Efnasambönd og framboð fyrir örverur í jarðhitavatni - verkefni lokið
Fréttatilkynning verkefnisstjóra
Our data suggests that in particular in water with pH~6 and above, Fe speciation may be controlled by equilibrium with Fe(III) hydroxide solid phase, but in acid waters equilibrium may not have been reached with Fe(II) and Fe(III) being controlled by other factors such as source(s), kinetics, and microbial reactions.
In the project "Speciation and bioavailability in geothermal waters", funded by the Rannis START postdoctoral fund, various sampling and analytical methods to determine species concentrations of biogeochemically important elements in geothermal waters were developed and applied in the field analysis of natural geothermal waters, including chromatography, spectrophotometry, voltammetry and size fractionation methods. Special emphasis was on iron speciation and geochemistry, for which a field-deployable ion chromatography spectrophotometry method (IC-Vis) was developed and applied for the field determination of Fe(II) and Fe(III) concentrations in geothermal water over a range of pH values, chemical composition and absolute and relative Fe(II) and Fe(III) concentrations. This allowed assessment of the most important reactions involving Fe in geothermal water. Our data suggests that in particular in water with pH~6 and above, Fe speciation may be controlled by equilibrium with Fe(III) hydroxide solid phase, but in acid waters equilibrium may not have been reached with Fe(II) and Fe(III) being controlled by other factors such as source(s), kinetics, and microbial reactions. In circum-neutral pH waters, the presence of colloidal/nanoparticulate Fe, passing the standard 0.2 μm filter pore size, is suggested. With the aim to assess the role of colloid-associated metals in <100C natural water in Iceland, techniques to distinguish between the elements present in different size fractions, namely as truly dissolved, colloidal and nanoparticulate phases, were tested and applied for the first time for <100°C natural water in Iceland. Our results show that most major elements including Cl, F, Si, Ca, Mg, Na, and K are largely present in the truly dissolved phase in all considered water types, including geothermal ground and surface water of various pH and temperatures <100C as well as cold surface and ground water. In contrast, in all water types expect for steam-heated water with pH<4, Fe and Al are predominantly present in the colloidal form. Trace elements show variable behavior from truly dissolved (e.g. B, Rb) to predominantly colloid-associated (e.g .Ti). In general, there is a systematic relationship between the water pH and water type and the importance of colloidal forms, with truly dissolved phase dominating in the steam-heated water having pH<4, and lesser role of colloids in alkaline geothermal water compared to near-neutral conditions including cold surface and groundwater. Additionally, voltammetric methods, having great potential to continuous in-situ determination of species concentrations, were tested in thermal water in Iceland. The results of this project have been presented in international conferences and peer-reviewed scientific articles.
Heiti verkefnis: Efnasambönd og framboð fyrir
örverur í jarðhitavatni / Speciation and bioavailability in geothermal waters
Verkefnisstjóri: Hanna Sisko Kaasalainen, Jarðfræðistofnun Háskóla Íslands
Tegund styrks: Rannsóknastöðustyrkur – START
Styrkár: 2012-2015
Fjárhæð styrks: 18,454 millj. kr. alls
Tilvísunarnúmer Rannís: 120250
