By using radiotracer technique

the sorption and desorption behaviors of iridium in marine sediment-seawater system were studied through the sorption and desorption experiments and visible absorption spectrum analysis. The results indicated that

in the range of very low iridium concentration

the sorption and desorption isotherms were linear

and the sorption-desorption process was irreversible. Iridium in the form of IrCl62- was very easy to be sorbed by the sediments. Once being sorbed by the sediments

Ir was hard to be desorbed. In the sedimentary process

the sediment continuously absorbed the species of IrCl62- from the seawater

which might lead to the Ir accumulation in the sediment. The sorption ability of the Danish K/T Fish Clay was weaker than that of the coastal sediment

which indicated that the excessively high Ir content in the Fish Clay might be caused by the other enrichment mechanisms

such as volcanic or extraterrestrial origin.