The Speciation Of As In The Dongting Lake Area Of Hunan Province And Its Environmental Significance

With the rapid development of the economy,the pollution of air,water and soil in some parts of China has become increasingly severe.Among them,soil heavy metal pollution is one of the main hidden dangers that threaten human health.Heavy metals in the soil cannot be eliminated naturally,and their effective speciation is dissolved in water and absorbed by plants easily,directly affecting the safety of food and water.In order to explore the main speciation and environmental significance of heavy metal elements in contaminated soil,this paper selects the Dongting Lake area in Hunan Province as the research area,and uses the soil with abnormal arsenic elements as the research object.The main mineral composition of soil samples was analyzed by using X-ray diffraction and Fourier transform infrared spectroscopy.The content of macroeletics in soil samples was analyzed by X-ray fluorescence spectrometry.The content of heavy metals in soil samples was analyzed by atomic absorption spectrometry.It is the most important is that the chemical presence of arsenic in contaminated soil samples was analyzed by using current soil sequential extraction.The valence state of arsenic in different soil and sediment samples was analyzed by liquid chromatography-inductively coupled plasma mass spectrometry.Based on the summary analysis,the one-step extraction method for extracting bioavailable arsenic from soil(sediment)samples using L-cysteine solution was proposed,and the experimental conditions for L-cysteine solution extraction were optimized.Finally,by the soil leaching experiment,the environmental significance of the state of arsenic was discussed.The main results of the thesis are as follows:(1)The results of X-ray diffraction and Fourier transform infrared spectroscopy indicate that the main minerals in the soil samples in the study area are quartz,feldspar,illite,kaolinite and andreattite.The content of montmorillonite and Illite in the paddy soils is obviously higher than that of farmland soil and water system sediments;(2)The results of atomic absorption spectrometry indicate that the main pollutants in the study area are copper,zinc,cadmium and arsenic.(3)The results of sequential extraction of arsenic in soil and water sediment samples indicate that the arsenic element in the study area mainly exists in the form of residual state,accounting for about 80% of the total;(4)The results of liquid chromatography inductively coupled plasma mass spectrometry showed that the content of trivalent arsenic in paddy soil samples was higher than the stream sediment samples,which was consistent with the redox environment of paddy soil.(5)After repeated conditions exploration,the 10 g/L L-cysteine solution was determined as the high-efficiency extractant of bioavailable arsenic in the soil of the study area.The optimal extraction conditions were ultrasonic extraction at 40±3 °C.(6)The results of leaching experiments showed that the concentration of arsenic in acidic and alkaline leaching filtrate increased first and then decreased with the increase of leaching time,and the concentration of arsenic in neutral leachate decreased first.Finally,it tends to be stable,indicating that the arsenic elements in different forms have undergone mutual transformation during the leaching experiment.By comparing the concentration of arsenic in the leaching filtrate of different pH values,it is found that the acidic and alkaline leaching filtrate will accelerate the activation of arsenic,increase the content of bioavailable arsenic and aggravate environmental pollution.