Study On Characters Of Ammonia Nitrogen Adsorption And Desorption Desorption Of Sediment In Xiangjiang River

The adsorption and desorption characteristics of ammonia nitrogen in water onXiangjiang River (Hengyang Section) sediment were studied in this experiment.Firstly, the effects of amount of sediment, initial concentration of ammonia nitrogen,pH and temperature on the adsorption capacity were investigated. Secondly, theeffects of the amount of sediment, sediment particle size, pH and temperature on thedesorption capacity were researched. Lastly, the adsorption kinetics, adsorptionisotherm, adsorption thermodynamics and desorption kinetics of the sediment toammonia nitrogen were analyzed.Sediment has a certain adsorption capacity to ammonia nitrogen. The adsorptioncapacity was strongly dependent on amount of sediment, initial concentration ofammonia nitrogen in water, pH and temperature. The adsorption capacity increasedwith reducing amount of sediment, increasing initial ammonia nitrogen concentrationand decreasing temperature. When the pH of the solution increased from3to6, theabsorption capacity increased with increasing of pH. On the contrary, when the pHincreased from6to9, the absorption capacity decreased with increasing of pH.The adsorption kinetics of ammonia nitrogen were fitted well to Lagergrenpsedo-second order equation and the adsorption isotherms of ammonia nitrogen werefitted well to Freundlich and Langmuir equation. But Langmuir equation can explainthe adsorption isotherms better. The thermodynamic analysis showed that theadsorption reaction was a spontaneous process for ΔG of adsorption was negative.The adsorption reaction was an exothermic reaction process for ΔH was negative,,The reaction is based on physical adsorption for the ΔH was less than40J/mol,Besides, the adsorption of ammonia nitrogen was a process with decreasing entropy.The ammonia nitrogen adsorbed by sediment will released under certainconditions. The main factors including amount of sediment, sediment particle size, pHand temperature could affecting the desorption capacity. The desorption capacity of ammonia nitrogen was increased with decreasing sediment particle size, reducingamount of sediment and rising temperature. The desorption capacity of ammonianitrogen was the smallest with neutral pH solution.The desorption process of ammonia nitrogen cannot be described by thefirst-order kinetic model, but change some outside conditions can make it follow thefirst-order kinetic model. The fitting correlation coefficients (R2) of the diffusionequation were between0.6779and0.9893. Therefore, diffusion equation cannotdescribe the desorption of ammonia nitrogen very well. In comparison, the fittingcorrelation coefficients (R2) of the Elovich equations were greater than0.9，whichcould be used to describe the desorption process and demonstrated the desorption ofammonia nitrogen was a non-homogeneous diffusion process.