Effective and economically viable method to remove elevated metal(loid)s from farm and industrial lands remains a major challenge. In this study, magnetic biochar-based adsorbents with Fe3O4 ...particles embedded in a porous biochar matrix was synthesized via iron (Fe) treated biochar or thermal pyrolysis of Fe treated cedar sawdust. Application and separation of the adsorbent to a multi-contaminated soil slurry simultaneously removed 20–30% of arsenic, cadmium and lead within 24 h. Fast removal of multi-metal(loid)s result from the decrease in all operationally defined fractions of metal(loid)s, not limited to the exchangeable fraction. The direct removal of arsenic-enriched soil particles was observed via micro X-ray fluorescence maps. Furthermore, through comparison of biochars with different production methods, it has been found that magnetization after pyrolysis treatment leads to stronger metals/metalloids adsorption with a higher qe (bound sorbate) than other treatments but pyrolysis after magnetization stabilized Fe oxides on the biochar surface, indicating a higher biochar recovery rate (∼65%), and thus a higher metal(loid)s removal efficiency. The stability of Fe oxides on the surface of biochar is the determining factor for the removal efficiency of metal(loid)s from soil.
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•Magnetized biochar simultaneously removed As, Cd and Pb from soil.•The direct removal of arsenic-enriched soil particles was observed.•Stability of the magnetic biochar in soil determines removal efficiency.
Magnetic biochar efficiently removed multi-metal(loid)s from soil, with the removal rate mainly determined by the separation process rather than adsorption.
More than 100 million people in Asia are presently exposed to groundwater with arsenic (As) concentrations exceeding the World Health Organization standard of 10μgL−1. Arsenic contaminated ...groundwater within basins of the central portion of the Yangtze River has recently been reported, but the processes controlling arsenic concentrations have yet to be resolved. We examined the hydrologic and geochemical factors controlling arsenic within the Jianghan Plain, an inland sedimentary basin of the Yangtze River, where arsenic concentrations exhibit strong seasonal variability driven by surface and groundwater mixing (Schaefer et al., 2016). Hydrologic fluctuations alter redox conditions in the aquifer, leading to oscillations between arsenic/iron reduction and oxidation. Here we investigate the depth-distribution of solid and aqueous phase iron and arsenic species and, through a series of laboratory manipulations, constrain the biogeochemical processes controlling seasonal changes in groundwater arsenic concentrations. In sediment incubations from ∼20m below the surface, where solid-phase arsenic concentrations exceed 100mgkg−1, both unamended and glucose-amended sediment samples result in arsenic release to the aqueous phase. In situ carbon was capable of promoting As release in the sediment. In contrast, sediment batch incubations from other depths resulted in limited As release. Solid phase arsenic in the enriched zone was relatively oxidized but may become reduced over short time periods. In sediments below the As-enriched zone, glucose amendment resulted in arsenic reduction, but arsenic release to the aqueous phase was restricted by the subsequent formation of arsenic sulfide minerals. Buried sedimentary arsenic coupled with anaerobic microbial respiration of subsurface organic carbon within the Jianghan Plain aquifer leads to rapid release of As to groundwater. Arsenic release from sediments at ∼20m depth is sufficient to explain arsenic concentrations throughout the aquifer, and provides a mechanism to explain how shifts in hydrology result in seasonally variable arsenic concentrations in groundwater.
Arctic tundra stores large quantities of soil organic matter under varying redox conditions. As the climate warms, these carbon reservoirs are susceptible to increased rates of decomposition and ...release to the atmosphere as the greenhouse gases carbon dioxide (CO2) and methane (CH4). Geochemical interactions between soil organic matter and minerals influence decomposition in many environments but remain poorly understood in Arctic tundra systems and are not considered in decomposition models. The accumulation of iron (Fe) oxyhydroxides and organo-iron precipitates at redox interfaces may be particularly important for carbon cycling given that ferric iron Fe(III) species can enhance decomposition by serving as terminal electron acceptors in anoxic soils or inhibit microbial decomposition by binding organic molecules. Here, we examine chemical properties of solid-phase Fe and organic matter in organic and mineral horizons within the seasonally thawed active layer of Arctic tundra on the North Slope of Alaska. Spectroscopic techniques, including micro-X-ray fluorescence (μXRF) mapping, micro-X-ray absorption near-edge structure (μXANES) spectroscopy, and Fourier transform infrared spectroscopy (FTIR), were coupled with chemical sequential extractions and physical density fractionations to evaluate the spatial distribution and speciation of Fe-bearing phases and associated organic matter in soils.
Organic horizons were enriched in poorly crystalline and crystalline iron oxides, and approximately 60% of total Fe stored in organic horizons was calculated to derive from upward translocation from anoxic mineral horizons. Ferrihydrite and goethite were present as coatings on mineral grains and plant debris, and in aggregates with clays and particulate organic matter. Minor amounts of ferrous iron Fe(II) were present in iron sulfides (i.e., pyrite and greigite) in mineral horizon soils and iron phosphates (vivianite) in organic horizons. Concentrations of organic carbon in the organic horizons (28±5wt.% C) were approximately twice the concentrations in the mineral horizons (14±2wt.% C), and organic matter was dominated by base-extractable and insoluble organics enriched in aromatic and aliphatic moieties. Conversely, water-soluble organic molecules and organics solubilized through acid-dissolution of iron oxides comprised <2% of soil organic C and were consistent with a mixture of alcohols, sugars, and small molecular weight organic acids and aromatics released through decomposition of larger molecules. Integrated over the entire depth of the active layer, soils contained 11±4kgm−2 low-density, particulate organic C and 19±6kgm−2 high-density, mineral-associated organic C, indicating that 63±19% of organic C in the active layer was associated with the mineral fraction.
We conclude that organic horizons were enriched in poorly crystalline and crystalline iron oxide phases derived from upward translocation of dissolved Fe(II) and Fe(III) from mineral horizons. Precipitation of iron oxides at the redox interface has the potential to contribute to mineral protection of organic matter and increase the residence time of organic carbon in arctic soils. Our results suggest that iron oxides may inhibit organic carbon degradation by binding low-molecular-weight organic compounds, stabilizing soil aggregates, and forming thick coatings around particulate organic matter. Organic matter released through acid-dissolution of iron oxides could represent a small pool of readily-degradable organic molecules temporarily stabilized by sorption to iron oxyhydroxide surfaces. The distribution of iron in organic complexes and inorganic phases throughout the soil column constrains Fe(III) availability to anaerobic iron-reducing microorganisms that oxidize organic matter to produce CO2 and CH4 in these anoxic environments. Future predictions of carbon storage and respiration in the arctic tundra should consider such influences of mineral stabilization under changing redox conditions.
•Fe speciation in redox-stratified peats is reported.•Fe2+ and Fe3+ co-occur irrespective of redox conditions.•Complexation of Fe with organic matter is the primary stabilization mechanism.•Fe ...(oxy)hydroxide is identified as a secondary Fe species.
The speciation of iron (Fe) in organic matter (OM)-rich environments under in situ variable redox conditions is largely unresolved. Peatlands provide a natural setting to study Fe–OM interactions. Utilizing chemical, spectroscopic and theoretical modeling approaches, we report the chemical forms, oxidation states and local coordination environment of naturally occurring Fe in the vertically redox-stratified Manning peatlands of western New York. In addition, we report dominant carbon, sulfur and nitrogen species that can potentially stabilize the various Fe species present in these peatlands. Our results provide clear direct and indirect evidence for the co-occurrence of ferrous (Fe2+) and ferric (Fe3+) iron species in peats under both oxic and anoxic conditions. Iron is mostly present within the operationally defined organic and amorphous (i.e., short range ordered, SRO) fractions; ferric iron primarily as magnetically isolated paramagnetic Fe3+ in Fe(III)-organic complexes, but also in mineral forms such as ferrihydrite; ferrous iron in tetrahedral coordination in Fe(II)-organic complexes with minor contribution from pyrite. All of the Fe species identified stabilize Fe(III) and/or Fe(II) in anoxic and oxic peats. Fundamental differences are also observed in the relative proportion of C, S and N functionalities of OM in oxic and anoxic peats. Aromatic CC, ester, phenol and anomeric C (ROCOR), as well as thiol, sulfide and heterocyclic N functionalities are more prevalent in anoxic peats. Collectively, our experimental evidence suggests iron forms coordination complexes with O-, S- and N-containing functional groups of OM. We posit the co-occurrence of organic and mineral forms of Fe(II) and Fe(III) in both oxic and anoxic peat layers results from dynamic complexation and hydrolysis-precipitation reactions that occur under variable redox conditions. Our findings aid in understanding the crucial role OM plays in determining Fe species in soils and sediments.
Melanin is a ubiquitous biological pigment found in bacteria, fungi, plants, and animals. It has a diverse range of ecological and biochemical functions, including display, evasion, photoprotection, ...detoxification, and metal scavenging. To date, evidence of melanin in fossil organisms has relied entirely on indirect morphological and chemical analyses. Here, we apply direct chemical techniques to categorically demonstrate the preservation of eumelanin in two > 160 Ma Jurassic cephalopod ink sacs and to confirm its chemical similarity to the ink of the modern cephalopod, Sepia officinalis . Identification and characterization of degradation-resistant melanin may provide insights into its diverse roles in ancient organisms.
The Paleocene high volatile B bituminous Raša coal, mined on the Istrian Peninsula, Croatia, for nearly 400 years up to 1999, is notable in having a superhigh organic sulfur (SHOS) content, exceeding ...11% in some cases. The latter feature contributed to interest in the coal, far outweighing its status as a locally-used coal. Investigation by organic petrology, X-ray diffraction mineralogy, X-ray fluorescence and ICP-MS chemistry, SEM-EDS and TEM-EDS-SAED, micro-FTIR spectroscopy, and Raman spectroscopy showed that the Raša coal is dominated by vitrinite-group macerals, CaO and SO3, carbonate minerals with contributions by Sr- and Ba-sulfates at the sub-micron scale, and the contribution of sulfur to the organic structure. Compared to Chinese SHOS coals and world ash, a majority of analyzed trace elements in Raša coal and ash, respectively, were depleted (up to 0.8 times), with the exception of V, Se, Sr, and Ba, which were increased 1.7 to 26 times. This fact, supported by elevated trace element concentrations in dripstone, are evidence for weathering of Raša coal by underground water, which is contaminating the local environment with trace elements, selenium in particular. Results of this study warrant further research.
•The Paleocene Raša coalm Istria, Croatia, was mined for nearly 400 years.•The coal is noted to be a superhigh organic sulfur coal.•FTIR and Raman spectroscopy showed CS, C–S, and S–S bonds.•TEM indicated the presence of Sr and Ba sulfates, alglesite, and REE-bearing niobate.
The kaolinite-group minerals kaolinite, dickite, nacrite, halloysite including its metaform and their associates allophane and imogolite are phyllosilicates characterized by a rather simple chemical ...composition of Si, Al, O, and H. These elements contribute for the most part to the built-up of the continental earth crust, which down to a depth of approx. 1.5km, consists of 75% of sedimentary rocks. In a sense, kaolinite-group minerals accommodating these elements in their structure chemically reflect the uppermost part of the crust. It is not a surprise that kaolin is very widespread particularly in those sedimentary rocks which came into existence under near-ambient conditions and, as a further consequence, is a mirror image of those processes taking place in the topmost parts of the crust. In a tripartite subdivision (primary: magmatic/structure bound, secondary: sedimentary, tertiary: metamorphic), the following environments bearing kaolin exist: Primary environments of kaolinization: (1) Vein-type deposits, (2) (sub) volcanic and pyroclastic deposits, (3) skarn to epithermal deposits, (4) granitic rocks and their affiliated rocks (pegmatites and greisen). Secondary environments of kaolinization:(1) kaolin and soil (ferralsols, plinthosols, nitisols, podzols, vertisols, andosols), (2) layered residual kaolin deposits (mixed-type residual kaolin-bauxite deposits, exposed residual kaolin, hidden residual kaolin), (3) vein-like kaolin, (4) alluvial-fluvial environments (alluvial fans, fluvial braided streams, fluvial meandering streams),(5) prograding fluvial deltas (prograding into a playa (dry delta), prograding into a marine or lacustrine basin (wet delta)),(6) lakes and ponds (permanent and ephemeral lakes), (7) coal-bearing environments (suspended load deposits in coal swamps, underclays, composite residual and hydrothermal kaolinization in coal swamps, kaolin tonsteins), (8) marine terrigenous shoreline deposits (open - tide-dominated estuary, blind - wave-dominated estuary, sealed-off lagoon). Tertiary environments of kaolinization: (1) burial diagenesis, (2) very-low grade regional dynamo metamorphism, (3) contact metamorphism. The above tripartite subdivision of kaolin has been established so as to be in accordance with other lithologies which formed through magmatic, sedimentary, and metamorphic processes and to link the present classification scheme directly with the "Chessboard classification scheme of mineral deposits" (Dill, 2010b). While in many classification schemes of mineral deposits kaolin and its minerals were only considered as an "ore" in the category non-metallic deposits and industrial minerals, in the current review the barriers between economic geology and its neighboring disciplines like sedimentology, pedology, geomorphology, petrography and palaeoclimatology have been torn down and the kaolin looked at from different angles, as soil, rock and ore. Kaolin and kaolinitic clays are taken as the type-lithology of the near-surface continental environments. Together with bentonites, bentonitic clays and a varied spectrum of argillites they form part of a group of lithologies, encompassing besides bauxite, ferrites (ferricretes) and laterite, all of which developed close to the interface between atmosphere, pedosphere, hydrosphere, and lithosphere. To accentuate the intimate relation between the various lithologies mentioned in the previous paragraph, a classification scheme has been designed. It makes use in part of pre-existing ternary plots to take also account of these interferences with the different geoscientific disciplines such as sedimentology or pedology. In addition to that, an overview of the various field and laboratory methods to identify and quantify kaolin/kaolinite-group minerals is given. The succeeding parameters, features and settings are crucial as to the kaolinization in the magmatic, sedimentary and metamorphic environments. Geodynamic setting The sites most favorable to develop large (economic) kaolin deposits are located along the passive continental margin and in epicontinental basins. Almost all of the kaolin deposits have to be attributed to the secondary deposits. Rate of uplift and weathering Cratonic crustal sections stable over a long period of time with little vertical displacement are crustal sections favorable for kaolin formation and preservation. During slow uplift, chemical weathering operative in the peneplained hinterland and on the sedimentary bodies in the foreland helped to decompose labile constituents from the parent material and enhance the quality and increase the thickness of the kaolin. Reducing the slope angle or the paleogradient, i.e., moving from the alluvial-colluvial fan system towards deltaic and swampy environments raises the likelihood of kaolin concentration of economic grade. The drainage pattern and hydrography The fluvial drainages system most proximal to the residual kaolin and most favorable for kaolin is the braided-stream drainage system. In the meandering-river system two different types "bar sand kaolin" and the "overbank kaolin deposits" occur. Kaolin accumulation may be tracked down to the coastal marine deposits under humid climatic conditions. Rivers are accountable for a steady supply of suspended load, the tidal processes is held most effective in concentrating the fine-grained raw material and wave action in combination with the transgression and regression of strandlines act as a seal and preserve the kaolin deposit. The tidal analogues developing under arid climatic conditions, also known as coastal sabkha, are of no relevance for kaolin concentration. The most well-balanced state between concentration and preservation of kaolin is achieved in the blind estuary under a mesotidal regime. Organic matter and the redox regime The organic matter has no effect on the formation of kaolin in the primary deposits. In the secondary kaolin...
A series of laboratory experiments were conducted to examine how partitioning of Fe among solid reaction products and rates of H sub(2) generation vary as a function of temperature during ...serpentinization of olivine. Individual experiments were conducted at temperatures ranging from 200 to 320 degree C, with reaction times spanning a few days to over a year. The extent of reaction ranged from <1% to similar to 23%. Inferred rates for serpentinization of olivine during the experiments were 50-80 times slower than older studies had reported but are consistent with more recent results, indicating that serpentinization may proceed more slowly than previously thought. Reaction products were dominated by chrysotile, brucite, and magnetite, with minor amounts of magnesite, dolomite, and iowaite. The chrysotile contained only small amounts of Fe (X sub(Fe) = 0.03-0.05, with similar to 25% present as ferric Fe in octahedral sites), and displayed little variation in composition with reaction temperature. Conversely, the Fe contents of brucite (X sub(Fe) = 0.01-0.09) increased steadily with decreasing reaction temperature. Analysis of the reaction products indicated that the stoichiometry of the serpentinization reactions varied with temperature, but remained constant with increasing reaction progress at a given temperature. The observed distribution of Fe among the reaction products does not appear to be entirely consistent with existing equilibrium models of Fe partitioning during serpentinization, suggesting improved models that include kinetic factors or multiple reaction steps need to be developed. Rates of H sub(2) generation increased steeply from 200 to 300 degree C, but dropped off at higher temperatures. This trend in H sub(2) generation rates is attributable to a combination of the overall rate of serpentinization reactions and increased partitioning of Fe into brucite rather than magnetite at lower temperatures. The results suggest that millimolal concentration of H sub(2) could be attained in moderately hot hydrothermal systems like Lost City during fluid circulation on timescales of a few years.
Abstract Global magmatic trends inferred from gamma‐ray, visible/near‐infrared, and thermal infrared spectrometers on Mars‐orbiting spacecraft have been used to constrain planetary petrogenetic ...processes and global thermal evolution models. Inferred magmatic trends include temporal variations in the relative proportions of low‐Ca and high‐Ca pyroxenes, and in the abundances of potassium (and total alkalis), silica, FeO* (total iron expressed as FeO), and thorium. These patterns are evaluated for consistency with the compositions of surface igneous rocks of different ages analyzed by Mars rovers and of martian meteorites. Trends of decreasing low‐Ca pyroxene/total pyroxene ratios and of decreasing potassium (and total alkalis), with time are generally supported by surface rock analyses. However, significant differences in the GRS‐measured silica in Amazonian volcanoes and in martian meteorites of equivalent age result from contamination by silica‐rich dust and are problematic for a silica trend. Comparison of FeO* in Noachian and Amazonian surface data shows no decrease. An inferred temporal trend in thorium is in conflict with the complex enrichment and depletion patterns of incompatible trace elements in martian meteorites of various ages. A dearth of analyses of Hesperian‐age surface rocks precludes a firm evaluation of inferred Noachian‐Hesperian trends and Hesperian‐Amazonian trends, but abundant Noachian rocks and a few Hesperian rocks at rover sites, and Amazonian martian meteorites, collectively representing at least 16 surface locations, afford useful comparisons with orbital remote‐sensing data.
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