The dissolution rate of chrysotile
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The dissolution reaction for chrysotile for pH's less than nine is: Mg3Si205(OH)4 + 6H+ = 3Mg2+ + 2H4Si04 + 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 (Â±3.05) x 10-10 moles m-2 sec-I. 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 Î¼m) 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.
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