An experimental study about the effects of phosphorus loading in river sediment on the transport of lead and cadmium at sediment- water interface

摘要

Phosphorus (P) in the river sediment plays an important role in the fate and transport of heavy metals at sediment-water interface of the aquatic eutrophication environment To explicate the effect of P loading, the sediments with different P contents were employed in this study to experimentally investigate the adsorption/desorption of Pb~(2+) and Cd~(2+) and the releasing behavior of P during the adsorption/desorption processes. Results illustrated a strong affinity between Pb~(2+) ions and the P-containing sediments in both single Pb and binary Pb + Cd systems. In single-metal systems, the Pb~(2+) adsorption capacities of all types of sediments (15.04-19.44 mg g~(-1)) were higher than those for Cd~(2+) (4.68-5.56 mg g~(-1)). While in binary-metal systems, the Pb~(2+) adsorption was slightly influenced by the coexisting Cd~(2+), but the Cd~(2+) adsorption capacities were decreased by over 5 times. Moreover, the adsorption amount and retention ability of Pb~(2+) on sediment were enhanced by increasing content of P in the sediment Meanwhile, the releasing of P was also closely depended and significantly inhibited by the Pb~(2+) attached on the sediment. The P release amounts during the desorption processes of Pb- and Pb + Cd-loaded sediments were over 50 times lower than those from the raw sediments (sediments without heavy metals adsorbed), but the values decreased by a factor of two for the single Cd-loaded sediments. Furthermore, the results of X-ray photoelectron spec-troscopy indicated the crucial role of P loading in Pb transport in the sediment and overlaying water. The findings in this study showed important implications for the transport of heavy metals and P at the sediment-water interface and offered new insights for further explicating the mechanisms of secondary pollution caused by heavy metals and P in aquatic eutrophication environment.