Chlorite: Geochemical properties, Dissolution kinetics and Ni(II) sorption Åsa Zazzi Doctoral Thesis in Chemistry KTH Chemical Science and Engineering Stockholm, Sweden, 2009 ________________________________________________________________ AKADEMISK AVHANDLING Som med tillstånd av Kungliga Tekniska Högskolan i Stockholm framlägges till offentlig granskning för avläggande av Filosofie Doktorsexamen i Kemi fredagen den 24 april 2009, kl. 10.00 i D2, Lindstedsvägen 5, Entreplan, Stockholm. Fakultetsopponent är Ph. D. Peter Vilks, AECL, Whiteshell Laboratories, Canada. Avhandlingen försvaras på engelska. Chlorite: Geochemical properties, Dissolution kinetics and Ni(II) sorption Åsa Zazzi Doctoral Thesis KTH Chemical Science and Engineering Royal Institute of Technology Stockholm, Sweden, 2009 ISBN 978-91-7415-247-0 ISSN 1654-1081 TRITA-CHE Report 2009:9 © Åsa Zazzi, Mars 2009 Printed by E-PRINT AB, Stockholm 2009. När man är en björn med en mycket liten hjärna och tänker ut saker, upptäcker man att en idé som verkade vara riktigt idéaktig inne i hjärnan, är annorlunda när den kommer ut i det fria och andra människor ser på. Nalle Puh When you are a Bear of Very Little Brain, and Think of Things, you find sometimes that a Thing which seemed very Thingish inside you, is quite different when it gets out into the open and has other people looking at it. Winnie the Pooh Abstract 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. i ii Sammanfattning 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. iii iv List of publications This thesis is based on the following papers: I. The effect of pH on chlorite dissolution rates at 25º C Åsa B. Gustafsson1 and Ignasi Puigdomenech In: Scientific Basis for Nuclear Waste Management, XXVI (R. J. Finch, D. B. Bullen, eds.), Material Research Society, Boston, MA, USA, 2002, vol. 757, p. 649-655. II. Study of Ni(II) Sorption on Chlorite-A Fracture Filling Mineral In Granites Å. Gustafsson1, M. Molera, and I. Puigdomenech In: Scientific Basis for Nuclear Waste Management XXVIII (J.M. Hanchar, S. Stroes-Gascoyne, L. Browning, eds.), Material Reseach Society, San Fransisco, CA, USA, 2004, vol. 824 p. 373-379. III. Structural Investigations of natural and synthetic chlorite minerals by X-ray diffraction, Mössbauer spectroscopy and Solid-state Nuclear Magnetic Resonance Åsa Zazzi, Tomas K. Hirsch, Ekaterina Leonova, Andrei Kaikkonen, Jekabs Grins, Hans Annersten, and Mattias Edén In: Clays and Clay Minerals; April 2006; v. 54; no. 2; p. 252-265 IV. Ni(II) sorption on natural Chlorite Åsa Zazzi, Anna-Maria Jakobsson and Susanna Wold Submitted to: Applied Geochemistry V. Ni(II) sorption on the fracture filling mineral Chlorite Åsa Zazzi and Susanna Wold Accepted for publication in: Scientific Basis for Nuclear Waste Management XXXII (R.B. Bebak, N.C. Hyatt and D.A. Pickett, eds). Material Research Society, Boston, MA, USA, 2008, vol 1124. VI. Dissolution rates and stoichiometry of two different chlorites as a function of pH Åsa Zazzi, Maria E. Malmström and Susanna Wold Manuscript 1 Maiden name, changed to Zazzi by way of matrimony. v vi Comment on my contribution to the publications Paper I: I performed the experimental work, participated in evaluation of the data and wrote most part of the manuscript. Paper II: I participated in the design of experiments and performed most of the experimental work. I performed parts of the simulations, participated in evaluation of the data and wrote the manuscript. Paper III: I provided the chlorite samples, prepared the synthetic chlorite and wrote parts of the Introduction section of the manuscript. Paper IV: I designed most of the experiments and performed most of the experimental work. I participated in discussions about the simulations as well as in evaluation of data and wrote most of the manuscript. Paper V: I designed and performed the experiments, evaluated the data and wrote the manuscript. Paper VI: I designed and performed the experiments, participated in data evaluation and prepared parts of the manuscript. vii viii List of abbreviations Abbreviations used in text. AFM Atomic Force Microscopy BET Brunauer-Emmett-Teller, a method for measuring the surface area of powders CCM Constant Capacitance Model CEC Cation Exchange Capacity DLM Diffuse layer model ICP-MS Inductively Couple Plasma equipped with Mass Spectrometry ICP-OES Inductively Couple Plasma equipped with Atomic Emission Spectroscopy KBS-3 Kärnbränslesäkerhet-3, the Swedish concept for spent nuclear fuel, the abbreviation is always used. LSC Liquid Scintillation Counting MES 2-(N-morpholino)ethanesulfonic acid MUSIC Multi Site Complexation Model NEM Non Electrostatic Model SCM Surface Complexation Model SEM Scanning Electron Microscopy SEM-EDS Scanning Electron Microscopy-Energy Dispersive Spectroscopy SKB Swedish Nuclear Fuel and Waste Management Company TLM Triple Layer Model TOT Tetrahedral-Octahedral-Tetrahedral coordination TRIS 2-Amino-2-hydroxymethyl-1,3-propanediol UV-VIS Ultraviolet-Visible Spectroscopy XRD X-ray Diffraction ix x Table of contents Abstract ................................................................................................................................................. i Sammanfattning............................................................................................................................ iii List of publications ........................................................................................................................ v Comment on my contribution to the publications.................................................vii List of abbreviations.................................................................................................................... ix 1. Introduction................................................................................................................................. 1 1.1 Background .......................................................................................................................... 1 1.2