The dissolution rate of chrysotile

Chrysotile can be linked to three diseases: lung cancer, asbestosis, and mesothelioma. The duration and intensity of exposure along with fiber size appear to play an important role in the development of the diseases. Chrysotile is part of the serpentine group which has the general composition of Mg₃Si₂O₅(OH)₄. The fluids in lung tissue contain very low concentrations of magnesium and silicon. As a result they are quite undersaturated with respect to chrysotile and chrysotile will dissolve. Its persistence in lung tissue is simply a result of its dissolution kinetics. The purpose of this study was to estimate the lifetime of a respirable size fiber of chrysotile in lung tissue. The dissolution reaction for chrysotile for pH's less than nine is: Mg₃Si₂O₅(OH)₄ + 6H⁺ = 3Mg²⁺+ 2H₄4SiO₄ + H₂0 This reaction proceeds in two steps. First, the magnesium hydroxide layer of the serpentine dissolves leaving behind the silica structure of the fiber. Then the silica dissolves. Therefore, the fiber lifetime depends upon the rate of silica release. Over the range of undersaturation expected for lung tissue, the rate of silica release was found to be independent of pH with the average rate being 5.94 (±3.05) x 10⁻¹⁰ moles m⁻² sec⁻¹. A shrinking fiber model was used to determine the relationship between dissolution time and fiber diameter. It was found that the most hazardous sized fiber of chrysotile (1 μm) would completely dissolve in about 9 months, consideration of one standard deviation above and below the mean of the rate constant gives estimates of the lifetime of a fiber ranging from 6 to 19 months.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Geology

Department dc:contributor.department

Geology

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

1991

Author dc:creator

• Hume, Lily Ann

Chair dc:contributor.committeechair

• Rimstidt, J. Donald

Committee members dc:contributor.committeemember

• Craig, James R.
• Zelazny, Lucian W.

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

etd-06082009-171119

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/33485