Study On The Migration And Transformation Mechanism Of Cyanamide In Soil And Groundwater And Its Pollution Remediation

Cyanamide is widely used because it can provide a large amount of cooling capacity for fruit trees,which makes the dormancy period of fruit trees end ahead of schedule,and its residue is low and easy to degrade.However,in the process of use,it will inevitably cause pesticide residues and enter the soil through precipitation and surface runoff,which will destroy microorganisms and organic matter in the soil and easily cause ecological imbalance.Cyanamide will also enter the groundwater through the soil,pollute the water source,and then cause secondary pollution,thus posing a great threat to the environment and human diet.In this paper,taking cyanamide as the research object,the treated soil and water source were selected as the test soil and water source,and the effects of different factors on the migration and transformation of cyanamide in soil were studied by solid phase extraction combined with high performance liquid chromatography.A simulated shallow groundwater device was designed,and the effects of different factors on the migration and transformation of monoamine in shallow groundwater were studied.By modifying LTA zeolite nanoparticles,the remediation of water pollution by cyanamide was studied.The research results are as follows:(1)The standard solution of cyanamide was detected by solid phase extraction and high performance liquid chromatography,and the standard curve of cyanamide was established.The correlation coefficient of the linear equation was 0.99997.(2)In soil,the initial concentration has the greatest influence on the migration and transformation behavior of monoamine.When soil depth,p H,temperature and migration time affect the migration and transformation behavior of cyanamide,they will all be affected by some characteristics of cyanamide itself: when the soil is deep,the temperature is high and the migration time is long,cyanamide will inevitably decompose,while when the p H is less than3 or greater than 8,it will be transformed into other substances(such as urea and dicyandiamide)because of its high activity.(3)The migration and transformation behavior of cyanamide in shallow groundwater is influenced by the migration and transformation behavior of cyanamide in soil,and the influence law of different factors on the residual concentration of cyanamide in shallow groundwater is basically the same as that of different factors on the residual concentration of cyanamide in soil.Because it takes a long time for cyanamide to enter shallow groundwater,the residual concentration of cyanamide in shallow groundwater is obviously lower than that in soil.Cyanamide will have a solid-liquid distribution process with the soil after entering the shallow groundwater,which will reduce the concentration of monoamine in the lowest soil,leaving many adsorption sites,leading to the continuous downward migration of monoamine in the upper soil and occupying the adsorption sites in the lower soil,which will increase the content of monoamine in the lower soil,but this increase is not sustainable,and will stop when a new solid-liquid balance is reached,making the residual concentration of monoamine in the shallow groundwater higher than half of that in the same experimental conditions.(4)The modification of LTA zeolite nanoparticles was confirmed by XRD and FTIR.The elemental composition and content of modified LTA zeolite nanoparticles were determined.The most obvious difference between modified LTA zeolite nanoparticles and unmodified LTA zeolite nanoparticles was the increase of Si/Al ratio.Due to the increase of Si/Al ratio,the thermal stability and chemical stability of the product were significantly improved,which could be used to remove cyanamide from polluted aqueous solution.The adsorption process of cyanamide is influenced by many factors,such as adsorption time,initial concentration of cyanamide,p H,dosage of adsorbent and so on.The modified adsorbent is suitable for use in the system with p H lower than 7.When the dosage of adsorbent is 0.5 g/L,the removal rates of cyanamide can reach 98.5%,85.2%,79.8%,67.5% and 51% respectively in the adsorption system with the initial concentration of cyanamide of 10,25,40,50 and 75 mg/L,and the equilibrium adsorption time is 60 min.