Iron-rich Water Research Articles

Productivity and organic carbon loading control uranium isotope behavior in ancient reducing settings: Implications for the paleoredox proxy

Uranium isotopes in ancient sedimentary rocks have emerged as a powerful proxy for the oxygenation history of Earth surface environments. Proper quantitative interpretation of δ238U data hinges, however, on an understanding of isotopic fractionation associated with uranium removal to sediments under different redox conditions. Whereas oxygenated environments are plentiful in the modern ocean, euxinic settings are scarce today, and persistently ferruginous settings are not a feature in the modern ocean, leaving lakes as our best analogs for iron-rich waters. These challenges to studying δ238U behavior under contemporaneous oxic, euxinic (sulfidic), and ferruginous (iron-rich) marine conditions limit our ability to apply the isotope proxy to ancient oceans. Here, we present δ238U data from five coeval cores through the Lower Mississippian Sunbury Shale of the semi-restricted Appalachian Basin (North America), which were deposited across a strong redox gradient from intermittently oxic conditions proximal to the Catskill Delta, to ferruginous conditions in the central basin axis and euxinic conditions along the basin-bounding Cumberland Sill. Overall, we find that both euxinic and ferruginous environments are capable of imparting high degrees of uranium isotope fractionation and that δ238U values covary more strongly with total organic carbon (TOC) and trace metal abundances than they do with the presence of euxinic versus ferruginous conditions. We suggest uranium sorption or incorporation into sinking organic matter in the water column as a mechanism for generating positive covariation between δ238U and TOC, particularly at lower TOC concentrations. We also compare our δ238U data to broadly coeval carbonates from Nevada, which can be used to estimate Early Mississippian seawater δ238U values. We find that Sunbury Shale cores deposited under stably anoxic conditions (both euxinic and ferruginous) and under consistently brackish salinities away from freshwater sources record an increasing δ238U trend through time that loosely mirrors the record for carbonates (and thus estimates for seawater) with an offset of ∼0.4‰ to 1.1‰, depending on the inferred offset between carbonate and seawater. In contrast, cores deposited close to the Catskill Delta and in a shallow oceanic-restricted basin transition across the Cumberland Sill record a decreasing δ238U trend through time, opposite the inferred seawater trend and suggestive of entirely local controls on δ238U values. Ultimately, these data suggest that highly productive environments with high rates of organic carbon loading can exert a strong control on the global δ238U mass balance regardless of whether euxinic or ferruginous conditions are present. These results necessitate a partial reassessment of the processes controlling δ238U variability in seawater and sedimentary rocks through Earth history.

Fate of micropollutants in a lab-scale urban wastewater system: Impact of iron-rich drinking water treatment sludge

Iron rich drinking water treatment sludge (Fe-DWTS) could be a potential alternative for Fe salts in controlling sulfide in the sewer network. This study investigated the impact of in-sewer dosed Fe-DWTS on the fate of 26 different intrinsic organic micropollutants in wastewater by using a lab-scale integrated system consisting of sewer reactors and a sequential batch reactor (SBR) to simulate urban wastewater collection and treatment. The batch results revealed that seven among these 26 compounds had higher removal in the Fe-DWTS dosed sewer reactor compared to the control sewer reactor. In contrast, the removal of 7 out of the 26 investigated compounds were reduced, along with the biofilm methanogenic activity due to the long-term Fe-DWTS dosing. Cycle experiments in the SBR showed that the removal of acesulfame was enhanced and the formation of carbamazepine, desvenlafaxine, tramadol and hydrochlorothiazide were reduced, compared to their behaviour in the control SBR. However, the long-term experiments showed no adverse or beneficial effect of in-sewer dosed Fe-DWTS on the removal of most micropollutants in the SBR. Codeine, trimethoprim and gabapentin were exceptions with slightly higher concentrations in the experimental SBR effluent, possibly due to change in microbial composition.

Porous 3D-Biocomposite Adsorbent for Iron Reclamation and Use in Agricultural Applications

The essential nutrients (e.g., iron) for food production are nonrenewable resources, which cannot satisfy the need of a fast-growing global population. Meanwhile, excessive irons accumulated in iron-rich water pose an adverse effect on human and ecosystem health. Thus, it is necessary to develop a cost-effective and eco-friendly adsorbent for reclaiming irons from iron-accumulated water and which cannot satisfy the need of a fast-growing global population. Meanwhile, excessive irons accumulated in iron-rich water pose an adverse effect on human and ecosystem health. Thus, it is necessary to develop a cost-effective and eco-friendly adsorbent for reclaiming irons from iron-accumulated water and these irons for growing crops. In this study, a simple gelation–solidification process aided by phase separation is developed to fabricate a biodegradable alginate/polyvinyl alcohol/lignosulfonate (SA/PVA/LS) three-dimensional (3D) biocomposite adsorbent. Calcium chloride and boric acid are used as cross-linkers between polymers with hydroxyl groups. This bioadsorbent owns a multiporous architecture, ample functional groups, and enhanced total pore volume. A multilayer adsorption mechanism endows it with a high iron adsorption capacity (52 mg/g) via Langmuir simulation and a physiochemical adsorption mechanism. The porous 3D structure of the biocomposite could be observed from SEM and CT scanning. After iron loading, it can be applied as an excellent substitute for a commercial EDTA-Fe micronutrient to promote plant growth with a comparable ratio of root to shoot length. This eco-friendly, highly efficient, and filled 3D bioadsorbent is expected to open a door to achieving circular recovery of plant essential plant nutrients from waste resources for crop production.

In situ stabilization of arsenic and lead in contaminated soil using iron-rich water treatment residuals.

Arsenic (As) and lead (Pb) are common soil contaminants, environmentally hazardous, and threats to public health. Addition of soluble phosphate is known to be effective for in situ remediation of Pb-contaminated soils, but phosphate additions displace As from the soil particles and increase As concentration in soil solution. This study examined the dual use of iron (Fe) and phosphorus (P) amendments to soil that was highly contaminated with As and Pb. The test soil originated from a former smelter site in Utah with As and Pb concentrations of 66,400mgPbkg-1 and 7,520mg As kg-1 . Goethite, ferrihydrite, and Fe-rich water treatment residuals (Fe-WTRs) were added to immobilize As, and soluble P was added to reduce Pb lability. The Fe amendments were added in Fe/As molar ratios ranging from 1:1 to 1:10, and P was added in P/Pb molar ratios ranging from 0.2:1 to 5:1. Iron-rich water treatment residuals were found to be the most effective Fe amendment. When Fe-WTR and P were added simultaneously, the P concentrations required to immobilize Pb resulted in increased mobilization of As, even when Fe-WTR were added at 10:1 Fe/As. However, when P was added first at 5:1 P/Pb, incubated for 1 wk, and then amended with Fe-WTR at 10:1 Fe/As, both Pb and As were significantly immobilized. The proposed process is a practical remediation approach to soils co-contaminated with Pb and As while encouraging re-use of Fe-WTR as a sustainable amendment.

Modified chemical mineralization-alkali neutralization technology: Mineralization behavior at high iron concentrations and its application in sulfur acid spent pickling solution

Mineralization coupled with neutralization is a dual-function technology for disposing acidic iron-rich waters, which can recover the valuable iron in the form of secondary mineral and concurrently purify the wastewater. In this study, a modified technology for treating high Fe wastewater (sulfur acid spent pickling liquor, 62 g Fe/L) was proposed based on the specific investigation of the mineralization behaviors in Fe concentration range of 20–70 g/L. Results showed that high SO42−/Fe2+ molar ratio (> 2.0) tended to trigger gelation phenomena at Fe concentrations above 30 g/L. Fe specie distribution suggested that the insufficient polymerization among Fe-OH complexes might be responsible for the gelation phenomena, since the strong Fe-SO4 coordination almost completely suppressed the Fex(OH)y(3x-y)+ form (a general terms of Fe3+ hydrolysates and their polymers). Modified mineralization strategies were proposed, including pretreatment with dilution or BaCl2/CaCl2 precipitation, of which CaCl2 pretreatment was a versatile and low-cost method. Following CaCl2 pretreatment, chemical mineralization converted above 90% of iron into secondary mineral, which therefore drastically reduced the alkali consumption (from 164.2 g/L to 1.4 g/L) and sludge yield (from 328.1 g/L to 2.4 g/L) in subsequent neutralization treatment. The resultant mineral was identified as schwertmannite, and exhibited efficient adsorption capacity toward arsenite (364.2 mg/g). The modified chemical mineralization-alkaline neutralization is a cost-effective technology for the treatment of the acidic iron-rich waters. In practical applications, several regulating strategies should be further explored to improve the mineral purity, and the mineralization conditions must be optimized according to the Fe and SO42− concentrations in wastewater.

A Modified Non Electrical Filter for Decontamination of Iron Rich Water for Rural Application

A non-electrical filter is designed to cater the need of providing iron free water in forward and rural areas. The features of the unit are equipped with the aeration system and activated sand chemically coated by iron oxide as catalytic and filtering media which can bring down iron concentration from 12 mg/L to desirable limit. It increases the pH of water from acidic to pH above 7. This is in contrast to some indigenous water filter which existed in the North Eastern India that tend to remove iron below 4 mg/L. The modified filter is effective in reducing excess total dissolved solids (TDS) from drinking water. All other physical parameters found to be within the prescribed limit. It can give iron free water with output capacity of 25L/hr. The added advantage of the unit is the provision for back washing of the filter media and collection point of the precipitated iron at the lower bottom of the tank for safe discharge.

Biofouling, metal sorption and aggregation are related to sinking of microplastics in a stratified reservoir

Microplastic particles entering aquatic systems are rapidly colonized by microbial biofilms. The presence of microbial biomass may cause sinking of particles and as a consequence prevent their transport to the oceans. We studied microbial colonization of different polymer particles exposed in the epi-, meta- and hypolimnion of a freshwater reservoir during late summer for 47 days. Parameters measured included biofilm formation, metal sorption and sinking velocities. Microbial biofilms contained bacteria, cyanobacteria and algae as well as inorganic particles such as iron oxides. Regardless of biofilm thickness and biovolumes of different biofilm constituents, single polyethylene (PE) particles stayed buoyant, whereas the sinking velocity of single polystyrene (PS) and polyethylene terephthalate (PET) particles did not change significantly compared to initial values. During exposition, a mixing event occurred, by which anoxic, iron-rich water from the hypolimnion was mixed with water from upper layers. This induced aggregation and sinking of hypolimnetic PE particles together with organic matter, cyanobacteria colonies and iron minerals.

Dissolved iron in the Bermuda region of the subtropical North Atlantic Ocean: Seasonal dynamics, mesoscale variability, and physicochemical speciation

Water-column data from seven cruises in 2007–2008 reveal pronounced temporal and spatial variations in the distribution of dissolved iron (DFe, <0.4 μm) over the upper 1000 m of the Sargasso Sea near Bermuda, in the western subtropical North Atlantic Ocean. In near-surface waters, DFe exhibits a clear seasonal cycle, increasing from ~0.1–0.3 nM in spring to ~0.4–1.0 nM in summer-early fall. The observed seasonal ranges appear to reflect the extent of winter convective mixing and of summer dust deposition, both of which are closely tied to atmospheric circulation processes. Surface DFe concentrations also show significant (~two-fold) submesoscale lateral variations during summer, perhaps as a result of lateral inhomogeneities in wet deposition and wind-driven mixing. The summer vertical profiles reveal pronounced DFe minima and sometimes deeper maxima in the lower euphotic zone, which likely reflect biological uptake and shallow remineralization, and eddy-driven lateral gradients in these processes. Significant variability is also seen in the mesopelagic zone, with a DFe concentration range of ~0.4–0.7 nM at 1000 m depth, which may reflect mesoscale isopycnal displacements and/or lateral advection of iron-rich waters in the lower thermocline. Physicochemical iron speciation measurements indicate that the major fraction of DFe that accumulates in surface waters of the Sargasso Sea during summer is colloidal-sized Fe(III), which appears to be complexed by strong, iron-binding organic ligands. Concentrations of soluble iron (sFe, <0.02 μm) were considerably lower than DFe in the upper euphotic zone during summer, except over the subsurface DFe minima, where sFe accounts for ~50–100% of the DFe pool. Labile Fe(II), on average, accounted for around 20% of DFe, with maximum concentrations of around 0.1 nM in near-surface waters and in the lower thermocline. The seasonal-scale DFe changes that we have documented near Bermuda are of the same magnitude as basin-scale lateral gradients across the North Atlantic, underscoring the importance of time-series observations in understanding the behavior of trace elements in the upper ocean.

Sources and transformations of iron in the sediments of the Gulf of Aqaba (Red Sea)

The Gulf of Aqaba is an oligotrophic marine system with an oxygen-rich water column. Aeolian dust from the Arabian, Sinai, and Sahara deserts is an important source of sedimentary material to the gulf, especially at 700 m water depth. The head of the gulf is affected by sediment transport from the Arava desert during winter flash floods. In this work, we have studied the speciation of iron in the dust, dry creek sediments and sediments of the Gulf of Aqaba at various water depths in order to understand sources and transformations of iron. Two sources of iron, dust and flash floods transported material, were found to possess distinct geochemical signatures: dust was found to be enriched in total and highly reactive iron relative to the sediments in creek beds. Combination of these two sources leads to an increase of highly reactive iron in sediments with water depth. This increase, in turn, results in formation of a lateral redox gradient with sulfidic pore-waters near the shore, and ferruginous-manganous pore-waters and cryptic sulfur cycling at the deeper water sites. Another result of dry aeolian deposition of desert dust to the sediments of the Gulf of Aqaba, overlaid by deep well‑oxygenated waters, is anomalously high ratios of highly reactive to total iron, which have been proposed to be diagnostic for anoxic, iron-rich water columns, when applied as a paleoproxy.

High Diversity in Iron Cycling Microbial Communities in Acidic, Iron-Rich Water of the Pyhäsalmi Mine, Finland

Microbial communities of iron-rich water in the Pyhäsalmi mine, Finland, were investigated with high-throughput amplicon sequencing and qPCR targeting bacteria, archaea, and fungi. In addition, the abundance ofLeptospirillumandAcidithiobacilluswas assessed with genus-specific qPCR assays, and enrichment cultures targeting aerobic ferrous iron oxidizers and ferric iron reducers were established. The acidic (pH 1.4–2.3) mine water collected from 240 m, 500 m, and 600 m depth from within the mine had a high microbial diversity consisting of 63-114 bacterial, 10-13 archaeal, and 104-117 fungal genera. The most abundant microorganisms in the mine water were typical acid mine drainage (AMD) taxa, such as acidophilic, iron-oxidizingLeptospirillum,Acidiphilum,Acidithiobacillus,Ferrovum, andThermoplasma. The fungi belonged mostly to the phylum Ascomycetes, although a great part of the fungal sequences remained unclassified. The number of archaeal 16S rRNA genes in the mine water was between 0.3 and 1.2 × 107copies mL−1in the samples from 500 m and 600 m, but only 3.9 × 103at 240 m and archaea were in general not enriched in cultures. The number of fungal 5.8S rRNA genes was high only in the mine water from 500 m and 600 m, where 0.2–3.4 × 104spore equivalents mL−1were detected. A high number ofLeptospirillum16S rRNA genes, 0.6–1.6 × 1010copies mL−1, were detected at 500 m and 600 m depth and in cultures containing ferrous iron, showing the importance of iron oxidizers in this environment. The abundance of bacteria in general was between 103and 10616S rRNA gene copies mL−1. Our results showed a high microbial diversity in the acid- and iron-impacted waters of the Pyhäsalmi mine, whereLeptospirillumbacteria were especially prominent. These iron oxidizers are also the main nitrogen-fixing microorganisms in this ecosystem.

Gulf Stream rings as a source of iron to the North Atlantic subtropical gyre

Substantial amounts of nitrogen fixation occur in the North Atlantic subtropical gyre, due to the activity of cyanobacteria with high iron requirements. Iron is delivered to this region by dust from the Sahara Desert. However, this dust deposition is typically localized and episodic. Therefore, other sources of iron may also be important. Here, we report observations of dissolved iron concentrations in a Gulf Stream cold-core ring, which transported iron-rich water from near the continental slope into the subtropical gyre. We find that iron concentrations were elevated in the ring compared with subtropical waters, reflecting its source waters. Using iron data from these source waters and the identification of ring activity in satellite data, we estimate that cold-core rings provide a net flux of 0.3 ± 0.17 × 108 mol Fe yr−1 across the northwestern gyre edge, on the order of 15% of our median estimates of gyre-wide supply of iron by dust deposition. We suggest that iron supply from cold-core rings is an important source of iron to the northwestern gyre edge. We conclude that mesoscale ocean circulation features may play an important role in subtropical nutrient and carbon cycling.

Influence of Tropical Instability Waves on Phytoplankton Biomass near the Marquesas Islands

The Marquesas form an isolated group of small islands in the Central South Pacific where quasi-permanent biological activity is observed. During La Niña events, this biological activity, shown by a net increase of chlorophyll-a concentration (Chl, a proxy of phytoplankton biomass), is particularly strong. It has been hypothesized that this strong activity is due to iron-rich waters advected from the equatorial region to the Marquesas by tropical instability waves (TIWs). Here we investigate this hypothesis over 18 years by combining satellite observations, re-analyses of ocean data, and Lagrangian diagnostics. Four La Niña events ranging from moderate to strong intensity occurred during this period, and our results show that the Chl plume within the archipelago can be indeed influenced by such equatorial advection, but this was observed during the strong 1998 and 2010 La Niña conditions only. Chl spatio-temporal patterns during the occurrence of other TIWs rather suggest the interaction of large-scale forcing events such as an uplift of the thermocline or the enhancement of coastal upwelling induced by the tropical strengthening of the trades with the islands leading to enhancement of phytoplankton biomass within the surface waters. Overall, whatever the conditions, our analyses suggest that the influence of the TIWs is to disperse, stir, and, therefore, modulate the shape of the existing phytoplankton plume.

Mutual effect of Phragmites australis, Arundo donax and immobilization agents on arsenic and trace metals phytostabilization in polluted soils

This study assessed the suitability of Phragmites australis and Arundo donax for the aided phytostabilization of metal(loid)s in polluted soils treated with an iron-rich water treatment residue (Fe-WTR), a municipal solid waste compost (MSW-C) and their combination (Fe-WTR+MSW-C). The three soils under study (S1, S2, S3) showed very high total concentrations of As (from 371 to 22,661mg·kg−1 d.w.) and variable amounts of co-occurring trace metals (TMs) (i.e. Pb, 74–2162; Zn, 57-1535 and Cu, 19–412mg·kg−1 d.w.). Results showed that P. australis and A. donax biomass was significantly increased in all the amended soils and followed the order: MSW-C>Fe-WTR+MSW-C>Fe-WTR>Control. For both plant species grown in the amended soils, metal(loid)s concentration in below ground organs were higher than those in above ground tissues. In S1 soil (the most polluted and acidic; pH3.77), the highest As bioaccumulation factors (BAFs) were recorded for plants grown on untreated soil (approx. 45% higher with respect to those recorded for plants in treated soils), where the concentration of labile As was significantly higher with respect to amended soils. By contrast, in S2 and S3 soils, the most effective As bioaccumulator plants were grown on soils treated with compost, even if the addition of this amendment induced a decrease of the soil As extractability. Similar results were detected for TMs in S1 soil, where P. australis and A. donax grown on soil amended with compost showed the highest Pb, Zn and Cu BAFs, while variable results were detected in S2 soil. The lowest As translocation factors (TFs ≪1.0) were detected for plants grown on compost-amended soils (25 and 51, 34 and 50, 64 and 55% lower with respect to P. australis and A. donax control plants in S1, S2 and S3 soils respectively), while TMs translocation from roots to shoots was more variable and depending on soil, TMs, amendment and plant species.Overall, our results indicate the suitability of P. australis and A. donax, and of Fe-WTR and MSW-C, for the aided phytostabilization of soils contaminated with arsenic and trace metals.

Chalcopyrite dissolution: Scanning photoelectron microscopy examination of the evolution of sulfur species with and without added iron or pyrite

Dissolution and oxidation of sulfide minerals play key roles in both acid and metalliferous rock drainage and supergene enrichment. Surface speciation heterogeneity, critical to understanding mechanisms of mineral sulfide dissolution, has to date largely not been considered. To this end synchrotron scanning photoelectron microscopy (SPEM) was employed to examine freshly fractured and partially dissolved chalcopyrite (CuFeS2) surfaces (pH 1.0 HClO4 solution, redox potential 650mV relative to a standard hydrogen electrode, 75°C). S2− (bulk), S22− and Sn2− were found to be present on all samples at varying concentrations. Oxidation was observed to take place heterogeneously at the sub-micron scale. As compared to chalcopyrite partially dissolved for 5days, extended dissolution to 10days did not show appreciably enhanced oxidation of surface species; however surface roughness increased markedly due to the growth/overlap of oxidised sulfur species. On addition of 4mM iron both S0 and SO42− were observed but not SO32−, indicating that the greater Fe3+ activity/concentration promotes heterogeneous sulfur oxidation. On contact of pyrite (FeS2) with chalcopyrite, significantly greater chalcopyrite surface oxidation was observed than for the other systems examined, with S0, SO32− and SO42− being identified heterogeneously across the surface. It is proposed that chalcopyrite oxidative dissolution is enhanced by increasing its cathodic area, e.g. contacting with pyrite, while increased Fe3+ activity/concentration also contributes to increased dissolution rates. The high degree of surface heterogeneity of these surface products indicates that these surfaces are not passivated by their formation. These results suggest that chalcopyrite dissolution will be accelerated when in contact with pyrite at solution redox potential intermediate between the rest potentials of chalcopyrite and pyrite (560mV and 660mV, respectively) and/or iron rich acidic waters with resulting enhanced formation of secondary sulfur containing species and release of copper and iron. This in turn suggests accelerated supergene formation and enhanced metalliferous drainage under these conditions.

Use of municipal solid wastes for chemical and microbiological recovery of soils contaminated with metal(loid)s

Iron-rich water treatment residues (Fe-WTRs) and municipal solid waste compost (MSWC) were added together at two different total rates (i.e. 0.5% Fe-WTRs+0.5% MSWC and 1% Fe-WTRs+1% MSWC) to a degraded sub-alkaline soil (pH 8.0) contaminated with Sb (∼110 mg kg−1 soil), Pb (∼1200 mg kg−1), Cd (∼23 mg kg−1), and Zn (∼5400 mg kg−1). A large number of chemical and biological endpoints were evaluated to assess the efficacy of the treatments after five months of incubation. Both treatments significantly reduced the labile fractions of the metal(loid)s in soil, especially Sb, while increasing the abundance of culturable heterotrophic bacteria, actinomycetes and fungi (i.e. up to 6.3-, 1.6- and 4.1-fold higher than control respectively). Soil enzyme activities, i.e. dehydrogenase, β-glucosidase and urease, were also significantly enhanced in the treated soils (i.e. up to ∼12-, 3- and 2-fold higher than control respectively). The amendment addition affected the structure of the soil microbial community as highlighted by the higher metabolic potential and catabolic versatility of treated soils (Biolog CLPP) and by the significantly higher α-diversity values based on high throughput partial 16S rRNA gene sequencing. Moreover, analysis of the dominant operational taxonomic units (OTUs) showed differences in the microbial communities of untreated and treated soils. Plant growth (Helichrysum italicum) in the treated soils was greatly stimulated while metal(loid)s uptake was significantly reduced. Overall, the results indicated that the applied treatment could be ideal for the chemical and (micro)biological recovery of sub-alkaline soils contaminated with Sb and co-occurring metals, and H. italicum appears to be a promising plant species for aided phytostabilisation of such soils.

Dakhla–Kharga iron-rich paleosols, Western Desert, Egypt: geology, geochemistry, and mineralization

The purpose of the present paper is to identify the source of iron oxides as well as the paleo-oxygenation conditions by using major oxide and trace element geochemistry of the Quseir and Sabaya formations exposed at the Dakhla–Kharga basin, Western Desert, Egypt. The iron-rich paleosol occurs chiefly overlying different Upper Cretaceous rocks, particularly the red clay of the Campanian Quseir Formation at the Dakhla Oasis or the Cenomanian Sabaya Formation at the Kharga Oasis. The iron-rich paleosols consist mainly of massive yellow goethite-rich beds with high concentrations of Fe(OH). The presence of high Fe/Mn ratio with a wide range of variation indicates that the sources of the iron-rich paleosols are from the discharge of iron-rich Nubian Aquifer water controlled largely by localized fractures which formed spring mounds deposited of Pleistocene age. These mounds were exposed to subaerial weathering that resulted in the formation of lateritic goethite ore during tropical climatic periods. There is evidence of hydrothermal vents (hot spring) such as found native Au, magnetite. and high concentrations of zirconium, cobalt. and vanadium. In the depositional history of Mut and Zayat ironstones, four main processes will be clarified as follows: (1) the syn-depositional, (2) diagenetic, (3) hot spring processes, and (4) post-diagenetic (soil formation). At the end, the high Fe2O3 concentrations and replacement of lithic fragments by microcrystalline goethite indicate that the Dakhla–Kharga sedimentary rocks were subjected to ferrugination. These alterations thought to be result of either post-depositional hydrothermal alteration or syn-depositional interaction with seawater at low temperatures or some combination of the two processes.

Influence of iron-rich water treatment residues and compost on the mobility of metal(loid)s in mine soils

Two different amendments, an iron-rich water treatment residue (Fe-WTR), a municipal solid waste compost (MSW-C) and their combination (Fe-WTR+MSW-C) were added at different rates (from 2 to 4% w/w) to three mining soils (S1, S2, S3) mainly polluted with As (from 371 to 22,661mg·kg−1d.w.) and different co-occurring trace metals (i.e. Pb, Zn and Cu) to evaluate their effectiveness as metal(loid)s-immobilizing agents. After four months of soil-amendment contact, sequential extractions revealed that MSW-C and Fe-WTR induced an increase of the residual As (non-extractable) fraction. Compost was the most effective amendment at increasing the residual As in treated soils (e.g. +16% in S1-MSW-C with respect to untreated S1), although its addition increased at the same time the exchangeable and water-soluble As fraction and the extractability of Pb, Zn and Cu, especially in S1-MSW-C. Leaching experiments highlighted a similar trend, with the highest cumulative fraction of As leached recorded in S1 and S2 soils amended with MSW-C (3.8 and 1.4-fold higher than respective controls), and the lowest recorded in S1 and S2 soils amended with Fe-WTR (1.2 and 1.8-fold lower than respective controls). On the other hand, Fe-WTR and Fe-WTR+MSW-C were the most effective at reducing the total cumulative concentration of metal (Pb, Zn and Cu) in soil leachate. The results of this study show that the amendments considered influenced with a different extent metal(loid)s mobility, and this was depending on soil and amendment characteristics, as well as the type and amount of contamination.

The relative roles of modified circumpolar deep water and benthic sources in supplying iron to the recurrent phytoplankton blooms above Pennell and Mawson Banks, Ross Sea, Antarctica

The role that dissolved iron (dFe) rich Circumpolar Deep Water (CDW) might play in sustaining the consistently observed discrete patches of high chlorophyll biomass over Pennell Bank (PB) and Mawson Bank (MB) in the Ross Sea, was investigated during January/February 2011. Over a 26-day period, hydrographic and trace metal clean water sampling was carried out adjacent to both of these banks, in some cases repeatedly. Particulate sampling was also accomplished at selected stations by in situ pumping. The results indicate that the dFe content of the CDW is in fact reduced by on-shelf mixing with Antarctic Surface Water as it transitions into modified CDW (MCDW). Our stations above PB, where the maximum bloom is encountered, show no evidence of MCDW presence. In contrast, above MB, where there is a smaller persistent bloom, MCDW was observed. Although both of these stations displayed the imprint of sedimentary Fe input connected to the strong tidal cycles above the banks, the stronger near-bottom density gradient that MCDW produces appears to contribute to reduced vertical mixing of the sedimentary source. Thus, ironically, the presence of MCDW may be hindering the Fe supply to the surface waters, rather than being the source, as originally hypothesized.

A new method for thioarsenate preservation in iron-rich waters by solid phase extraction

In order to preserve iron-rich samples for arsenic speciation analysis, mineral acids or EDTA are typically added to prevent oxidation and precipitation of iron. However, when sulfide is present, and thioarsenates ([HAsVS−IInO4−n]2−, n = 1–4) can form, these methods are unsuitable due to arsenic sulfide precipitation or artifact speciation changes. Here, a new method based on separating the anionic arsenic species from cationic iron in the presence of sulfide via solid phase extraction (SPE) has been investigated. Synthetic solutions containing arsenite, arsenate, monothioarsenate, and trithioarsenate were passed through the anion-exchange resin AG2-X8, after which the resin was washed, eluted, and speciation of each step analyzed by IC-ICP-MS. Retention on the resin of 96.8 ± 0.2%, 98.8 ± 0.2%, and 99.6 ± 0.3% was found for arsenate, monothioarsenate, and trithioarsenate, respectively. Cationic iron (90 μM Fe(II)) was not retained (0.4 ± 0.2%). Uncharged arsenite passed through the resin in the absence of sulfide, while 47.3% of arsenite were retained at tenfold sulfide excess via thiol groups binding to the organic resin structure. Elution with 3 × 15 mL of 0.5 M salicylate, including a soak time, resulted in quantitative recovery of all retained species. Stability of the retained species on the resin was tested with iron-rich, natural waters from a Czech mineral spring. Arsenate, monothioarsenate, dithioarsenate, and trithioarsenate were successfully separated from iron and recovered after 6 d. Thus, SPE presents a viable answer to the problem of preserving arsenic in the presence of both iron and sulfide.

Reactive transport modeling of redox processes to assess Fe(OH)3 precipitation around aquifer thermal energy storage wells in phreatic aquifers

Well clogging due to iron (hydr)oxide precipitation can negatively influence the performance, or even cause failure, of aquifer thermal energy storage (ATES) wells in aquifers with varying redox conditions. The interactions between physical and chemical processes during ATES operation are, however, not well understood. The reactive transport modeling code PHT3D is used to assess the effects of alternating pumping by ATES systems near the redox boundary on the precipitation of iron hydroxides for two cases, Leuven and Antwerp in the north of Belgium. Results show in both investigated cases that initial mixing plays an important role in the development of Fe(OH)3 precipitation around the wells, with the highest concentration of Fe(OH)3 around the cold well. The initial injection into the warm well causes both the initial mixing and temperature effects to counteract each other, so that the Fe(OH)3 concentration at the cold well is lower and closer to those of the warm well. Since the temperature dependence of the reaction rate of Fe(OH)+, Fe(OH)2 and other reactive species is not taken into account, the impact of the temperature effect on iron (hydr)oxide precipitation should not be viewed quantitatively. However, avoiding the mixing of oxygen/nitrate rich water with iron rich water remains the best strategy to prevent well clogging. Feasibility studies for ATES should therefore assess water quality variations with depth, and use this information to optimize filter screen settings. In this way, the well screen setting can be optimized and the risk of well clogging due to iron (hydr)oxide precipitation is reduced.