Biomedical subjects

L Lövgren

Publications and source records attributed to L Lövgren.

4 recordsLinked to original sources

PubMed1999

Strontium Sorption on Hematite at Elevated Temperatures.

Acid-base reactions and surface complexation of Sr(II) at the hematite/water interface have been studied by means of potentiometric titrations at three different temperatures: 25, 50, and 75 degrees C. Equilibrium measurements were performed in 0.1 M NaCl. In the evaluation of equilibrium models for the acid-base reactions and complexation reactions in the three-component system H(+) &bond;(&tbond;FeOH)&bond;Sr(2+), the constant capacitance model was applied. During the titrations with Sr, aliquots of the suspension were sampled at in several points. The aqueous concentrations of Sr were analyzed by atomic absorption spectrometry. Treatment of data included tests for formation of both inner-sphere and outer-sphere complexes of different stoichiometric composition. The proposed equilibrium model consists of the following surface complexes of inner sphere type: &tbond;FeOHSr(2+) and &tbond;FeOSrOH. Besides the stability constants for the surface complexes, the thermodynamic parameters DeltaH and DeltaS were evaluated. The combined effect of a decrease in pH(pzc) with increasing temperature and positive enthalpies of surface complex formation favors adsorption of Sr at elevated temperatures. Copyright 1999 Academic Press.

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PubMed1999

Competitive Metal Ion Adsorption in Goethite Systems Using In Situ Voltammetric Methods and Potentiometry.

Competitive complexation with respect to the binary-metal ion combinations Cu(II)-Zn(II), Cu(II)-Pb(II), and Pb(II)-Zn(II) were studied at the goethite (alpha-FeOOH)-water interface (25 degrees C, I = 0.1 M NaNO(3)). In addition to potentiometric titrations and batch adsorption experiments, an in situ voltammetric technique was utilized. Sorption studies were performed within the ranges 3.5 </= pH </= 8.5, 10(-6) </= [M(II)](tot) </= 10(-3 )M, and with solid concentrations between 0.09 and 9 g dm(-3). The results obtained (metal uptake and proton release curves) were compared with corresponding predicted values, based upon previously determined thermodynamic surface complexation models for the different single-metal ion goethite systems. The surface complexation modeling was based upon the constant capacitance concept. The results showed that the Cu(II) and Zn(II) surface complexation submodels were combinatory in all two-metal systems studied, both at 10(-3) M and at 10(-6 )M concentrations of the metals. For Pb(II) a somewhat stronger adsorption to goethite than predicted by the previously determined submodel was observed in all two-metal systems studied. These deviations could be corrected for by a moderate adjustment of the equilibrium constant for the most acidic surface complex &tbond;FeOHPb(2+). It can also be concluded that the in situ voltammetric technique can be applied to measure trace concentrations of at least two metal ions simultaneously occurring in goethite suspensions under varying experimental conditions with good accuracy. Copyright 1999 Academic Press.

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PubMed1998

Comparison of the Adsorption of o-Phthalate on Boehmite (gamma-AlOOH), Aged gamma-Al2O3, and Goethite (alpha-FeOOH).

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. Copyright 1998 Academic Press.

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PubMed1997

In Situ Voltammetric Determinations of Metal Ions in Goethite Suspensions: Single Metal Ion Systems.

In the present paper voltammetric techniques have been used to study the sorption of Pb(II), Cd(II), Zn(II), and Cu(II) at low concentrations ( approximately 10(-6) M) in goethite (alpha-FeOOH) suspensions with varying solid concentrations as a function of pH. Metal ion adsorption on the cell walls was minimized by using a Teflon cell. Measurements in the absence of goethite showed the applicability of the voltammetric techniques for trace analysis in a wide pH range. The analysis seems to be limited mainly by the onset of metal ion hydrolysis at high pH values, where neutral and negatively charged species are formed. The results obtained in the presence of goethite were compared with previously determined surface complexation models, evaluated from relatively high metal ion ( approximately 10(-3) M) and solid concentrations ( approximately 10 g/L). Application of these models to more dilute conditions could thus be questioned. The results obtained indicated that no "high-affinity" sites are present on the surface of alpha-FeOOH. The voltammetric measurements showed good agreement for the Zn(II) and Cu(II) goethite systems. In the case of Pb(II), deviations between calculated and experimentally determined metal ion concentrations were detected at pH >7 and a molar ratio of Pb(II) to the surface concentration of goethite of 0.17. These deviations may be explained by assuming either formation of polymeric species or surface precipitates at high total concentrations (instead of the previously suggested surface complex identical withFeOPbOH) or slow adsorption kinetics at low concentrations. Also in the Cd(II) goethite system, a corresponding weaker adsorption than predicted was found. These observations strongly emphasize the importance of evaluating surface complexation models from data within concentration ranges as wide as possible. This holds for all components including the solid concentration. Copyright 1997 Academic Press.

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