Iron-containing Clays Research Articles

Characterization of Kazakhstan’s Clays by Mössbauer Spectroscopy and X-ray Diffraction

Studies of the mineralogical composition were carried out, and the features of the clays from the deposits of Kazakhstan were established using Mössbauer spectroscopy (MS) and X-ray diffraction analysis (XRD). According to the XRD results, all the samples were mixed-layer clays of the kaolinite–illite type. The lattice parameters of the kaolinite were determined, and it was shown that its structure was disordered and contained a certain amount of impurity in some of the clay samples. A special feature of two of the samples was the additionally identified muscovite polytype 2M1. The spectra of the iron-containing clays were amenable to being resolved into separate components, with similar Mössbauer parameters of the kaolinite, muscovite, illite, and glauconite. The oxidation state of the iron was determined using MS. The predominant part of paramagnetic iron in most samples was in the trivalent state. The primary minerals contributing to Fe2+ were illite and muscovite. The results obtained during the study of the clay samples with complex mineralogical compositions using MS and XRD methods both complemented one another and were found to be in good agreement.

Bleaching of red clay using Na2S2O4 and NaBH4 in acidic solution

Bleaching of red clay is carried out by reacting iron-containing clay with the system of two reducing agents Na2S2O4, and NaBH4, in an acidic environment. The treatment process is performed with the help of ultrasonic equipment, as well as mixing operations performed at high temperature. Several physical-chemical methods such as XRF, XRD, and FTIR were used to evaluate clay samples before and after treatment. The results showed effective iron-removal in red clay. Comparison of whiteness between the processed sample and the original sample is performed by measuring parameters in the CIE L*a*b* color-system. The analysis shows that the whiteness of the treated sample reached 78.72%, showing that the treated clay has clearly improved its whiteness, and can be applied in making high-end ceramic products that require the clay with high whiteness.

A H2O2-free heterogeneous Fenton process for the degradation of lincomycin using natural structural iron-containing clay mineral and dimethoxyhydroquinone with in situ generated hydroxyl radicals.

The heterogeneous Fenton process is a strategy for overcoming the greatest shortcomings of traditional homogeneous Fenton, i.e. the high generation of ferric hydroxide sludge and effectivity in a limited pH range. In this study, we constructed a heterogeneous Fenton system with natural iron-bearing clay mineral (nontronite) and dimethoxyhydroquinone (DMHQ) to degrade lincomycin (LCM) without the addition of H2O2. The degradation mechanism was derived from the hydroxyl radicals (•OH) produced from the oxygenation of Fe(II) in nontronites, which was reduced by DMHQ. Acidic conditions and low concentrations of LCM were favourable for LCM degradation. When the solution pH increased from 3 to 7, the final LCM removal ratio decreased from 95 to 46%. However, LCM can still be degraded by 46% under neutral conditions and 20% at the LCM concentration of 500 μmol/L. The nontronite has good reusability, and the LCM degradation efficiency in the fourth cycle still exceeded 90% of the original efficiency. The degradation sites of LCM mainly occurred in the methyl thioether moiety and the aliphatic amine group on the pyrrolidine ring, with the final product of CO2. This research presents a new eco-friendly and cost-effective method for the heterogenous Fenton process without external H2O2.

Effects of Organic Ligands on the Antibacterial Activity of Reduced Iron-Containing Clay Minerals: Higher Extracellular Hydroxyl Radical Production Yet Lower Bactericidal Activity.

Reduced iron-containing clay (RIC) minerals have been documented to exhibit antibacterial activity through a synergistic action of extracellular membrane attack and intracellular oxidation of cellular components. However, the relative importance between extracellular and intracellular processes has remained elusive. Here, metal-chelating organic ligands (lactate, oxalate, citrate, and ethylene diaminetetraacetic acid (EDTA)) were amended to the bactericidal assays such that the importance of the two processes could be evaluated. Reduced nontronite (rNAu-2) was used as a model clay mineral to produce extracellular hydroxyl radical (•OH) upon oxygenation. The presence of Fe-chelating ligands increased •OH yield by 3-5 times. Consequently, bacterial cell membrane attack was enhanced, yet the antibacterial activity of RIC diminished. Additional experiments revealed that the ligands inhibited soluble metal ions from adsorption onto the bacterial cell membrane and/or penetration into the cytoplasm. Consequently, intracellular Fe concentration for the ligand-treated group was nearly 2 orders of magnitude lower than that for no-ligand control, which greatly decreased intracellular accumulation of reactive oxygen species (ROS) and increased cell survival. These results highlight that destruction of intracellular contents (proteins and DNA) is more important than oxidative degradation of membrane lipids and cell envelope proteins in causing bacterial cell death by RIC.

Cr(VI) Reduction by Siderophore Alone and in Combination with Reduced Clay Minerals.

Siderophores and iron-containing clays are known to influence the transformation of chromium in the environment. The role of clays in hexavalent chromium [Cr(VI)] reduction has been reported extensively. However, the mechanisms of Cr(VI) reduction by siderophores and their combination with iron-bearing clays are poorly known. Herein, we report the kinetics and products of Cr(VI) reduction by a siderophore alone or in combination with reduced clays. Results showed that Cr(VI) reduction by a tri-hydroxamate siderophore─desferrioxamine B (DFOB)─at a pH of 6 was achieved by one-electron transfer via the formation of Cr(V) intermediate. The formed Cr(V) was further reduced to organically complexed Cr(III). The Cr(VI) reduction rate and extent in the presence of both DFOB and reduced clays unexpectedly decreased relative to that with reduced clays alone, despite both serving as Cr(VI) reductants. The interaction between DFOB and clays (e.g., adsorption/intercalation, dissolution, and/or oxidation) was primarily responsible for Cr(VI) reduction inhibition. The extent of inhibition increased at higher DFOB concentrations in the presence of iron-rich nontronite but decreased in the presence of iron-poor montmorillonite, which may be related to their different Cr(VI) reduction mechanisms. This study highlights the importance of siderophores in chromium transformation and its impact on the reactivity of iron-bearing clays toward heavy metal reduction in the environment.

Mechanisms of Enhanced Antibacterial Activity by Reduced Chitosan-Intercalated Nontronite

Previous studies have documented the antibacterial activity of certain iron-containing clays. However, the repulsion between negatively charged bacteria and the clay surface makes this process inefficient. The objective of this study is to improve the bactericidal efficiency of clays by reversing their surface charge from negative to positive. To achieve this objective, positively charged chitosan, a nontoxic and biodegradable polymer, was intercalated into nontronite NAu-2. Chitosan-intercalated NAu-2 (C-NAu-2) was chemically reduced to obtain reduced C-NAu-2 (rC-NAu-2). Relative to reduced nontronite (rNAu-2), the antibacterial activity of rC-NAu-2 is higher and more persistent over a pH range of 6-8. The close spatial association between positively charged rC-NAu-2 and negatively charged bacteria increases the chances of cell membrane attack by extracellular ROS, the influx of soluble Fe2+ into the bacterial cell, and the yield of intracellular ROS. All these factors contribute to the enhanced antibacterial activity of rC-NAu-2. In contrast to rNAu-2 treated E. coli cells, where membrane damage and intracellular ROS/Fe accumulation are restricted to the polar regions, the close bacteria-clay association in rC-NAu-2 results in nonselective membrane damage and more uniform intracellular ROS/Fe distribution across whole bacterial cells. These results advance the antibacterial model by highlighting the importance of bacteria-clay interactions to the antibacterial activity of Fe-bearing clays.

Development of modified kaolins for the removal of As (III) in waters

Some inorganic species of arsenic (As) present in drinking waters are highly dangerous for human health. Adsorption technique is considered a promising technology for the selective removal of As from aqueous systems. Iron (Fe), and iron-containing clays are adsorbents commonly used for arsenic elimination from water due to the strong affinity between Fe and inorganic species of As. Natural and acid-treated kaolinites, impregnated with iron oxides (30 % and 20 % of the Fe (III)) were developed in the present work. The selected clays were physico-chemically characterised, and the As adsorption capability was tested in batch experiments at pH = 7. Arsenic removal studies showed 97% effectiveness for the 30% iron sedimented kaolinite at 1 h of treatment, being the most effective developed material. These preliminary results showed that the Fe (III) impregnated kaolinites could be considered as promising adsorbent materials for As removal from aqueous systems.

Iron-containing clay and hematite iron ore in slurry-phase anaerobic digestion of chicken manure

It is shown in this review that addition of clay minerals and hematite iron ore can significantly enhance anaerobic digestion of chicken manure. Liquid-phase anaerobic digestion of chicken manure consumes a lot of fresh water and energy to keep waste as a suspension. Meanwhile, anaerobic digestion of chicken manure in clay slurry without stirring could minimize energy and water consumption because the initial acceptable content of organic solids can be increased. For example, this content can be increased from 5% (w v-1) in suspension of chicken manure for liquidphase anaerobic digestion up to 15% (w v-1) in the slurry of chicken manure for slurry-phase anaerobic digestion than can save up to 13.3 L of water per kilogram of dry organic solids. The slurry-phase anaerobic digestion of nitrogen-, sulphur-, and fat-containing organic wastes can be enhanced using microbial reduction of Fe(Ⅲ) in clay or in hematite iron ore. This is due to adsorption or precipitation of such inhibitors of microbial acidogenesis and methanogenesis as ammonium, sulphide, long-chain fatty acids, humic and fulvic acids with clay or ferrous ions. For example, maximum concentration of ammonium decreased from 11.4 g L-1 during liquid-phase anaerobic digestion to 1.4 g L-1 during slurry-phase process due to adsorption of ammonium ions on clay. Addition of iron-containing clay to slurry-phase anaerobic reactor removed dissolved sulphide totally due to its precipitation with ferrous ions that are produced by bioreduction of Fe(Ⅲ) in clay. Slurry-phase anaerobic digestion enhanced with bioreduction of Fe(Ⅲ) minerals is also more effective process in terms of environmental safety than widely used liquid-phase anaerobic digestion because of an absence of water supply and wastewater effluent.

Electron Transfer of <i>Shewanella oneidensis</i> MR-1 at Clay-Modified ITO Electrode

The electrode material is an important aspect for the efficiency and costs in the microbial fuel cells (MFCs). Enhancing of current production and bacteria attachment to the electrode are essential goals for developing the performance of MFCs. In this study, the role of the structural iron present in clays in enhancing the electron transfer of Shewanella oneidensis MR-1 was investigated. Two types of clay containing different amounts of iron situated in the octahedral sites were used to modify ITO (indium tin oxide) electrodes, namely nontronite NAu-1, and montmorillonite (Wyoming) SWy-1. Synthetic montmorillonite SYn-1 which is iron-free clay was used for comparison. The interaction between the bacterial cells and the clays was studied by potential-step chronoamperometry, cyclic voltammetry, confocal microscopy, and scanning electron microscopy (SEM). The obtained results showed that the current densities generated upon ITO electrode modification using the NAu-1 and SWy-1 iron-containing clays were 19 and 3 times higher than that produced using the bare ITO electrode. No current density was obtained when utilizing the synthetic montmorillonite SYn-1 clay. SEM and confocal microscopy observations confirmed the increased coverage percentage of the bacterial cells attached to the clay-modified electrodes compared to the bare ITO.

Mineralogy and physicochemical features of Saharan dust wet deposited in the Iberian Peninsula during an extreme red rain event

Abstract. The mineralogy and physicochemical features of Saharan dust particles help to identify source areas and determine their biogeochemical, radiative, and health effects, but their characterization is challenging. Using a multianalytical approach, here we characterized with unprecedented level of detail the mineralogy and physicochemical properties of Saharan dust particles massively wet deposited ( ∼ 18 g m−2) following an extreme red rain event triggered by a northern African cyclone that affected the southern Iberian Peninsula during 21–23 February 2017. Abundant palygorskite and illite, and relatively high carbonate contents, well-known northern and north-western Saharan dust indicators, along with low chlorite content and significant amounts of smectites and kaolinite, whose abundance increases southwards in the western Sahara, complemented by satellite imagery and back/forward trajectories, show that the most probable dust source areas were (i) southern/central Algeria, northern Mali, and northwestern Niger, and (ii) northern Algeria, southern Tunisia, and northwestern Libya. Scanning and transmission electron microscopy analyses, including Z-contrast high angle annular dark field (HAADF) imaging and analytical electron microscopy (AEM), show that clay minerals include abundant structural Fe (55 % of the total Fe) and typically form nanogranular aggregates covered or interspersed with amorphous/poorly crystalline iron oxyhydroxide nanoparticles (ferrihydrite), which account for ∼ 18 % of the free Fe, the rest being goethite and hematite. These nanogranular aggregates tend to form rims lining large silicate and carbonate particles. Such internally mixed iron-containing phases are the main contributors to the observed absorption of solar and thermal radiation, and along with the abundant coarse/giant particles ( > 10 µm) strongly affect the dust direct radiative forcing. The lack of secondary sulfates in aggregates of unaltered calcite internally mixed with clays/iron-rich nanoparticles shows that iron-rich nanoparticles did not form via atmospheric (acid) processing but were already present in the dust source soils. Such iron-rich nanoparticles, in addition to iron-containing clay (nano)particles, are the source of the ∼ 20 % soluble (bioavailable) iron in the studied desert dust. The dust particles are a potential health hazard, specifically the abundant and potentially carcinogenic iron-containing palygorskite fibers. Ultimately, we show that different source areas are activated over large desert extensions, and large quantities of complex dust mixtures are transported thousands of kilometers and wet-deposited during such extreme events, which dwarf any other Saharan dust event affecting southwestern Europe. The past, present, and future trends, as well as impacts, of such extreme events must be taken into account when evaluating and modeling the manifold effects of the desert dust cycle.

Reduced Iron-Containing Clay Minerals as Antibacterial Agents.

Previous work documented the general antibacterial mechanism of iron containing clays that involved hydroxyl radical (•OH) production from soluble Fe2+, and attack of cell membrane and intracellular proteins. Here we explore the role of clay structural Fe(II) in •OH production at near neutral pH and identify a lipid involved in the antibacterial process. Structural Fe(III) in nontronite NAu-2 was reduced (rNAu-2) and E. coli, a model bacterium, was exposed to rNAu-2 in oxic suspension. The antibacterial activity of rNAu-2 was dependent on pH and Fe(II) concentration, where E. coli were completely killed at pH 6, but survived at pH 7 and 8. In the presence of a •OH scavenger or in anaerobic atmosphere, E. coli survived better, suggesting that cell death may be caused by •OH generated from oxidation of structural Fe(II) in rNAu-2. In-situ imaging revealed damage of a membrane lipid, cardiolipin, in the polar region of E. coli cells, where reactive oxygen species and redox-active labile Fe were enriched. Our results advance the previous antibacterial model by demonstrating that the structural Fe(II) is the primary source of •OH, which damages cardiolipin, triggers the influx of soluble Fe2+ into the cell, and ultimately leads to cell death.

Oxidation of tetrahydrofuran to butyrolactone catalyzed by iron-containing clay

Earth-abundant iron-containing clay can be applicable as an oxidation catalyst for butyrolactone production from biomass-derived tetrahydrofuran using hydrogen peroxide as oxidant at mild condition.

Laser flash photolysis study of photocatalytic properties of pillared interlayered clays and Fe,Al-silica mesoporous catalysts

Laser flash photolysis was applied to determine the primary photochemical processes over iron-containing clay (montmorillonite KSF), pillared interlayered clays (PILCs) and mesoporous mesophase iron silicate materials (MMMs). For KSF, the homogeneous photochemical reaction of Fe(III) leached from the clay material resulted in the formation of OH radicals, which were monitored by means of their reaction with methyl viologen dication (MV(2+)). For PILCs and MMMs, no leaching of Fe(III) to the solution nor hydroxyl radical formation were observed. Nevertheless, these catalysts were found to exhibit a sufficient effect on phenol photoionization. The increase in quantum yields of PhO radicals is caused by the effect of PILCs and MMMs and is explained by heterogeneous processes on the surface of catalyst particles.

Kinetics and efficiency of H2O2 activation by iron-containing minerals and aquifer materials

To gain insight into factors that control H2O2 persistence and OH yield in H2O2-based in situ chemical oxidation systems, the decomposition of H2O2 and transformation of phenol were investigated in the presence of iron-containing minerals and aquifer materials. Under conditions expected during remediation of soil and groundwater, the stoichiometric efficiency, defined as the amount of phenol transformed per mole of H2O2 decomposed, varied from 0.005 to 0.28%. Among the iron-containing minerals, iron oxides were 2–10 times less efficient in transforming phenol than iron-containing clays and synthetic iron-containing catalysts. In both iron-containing mineral and aquifer materials systems, the stoichiometric efficiency was inversely correlated with the rate of H2O2 decomposition. In aquifer materials systems, the stoichiometric efficiency was also inversely correlated with the Mn content, consistent with the fact that the decomposition of H2O2 on manganese oxides does not produce OH. Removal of iron and manganese oxide coatings from the surface of aquifer materials by extraction with citrate–bicarbonate–dithionite slowed the rate of H2O2 decomposition on aquifer materials and increased the stoichiometric efficiency. In addition, the presence of 2 mM of dissolved SiO2 slowed the rate of H2O2 decomposition on aquifer materials by over 80% without affecting the stoichiometric efficiency.

CATALYTIC WET HYDROGEN PEROXIDE OXIDATION OF 4-CHLOROPHENOL OVER IRON-EXCHANGED CLAYS

Chlorophenols were selected for this study because most of them are toxic and difficult to biodegrade. They represent a particular group of priority toxic pollutants listed by the US EPA in the Clean Water Act and by the European Decision 2455/2001/EC. The efficiency of advanced oxidation processes for degradation of chlorophenols has been extensively documented. The catalytic wet hydrogen peroxide oxidation process, involving oxidation with H2O2 and solid catalysts in mild reaction conditions, was found to be very attractive for different pollutants; however, data regarding the degradation of chlorophenols are very scarce. The aims of this paper were: (i) to prepare and characterize a series of iron-exchanged montmorillonites and (ii) to assess their catalytic performances in a Fenton-like process for the oxidation of para-chlorophenol. DR-UV-VIS spectroscopy was tentatively used to elucidate the structure of the iron oxo sites intervening in the reaction. This approach has been used previously for ion-exchanged zeolites and was able to distinguish between isolated Fe(III) species and FexOy clusters of different nuclearity. The catalytic tests, performed at room temperature, showed that all iron-containing clays were very active, leading to the complete oxidation of parachlorophenol and a significant reduction of TOC values. 4-chlorocatechol was the major reaction intermediate found in the CWHPO of 4-CP, followed by hydroquinone and traces of benzoquinone, 5-chloro-1,2,4-benzenetriol, 1,2,4-benzenetriol and 3chloro-muconic acid. The leaching test indicates that the catalytic activity is mainly due to leached iron ions, at least in the second part of the process.

Synthesis, characterization and catalytic application for wet oxidation of phenol of iron-containing clays

High-surface-area pillared clays (PILC) were prepared from naturally occurring montmorillonites by exchanging interlayer ions to polyoxocations containing (i) aluminum (Al13-PILC), (ii) iron adsorpted onto Al13-PILC, and (iii) iron and aluminum located within the same complex (Fe0.8Al12.2-PILC). The obtained Fe0.8Al12.2-PILCs were characterized by DR–UV–vis and IR spectroscopy, XRD, ESR, scanning electron microscopy and low temperature N2 adsorption measurements. Important factors affecting catalyst activity and phenol removal efficiencies have been studied, i.e. the effect of pH, temperature, catalyst concentration and stability of the catalyst.

Effect of iron compounds on the treatment of fat-containing wastewaters

Effects of iron compounds on methanogenic fermentation the water polluted with fatty acids were studied. A natural readily available source of iron applicable to biological treatment of liquid wastes was searched for. A positive effect of iron on the methanogenic fermentation of fats and their degradation products--long-chain fatty acids--in aqueous media was demonstrated. It is recommended to add iron-containing clay, as an inexpensive and easily available iron source, in amounts providing the binding of the long-chain fatty acids present in wastewaters.

Direct Evidence of Clay-Mediated Charge Transfer

The charge transfer (CT) from montmorillonite K10 (iron-containing clay) was studied by monitoring the reaction of halides (Cl-, Br-, and I-) with the intercalated photosensitizer, 10-methylacridinium (AcH+). The electrodes, which were fabricated by the AcH+-intercalated clays (denoted clay/AcH+), showed no current responses to bromide and chloride. However, there was a significant current response corresponding to the reduction of iodine and this response was enhanced by light irradiation. These differences in the electrochemical behavior suggested the electron transfer on the clay/AcH+ surface was regulated by the electrochemically active iron species in the clay. The lifetime of AcH+ is ca. 36 ns, whereas for AcH+(clay), it is as fast as the instrumental response (<10 ns), indicating the clay can efficiently quench the excited acridinium, AcH+*. Moreover, a long-lived species, attributed to I2-•, was recorded in KI solutions (pH 4) containing either AcH+ or clay/AcH+. In contrast, the transient species, presumed to be Br2-•, was only observed in the solutions containing free AcH+. Both electrochemical and laser spectroscopic results indicated that the electron transfer between AcH+* and I- is mediated by the iron species in montmorillonite K10.

Catalytic properties of materials derived from iron-containing clays

The catalytic activities of iron-containing fireclays reduced at 1020°C, determined using the Fischer-Tropsch hydrocarbon synthesis reaction in a wax-slurry reactor, are proportional to the intensity of an unusual singlet peak in the Mossbauer spectra of the reduced samples. This singlet peak is attributed to γ-Fe, a metastable high-temperature form which appears to be stabilized by the cubic host lattice resulting from kaolinite decomposition at ca. 980°C. The enhanced activity of γ-Fe is discussed in terms of steric factors related to the structure of this phase. The effects of different thermal pretreatments and additions of alkali promotors on the catalytic activity are also discussed.

Simulation of the Viking biology experiments: an overview.

Several ground-based investigations have been carried out since the Viking biology results were received from Mars. Many of these have resulted in reasonable simulations of the Martian data, using as analogues of Mars either strong oxidants, UV-treated materials, iron-containing clays, or iron salts. The ambiguity between the GCMS experiment, in which no organic compounds were found on Mars, and the Labeled Release experiment, in which added organics were decomposed, may well be accounted for by these simulations.