Fate of corrosion products released from stainless steel in marine sediments and seawater. Part 4: Hatteras abyssal red clay Page: 11 of 32
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Table 5 lists the distribution of indigenous metals among different
chemical fractions and shows that -50-60% of the extractable fractions of Cr,
Mn, Fe, Co, and Zn were associated with materials soluble in 1N hydroxylamine
hydrochloride in 25% acetic acid. Materials soluble in this reagent are
generally amorphous Mn and Fe oxides coating the clay mineral substrate
(Chester and Hughes, 1967). Most of the remaining extractable Cr (-40%),
and about a third of the extractable Cu appear to have been weakly complexed.
Major fractions (25-36%) of Mn, Co and Ni were extracted by DTPA and may
have been present as adsorbed cations. Organic complexation appears to
account for a large amount (25-40%) of extractable Fe, Ni, Cu and Zn.
The data on Table 5 also show that about two-thirds of total Mn and Cu
were extracted by the methods employed, whereas about 40-50% Co, Ni and Zn
and less than 10% of Cr and Fe were removed. With respect to three other
sediments having somewhat different properties (Table 6), the distribution of
extractable Cr, Mn, Fe and Cu in Hatteras abyssal red clay most strongly
resembles that of the Northeast Pacific red clay.
CORROSION PRODUCT DISTRIBUTION
Neutron-activated 347 stainless steel specimens were exposed to sediment
slurry under aerobic and non-oxygenated conditions for a period of 94 days.
The conditions of exposure, the 60Co activity of the stainless steel specimens,
and the amounts of 60Co released are given in Table 7. The redox potential
measurements for air-sparged and N2, C02-sparged sediment slurries were +410
and +60 mv, respectively, at the end of the experimental period. The lack of
sufficient degradable organic matter apparently inhibited the formation of
true anoxic conditions, i.e., Eh <-150 mv.
The total activity of 60Co released to the sediment (Table 7) was
determined by radioanalyses of aliquots of the exposure medium. The quantity
of corrosion products released was estimated by comparing the 60Co activity
in the exposure medium with that of the whole metal specimen. The data in
Table 7 indicate that, on the basis of weight of material released per year
per unit area of exposed stainless steel surface, the presence of 02 produced
increased corrosion: 3.2 pg year-1 cm-2 were released into aerated sediment
and 1.0 pg year-1 cm-2 were released when 02 was absent. Increased corrosion
in the aerated vs non-oxygenated system was also observed for corrosion
experiments using Northeast Pacific red clay (Schmidt, 1982a).
Aerated Sediment.
Samples of Hatteras abyssal red clay slurry containing corrosion products
were subjected to sequential extraction according to the procedure outlined in
Table 1 and Figure 1. The results of 60Co assay of the extracts are presented
in Table 8 and summarized in Table 10 and Figure 3. Fractions 1 through 8
(Table 8) are relatively labile substances and constitute about 84% of the
60Co activity released (Table 10). Among these fractions, about 7% is soluble
or easily dissolved. Materials extracted by DTPA (assumed to be adsorbed
cations) are most prominent, accounting for 57% of the labile material. The4
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Schmidt, R. L. Fate of corrosion products released from stainless steel in marine sediments and seawater. Part 4: Hatteras abyssal red clay, report, July 1, 1982; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc1061471/m1/11/: accessed July 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.