Enhanced Cd2+ removal from aqueous solution using olivine and magnesite combination: New insights into the mechanochemical synergistic effect.

In this study, an efficient stabilizer material for cadmium (Cd2+) treatment was successfully prepared by simply co-milling olivine with magnesite. Several analytical methods including XRD, TEM, SEM and FTIR, combined with theoretical calculations (DFT), were used to investigate mechanochemical interfacial reaction between two minerals, and the reaction mechanism of Cd removal, with ion exchange between Cd2+ and Mg2+ as the main pathway. A fixation capacity of Cd2+ as high as 270.61 mg/g, much higher than that of the pristine minerals and even the individual/physical mixture of milled olivine and magnesite, has been obtained at optimized conditions, with a neutral pH value of the solution after treatment to allow its direct discharge. The as-proposed Mg-based stabilizer with various advantages such as cost benefits, green feature etc., will boosts the utilization efficiency of natural minerals over the elaborately prepared adsorbents.

Inhibition of jarosite heterogeneous crystallization on anglesite via in-situ formation of competitive substrate.

Heterogeneous crystallization is a common occurrence during the formation of solid wastes. It leads to the encapsulation of valuable/hazardous metals within the primary phase, presenting significant challenges for waste treatment and metal recovery. Herein, we proposed a novel method involving the in-situ formation of a competitive substrate during the precipitation of jarosite waste, which is an essential process for removing iron in zinc hydrometallurgy. We observed that the in-situ-formed competitive substrate effectively inhibits the heterogeneous crystallization of jarosite on the surface of anglesite, a lead-rich phase present in the jarosite waste. As a result, the iron content on the anglesite surface decreases from 34.8% to 1.65%. The competitive substrate was identified as schwertmannite, characterized by its loose structure and large surface area. Furthermore, we have elucidated a novel mechanism underlying this inhibition of heterogeneous crystallization, which involves the local supersaturation of jarosite caused by the release of ferric and sulfate ions from the competitive substrate. The local supersaturation promotes the preferential heterogeneous crystallization of jarosite on the competitive substrate. Interestingly, during the formation of jarosite, the competitive substrate gradually vanished through a dissolution-recrystallization process following the Ostwald rule, where a metastable phase slowly transitions to a stable phase. This effectively precluded the introduction of impurities and reduced waste volume. The goal of this study is to provide fresh insights into the mechanism of heterogeneous crystallization control, and to offer practical crystallization strategies conducive to metal separation and recovery from solid waste in industries.

Taxonomic and functional characterization of biofilms from a photovoltaic panel reveals high genetic and metabolic complexity of the communities.

AIMS: Biofilms are complex microbial cell aggregates that attach to different surfaces in nature, industrial environments, or hospital settings. In photovoltaic panels (PVs), biofilms are related to significant energy conversion losses. In this study, our aim was to characterize the communities of microorganisms and the genes involved in biofilm formation. METHODS AND RESULTS: In this study, biofilm samples collected from a PV system installed in southeastern Brazil were analyzed through shotgun metagenomics, and the microbial communities and genes involved in biofilm formation were investigated. A total of 2030 different genera were identified in the samples, many of which were classified as extremophiles or producers of exopolysaccharides. Bacteria prevailed in the samples (89%), mainly the genera Mucilaginibacter, Microbacterium, Pedobacter, Massilia, and Hymenobacter. The functional annotation revealed >12 000 genes related to biofilm formation and stress response. Genes involved in the iron transport and synthesis of c-di-GMP and c-AMP second messengers were abundant in the samples. The pathways related to these components play a crucial role in biofilm formation and could be promising targets for preventing biofilm formation in the PV. In addition, Raman spectroscopy analysis indicated the presence of hematite, goethite, and ferrite, consistent with the mineralogical composition of the regional soil and metal-resistant bacteria. CONCLUSIONS: Taken together, our findings reveal that PV biofilms are a promising source of microorganisms of industrial interest and genes of central importance in regulating biofilm formation and persistence.

Molecular characterization on the fractionation of organic phosphorus induced by iron oxide adsorption using ESI-FT-ICR MS.

The interaction between organic phosphorus (OP) and iron oxide significantly influences the phosphorus cycle in the natural environment. In shallow lakes, intense oxidation-reduction fluctuations constantly alter the existing form of iron oxides, but little is known about their impact on the adsorption and fractionation of OP molecules. In this study, electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS) was used to investigate the fractionation of OP from alkali-extracted sediment induced by crystalline goethite and amorphous ferrihydrite adsorption at a molecular scale. The results showed that ferrihydrite and goethite both exhibited high OP adsorption, and the adsorption amount decreased as the pH increased. The adsorption kinetics matched the pseudo-second-order equation. The ESI-FT-ICR MS analysis showed that 91 P-containing formulas were detected in the alkaline-extracted sediment solution. Ferrihydrite and goethite adsorbed 51 and 24 P-containing formulas, respectively, with adsorption rates of 56.0 % and 26.4 %. Ferrihydrite could adsorb more OP compounds than goethite, but no obvious molecular species selectivity was observed during the adsorption. The P-containing compounds, including unsaturated hydrocarbons-, lignin/carboxyl-rich alicyclic molecule (CRAM)-, tannin-, and carbohydrate-like molecular compounds, were more suitable for iron oxide adsorption. The double bond equivalence (DBE) is a valuable parameter that indicates OP fractionation during adsorption, and P-containing compounds with lower DBE values such as lipid- and protein-like molecular were prone to remain in the solution after adsorption. These research results provide insights into the biogeochemical cycling process of P in the natural environment.

Insights into the Photochemical Mechanism of Goethite: Roles of Different Types of Surface Hydroxyl Groups in Reactive Oxygen Species Generation and Fe(III) Reduction.

The surface photochemical activity of goethite, which occurs widely in surface soils and sediments, plays a crucial role in the environmental transformation of various pollutants and natural organic matter. This study systemically investigated the mechanism of different types of surface hydroxyl groups on goethite in generating reactive oxygen species (ROSs) and Fe(III) reduction under sunlight irradiation. Surface hydroxyl groups were found to induce photoreductive dissolution of Fe(III) at the goethite-water interface to produce Fe2+(aq), while promoting the production of ROSs. Substitution of the surface hydroxyl groups on goethite by fluoride significantly inhibited the photochemical activity of goethite, demonstrating their important role in photochemical activation of goethite. The results showed that the surface hydroxyl groups (especially the terminating hydroxyl groups, ≡FeOH) led to the formation of Fe(III)-hydroxyl complexes via ligand-metal charge transfer on the goethite surface upon photoexcitation, facilitating the production of Fe2+(aq) and •OH. The bridging hydroxyl groups (≡Fe2OH) were shown to mainly catalyze the production of H2O2, leading to the subsequent light-driven Fenton reaction to produce •OH. These findings provide important insights into the activation of molecular oxygen on the goethite surface driven by sunlight in the environment, and the corresponding degradation of anthropogenic and natural organic compounds caused by the generated ROSs.

Treatment of tetracycline in an aqueous solution with an iron-biochar/periodate system: Influencing factors and mechanisms.

In this study, a potassium ferrate (K2FeO4)-modified biochar (Fe-BC) was prepared and characterized. Afterwards, Fe-BC was applied to activated periodate (PI) to degrade tetracycline (TC), an antibiotic widely used in animal farming. The degradation effects of different systems on TC were compared and the influencing factors were investigated. In addition, several reactive oxygen species (ROS) generated by the Fe-BC/PI system were identified, and TC degradation pathways were analyzed. Moreover, the reuse performance of Fe-BC was evaluated. The results exhibited that the Fe-BC/PI system could remove almost 100% of TC under optimal conditions of [BC] = 1.09 g/L, initial [PI] = 3.29 g/L, and initial [TC] = 20.3 mg/L. Cl-, HCO3-, NO3-, and humic acid inhibited TC degradation to varying degrees in the Fe-BC/PI system due to their quenching effects on ROS. TC was degraded into intermediates and even water and carbon dioxide by the synergistic effect of ROS generated and Fe on the BC surface. Fe-BC was reused four times, and the removal rate of TC was still maintained above 80%, indicating the stable nature of Fe-BC.

Generic phosphate affinity constants of the CD-MUSIC-eSGC model to predict phosphate adsorption and dominant speciation on iron (hydr)oxides.

Estimating the availability of phosphorus in soils and sediments is complicated by the diverse mineralogical properties of iron (hydr)oxides that control the environmental fate of phosphorus. Despite various surface complexation models have been developed, lack of generic phosphate affinity constants (logKPO4s) for iron (hydr)oxides hinders the prediction of phosphate adsorption to iron (hydr)oxides in nature. The aim of this work is to derive generic logKPO4s for the Charge Distribution-Multisite Complexation extended-Stern-Gouy-Chapman (CD-MUSIC-eSGC) model using a large phosphate adsorption database and previously derived generic protonation parameters. The optimized logKPO4s of goethite, hematite and ferrihydrite are located in a much narrower range than those in the RES3T database. Specifically, the logKPO4 ranges of FeOPO3, FeOPO2OH, FeOPO(OH)2, (FeO)2PO2, and (FeO)2POOH complexes were 17.40-18.00, 24.20-27.40, 27.90-29.80, 26.50-29.60, and 30.70-33.40, respectively. A simplified CD-MUSIC-eSGC model with species FeOPO2OH and (FeO)2PO2 and generic logKPO4 values 26.0 ± 0.9 and 27.9 ± 0.8, respectively, provides an accurate prediction of phosphate adsorption and dominant speciation to the iron (hydr)oxides at environmental pH and phosphate levels. For ferrihydrite at low pH and high phosphate levels the species FeOPO(OH)2 and (FeO)2POOH cannot be neglected. The simplified model expands the application boundaries of CD-MUSIC-eSGC model in predicting the phosphate adsorption on natural iron (hydr)oxides without laborious characterization.

(SiFA)SeFe: A Hydrophilic Silicon-Based Fluoride Acceptor Enabling Versatile Peptidic Radiohybrid Tracers.

The radiohybrid (rh) concept to design targeted (and chemically identical) radiotracers for imaging or radionuclide therapy of tumors has gained momentum. For this strategy, a new bifunctional Silicon-based Fluoride Acceptor (SiFA) moiety (SiFA)SeFe was synthesized, endowed with improved hydrophilicity and high versatility of integration into rh-compounds. Preliminary radiolabeling and stability studies under different conditions were conducted using model bioconjugate peptides. Further, three somatostatin receptor 2 (sstR2)-targeted rh-compounds ((SiFA)SeFe-rhTATE1-3, TATE = (Tyr3)-octreotate) were developed. Compound (SiFA)SeFe-rhTATE3, enables labeling with 18F for PET imaging or chelation of 177Lu for therapy. The rh-compounds possess comparable receptor binding affinity and in vitro performance as good as the clinically proven gold standards. SstR2-specificity was further shown for (SiFA)SeFe-rhTATE2 using the chicken chorioallantoic membrane (CAM) model. The biodistribution of two compounds in mice showed high accumulation in tumors and excretion via the kidneys, demonstrating the clinical applicability of the (SiFA)SeFe moiety.

Potential of CO2 sequestration by olivine addition in offshore waters: A ship-based deck incubation experiment.

Ocean alkalinity enhancement is considered as an effective atmospheric CO2 removal approach, but currently, little is known about the carbon sequestration potential of implementing olivine addition in offshore waters. We investigated the effect of olivine addition on the seawater carbonate system by carrying out a deck incubation experiment in the Northern Yellow Sea; the dissolution rate of olivine was calculated based on the increase in seawater alkalinity (TA), and the CO2 sequestration potential was evaluated. The results showed that the dissolution of olivine increased seawater TA and decreased partial pressure of CO2, resulting in oceanic CO2 uptake from the atmosphere through sea-air exchange; it also increased seawater pH and mitigated ocean acidification to a certain extent. The addition of 1 ‰ olivine had a more significant effect on the seawater carbonate system than 0.5 ‰ olivine addition. The average dissolution rate constant of olivine was 1.44 ± 0.15 µmol m-2 d-1. Assuming that olivine settles completely on the seabed due to gravity, the theoretically maximum amount of CO2 removed by applying 1 tonne of olivine per square meter area in the Northern Yellow Sea is only 2.0 × 10-4 t/m2. Therefore, when olivine addition is implemented in the offshore waters, it is necessary to consider reducing the olivine size, prolonging the settling time of olivine in the water column; and spreading olivine in well-mixed waters to prolong the residence time through repeated resuspension, thus increasing its potential in carbon sequestration.

Impact of ionic strength on goethite colloids co-transported with arsenite (As3+) through a saturated sand column under anoxic condition: Experiment and mathematical modeling.

The knowledge about co-transport of goethite and As3+ to investigate the effect of goethite colloids on As3+ transport under various degrees of seawater intrusion, particular extremely conditions, in groundwater environment is still limited. The main objective is to investigate the influence of seawater intrusion on the sorption, migration, and reaction of As3+and goethite colloids into sand aquifer media under anoxic conditions by using the bench-scale and reactive geochemical modeling. The research consisted of two parts as follows: 1) column transport experiments consisting of 8 columns, which were packed by using synthesis groundwater at IS of 0.5, 50, 200, and 400 mM referring to the saline of seawater system in the study area, and 2) reactive transport modeling, the mathematical model (HYDRUS-1D) was applied to describe the co-transport of As3+ and goethite. Finally, to explain the interaction of goethite and As3+, the Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation was considered to support the experimental results and HYDRUS-1D model. The results of column experiments showed goethite colloids can significantly inhibit the mobility of As3+ under high IS conditions (>200 mM). The Rf of As3+ bound to goethite grows to higher sizes (47.5 and 65.0 µm for 200 and 400 mM, respectively) of goethite colloid, inhibiting As3+ migration through the sand columns. In contrast, based on Rf value, goethite colloids transport As3+ more rapidly than a solution with a lower IS (0.5 and 50 mM). The knowledge gained from this study would help to better understand the mechanisms of As3+ contamination in urbanized coastal groundwater aquifers and to assess the transport of As3+ in groundwater, which is useful for groundwater management, including the optimum pumping rate and long-term monitoring of groundwater quality.

Enhanced methane production from waste activated sludge by potassium ferrate combined with thermal hydrolysis pretreatment.

Anaerobic digestion of waste activated sludge (WAS) was one of the directions of sludge treatment, but how to effectively improve the production of methane as a resource product of anaerobic digestion of sludge still needs further research. The study examined how the combination of potassium ferrate (PF) and thermal hydrolysis (TH) pretreatment affected methane production from sludge. The results demonstrated a positive synergistic effect on methane production with PF-TH pretreatment. Specifically, by employing a 0.05 g/g TSS (total suspended solids) PF in conjunction with TH at 80 °C for 30 min, the methane yield increased from 170.66 ± 0.92 to 232.73 ± 2.21 mL/g VSS (volatile suspended solids). The co-pretreatment of PF and TH has been substantiated by mechanism studies to effectively enhance the disintegration and biodegradability of sludge. Additionally, the variation of microbial community revealed an enrichment of active microorganisms associated with anaerobic digestion after treated with PF + TH, resulting in a total abundance increase from 11.87 to 20.45% in the PF + TH group.

Unveiling the Mechanism and Kinetics of Pollutant Attenuation by Free Radicals Triggered from Goethite in Water Distribution Systems.

Investigating the fate of persistent organic pollutants in water distribution systems (WDSs) is of great significance for preventing human health risks. The role of iron corrosion scales in the migration and transformation of organics in such systems remains unclear. Herein, we determined that hydroxyl (•OH), chlorine, and chlorine oxide radicals are generated by Fenton-like reactions due to the coexistence of oxygen vacancy-related Fe(II) on goethite (a major constituent of iron corrosion scales) and hypochlorous acid (HClO, the main reactive chlorine species of residual chlorine at pH ∼ 7.0). •OH contributed mostly to the decomposition of atrazine (ATZ, model compound) more than other radicals, producing a series of relatively low-toxicity small molecular intermediates. A simplified kinetic model consisting of mass transfer of ATZ and HClO, •OH generation, and ATZ oxidation by •OH on the goethite surface was developed to simulate iron corrosion scale-triggered residual chlorine oxidation of organic compounds in a WDS. The model was validated by comparing the fitting results to the experimental data. Moreover, the model was comprehensively applicable to cases in which various inorganic ions (Ca2+, Na+, HCO3-, and SO42-) and natural organic matter were present. With further optimization, the model may be employed to predict the migration and accumulation of persistent organic pollutants under real environmental conditions in the WDSs.

Multicomponent and Surface Charge Effects on PFOS Sorption and Transport in Goethite-Coated Porous Media under Variable Hydrochemical Conditions.

Perfluorooctanesulfonate (PFOS), a toxic anionic perfluorinated surfactant, exhibits variable electrostatic adsorption mechanisms on charge-regulated minerals depending on solution hydrochemistry. This work explores the interplay of multicomponent interactions and surface charge effects on PFOS adsorption to goethite surfaces under flow-through conditions. We conducted a series of column experiments in saturated goethite-coated porous media subjected to dynamic hydrochemical conditions triggered by step changes in the electrolyte concentration of the injected solutions. Measurements of pH and PFOS breakthrough curves at the outlet allowed tracking the propagation of multicomponent reactive fronts. We performed process-based reactive transport simulations incorporating a mechanistic network of surface complexation reactions to quantitatively interpret the geochemical processes. The experimental and modeling outcomes reveal that the coupled spatio-temporal evolution of pH and electrolyte fronts, driven by the electrostatic properties of the mineral, exerts a key control on PFOS mobility by determining its adsorption and speciation reactions on goethite surfaces. These results illuminate the important influence of multicomponent transport processes and surface charge effects on PFOS mobility, emphasizing the need for mechanistic adsorption models in reactive transport simulations of ionizable PFAS compounds to determine their environmental fate and to perform accurate risk assessment.

The pH-dependent role of different manganese oxides in the fate of arsenic during microbial reduction of arsenate-bearing goethite.

Manganese oxides reduce arsenic (As) toxicity by promoting aqueous-phase As(III) oxidation and immobilization in natural aquatic ecosystems. In anaerobic water-sediment systems, arsenic exists both in a free state in the liquid phase and in an adsorbed state on iron (Fe) minerals. However, the influence of different manganese oxides on the fate of As in this system remains unclear. Therefore, in this study, we constructed an anaerobic microbial As(V) reduction environment and investigated the effects of three different manganese oxides on the fate of both aqueous-phase and goethite-adsorbed As under different pH conditions. The results showed that δ-MnO2 had a superior As(III) oxidation ability in both aqueous and solid phase due not only to the higher SSA, but also to its wrinkled crystalline morphology, less favorable structure for bacterial reduction, structure conducive to ion exchange, and less interference caused by the formation of secondary Fe-minerals compared to α-MnO2 and γ-MnO2. Regarding aqueous-phase As, δ-MnO2, α-MnO2, and γ-MnO2 required an alkaline condition (pH 9) to exhibit their strongest As(III) oxidation and immobilization capability. For goethite-adsorbed As, under microbial-reducing conditions, all manganese oxides had the highest As immobilization effect in neutral pH environments and the strongest As oxidation effect in alkaline environments. This was because at pH 7, Fe(II) and Mn(II) formed hydrated complexes, which was more favorable for As adsorption. At pH 9, the negatively charged state of goethite hindered As adsorption but promoted the adsorption and oxidation of As by the manganese oxides. Our research offers new insights for optimizing As removal from water using various manganese oxides and for controlling the mobilization of As in water-sediment system under different pH conditions.

Solid-liquid partitioning and speciation of Pb(II) and Cd(II) on goethite under high pH conditions, as examined by subnanomolar heavy metal analysis, X-ray absorption spectroscopy, and surface complexation modeling.

The adsorption of heavy metals on iron oxides generally increases with pH and is almost complete at neutral to slightly alkaline pH. However, almost complete adsorption on a linear scale does not imply sufficient removal of the heavy metals in terms of their toxicity. Here, we elucidated the chemical reactions that determine the solid-liquid partitioning of Pb(II) and Cd(II) on goethite at high pH. While the removal of both heavy metals was almost complete on a linear scale above pH 7 for Pb(II) and pH 9 for Cd(II), the dissolved metal concentrations decreased on a logarithmic scale with pH, reaching minima at around pH 10 for Pb(II) and pH 10-11 for Cd(II), and then they increased with pH thereafter. The XAFS spectra of Pb(II)- or Cd(II)-adsorbed goethite prepared at pH > 11 were almost the same as those at neutral pH, suggesting that removal of the heavy metals from solution was achieved by a single adsorption reaction over the entire pH range. Based on the observed macroscopic and microscopic adsorption behaviors at high pH, a robust surface complexation model was developed to predict the solid-liquid partitioning of divalent heavy metals over the entire pH range.

Iron minerals enhance Fe(II)-mediated abiotic As(III) oxidation.

The abiotic oxidation of As(III) is simultaneously mediated by the oxidation of Fe(II) in microaerobic environment, but the role of Fe minerals in the Fe(II)-mediated As(III) oxidation have been neglected. This work mimicked the microaerobic environment and examined the mechanisms of Fe(II) mediated the As(III) oxidation in the presence of Fe minerals using a variety of iron minerals (lepidocrocite, goethite, etc.). The results indicated the Fe(II) and As(III) oxidation rate were improved with Fe minerals, while As(III) oxidation efficiency increased by 1.3-1.8 times in comparison to that without minerals. Fe(II) mediated the As(III) oxidation happened on Fe minerals surface in the presence of Fe minerals. The As(III) oxidation efficiency increased with increasing Fe mineral concentrations (from 0.5 to 2 g L-1) but decreased with increasing pH values. Reactive oxygen species (ROS) that play a crucial role in As(III) oxidation were Fe(IV) and ·O2-, accounting for 42.7%-47.9% and 24.1%-29.8%, respectively. The Fe minerals facilitated the oxidation of As(III) by ROS and stimulated the release of ROS through the adsorbed-Fe(II) oxidation, both of which favored As(III) oxidation. This work highlighted the potential mechanisms of Fe minerals in promoting Fe(II) mediated the As(III) oxidation in microaerobic environment, especially in terms of As(III) oxidation efficiency, shedding a valuable insight on optimization of arsenic contaminated wastewater treatment processes.

Influence of macromolecules and electrolytes on heteroaggregation kinetics of polystyrene nanoplastics and goethite nanoparticles in aquatic environments.

Fate and transport of nanoplastics in aquatic environments are affected by their heteroaggregation with minerals in the presence of macromolecules. This study investigated the heteroaggregation of polystyrene nanoplastics (PSNPs) with goethite nanoparticles (GNPs) under the influence of macromolecules [humic acid (HA), bovine serum albumin (BSA), and DNA] and electrolytes. Under 1 mg C/L macromolecule, raising electrolyte concentration promoted heteroaggregation via charge screening, except that calcium bridging with HA also enhanced heteroaggregation at CaCl2 concentration above 5 mM. At all NaCl concentrations and CaCl2 concentration below 5 mM, 1 mg C/L macromolecules strongly retarded heteroaggregation, ranking BSA > DNA > HA. Raising macromolecule concentration strengthened such stabilization effect of all macromolecules in NaCl solution and that of DNA and BSA in CaCl2 solution by enhancing steric hindrance. However, 0.1 mg C/L BSA slightly promoted heteroaggregation in CaCl2 solution due to stronger electrostatic attraction than steric hindrance. In CaCl2 solution, raising HA concentration strengthened its destabilization effect via calcium bridging. Macromolecules having more compact globular structure and higher molecular weight may exert greater steric hindrance to inhibit heteroaggregation more effectively. This study provides new insights on the effects of macromolecules and electrolytes on heteroaggregation between nanoplastics and iron minerals in aquatic environments.

Green preparation of regenerable biohybrids with xanthan gum-stabilized biogenic mackinawite nanoparticles for efficient treatment from high-concentration uranium wastewater.

The high efficiency, economy, sustainability and no secondary pollution of U(VI) removal is an important and challenging topic for U(VI) wastewater treatment. Here, the regenerable biohybrids with xanthan gum (XG) stabilized biogenic mackinawite nanoparticles (BX-FeS) were prepared, where XG acted as carrier facilitated the Fe2+ attachment and induced the low size, high stability and activity of nearly spherical FeS nanoparticles. Results showed that BX-FeS kept high activity after storing two years and good performance for U(VI) removal in broad pH range and co-existence of ions, and had greater removal efficiency (97.9 %) than biogenic B-FeS (67.1 %). Moreover, BX-FeS preformed high adsorption capacity in uranium wastewater (658.0 mg/g), and lower cost compared with zerovalent-iron and silica gel. Importantly, BX-FeS maintained high activity within three regeneration cycles driven by Desulfovibrio desulfuricans, inhibited the secondary pollution (Fe3+, SO42-) of reaction. This study provides a new strategy for sustainable and efficient treatment of U(VI) wastewater.

New insights into the controversy of reactive mineral-controlled arsenopyrite dissolution and arsenic release.

Serious arsenic (As) contaminations could commonly result from the oxidative dissolution of As-containing sulfide minerals, such as arsenopyrite (FeAsS). Pyrite (Py) and calcite (Cal) are two typically co-existing reactive minerals and represent different geological scenarios. Previous studies have shown that a high proportion of Py can generate a stronger galvanic effect and acid dissolution, thereby significantly promoting the release of arsenic. However, this conclusion overlooks calcite's antagonistic effect on the release of As in the natural environment. That antagonistic effect could remodel the linear relationship of pyrite on the oxidative dissolution of arsenopyrite, thus altering the environmental risk of As. We examined As release from arsenopyrite along a gradient of Py to Cal molar ratios (Py:Cal). The results showed that the lowest As release from arsenopyrite was surprisingly found in co-existing Py and Cal systems than in the singular Cal system, let alone in the singular Py system. This phenomenon indicated an interesting possibility of Py assistance to Cal inhibition of As release, though Py has always been regarded as a booster, also evidenced in this research, for As release from arsenopyrite. In singular systems of Py and Cal, As continued to be released for 60 days. However, in co-existing Py and Cal systems, As was released non-linearly in three stages over time: initial release (0-1 Day), immobilization (1-15 Days), and subsequent re-release (>15 Days). This is a new short-term natural attenuation stage for As, but over time, this stage gradually collapses. During the re-release stage (> 15 Days), a higher molar ratio of Py:Cal (increasing from 1:9 to 9:1) results in a lower rate constant k (mg·L-1·h-1) of As release (range from 0.0011 to 0.0002), and a higher abundance of secondary minerals formed (up to 26 mg/g goethite and hematite at Py: Cal=9:1). This demonstrates that increasing the Py:Cal molar ratio results in the formation of more secondary minerals which compensate for the higher potential antagonistic mechanisms generated by pyrites, such as acid dissolution and galvanic effect. These results explain the mechanisms of the high-risk characteristics of As both in acidic mine drainage and karst aquifers and discover the lowest risk in pyrite and calcite co-existing regions. Moreover, we emphasize that reactive minerals are important variables that can't be ignored in predicting As pollution in the future.

Going deeper into plutonium sorption affected by redox.

Sorption of Pu(VI) onto synthesized goethite under oxidizing and normal conditions was investigated, which revealed its pH dependence on different solid/liquid ratios. Pu speciation upon sorption on the solid phase was characterized via extended X-ray absorption fine structure (EXAFS) spectroscopy, while that in solution was assessed using ultraviolet-visible (UV-Vis) spectroscopy and liquid-liquid extraction. The obtained results demonstrate differences in plutonium behavior in the studied systems. Pu(VI) remains hexavalent on the goethite surface and in solution under oxidizing conditions. While Pu(IV) is stabilized on the mineral and Pu(V) is found in solution under normal conditions. This study provides the thermodynamic descriptions of these reactions.