Calcium dihydroxide

CHEMICAL SUBSTANCE IDENTIFICATION

Chemical name                 

 Calcium dihydroxide[1]

Synonyms                           

calcium hydroxide/caustic lime/hydrated lime/slaked lime [1]

IUPAC name

calcium dihydroxide [1]

CAS No

1305-62-0 [1]

REACH registration number

fully registered [1]

EC No

Molecular formula              

 CaH₂O₂ [1]

Substance group/chemical family

 Mono constituent substance/ inorganic [1]

Appearance

Physical state

Odour

Form

Colour

solid @  20°C and 1013 hPa [1]

Odourless (86%), Other (14%) [1]

Powder (71%), Crystalline (29%) [1]

colourless or white [3]

USES AND HANDLING ISSUES

Relevant identified uses

In mortar, plaster, cement and other binding and paving materials; in lubricants, drilling fluid, pesticides, fireproofing coatings, water paint; as egg preservative; manufacture of paper pulp; in SBR rubber vulcanization; in water treatment; as absorbant for carbon dioxide; dehairing hides, calcium salts, causticizing soda, depilatory, whitewash, soil conditioner, ammonia recovery in gas manufacturing, disinfectant, water softening, purification of sugar juices, petrochemicals, food additive as buffer and neutralizing agent, shell-forming agent (poultry) [3]

Handling considerations

Avoid contact with skin and eyes. Wear protective equipment. Keep dust levels to a minimum. Minimise dust generation. Enclose dust sources, use exhaust ventilation (dust collector at handling points). Handling systems should preferably be enclosed. When manually handling bags usual precautions should be paid to the risks outlined in the Council Directive 90/269/EEC.
Precautions for safe storage: Store under dry conditions. Minimise contact with air and moisture. Bulk storage should be in purpose – designed silos. Keep away from acids, significant quantities of paper, straw, and nitro compounds. Keep out of reach of children. Do not use aluminium for transport or storage if there is a risk of contact with water. [2]

PHYSICO-CHEMICAL PROPERTIES

Molecular weight                                  

74.09 g/mol [3]

Bulk density/Specific gravity

2.22 - 2.26 @ 20 - 22.5 °C [1]

pH

12.4 (aqueous solution saturated at 25 °C) [3]

Particle size

EC

Melting/Freezing point

450 - 580 °C @ 101.3 kPa [1]

Boiling point

Flash point

Flammability

Non flammable (100%) [1]

Vapour density

Vapour pressure

Solubility in water

999 - 1 844.9 mg/L @ 20 °C and pH 12.4 [1]

Solubility in organic solvents

Insoluble in ethanol, sugar. Soluble in glycerol.  Insoluble in alcohol. [3]

Solubility in inorganic solvents

Soluble in  ammonium chloride solution; soluble in acids with evolution of much heat [3]

Hydrolysis

Ionicity in water

Surface tension

72 mN/m @ 1000 mg/L and 20 °C [1]

Dispersion properties

Explosiveness

Non-explosive (100%) [1]

Other properties

Non oxidising (100%) [1]

Stability and reactivity

Chemical stability

Readily absorbs carbon dioxide from air forming calcium carbonate. [3]

Reactivity hazards

Phosphorus boiled with alkaline hydroxides yields mixed phosphines which may ignite spontaneously in air. [3]

Violent reaction with maleic anhydride, nitroethane, nitromethane, nitroparaffins, nitropropane, phosphorus. [3]

Reaction with polychlorinated phenols + potassium nitrate forms extremely toxic products. [3]

Corrosivity

Polimerization

Incompatibility with various substances

Phosphorus boiled with alkaline hydroxides yields mixed phosphines which may ignite spontaneously in air. [3]

Special remarks on reactivity

Physical, chemical and biological coefficient

Koc

Kow

pKa

12.6 @ 20 °C [1]

For calcium dihydroxide the pH of a saturated solution was 12.4, which correlated to the pKa of 12.6 reported in the literature for the Calcium (II) ion. [2]

log Kp

Henry-constant

ENVIRONMENTAL FATE AND BEHAVIOUR

Artificial pollution sources

Calcium hydroxide's production and use may result in its release to the environment through various waste streams; its use in drilling fluid, mortar, plaster, cement and other binding and paving materials and as a soil conditioner will result in its direct release to the environment. [3]

General terrestrial fate

In soil as well as in sediment-water systems, calcium (di)hydroxide will react and release calcium ions and hydroxyl ions. Therefore, relevant information on adsorption/desorption of calcium (di)hydroxide can be broadened to data on adsorption/desorption of calcium. The behaviour of hydroxyl ions depends on the pH buffer capacity of the tested medium. The pH buffer capacity is controlled by a whole range of processes (mineral dissolution/precipitation, protonation/deprotonation of pH dependent charge sites, reaction with CO2, biological processes etc.).

Therefore, determining a Kd-value for calcium dihydroxide is not relevant. Reliable Kd-values for calcium range from 5.3 L/kg to 49.1 L/kg and are added as supportive information. The Kd-concept is not relevant for hydroxyl ions, since the behaviour of these ions depends on the pH buffer capacity of the tested medium. [2]

General aquatic fate

When mixing calcium (di)hydroxide with water, the substance will be completely dissociated into its ions as the water solubility is relatively high compared to the environmental background concentration of calcium and due to dilution effects. Depending on the properties of the test medium, calcium (di)hydroxide will be strongly neutralised in the initial period after application, by formation of calcium carbonate. [2]

Aquatic toxicity is the function of an alkalinity effect. Addition of lime to soft water lakes has increased biological activity, possibly by providing a carbon dioxide reservoir. [3]

General atmospheric fate

Calcium hydroxide does not degrade by photooxidation; it is neutralized by absorption of atmospheric carbon dioxide. [3]

General persistence and degradability

Abiotic degradation and metabolites

Biodegradation and metabolites

Biotic degradation is not relevant for inorganic substances. [2]

Bioconcentration

no bioaccumulation potential [2,3]

Bioaccumulation is not relevant for calcium dihydroxide. In the aquatic environment and in soil, exposure to calcium dihydroxide actually comes down to exposure to calcium and hydroxyl ions. There will be no intake of calcium dihydroxide as such from water or soil, nor will calcium dihydroxide prevail under its original form in the organisms. Moreover, both the intake of the essential element calcium and the internal pH (hydroxyl ions) of an organism are actively regulated (homeostasis). [2]

Volatilization

Photolysis

Hydrolysis

Soil adsorption and mobility

In soil as well as in sediment-water systems, calcium (di)hydroxide will react and release calcium ions and hydroxyl ions. Therefore, relevant information on adsorption/desorption of calcium (di)hydroxide can be broadened to data on adsorption/desorption of calcium. The behaviour of hydroxyl ions depends on the pH buffer capacity of the tested medium. The pH buffer capacity is controlled by a whole range of processes (mineral dissolution/precipitation, protonation/deprotonation of pH dependent charge sites, reaction with CO2, biological processes etc.).

Therefore, determining a Kd-value for calcium dihydroxide is not relevant. Reliable Kd-values for calcium range from 5.3 L/kg to 49.1 L/kg and are added as supportive information. The Kd-concept is not relevant for hydroxyl ions, since the behaviour of these ions depends on the pH buffer capacity of the tested medium. [2]

ENVIRONMENTAL CONCENTRATIONS

Measured data

ECOTOXICOLOGICAL INFORMATION

General adverse effects on ecosystem

Acute toxicity (LC50, EC50)

Aquatic systems

LC50 (4 days) for freshwater fish: 50.6 mg/L [1]

LC50 (4 days)  for marine water fish: 457 mg/L [1]

EC50 / LC50 (48h) for freshwater invertebrates: 49.1 mg/L [1]

EC50 / LC50 (4 days) for marine invertebrates: 158 mg/L [1]

EC50 (72h) for freshwater algae: 184.57 mg/L [1]

EC50 (3 h) for microorganisms: 300.4 mg/L [1]

Terrestrial systems

Chronic toxicity (NOEC, LOEC)

Aquatic systems

EC10 / LC10 or NOEC (14 days) for marine invertebrates: 32 mg/L [1]

Terrestrial systems

EC10 / LC10 / NOEC (28 days) for terrestrial macroorganisms except arthropods: 2 g/kg soil dw [1]

EC10 / LC10 / NOEC (21 days) for terrestrial plants: 1.08 g/kg soil dw [1]

EC10 / NOEC (3.2 months) for soil microorganisms: 4 g/kg soil dw [1]

HUMAN HEALTH EFFECTS and PROTECTION

Routes of human exposures

Occupational exposure to calcium hydroxide may occur through inhalation of dust and dermal contact with this compound at workplaces where calcium hydroxide is produced or used. Use data indicate that the general population may be exposed to calcium hydroxide via ingestion of food and drinking water, and dermal contact with consumer products containing calcium hydroxide.  [3]

General effects

irritation eyes, skin, upper respiratory system; eye, skin burns; skin vesiculation; cough, bronchitis, pneumonitis [3]

Endocrine disruption

Mutagenicity

The results of in vitro gene mutation studies in bacteria, in vitro chromosome aberration studies in mammalian cells and in vitro gene mutation studies in mammalian cells performed using calcium dihydroxide or calcium carbonate were all negative. It is concluded that both calcium dihydroxide and calcium carbonate are not genotoxic and neither chemical nor mixtures of these chemicals warrants classification for mutagenicity under CLP. [2]

Carcinogenicity

Neither calcium, calcium dihydroxide nor calcium carbonate are carcinogenic. Classification for carcinogenicity is not warranted. [2]

Reprotoxicity

Calcium is an essential mineral nutrient for mammals including humans. Based on evaluation of a wealth of human medical and nutritional data it is concluded that calcium, therefore also calcium dihydroxide and calcium carbonate, does not pose any hazard for reproduction and/or developmental toxicity. Classification for toxicity to reproduction is not warranted. [2]

Teratogenicity

Calcium is an essential mineral nutrient for mammals including humans. Based on evaluation of a wealth of human medical and nutritional data it is concluded that calcium, therefore also calcium dihydroxide and calcium carbonate, does not pose any hazard for reproduction and/or developmental toxicity. Classification for toxicity to reproduction is not warranted. [2]

Skin, eye and respiratory irritations

Adverse effect observed (irritating) (skin, eye, respiratory) [1]

Based on experimental results and human data, calcium dihydroxide requires classification as Skin Irrit 2 (H315 – Causes skin irritation).

Based on experimental results and human data, calcium dihydroxide requires classification as Eye Damage 1 (H318 - Causes serious eye damage).

Based on human data as summarised and evaluated in the SCOEL recommendation it is proposed to classify calcium dihydroxide as STOT SE 3 (H335 - May cause respiratory irritation). [2]

Metabolism:

absorption, distribution & excretion

Exposure limits

DNEL(Workers, inhalation, local effects, long term):  1 mg/m³ [1]

DNEL (Workers, inhalation, local effects, acute/short term):  4 mg/m³ [1]

DNEL(General population, inhalation, local effects, long term):  1 mg/m³ [1]

DNEL (General population, inhalation, local effects, acute/short term):  4 mg/m³ [1]

According to OSHA [3]:

REL-TWA (Time Weighted Average): 5 mg/m³

PEL-TWA (8-Hour Time Weighted Average): 15 mg/m³ (total dust), 5 mg/m³ (respirable fraction)

According to ACGIH [3]:

TLV 8 hr Time Weighted Avg (TWA): 5 mg/ m³.

Drinking water MAC

Other information

Animal toxicity data

Acute toxicity (LD50)

 LD50 2 000 mg/kg bw (rat, oral route) No adverse effect observed Discriminating dose 2 000 mg/kg bw [1]

LC50 (4 h) 6.04 mg/L air (rat, inhalation route) Adverse effect observed Discriminating conc. 6 040 mg/m³ [1]

LD50 2 500 mg/kg bw (rabbit, dermal route) No adverse effect observed Discriminating dose 2 500 mg/kg bw [1]

Chronic toxicity (NOEL, LOEL)

Inhalation route - systemic effects (repeated dose toxicity) [1]: No adverse effect observed NOAEC 107 mg/m³ (subacute, rat)

No adverse effect observed NOAEC 107 mg/m³ (subacute, rat)

ENVIRONMENTAL STANDARDS AND REGULATIONS

REACH/CLP

Danger! According to the classification provided by companies to ECHA in REACH registrations this substance causes serious eye damage, causes skin irritation and may cause respiratory irritation.

Additionally, the classification provided by companies to ECHA in CLP notifications identifies that this substance causes severe skin burns and eye damage. [1]

According to  REACH registrations [1]:

H318: Causes serious eye damage

H315: Causes skin irritation

H335: May cause respiratory irritation

not classified

According to some CLP  notifications [1]:

H318: Causes serious eye damage

H315: Causes skin irritation

H335: May cause respiratory irritation

H314: Causes severe skin burns and eye damage

H370:  Causes damage to organs

H373:  May cause damage to organs through prolonged or repeated exposure

EINECS regulation

listed

OSHA regulations etc.

Disposal considerations

OTHER INFORMATION, SPECIAL REMARKS

Classification and proposed labelling with regard to toxicological data

CREATED, LAST UPDATE

Created

2020.06.09

Last update

2020.06.10

REFERENCES

[1] ECHA, Calcium dihydroxide, brief profile,  https://echa.europa.eu/hu/brief-profile/-/briefprofile/100.013.762,  Accessed: 2020.06.09.

[2] ECHA, Calcium dihydroxide, https://echa.europa.eu/hu/registration-dossier/-/registered-dossier/16187, Accessed: 2020.06.10.

[3]PubChem, Calcium-hydroxide. https://pubchem.ncbi.nlm.nih.gov/compound/Calcium-hydroxide#section=Structures, Accessed: 2020.06.10.