Titanium oxide sulphate

Hydrolysis

Administrative data

Endpoint:

hydrolysis

Type of information:

other: introductory part of a scientific publication

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Data taken from a scientific publication; study well documented, meets generally accepted scientific principles.

Data source

Reference

Reference 1

Reference Type:

secondary source

Title:

Unnamed

Year:

2007

Report date:

2007

Reference 2

Reference Type:

publication

Title:

Effect of TiOSO4 hydrothermal hydrolysis conditions on TiO2 morphology and gas-phase oxidative activity

Author:

Bavykin et al.

Year:

2007

Bibliographic source:

Research on Chemical Intermediates, 33, 449-464

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other:

Deviations:

not specified

Principles of method if other than guideline:

Data taken from the introductory part of a scientific publication, no details on methodology given.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

TiOSO4

IUPAC Name:

TiOSO4

Details on test material:

Chemical formula: TiOSO4
Substance name as mentioned in the study report: titanyl sulphate

Radiolabelling:

no

Study design

Analytical monitoring:

not specified

Results and discussion

Dissipation DT50 of parent compound

pH:

0

Temp.:

100 °C

DT50:

< 1 h

Type:

not specified

Remarks on result:

other: pH reflecting conditions with sulphuric acid in the reactor vessel.

Details on results:

No actually measured data on half-life time of TiOSO4 under reactor conditions (temperature ca. 100 °C, pH highly acidic) are given, however they can assumed to be very short. Based on evidence available, target compound TiOSO4 only can get stabilised in aqueous medium under the presence of sulphuric acid at highly acidic pH conditions. Therefore it is to be concluded that under environmentally and physiologically relevant pH conditions TiOSO4 will be transformed instantaneously to final hydrolysis product TiO2.

Any other information on results incl. tables

Short description of the step of hydrothermal hydrolysis during titanium dioxide pigment production (quoted from Grzmil):

"The hydroIysis of titanyl sulphate is one of the most important steps in titanium pigment production with a decisive impact on the pigment properties of the final product. During hydrolysis, the hydrated titanium dioxide precipitates from the titanyl sulphate solution in sulphuric acid. The hydrolysis of sulphate solutions of titanium is a complex physicochemical process which decides about the product. It is generally accepted that TiO2 particles grow to colloidal size and then the precipitation of the deposit takes place. There are different mechanisms of TiO2 formation from the titanyl sulphate solution, which depend on concentrations of TiOSO4. At high concentrations of titanyl sulphate, titanium is mainly present in -Ti2 +-O-Ti2 +-O- chains. On the other hand, when the concentration of TiOSO4 is low, titanyl ions are present mainly in the monomeric form. Under the hydrolysis condition, the chains attach to OH-groups (high concentration of TiOSO4). The solubility of partially hydrolysed -Ti(OH)2 -O-Ti(OH)2 -O- chains is lower than that of their precursers. This results in oversaturation and coagulation to 3TiO2 x 4H2O particles. Hydrolysis of the monomeric form (low concentration of TiOSO4) results in the formation of hydrolysed monomeric form of TiO(OH)2 (Bavykin et al., 2007). The hydrolysis process can be carried out by means of either the Blumenfeld (1924) or the Mecklenburg (1930) method."

Applicant's summary and conclusion

Validity criteria fulfilled:

not applicable

Conclusions:

Based on evidence available, target compound TiOSO4 only can get stabilised in aqueous medium under the presence of sulphuric acid at highly acidic pH conditions. Therefore it is to be concluded that under environmentally and physiologically relevant pH conditions TiOSO4 will be transformed instantaneously to final hydrolysis product TiO2.

Executive summary:

The publication of Grzmil 2007 gives a brief description of the step of hydrothermal hydrolysis during the industrial process of titanium dioxide pigment production. As not relevant for describing the behaviour of TiOSO4 under physiologically or environmentally relevant conditions, this publication shall be given as supporting information.

According to the publication, during hydrolysis the hydrated titanium dioxide precipitates from the titanyl sulphate solution in sulphuric acid. It is generally accepted that TiO2 particles grow to colloidal size and then the precipitation of the deposit takes place. There are different mechanisms of TiO2 formation from the titanyl sulphate solution, which depend on concentrations of TiOSO4. At high concentrations of titanyl sulphate, titanium is mainly present in -Ti2 +-O-Ti2 +-O- chains. On the other hand, when the concentration of TiOSO4 is low, titanyl ions are present mainly in the monomeric form. Under the hydrolysis condition, the chains attach to OH-groups (high concentration of TiOSO4). The solubility of partially hydrolysed -Ti(OH)2 -O-Ti(OH)2 -O- chains is lower than that of their precursers. This results in oversaturation and coagulation to 3TiO2 x 4H2O particles. Hydrolysis of the monomeric form (low concentration of TiOSO4) results in the formation of hydrolysed monomeric form of TiO(OH)2.

In summary, no actually measured data on half-life time of TiOSO4 under reactor conditions (temperature ca. 100 °C, pH highly acidic) are given, however they can assumed to be very short. Based on evidence available, target compound TiOSO4 only can get stabilised in aqueous medium under the presence of sulphuric acid at highly acidic pH conditions. Therefore it is to be concluded that under environmentally and physiologically relevant pH conditions TiOSO4 will be transformed instantaneously to final hydrolysis product TiO2.