Diatomaceous Silica Research Articles

Diatomaceous Silica in Environmental Applications: A Case Study from the Lacustrine Deposit of Limnos Island, Aegean Sea, Greece

Diatomitic and clastic-volcanoclastic marly samples from the Paranisia area of Limnos Island, were studied mineralogically by X-ray diffraction (XRD), chemically by X-ray fluorescence spectroscopy (XRF) and morphologically by scanning electron microscopy (SEM-EDS), together with some physical properties such as the insulation block density, specific surface area and porosity. The diatomaceous samples were classified as porcelaneous or clayey (moler type) diatomite. Opal-CT forms microplates disseminated in the groundmass and are diagenetically formed in expense of opal-A dissolution. The purest diatomaceous beds have been transformed into opaline beds (opal-CT-rich rocks), whereas the clayey beds were not influenced by diagenetic transformations. The studied diatomites from Limnos Island are suitable materials for environmental uses, as an absorbent, for the production of insulation bricks or as lightweight aggregates.

Methodological Aspects of Obtaining and Characterizing Composites Based on Biogenic Diatomaceous Silica and Epoxy Resins.

Diatomaceous earth are sediments of unicellular algal skeletons with a well-defined hierarchical structure. Despite many tests conducted on systems using diatomaceous earth and epoxy resins, we can find many differences in the methods of acquisition and characteristics of the composite, which may considerably affect the results. In our study, we have conducted tests to verify the impact of the method of obtaining samples and the degassing of the composite on its mechanical properties and standard deviation. The samples were cast in glass moulds and silicone moulds and then subjected to testing for their mechanical and functional properties, imaging with the use of an optical microscope and a scanning electron microscope. The tests have shown that, for samples cast in glass moulds, there is no heterogeneity within the area of the tested sample, as in the case of samples cast in silicone moulds. Silicone moulds allow for quite effective self-degassing of the resin due to the large area-to-mass ratio, and the small remaining air vesicles have a limited effect on the mechanical properties of the samples. The filler used also played a significant role. For systems containing base and rinsed diatomite, it is clear that the degassing of mixtures increases the tensile strength. For treated diatomite, the elongation at break grew along with increasing filler concentration, while for base diatomite, the improvement was observed for flexural strength and impact strength. A non-modified epoxy resin shows a tensile strength at 19.91 MPa (silicone mould cast). At the same time, the degassed, glass mould-cast systems containing 12% of base and rinsed diatoms showed a tensile strength of 27.4 MPa and 44.7 MPa, respectively. We have also observed that the higher the filler concentration, the higher were the tensile strength values, which for the rinsed diatoms reached over 55.1 MPa and for the base diatoms were maximum of 43.8 MPa. The tests, therefore, constitute a set of guidelines and recommendations for testing with the use of fillers showing an extended inner structure.

Proposing a potential strategy concerning Mineral-enhanced Biological Pump (MeBP) for improving Ocean Iron Fertilization (OIF)

Ocean iron fertilization (OIF) is a geoengineering strategy aimed at mitigating global warming by reducing the amount of atmospheric CO2. However, the efficacy by which OIF vertically exports organic carbon of bloomed phytoplankton (mostly, diatoms) to the deep sea is low because of the remineralization of organic carbon during the sinking of diatomaceous silica (BSi). To address the low efficiency of the vertical C export of OIF, a potential strategy for enhancing oceanic biological pump using clay minerals, so-called mineral-enhanced biological pump (MeBP), is proposed herein. Under ideal operation of MeBP, the purposefully added clay minerals are supposed to agglomerate with BSi, facilitating an increase in the quantity of BSi settling and a decrease of organic carbon loss. Meanwhile, the structural Al of clay minerals would be assimilated by diatoms due to the biological dissolution of the clays, inhibiting the dissolution of BSi during its sinking. The abovementioned effects would significantly improve the efficiency of the vertical C export of OIF. The preliminary evidence and arguments in support of MeBP are presented.

Efficient sorption performance of carbon-diatomaceous silica compounds towards phenol

Phenol removal as organic pollutant model has been studied on new composite adsorbents prepared from carbon and natural diatomaceous silica mixtures in different proportions (KCp1, KCp2, and KCp3 with 10, 20, and 30% of carbonaceous matter, respectively). SEM observations clearly showed the porous aspect evolution when mixing carbon with the macroporous diatomite skeleton, further proved by TEM images that revealed a co-existence of two distinct pore sizes. FTIR and XRD characterization mainly demonstrated the disappearance of calcium carbonate species as consequence of the undertaken treatments in presence of carbon. N2 sorption analysis at 77 K confirmed the obtaining of more developed textural properties with enhanced BET surfaces, and the creation of narrower porosity. The best area was obtained for KCp3 (336 m2/g) as compared to the starting carbon and diatomite surfaces (118 and 8 m2/g, respectively). The influence of several parameters such as contact time, temperature, pH, and initial concentration on the performance of the resultant materials in terms of phenol adsorption was investigated. The pH ≤ 8 favored the phenol removal, whereas the temperature did not have a great impact in the selected range (30-60°C). The sorption isotherms followed well the Freundlich and, more accurately, Langmuir models with the highest adsorption capacity recorded for KCp3 (98.5 mg.g−1). A fast kinetic was revealed whose data best fitted with the pseudo-second-order model with a correlation factors values of R2=0.996, 0.999, and 0.992 for KCp1, KCp2, and KCp3 respectively. More than 50% of the maximum adsorption ratio was achieved in half the time needed for saturation. The new composites offer promising prospects as inexpensive sorbents for use with competitive capacities in the industrial water treatment.

Ruthenium recovery from alkaline radioactive feeds using an extraction chromatography resin containing Aliquat 336

The knowledge of ruthenium speciation under aqueous alkaline conditions was applied for the recovery of radio-ruthenium from the alkaline radioactive feeds using a Chromosorb W (dimethyldichlorosilane treated, acid washed celite diatomaceous silica; mesh size 60/80) based extraction chromatography resin (ECR) loaded with Aliquat 336, a quaternary ammonium compound. The experimental conditions were optimized for the uptake of Ru from alkaline feeds and its subsequent desorption using batch studies. Although the precipitation of the black RuO2·xH2O at the ECR surface helps in the quantitative (up to 500 ppm Ru) uptake of ruthenium, it’s desorption was not favorable. About 75% of the Ru was desorbed from the ECR by the batch method using sequential washing by alkaline hypochlorite solution and nitric acid solution. The sorption isotherm was studied for the above system under optimized conditions and the uptake data conformed to the Langmuir isotherm model while chemisorption was suggested to be the mechanism. Column studies, under optimized conditions, showed ~82% Ru recovery in the first cycle which sharply decreased to ~60% in the subsequent runs. The FTIR studies were undertaken to understand the mechanism for the ruthenium extraction from alkaline medium and it’s desorption from the resin.

Nanostructured interfaces between photosynthetic bacterial Reaction Center and Silicon electrodes

ABSTRACT:Optimizing interfaces between photosynthetic natural photoconverters, like photosynthetic bacterial Reaction Centers (RCs) and electrode surfaces represents a challenge in the progress of bio-optoelectronic devices. The features of the surfaces may result detrimental for the tertiary and quaternary structures of the RC, even resulting in the denaturation of the enzyme. Functional surfaces possessing both confinement capability and conductive features able to preserve the conformation of the biomolecule and its bioelectronic behaviours are highly needed. In this work, the RC is adsorbed on diatomaceous silica and plasma treated hydrophobic silicon based materials. Both the materials are demonstrated to be able to preserve and enhance the RC photoconverting activity. In particular, we evaluate the functioning of isolated bacterial RC interacting with flat pSi electrode through two nanotextured interfaces designed to address the RC: a thin conductive silicon film nanotextured in pillars via plasma treatment, and a cast film of nanostructured dielectric biosilica obtained from diatomaceous earth. The characterization of these interfaces, together with the RC photocurrent production measurements, pave the way to new generation RC based bio-devices for photocurrent investigation.

The chemical form of silicon in marine Synechococcus

The widely distributed marine picocyanobacterium Synechococcus is found throughout the upper oceans. Recent observations that Synechococcus accumulates silicon indicate that it may influence the global cycle of this element. While diatoms, the organisms that dominate the marine Si cycle, have absolute Si requirements due to their precipitation of exoskeleton frustules composed of hydrated opal-A (i.e., biogenic silica), no requirements or biological roles are known for the Si associated with Synechococcus. Even less is known about the biochemical form(s) of Si in picocyanobacteria or whether it differs from diatomaceous silica. Using bulk X-ray absorption near-edge spectroscopy (XANES) across the Si K-edge, we investigated the chemical speciation of Si in dried Synechococcus laboratory isolates from several clades, representing both coastal and oligotrophic isolates grown at a range of Si(OH)4 concentrations. Silicon associated with Synechococcus is bound to oxygen and is spectroscopically distinct from opal-A precipitated by diatoms. The closest XANES spectral analogues found in the literature are dried Mg-Si gels precipitated under basic conditions, suggesting that some Synechococcus Si may be present in vivo as a hydrated siliceous network with Mg and/or Ca cations. Slight spectral variations across isolates and growth conditions suggest strain-specificity in Si chemistry and the potential for siliceous phases to bind organic matter.

The Manufacturing of Metallurgical Grade Silicon from Diatomaceous Silica by an Induction Furnace

The Manufacturing of Metallurgical Grade Silicon from Diatomaceous Silica by an Induction Furnace

Preparation of hierarchically porous diatomite/MFI-type zeolite composites and their performance for benzene adsorption: The effects of desilication

Hierarchically porous diatomite/MFI-type zeolite composites were prepared by transforming the natural diatomaceous silica into MFI-type zeolite by a vapor-phase transport method, followed by a desilication treatment. The morphology and macroporosity of the diatomite were well preserved in the parent diatomite/MFI-type zeolite composite (Dt/Z). Treatment of Dt/Z by desilication in aqueous 0.2M NaOH solution at 60°C for 1h resulted in a mesopore size distribution centered at approximately 7nm, without significantly altering the macroporosity and microporosity of the resulting composite. Further desilication treatment (10h) broadened the mesopore size distribution, whereas the macropores sourced from the diatomite support were significantly damaged and a fraction of the micropores was narrowed to approximately 0.49nm. Under the optimal desilication condition (1h), the desilication-treated Dt/Z sample (Dt/Z-A1h) exhibited a higher adsorption capacity, better affinity, and faster adsorption kinetics toward benzene than the parent Dt/Z, as evaluated via a gravimetric method using an Intelligent Gravimetric Analyzer. The excellent benzene adsorption performance of Dt/Z-A1h was attributed both to the increase in porosity and the formation of terminal silanol groups on the surface of newly developed pores after the desilication treatment.

Extent of diagenetic transformations in severely altered biogenic silica deposits from Tunisia: new insights from mineralogy and geochemistry

Sedimentary biogenic silica from Redeyef in Gafsa basin (southern Tunisia) was analysed for its 29Si and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra and complemented by X-ray diffraction and SEM observations. The 29Si MAS NMR spectrum is characterized by the abundance of hydroxylated silicon, displayed in resonance intensities and reflects a clear tendency towards dissolution of diatomaceous amorphous silica and the occurrence of the hydrated silica, which is the main component that ensures the diagenetic transition via the mechanism of dissolution–precipitation to other more crystalline silica phases, after the lost of its hydroxyls groups (water) by heating (burial). 27Al MAS NMR reveals two coordinations of Al; the octahedrally coordinated Al suggests the presence of clay relics trapped during crystal growth or a microcrystalline zeolite (clinoptilolite detected by SEM observations), while the tetrahedrally coordinated Al suggests the presence of minor quantities of minerals with tetrahedral Al, such as an Al-rich fluid and/or minerals such as feldspars.

A laser fluorination method for oxygen isotope analysis of biogenic silica and a new oxygen isotope calibration of modern diatoms in freshwater environments

An empirical calibration for the oxygen isotope fractionation between biogenic silica and water was determined for diatom frustules sampled from living diatom communities in the Jemez Mountains of northern New Mexico, USA. Over a temperature range from 5.1 to 37.8 °C, the silica–water fractionation is defined by the equation 1000 ln α(silica–water) = 2.39(±0.13) × 106T−2 + 4.23(±1.49). This relationship is in close agreement with other published silica–water fractionation factors for laboratory cultured diatom samples; however, it is as much as 8‰ lower than equilibrium quartz–water fractionations and 3–4‰ lower than observed silica–water fractionations in diatomaceous silica collected from sediment traps and sediment cores. There are three possible explanations for the disparate silica–water fractionation factors observed in diatom silica: (1) silica does not precipitate in equilibrium with ambient water, (2) silica does precipitate in equilibrium with ambient water, but the silica–water fractionation factor for diatom silica is considerably less than the equilibrium fractionation factor for quartz–water, or (3) silica precipitation is influenced by a ‘vital’ effect, where the δ18O value of the water inside the diatom cell walls is lower than the δ18O values of ambient water. Post-mortem loss of organic material results in an alteration or ‘maturation’ of diatom silica in which silica reequilibrates with a silica–water fractionation closer to the equilibrium quartz–water fractionation. Alteration is likely to occur rapidly after the diatom frustule loses its organic coating, either as it settles through the water column or at the sediment–water interface; δ18O values recorded by paleo-diatom silica therefore do not record growing conditions but more likely record conditions at the sediment–water interface. In the case of lacustrine environments, where the bottom water remains at a nearly constant 4 °C, the reequilibration of diatom silica with bottom conditions could reduce or remove the conflating effects of temperature on δ18O values recorded by paleo-diatom silica and provide direct information on the δ18O value of the lake water.

Seawater-mediated interactions between diatomaceous silica and terrigenous sediments: Results from long-term incubation experiments

Reactors containing frustules of the cultured diatom Thalassiosira punctigera suspended in seawater were incubated with or without added sediment from the Mississippi River Delta or the Congo River Fan. The diatom frustules were separated from the terrigenous sediments by a dialysis membrane, thereby only allowing the exchange of dissolved species. One series of incubations was carried out in the laboratory, at room temperature (21 °C) and for a period of 10 months. Another series of reactors was deployed along a mooring in the Mozambique Channel at three water depths (500, 1250, and 2000 m), for a period of 22 months. Chemical analyses after total destruction of frustules collected at the end of the incubations showed elemental transfer from seawater (Mg and K) and the sediments (Al, Fe, Mn, P and Ca) to the frustules. In the presence of the terrigenous sediments, the dissolved silicate concentrations at the end of the incubations were systematically lower that those measured in the incubations without the sediments. In addition, electron microscopy revealed the formation of new mineral precipitates. These included amorphous deposits on the frustules containing Si, Fe, Al, Mg, K and P, as well as euhedral clay crystallites. Differences were observed between the incubations performed in the laboratory and those deployed at sea, likely as a result of differences in redox conditions, temperature and reaction time. Overall, the interactions between biogenic silica, seawater and lithogenic minerals reduce the regeneration of nutrient silicon fixed by siliceous organisms. These interactions take place on relatively short time scales (months to years), and affect not only the marine cycle of silicon, but also those of other major and minor elements, such as Al, Fe, Mn, K, and Mg.

Adsorption of methylene blue by acid and heat treated diatomaceous silica

Diatomite, an abundant inorganic material in Jordan, was treated with sulfuric acid and heat treated in order to improve its performance as an adsorbent. The acid treated diatomite (ATD) was used to adsorb methylene blue from aqueous solutions. The equilibrium data were fitted to different adsorption isotherms and the best fit was obtained using Langmuir isotherm with R 2 value of about unity. The maximum loading capacity, Q max was found 126.6 mg/g at 30EC and increases slightly as the temperature increases. The kinetics data were best described by the pseudosecond order model with a value of the model constant k 2 of 1.056 (g/mg h) at 30EC and an initial dye concentration of 50 mg/l. The thermodynamic parameters such as the standard enthalpy (ΔH 0), standard entropy (ΔS 0) and standard free energy (ΔG 0) were evaluated. The obtained results indicated the adsorption of basic dyes onto ATD is endothermic and spontaneous process and confirmed the applicability of this modified inorganic material as an efficient adsorbent for basic dyes.

Thermal insulators made with rice husk ashes: Production and correlation between properties and microstructure

Extruded and pressed thermal insulators were obtained with the utilization of rice husk ashes, which is a residue from the beneficiation process of rice with high silica content. The thermal insulators were characterized both chemically (composition) and physically (particle size, porosity, density and thermal conductivity), and their properties were correlated to their microstructure. The thermal conductivity of these insulators was determined by the hot plates method, according to the ASTM-E 1225-87 Standard, and the measured values were then compared to a commercial thermal insulator made from diatomaceous silica. The morphology of the preset phases (solid and porous), as well as their distribution, was determined by means of scanning electron microscopy.

Influences of pretreatment temperature on the surface silylation of diatomaceous amorphous silica with trimethylchlorosilane

Diatomaceous amorphous silica samples were modified by silylation using trimethylchlorosilane (TMCS). The resultant materials were characterized by using thermogravimetry (TG), 1H magic-angle spinning nuclear magnetic resonance (1H MAS NMR), Fourier transform infrared spectroscopy (FTIR) and chemical analysis. The degree of silylation was found to increase with the increasing temperature of thermal pretreatment on diatomaceous silica prior to silylation. Increment of the pretreated temperature leads to stepwise removal of physisorbed water followed by the dehydration of capping water that H-bonded with the surface silanols, resulting in exposure of more and more isolated and H-bonded silanols previously covered by water molecules. Among these exposed silanols, isolated silanols show high activity for silylation reaction but H-bonded ones show poor activity. The maximum degree of surface attachment of TMCS grafted onto the diatomaceous silica (about 1.81mmol TMCS groups per gram of silica) was shown in the sample pretreated at 1100°C, in which the amount of exposed isolated silanols get the maximum. The fundamental information derived from this work is of significance in well understanding the surface silylation reaction of diatomaceous silica and providing useful information for related industrial production.

Transfer and early diagenesis of biogenic silica oxygen isotope signals during settling and sedimentation of diatoms in a temperate freshwater lake (Lake Holzmaar, Germany)

We have investigated the transfer of oxygen isotope signals of diatomaceous silica ( δ 18O diatom) from the epilimnion (0–7 m) through the hypolimnion to the lake bottom (∼20 m) in freshwater Lake Holzmaar, Germany. Sediment-traps were deployed in 2001 at depths of 7 and 16 m to harvest fresh diatoms every 28 days. The 7 m trap collected diatoms from the epilimnion being the main zone of primary production, while the 16 m trap collected material already settled through the hypolimnion. Also a bottom sediment sample was taken containing diatom frustules from approximately the last 25 years. The δ 18O diatom values of the 7 m trap varied from 29.4‰ in spring/autumn to 26.2‰ in summer according to the temperature dependence of oxygen isotope fractionation and represent the initial isotope signal in this study. Remarkably, despite the short settling distance δ 18O diatom values of the 7 and the 16 m trap were identical only during spring and autumn seasons while from April to September δ 18O diatom values of the 16 m trap were roughly ∼1.5‰ enriched in 18O compared to those of the 7 m trap. Isotopic exchange with the isotopically lighter water of the hypolimnion would shift the δ 18O diatom value to lower values during settling from 7 to 16 m excluding this process as a cause for the deviation. Dissolution of opal during settling with intact organic coatings of the diatom cells and near neutral pH of the water should only cause a minor enrichment of the 16 m values. Nevertheless, opal from the bottom sediment was found to be 2.5‰ enriched in 18O compared to the weighted average of the opal from the 7 m trap. Thus, resuspension of bottom material must have contributed to the intermediate δ 18O diatom signal of the 16 m trap during summer. Dissolution experiments allowed further investigation of the cause for the remarkably enriched δ 18O diatom value of the bottom sediment. Experiments with different fresh diatomaceous materials show an increase of opaline 18O at high pH values which is remarkably reduced when organic coatings of the cells still exist or at near neutral pH. In contrast, high pH conditions do not affect the δ 18O diatom values of sub-fossil and even fossil opal. IR analyses show that the 18O enrichment of the sedimentary silica is associated with a decrease in Si–OH groups and the formation of Si–O–Si linkages. This indicates a silica dehydroxylation process as cause for the isotopic enrichment of the bottom sediment. Silica dissolution and dehydroxylation clearly induce a maturation process of the diatom oxygen isotope signal presumably following an exponential behaviour with a rapid initial phase of signal alteration. The dynamics of this process is of particular importance for the quantitative interpretation of sedimentary δ 18O diatom values in terms of palaeothermometry.

Lassa Fever, Nigeria, 2003 and 2004

Lassa Fever, Nigeria, 2003 and 2004

Mesoporosity in diatoms via surfactant induced silica rearrangement

Mesoporosity has been introduced into the micron-sized pore walls of diatoms. The technique used involves dissolution and rearrangement of diatomaceous silica, via interactions with the surfactant hexadecyltrimethylammonium bromide. The resulting biomineral possesses ordered hexagonal and disordered mesostructure, and has a BET surface area of 284 m 2 g −1. Electron microscopy, X-ray diffraction and nitrogen adsorption studies have been used to confirm the presence of mesoporosity in the material, and the stability of the micron-sized diatom architecture under the reaction conditions.

A modern vs. Permian black shale—the hydrography, primary productivity, and water-column chemistry of deposition

The sediment currently accumulating in the Cariaco Basin, on the continental shelf of Venezuela, has an elevated organic-carbon content of approximately 5%; is accumulating under O 2-depleted bottom-water conditions (SO 4 2− reduction); is composed dominantly of foraminiferal calcite, diatomaceous silica, clay, and silt; and is dark greenish gray in color. Upon lithification, it will become a black shale. Recent studies have established the hydrography of the basin and the level of primary productivity and bottom-water redox conditions. These properties are used to model accumulation rates of Cd, Cr, Cu, Mo, Ni, V, and Zn on the seafloor. The model rates agree closely with measured rates for the uppermost surface sediment. The model is applied to the Meade Peak Phosphatic Shale Member of the Phosphoria Formation, a phosphate deposit of Permian age in the northwest United States. It too has all of the requisite properties of a black shale. Although the deposit is a world-class phosphorite, it is composed mostly of phosphatic mudstone and siltstone, chert, limestone, and dolomite. It has organic-carbon concentrations of up to 15%, is strongly enriched in several trace elements above a terrigenous contribution and is black. The trace-element accumulation defines a mean primary productivity in the photic zone of the Phosphoria Basin as moderate, at 500 g m −2 year −1 organic carbon, comparable to primary productivity in the Cariaco Basin. The source of nutrient-enriched water that was imported into the Phosphoria Basin, upwelled into the photic zone, and supported primary productivity was an O 2 minimum zone of the open ocean. The depth range over which the water was imported would have been between approximately 100 and 600 m. The mean residence time of bottom water in the basin was approximately 4 years vs. 100 years in the Cariaco Basin. The bottom water was O 2 depleted, but it was denitrifying, or NO 3 − reducing, rather than SO 4 2− reducing.

Characterization of diatomaceous silica by Raman spectroscopy

The network characteristic of a selection of diatomaceous silica derived from China has been investigated using Raman spectroscopy. Before any thermal treatment of the sample, two prominent bands of 607 and circa 493 cm −1 are resolved in the Raman spectra of diatomaceous silica, corresponding to the (SiO) 3-ring breathing mode of D 2-line and the O 3SiOH tetrahedral vibration mode of D 1-line, respectively. This is more similar to the pyrogenic silica rather than the silica gel. For the latter, to obtain a (SiO) 3-ring, the sample must be heated between 250 and 450 °C. Significant difference is also found between the diatomaceous silica and other natural silicas, e.g. in the Raman spectra of sedimentary and volcanic opals, neither D 1 nor D 2 band is detected in previous reports.