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
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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.Abstract: Surface waters were collected from the Jiulong River Estuary for determination of activity concent rations of uranium isotopes in different size fractions,namely,>53 Lm,10~53 Lm,2~10 Lm, 0.4~2 Lm,10 000 u~0.4 Lm and<10 000 u fractions by microfiltration and crossOflow ultrafiltration techniques.Our results indicated that most of the dissolved uranium(<0.4 Lm)existed in the low molecular mass fraction(<10 000 u),and the colloidal 238U(10 000 u~0.4 Lm)only contributed <1% of the dissolved 238U.The fractions of colloidal uranium in the dissolved phases decreased with the increasing salinity.
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Key words:
- uranium isotopes /
- size fractionation /
- Jiulong River Estuary
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