Calcium dihydroxide

Endpoint summary

Additional information

Appearance/physical state/colour: Based on the available data, calcium dihydroxide is an odourless, colourless crystalline substance.

Melting point: In a standard test, the melting point for calcium dihydroxide (92.1 % purity) was determined to be > 450°C. Literature data for calcium carbonate also show the melting point to be greater than 450°C. In a Thermogravimetric analysis study, a sample of hydrated lime (calcium dihydroxide content of 91.3 %) was found to begin decomposition at 360 °C and to melt at 510 °C, whilst a sample with calcium dihydroxide of 60.0 % and calcium carbonate content of 35.9 %, respectively, showed decomposition at 356 °C and 571 °C with melting at approximately 490 °C and approximately 800 °C.

Boiling point: According to Annex VII, section 7.3, column 2 of Regulation No. 1907/2006, a boiling point study is not required for solids that either melt above 300 °C or decompose before boiling. The melting point of calcium dihydroxide is >450 °C and the melting point of grades of calcium dihydroxide containing calcium carbonate up to 35% is also expected to be >450 °C. Hence a boiling point study is not required.

Relative density: The relative density of calcium dihydroxide (hydrated lime; purity = 98.2%) measured in accordance with OECD TG 109 using the pycnometer method is 2.22.

The relative density of calcium carbonate, based on a weight of evidence using data from several peer reviewed handbooks, is 2.7. Thus it may be expected that grades of calcium dihydroxide with up to 35% calcium carbonate will have a relative density in the range of 2.2 - 2.7.

Particle size distribution (Granulometry): Total Dustiness (airborne fraction): 143.50 mg/g (experimental results, DMT Report). Mass median aerodynamic diameter of airborne fraction: 12.62 µm (GSD: 4.61 µm) (distribution fitted to cascade impactor data). Fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD): Head (ET): 50.7 %; Tracheobronchial (TB): 1.4 %; Pulmonary (PU): 4.0 %

Vapour pressure: According to Annex VII, section 7.5, column 2 of Regulation No. 1907/2006, a vapour pressure study is not required for solids that melt above 300 °C. Calcium dihydroxide is a solid with a melting point of > 450 °C and the melting point of grades of calcium dihydroxide containing calcium carbonate up to 35% is also expected to be >450 °C. Hence, a vapour pressure study is not required for this substance.

Partition coefficient: According to Annex VII, section 7.8, column 2 of Regulation No. 1907/2006, a study of the n-octanol/water partition coefficient does not need to be performed for an inorganic substance.

Water solubility of calcium dihydroxide: The water solubility of calcium dihydroxide (purity = 92.1 %) was determined in a study performed according to EU Method A.6. In this study, a value of 1844.9 mg/L was obtained, and the pH of the solution was 12.4.

The water solubility of calcium carbonate, as determined in a study performed according to OECD TG 105, is 16.6 mg/L at 20 °C.

A water solubility study was performed using a method based on EU test method A.6. Two grades of hydrated lime were used, the first containing 91.3 % calcium dihydroxide, whilst the second contained 60.0 % calcium dihydroxide and 35.9 % calcium carbonate. The water solubility for the grade with high calcium dihydroxide content was 935 mg Ca/L (equivalent to 1725 mg Ca(OH)2/L) whilst for the high calcium carbonate content grade the water solubility was 910 mg Ca/L (equivalent to 1680 Ca(OH)2/L). For both grades the pH of the solution was 12.4.

Surface tension: The surface tension of calcium dihydroxide (hydrated lime; purity = 98.2%) was determined by the OECD harmonised ring method in accordance with OECD TG 115. The surface tension of a 1 g/l aqueous solution of the substance was found to be 72.0 mN/m. As the result is greater than 60 mN/m, calcium dihydroxide was not considered to be surface active.

No data are available for calcium carbonate. However, based on structure, surface activity is not expected. Therefore, grades of calcium dihydroxide containing up to 35%% calcium carbonate are also not expected to be surface active.

Flash point: According to Annex VII, section 7.9, column 2 of Regulation No. 1907/2006, a study of the flash point does not need to be performed for an inorganic substance.

Auto-flammability: Calcium dihydroxide purity = 92.1 %) showed no relative self-ignition temperature below 400 °C in a test performed according to EU Method A.16.

Calcium carbonate was found to be not auto flammable in a study performed using Method N.4 of the UN Recommendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, 4th revised edition, 2003. On this basis it may be concluded that grades of calcium dihydroxide containing up to 35% calcium carbonate will not be auto flammable.

Flammability: Calcium dihydroxide is not flammable based on the results of a preliminary screening test performed according to EU Method A.10.

Similarly, calcium carbonate (purity = 92.1 %) is not flammable based on the results of a preliminary screening test performed according to Method N.1 of the UN Recommendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, 4th revised edition, 2003. Therefore it may be concluded that grades of calcium dihydroxide containing up to 35% calcium carbonate will also be not flammable.

Explosiveness: According to the provisions of EU A.14 method, expert judgement considered calcium dihydroxide to be void of any chemical structures commonly associated with explosive properties.

The explosive properties of calcium carbonate have also been predicted negative based on the chemical structure and experience of handling and use. Therefore grades of calcium dihydroxide containing up to 35% calcium carbonate may also be predicted to have no explosive properties.

Oxidising properties: According to the provisions of EU A.17 method, expert judgement considered calcium dihydroxide as a non-oxidising substance.

The structure of calcium carbonate was assessed for chemical groups that would indicate oxidising properties and was found to contain no such groups. Therefore, the oxidising properties of calcium carbonate have been predicted negative based on the chemical structure and experience of handling and use. On this basis all grades of calcium dihydroxide may be considered to be non-oxidising, irrespective of the calcium carbonate content.

Stability in organic solvents and identity of relevant degradation products: This study does not need to be conducted for inorganic substances (cf. section 7.15 Column 2 Annex IX of Regulation (EC) 1907/2006).

Dissociation constant: The dissociation constants in water of calcium dihydroxide could not be deternined using OECD TG 112 as the test item was an inorganic and the test methods were not applicable. Alternatively, the pH of a saturated solution of the test item was measured to be 12.4 which correlated with the value of 12.6 found in the literature for the pKa of calcium (II) ion.

For calcium carbonate, no experimental testing was considered possible according to OECD TG 112 for the following reasons:

1). The test material has been determined to be essentially insoluble in water. Therefore, determination of the dissociation constant(s) using a potentiometric titration, spectrophotometric and/or conductivity method would not be feasible.

2). The test material contains no significant chromophoric group(s) and thus, will absorb very little in the ultra-violet/ visible region of the spectrum. Therefore, determination of the dissociation constant(s) using a spectrophotometric method would not be practical.

Therefore, experimentally determined dissociation constants were taken from Albert and Serjeant, Ionisation Constants of Acids and Bases, A Laboratory Manual, 1971. The values presented below are those for carbonic acid, the free acid form of the test material:

pKa1 = 10.4 (functional group - carboxylic acid)

pKa2 = 6.4 (functional group - carboxylic acid)

Viscosity: Viscosity is a property of liquids. Since calcium dihydroxide is a solid at ambient temperature (ca. 20 °C) such a study does not need to be conducted for this substance (melting point: >450 °C, which is in accordance with section 1, Annex XI of Regulation (EC) 1907/2006 (REACH).

Calcium carbonate is a solid which remains solid at temperatures significantly above room temperature (melting point >825 °C). OECD Guideline no. 114 on the viscosity of liquids, indicates that the substances to be tested must be liquid at room temperature, and therefore a study of the viscosity of calcium carbonate is not required.