咸水环境下沉积物中镭的解吸特点

Characteristics of Radium Desorption from Sediments in the Salt Water Environment

海底沉积物向上覆水体扩散的镭是海洋水体中镭同位素的重要来源之一。为了研究沉积物中镭同位素的解吸和扩散特点,进行了不同盐度和不同粒度条件下^224Ra和^226Ra解吸的模拟实验,并通过多个时间段的沉积物培养实验获取^224Ra和^226Ra的扩散通量。实验结果表明：随着水体盐度增大,沉积物中^224Ra、^226Ra的解吸量随之增加,在盐度为25时,解吸量基本达到最大值;在同一咸水环境条件下,4个粒级（2000-1000μm、1000-500μm、500-250μm、250-125μm）的沉积物的^224Ra、^226Ra解吸量比较接近,粒级〉2000μm的224Ra、226Ra解吸量略高于上述4个粒级,而粒级〈125μm的^224Ra、^226Ra解吸量远大于上述5个粒级;胶州湾沉积物中^224Ra和^226Ra的平均扩散通量分别为0.85 Bq·m^-2·d^-1和0.022 Bq·m–2·d^-1。

Radium diffusion from sediments to overlying water is one of the important sources of radium isotopes in ocean water. A series of laboratory desorption/diffusion experiments were conducted to help elucidate the characteristics of sediments on ^224Ra and ^226Ra desorption and diffusion,which included 1） ^224 Ra and ^226 Ra desorption from sediments in water of different salinities,2） 224Ra and 226Ra desorption from sediments of different grain sizes in water of the same salinity,3） ^224Ra and ^226Ra diffusive fluxes by observing Ra enrichment with time in the overlying water of incubated sediments. The experimental results show that there is an increase in the amount of ^224Ra and ^226Ra with the increase of salinity from 5 to 30,and Ra desorption is strongest at the salinity of 25. Under the same salt water condition,^224Ra and ^226Ra desorption activities of the four grain sizes（2000-1000 μm,1000-500 μm,500-250 μm and 250-125 μm） of sediments are very close to each other. When the grain sizes of sediments are larger than 2000μm,the ^224Ra and ^226Ra desorption activities are slightly higher than those of the sediments of the above-mentioned four grain sizes. When the grain sizes of sediments are less than 125 μm,the ^224Ra and ^226Ra desorption activities are much larger than those of the above-mentioned five grain sizes. The average diffusive fluxes of ^224Ra and ^226Ra of sediments from Jiaozhou Bay are 0.85 Bq·m-2·d^-1 and 0.022 Bq·m^-2·d^-1,respectively.