O
18
x
SiO
2
mol%
Na
2
O
Figure 7.21 Crystallization field in Na
2
O
a
ZrO
2
a
SiO
2
system
[95]
.
refine the composition of some phases. Thus, the phase earlier described as
Na
14
Zr
2
Si
10
O
31
based on the data of chemical analysis
[97,98]
has, in fact, the
composition Na
8
ZrSi
6
O
18
. Its structure is analogous to Na
8
SnSi
6
O
18
[99]
.
Na
6
Zr
2
Si
3
O
15
(composition based on the data of the chemical analysis)
[100]
has
the same structure as the synthetic germanate Na
3
HZrGe
2
O
8
(
Table 7.13
).
The general scheme of zirconium silicate crystallization in hydrothermal solu-
tion with an increase in alkali concentration and temperature is shown in
Figure 7.22
.
Analogs of zirconium mineral (zircon, elpidite, vlasovite, catapleite, parakeldy-
shite) and Na
4
Zr2Si
5
O
16
H
2
O silicate (still not observed in nature) are formed in
the region of solutions with the lowest concentrations. In highly concentrated solu-
tions, the silicates with the lowest silicon content are crystallized: Na
4
Zr
2
Si
3
O
12
and Na
2
ZrSiO
5
. This system illustrates the role of the solvent in the formation of