Evaluation of acid mine drainage forming potential of a low-grade copper waste dump of Miduk mine according to chemical static methods, mineralogical studies and multivariate statistical analyses

The oxidation of sulphide minerals especially pyrite is the main source of acid production in mine waste rocks. Other sulphide minerals including chalcopyrite, covellite, and galena may be also responsible for acid production. Huge waste rock dumps with high sulphide content may generate acidic drainages as a result of oxidation and hydrolysis processes. Accordingly, acid production and neutralization potential of waste rocks were evaluated based on common Acid-Base Accounting (ABA) and Net Acid Generation (NAG) methods at dump No.7 from Miduk Mine. The results of chemical methods were compared with the mineralogical studies. Mineralogical analyses including X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe micro analysis (EPMA) were employed to comprehensively study primary sulphides and secondary minerals. There was a strong possibility to generate acid mine drainage (AMD) with very high metal content in dump No. 7. According to the results of NAPP and NAG pH, all samples were classified as potential acid forming (PAF). The lowest and the highest NAPP were determined in samples HB1 and HC1S with values 200.08 and 654.14 kgH2SO4/t. Regarding paste pH and NAG pH classification, all samples were categorised as extremely acid forming (EAF) and acid forming (AF) groups. Due to high pyrite oxidation, the portion of sulphate sulphur was ranged between 1.28 and 7.28 wt. According to both hierarchical cluster analysis (HCA) and principal component analysis (PCA), pH has an important role in the dissolution of waste materials. In addition, there was a strong positive correlation between Fe, Pb and As indicating the fact that they may have the same secondary mineral source in the soluble phase of the wastes. The results of the present study could be applied in the prediction of AMD generation and mine waste management.