Progress Semester 4
Nik Berninger: CNRS Toulouse |
Reaction kinetics of Mg-carbonates. Microscopic experiments at 100 °C demonstrated a clear change in surface reactivity on the (104) surface of magnesite as a function of aqueous calcium concentration. Low concentration of aqueous Ca promoted obtuse step advancement while higher concentration inhibited obtuse step advancement rates. Macroscopic experiments at 100 °C did not show any significant change in bulk precipitation rates. These findings suggest that obtuse step advancement rates – unlike acute step advancement rates - are not controlling magnesite growth rates. 7. For more information, please click here. |
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Diwaker Jha: Uni Copenhagen |
During this reporting period, I finalized a paper and the code "Adaptive Ring Artifact Suppression for Tomography Applications" and submitted it to Applied Physics Letters. I also found out that flow related properties derived from tomograms can be highly influenced by the resolution of the tomograms. |
For more information on multiscale mapping of 3D Nanotomograms, please click here. |
Jan Prikryl: Uni Iceland |
Carbonate mineral scaling is commonly associated with geothermal fluid utilization, both in the reservoir as well as in production and re-injection wells and surface pipelines. The problematic aspect is to visually investigate on-going geochemical processes. The lack of information on porosity changes, total reactive surface area, fluid-rock kinetics makes it difficult to predict such interaction and leads to malfunction during geothermal utilization. Understanding the CO2-water-rock interaction at geothermal conditions is therefore of significant importance. For this reason batch-type experiments (CO2-H2O-olivine) were conducted as a function of time and acid supply under hydrothermal conditions. Such a series of experiments tells us more about typical dissolution, nucleation, crystal growth macroscopic patterns of secondary phases or how reactive surface area evolves with time. For dissolution patterns olivine, crystalline basalt and basaltic glass powders were dissolved in 1D flow-through columns. These experimental examples of porous media can answer how mass transfer is affected with distance in porous media. Moreover how porosity and reactive surface area is evolving with reaction progress. Morphology of typical grains in porous media: For more information, please click here. |
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Daniela Meier: Uni Leeds |
Abstract of paper in press with Mineralogical Magazine for update on scaling plate story: Precipitation of amorphous silica (SiO2) in geothermal power plants, although a common factor limiting the efficiency of geothermal energy production, is poorly understood and no universally applicable mitigation strategy to prevent or reduce precipitation is available. This is primarily due to the lack of understanding of the precipitation mechanism of amorphous silica in geothermal systems. In this study we present data about microstructures and compositions of precipitates formed on scaling plates inserted at five different locations into the pipelines at the Hellisheiði power station (SW-Iceland). Precipitates on these plates formed during 6 to 8 weeks of immersion in 120 or 60°C hot, fast flowing and silica supersaturated geothermal fluids (around 800 ppm of SiO2). Although the composition of the precipitates is fairly homogeneous, with silica being the dominant component and Fe-sulphides as a less common phase, the microstructures of the precipitates are highly variable and dependent on the location within the geothermal pipelines. The silica precipitates have grown through aggregation and precipitation of silica particles that precipitated homogeneously in the geothermal fluid. We identified 5 main factors that may control the precipitation of silica: (1) temperature, (2) fluid composition, (3) fluid flow regime, (4) distance along flow path and (5) immersion time. On all scaling plates, a corrosion layer was found underlying the silica precipitates indicating that once formed the presence of a silica layer likely protects the steel pipe surface against further corrosion. Yet silica precipitates influence the flow of the geothermal fluids and therefore can limit the efficiency of geothermal power stations. Abstract submitted to the International Carbon Conference for update on precipitates form heat exchanger: According to a recent report [1] only around 223 TWh of geothermal energy, both electricity and thermal energy, were produced in 2012. Besides high exploration, development and running costs, the development of geothermal resources is often limited by corrosion and scaling problems. One of the most common scaling problems in geothermal power stations world-wide is the precipitation of amorphous silica. However, there is still no universally applicable solution to mitigate silica precipitation because our understanding of the pathways and mechanisms of silica precipitation under conditions prevalent in geothermal power plants (i.e. high temperatures and high flow rates) is still in its infancy. Here we present results from a study of silica precipitates that formed inside the heat exchanger unit used for the production of thermal energy at the Hellisheiði power station in SW Iceland. Amorphous silica precipitated over ~ 6 months from a fast flowing (400 l/s), 120°C hot solution containing around 800 ppm of SiO2. The precipitates that were removed during a routine cleaning operation were dried and characterized for composition and structural features. All precipitates were nearly pure amorphous silica as confirmed by X-ray diffraction and FTIR spectroscopy. Scanning electron microscopy revealed that precipitates were composed of individual spheres 0.5 to 20 μm in diameter. These small individual spheres were cemented together into larger, up to 1 mm spherical aggregates by the continual polymerization of monosilicic acid (H4SiO4). These aggregated structures had a total specific surface area of ~ 0.24 m2/g. Interestingly, nuclear magnetic resonance measurements revealed a low overall porosity of ~ 8%, but with a high proportion of pores in the nm-range, and only ~ 17% of the pores reaching ~ 0.2 μm. The silica precipitates showed very intricate three-dimensional structures that were analysed by X-ray computed tomography. Information about the 3D resolved structure of samples combined with the bulk analyses helps us quantify and likely also model better the formation processes and allows us to assess the impact of these precipitates on fluid flow through the heat exchanger. Reduction in flow due to precipitation impacts the production of thermal energy at Hellisheiði power station and both compositional and structural knowledge about these precipitates can help mitigate the costly scaling problem. [1] REN21 2013. Renewables 2013 Global Status Report. Paris: REN21 Secretariat. |
Giulia Montanari: Uni Copenhagen |
Growth inhibitors on carbonates The study of CaCO3 formation and growth is very important not only for a better understanding of biomineralisation, but also for improving industrial processes, for example the inhibition of CaCO3 scales inside pipelines, boreholes and heat exchangers. Different CaCO3 polymorphs (vaterite, calcite, aragonite) with varying morphologies and size can form as a result of different physico-chemical conditions, such as pH, supersaturation, ionic strength, presence of inorganic and organic additives or temperature. Over the last few months, I studied the early stages of CaCO3 crystal growth to probe how potential organic compounds affect CaCO3 polymorph, growth rate, crystal morphology and size. Experiments were carried out at room temperature with UV-Vis spectrophotometer to follow in-situ the formation of CaCO3 crystals and their growth as a function of CaCO3 saturation, Ca:CO3 ratio and the presence of organic additives. These time-resolved turbidity measurements allow quantification of induction period for crystal formation, growth rate and inhibitory effect of added organic compounds. Samples were removed during the reactions for XRD, SEM and XPS analyses to check for CaCO3 polymorph, crystal morphology and size and sorbed organic compounds. With a decrease in saturation index, induction period for crystal formation increased and a higher percentage of calcite over vaterite crystal was observed (XRD and SEM analysis). The presence of organic additives, like aspartic acid, added to the NaHCO3 solution, greatly affected the type of polymorph forming as well as the growth rate and induction time: vaterite became more stable and the amount of precipitate decreased with increasing concentration of the amino acid, while induction time increased. |
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Biyun Zhen Wu: Uni Copenhagen |
During this reporting period, I had a two-month stay at Geosciences Environment Toulouse (GET), Centre National de la Recherche Scientifique (CNRS), Universite Paul Sabatier, France as part of my secondment. The purpose of this visit was to carry out kinetic experiments on barite as part of my research within the EU-MINSC project. Many experiments were done at different conditions using batch low and high temperature reactors and analyses were conducted with ICP-AES. This opportunity was a great chance for exchanging knowledge and gaining experience within the applied geochemistry environment. First, of all I am thankful for supervision from Dr. Eric H. Oelkers, whose guidance and support were very valuable and meaningful for the research. I also got valuable training and support from the fellows from other networks: Ulf-Niklas Berninger from MINSC, Martin Voigt and Christian Grimm from C02-REACT and Andrea Perez from MetTrans; help and encouragement from experienced researches, such as Thomas Rinder and Aridane Gonzalez Gonzalez, from specialised technicians for operating the high temperature reactors and analytical equipment, namely Alain Castillo and Philippe Besson, and assistance from Clare Desplats. I had a really great, helpful team during my stay. |
Cristina Ruiz Agudo: Uni Münster |
Our in situ AFM observations show that the commercial copolymer used in our studies (maleic acid/allyl sulfonic acid copolymer with phosphonate groups, partial sodium salt) in concentrations as low as 1 ppm completely blocks barite surface growth, probably due by the adsorption of an inhibitor layer to barite (001) surfaces. At lower copolymer concentrations (0.1 ppm and 0.5 ppm) tested here, this commercial copolymer has an important impact on the (001) barite face promoting 2D nucleation before inhibiting it. The growth mechanism in the presence of 0.5 ppm inhibitor, observed in AFM experiments, is changed, such that nanoparticle attachment to the surface occurred instead of 2D islands nucleation and spreading. This is probably due to the copolymer which stabilizes barite nanoparticles. |
Fernando Berro Jimenez: West Systems |
Running experiments and taking some conclusions such as the final layout and the instrument to buy have been the main part of these six months. These experiments were necessary to verify the linearity and stability of the yellow colorimetric method. Linearity seems to be stable up to about 55-60 ppm of SiO2. Although the range and the linearity are a little bit lower than spectrophotometers in laboratories, this instrument is good enough, considering that the whole process runs continuously and with automatic devices. Linearity is always R2>0,99 After these crucial experiments we have decided which instruments we must acquire and the final disposition of the system. |
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Christopher Hawkins: Uni Oslo |
The past six months have been spent doing the following: Month 1: Further simulations regarding turbulent mixing. Analysis of turbulent simulation results. The paper on turbulent mixing is almost complete which will provide a key link between physics, chemistry and engineering in the domain of turbulent pipe flow. |
Prathap Moola: Reykavik Energy |
Fluid rock interaction experiments were conducted on six common hydrological tracers namely amino G acid, amino rhodamine G, fluorescein sodium salt, napthionic acid, rhodamine B and pyranine in solutions of pH 3 and 9 with porous rocks gibbsite and goethite respectively. Tracers were injected at a fixed flow rate through Teflon column dry packed with rock material and the tracer concentration was monitored through spectrophotometer. A breakthrough curve was generated. The outcome of the data obtained from experiments suggest that tracers were bind inside the column due to the effect of adsorption. Static batch sorption experiments will be conducted to calculate the equilibrium constant for tracers with goethite and gibbsite in solutions of pH 2-10. |
Taher Rabizadeh: Uni Leeds |
The kinetics of calcium sulfite nucleation and growth were studied by UV-VIS and the solid products were characterized during and at the end of each reaction for their mineralogical composition by X-ray diffraction (XRD) and for their morphological features by scanning electron microscopy. The data that I produced show that the addition of magnesium nitrate increased the calcium sulfate induction time. Also at the same concentration, magnesium nitrate increased the indcution time more than magnesium chloride. Furthermore, it was observed that gypsum crystals have higher solubility in nitrate solution rather than a chloride one. The ion chromatography experiments reveald that the concentration of magnesium ion during the reaction remained constant. |
