Sulfur chemistry and isotope systematics in natural geothermal systems

The project aims at studying the speciation and source of various sulfur compounds and isotopes in natural geothermal systems including SO42-, H2S, SO32-, H2-xS-x, SxO62-, S2O32- and SO2 in geothermal fluids and δ33S, δ34S and δ36S for SO4, H2S and SO2 and S2O3 if possible.  

  • People: Nicole Keller, Andri Stefánsson, Jóhann Gunnarsson Robin, Hanna Kaasalainen, Suhei Ono. 
  • Funding: Georg (2012-2014), Landsvirkjun (2011-2013)

H2S mineralization and sequestration

H2S is commonly emitted into the atmosphere from geothermal power plants, causing potential environmental problems. One possibility disposal method for H2S is injection back into the geothermal systems whereas H2S may mineralise forming sulphides. The project is aimed at defining the geochemistry of geothermal H2S sequestration and its geochemical feasibility. Emphasis will be made on studying the rate of H2S mineralization, possible oxidation to sulphuric acid and together with geochemical modelling assess the optimal conditions of H2S disposal.  The project is a joint effort between scientists that have contributed to this subject  in years passed.

  • People: Snorri Guðbrandsson, Andri Stefánsson
  • Funding: Landsvirkjun (2013-2014), Georg (2012-2014)

The geochemistry of CO2 in hydrothermal waters

Carbon is one of the most important element in hydrothermal systems, present in various oxidations states in secondary minerals, the gas phase and dissolved in water. To gain deeper insight into the hydrothermal carbonate geochemistry and mass movement evidences from natural systems, experiments and numerical models needs to be combined. The present limitations are largely due to incomplete and inconsistent thermodynamic and kinetic datasets and theories commonly used on carbonate solubilities, dissolution and precipitation kinetics and aqueous speciation. The research project "The geochemistry of CO2 in hydrothermal waters" aims to improve our understanding of transport, speciation and solubility of carbonate carbon in hydrothermal systems. The project will focus on (1) measuring experimentally the solubility of magnesite to 300°C using hydrogen cell in-situ pH determination, (2) direct measurements of speciation and complex stabilities of Mg-carbonate complexation reactions using combined IR and Raman spectroscopy and acid-base titrations and theroretical density functional calculations and (3) using these results and literature data, developing of internally consistent thermodynamic and kinetic data sets involving carbonate minerals, aqueous species and gases in the system Na-Ca-Mg-Fe(II)-CO2-H2O for common application. The study will involve active collaboration by scientists at the University of Iceland and University of Toulouse.

  • People: Andri Stefánsson, Pascale. Bénézeth (CNRS Toulouse), Jacques Schott (CNRS Toulouse)
  • Funding: RANNÍS (2011-2013), CNRS Toulouse and Paul Sabatier University (2010-2011)


MINSC is a European FP7 Marie Curie Initial Training Network (ITN) that addresses the current and future challenges of mineral scale formation. The research themes of MINSC relate to the mechanisms of nucleation, growth and inhibition of mineral scale formation through experimental and field projects. Scale formation is a common and costly phenomenon in many industrial processes that deal with water or other fluid handling systems (i.e., wells, heat exchangers, tanks and delivery lines, etc.), where mineral precipitation in pipes, on equipment or as fracture filling has a detrimental effect on process efficiency, cost and lifetime of processing technologies. Scale formation is encountered in a large number of industries including paper-making, chemical manufacturing, cement operations, food processing, as well as non-renewable, (i.e., oil and gas) and renewable (i.e., geothermal) energy production.

  • People: Prathap Moola, Jan Přikryl, Andri Stefánsson, Bergur Sigfússon
  • Collaborators: Various Partners of the MINSC project


The overall purpose of the project is to construct an integrated, dynamic geochemical model of geothermal systems at Reykjanes and Krafla, Iceland. Using data on fluid chemistry and mineralogy and geochemical modelling the origin of the geothermal fluids will be assessed together with quantifying the processes govern their compositions and the associated chemical and mineralogical transformations of rocks with which the fluids interact.

  • People: Matylda Heřmanská and Andri Stefánsson
  • Collaborators: Various Partners of the COTHERM project

Iron chemistry and speciation in hydrothermal waters

Iron (Fe) is particularly important in environmental biogeochemistry, and the transformations between the dissolved, solid and colloidal FeII and FeIII play a key role in the release and sequestration of many trace elements and contaminants, mineral formation and dissolution, and Fe bioavailability. Thus, in order to understand the chemical and biochemical reactions of Fe it is essential but non-trivial to determine its speciation. In this project we  test and develop sampling and analytical methods including ion chromatography and size fractionation for Fe species determination and study the chemistry and speciation of Fe in natural hydrothermal waters in Iceland.

  • People: Hanna Kaasalainen, Andri Stefánsson, Greg Druschel (IUPUI)
  • Funding: Rannís (2013-2015), Landsvirkjun (2013-2015)

Speciation and bioavailability in geothermal waters

The geochemical behaviour of elements in geothermal waters depends largely on their speciation. Our aim is to developed analytical methods to determine aqueous species concentrations of biogeochemically important elements (Fe, Mn, S, O) in (geothermal) waters, including use of for example voltammetry and ion chromatography and to test size fractionation methods to separate the true dissolved, colloidal, nanoparticle and suspended material. The concentrations of selected aqueous species will be analyzed in natural (geothermal) waters and the most important chemical reactions involving the species in question will be assesseed.

  • People: Hanna Kaasalainen, Greg Druschel, Andri Stefánsson (IUPUI)
  • Funding: Rannís (2013-2015), Landsvirkjun (2013-2015)

The unique microbial ecosystems in Vonarskard

Vonarskarð is a geothermal area situated between Vatnajökull and Tungnafellsjökull in the Icelandic highlands. A survey for microbial diversity performed in 2008 revealed numerous unique thermal ecosystems in Vonarskarð with high proportions of unidentified bacteria and archaea. The objective of the proposed project is to thoroughly examine these ecosystems and to assert which factors control microbial hot spring community structures. The selected communties are a white sulphur mat (50°C, pH 5), a green photosynthetic mat (40°C, pH 6) and an orange anoxygenic photosynthetic mat (63°, pH 7). Specimens will be acquired and separated into samples representing different depths of the mats. The morphology and mineral features of the mats will be examined using a wide range of microscopic methods including SEM-EDS. Detailed geochemical analyses will be performed on aqueous and mat samples. High-resolution data will be obtained on the composition of bacterial and archaeal species in each sample using 454 pyrosequencing of 16S rRNA genes. Furthermore, thermodynamic calculations, metagenomic analysis and studies on cultured representatives will demonstrate the partitioning of metabolic functions within the mats. Results from the different approaches will be integrated to delineate the three ecosystems and to infer the interrelation of the mat communities and geochemical processes. Furthermore, insight will be gained into the effects of poorly known microbial groups on biogeochemical cycling. The proposed project represents the first geomicrobial study performed in Iceland. It recruits scientist with expertise in microbiology, geology, geochemistry, molecular biology, electron microscopy, statistics, evolution and ecology.

  • People: Sólveig Pétursdóttir and others at Matís, Andri Stefánsson, Nicole Keller, Jóhann Gunnarsson Robin, Snorri Guðbrandsson, Hanna Kaasalainen
  • Funding: Rannís (2011-2013)

Trace element chemistry of volcanic gas

Volatile trace elements provide information on the physical and chemical origin and processes in volcanic geothermal systems. In such systems liquid and vapor phases are often present. Accordingly, volatile metals and metalloids may be transported by both phases and even become enriched in the vapor phase. Many of the elements enriched in the vapor phase (e.g. As, Pb, Cu) are of economic and environmental interest. The role of the vapor phase as a media for trace element transport has been largely ignored until recently. The speciation and transport mechanism, as well as the origin of the elements in the vapor are often poorly understood, and difficulties are associated with sampling and analysis of volcanic vapor condensates. The objectives of this study are to develop reliable sampling methods for trace element determination in volcanic vapor and characterize the concentrations and transport mechanism of elements in the vapor phase in active volcanic geothermal systems. 

  • People: Hanna Kaasalainen, Andri Stefánsson
  • Funding: Rannis, NordVulk

Chemistry of trace elements in geothermal waters

Trace elements present in geothermal fluids may be useful in studying the various processes occurring in active geothermal systems, such as primary rock leaching, precipitation and dissolution reactions, boiling and phase segregation, cooling, mixing and mass precipitation. Such trace elements show a wide range of chemical behavior from alkali to transition metals and metalloids and The objectives of this study are to characterize trace element composition of natural geothermal waters including surface geothermal waters covering the pH range from 2 to >9 and aquifer fluids discharged by sub-boiling and high-temperature wells, and to understand the most important processes controlling the trace element chemistry in surface geothermal waters and aquifer fluids in Iceland. 

  • People: Hanna Kaasalainen, Andri Stefánsson, Stefán Arnórsson, Niels Giroud
  • Funding: Rannis, NordVulk 

The Source of CO2 in geothermal waters traced by δ13C

The project aims at studying the origin of carbon in low temperature geothermal waters using C-13.  The contribution from organic matter, mineralogical source and atmospheric source will be assessed as well as the geochemical behavior of CO2 in geothermal waters.

  • People: Ríkey Kjartansdóttir, Andri Stefánsson, Árný E. Sveinbjörnsdóttir

Geochemical modeling software

The objective of this project is to develop new software for computing equilibria between dissolved aqueous species, rock minerals, and gases in steam. In particular, this code is intended to handle aqueous speciation calculations; fluid mixing; reaction progress calculations, such as the dissolution of primary rock minerals and the precipitation of alteration minerals; boiling and condensation processes; and redox equilibria.

  • Jón Örn Bjarnason, Stefán Arnórsson
  • Funding: HS Orka, Landsvirkjun, Orkustofnun, Reykjavík Energy

Past projects

  • Speciation of Arsenic in geothermal waters (Nicole Keller, Andri Stefánsson, Bergur Sigfússon)