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Papers by Lars-olof Öhman

Research paper thumbnail of Equilibrium approaches to natural water systems—7. Complexation reactions of copper(II), cadmium(II) and mercury(II) with dissolved organic matter in a concentrated bog-water

Water Research, 1989

ABSTRACT Trace metal complexation by the dissolved organic matter in a concentrated bog-water has... more ABSTRACT Trace metal complexation by the dissolved organic matter in a concentrated bog-water has been studied using a potentiometric method (glass electrode). Bog-waters, sampled on five different times, were concentrated with a freezing-out technique and the complexation reactions involving Cu2+, Cd2+ and Hg2+ were investigated in 0.1 M ionic media. In the mercury(II) system, chloride was used as a competing ligand. Formation of binary CuL, CdL and HgL complexes was found. In the mercury(II) system a ternary HgH−1L complex was formed as well. The following values were obtained: log kCuL = 3.63 (Oct. 1983), 4.10 (Feb. 1984) and 3.99 (Sept. 1984); log kCdL = 2.84 (Jan. 1986); log kHgL = 10.37 and pKaHgL = 4.40 (Aug. 1985). Experimental data were evaluated using the least squares computer program LET-AGROPVRID. Distribution diagrams describing the speciation in experimental and natural conditions were constructed using the computer program SOLGASWATER.

Research paper thumbnail of Equilibrium and Structural Studies of Silicon(IV) and Aluminium(III) in Aqueous Solution. XXV. Composition and Stability of Aluminium Complexes with Methylmalonic Acid and Alanine

Acta Chemica Scandinavica, 1990

Research paper thumbnail of Corrosion of dense polycrystalline alpha-Al2O3 in NaHCO3-buffered water solution of pH 8.5 at 40-degrees-C-100-degrees-C

American Ceramic Society Bulletin

Research paper thumbnail of Stable and metastable complexes in the system H+-Al3+-Citric acid

Research paper thumbnail of Citrate as the main small molecule binding Al3+ in serum. Clin Chem

Clinical Chemistry

A recent proposal (Clin Chem 1992;38:1809-18) that inorganic phosphate is the predominant small m... more A recent proposal (Clin Chem 1992;38:1809-18) that inorganic phosphate is the predominant small molecule binding J3 in blood serum is shown to be incorrect. Experiments in which Al3 is added to solutions containing phosphate and citrate in the same proportions as in serum clearly show that citrate prevents formation of any aluminum phosphate precipitate, and analysis of these data indicates that the assumed binding constants for soluble phosphate are two orders of magnitude too strong. Consideration of the effect of competitive binding of alkaline earth metal ions to citrate on Al3 binding and of a set of transferrin-Al3 stability constants leads to the conclusion that the proportions are in close agreement with previously published results. We conclude on the basis of stability constants that, of the Al3 in blood serum, -89% (±5%) binds to transferrin and -11% (±5%) to citrate.

Research paper thumbnail of Equilibrium and structural studies of silicon(IV) and aluminum(III) in aqueous solution. 31. Aqueous complexation between silicic acid and the catecholamines dopamine and L-DOPA

Research paper thumbnail of Dissolution of feldspars in the presence of natural, organic solutes

European Journal of Soil Science, 2006

ABSTRACT

Research paper thumbnail of Materials aspects of titanium-doped aluminas: 14%Ti/γ-Al2O3/Cu and sulfided Al2O3–TiO2/NiMo

Materials Chemistry and Physics, 2002

ABSTRACT Materials aspects of titanium-doped alumina catalysts are discussed in light of a partly... more ABSTRACT Materials aspects of titanium-doped alumina catalysts are discussed in light of a partly new synthesis route, ion exchange reactions and sulfidation. Starting with a solution of the isopropoxides of aluminum and titanium, we aimed at an Al:Ti ratio of 6:1, which corresponds to the maximum acidity of the final product. Transmission electron micrographs showed that the synthesis gave a product of nearly monodisperse, rectangular particles and X-ray diffractograms revealed an amorphous to nano-crystalline structure reminiscent of γ-Al2O3. The Brunauer–Emmet–Teller area was 340 m2 g−1 and the H+ titration found 3 acidic sites nm−2. These numbers indicate that the titanium modification may fourfold increase the ion exchange capacity of a regular alumina. The importance of titanium modification for catalysis is discussed in connection with selective catalytic reduction with hydrocarbon reactions over Cu/14%Ti–Al2O3 and hydrogenation of 1-Me-naphthalene over sulfided NiMo/Al2O3–TiO2. The Ti4+ ions in the alumina lattice are almost irreducible, but infrared spectra suggested that these ions act as dispersion agents not only for adsorbed Cu2+ ions, but also for a supported phase of sulfided NiMo. Finally, we show that a simple weight control can be used to monitor the sulfidation and to indicate if the synthesis has produced a separate, reducible titania phase.

Research paper thumbnail of Surface Complexation and Precipitation at the H + −Orthophosphate−Aged γ-Al 2 O 3 /Water Interface

Research paper thumbnail of Balance between Surface Complexation and Surface Phase Transformation at the Alumina/Water Interface

Langmuir, 1998

ABSTRACT This paper synthesizes and expands on the results of a recent series of investigations a... more ABSTRACT This paper synthesizes and expands on the results of a recent series of investigations aimed at characterizing the interactions of orthophosphate, phenylphosphonate, and clodronate ions with hydrous alumina surfaces. The paper shows that γ-Al2O3 is a thermodynamically unstable substance in water, which undergoes a (surface) phase transformation into bayerite, β-Al(OH)3. Furthermore, it also shows that while phenylphosphonate ions are exclusively adsorbed via surface complexation to the alumina surfaces, clodronate ions dissolve the alumina phase and precipitate as an aluminum clodronate phase. Orthophosphate ions show a transient behavior in this respect, and the limits for, and consequences of, AlPO4(s) formation are determined via a series of chemical modeling calculations. The paper finally shows that, with respect to phenylphosphonate surface complexation, care must be taken when macroscopically derived stoichiometric compositions are used to assign microscopic surface complex structures.

Research paper thumbnail of Equilibrium and structural studies of silicon(IV) and aluminum(III) in aqueous solution. 17. Stable and metastable complexes in the system hydrogen (+)-aluminum(3+)-citric acid

Inorganic Chemistry, 1988

The kinetic route for complexation of citric acid (H3Cit) to Ai3+ was studied by time-dependent p... more The kinetic route for complexation of citric acid (H3Cit) to Ai3+ was studied by time-dependent potentiometric measurements in the range 3 < -log [H'] < 7. It is shown,that two mononuclear species, A1(H-lCit)-and Al(OH)(H-lCit)2-, determine the speciation in freshly prepared solutions. As the solutions age, these are converted into the thermodynamically more stable species A1,(OH)(H-1Cit)3'. In the paper, distribution diagrams showing this conversion as a functionof time and -log [H+] are presented.

Research paper thumbnail of Multicomponent polyanions. 39. Speciation in the aqueous hydrogen ion-molybdate(MoO42-)-hydrogenphosphate(HPO42-) system as deduced from a combined Emf-phosphorus-31 NMR study

Inorganic Chemistry, 1986

ABSTRACT

Research paper thumbnail of Equilibrium and structural studies of silicon(IV) and aluminum(III) in aqueous solution. 21. A potentiometric and aluminum-27 NMR study of the system proton-aluminum(3+)-molybdate (MoO42-)

Inorganic Chemistry, 1989

Research paper thumbnail of Equilibrium and structural studies of silicon (IV) and aluminum (III) in aqueous solution. 16. Complexation and precipitation reactions in the proton-aluminum(3+)-phthalate system

Inorganic Chemistry, 1988

The kinetic route for complexation of citric acid (H3Cit) to Ai3+ was studied by time-dependent p... more The kinetic route for complexation of citric acid (H3Cit) to Ai3+ was studied by time-dependent potentiometric measurements in the range 3 < -log [H'] < 7. It is shown,that two mononuclear species, A1(H-lCit)-and Al(OH)(H-lCit)2-, determine the speciation in freshly prepared solutions. As the solutions age, these are converted into the thermodynamically more stable species A1,(OH)(H-1Cit)3'. In the paper, distribution diagrams showing this conversion as a functionof time and -log [H+] are presented.

Research paper thumbnail of Comment on “speciation of aqueous mononuclear Al(III)-hydroxo and other Al(III) complexes at concentrations of geochemical relevance by aluminum-27 nuclear magnetic resonance spectroscopy” by B. C. Faust, W. B. Labiosa, K. H. Dai, J. S. MacFall, B. A. Browne, A. A. Ribeiro, and D. D. Richter

Geochimica et Cosmochimica Acta, 1997

Research paper thumbnail of Comment on “Aluminum speciation and equilibria in aqueous solution: IV. A potentiometric study of aluminum acetate complexation in acidic NaCl brines to 150°C” by D. A. Palmer and J. L. S. Bell

Geochimica et Cosmochimica Acta, 1995

In order to further develop understanding of the possible role for acetate on mobilizing aluminiu... more In order to further develop understanding of the possible role for acetate on mobilizing aluminium from sedimentary basinai brines, recently presented a series of thermodynamic data describing the formation of aqueous aluminium-acetate complexes, as a function of temperature and ionic strength. Although the basic experimental data upon which this equilibrium study is based seem to be of the highest precision, I unfortunately feel that the experimental conditions were inadequately chosen and, furthermore, that the species chosen to represent this complexation, are incorrect.

Research paper thumbnail of Equilibrium and Structural Studies of Silicon(IV) and Aluminium(III) in Aqueous Solution. 4. A Potentiometric Study of Polynuclear Aluminium(III) Hydroxo Complexes with Gallic Acid in Hydrolyzed Aluminium(III) Solutions

Three component equilibria between H +, silicic acid, and the catecholamines dopamine and L-DOPA ... more Three component equilibria between H +, silicic acid, and the catecholamines dopamine and L-DOPA were studied by means of potentiometric (glass electrode) measurements in 0.6 M Na(CI) medium at 25 ° C. Experimental data cover the ranges 2 < -log[H +] < 9.5, 0.002 < B < 0.005 M; 0.005 < C < 0.016 M, and 1 < C/B < 6 (B and C stand for the total concentration of Si and catecholamine, respectively). In acidic and near-neutral solutions no interactions were registered while, in slightly alkaline solutions, both systems are characterized by a formation of mononuclear tris-complexes SiL 3 containing pyrocatechol-type bonds. The species forming at -log[H +] = 7.5 have fully protonated amine side-chains which, at somewhat higher -log[H +] values, start to deprotonate. Simultaneously, a decomposition of the octahedrally coordinated complex is occurring and the hydrolytic species SiO(OH) 3-becomes increasingly important. With dopamine, the equilibrium constants characterizing the system are log K (Si(OH) 4 + 3H 3L+,~ -Si(HL) 3 ++ 2H ++ 4H20) -9.70 -I-0.03 and log K (Si(OH) 4 + 3H3L+~ -~ SiL(HL) 2 + 3H++ 4H20) -19.33 + 0.03. The corresponding equilibrium reactions with L-DOPA are log K (Si(OH) 4 + 3H3L ~ Si(HL)32-+ 2H + + 4H20) -10.08 + 0.05 and log K (Si(OH) 4 + 3H3L ~-~ SiL(HL)23-+ 3H + + 4H20) -19.35 + 0.07. Data were analyzed using the least-squares computer program LETAGROPVRID.

Research paper thumbnail of Equilibrium and Structural Studies of Silicon(IV) and Aluminium(III) in Aqueous Solution. 1. The Formation of Ternary Mononuclear and Polynuclear Complexes in the System Al(3+)Gallic Acid--OH-. A Potentiometric Study in 0.6 M Na(Cl)

Acta Chemica Scandinavica

Research paper thumbnail of Equilibrium and Structural Studies of Silicon(IV) and Aluminium(III) in Aqueous Solution. 7. Redox, Hydrolysis and Complexation Equilibria in the System Al(3+)-1,2Naphthoquinone4-sulfonate/1,2-Dihydroxy-naphthalene-4-sulfonate-OH(-). A Potentiometric Study in 0.6 M Na(Cl)

Acta Chemica Scandinavica

Research paper thumbnail of Equilibrium and Structural Studies of Silicon(IV) and Aluminium(III) in Aqueous Solution. 8. A Potentiometric Study of Aluminium(III) Salicylates and Aluminium(III) Hydroxo Salicylates in 0.6 M Na(Cl)

Acta Chemica Scandinavica

Research paper thumbnail of Equilibrium approaches to natural water systems—7. Complexation reactions of copper(II), cadmium(II) and mercury(II) with dissolved organic matter in a concentrated bog-water

Water Research, 1989

ABSTRACT Trace metal complexation by the dissolved organic matter in a concentrated bog-water has... more ABSTRACT Trace metal complexation by the dissolved organic matter in a concentrated bog-water has been studied using a potentiometric method (glass electrode). Bog-waters, sampled on five different times, were concentrated with a freezing-out technique and the complexation reactions involving Cu2+, Cd2+ and Hg2+ were investigated in 0.1 M ionic media. In the mercury(II) system, chloride was used as a competing ligand. Formation of binary CuL, CdL and HgL complexes was found. In the mercury(II) system a ternary HgH−1L complex was formed as well. The following values were obtained: log kCuL = 3.63 (Oct. 1983), 4.10 (Feb. 1984) and 3.99 (Sept. 1984); log kCdL = 2.84 (Jan. 1986); log kHgL = 10.37 and pKaHgL = 4.40 (Aug. 1985). Experimental data were evaluated using the least squares computer program LET-AGROPVRID. Distribution diagrams describing the speciation in experimental and natural conditions were constructed using the computer program SOLGASWATER.

Research paper thumbnail of Equilibrium and Structural Studies of Silicon(IV) and Aluminium(III) in Aqueous Solution. XXV. Composition and Stability of Aluminium Complexes with Methylmalonic Acid and Alanine

Acta Chemica Scandinavica, 1990

Research paper thumbnail of Corrosion of dense polycrystalline alpha-Al2O3 in NaHCO3-buffered water solution of pH 8.5 at 40-degrees-C-100-degrees-C

American Ceramic Society Bulletin

Research paper thumbnail of Stable and metastable complexes in the system H+-Al3+-Citric acid

Research paper thumbnail of Citrate as the main small molecule binding Al3+ in serum. Clin Chem

Clinical Chemistry

A recent proposal (Clin Chem 1992;38:1809-18) that inorganic phosphate is the predominant small m... more A recent proposal (Clin Chem 1992;38:1809-18) that inorganic phosphate is the predominant small molecule binding J3 in blood serum is shown to be incorrect. Experiments in which Al3 is added to solutions containing phosphate and citrate in the same proportions as in serum clearly show that citrate prevents formation of any aluminum phosphate precipitate, and analysis of these data indicates that the assumed binding constants for soluble phosphate are two orders of magnitude too strong. Consideration of the effect of competitive binding of alkaline earth metal ions to citrate on Al3 binding and of a set of transferrin-Al3 stability constants leads to the conclusion that the proportions are in close agreement with previously published results. We conclude on the basis of stability constants that, of the Al3 in blood serum, -89% (±5%) binds to transferrin and -11% (±5%) to citrate.

Research paper thumbnail of Equilibrium and structural studies of silicon(IV) and aluminum(III) in aqueous solution. 31. Aqueous complexation between silicic acid and the catecholamines dopamine and L-DOPA

Research paper thumbnail of Dissolution of feldspars in the presence of natural, organic solutes

European Journal of Soil Science, 2006

ABSTRACT

Research paper thumbnail of Materials aspects of titanium-doped aluminas: 14%Ti/γ-Al2O3/Cu and sulfided Al2O3–TiO2/NiMo

Materials Chemistry and Physics, 2002

ABSTRACT Materials aspects of titanium-doped alumina catalysts are discussed in light of a partly... more ABSTRACT Materials aspects of titanium-doped alumina catalysts are discussed in light of a partly new synthesis route, ion exchange reactions and sulfidation. Starting with a solution of the isopropoxides of aluminum and titanium, we aimed at an Al:Ti ratio of 6:1, which corresponds to the maximum acidity of the final product. Transmission electron micrographs showed that the synthesis gave a product of nearly monodisperse, rectangular particles and X-ray diffractograms revealed an amorphous to nano-crystalline structure reminiscent of γ-Al2O3. The Brunauer–Emmet–Teller area was 340 m2 g−1 and the H+ titration found 3 acidic sites nm−2. These numbers indicate that the titanium modification may fourfold increase the ion exchange capacity of a regular alumina. The importance of titanium modification for catalysis is discussed in connection with selective catalytic reduction with hydrocarbon reactions over Cu/14%Ti–Al2O3 and hydrogenation of 1-Me-naphthalene over sulfided NiMo/Al2O3–TiO2. The Ti4+ ions in the alumina lattice are almost irreducible, but infrared spectra suggested that these ions act as dispersion agents not only for adsorbed Cu2+ ions, but also for a supported phase of sulfided NiMo. Finally, we show that a simple weight control can be used to monitor the sulfidation and to indicate if the synthesis has produced a separate, reducible titania phase.

Research paper thumbnail of Surface Complexation and Precipitation at the H + −Orthophosphate−Aged γ-Al 2 O 3 /Water Interface

Research paper thumbnail of Balance between Surface Complexation and Surface Phase Transformation at the Alumina/Water Interface

Langmuir, 1998

ABSTRACT This paper synthesizes and expands on the results of a recent series of investigations a... more ABSTRACT This paper synthesizes and expands on the results of a recent series of investigations aimed at characterizing the interactions of orthophosphate, phenylphosphonate, and clodronate ions with hydrous alumina surfaces. The paper shows that γ-Al2O3 is a thermodynamically unstable substance in water, which undergoes a (surface) phase transformation into bayerite, β-Al(OH)3. Furthermore, it also shows that while phenylphosphonate ions are exclusively adsorbed via surface complexation to the alumina surfaces, clodronate ions dissolve the alumina phase and precipitate as an aluminum clodronate phase. Orthophosphate ions show a transient behavior in this respect, and the limits for, and consequences of, AlPO4(s) formation are determined via a series of chemical modeling calculations. The paper finally shows that, with respect to phenylphosphonate surface complexation, care must be taken when macroscopically derived stoichiometric compositions are used to assign microscopic surface complex structures.

Research paper thumbnail of Equilibrium and structural studies of silicon(IV) and aluminum(III) in aqueous solution. 17. Stable and metastable complexes in the system hydrogen (+)-aluminum(3+)-citric acid

Inorganic Chemistry, 1988

The kinetic route for complexation of citric acid (H3Cit) to Ai3+ was studied by time-dependent p... more The kinetic route for complexation of citric acid (H3Cit) to Ai3+ was studied by time-dependent potentiometric measurements in the range 3 < -log [H'] < 7. It is shown,that two mononuclear species, A1(H-lCit)-and Al(OH)(H-lCit)2-, determine the speciation in freshly prepared solutions. As the solutions age, these are converted into the thermodynamically more stable species A1,(OH)(H-1Cit)3'. In the paper, distribution diagrams showing this conversion as a functionof time and -log [H+] are presented.

Research paper thumbnail of Multicomponent polyanions. 39. Speciation in the aqueous hydrogen ion-molybdate(MoO42-)-hydrogenphosphate(HPO42-) system as deduced from a combined Emf-phosphorus-31 NMR study

Inorganic Chemistry, 1986

ABSTRACT

Research paper thumbnail of Equilibrium and structural studies of silicon(IV) and aluminum(III) in aqueous solution. 21. A potentiometric and aluminum-27 NMR study of the system proton-aluminum(3+)-molybdate (MoO42-)

Inorganic Chemistry, 1989

Research paper thumbnail of Equilibrium and structural studies of silicon (IV) and aluminum (III) in aqueous solution. 16. Complexation and precipitation reactions in the proton-aluminum(3+)-phthalate system

Inorganic Chemistry, 1988

The kinetic route for complexation of citric acid (H3Cit) to Ai3+ was studied by time-dependent p... more The kinetic route for complexation of citric acid (H3Cit) to Ai3+ was studied by time-dependent potentiometric measurements in the range 3 < -log [H'] < 7. It is shown,that two mononuclear species, A1(H-lCit)-and Al(OH)(H-lCit)2-, determine the speciation in freshly prepared solutions. As the solutions age, these are converted into the thermodynamically more stable species A1,(OH)(H-1Cit)3'. In the paper, distribution diagrams showing this conversion as a functionof time and -log [H+] are presented.

Research paper thumbnail of Comment on “speciation of aqueous mononuclear Al(III)-hydroxo and other Al(III) complexes at concentrations of geochemical relevance by aluminum-27 nuclear magnetic resonance spectroscopy” by B. C. Faust, W. B. Labiosa, K. H. Dai, J. S. MacFall, B. A. Browne, A. A. Ribeiro, and D. D. Richter

Geochimica et Cosmochimica Acta, 1997

Research paper thumbnail of Comment on “Aluminum speciation and equilibria in aqueous solution: IV. A potentiometric study of aluminum acetate complexation in acidic NaCl brines to 150°C” by D. A. Palmer and J. L. S. Bell

Geochimica et Cosmochimica Acta, 1995

In order to further develop understanding of the possible role for acetate on mobilizing aluminiu... more In order to further develop understanding of the possible role for acetate on mobilizing aluminium from sedimentary basinai brines, recently presented a series of thermodynamic data describing the formation of aqueous aluminium-acetate complexes, as a function of temperature and ionic strength. Although the basic experimental data upon which this equilibrium study is based seem to be of the highest precision, I unfortunately feel that the experimental conditions were inadequately chosen and, furthermore, that the species chosen to represent this complexation, are incorrect.

Research paper thumbnail of Equilibrium and Structural Studies of Silicon(IV) and Aluminium(III) in Aqueous Solution. 4. A Potentiometric Study of Polynuclear Aluminium(III) Hydroxo Complexes with Gallic Acid in Hydrolyzed Aluminium(III) Solutions

Three component equilibria between H +, silicic acid, and the catecholamines dopamine and L-DOPA ... more Three component equilibria between H +, silicic acid, and the catecholamines dopamine and L-DOPA were studied by means of potentiometric (glass electrode) measurements in 0.6 M Na(CI) medium at 25 ° C. Experimental data cover the ranges 2 < -log[H +] < 9.5, 0.002 < B < 0.005 M; 0.005 < C < 0.016 M, and 1 < C/B < 6 (B and C stand for the total concentration of Si and catecholamine, respectively). In acidic and near-neutral solutions no interactions were registered while, in slightly alkaline solutions, both systems are characterized by a formation of mononuclear tris-complexes SiL 3 containing pyrocatechol-type bonds. The species forming at -log[H +] = 7.5 have fully protonated amine side-chains which, at somewhat higher -log[H +] values, start to deprotonate. Simultaneously, a decomposition of the octahedrally coordinated complex is occurring and the hydrolytic species SiO(OH) 3-becomes increasingly important. With dopamine, the equilibrium constants characterizing the system are log K (Si(OH) 4 + 3H 3L+,~ -Si(HL) 3 ++ 2H ++ 4H20) -9.70 -I-0.03 and log K (Si(OH) 4 + 3H3L+~ -~ SiL(HL) 2 + 3H++ 4H20) -19.33 + 0.03. The corresponding equilibrium reactions with L-DOPA are log K (Si(OH) 4 + 3H3L ~ Si(HL)32-+ 2H + + 4H20) -10.08 + 0.05 and log K (Si(OH) 4 + 3H3L ~-~ SiL(HL)23-+ 3H + + 4H20) -19.35 + 0.07. Data were analyzed using the least-squares computer program LETAGROPVRID.

Research paper thumbnail of Equilibrium and Structural Studies of Silicon(IV) and Aluminium(III) in Aqueous Solution. 1. The Formation of Ternary Mononuclear and Polynuclear Complexes in the System Al(3+)Gallic Acid--OH-. A Potentiometric Study in 0.6 M Na(Cl)

Acta Chemica Scandinavica

Research paper thumbnail of Equilibrium and Structural Studies of Silicon(IV) and Aluminium(III) in Aqueous Solution. 7. Redox, Hydrolysis and Complexation Equilibria in the System Al(3+)-1,2Naphthoquinone4-sulfonate/1,2-Dihydroxy-naphthalene-4-sulfonate-OH(-). A Potentiometric Study in 0.6 M Na(Cl)

Acta Chemica Scandinavica

Research paper thumbnail of Equilibrium and Structural Studies of Silicon(IV) and Aluminium(III) in Aqueous Solution. 8. A Potentiometric Study of Aluminium(III) Salicylates and Aluminium(III) Hydroxo Salicylates in 0.6 M Na(Cl)

Acta Chemica Scandinavica