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Weathering of mine waste rock can result in high concentrations of zinc (Zn) and cadmium (Cd) in surface and ground water. Design and implementation of mitigation measures requires an understanding of the mineralogical occurrence of Zn and Cd within the waste rock as well as the subsequent weathering and leaching processes. Recent geochemical studies have focused on the characterization of selenium and arsenic leaching from sphalerite and pyrite in waste rock from coal mines in the Elk Valley, British Columbia, Canada. Data collected from these studies provide an opportunity to evaluate the distribution and behavior of Zn and Cd. The abundance and mineralogical association of Zn and Cd were determined in waste rock placed at different times in the dump and leaching of Zn and Cd at the dump-scale was estimated by analyzing porewater and effluent water samples in a rock drain. Mean contents of Zn and Cd in the waste rock samples (n = 260) were 152 mg/kg (range: 48.4–591 mg/kg) and 3.02 mg/kg (range: 0.97–7.56 mg/kg), respectively. Electron microprobe analysis showed Zn and Cd are present in rock samples as primary sphalerite and sorbed onto secondary Fe oxides. The mean concentrations of Zn and Cd in porewater in the dump (n = 121) were 231 μg/L (range: 4.27–1046 μg/L) and 0.61 μg/L (range: <0.01–6.85 μg/L), respectively. The sorption onto secondary Fe oxides is identified as the sink for aqueous Zn and Cd in the dump. Under the oxidizing conditions that exist throughout much of the dump, Fe oxides will likely be a long-term sink for aqueous Zn and Cd. Mean concentrations of Zn and Cd in the rock drain water were 56.4 μg/L (range: 1.2–523 μg/L, n = 213) and 1.53 μg/L (range: 0.004–3.92 μg/L, n = 209), respectively. As such, these low concentrations are attributed to dilution by drain waters sourced upstream of the dump and sorption of Zn and Cd onto secondary Fe oxides and calcite precipitated in the drain within 200 m after discharge from the dump. The relative increase of Cd concentration in rock drain water compared to porewater can be because of its lower affinity for the sorption onto secondary Fe oxides and calcite. This study suggests that the mobility of Zn and Cd from the weathering of any low sulfide – high carbonate waste rocks will be limited because the precipitation of secondary Fe oxides and calcite provide a strong internal geochemical control on Zn and Cd mobilization. [Display omitted] • Oxidation of sphalerite releases Zn and Cd into porewater of oxic coal waste rock dumps. • Sorption onto secondary Fe-oxides is a sink for Zn and Cd within dumps. • Sorption onto secondary Fe-oxides and calcite control Zn and Cd in rock drain water discharged from the dump. • Mobility of Zn and Cd from weathering of low sulfide–high carbonate waste rocks is limited. [ABSTRACT FROM AUTHOR]

Nano-sized powders of iron oxides have been synthesized electrochemically at temperatures in the range of 295–361 K, and current densities in the range of 200–1000 mA dm−2. The structure and morphology of the powders were investigated by X-ray diffraction and scanning electron and transmission electron microscopy techniques. Their infrared absorption spectra, specific heat Cp( T) and magnetic susceptibility χ( T) temperature dependences are also determined. The obtained powders consist of two phases, each possessing distinguished characteristics: the one formed of large plates and the other of whiskers. By appropriate adjustment of the synthesis conditions, it is possible to change features and relative abundances of the two phases, and that way to control morphology and other powder properties. Relaxation and transformation of the phases under external influences was also investigated, and the optimal procedure for preparation and stabilization of iron oxide nano-sized powders with desired characteristics was established. [ABSTRACT FROM AUTHOR]

Uranium (U) is a common contaminant at numerous surface and subsurface sites in proximity to areas involved with weapons manufacturing and atomic energy related activities. This paper covers some important aspects of the aqueous hexavalent uranium [U(VI)] interactions with soil minerals that are present in contaminated soils and sediments. The retention of U via interactions with soil minerals has significant consequences for the prediction of its short- and long-term behavior in soils and geological systems. Studies of the nature and type of these interactions have provided the necessary evidence for assessing the geochemical behavior of U in natural systems under different physical, biogeochemical, hydrological, and reducing or oxidizing conditions. Over the last 20 years, aqueous U(VI): soil mineral interactions have been studied by geochemists, soil chemists, clay and soil mineralogists, and the progress in some areas is remarkable. Although a mechanistic description and understanding of the complex interactions involving U and soil minerals in natural systems is currently difficult, results from carefully designed and executed field and laboratory experiments with these materials have improved our understanding of the heterogeneous system’s behavior and U contaminant mobility and transport. There are, however, areas that warrant further exploration and study. Numerous research publications were reviewed in this paper to present recent important findings to reveal the current level of the understanding of the U(VI) interactions with soil minerals, and to provide ideas for future needs and research directions. [ABSTRACT FROM AUTHOR]

• Heavy Zn isotopes are preferentially adsorbed on the surface of secondary Fe oxides. • Fe oxides precipitates under oxidizing conditions with the recession of groundwater. • Fe oxide-rich soils controls the heavier riverine δ66Zn relative to unweathered rocks. Zinc (Zn) is an essential micronutrient released into soils during rock weathering, and Zn isotope composition has been emerging as a powerful tracer involved in the Earth's surface processes. To explore the soil development in dry tropical regions and evaluate the influence on the global Zn cycles, stable Zn isotope data were presented for the two pristine low-humic gleysol profiles from the Mun River Basin (MRB), northeast Thailand. The samples exhibit the δ66Zn (relative to JMC 3-0749L standard) from −0.69‰ to 0.32‰. Therein, the Fe nodule-containing soils exhibit a light shift of δ66Zn relative to parent red siltstones (Δ66Zn nodule-containing soil – p of S1 = −0.60‰) and the other soils (Δ66Zn II- other zones = −0.66‰ – −0.50‰), indicating that the preferential retention of light Zn isotopes in residual soils is attributed to the adsorption of heavy Zn isotopes onto the surface of secondary Fe oxides. Due to the water insufficiency in the MRB, the redox conditions to control the oxide precipitation are driven by the seasonal alteration of groundwater levels. With the recession of groundwater, Fe oxides precipitate and adsorb heavy Zn isotopes. Besides, heavy Zn isotopes are also incorporated in clay fraction. On the contrary, the saturated water is likely to disrupt the interactions of Zn with Fe phases and clay minerals. In addition, low content of organic matter and Mn oxides and the absence of sulfides limitedly contribute to the light Zn pool in soils. Conclusively, the isotopic signature of Zn indicates that Fe oxide-rich soils are likely to control the heavier Zn isotope composition of dissolved load in rivers relative to continental rocks in dry tropical regions. [ABSTRACT FROM AUTHOR]

Abstract: The susceptibility of loess soils in the lower Mississippi to runoff and erosion losses varies as a function of landscape position and mapping units. This study was conducted to determine the effects of soil drainage on physical and chemical properties that influence erodibility through their control of aggregate stability. Soil samples were collected from the A- and B-horizons of the five representative pedons in the Memphis catena whose drainage class varied from well-drained to poorly-drained. The fine earth fraction (<2 mm) of each soil was characterized for a range of basic soil physical and chemical properties. Additional sub-samples (<8 mm) were placed in a rainfall simulator pan (0.6 m×0.6 m test area) and subjected to simulated rainfall at an intensity of 64 mm h−1. Soil erodibility was assessed by the use of an aggregation index (AI) computed from water dispersible clay (WDC) relative to total clay contents. The data show that as soil drainage classes became wetter, the percentage of sediment <53 µm increased with a decrease in soil AI resulting from a loss of Fe, Al, and Si oxide cementing agents. These results suggest that cementing agents responsible for soil aggregate stabilization are mobilized under conditions of relatively low redox potentials which increase soil erodibility. [Copyright &y& Elsevier]

The sorption characteristics of pentachlorophenol (PCP) in the surficial sediments were investigated using a selective extraction procedure. The results show that the Γ max of PCP sorption decreased from 1.60μmolg−1 to 0.69μmolg−1 by approximately 60% after selective removal of organic materials from the sediments. The sorption of PCP in the sediments after selective removal of Mn oxides increased nearly up to 600% (from 1.60μmolg−1 to 11.11μmolg−1) and, to a less degree, the PCP sorption in the sediments after simultaneous removal of Fe/Mn oxides (Γ max =3.53μmolg−1). The analysis of the data using an additional model indicates that the contribution of Mn oxides to PCP sorption was negative, and Fe oxides and organic materials both have greater potential for sorption of PCP with less contribution from residues including Mn and Fe oxides in the residual fractions determined by a sequential extraction procedure and clay and silicate minerals. The differences in the decreased degrees of PCP sorption with increasing of Cu suggest that competition between Cu and PCP for sorption sites mainly takes place on Fe oxides. [Copyright &y& Elsevier]

Abstract: The adsorption of selenium species on crushed granite is investigated directly linking to its internal iron-related minerals. Experimental results demonstrated that granite has higher affinity toward Se(IV) adsorption than Se(VI) adsorption. Se(IV) adsorption on granite is insensitive to background electrolytes while the effect of ionic strength on Se(VI) adsorption is not observed, which is attributed to the overloading of Se(VI) ions. Results of chemical sequential extraction showed that the removal of crystalline iron oxides dramatically reduces Se(IV) adsorption, which corresponds to the disappearance of goethite signal within XRD pattern. Based on our results, it is proposed that goethite within granite dominates Se adsorption in crushed granite. Although these goethites probably stem from some sample preparation processes including drilling in situ, crushing, washing and drying granite samples in laboratory, the formation of goethite enhances the granite affinity toward Se species adsorption. Images of SEM/EDS furthermore revealed that goethite is embedded within the fractures. In addition, quantification by standard addition method by spiking goethite suspension indicates that only around 20% of goethite minerals are available during Se(IV) adsorption. [Copyright &y& Elsevier]

Changes in the soil chemical environment can be expected to increase the leaching of trace metals bound in soils. In this study the mobility of trace metals was monitored in a column experiment for two contaminated urban soils. Four different treatments were used (i.e. rain, acid rain, salt and bark). Leachates were analysed for pH, dissolved organic carbon (DOC) and for seven trace metals (cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn)). The salt treatment produced the lowest pH values (between 5 and 6) in the effluent whereas the DOC concentration was largest in the bark treatment (40–140 mg L−1) and smallest in the salt and acid treatments (7–40 mg L−1). Cadmium, Ni and Zn were mainly mobilised in the salt treatment, whereas the bark treatments produced the highest concentrations of Cu and Pb. The concentrations of Cu, Cr, and Hg were strongly correlated with DOC ( r 2 = 0.90, 0.91 and 0.96, respectively). A multi-surface geochemical model (SHM-DLM) produced values for metal dissolution that were usually of the correct magnitude. For Pb, however, the model was not successful indicating that the retention of this metal was stronger than assumed in the model. For all metals, the SHM-DLM model predicted that soil organic matter was the most important sorbent, although for Pb and Cr(III) ferrihydrite was also important and accounted for between 15 and 50% of the binding. The results confirm the central role of DOC for the mobilization of Cu, Cr, Hg and Pb in contaminated soils. [ABSTRACT FROM AUTHOR]

Abstract: Tannic acid (TA) and condensed tannin (CT) are strongly retained by mineral phases consisting of quartz (Qtz) with or without coatings of either goethite (Gt) or ferrihydrite (Fh). We investigated the impact of evaporation of the carrier solvent after addition of solutions of TA and CT to the mineral phases on tannin retention. These experiments were performed in solutions ranging from acidic to alkaline pH to study the effect of pH on tannin retention and the release of Fe from the mineral phases. It was found that pH had little influence on the interactions between the tannins and the minerals under natural soil pH conditions (pH 4–8) and that evaporation of the carrier solvent followed by re-extraction resulted into stronger retention of the tannins than if the evaporation step was omitted, especially for CTs. Tannins promoted the release of Fe, Al and Si from the mineral phases into the solution, with Fe concentrations increasing in the order Qtz>Qtz–Fh>Qtz–Gt. Qtz–Fh was the strongest adsorbent, and CT was retained stronger than TA. These results confirm that TA and the CTs used are efficient Fe, Al and Si mobilising agents. In natural soil, the fate of tannins after entering the mineral soil is probably affected by the soil''s moisture regime and especially by the abundance and type of Fe (oxy)(hydr)oxides. Also, in quartzitic soil poor in secondary oxides, tannins may be tightly bound to Qtz surfaces. We suggest that under natural conditions, where evaporation and rewetting occur continuously, tannins can be attenuated by mineral soil constituents but can also act as carriers of metals or metal (hydr)oxides. [Copyright &y& Elsevier]

An iron oxide–clinoptilolite system was synthesized by adding natural clinoptilolite in an iron nitrate solution under strongly basic condition. The newly synthesized material has a red–brown color. A combination of XRD, FTIR and EPR spectroscopies, as well as specific surface area measurements and TG/DSC thermal analyses provided information on the type of Fe species located on the zeolite surface. Clinoptilolite seems to maintain its structure, while Fe3+ species are in a symmetric environment (Th or Oh). The new material has a noteworthy high value of specific surface area (151m2 g−1) and is fully iron exchanged (Fe/Al=1.23). Differences in FTIR and TG/DSC spectrograms between the Fe–Clin system and untreated Clin were reported and explained. According to Cu adsorption/desorption experiments, carried out after the synthesis and characterization procedures, the Fe–Clin system is a promising new material since it adsorbs significantly larger Cu concentrations than clinoptilolite. This fact is owed to its high specific surface area and to its high negative surface charge. Desorption of Cu was also examined and it was observed that the Fe–Clin system desorbs smaller Cu amounts than untreated clinoptilolite. [Copyright &y& Elsevier]

Iron (Fe) chlorosis, an Fe deficiency commonly observed in grapevines cultivated on calcareous soils, generally inhibits plant growth and decreases yield. The objective of this research was to relate the incidence of Fe chlorosis in vines of the Montilla‐Moriles area, southern Spain, to indigenous soil properties. Thirty‐five grapevines ( V. vinífera L. cv. Pedro Ximenez grafted on V. berlandieri×V. rupestris 110 Ritcher) showing different degree of Fe chlorosis were selected from 13 vineyards. The leaf chlorophyll concentration (estimated by the SPAD value measured with a Minolta meter) was positively correlated with the contents in different soil Fe forms but not with alkalinity‐related soil properties (pH, calcium carbonate equivalent, and active lime). The acid NH 4 oxalate‐extractable Fe (Fe o ) was the most useful simple variable to predict the occurrence of Fe chlorosis. A Fe o /active lime ratio of 25×10 –4 was found to be useful to class soils into two groups according to the probability of inducing Fe chlorosis. [ABSTRACT FROM AUTHOR]

Abstract: This paper intends to shed light on the interactions between tannin and mineral soil particles. For that purpose, aqueous solution of condensed tannin (CT) (derived from Black pine (Pinus nigra var. maritima)) and commercially available tannic acid (TA) were added to purified quartz (Qtz) sand and quartz sand coated with either goethite (Gt) or ferrihydrite (Fh). After solvent removal by evaporation the samples were extracted by water. The extracts were analysed for organic carbon, total phenolics and CT. The extractability of the two tannins was small and increased in the order Qtz–Fh&#60;Qtz–Gt&#60;Qtz. For all mineral samples, TA was more extractable than CT. Bonding of tannins to the mineral samples and the partial peptisation of the Fe oxide coatings upon the binding resulted in complex tannin release curves. Our results suggest that the inextractability of tannins from natural soils and the absence of tannins in soil leachates might be caused by strong adsorption on soil minerals such as Qtz and Fe (oxy)(hydr)oxides. The results of competition experiments with mixtures of both tannins demonstrate that the CTs, and TA in particular, can release large amounts of Fe (oxides), suggesting that the tannins are excellent metal-mobilising agents. We therefore suggest that the fate of tannins in the mineral soil environment is highly dependent on the abundance of weakly bonded secondary oxides. [Copyright &y& Elsevier]

Abstract: This study was carried out in order to understand the early diagenetic redistribution of phosphorus and relevant mass balance in the sediments of the East Sea. In two cruises during May 1993 and October 1995, 11 box cores were collected in the southwestern part of the East Sea. Dissolved phosphorus and iron were analyzed in the porewater from the cores. Sediment samples were analyzed for solid-phase P species and solid-phase Fe oxyhydroxide by sequential extraction. Phosphorus speciation results show that organic P is the major chemical form of phosphorus in young sediments within the upper 50 cm of sediment. However, the authigenic fraction of total P increases with depth, indicating the precipitation of carbonate fluorapatite (CFA) in the sediments. The authigenic CFA (Ca5(PO4)2.6(CO3)0.4F) was formed and buried at rates of 11–110 μmol cm−2 kyr−1. The main source of dissolved phosphorus for the precipitation of CFA is organic P. Dissolved phosphorus, released from the decomposition of organic P, diffuses upward to return to bottom water, or is sorbed to iron oxides in the oxidized sediments. As sedimentation proceeds, the iron oxide-bound P is released in the reduced layer and enters the dissolved phase, which contributes P to the formation of CFA in addition to that contributed by the organic P. The burial flux of reactive P (iron oxide-bound P+authigenic P+organic P) is 0.09–0.53 g P m−2 yr−1 that accounts for 18–58% of the reactive P arriving at the sediment/water interface. The burial flux of reactive P is high in the upper and lower continental margin sediment. The burial flux of reactive P in the Ulleung Basin sediment is less than those in the continental margin sites by a factor of 6, indicating that the reactive P burial flux is mainly dependent on sedimentation rate. [Copyright &y& Elsevier]

The rare earth element (REE) contents of soils and pan sediments of the Darling Hills granitic terrain of southwestern South Africa were determined to study the behavior of REE during weathering in a semi-arid, Mediterranean climate. The P-rich, S-type bedrock granite has a middle REE (MREE) enrichment relative to post-Archean Australian sedimentary rocks (PAAS) that primarily reflects the REE content of feldspar and accessory apatite. Initial chemical weathering of the granite results in the loss of REE, particularly Ce, Eu and the heavy REE (HREE). The enrichment of REE in soils relative to bedrock granite corresponds to clay mineral and amorphous Fe oxide content in the case of the light REE (LREE) and precipitation of pedogenic calcite in the case of the HREE. Quartz sand dilutes the REE content, and concentration of K-feldspar produces positive Eu anomalies. Cerium is rapidly precipitated during weathering and retained in clayey, upper soil horizons as insoluble CeO2. Most pan sediments have a bowl-shaped REE pattern that is derived from the accumulation of eroded catchment soils modified by precipitation of evaporative carbonates. REE enrichment, particularly LREE, and the large negative Ce anomaly of oxidized basal pan sediment relative to the bedrock granite suggest that REE entering the pan by groundwater flow are sorbed onto amorphous Fe oxides. In contrast, goethite-rich nodules from the pan have a low REE content and show HREE enrichment relative to the granite. Precipitation of pedogenic calcite and evaporative pan carbonates greatly increases the retention of the HREE in these semi-arid soils. Diagenetic pan dolomite has a REE pattern similar to pedogenic and evaporative calcite, but with a significantly lower REE content. The REE patterns indicate that, although most abundant in the bedrock granite, the MREE are least retained by soils during weathering. The LREE are generally retained by clayey and amorphous Fe-oxide-rich soils and sediments, whereas HREE are retained by precipitation of soil and pan carbonates. [Copyright &y& Elsevier]

Free ferric oxides of a red bed series were analyzed by rock-magnetic techniques (IRM component analysis) and by two less traditional methods: visible spectroscopy and voltammetry. All three methods have low limits of detection, making them suited for this type of analysis. The red bed samples studied contained clay minerals, quartz, and calcium carbonate as major constituents. Free Fe oxides occurred at a concentration of 0.3–2.1%, i.e. in the majority of the samples below the detection limit of X-ray powder diffraction. The combination of the employed analytical techniques enabled to characterize the mineralogy of free ferric oxides and to estimate the ratio of goethite and to hematite. This ratio changes substantially within the section that probably indicates paleoclimatic changes. [Copyright &y& Elsevier]

The role of Fe oxyhydroxides dynamic on metal bioavailability was studied in the Rio Doce estuary after the largest mining disaster in the world. Soon after the disaster in 2015, metals were associated with Fe oxyhydroxides under a redox-active estuarine environment. Our results indicate that organic matter inputs from plant colonization on deposited tailings over estuarine soils led to a reductive dissolution of Fe oxyhydroxides within two years. Soil pseudo-total Fe content decreased by 70% between 2015 and 2017, while the total metal contents (Cr, Cu, Ni, Pb, and Zn) decreased by 79% in the soil. The losses of Fe and metals coupled to changes in Fe oxides crystallinity reveal a future ephemeral control of Fe oxyhydroxides over metal immobilization. Our results suggest a potential chronic contamination at the estuary and points to an aggravating scenario for the following years due to the increasing dominance of poorly crystalline Fe oxyhydroxides. • Massive Fe and metal losses took place within two years after the Samarco disaster. • Inputs of organic matter increase the dissolution of Fe oxides within mine tailings. • Loss in the crystallinity of Fe oxides weakens the soil capacity to immobilize metals. • A chronic contamination is expected at Rio Doce estuary for the following years. [ABSTRACT FROM AUTHOR]

Zinc (Zn) deficiency constrains crop yield and quality, but soil factors influencing Zn availability to plants and reactions of applied Zn fertilizer are not fully understood. This work is aimed at studying Zn availability in soil and the use efficiency of Zn fertilizers by plants as affected by soil properties and particularly by soil available P. We performed a pot experiment involving four consecutive crops fertilized with Zn sulfate using 36 soils. The cumulative Zn uptake and dry matter yield in the four crops increased with increased initial diethylenetriamine pentaacetic acid extraction of Zn (DTPA-Zn) (R2 = 0.75 and R2 = 0.61; p < 0.001). The initial DTPA-Zn increased with increased Olsen P (R2 = 0.41; p < 0.001) and with increased ratio of Fe in poorly crystalline to Fe in crystalline oxides (R2 = 0.58; p < 0.001). DTPA-Zn decreased with increased cumulative Zn uptake, but not in soils with DTPA-Zn < 0.5 mg kg−1. Overall, the available Zn is more relevant in explaining Zn uptake by plants than applied Zn sulfate. However, in Zn-deficient soils, Zn fertilizer explained most of the Zn uptake by crops. Poorly crystalline Fe oxides and P availability exerted a positive role on Zn availability to plants in soil. [ABSTRACT FROM AUTHOR]

The availability of phosphorus (P) in estuarine ecosystems is ultimately controlled by the nature of interactions between dissolved P and the soil components (e.g., soil minerals), especially iron (Fe) oxyhydroxides. P retention on Fe oxyhydroxides and its subsequent availability depends on mineral crystallinity and susceptibility to dissolution. However, in estuarine soils, geochemical conditions (e.g., redox oscillation and high soil organic matter content) may alter the fate of P and decrease the environmental quality of estuarine waters. The large input of Fe-rich tailings into the Rio Doce Estuary in Brazil in 2015 after a rupture of a Fe ore tailings dam (i.e., "Mariana mine disaster") offers a unique framework to evaluate the Fe oxyhydroxides role in P availability in estuarine soils, their potential effects on the cycling of P and eutrophication. We observed a significant correlation between Fe minerals and the P content in the estuary soils, suggesting that P enrichment was promoted by the deposited Fe-rich tailings. Adsorption isotherm curves indicated that mine tailings had a strong affinity for P due to presence of crystalline Fe oxyhydroxides in the tailings. Significant losses of Fe (62%) and P (56%) from the estuarine soil was observed two years after the initial impact and in response to redox conditions oscillations. Additionally, the content of high crystallinity Fe oxyhydroxides decreased significantly, whereas that of low crystallinity Fe oxyhydroxides showed an increase over time. These changes were associated with the dissimilatory Fe reduction, which led an increase in the concentrations of readily available P (2015: 2.30 ± 0.41 mg kg−1; 2017: 3.83 ± 1.82 mg kg−1; p < 0.001) in the studied soils. Moreover, in 2017, the dissolved P content exceeded the recommended environmental safety limits by five times. Our results indicate that Fe oxyhydroxides are a continuous source of dissolved P for the ecosystem, and Fe-rich tailings deposited in the estuarine ecosystem may be linked to a potential eutrophication. Image 1 • The Fe-rich mine tailings acted as an adsorbent carrier for phosphorus to the estuary. • Phosphorus is associated to both low and high crystallinity Fe oxy-hydroxides. • Redox changes induced both Fe oxides reductive dissolution and crystallinity changes. • Fe oxides transformations resulted in an ephemeral control over P bioavailability. • Dissolved P at the estuary exceeded in 5 times the Brazilian legislation threshold. [ABSTRACT FROM AUTHOR]

In this study, the effect of unstable pe + pH levels on the transformation of Fe oxides in different-sized soil fractions and its impact on Cd speciation were explored. Paddy soil samples collected from two locations in China were cultivated for two months under one of four pe + pH conditions: flooding + N 2 (T1), flooding (T2), 70% water holding capacity (T3), and 70% water holding capacity + O 2 (T4). Chemical analysis and X-ray diffraction (XRD) were used to identify the mineralogical phases and species of Fe and Cd in paddy soils. The results show that the decrease of soil pe + pH level favored the transformation of well-crystallized Fe oxides (Fe c), such as hematite and goethite, into poorly-crystallized (Fe o) and organically-complexed (Fe p) forms. The transformation promoted the binding of Cd to Fe oxides and was primarily responsible for up to a 41.8% decrease of soil DTPA (diethylenetriaminepentaacetic acid)-extractable-Cd content. In addition, the decline in pe + pH value reduced Fe concentrations in soil particle fractions of 0.2–2-mm (17.8%–30.6%) and <0.002-mm (20.7%–31.7%) of the two flooding treatments. The decreased Fe concentrations were closely associated with less Fe c contents in these same fractions and more Fe o and Fe p in coarser aggregates (P < 0.01). Importantly, the increase in contents of Fe o and Fe p in the 0.002–2 mm fraction were significantly correlated with content of Fe-/Mn-oxide-bound Cd (OX-Cd) in larger particle-size fractions (P < 0.01). Furthermore, the increasing content of OX-Cd played a crucial role in reducing DTPA-Cd content. This study demonstrates that low pe + pH values favor the transformation of crystalline Fe oxides into a poorly-crystallized and organically-complexed phase, which facilitates Cd accumulation in coarser aggregates and enhances Cd stability in paddy soils. Unlabelled Image • Low pe + pH condition induces the decline in level of crystallinity of Fe oxides. • Low-crystalline Fe oxides exhibit high adsorption affinity of Cd in paddy soil. • Soil pe + pH decline favours the accumulation of Fe o and Fe p in larger aggregates. • Fe redistribution in different-sized aggregates affects Cd availability in soil. [ABSTRACT FROM AUTHOR]

• With inorganic P addition, labile P is initially high, but decreases under oxidising conditions. • The decrease in labile P is likely due to binding to Fe oxides. • With P added as manure, labile P is initially lower than with inorganic P, but remains stable over time. • With manure, oxalate extractable Fe and P are high under oxidizing conditions, but low when submerged. • Organic acid anions released during manure decomposition can reduce P binding to Fe oxides. Phosphorus availability in acid soils is influenced by interactions of P and Fe-oxides which are modulated by soil water content. Decomposition of organic material influences these interactions. But little is known about the effect of P added as inorganic P or manure on P pools in an acid sulfate soil under varying water content. Sandy acid sulfate soil (pH adjusted to 5.5) was amended with 400 mg P kg−1 as inorganic P, manure or combinations of inorganic P and manure. Amendment treatments included inorganic P alone (100F), manure alone (100M) and P added as 50% inorganic P + 50% manure (50M/50F) as well as an unamended control. The soil was submerged for 2 weeks, then the overlying water was removed and the soil dried to maximum water-holding capacity. The soil was incubated for 4 weeks at this water content followed by submergence for 2 weeks. In the unamended control, P pools were very low and not affected by soil water content. At the end of the first submergence, labile phosphate and oxalate extractable P were two-fold higher in 100F than in 100M and 50M/50F. Oxalate extractable Fe was higher in 100M than 100F and remained unchanged until the end of the experiment. In the following moist incubation and after the second submergence, labile phosphate remained unchanged in 100M, but halved in 100F. Labile phosphate strongly increased in 50M/50F and was about two-fold higher than in the other two amended treatments. Oxalate extractable P was two-fold higher in the moist period than at the end of the first submergence in manure treatments and 30% higher in 100F. It then decreased again after re-submergence in the manure treatments and became lower than in 100F. It can be concluded that with inorganic P addition, labile phosphate was initially very high, but then strongly decreased in the moist period due to removal of phosphate with the overlying water and to binding of P to amorphous Fe where it remained after re-submergence. With manure on the other hand, labile phosphate was lower than with 100F initially, but then remained stable. Phosphate in the overlying water was low with manure which indicates that, in contrast to inorganic P addition, the threat of P transfer into the surrounding environment is low. [ABSTRACT FROM AUTHOR]

Avoiding chemical and physical artifacts during sampling is crucial for realistic analyses of mineral and other colloids in soil. We developed a sampler, which allows for the in situ collection of Fe oxides that precipitate in their natural environment in a Bg horizon of a Calcaric Gleysol. Simultaneous measurements of redox-sensitive parameters confirmed temporal changes from Fe-reducing to Fe-oxidizing conditions on site. [ABSTRACT FROM AUTHOR]

• DTPA extractable Zn had little value to predict Zn deficiency. • Clay and Olsen P negatively affected Zn uptake in calcareous soils. • In non-calcareous soils, crystalline Fe oxides negatively affected Zn uptake. • Estimate of Zn uptake requires discriminating soils according to its carbonate content. • Soil properties related to Zn adsorption should be considered in Zn uptake estimation. Zinc deficiency is an extended agronomic problem, particularly in staple food crops such as cereals. The availability of Zn to plants is ruled by soil properties, biological factors in the rhizosphere, and interaction with other nutrients. These factors may constrain the predictive value of Zn availability indices. This work aimed at assessing the soil factors that affect the absorption of Zn by plants and improving the predictive value of conventional indices. To this end, an experiment was performed using durum wheat (Triticum durum L.) grown on a set of soils developed under Mediterranean climate. In calcareous soils, Zn uptake by plants decreased with increased clay content and Olsen P (P Olsen), meanwhile in non-calcareous soils it decreased with increased crystalline Fe oxides content. Biological factors such as microbial activity and organic anion exudation in the rhizosphere contribute to Zn uptake by plants. No relationship was found between Zn uptake by plants and the DTPA extractable Zn (Zn DTPA). Pyrophosphate extractable Zn (Zn Pyro) was only related to Zn uptake by plants in calcareous soils (R2 = 0.29; P < 0.01). The best estimation of Zn uptake by plants in calcareous soils was obtained with a model involving Zn Pyro /P Olsen ratio and clay content (R2 = 0.57; P < 0.001). In non-calcareous soils, Zn uptake by plants was accurately estimated with a model involving Fe bound to crystalline oxides and rhizospheric oxalate (81% of the variance explained). Results reveal the need of discriminating soils according to its carbonate content and the use of soil properties related to Zn adsorption capacity, such as clay and Fe oxide content, and Olsen P for accurate estimation of Zn uptake by plants. [ABSTRACT FROM AUTHOR]

• Biomass waste and hydrochar were used as feedstock for Fe oxide-biochar composites. • Fe increased the carbonization degree during pyrolysis of biomass waste or hydrochar. • Hydrochar leads to Fe oxide-biochar composite with lower ash content. • Hydrochar leads to Fe oxide-biochar composite with high microporosity. The synthesis of biochar-metal oxide composites for removing heavy metals from aqueous solutions or remediating polluted soils has attracted increased attention. Amongst them, Fe oxide composites stand out due to possible magnetic properties and low price. Two types of Fe oxide-biochar composites were prepared by impregnation with ferric sulfate salts of biomass waste or corresponding hydrochar, followed by pyrolysis at 550 °C for 5 h. During pyrolysis, Fe increased carbonization, leading to biochar with low H/C values. Properties of Fe oxide-biochar composite greatly depend on the feedstock. The Fe content in the final Fe oxide-biochar was higher than in biochar obtained by direct pyrolysis of biomass waste. Some of Fe was in the form of FeS. Impregnation of hydrochar followed by pyrolysis lead to a Fe oxide-biochar composite with lower ash content and higher micro- and macro-porosity. In this case, the Fe was in the form of Fe oxides. [ABSTRACT FROM AUTHOR]

Iron (Fe) oxides are intimately coupled with phosphorus and closely associated with the bioavailability of potential toxic elements (PTEs) in soil. Thus, Fe oxides may influence the stabilization of PTEs in contaminated soils amended by phosphorus. To evaluate the effects of hematite (HMT) on the stabilization of PTEs, 1–5% (by weight) of HMT was added into a contaminated red soil amended with hydroxyapatite (HAP) to simulate naturally occurring Fe oxides. The stabilization efficiencies of soil copper (Cu) and cadmium (Cd) amended with HAP in soils with low, moderate, and high content of HMT were assessed after a 60-day incubation. HAP treated the soil with high rate HMT decreased the CaCl 2 -extractable and acid-soluble fractions of Cu and Cd than that of HAP alone. In particular, CaCl 2 -extactable Cu and Cd in the soil with 5% HMT amended by HAP were 91–95% and 41–68% lower than those amended with only HAP. High content of HMT in soil could decrease the concentration of labile phosphorus in the presence of HAP, but it did not increase the concentration of NaOH-extractable inorganic phosphorus (the fraction bound to Fe oxides). The concentrations of free and crystalline Fe oxides were significantly increased by adding high dosages of HMT with or without HAP. High content of HMT in soil amended by HAP reduced metal phytotoxicity and uptake by wheat shoots than the soil containing HAP without HMT. The results indicate that HMT can promote Cu and Cd stabilization while decrease labile phosphorus in red soil amended with HAP, suggesting that phosphorus-based amendments combined with Fe oxides can be used to stabilize PTEs in contaminated red soils. Image 1 • A contaminated red soil with 1–5% hematite was treated by hydroxyapatite (HAP) for 60 d. • Hematite decreased Cu and Cd bioavailability in the soil amended with HAP. • Hematite decreased soil labile phosphorus content in the presence of HAP. • Hematite promoted the reduction of wheat phytotoxicity in red soil amended with HAP. • Hematite promoted the stabilization of Cu and Cd in red soil amended with HAP. [ABSTRACT FROM AUTHOR]

Iron electronic transitions produce intense colors in minerals with moderate to high Fe content, which phenomenon allows using color and visible spectroscopy to identify and quantify Fe-bearing minerals. This approach is especially useful for Mars investigation due to the limited analytical instruments available at Mars. The challenges are: (1) overlap between Fe electronic absorption bands of Fe-bearing minerals, (2) band wavelengths are modified by chemical and structural variables, and (3) particle size effects can modify mineral color. The magnitude of these difficulties, however, depends on the mineral mixture investigated. In this study, we further probe the potential of visible-range data for investigation of Fe-minerals. The samples were mineral mixtures from the Riotinto area (SW Spain) that resulted from acidic alteration and contained Fe in oxy-hydroxides, hydroxysulfates and phyllosilicates. Samples were studied using visible/near-infrared spectroscopy, X-ray diffraction and thermogravimetry. The wavelength range 320–1000 nm was investigated using spectral second derivatives and CIELAB color parameters. Hematite was readily detected, below X-ray diffraction detection limits, from the band at 520–560 nm. Jarosite was readily identified by the combined presence of bands at ~390 and ~ 440 nm. Thermogravimetric and CIELAB color analyses indicated goethite as the most common Fe-rich mineral in the samples. Correlations between CIELAB color parameters were controlled by goethite, where jarosite-rich specimens aligned with the correlations but some samples containing hematite plotted outside them. Quantification of goethite was attempted as calibrated against thermogravimetric data. Calibration was not possible below ~10 wt% goethite. Above this value, results from spectral second derivatives allowed quantification up to the maximum goethite content of ~35 wt% (linear correlation with R2 = 0.89). Goethite quantification with CIELAB color parameters was hindered by hematite. In samples with very low or no hematite, goethite quantification was possible with parameters L * 10 (R2 = 0.83) and h ab,10 (R2 = 0.65), also up to ~35 wt% goethite. Consequently, if accurate calibration is possible and depending on mineral mixture components, spectroscopic and CIELAB color parameters should allow goethite quantification in a wide concentration range. • Hematite detectability in mineral mixtures is high due to absorption at 520–560 nm. • Jarosite is also readily detectable due to the combined bands at 390 and 440 nm. • Goethite and jarosite share color characteristics determined with CIELAB parameters. • Hematite modifies CIELAB color characteristics of goethite-jarosite mixtures. • Goethite quantification is possible by spectral and color methods to at least 35 wt%. [ABSTRACT FROM AUTHOR]

To design more efficient and versatile sorbent materials for wastewater treatment three magnetic beidellite composites with different cation exchange capacity and total specific surface area have been synthetized, characterized and used as Cs+ and Sr2+ sorbents. Total loaded Fe concentration and its distribution on the magnetic composites seems to be related to the total specific surface area. The higher saturation magnetization, 13.7 ± 0.7 Am2/kg, was achieved for the sample with the higher total specific surface area. The main magnetic phases after the synthesis are magnetite and maghemite, whose particle size ranged between 28 and 114 nm, respectively. The Cs+ and Sr2+ sorption capacities of raw and magnetic beidellite composites were similar. The sorption takes place at two different sorption sites of the beidellite composites: the external surface, as indicated by zeta potential changes, and the interlayer space, as revealed by diffraction patterns. • Synthetics beidellite were used as base material for magnetic composite obtention. • Fe concentration and distribution on the composites depends on the used beidellite. • Saturation magnetization also depends on the used base beidellite. • Composites have sorbed Cs and Sr. At the same conditions, more Sr than Cs. • The Fe oxides seems do not affect the adsorption capacity of beidellite samples. [ABSTRACT FROM AUTHOR]

Over the last few years, phosphorus (P) has attracted the global interest because it is finite and non-renewable resource. However, some aspects of P dynamics in soils are still unclear and novel insights are necessary to better understand the very complex geochemistry of P and to conclusively evolve the traditional soil P management practices. An explicit example is the very limited research on P behavior in redoximorphic soils. These soils are characterized by specific morphological features, such as Fe-Mn concretions and nodules, and cover large areas around the world. In redoximorphic soils, biogeochemical processes change dramatically as a result of oxygen being periodically excluded from the soil environment affecting the geochemistry of nutrients and trace elements. Fe-Mn concretions and nodules are significant pedogenic components containing high amounts of Fe and Mn oxides and show high sorption capacity for various elements. This paper summarizes the current knowledge on the processes determining the formation of Fe-Mn concretions and nodules in redoximorphic soils and on their impact on soil P dynamics. Depending on soil properties, during Fe-Mn concretions and nodules formation and growth following repeated redox cycles, P can be trapped in the concretions/nodules which act as a sink for P and as a barrier to P movement from land to water bodies. Since very little scientific work on this issue has been done, intensive future work is needed to figure out the complex role of Fe-Mn concretions and nodules on P dynamics in redox-sensitive soils. Unlabelled Image • Fe-Mn concretions and nodules are among the most important pedogenic components. • Formation of Fe-Mn concretions and nodules is a complex biogeochemical process. • Cations and anions enriched in Fe-Mn concretions and nodules with respect to host soil • Fe-Mn concretions and nodules have a high capacity for P sequestration. • Fixation of P in Fe-Mn concretions and nodules has serious agronomic implications. [ABSTRACT FROM AUTHOR]

Arsenic (As) is a trace element in the Earth's crust that often occurs with gold mineralization, where it is found in association with sulfide-bearing minerals such as pyrite (FeS 2). Our study evaluated the mobility of As in creeks that traverse a gold mineralization area in Paracatu, Brazil. The results relate As mobility in water draining actively mined areas to season, wet and dry, and to the impact of in-stream channels lined with limestone that are used to neutralize acid mine drainage. Passage of the creek water through channels lined with limestone decreased soluble As to concentrations below the drinking water threshold in 13 out of 31 samples (10 μg.L−1). The soluble As concentrations were generally higher during the wet season. Arsenic speciation in water was mainly influenced by the season and by the proximity to mineralization zones in the areas that are actively mined. The organic arsenic species DMA (dimethylarsinate) was detected near the mineralized area during the wet season. Sediment-associated As varied with season and with sampling site, but was consistently high at one headwater spring; the highest observed value was 8750 mg As kg−1. We applied selective sequential extraction techniques to assess the portioning of As in the creek sediments. Two of the most mobile fractions of sediment-associated As, the adsorbed and very poorly crystalline fractions, showed a strong seasonal dependence which supported mobilization of As during the wet season. The amorphous Fe oxide fraction followed the same trend but contributed less As, and As associated with the crystalline Fe oxide fraction showed little fluctuation with season. • The Fe and Al (hydr)oxides controlled the seasonal mobility Arsenic, especially very poorly crystalline fractions. • The speciation of As in water was affected by the seasonality of the water flow and its proximity to the mineralized area. • Arsenic (V) was the dominant species during the dry season and the proportion of As(III) increased during the wet season. [ABSTRACT FROM AUTHOR]