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Chemical, Hr-Xrd and Spectroscopic Approaches to Short-Time Dissolution Behavior of Kaolin1tic Soils

Published online by Cambridge University Press:  10 February 2011

N. Malengreau  and
G. Sposito
N. Malengreau
Affiliation:
Department of Environmental Science, Policy and Management, Ecosystem Sciences Division, University of California, Berkeley, CA94720, USA.
G. Sposito
Affiliation:
Department of Environmental Science, Policy and Management, Ecosystem Sciences Division, University of California, Berkeley, CA94720, USA.
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Abstract

Batch experiments were conducted at varying proton concentrations on a representative tropical soil in order to investigate its dissolution behavior over a 12h period. The release kinetics of Al, Fe, Si and C were investigated over a 2 to 6 pH range. The pH-dependence exhibited a “point of minimum dissolution” at pH ≈ p.z.n.c. Light scattering measurements on supernatant solutions indicated that colloids were dispersed mainly at pH > p.z.n.c. These results suggested a two-pathway dissolution process, with organic matter playing a role in both pathways. High-resolution X-ray diffraction as well as electron spin resonance and diffuse reflectance spectroscopies, were applied to characterize solid-phase transformations in the course of dissolution. With the exception of quartz, all mineralogical phases (kaolinite, and minor phases such as Fe-, Al- and Ti-oxides) remained unchanged or were slightly affected. A significant loss of quartz (about 10% by mass) was observed after a 12h dissolution at pH 2. Minor phases might have played an important role in stabilizing kaolinite, and dissolved silica may have hindered the dissolution of minor phases.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 432: Symposium S – Aqueous Chemistry and Geochemistry of Oxides , 1996 , 289
Copyright
Copyright © Materials Research Society 1997

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