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Appendices 5-13 - Nautilus Cares - Nautilus Minerals

Appendices 5-13 - Nautilus Cares - Nautilus Minerals

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Concentration (ug/kg ore) (log scale)<br />

100000<br />

10000<br />

1000<br />

100<br />

10<br />

1<br />

Cu Zn Cd Pb<br />

6 Deg<br />

12 Deg<br />

24 Deg<br />

Figure 5: Mass of metal (!g) dissolved per kg of ore at 6, 12 and 24 o C (note 6 o C<br />

data from Phase 1 experiment).<br />

Metal sulfides are generally very insoluble, but they are thermodynamically unstable<br />

in the presence of oxygen and water, undergoing complex oxidation/reduction<br />

reactions (Richardson, 1995, Tsang and Parry, 2004). The result of the oxidation is<br />

the production of sulfate and mobilization of metals. The overall oxidation of metal<br />

sulfides can be described by equation 1, but this is an oversimplification of a complex<br />

multi-step reaction.<br />

MS(s) + 2O2 "> M 2+ + SO4 2- (1)<br />

The results from these elutriation experiments clearly show the mobilization of metals<br />

and concomitant release of sulfate (Table 5 and 6 and Figure 6). The Phase 1<br />

experiment showed that virtually all the sulfate was released at time zero with little<br />

increase over time (Table 5). This would indicate that there was an existing oxidized<br />

surface on the ore sample. Figure 6 shows there is an increase in release of sulfur<br />

with temperature, however the substantial increase at 24 o C is largely due to one of the<br />

replicates being approximately 100mg/L higher than the other 2 (Table 6).<br />

14

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