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Environmental fate & pathways

Hydrolysis

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Administrative data

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Cross-referenceopen allclose all
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study

Data source

Reference
Reference Type:
publication
Title:
Current considerations for the dissolution kinetics of solid oxides with silica
Author:
Löbbus M, Vogelsberger W, Sonnefeld J, Seidel A
Year:
1998
Bibliographic source:
Langmuir 14(16), 4386-4396 (American Chem. Society)

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
other: OECD 105 (water solubility)
Principles of method if other than guideline:
Development of a dissolution model for silicon oxides, taking into account Si-O bond cleavage and formation as well as protolysis of silanol groups. Three different models, pH dependent surface potential, diffuse double layer, and gel layer, are investigated.
Experiments carried out with a well-defined amorphous silica (Monospher 250 (Merck Darmstadt) included dependence on pH and NaCl concentration at 40 °C.
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Radiolabelling:
no

Study design

Analytical monitoring:
yes

Results and discussion

Preliminary study:
not relevant
Transformation products:
yes
Identity of transformation products
No.:
#1
Reference
Reference substance name:
Unnamed
IUPAC name:
orthosilicic acid / silicate ion
Identifier:
common name
Identity:
orthosilicic acid / silicate ion
Dissipation DT50 of parent compound
Key result
Remarks on result:
not determinable because of methodological limitations

Any other information on results incl. tables

The surface of silica may be covered by a partial hydrolysed gel layer when in contact with water (p. 4389). This layer is in equilibrium with the outer aqueous phase and constitutes a diffusion barrier for ions and water.

It is known and generally recognised that proton and hydroxide ion promoted dissolution plays a more prevailing role in the dissolution process than a simple hydrolysis of siloxane bridges (p. 4390).

The experimental part showed that there was a distinct pH dependence in the rate of dissolution, increasing with the pH increasing. However, the free dissolved SiO2 reached a maximum independent of the pH (Report, Table 1, Fig.. 4). It is concluded that the total amount of silica dissolved is relatively constant in a broad range of pH (1.1 < pH < 8.9) (p. 4393).

The level of maximum solubility was about 2.7 mmol SiO2/L (here: Monosphere, see also 4.8 Water solubility).

The degree of hydrolysis that may be involved in the dissolution process could not yet be solved.

Applicant's summary and conclusion