Establishment for the measurement of silicate species dissolved in natural waters and analysis of their data

人们对天然水的化学成分进行了深入的研究，然而，分析二氧化硅化学成分的方法还没有建立起来。本研究的最终目的是阐明全球范围内二氧化硅的行为和循环：天然水体中溶解的硅酸盐种类以及水相和固相之间的化学行为。众所周知，二氧化硅溶于钠和氯化钙溶液中。天然水体中含有钠、钙、钾、氯化物、硝酸盐、硫酸盐离子等多种离子，它们以不同的成分影响二氧化硅的行为。以河口为例，在河海混合的地方，溶解的二氧化硅通过混凝和盐析作用形成沉积物，但其机理尚未明确。在实验室基础数据的基础上，从硅酸盐物种分子水平的角度对盐析效应进行了阐述。结果表明，硅酸盐配合物中硅醇基（Si-OH）的质子很容易被钠离子和钙离子取代，钙离子与硅酸盐离子形成双齿配合物。另一方面，硅酸盐离子不能与锂离子和镁离子形成络合物。这表明离子半径是与硅酸盐离子形成配合物的重要因素。最重要的结果是，一般认为硅酸盐离子是单体，但在溶液中，二聚体、线性四聚体和环四聚体是比单体更稳定的配合物。本研究的结果已在后面列表的论文中报道。对于本研究的应用，可以对天然温泉和深海中溶解的二氧化硅种类进行表征。

The chemical compositions of natural waters have been well studied, however, the method to analyze the chemical species of silica as they are, has not been established. The final purpose of this study is to elucidate the behavior and circulation of silica in the global scale : the silicate species dissolved in natural waters and the chemical behavior between aquatic phase and solid phases.It is known that silica is dissolved in sodium and calcium chloride solutions. In the natural waters, many kinds of ions, such as sodium, calcium, potassium, chloride, nitrate, sulfate ions and so on, are contained with various compositions to affect the behavior of silica. Fox example, the estuary, where river and sea water are mixed, the dissolved silica becomes deposits by the coagulation and salting-out effect, but their mechanism has not been cleared. The salting-out effect could be elucidated from the view point of molecular level of silicate species on the basic data in laboratory. As the result, it is shown that the proton of silanol group (Si-OH) in silicate complex is easily replaced by sodium ion and calcium ion, and calcium ion makes complex with silicate ion with bidentate. On the other hand, silicate ion cannot make complex with lithium ion and magnesium ion. This shows that the ionic radii is the important factor to make complex with silicate ion. The most important results are mentioned that, generally, silicate ion is considered to be monomer, however, in the solution, dimer, linear tetramer and cyclic tetramer are more stable complexes than monomer in the solution.The results of this study have been reported in the papers in the later list. For the applications of this study, the silica species dissolved in natural hot springs and deep seawaters could be characterized.