The Arlanda area is a construction intensive area facing problems with risk of leaching of arsenic (As) from the bedrock to surface- and groundwater. Construction projects in the area have had problems with high levels of As in the bedrock and the risk of leaching increases through processing of aggregates and blasting of the bedrock. Additionally, there are high concentrations of As in potable water and elevated concentrations are correlated with occurrences of metasedimentary rock, but may also be related to other rock types. The existing geological information of the area was collected in the 1960´s and modern petrographic information as well as modelling of P-T and redox conditions are needed to understand the As mineralogy of the bedrock. Methods used in this project include field work, optical microscopy, electron microprobe analyses, geothermometry calculations, pseudosection modelling in Perple_X and geochemical modelling in PHREEQC. The results indicate that the As-rich bedrock domain include rocks of both igneous and sedimentary origin. As-bearing minerals löllingite and arsenopyrite were found in the matrix of two of the metasedimentary rock samples, while no As-minerals were found in metavolcanic samples. P-T estimates from several geothermobarometry models all suggest amphibolite facies metamorphism for the area, with pressure of 3.0-5.5 kbar and temperature of 490-640 °C. Simple modelling of equilibration of löllingite and arsenopyrite in pure water indicate that As(III) is the dominating oxidation state of As and that the molality of As increases with increasing T and decreasing pH. The results of this thesis provide new information on the petrography and P-T conditions for metamorphism of As-bearingsupracrustal rocks in the Arlanda area, but future research is needed to be able to predict the spatial occurrence of As in the bedrock. / Arlandaområdet är ett av de mest expansiva områdena i Sverige där en stor mängd infrastrukturprojekt är planerade under de närmaste 5-20 åren. Tidigare byggnadsprojekt i området har dock stött på problem med höga bakgrundshalter av arsenik (As) i berggrunden och det finns även en risk för urlakning av As från berggrunden till både yt-och grundvatten. Denna risk ökar under byggnadsarbeten i och med till exempel sprängning av berg. Ytterligare ett problem är att det i området runtomkring Arlanda ofta är höga halter av arsenik i dricksvattenbrunnar. Från data över As-halter i bergborrade brunnar har man kunnat se att höga halter av As ofta förekommer i metasedimentära bergarter, men även kan uppträda i andra bergarter. Den tillgängliga geologiska informationen över området är insamlad på 60-talet och ny petrografisk information, samt modellering av tryck- och temperaturförhållanden är nödvändig för att förstå förekomst av As i berggrunden. Målet med detta projekt är att med hjälp av fältarbete, optisk- och elektronmikroskopering, samt termodynamisk modellering få djupare kunskap kring ytbergarterna i området och utvärdera förekomsten av arsenik i dessa. Under vilka tryck- och temperaturförhållanden som de metamorfa bergarterna omvandlats studeras genom beräkningar från mineralsammansättningar samt modellering i programmet Perple_X. Resultatet från projektet visar att bergarter i As-anrikade zoner är av både magmatiskt och sedimentärt ursprung. Arsenikmineralen löllingit och arsenikkis dokumenterades endast i bergarter av sedimentärt ursprung. Bergarternas kemiska sammansättning tyder också på att de högsta As-halterna finns i de metasedimentära bergarterna. Modellering i PHREEQC visar att As(III) är den dominerande formen av As när löllingit och arsenikkis reagerar med vatten. Tryck- och temperaturberäkningar samt tryck- och termodynamisk modellering tyder på metamorfos under amfibolitfacies, med tryck omkring 3.0-5.5 kbar och temperatur omkring 490-640 °C. Resultaten från detta projekt ger ny information om de metamorfa bergarterna i Arlanda området och förekomst av As i dessa. Vidare studier är nödvändiga för att kunnaförutse i vilken form och i vilka bergarter As förekommer.

The Scandinavian Caledonides form a mountain range comprising nappe stacks of numerous far-travelled thrust sheets. The thrust sheets consist of diverse lithologies representing pre- and synorogenic sedimentary and igneous rocks subsequently metamorphosed to various degrees, from the Late Neoproterozoic to Middle Devonian. In particular, (ultra)-high-grade metamorphic rocks have been recorded in the Seve Nappe Complex (SNC), extending >1000 km along strike of the Scandinavian Caledonides. Included in the SNC of northern Sweden is the Vássačorru Igneous Complex (VIC), consisting of bimodal magmatic suites, that formed c. 845 Ma. Fieldwork was conducted in the Kebnekaise mountains of northern Sweden, focusing on the high-grade Aurek metagabbro within the VIC of the SNC. Aurek is a key locality representing both initial stages of Iapetus Ocean formation in the Ediacaran and later stage Caledonian subduction affinities, from the collision between Laurentia and Baltica. In this study, petrological description, zircon U-Pb geochronology, mineral chemistry analysis, whole rock composition, and thermodynamic modeling was performed. Zircon U-Pb geochronology yielded protolith ages of 609±2.5 Ma, and 614±2.3 Ma, suggesting the Aurek metagabbro to not be part of the VIC, as has previously been described. The age of Aurek can instead be correlated to the Kebnekaise Dyke Swarms at c. 607 Ma, in the Kebnekaise mountains. Whole rock major and trace element data of e.g., Al2O3 (15.0 – 25.0 ppm) versus SiO2 (46.0 – 53.0 ppm), Rb (2.0 – 18.0 ppm), Zr (8.0 – 58.0 ppm) versus Y (2.7 – 18.0 ppm), Th/Yb ratio 0.25 – 2.0 and Nb/Yb ratio 1.30 – 5.14, indicate assimilation of continental crust. These major and trace element signatures show that the protolith of the Aurek metagabbro probably was emplaced in a continental rift setting in the Ediacaran. Semi-quantitative thermodynamic modeling from this study present blueschist to amphibolite facies conditions for the Aurek metagabbro at 11.8 – 12.6 kbar and 480 – 565 oC, confirming the unit experienced subduction, possibly in the Late Cambrian to Early Ordovician. The metamorphic grade and protolith age show similar features to correlative rock sequences in the Tsäkkok Lens, south of Aurek, in Norrbotten. Consequently, this study concludes that subduction, exhumation and subsequent deformation for Aurek, probably was equivalent to those of the Tsäkkok Lens, extending the HP affinities of the SNC further north in the Swedish Caledonides. / Skandinaviska Kaledoniderna utgör en bergskedja bestående av olika skollor som transporterats hundratals kilometer från sin ursprungskälla. Skollorna består av varierande bergarter som representerar olika utvecklingsskeden i formationen av Kaledoniderna under senare Neoproterozoikum och mellan Devon. Utmärkande har höggradiga metamorfiska bergarter återfunnits i Seveskollan som sträcker sig >1000 km längs med strykningsriktningen av de Skandinaviska Kaledoniderna. I norra Sverige inkluderar Seveskollan det magmatiska Vássačorru-komplexet, bestående av bimodal magmatism som bildats ca 845 Ma. Fältarbete utfördes kring Kebnekaisebergen i norra Sverige, med fokus på höggradig metagabbro från Aurek, ett område inom det magmatiska Vássačorru-komplexet. Aurek är ett viktigt område som representerar både initiala stadier av Iapetushavets bildande och efterföljande formationer från kollisionen mellan Laurentia och Baltica plattorna. I denna studie utfördes petrologisk beskrivning av mineral, U-Pb geokronologi av zirkon, kemisk analys av mineral och bulkkomposition av bergarter, samt termodynamisk modellering. U-Pb dateringen av zirkon resulterade i en ursprungsålder på 609±2,5 Ma och 614±2,3 Ma för metagabbro från Aurek. Detta indikerar att metagabbro i Aurek inte är en del av det magmatiska Vássačorru-komplexet, något som tidigare antagits. Åldern kan istället korreleras till Kebnekaise-gångkomplexet med en ålder på ca 607 Ma. Huvud- och spårelement i Aureks metagabbro tyder på assimilering av kontinentalskorpa, vilket föreslår att ursprungsbergarten till metagabbro i Aurek bildades i en kontinental spridningszon. Den termodynamiska modelleringen resulterade i metamorfiska förhållanden på mellan 11,8 – 12,6 kbar och 480 – 565 oC för bergarterna, vilket påvisar att den tektoniska miljön som senare präglat bergarterna förmodligen var associerad med en subduktionszon.

The use of waste (or recycled) wood as a fuel in heat and power stations is becoming more widespread in Sweden (and Europe), because it is CO2 neutral with a lower cost than forest fuel. However, it is a heterogeneous fuel with a high amount of chlorine, alkali and heavy metals which causes more corrosion than fossil fuels or forest fuel. A part of the boiler which is subjected to a high corrosion risk is the furnace wall (or waterwall) which is formed of tubes welded together. Waterwalls are made of ferritic low-alloyed steels, due to their low price, low stress corrosion cracking risk, high heat transfer properties and low thermal expansion. However, ferritic low alloy steels corrode quickly when burning waste wood in a low NOx environment (i.e. an environment with low oxygen levels to limit the formation of NOx). Apart from pure oxidation two important forms of corrosion mechanisms are thought to occur in waste environments: chlorine corrosion and alkali corrosion. Although there is a great interest from plant owners to reduce the costs associated with furnace wall corrosion very little has been reported on wall corrosion in biomass boilers. Also corrosion mechanisms on furnace walls are usually investigated in laboratories, where interpretation of the results is easier. In power plants the interpretation is more complicated. Difficulties in the study of corrosion mechanisms are caused by several factors such as deposit composition, flue gas flow, boiler design, combustion characteristics and flue gas composition. Therefore, the corrosion varies from plant to plant and the laboratory experiments should be complemented with field tests. The present project may thus contribute to fill the power plant corrosion research gap. In this work, different kinds of samples (wall deposits, test panel tubes and corrosion probes) from Vattenfall’s Heat and Power plant in Nyköping were analysed. Coated and uncoated samples with different alloys and different times of exposure were studied by scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), X-ray diffraction (XRD) and light optical microscopy (LOM). The corrosive environment was also simulated by Thermo-Calc software. The results showed that a nickel alloy coating can dramatically reduce the corrosion rate. The corrosion rate of the low alloy steel tubes, steel 16Mo3, was linear and the oxide scale non-protective, but the corrosion rate of the nickel-based alloy was probably parabolic and the oxide much more protective. The nickel alloy and stainless steels showed good corrosion protection behavior in the boiler. This indicates that stainless steels could be a good (and less expensive) alternative to nickel-based alloys for protecting furnace walls. The nickel alloy coated tubes (and probe samples) were attacked by a potassium-lead combination leading to the formation of non-protective potassium lead chromate. The low alloy steel tubes corroded by chloride attack. Stainless steels were attacked by a combination of chlorides and potassium-lead. The Thermo-Calc modelling showed chlorine gas exists at extremely low levels (less than 0.1 ppm) at the tube surface; instead the hydrated form is thermodynamically favoured, i.e. gaseous hydrogen chloride. Consequently chlorine can attack low alloy steels by gaseous hydrogen chloride rather than chlorine gas as previously proposed. This is a smaller molecule than chlorine which could easily diffuse through a defect oxide of the type formed on the steel. / <p>QC 20130423</p>