| 1. |
- Dario, Mårten, et al.
(författare)
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Sorption of Cd to colloidal ferric hydroxides : impact of pH and organic acids
- 1997
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Ingår i: Chemical speciation and bioavailability. - 0954-2299 .- 2047-6523. ; 9:1, s. 3-14
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Tidskriftsartikel (refereegranskat)abstract
- The sorption (both ad- and desorption) of Cd to or from colloidal ferric hydroxides as a function of pH, the concentration of organic acids (acetic acid (AA), EDTA, fulvic acid (FA) and malonic acid (MA)), the precipitation procedure for the ferric hydroxide as well as the contact time were investigated in the present study. The concentrations of Cd, colloids and organic acids were chosen to be representative of natural surface waters. The ferric hydroxide were either precipitated in presence of FA or the acid was mixed with the colloids after the purification steps. The presence of FA during the precipitation of ferric hydroxide, had an impact on the size distribution of the solid phase, but it did not have any influence on the sorption behaviour of Cd. The adsorption process was found to be relatively fast and largely pH-dependent. It was fully reversible when the pH was decreased, however, with somewhat slower kinetics. The addition of up to 1 mmol L-1 AA or MA did not cause any measurable desorption of Cd, probably due to the relatively weak complexes formed between Cd(II)-ions and the anions of the acids. Thermodynamic calculations of the distribution between different soluble Cd-species indicated that EDTA and FA would form stronger complexes with Cd. This was indicated in the experiments as enhanced adsorption at low pH-values due to the adsorption of Cd(II)-organic species, and an increase in the soluble fraction at high pH-values caused by competition for Cd(II)-ions between complex forming groups on the surfaces and the soluble organic ligands.
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| 2. |
- HOFSLAGARE, O, et al.
(författare)
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THE EFFECT OF ARSENATE AND ARSENITE ON PHOTOSYNTHESIS IN SCENEDESMUS-OBLIQUUS - A POTENTIOMETRIC STUDY IN A CLOSED CO2-SYSTEM
- 1994
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Ingår i: Chemical speciation and bioavailability. - 0954-2299 .- 2047-6523. ; 6:4, s. 95-102
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Tidskriftsartikel (refereegranskat)abstract
- A potentiometric titration method was used to study the adverse effect of arsenate (As(V) and arsenite (As(III) on inorganic carbon uptake in suspensions of the green alga Scenedesmus obliquus. The measurements were performed in a closed CO2-system with diluted synthetic seawater (1 parts per thousand salinity) as ionic medium. Usually, the algal chlorophyll concentration was 0.4 mg dm-3, while the arsenate- and arsenite-concentrations were varied within the limits 0.1 to 200 mumol dm-3. In some experiments arsenate toxicity was studied in the presence of 1 to 100 mumol dm-3 of phosphate (P(V)). With concentrations of arsenate or arsenite less than 0.1 mumol dm-3 no toxic effects were observed. However, at As-concentrations of 200 mumol dm-3, the algal carbon uptake was reduced by 41% with arsenate and 29% with arsenite, i.e., arsenate is more toxic to Scenedesmus obliquus than arsenite. The toxicity of arsenate was negligible in the presence of a ten fold excess of phosphate. This is probably due to chemical similarities between arsenate and phosphate causing competition between the ions for the binding sites. The importance of taking the speciation as well as the buffer capacity of the algal system into account, when calculating the carbon uptake, is also discussed.
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| 3. |
- Nilsson, Nils, et al.
(författare)
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Phosphate complexation at the surface of goethite
- 1992
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Ingår i: Chemical speciation and bioavailability. - : Informa UK Limited. - 0954-2299 .- 2047-6523. ; 4:4, s. 121-130
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Tidskriftsartikel (refereegranskat)abstract
- Phosphate complexation at the goethite-water interface has been studied in 0.1 M Na(NO3) medium at 298.2 K in the range 3.0 <—log[H+] < 9.0. Equilibrium measurements were performed as potentiometric titrations supplemented with spectrophotometric phosphate analyses. The experimental data were evaluated on the basis of the constant capacitance model and with the aid of the computer program FITEQL, version 2.0.The acid/base properties of the goethite-water interface have been investigated earlier and are described by two intrinsic equilibrium constants logβs 1,1,0(int) = 7.47 and logβs-1,1,0(int) = −9.51 and with a specific capacitance of 1.28 F m−2. The binding between phosphate and goethite was found to be strong within the investigated -log[H+] range, and the amount of adsorbed phosphate is slowly decreasing with increasing—log[H+] value. The model describing the phosphate complexation is represented by the following equilibria and intrinsic constants:Further support for the proposed model is given by zeta-potential measurements.
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| 4. |
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