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Surface alteration of plagioclase during acid dissolution
Author(s) -
Seyama Haruhiko,
Kinoshita Kaoru,
Soma Mitsuyuki
Publication year - 2002
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.1302
Subject(s) - plagioclase , dissolution , x ray photoelectron spectroscopy , leaching (pedology) , chemistry , silicate minerals , quartz , chemical composition , silicate , inorganic chemistry , surface layer , analytical chemistry (journal) , layer (electronics) , materials science , chemical engineering , geology , environmental chemistry , metallurgy , organic chemistry , soil science , engineering , soil water
To examine the dissolution mechanism of silicate minerals in acidic solution, XPS was applied to plagioclase samples (Na 0.5 Ca 0.5 Al 1.5 Si 2.5 O 8 ) treated with 5 × 10 −2 , 5 × 10 −4 or 5 × 10 −6 mol l −1 H 2 SO 4 for 3 h, 1 day and 1 week. The atomic abundances of Na, Ca and Al relative to Si in the surface layer of acid‐leached (5 × 10 −2 mol l −1 H 2 SO 4 ) plagioclase decreased with increasing reaction time. The Si 2s and O 1s photoelectron spectra were shifted to higher binding energies during dissolution, and their binding energies were comparable to those of quartz after treatment for 1 week. From the preferential leaching of Na, Ca and Al, and the chemical shifts of the Si 2s and O 1s spectra, the formation of hydrous silicon dioxide on the mineral surface was deduced. The surface chemical composition of plagioclase changed in the same manner during dissolution by H 2 SO 4 at a low concentration (5 × 10 −4 mol l −1 ), although the magnitude of the decrease in surface concentrations of Na, Ca and Al was lower, suggesting the formation of a thinner altered surface layer. In addition, Al was less depleted than Na or Ca. Thus Na and Ca are more susceptible to acid leaching than Al. However, after dissolution in 5 × 10 −6 mol l −1 H 2 SO 4 , the relative surface abundance of Al was slightly higher than that of the untreated sample. Surface enrichment in Al is probably associated with the formation of hydrous oxides of Si and Al. Copyright © 2002 John Wiley & Sons, Ltd.