Geoscience Reference
In-Depth Information
S
6
5
4
3
2
1
10% H
3
PO
4
300
310
320
330
340
360
350
Figure 5.16 Solubility of berlinite in orthophosphoric acid above 300
C
[75]
.
earlier failures in the growth of AlPO
4
crystals. It was only in the late 1970s and
early 1980s that reports on the solubility of AlPO4 appeared in the literature. The
problem associated with the growth of large single crystals of AlPO
4
is directly
related to the lack of a systematic study of the solubility and partly to the P
2
O
5
pressure. Although, several reports have appeared on the solubility measurements
with reference to various parameters, still there is no unanimity in the results.
The solubility of berlinite was first determined by Jahn and Kordes (1950)
[75]
in
orthophosphoric acid above 300
C and it was found positive (
Figure 5.16
).
Subsequently, Stanley (1954)
[76]
reported a negative solubility for berlinite in
6.1 M H
3
PO
4
(
Figure 5.17
). The solubility of ALPO
4
varies widely with the type of
solvent used. Some authors claim that solubility of AlPO
4
in HCl is similar to that
in H
3
PO
4
. The most important difference is the higher solubility at comparable
mineralizer concentration.
The authors
[83]
have made an attempt to study the solubility of AlPO
4
in some
new solvents like HCOOH, NH
4
Cl, Na
2
CO
3
,NH
4
H
2
PO
4
, NaF, KF, and LiF. The
solubility of AlPO
4
(in wt%) as a function of temperature and at a pressure of
2 kpsi in 2 M HCOOH solution is shown in
Figure 5.18
.
It has been shown that the solubility of AlPO
4
in H
2
SO
4
is retrograde with
respect to temperature and higher than in H
3
PO
4
and HCl at comparable tempera-
ture, pressure, and acid molarity. However, the viscosity of sulfuric and phosphoric
acid solutions is greater than that of HCl. Hence, the addition of HCl to H
2
SO
4
would form a more efficient solvent for the growth of AlPO
4
[84]
.
Figure 5.19
shows solubility as a function of temperature in H
2
SO
4
1
HCl mixtures. The
