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Chlorite: Geochemical properties, Dissolution kinetcis and Ni(II) sorption
KTH, School of Chemical Science and Engineering (CHE), Chemistry. (Zoltan Szabo)
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 [en]
chlorite, dissolution kinetics, Ni(II) sorption, surface complexation
National Category
Other Basic Medicine
Identifiers
URN: urn:nbn:se:kth:diva-10139ISBN: 978-91-7415-247-0 (print)OAI: oai:DiVA.org:kth-10139DiVA: diva2:209484
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
List of papers
1. The effect of pH on chlorite dissolution rates at 25 degrees C
Open this publication in new window or tab >>The effect of pH on chlorite dissolution rates at 25 degrees C
2003 (English)In: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVI, 2003, Vol. 757, 649-655 p.Conference paper, Published paper (Refereed)
Abstract [en]

The Swedish nuclear industry is planing to dispose spent nuclear fuel encapsulated in copper canisters in granitic bedrock at a depth of approx. 500 m. The reducing capacity of the geosphere is important for canister corrosion and radionuclide migration. The main inorganic reductants are Fe(II)-containing minerals: biotite in the bedrock, and pyrite and chlorite in the fracture filling minerals as well as in the buffer and backfill. As a consequence, the dissolution of chlorite is an important parameter when considering the reducing capacity available to groundwaters around the repository. The weathering rates of a chlorite sample from Taberg in central Sweden has been studied in 0.01 M NaCl media at (25+/-1)degreesC in the pH region 2-12. The chlorite was characterized before and after grinding and sieving, and was found to have a relatively low Fe-content, with the formula ((Mg9.44Fe0.72Al1.68)-Al-II)(Si6.47Al1.40Fe0.13III)O-20(OH)(16). Kinetic experiments were performed using a thin-film continuous flow-through technique with flow rates of 5 mL/h or 2.7 mL/h. Ibis technique prevents the precipitation of secondary phases such as iron(III) hydroxides. Solution samples were taken after a reaction time of 0-30 days. The contents of released Al, Fe, Mg and Si were analyzed using an Inductively Coupled Plasma emission spectroscopy (ICP-AES) technique and then normalized to the Brunauer-Emmet-Teller (BET) surface area and flow-rate in order to obtain rates of dissolution. The dissolution rate of the chlorite studied was pH-dependent, and a minimum was observed in the neutral pH region. The dissolution rate (based on Si data) decreased from 7x10(-11) mol/(m(2) s) at pH=2 to 4x10(-13) mol/(m(2) s) at pHapproximate to7 and then increased to 3x10(-12) mol/(m(2) s) at pH=12.

Series
Materials research society symposium proceedings, ISSN 0272-9172
Keyword
precipitation kinetics; biotite dissolution; minerals; 80-degrees-c; temperature; dependence; kaolinite; iron; fuel
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-24159 (URN)000186634300088 ()1-55899-694-X (ISBN)
Conference
26th Symposium on the Scientific Basis for Nuclear Waste Management held at the 2002 MRS Fall Meeting BOSTON, MA, DEC 02-05, 2002
Note
QC 20100819Available from: 2010-08-19 Created: 2010-08-19 Last updated: 2010-08-19Bibliographically approved
2. Study of Ni(II) sorption on chlorite - a fracture filling mineral in granites
Open this publication in new window or tab >>Study of Ni(II) sorption on chlorite - a fracture filling mineral in granites
2004 (English)In: 28th Symposium on the Scientific Basis for Nuclear Waste Management held at the 2004 MRS Spring Meeting San Francisco, CA, APR 13-16, 2004, 2004, Vol. 824, 373-378 p.Conference paper, Published paper (Refereed)
Abstract [en]

Chlorite is an Fe(II)-containing phyllosilicate which is often present as a fracture filling mineral in e.g. granitic rocks. It may therefore be significant in influencing redox conditions and sorption processes in granitic groundwaters. The sorption properties of chlorite may therefore be important when modelling the migration of radionuclides under reducing conditions around nuclear waste repositories or in sites contaminated by mining waste. The sorption behaviour of Ni(II) onto a natural chlorite (Karlsborg, Sweden) was investigated using a batch technique. The effects of three different background electrolyte concentrations (0.01 M, 0.1 M and 0.5 M NaClO4) different pH values (ranging from 4 to 11) and different Ni(II) concentrations (10(-6) and 10(-8) M) were studied under anoxic conditions in a glove-box. Ni(II) solutions were spiked with 63 Ni and beta-Liquid scintillation counting (LSC) was used to determine the concentration of nickel in the bulk solution, allowing the calculation of solid-water distribution coefficients for the metal ion. The results of the sorption experiments show strong pH dependence at pH > 5, but the sorption is independent of ionic strength. The maximum adsorption is found in the pH range between 7 and 11 with K-d values approximate to10(3) cm(3)/g. A diffuse double layer model has been used to describe the experimental results.

Series
Materials research society symposium proceedings, ISSN 0272-9172
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:kth:diva-24160 (URN)000224543500056 ()2-s2.0-14944372867 (Scopus ID)
Note
QC 20100819Available from: 2010-08-19 Created: 2010-08-19 Last updated: 2011-10-31Bibliographically approved
3. Structural investigations of natural and synthetic chlorite minerals by X-ray diffraction, Mossbauer spectroscopy and solid-state nuclear magnetic resonance
Open this publication in new window or tab >>Structural investigations of natural and synthetic chlorite minerals by X-ray diffraction, Mossbauer spectroscopy and solid-state nuclear magnetic resonance
Show others...
2006 (English)In: Clays and clay minerals, ISSN 0009-8604, E-ISSN 1552-8367, 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.

Keyword
Al-27 NMR, cation distributions, chlorite, layered mineral, mineral structure, Mossbauer spectroscopy, Si-29 NMR, XRD
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-24161 (URN)10.1346/CCMN.2006.0540210 (DOI)000237465700010 ()2-s2.0-33646558014 (Scopus ID)
Note

QC 20100819

Available from: 2010-08-19 Created: 2010-08-19 Last updated: 2017-12-12Bibliographically approved
4. Ni(II) sorption on natural chlorite
Open this publication in new window or tab >>Ni(II) sorption on natural chlorite
2012 (English)In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 27, no 6, 1189-1193 p.Article in journal (Refereed) Published
Abstract [en]

Sorption of Ni(II) onto chlorite surfaces was studied as a function of pH (5-10), ionic strength (0.01-0.5 M) and Ni concentration (10(-8)-10(-6) M) in an Ar atmosphere using batch sorption with radioactive Ni-63 as tracer. Such studies are important since Ni(II) is one of the major activation products in spent nuclear fuel and sorption data on minerals such as chlorite are lacking. The sorption of Ni(II) onto chlorite was dependent on pH but not ionic strength, which indicates that the process primarily comprises sorption by surface complexation. The maximum sorption was at pH similar to 8(K-d = similar to 10(-3) cm(3)/g). Desorption studies over a period of 1-2 weeks involving replacement of the aqueous solution indicated a low degree of desorption. The acid-base properties of the chlorite mineral were determined by titration and described using a non-electrostatic surface complexation model in FITEQL. A 2-pK NEM model and three surface complexes, Chl_OHNi2+, Chl_OHNi(OH)(+) and Chl_OHNi(OH)(2), gave the best fit to the sorption results using FITEQL. The high K-d values and low degree of desorption observed indicate that under expected groundwater conditions, a large fraction of Ni(II) that is potentially leachable from spent nuclear fuel may be prevented from migrating by sorption onto chlorite surfaces.

Keyword
Chlorite minerals, Groundwater, Ionic strength, Radioactive wastes
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-24162 (URN)10.1016/j.apgeochem.2012.03.001 (DOI)000303464500014 ()2-s2.0-84860355599 (Scopus ID)
Note
QC 20120528. Updated from submitted to published.Available from: 2010-08-19 Created: 2010-08-19 Last updated: 2017-12-12Bibliographically approved
5. Ni(II) Sorption on the Fracture Filling Mineral Chlorite
Open this publication in new window or tab >>Ni(II) Sorption on the Fracture Filling Mineral Chlorite
2009 (English)In: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXXII, 2009, Vol. 1124, 531-536 p.Conference paper, Published paper (Refereed)
Abstract [en]

Abundance of the mineral chlorite as fracture filling material in granitic bedrock motivates sorption studies for quantification of the retention of radionuclides on this mineral. The activation product Ni-63 is an important component in spent nuclear fuel, accounting for a large contribution to the high activity level, and further motivates sorption studies of Ni on chlorite. Earlier sorption studies have been performed on larger mineral pieces; however, it is questionable if these data are representative for fracture filling material. Chlorite from a borehole core from Oskarshamn, Sweden, from the depth of 944 m has been characterized and the chemical composition determined prior to the experiments. The thickness of the fracture filling mineral is at maximum a couple of millimeters; therefore, careful removal of the thin chlorite layer from the core was performed with a carbide tool. The fraction was sieved to a size distribution of 63-118 mu m and ultrasonically washed. The major oxides were found to be 34.4 % SiO2, 21.6 % MgO, 15.4 % Al2O3 and 12.9 % Fe2O3 determined by Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) analysis. Sorption of Ni(II) to the sample was performed in 0.1 M NaClO4 with a batch technique inside a glove-box with Ar-atmosphere, using Ni-63 as a tracer with the Ni carrier concentration of 10(-6) and 10(-8) M. The percent sorption in these experiments was 57% at pH 5.5, 85 % at pH 6.5 and 92 % at pH 8.3, with the last value corresponding to maximum sorption No significant differences between the experiments performed in the two concentrations of 10(-6) and 10(-8) M were found. The degree of sorption on this fracture filling material is of the same magnitude as earlier studies of Ni sorption on chlorite provided from larger mineral pieces, using the same size fraction of the material. Sorption of Ni is, as expected, strongly pH dependent and Ni-63 escaping a breached canister will, reaching chlorite within the surrounding bedrock, be retarded due to strong sorption.

Series
Materials Research Society Symposium Proceedings, ISSN 0272-9172
Keyword
dissolution rates; ph; 25-degrees-c
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-24163 (URN)000270898900070 ()2-s2.0-70449382071 (Scopus ID)
Conference
32nd Symposium on Scientific Basis for Nuclear Waste Management held at the 2008 MRS Fall Meeting Boston, MA, DEC 01-05, 2008
Note
QC 20100819Available from: 2010-08-19 Created: 2010-08-19 Last updated: 2010-08-19Bibliographically approved
6. Dissolution rates and stoichiometry of two different chlorites as a function of pH
Open this publication in new window or tab >>Dissolution rates and stoichiometry of two different chlorites as a function of pH
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-24164 (URN)
Note

QC 20100819

Available from: 2010-08-19 Created: 2010-08-19 Last updated: 2014-09-22Bibliographically approved

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