Constraining the preservation of organic compounds in Mars analog nontronites after exposure to acid and alkaline fluids

The presence of organic matter in lacustrine mudstone sediments at Gale crater was revealed by the Mars Science Laboratory Curiosity rover, which also identified smectite clay minerals. Analogue experiments on phyllosilicates formed under low temperature aqueous conditons have illustrated that these are excellent reservoirs to host organic compounds against the harsh surface conditions of Mars. Here, we evaluate whether the capacity of smectites to preserve organic compounds can be influenced by a short exposure to different diagenetic fluids. We analyzed the stability of glycine embedded within nontronite samples previously exposed to either acidic or alkaline fluids (hereafter referred to as “treated nontronites”) under Mars-like surface conditions. Analyses performed using multiple techniques showed higher photodegradation of glycine in the acid-treated nontronite, triggered by decarboxylation and deamination processes. In constrast, our experiments showed that glycine molecules were preferably incorporated by ion exchange in the interlayer region of the alkali-treated nontronite, conferring them a better protection against the external conditions. Our results demonstrate that smectite previously exposed to fluids with different pH values influences how glycine is adsorbed into their interlayer regions, affecting their potential for preservation of organic compounds under contemporary Mars surface conditionsEuropean Commission | Ref. FP7 n. 307496European Commission | Ref. H2020 n. 818602Ministerio de Economía | Ref. MDM-2017-0737Ministerio de Economía | Ref. ESP2017-89053-C2-1-

Tracking the weathering of basalts on Mars using lithium isotope fractionation models

An edited version of this paper was published by AGU. Copyright (2015) American Geophysical UnionLithium (Li), the lightest of the alkali elements, has geochemical properties that include high aqueous solubility (Li is the most fluid mobile element) and high relative abundance in basalt-forming minerals (values ranking between 0.2 and 12 ppm). Li isotopes are particularly subject to fractionation because the two stable isotopes of lithium - 7Li and 6Li - have a large relative mass difference (∼15%) that results in significant fractionation between water and solid phases. The extent of Li isotope fractionation during aqueous alteration of basalt depends on the dissolution rate of primary minerals - the source of Li - and on the precipitation kinetics, leading to formation of secondary phases. Consequently, a detailed analysis of Li isotopic ratios in both solution and secondary mineral lattices could provide clues about past Martian weathering conditions, including weathering extent, temperature, pH, supersaturation, and evaporation rate of the initial solutions in contact with basalt rocks. In this paper, we discuss ways in which Martian aqueous processes could have lead to Li isotope fractionation. We show that Li isotopic data obtained by future exploration of Mars could be relevant to highlighting different processes of Li isotopic fractionation in the past, and therefore to understanding basalt weathering and environmental conditions early in the planet's historyData supporting our models and calculations are available as supporting information. The research leading to these results is a contribution from the Project ‘icyMARS’’, funded by the European Research Council, Starting Grant no 307496. This work was also partially supported by the European FEDER program and the Spanish Ministry of Science (MICINN) through the project CGL2011–30079. Comments by R. James and four anonymous reviewers helped us to clarify and strengthen our wor

Silicates weathering on Mars : lithium and its isotopes as geochemical tracers

La geoquímica isotópica del Litio (Li) ha experimentado un crecimiento importante en los últimos años. Es una técnica de análisis isotópico que proporciona información acerca de los flujos derivados de la meteorización de silicatos provenientes de diferentes áreas. Dicha técnica nos permite discriminar entre los procesos de meteorización química, ligados esencialmente a las variaciones del CO2 atmosférico, y de meteorización física, asociados a procesos tectónicos. El Li está presente en concentraciones del orden de ppm en la mayoría de los minerales del basalto donde, debido a su pequeño radio iónico, sustituye al Mg+2 en las estructuras cristalinas [1, 2]. Los dos isótopos estables del Li, 6Li y 7Li, presentan una apreciable diferencia de masa atómica produciendo fraccionamiento isotópico en las fases secundarias resultantes del proceso de meteorización, proporcionando información relevante de los mecanismos y condiciones físico-químicas en que tuvo lugar [3, 4]. La disolución de los minerales primarios de las rocas ígneas no produce por sí misma un fraccionamiento apreciable [5], éste tiene lugar como resultado de los procesos de intercambio de iones entre el agua y los minerales secundarios resultantes del proceso de meteorización, principalmente arcillas [6, 7]. Las arcillas incorporan preferentemente el isótopo ligero en su estructura y dan lugar progresivamente a una firma isotópica más pesada en la fase líquida. Sin embargo, este proceso actúa siempre en el mismo sentido, los valores finales del fraccionamiento isotópico son muy dependientes del proceso concreto de meteorización que ocurre en cada sistema y, en particular, de la influencia de factores como la temperatura, pH, o condiciones redox. El acoplamiento entre estos factores condicionan selectivamente el tipo y cantidad de minerales secundarios, como resultado de los procesos de cristalización-disolución asociados a la meteorización química y por tanto, a la evolución isotópica del Li en el sistema.A xeoquímica isotópica do Litio (Li) experimentou un crecemento importante nos últimos anos. É unha técnica de análise isotópica que proporciona información acerca dos fluxos derivados da meteorización de silicatos provenientes de diferentes áreas. A devandita técnica permítenos discriminar entre os procesos de meteorización química, ligados esencialmente ás variacións do CO2 atmosférico, e de meteorización física, asociados a procesos tectónicos. O Li está presente en concentracións da orde de ppm na maioría dos minerais do basalto onde, debido ao seu pequeno radio iónico, substitúe o Mg+2 nas estruturas cristalinas [1, 2]. Os dous isótopos estables do Li, 6Li e 7Li, presentan unha apreciable diferenza de masa atómica producindo fraccionamento isotópico nas fases secundarias resultantes do proceso de meteorización, proporcionando información relevante dos mecanismos e condicións físico-químicas en que tivo lugar [3, 4]. A disolución dos minerais primarios das rochas ígneas non produce por si mesma un fraccionamento apreciable [5], este ten lugar como resultado dos procesos de intercambio de ións entre a auga e os minerais secundarios resultantes do proceso de meteorización, principalmente arxilas [6, 7]. As arxilas incorporan preferentemente o isótopo lixeiro na súa estrutura e dan lugar progresivamente a unha firma isotópica máis pesada na fase líquida. Non obstante, este proceso actúa sempre no mesmo sentido, os valores finais do fraccionamento isotópico son moi dependentes do proceso concreto de meteorización que acontece en cada sistema e, en particular, da influencia de factores como a temperatura, pH, ou condicións redox. O acoplamento entre estes factores condicionan selectivamente o tipo e cantidade de minerais secundarios, como resultado dos procesos de cristalización-disolución asociados á meteorización química e polo tanto, á evolución isotópica do Li no sistema.Lithium (Li) isotope geochemistry has experienced a significant growth in recent years. It is an isotopic analysis technique that provides important information about the flows derived from weathering of silicates of different sources. This technique allows us discrimination between chemical weathering processes, linked essentially to variations in CO2 atmospheric associated to climate changes, and physical weathering induced by tectonic processes. Usually, Li is present in concentrations on the ppm range in most of basalt bearing minerals where, due to its small ionic radius, replaces Mg2+ in the crystal structures of primary silicates of igneous rocks [1, 2]. Both stable isotopes of Li, 6Li and 7Li, have important differences in relative mass resulting in a significant isotopic fractionation in the solid phases derived from the weathering processes, providing important clues about chemical weathering processes [3, 4]. Although, the dissolution of primary minerals in igneous rocks by itself does not produce appreciable fractionation [5], the isotopic fractionation occurs as a result of ion exchange processes between water and secondary minerals derived from weathering process, mainly clays [6, 7]. These clays lead the preference incorporation of the lighter isotope in the structure and progressively produce a heavier isotopic signature in the liquid phase. Despite this process always acts in the same direction, the final isotopic fractionation values are highly dependent of the particular weathering process that occurs in each system and, in particular, of the influence of factors such as temperature, pH, or redox conditions. The coupling between these factors determines the type and the amount of secondary minerals resulting from dissolution-crystallization processes associated with the chemical weathering and hence, the isotopic evolution of Li in the system

Pyrite nanoparticles as a Fenton-like reagent for in situ remediation of organic pollutants

The Fenton reaction is the most widely used advanced oxidation process (AOP) for wastewater treatment. This study reports on the use of pyrite nanoparticles and microparticles as Fenton reagents for the oxidative degradation of copper phthalocyanine (CuPc) as a representative contaminant. Upon oxidative dissolution in water, pyrite (FeS2) particles can generate H2O2 at their surface while simultaneously promoting recycling of Fe3+ into Fe2+ and vice versa. Pyrite nanoparticles were synthesized by the hot injection method. The use of a high concentration of precursors gave individual nanoparticles (diameter: 20 nm) with broader crystallinity at the outer interfaces, providing a greater number of surface defects, which is advantageous for generating H2O2. Batch reactions were run to monitor the kinetics of CuPc degradation in real time and the amount of H2O2. A markedly greater degradation of CuPc was achieved with nanoparticles as compared to microparticles: at low loadings (0.08 mg/L) and 20 h reaction time, the former enabled 60% CuPc removal, whereas the latter enabled only 7% removal. These results confirm that the use of low concentrations of synthetic nanoparticles can be a cost effective alternative to conventional Fenton procedures for use in wastewater treatment, avoiding the potential risks caused by the release of heavy metals upon dissolution of natural pyrites

Long-lasting habitable periods in Gale crater constrained by glauconitic clays

International audienc