Abstract

Tailings of Dukum mine in the vadose and saturated zone were investigated to reveal the mobility of metal elements and the condition of mineralogical solubility according to redox environments throughout the geochemical analysis, thermodynamic modelling, and mineralogical study for solid-samples and water samples(vadose zone; distilled water: tailings=5:1 reacted, saturated zone; pore-water extracted). In the vadose zone, sulfide oxidation has generated low-pH(2.72~6.91) condition and high concentration levels of SO₄^2- (561~1430 mg/L) and other metals(Zn:0.12~157 mg/L, Pb:0.06~0.83 mg/L, Cd :0.06~1.35 mg/L). Jarosite(KFe₃(SO₄)₂(OH)₆) and gypsum(CaSO₄ · 2H₂O) were identified on XRD patterns and thermodynamics modelling. In the saturated zone, concentration of metal ions decreased because pH values were neutral(7.25~8.10). But Fe and Mn susceptible to redox potential increased by low-pe values(7.40~3.40) as the depth increased. Rhodochrosite(MnCO₃) identified by XRD and thermodynamics modelling suggested that Mn⁴⁺ or Mn³⁺ was reduced to Mn²⁺. Along pH conditions, concentrations of dissolved metal ions has been most abundant in vadose zone
throughout borehole samples. It was observed that pH had more effect on metal solubilities than redox potential. However, the release of co-precipitated heavy metals following the dissolution of Fe-Mn oxyhydroxides could be the mechanism by which reduced condition affected heavy metal solubility considering the decrease of pe as depth increased in the saturated zone.

Keywords tailings, redox, transition metal, solubility, saturated index