Study On Passivation Of Modified Peat Soil To Mercury Pollution In Paddy Field

Mercury is one of the most toxic heavy metals.It has strong neurotoxicity and teratogenicity,and has been listed as a priority control pollutant by many countries（institutions）such as China and the United Nations Environment Program.Among the mercury pollution,soil pollution is a serious problem and it is becoming increasingly serious.In China’s mercury-contaminated areas,there are still many places where large-scale use of mercury-contaminated soil is used for rice cultivation,and rice’s ability to enrich more toxic methylmercury is much higher than other crops,posing a serious threat to the dietary safety of local residents.Therefore,it is imminent to carry out the work about the rehabilitation of the mercury-contaminated soil in rice fields.It is of great theoretical basis and practical significance to explore a repair material that can effectively reduce total mercury and methylmercury in rice.In this thesis,peat soil is used as a raw material and modified by different methods to prepare modified peat soil.Firstly,through soil culture experiments,the modified peat soil with good effect was preliminarily screened out.Then,the screened modified peat soil was subjected to adsorption and desorption experiments to study its maximum adsorption capacity and desorption degree of mercury,and through infrared spectroscopy analysis,preliminary discussion of its adsorption mechanism.Finally,a rice pot experiment was conducted to study its repairing effect and mechanism.The paper mainly obtained the following results:（1）The results of soil culture experiments show that the addition of herbal peat soil can significantly inhibit the content of methylmercury,water-soluble and exchangeable mercury in the soil,and the passivation effect after modification is significantly increased,and the passivation effect is better mercaptoacetic acid and selenide mixed modified group,mercaptopropyl modified group,mercaptoacetic acid modified group and sodium selenite reorganization.Under the condition of adding2%of soil mass ratio,for different proportions of mercapto materials modified peat,within the range of 1:0.1～1:1（peat soil:mercapto substance=g:ml）,it has a certain effect of reducing methylmercury in the soil.For the ratio of 1000:0.25～1000:10（peat soil:Selenide=g:g）Selenide modification,different proportion of sodium selenium modification has no obvious effect on the reduction of methylmercury content in the soil.But for different proportion of sodium selenite modification,the greater the modification ratio,the better the effect of reducing methylmercury in soil..（2）The results of adsorption and desorption experiments show that:after modification with mercaptopropyl,the thiol content of peat soil is obviously increased,and the adsorption capacity of peat soil to Hg²⁺is increased,so that the adsorption equilibrium time is shortened obviously.The maximum adsorption capacity of peat soil to Hg²⁺increased from 74.764 mg/g to 174.361 mg/g after 1:1 mercaptopropyl modification.The adsorption kinetics of each group conformed to the quasi-second-order kinetic equation.The Langmuir equation fits best in the isothermal adsorption process.And the mercaptopropyl modified peat soil has a low desorption rate.Infrared spectroscopy analysis shows that the adsorption of peat soil to Hg²⁺is mainly through the complex adsorption of mercury,such as hydroxyl,carbonyl and other functional groups.（3）The experimental results of potted rice in herbaceous peat soil showed that the total mercury and methylmercury content of rice in the control group were 202.93±26.41μg/kg and 133.96±8.6μg/kg respectively.The average reduction rates of total mercury and methylmercury were 27.44%and 45.97%respectively.After mercaptopropyl modification（1:1）,the total mercury and methylmercury content in rice decreased further,with the content of 25.33±5.07μg/kg and 8.33±1.46μg/kg,the average reduction rates reached 87.52%and 93.79%,respectively.（4）The moss peat soil rice pot experiment results show that:the addition of mercaptopropyl modified moss peat soil can significantly reduce the content of rice mercury in clay and sandy soil,and the reduction effect of rice mercury in clay is significantly better than sand.In clay,when the mercaptopropyl modification ratios are1:0.2,1:0.5,and 1:1,the average reduction rate of total mercury in rice is 79.14%,90.81%,93.14%,and that of methyl mercury in rice was 82.72%,92.01%and93.87%,respectively.In sandy soil,the average reduction rates of total mercury and methylmercury content in rice with 1:0.5 mercaptopropyl modified group were54.28%and 62.18%,respectively.The addition of mercaptopropyl modified moss peat soil in the clay and sandy soils during the middle growth stage of rice further reduces the total mercury in the interstitial water and the bioavailable mercury（dissolved and exchangeable mercury,special adsorption state）and oxidation in the soil the content of mercury in the form of mercury.And the mercapto group has a strong adsorption capacity for methylmercury,which can adsorb and fix methylmercury in the soil,thereby inhibiting the absorption of total mercury and methylmercury in the soil by rice and reducing the total mercury and methylmercury content in rice.