Figure 4
Calculated saturation index for each sample using the pH, Fe, Zn, and acid-volatile sulfide (AVS) concentrations measured in unfiltered samples: a) ZnS(s) (sphalerite) saturation index at four temperatures (1 bar); b) FeS2(s) (pyrite) and FeS(s) (mackinawite) saturation indices (25°C, 1 bar). Calculations at 25°C, 1 bar, were conducted using the thermodynamic database in MINEQL+. Saturation indices corresponding to 100°C, 150°C, and 240°C were calculated using equilibrium constants listed in Table 2. The calculations assumed 0.55 M Cl- and ionic strength corrections by the Davies equation for I = 0.5 M. N/A denotes that the total AVS was not available or total Zn concentration was below the analytical detection limit (< 0.3 μM) by ICP-OES.