Effect of manganese salts on recovery of potassium from K-feldspar by means of a calcination reaction in the chloride salts-calcium carbonate system

Amorphous calcium carbonate (ACC) has been observed, or inferred to exist, in the majority of the major phyla of marine calcifying organisms. The CaCO3 produced by these organisms represents one of the largest long-term carbon sinks on Earth&#8217;s surface, such that identifying how calcification will respond to anthropogenic climate change is an urgent priority. A substantial portion of our knowledge of the biomineralisation process of these organisms is derived from inferences based on skeletal geochemical data, yet such models typically do not include an ACC component because little is known about trace element and isotope fractionation into ACC. In order to address this, we present, to our knowledge, the first structural and geochemical data of ACC precipitated from seawater under varying carbonate system conditions, seawater Mg/Ca ratios, and in the presence of three of the most common intracrystalline amino acids (aspartic acid, glutamic acid, and glycine). Based on these data we identify the carbonate system conditions necessary to produce ACC from seawater [Evans et al., 2019], and identify the dominant controls on ACC geochemistry. As an example, we utilise these data to build a simple biomineralisation model for the low-Mg (e.g. planktonic) foraminifera, based on precipitation of low-Mg calcite through an ACC precursor phase in a semi-enclosed pool. This exercise demonstrates that the observed shell geochemistry of this group of organisms can be fully reconciled with a model that includes an ACC component, and moreover that constraints can be placed on the degree of ACC utilisation and the ACC-calcite transformation process. More broadly, the exercise demonstrates that knowledge of the characteristics and geochemistry of ACC is important in the development of a process-based understanding of marine calcification.Evans, D., Webb, P., Penkman, K. Kr&#246;ger, R., & Allison, N. [2019] The Characteristics and Biological Relevance of Inorganic Amorphous Calcium Carbonate (ACC) Precipitated from Seawater. Crystal Growth & Design 19: 4300.

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Raman Studies of Pressure and Temperature Induced Phase Transformations in Calcite

MRS Proceedings ◽

10.1557/proc-205-253 ◽

1990 ◽

Vol 205 ◽

Author(s):

Gregory J. Exarhos ◽

Nancy J. Hess

Keyword(s):

Calcium Carbonate ◽

Diamond Anvil Cell ◽

Vibrational Mode ◽

Time Dependent ◽

Stress Dependence ◽

Raman Intensity ◽

Carbonate System ◽

Unequivocal Identification ◽

Diamond Anvil ◽

T Phase

AbstractPhase stability in the calcium carbonate system was investigated as a simultaneous function of pressure and temperature up to 40 kbar and several hundred degrees Kelvin using micro-Raman techniques to interrogate samples constrained within a resistively heated diamond anvil cell. Measured spectra allow unequivocal identification of crystalline phases and are used to refine the P, T phase diagram. Calcium carbonate was found to exhibit both reversible and irreversible transformation phenomena among the four known phases which exist under these conditions. Time-dependent Raman intensity variations as the material is perturbed from its equilibrium state allow real-time kinetics measurements to be performed. Evidence suggests that the order of certain observed transformations may be pressure dependent. The utility of Raman spectroscopy to follow transformation phenomena and to estimate fundamental thermophysical properties from the stress dependence of vibrational mode frequencies is demonstrated.

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Chapter 4 The Oceanic Carbonate System and Calcium Carbonate Accumulation in Deep Sea Sediments

Geochemistry of Sedimentary Carbonates - Developments in Sedimentology ◽

10.1016/s0070-4571(08)70333-9 ◽

1990 ◽

pp. 133-177 ◽

Cited By ~ 1

Keyword(s):

Calcium Carbonate ◽

Deep Sea ◽

Carbonate System ◽

Deep Sea Sediments

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From solutes to solids: towards a supramolecular view on mineralization processes

10.5194/egusphere-egu2020-21861 ◽

2020 ◽

Author(s):

Stephan Wolf

Keyword(s):

Calcium Carbonate ◽

Solid State ◽

Experimental Evidence ◽

Solution Chemistry ◽

Formation Mechanisms ◽

Crystal Formation ◽

Carbonate System ◽

Controlled Conditions ◽

Kinetically Controlled ◽

Mineralization Processes

The formation of a solid-state material from solution is a ubiquitous process of fundamental importance not only for synthesis in solid-state chemistry but for a wide range of disciplines such as geosciences and biology. However, established classical crystallization theories fall short in explaining the outcome of crystallization and mineralization processes in complex environments, such as in biomineralizing organisms or geochemical and industrial settings. &#160;The misfit between classical textbook knowledge and the plurality of conflicting experimental evidence facilitated the advent of an array of new crystallization concepts. These so-called nonclassical crystallization processes are fuelled by the attachment of multiatomic assemblies rather than by attachment of single ions drive crystal formation. Some of these models, such as oriented attachment, were unequivocally backed by experimental evidence and thus accepted by the science community. Other models have encountered distinct resistance from peers. At the centre of this intense dispute, we find the calcium carbonate system, which is of crucial importance for a range of disciplines. For this system, in particular, the existence of prenucleation clusters in the form of dynamically ordered liquid-like polyoxoanions (DOLLOP) has been suggested, and it has been claimed that nonclassical nucleation processes take place. However several groups have challenged this claim, claiming an entirely classical crystallization behaviourBased on our results, we will draw a different picture of calcium carbonate formation. We show that the issues with this very systems root in its solute chemistry and the fact that this renders a calcium carbonate solution into a multicomponent system. We show liquid-liquid phase separation of near-neutral calcium carbonate solutions along with the first ultrastructural model of amorphous calcium carbonate (ACC). This findings give insight into the formation mechanisms of calcium carbonate under kinetically controlled conditions. Our findings further demonstrate that the formation of a liquid-condensed mineral precursor phase is not solely a &#8220;quirk of the peculiar calcium carbonate system&#8221; but a general phenomenon: it is an early stage precursor in the formation pathway of calcium carbonate under geo- and biochemical relevant conditions. Moreover, we show that this unexpected demixing behaviour is widespread, many inorganic components go through spinodal decomposition, when the reaction conditions are kinetically controlled and the solution chemistry disadvantage burst nucleation. Our data suggest that it is not the misconception and oversimplification of classical theories but our oversimplification of the solution chemistry which causes the current dispute on classical vs nonclassical nucleation of inorganic compounds. Currently, we see no need for invoking &#8220;non-classical&#8221; notions of nucleation since our exceptional observations can entirely be explained by established physicochemical concepts apart from CNT. Our results raise the awareness that a supramolecular solution and coordination chemistry provides the key to a thorough understanding of the genesis of inorganic solids under kinetically controlled conditions.

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The Gulf of St. Lawrence Biogeochemical Model: A Modelling Tool for Fisheries and Ocean Management

Frontiers in Marine Science ◽

10.3389/fmars.2021.732269 ◽

2021 ◽

Vol 8 ◽

Author(s):

Diane Lavoie ◽

Nicolas Lambert ◽

Michel Starr ◽

Joël Chassé ◽

Olivier Riche ◽

...

Keyword(s):

Calcium Carbonate ◽

Dissolved Oxygen ◽

Phytoplankton Bloom ◽

Biogeochemical Model ◽

Carbonate System ◽

Lawrence Estuary ◽

Ocean Management ◽

System Components ◽

St Lawrence Estuary

The goal of this paper is to give a detailed description of the coupled physical-biogeochemical model of the Gulf of St. Lawrence that includes dissolved oxygen and carbonate system components, as well as a detailed analysis of the riverine contribution for different nitrogen and carbonate system components. A particular attention was paid to the representation of the microbial loop in order to maintain the appropriate level of the different biogeochemical components within the system over long term simulations. The skill of the model is demonstrated using in situ data, satellite data and estimated fluxes from different studies based on observational data. The model reproduces the main features of the system such as the phytoplankton bloom, hypoxic areas, pH and calcium carbonate saturation states. The model also reproduces well the estimated transport of nitrate from one region to the other. We revisited previous estimates of the riverine nutrient contribution to surface nitrate in the Lower St. Lawrence Estuary using the model. We also explain the mechanisms that lead to high ammonium concentrations, low dissolved oxygen, and undersaturated calcium carbonate conditions on the Magdalen Shallows.

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