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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
other: handbook data
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: peer-reviewed expert judgement
Principles of method if other than guideline:
Qualitative statement
GLP compliance:
no
Preliminary study:
no data
Transformation products:
not specified
Remarks on result:
not measured/tested
Remarks:
See "Any other information on results incl. tables"

The basic consideration is that silica dissolves according to : SiO2 + H2O = Si(OH)4. At low concentrations most species are present as monomers, at higher concentrations polymerisation will occur. Most soluble silicates are in the form: M2O . mSiO2 . nH2O where M = alkali metal, predominantly Na, but also K. The index m (molar ratio) ranges between 0.5 - 4, most commonly m = 3.3. Stability depends to a large extent on pH, above pH 10.6 the solutions are chemically stable. The increase of ionic strength accelerates nucleation and deposition and decreases the SiO2 solubility. Coating of surfaces by organic matter may hamper dissolution, but at the same time Si(OH)4 may form complexes with organic matter, a process which favours dissolution.

Description of key information

Key value for chemical safety assessment

Additional information

The basic consideration is that silica dissolves according to: SiO2+ H2O = Si(OH)4. At low concentrations most species are present as monomers, at higher concentrations polymerisation will occur. Most soluble silicates are in the form: M2O x mSiO2 x nH2O where M = alkali metal, predominantly Na, but also K. The index m (molar ratio) ranges between 0.5 - 4, most commonly m = 3.3. Stability depends to a large extent on pH, above pH 10.6 the solutions are chemically stable. The increase of ionic strength accelerates nucleation and deposition and decreases the SiO2solubility. Coating of surfaces by organic matter may hamper dissolution, but at the same time Si(OH)4may form complexes with organic matter, a process which favours dissolution (Falcone 1997).