Mn and Zn incorporation into calcite as a function of chloride aqueous concentration
Mn and Zn incorporation into calcite as a function of chloride aqueous concentration
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DOI：
10.1016/s0016-7037(00)00375-6
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发表时间：
2000-07
影响因子：
5
通讯作者：
M. Temmam;J. Paquette;H. Vali
中科院分区：
文献类型：
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作者：
M. Temmam;J. Paquette;H. Vali
在螺旋生长的方解石菱面体{101 4}，二价金属取代Ca 2+的差异纳入由于空间差异固有的不对称扭结网站暴露在不等价的增长步骤。因此，比Ca 2+“大”的离子（例如，Sr 2+和Ba 2+）表现出与“较小”离子（例如，Mn 2+和Co 2+）。然而，Zn 2+表现出相同的掺入趋势，从强NH 4Cl电解质进行的共沉淀实验中的大离子。在这项研究中，我们比较了不同氯化物含量的溶液中Zn和Mn的掺入趋势，以测试“大”ZnCln 2 −水溶液络合物的吸附影响Zn的位置偏好的可能性。Mn和Zn的掺入趋势在对称非等效生长阶段相反。从0.4 M的氯化铵溶液，其中锌水溶液的形态主要是由“自由”的水离子，锌保持其网站的几何约束较少的表面网站的偏好。因此，Zn表现出与表面位点的特定相互作用，其掺入趋势不受ZnCln 2 − n络合物的流行控制。必须考虑其他因素，如电子配置。方解石的表面微观形貌被发现是敏感的NH 4Cl和Zn的水溶液浓度的变化。NH 4Cl浓度的降低导致生长丘密度的增加。Zn的强吸附行为增加了表面粗糙度，降低了生长速率，扰乱了螺旋生长机制，并触发了沿沿着宏观台阶的离散表面沉淀（约0.2 μm）的形核。Cl掺入的增加，尽管其水溶液浓度的降低，通过稀释的母溶液，表明方解石溶液界面处的表面粗糙度是杂质元素掺入的非平衡过程中涉及的另一个因素。由于Cl水溶液浓度的降低，Mn和Zn掺入到方解石中的显着增加证明了氯化物作为方解石和低温水性流体之间的微量金属离子的分区中的重要因素的作用。更重要的是，锰微分掺入的幅度也增加了稀释，这表明通常从散装固体分析计算的分配系数可能严重低估了对微量元素掺入的表面结构效应。
During spiral growth of the calcite rhombohedron {101 4}, divalent metals substituting for Ca2+are differentially incorporated due to steric differences inherent to the asymmetric kink sites exposed at nonequivalent growth steps. Hence, ions “larger” than Ca2+(e.g., Sr2+and Ba2+) exhibit an incorporation trend opposite to that of “smaller” ions (e.g., Mn2+and Co2+). However, Zn2+exhibits the same incorporation trend as large ions in coprecipitation experiments conducted from strong NH4Cl electrolytes. In this study we compared the incorporation trends of Zn and Mn from solutions with various chloride content to test the possibility that the adsorption of “large” ZnCln2−naqueous complexes influences the site preference of Zn. The incorporation trends of Mn and Zn were opposite at the symmetrically nonequivalent growth steps. From a 0.4 M NH4Cl solution, where Zn aqueous speciation was thermodynamically dominated by the “free” aquo ion, Zn maintained its site preference for the geometrically less constrained surface sites. Thus, Zn exhibits a particular interaction with surface sites and its incorporation trend is not controlled by the prevalence of ZnCln2−ncomplexes. Other factors like the electronic configuration must be considered. The surface microtopography of calcite was found to be sensitive to changes in the aqueous concentrations of NH4Cl and Zn. Decreases in NH4Cl concentration resulted in an increase of the density of growth hillocks. The strong adsorbing behaviour of Zn increased the surface roughness, decreased the rate of growth, perturbed the spiral growth mechanism, and triggered the nucleation of discrete surface precipitates (∼0.2 μm) along macrosteps. An increase of Cl incorporation, despite the decrease of its aqueous concentration by dilutions of the parent solution, suggests that surface roughness at the calcite-solution interface is another factor involved in the nonequilibrium process of impurity element incorporation. The significant increase in Mn and Zn incorporation into calcite due to decreases in Cl aqueous concentration demonstrates the role of chloride as an important factor in the partitioning of trace metal ions between calcite and low-temperature aqueous fluids. More importantly, the magnitude of Mn differential incorporation also increased with dilutions which indicates that distribution coefficients commonly calculated from bulk solid analyses may underestimate seriously the surface structural effect imposed on trace element incorporation.