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Specific surface area of some minerals commonly found in granite
KTH, School of Industrial Engineering and Management (ITM), Industrial Ecology.
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The specific surface area, determined by the BET method, is a parameter often used to scale results of mineral studies of surface reactions in terms of rate and capacity to the field scale. Such extrapolations of results from small-scale laboratory experiments to the field-scale are important within many environmental applications. An example of this is for the prediction of radionuclide retention in the bedrock surrounding a deep repository for radioactive waste, following failure of the engineered barriers, where radionuclides may sorb onto minerals constituting the geological environment.

As a first step, the approach used in this work is to study the relationship between specific surface area and the particle size (0.075-8 mm) and to approach the field scale via measurements on large, centimetre-sized pieces, for seven natural minerals commonly found in granite: apatite, biotite, chlorite, K-feldspar, hornblende, labradorite and magnetite. The underlying assumption is that sorption of radionuclides can be related to specific surface area of a particular mineral in a continuation of this project.The results show that the phyllosilicates biotite and chlorite have a specific surface area that is about 10 times larger than the other minerals. Over the range of particle size fractions studied, the specific surface area varies between 0.1 and 1.2 m2g-1 for biotite and chlorite. The other studied minerals have specific surface areas varying between 0.01 m2g-1 for the largest fraction and up to 0.06 - 0.12 m2g-1 for the smallest. Results show linear relationships between the specific surface area and the inverse of the particle size for all studied minerals for small particle sizes, as expected. For some minerals, however, the data seemingly can be divided in two linear trends, where a change in internal surface area, surface roughness and/or particle geometry as the particle size decreases may explain this behaviour.

Interestingly, for larger particles, there is a deviation from the linearity observed for small particles. Tentatively, this behaviour is attributed to a disturbed zone, created by the mechanical treatment of the material during particle size reduction, extending throughout small particles, but not altering an undisturbed core of the larger particles. In agreement with this, measurements on large pieces show a surface area 5 to 150 times lower than expected from the linear trends observed for the crushed material, implying an overestimation of the surface area and possibly also of the sorption capacities of the rock material from simple extrapolations of experimental results employing finely crushed material to the field situation.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , x, 69 p.
Series
Trita-IM, ISSN 1402-7615 ; 2011:32
Keyword [en]
Granite, Mineral, Surface area, BET, Sorption, Particle size
National Category
Geochemistry
Identifiers
URN: urn:nbn:se:kth:diva-41259ISBN: 978-91-633-9472-0 (print)OAI: oai:DiVA.org:kth-41259DiVA: diva2:443320
Presentation
2011-10-13, V1, Teknikringen 76, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Projects
Äspö Radionuclide sorption
Note
QC 20110929Available from: 2011-09-29 Created: 2011-09-23 Last updated: 2011-09-29Bibliographically approved
List of papers
1. Dependency of BET surface area on particle siz for some granitic minerals
Open this publication in new window or tab >>Dependency of BET surface area on particle siz for some granitic minerals
2011 (English)In: Proc. radiochem. acta, Vol. 1, 75-82 p.Article in journal (Refereed) Published
Abstract [en]

In order to assess the geochemical retention properties of rocks, which will be the final barrier for radionuclide transport to the biosphere in the case of a failed deep underground repository for spent nuclear fuel, radionuclide sorption experiments are usually made with crushed material. This raises the issue of extrapolating results obtained from laboratory experiments to the field scale. As sorption is generally related to the surface area of the geological material, it is then important to consider the dependency of the specific surface area on the particle size. In this work, BET surface area determinations of samples of different particle sizes are conducted on two minerals commonly found in granite: labradorite and magnetite. The results show a linearre lationship between BET surface area and the inverse of the particle size, up to a certain particle size. Furthermore, results also show that the specific surface area for intact, larger pieces is much smaller than the one predicted by a linear extrapolation of results on crushed material. Therefore, extrapolation of BET area for fine particles to the field situation will lead to an overestimation of the surface area and thereby also the radionuclide sorption, if sorption coefficients are extrapolated as well. Also of importance is that these results show that sorption experiments on crushed material may dominantly reflect properties of new surface, created during the mechanically treatment of the samples.

Keyword
Surface area, Particle size, Radionuclide, Magnetite, Plagioclase
National Category
Geochemistry
Identifiers
urn:nbn:se:kth:diva-41534 (URN)
Note

QC 20110929

Available from: 2011-09-29 Created: 2011-09-29 Last updated: 2017-06-09Bibliographically approved
2. Correlation between particle size and surface area for chlorite and K-feldspar
Open this publication in new window or tab >>Correlation between particle size and surface area for chlorite and K-feldspar
2010 (English)In: Water-Rock Interaction - Proceedings of the 13th International Conference on Water-Rock Interaction, WRI-13 / [ed] P. Birkle, I.S. Torres-Alvorado, 2010, 717-720 p.Conference paper, Published paper (Refereed)
Abstract [en]

The specific surface area as determined by BET analysis is often used for scaling mineral surface reaction capacities and rates between particles of different sizes as found in nature. Generally, an inverse proportionality between BET area and particle size is assumed, based on geometry. However, macroscopic laboratory studies of mineral surface reactions generally employ crushed material that may have been mechanically disturbed, potentially leading to an artificial increase in the specific surface area, and a change in the apparent surface reactivity. In this study, we determine the BET area for natural K-feldspar and chlorite samples from Sweden as function of particle size in a first step towards relating the surface reactivity for these minerals to grain size.

Keyword
BET analysis, Crushed materials, Different sizes, Grain size, K-feldspar, Laboratory studies, Particle size and surfaces, Surface reactivity
National Category
Geochemistry
Identifiers
urn:nbn:se:kth:diva-41536 (URN)2-s2.0-84860204698 (Scopus ID)978-041560426-0 (ISBN)
Conference
13th International Conference on Water-Rock Interaction, WRI-13; Guanajuato; Mexico; 16 August 2010 through 20 August 2010
Note

QC 20110929

Available from: 2011-09-29 Created: 2011-09-29 Last updated: 2014-09-03Bibliographically approved

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Licentiat_Isabelle Dubois(2745 kB)544 downloads
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