Person: Fernández Díaz, María Lourdes
Loading...
First Name
María Lourdes
Last Name
Fernández Díaz
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Geológicas
Department
Mineralogía y Petrología
Area
Cristalografía y Mineralogía
Identifiers
133 results
Search Results
Now showing 1 - 10 of 133
Item Estudio de la influencia del carbonato en el crecimiento de la barita a nanoescala.(Macla, 2004) Sánchez Pastor, Nuria; Pina Martínez, Carlos Manuel; Astilleros García-Monge, José Manuel; Fernández Díaz, María LourdesItem Cristalización secuencial de carbonatos cálcicos y yeso en un sistema difusión-reacción(Macla, 2004) López Guijarro, R.; Pina Martínez, Carlos Manuel; Fernández Díaz, María LourdesItem Crystallizationof ikaite and its pseudomorphic transformation into calcite: Raman spectroscopy evidence(Geochimica et cosmochimica acta, 2016) Sánchez Pastor, Nuria; Oehlerich, Markus; Astilleros García-Monge, José Manuel; Kalliwoda, Melanie; Mayr, Christoph C.; Fernández Díaz, María Lourdes; Schmahl, Wolfgang W.; Geochemical Society; ElsevierIkaite (CaCO3·6H2O) is a metastable phase that crystallizes in nature from alkaline waters with high phosphate concentrations at temperatures close to 0 °C. This mineral transforms into anhydrous calcium carbonate polymorphs when temperatures rise or when exposed to atmospheric conditions. During the transformation in some cases the shape of the original ikaite crystal is preserved as a pseudomorph. Pseudomorphs after ikaite are considered as a valuable paleoclimatic indicator. In this work we conducted ikaite crystal growth experiments at near-freezing temperatures using the single diffusion silica gel technique, prepared with a natural aqueous solution from the polymictic lake Laguna Potrok Aike (51°57′S, 70°23′W) in Patagonia, Argentina. The ikaite crystals were recovered from the gels and the transformation reactions were monitored by in situ Raman spectroscopy at two different temperatures. The first spectra collected showed the characteristic features of ikaite. In successive spectra new bands at 1072, 1081 and 1086 cm−1 and changes in the intensity of bands corresponding to the OH modes were observed. These changes in the Raman spectra were interpreted as corresponding to intermediate stages of the transformation of ikaite into calcite and/or vaterite. After a few hours, the characteristics of the Raman spectrum were consistent with those of calcite. While ikaite directly transforms into calcite at 10 °C in contact with air, at 20 °C this transformation involves the formation of intermediate, metastable vaterite. During the whole process the external shape of ikaite crystals was preserved. Therefore, this transformation showed the typical characteristics of a pseudomorphic mineral replacement, involving the generation of a large amount of porosity to account for the large difference in molar volumes between ikaite and calcite. A mechanism involving the coupled dissolution of ikaite and crystallization of calcite/vaterite is proposed for this replacement.Item The role of sulfate in the hydrothermal replacement of aragonite single crystals by calcite(Earth and Planetary Science Letters, 2024) Forjanes Pérez, Pablo Cayetano; Astilleros García-Monge, José Manuel; Fernández Díaz, María LourdesAragonite (CaCO3) is a stable calcium carbonate phase under high pressure conditions. However, its formation in (sub)surface environments, where calcite is the stable polymorph, is widespread. Regardless of its origin, aragonite is expected to undergo transformation into calcite under moderate pressures and temperatures. However, this transformation does not always take place, which results in the presence of abundant aragonitic relics in the geological record. Traditionally, this preservation has been explained by the presence of chemical inhibitors that prevent the conversion of aragonite to calcite. While it is widely accepted that magnesium (Mg) plays a key role in the polymorphic selection of CaCO3, the influence of other ions has also been suggested. This work evaluates the effect that different concentrations of sulfate (SO42−) in the fluid has on the progress of the aragonite-to-calcite transformation at 220 °C. Our results show that, upon reaction with deionized water or sulfate-poor solutions ([SO42−]aq < 0.1 mM), aragonite single crystals are extensively replaced by calcite aggregates (crystal size > 15 µm) through an interface coupled dissolution-precipitation reaction. The replacement starts at the aragonite crystal surfaces and advances inwards thanks to the development of an extensive network of fractures. Contrarily, when the solution bears higher concentrations of sulfate ([SO42−]aq > 0.1 mM), only a thin layer of smaller crystals of calcite (< 10 µm) form on the aragonite substrates, without any further transformation taking place. We interpret that these smaller crystals exert too little crystallization pressure and fail to promote the development of a network of fractures. In the absence of this network, the aragonite-calcite transformation cannot take place. The transformation does not occur neither when the experiments are conducted with deionized water and fragments of gypsum or anhydrite together with the aragonite grains. The results of this study shed light on the influence of dissolved sulfate in the kinetics of the fluid-driven transformation of aragonite into calcite. These results are useful to understand the preservation of aragonite in a variety of current geological settings and provide valuable insights for better understanding the diagenesis of sedimentary carbonates.Item Relaciones entre morfología y composición en los cristales de la solución sólida (Ba,Sr) SO4(Macla, 2004) Sánchez Pastor, Nuria; Pina Martínez, Carlos Manuel; Fernández Díaz, María LourdesItem Pb removal efficiency by Calcium carbonates: biogenic versus abiogenic materialsc(Crystal Growth and Design, 2023) Roza Llera, Ana; Di Lorenzo, Fulvio; Churakov, Sergey V.; Jiménez, Amalia; Fernández Díaz, María LourdesThe sorption of heavy metals on mineral surfaces plays a key role in controlling the fate and bioavailability of harmful elements through dissolution–precipitation reactions. Here, we investigate the efficiency of Pb removal from highly contaminated waters by two calcium carbonate hard tissues, scallop shells (up to 99.9 mol %; -biocalcite) and cuttlefish bones (up to 90.0 mol %; bioaragonite), which template the precipitation of the highly insoluble mineral cerussite (PbCO3). The experiments show that both biomaterials are about five times more effective Pb scavengers (5 mmol of cerussite precipitated/g sample) than their inorganic counterparts (∼1 mmol/g). We relate this enhanced Pb scavenging capacity of biocarbonates to their composite organic–inorganic nature, which modulates their specific nano- and microstructural features and defines their larger surface areas, solubility, and reactivity compared to those of their inorganic counterparts. The oriented growth of cerussite progressively passivates the bioaragonite surface, reducing its long-term Pb scavenging capacity. In contrast, the randomly oriented growth of cerussite crystals on biocalcite prevents surface passivation and explains why biocalcite outperforms bioaragonite as a long-term Pb scavenger. The use of biocarbonates could be a key for designing more efficient decontamination strategies for heavy metal-polluted waters.Item Mechanism and kinetics of the pseudomorphic replacement of anhydrite by calcium phosphate phases at hydrothermal conditions(American Mineralogist, 2023) Roza Llera, Ana; Jiménez, Amalia; Fernández Díaz, María LourdesMineral replacement reactions mediated by fluids are common in sedimentary basins, where they influence geochemical cycles. Phosphorous (P) pollution of soils, sediments and water bodies is currently a widespread problem. Some apatite accumulations in sediments may have formed through the interaction of P-bearing aqueous solutions with mineral surfaces that result in mineral replacement reactions. Here, we investigate the pseudomorphic replacement of anhydrite single crystals by aggregates of β-tricalcium phosphate and hydroxyapatite upon interaction with a P-bearing solution at temperatures between 120 and 200 °C. SEM imaging is used to study the texture of the aggregates. Rietveld refinement of the X-ray diffraction patterns and Raman spectra analysis of the reacted samples provide information on the kinetics of the replacement. At all temperatures β-tricalcium phosphate forms alongside hydroxyapatite at early stages of the replacement reaction. At T ≥ 180 °C, hydroxyapatite/β-tricalcium phosphate ratio rapidly increases, and hydroxyapatite is the only phase in fully replaced samples. At T < 180 °C hydroxyapatite/β-tricalcium phosphate ratio increases slowly and fully replaced samples still contain significant amounts of β-tricalcium phosphate. The progress of the replacement is facilitated by the formation of porosity. The evolution of the hydroxyapatite/β-tricalcium phosphate ratio and the crystal habit of both phases strongly influence the arrangement of this porosity. The empirical activation energy Ea (kJ/mol) of the replacement reaction is determined by the Avrami and the iso-conversion methods. Both approaches yield an Ea of ~40 kJ/mol. Anhydrite dissolution appears as the rate-limiting process and the overall kinetics of the replacement reaction is controlled by the rate diffusion of dissolved species through the porosity network. The ripening of the metastable β-tricalcium phosphate into hydroxyapatite affects the characteristics of the porosity network and further modulates the kinetics of the replacement. These results may improve the understanding of the mechanisms of P-sequestration by mineral surfaces through coupled dissolution–precipitation reactions and shed light on the origin of apatite accumulations associated to evaporitic sedimentary rocks.Item Crecimiento epitaxial de celestina sobre la superficie (001) de la barita(Macla, 2004) Sánchez Pastor, Nuria; Pina Martínez, Carlos Manuel; Astilleros García-Monge, José Manuel; Fernández Díaz, María LourdesItem Cinética de disolución de superficies (𝟏𝟎𝟏̅𝟒) de calcita en presencia de diferentes sales de Cu2+ disueltas en agua(Macla, 2023) Pérez Garrido, Carlos; Astilleros García-Monge, José Manuel; Fernández Díaz, María LourdesLas interacciones de polimorfos del carbonato cálcico (CaCO3), principalmente calcita y aragonito, con soluciones acuosas que contienen metales contaminantes tiene un gran interés medioambiental ya que las superficies de estas fases minerales tienen la capacidad de secuestrar de forma eficaz dichos contaminantes mediante procesos acoplados de disolución-precipitación y/o adsorción (Godelitsas et al., 2003; Prieto et al., 2003). Este estudio pretende, por un lado, valuar los cambios producidos sobre las superficies de calcita en contacto con soluciones acuosas ricas en Cu2+ de diferente concentración, y por otro, estudiar la posible influencia en esos cambios de los aniones que pueden acompañar a este catión, para lo que se han utilizado soluciones de tres sales diferentes CuCl2·2H2O, CuSO4·5H2O y Cu(NO3)2·H2O.Item Interacción de Anhidrita con Soluciones Acuosas que Contienen Plomo. I. Evolución Fisicoquímica del Sistema(2011) Morales Sánchez, Juan; Astilleros García-Monge, José Manuel; Jiménez, Amalia; Fernández Díaz, María Lourdes