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Hydrolysis

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Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
supporting 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 and stability 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
Remarks:
(laboratory certified according to ISO/TS 16949)
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
Not applicable
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
No data
Buffers:
aqueous hydrofluoric acid and lithium hydroxide
Details on test conditions:
SOLUBILITY (TIME DEPENDENCE)

A series of test was carried out by weighing an amount of approximately 4 grams of Li3ALF6 into a PE broad-neck bottle along with 200 mL de-ionized water and stirred for 2 hours, 4 hours, 1 day, 2 days and 7 days. After stirring at room temperature the suspensions were filtered and the solid dried at 120°C and re-weighed.
Further on, 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:
- XRD on the solids and evaporated solutions
- Fluoride content of solution (F-electrode after steam distillation)
- Lithium content of solution (ICP)
- Aluminium content of solution (ICP)

The solubility was determined based on the measured lithium content of the solutions:

S (g/kg) = determined concentration Li (g/kg) * molar mass of Li3AlF6 / molar mass of Li / 3

SOLUBILITY AS FUNCTION OF pH

An amount of approximately 4 grams of Li3AlF6 was weighted into a PE broad-neck bottle along with 200 mL de-ionized water and stirred. The pH of the suspensions 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. After that time the suspensions were filtered and the solid dried at 120°C and reweighed.
Further on, 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:
- XRD on the solids and evaporated solutions
- Fluoride content of solution (F-electrode after steam distillation)
- Lithium content of solution (ICP)
- Aluminium content of solution (ICP)

The solubility was determined based on the measured lithium content of the solutions:

S (g/kg) = determined concentration Li (g/kg) * molar mass of Li3AlF6 / molar mass of Li / 3
Duration:
2 d
Temp.:
20 °C
Duration:
7 d
Temp.:
20 °C
Number of replicates:
No data
Positive controls:
no
Negative controls:
no
Preliminary study:
See the section "details on results"
Test performance:
See the section "details on results"
Transformation products:
no
Details on hydrolysis and appearance of transformation product(s):
See the section "details on results"
Key result
pH:
4
Temp.:
20 °C
Remarks on result:
hydrolytically stable based on preliminary test
Key result
pH:
7
Temp.:
20 °C
Remarks on result:
hydrolytically stable based on preliminary test
Key result
pH:
9
Temp.:
20 °C
Remarks on result:
hydrolytically stable based on preliminary test
Other kinetic parameters:
See the section "details on results"
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.

See tables reported in the section "water solubility".

Validity criteria fulfilled:
not applicable
Conclusions:
The substance is not hydrolysed in water.
Executive summary:

 In this study the water solubility and stability 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 and therefore it is considered as not hydrolysed in water.

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.

Endpoint:
hydrolysis
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:

Description of key information

Based on the chemical structure of Lithium Cryolite, it is expected to dissociate in water into various ions. Therefore, Lithium cryolite is not hydrolysed in water. Based on the OECD Testing Guideline 111, it is considered that the half-life of Lithium cryolite in water is above 1 year at 20°C.

Key value for chemical safety assessment

Half-life for hydrolysis:
1 yr
at the temperature of:
20 °C

Additional information

Based on its chemical structure, Lithium cryolite is easily dissociated into various ions in water. Therefore, it is not hydrolysed. This is supported by a reliable key study on water solubility and stability of Lithium cryolite 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. Therefore, the substance is considered as not hydrolysed.

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.