Abstract:A five-year, humidity-cell experiment was used to study the weathering evolution of a low-sulfide, granitic waste rock at 5 and 22 °C. Only the rock with the highest sulfide content (0.16 wt %) released sufficient acid to overcome a limited carbonate acid-neutralization capacity and produce a substantial decline in pH. Leached SO 4 and Ca quickly increased then decreased during the first two years of weathering. Sulfide oxidation continued to release acid and SO 4 after carbonate depletion, resulting in an increase in acid-soluble elements, including Cu and Zn. With the dissolution of Al-bearing minerals, the pH stabilized above 4, and sulfide oxidation continued to decline until the end of the experiment. The variation in activation energy of sulfide oxidation correlates with changes in sulfide availability, where the lowest activation energies occurred during the largest releases of SO 4 . A decrease in sulfide availability was attributed to consumption of sulfide and weathered rims on sulfide grains that reduced the oxidation rate. Varying element release rates due to changing carbonate and sulfide availability provide identifiable
OPEN ACCESSMinerals 2014, 4 258 geochemical conditions that can be viewed as neutralization sequences and may be extrapolated to the field site for examining the evolution of mineral weathering of the waste rock.
The OB/OD site is located near the western edge of the Tularosa Basin (fig. 1) at an altitude of approximately 5,700 ft on the pediment slope of the San Augustin and San Andres Mountains. A thin soil profile consisting mostly of granite wash covers much of the terrain, but granite outcrops are visible across the surface of the pediment. Vegetation consists mostly of perennial grasses, woody brushes, yucca, prickly
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