2D Acid Rock Drainage Kinetics

Rock & air exposure

Crushing (surface area) 55%

Oxygen availability 60%

Limestone remediation 0%

pH over time

drainage pH neutral (pH 7)

Readouts

Drainage pH

6.9

Acid rate

0.0

Metal mobilization

Low

Limestone consumed

0.0

How it works

Acid rock drainage forms when the mineral pyrite (FeS₂), common in mine waste and exposed rock, meets both oxygen and water. The reaction is real and well studied:

4 FeS2 + 15 O2 + 14 H2O
    -> 4 Fe(OH)3 + 8 H2SO4

Crushing (surface area) — the reaction only happens at the mineral surface, so crushing the same amount of rock into smaller fragments exposes far more surface and speeds up acid generation, exactly as it does at real mine sites.
Oxygen availability — pyrite oxidation needs O₂; flooding or sealing a waste pile away from air starves the reaction, while a loose, well-aerated pile reacts fastest.
Drainage pH — starts near neutral and falls as sulfuric acid (H₂SO₄) accumulates in the water; the rate of the pH drop depends directly on how fast pyrite is oxidizing above.
Metal mobilization — iron, aluminum and manganese hydroxides that are insoluble near neutral pH become increasingly soluble as pH drops, so the water carries more dissolved heavy metals the more acidic it gets — a major secondary contamination pathway.
Limestone remediation — crushed limestone (CaCO₃) dissolves and neutralizes acid, raising pH back toward neutral and re-precipitating metals out of solution; this is the standard passive-treatment method used at real sites.

Pyrite fragment Oxygen (O₂) Acid (H₂SO₄) Metal ion (Fe/Al/Mn) Limestone