Mathematical modeling the pyrite and chalcopyrite oxidation and pollution transportation in the Sarcheshmeh copper mine tailings

Mineral processing operation at the Sarcheshmeh porphyry copper mine has produced huge quantities of tailings materials containing sulfide minerals mainly pyrite and chalcopyrite. The tailings have been geochemically and mineralogically characterized to evaluate and gain insight into pyrite and chalcopyrite oxidation processes، acid mine drainage generation (AMD)، and transportation of the oxidation products. Five vertical trenches up to 4. 2 m deep were excavated from the tailings surface، and altogether 70 solid samples were taken in 0. 3 m intervals. The results show that pyrite with a content range of 4-6% was the main sulfide mineral found in the tailings which has major role in AMD generation. The lowest pH values were 2. 9، 3. 3، 3. 3، 3. 9 and 3. 0 which were determined at profiles A، B، C، D and E، respectively. The depth of oxidation zone in tailings varies between 1. 8 and 2 m at all five profiles. This paper also presents a numerical finite volume model to simulate sulfide minerals oxidation، AMD generation and transportation of the oxidation products. A shrinking core concept describes oxidation process. Gaseous diffusion was the main mechanism for oxygen transport through the tailings. The governing equations of the model were numerically solved using PHOENICS software. The role of Thiobacillus ferrooxidans bacteria was also considered in the oxidation and leaching processes. A close agreement was achieved between the field data and modeling results for pyrite and chalcopyrite oxidation. In this paper، capping the tailings as a reclamation scenario is further simulated to gain insight into how pollutants produced by pyrite oxidation in the tailings disposal site could be reduced if a cap is used to limit oxygen diffusion and surface recharge infiltration. The simulated results of scenario with cap show that oxygen source removal limited the oxidation process. However، transportation of the oxidation products continued for long time.