13. High and low temperature geochemistry, cosmochemistry and geochronology

13.1. Geomicrobiology of the past and present

13.2. Bio-mineral interactions

13.3. Inorganic Geochemistry

13.1. Geomicrobiology of the past and present

                       ORAL PRESENTATIONS                    

Ocean redox conditions between the Snowballs – geochemical constraints from Arena Formation, East Greenland

Tais W. Dahl¹, Eva L. Scheller², Alexander J. Dickson³, Donald E. Canfield⁴, Christoph Korte⁵ and Kasper K Kristiansen^5
1Natural History Museum of Denmark, University of Copenhagen, Denmark, ²Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, USA, ³Department of Earth Sciences, University of Oxford, United Kingdom, ⁴University of Southern Denmark, Odense M, Denmark, ⁵Institute of Geology and Natural Resources, University of Copenhagen, Denmark
The emergence of animal ecosystems is largely believed to have occurred in increasingly oxygenated oceans after the termination of the Sturtian and Marinoan glaciations. This transition has led to several hypotheses for the mechanism driving ocean oxygenation and animal evolution. One hypothesis is that enhanced weathering increased oceanic nutrient levels, primary productivity and organic carbon burial, and ultimately oxygenated the atmosphere and oceans. Another hypothesis suggests that an animal-driven reorganization of the marine biogeochemical cycles might have oxygenated the oceans. Through molybdenum (Mo), carbon, sulfur isotopes and iron speciation results from the Arena Fm, East Greenland, this study constrains ocean redox conditions after the Sturtian deglaciation and before the major radiation of animals. Carbon and sulfur isotope stratigraphy is used to correlate the Arena Fm with other formations worldwide between the Sturtian and Marinoan glaciations (~720–635 Ma). The lower part of the Arena Fm consists of black shales deposited under locally euxinic conditions as evidenced by high proportions of highly reactive iron and pyrite. These black shales display muted Mo enrichments, low Mo/TOC compared to overlying shales and Phanerozoic euxinic sediments. The δ⁹⁸Mo values are consistent with other Cryogenic euxinic basins and well below that of the modern oceans. The combination of low [Mo] and δ⁹⁸Mo suggests that widespread anoxia prevailed in the oceans at this time. These results are consistent with most other studies from this time suggesting that ocean oxygenation was not linked to Snowball Earth deglaciation, but was delayed until animals effectively entered the scene.

Primordial cellular oxygen sensing key to animal evolution in the oxic realm

Emma Hammarlund^1
1Lund University
Microbes sense environmental oxygen through mechanisms that since have been inherited through evolution all the way to vertebrate animals[1]. The inherited and modified mechanisms in animals now couple to cell responses that are crucial for the maintenance of tissue. However, to what extent an evolution of the oxygen sensing mechanisms mattered for the evolution animals remains largely unexplored.

Oxygen sensing mechanisms have primarily been explored in the field of tumor biology, since they associate with tissue hypoxia[2] and the maintenance of cancer stem cells. Cancer stem cells possess the capacity to form new tissue. In these studies, the hypoxia-inducible transcription factors (HIFs) are central, by how they are guided by ambient tissue oxygenation and how they associate to stem cell-like features (stemness)[3]. Insights from tumor biology, on how HIFs regulate tissue formation, emphasize that refined control of primordial oxygen sensing mechanisms must play a role for large life in the oxic environment. Indeed, by acknowledging a few observations from the fields of stem cells science and tumor biology, it appears a paradox that animals renew tissue in the oxic environment at all.

Based on transdisciplinary observations regarding the role of the oxygen sensing mechanisms – inherited from microbes – I present a model of evolving stemness control that may have facilitated animals to enter and diversify in the oxic environment. The model challenges the view that an increased extent of oxic niches resulted in the Cambrian explosion. Implications of the model is compared to observations in the geological record.

References
1.        Taylor, B.L. and I.B. Zhulin, PAS domains: internal sensors of oxygen, redox potential, and light. Microbiology and Molecular Biology Reviews, 1999. 63(2): p. 479-506.

2. Semenza, G.L., Hypoxia-inducible factors in physiology and medicine. Cell, 2012. 148(3): p. 399-408.
3. Pietras, A., et al., HIF-2α maintains an undifferentiated state in neural crest-like human neuroblastoma tumor-initiating cells. Proceedings of the National Academy of Sciences, 2009. 106(39): p. 16805-16810.

Microbial element cycling and transport: from ancient sedimentary basins to the Plastisphere

Nicole R. Posth¹, Serguei Chiriaev², Elena Gorokhova³, Thomas R. Neu⁴ and Jakob Strand^5
1Geology, Dept of Geosciences & Natural Resource Management, University of Copenhagen, DK, ²SDU NanoSYD, IRCA, Mads Clausen Institute, SDU, Sønderborg, ³Dept of Environmental Science & Analytical Chemistry- ACES, Stockholm University, ⁴Microbiology of Interfaces, Helmholtz Centre for Environmental Research (UFZ) Magdeburg, ⁵Dept of Bioscience, Aarhus University
Microorganisms play a key role in biogeochemical processes in aquatic environments, closing all major element cycles and influencing element transport and burial. Experiments with modern, model organisms have been used to constrain the role of microbes in ancient aqueous environments. Both the acquired knowledge and the analytical methods used in these studies of the Earth´s past are also useful to clarify the role of microorganisms in contemporary and future evolving environments.

The pollution of oceans through plastic debris has emerged as a new global challenge. The introduction of these synthetic particles to aquatic systems raises environmental health concerns, but these particles may also alter the transport and burial of microbial organic matter and influence global biogeochemical cycles. Both in the water column and sediment, bacteria are found as free-living cells or surface-oriented biofilms. While biofilm found on marine plastic implies a new ecological niche, named the Plastisphere, our knowledge of marine plastic-microbe interaction is still nascent. Plastic acts as a vector for microbial communities, offers a surface for abiotic and biotic element cycling, and may even be a microbial carbon source. Indeed, microorganisms may play a key role in degrading, transporting and incorporating (micro)plastic into biogeochemical cycles. In this new study, we combine microbial community profiles, bioimaging, isotope, and elemental analysis to elucidate plastic-associated element cycling. Focus on the interaction between microbes, the plastic surface and their environment, as well as the effect of transport and diagenesis will inform the influence of these particles on element cycling.

Mechanistic insight into microbial formation of iron oxides: implications for development of banded iron formations and our atmosphere

Karina K. sand¹, Stanislav Jelavić¹ and James J. DeYoreo^2
1Department of Chemistry, University of Copenhagen, Denmark, ²Physical Sciences Division, Pacific Northwest National, Laboratory, Richland, WA, USA.
Microbial control over mineralization is a widespread phenomena that has shaped the near-surface mineralogy and chemistry of the earth, oceans and atmosphere. However, the mechanistic understanding of these interactions is poorly constrained. We quantitively addressed the mechanisms behind the controls that microbial extracellular polymeric substances (EPS) exert in directing mineral formation and transformation. We captured the collective bond behavior of model and natural EPS during interaction with the two common iron oxides, hematite and ferrihydrite. Subsequently, we applied nucleation theories to the measurements and obtained information on the mechanistic controls for iron oxide formation on the polymers. One of the main findings is that EPS, as well as less complex polysaccharides, strongly bind iron species and iron oxides to such an extent that they modulate the interfacial free energy of the iron oxide-polymer system, thus promoting nucleation on the polymer matrix by decreasing the nucleation barriers. These findings have implications for mineral formation in both oxic and anoxic conditions and may explain the mechanisms behind the development of banded iron formations (Lalonde et al., 2012) and oxygen buildup during the Great Oxidation Event (Canfield, 1998).

References
Canfield, D.E., 1998. A new model for Proterozoic ocean chemistry. Nature 396, 450–453. doi:10.1038/24839

Lalonde, K., Mucci, A., Ouellet, A., Gélinas, Y., 2012. Preservation of organic matter in sediments promoted by iron. Nature 483, 198–200. doi:10.1038/nature10855

Pore space sealing using microbially mediated calcite precipitation: a lab to field scale study

Dominique J. Tobler¹, Mark O. Cuthbert², Michael S. Riley³, Stephanie Handley-Sidhu⁴ and Vernon R. Phoenix^5
1Nano-Science Center, Department of Chemistry, University of Copenhagen, Denmark, ²School of Earth and Ocean Sciences, Cardiff University, United Kingdom, ³School of Geography, Earth and Environmental Sciences, University of Birmingham, United Kingdom, ⁴School of Geography, Earth and EnvironmentalSciences, University of Birmingham, United Kingdom., ⁵Civil and Environmental Engineering, University of Strathclyde, United Kingdom
Microbially driven calcite precipitation (via ureolysis) has shown great potential in a wide range of applications, including solid-phase capture, concrete crack remediation, soil stabilisation and carbon sequestration. Here, this process is investigated as a means of reducing the primary porosity and/or secondary fracture porosity of host rocks surrounding nuclear waste repositories in order to control or prevent radionuclide transport. To determine a suitable field injection approach, a series of bench scale experiments were undertaken in the laboratory. First, batch experiments focused on the kinetics of calcite precipitation as a function of bacterial mass, urea and Ca²⁺ concentration and anaerobic vs aerobic conditions. Results showed that the ureolytic bacteria performed equally well under both oxygen poor and oxygen rich conditions. In the next stage, flow-through experiments in various media (sand columns, rock cores) were carried out to examine the homogeneity and extent of the pore space fill along the column / core as a function of injection strategies. It emerged that a staged injection strategy, where we alternate between bacterial and reactant injection, yields the most homogeneous calcite fill, reducing overall porosity by up to 45 %. Ultimately, this approach was tested at the field scale, led by University of Birmingham, to seal a fractured rock (dacite) at ~28 m depth, in a quarry in Leicestershire, UK. Within few injection cycles, the single fracture was substantially plugged by calcite, yielding a significant transmissivity decrease over several meters.

13.2. Bio-mineral interactions

                       ORAL PRESENTATIONS                    

Crystallization kinetics of apatite model systems

Henrik Birkedal^1
1Department of Chemistry & iNANO, Aarhus University, Denmark
The formation of biominerals remains shrouded in mystery. A plethora of mechanisms have been proposed [1,2]. To obtain detailed insights into the formation of such minerals, we have present results of studies of apatite formation.

We use in situ X-ray diffraction to map crystallization kinetics [2-5] and found that at high pH apatite forms from amorphous calcium phosphate precursors. Choices of pH and counterions have significant impacts on crystallization kinetics and the shape of the resulting nanocrystals.

We show that using dense organic gels afford chemical garden type formation of hollow tubes with apatitic (and other minerals depending on choice of conditions) walls [6] while coupling sedimentation and particle aggregation results in large transparent nanocrystal aggregates [7]. Organic additives change crystallization kinetics and crystal size/shape [3,4,7] and may even dramatically alter the crystallization pathway by introducing metastable mesoscopic states prior to nucleation [8]. These results illustrate the complex nature of (bio)mineral formation.

References

[1] De Yoreo, J. J.; Gilbert, P. U. P. A.; Sommerdijk, N. A. J. M.; Penn, R. L.; Whitelam, S.; Joester, D.; Zhang, H.; Rimer, J. D.; Navrotsky, A.; Banfield, J. F.; Wallace, A. F.; Michel, F. M.; Meldrum, F. C.; Cölfen, H.; Dove, P. M. Science 2015, 349, aaa6760.

[2] H. Birkedal in New perspectives on mineral nucleation and growth: From solution precursors to solid materials (Eds. A. E. S. van Driessche, M. Kellermeier, L. G. Benning, D. Gebauer) Springer 2017, 99, 199-210.

[3] Ibsen, C. J. S.; Birkedal, H. Nanoscale 2010, 2, 2478-2486.

[4] Ibsen, C. J. S.; Birkedal, H. Journal of Applied Crystallography 2012, 45, 976-981.

[5] Ibsen, C. J. S.; Chernyshov, D.; Birkedal, H.  Chem. Eur. J. 2016, 22, 12347–12357.

[6] Ibsen, C. J. S.; Mikladal, B. F.; Jensen, U. B.; Birkedal, Chem. Eur. J. 2014, 20, 16112-16120.

[7] Jensen, A. C. S.; Ibsen, C. J. S.; Birkedal, H. Cryst. Growth Des. 2014, 14, 6343-6349.

[8] Ibsen, C. J. S.; Gebauer, D.; Birkedal, H. Chem. Mater. 2016, 28.

In, on or in between: tracking the persistence of proteins in the past

Matthew Collins^1
1University of Copenhagen
It is a time of great change in the use of biomolecules in archaeology and geology.  As a young lecture at the Fossil Fuels and Environmental Geochemistry Institute in Newcastle, I was used to thinking that it was small robust molecules which typified organic geochemistry. Today leading Scandinavia Archaeologist Kristian Kristiansen (Gothenburg) is arguing that his discipline is undergoing a third science revolution, in which genetics allied to isotope geochemistry and data modelling is casting aside postmodern notions and returning to older concepts of cultural change. Of these three pillars, both bigger geochemical datasets and better modelling strategies were foreseen, the explosion in genetic data was not. Genetics and proteomics are now potential tools for archaeologists and geoscientists because extraordinary technological advances, driven by the biosciences, are luckily well suited to the fragmented remains which accumulate over time.  Using new genomic methods, the last decade has revealed how remarkably well large fragile organic molecules persist and can be recovered and interrogated.

Proteins survive longer than DNA – therefore if genomics has revolutionised archaeology will proteomics revolutionise geosciences…?  Er, no, probably not.  Nevertheless in this presentation I will explore what we know about protein survival.  How long do proteins survive into geological time, where and how does they survive, and what use might they be upon recovery? As I am speaking in the bio-mineral interactions session, it probably comes as no surprise that it is minerals which seem to key to answering these questions.

Biomimetic approach to material design

Anne Rath Nielsen¹, Daniel J. Murray², Behzad Rad², Susan L.S. Stipp³, Ronald N Zuckermann² and Karina K. Sand^4
1University of Copenhagen, Department of Chemistry, Materials Chemistry Section, ²Molecular Foundry, Lawrence Berkeley National Lab, California, USA, ³Materials Chemistry, Nano-Science Center, Department of Chemistry, University of Copenhagen, Denmark, ⁴Geography & Earth Sciences, Aberystwyth University, UK
Biomineralising organisms are experts in controlling the interplay between polymers and minerals to obtain strong and functional materials. The use of bio inspired polymers to control and direct growth of calcium carbonate, could provide a pathway towards the fabrication of novel tough and strong composite materials. An important step in this direction is to gain control of the calcium carbonate nucleation and growth processes, which requires thorough characterization of the organic/inorganic interactions.

Bio inspired peptoid polymers (N-substituted glycines) can be synthesized with precision sequence control and are known to form ultrathin two-dimensional nanosheets [1]. A recent study has shown that nanosheets with surface exposed acidic chains can template formation of stable amorphous CaCO₃ (ACC) [2]. This has inspired us to investigate the CaCO₃ nucleation rates and growth on functionalised substrates as a function of time using a custom build flow cell system. We used model systems of chosen self-assembled monolayers (SAMs) to map the effect of specific functional groups as well as studied direct nucleation and growth on immobilized peptoid polymers.

This study provides insight into the different energy barriers provided by the different surfaces. Knowledge of the kinetics and thermodynamics of the crystallisation process is an important first step for guiding the crystallization towards fabrication of bio inspired composite materials.

References
[1] Nam K.T., Shelby S.A., Choi P.H., Marciel A.B., Chen R., Tan L., Chu T.K., Mesch R.A., Lee BC., Connolly M.D., Kisielowski C., and Zuckermann R.N. (2010) Free-floating ultrathin two-dimensional crystals from sequence-specific peptoid polymers. Nature materials, 9, 454-460

[2] Jun J.M.V., Altoe M.V.P., Aloni S., and Zuckermann R.N. (2015) Peptoid nanosheets as soluble, two-dimensional templates for calcium carbonate mineralization. Chem. Comm., 51, 10218.

Sub-micron resolution diffraction and fluorescence tomography reveals bone microstructure

Nina Wittig¹, Simon Frølich¹, Mie Birkbak¹, Jonas Palle¹, Maja Østergaard¹, Kathryn Spiers², Jan Garrevoet² and Henrik Birkedal^1
1Department of Chemistry & iNANO, Aarhus University, Denmark, ²DESY Photon Science, Hamburg, Germany
The structures of many materials including biominerals are highly complex. Understanding their structure is challenging and calls for methods with sensitivity across several length scales in 3D. Multimodal X-ray tomographies are such techniques [1]. Here, we apply diffraction scattering computed tomography (DSCT) to reveal the crystalline properties and fluorescence tomography (FT) to probe element distributions in bone using a 400 nm X-ray beam.

Bone displays essential structural features ranging from the nano- to macro-scale. The links between bone structure and function remain poorly understood. The osteon is a building block in human long bones. In osteons, mineralized collagen fibrils are arranged in a twisted plywood structure surrounding a Haversian canal. While it has been shown that the indentation modulus varies periodically with the osteon lamellae and that this is positively correlated with the mineral content [2], it remains uncear how the mineral phase’s properties varies across the osteon. The same holds for oligo elements such as Sr. To unravel the structure of osteons, we combine DSCT and FT with sub-micron resolution. This experiment combines the capabilities of diffraction and fluorescence with those of computed tomography to allow for reconstruction of a diffractogram and a fluorescence spectrum in each volume element within the sample [1]. The resulting >1.5 million diffractograms were Rietveld refined using MultiRef [3] to obtain typical crystallographic parameters, including unit cell parameters, profile parameters etc. This revealed distinct variations in mineral properties and element distributions with distance from the osteon center.

References
[1] Birkbak et al. (2015) Nanoscale 7, 18402-18410.

[2] Gupta et al. (2006) J. Mater. Res. 21, 1913–1921 .

[3] Frølich & Birkedal (2015) J. Appl. Cryst. 48, 2019-2025.

                       POSTER PRESENTATIONS                    

Quantification of molecular bonding: Implications for origin of life and the iron cycle

Stanislav Jelavić¹ and Karina K Sand^2
1University of Copenhagen, Nano-Science Center, Department of Chemistry, Copenhagen, Denmark, ²Aberystwyth University, Geography & Earth Sciences, Aberystwyth, United Kingdom.
Mineral-polymer interactions are vital for many life forms have probably played a significant role in the origin of life through polymerization of nucleotides. To form functional biopolymers, the preexisting monomers had to be preconcentrated from dilute prebiotic solutions and the thermodynamic barrier to polymer formation had to be surpassed. Both these processes has been found to be encouraged by mineral adsorption. Element cycles of carbon and iron are also strongly impacted by mineral-polymer interactions. E.g.  microbial production of iron oxides occurs on such a vast scale that it impacts the global iron cycle and has been responsible for major biogeochemical events such as the creation of an oxygen-rich atmosphere. Despite the significance of the polymer-mineral interaction, little insight into the thermodynamic and kinetic properties of the polymer-mineral bond is available at a mechanistic level.

Dynamic force spectroscopy (DFS) can directly capture the bond behavior of interacting bonds between molecules and mineral surfaces. We have used this atomic force microscopy technique to investigate the thermodynamic and kinetic bond parameters describing bond behavior and energetics of nucleotide adsorption and RNA polymerisation on clay mineral surfaces as well as the mechanism behind the observed enhanced iron oxide formation on bacterial polymers. Our results highlight the strength of DFS as a tool of investigating the determining mechanisms behind mineral-organic interactions.

Using LA-ICPMS to investigate seasonality in Cod otolith microchemistry

Kristian Nielsen¹, Simon Hansen², Tonny Thomsen² and Karin Hüssy^1
1Technical University of Denmark, National Institute of Aquatic Resources, ²Geological Survey of Denmark and Greenland, Department of Petrology and Economic Geology
Fish ages are traditionally determined by visually inspecting the ring structures in fish ear stones (otoliths). These ages are important in fish stock management, e.g. when assessing fishing pressure, growth patterns or stock conditions. For the eastern Baltic cod the methods of visual age determination has always been problematic, and in recent years this has worsened, causing problems for the stock management. In this project we aim to develop an alternative age determination method using the chemical composition of otoliths. We have analysed 132 otoliths using LA-ICPMS line transects which provide a chronological record of the fish’s entire life from hatch to catch. The elements analysed were Mg, P, Ca, Mn, Cu, Zn, Sr and Ba, which are the most abundant elements in otoliths. The otoliths are recaptures from a mark-recapture experiment, where cod were tagged with an external tag and an internal chemical marker by injecting SrCl2, which incorporates into the otolith during growth. During LA-ICPMS analysis, the Sr marker was detected by screening with a 3 µm laser spot size, whereas the analyses were performed using a beam size of 40 µm at 5 µm/s progressing rates. The Sr marker acts as a time stamp that allows evaluation of the LA-ICPMS elemental analysis in time. The aim is to investigate if some of the analyzed elements vary on a seasonal basis, and how well this can be used for age determination. The presentation will include method details and preliminary results of this on-going project.

Manganese speciation and distribution in foraminiferal calcite under varying environmental conditions

Nadine Quintana Krupinski¹, Sam Webb², Per Persson¹, Marit-Solveig Seidenkrantz³, Takashi Toyofuku⁴ and Helena Filipsson^1
1Lund University, ²Stanford Synchrotron Radiation Lightsource, ³Aarhus University, ⁴JAMSTEC
Benthic foraminiferal Mn/Ca, though often referred to as an indicator of authigenic contamination, has recently been suggested as a bottom water oxygen proxy. However, our understanding of Mn incorporation into benthic foraminifera is incomplete, and roles of potential contaminant phases need to be clarified. To evaluate whether Mn can indicate past hypoxia, we need to understand where/how Mn occurs in benthic foraminifera: is it incorporated into the calcite as a Mn-bearing carbonate species, and are other forms of Mn present? We also study how/whether changing environmental conditions and vital processes may affect Mn speciation and distribution.

We use synchrotron methods (X-ray absorption spectroscopy (XAS)) and micro-X-ray fluorescence (μXRF) mapping) to evaluate how Mn is incorporated into the benthic foraminifera calcite lattice (its distribution and speciation). We complement this with solution ICP-MS to determine mean Mn/Ca values for pooled foraminifera from the same samples. We use field-collected samples of living benthic foraminifera (to avoid diagenetic effects) from two oxygen conditions to evaluate whether differing environmental conditions affect Mn distribution and coordination.

Spectral data (XAS) indicate that Mn in the foraminiferal tests occurs as a Mn-carbonate, while small external debris with high Mn in these uncleaned foraminifera generally has Mn-oxide-type spectra (removable via cleaning methods). μXRF maps show that in many species, Mn is fairly evenly distributed at low-moderate concentration throughout the test, potentially suggesting stable oxygenation conditions. However, other species have specific high-Mn chambers, perhaps suggesting intervals of greater oxygen stress or a response to foraminiferal processes that alter the microenvironment.

13.3. Inorganic Geochemistry

                       ORAL PRESENTATIONS                    

Microscopic view of hydrogen motion in Clay minerals from neutron scattering

Heloisa Bordallo^1
1Niels Bohr Institute – University of Copenhagen
Neutron science is the science of everyday life, providing a microscopic view of the materials we rely on for modern life. Neutrons, similarly to X-rays, penetrate matter. However, unlike X-rays, neutrons interact with matter in a different manner, thus allowing the identification of elements with very low molecular weight, including hydrogen. For this reason, neutron spectroscopy brings unique information about hydrogen mobility and can contribute for better understanding the mechanisms that govern processes in clay dominated environments.

In this talk I will discuss on this promising approach by presenting a couple of specific examples  of quasi-elastic neutron scattering experiments. The first is related to the investigation of how the transport mechanisms (of water or ions) are affected by an applied electric field. To shed light into this question, we have focused specifically on the dynamics of water in clays through investigating the origin of changes observed in water resistance under in-situ electric field stimuli.   The second focus on in-situ measurements performed during controlled exposure to water vapour and how the dynamics of adsorbed water change over a large range of unsaturated conditions. Using this approach we were able to confirm that true material equilibrium at intermediate hydration states is a time dependent phenomenon. The overall knowledge acquired using neutron spectroscopy opens new possibilities in the mitigation of soil contamination and geo-environmental engineering, where the role played by water controls the system properties.

References
R. Ignazzi, W. P Gates, S. O. Diallo, D. Yu, F. Juranyi, F. Natali, and H. N. Bordallo (2017) Electric Field Induced Polarization Effects Measured by In Situ Neutron Spectroscopy. Journal of Physical Chemistry C, DOI: 10.1021/acs.jpcc.7b08769.

104. P. Gates, L. P. Aldridge, G. G. Guzman, R. A. Mole, D. Yu, G. N. Iles, A. Klapproth, H. N. Bordallo (2017) Water desorption and absorption isotherms of sodium montmorillonite: A QENS study. Applied Clay Science, 147, 97–104.
105. C. Berg, K. N. Dalby, N. Tsapatsaris, D. V. Okhrimenko, H. O. Sørensen, D. Jha, J. P. Embs, S. L. S. Stipp, and H. N. Bordallo (2017) Water Mobility in Chalk: A Quasielastic Neutron Scattering Study. Journal of Physical Chemistry C, 121, 14088–14095.

W.P. Gates, H.N. Bordallo, L.P. Aldridge, T. Seydell, H. Jacobsen, V. Marry and G. Jock Churchman (2012) Neutron Time-of-Flight Quantification of Water Desorption Isotherms of Montmorillonite. Journal of Physical Chemistry C, 116, 5558-70.

H.N. Bordallo, L. P. Aldridge, G. Jock Churchman, W. P. Gates, M. T. F. Telling, K. Kiefer, P. Fouquet, T. Seydel and S. A. J. Kimber (2008) Quasi-Elastic Neutron Scattering Studies on Clay Interlayer Space Highlighting the Effect of the Cation in Confined Water Dynamics. Journal of Physical Chemistry C, 112, 19982-91.

Turbostratic disorder: Lessons learned from Fe-bearing Layered Double Hydroxides.

Knud Dideriksen¹, Laura Voigt², Marco Mangayayam¹, Case van Genuchten³, Cathrine Frandsen⁴, Kristen M. Ø. Jensen¹, S. L. S. Stipp¹ and Dominique J. Tobler^1
1Nano-Science Center, Department of Chemistry, University of Copenhagen, Denmark, ²Department of Chemistry, Technical University of Denmark, Denmark, ³Dept. of Earth Sciences-Geochemistry, Utrecht University, Utrecht 3508TA, The Netherlands, ⁴Department of Physics, Technical University of Denmark, Denmark
Turbostratic disorder exists in ordered materials with highly anisotropic bond strength (e.g., clays) and affects their properties (e.g., stability and ion exchange). It arises when sheets of strongly bonded atoms, stacked along the direction of weaker bonding, are displaced so that atomic alignment across sheets is lost. Layered double hydroxides (LDH) are composed of Me^II-Me^III hydroxide sheets separated by interlayers with water and weakly held anions. To probe short range order (1-40 Å) in synthetic LDHs in the sulphate green rust (Fe^III) – nikischerite (Al^III) series, we performed pair distribution function (PDF) analysis of high energy X-ray scattering data. Results show that structural coherence along the c axis decreases with increasing Al content, although Bragg peaks are clear for basal planes. The PDF for synthetic nikischerite is best matched by the calculated pattern for coherent scattering domains composed of a single metal hydroxide sheet. Parallel to the decrease in the structural coherence between layers, the coherence within layers also decreases markedly to ~6 nm for synthetic nikischerite. Thus, this material does not simply have unaligned, but otherwise structurally developed sheets. Instead, crystals are mosaic with coherent scattering domains that decrease in all directions. In fact, the aspect ratio of the large green rust sulphate crystals is comparable to that of the small coherent scattering domains in synthetic nikischerite. Given that the structure of disordered material is very complicated to characterise with traditional techniques, we speculate to what degree silicate clay minerals have mosaic crystals rather than only turbostratic disorder.

CaCO₃ scaling: Nucleation and growth inhibition of aragonite by MgSO₄

Mia Rohde Nielsen¹, Juan Diego Rodriguez-Blanco², Karina Sand¹ and Susan Stipp^1
1Nano-Science Center, Department of Chemistry, University of Copenhagen, Denmark, ²Department of Geology, Trinity College Dublin, Dublin, Ireland
Mg²⁺ and SO₄^2- are abundant in seawater and in hydrothermal fluids and are hence naturally present where calcium carbonate minerals form. Both ions are known to influence nucleation and growth of CaCO₃ polymorphs but reports of aragonite growth inhibition by Mg²⁺ (±SO₄^2-) are contradictory. We used UV-vis spectroscopy to explore the influence of Mg²⁺ and SO₄^2- on nucleation and growth rates of crystalline CaCO₃ phases and we examined the solids using scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD). SO₄^2- promoted formation of vaterite, extended the induction time for nucleation and decreased growth rate. Mg²⁺ (±SO₄^2-) promoted formation of aragonite in preference to calcite. Aragonite nucleation and growth was inhibited by Mg²⁺ alone and in combination with SO₄^2-. Mg²⁺ clearly prolonged induction time and inhibited aragonite growth proportional to Mg²⁺ concentration. The results suggest an environmentally friendly method to inhibit aragonite scale formation, for example in desalination plants.

Figure 1. Crystallization of CaCO₃ (measured as absorbance) as a function of time. Insert: SEM images of end products.