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Background: Hyponatremia is a common electrolyte disturbance in patients with neurological disease; however, its predictive role for outcome in patients with supratentorial spontaneous intracerebral hemorrhage (sICH) is controversial. This study aims to explore the association between hyponatremia within 7 days after bleeding and 90-day mortality in patients with supratentorial sICH., Methods: A retrospective analysis was conducted at our institution. Patients with sICH meeting the inclusion criteria were enrolled in this study. Multivariate regression analyses were performed to determine the predictive value of hyponatremia (serum sodium <135 mmol/L) for 90-day mortality and functional outcome. Subgroup analysis was performed based on the degree and duration of hyponatremia and therapeutic strategies. The Spearman correlation test was performed to explore the relationship between hyponatremia severity and duration with variables in a multivariate regression model. Kaplan-Meier curve was depicted to reveal the relationship between hyponatremia and mortality. The receiver operating characteristic (ROC) curve was plotted to show the diagnostic effect of the minimum concentration of serum sodium (sodium min ) on 90-day mortality., Results: A total of 960 patients were enrolled, 19.6% (188) of whom were patients with hyponatremia and 26.0% (250) had 90-day mortality. The incidence of hyponatremia was roughly 2.5 times in non-survivors compared with survivors (34.8% vs. 14.2%). Multivariate regression analysis revealed that hyponatremia was the independent predictor of 90-day mortality (OR 2.763, 95%CI 1.836-4.157) and adverse outcome (OR 3.579, 95%CI 2.332-6.780). Subgroup analysis indicated an increased trend in mortality risk with both duration (more or less than 48 h) and severity of hyponatremia (mild, moderate, and severe) and confirmed the predictive value of hyponatremia for mortality in patients undergoing surgical intervention (external ventricular drainage, craniotomy, and decompressive craniectomy; all p < 0.05). The Spearman correlation test indicated no moderate or strong relationship between hyponatremia severity and duration with other variables in the multivariate model (all |r s | < 0.4). The ROC curve suggested the moderate diagnostic performance of sodium min for mortality in both general patients and subgroups of therapeutic method patients (AUC from 0.6475 to 0.7384)., Conclusion: Hyponatremia occurring in the first 7 days after bleeding is an independent predictor of 90-day morality and adverse outcome. Rigorous electrolyte scrutiny in patients treated surgically is required., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Qian, Zheng, He, Zhou, Tang and Xing.)

We performed a single-center retrospective cohort study of 66 consecutive ABO incompatible kidney transplants (ABOiKT) performed without B-cell depleting therapy. Outcomes were compared to an earlier era performed with rituximab ( n = 18) and a contemporaneous cohort of ABO compatible live donor transplants (ABOcKT). Acute rejection within 3 months of transplant was significantly more common after rituximab-free ABOiKT compared to ABOiKT with rituximab (OR 8.8, p = 0.04) and ABOcKT (OR 2.9, p = 0.005) in adjusted analyses. Six recipients of rituximab-free ABOiKT experienced refractory antibody mediated rejection requiring splenectomy, and a further two incurred early graft loss with no such episodes amongst ABOiKT with rituximab or ABOcKT cohorts. Patient and graft survival were similar between groups over a median follow-up of 3.1 years. This observational evidence lends strong support to the continued inclusion of rituximab in desensitization protocols for ABOiKT., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Bleasel, Wan, Chadban, Ying, Gracey, Aouad, Chen, Utsiwegota, Mawson and Wyburn.)

Background: Both intrasuprasellar and suprasellar Rathke cleft cysts (RCCs) have suprasellar components, and we aimed to explore their clinical features and surgical outcomes., Method: Patients with surgically treated intrasuprasellar or suprasellar RCCs were retrospectively analyzed. All patients with intrasuprasellar RCCs were treated with the standard endoscopic endonasal approach (EEA, group I); the patients with suprasellar RCCs received the extended EEA (group II) or supraorbital keyhole approach (SKA, group III) according to the relevant indications. A surgical strategy of maximal safe resection aiming to protect neuroendocrine function was adopted. In addition, patients (distinguished from the above 3 groups) who had aggressive resection of suprasellar RCC were also enrolled for comparison of different surgical strategies., Results: A total of 157 patients were eligible, including 121 patients with intrasuprasellar RCCs in group I, 19 patients with suprasellar RCCs in group II, and 17 patients with suprasellar RCCs in group III. Preoperatively, the patients with suprasellar RCC (groups II and III) more commonly presented with visual dysfunction, diabetes insipidus (DI), and hyperprolactinemia than the patients with intrasuprasellar RCCs (all p<0.05). A higher incidence of hypopituitarism and a larger diameter were observed for intrasuprasellar RCCs (both p<0.05). Postoperatively, group II had a higher rate of new-onset DI, hyponatremia, and recurrence than group I (all p<0.025) and similar outcomes to group III. For suprasellar RCCs, comparison of the maximal safe resection vs. aggressive resection (supplementary patients: 14 with extended EEA, 12 with SKA) showed similar improvement and recurrence, with higher rates of DI and hyponatremia with the latter strategy (all p<0.05)., Conclusions: Suprasellar RCC is associated with more complicated preoperative presentations, intricate postoperative complications, and frequent recurrence compared with intrasuprasellar RCC. Under rational indications, both extended EEA and SKA achieve satisfactory outcomes. The strategy of maximal safe resection is recommended for greatest functional preservation., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Electron transfer (ET) is the essence of most biogeochemical processes related to element cycling and contaminant attenuation, whereas ET between different minerals and the controlling mechanism remain elusive. Here, we used surface-associated Fe(II) as a proxy to explore ET between reduced nontronite NAu-2 (rNAu-2) and Fe (hydr)oxides in their coexisting systems. Results showed that ET could occur from rNAu-2 to ferrihydrite but not to goethite, and the ET amount was determined by the number of reactive sites and the reduction potential difference between rNAu-2 and ferrihydrite. ET proceeded mainly through the mineral-mineral interface, with a negligible contribution of dissolved Fe 2+ /Fe 3+ . Control experiments by adding K + and increasing salinity together with characterizations by X-ray diffraction, scanning electron microscopy/energy-dispersive spectrometry, and atomic force microscopy suggested that ferrihydrite nanoparticles inserted the interlayer space in rNAu-2 where structural Fe(II) in rNAu-2 transferred electrons mainly through the basal plane to ferrihydrite. This study implicates the occurrence of ET between different redox-active minerals through the mineral-mineral interface. As minerals at different reduction potentials often coexist in soils/sediments, the mineral-mineral ET may play an important role in subsurface biogeochemical processes.

Backgroud: Recurrence of Rathke's cleft cyst (RCC) is not uncommon after surgery, and the associated factors and incidence of relapse deserve a systematic summary., Methods: This study was conducted in accordance with Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines. The Pubmed, Embase, Cochrane, and Web of Science databases were searched until September 12, 2022. Studies with significant results of recurrent factors or specific incidences of RCC recurrence and mean/median follow-up time were included. Based on a protocol of a 2-year interval grouping, included studies were categorized into four groups with follow-up periods  <24 months, 24-48 months, 48-72 months, and ≥72 months, respectively. Quality assessment was performed using the NOS score. Pooled estimations were computed by using a random-effects model in the STATA "metaprop" command. Publication bias was assessed visually through a funnel plot and statistically through Egger's linear regression test and Begg's correlation test., Results: A total of 44 studies were included containing 2,539 cases. Squamous metaplasia was the most commonly reported factor, followed by the extent of cyst removal. The other factors were reported individually. The pooled overall incidences of RCC recurrence after surgery in four groups of the follow-up period were 7.4% (95%CI = 4.1-11.3%) in <24 months, 13.1% (95%CI = 9.7-17.0%) in 24-48 months, 13.7% (95%CI = 7.7-21.0%) in 48-72 months, and 33.8% (95%CI = 19.6-49.6%) in ≥72 months. The pooled symptomatic incidences were 2.3% (95%CI = 0.4-5.1%) in <24 months, 5.6% (95%CI = 3.6-7.9%) in 24-48 months, 5.9% (95%CI = 2.4-10.6%) in 48-72 months, and 14.1% (95%CI = 6.0-24.5%) in ≥72 months. A dramatic increase in recurrent incidence was observed when the follow-up period was more than 72 months in both overall and symptomatic recurrence. A similar trend of recurrence was found in subgroup analyses stratified by publication year, cohort size, and cyst resection strategy., Conclusion: This study systematically reviewed recurrent factors and described the profile of trends in RCC recurrent incidence after surgery with a follow-up time based on a protocol of a 2-year interval, finding a dramatic increase in recurrent rates with a follow-up period of more than 72 months. This encouraged us to put forward a recommendation of at least a 6-year follow-up after surgery for patients with RCC., Systematic Review Registration: https://www.crd.york.ac.uk/prospero/, identifier: CRD42021278970., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Qian, Zhou, Zhang, Yu and Wang.)

Hydrogen peroxide (H 2 O 2 ) and hydroxyl radical ( • OH) production during oxygenation of reduced iron (Fe(II)) and natural organic matter (NOM) in the subsurface has been increasingly discovered, whereas the effect of the C/Fe molar ratio in Fe(II) and NOM coexisting systems remains poorly understood. In this study, aqueous Fe(II) and reduced humic acid (HA red ) mixture at different C/Fe molar ratios (0-20) were oxygenated. Results show that both H 2 O 2 and • OH accumulation increased almost linearly with the increase in the C/Fe ratio, with a more prominent increase in • OH accumulation at high C/Fe molar ratios. At low C/Fe molar ratios (C/Fe ≤ 1.6), electrons mainly transferred from dissolved inorganic Fe(II), surface-adsorbed Fe(II), and a low proportion of HA-complexed Fe(II) to O 2 ; with the increase in the C/Fe ratio to a high level (C/Fe ≥ 5), the main electron source turned to HA-complexed Fe(II) and free HA red . The changes in the electron source and electron transfer pathway with the increase in the C/Fe ratio increased the yield of • OH relative to H 2 O 2 . This study highlights the important role of the C/Fe ratio in controlling H 2 O 2 and • OH production and therefore in accurately evaluating the associated environmental impacts.

Dark formation of hydroxyl radicals (•OH) from soil/sediment oxygenation has been increasingly reported, and solid Fe(II) is considered as the main electron donor for O 2 activation. However, the role of solid organic matter (SOM) in •OH production is not clear, although it represents an important electron pool in the subsurface. In this study, •OH production from oxygenation of reduced solid humic acid (HA red ) was investigated at pH 7.0. •OH production is linearly correlated with the electrons released from HA red suspension. Solid HA red transferred electrons rapidly to O 2 via the surface-reduced moieties (hydroquinone groups), which was fueled by the slow electron transfer from the reduced moieties inside solid HA. Cycling of dissolved HA between oxidized and reduced states could mediate the electron transfer from solid HA red to O 2 for •OH production enhancement. Modeling results predicted that reduced SOM played an important or even dominant role in •OH production for the soils and sediments possessing high molar ratios of SOC/Fe(II) (e.g., >39). The significant contribution of SOM was further validated by the modeling results for oxygenation of 88 soils/sediments in the literature. Therefore, reduced SOM should be considered carefully to comprehensively understand •OH production in SOM-rich subsurface environments.

Backgroud: Delayed postoperative hyponatremia (DPH) is common for sellar lesions. However, the true prevalence and associated factors of DPH after endoscopic endonasal surgery (EES) for Rathke's cleft cyst (RCC) have not been studied in a large patient cohort., Methods: A retrospective analysis was conducted over 6 years at our institution, and patients with RCC treated by EES were enrolled according to our inclusion criteria. Patient demographics, clinical characteristics, images, and surgical procedures were documented. Serum sodium was routinely measured before surgery, on postoperative day 1, and every 2 days thereafter until discharge. For patients with DPH, electrolyte, hematocrit, serum protein levels, and plasma and urinary osmolality were daily measured to explore potential etiology., Results: Of the 149 eligible patients, 25 (16.8%) developed DPH, which was similar to other sellar lesions, except craniopharyngioma, in the same period in our institution. Significant risk factors suggested by univariate analysis were cyst location, requirement of postoperative hydrocortisone therapy, postoperative meningitis, intraoperative cerebrospinal fluid (CSF) leakage, and subtotal resection (STR) of the cyst wall (all p  < 0.05). In addition, other supplementary 11 cases of suprasellar RCC with different surgical strategies (aggressive resection) and relevant factors were enrolled into multivariate analysis. Suprasellar location [odds ratio (OR) 8.387, 95% confidence interval (CI) 1.014-69.365, p  = 0.049], requirement of postoperative hydrocortisone therapy (OR 4.208, 95%CI 1.246-14.209, p  = 0.021), and intraoperative CSF leakage (OR 6.631, 95%CI 1.728-25.440, p  = 0.006) were found to be the independent predictors of DPH., Conclusion: DPH is a common complication after EES for RCC. Suprasellar location, requirement of postoperative hydrocortisone therapy, and intraoperative CSF leakage are the most reliable risk factors. Cortisol deficiency and syndrome of inappropriate antidiuretic hormone (SIADH) are considered as the main etiologies of DPH in RCC. Conservative excision of the cyst wall may reduce DPH occurrence., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2022 Qian, Zhou, Yu, Huo and Wang.)

Iron electrocoagulation is designed for sustainable high-efficiency and high-flexibility water purification applications. Recent advances reported that hydroxyl radicals (•OH)-based oxidative transformation of organic contaminants can occur in iron electrocoagulation. However, there is still a lack of mechanistic understanding the production of •OH in bicarbonate electrolyte, which presents a critical knowledge gap in the optimization of iron electrocoagulation technology towards practical application. Combined with contaminant degradation, radical quenching experiments, and spectroscopic techniques, we found that •OH was produced at rate of 16.1 μM∙h  -   1 during 30-mA iron electrocoagulation in bicarbonate electrolyte through activation of O 2 by Fe(II) under pH-neutral conditions. High yield of •OH occurred at pH 8.5, likely due to high adsorbed Fe(II) that can activate O 2 to enhance •OH production. Mössbauer and X-ray photoelectron spectroscopy measurements substantiated that Fe(II)-adsorbed lepidocrocite was the dominant solid Fe(II) species at pH 8.5. A process-based kinetic modeling was developed to describe the dynamic of •OH production, Fe(II) oxidation, and contaminant degradation processes in iron electrocoagulation. Findings of this study extend the functionality of electrocoagulation from phase separation to •OH-based advanced oxidation process, which provides a new perspective for the development of electrocoagulation-based next generation sustainable water purification technology., (Copyright © 2022 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Hydroxyl radical (•OH) production by electron transfer from Fe(II)-bearing clay minerals to oxygen has been increasingly reported. However, the influence of ubiquitous coexisting humic acid (HA) on this process is poorly understood. Here, we investigated the effect of different HA on •OH production during the oxygenation of reduced nontronite NAu-2 (rNAu-2), montmorillonite, and sediment. Results showed that HA could enhance •OH production, and the enhancement was related to the content of reactive Fe(II) in rNAu-2 and the electron-accepting capacity of HA. Coexisting HA leads to a new electron-transfer pathway from Fe(II) in rNAu-2 to HA (instead of the HA-Fe complex) and then to O 2 , changing the first step of O 2 reduction from one- to two-electron transfer process with H 2 O 2 as the main intermediate. Reduced HA decomposes H 2 O 2 to •OH at a higher yield (13.8%) than rNAu-2 (8.8%). Modeling results reveal that the HA-mediated electron-transfer pathway contributes to 12.6-70.2% of H 2 O 2 generation and 13.2-62.1% of •OH formation from H 2 O 2 decomposition, with larger contributions at higher HA concentrations (5-100 mg C/L). Our findings implicate that HA-mediated electron transfer can expand the area of •OH production from the mineral surface to the aqueous phase and increase the yield of •OH production.

Reductive transformation of organic contaminants by FeS in anoxic environments has been documented previously, whereas the transformation in oxic environments remains poorly understood. Here we show that phenol can be efficiently oxidized in oxic FeS suspension at circumneutral pH value. We found that hydroxyl radicals (•OH) were the predominant reactive oxidant and that a higher O 2 content accelerated phenol degradation. Phenol oxidation depended on •OH production and utilization efficiency, i.e., phenol degraded per •OH produced. Low FeS contents (≤1 g/L) produced less •OH but higher utilization efficiency, while high contents produced more •OH but lower utilization efficiency. Consequently, the most favorable conditions for phenol oxidation occurred during the long-term interaction between dissolved O 2 and low levels of FeS (i.e., ≤1 g/L). Mössbauer spectroscopy suggests that FeS oxidation to lepidocrocite initially produced an intermediate Fe(II) phase that could be explained by the apparent preferential oxidation of structural S(-II) relative to Fe(II), rendering a higher initial •OH yield upon unit of Fe(II) oxidation. Trichloroethylene can be also oxidized under similar conditions. Our results demonstrate that oxidative degradation of organic contaminants during the oxygenation of FeS can be a significant but currently underestimated pathway in both natural and engineered systems.

Fe(II)-bearing clay minerals are important electron sources for Cr(VI) reduction in subsurface environments. However, it is not clear how iron (oxyhydr)oxides impact Cr(VI) reduction by Fe(II)-bearing clays as the two minerals can coexist in soil and sediment aggregates. This study investigated Cr(VI) reduction in the mixed suspensions of reduced nontronite NAu-2 (rNAu-2) and ferrihydrite (Fe(II)/Cr(VI) = 3:1). When the mineral premixing time increased from 0 to 72 h, Cr(VI) reduction was accelerated prominently in the initial stage, while Cr(VI) sorption was inhibited drastically. Mineral premixing led to electron transfer from structural Fe(II) in rNAu-2 to ferrihydrite with formation of reactive-surface-associated Fe(II), which catalyzed ferrihydrite transformation to lepidocrocite. Reactive-surface-associated Fe(II) accelerated Cr(VI) reduction initially, and ferrihydrite transformation to lepidocrocite was responsible for the inhibited sorption. When the reactive-surface-associated Fe(II) was consumed in the initial stage, the Cr(VI) reduction rate decreased dramatically due to the limitation of slow electron transfer from structural Fe(II) in rNAu-2 to surface-reactive sites. The main reduction sites shifted from rNAu-2 to ferrihydrite/lepidocrocite when rNAu-2 coexisted with ferrihydrite. Our findings demonstrate that electron transfer between minerals has important implications for Cr(VI) and other high-valence contaminant reduction by Fe(II)-bearing clay minerals in subsurface environments.

Iron electrocoagulation (Fe EC) is normally considered as a separation process. Here, we found that Fe(II)-O 2 interactions in Fe EC systems could produce reactive oxidants, mainly hydroxyl radicals (•OH), for refractory organic contaminant transformation. Production of reactive oxidants, probed by benzoate conversion to p -hydroxybenzoic acid ( p -HBA), depended on dissolved oxygen (DO) concentration and Fe(II) speciation. Measurable levels of DO were required for significant p -HBA production. Fe precipitates evolved from lepidocrocite to magnetite when DO decreased to below the detection limit. Both experiments and kinetic modeling suggest that the main Fe(II) species contributing to reactive oxidants (mainly •OH) production changed from aqueous Fe(II) initially to lepidocrocite-sorbed Fe(II) with progressive precipitates formation. When DO was not measurable at high currents (≥50 mA or 100 mA/L), reactive oxidant production was ineffective because of pH rise and Fe(II) preservation in magnetite, but it could be enhanced drastically by aeration. The reactive oxidants produced at 30 mA (or 60 mA/L) could degrade about 47% of 10 μM aniline and 34% of sulfanilamide within 6 h of Fe EC treatment. Our findings highlight the importance of reactive oxidants for refractory organic contaminants oxidation in Fe EC systems.

Perturbation of Fe(III)-bearing oxic environments by reduced species such as sulfide occurs widely in natural and engineered systems. However, whether hydroxyl radicals (OH) can be produced in these environments remains unexplored. Here we show that sulfide drives OH production in Fe(III) oxyhydroxides suspensions under neutral and oxic conditions. For lepidocrocite, ferrihydrite and goethite suspensions at 11.2 mM Fe, the addition of 0.5 mM sulfide produced 14.2, 14.3 and 22.4 μM OH within 120 min, respectively. With addition of sulfide to lepidocrocite suspensions at 11.2 mM Fe, the cumulative OH concentration within 120 min increased from 0 to 14.2, 25.2, 52.6 and 63.1 μM when sulfide dosage increased from 0 to 0.5, 2.5, 5 and 7.5 mM, respectively. At a fixed sulfide dosage of 5 mM, the cumulative OH concentration increased with increasing the number of sulfide additions. The mechanisms of OH production were attributed to the generation of surface-bound Fe(II), most likely in the form of >Fe II OH 2 + , and Fe(II) in the solid phase or FeS from the reactions between sulfide and Fe(III), followed by O 2 activation. OH production could take place until depletion of sulfide. Finally, we found that the generated OH could oxidize the coexisting redox-active substances like phenol under neutral and oxic conditions. Our findings reveal that sulfide perturbation of Fe(III)-bearing oxic environments is a new source of OH, and contaminants oxidation by OH necessitates consideration in these environments., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Dissolved Mn(III) species have recently been recognized as a significant form of Mn in redox transition zones, but their speciation, stability, and reactivity are poorly understood. Besides acting as the intermediate for Mn redox chemistry, Mn(III) can undergo disproportionation producing insoluble Mn oxides and aqueous Mn(II). Using pyrophosphate(PP) as a model ligand, we evaluated the thermodynamic and kinetic stability of Mn(III) complexes. They were stable at circumneutral pH and were prone to (partial) disproportionation at acidic or basic pH. With an initial lag phase, the kinetics of Mn(III)-PP disproportionation was autocatalytic with the produced Mn oxides promoting the disproportionation. X-ray diffraction and the average Mn oxidation state indicated that the solid products were not pure Mn(IV) oxides but a mixture of triclinic birnessite and δ-MnO 2 . Addition of synthetic analogs of the precipitates eliminated the lag phase, confirming their catalytic roles. Thermodynamic calculations adequately predicted the stability regime of Mn(III)-PP. The present results refined the constant for Mn(PP) 2 5- formation, which allows a consistent and quantitative prediction of equilibrium speciation of Mn(III)-Mn(II)-birnessite with PP. A simple and robust model, which incorporated the thermodynamic constraints, autocatalytic rate law, and verified reaction stoichiometry, successfully simulated all kinetic data.

The reaction of manganese oxides with Cr(III)-bearing solids in soils and sediments can lead to the natural production of Cr(VI) in groundwater. Building on previous knowledge of MnO 2 as an oxidant for Cr(III)-containing solids, this study systematically evaluated the rates and mechanisms of the oxidation of Cr(III) in iron oxides by δ-MnO 2 . The Fe/Cr ratio (x = 0.055-0.23 in Cr x Fe 1-x (OH) 3 ) and pH (5-9) greatly influenced the Cr(VI) production rates by controlling the solubility of Cr(III) in iron oxides. We established a quantitative relationship between Cr(VI) production rates and Cr(III) solubility of Cr x Fe 1-x (OH) 3 , which can help predict Cr(VI) production rates at different conditions. The adsorption of Cr(VI) and Mn(II) on solids shows a typical pH dependence for anions and cations. A multichamber reactor was used to assess the role of solid-solid contact in Cr x Fe 1-x (OH) 3 -MnO 2 interactions, which eliminates the contact of the two solids while still allowing aqueous species transport across a permeable membrane. Cr(VI) production rates were much lower in multichamber than in completely mixed batch experiments, indicating that the redox interaction is accelerated by mixing of the solids. Our results suggest that soluble Cr(III) released from Cr x Fe 1-x (OH) 3 solids to aqueous solution can migrate to MnO 2 surfaces where it is oxidized.

Many karst areas are impacted by acid mine drainage (AMD) which is characterized by low pH, high concentrations of dissolved Fe(II) and toxic contaminants. During the flow of AMD in karst areas, the increase in pH facilitates the oxygenation of Fe(II). Whereas, the oxidizing capacity for Fe(II) oxygenation in AMD is poorly understood. In light of the recent finding that hydroxyl radicals (OH) can be produced from Fe(II) oxygenation, this study experimentally measured the cumulative concentrations of OH produced from oxygenation of simulated AMD (8.93 mM Fe 2+ , pH 3) in the presence of limestone (CaCO 3 ). With the increase in CaCO 3 dosages from 0.67 to 2.78 g/L, Fe(II) oxidation rate increased accordingly, but the maximum concentration of cumulative OH appeared at the CaCO 3 dosage of 1.39 g/L, being 59.3 μM within 24 h. The production of OH was mainly attributed to the rise of AMD pH due to dissolution of limestone, rendering the appearance of adsorbed Fe(II) on the newly formed lepidocrocite and ferrihydrite and complexed Fe 2+ by carbonate (i.e., siderite). Oxygenation of these Fe(II) species was accountable for the production of OH. An appropriate pH (i.e., 5-6) was required for the moderate rate of Fe(II) oxidation, corresponding to the maximum production of OH. The OH produced from AMD oxygenation can concurrently oxidize the contaminants of arsenic and p-aminobenzenesulfonamide. Findings from this study suggest that the oxidizing impact of OH on contaminants transformation as well as organic carbon mineralization should be concerned for the oxygenation of AMD in karst areas., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Electrochemical cathodes are often used to reduce contaminants or produce oxidizing substances (i.e., H2O2). Alkaline conditions develop automatically around the cathode in electrochemical processes, and O2 diffuses onto the cathode easily. However, limited attention is paid to contaminant transformation by the reactive species produced on the cathode under oxic and alkaline conditions due to the inapplicability of pH for Fenton reaction. In this study, a new oxidation mechanism on the cathode is presented for contaminant transformation under automatically developed alkaline conditions. In an electrochemical sand column, 6.67 μM As(III) was oxidized by 36% when it passed through the cathode under the conditions of 30 mA current, an initial pH of 7.5 and a flow rate of 2 mL/min. Under the alkaline conditions (pH 10.0-11.0) that developed automatically around the cathode, the reduction potential of As(III) decreased greatly, allowing a pronounced oxidation by the small quantities of H2O2 produced from O2 reduction on the cathode. As(III) oxidation was further increased by the presence of soil pore water and groundwater solutes of HCO3-, Ca2+, Mg2+ and humic acid. The new oxidation mechanism found for the cathode under localized alkaline conditions supplements the fundamentals of contaminant transformation in electrochemical processes.

Pd-catalytic process is effective for reducing a wide range of contaminants in groundwater. However, limited attention is paid to Cr(VI) reduction presumably due to the weakly oxidizing potential of Cr(VI) under circumneutral conditions. In this study, a new concept of in situ reducing Cr(VI) in groundwater by a hybrid electro-Pd process with automatic pH adjustments is proposed and justified. In an undivided electrolytic cell, Cr(VI) at 5 mg/L is reduced by 95% within 30 min under conditions of pH 3, 1 g/L Pd/Al2O3 and 20 mA current. Reduction of Cr(VI) increases with decreasing pH and increasing current and Pd/Al2O3 dosage. Inhibition of anodic O2 is significant but decreases with drop of pH. Atomic H is assigned as the predominant reactive species contributing to Cr(VI) reduction. Although H2O2 is effective for reducing Cr(VI), its production on Pd surface is completed inhibited by the presence of Cr(VI). The concept is ultimately justified using a specially configured three-electrode column. Cr(VI) is effectively reduced to Cr(3+) in the locally acidic Pd zone, and Cr(3+) is then precipitated in the downstream neutral zone. This hybrid electro-Pd process could be potentially applied in the in situ remediation of Cr(VI)-contaminated groundwater., (Copyright © 2013 Elsevier Ltd. All rights reserved.)