Disodium disilicate

Water solubility

Description of key information

The test substance disodium disilicate (delta-crystalline) was examined for its water solubility. Following the results of the flask method and the experimental uncertainties affecting the analytical methods the water solubility of the test substance was defined in this study to be soluble at 20 °C ≥ 700 g/L (very soluble).

Key value for chemical safety assessment

Water solubility:

700 g/L

at the temperature of:

20 °C

Additional information

The water solubility of disodium disilicate (delta-crystalline) was determined according to EC – guideline 92/69/EEC A.6, Flask – method except for the following deviations.

-  Due to the expected high solubility of the test item in water (> 500 g/L) the weighed amount of the test item could not be the fivefold amount required for saturation

-  Because of the known dependence of the test items solubility on the time of equilibration, the time of stirring was extended in amendment to the described procedure in the test guideline.

- The low hydration rate of the test item prevents the accomplishment of the preliminary test according to the testing guideline

-  Therefore sufficiently great amounts of disodium disilicate (delta-crystalline) were added with water. These mixtures were subsequently stirred in a temperature – controlled water bath for at minimum 8 days. After phase separation (centrifugation) at test temperature the concentration of the test item was determined by two independent analytical methods.

-  Gravimetrically by drying weighed aliquots of the saturated solution at 450°C until constant weight occurred.

-  Determination of the content of silicon in the saturated solution by ICP-OES analysis. The water solubility of the test item was calculated from the determined Si – concentration and the certified content of Si in the test item (31% w/w).

Both analytical methods were affected by experimental uncertainties:

Firstly, the high viscosity of the saturated solution which made it very difficult to admeasure an exact volume of the samples. Secondly, the slight turbidity of the samples showed that there were still some undissolved particles which could not be separated by centrifugation or filtration and thirdly the saturated solutions were very unwilling to release the bound water also by drying at high temperatures.

The following water solubility´s were determined by the two analytical methods:

Gravimetric analysis (drying at 450°C): Cwater solubility = 880 ± 13 g/L

ICP-OES analysis (Si): Cwater solubility = 727 ± 21 g/L

Due to the uncertainties mentioned above and because of the fact that both results attested the test item nearly miscibility with water the water solubility of disodium disilicate (delta-crystalline) as the result of this study was defined as follows:

Cwater solubility of disodium disilicate (delta-crystalline) at 20°C > 700 g/L.