THE GEOCHEMISTRY OF URANIUM AND THORIUM IN COASTAL MARINE-SEDIMENTS AND SEDIMENT PORE WATERS
THE GEOCHEMISTRY OF URANIUM AND THORIUM IN COASTAL MARINE-SEDIMENTS AND SEDIMENT PORE WATERS
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DOI：
10.1016/0016-7037(86)90344-3
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发表时间：
1986-05-01
影响因子：
5
通讯作者：
SURPRENANT, LD
中科院分区：
文献类型：
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作者：
COCHRAN, JK;CAREY, AE;SURPRENANT, LD
美国马萨诸塞州Buzzards湾泥质沉积物中铀和钍同位素孔隙水剖面，可以评估成岩氧化还原反应对这些元素地球化学行为的影响。铀具有明显的最小孔隙水浓度。1.2 dpm/kg)，接近沉积物水界面（0 ~ 3 cm），与孔隙水Fe最大值相吻合。U浓度随深度增大，达到最大值，大于上覆海水的值，然后减小。在没有大型动物的情况下进行的实验室沉淀池实验也显示出近界面的最小值和增加，沉积物培养实验显示，孔隙水中U的去除约40天达到恒定值。234 u / 23。+ -。所有样品的活度比均等于海水值。HCl溶液中孔隙水U的氧化态分离（用阴离子交换法）表明，U以U（VI）的形式存在于孔隙水中。孔隙水铀和铁最大值的重合符合U（VI）还原为U（IV）并在与Fe还原深度（或pe）大致相同的深度（或pe）从溶液中去除的假设。孔隙水U随深度的增加似乎与自生（海水）U（VI）释放到溶液中有关，可能是由于碱度和pH值的增加以及与U相关的有机物被氧化。沉积物柱中较低的深度浓度可能与孔隙水中硫化氢等有效U还原剂的增加或大型动物的活动有关。相比之下，长寿命钍同位素232Th和230Th的孔隙水剖面显示出较低的活度。2 dpm/kg)，随深度变化相对较小，但数值大于上覆水。固相活度同样随深度不变，其分布可能受孔隙水与固相之间的吸附平衡控制。短寿命同位素234在上部5cm处孔隙水活动最大，而在沉积物柱的其他位置几乎为零。沉积物上部几厘米处普遍含有上覆水柱中清除的过量234，并由生物扰动分布，孔隙水中的Fe和Mn剖面显示出最大值，表明Fe和Mn氢氧化物的还原和溶解。孔隙水的234号剖面可以解释为Fe/Mn氧化物表面涂层的还原和溶解使234号从固相中释放出来。
Pore water profiles of uranium and thorium isotopes in the muddy sediments of Buzzards Bay, Massachusetts, USA, permit an assessment of the effect of diagenetic redox reactions on the geochemical behavior of these elements. Uranium shows a pronounced minimum pore water cncentration (.apprx. 1.2 dpm/kg) near the sediment water interface (0-3 cm) which coincides with the pore water Fe maximum. U concentrations increase with depth to a broad maximum which is greater than the overlying seawater value, then decrease. Laboratory sediment tank experiments maintained without macrofauna also show the near-interface minimum and increase, and sediment incubation experiments show removal of U from the pore water to a constant value by about 40 days. The 234U/23.+-. activity ratio is equal to the seawater value in all samples. Oxidation state separations of pore water U in HCl solution (using anion exchange) demonstrate that U is present in the pore water as U(VI). The coincidence of the pore water uranium and Fe maximum is consistent with the hypothesis of reduction of U(VI) to U(IV) and removal from solution at about the same depth (or pe) as Fe is reduced. Increases in pore water U with depth appear to be related to release of authigenic (seawater) U(VI) to solution, possibly as alkalinity and pH increase and organic matter with which the U is associated is oxidized. Lower concentrations at depth in the sediment column may be linked to increases of effective U reducing agents like hydrogen sulfide in the pore water or to the activities of macrofauna. In contrast, pore water profiles of the long-lived Th isotopes 232Th and 230Th show low activities (.ltorsim. 02 dpm/kg) and relatively little change with depth, although values are greater than those in the overlying water. Solid phase activities are similarly constant with depth, and the distribution may be controlled by a sorption equilibrium between pore water and the solid phase. The short-lived isotope 234Th shows greatest pore water activities in the upper 5 cm and is present at virtually zero activities elsewhere in the sediment column. The upper few centimeters of the sediment generally contain excess 234Th scavenged from the overlying water column and distributed by bioturbation, as well as pore water Fe and Mn profiles which show maxima indicating reduction and dissolution of Fe and Mn oxyhydroxides. The pore water 234Th profile can be explained by release of 234Th from the solid phase as Fe/Mn oxide surface coatings are reduced and dissolved.