The oxidation of metallic particles, e.g., sulphide minerals, present in unconsolidated soils is a source of harmful dissolved ions which poses a contamination risk to groundwater and surface water. When associated with mine waste deposits such as tailings impoundments, the contaminated water discharges are known as acid mine drainage (AMD); this is a major environmental concern in the mining industry. Therefore, methodologies which can help to improve the long-term stability assessment of mine waste deposits and monitoring of contamination risk by AMD are needed. This thesis shows that the dc-resistivity method was suitable for imaging the subsurface structure of the Haveri Au-Cu mine tailings (SW Finland). When coupled with geochemical and mineralogical studies of tailings samples it was possible to characterize a potential reactive zone of AMD generation, as well as to delimit the associated contaminated water (i.e., the AMD discharge) inside the tailings material. The oxidation-reduction reactions at the metal sulphide mineral-electrolyte interface, i.e., the mechanisms which generate the AMD discharges, were investigated by means of the spectral induced polarization (SIP) method at the laboratory scale. The SIP response to oxidation of sulphide minerals (pyrite and pyrrhotite) promoted by dissolved and atmospheric O2 was analysed for synthetic mixtures of silica sand, whereas the SIP response to oxidation promoted by dissolved Fe3+ was analysed on a pyrite-sand mixture and real tailings material, respectively. The effect of redox-passive ions (non-oxidizing agents) and pore water pHw on the SIP response was also investigated. The SIP method shows unique sensitivity in detecting oxidation of sulphide minerals linked to a reduction in the capacitive properties at the metallic mineral surface-electrolyte interface, which diminishes the polarization magnitude given in terms of the imaginary conductivity and total chargeability. This SIP oxidation diagnostic is supported by the electrochemical model of Wong, which defines the IP-phenomenon on the basis of the activation of charge-transfer oxidation-reduction reactions or faradaic process at the metal mineral-electrolyte interface. Similarly, the SIP method is able to distinguish the in-situ oxidation-driven textural features of tailings (i.e., the oxidation degree of sulphide minerals) under saturated conditions. Additionally, the evolving physicochemical conditions from basic (reductive) to acid (oxidant) in the porous medium containing metal sulphide minerals, as expected during the development of AMD discharges, is well defined by the shift of the maximum relaxation of the SIP response towards higher frequencies, significantly impacting the relaxation time.
|Translated title of the contribution||Indusoidun polarisaation spektritutkimukset metallisten sulfidimineraalien läsnäollessa: mahdollinen sovellus happamien kaivosvesien muodostumisen seurantaan|
|Publication status||Published - 2015|
|MoE publication type||G5 Doctoral dissertation (article)|
- metallic sulphides
- acid mine drainage
- imaginary conductivity
- spectral induced polarization