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Formation of secondary minerals and its effect on anorthite dissolution

1998; Mineralogical Society of America; Volume: 83; Issue: 11-12 Part 1 Linguagem: Inglês

10.2138/am-1998-11-1209

1945-3027

Takashi Murakami, Toshihiro Kogure, Hiroyuki Kadohara, Toshihiko Ohnuki,

Clay minerals and soil interactions

Other| December 01, 1998 Formation of secondary minerals and its effect on anorthite dissolution Takashi Murakami; Takashi Murakami University of Tokyo, Mineralogical Institute, Tokyo, Japan Search for other works by this author on: GSW Google Scholar Toshihiro Kogure; Toshihiro Kogure Search for other works by this author on: GSW Google Scholar Hiroyuki Kadohara; Hiroyuki Kadohara Search for other works by this author on: GSW Google Scholar Toshihiko Ohnuki Toshihiko Ohnuki Search for other works by this author on: GSW Google Scholar Author and Article Information Takashi Murakami University of Tokyo, Mineralogical Institute, Tokyo, Japan Toshihiro Kogure Hiroyuki Kadohara Toshihiko Ohnuki Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X GeoRef, Copyright 2004, American Geological Institute. American Mineralogist (1998) 83 (11-12_Part_1): 1209–1219. https://doi.org/10.2138/am-1998-11-1209 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Takashi Murakami, Toshihiro Kogure, Hiroyuki Kadohara, Toshihiko Ohnuki; Formation of secondary minerals and its effect on anorthite dissolution. American Mineralogist 1998;; 83 (11-12_Part_1): 1209–1219. doi: https://doi.org/10.2138/am-1998-11-1209 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract To examine the relationship between product secondary minerals and dissolution of anorthite (An 95 Ab 5 from Fugoppe, Hokkaido, Japan), anorthite batch dissolution experiments were carried out. The dissolution experiments were done at 90, 150, and 210 degrees C for 3 to 355 days at pH 4.56 measured at 25 degrees C, which corresponds to 4.69, 4.97, and 5.40 at the respective experimental temperatures. A sequence of secondary minerals including boehmite, "modified boehmite," and kaolinite formed with increasing time. Modified boehmite, probably a metastable phase, is basically similar to boehmite in structure, but their stacking orders of the A1 octahedral layers as well as morphologies and chemistries are different. Modified boehmite shows laminations normal to the b* axis and contains 3 to 30 mol% Si. Silicon may be present between the A1 octahedral layers of modified boehmite. The anorthite dissolution is incongruent under the above conditions and approximated by a two-stage process. The first is characterized by the formation of boehmite, and the second by formation of modified boehmite. The dissolution rate in the second stage is slower than the first by approximately one order of magnitude because of the saturation state with respect to anorthite. To estimate the effect of the formation of secondary minerals on the anorthite dissolution, Gibbs free energies of anorthite dissolution (Delta G) were calculated, assuming conditions without the formation of secondary minerals. The calculations reveal that the formation of secondary minerals decreases the Delta G values significantly, and thus we can predict that the dissolution rates of anorthite increase due to the influence of the secondary minerals on Delta G. Modified boehmite functions as a sink for Si, and thus accelerates the dissolution rate of anorthite. The results indicate that the overall dissolution rate near equilibrium is affected by both the saturation with respect to a primary mineral and the formation of secondary minerals, but in the opposite sense. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.