ABSTRACT:The waste produced by coal washing process produces many environmental problems. In this study, the pollution problems associated with the waste produced by Alborz Sharghi Coal Washing Plant was investigated by mathematical modeling. The study area is located at 11 km. to Razmjah coal region and 45 km. to Tehran-Mashhad road in the north part od Iran. To achieve the goal, a few samples were taken from different depths at three points on the waste dump in order to investigate pyrite oxidation and pollution generation. The samples were then analysed, using an AA-670 Shimadzu atomic absorption to determine the fraction of pyrite remained within the waste particles. A numerical finite volume model using Phoenics package has been developed to simulate pyrite oxidation and pollution generation from the Alborz Sharghi coal washing waste dump. The pyrite oxidation reaction is described by the shrinking-core model. Gaseous diffusion is the main mechanism for the transport of oxygen through the waste. The results of numerical modelling were compared with the field observations and close agreement was achieved. A simple mathematical model incorporating advection and hydrodynamic dispersion processes was also presented in order to verify the results of geophysical time-laps method showing transportation of the pollutants through the downstream of the waste dump. Both mathematical model and geophysical time-laps method are agreed in the identification of pollutant transport emanated from the waste dump. The results of such investigations can be used for designing an effective environmental management program.

Pyrite oxidation and release of the oxidation products from a low-grade coal waste dump to stream, groundwater and soil was investigated by geochemical and hydrogeochemical techniques at Alborz Sharghi coal washing plant, Shahrood, northeast Iran. Hydrogeochemical analysis of water samples indicates that the metal concentrations in the stream waters were low. Moreover, the pH of the water showed no considerable change. The analysis of the stream water samples shows that except the physical changes, pyrite oxidation process within the coal washing waste dump has not affected the quality of the stream water. Water type was determined to be calcium sulphate. The results of the analysis of groundwater samples indicate that the pH varies from 7.41 to 7.51. The concentrations of the toxic metals were low. The concentration of SO4 is slightly above than its standard concentration in potable water. It seems that the groundwater less affected by the coal washing operation in the study area. Geochemical analysis of the sediment samples shows that Fe concentration decreases gradually downstream the waste dump with pH rising. SO(4) decreases rapidly downstream direction. Copper, Zn and Co concentrations decrease with distance from the waste dump due to a dilution effect by the mixing of uncontaminated sediments. These elements, in particular, Zn are considerably elevated in sediment sample collected at the nearest distance to the waste dump. There is no doubt that such investigations can help to develop an appropriate water remediation plan.

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