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Structural investigations of natural and synthetic chlorite minerals by X-ray diffraction, Mossbauer spectroscopy and solid-state nuclear magnetic resonance
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
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2006 (English)In: Clays and clay minerals, ISSN 0009-8604, ISSN 0009-8604, Vol. 54, no 2, 252-265 p.Article in journal (Refereed) Published
Abstract [en]

The structures of one synthetic and two natural chlorites of the chlinochlore type were explored using X-ray diffraction, magic-angle spinning nuclear magnetic resonance (NMR) and Mossbauer spectroscopy. Rietveld refinements indicated that all structures are of the trioctahedral ordered IIb polytype. Mossbauer spectra provided the ratio Fe-II/Fe-III but gave no evidence for the presence of Fe-III in the brucite-like sheet. We also report unit-cell parameters, Mossbauer isomeric shifts, Si-29 NMR chemical shifts as well as Al-27 isotropic shifts and quadrupolar coupling parameters. Very broad Si-29 NMR peaks from the natural samples prevented us from obtaining accurate information on the Si-Al ordering in the tetrahedral sheets; the limitations of Si-29 NMR as applied to natural chlorites are discussed. High-resolution 3QMAS NMR resolved the Al-27 signal of the M4 octahedral site in the brucite-like sheet from the other three Al signals of crystallographically inequivalent octahedral positions.

Place, publisher, year, edition, pages
2006. Vol. 54, no 2, 252-265 p.
Keyword [en]
Al-27 NMR, cation distributions, chlorite, layered mineral, mineral structure, Mossbauer spectroscopy, Si-29 NMR, XRD
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-24161DOI: 10.1346/CCMN.2006.0540210ISI: 000237465700010Scopus ID: 2-s2.0-33646558014OAI: oai:DiVA.org:kth-24161DiVA: diva2:344376
Note

QC 20100819

Available from: 2010-08-19 Created: 2010-08-19 Last updated: 2014-04-07Bibliographically approved
In thesis
1. Chlorite: Geochemical properties, Dissolution kinetcis and Ni(II) sorption
Open this publication in new window or tab >>Chlorite: Geochemical properties, Dissolution kinetcis and Ni(II) sorption
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In Sweden, among other countries, a deep multi-barrier geological repository, KBS-3, is planned for the burial of nuclear waste. One of the barriers is identified as the grantic bedrock itself and in this environment chlorite is present at surfaces in fracture zones.

This thesis is focused on characterisation of chlorite samples and studies of their dissolution and sorption behaviour, in order to verify chlorites capacity to retard possible radionuclide migration in the case of leaking canisters.

Chlorite dissolution of has been studied in the pH interval 2-12, and as expected the dissolution is highest at acidic pH and at most alkaline pH, whereas dissolution is lowest at near neutral pH values. Chemical and physical properties of chlorites clearly influence the dissolution rates, and at steady-state dissolution rates in the interval 10-12 ‑ 10-13 mol g-1 s-1 was observed.

Sorption studies were performed since Ni(II) is one of the important activation products in spent nuclear fuel and sorption data on minerals like chlorite are lacking. Ni(II) sorption onto chlorite was studied using batch technique as a function of; pH, concentration of Ni(II), ionic strength and solid concentrations. As expected, the sorption of Ni(II) onto chlorite was pH dependent, but not ionic strength dependent, with a sorption maximum at pH ~ 8, and with a Kd of ~ 103 cm3/g. This confirms that the Ni(II) sorption onto chlorite is primarily acting through surface complexation. The acid-base properties were determined by titrations and described by a non-electrostatical surface complexation model in FITEQL. Further, the sorption results were fit with a 2-pK NEM model and three surface complexes, Chl_OHNi2+, Chl_OHNi(OH)+ and Chl_OHNi(OH)2, gave the best fit using FITEQL.

Abstract [sv]

Sverige är ett av de länder som planerar ett geologiskt slutförvar kallad KBS-3, bestående av ett antal barriärer, för placering utav det använda kärnbränslet. En av dessa barriärer är identifierad som själva berggrunden där det tilltänkta förvaret kommer att byggas och i denna miljö förekommer klorit på granitytor i sprickzoner.

Denna doktorsavhandling karakteriserar kloriter och studerar deras upplösnings- och sorptionsbeetende, för att kunna bestämma huruvida kloriter är utav betydelse som naturlig barriär för eventuell radionuklidtransport från det använda kärnbränslet.

Upplösning av klorit har undersökts i pH intervallet 2-12 och graden av upplösningen är som förväntat högst vid sura respektive mest basiska pH och lägst där pH är neutralt. Denna studie bekräftar att den kemiska sammansättning och de fysikaliska egenskaper hos kloriterna påverkar upplösningshastigheterna och vid steady‑state har upplösningshastighet bestämts till 10-12 ‑ 10-13 mol g-1 s-1.

Sorptionsstudier genomfördes då Ni(II) är en viktig aktiveringsprodukt och data rörande Ni(II) sorption till klorit saknas. Ni(II) sorption till klorit har studerats i; varierande pH, olika initiala Ni(II) koncentrationen, olika jonstyrka och olika fastfas förhållanden där individuella satser i serie har nyttjats. Som förväntat är sorptionen av Ni(II) till klorit pH beroende men inte jonstyrkeberoende och ett sorpions maximum observerades vid pH ~ 8, med ett Kd‑värde på ~ 103 cm3/g. Från detta dras slutsatsen att sorptionen av Ni(II) till klorit sker mestadels genom ytkomplexering. Syra-bas egenskaperna hos kloriterna bestämdes genom titreringar och bekrevs med en icke‑elektrostatisk modell i FITEQL. Vidare har passning av sorptionsresultaten utförts med en 2-pK NEM-modell och tre ytkomplex, Chl_OHNi2+, Chl_OHNi(OH)+ och Chl_OHNi(OH)2, vilket gav den bästa passningen av data med FITEQL.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. xii, 81 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:9
Keyword
chlorite, dissolution kinetics, Ni(II) sorption, surface complexation
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:kth:diva-10139 (URN)978-91-7415-247-0 (ISBN)
Public defence
2009-04-24, D2, Lindstedsvägen 5, entreplan, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100819Available from: 2009-05-05 Created: 2009-03-25 Last updated: 2010-08-19Bibliographically approved

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