[pfdietz]

It's also possible to neutralize acid drainage with non-carbonate minerals, for example olivine.

The sulfide tailings of some mining regions, as in Spain, may in the future become exploited as sources of sulfur. Today most sulfur comes from desulfurization of oil and natural gas, but in a post-fossil fuel age that source will not be available, so the large amounts of pyrite in these tailings could be exploited instead.

[littlexsparkee]

That's the other component I didn't grok at first - the sheer amount of tailings and their contribution to carbon footprint since mining could result in 200:1 waste pyrite to copper. Looking at near term emissions from mining underestimates the share of emissions from these ores since this process can take decades to centuries to unfold. Neutralization with something like limestone would be a high emissions process itself IIUC.

[pfdietz]

Yes, limestone is where the CO2 comes from.