Sulfide bisulfide complexes

For these reasons, it is useful to evaluate the effects of forming or not forming aqueous sulfide complexing agents and sulfide precipitates on radionuclide solubilities and aqueous speciation. Therefore, calculations were performed for key radionuclides for two cases (1) reduction of sulfate to sulfide and bisulfide was allowed to occur as Eh was lowered and (2) sulfate reduction as a function of Eh was prohibited so that sulfate was the only sulfur complexing agent available at all Eh values. 

Figure 3. Rough ratios of equilibrium concentrations for inorganic (31.321 and organic (20-221 copper species to those of the aquo ion Cu2+, with sulfide complexes plotted as functions of free bisulfide ion level and set at the lower limit in Table II.

Polysulfides and Sulfide. The polysulfide complexes of Ag and Cu have been added to the model in an attempt to reduce the apparent oversaturation with Ag2S(s) calculated for San Francisco Bay waters (12). Calculation of the activity of polysulfide iotis requires the assumptions 1) the quantity of Sg (free sul-fur) is not a limitation on its reaction with bisulfide (HS ) to form polysulfides and 2) polysulfides are in equilibrium with bisulfide. 

In this context, pioneering investigations of the metal behavior under anoxic conditions in the Gotland Basin have been described in detail by Kremling (1983). Models have been developed by comparing field measurements with equilibrium calculations to predict the maximum solubility of metals in anoxic waters. Furthermore, it has been demonstrated that the solubility of the individual trace metals is controlled by the formation of bisulfide or poly sulfide complexes. 

From the reactions (1.86) and (1.87) and chemical equilibrium involving Cu-and Fe-chloro-complexes, iso-concentration contours for Cu- and Fe-minerals are drawn on logfo -pH diagram (Fig. 1.32 Crerar and Barnes 1976). Above calcida-tions were carried out, assuming that Cu- and Fe-chloro-complexes are dominant Cu- and Fe-species (Crerar and Barnes 1976). Bisulfide-, thio- and carbonate-complexes are also important in determining solubility of sulfides as well as chloro-complexes (Table 1.5, Brimhall and Crerar (1987)). Above argument clearly indicates that dominant base metal complexes in hydrothermal solution depend on concentration of ligand, pH, foj, temperature and so on. 

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