Pre and Post Reaction of Mine Waste Pile Pyrite Acidification
Faculty Mentor Information
Dr. Jeff Langman, University of Idaho
Presentation Date
7-15-2026
Abstract
Our research looks into understanding acid rock drainage (ARD) generated from the 60 million-tonne pyritic Main Waste Stockpile at the Red Dog Mine, Alaska. We employed a five-step, non-sequential extraction on samples from a 52-m depth profile, conducted before and after 5-day saturated tests. This procedure allowed us to isolate mineralogical fractions contributing to the potential release of iron (Fe) and sulfur (S) with introduction of water, ranging from highly soluble secondary sulfates to poorly crystalline Fe(III) oxyhydroxides and primary sulfides. Results indicated early-stage acid generation is driven by rapid depletion of water-soluble "stored acidity," such as from the dissolution of melanterite, while previously unresolved reservoirs of iron reside in the poorly crystalline oxyhydroxide fraction. Extractions revealed depth-dependent variations, with the highest concentrations of iron and sulfate located at the base of the stockpile. Despite the rapid release of the labile pools during saturation, the primary sulfide fraction remained highly stable across all post-batch samples. This confirms that the majority of the original pyrite mass remains unreacted. By linking these fraction-specific mass balances with aqueous chemistry, we refine interpretations of early-stage weathering mechanisms, supporting long-term ARD predictions, emphasizing that the stockpile will remain a source of acid generation for centuries.
Pre and Post Reaction of Mine Waste Pile Pyrite Acidification
Our research looks into understanding acid rock drainage (ARD) generated from the 60 million-tonne pyritic Main Waste Stockpile at the Red Dog Mine, Alaska. We employed a five-step, non-sequential extraction on samples from a 52-m depth profile, conducted before and after 5-day saturated tests. This procedure allowed us to isolate mineralogical fractions contributing to the potential release of iron (Fe) and sulfur (S) with introduction of water, ranging from highly soluble secondary sulfates to poorly crystalline Fe(III) oxyhydroxides and primary sulfides. Results indicated early-stage acid generation is driven by rapid depletion of water-soluble "stored acidity," such as from the dissolution of melanterite, while previously unresolved reservoirs of iron reside in the poorly crystalline oxyhydroxide fraction. Extractions revealed depth-dependent variations, with the highest concentrations of iron and sulfate located at the base of the stockpile. Despite the rapid release of the labile pools during saturation, the primary sulfide fraction remained highly stable across all post-batch samples. This confirms that the majority of the original pyrite mass remains unreacted. By linking these fraction-specific mass balances with aqueous chemistry, we refine interpretations of early-stage weathering mechanisms, supporting long-term ARD predictions, emphasizing that the stockpile will remain a source of acid generation for centuries.