Geochemical modelling of acid mine drainage in mill tailings : Quantification of kinetic processes from laboratory to field scale

• Main Author: Salmon, Sally Ursula
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: KTH, Byggvetenskap 2003
• Subjects: geochemistry; biogeochemistry; Kristineberg; Northern Sweden
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3638

Assessment of the potentially acidic, heavy metal-ladenleachates that leave deposits of sulfide ore mill tailings andevaluation of various possible options for mill tailingremediation are scientific problems of increasing practicalimportance. High costs may be associated with the mill tailingremediation, not least after recent changes in Swedish andEuropean environmental legislation. This thesis presents amethodology for studying and quantifying geochemical processesthat contribute to generation of so-called acid mine drainage(AMD). The methodology builds from first principles regardinggeochemical processes, and is based on geochemicalcharacterisation of the mill tailings combined with explicitmodel quantification of the effect of factors, such astemperature, pH, and mineral (BET) surface area, that influencemineral weathering rates. Application of the modellingmethodology to a case study site, Impoundment 1, Kristineberg,northern Sweden, including quantification of slow processesthrough literature rate laws, successfully reproduced the pHand relative concentrations of major ions in the impoundmentgroundwater. Absolute concentrations of most major ions, withthe exception of Zn, were 1-2 orders of magnitude higher in themodel than in the field, which is consistent with the commonlyobserved scale dependence of mineral weathering rates; however,application of a single calibration factor, Xr=10-2, to all weathering rate expressions, sufficed toaccount for this apparent scale dependence. Subsequent laboratory determination of mineral weatheringrates in Impoundment 1 tailings indicated that rates for themajor minerals pyrite (FeS2) and aluminosilicates were in fact 1-2 orders ofmagnitude lower in the ~50-year-old tailings than ratesreported in the literature. Weathering rates of chalcopyrite(CuFeS2) and sphalerite (ZnS) were by contrast 1-3 ordersof magnitude greater than predicted by the literature rate lawsthat were used in the modelling study. While the mechanism ofZn release requires further investigation for ...