Oxidation mechanism of pyrite in a thiosulfate solution: electrochemical impedance (EIS) and in situ Raman spectroscopy.

Ammoniacal thiosulfate has been used lately as an alternative lixiviant for leaching gold from sulfides ores which are not amenable for cyanidation. However, the oxidation of the sulfide minerals generates products that inhibit the dissolution of gold and can promote the degradation of the leaching solution. The complexity of the ammoniacal thiosulfate leaching system has prevented the unification and clarification of the mechanisms of oxidation of sulfide ores used for gold extraction. In this study, a method combining polarization curves, Electrochemical impedance spectroscopy (EIS), and in situ Raman spectroscopy was implemented to investigate the oxidation process of high-purity pyrite. Pyrite samples were dispersed in carbon paste electrode (CPE-Py). The polarization curves of CPE-Py exhibited an increase in current values for overpotentials greater than 0.1 V, indicating the initiation of mineral oxidation processes. Subsequently, a maximum current was observed initially, followed by subsequent decrease, indicating the occurrence of passivation processes on the electrode surface. Hydrodynamic polarization curves demonstrated that the overpotential at which the passivation process occurs is independent of mass transport, suggesting that the passivation products were formed through solid-state transformation. Impedance spectra revealed that at overpotentials below 0.1 V, a partially resolved capacitive semicircle was observed, which was associated with the resistance encountered when charge was transferred between the solution and the surface layer interface. This resistance decreased as the polarization overpotential increased, implying a decrease in charge transfer kinetics. At higher overpotentials (0.3 V-0.4 V), a second capacitive semicircle appeared, linked to the oxidation of one or several species present in the mineral. In situ Raman spectroscopy was utilized to identify the oxidation species of pyrite in ammonia-thiosulfate ((NH4)2S2O3) leaching solution at a pH = 10.2. The composition of the species varied depending on the applied anodic potential. At low anodic potentials (0.1 V), Fe(OH)2 and thiosulfate (S2O32-) were formed, while at high anodic potentials (0.4 V), iron products such as Fe3O4 and γ-FeOOH, as well as sulfide species including thiosulfate, tetrathionates and sulfates (S2O32-, S4O6-2 and SO42-) were formed.

Annealing effects on the magnetic and magnetotransport properties of iron oxide nanoparticles self-assemblies.

In magnetic tunnel junctions based on iron oxide nanoparticles the disorder and the oxidation state of the surface spin as well as the nanoparticles functionalization play a crucial role in the magnetotransport properties. In this work, we report a systematic study of the effects of vacuum annealing on the structural, magnetic and transport properties of self-assembled ∼10 nm Fe3O4nanoparticles. The high temperature treatment (from 573 to 873 K) decomposes the organic coating into amorphous carbon, reducing the electrical resistivity of the assemblies by 4 orders of magnitude. At the same time, the 3.Fe2+/(Fe3++Fe2+) ratio is reduced from 1.11 to 0.13 when the annealing temperature of the sample increases from 573 to 873 K, indicating an important surface oxidation. Although the 2 nm physical gap remains unchanged with the thermal treatment, a monotonous decrease of tunnel barrier width was obtained from the electron transport measurements when the annealing temperature increases, indicating an increment in the number of defects and hot-spots in the gap between the nanoparticles. This is reflected in the reduction of the spin dependent tunneling, which reduces the interparticle magnetoresistance. This work shows new insights about influence of the nanoparticle interfacial composition, as well their the spatial arrangement, on the tunnel transport of self-assemblies, and evidence the importance of optimizing the nanostructure fabrication for increasing the tunneling current without degrading the spin polarized current.

Synthesis of Iron Oxides and Influence on Final Sizes and Distribution in Bacterial Cellulose Applications.

Iron oxide nanoparticles have been investigated due to their suitable characteristics for diverse applications in the fields of biomedicine, electronics, water or wastewater treatment and sensors. Maghemite, magnetite and hematite are the most widely studied iron oxide particles and have ferrimagnetic characteristics. When very small, however, these particles have superparamagnetic properties and are called superparamagnetic iron oxide nanoparticles (SPIONs). Several methods are used for the production of these particles, such as coprecipitation, thermal decomposition and microemulsion. However, the variables of the different types of synthesis must be assessed to achieve greater control over the particles produced. In some studies, it is possible to compare the influence of variations in the factors for production with each of these methods. Thus, researchers use different adaptations of synthesis based on each objective and type of application. With coprecipitation, it is possible to obtain smaller, more uniform particles with adjustments in temperature, pH and the types of reagents used in the process. With thermal decomposition, greater control is needed over the time, temperature and proportion of surfactants and organic and aqueous phases in order to produce smaller particles and a narrower size distribution. With the microemulsion process, the control of the confinement of the micelles formed during synthesis through the proportions of surfactant and oil makes the final particles smaller and less dispersed. These nanoparticles can be used as additives for the creation of new materials, such as magnetic bacterial cellulose, which has different innovative applications. Composites that have SPIONs, which are produced with greater rigour with regards to their size and distribution, have superparamagnetic properties and can be used in medical applications, whereas materials containing larger particles have ferromagnetic applications. To arrive at a particular particle with specific characteristics, researchers must be attentive to both the mechanism selected and the production variables to ensure greater quality and control of the materials produced.

Magnetic mining waste based-geopolymers applied to catalytic reactions with ozone.

The demand for sustainable and low-cost materials for wastewater treatment is increasing considerably. In this scenario, geopolymers have gained great interest, due to their good mechanical properties, their ability to be produced from industrial waste and their adsorbent or catalytic properties. In this study, novel magnetic mining waste based-geopolymers were produced by incorporating a residue from phosphate waste rocks, which were extensively characterized (XRD, TGA/DTA, SEM, BET, XRF, FTIR, Mössbauer, ss-NMR and XPS). The materials produced showed formation of a dense framework, even with 75% incorporation of the residue. The iron oxides and their magnetic properties remained unchanged, and their application in advanced oxidation reactions were evaluated, in particular, as catalysts in ozonation reactions. All of the geopolymers presented catalytic activity in the ozonation reaction, with catalytic ozone decomposition values of up to 2.98 min-1, which is 99 times greater than non-catalyzed reactions. Moreover, the reuse (performed in three cycles) and hot filtration-like experiments demonstrated, respectively, the regenerability and heterogeneous catalytic properties of the produced materials, showcasing the potential of these waste materials for catalytic geopolymer production. demonstrating the potential of this waste to produce catalytic geopolymers.

Ferrihydrite synthesis in the presence of amino acids and artificial seawater.

Ferrihydrite is widespread in clays, soils, and living organisms and was found on Mars. This iron-mineral could be found on the prebiotic Earth, which also contained simple monomeric amino acids. For prebiotic chemistry, it is important to understand how amino acids have an effect on the process of iron oxide formations. There are three important results in this work: (a) preconcentration of cysteine and aspartic acid, (b) formation of cystine and probably the cysteine peptide occurred during ferrihydrite syntheses, and (c) amino acids have an effect on iron oxide synthesis. For samples containing aspartic acid and cysteine, their presence on the surface or mineral structure can be confirmed by FT-IR spectra. Surface charge analysis showed a relatively high decrease for samples synthesized with cysteine. Scanning electron microscopy did not show marked morphological differences among the samples, except for the seawater sample containing cysteine, which had a lamina-shaped morphology surrounded by circular iron particles, indicating the possible formation of a cysteine structure involving iron oxide particles. The thermogravimetric analysis of the samples indicates that the presence of salts and amino acids in the synthesis of ferrihydrite has an effect on the thermal behavior of the iron oxide/amino acids and modifying the water-loss temperature. The heating of the cysteine samples, synthesized in distilled water and artificial seawater, showed several peaks of degradation of cysteine. In addition, heating of the aspartic acid samples produced the polymerization of this amino acid and peaks of degradation of it. FTIR spectra and XRD patterns did not indicate the precipitation of methionine, 2-aminoisobutyric acid, lysine, or glycine with the iron oxide formations. However, the heating of the glycine, methionine and lysine samples, synthesized in artificial seawater, showed peaks that could be attributed to the degradation of them. Then this could be an indication that these amino acids precipitate with the minerals during the syntheses. Also, the dissolution of these amino acids in artificial seawater prevents the formation of ferrihydrite.

Redox phase transformations in magnetite nanoparticles: impact on their composition, structure and biomedical applications.

Magnetite nanoparticles (NPs) are one of the most investigated nanomaterials so far and modern synthesis methods currently provide an exceptional control of their size, shape, crystallinity and surface functionalization. These advances have enabled their use in different fields ranging from environmental applications to biomedicine. However, several studies have shown that the precise composition and crystal structure of magnetite NPs depend on their redox phase transformations, which have a profound impact on their physicochemical properties and, ultimately, on their technological applications. Although the physical mechanisms behind such chemical transformations in bulk materials have been known for a long time, experiments on NPs with large surface-to-volume ratios have revealed intriguing results. This article is focused on reviewing the current status of the field. Following an introduction on the fundamental properties of magnetite and other related iron oxides (including maghemite and wüstite), some basic concepts on the chemical routes to prepare iron oxide nanomaterials are presented. The key experimental techniques available to study phase transformations in iron oxides, their advantages and drawbacks to the study of nanomaterials are then discussed. The major section of this work is devoted to the topotactic oxidation of magnetite NPs and, in this regard, the cation diffusion model that accounts for the experimental results on the kinetics of the process is critically examined. Since many synthesis routes rely on the formation of monodisperse magnetite NPs via oxidation of wüstite counterparts, the modulation of their physical properties by crystal defects arising from the oxidation process is also described. Finally, the importance of a precise control of the composition and structure of magnetite-based NPs is discussed and its role in their biomedical applications is highlighted.

Reactive Oxygen Species in Emulated Martian Conditions and Their Effect on the Viability of the Unicellular Alga Scenedesmus dimorphus.

Formation of oxygen-based free radicals from photochemical decomposition of hydrogen peroxide (H2O2) on Mars may be a key factor in the potential survival of terrestrial-like organisms on the red planet. Martian conditions that generate reactive oxygen species involve the decomposition of H2O2 at temperatures of around 278 K under relatively high doses of C-band ultraviolet radiation (UVC). This process is further amplified by the presence of iron oxides and perchlorates. Photosynthetic organisms exhibit a number of evolutionary traits that allow them to withstand both oxidative stress and UVC radiation. Here, we examine the effect of free radicals produced by the decomposition of H2O2 under emulated martian conditions on the viability of Scenedesmus dimorphus, a unicellular alga that is resistant to UVC radiation and varying levels of perchlorate and H2O2, both of which are present on Mars. Identification and quantification of free radicals formed under these conditions were performed with Electron Paramagnetic Resonance spectroscopy. These results were correlated with the viability of S. dimorphus, and the formation of oxygen-based free radicals and survival of the alga were found to be strongly dependent on the amount of H2O2 available. For H2O2 amounts close to those present in the rarefied martian environment, the products of these catalytic reactions did not have a significant effect on the algal population growth curve.

The Effect of Goethites on the Polymerization of Glycine and Alanine Under Prebiotic Chemistry Conditions.

After pre concentration of monomers, polymerization is the second most important step for molecular evolution. The formation of peptides is an important issue for prebiotic chemistry and consequently for the origin of life. In this work, goethite was synthesized by two different routes, named goethite-I and goethite-II. Although both samples are goethite, Far-FT-IR spectroscopy and EPR spectroscopy showed differences between them, and these differences had an effect on the polymerization of glycine and alanine. For the amino acid polymerization, three protocols were used, that resembled prebiotic Earth conditions: a) amino acid plus goethite were mixed and heated at 90 °C for 10 days in solid state, b) a wet impregnation of the amino acid in the goethite, with subsequent heating at 90 °C for 10 days in solid state, and c) 10 wet/dry cycles each one for 24 h at 90 °C. Experiments with glycine plus goethite-II, using protocols B and C, produced only Gly-Gly. In addition, for the C protocol the amount of Gly-Gly synthesized was 3 times higher than the amount of Ala-Ala. Goethite-I presented a decrease in the EPR signal, when it was submitted to the protocols with and without amino acids. It is probable the decrease in the intensity of the EPR signal was due to a decrease in the imperfections of the mineral. For all protocols the mixture of alanine plus goethite-I or goethite-II produced c(Ala-Ala). However, for wet/dry cycles, protocol C presented higher yields (p < 0.05). In addition, Ala-Ala was produced using protocols A and C. The c(Ala-Ala) formation fitted a zero-order kinetic equation model. The surface areas of goethite-I and goethite-II were 35 m2 g-1 and 37 m2 g-1, respectively. Thermal analysis indicated that the mineral changes the thermal behavior of the amino acids. The main reactions for the thermal decomposition of glycine were deamination and dehydration and for alanine was deamination.

Manganese: The overlooked contaminant in the world largest mine tailings dam collapse.

Manganese (Mn) is an abundant element in terrestrial and coastal ecosystems and an essential micronutrient in the metabolic processes of plants and animals. Mn is generally not considered a potentially toxic element due to its low content in both soil and water. However, in coastal ecosystems, the Mn dynamic (commonly associated with the Fe cycle) is mostly controlled by redox processes. Here, we assessed the potential contamination of the Rio Doce estuary (SE Brazil) by Mn after the world's largest mine tailings dam collapse, potentially resulting in chronic exposure to local wildlife and humans. Estuarine soils, water, and fish were collected and analyzed seven days after the arrival of the tailings in 2015 and again two years after the dam collapse in 2017. Using a suite of solid-phase analyses including X-ray absorption spectroscopy and sequential extractions, our results indicated that a large quantity of MnII arrived in the estuary in 2015 bound to Fe oxyhydroxides. Over time, dissolved Mn and Fe were released from soils when FeIII oxyhydroxides underwent reductive dissolution. Due to seasonal redox oscillations, both Fe and Mn were then re-oxidized to FeIII, MnIII, and MnIV and re-precipitated as poorly crystalline Fe oxyhydroxides and poorly crystalline Mn oxides. In 2017, redox conditions (Eh: -47 ± 83 mV; pH: 6.7 ± 0.5) favorable to both Fe and Mn reduction led to an increase (~880%) of dissolved Mn (average for 2015: 66 ± 130 µg L-1; 2017: 582 ± 626 µg L-1) in water and a decrease (~75%, 2015: 547 ± 498 mg kg-1; 2017: 135 ± 80 mg kg-1) in the total Mn content in soils. The crystalline Fe oxyhydroxides content significantly decreased while the fraction of poorly ordered Fe oxides increased in the soils limiting the role of Fe in Mn retention. The high concentration of dissolved Mn found within the estuary two years after the arrival of mine tailings indicates a possible chronic contamination scenario, which is supported by the high levels of Mn in two species of fish living in the estuary. Our work suggests a high risk to estuarine biota and human health due to the rapid Fe and Mn biogeochemical dynamic within the impacted estuary.

The first evidence of accumulation and avoidance behavior of macroinvertebrates in a forest soil spiked with human-made iron nanoparticles: A field experiment.

Both earthworms and terrestrial isopods have been used to evaluate the quality of contaminated soil by NPs. However, most experiments have been conducted in the laboratory and under greenhouse conditions. Besides, little is known of Fe accumulation in earthworms from iron NPs (Fe NPs) under natural conditions. Therefore, the objective of this research was to evaluate the effect of manufactured NPs on the accumulation of Fe in macroinvertebrates from forest soil. Our results revealed that earthworms consume low amounts of Fe in a concentration of 1000 mg Fe NPs kg-1 of dry soil, with a behavior constant over time. Besides, we observed that earthworms could not detect Fe at low concentrations (1 or 10 mg Fe NPs kg-1), so they do not limit soil consumption, which translates into high amounts of Fe in their bodies. By contrast, the content of Fe in organisms is inversely proportional to increasing concentrations in the soil (R2 = -0.41, p < 0.05). Therefore, although studies are needed, in addition to considering environmental factors and the physicochemical properties of the soil, endogenous worms in the evaluated area could, under natural conditions, be useful to inform us of contamination of NP manufactured from Faith. Besides, for future research, a novel methodology should be considered to demonstrate more realistic avoidance behavior under field conditions.

The Use of a Sequential Extraction Technique to Characterize Soil Trace Evidence Recovered from a Spade in a Murder Case in Brazil.

Soil trace evidence can be useful in criminal investigations. A homicide which had occurred in South Brazil been concluded through the courts with a guilty conviction. A spade with soil traces adhering to it was seized from the confessed killer's house, it having been established that it had been used to bury parts of the victim's body. In the context of this confession, it provided an opportunity to test a protocol of analysis and verify the potential of discriminate soil sample analysis in such case works. This allowed us to test the practice of sequential analysis which had been developed for forensic case works in Brazil, with three sequential extractions: (i) 0.2 mol/L pH 3.0 ammonium oxalate; (ii) dithionite-citrate-bicarbonate; and (iii) 0.5 mol/L NaOH. It was possible to predict the sequence of events related to the homicide by using the sequential extraction technique and to conclude that: (i) the A horizon soil from the burial location of the torso was found to be very similar to the soil samples which had been recovered from the spade, which was able to be established despite there only being a small amount of soil adhering to the spade; (ii) the location where the legs were buried contributed a low amount of soil adhering to the spade. Therefore, it is suggested that, where possible, sequential extractions should be prioritized from a questioned sample to best provide information about the likely sequence of contact places and this test likely scenarios and criminal events.

Lead-contaminated soils with contrasting texture remediated with phosphate: chemical fractionation and chloropyromorphite stability.

Pb can be stabilized in soil as Pb-P mineral. The aims of this study were to access the distribution of Pb in organic and mineral fractions of contrasting texture of soil Pb-contaminated and remediated with P and Cl and to evaluate the stability of chloropyromorphite in these soils. A clay loam Oxisol (sandstone) and a clayey Ultisol (basalt) were used in a factorial experiment, with three replications: two soils, two Pb contamination levels, two soil pH values, and four P doses. The Pb concentrations were determined in seven soil phases. Release kinetics of Pb were performed with 0.1 mol L-1 pH 2.5 citric acid. The transfer of soil Pb to chloropyromorphite was dependent on the level of contamination in the clay loam Oxisol. In the lowest P dose (molar ratios P:Pb 3:5), the main source was the Pb complexed in the organic matter and in the highest P dose (molar ratios P:Pb 12:5) was the Pb adsorbed by inner sphere in gibbsite and kaolinite. The release of Pb in the citric acid was dependent on the texture and mineralogy of the soils. Pb recovery applied to the clay loam Oxisol was around 100% (biphasic kinetic), while for the clayey Ultisol, the recovery ranged from 43 to 52% (single-phase kinetic). Remediation of Pb-contaminated soils with P and Cl is more efficient in clayey and oxidic soils since chloropyromorphite formation is faster and its solubilization is slower, an important combination in environmental terms.

Unexpected Thiocyanate Adsorption onto Ferrihydrite Under Prebiotic Chemistry Conditions.

The most crucial role played by minerals was in the preconcentration of biomolecules or precursors of biomolecules in prebiotic seas. If this step had not occurred, molecular evolution would not have occurred. Thiocyanate is an important molecule in the formation of biomolecules as well as a catalyst for prebiotic reactions. The adsorption of thiocyanate onto ferrihydrite was carried out under pH and ion composition conditions in seawater that resembled those of prebiotic Earth. The seawater used in this work had high Mg2+, Ca2+ and SO42- concentrations. The most important result of this work was that ferrihydrite adsorbed thiocyanateata pH value (7.2 ± 0.2) that usually does not adsorb thiocyanate. The high adsorptivity of Mg2+, Ca2+ and SO42-onto ferrihydrite showed that seawater ions can act as carriers of thiocyanate to the ferrihydrite surface, creating a huge outer-sphere complex. Kinetic adsorption and isotherm experiments showed the best fit for the pseudo-second-order model and an activation energy of 23.8 kJ mol-1forthe Langmuir-Freundlich model, respectively. Thermodynamic data showed positive ΔG values, which apparently contradict the adsorption isotherm data and kinetic data that was obtained. The adsorption of thiocyanate onto ferrihydrite could be explained by coupling with the exergonic SO42- adsorption onto ferrihydrite. The FTIR spectra showed no difference between the C≡N stretching peaks of adsorbed thiocyanate and free thiocyanate, corroborating the formation of an outer-sphere complex. All the results demonstrated the importance of the artificial seawater composition for the adsorption of thiocyanate and for understanding prebiotic chemistry.

Mineralogy, magnetic susceptibility and geochemistry of Fe-rich Oxisols developed from several parent materials

Fe-rich Oxisols on mafic rocks in Brazil generally have high magnetic susceptibility with high contents of some trace elements. These are taxonomically similar soils; however, differences in magnetic and geochemical properties may affect agricultural or environmental usability and subsequent management. This study investigated the pedogenesis of Fe-rich Oxisols from various parent materials and evaluated the lithogenetic influence on magnetic susceptibility and trace elements contents. Soil samples were collected from Bw horizons in 13 Rhodic Oxisols and a Typic Oxisol developed from several parent materials in Minas Gerais State, Brazil. Soils were analyzed by X-ray diffractometry (XRD) and magnetometry. Soil chemical analyses consisted of sulfuric and total (tri-acid) digestions and selective Fe oxides dissolutions and statistical correlations were determined. Fe-rich Oxisols presented a typical mineralogical composition of highly weathered soils with structural stability. The results confirm the difficulty to identify accurately magnetic minerals in different grain sizes using XRD. However, coarse fractions still exert dominant influence on the magnetic properties of the Fe-rich Rhodic Oxisols. In addition, coarse fractions probably contribute to the enrichment of superparamagnetic particles for the clay fraction. Although highly weathered, Fe-rich Oxisols may have their geochemical attributes still controlled by the parent material, where trace elements seem to be correlated with the magnetic minerals in the coarse fractions. Thus, the natural replacement of some trace elements from soil-solution equilibrium reactions during plant development could be more effective in soils with higher magnetic particles concentrations in the coarse fractions.(AU)

Mineralogy, magnetic susceptibility and geochemistry of Fe-rich Oxisols developed from several parent materials

Fe-rich Oxisols on mafic rocks in Brazil generally have high magnetic susceptibility with high contents of some trace elements. These are taxonomically similar soils; however, differences in magnetic and geochemical properties may affect agricultural or environmental usability and subsequent management. This study investigated the pedogenesis of Fe-rich Oxisols from various parent materials and evaluated the lithogenetic influence on magnetic susceptibility and trace elements contents. Soil samples were collected from Bw horizons in 13 Rhodic Oxisols and a Typic Oxisol developed from several parent materials in Minas Gerais State, Brazil. Soils were analyzed by X-ray diffractometry (XRD) and magnetometry. Soil chemical analyses consisted of sulfuric and total (tri-acid) digestions and selective Fe oxides dissolutions and statistical correlations were determined. Fe-rich Oxisols presented a typical mineralogical composition of highly weathered soils with structural stability. The results confirm the difficulty to identify accurately magnetic minerals in different grain sizes using XRD. However, coarse fractions still exert dominant influence on the magnetic properties of the Fe-rich Rhodic Oxisols. In addition, coarse fractions probably contribute to the enrichment of superparamagnetic particles for the clay fraction. Although highly weathered, Fe-rich Oxisols may have their geochemical attributes still controlled by the parent material, where trace elements seem to be correlated with the magnetic minerals in the coarse fractions. Thus, the natural replacement of some trace elements from soil-solution equilibrium reactions during plant development could be more effective in soils with higher magnetic particles concentrations in the coarse fractions.

Combining X-Ray Whole Powder Pattern Modeling, Rietveld and Pair Distribution Function Analyses as a Novel Bulk Approach to Study Interfaces in Heteronanostructures: Oxidation Front in FeO/Fe3 O4 Core/Shell Nanoparticles as a Case Study.

Understanding the microstructure in heterostructured nanoparticles is crucial to harnessing their properties. Although microscopy is ideal for this purpose, it allows for the analysis of only a few nanoparticles. Thus, there is a need for structural methods that take the whole sample into account. Here, a novel bulk-approach based on the combined analysis of synchrotron X-ray powder diffraction with whole powder pattern modeling, Rietveld and pair distribution function is presented. The microstructural temporal evolution of FeO/Fe3 O4 core/shell nanocubes is studied at different time intervals. The results indicate that a two-phase approach (FeO and Fe3 O4 ) is not sufficient to successfully fit the data and two additional interface phases (FeO and Fe3 O4 ) are needed to obtain satisfactory fits, i.e., an onion-type structure. The analysis shows that the Fe3 O4 phases grow to some extent (≈1 nm) at the expense of the FeO core. Moreover, the FeO core progressively changes its stoichiometry to accommodate more oxygen. The temporal evolution of the parameters indicates that the structure of the FeO/Fe3 O4 nanocubes is rather stable, although the exact interface structure slightly evolves with time. This approach paves the way for average studies of interfaces in different kinds of heterostructured nanoparticles, particularly in cases where spectroscopic methods have some limitations.

The Samarco mine tailing disaster: A possible time-bomb for heavy metals contamination?

In November 2015, the largest socio-environmental disaster in the history of Brazil occurred when approximately 50 million m3 of mine tailings were released into the Doce River (SE Brazil), during the greatest failure of a tailings dam worldwide. The mine tailings passed through the Doce River basin, reaching the ecologically important estuary 17 days later. On the arrival of the mine wastes to the coastal area, contamination levels in the estuarine soils were measured to determine the baseline level of contamination and to enable an environmental risk assessment. Soil and tailings samples were collected and analyzed to determine the redox potential (Eh), pH, grain size and mineralogical composition, total metal contents (Fe, Mn, Cr, Zn, Ni, Cu, Pb and Co) and organic matter content. The metals were fractionated to elucidate the mechanisms governing the trace metal dynamics. The mine tailings are mostly composed of Fe (mean values for Fe: 45,200 ±â€¯2850; Mn: 433 ±â€¯110; Cr: 63.9 ±â€¯15.1; Zn: 62.4 ±â€¯28.4; Ni: 24.7 ±â€¯10.4; Cu: 21.3 ±â€¯4.6; Pb: 20.2 ±â€¯4.6 and Co: 10.7 ±â€¯4.8 mg kg-1), consisting of Fe-oxyhydroxides (goethite, hematite); kaolinite and quartz. The metal contents of the estuarine soils, especially the surface layers, indicate trace metal enrichment caused by the tailings. However, the metal contents were below threshold levels reported in Brazilian environmental legislation. Despite the fact that only a small fraction (<2%) of the metals identified are readily bioavailable (i.e. soluble and exchangeable fraction), trace metals associated with Fe oxyhydroxides contributed between 69.8 and 87.6% of the total contents. Control of the trace metal dynamics by Fe oxyhydroxides can be ephemeral, especially in wetland soils in which the redox conditions oscillate widely. Indeed, the physicochemical conditions (Eh < 100 mV and circumneutral pH) of estuarine soils favor Fe reduction microbial pathways, which will probably increase the trace metal bioavailability and contamination risk.

Trypsin purification using magnetic particles of azocasein-iron composite.

This work presents an inexpensive, simple and fast procedure to purify trypsin based on affinity binding with ferromagnetic particles of azocasein composite (mAzo). Crude extract was obtained from intestines of fish Nile tilapia (Oreochromis niloticus) homogenized in buffer (01g tissue/ml). This extract was exposed to 100mg of mAzo and washed to remove unbound proteins by magnetic field. Trypsin was leached off under high ionic strength (3M NaCl). Preparation was achieved containing specific activity about 60 times higher than that of the crude extract. SDS-PAGE showed that the purified protein had molecular weight (24kDa) in concordance with the literature for the Nile tilapia trypsin. The mAzo composite can be reused and applied to purify trypsin from other sources.

Effects of hematite and ferrihydrite nanoparticles on germination and growth of maize seedlings.

Engineered iron oxide nanoparticles (IO-NPs) have been used extensively for environmental remediation. It may cause the release IO-NPs to the environment affecting the functions of ecosystems. Plants are an important component of ecosystems and can be used for the evaluation of overall fate, transport and exposure pathways of IO-NPs in the environment. In this work, the effects of engineered ferrihydrite and hematite NPs on the germination and growth of maize are studied. The germination and growth of maize were done with treatments at different concentrations of hematite and ferrihydrite NPs, namely 1, 2, 4, and 6 g/L. Biological indicators of toxicity or stress in maize seedlings were not observed in treatments with engineered hematite and ferrihydrite NPs. In contrast, the NPs treatments increased the growth of maize and the chlorophyll content, except for hematite NPs at 6 g/L, where non-significant effects were found. The translocation of engineered ferrihydrite and hematite NPs in maize stems was demonstrated using confocal laser scanning microscopy.

Relationship between heavy metals and minerals extracted from soil clay by standard and novel acid extraction procedures.

Strong acid digestions are commonly used to determine heavy metal (HM) contents in soils. In order to understand more fully the acid digestion processes, a logical step is to determine the extent of dissolution of mineral phases. The aims of this study were to compare the efficiency of extraction of HM by different acid digestions and to monitor the associated dissolution of the clay fraction. The context of the study was to develop a milder chemical extraction method (microwave-assisted 1 mol L-1 HNO3 closed system (NACS)), which recovers more reactive HM and with little dissolution of minerals. The different acid digestion methods dissolved different amounts of minerals from the clay fraction. Both aqua regia (AR) and EPA 3051 dissolved all of the Fe and Al oxides, and the dissolution of kaolin was limited to thinner particles (c dimension), smaller particles in a and b dimensions and grains with lower crystallinity. The lower recovery of HM for AR compared with EPA 3051 was related to the large amount of short-range order phases formed during the AR extraction as these phases have the capacity to re-adsorb HM. The new method (NACS) has the potential to replace other methods of determining bioavailable forms of HM, such as AR and EPA 3051. The contents of Pb, As, Co, Zn, and Cu determined by EPA 3051 and EPA 3052 were quite close.