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Effect of dissolved organic matter on ammonium sorption kinetics and equilibrium to Chinese clinoptilolite

In the in-situ remediation of ammonium in groundwater by a sequential reactive barrier filled with zeolite, it is of great importance to understand the mechanisms of sorption to zeolite. In this study, the effect of dissolved natural organic matter on sorption to natural Chinese clinoptilolite was studied by batch experiments taking humic acid (HA) as a model substance. The surface of clinoptilolite was characterized by scanning electronic microscopy (SEM). A needle cluster of sorbed HA could be observed on the surface of the clinoptilolite. The negative effect of HA on sorption is thought to be their competition for sorption sites, the surface coverage and blockage of the pores of clinoptilolite by HA. The fitting results of kinetic sorption data indicated that the rate-controlling step for sorption by clinoptilolite in both and systems is the heterogeneous chemisorption. The existence of HA (10 mg/L) significantly reduced the initial sorption rate of , but the effect of a further concentration increase of HA was slight. The effect of HA on maximum sorption capacity was found to be insignificant in the experiments. A high aqueous Ca 2+ concentration can decrease the negative effect of HA on sorption by precipitation of calcium humate.