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Cation adsorption properties of substituted kraft fibres: an experimental and thermodynamic modelling study
Umeå University, Faculty of Science and Technology, Chemistry.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Acid/base and metal ion adsorption properties have been investigated for a range of chemically modified bleached Kraft fibre materials (pulps). The studies were performed via potentiometric titrations, Flame Atomic Absorbtion (and Emission) Spectroscopy, Inductively Coupled Plasma Optical Emission Spectroscopy and Extended X-ray Absorbtion Fine Structure measurements. As a result of a chemical modification procedure, the total concentration of acidic carboxylate groups in the fibre materials ranged between 43 and 590 μmol/g.

The preferable surface potential model for modelling the ionic strength dependent acid/base properties of fibre materials with low charge densities, i.e. unmodified fully bleached Kraft fibre materials, was found to be the Basic Stern Model. For fibre materials with high total charge, ≳100 μmol/g, this model resulted in poor fits to data, and for such materials a number of Constant Capacitance Models, one at each ionic strength, must be recommended.

With respect to metal ion adsorption, the results have indicated that the unspecific Donnan theory could correctly model the simultaneous adsorption of several metal ions, i.e. K+, Na+, Mg2+, Ca2+ and Cu2+, provided that the salt concentration in the fibre suspension is low. In suspensions of high salt concentration it was, however, found that this very same model strongly underestimated the adsorption of Ca2+ and Cu2+. Here, the Donnan model had to be complemented by specific ion exchange equilibria. These results were corroborated by spectroscopic evidence of specific interactions between Cu2+-ions and fibres. The spectroscopic indication of a complex formed between two fibre surface carboxylate groups and one Cu2+-ion, agree with the specific ion exchange model. It was therefore concluded that specific metal ionfibre interactions cannot be neglected, especially at high salt concentrations.

The interactions occurring between the polycation GaO4Al12(OH)24(H2O)127+ and fibre materials were studied by both adsorption and spectroscopic measurements. These indicate that GaO4Al12(OH)24(H2O)127+ is surprisingly stable in fibre suspensions and that intact GaO4Al12(OH)24(H2O)127+- ions are strongly adsorbed onto the fibres. Also for this ion, specific interactions has to be considered, since the strong adsorption registered was too strong to be explained by Donnan equilibria. In the thesis, the stochiometric composition and an equilibrium constant characterising these interactions is presented.

Place, publisher, year, edition, pages
Umeå: Kemi , 2008. , 49 p.
Keyword [en]
Kraft fibres, Donnan equilibria, ion exchange, acid/base properties, potentiometric titrations, thermodynamic modelling, NPEs, GaAl12 7+, EXAFS
National Category
Other Basic Medicine
Identifiers
URN: urn:nbn:se:umu:diva-1891ISBN: 987-91-7264-672-8 OAI: oai:DiVA.org:umu-1891DiVA: diva2:142326
Public defence
2008-11-14, KB3A9, KBC-Huset, Umeå Universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2008-10-24 Created: 2008-10-24 Last updated: 2009-07-03Bibliographically approved
List of papers
1. Alternative models for describing the acid/base properties of bleached softwood fibres
Open this publication in new window or tab >>Alternative models for describing the acid/base properties of bleached softwood fibres
2005 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 20, no 4, 378-382 p.Article in journal (Refereed) Published
Abstract [en]

To evaluate the capacity of different thermodynamic models to mimic the build-up of charge on fully bleached softwood fibres as a function of -log[H+] and ionic strength (0.01-0.6 M NaCl), the model of an Ideal Monoprotic Acid, the Constant Capacitance Model (CCM), the Basic Stern Model (BSM), and the Diffuse Layer Model (DLM) were compared. The Ideal Monoprotic Acid, IMA, model consistently yielded a too steep increase in the build up of charge with -log[H+] and thereby indicated the need for applying a surface potential model. The "best" of these, with respect to describing the experimental data, was found to be the Constant Capacitance Model, which utilises an individual equilibrium constant and an individual capacitance value at each ionic strength modelled. However, the Basic Stern Model, which uses only two variables over the entire ionic strength interval, was found to describe data almost as well. Therefore, in modelling applications where a variation in the salt concentration is significant, the Basic Stern Model must be judged as being superior to the Constant Capacitance Model. As for the IMA model, the Diffuse Layer Model, finally, was found to yield a too steep increase in the fibre charge with rising -log[H]. Nevertheless, it was found to model the variation of the apparent acidity with ionic strength, relatively well.

Keyword
bleached softwood kraft fibre, ionic strength; acid/base properties, surface charge, equilibrium modelling
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-13318 (URN)10.3183/NPPRJ-2005-20-04-p378-382 (DOI)
Available from: 2007-05-08 Created: 2007-05-08 Last updated: 2012-04-18Bibliographically approved
2. Acid/base and metal adsorption properties of CMC-type softwood Kraft pulps of different charge
Open this publication in new window or tab >>Acid/base and metal adsorption properties of CMC-type softwood Kraft pulps of different charge
2006 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 21, no 3, 372-381 p.Article in journal (Refereed) Published
Abstract [en]

Pulp materials ranging in charge from zero to 280 mmol/g were synthesised and characterised with respect to ion exchange properties. Both the Constant Capacitance and the Basic Stern Models were found applicable to simulate the acid/base properties. For all materials, the Donnan distribution model gave a good description for the metal binding properties.

Keyword
Basic Stern Model, Carboxymethyl cellulose (CMC), Carboxymethylation, Cellulose fibres, Constant capacitance model, Donnan Distribution Model, Ionic strength dependence, Kraft pulp, Metal ions, Potentiometric titration
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-12741 (URN)10.3183/NPPRJ-2006-21-03-p382-394 (DOI)
Available from: 2007-05-08 Created: 2007-05-08 Last updated: 2012-04-18Bibliographically approved
3. A multitechnique study of the interactions between H+, Na+, Ca2+ and Cu2+, and two types of softwood Kraft fibre materials
Open this publication in new window or tab >>A multitechnique study of the interactions between H+, Na+, Ca2+ and Cu2+, and two types of softwood Kraft fibre materials
2008 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 328, no 2, 248-56 p.Article in journal (Refereed) Published
Abstract [en]

Aiming for a better understanding of the interactions between water suspended cellulose fibres and metal ions, this study was focused on characterising the interactions between Ca2+, Cu2+ and two different fibre materials—a fully bleached softwood Kraft pulp, and a chemically modified fully bleached softwood Kraft fibre material. The study was conducted as a function of pH (2–7), and both in the absence and presence of an excess of Na+ ions, 0–100 mM Na(Cl). For both fibre materials, adsorption data collected in the absence of Na+ were fully explained by the unspecific Donnan ion-exchange model. However, in an excess of Na(Cl), data clearly indicated that higher amounts of divalent metal ions adsorbed, than predicted by the Donnan model. Therefore, to model these data, specific metal ion–fibre surface complexes were assumed to form, in addition to the Donnan ion-exchange. A neutral surface species involving two surface carboxylate groups and one metal ion was, for both metal ions, found to yield a good description of data at all ionic strengths. In the case of Cu2+, the existence of this complex was corroborated by Cu K-edge EXAFS data, suggesting that copper ions interacts directly with carboxyl groups present int the fibres. EXAFS data also indicate that one Cu2+ interacts with two carboxyls.

Graphical abstract

In combination with unspecific Donnan interactions, specific interactions between divalent metal ions (Ca2+ and Cu2+) and cellulose fibre carboxylic groups were evidenced from both macroscopic adsorption data and spectroscopic measurements.

Keyword
Metal ions, Kraft fibres, Donnan, Adsorption, Ion exchange, Surface complexes, EXAFS, Affinity
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-10631 (URN)doi:10.1016/j.jcis.2008.09.027 (DOI)
Available from: 2008-12-15 Created: 2008-12-15 Last updated: 2012-04-18Bibliographically approved
4. A study of the stability and adsorption behaviour of the ε-Keggin GaO4Al12(OH)24(H2O)127+ polycation in suspensions of fibre materials
Open this publication in new window or tab >>A study of the stability and adsorption behaviour of the ε-Keggin GaO4Al12(OH)24(H2O)127+ polycation in suspensions of fibre materials
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-3562 (URN)
Available from: 2008-10-24 Created: 2008-10-24 Last updated: 2012-04-18Bibliographically approved
5. Comparison between specific surface complexation and Donnan models for describing the adsorption of cations on Kraft fibres – a review
Open this publication in new window or tab >>Comparison between specific surface complexation and Donnan models for describing the adsorption of cations on Kraft fibres – a review
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-3563 (URN)
Available from: 2008-10-24 Created: 2008-10-24 Last updated: 2012-04-18Bibliographically approved

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