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The present study evaluates the color wastewater treatment in the textile industry by the persulfate/ dithionite (PS/DTN) process. This study was performed on a laboratory scale in a reactor with a batch system. The wastewater was taken from the textile industry, and the efficiency of the PS/DTN process in the treatment and removal of COD of this wastewater was optimized by the operational parameters of pH, PS, DTN, and reaction time. Optimal values of these parameters were obtained at pH = 3, PS = DTN = 1.5 g/L, and reaction time = 90 min. Although in optimal condition, the removal efficiency of COD and TOC reached 64.9 and 54.5%; it does not meet the required discharge conditions and standards. On the other hand, it was observed that this process has a good ability to improve the biodegradability properties of textile wastewater, and the results showed a good increase in BOD5/COD and average oxidation state (AOS) and carbon oxidation state (COS) indexes to 0.47, 0.7, and by 2.4. Dominant radical contributed to the system for oxidation was found to be SO 4 ∙ - based on the scavenger radical test. According to the findings, it can be suggested that this system can be proposed as a pre-treatment step to reduce the toxicity of wastewater and reduce the input COD load to the biological system. [ABSTRACT FROM AUTHOR]

Wet‐chemical extraction of soil to quantify pedogenic species or to remove specific compounds prior to other analyses is an established approach in analytical soil mineralogy and soil chemistry. Interpretation and informational value of data derived from long‐established and frequently used extractions, for instance involving dithionite, oxalate/oxalic acid in the dark (AOD), and pyrophosphate (PYR), suffers from nonuniform practical regulation and missing knowledge about potential methodical limitations. In this review, we analyzed potential pitfalls of these frequently used extractions, with the focus on selectivity and completeness of the methods as derived from effects of time dependency and of phase separation. Major problems we identified comprised that time‐dependency of extraction differed between analytical targets, that a multitude of species is attacked, reducing the selectivity for the original analytical target, and that studies on extraction from model compounds, including analytical targets and nontargets, are not universally present. The latter aspect is crucial for the completeness of AOD and PYR extraction that has not been proven for all potential analytical targets of the methods yet. We practically tested citrate (CIT) extraction of aluminum (Al) and iron (Fe) in organic association, using selected models of soil constituents. Apart from a synthesized poorly ordered Si‐rich short‐range ordered aluminosilicate, CIT did not extract Al from nontarget phases, confirming previous studies, but did extract Al and Fe completely from organic associations. In addition to recommendations on the practical use of dithionite‐based, AOD, citrate‐ascorbate (CA), and CIT extraction, we suggest replacing highly problematic PYR extraction by CIT extraction for metals in organic association in soil and using AOD extraction in combination with CA and CIT extraction to avoid potential misinterpretation of ambiguous data. [ABSTRACT FROM AUTHOR]

The study examined the composition and forms of iron and aluminium oxides in benchmark soils of central southwestern Nigeria. Soils developed from distinct parent rock types, including coarse-grained granite and gneiss, fine grained biotite gneiss and schist, and the amphibolite complex which correspond to the parent rocks of the soils of Iwo (Typic Paleustults), Egbeda (Rhodic Kandiustults) and Itagunmodi (Typic Haplustults) Associations, respectively, were selected for the study. Notably, these soils collectively encompass approximately 60% of the total land area in central southwestern Nigeria. The less than 2 mm soil fractions were pre-treated with hydrogen peroxide to remove soil organic matter. Thereafter, oxides of Fe and Al were extracted using three different extractants: dithionite-citrate-bicarbonate (DCB) mixtures, acidified ammonium oxalate and sodium pyrophosphate solution. The quantification of Fe and Al oxides contents in the respective extracts were carried out using Inductively Coupled Plasma—Atomic Emission Spectrometry. The research findings indicated that the DCB extractable forms of Fe and Al oxides were more abundant compared to other forms of these oxides, and a substantial portion of these oxides within the soils existed in crystalline form. Among the soil series studied, Itagunmodi series exhibited the highest amount of DCB- and oxalate extractable Fe oxides, while Iwo series had the highest content of Fe and Al oxides extracted by sodium pyrophosphate solution. Importantly, the presence of Fe oxides were found to negatively impact the reactivity of SOM in the soils. [ABSTRACT FROM AUTHOR]

Advanced Reduction Processes (ARP) are emerging technology that allows the breakdown of oxidation-resistant pollutants by producing reductant radicals such as hydrated electrons (eaq–) and hydrogen radicals (H•). Because of that, it is a suitable treatment method for recalcitrant compounds such as 2,4,6-trinitrotoluene (TNT). Although the requirements of the process cannot be fully defined, it's promising for wastewater treatment due to its short reaction times and easy operation. In this study, the TNT degradation efficiency of UV (253.7 nm wavelength) combined with reducing agents such as sulfite, dithionite, and sulfide was investigated. Important process parameters such as agent selection, pH, agent dose, initial TNT concentration, and UV intensity were optimized. Almost 100% TNT removal was observed by dithionite/UV process after 30 min under optimum conditions (1.5 mM dithionite, pH = 7, 8000 μW/cm2 UV, initial TNT concentration = 25 mg/L). For dithionite, molar absorption and quantum yield for TNT were calculated at 254 nm wavelength ε = 87.33 1/M·cm and φ = 0.199 mol/Einstein, respectively. [ABSTRACT FROM AUTHOR]

Whereas dithionite has been extensively used as a reducing agent in soil and sediment remediation, here, we demonstrate that it can be used as a potential source of oxidizing radical in oxic soils with potential application in organic pollutant remediation. Benzoic acid was used as a probe compound and the generation of its oxidative product para-hydroxybenzoic acid (p-HBA) was detected to quantify the production of oxidative radicals (ROS). By increasing the dithionite concentration from 2.5–10 Mm, the accumulated P-HBA concentration in 120 min increased from 15.0–27 µM. Whereas, above 10 mM, the p-HBA concentration decreased due to radical scavenging. Increasing soil dosage from 2.5–15 g/100 mL the accumulated p-HBA amount increased from 22.8–33.7 µM. Temperature 25–35 oC and pH 6.2–7.5 were favoured for p-HBA generation. Furthermore, we investigated the roles of different active intermediates in the reaction system and proposed the mechanism behind the ROS genearation. This study suggested that dithionite can be used as an active reagent for advanced oxidation remediation in oxic soil medium. [ABSTRACT FROM AUTHOR]

It is of great scientific and practical importance to explore the mechanisms of accelerated degradation of Hexachlorobenzene (HCB) in soil. Both iron oxide and dithionite may promote the reductive dechlorination of HCB, but their effects on the microbial community and the biotic and abiotic mechanisms behind it remain unclear. This study investigated the effects of goethite, dithionite, and their interaction on microbial community composition and structure, and their potential contribution to HCB dechlorination in a paddy soil to reveal the underlying mechanism. The results showed that goethite addition alone did not significantly affect HCB dechlorination because the studied soil lacked iron-reducing bacteria. In contrast, dithionite addition significantly decreased the HCB contents by 44.0–54.9%, while the coexistence of dithionite and goethite further decreased the HCB content by 57.9–69.3%. Random Forest analysis suggested that indicator taxa (Paenibacillus, Acidothermus, Haliagium, G12-WMSP1, and Frankia), Pseudomonas, richness and Shannon’s index of microbial community, and immobilized Fe content were dominant driving factors for HCB dechlorination. The dithionite addition, either with or without goethite, accelerated HCB anaerobic dechlorination by increasing microbial diversity and richness as well as the relative abundance of the above specific bacterial genera. When goethite and dithionite coexist, sulfidation of goethite with dithionite could remarkably increase FeS formation and then further promote HCB dechlorination rates. Overall, our results suggested that the combined application of goethite and dithionite could be a practicable strategy for the remediation of HCB contaminated soil.

Persulfate-based processes are a sort of advanced treatment that is effective in the degradation of a variety of pollutants. The capability of persulfate (PS) activated by dithionite (DTN) and ultraviolet (UV) to remove pentachlorophenol (PCP) as an organic pollutant from aqueous media was studied. In both processes, the PCP removal efficiency was measured using a variety of factors, such as the initial PCP concentration, PS concentration, DTN concentration, solution pH, and reaction time. An experimental design based on an orthogonal array was proposed, utilizing the Taguchi method for each process to investigate the impacts of experimental parameters involved in PCP removal. With a concentration of 25 mg/L PCP, 20 mg/L PS, and 10 mg/L DTN, pH 11, and a time of 10 min, optimal conditions for PCP removal in the DTN/PS process were determined (removal efficiency = 97.28%). Additionally, optimum UV/PS conditions were determined, including a concentration of 25 mg/L PCP, 100 mg/L PS, pH 11, and a reaction time of 40 min (removal efficiency = 98.78%). An analysis of variance (ANOVA) showed that PS is the most effective agent in removing PCP in both processes (25.08% in the DTN/PS process and 57% in the UV/PS process). Additionally, the COD and TOC removal rates in the DTN/PS process were 75.2% and 41%, and 82.3% and 61% in the UV/PS process, respectively. Furthermore, using LC-MS, the PCP degradation intermediates were detected, and possible transformation pathways were suggested. Overall, this study aims to shed light on the use of AOPs-SR to remove organic pollutants in water treatment. Based on the characteristics impacting each process, the DTN/PS method may be said to be superior to the UV/PS process (less reaction time, less persulfate) and the key reactants in both reactions are sulfate radicals. The quantity of mineralization in both procedures is nearly the same. As a result, these methods, notably DTN/PS, have a higher likelihood of removing more chlorinated organic chemicals. [ABSTRACT FROM AUTHOR]

The wide occurrence of emerging contaminants (ECs) was drawing more attention due to the potential hazard and threat on human and environment. Carbamazepine (CBZ) is a widely prescribed medication that has garnered considerable research interest with the exposures exceeding the environmental carrying capacity. We have established the innovative heterogeneous advanced oxidation process (AOPs) based on the activated dissolved oxygen (DO) coupled with S(III) and natural iron ore (siderite). In S(III)/O 2 /siderite system, we investigated the degradation efficiency, reactive species generation mechanism, and degradation pathway of CBZ. CBZ degradation and mineralization rate were 90% above and ∼15% with the reaction time of 40 min. The degradation of CBZ conformed to a pseudo-first-order kinetic model, with an activation energy determination of 76.36 kJ/mol. The optimal initial solution pH was the weak acid condition (pH = 4–6) for CBZ degradation. Moreover, the inhibition effects of coexisting substance including Cl−, HCO 3 −, and natural organic matter (NOM) on CBZ removal were observed, while the coexisted SO 4 2− exhibited no significant influence. In addition, the reactive species generated in S(III)/O 2 /siderite system were predominantly identified as sulfate radical (SO 4 ∙- ) and hydroxyl radical (∙OH). The crucial intermediate complexes, Fe(III)S(IV)O 3 (+) and Fe(II)HS(IV)O 3 (+), was proposed to form in the initial stages of the reaction, which upon decomposition, yielded SO 4 ∙- along with other reactive species. The degradation pathway of CBZ primarily involved deamination, oxidative ring-opening, hydroxylation, decarboxylation, and ketone degradation processes. This work provides the effective approach for the CBZ degradation with the mild reaction conditions and the sustainable technology for ECs treatment and control. [Display omitted] • Activated dissolved oxygen was effective for CBZ degradation coupled with S(III) and siderite. • SO 4 ∙- and ∙OH were the dominant reactive species in S(III)/O 2 /siderite system for CBZ degradation. • Fe(III)S(IV)O 3 (+) is the crucial intermediate complex for reactive species production. • Five degradation mechanisms of CBZ were proposed in S(III)/O 2 /siderite system. [ABSTRACT FROM AUTHOR]

The electron accepting capacity (EAC) of soil plays a pivotal role in the biogeochemical cycling of nutrients and transformation of redox-labile contaminants. Prior EAC studies of soils and soil constituents utilized different methods, reductants, and mediators, making cross-study comparison difficult. This study was conducted to quantify and compare the EACs of two soil constituents (hematite and Leonardite humic acid) and 12 soils of diverse composition, using chemical redox titration (CRT) with dithionite as the reductant and mediated electrochemical reduction (MER) with diquat as the mediator. The EACs of hematite and humic acid measured by CRT (EAC CRT ) and MER (EAC MER ) are similar and close to the theoretical/reported values. For soils, EAC CRT and EAC MER increased with iron and organic carbon (TOC) contents, suggesting iron and carbon were the main contributors to soil EAC. EAC CRT > EAC MER for all soils, and their difference (ΔEAC = EAC CRT - EAC MER ) increased with TOC, presumably due to the longer contact time in CRT and thus more complete reduction of carbonaceous redox moieties. We propose an equation that relates EAC CRT to EAC MER (ΔEAC = 1796 f from dithionite-reducible Fe and TOC (EAC TOC + 32) and another that predicts EAC CRT from dithionite-reducible Fe and TOC (EAC CRT = 2705 μmol e - /g C × f TOC + 17907 μmol e - /g Fe × f Fe dithionite-reducible ). Our results suggest that at least 10-15% of soil organic carbon contributed to EAC CRT .

Fluoroalkylations have received increasing attention in the academic and industrial environment due to the particular properties of the active ingredients that are strongly influenced by fluoroalkyl substituents. The inherent difficulties of introducing a fluoroalkyl substituent into advanced intermediates has triggered the development of an enormous number of specialized reagents, which, however, are often not suitable for large scale applications. In contrast to this reagent based fluoroalkylation approach, the direct activation of industrially readily available fluoroalkyl halides could be more suitable for a large-scale process. In this way the dithionite initiated fluoroalkylation as well as newly developed catalytically activated fluoroalkylation protocols were considered for industrial large-scale applications.

Dithionite remained in the foodstuff may pose a great threat to the health of consumers. Three xanthylium-based probes were synthesized and their responses to dithionite were explored. Probe SH-1 could respond to dithionite selectively in PBS buffer (15% DMSO, 10 mM, pH = 7.4). Upon the addition of dithionite, the fluorescent emission of SH-1 at 684 nm dropped quickly (within 10 s) and the fluorescence decline was proportional to the concentration of dithionite (0–7.0 μM). The limit of detection was determined to be 0.139 μM. Then, the sensing mechanism was tentatively presented and the structure of resulted adduct (SH-1-SO 3 − ) which was the reaction product of SH-1 and dithionite via a Micheal addition reaction followed by an oxidation reaction was verified. Moreover, white granulated sugar was subjected to the standard spike experiments and the results demonstrated a great potential of SH-1 for the quantitative monitoring of dithionite in foodstuffs. [Display omitted] • A xanthylium-based fluorescent probe for fast dithionite detection (within 10 s) was developed. • SH-1 could discriminate dithionite and bisulfite effectively with a LOD of 0.139 μM. • SH-1 exhibited a great potential for dithionite detection in sugar and other foodstuffs. [ABSTRACT FROM AUTHOR]

Mining uranium by in situ recovery (ISR) typically involves injecting an oxidant and a complexing agent to mobilize and extract uranium in a saturated ore zone. This strategy involves less infrastructure and invasive techniques than traditional mining, but ISR often results in persistently elevated concentrations of U and other contaminants of concern in groundwater after mining. These concentrations may remain elevated for an extended period without remediation. Here, we describe a field experiment at an ISR facility in which both a chemical reductant (sodium dithionite) and a biostimulant (sodium acetate) were sequentially introduced into a previously mined ore zone in an attempt to establish reducing geochemical conditions that, in principle, should decrease and stabilize aqueous U concentrations. While several lines of evidence indicated that reducing conditions were established, U concentrations did not decrease, and in fact increased after the amendment deployments. We discuss likely reasons for this behavior, and we also discuss how the results provide insights into improvements that could be made to the restoration process to benefit from the seemingly detrimental behavior. [ABSTRACT FROM AUTHOR]

[Display omitted] 1-R-2,4-Dinitrobenzenes are regioselectively reduced with sodium dithionite at near-neutral pH into the product having amino group ortho to the substituent R. Although the yields of products varied from moderate to good, the procedure does not involve the use of transition metals. [ABSTRACT FROM AUTHOR]

A convenient two-step method is described for the detection of nitrotyrosine-containing proteins. First, nitrotyrosines are reduced to aminophenols using sodium dithionite. Following this, an oxidative coupling reaction is used to attach anilines bearing fluorescence reporters or affinity probes. Features of this approach include fast reaction times, pmol-level sensitivity, and excellent chemoselectivity.

The applicability of the dithionite/persulfate (DTN/PS) process for the degradation of pentachlorophenol (PCP) as an organic contaminant from aqueous solutions was investigated. Effective operational parameters, including the initial PCP concentration (25, 50, 100, and 150 mg/L), PS concentration (5, 10, 15, and 20 mg/L), DTN concentration (2.5, 5, 7, and 10 mg/L), solution pH (5, 7, 9, and 11), and reaction time (3, 5, 7, and 10 min) were investigated. To identify the influences of experimental factors involved in PCP degradation, an experimental design based on an orthogonal array was proposed using the Taguchi method. Based on the results, 97.28% of the PCP was removed at the optimal conditions (initial concentration of 25 mg/L, Na-PS (sodium persulfate) concentration of 20 mg/L, Na-DTN (sodium dithionite) concentration of 10 mg/L, pH of 11, and reaction time of 10 min) in the DTN/PS process. Moreover, COD and TOC removal rates were 75.2% and 41% in the DTN/PS process, respectively. An analysis of variance (ANOVA) indicated that PS is the most effective agent in removing PCP in the DTN/PS process. The compounds of phenol, 3,4-dichlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, oxalic acid, propionic acid, tetrachloro-o-benzoquinone, and butanedioic acid were identified as intermediates.

mKate red-to-green photoconversion is a non-canonical type of phototransformation in fluorescent proteins, with a poorly understood mechanism. We have hypothesized that the daughter mKate2 protein may also be photoconvertible, and that this phenomenon would be connected with mKate(2) chromophore photoreduction. Indeed, upon the intense irradiation of the protein sample supplemented by sodium dithionite, the accumulation of green as well as blue spectral forms is enhanced. The reaction was shown to be reversible upon the reductant's removal. However, an analysis of the fluorescence microscopy data, absorption spectra, kinetics and time-resolved fluorescence spectroscopy revealed that the short-wavelength spectral forms of mKate(2) exist before photoactivation, that their fractions increase light-independently after dithionite addition, and that the conversion is facilitated by the photobleaching of the red chromophore form. [ABSTRACT FROM AUTHOR]

The reaction of the air-tolerant CO dehydrogenase from Oligotropha carboxidovorans with H2 has been examined. Like the Ni-Fe CO dehydrogenase, the enzyme can be reduced by H2 with a limiting rate constant of 5.3 s(-1) and a dissociation constant Kd of 525 μM; both kred and kred/Kd, reflecting the breakdown of the Michaelis complex and the reaction of free enzyme with free substrate in the low [S] regime, respectively, are largely pH-independent. During the reaction with H2, a new EPR signal arising from the Mo/Cu-containing active site of the enzyme is observed which is distinct from the signal seen when the enzyme is reduced by CO, with greater g anisotropy and larger hyperfine coupling to the active site (63,65)Cu. The signal also exhibits hyperfine coupling to at least two solvent-exchangeable protons of bound substrate that are rapidly exchanged with solvent. Proton coupling is also evident in the EPR signal seen with the dithionite-reduced native enzyme, and this coupling is lost in the presence of bicarbonate. We attribute the coupled protons in the dithionite-reduced enzyme to coordinated water at the copper site in the native enzyme and conclude that bicarbonate is able to displace this water from the copper coordination sphere. On the basis of our results, a mechanism for H2 oxidation is proposed which involves initial binding of H2 to the copper of the binuclear center, displacing the bound water, followed by sequential deprotonation through a copper-hydride intermediate to reduce the binuclear center.

The study is a first investigation of the feasibility to preserve recycled fillers (e.g. calcium carbonate, kaolin) from deinking paper sludge for newspaper production using an alternative approach respect to the actual methods. Deinking paper sludge was incinerated at 575 °C. The thermal stability of the incinerated sludge (ash) was evaluated by infrared analysis. Subsequently, the resulting ash was bleached by sodium dithionite. The particle size of the ashes was analysed by laser diffraction. The effect of recycled fillers on recycled paper pulp, after blending, was evaluated by the analysis of the physical and optical properties of the obtained paper sheets. Analysis showed the conservation of the calcium carbonate and other fillers' molecular structure, both after incineration of the sludge and after bleaching. The dithionite treatment of the ashes resulted in ISO brightness levels of more than 70. The brightness was stable over one month. Paper sheets made by blending the bleached ashes with recycled paper showed an improvement of brightness and opacity but a decrease in terms of porosity and breaking length compared to paper sheets made without any filler. The proposed method still requires further studies to evaluate the economical application but offers an opportunity for the recycling of inorganic materials and valorisation of the sludge. [ABSTRACT FROM AUTHOR]

The present study deals with chemical leaching tests conducted on Batn El-Ghoul kaolin clay deposit, south Jordan. Mineral identification and characterization studies were conducted using X-ray diffraction. The chemical analyses were performed by X-ray fluorescence. The chemical leaching study with sodium dithionite (Na2S2O4) as leachant was accomplished with the fraction below 44 μm, after classification by screening. The main objective of this study was to evaluate the conditions of chemical leaching for removal of the colouring materials and to improve the brightness. The leaching tests improved the brightness from 56% to 86%. The corresponding iron-oxide removal was in the order of 94%. Removal of 94% iron gives a product containing 0.48% Fe2O3, which is fit for industrial applications such as fine ceramics and as a filler materials in paper, plastic and rubber industries.

This works reports that tetrasulfonated cobalt(II) phthalocyanine (Co(II)TSPc) catalyzes reduction of selenite (SeO32−), the one of the most toxic form of selenium, to slightly toxic Se(0) by dithionite (S2O42−) in neutral aqueous solutions. The overall reaction mechanism involves rapid reduction of Co(II)TSPc to Co(I)TSPc by dithionite followed by slower oxidation of Co(I)TSPc by selenite. Reaction of Co(I)TSPc with selenite proceeds via two consecutive steps, i.e. the formation of complex between reactants followed by electron transfer from Co(I)-ion to selenite and dissociation of reduced selenite species from Co(II)-ion. [ABSTRACT FROM AUTHOR]

Introduction: In recent years, sodium hydro sulfurous anhydride (Dithionite) has been used as an additive for better preservation, increase of visual appearance and improvement of fermentation action in breads products. The purpose of this study was to determine and quantify the concentration of dithionite in breads produced in Hamadan. Methods: In this descriptive study, the concentration of Dithionite in bread in breads produced in Hamadan from July to September 2016 was determined. The study population was the whole of active industrial bakeries in the city of Hamadan. The sampling was conducted after listing the bakeries producing bread by referring randomly to the bakeries and taking samples and transmitting them to the laboratory. Finally, the content of dithionite was quantified based on the Iranian National Standard (no: 2628). Results: The findings indicated that dithionite concentration in all samples in different months was zero, which meets the standard. Conclusion: The results of this study indicated that dithionite, as an additive, has not been used in processing of the bread; hence, it cannot be considered as a threat to human health.

Sodium dithionite (Na2S2O4) may have the potential to be used as a reducing agent for the stabilization of glucomannan in kraft cooking for increased pulp yield. However, due to the fact that dithionite decomposes under the conditions of kraft pulping, studies of the effects of dithionite in kraft pulping are non-conclusive; sometimes clearly showing an increased yield, and in other studies no effect at all. The specific conditions influencing dithionite degradation are also unclear. For that reason, this study was conducted to determine the thermal and chemical stability of sodium dithionite with respect to specific factors, such as the pH, temperature, heating time, and the concentration of sodium dithionite solution. The study was performed under anaerobic conditions using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The thermal and alkali stability of the sodium dithionite solution was shown to decrease with increasing temperature, heating time, and concentration of the solution at the alkaline conditions studied. The thermal stability decreased rapidly at weak alkalinity (pH 9) as well as in high alkalinity (pH 14), whereas the sodium dithionite was rather stable at moderate alkalinity (pH 11.5 to pH 13).

• Persulfate and dithionite act synergistically for ATZ degradation. • Various reactive species (SO 2 −, SO 3 −, SO 4 −, OH, etc) are involved in the PS/DTN system. • ATZ degradation pathway has been proposed based on the identified intermediates. Efficient and environmentally friendly activation methods of persulfate (PS) have gained growing attention in the remediation of water or soil polluted by organic contaminants. Among all, the exploration of effective and applicable method for the PS activation becomes one of the hottest topics in the field of organic degradation. Dithionite (DTN) was employed in this study to activate PS and applied to degrade Atrazine (ATZ) without secondary pollution. ATZ could be completely degraded within 90 min by PS/DTN system. ATZ degradation by PS obeyed the pseudo-first-order kinetics and the rate constant values increased from (4.71–5.05) × 10−3 min−1 to (4.59–5.09) × 10−2 min−1 with the addition of DTN. Sulfate radicals were verified to be the dominant reactive species through the radical scavenging experiment. PS/DTN system can remain a strong oxidative ability in the range of pH below 9.0. The presence of Cl−, natural organic matter (NOM), and high concentration of HCO 3 − may inhibit the removal of ATZ while the low concentration of HCO 3 − can slightly promote the degradation. It was found that the degradation pathways of ATZ by PS/DTN involved de-chlorination and hydroxylation, de-alkylation, and de-amination by the reactive species. The study reveals that PS/DTN system has the broad application prospect in the treatment of refractory pollutants. [ABSTRACT FROM AUTHOR]

Abstract Oxalic acid can effectively extract arsenic bound to amorphous iron oxides via dissolution of iron oxides containing arsenic. Therefore, soil washing with oxalic acid is a promising method to remediate arsenic-contaminated soil, since arsenic is often associated with amorphous iron oxides in soil. However, high cost of oxalic acid compared to the other inorganic acids commonly used for remediation of metal-contaminated soils is the main disadvantage of using oxalic acid for soil washing. In this study, in order to increase the economic feasibility of soil washing using oxalic acid, selective recovery of iron and oxalate as resources was suggested via two step reduction reaction using dithionite as a reductant during soil-washing wastewater treatment. In the first step, high levels of oxalate and iron present in wastewater was recovered as a ferrous oxalate phase. Under mild reducing conditions, ferric iron in the wastewater was reduced to ferrous iron, which could form a complex with oxalate and precipitate as the ferrous oxalate phase with low solubility. The ferrous oxalate phase did not affect dissolved arsenic retention in this step. The recovered ferrous oxalate phase can be applied in the industry as useful resources, which can contribute to the sustainable development and cleaner production. In the second step, arsenic in wastewater was removed by forming a realgar-like phase from the reaction with dithionite. Sulfide produced by the decomposition of dithionite reacted with arsenic and other metals in wastewater, and formed sulfide phases such as realgar (As 4 S 4)/orpiment (As 2 S 3) and lead sulfide (PbS). Highlights • Two-step reduction reaction for the feasibility of soil-washing with oxalate. • Ferrous oxalate was selectively recovered from wastewater in the 1st-step reaction. • As in wastewater was precipitated as a realgar-like phase in the 2nd-step reaction. [ABSTRACT FROM AUTHOR]

The remediation efficiency of soils containing energetic materials (EM) is assessed using SW-846 USEPA Method 8330B. However, the extraction, which is performed by sonicating the soil samples in acetonitrile for several hours, could lead to additional degradation of EM during sample processing, and consequently, to an overestimation of remediation efficiency. To verify this, soil samples that were spiked with controlled amounts of EM were briefly exposed to remediation reagents, such as MuniRem® (a commercial sodium dithionitebased formulation) or hydrated lime, and analyzed using SW-846 USEPA Method 8330B. The most affected EM of this study was 2,4,6-trinitrotoluene (TNT), for which complete degradation was observed after exposure to hydrated lime or pH-buffered MuniRem®. Losses of 1,3,5-trinitro-1,3,5-triazinane (RDX) reached 30 ± 20% upon treatment with full pH-buffered MuniRem® and 90 ± 10% when exposed to lime. The concentrations of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) were near the method's lower limit of quantification, and subjected to large errors, which prevented us from drawing any clear conclusions regarding its degradation under the studied experimental conditions. These results highlight the necessity of performing appropriate soil sample treatments to quench the remaining hydrated lime or sodium dithionite prior to the extraction and analysis steps with SW-846 USEPA Method 8330B. Quenching of remaining remediation reagents may possibly be also required for other remediation reagents and EM. [ABSTRACT FROM AUTHOR]

Abstract Closed-system experiments were conducted to investigate the decomposition of sodium dithionite in aqueous solutions under varying pH and starting concentrations to simulate the deployment of dithionite as an in-situ redox barrier. Co-determination of dithionite and its degradation products was conducted using UV–Vis spectrometry, iodometric titration, and ion chromatography. In unbuffered solutions, dithionite reacted rapidly, whereas in near-neutral solutions (pH ∼7), it persisted for ∼ 50 days and in alkaline solution (pH ∼9.5) for >100 days. These are the longest lifetimes reported to date, which we attribute to not only excluding oxygen but also preventing outgassing of H 2 S. Thoroughly constraining the reaction products has led to the following hypothesized reaction: 4 S 2 O 4 2− + H 2 O → HS− + SO 3 2−+2 SO 4 2− + S 4 O 6 2− + H+ which represents relatively rapid degradation at near-neutral pH values. At the more alkaline pH, and over longer time scales, the reaction is best represented by: 3 S 2 O 4 2− + 3 H 2 O → 2HS- + SO 3 2−+3 SO 4 2−+ 4 H+ the following kinetic rate law was developed for the pH range studied: dC i dt = S i 10 − 4.81 { H + } 0.24 { S 2 O 4 2 - } , where dC i dt is the rate of change of the i t h chemical component in the simplified equation (mole L−1 s−1) and S i is the stoichiometric coefficient of the ith chemical. The kinetic rate law was used to calculate a pseudo first order half-life of 10.7 days for near-neutral pH and 33.6 days for alkaline pH. This work implies that if hydrogen sulfide is contained within the system, such as in the case of a confined aquifer below the water table, dithionite decomposes more slowly in alkaline aqueous solution than previously thought, and thus it may be more cost-effectively distributed in aquifers than has been previously assumed. Highlights • Sodium dithionite concentrations in alkaline aqueous solutions were measured by UV–vis spectrometry for up to 105 days. • Analysis of degradation products revealed that sulfite, hydrogen sulfide, sulfate, and polythionates are present. • The closed system created in this study ensured no loss of hydrogen sulfide, which slowed the loss of dithionite. • The kinetic rate law developed yields a half-life of 10.7 days at near-neutral pH and 33.6 days at alkaline pH. [ABSTRACT FROM AUTHOR]

This study investigates removal of selenite [Se(IV)] by reductive precipitation during treatment with an Advanced Reduction Process (ARP) that uses dithionite activated by ultraviolet (UV) irradiation. Our screening experiments evaluated a number of ARP and found that the dithionite/UV ARP was most effective in removing soluble selenite. Furthermore, this work considers effects of operating conditions such as dithionite dose, solution pH, initial selenite concentration, and light intensity on reduction of Se(IV). Selenite [Se(IV)] was completely removed in 120 min when initial Se(IV) concentration was 0.023 mM, dithionite dose was 1 mM, and the initial pH was ∼4.5. Higher dithionite doses, lower pH, and higher incident UV irradiance increased soluble Se(IV) removal. Selenium in the solids was effectively removed from solution by conversion to solids that were removed by filtration. Scanning emission microscopy/energy dispersive X-ray spectroscopy (EDS), X-ray diffraction, and X-ray Photoelectron Spectroscopy results showed that Se(IV) was reduced by the dithionite/UV ARP to form solids identified as elemental Se or as a compound composed of both Se and S (e.g., SemSn). Elemental Se was the primary solid, especially at higher initial Se(IV) concentrations. In the dithionite/UV ARP, rapid removal of soluble Se(IV) at low pH is attributed to photolysis of dithionite or a dithionite decomposition product (e.g., bisulfite, metabisulfite, thiosulfate, and trithionate) that is initially present in the dithionite solution. [ABSTRACT FROM AUTHOR]

The present study deals with chemical leaching tests conducted on Batn El-Ghoul kaolin clay deposit, south Jordan. Mineral identification and characterization studies were conducted using X-ray diffraction. The chemical analyses were performed by X-ray fluorescence. The chemical leaching study with sodium dithionite (Na2S2O4) as leachant was accomplished with the fraction below 44 μm, after classification by screening. The main objective of this study was to evaluate the conditions of chemical leaching for removal of the colouring materials and to improve the brightness. The leaching tests improved the brightness from 56% to 86%. The corresponding iron-oxide removal was in the order of 94%. Removal of 94% iron gives a product containing 0.48% Fe2O3, which is fit for industrial applications such as fine ceramics and as a filler materials in paper, plastic and rubber industries. [ABSTRACT FROM AUTHOR]

This article reports on the application of an advanced reduction process (ARP) that combines ultraviolet (UV) irradiation and dithionite to remove selenium from solution. Batch kinetic removal of selenite (Se(IV)) and selenate (Se(VI)) with the dithionite/UV ARP at different pH were evaluated under anaerobic conditions and a removal mechanism was proposed. Resolubilization of selenium was observed for all pH (7, 8, and 9) after 15 to 20 min, which was the time when dithionite was completely consumed. A hypothesis was proposed that selenium first was reduced to elemental Se by radicals formed from photolysis of dithionite. Then, it was resolubilized by reaction with oxidizing radicals formed by photolysis of dithionite degradation products. A kinetic model for dithionite photolysis and a second-order model for precipitation of selenium were developed to describe selenium removal. Experimental data were used in nonlinear regressions to estimate quantum yields and second-order rate constants. Lowest quantum yields were observed at pH 8 for experiments with both selenite and selenate. The rate of selenite removal from solution was not affected by pH, but the rate of selenate removal was faster at pH 8 than at pH 7 and 9. [ABSTRACT FROM AUTHOR]

It is of great scientific and practical importance to explore the mechanisms of accelerated degradation of Hexachlorobenzene (HCB) in soil. Both iron oxide and dithionite may promote the reductive dechlorination of HCB, but their effects on the microbial community and the biotic and abiotic mechanisms behind it remain unclear. This study investigated the effects of goethite, dithionite, and their interaction on microbial community composition and structure, and their potential contribution to HCB dechlorination in a paddy soil to reveal the underlying mechanism. The results showed that goethite addition alone did not significantly affect HCB dechlorination because the studied soil lacked iron-reducing bacteria. In contrast, dithionite addition significantly decreased the HCB contents by 44.0–54.9%, while the coexistence of dithionite and goethite further decreased the HCB content by 57.9–69.3%. Random Forest analysis suggested that indicator taxa (Paenibacillus , Acidothermus , Haliagium , G12-WMSP1, and Frankia), Pseudomonas , richness and Shannon's index of microbial community, and immobilized Fe content were dominant driving factors for HCB dechlorination. The dithionite addition, either with or without goethite, accelerated HCB anaerobic dechlorination by increasing microbial diversity and richness as well as the relative abundance of the above specific bacterial genera. When goethite and dithionite coexist, sulfidation of goethite with dithionite could remarkably increase FeS formation and then further promote HCB dechlorination rates. Overall, our results suggested that the combined application of goethite and dithionite could be a practicable strategy for the remediation of HCB contaminated soil. [Display omitted] • POPs are an important environmental issue for their high toxicity and persistence. • Goethite did not affect HCB dechlorination with few iron-reducing bacteria. • Dithionite addition accelerated HCB dechlorination by influencing soil microbes. • Sulfidation of goethite with dithionite increased FeS and promoted HCB dechlorination. [ABSTRACT FROM AUTHOR]