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Dissolved and suspended transport of tungsten, molybdenum, and vanadium in natural waters
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. (Applied geochemistry)ORCID iD: 0000-0003-3424-9552
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Some transition metals and metalloids occur primarily as oxyanions in natural waters including antimony, arsenic, chromium, molybdenum, tungsten and vanadium. These oxyanions can pass through cell walls along the same pathways as phosphate or sulfate. Some of these oxyanions are essential for life, but in high concentrations they become all toxic. Recent studies showed that tungsten probably is posing a risk to human health. The growing use of tungsten in industrial and military applications probably leads to an increased release of tungsten to the environment. It has also been shown that the use of studded winter tires in Sweden significantly increases tungsten concentrations in road runoff. Still, little is known about the geochemical cycling of tungsten in the environment as it has been considered to be a more or less inert element. Only a few studies deal with tungsten in natural waters. For example, for the Baltic Sea no concentration data have been published before this work and data on the suspended particulate fraction of tungsten in terrestrial and marine waters are scarce.

This thesis contributes to the understanding of the distribution and behavior of tungsten, molybdenum and vanadium in natural waters under changing redox conditions, varying pH and different seasons. Particular attention is paid to the suspended particulate fraction of these elements, which is often neglected even though it can be of great importance. Tungsten, molybdenum and vanadium primarily occur as oxyanions in solution and can be adsorbed to particles, which determines their mobility.

Molybdenum usually is very mobile, while vanadium has a tendency to adsorb to iron oxyhydroxides or to form organic complexes. Tungsten has many similarities with molybdenum, but it seems to be less mobile than molybdenum in natural waters.

Tungsten and molybdenum have a similar abundance in the upper continental crust, but in the ocean molybdenum is almost 2000 times more abundant. A strong fractionation of these two elements occurs from land to the ocean, indicating a removal of W during mixing of river and seawater.

This study comprises data from small streams in the boreal landscape of northern Sweden, major rivers (Kalix River and Råne River) and their estuaries discharging into the Baltic Sea. In the marine environment, sediment cores from the Bothnian Bay and water profiles at the stratified Landsort Deep have been studied. Apart from the spatial distribution, the temporal behavior of tungsten, molybdenum, and vanadium in was investigated. In the boreal environment snowmelt is playing a major role for their transport.

All water samples were filtered through 0.22 pore size filters to define dissolved and suspended particulate fractions. The particulate fraction of all studied elements increases from streams to rivers. Especially during spring flood, particle transport becomes even more important. About 80% tungsten, 70% vanadium and 30% molybdenum occur in the particulate fraction during this event. During estuarine mixing, tungsten and molybdenum are released from the particles again. However, vanadium seems to be removed in both fractions, probably due to a different adsorption behavior. In the dissolved fraction molybdenum increased and vanadium decreased from land to the sea, while tungsten showed small variation in all surface waters.

All three elements are affected by manganese redox cycling at the transition zone between oxic and sulfidic water at the Landsort Deep in the Baltic Sea. Adsorption of these oxyanions to the freshly formed manganese oxides plays an important role for their transport to the sulfidic zone. In contrast to molybdenum, dissolved tungsten is accumulated in the sulfidic environment. There is no effective removal mechanisms like for molybdenum, which is adsorbed to sulfides. Also in the sediment, redox cycling of manganese and iron affects the distribution of tungsten and molybdenum close to the water-sediment interface.

Place, publisher, year, edition, pages
Luleå University of Technology, 2018.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keyword [en]
tungsten, molybdenum, vanadium, Baltic Sea, redox cycling, suspended particles, boreal rivers
National Category
Geochemistry
Research subject
Applied Geology
Identifiers
URN: urn:nbn:se:ltu:diva-66852ISBN: 978-91-7790-013-9 (print)ISBN: 978-91-7790-014-6 (electronic)OAI: oai:DiVA.org:ltu-66852DiVA: diva2:1161564
Public defence
2018-02-09, F341, Luleå tekniska universitet, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2017-12-04 Created: 2017-11-30 Last updated: 2017-12-04Bibliographically approved
List of papers
1. Distribution of dissolved and suspended particulate molybdenum, vanadium, and tungsten in the Baltic Sea
Open this publication in new window or tab >>Distribution of dissolved and suspended particulate molybdenum, vanadium, and tungsten in the Baltic Sea
2017 (English)In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 196, 135-147 p.Article in journal (Refereed) Published
Abstract [en]

In natural waters, dissolved oxyanions often dominate over the particle-bound element fraction. Still, the scavenging of oxyanions by suspended particles might contribute significantly to their dynamic cycling and distribution. To investigate how oxyanions are affected by manganese (Mn) redox cycling, detailed depth profiles across the pelagic redox zone at the Landsort Deep, Baltic Sea, were collected for molybdenum (Mo), vanadium (V), and tungsten (W), for both dissolved (<0.22 µm) and suspended particulate (>0.22 µm) fractions.

All three oxyanions show a non-conservative behavior in the stratified Landsort Deep. Strong linear correlations with Mn in the particulate fraction in the redox zone of the Landsort Deep suggest that Mn redox cycling influences their distribution. In the dissolved fraction, Mo, V, and W exhibited rather different behavior. Molybdenum was depleted below the redox zone, while V was depleted only within the redox zone. Tungsten concentrations increased within the redox zone, being three times higher in the sulfidic zone than in the surface water. Unlike Mo, W shows no tendency for adsorption or co-precipitation under the prevailing weak sulfidic conditions in the deep water of the Landsort Deep and is, therefore, not exported to the underlying sediment.

The Landsort Deep data were compared with data from the northern Baltic Sea (Bothnian Bay, Kalix River and Råne River estuaries), where particulate iron (Fe) occurs in high abundance. The particulate fractions of Mo, V, and W decreased during mixing in these estuaries. Vanadium showed the most drastic reduction, with a decrease in dissolved and particulate fractions, indicating that different processes influence the distribution of these oxyanions.

Place, publisher, year, edition, pages
Elsevier, 2017
Keyword
redox cycling, iron, manganese, molybdenum, tungsten, vanadium, suspended particles, Baltic Sea
National Category
Geochemistry
Research subject
Applied Geochemistry
Identifiers
urn:nbn:se:ltu:diva-65419 (URN)10.1016/j.marchem.2017.08.010 (DOI)000415773500013 ()
Funder
Swedish Research Council
Note

Validerad;2017;Nivå 2;2017-11-01 (andbra)

Available from: 2017-08-30 Created: 2017-08-30 Last updated: 2017-12-14Bibliographically approved
2. Geochemistry of tungsten and molybdenum during fresh water transport and estuarine mixing
Open this publication in new window or tab >>Geochemistry of tungsten and molybdenum during fresh water transport and estuarine mixing
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The geochemistry of tungsten (W) in the environment is still poorly studied. Tungsten is little mobile and usually occurs in low concentrations in natural waters. For this study, we analyzed W together with molybdenum (Mo) in the dissolved and particulate fraction of two boreal estuaries during different seasons. Additionally, we sampled first-order streams, draining different landscape types, and the receiving northern Baltic Sea. Furthermore, surface sediment from the estuaries was analyzed to get a comprehensive overview of the distribution of W and Mo in a boreal environment.

Both elements showed different distribution patterns during different seasons. While they decreased in dissolved concentrations during spring discharge, their concentrations were elevated in winter and exhibited non-conservative behavior along the salinity gradient in the estuaries. In the particulate fraction, we found an opposing behavior for Mo and W, with higher particulate W and lower particulate Mo during spring discharge.

Molybdenum and W underwent fractionation from land to sea, indicating different mobility for these oxyanions. The Mo/W ratio in the dissolved fraction was mainly determined by the Mo concentration as the W concentration varied only in a narrow range from first-order streams to the Bothnian Bay. In the particulate fraction, the Mo/W ratio appeared to be affected by scavenging processes and showed only small variations. 

Keyword
Tungsten, Molybdenum, Suspended particles, Estuarine mixing
National Category
Geochemistry
Research subject
Applied Geochemistry
Identifiers
urn:nbn:se:ltu:diva-66850 (URN)
Funder
Swedish Research Council, 150 119
Available from: 2017-11-30 Created: 2017-11-30 Last updated: 2017-11-30
3. Seasonal behavior of molybdenum, vanadium, and tungsten in boreal rivers
Open this publication in new window or tab >>Seasonal behavior of molybdenum, vanadium, and tungsten in boreal rivers
(English)Manuscript (preprint) (Other academic)
Keyword
tungsten, vanadium, molybdenum, spring flood, suspended particles, Kalix River
National Category
Geochemistry
Research subject
Applied Geochemistry
Identifiers
urn:nbn:se:ltu:diva-66851 (URN)
Available from: 2017-11-30 Created: 2017-11-30 Last updated: 2017-11-30
4. Changes in trace metal sedimentation during freshening of a coastal basin
Open this publication in new window or tab >>Changes in trace metal sedimentation during freshening of a coastal basin
Show others...
2014 (English)In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 167, 2-12 p.Article in journal (Refereed) Published
Abstract [en]

Holocene freshening has turned the Bothnian Bay, northern Baltic Sea into an oligotrophic basin. Sequestering of trace elements has changed significantly during the oligotrophication process. In principle, trace metals have been transferred from permanently buried sulfides to Fe–Mn-oxyhydroxides in the top layers of the sediment. The oxyhydroxide layers restrict the flux of trace metals from the sediment to the oxic bottom water. Hence, Fe–Mn cycling in the suboxic sediment enriches a number of trace metals in the surface sediment. Arsenic, Sn, Ge and Bi show enrichment in the Fe-oxyhydroxide layer, whereas Mo, Cd, Ni, Co, Cu, and Sb are enriched in the uppermost Mn-oxyhydroxide layer. This natural redox cycling in the sediment obscures pollution effects.The oligotrophication process started approximately 3500 years ago, reflected in decreasing deposition of Zn, a proxy for phytoplankton production, and formation of Mn oxyhydroxide layers. Similarly, Ba/Al data indicate a decrease in the pelagic input of plankton. Barium data also suggest that dissolved sulfide in the sediment never reached high concentrations. Germanium is closely related to Ba, suggesting that Ge can be used as a proxy for phytoplankton production. Vanadium, U, Re, and Mo all indicate that the bottom water never has been significantly sulfidic during the last 5500 years. Rhenium data indicate that the organic carbon oxidation rate has decreased during the last 5500 years. Cadmium follows the organic matter distribution, but started to increase 1000 YBP (years before present). The reason for this enhanced input of Cd is unclear.

Keyword
Earth sciences - Exogenous eart sciences, Geovetenskap - Exogen geovetenskap
National Category
Geochemistry Geophysics
Research subject
Applied Geology; Exploration Geophysics
Identifiers
urn:nbn:se:ltu:diva-5774 (URN)10.1016/j.marchem.2014.06.010 (DOI)3f465607-16e1-43ab-b560-6484e509aba7 (Local ID)3f465607-16e1-43ab-b560-6484e509aba7 (Archive number)3f465607-16e1-43ab-b560-6484e509aba7 (OAI)
Note
Validerad; 2014; 20140812 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-30Bibliographically approved

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