The durability of a potassium permanganate protective coating (passivation) on potentially acidic waste rock was examined for preventing acid generation. There is limited biological and physical data on the environmental impact and durability of passivation technology. The objective was to determine if exposure of passivated acid waste rock to repeated cycles of intensive root growth would affect coating stability. Passivated treatments were compared to limed waste rock in columns with and without plants. Passivation stability was determined by measuring the pH, electrical conductivity (EC), iron, and sulfate of drainage leachate and saturated paste extracts by the use of a hydrogen peroxide stability test. The treatments were kept at field capacity and were leached once a month with reverse osmosis (RO) water. The stability study showed 1) no root system effects on passivation stability: and 2) no difference in expression of potential acidity of waste rock between passivation and adding lime at the rate of 15% (by weight) to the waste rock.