Geoscience Reference
In-Depth Information
700
C and pressures of 750
Using pure LiCl solutions at 400
3000 atm, we
may synthesize
α
-eucryptite LiAlSiO
4
,
β
-spodumene
β
-LiAlSi
2
O
6
, and petalite
LiAlSi
4
O
10
.The
α
-eucryptite is mainly formed for high Al
2
O
3
/SiO
2
ratios in the
original charge (
1:1),
β
-spodumene for smaller ratios (1:2
1:3), and petalite for
B
a high concentration of silica (ratio A/S
1:8). In the neighborhood of the ratio
B
Al
2
O
3
/SiO
2
B
-spodumene and quartz.
The concentration of LiCl solutions, and the temperature and pressure within
the limits indicated, have little effect on the phase formation in the LiCl
1:5, we observe paragenesis of
β
a
Al
2
O
3
a
SiO
2
a
H
2
O system.
The pH of the solution, together with the Al
2
O
3
/SiO
2
ratio, constitutes the sec-
ond most important factor in the crystallization. Reducing the alkalinity of the solu-
tion (in LiCl
HCl solutions) has practically no effect on the phase formation, but
on increasing the alkalinity (in LiCl
1
LiOH or LiOH solutions) new compounds
appear and the ranges of crystallization of the phases already noted alter. First of
all, lithium silicate Li
2
SiO
3
appears. For a ratio of Al
2
O
3
/SiO
2
5
1
1:1 lithium silicate
is synthesized for high values of the alkalinity, but with increasing concentration of
SiO
2
in the original mixture the range of its stability moves in the low pH direction
(
Figure 7.42
). In alkaline solutions, the field of formation of petalite also widens,
and the latter is synthesized for higher Al
2
O
3
/SiO
2
ratios (
B
1:2 for pH
.
10) than
in LiCl solutions. The range of existence of
-spodumene, on the other hand, con-
tracts slightly on increasing the alkalinity (
Figure 7.42
), and for pH
β
10 it
.
becomes unstable, being replaced by
α
-eucryptite and lithium silicate.
The densest of all phases synthesized is
-spodumene, which clearly indicates
that the stability range lies at much higher pressures. In other words, at pressures of
under 4000 atm and in the absence of impurities, no spodumene is formed. The
commonly used impurities are Cr
3
1
and Fe
3
1
. The
α
-spodumene is synthesized in
LiCl solutions at pressures over approximately 6000 atm. At lower pressures, it
α
Figure 7.42 Fields of stability
of lithium silicates in relation to
the pH of the solution and the
ratio of the original charge
components at T
5
600
700
and P
5
2000
3000 atm. (1)
α
-LiAlSiO
4
; (2)
β
-LiAlSi
2
O
6
;
(3) LiAlSi
4
O
10
;(4)Li
2
SiO
3
[200]
.
pH
11
8
5
3
0
1:1
1:2
1:3
1:8
Al
2
O
3
/SiO
2
1
2
3
4
