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Physical & Chemical properties

Water solubility

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Reference
Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
no data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
This study does not follow normalised testing guideline and GLP, but was performed according to an relevant method for this type of inorganic substance.
Reason / purpose:
reference to same study
Qualifier:
no guideline followed
Principles of method if other than guideline:
In this study the water solubility of Lithium cryolite has been determined as function of time and pH.
In the time-dependence experiment, a defined quantity of test item has been put in de-ionized water and stirred during different duration from 2 hours to 7 days at room temperature.
In the pH-dependence experiment, a defined quantity of test item has been put in de-ionized water and the pH of the suspension was set to 4, 7 and 9 by adding small amounts of aqueous hydrofluoric acid or lithium hydroxide. The suspensions were stirred for two days at room temperature.
In both experiments, the suspensions were then filtered and the solid dried at 120°C and re-weighted. Analyses of the solutions and solids were conducted in order to determine the solubility and to qualitatively describe the eventual hydrolysis process occurring in the solutions.
GLP compliance:
no
Other quality assurance:
other: (laboratory certified according to ISO/TS 16949)
Type of method:
flask method
Key result
Water solubility:
1.1 g/L
Conc. based on:
test mat.
Loading of aqueous phase:
20 g/L
Incubation duration:
2 d
Temp.:
20 °C
pH:
>= 6.1 - <= 6.3
Remarks on result:
other: no significant time functionality dependency.
Details on results:
OBSERVATIONS IN SOLUBILITY (TIME DEPENDENCE)
The suspensions formed consisted of very small particles with a height adhesion to surfaces. Because of this, the residue could be only partially applied to the filter paper, making a gravimetric determination of the solubility impossible (adhesion to Buechner funnel). This has been demonstrated by a partial repetition of the experiments where glass filter crucibles were used instead of Buechner funnel.
The solubility of Li3AlF6 shows only minimal time dependence, after 2 hours a solubility of 1.10 g/kg and after 7 days of 1.13 g/kg was determined.
pH values between 6.1 and 6.3 were measured in the clear filtered solutions.

A reproducible measurement of the fluoride content with a fluoride selective electrode was only possible after steam distillation by adding of H3PO4 in order to transfer the complex ions into a non-complex form (F-). Therefore the fluoride in the Li3AlF6 solutions is presumably mainly present as (AlF6)3- complex.

OBSERVATIONS IN SOLUBILITY AS FUNCTION OF pH
The suspensions formed consisted of very small particles with a height adhesion to surfaces. Because of this, the residue could be only partially applied to the filter paper, making a gravimetric determination of the solubility impossible (adhesion to Buechner funnel).
The pH could not be continuously adjusted. Thus the pH of the solutions primarily adjusted to pH7 and 9 decreased during the experiment significantly (pH 4 : 4, pH 7 : 5.5, pH 9 : 5.9).

The undissolved residue increases with the increase of the pH, while the solubility determined by the lithium content of the solution does not change significantly. The slightly increased value for pH 9 is considered to be an effect of the pH adjustment by adding LiOH.

ln native and acidic solution there is no remarkable evidence of hydrolysis, being the mol ration of Li, Al and F in solution close to the theoretical 3:1:6 of Li3AIF6. Lithium cryolite will most probably mainly dissociate into Li+ and (AIF6)3-. This is also supported by the results of the XRD analysis.
However, the reduced aluminium content in the clear pH 9 solution may probably result from a precipitation of aluminium fluoride, aluminium hydroxifluoride or aluminium hydroxide.

Table 1: Results of solubility - time dependence

Li3AlF6
BWF11016
Buechner tunnel with filter paper filter crucible
  2 hours 4 hours 1 day 2days 7 days 2 hours 2 hours
initial weight [g] 3,99 4,01 4,04 4,00 4,00 4,00 4,00
residue (1) [g] 3,57 3,66 3,63 3,62 3,61 3,797 3,795
pH filtrate (2) 6,1 6,2 6,3 6,3 6,3    
F- (electrode) (3)
[mg/kg]
665 666 698 705 678    
Al (ICP)(4)
[mg/kg]
157 164 176 179 167 155 153
Li (ICP) (4)
[mg/kg]
141 143 144 144 146 153 153
Solubility [g/kg]
(Li content, solution)
1,10 1,11 1,12 1,12 1,13 1,19 1,19
Solubility [g/1] (5)
gravimetrie
          1,02 1,03
Sum of F,AI,Li [g/kg] 0,96 0,97 1,02 1,03 0,99    
w%F 69,06 68,45 68,57 68,58 68,42 - -
w%AI 16,30 16,86 17,29 17,41 16,85 - -
w%Li 14,64 14,70 14,15 14,01 14,73 - -
Mol ratio Li 3,0 3,0 3,0 3,0 3,0 3,0 3,0
Mol ratio Al 0,9 0,9 0,9 1,0 0,9 0,8 0,8
Mol ratio F 5,2 5,1 5,3 5,4 5,1 - -
XRD residue (6) Li3AlF6 Li3AlF6 Li3AlF6 Li3AlF6 Li3AlF6
Evaporation residue (7) - - - Li3AlF6
LiF (small)
-
(1) solid after filtration and drying at 120° C
(2) pH of the filtered solution
(3) fluoride selective electrode (H3P04, steam distillation)
(4) inductively coupled plasma
(5) S (g/1) = (suspended mass Li3AIF6- Solid recovered on filter after drying) *5
(6) dried solid on filter
(7) solid after vaporisation of solution

Table 2 : Results of the solubility as function of pH

Li3AlF6
BWF11016
pH4 pH 7 pH9
initial weight [g] 4,00 3,99 4,04
residue (1) [g] 3,22 3,26 3,75
pH filtrate (2) 4,0 5,5 5,9
F- (electrode) (3)
[mg/kg]
726 683 489
Al (ICP)(4)
[mg/kg]
173 166 54
Li (ICP) (4)
[mg/kg]
145 143 154
Solubility [g/kg]
(Li content, solution)
1,13 1.11 1,20
Sum of F,AI,Li [g/kg] 1,0 1,0 0,7
Mol ratio Li 3,0 3,0 3,0
Mol ratio Al 0,9 0,9 0,3
Mol ratio F 5,5 5,2 3,5
XRD residue (6) Li3AlF6 Li3AlF6 Li3AlF6
Evaporation residue (7) Li3AlF6
LiF (small)
Li3AlF6
LiF (small)
Li3AlF6
LiF (small)
(1) solid after filtration and drying at 120° C
(2) pH of the filtered/decanted solution
(3) fluoride selective electrode (H3P04, steam distillation)
(4) inductively coupled plasma
(5) filtered/decanted solution
(6) dried solid on filter
Conclusions:
Interpretation of results (migrated information): soluble (1000-10000 mg/L)
Lithium hexafluoroaluminate demonstrates a solubility of 1.1 g/kg ± 0.1 g/kg without significant time functionality.
Executive summary:

In this study the water solubility of Lithium cryolite has been determined as function of time and pH.

In the time-dependence experiment, a defined quantity of test item (4g) has been put in de-ionized water (200 mL) and stirred during different duration from 2 hours to 7 days at room temperature.

In the pH-dependence experiment, a defined quantity of test item (4g) has been put in de-ionized water (200 mL) and the pH of the suspension was set to 4, 7 and 9 by adding small amounts of aqueous hydrofluoric acid or lithium hydroxide. The suspensions were stirred for two days at room temperature.

In both experiments, the suspensions were then filtered and the solid dried at 120°C and re-weighted. Analyses of the solutions and solids were conducted in order to determine the solubility and to qualitatively describe the eventual hydrolysis process occurring in the solutions. These analyses included Fluoride, Lithium and Aluminium content of solution. The solubility of Lithium Cryolithe was determined based on the measured lithium content of the solutions and considering the molar mass of the different entities.

In both experiments, the suspensions formed consisted of very small particles with a height adhesion to surfaces. Because of this, the residue could be only partially applied to the filter paper, making a gravimetric determination of the solubility impossible (adhesion to Buechner funnel).

The solubility of Li3AlF6 shows only minimal time dependence, after 2 hours a solubility of 1.10 g/kg and after 7 days of 1.13 g/kg was determined. pH values between 6.1 and 6.3 were measured in the clear filtered solutions.

A reproducible measurement of the fluoride content with a fluoride selective electrode was only possible after steam distillation by adding of H3PO4 in order to transfer the complex ions into a non-complex form (F-). Therefore the fluoride in the Li3AlF6 solutions is presumably mainly present as (AlF6)3- complex.

In the pH-dependence experiment, the pH could not be continuously adjusted. Thus the pH of the solutions primarily adjusted to pH7 and 9 decreased during the experiment significantly (pH 4 : 4, pH 7 : 5.5, pH 9 : 5.9).

The undissolved residue increases with the increase of the pH, while the solubility determined by the lithium content of the solution does not change significantly. The slightly increased value for pH 9 is considered to be an effect of the pH adjustment by adding LiOH.

Based on the above data, Lithium cryolite demonstrates a solubility of 1.1 g/L ± 0.1 g/L at room temperature without significant time functionality.

ln native and acidic solution there is no remarkable evidence of hydrolysis, being the mol ration of Li, Al and F in solution close to the theoretical 3:1:6 of Li3AIF6. Lithium cryolite will most probably mainly dissociate into Li+ and (AIF6)3-. This is also supported by the results of the XRD analysis.

However, the reduced aluminium content in the clear pH 9 solution may probably result from a precipitation of aluminium fluoride, aluminium hydroxifluoride or aluminium hydroxide.

Description of key information

Lithium cryolite demonstrates a solubility of 1.1 g/L ± 0.1 g/L at room temperature without significant time functionality.

Key value for chemical safety assessment

Water solubility:
1.1 g/L
at the temperature of:
20 °C

Additional information

One reliable key study is available for this endpoint. In this study the water solubility of Lithium cryolite has been determined as function of time and pH.

In the time-dependence experiment, a defined quantity of test item (4g) has been put in de-ionized water (200 mL) and stirred during different duration from 2 hours to 7 days at room temperature.

In the pH-dependence experiment, a defined quantity of test item (4g) has been put in de-ionized water (200 mL) and the pH of the suspension was set to 4, 7 and 9 by adding small amounts of aqueous hydrofluoric acid or lithium hydroxide. The suspensions were stirred for two days at room temperature.

In both experiments, the suspensions were then filtered and the solid dried at 120°C and re-weighted. Analyses of the solutions and solids were conducted in order to determine the solubility and to qualitatively describe the eventual hydrolysis process occurring in the solutions. These analyses included Fluoride, Lithium and Aluminium content of solution. The solubility of Lithium Cryolithe was determined based on the measured lithium content of the solutions and considering the molar mass of the different entities.

In both experiments, the suspensions formed consisted of very small particles with a height adhesion to surfaces. Because of this, the residue could be only partially applied to the filter paper, making a gravimetric determination of the solubility impossible (adhesion to Buechner funnel).

The solubility of Li3AlF6 shows only minimal time dependence, after 2 hours a solubility of 1.10 g/kg and after 7 days of 1.13 g/kg was determined. pH values between 6.1 and 6.3 were measured in the clear filtered solutions.

A reproducible measurement of the fluoride content with a fluoride selective electrode was only possible after steam distillation by adding of H3PO4 in order to transfer the complex ions into a non-complex form (F-). Therefore the fluoride in the Li3AlF6 solutions is presumably mainly present as (AlF6)3- complex.

In the pH-dependence experiment, the pH could not be continuously adjusted. Thus the pH of the solutions primarily adjusted to pH7 and 9 decreased during the experiment significantly (pH 4 : 4, pH 7 : 5.5, pH 9 : 5.9).

The undissolved residue increases with the increase of the pH, while the solubility determined by the lithium content of the solution does not change significantly. The slightly increased value for pH 9 is considered to be an effect of the pH adjustment by adding LiOH.

Based on the above data, Lithium cryolite demonstrates a solubility of 1.1 g/L ± 0.1 g/L at room temperature without significant time functionality.

ln native and acidic solution there is no remarkable evidence of hydrolysis, being the mol ration of Li, Al and F in solution close to the theoretical 3:1:6 of Li3AIF6. Lithium cryolite will most probably mainly dissociate into Li+ and (AIF6)3-. This is also supported by the results of the XRD analysis.

However, the reduced aluminium content in the clear pH 9 solution may probably result from a precipitation of aluminium fluoride, aluminium hydroxifluoride or aluminium hydroxide.