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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
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