Impact of Iron Ore Mining on the Concentration of some Heavy Metals and Soil Pollution Zoning (Case Study: Sangan Iron Ore Mine, Khaf-Iran)

One of the most fundamental global environmental challenges in the past two decades has been the issue of soil pollution and degradation. Soil, as an important environmental element, has played a significant role in food production, human health, and living organisms, but various factors, by both human and naturally have destroyed it. The exploitation of natural resources with activities such as mining and quarrying, as an anthropogenic action (caused by human activities), is one of the most important factors of human intervention in nature and also one of the environmental hazards of soil degradation, which has caused the spread of desertification. Sangan iron mines in Khaf city are the largest mines in the northeast of Iran. According to the geomorphological disturbances caused by the activity of Khaf iron ore mines and the geological composition of the region, there is a potential for causing pollution and destroying the soil around the mine. This research was conducted with the aim of evaluating the impact of mining activity on concentration of some heavy metals such as lead, iron, nickel, copper, and arsenic in the soil around the iron ore mine in Sangan area of Khaf city in Khorasan Razavi province. Realizing the polluted hotspots due to the concentration of heavy metals, as one of the important signs of soil pollution and the spread of desertification, is one of the goals of this research, and the results can be effective in making appropriate management decisions to prevent soil pollution and further destruction.

In order to conduct this research, 60 soil samples were systematically taken from a depth of 0-20 cm from two areas adjacent to the mine and control. The concentration of aqua regia extracted heavy metals was measured using an inductively coupled plasma-optical emission spectroscopy (ICP-OES). In the first stage, the results were descriptive, and in the second part, after performing tests related to the normality of the data, they were inferential using the parametric independent t-test and Pearson's correlation coefficient in the statistical environment of the SPSS software. In order to quantify the level of soil contamination with heavy metals, geochemical indices including contamination factor, pollution load index, and enrichment factor were used. The pollution load zoning map of the area adjacent to the mine as well as the average enrichment map of lead and arsenic elements were prepared using the inverse distance weighting interpolation method in the ArcGIS environment.

The results of this research showed that the average concentrations of arsenic, copper, nickel, lead, and iron elements in the area near the mine were 12.71, 25.54, 34.59, 48.64, and 38860 mg/kg and in the control area were 8.57, 15.97, 32.13, 16.96, 29110 mg/kg, respectively. The comparison of the coefficient of variation (dispersion criterion) of heavy metals showed that the highest coefficient of variation among the metals is related to the lead with a value of 42.8%, as well as the coefficient of variation for other metals in the area adjacent to the mine also has a relatively high dispersion compared to the control area. In addition, it was found in all elements except for nickel (p<0.05), which indicates a significant difference in the average concentrations between the control area and the area adjacent to the mine. The correlation between lead element and nickel, copper and arsenic variables was inverse and there was a positive and very strong correlation between iron and copper and nickel with values of 0.8 and 0.76 respectively and nickel and copper with values of 0.82. The pollution coefficient of the lead elements in the area adjacent to the mine showed moderate to significant pollution levels, which is more polluted than other elements. The pollution load in the area near the mine showed that the value of this index was greater than one in the samples closer to the mining areas, which indicates the high contamination of the surface soil with these elements. Lead and arsenic elements in the area adjacent to the mine showed moderate to relatively intense enrichment. From the examination of all the pollution indicators used in this research, as well as the positive and very strong correlation between copper and nickel, the presence of these two elements in the soil of the study area showed no pollution. The comparison of the results obtained from the analysis of soil samples in the two areas of the control and adjacent to the mine showed an increase in the concentration of heavy metals (iron, lead, and arsenic, copper) in the area adjacent to the mining.

The results obtained from the analysis of soil samples and pollution indicators in the two control areas adjacent to the Sangan iron ore mine in Khaf city showed that the presence of iron ore industrial and mining sites in the study area and the spread of its wastes and tailings by seasonal and local winds, as well as the activities of humanity and the spread of these pollutants to other areas, can be one of the main reasons for the increase in the concentration of metal pollutants in the soils of this region.