Integrated Time-Lapse Geoelectrical-Geochemical Investigation at a Reactive Coal Washing Waste Pile in Northeastern Iran

Geochemical and geoelectrical methods were used to investigate pyrite oxidation at a coal waste pile at Alborz Sharghi, in northeastern Iran. The geochemical studies revealed that the fraction of pyrite remaining increased with depth, indicating that pyrite oxidation is limited to the shallower depths of the waste pile. A comprehensive time-lapse geoelectrical investigation, consisting of a one-dimensional (1D) electrical sounding with a Schlumberger array at the sampling locations and two-dimensional (2D) geoelectrical surveys along four parallel profiles with a dipole-dipole array, was conducted on the surface of the pile. A strong correlation (r(2) = 0.88) was observed between the fraction of pyrite remaining and the apparent resistivity values of the 1D surveys. The 2D surveys indicate horizontal layering within the pile, which demarcates the difference between a shallow oxidation zone and a deeper non-oxidation zone. The time-lapse technique showed that water plays an important role in the resistivity changes within the pile.