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About supersaturation and growth rates of hydrargillite Al(OH)3 in alumina caustic solutions
Journal of Crystal Growth 130 (1993) 411—415 North-Holland
Jo~o~
CRYSTAL GROWTH
About supersaturation and growth rates of hydrargillite Al(OH)3 in alumina caustic solutions Stéphane Veesler Roland Boistelle 2 ‘K, CNRS, Campusand de Luminy, Case 913, F-13288 Marseille CRMC
Cedex 09, France
Received 1 December 1992; manuscript received in final form 18 January 1993
Growth rates of hydrargillite crystals, Al(OH) 3, growing from concentrated caustic solutions, are traditionally plotted and discussed as a function of the difference between actual concentration and solubility of alumina. This way to express supersaturation is probably due to practical or technical reasons, as hydrargillite is mainly grown in industrial plants. However, as the solubility of hydrargillite is greatly affected by the presence of caustic soda there are as many growth rate curves as there are solutions at different soda concentrations, if supersaturation is expressed as a concentration difference. In the present paper we show that all growth rates, measured in different caustic solutions, lie on a single curve if supersaturation is normalized with respect to solubility, i.e. expressed as a ratio of actual concentration over solubility. Accordingly, growth rates become independent of the caustic concentrations when growth takes place at the same supersaturation.
1. Introduction
ical potentials of supersaturated and saturated solutions,
In the Bayer process, the production of alumina from bauxite first consists in crystallizing hydrargillite, Al(OH)3, from a caustic solution supersaturated in sodium aluminate. This solution, commonly named pregnant liquor, is made of water, caustic soda and dissolved hydrargillite. In a recent study [11,we were concerned with the definition of supersaturation and the influence of NaOH on the growth rates of hydrargillite crystals. To approach these problems, we have analysed the data given in the literature and propose to normalize supersaturation with respect to solubility of hydrargillite at each caustic concentration.
~P-
=
kBT
In
13,
(1)
where 13, the supersaturation ratio, is the ratio of the ionic product over the solubility product ~ of all species involved in the crystallization of the solid phase; T is the temperature and k8 the Boltzmann constant. Dissolution of hydrargillite in caustic solutions leads to the formation of several ions and soluble complexes. However, the concentrations of all species but one are negligible [21,so that dissolution corresponds to the reaction OH)3+OH~A1(OH),~I. The thermodynamic solubility product is
(2)
2. Supersaturation (A1(oH)~~)0 In electrolytic solutions, supersaturation should be expressed as the difference between the chem*
Laboratoire associé aux Universités d’Ajx—Marseille II et III.
0022-0248/93/$06.00 © 1993
—
~
=
(0H)0 =
[Ai(oH)fl 0y0(A1(OH)~~) [0H]0y0(0H)
Elsevier Science Publishers B.V. All rights reserved
.
(3)
412
S. Veesler, R. Boistelle
/ Supersaturation
and growth rates of hydrargillite
l’he parentheses and brackets refer to activities and concentrations respectively: y is the activity coefficient of the species under considera-
where R is the molar gas constant and ~.4Gthe activation free energy for crystallization. The kinetic coefficient k0 depends on temperature and
tion, the subscript zero referring to equilibrium, According to eqs. (2) and (3), /3 should be written
solution composition. C and C0 are the actual and equilibrium concentrations of dissolved Al(OH)3 but, traditionally, for explaining the growth rates of hydrargillite crystals, C and Co are expressed as grams of Al203 per liter of solution. As an example, a 2 molar Al(OH)3 solution contains 102 g Al(OH)3 i.e. 156 g A1203, the conversion factor A1203 A1(OH)3 being 1.53. In addition, the NaOH concentrations are always transformed into Na20 concentrations (2NaOH Na~O+ H20), 40 g NaOH/l for instance being 31 g Na20/l. Actually, the choice of C C0 in eq. (6) is not really judicious in the present case, because in the ternary system Al(OH)3 + NaOH + H20 (A1203 + Na20 + H20), the solubility of hydrargillite changes drastically with NaOH concentration. Accordingly, the caustic concentration must be known precisely, the difference C C0 depending on the units taken for A1203 concentrations. On the other hand, the non-dimensional numbers /3 C/C0 and o~ (C C0)/C0 j~ dude the effect of NaOH on solubility and do not suffer this drawback. Hereafter, we intend to show that results obtamed in different caustic solutions can be anal-
[Al(OH)~][OH]oy(A,(QH)~-)y~OH-) =
[Al(OH)~]O[oH~]y~M(OH)~)y(OU_) (4) .
Unfortunately, there is no information in the literature concerning the activity coefficients in highly concentrated alumina caustic solutions, so that we temporarily assume that the ratio between the different activity coefficients in eq. (4) is one. This is similar to the approximation of Davies [31,which supposes that the activity coefficients depend only on the species valence and ionic strength of the solution. Finally, if the NaOH concentrations are not too different in supersaturated and saturated solutions, eq. (4) reduces to
=
[Jsd(oH)~1 [AJ(oH)~1~’
—~
—
—
—
(5)
This equation, which is commonly written /3 C/C0, is rarely used by the authors dealing with hydrargillite crystallization, most results being discussed in terms of the difference (C C0), as in a chemical reaction. =
—
=
Only a few authors [4—11]studied the crystallization of hydrargillite from caustic solutions. They mainly aimed at describing the growth mechanisms of Al(OH)3 or improve the crystallization process in industrial plants (Bayer process). In all cases, the linear growth rates G of hydrargillite crystals were discussed on the basis of equations like 1, (6) G k(C C0)’ =
—
with k=k0 exp(—ziG/RT),
(7)
—
ysed in a simple way using /3 or a- instead of C C0 for expressing supersaturation. The solubility data of hydrargillite we used for unit conversions were taken from a review of solubility data by Misra [12]. Concerning the linear growth rates of hydrargillite, only the data of King [4] and White and Bateman [8] could be analysed, because all raw data were available. The results of Overbey and Scott [51and Mordini and Cristol [61could not be analysed due to a lack of information on the raw data. Halfon and Kaliaguine [7] on the one hand and Misra and White [10] on the other hand did not report any influence of caustic soda. However, in both cases,over the limited caustic concentrations were only varied ranges (107—114 and 80—120 g/l in Na 20 units respectively) and it is likely that its influence was hidden by some scattering of the experimental points. —
3. Growth rates of Al(OH)3
=
S. Veesler, R. Boistelle
/ Supersaturation and
4. Discussion
growth rates of hydrargillite
413
20 84 gil
In table 1, we summarize the data of White and Bateman [81, who measured the overall growth rates G of Al(OH)3 aggregates at 89.5°C in different caustic Na20 solutions at different supersaturations (C C0). These data and Misra’s equation [12] were used to calculate the a- values. In the diagram of G =f(C C0), the experimental points lie on 4 curves (fig. 1), each of them corresponding to the specific caustic concentrations given in table 1. Once supersaturations are normalized with respect to solubility, all points lie on one single curve (fig. 2). The measurements of King [4] were carried out at 80°Con single crystals along the c axis of hydrargillite or perpendicular to this direction (table 2). In the plot of G =f(C C0), there is an important scattering of the experimental points due to the influence of Na20 on the solubility of hydrargillite (fig. 3a). Once supersaturations are normalized, all points but one also lie on the same curve (fig. 3b). In both these figures, only
147 g/l
/
•
/ ~.
9/I
/
/
gIl
113
10
—
, 5
—
0
—~
0
20
40
60 C~C0gil
80
100
1 20
Fig. 1. Growth rates of hydrargillite at different concentrations of caustic soda expressed in Na20 units (after ref. 18]).
—
20
C0 (g/l)
C-C0 (g/l)
u
84 84 84
56.5 56.5 56 5
20 30 40
0.35 0.53 0 71
3.40 6.60 17 00
113 113 113 113
82.9 82.9 82.9 82.9
20 30 40 50
0.24 0.36 0.48 0.60
1.65 3.20 6.50 10.00
147 147 147 147 147
119.0 119.0 119.0 119.0 119.0
20 30 40 60 90
0.17 0.25 0.33 0.50 0.75
0.93 1.88 3.71 7.30 17.50
165 165 165 165
141.4 141.4 141.4 141.4
30 40 60 100
0.21 0.28 0.42 0.71
1.12 2.00 4.30 15.00
.
~ 1 5
-
~
~
Table! Growth rates G of hydrargillite at 89.5°C[8] as a function of normalized supersaturation in different caustic solutions Na20 (g/l)
.
-
~—
—
g~
_______
.
147 ~/l 165 gil
~
:
/
S
5
G (gm/h)
0
0.2
0 .
0.4
.
0.6
0.8
.
Fig. 2. Growth rates displayed in figure 1 after normalization of supersaturation.
Table 2 Growth rates G of hydrargillite single crystals at 80°C[4] parallel and normal to the c axis of the crystals Na20 (g/l) 106.4 128.8 106.4 107.1 69.9 106.4
C0 (g/l) 64.2 83.2 64.2 64.7 37.7 64.2
C — C0 (g/l) 45.0 59.8 53.7 61.9 41.2 71.4
o0.70 0.72 0.84 0.96 1.09 1.11
G (II c) (~sm/h) 1.4 1.9 2.7 4.5 4.1 9.2
G (Ic) (j.~m/h) 1.1 1.7 2.2 3.5 3.5 7.0
414
S. Veesler, R. Boistelle
a
0
/ Supersaturation and growth rates of hydrargillite
l06~4 9/’.
—
~
8
8 -
E
E
_..9
~
c~.7
4
5/
•
2
(D
4
+
.
.
c.l2.8~4/l4 : .
2
0
0 60 65 70 75 0.6 0.7 0.8 0.9 I 1.1 1.2 c-c 0 gil a Fig. 3. Growth rates of hydrargillite single crystals along their c axis (after ref. [4]):(a) as a function of concentration difference; (b) after supersaturation normalization. 40
45
50
55
the growth rates along the c axis have been plotted to avoid overlapping, At constant temperature, 80 and 89.5°Cin the present case, the growth rate is only dependent on supersaturation, when it is expressed as /3, because caustic concentration and supersaturation are inter-dependent variables. In other terms, solubility of Al(OH)3 decreases, for instance, with decreasing caustic concentration. This would resuit in an increase of supersaturation and consequently of the crystal growth rate if the actual concentration of solute remains unchanged. On the other hand, if supersaturation /3 is readjusted to the same initial value, taking the solubility variation into account, then the crystal growth rate remains constant. From this standpoint, the growth rate is independent of caustic concentration. It is noteworthy that Overbey and Scott [5] proposed a model for explaining the growth rate of hydrargillite (actually the liquor decomposition versus time) on the basis of the second order rate equation given by Pearson [11]. This equation can be written with our symbols dC1 —
dt
of refs. [5,11], the results may be fitted by this equation, but actually the term in parentheses has no real physical significance as N should not be added to C0 to define supersaturation.
5. Conclusion Both examples we have given show clearly that expressing supersaturation as a nondimensional number, normalized with respect to solubility, is more appropriate than expressing supersaturation as a concentration difference. The same concentration differences do not correspond to the same supersaturations, as they are dependent on solubilities which in turn depend on caustic concentrations. From the present analysis, if normalized supersaturations are used, including the caustic effect on solubility, it also turns out that the caustic concentration does not affect the growth rates of hydrargillite, at least for Na2O concentrations ranging from 80 to 165 g/l.
_____
=
~
C0
+ N)
(8)
where A~is the overall area of the crystallites present in the liquor and N the concentration of NaOH at equilibrium. According to the authors
Acknowledgments The authors are indebted to Aluminium Pechiney for financial support and to Mrs. D. Laporte and M.C. Toselli for technical assistance.
S. Veesler, R. Boistelle
/ Supersaturation and
References [1] S. Veesler, Cristallisation de l’hydrargillite: cinétique et attrition, Thesis, Université Aix—Marseille III (1991). [2] C.F. Baes and R.E. Mesmer, The Hydrolysis of Cations (Wiley, New York, 1976) p. 1 [3] C.W. Davies, J. Chem. Soc. 19 (1938) 2093. [4] W.R. King, in: Light Metals, Conf. Proc. (1973) p. 551. [5] T.L. Overbey and CE. Scott, in: Light Metals, Conf. Proc. (1978) p. 163. [6] J. Mordini and B. Cristol, in: Proc. Yugoslav Intern. Symp. on Aluminium, Univ. Edvarda Kardelja, Ljubljana, 1982, p. 168.
17]
growth rates of hydrargillite
415
A. Halfon and S. Kaliaguine, Can. J. Chem. Eng. 54 (1976) 160.
[8] E.T. White and S.H. Bateman, in: Light Metals, Conf. Proc. (1988) p. 157. [9] D.R. Audet and J.E. Larocque, in: Light Metals, Conf. Proc. (1989) p. 21. [10] C. Misra and E.T. White, Chem. Eng. Progr. Symp. Series 67, No. 110 (1971) 53. [11] T.G. Pearson, The Chemical Background of the Aluminium Industry, Monograph No. 3 (Royal Institute of Chemistry, London, 1955). [12] C. Misra, Chem. md. 20 (1970) 619.
Jo~o~
CRYSTAL GROWTH
About supersaturation and growth rates of hydrargillite Al(OH)3 in alumina caustic solutions Stéphane Veesler Roland Boistelle 2 ‘K, CNRS, Campusand de Luminy, Case 913, F-13288 Marseille CRMC
Cedex 09, France
Received 1 December 1992; manuscript received in final form 18 January 1993
Growth rates of hydrargillite crystals, Al(OH) 3, growing from concentrated caustic solutions, are traditionally plotted and discussed as a function of the difference between actual concentration and solubility of alumina. This way to express supersaturation is probably due to practical or technical reasons, as hydrargillite is mainly grown in industrial plants. However, as the solubility of hydrargillite is greatly affected by the presence of caustic soda there are as many growth rate curves as there are solutions at different soda concentrations, if supersaturation is expressed as a concentration difference. In the present paper we show that all growth rates, measured in different caustic solutions, lie on a single curve if supersaturation is normalized with respect to solubility, i.e. expressed as a ratio of actual concentration over solubility. Accordingly, growth rates become independent of the caustic concentrations when growth takes place at the same supersaturation.
1. Introduction
ical potentials of supersaturated and saturated solutions,
In the Bayer process, the production of alumina from bauxite first consists in crystallizing hydrargillite, Al(OH)3, from a caustic solution supersaturated in sodium aluminate. This solution, commonly named pregnant liquor, is made of water, caustic soda and dissolved hydrargillite. In a recent study [11,we were concerned with the definition of supersaturation and the influence of NaOH on the growth rates of hydrargillite crystals. To approach these problems, we have analysed the data given in the literature and propose to normalize supersaturation with respect to solubility of hydrargillite at each caustic concentration.
~P-
=
kBT
In
13,
(1)
where 13, the supersaturation ratio, is the ratio of the ionic product over the solubility product ~ of all species involved in the crystallization of the solid phase; T is the temperature and k8 the Boltzmann constant. Dissolution of hydrargillite in caustic solutions leads to the formation of several ions and soluble complexes. However, the concentrations of all species but one are negligible [21,so that dissolution corresponds to the reaction OH)3+OH~A1(OH),~I. The thermodynamic solubility product is
(2)
2. Supersaturation (A1(oH)~~)0 In electrolytic solutions, supersaturation should be expressed as the difference between the chem*
Laboratoire associé aux Universités d’Ajx—Marseille II et III.
0022-0248/93/$06.00 © 1993
—
~
=
(0H)0 =
[Ai(oH)fl 0y0(A1(OH)~~) [0H]0y0(0H)
Elsevier Science Publishers B.V. All rights reserved
.
(3)
412
S. Veesler, R. Boistelle
/ Supersaturation
and growth rates of hydrargillite
l’he parentheses and brackets refer to activities and concentrations respectively: y is the activity coefficient of the species under considera-
where R is the molar gas constant and ~.4Gthe activation free energy for crystallization. The kinetic coefficient k0 depends on temperature and
tion, the subscript zero referring to equilibrium, According to eqs. (2) and (3), /3 should be written
solution composition. C and C0 are the actual and equilibrium concentrations of dissolved Al(OH)3 but, traditionally, for explaining the growth rates of hydrargillite crystals, C and Co are expressed as grams of Al203 per liter of solution. As an example, a 2 molar Al(OH)3 solution contains 102 g Al(OH)3 i.e. 156 g A1203, the conversion factor A1203 A1(OH)3 being 1.53. In addition, the NaOH concentrations are always transformed into Na20 concentrations (2NaOH Na~O+ H20), 40 g NaOH/l for instance being 31 g Na20/l. Actually, the choice of C C0 in eq. (6) is not really judicious in the present case, because in the ternary system Al(OH)3 + NaOH + H20 (A1203 + Na20 + H20), the solubility of hydrargillite changes drastically with NaOH concentration. Accordingly, the caustic concentration must be known precisely, the difference C C0 depending on the units taken for A1203 concentrations. On the other hand, the non-dimensional numbers /3 C/C0 and o~ (C C0)/C0 j~ dude the effect of NaOH on solubility and do not suffer this drawback. Hereafter, we intend to show that results obtamed in different caustic solutions can be anal-
[Al(OH)~][OH]oy(A,(QH)~-)y~OH-) =
[Al(OH)~]O[oH~]y~M(OH)~)y(OU_) (4) .
Unfortunately, there is no information in the literature concerning the activity coefficients in highly concentrated alumina caustic solutions, so that we temporarily assume that the ratio between the different activity coefficients in eq. (4) is one. This is similar to the approximation of Davies [31,which supposes that the activity coefficients depend only on the species valence and ionic strength of the solution. Finally, if the NaOH concentrations are not too different in supersaturated and saturated solutions, eq. (4) reduces to
=
[Jsd(oH)~1 [AJ(oH)~1~’
—~
—
—
—
(5)
This equation, which is commonly written /3 C/C0, is rarely used by the authors dealing with hydrargillite crystallization, most results being discussed in terms of the difference (C C0), as in a chemical reaction. =
—
=
Only a few authors [4—11]studied the crystallization of hydrargillite from caustic solutions. They mainly aimed at describing the growth mechanisms of Al(OH)3 or improve the crystallization process in industrial plants (Bayer process). In all cases, the linear growth rates G of hydrargillite crystals were discussed on the basis of equations like 1, (6) G k(C C0)’ =
—
with k=k0 exp(—ziG/RT),
(7)
—
ysed in a simple way using /3 or a- instead of C C0 for expressing supersaturation. The solubility data of hydrargillite we used for unit conversions were taken from a review of solubility data by Misra [12]. Concerning the linear growth rates of hydrargillite, only the data of King [4] and White and Bateman [8] could be analysed, because all raw data were available. The results of Overbey and Scott [51and Mordini and Cristol [61could not be analysed due to a lack of information on the raw data. Halfon and Kaliaguine [7] on the one hand and Misra and White [10] on the other hand did not report any influence of caustic soda. However, in both cases,over the limited caustic concentrations were only varied ranges (107—114 and 80—120 g/l in Na 20 units respectively) and it is likely that its influence was hidden by some scattering of the experimental points. —
3. Growth rates of Al(OH)3
=
S. Veesler, R. Boistelle
/ Supersaturation and
4. Discussion
growth rates of hydrargillite
413
20 84 gil
In table 1, we summarize the data of White and Bateman [81, who measured the overall growth rates G of Al(OH)3 aggregates at 89.5°C in different caustic Na20 solutions at different supersaturations (C C0). These data and Misra’s equation [12] were used to calculate the a- values. In the diagram of G =f(C C0), the experimental points lie on 4 curves (fig. 1), each of them corresponding to the specific caustic concentrations given in table 1. Once supersaturations are normalized with respect to solubility, all points lie on one single curve (fig. 2). The measurements of King [4] were carried out at 80°Con single crystals along the c axis of hydrargillite or perpendicular to this direction (table 2). In the plot of G =f(C C0), there is an important scattering of the experimental points due to the influence of Na20 on the solubility of hydrargillite (fig. 3a). Once supersaturations are normalized, all points but one also lie on the same curve (fig. 3b). In both these figures, only
147 g/l
/
•
/ ~.
9/I
/
/
gIl
113
10
—
, 5
—
0
—~
0
20
40
60 C~C0gil
80
100
1 20
Fig. 1. Growth rates of hydrargillite at different concentrations of caustic soda expressed in Na20 units (after ref. 18]).
—
20
C0 (g/l)
C-C0 (g/l)
u
84 84 84
56.5 56.5 56 5
20 30 40
0.35 0.53 0 71
3.40 6.60 17 00
113 113 113 113
82.9 82.9 82.9 82.9
20 30 40 50
0.24 0.36 0.48 0.60
1.65 3.20 6.50 10.00
147 147 147 147 147
119.0 119.0 119.0 119.0 119.0
20 30 40 60 90
0.17 0.25 0.33 0.50 0.75
0.93 1.88 3.71 7.30 17.50
165 165 165 165
141.4 141.4 141.4 141.4
30 40 60 100
0.21 0.28 0.42 0.71
1.12 2.00 4.30 15.00
.
~ 1 5
-
~
~
Table! Growth rates G of hydrargillite at 89.5°C[8] as a function of normalized supersaturation in different caustic solutions Na20 (g/l)
.
-
~—
—
g~
_______
.
147 ~/l 165 gil
~
:
/
S
5
G (gm/h)
0
0.2
0 .
0.4
.
0.6
0.8
.
Fig. 2. Growth rates displayed in figure 1 after normalization of supersaturation.
Table 2 Growth rates G of hydrargillite single crystals at 80°C[4] parallel and normal to the c axis of the crystals Na20 (g/l) 106.4 128.8 106.4 107.1 69.9 106.4
C0 (g/l) 64.2 83.2 64.2 64.7 37.7 64.2
C — C0 (g/l) 45.0 59.8 53.7 61.9 41.2 71.4
o0.70 0.72 0.84 0.96 1.09 1.11
G (II c) (~sm/h) 1.4 1.9 2.7 4.5 4.1 9.2
G (Ic) (j.~m/h) 1.1 1.7 2.2 3.5 3.5 7.0
414
S. Veesler, R. Boistelle
a
0
/ Supersaturation and growth rates of hydrargillite
l06~4 9/’.
—
~
8
8 -
E
E
_..9
~
c~.7
4
5/
•
2
(D
4
+
.
.
c.l2.8~4/l4 : .
2
0
0 60 65 70 75 0.6 0.7 0.8 0.9 I 1.1 1.2 c-c 0 gil a Fig. 3. Growth rates of hydrargillite single crystals along their c axis (after ref. [4]):(a) as a function of concentration difference; (b) after supersaturation normalization. 40
45
50
55
the growth rates along the c axis have been plotted to avoid overlapping, At constant temperature, 80 and 89.5°Cin the present case, the growth rate is only dependent on supersaturation, when it is expressed as /3, because caustic concentration and supersaturation are inter-dependent variables. In other terms, solubility of Al(OH)3 decreases, for instance, with decreasing caustic concentration. This would resuit in an increase of supersaturation and consequently of the crystal growth rate if the actual concentration of solute remains unchanged. On the other hand, if supersaturation /3 is readjusted to the same initial value, taking the solubility variation into account, then the crystal growth rate remains constant. From this standpoint, the growth rate is independent of caustic concentration. It is noteworthy that Overbey and Scott [5] proposed a model for explaining the growth rate of hydrargillite (actually the liquor decomposition versus time) on the basis of the second order rate equation given by Pearson [11]. This equation can be written with our symbols dC1 —
dt
of refs. [5,11], the results may be fitted by this equation, but actually the term in parentheses has no real physical significance as N should not be added to C0 to define supersaturation.
5. Conclusion Both examples we have given show clearly that expressing supersaturation as a nondimensional number, normalized with respect to solubility, is more appropriate than expressing supersaturation as a concentration difference. The same concentration differences do not correspond to the same supersaturations, as they are dependent on solubilities which in turn depend on caustic concentrations. From the present analysis, if normalized supersaturations are used, including the caustic effect on solubility, it also turns out that the caustic concentration does not affect the growth rates of hydrargillite, at least for Na2O concentrations ranging from 80 to 165 g/l.
_____
=
~
C0
+ N)
(8)
where A~is the overall area of the crystallites present in the liquor and N the concentration of NaOH at equilibrium. According to the authors
Acknowledgments The authors are indebted to Aluminium Pechiney for financial support and to Mrs. D. Laporte and M.C. Toselli for technical assistance.
S. Veesler, R. Boistelle
/ Supersaturation and
References [1] S. Veesler, Cristallisation de l’hydrargillite: cinétique et attrition, Thesis, Université Aix—Marseille III (1991). [2] C.F. Baes and R.E. Mesmer, The Hydrolysis of Cations (Wiley, New York, 1976) p. 1 [3] C.W. Davies, J. Chem. Soc. 19 (1938) 2093. [4] W.R. King, in: Light Metals, Conf. Proc. (1973) p. 551. [5] T.L. Overbey and CE. Scott, in: Light Metals, Conf. Proc. (1978) p. 163. [6] J. Mordini and B. Cristol, in: Proc. Yugoslav Intern. Symp. on Aluminium, Univ. Edvarda Kardelja, Ljubljana, 1982, p. 168.
17]
growth rates of hydrargillite
415
A. Halfon and S. Kaliaguine, Can. J. Chem. Eng. 54 (1976) 160.
[8] E.T. White and S.H. Bateman, in: Light Metals, Conf. Proc. (1988) p. 157. [9] D.R. Audet and J.E. Larocque, in: Light Metals, Conf. Proc. (1989) p. 21. [10] C. Misra and E.T. White, Chem. Eng. Progr. Symp. Series 67, No. 110 (1971) 53. [11] T.G. Pearson, The Chemical Background of the Aluminium Industry, Monograph No. 3 (Royal Institute of Chemistry, London, 1955). [12] C. Misra, Chem. md. 20 (1970) 619.