| Heavy metal mercury is a kind of pollutants which have high toxicity to animals, plants and humans, with high biological enrichment, easy migration and persistent pollution characteristics. It is very easy to migrate in the soil, air and water environment and enrich the food chain in the high animal, which is a serious threat to human health. The exploitation of mercury mine will lead to a certain degree of mercury pollution in the surrounding environment. Therefore, it is of great significance to study the mercury pollution and its adsorption and desorption in the surrounding soils and sediments of mercury mining area.In this paper, a mercury mine in Xiushan County of Chongqing surrounding pollution area and control area of the soils and stream sediments as the research object, its physical and chemical properties and mercury speciation were studied to evaluate the mercury pollution. The isothermal adsorption desorption, adsorption kinetics of Hg2+ and the influence of pH and Cl~- on the adsorption process were also studied. Preliminary conclusions are as follows:(1) The total mercury content in the polluted soils and sediments surrounding mercury ore area 568.76mg/kg and 75.53mg/kg respectively, are far more than the Chongqing soil heavy metal mercury background values and the soil environment quality standard(GB15618-1995) secondary standard value. Mercury area upstream against the stream sediments have also been a certain degree of mercury pollution; Mercury in contaminated samples was mainly in the form of organic combined state and residual state, biological effective state content is low. RAC heavy metal speciation risk assessment method shows that the risk of bioavailable heavy metals in soil and sediment is low.(2) The ecological risk assessment of soil and sediment was carried out by using single factor index method, geo accumulation index method and potential ecological risk index method. The results showed that the soil of the control area was not polluted, and the remaining soil and sediment were seriously polluted by mercury, and the potential ecological risk was very high.(3) The process of soil and sediment adsorption of Hg2+ is similar under the condition of neutral pH and 25±1?, When the soil and the sediment of the control area reach the adsorption equilibrium, the saturated adsorption amount is 1848.77mg/kg, 941.25mg/kg; Langmuir, Freundlich and TemKin three curves can be well fitted to the adsorption of Hg2+ in soil and sediment, but the Langmuir fitting degree is higher. Adsorption of Hg2+ in soil and sediment is bigger, the greater desorption. Soil for Hg2+ a linear relationship with the amount of adsorption and desorption, and sediment linear relationship is not obvious. The maximum desorption rates of soil and sediment were 0.92% and 1.32%, respectively, and desorption rate was low, which indicated that Hg2+ was difficult to be desorption once it entered the soil or sediment.(4) Sorption of Hg2+ by soil and sediment was very rapid during the first few minutes of the sorption process. In the initial 5min, the adsorption amount of Hg2+ on Soil and sediment reached 72.64% and 62.68% respectively, achieving the adsorption saturation within 200 min, which illustrates the soil and sediment adsorption of Hg2+ adsorption phase can be divided into fast and slow adsorption phase. Elovich equation and double constant equation of adsorption dynamics of linear fitting have reached the significant level, Elovich equation can better fitting soil adsorption kinetics of Hg2+, and double constant equation is better suitable for sediment.(5) The adsorption capacity of soil and sediment on Hg2+ increased first and then decreased with the increasing of the pH, which showed a single peak curve. When the pH was about 7, the adsorption amount of Hg2+ in soil reached the maximum, while the sediment was 8 at pH. Acidic conditions conducives to soil and sediment adsorption of Hg2+. Cl~- ion has a great influence on adsorption process, when the Cl~- ion concentration is lower than 10-5M, its influence is small, with the increase of initial concentration of Cl~- ions, the adsorption quantity of soil and sediment of Hg2+ less and less, but the soil and sediment has not lost on mercury adsorption ability, just because of the existence of Cl~- ions cause its adsorption capacity on mercury weaken greatly. |
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