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Iron and aluminium speciation in Swedish freshwaters: Implications for geochemical modelling
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Speciation governs transport and toxicity of trace metals and is important to monitor in natural waters. Geochemical models that predict speciation are valuable tools for monitoring. They can be used for risk assessments and future scenarios such as termination of liming. However, there are often large uncertainties concerning the speciation of iron and aluminium in the models, due to the complicated chemistry of these metals. Both are important in governing the speciation of other metals, due to (i) their capacity to form minerals onto which metals can adsorb and (ii) their ability to compete for binding sites to natural organic matter (NOM). Aluminium is also potentially toxic and is therefore closely monitored in acidified freshwaters. In this study different phases of iron in Swedish lakes were characterised. This required a good method for preconcentrating the iron colloids. A new method was developed in this thesis that uses an anion-exchange column to isolate the iron colloids prior to characterisation with extended X-ray absorption fine structure (EXAFS) spectroscopy. Iron was present as ferrihydrite in particles but was also strongly monomerically complexed to NOM in two Swedish lakes. Based on the results an internally consistent process-based geochemical equilibrium model was presented for Swedish freshwaters. The model was validated for pH (= 9 400) and inorganic monomeric aluminium (Ali) (n = 3 400). The model could simulate pH and Ali simultaneously, and be used for scenario modelling. In this thesis, modelling scenarios for decreases and complete termination of liming are presented for the 3 000 limed Swedish lakes. The results suggest that liming can be terminated in 30 % of the Swedish lakes and decreased in many other lakes.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , xiv, 51 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1065
Keyword [en]
Geochemical equilibrium modelling, pH, adsorption to ferrihydrite, metal-NOM complexation, liming, EXAFS spectroscopy
National Category
Geochemistry
Identifiers
URN: urn:nbn:se:kth:diva-94528ISBN: 978-91-7501-373-2 (print)OAI: oai:DiVA.org:kth-94528DiVA: diva2:526350
Public defence
2012-10-05, V1, Teknikringen 76 1 tr, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2007-4468
Note

QC 20120919

Available from: 2012-05-11 Created: 2012-05-09 Last updated: 2012-09-19Bibliographically approved
List of papers
1. Speciation of aluminium, arsenic and molybdenum in excessively limed lakes
Open this publication in new window or tab >>Speciation of aluminium, arsenic and molybdenum in excessively limed lakes
2009 (English)In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 407, no 18, 5119-5127 p.Article in journal (Refereed) Published
Abstract [en]

The possible existence of the potentially toxic oxyanions of Al (AI(OH)(4)(-)). As (HAsO42-), and Mo (MoO42-) was examined in excessively limed lakes. In-situ dialysis (MWCO 1 kDa) was performed in the surface and bottom waters of two excessively limed lakes (pH 7.1-7.7) and one acidic lake (pH similar to 5.4). The dialysable metal concentrations were compared to the equilibrium distribution of species as calculated with the geochemical code Visual MINTEQ incorporating the CD-MUSIC and Stockholm Humic models for complexation onto colloidal ferrihydrite and dissolved organic matter. Arsenic and molybdenum in the excessively limed lakes were to a large extent present in the dialysable fraction (>79% and >92% respectively). They were calculated to exist as free or adsorbed oxyanions. Most of the Al was observed to reside in the colloidal fraction (51-82%). In agreement with this, model predictions indicated aluminium to be present mostly as colloids or bound to dissolved organic matter. Only a small fraction was modelled as AI(OH)(4)(-) ions. In most cases, modelled values were in agreement with the dialysis results. The free concentrations of the three oxyanions were mostly low compared to toxic levels.

Keyword
Trace metals, Lakes, Liming, In-situ dialysis, Geochemical modeling, trace-metal speciation, fresh-waters, aquatic environments, charge-distribution, humic substances, aqueous aluminum, organic-matter, surface waters, natural-waters, toxicity
Identifiers
urn:nbn:se:kth:diva-18703 (URN)10.1016/j.scitotenv.2009.05.034 (DOI)000269228000018 ()2-s2.0-67650999500 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Chemical Equilibrium Modeling of Organic Acids, pH, Aluminum, and Iron in Swedish Surface Waters
Open this publication in new window or tab >>Chemical Equilibrium Modeling of Organic Acids, pH, Aluminum, and Iron in Swedish Surface Waters
2010 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 44, no 22, 8587-8593 p.Article in journal (Refereed) Published
Abstract [en]

A consistent chemical equilibrium model that calculates pH from charge balance constraints and aluminum and iron speciation in the presence of natural organic matter is presented. The model requires input data for total aluminum, iron, organic carbon, fluoride, sulfate, and charge balance ANC. The model is calibrated to pH measurements (n = 322) by adjusting the fraction of active organic matter only, which results in an error of pH prediction on average below 0.2 pH units. The small systematic discrepancy between the analytical results for the monomeric aluminum fractionation and the model results is corrected for separately for two different fractionation techniques (n = 499) and validated on a large number In = 3419) of geographically widely spread samples all over Sweden. The resulting average error for inorganic monomeric aluminum is around 1 mu M. In its present form the model is the first internally consistent modeling approach for Sweden and may now be used as a tool for environmental quality management Soil gibbsite with a log *K-s of 8.29 at 25 degrees C together with a pH dependent loading function that uses molar Al/C ratios describes the amount of aluminum in solution in the presence of organic matter if the pH is roughly above 6.0.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2010
Keyword
HUMIC SUBSTANCES, FRESH-WATERS, BINDING, LAKES, SPECIATION, BOREAL, SOILS, SNOWMELT, FE(III), MATTER
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-27088 (URN)10.1021/es102415r (DOI)000284248300038 ()2-s2.0-78449233251 (Scopus ID)
Note

QC 20101210

Available from: 2010-12-10 Created: 2010-12-06 Last updated: 2017-12-11Bibliographically approved
3. Iron speciation in soft-water lakes and soils as determined by EXAFS spectroscopy and geochemical modelling
Open this publication in new window or tab >>Iron speciation in soft-water lakes and soils as determined by EXAFS spectroscopy and geochemical modelling
Show others...
2013 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 105, 172-186 p.Article in journal (Refereed) Published
Abstract [en]

Complexation of iron by organic matter can potentially compete with toxic metals for binding sites. Iron(III) forms both monomeric and di/trimeric complexes with fulvic and humic acids, but the nature and extent of complexation with natural organic matter samples from soft-water lakes has not been extensively studied. The aim of this study was to determine the coordination of iron in complexes with organic matter in two soft-water lakes and in the surrounding Oe soil horizons. Iron K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy was performed on particles and large colloids (>0.45. μm) collected by in-line pre-filtration, and on smaller colloids isolated both on an AGMP-1 anion-exchange column and by concentration using 1000. Da ultrafiltration. The results showed that iron(III) was mainly present in monomeric complexes with organic matter, both in the lake water smaller colloids and in the soil samples. Evidence for iron(III) (hydr)oxides was found for the lake particles, in the ultrafiltration retentates, and in some of the soils. Overall, the results suggest that complexation of iron(III) to organic matter prevents hydrolysis into polymeric forms. Strong complexation of iron(III) would lead to competition with other metals for organic-matter binding sites.

Keyword
Ultrafiltration, natural organic matter, ferrozine method, anion-exchange column, colloids, ferrihydrite
National Category
Geochemistry
Identifiers
urn:nbn:se:kth:diva-94536 (URN)10.1016/j.gca.2012.11.035 (DOI)000315194800011 ()2-s2.0-84872550254 (Scopus ID)
Funder
Swedish Research Council, 2007-4468Knut and Alice Wallenberg Foundation
Note

QC 20130215. Updated from manuscript to article in journal.

Available from: 2012-05-11 Created: 2012-05-09 Last updated: 2017-12-07Bibliographically approved
4. Modelling of pH and inorganic aluminium after termination of liming in 3 000 Swedish lakes
Open this publication in new window or tab >>Modelling of pH and inorganic aluminium after termination of liming in 3 000 Swedish lakes
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Significant resources are spent on counteracting the effects of acidification, mainly by liming. Due to a lower sulphur and nitrogen deposition in Europe and North America, authorities are reducing liming, changing directives and strategies for remediation. However, as the acid-base buffer capacity differs in different water bodies, the desirable reduction of the lime dose is variable. In this study, a geochemical model is used to predict pH and inorganic monomeric aluminium (Ali) when liming reduced and finally terminated in the 3 000 Swedish lakes that have been subject to liming. The model used estimations of Ca and Mg concentrations not affected by liming based upon the Ca/Mg ratio in nearby unlimed reference lakes. For modelling of pH and inorganic aluminium we used the geochemical model program Visual MINTEQ including the Stockholm Humic Model recently calibrated for Swedish fresh water. The predictions were confirmed by results from six monitored lakes, in which liming had been terminated. The use of geochemical modelling proved to be a promising tool for the calculation of accurate lime requirements in acid waters. For simulations in which liming was completely terminated, the pH value decreased with, on average, 0.9 pH units to pH 5.9, whereas Ali increased with 18 μg L-1 to 31 μg L-1. If liming was reduced by half, the pH would drop only 0.3 pH units and Aliwould increase with 2 μg L-1. Lakes in the south-western part of Sweden were predicted to reach a lower pH and higher Ali, as could be expected due to their larger historical S deposition. The results indicate that liming can be terminated in certain areas and be reduced without large pH reductions in the fresh water.

Keyword
Acidification, surface water, geochemical equilibrium model, pH, Ali, Visual MINTEQ
National Category
Geochemistry
Identifiers
urn:nbn:se:kth:diva-94537 (URN)
Note
QS 2012Available from: 2012-05-11 Created: 2012-05-09 Last updated: 2012-05-11Bibliographically approved
5. Phosphate effects on copper(II) and lead(II) sorption to ferrihydrite
Open this publication in new window or tab >>Phosphate effects on copper(II) and lead(II) sorption to ferrihydrite
(English)Manuscript (preprint) (Other academic)
Keyword
Surface complex, heavy metal, iron oxide, adsorption, CD-MUSIC model; EXAFS spectroscopy
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-94538 (URN)
Note
QS 2012Available from: 2012-05-11 Created: 2012-05-09 Last updated: 2012-05-11Bibliographically approved

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