The adsorption characteristics and adsorption thermodynamics parameter of phosphate on lake sediments

Abstract

The adsorption isotherms,kinetics and thermodynamics parameters of phosphate on three sediments that are in different trophic levels respectively were studied in simulated condition,and the differences of phosphate adsorption on different sediments were also compared.The conclusions are as follows. (1) The Qmax,K,m,NAP and EPC_(0) of phosphate adsorption on the sediments from the East Taihu and the Gonghu lakes were almost the same,and the Qmax,K,NAP and EPC_(0) of the two sediments were lower than that from the Wuli Lake,but m was higher.That means the Qmax and K of the sediment from the heavily polluted Wuli Lake were higher than that from the slightly polluted East Taihu and Gonghu lakes.At the same time NAP and EPC_(0) of the Wuli Lake were also higher,the risk of phosphorus release of the sediment from the lake was higher,and m was lower.So the polluted state of sediment has significant effect on its phosphate adsorption.For the sediments from the East Taihu and the Gonghu lakes,they maintained a phosphate adsorption-desorption equilibrium state between the sediments and the overlying water,and for the sediment from the Wuli Lake,it tended to release phosphate into the lake′s overlying water. (2) The phosphate adsorption rate of the lake sediment within 0.5 h was the highest,and was 10 times or 100 times higher than that sampled in other time intervals,so the majority of phosphate adsorption on sediment was completed within 0.5 h.The phosphate adsorption rate within 0.5 h of the sediments from the Gonghu Lake was almost the same as the sediment from the East Taihu Lake,and the rate of the two sediments was higher than that from the Wuli Lake.Phosphate adsorption on sediment mainly depends on its physical and chemical properties such as distribution of sediment grain size.In this study,the adsorption rate within 0.5 h had no strong positive correlation with its volume percentage of fine particles less than 63μm.This suggests that the phosphate adsorption on the sediments studied was not only affected by its volume percentage of the fine particles,but also by its other physical and chemical properties. (3) The adsorption isotherms of phosphate on the sediments from the Wuli,the Gonghu and the East Taihu lakes at 283 K,298 K and 308 K were studied.The results show that the adsorption process of phosphate on the sediments was the endothermic reaction as the phosphate adsorption rate increased along with the increase of temperature.ΔH~(0) of the sediments from the East Taihu,the Wuli and the Gonghu lakes were 7.84,15.49 and 8.59 kJ·mol~(-1),and ΔG~(0) were 8.50,5.95 and 8.07 kJ·mol~(-1),respectively.The effect of phosphate adsorption by temperature was lower for the sediment from the Wuli Lake,and higher for the sediments from the East Taihu and the Gonghu lakes in this study.