Sounds well intentioned. But..

I feel that there are any metrics supporting claims of environmental benefits, like saving water, treating water, removing pollutants.

Is iron oxide a pollutant? By itself I would not have though so.

What makes this different from finding a mineral resource and extracting it to sell?

EDIT: A couple of informative and interesting follow up links

Wikipedia on Acid mine drainage.

Professor [Carl Kirby] paints a bright picture with 'yellow boy' [from Pennsylvania's acid mine drainage]