Reactions of radium and barium with the surfaces of carbonate minerals
Reactions of radium and barium with the surfaces of carbonate minerals
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DOI：
10.1016/j.apgeochem.2011.04.012
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发表时间：
2011-07-01
影响因子：
3.4
通讯作者：
Livens, Francis R.
中科院分区：
文献类型：
--
作者：
Jones, Mark J.;Butchins, Laura J.;Livens, Francis R.
镭-226是一种天然存在的放射性同位素，具有潜在的重大放射性影响，其环境行为令人担忧。研究了示踪剂（0.1-1 nM）溶解的Ra及其化学类似物Ba与一系列碳酸盐矿物表面的反应。所有的矿物反应与Ra，但，而方解石，白云石，菱锶矿，菱锰矿，铁白云石和毒重石都显示增加的吸收与Ra浓度的增加，这表明共沉淀反应（因此与相形成限制吸收），菱铁矿，菱镁矿和铁白云石显示行为表明简单的吸附（随着Ra浓度的增加，或与[Ra]的依赖性降低吸收）。特别是菱镁矿的吸附能力较低，钡的浓度较高（0.1-1 mM），因此除了本体吸收测量外，还可以使用表面分析和成像技术。虽然研究了相同的八种碳酸盐，但可测量的吸收仅发生在白云石、菱镁矿和菱铁矿上。对于菱铁矿和菱镁矿，有一个近似的线性关系之间的增加固体和溶液相钡浓度。表明吸附过程简单。白云石表现出更复杂的行为，表明在最低浓度下的简单吸附和在较高浓度（>0.4 mmol L（-1））下的相形成。后一种观察结果与毒重石形成的光谱学证据一致。与Ba反应的三种碳酸盐基质的表面分析和成像显示出多样性的行为，部分原因是在这些实验中使用天然矿物。毒重石通常以表面沉淀物的形式形成，尽管存在甚至痕量的SO（4）（2-）也会导致重晶石的形成。表面相显示出一系列特征形貌，表面结构具有模板生长效应。甚至少量的Fe（氢）氧化物相作为碳酸盐上的蚀变产物或沉淀物的存在也是重要的，因为Ba对这些相具有强亲和力。(C)2011爱思唯尔有限公司版权所有。
Radium-226 is a naturally-occurring radioisotope with potentially significant radiological impact and whose environmental behaviour is of concern. The reactions of tracer (0.1-1 nM) dissolved Ra and its chemical analogue Ba with the surfaces of a range of carbonate minerals have been studied. All of the minerals react with Ra but, whereas calcite, dolomite, strontianite, rhodocrosite, ankerite and witherite all show increased uptake with increasing Ra concentration, suggesting a coprecipitation reaction (hence with phase formation limiting uptake), siderite, magnesite and ankerite show behaviour suggesting simple sorption (with decreasing uptake as Ra concentration increases, or with no dependence on [Ra]). Magnesite, in particular, has a low sorption capacity.Barium has been used at higher (0.1-1 mM) concentrations to enable the use of surface analytical and imaging techniques in addition to bulk uptake measurements. Although the same eight carbonates were studied, measurable uptake occurs only on dolomite, magnesite and siderite. For siderite and magnesite, there is an approximately linear relationship between the increasing solid and solution phase Ba concentrations. suggesting a simple sorption process. Dolomite shows more complex behaviour suggesting simple sorption at the lowest concentrations and phase formation at higher concentrations (>0.4 mmol L(-1)). The latter observation is consistent with spectroscopic evidence for the formation of witherite. Surface analysis and imaging of the three carbonate substrates that react with Ba show a diversity of behaviour, partly as a result of using natural minerals in these experiments. Witherite is commonly formed as a surface precipitate although the presence of even trace SO(4)(2-) leads to barite formation. The surface phases display a range of characteristic morphologies, and the surface structure has the effect of templating growth. The presence of even minor amounts of Fe (hydr)oxide phases as alteration products or precipitates on the carbonates is also important, since Ba has a strong affinity for these phases. (C) 2011 Elsevier Ltd. All rights reserved.