Interactions between microorganisms and clay minerals are ubiquitous in nature and are involved in the formation and transformation of clay minerals and the global cycles of many elements. The ...fungi/actinomyces in microbes are also associated with clay minerals, but bacteria are more widely linked. These interactions are also involved in the adsorption and fixation of heavy metals and the decomposition of organic pollutants in soil. Knowledge of these interactions can be utilised for the refinement and purification of clay minerals in industry. This review provides an overview of recent studies and obtains insights into the interactions between microorganisms and clay minerals. Microorganisms can induce the nucleation and growth of clay minerals. The metabolism of microorganisms can also degrade and transform clay minerals. The interaction between microorganisms and clay minerals promots the transformation of smectite to illite (S-I) and vice versa (I-S). Such interactions significantly contribute to the global cycles of various elements, such as Al, Si, Mg, Fe, P, S, C, and N. Microorganisms and clay minerals can form complexes and composite materials that adsorb heavy metals such as Cu, Cr, Cd, Pb, Zn, Co, Ni, Ag, and Hg. Microorganism adhesion to clay minerals is involved in the synergistic adsorption and decomposition of organic pollutants in soil and water. This literature review indicates that knowledge of the interactions between microorganisms and clay minerals has been significantly deepened over recent years. However, the interaction between microorganisms and clay minerals under natural geological conditions and the inherent mechanisms involved are not yet well understood. Future work on interactions between microorganisms and clay minerals has great implications for handling atmospheric micro/nano particle pollutants, understanding the formation, alteration and diagenesis of clay minerals and other related minerals, tracking primitive life on Earth and exploring extraterrestrial planets.
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•Recent insights into interactions between microorganisms and clay minerals•Roles of microorganisms in formation and transformation of clay minerals•Global cycles of elements, soil formation and organic matter preservation•Adsorption and elimination of pollutants and purification of clay minerals•Future work on interactions between microorganisms and clay minerals
Polymers based on 2-(acetoacetoxy)ethyl methacrylate, charged with iron or sodium, were thermally heated at 150 °C. Both polymers were studied and characterized by SEM, TEM, STEM microscopy and SAEDF ...techniques. The morphological investigation revealed that, upon heating, both polymers were endowed with microholes, sometimes perfectly ordered, whose dimensions varied from 4-5 nm to approximately 500 nm. In the case of an Fe-containing copolymer, unexpectedly, iron did not fill in the cavities, thus implying that it was "dispersed" in the polymeric matrix. Electronic microdiffraction documented that both polymers exhibited a proto-crystallinity, likely induced by thermal heating.
The synthesis of zeolites from three samples of fly ash was carried out through a low-temperature (25–60
°C) hydrothermal process with a NaOH pre-fusion treatment preceded by sonication. The results ...were compared with those of conventional hydrothermal syntheses. XRD and SEM investigations demonstrate that the application of ultrasonic treatment facilitates the formation of zeolites at a lower-temperature (25
°C) than syntheses not preceded by sonication. No significant difference in type, temperature of crystallization, or amount of zeolites synthesized was noted between the three different samples of fly ash, implying that the chemical composition of fly ash had little influence on the zeolite product within the compositional range of these fly ash precursors. Although there appears to be a correlation between the SiO
2/Al
2O
3 ratio of the fly ash and the temperature of zeolite formation by conventional synthesis, no correlation was apparent when ultrasonic pre-treatment was used at low-temperatures.
Near-infrared remote sensing data of Mars have revealed thousands of ancient deposits of Fe/Mg-rich smectitic clay minerals within the crust with relevance to past habitability. Diagnostic metal–OH ...infrared spectroscopic absorptions used to interpret the mineralogy of these phyllosilicates occur at wavelengths of 2.27–2.32 μm, indicating variable Fe/Mg ratios in the clay structures. The objective of this work is to use these near infrared absorptions to constrain the mineralogy of smectites on Mars. Using Fe/Mg-rich seafloor clay minerals as mineralogical and spectroscopic analogs for Martian clay minerals, we show how crystal–chemical substitution and mixed layering affect the position of the diagnostic metal–OH spectral feature in smectitic clay minerals. Crystal-chemistry of smectites detected on Mars were quantitatively constrained with infrared data and categorized into four mineralogical groups. Possible alteration processes are constrained by comparisons of clay chemistry detected by remote sensing techniques to the chemistry of candidate protoliths. Of the four groups identified, three of them indicate significant segregation of Fe from Mg, suggestive of alteration under water-rich and/or oxidizing conditions on Mars. The fourth group (with low Fe/Mg ratios) may result from alteration in reducing or water-limited conditions, potentially in subsurface environments. Some samples are interstratified di–trioctahedral clay minerals that have characteristics of dioctahedral clay minerals but clear chemical evidence for trioctahedral sheets. Approximately 70% of smectite deposits previously detected on Mars are classified as Fe-rich (FeO/MgO > 10). Only 22% of detections are trioctahedral and relatively Mg-rich. An additional ∼8% are difficult to characterize, but might be very Fe-rich. The segregation of Fe from Mg in Martian clay minerals suggests that Mg should be enriched in other contemporaneous deposits such as chlorides and carbonates.
•We constrain the mineralogy and chemistry of Martian smectitic clays from infrared data.•Martian smectites include mixed-layer varieties such as complex di–trioctahedral clays.•Most Martian smectitic clays are dioctahedral and Fe-rich, with FeO/MgO ratios >10.•Clay-forming alteration processes on Mars segregated Fe from Mg.
In this study Italian coal fly ash was converted into several types of zeolite in laboratory experiments with temperatures of crystallization ranging from 35 up to 90
°C. Distilled and seawater were ...used during the hydrothermal synthesis process in separate experiments, after a pre-treatment fusion with NaOH.
The results indicate that zeolites could be formed from different kind of Italian coal fly ash at low temperature of crystallization using both distilled and seawater. SEM data and the powder patterns of X-ray diffraction analysis show that faujasite, zeolite ZK-5 and sodalite were synthesized when using both distilled and seawater; zeolite A crystallized only using distilled water. In particular the experiments indicate that the synthesis of zeolite X and zeolite ZK-5 takes place at lower temperatures when using seawater (35 and 45
°C, respectively). The formation of sodalite is always competitive with zeolite X which shows a metastable behaviour at higher temperatures (70–90
°C).
The chemical composition of the fly ash source could be responsible of the differences on the starting time of synthesized zeolite with distilled water, in any case our data show that the formation of specific zeolites takes place always at lower temperatures when using seawater.
A number of water purification processes have been developed in recent years based on the utilisation of low-cost materials with high pollutant removal efficiency. Among these materials, fly ash and ...zeolite synthesised from fly ash are two examples of high-efficiency adsorbents. Column absorption tests were performed in order to compare the manganese sorption behaviour of an Italian coal fly ash and zeolite synthesised from it. Different masses of both materials (10–60 g) were exposed to solutions containing a total metal concentration of 10 mg/L. Batch adsorption studies were also conducted to determine the effect of time on the removal on Mn sequestration. The results indicate that both materials are effective for the removal of Mn from aqueous solution by precipitation due to the high pH of the solid/liquid mixtures. However, the leaching tests reveal that the amount of Mn removed from the fly ash was greater than that leached from the zeolite, thereby indicating that the metal is partially sequestrated by zeolite.
•Fly ash and synthetic zeolites were used for removal of Mn from aqueous solutions.•Precipitation mechanism determines the Mn reduction using both fly ash and zeolite.•Adsorption mechanism takes place at zeolite surface.•The proposed Mn-sequestration mechanisms are supported by leaching tests.
Seafloor hydrothermal sites generate abundant Mg- and Fe-rich clays. These clays are structurally and compositionally interesting because these environments are characterized by large, dynamic ...temperature and chemical gradients in their deposition environment, which promote the formation of chemically and structurally complex clays, including interstratified phases. The system is also interesting as a proxy for the study of the large Mg- and Fe-rich phyllosilicate deposits on Mars, which are broadly characterized as smectitic clay of hydrothermal, volcanic or sedimentary origin. Thirty submarine samples and four terrestrial ones, for comparison, were studied by means of X-ray diffraction (XRD), thermogravimetry (TG), mid-IR and Mössbauer spectroscopies and chemical analysis. The samples include nontronite and the mixed-layer phases glauconite–nontronite, talc–nontronite and talc–saponite. Some of the talc–saponite samples have Fe contents well above those typical for these Mg-rich, trioctahedral phases (up to 1.69 Fe per O10OH2, in the tetrahedral and octahedral sheets). Tetrahedral Fe ranges from 0 to 0.66atoms per O10OH2 across the samples. As found in previous studies of similar specimens, Fe promotes the retention of molecular water that is released upon heating above 200C, and is mainly emplaced in non-expandable layers (talc and glauconite layers). In talc–nontronite and talc–saponite octahedral Fe (both di- and trivalent) appears to be bound to this trapped molecular water, whereas in glauconite–nontronite the bond appears to be with tetrahedral Fe. Samples typically show more than one dehydroxylation event in the TG analysis. The weight loss at each dehydroxylation event is broadly consistent with the proportion of individual layers as determined by means of XRD, but there is no good correlation between both. By contrast, the weight loss at each dehydroxylation event correlates with the chemistry of the layers, where certain cations promote chemical domains in the octahedral sheet (e.g., trioctahedral, nontronite-like, and montmorillonite-like) that dehydroxylate at the several temperatures. The correlations found for talc–nontronite and glauconite–nontronite samples suggest that the distribution of cations in the octahedral sheets of most, but not all, samples is intermediate between total dispersion and total segregation, perhaps random. The talc–nontronite samples have talc layers with cation-deficient octahedral sheets. The above results are best explained by layers of polar character, where the octahedral sheets are composed of domains with different chemical characteristics corresponding to the two types of layers in the interstratified clay. The existence of molecular water (bands at 1635 and 3300–3500cm−1, or ~6.1 and 2.9–3.1μm, respectively) bound in non-expanding layers is relevant to the mineral characterization of Martian Fe-rich clays with spectroscopic methods, where molecular water is so far assumed to be linked to smectite. The variety of mixed-layer clays in which Fe is found in the submarine samples suggests that mixed-layering may be important in Martian clays, which are spectroscopically variable but generally Fe-rich.
•Seafloor hydrothermal clays are mainly mixed-layer Mg- and Fe-rich phases.•Non-expandable clay layers trap molecular water near the structural Fe.•Water in Fe-, Mg-rich clay on Mars may not necessarily indicate smectite.•Octahedral sheets in clay layers have domains of different composition.•Clay layers are polar and do not correspond to mineral end-members.
The effect of citrate and oxalate on tremolite dissolution rate was measured at 37°C in non-stirred flow-through reactors, using modified Gamble’s solutions at pH 4 (macrophages), 7.4 (interstitial ...fluids) and 5.5 (intermediate check point) containing 0, 0.15, 1.5 and 15mmolL−1 of citrate or oxalate. The dissolution rates calculated from Si concentration in the output solutions without organic ligands depend on pH, decreasing when the pH increases from −13.00 (pH 4) to −13.35 (pH 7.4)molg−1s−1 and following a proton-promoted mechanism. The presence of both ligands enhances dissolution rates at every pH, increasing this effect when the ligand concentration increases. Citrate produces a stronger effect as a catalyst than oxalate, mainly at more acidic pHs and enhances dissolution rates until 20 times for solutions with 15mmolL−1 citrate. However, at pH 7.4 the effect is lighter and oxalate solutions (15mmolL−1) only enhances dissolution rates eight times respect to free organic ligand solutions. Dissolution is promoted by the attack to protons and organic ligands to the tremolite surface. Magnesium speciation in oxalate and citrate solutions shows that Mg citrate complexes are more effective than oxalate ones during the alteration of tremolite in magrophages, but this tendency is the opposite for interstitial fluids, being oxalate magnesium complexes stronger. The biodurability estimations show that the destruction of the fibers is faster in acidic conditions (macrophages) than in the neutral solutions (interstitial fluid). At pH 4, both ligands oxalate and citrate reduce the residence time of the fibers with respect to that calculated in absence of ligands. Nevertheless, at pH 7.4 the presence of ligands does not reduce significantly the lifetime of the fibers.
The major geochemical forms of Cr, Ni, Cu, Zn, Pb, and V in a soil from an industrial polluted site in the south of Italy were determined by means of synchrotron X-ray microanalytical techniques such ...as coupled micro-X-ray fluorescence/micro-X-ray diffraction and micro-X-ray absorption near edge structure spectroscopy in combination with bulk extraction methods (sequential extraction procedures, EDTA extractions, and toxicity leaching characteristic procedure tests). Cr, Ni, Zn, and Cu were found in spinel-type geochemical forms (chromite, trevorite, franklinite, zincochromite, and cuprospinel) and often in association with magnetite and hematite. V was mainly present as V(V) associated with iron-oxides or in the form of volborthite Cu3(OH)2V2O7·2H2O. Pb was speciated as minium (Pb3O4), lanarkite Pb2O(SO4), and, in association with Cr(VI), as crocoite (PbCrO4). In general, despite a high total concentration, metals appear to be speciated for the most part as rather insoluble geochemical forms. However, particular attention should be paid to Zn, Cu, V, and Pb that show non-negligible mobilizable fractions. On the basis of the geochemical forms identified, among others, two major former industrial activities were tentatively ascribed as being responsible for the observed major pollution: polyvinyl chloride and cement−asbestos productions.
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