Taconite tailings are the ore-bearing, by-product rocks of iron mining, predominantly consisting of silicate and fine magnetite crystals. In recent years, the use of taconite tailings in pavement construction has increased considerably due to their superior mechanical properties. However, an environmental impact assessment of taconite tailings is required before their potential use in construction purposes. Taconite tailings may leach heavy and toxic metals, which could contaminate the soil, surface, and groundwater. Coarse, sand, fine, and composite sized taconite tailings were subjected to pH-dependent leaching tests in the pH range of 2 to 13 to investigate the leaching behavior of aluminum (Al), chromium (Cr), magnesium (Mg), and sulfate (SO4). In addition, Toxic Characteristic Leaching Procedure (TCLP), Synthetic Precipitation Leaching Procedure (SPLP), Water Leach Test (WLT), and U.S. Geological Survey leach test (USGS) were performed to evaluate the leaching behavior of taconite tailings in different environmental conditions. The test results show the highest concentrations of metals were leached from fine sized taconite, whereas the lowest amount of metal concentrations were leached from coarse sized taconite tailings. Magnesium and sulfate demonstrate a cationic leaching pattern, and aluminum and chromium indicate an amphoteric leaching pattern. Taconite tailings leached the highest metal concentrations in TCLP effluent; therefore, it is recommended as the most conservative test procedure to evaluate the leaching of these metals from taconite tailings.