Nanostructured calcite precipitated under hydrothermal conditions in the presence of organic and inorganic selenium
Nanostructured calcite precipitated under hydrothermal conditions in the presence of organic and inorganic selenium
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DOI：
10.1016/j.chemgeo.2011.09.007
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发表时间：
2011-11
期刊：
影响因子：
3.9
通讯作者：
G. Montes-Hernandez;G. Sarret;R. Hellmann;N. Menguy;D. Testemale;L. Charlet;François Renard
中科院分区：
文献类型：
--
作者：
G. Montes-Hernandez;G. Sarret;R. Hellmann;N. Menguy;D. Testemale;L. Charlet;François Renard
硒是一种重要的微量非金属，其全球循环受地球上地壳流体与岩石的相互作用、与土壤和生命系统中生物分子的相互作用以及灰烬中的大气传输控制。硒的循环通常与碳酸盐相密切相关，Se通常作为杂质掺入方解石晶体或吸附在碳酸盐纳米颗粒上。为了更好地理解水溶液中硒与碳酸盐的相互作用，我们研究了在水热条件下（30-90°C，25- 90 bar），在无机和有机硒化合物存在下，在CO2-H2O-Ca（OH）2介质中方解石的沉淀。水碳酸化反应在硒的存在下，在升高的温度和压力，相关的长期CO2封存在水库和其他自然地质系统，到目前为止还没有被调查，以我们所知。电子显微镜（FESEM和TEM）和同步辐射X射线吸收光谱（XAS）被用来在一个互补的方式来调查晶体的大小，结构顺序（结晶度），晶面的形态，晶体组织，和硒的形态在方解石样品。XAS数据分析显示了亚硒酸盐氧阴离子（SeO 32 −）掺入方解石晶体结构的明确证据。在低硒含量（1.3mg/g方解石），一个单一的网站，观察与硒包围六个钙原子，而额外的网站，可能对应于表面吸附网站，被发现与硒含量增加。XAS还表明，硒-L-胱氨酸（Secys）在碳酸化过程中被化学碎片化，固相中含有元素和氧化硒，在六角形或无定形形式，这取决于实验条件，与一个小比例的硒（IV）。此外，FESEM和TEM测量揭示了一个非常复杂的效果Secys上的颗粒大小和聚集/团聚过程中，导致以下方解石形态：菱面体，细长菱面体（c轴伸长），偏三角面体，星形和壳状晶体聚集体，和不规则的方解石多晶。这些聚集体和不规则的多晶体是由纳米级的方解石微晶（<100 nm）组成的，我们称之为纳米结构的方解石材料。仅在Secys存在下观察到的星星和壳状晶体聚集体可能是由于Secys的同时化学裂解导致的相关次生有机化合物存在下的晶体生长。总的来说，这项研究的结果表明，硒（生物或非生物来源）可以整合到热液条件下的方解石的晶体结构。这与不同环境中的地质过程有关，例如沿着洋中脊的热液系统，或与大量注入CO2以进行长期地质封存有关的地下水库。
Selenium is an important trace metalloid, whose global cycle is controlled by fluid–rock interactions in the Earth's upper crust, interactions with bio-molecules in soils and living systems, and atmospheric transport in ashes. The cycling of selenium is often intimately associated with carbonate phases, with Se being generally incorporated as an impurity in calcite crystals or adsorbed on carbonate nanoparticles. In order to better understand the interaction of aqueous selenium species with carbonates, we studied the precipitation of calcite under hydrothermal conditions (30–90°C, 25–90bar) in a CO2–H2O–Ca(OH)2medium in the presence of aqueous inorganic and organic selenium compounds. Aqueous carbonation reactions in the presence of selenium at elevated temperatures and pressures, relevant for long-term CO2sequestration in reservoirs and other natural geological systems, have until now not been investigated to the best of our knowledge. Electron microscopy (FESEM and TEM) and synchrotron X-ray absorption spectroscopy (XAS) were used in a complementary manner to investigate crystal size, structural order (crystallinity), morphology of crystal faces, crystal organization, and selenium speciation in the calcite samples. XAS data analysis showed clear evidence for the incorporation of selenite oxyanion (SeO32−) into the calcite crystal structure. At low Se content (1.3mg/g calcite), a single site was observed with Se surrounded by six Ca atoms, whereas additional sites, probably corresponding to surface sorption sites, were found with increasing Se content. XAS also showed that seleno-L-cystine (Secys) was chemically fragmented during carbonation, and the solid phase contained elemental and oxidized Se, in hexagonal or amorphous form depending on the experimental conditions, with a minor proportion of Se(IV). Moreover, FESEM and TEM measurements revealed a very complex effect of Secys on the particle size and aggregation/agglomeration process, leading to the following calcite morphologies: rhombohedra, elongated rhombohedra (c-axis elongation), scalenohedra, star-like and shell-like crystal aggregates, and irregular calcite polycrystals. The aggregates and irregular polycrystals, which we designate as nanostructured calcite material, were constituted of nanometer-sized calcite crystallites (<100nm). The star and shell-like crystal aggregates, which were observed only in the presence of Secys, may be due to crystal growth in the presence of associated secondary organic compounds due to a simultaneous chemical fragmentation of Secys. Overall, the results from this study show that selenium (of biotic or abiotic origin) can be integrated into the crystallographic structure of calcite under hydrothermal conditions. This has relevance for geological processes in diverse environments, such as hydrothermal systems along mid-ocean ridges, or underground reservoirs associated with massive injection of CO2for long-term geological sequestration.