九龙江河口区表层水铀同位素的粒级分布  

Size-fractionated uranium isotopes in surface waters in the Jiulong River Estuary in China

作　　者：吕娥[1] 张磊[1] 陈敏[1] 邱雨生[1] 邢娜[1] 杨伟锋[1] 李艳平[1] 黄奕普[1] 

机构地区：[1]厦门大学海洋系,福建厦门361005

出　　处：《海洋学报》2007年第4期59-68,共10页

基　　金：国家重点基础研究发展计划项目(2005CB422305);中国矿产资源研究开发协会"十五"科技攻关项目(DY105-02-04和DY105-02-01)

摘　　要：利用微滤和超滤技术研究了九龙江河口区表层水中铀及其同位素组成的粒级分布和地球化学行为.结果表明,溶解态(<0.4μm)中低分子量组分(<10 000 u)占主要份额,胶体态(10 000 u^0.4μm)238U所占比例不足1%,且随盐度的增加其所占份额逐渐降低.溶解态、低分子量组分和胶体态238U的比活度与盐度之间存在良好的线性正相关关系,证实它们在九龙江河口区呈现保守行为.在颗粒态(>0.4μm)中,各粒级组分238U所占份额主要受控于相应颗粒物的浓度,在盐度小于20的区域,各粒级颗粒组分238U占颗粒态的份额有如下变化次序:10~53μm>2~10μm>0.4~2μm>大于53μm,而在盐度大于30的近外海站位,该次序发生一些变化:0.4~2μm>10~53μm>2~10μm>大于53μm,最小粒级颗粒组分238U的贡献有所增加,反映了自生铀贡献的加强.九龙江河口区表层水中溶解态(包括低分子量组分和胶体态)的234U/238U)A.R.均大于1,显示出234U过剩的特征,而各粒级颗粒组分中的234U/238U)A.R.则接近于平衡值(1.0).这一现象与陆地岩石风化过程中水体对铀的淋滤释出量及234U的优先浸出有关.对232Th/238U质量比的研究显示,溶解态及其所包括的低分子量组分和胶体态的232Th/238U质量比均小于1,而颗粒态及其所包括的4个粒级组分中的232Th/238U质量比均大于1,反映了向外海输送过程中铀、钍地球化学行为的差异.Surface waters were collected from the Jiulong River Estuary for determination of activity con-centrations of uranium isotopes in different size fractions, namely, 〉53 /μm, 10b- 53 μm, 2- 10μm, 0.4-2 μm, 10 000 u-0. 4 μm and 〈10 000 u fractions by microfiltration and cross-flow ultrafiltration techniques. Our results indicated that most of the dissolved uranium （〈0. 4μm） existed in the low molec-ular mass fraction （〈 10 000 u）, and the colloidal ^238U （10 000 u-0. 4μm） only contributed 〈1% of the dissolved ^238U. The fractions of colloidal uranium linity. A positive linear relationship between ^238U in the dissolved phases decreased with the increasing saactivities and salinities was observed for the dissolved, the colloidal and the low molecular mass fractions, indicating a conservation behavior of uranium in Jiulong River Estuary. In the particulate phases （〉 0. 4μm）, the partitioning of uranium isotopes among different size fractions was controlled by the partitioning of particle concentrations. In the regions with salinity less than 20, the partitioning of ^238U among different size fractions was as follows： 10-53 μm 〉 2-10μm 0.4〉2 μm 〉 larger than 53 μm. However, the order at the offshore station with salinity larger than 30 was changed as follows： 0.4-2 μm 〉 10-53 μm 〉 2-10 μm 〉 larger than 53 μm. The fraction of the 0.4-2μm particles increased at the offshore station, suggesting the increased contribution of the autogenetic uranium. ^234 U/^238 U）A.R. in the dissolved phase, including the low molecular mass fraction and the colloidal fraction, was larger than 1, showing the occurrence of excess ^234 U. In contrast, ^234 U/^238 U） A. R. in all size fractions of the particulate phase was close to the equilibrium value （1.0）. The observed different values of ^234U/^238U）A.R, in the dissolved and particulate phases were ascribed to the preferential leaching of ^234U and the small amount of the leaching particulate uranium. The ^232 Th/^238U

关 键 词：铀同位素 粒级分布 九龙江河口 

分 类 号：P734.21[天文地球—海洋化学]