Here’s an infographic created by Kimberly Hiral for the High Country News explaining the application of biochar in abandoned mine cleanup. From the article:
To help revegetate and stabilize the acidic, plant-hostile soils around mine sites, scientists are borrowing a technique from agricultural research: They apply biochar, a charcoal formed by heating plant and wood waste in the absence of oxygen, to the soil. The carbon-dense char, used to boost soil fertility on farms, helps plants get established in barren mine sites, reducing contaminated runoff.
More restoration coverage here.