Interaction of cations with iron monosulfide (mackinawite) in dilute solutions and seawater /
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| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1992.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | The metastable iron sulfide mineral mackinawite commonly forms in anoxic sediments in the region where elevated concentrations of dissolved Mn[^2+], Co[^2+], and Ni[^2+] are also observed. There is, consequently, a potential for significant interactions between these dissolved metals and mackinawite. Adsorption of Mn[^2+], Co[^2+], and Ni[^2+] on mackinawite and their coprecipitation with mackinawite have been investigated in order to determine if such interactions are important for metal diagenesis in anoxic sediments. The very fine-grained nature of mackinawite results in adsorption being quantitatively much more important than coprecipitation for Mn2+. Adsorption of Mn[^2+], Co[^2+], and Ni[^2+] follow a Langmuir-type isotherm in dilute solutions. However, the adsorption of Co[^2+] in seawater cannot be explained by a Langmuir-type isotherm, possibly because of surface precipitation. The partition coefficient for Mn[^2+] with mackinawite in dilute solutions at 25°C is 4.8 ([plus or minus] 0.5) x 10^-3. It approximately doubles for every 20°C increase in temperature, and, over the range of conditions investigated, was found to be nearly independent of pH and the mole fraction of MnS. The partition coefficient is 1.8 ([plus or minus]0.35) x 10^-3 in seawater of S=35 at 25°C. It also decreases by about a factor of 3 at high precipitation rates, possibly because of the formation of a greater proportion of amorphous-FeS rather than mackinawite or an inability of the sorption reaction to keep up with the rate of formation of new surfaces. The partition coefficient of Co[^2+] decreases with decreasing temperature from 29 at 25°C to 5 at 5°C. The partition coefficient of Ni[^2+] in mackinawite decreases with decreasing temperature from 280 (25°C) to 50 (5°C). There are large deviations in Co[^2+] and Ni[^2+] partition coefficients from the ideal thermodynamic distribution coefficient, which may be explained by the high degree of supersaturation for these metal coprecipitation experiments or non-ideal behavior. Adsorption experiments showed that other metals (Cd[^2+], Cu[^2+], Cr[^3+], and Zn[^2+]) can be strongly adsorbed on mackinawite. However, these metals are not dominantly associated with pyrite and may, via diagenesis, be incorporated into other authigenic minerals such as carbonates. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Oceanography." |
| Physical Description: | xiv, 185 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |