Acid generating waste rock is environmentally harmful because water draining through the rock contains sulfuric acid, heavy metals, and high sulfate levels. This study examines the impact and durability of a potassium permanganate coating (passivation) on preventing acid generation from acid generating waste rock. There is limited biological and physical data on the environmental impact and durability of passivation technology. The objective of this study was to measure the effect of freeze/thaw (FT) cycles on the stability of passivated and nonpassivated waste rock (high and low acid potential). Passivation effectiveness was determined by measuring drainage leachate and soil/rock pH and EC and stability testing with hydrogen peroxide. Samples were kept at field capacity. Samples were froze at -5 deg C for 8 hrs and thawed at 5 deg C for 8 hrs (one FT cycle). Samples were leached every 15 FT cycles and soils were tested every 30 FT cycles until 120 FT cycles were completed. Preliminary results (60 FT cycles) indicate passivation significantly reduced soil and leachate acidity and high acid potential waste rock created significantly lower pH values when compared to low acid potential waste rock. There were few significant differences for leachates and the soil/rock material when 60 FT values were compared to 0 FT. Leachate and soil/rock results show significant decline in EC when 60 FT cycles are compared to 0 FT cycles with the exception of the non-passivated high acid where a significant increase was noted. FT cycles did not damage the permanganate coating as measured by the peroxide stability test. Passivation caused significantly higher pH values when passivated samples were compared to non-passivated samples in the peroxide test. Passivation was effective in reducing environmentally harmful effects of acid generating waste rock and 60 FT cycles did not reduce the passivation coating effectiveness.