Retention Of Uranium Research Articles

Phase migration and transformation of uranium in mineralized immobilization by wasted bio-hydroxyapatite

Abstract In this work, phase migration and transformation of uranium were investigated to understand the mechanism of uranium immobilization on bio-hydroxyapatite (Bio-HAP600), in which waste fish bone was successfully converted into a novel Bio-HAP600 by calcination at 600 °C. The physicochemical properties of Bio-HAP600 were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier Transform Infrared Spectrometer (FTIR) analyses. Sorption behaviors were investigated by batch experiments in comparison with commercial nano HAP. Phase transformation and fate of uranium during sorption process were investigated by SEM mapping and XRD analysis. Results showed that sorption equilibrium of Bio-HAP600 was achieved within 10 min. The maximum uranium sorption capacity of 384.6 mg/g was comparable to commercial available Nano-HAP. Chemical mineralization played a dominant role in the retention of uranium on Bio-HAP. Sorption of U (VI) was highly dependent on the content of P, Ca and O. Formation of nano flake crystal of autunite (Ca(UO2)2(PO4)2(H2O)6) was ascribed as the transformation and fate of uranium mineralization, contributing to the favorable immobilization of uranium. The results indicate that calcination of fish bone leading to Bio-HAP can be a feasible way to produce efficient uranium adsorbent for immobilizing uranium through forming nano flake crystals of autunite.

Multiple environmental factors influence 238U, 232Th and 226Ra bioaccumulation in arbuscular mycorrhizal-associated plants

Ecological consequences of low-dose radioactivity from natural sources or radioactive waste are important to understand but knowledge gaps still remain. In particular, the soil transfer and bioaccumulation of radionuclides into plant roots is poorly studied. Furthermore, better knowledge of arbuscular mycorrhizal (AM) fungi association may help understand the complexities of radionuclide bioaccumulation within the rhizosphere. Plant bioaccumulation of uranium, thorium and radium was demonstrated at two field sites, where plant tissue concentrations reached up to 46.93 μg g−1 238U, 0.67 μg g−1 232Th and 18.27 kBq kg−1 226Ra. High root retention of uranium was consistent in all plant species studied. In contrast, most plants showed greater bioaccumulation of thorium and radium into above-ground tissues. The influence of specific soil parameters on root radionuclide bioaccumulation was examined. Total organic carbon significantly explained the variation in root uranium concentration, while other soil factors including copper concentration, magnesium concentration and pH significantly correlated with root concentrations of uranium, radium and thorium, respectively. All four orders of Glomeromycota were associated with root samples from both sites and all plant species studied showed varying association with AM fungi, ranging from zero to >60% root colonisation by fungal arbuscules. Previous laboratory studies using single plant-fungal species association had found a positive role of AM fungi in root uranium transfer, but no significant correlation between the amount of fungal infection and root uranium content in the field samples was found here. However, there was a significant negative correlation between AM fungal infection and radium accumulation. This study is the first to examine the role of AM fungi in radionuclide soil-plant transfer at a community level within the natural environment. We conclude that biotic factors alongside various abiotic factors influence the soil-plant transfer of radionuclides and future mechanistic studies are needed to explain these interactions in more detail.

Retention of rare earth elements in authigenic phases following biogeochemical dissolution of ore from Elliot Lake, Ontario

The aim of this pilot study is to investigate the retention of uranium (U) and rare earth elements (REEs) by secondary phases following the biogeochemical mineral dissolution of quartz-pebble conglomerate originating from Elliot Lake, Ontario. An understanding of the geochemical controls of U and REE dissolution and subsequent retention in authigenic secondary phases following biogeochemical ore dissolution could provide information relevant to the environmental management of mine waste materials and economic element recovery. The retention of U, thorium (Th), REE, and base metals in secondary phases following biogeochemical ore dissolution formed on mineral surfaces, both in terms of their concentration and association with other elements present in the ore, is characterized in this study. The loss of mass of U (87%) from the quartz conglomerate ore is significantly higher than for the associated REE's, reflecting the mobile character of UO22+. A small but significant portion of the uranyl ions (13%) is retained in the ore sample, either as residual uraninite or as uranyl-phosphate complexes and minerals within Fe- and Al-rich surface coatings. The preliminary adsorption of phosphate (PO43−) ions on the surfaces of Al-Fe-(hydr)oxide mineral surface coatings forms negatively-charged surface sites within the porous media of the leached mineral material, providing adsorption sites for positively-charged metal species on the phosphate-bearing surface sites, allowing the formation of either ternary metal-phosphate-Al-Fe-(hydr)oxides complexes or nucleation of metal-phosphates, thus leading to the retention of U, REE, Th, Zn and Pb. Similarly, the observed retention of Pb, Zn, Cu and Ni is explained by the neoformation of authigenic minerals of the jarosite group within the pore spaces of Fe-, Al- and Si-rich coatings.

Plasma-grafted polyamine/hydrotalcite as high efficient adsorbents for retention of uranium (VI) from aqueous solutions

The high efficient adsorbent of polyamine/hydrotalcite (PANI/HT) composites has been fabricated by plasma-grafting techniques. In this study, the effect of environmental factors on the adsorption of U(VI) on PANI/HT was investigated by EXAFS, modeling and theoretical calculations. The characteristic results indicated that the large layer spacing of PANI/HT provided the massive interlayer ion exchange capacity for U(VI). The batch results illustrated that no effect of ionic strength on U(VI) adsorption at pH > 5.0 was observed, moreover the U-N and U-Si shells were observed at pH 5.0 and 7.0 by the EXAFS analysis, respectively, indicating that inner-sphere surface complexation dominated U(VI) adsorption at pH > 5.0. The desorption results showed that release of U(VI) from PANI/HT was irreversible, which indicated that the PANI/HT presented the large layer spacing to fix uranyl into cage space of the adjacent octahedral. The adsorption behaviors of U(VI) on PANI/HT can be well fitted by double layer modeling with ion exchange and inner-sphere surface complexation. According to theoretical calculations, the binding energies of U(VI) with carbonate (15.49 kcal/mol) were significantly higher than that of U(VI) with hydroxyl (8.35 kcal/mol), indicating that U(VI) was easily combined with carbonate compared to hydroxyl groups at high pH. These observations revealed that PANI/HT can be used as an excellent adsorbent for retardation of uranium species into sub-environments.

Effect of humic acid on uranium(VI) retention and transport through quartz columns with varying pH and anion type

Humic acid (HA)1 is ubiquitous in the environment and is an important factor in the migration behavior of U(VI) in the geological medium. The present work investigated the effect of HA on the migration behavior of U(VI) using quartz column experiments at different pH values and in the presence of various anions. The U(VI) adsorption characteristics and speciation were also studied to illuminate further the migration behavior of U(VI). Our results indicated that, at pH 6.0, HA slightly increased the migration velocity of U(VI) during the initial phase and reduced the quantity of eluted U(VI) because of the formation of HA-U(VI). The relative concentration (c/c0) of U(VI)was higher in the HA-U system at pH 8.0 than that at pH 5.0 because of the higher solubility of HA in basic solutions and the difference in charge of HA-U(VI). In the U-HA-anion system at pH 6.0, the breakthrough pore volumes (PVs2) of U(VI) in electrolytes containing Cl− and SO42− anions (PV = 8) are much higher than for solutions containing phosphate (PV = 3), while the HA migration behavior was not significantly affected by the type of anion. Thus, the fast migration of U(VI) under HA and phosphate was attributed to phosphate rather than HA. This result suggests that phosphate should be given more attention in predictions of U(VI) migration, especially in regions with high groundwater phosphate content.

Sodium silicate treatment for the attenuation of U(VI) by iron‐bearing sediments in acidic groundwater plumes

AbstractBACKGROUNDAnthropogenic activities, such as uranium mining and the nuclear industry, have resulted in groundwater contamination and the creation of uranium‐affected acidic plumes. In situ immobilization through base injection is a favorable way of uranium attenuation. The present study explores the use of sodium silicate for the restoration of neutral pH of the affected zone and consequently, uranium immobilization under circumneutral conditions.RESULTS70 mg L−1 sodium silicate restored the pH of uranium bearing, acidic groundwater to neutral in batch experiments consisting of Savannah River Site (SRS) soil and the aqueous phase. SRS soil main components are quartz, kaolinite and goethite and the U(VI) removal was ∼60%. Identical experiments consisting only of quartz and kaolinite showed only 19% U(VI) removal. Binding of uranium may be improved by inner‐sphere complexation and is not affected by the presence of competitive cations, such as Ca2+ and Mg2+. Recovery of uranium under acidic conditions (pH 3.5) was ∼60%, whereas sorption is not reversible under circumneutral conditions.CONCLUSIONSodium silicate restores the pH of acidic groundwater systems to circumneutral conditions, where uranium retention by iron bearing sediments is favored. Goethite is the soil's most reactive phase and contributes to stronger binding of uranium through inner‐sphere complexation. © 2017 Society of Chemical Industry

希土類元素・トリウムおよびウランの堆積岩中における保持状態：北海道幌延地域における調査例

希土類元素・トリウムおよびウランの堆積岩中における保持状態：北海道幌延地域における調査例

Compared in vivo efficiency of nanoemulsions unloaded and loaded with calixarene and soapy water in the treatment of superficial wounds contaminated by uranium

No emergency decontamination treatment is currently available in the case of radiological skin contamination by uranium compounds. First responders in the workplace or during an industrial nuclear accident must be able to treat internal contamination through skin. For this purpose, a calixarene nanoemulsion was developed for the treatment of intact skin or superficial wounds contaminated by uranium, and the decontamination efficiency of this nanoemulsion was investigated in vitro and ex vivo. The present work addresses the in vivo decontamination efficiency of this nanoemulsion, using a rat model. This efficiency is compared to the radio-decontaminant soapy water currently used in France (Trait rouge®) in the workplace. The results showed that both calixarene-loaded nanoemulsion and non-loaded nanoemulsion allowed a significant decontamination efficiency compared to the treatment with soapy water. Early application of the nanoemulsions on contaminated excoriated rat skin allowed decreasing the uranium content by around 85% in femurs, 95% in kidneys and 93% in urines. For skin wounded by microneedles, mimicking wounds by microstings, nanoemulsions allowed approximately a 94% decrease in the uranium retention in kidneys. However, specific chelation of uranium by calixarene molecules within the nanoemulsion was not statistically significant, probably because of the limited calixarene-to-uranium molar ratio in these experiment conditions. Moreover, these studies showed that the soapy water treatment potentiates the transcutaneous passage of uranium, thus making it bioavailable, in particular when the skin is superficially wounded.

Performance of AGR-1 high-temperature reactor fuel during post-irradiation heating tests

The fission product retention of irradiated low-enriched uranium oxide/uranium carbide tri-structural isotropic (TRISO) fuel compacts from the Advanced Gas-Cooled Reactor 1 (AGR-1) experiment has been evaluated at temperatures of 1600–1800°C during post-irradiation safety tests. Fourteen compacts (a total of ∼58,000 particles) with a burnup ranging from 13.4% to 19.1% fissions per initial metal atom (FIMA) have been tested using dedicated furnace systems at Idaho National Laboratory and Oak Ridge National Laboratory. The release of fission products 110mAg, 134Cs, 137Cs, 154Eu, 155Eu, 90Sr, and 85Kr was monitored while heating the fuel specimens in flowing helium. The behavior of silver, europium, and strontium appears to be dominated by inventory that was originally released through intact SiC coating layers during irradiation, but was retained in the compact at the end of irradiation and subsequently released during the safety tests. However, at a test temperature of 1800°C, the data suggest that release of these elements through intact coatings may become significant after ∼100h. Cesium was very well retained by intact SiC layers, with a fractional release <5×10−6 after 300h at 1600°C or 100h at 1800°C. However, it was rapidly released from individual particles if the SiC layer failed, and therefore the overall cesium release fraction was dominated by the SiC defect and failure fractions in the fuel compacts. No complete TRISO coating layer failures were observed after 300h at 1600 or 1700°C, and 85Kr release was very low during the tests (particles with failed SiC, but intact outer pyrocarbon, retained most of their krypton). Krypton release from TRISO failures was only observed after ∼210h at 1800°C in one compact. Post-safety-test examination of fuel compacts and particles has focused on identifying specific particles from each compact with notable fission product release and detailed analysis of the coating layers to understand particle behavior.

Impact of montmorillonate on the process of purification of waters containing uranium by ultra- and nanofiltration

The article has investigated the impact of montmorillonite (natural and modified) for purification of waters containing uranium by ultraand nanofiltration. It has been shown that maximally possible uranium retention coefficient by a nanofiltration membrane was obtained when a modifier with the molecular weight 2 kDa was used. Whereas for an ultrafiltration membrane a high index of purification is achieved when using a modifier with the molecular weight 10 kDa.

Exposure assessment of natural uranium from drinking water.

The uranium concentration in the drinking water of the residents of the Jaipur and Ajmer districts of Rajasthan has been measured for exposure assessment. The daily intake of uranium from the drinking water for the residents of the study area is found to vary from 0.4 to 123.9 μg per day. For the average uranium ingestion rate of 35.2 μg per day for a long term exposure period of 60 years, estimations have been made for the retention of uranium in different body organs and its excretion with time using ICRP's biokinetic model of uranium. Radioactive and chemical toxicity of uranium has been reported and discussed in detail in the present manuscript.

Physico-Chemical Heterogeneity of Organic-Rich Sediments in the Rifle Aquifer, CO: Impact on Uranium Biogeochemistry.

The Rifle alluvial aquifer along the Colorado River in west central Colorado contains fine-grained, diffusion-limited sediment lenses that are substantially enriched in organic carbon and sulfides, as well as uranium, from previous milling operations. These naturally reduced zones (NRZs) coincide spatially with a persistent uranium groundwater plume. There is concern that uranium release from NRZs is contributing to plume persistence or will do so in the future. To better define the physical extent, heterogeneity and biogeochemistry of these NRZs, we investigated sediment cores from five neighboring wells. The main NRZ body exhibited uranium concentrations up to 100 mg/kg U as U(IV) and contains ca. 286 g of U in total. Uranium accumulated only in areas where organic carbon and reduced sulfur (as iron sulfides) were present, emphasizing the importance of sulfate-reducing conditions to uranium retention and the essential role of organic matter. NRZs further exhibited centimeter-scale variations in both redox status and particle size. Mackinawite, greigite, pyrite and sulfate coexist in the sediments, indicating that dynamic redox cycling occurs within NRZs and that their internal portions can be seasonally oxidized. We show that oxidative U(VI) release to the aquifer has the potential to sustain a groundwater contaminant plume for centuries. NRZs, known to exist in other uranium-contaminated aquifers, may be regionally important to uranium persistence.

Uranium fate during crystallization of magnetite from ferrihydrite in conditions relevant to the disposal of radioactive waste

AbstractUranium incorporation into magnetite and its behaviour during subsequent oxidation has been investigated at high pH to determine the uranium retention mechanism(s) on formation and oxidative perturbation of magnetite in systems relevant to radioactive waste disposal. Ferrihydrite was exposed to U(VI)aq containing cement leachates (pH 10.5–13.1) and crystallization of magnetite was induced via addition of Fe(II)aq. A combination of XRD, chemical extraction and XAS techniques provided direct evidence that U(VI) was reduced and incorporated into the magnetite structure, possibly as U(V), with a significant fraction recalcitrant to oxidative remobilization. Immobilization of U(VI) by reduction and incorporation into magnetite at high pH, and with significant stability upon reoxidation, has clear and important implications for limiting uranium migration in geological disposal of radioactive wastes.

Uranium Binding Mechanisms of the Acid-Tolerant Fungus Coniochaeta fodinicola

The uptake and binding of uranium [as (UO2)(2+)] by a moderately acidophilic fungus, Coniochaeta fodinicola, recently isolated from a uranium mine site, is examined in this work in order to better understand the potential impact of organisms such as this on uranium sequestration in hydrometallurgical systems. Our results show that the viability of the fungal biomass is critical to their capacity to remove uranium from solution. Indeed, live biomass (viable cells based on vital staining) were capable of removing ∼16 mg U/g dry weight in contrast with dead biomass (autoclaved) which removed ∼45 mg U/g dry weight after 2 h. Furthermore, the uranium binds with different strength, with a fraction ranging from ∼20-50% being easily leached from the exposed biomass by a 10 min acid wash. Results from X-ray absorption spectroscopy measurements show that the strength of uranium binding is strongly influenced by cell viability, with live cells showing a more well-ordered uranium bonding environment, while the distance to carbon or phosphorus second neighbors is similar in all samples. When coupled with time-resolved laser fluorescence and Fourier transformed infrared measurements, the importance of organic acids, phosphates, and polysaccharides, likely released with fungal cell death, appear to be the primary determinants of uranium binding in this system. These results provide an important progression to our understanding with regard to uranium sequestration in hydrometallurgical applications with implications to the unwanted retention of uranium in biofilms and/or its mobility in a remediation context.

Potential use of native fungal strains for assisted uranium retention

Uranium-stabilizing ligands can be useful complexing agents for uranium in aqueous solution. The discovery of novel ligand candidates for selective uranium capture in artificial and natural waters could provide scope for their use in water remediation and metal recovery from low- and high grade ores. In this study we used seven fungal strains, isolated from shale waste, to monitor the uranium retention capacity from an aqueous solution. After four weeks of incubation, suspensions containing the fungal strains were filtered, and up to 100% of the total uranium inventory was removed from a 10mgL−1 solution. Approximately 70% of the total uranium removal is attributed to complexation and/or adsorption by particles in the malt extract and some 10% is adsorbed by the fungal biomass. The additional 20% uranium removed could be related to the excretion of fungal metabolites. From 58% to 90% of the uranium is removed within ten minutes. The formation of colloidal/particulate uranium is proposed to be controlled by organic ligands in the culture medium and organic ligands excreted by the fungi where phosphorus moieties seem to be important. Membrane fouling by the hydrocarbons is also suggested to contribute to a loss of uranium from the aqueous phase.

Cellular localization of uranium in the renal proximal tubules during acute renal uranium toxicity.

Renal toxicity is a hallmark of uranium exposure, with uranium accumulating specifically in the S3 segment of the proximal tubules causing tubular damage. As the distribution, concentration and dynamics of accumulated uranium at the cellular level is not well understood, here, we report on high-resolution quantitative in situ measurements by high-energy synchrotron radiation X-ray fluorescence analysis in renal sections from a rat model of uranium-induced acute renal toxicity. One day after subcutaneous administration of uranium acetate to male Wistar rats at a dose of 0.5 mg uranium kg(-1) body weight, uranium concentration in the S3 segment of the proximal tubules was 64.9 ± 18.2 µg g(-1) , sevenfold higher than the mean renal uranium concentration (9.7 ± 2.4 µg g(-1) ). Uranium distributed into the epithelium of the S3 segment of the proximal tubules and highly concentrated uranium (50-fold above mean renal concentration) in micro-regions was found near the nuclei. These uranium levels were maintained up to 8 days post-administration, despite more rapid reductions in mean renal concentration. Two weeks after uranium administration, damaged areas were filled with regenerating tubules and morphological signs of tissue recovery, but areas of high uranium concentration (100-fold above mean renal concentration) were still found in the epithelium of regenerating tubules. These data indicate that site-specific accumulation of uranium in micro-regions of the S3 segment of the proximal tubules and retention of uranium in concentrated areas during recovery are characteristics of uranium behavior in the kidney.

Alteration, adsorption and nucleation processes on clay–water interfaces: Mechanisms for the retention of uranium by altered clay surfaces on the nanometer scale

Nano-scale processes on the solid–water interface of clay minerals control the mobility of metals in the environment. These processes can occur in confined pore spaces of clay buffers and barriers as well as in contaminated sediments and involve a combination of alteration, adsorption and nucleation processes of multiple species and phases. This study characterizes nano-scale processes on the interface between clay minerals and uranyl-bearing solution near neutral pH. Samples of clay minerals with a contact pH of ∼6.7 are collected from a U mill and mine tailings at Key Lake, Saskatchewan, Canada. The tailings material contains Cu-, As-, Co-, Mo-, Ni-, Se-bearing polymetallic phases and has been deposited with a surplus of Ca(OH)2 and Na2CO3 slaked lime. Small volumes of mill-process solutions containing sulfuric acid and U are occasionally discharged onto the surface of the tailings and are neutralized after discharge by reactions with the slaked lime. Transmission electron microscopy (TEM) in combination with the focused ion beam (FIB) technique and other analytical methods (SEM, XRD, XRF and ICP-OES) are used to characterize the chemical and mineralogical composition of phases within confined pore spaces of the clay minerals montmorillonite and kaolinite and in the surrounding tailings material. Alteration zones around the clay minerals are characterized by different generations of secondary silicates containing variable proportions of adsorbed uranyl- and arsenate-species and by the intergrowth of the silicates with the uranyl-minerals cuprosklodowskite, Cu[(UO2)2(SiO3OH)2](H2O)6 and metazeunerite, Cu[(UO2)(AsO4)2](H2O)8. The majority of alteration phases such as illite, illite–smectite, kaolinite and vermiculite have been most likely formed in the sedimentary basin of the U-ore deposit and contain low amounts of Fe (<5at.%). Iron-enriched Al-silicates or illite–smectites (Fe >10at.%) formed most likely in the limed tailings at high contact pH (∼10.5) and their structure is characterized by a low degree of long-range order. Adsorption of U and nucleation of metazeunerite and cuprosklodowskite are strongly controlled by the presence of the adsorbed oxy-anion species arsenate and silica on the Fe-enriched silicates. Heterogeneous nucleation of nano-crystals of the uranyl minerals occurs most likely on adsorption sites of binary uranyl-, arsenate- and silica-complexes as well as on ternary uranyl–arsenate or uranyl–silicate complexes. The uranyl minerals occur as aggregates of misoriented nano-size crystals and are the result of supersaturated solutions and a high number of nucleation sites that prevented the formation of larger crystals through Oswald ripening. The results of this study provide an understanding of interfacial nano-scale processes between uranyl species and altered clay buffers in a potential Nuclear Waste repository as similar alteration conditions of clays may occur in a multi-barrier system.

Competing retention pathways of uranium upon reaction with Fe(II)

Biogeochemical retention processes, including adsorption, reductive precipitation, and incorporation into host minerals, are important in contaminant transport, remediation, and geologic deposition of uranium. Recent work has shown that U can become incorporated into iron (hydr)oxide minerals, with a key pathway arising from Fe(II)-induced transformation of ferrihydrite, (Fe(OH)3·nH2O) to goethite (α-FeO(OH)); this is a possible U retention mechanism in soils and sediments. Several key questions, however, remain unanswered regarding U incorporation into iron (hydr)oxides and this pathway’s contribution to U retention, including: (i) the competitiveness of U incorporation versus reduction to U(IV) and subsequent precipitation of UO2; (ii) the oxidation state of incorporated U; (iii) the effects of uranyl aqueous speciation on U incorporation; and, (iv) the mechanism of U incorporation. Here we use a series of batch reactions conducted at pH ∼7, [U(VI)] from 1 to 170μM, [Fe(II)] from 0 to 3mM, and [Ca] at 0 or 4mM coupled with spectroscopic examination of reaction products of Fe(II)-induced ferrihydrite transformation to address these outstanding questions. Uranium retention pathways were identified and quantified using extended X-ray absorption fine structure (EXAFS) spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Analysis of EXAFS spectra showed that 14–89% of total U was incorporated into goethite, upon reaction with Fe(II) and ferrihydrite. Uranium incorporation was a particularly dominant retention pathway at U concentrations ⩽50μM when either uranyl–carbonato or calcium–uranyl–carbonato complexes were dominant, accounting for 64–89% of total U. With increasing U(VI) and Fe(II) concentrations, U(VI) reduction to U(IV) became more prevalent, but U incorporation remained a functioning retention pathway. These findings highlight the potential importance of U(V) incorporation within iron oxides as a retention process of U across a wide range of biogeochemical environments and the sensitivity of uranium retention processes to operative (bio)geochemical conditions.

RETRACTED: The retention of uranium and europium onto sepiolite investigated by macroscopic, spectroscopic and modeling techniques

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Executive Editor-in-Chief. Concern was raised about the spectra shown in Figure 8E (sep_Eu2) and Figure 8F (sep_U2), which contained features that indicated data fabrication. The corresponding author was not able to provide reasonable explanations for these features and the Editor decided to retract the article. Moreover, the spectra shown by Figure 8F are highly similar to the spectra from Figure 7D of the article that the first author, the last author et al have previously published in Dalton Transactions 43 (2014) 3888–3896 https://doi.org/10.1039/C3DT52881B. One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not appeared in a publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents an abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

Uranium incorporation into aluminum-substituted ferrihydrite during iron(ii)-induced transformation.

Uranium retention processes (adsorption, precipitation, and incorporation into host minerals) exert strong controls on U mobility in the environment, and understanding U retention is therefore crucial for predicting the migration of U within surface and groundwater. Uranium can be incorporated into Fe (hydr)oxides during Fe(ii)-induced transformation of ferrihydrite to goethite. However, ferrihydrite seldom exists as a pure phase within soils or sediments, and structural impurities such as Al alter its reactivity. The presence of Al in ferrihydrite, for example, decreases the rate of transformation to goethite, and thus may impact the retention pathway, or extent of retention, of U. Here, we investigate the extent and pathways of U(vi) retention on Al-ferrihydrite during Fe(ii)-induced transformation. Ferrihydrite containing 0%, 1%, 5%, 10%, and 20% Al was reacted with 10 μM U and 300 μM Fe(ii) in the presence of 0 mM and 4 mM Ca(2+) and 3.8 mM carbonate at pH 7.0. Solid reaction products were characterized using U L3-edge EXAFS spectroscopy to differentiate between adsorbed U and U incorporated into the goethite lattice. Uranium incorporation into Al-ferrihydrite declined from ∼70% of solid-phase U at 0% and 1% Al to ∼30% of solid phase U at 20% Al content. The decrease in U incorporation with increasing Al concentration was due to two main factors: (1) decreased transformation of ferrihydrite to goethite; and, (2) a decrease of the goethite lattice with increasing Al, making the lattice less compatible with large U atoms. However, uranium incorporation can occur even with an Al-substituted ferrihydrite precursor in the presence or absence of Ca(2+). The process of U incorporation into Al-goethite may therefore be a potential long-term sink of U in subsurface environments where Al-substituted iron oxides are common, albeit at lower levels of incorporation with increasing Al content.