Ammonia Forms And Adsorption/Desorption Behavior In Soils From The Downstream Of Informal Landfill

The pollution problem of ammonium in underground water is becoming more and more serious.The informal landfill leachate is one of the pollution sources,and vadose zone is the necessary access for ammonium nitrogen to enter the groundwater.Soils were taken in contaminated area from the refuse landfill in Shuikousi as the object of study in the experiments.By the way of experimental and simulation analysis,the characteristics of ammonium in study area and their influencing factors were discussed,as well as the characteristics of ammonium adsorption and desorption.This study was carried out as a basis of further study on migration and transformation of ammonium in the soil,and to provide theoretical support for effective control of ammonia pollution in soil and groundwater.The main conclusions are as follows:(1)The average content of ammonium was 164.13±24.98 mg/kg.Ammonium forms ranged in the order of fixed ammonium > soluble ammonium > exchangeable ammonium.Correlation analysis showed that soluble ammonium occured mainly in the silt soil,affected by pH,Eh and organic matter content;exchangeable ammonium occured mainly in the size of 0.25-0.02 mm grit soils,affected by the redox environment;fixed ammonium occured mainly in the clay,mainly affected by particle size and mineral composition.(2)In the adsorption process,the adsorption amount ranged in the order of soluble ammonium > exchangeable ammonium > fixed ammonium.The whole dynamic processes of adsorption were affected by cation exchanges on medium surface,and fitted well with Langegren quasi-dynamic equations and Elovich equations.For the exchangeable ammonium and fixed ammonium,the early rapid adsoption were affected by the diffusion rate of NH4+,and fitted well with the parabola equations.The sorption isotherms were best fitted with Langmuir model,indicating that the adsorption of those three forms of ammonium was a single molecular layer adsorption.(3)In the desorption process,the release ability ranged in the order of soluble ammonium > exchangeable ammonium > fixed ammonium.The soluble ammonium affected most to the environment.The desorption kinetics curves of each form of ammonium fitted well with the Langegren quasi-dynamic equations.The isothermal desorption curve of each form of ammonium fitted well with the Freundlich model and the Henry model,as well as the Langmiur model.(4)The adsorption of ammonium was affected by both medium composition and environmental factors.Decrease of the particle size and temperature,as well as the increase of initial concentration,leads to the increase of adsorb ammount of ammonium.The increase of pH,promoted the adsorption of soluble ammonium,and inhibited the adsorption of exchangeable ammonium,and has little effect on the fixed ammonium adsorption process.Salinity in soils could inhibite the adsorption of ammonium,and the effect on exchangeable ammonium was most significant.(5)Desorption process was affected by environmental factors.The more ammonium originally adsorbed in soils,or the higher the temperature was,the more ammonium is released.The increasing pH showed inhibitory effect on desorption of ammonium,while salinity promoted desorption of ammonium.The influences of pH and salinity were most significant on exchangeable ammonium.