Adsorption characteristics of typical sediments from unsaturated zone of Beijing Plain, China

Adsorption of ammonia on representative sediments obtained from the Beijing plain was investigated in this study by means of batch experiment. It was found that the equilibrium time and the adsorption capacity increased with the decrease in the grain size of sediments. With the initial concentration of ammonia between 0 to 50 mg/L, the adsorption isotherm can be described by Henry, Langmuir and Freundlich models. The adsorption capacity elevated with the increase in the initial concentration of ammonia. The Henry coefficient and the adsorption capacity increased with the decrease of the grain size of the sediments. Adsorption of ammonia was affected by the total organic carbon (TOC) in the sediments. The correlations of TOC and Henry absorption coefficient were 050, 076 for sediments from Yongding River catchment and Chaobai River catchment, respectively. The adsorption capacity of ammonia decreased with the increase in the ratio of solid to liquid. Sediments from Chaobai River catchment, especially the finegrained sediments, had a higher capacity for ammonia adsorption than those from Yongding River catchment with the same lithology. The ammonia adsorption capacities of sediments from middle and lower reaches were higher than those from upper reaches in the same catchment.