1998 Fiscal Year Final Research Report Summary
Study on Mechanism of Chemical Weathering of Silicate Mineral by Surface Analysis
| Project/Area Number |
09640577
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | National Institute for Environmental Studies |
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Principal Investigator |
SEYAMA Haruhiko National Institute for Environmental Studies, Environmental Chemistry Division, Researcher, 化学環境部, 主任研究員 (40142096)
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| Co-Investigator(Kenkyū-buntansha) |
TANAKA Atsushi National Institute for Environmental Studies, Environmental Chemistry Division,, 化学環境部, 主任研究員 (80171734)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Weathering / Silicate Mineral / Mica / Surface Analysis / XPS / SIMS |
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| Research Abstract |
As a model of the chemical weathering of silicate minerals by acidic solution, surface alteration of acid-leached mica (biotite (K_<0.91>Na_<0.01>) (Fe_<2.61>Mg_<0.03>Mn_<0.09>Ti_<0.03>Al_<0.24>) Al_<1.22>Si_<2.78>O_<10> (OH, F) _2) was examined by secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). Iron, magnesium, potassium and aluminum were selectively leached during acid dissolution (0.05 moll^<-1>H_2S0_4), resulting in the formation of an altered layer rich in Si (SiO_2*nH_2O) on biotite surface. After acid dissolution for one week, the thickness of altered surface layer was estimated to be about 100 nm.
Although the dissolution conditions used in this study were drastic compared with those during natural weathering, the experimental results reflect the possible changes occurring in the surface chemical composition of biotite during chemical weathering. This work supports the following dissolution process for trioctahedral mica in acidic solution. At the initial stage, divalent cations (Fe^<2+> and Mg^<2+>) in the octahedral site and K^+ ion in the interlayer cation site are selectively removed. This is followed by leaching of Al^<3+> ion in the tetrahedral site, resulting in breakdown of the aluminosilicate layer of mica and the formation of an altered layer rich in Si (SiO_2*nH_2O) at the mica surface during acid dissolution. The release of Si from the top surface of the altered layer into solution is the slowest reaction in the dissolution process.The overall dissolution of mica proceeds gradually through these steps, the thickness of the altered layer depending on the rate of Si dissolution.
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