| 1. |
- Lindgren, J., et al.
(författare)
-
Charge determinations of cellulose fibres of different origin - Comparison between different methods
- 2002
-
Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 17:1, s. 89-96
-
Tidskriftsartikel (refereegranskat)abstract
- Eleven different pulps, both chemically and thermomechanically produced and of both softwood and hardwood origin, were acid/base characterised. The measurements were performed as series of potentiometric and conductometric titrations. The potentiometric titration data revealed that all pulp materials were characterised by two buffer regions with an intervening buffer minimum at pHapproximate to6 and, from these measurements, it was possible to evaluate the buffer capacity in the low pH region. The capacity of the second buffer region could not be quantified since drifting readings characterised the data and since the region extended beyond the area of accurate pH determinations. With the conductometric titration data it was not possible to strictly separate the two buffer regions, and it was concluded that the method, as used in the present work, determined the low pH region buffer capacity plus a minor part of the buffer capacity in the upper buffer region. This conclusion was based on a finding that the differences in buffer capacity, as evaluated with the two methods, was related to the relative amount of the weaker acidity at pH>6. From the potentiometric titration data it was also possible to evaluate additional information, namely the initial charge of the pulps and the thermodynamic acidity of the acidic groups on the fibre. In an attempt to determine the origin of the weaker acidity and to determine the practical importance of this weaker acidity, paper sheets were made from one of the softwood pulps at neutral and alkaline pH and these sheets were spectroscopically and physically characterised.
|
|
| 2. |
- Persson, Per, et al.
(författare)
-
Comparison of the adsorption of o-phthalate on boehmite (γ-AlOOH), aged γ-Al2O3, and goethite (α-FeOOH)
- 1988
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 206:1, s. 252-266
-
Tidskriftsartikel (refereegranskat)abstract
- This work is concerned with the adsorption of o-phthalate (1,2-benzenedicarboxylate) at the water-metal (hydr)oxide interface. Previously published infrared spectroscopic, potentiometric, and adsorption data characterizing the boehmite (gamma-AlOOH) system are compared with new data collected for o-phthalate adsorption on aged gamma-Al2O3 and goethite (alpha-FeOOH). The study focuses on identifying bonding mechanisms, stoichiometries, and stabilities of the formed complexes, and comparing these among the three systems. Furthermore, the effects of ionic strength and composition of the ionic medium are investigated. The infrared spectroscopic data provided direct, molecular-level evidence for the existence of two dominating surface complexes on all three solids. One was shown to be a deprotonated outer-sphere species and the other was an inner-sphere surface complex. The inner-sphere complexes on the three solids were structurally related, and they were tentatively assigned to a mononuclear, chelating structure involving both carboxylate groups. The outer-sphere complexes were shown to increase in relative importance at high pH and low ionic strengths, while low pH and high ionic strengths favored the inner-sphere complexes. The information gained from the infrared spectroscopic investigations was used as qualitative input in the formulation of the surface complexation models. New models, based on the extended constant capacitance approach, were presented for the o-phthalate/aged gamma-Al2O3 and o-phthalate/goethite systems.
|
|
| 3. |
|
|
| 4. |
- Andersson, Rickard, et al.
(författare)
-
Practical pulp washing implications of Donnan equlibria in the fiber line
- 2006
-
Ingår i: Nordic Pulp and Paper Research Journal. ; 21:2, s. 264-71
-
Tidskriftsartikel (refereegranskat)abstract
- The washing of dissolved lignin residues from fibers is significantly favored at low ionic strengths. This is shown to affect the standard procedures for COD analysis of pulp, and evaluations of washing efficiency. In the paper, strategies to take advantage of the effect, in storage towers and in washing equipment, are discussed.
|
|
| 5. |
- Andersson, Rickard, et al.
(författare)
-
The Donnan theory applied to pulp washing - Experimental studies on the removal of anionic substances from an assumed fiber lumen volume and from the fiber wall
- 2003
-
Ingår i: Nordic Pulp and Paper Research Journal. ; 18:4, s. 404-12
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied how anionic materials, i.e. methylorange, IndulinAT, and water soluble lignin residues from mill sampled pulps, are distributed between a restricted fiber wall liquor volume and the suspension liquor, as a function of the suspension liquor composition. The influence of time, temperature, and molecular size on the leaching of lignin residues from pulp fibers was also studied, as was the exchange of the residues between an assumed fiber lumen volume and the surrounding suspension liquor.It was shown that all the liquor up to a consistency of 35% can be considered as one homogeneous suspension liquor in all practical mill and laboratory situations. A gentle mechanical mixing or liquor displacement is sufficient to exchange the dissolved lignin residues between the assumed lumen volume and the surrounding suspension liquor. It was also shown that the level of mobile anionic material in the fiber wall liquor volume is significantly depleted at low salt concentrations and that the Donnan theory, which describes the fiber ion exchange properties, could be used to estimate the leaching of lignin residues from pulp fibers. Relatively low concentrations of magnesium, i.e. below 50 mM, or high concentrations of sodium ions, i.e. above 400 mM, seem to cause precipitation of these residues within the fiber wall, and reduce the amount of leachable lignin. This phenomenon is not accounted for by the Donnan theory. The leaching of high molecular weight lignin residues was found to be more sensitive to salt and temperature effects than low molecular weight residues.
|
|
| 6. |
- Athely, Karin, et al.
(författare)
-
Acid-base properties of oxygen-delignified kraft pulps
- 2001
-
Ingår i: Nordic Pulp & Paper Research Journal. ; 16:3, s. 195-203
-
Tidskriftsartikel (refereegranskat)abstract
- The acid-base properties of oxygen-delignified kraft pulps have been investigated in 0.02 and 0.10 mol/L (Na)Cl-media at 25 degreesC. The measurements have been performed with high precision potentiometric titrations in the pH-range of 3 to 5.5. The acid-base properties were ascribed to fibre-bound carboxylate groups. The acid-base reaction is affected by the charge arising in the fibre when the acid groups are deprotonated, and can be described by an intrinsic constant, beta (s)(1,1(intr.)) valid for an uncharged surface, and a capacitance of the electrical double layer, representing the influence of the surface charge. Two investigated softwood pulps were found to have similar acid-base properties having log beta (s)(1,1(intr.))-values of 3.20 and 3.25 respectively in 0.02 mol/L (Na)Cl, while the investigated hardwood pulp had a log beta (s)(1,1(intr.))-value of 3.45. When the strength of the ionic medium increased, the acid strength of the fibre-bound carboxylic acid groups increased. The influence of the charged groups on the acid-base properties is affected by the ionic strength and the distance between the acid groups on the fibre. The charged groups had the smallest influence on the acid-base properties in the hardwood, even though the amount of acid groups per unit weight was approximately twice that in the softwood.
|
|
| 7. |
- Clausén, Maria, et al.
(författare)
-
Characterisation of gallium(III)-acetate complexes in aqueous solution: A potentiometric, EXAFS, IR and molecular orbital modelling study
- 2002
-
Ingår i: Journal of Chemical Society Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1472-7773 .- 1364-5447. ; , s. 2559-64
-
Tidskriftsartikel (refereegranskat)abstract
- The aqueous gallium(III)-acetate system was studied in 0.6 M Na(Cl) at 25 °C using a multi-technique approach, including potentiometry, IR spectroscopy, EXAFS spectroscopy and molecular orbital calculations. The potentiometric data were satisfactorily explained by a model which includes one mononuclear and one binuclear complex. The corresponding equilibrium constants defined according to the reactionsGa3++ HAc GaAc2++ H+2Ga3++ HAc + 2H2O Ga2(OH)2Ac3++ 3H+are log –1,1,1=–2.08 ± 0.09 and log –3,2,1=–5.65 ± 0.06, respectively. The latter complex has a stoichiometry identical to that previously identified in the aluminium(III)-acetate system. Also in agreement with this system, the IR and EXAFS data strongly indicates that this complex consists of two edge-sharing Ga octahedra bridged with an acetate ion, and should be formulated [Ga2(µ-OH)2(µ-O2CCH3)]3+. This interpretation is further supported by the molcular orbital calculations.
|
|
| 8. |
- Clausén, Maria, et al.
(författare)
-
Spectroscopic studies of aluminum and gallium complexes with oxalate and malonate in aqueous solution
- 2003
-
Ingår i: Journal of Molecular Structure. ; 648:3, s. 225-35
-
Tidskriftsartikel (refereegranskat)abstract
- The local structures of Ga(III) in aqueous oxalate and malonate complexes were studied by means of Ga K-edge EXAFS spectroscopy. Irrespective of the number and type of coordinated ligands, the EXAFS results showed very regular first coordination shells consisting of six oxygen atoms. Scattering paths from more distant atoms revealed that both oxalate and malonate form mononuclear chelate structures where one oxygen from each carboxylate group binds to Ga(III). Again, very little variation in bond distances and no changes in coordination modes were detected as the number of ligands coordinated to Ga(III) was varied. Based on the very close resemblance of IR spectra of oxalate and malonate complexes of Al(III), and the corresponding complexes of Ga(III), it is believed that the local structures of the Al(III) complexes are similar to those of the Ga(III) complexes in terms of ligand coordination modes and distortions. This conclusion was corroborated by results from theoretical frequency calculations.
|
|
| 9. |
- Clausén, Maria, et al.
(författare)
-
Spectroscopic studies of aqueous gallium(III) and aluminum(III) citrate complexes
- 2005
-
Ingår i: JOURNAL OF INORGANIC BIOCHEMISTRY. - : Elsevier BV. - 0162-0134. ; 99:3, s. 716-26
-
Tidskriftsartikel (refereegranskat)abstract
- Aqueous gallium(III) citrate complexes have been studied in the 10(-2) M concentration range with extended X-ray absorption fine structure (EXAFS) and FTIR techniques. From EXAFS data, one mononuclear and one oligomeric species were identified at different Ga(III) to citrate ratios. The first shell of the mononuclear complex was found to be distorted, with average Ga-O bond lengths of 1.95 and 2.06 Angstrom, in agreement with the solid-state structure of Ga(Cit)(2)(3-) (Cit = citrate). Also the oligomeric species was found to have a distorted first shell, with average Ga-O bond lengths of 1.95 and 2.04 Angstrom. This complex was found to contain two Ga-Ga distances at 3.03 and 3.56 Angstrom, typical for edge and corner sharing GaO6 octahedra, respectively. The gallium(III) and aluminum(III) citrate systems were compared by means of FTIR, and were found to be analogous. The IR results suggest that the bond lengths derived from EXAFS for the 1:2 gallium(III) citrate complex also provide a good estimate of the corresponding distances in the mononuclear 1: 1 complex. Direct coordination of citrate to the metal ions in the oligomeric gallium(III) citrate complex was indicated from both EXAFS and IR results, and this complex is stoichiometrically analogous to the Al-3(H(-1)Cit)(3)(OH)(H2O)(4-) complex, which has been structurally determined. However, while the formation of the aluminum trimer has been shown to be slow, the gallium trimer was significantly more labile with a rate of formation indicated to be in the order of seconds or faster.
|
|
| 10. |
|
|
