Characteristics of Adsorption Kinetics and Isotherms of Phosphate on Sediments in Swan Lake

Adsorption kinetics and isotherms of phosphate on six sediments collected in Rongcheng Swan Lake(a nature lagoon) were determined in laboratory,and the relationship between the physical-chemical properties and the adsorption parameters of sediments was also discussed.The results indicated that the adsorption kinetics curve of phosphate at different sites all followed the second-order adsorption kinetic model.The adsorption reaction mainly occurred within 0-10 h,and the maximum adsorption rates occurred within 0-2 h.According to the Langmuir isotherm equation,phosphate adsorption capacity(Qmax) of surface sediments from Swan Lake varied from 294.12 mg/kg to 1 111.11 mg/kg.Phosphate sorption potential on the sediments from the northern and center areas was much higher than that from the south.The zero equilibrium phosphate concentration(EPC0) changed at the range of 0.002-0.033 mg/L,which had no significant positive correlation with the native absorption phosphate(NAP).At most sites the EPC0 values were lower than soluble reactive phosphorus concentration in the overlying water.The phosphorus in the sediments from the northwest and southeast of Swan Lake had a release potential into the overlying water.The NAP of sediments was closely related to the concentrations of organic matter(OM),total nitrogen,clay and aluminum extracted by ammonium oxalate(Alox),and the Qmax was closely related to Fe/Al-bound phosphorus(Fe/Al-P),OM,Alox and silt concentrations.In conclusion,amorphous aluminum oxide,organic matter and grain size in the sediments were the main effecting factors of phosphate adsorption.