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

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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.