57
Dissolved Cu in the bottom water and in the porewater was lower than the
international standard for drinking water (16 jaM, WHO). Therefore, under present
physicochemical conditions, no direct influence of dissolved Cu on the quality of
ground water and bottom water is to be expected.
SO42- reduction during the mineralization of organic matter leads to the production
of HS'. Highly insoluble metal-sulfides can form when traces of the HS" ion are
present in the porewater. Consequently, the mobility of these metals can be
significantly lowered (F6rstner and Wittmann 1979; Carignan and Nriagu 1985;
Dahrnke et al. 1991; Williams 1992; Morse and Arakaki 1993). Another possibility is
the coprecipitation of Cu with FeS:
Cu 2+ + HS" ---~ CuS + H +
Fe 2+ + HS" ---), FeS + H +
With electron microprobe analysis, Lee and Kittrick (1984a) found that sulfur
(33%) and Fe (27 %) are the most important associations for particulate Cu in
contaminated soil samples. X-ray dot pictures showed that Cu and the associated
elements are scattered rather than concentrated along the edge of the particles. This
indicates that Cu has been precipitated with sulfur as CuS or coprecipitated as
chalcopyrite (CuFeS2), instead of being adsorbed on the particle surface. In a
laboratory experiment, Wallmann (1992a) found that Cu concentration in a
suspension solution began to decrease when HS" was detected in the solution,
suggesting the formation of CuS in the solution.
HS- produced by the reduction of SO4 2- rapidly precipitates Fe 2+ in the form of
FeS nH20 (amorphous) or makinawite (FeS), which are further converted into pyrite.
Carignan and Lean (1991) reported that H2S concentrations in Williams Bay
sediments are controlled by the formation of iron monosutfides. They found that the
Ion Activity Products (IAP) of Fe 2+ and S 2- remains just above the solubility product
(Ksp) of mackinawite (FeS). Thus, Fe 2+ concentrations in the porewater can be used
to estimate HS- concentrations in anoxic sediments (Billen 1982, Morfett et al. 1988).
The formation of iron monosulfides is confn'med by the black color of the sediment
cores in the study area. The calculated HS" values range between 10 -7 and 10 -8 M,
which is in good agreement with the data from literature (Femex et al. 1986;
Carignan and Lean 1991).
The Saturation Index (SI) for CuS (covellite) is presented in Fig.4.24 and 4.25.
Strong supersaturation was found at all sites. The mostly probable explanation is that
Cu can be strongly complexed by organic colloids, which was not considered in the
calculation. This explanation is consistent with the observation that Cu has a strong
affinity for organic ligands. Boulegue et al. (1982) found that 90 % of dissolved Cu
was complexed as Cu-organo-sulfur complex in the porewater of Great Marsh,
Delaware. Similar results were reported by Elderfield (1981) for the porewater of
Narragansett Bay sediments.
Douglas et al. (1986) measured 22-67 % of dissolved Cu in the porewater from
Narragansett Bay. He found that the dissolved organic carbon (DOC) increased with
depth due to the mineralization of organic matter. This could enhance the mobility of
Cu by organic-Cu complexation. Indeed, dissolved Cu decreased with depth. It
Dissolved Cu in the bottom water and in the porewater was lower than the
international standard for drinking water (16 jaM, WHO). Therefore, under present
physicochemical conditions, no direct influence of dissolved Cu on the quality of
ground water and bottom water is to be expected.
SO42- reduction during the mineralization of organic matter leads to the production
of HS'. Highly insoluble metal-sulfides can form when traces of the HS" ion are
present in the porewater. Consequently, the mobility of these metals can be
significantly lowered (F6rstner and Wittmann 1979; Carignan and Nriagu 1985;
Dahrnke et al. 1991; Williams 1992; Morse and Arakaki 1993). Another possibility is
the coprecipitation of Cu with FeS:
Cu 2+ + HS" ---~ CuS + H +
Fe 2+ + HS" ---), FeS + H +
With electron microprobe analysis, Lee and Kittrick (1984a) found that sulfur
(33%) and Fe (27 %) are the most important associations for particulate Cu in
contaminated soil samples. X-ray dot pictures showed that Cu and the associated
elements are scattered rather than concentrated along the edge of the particles. This
indicates that Cu has been precipitated with sulfur as CuS or coprecipitated as
chalcopyrite (CuFeS2), instead of being adsorbed on the particle surface. In a
laboratory experiment, Wallmann (1992a) found that Cu concentration in a
suspension solution began to decrease when HS" was detected in the solution,
suggesting the formation of CuS in the solution.
HS- produced by the reduction of SO4 2- rapidly precipitates Fe 2+ in the form of
FeS nH20 (amorphous) or makinawite (FeS), which are further converted into pyrite.
Carignan and Lean (1991) reported that H2S concentrations in Williams Bay
sediments are controlled by the formation of iron monosutfides. They found that the
Ion Activity Products (IAP) of Fe 2+ and S 2- remains just above the solubility product
(Ksp) of mackinawite (FeS). Thus, Fe 2+ concentrations in the porewater can be used
to estimate HS- concentrations in anoxic sediments (Billen 1982, Morfett et al. 1988).
The formation of iron monosulfides is confn'med by the black color of the sediment
cores in the study area. The calculated HS" values range between 10 -7 and 10 -8 M,
which is in good agreement with the data from literature (Femex et al. 1986;
Carignan and Lean 1991).
The Saturation Index (SI) for CuS (covellite) is presented in Fig.4.24 and 4.25.
Strong supersaturation was found at all sites. The mostly probable explanation is that
Cu can be strongly complexed by organic colloids, which was not considered in the
calculation. This explanation is consistent with the observation that Cu has a strong
affinity for organic ligands. Boulegue et al. (1982) found that 90 % of dissolved Cu
was complexed as Cu-organo-sulfur complex in the porewater of Great Marsh,
Delaware. Similar results were reported by Elderfield (1981) for the porewater of
Narragansett Bay sediments.
Douglas et al. (1986) measured 22-67 % of dissolved Cu in the porewater from
Narragansett Bay. He found that the dissolved organic carbon (DOC) increased with
depth due to the mineralization of organic matter. This could enhance the mobility of
Cu by organic-Cu complexation. Indeed, dissolved Cu decreased with depth. It