Distribution and modeling of heavy metal pollution in the sediment and water mediums of Pakhir River, at the downstream of Sungun mine tailing dump, Iran

Abstract

Sungun sulfidic copper mine, with high potential to produce acid mine drainage, is located at northwest of Iran in the East Azerbaijan Province. To investigate the spatial distribution and vertical changes of heavy metals in alluvial deposits of this mine, sampling was conducted in two stages. Samples were collected from the surface and vertical profile of the river bed alluvium and also the waste dump. The sediment samples were analyzed for Cu, Zn, Mn, Cd and Al. Waste rocks samples were analyzed for Cu, Al, Cd, Mn, Zn, Mo, Fe, Pb, As, Ag, Hg, Na, Ca, K and Mg. Pollution indexes revealed that the most polluted sample was the one collected from Pakhir valley and Cu has the main role in the pollution of sediments. Comparison of metal concentrations in the sediment and water samples showed that there is almost a direct relationship between their concentrations. The highest concentration of heavy metals was detected in the upper 50 cm of ground surface and decreases downward in the sediment. Heavy metals less integrate in coarse grains due to the sediment texture and so leach to lower horizons without high amounts of adsorption in upper layers. HYDRUS-1D model was employed to simulate copper movement in the vertical profiles. Four scenarios including base case scenario, non-continuous source scenario, pulse source scenario and the worst case scenario were run to study the behavior of the pollutant in vertical transport through Pakhir alluvial sediments. After doubling the pollutant concentration, the plum reaches to the bottom of the profile faster than non-continuous source and pulse source scenarios. Also, the velocity of pollution movement in non-continuous source scenario is less than continuous scenario. Due to the sediment grain size, the transport velocity in all scenarios is fast and contamination in just a few hours can move several meters from the ground surface.