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Ion-adsorbed rare earth minerals are rich in medium and heavy rare earth (RE), which are important strategic resources. In this article, a novel approach for the extraction of RE from ion adsorbed minerals was developed. Through a comprehensive assessment of their extraction and separation performance, the hydrophobic deep eutectic solvents (HDES) with a composition of trioctylphosphine oxide (TOPO): dodecanol (LA): 2-thiophenoyltrifluoroacetone (HTTA) = 1:1:1 was determined as the optimal configuration. Under optimized conditions, only RE were extracted by the HDES, while Al, Ca, Mg were not extracted at all. The HDES based extraction obviated the need for diluent such as kerosene, eliminating the generation of impurity removal residues. The RE in the stripping solution could be successfully enriched by saponified lauric acid, achieving an impressive precipitation rate of 99.7%. The RE precipitate underwent further enrichment, resulting in a RE concentration of 176 g/L (REO = 210 g/L). Unlike industrial precipitants such as oxalic acid and ammonium bicarbonate, lauric acid can be effectively recycled, thereby avoiding a large amount of wastewater and carbon dioxide emissions. The obtained RE solution product exhibits high yield and purity, this study provides an eco-friendly and high-yield approach for extracting RE. [Display omitted] • Nine novel HDES composed of TOPO, LA and HTTA were prepared. • Impurities of Al, Ca, Mg were completely removed from RE with HDES extraction. • RE was enriched from 895 mg/L to 176 g/L with extraction-precipitation. • The separation process reveals eco-friendly and high-yield advantages for RE. [ABSTRACT FROM AUTHOR]

Electro-peroxone (EP) is a novel technique for the removal of refractory organic contaminants (ROCs), while the role of anode in this system is neglected. In this work, the EP system with graphite felt anode (EP-GF) and activated carbon fiber anode (EP-ACF) was developed to enhance ibuprofen (IBP) removal. The results showed that 91.2% and 98.6% of IBP was removed within 20 min in EP-GF and EP-ACF, respectively. Hydroxy radical (O ⋅ H) was identified as the dominant reactive species, contributing 80.9% and 54.0% of IBP removal in EP-ACF and EP-GF systems, respectively. The roles of adsorption in EP-ACF and direct electron transfer in EP-GF cannot be ignored. Due to the differences in mechanism, EP-GF and EP-ACF systems were suitable for the removal of O ⋅ H -resistant ROCs (e.g., oxalic acid and pyruvic acid) and non- O ⋅ H -resistant ROCs (e.g., IBP and nitrobenzene), respectively. Both systems had excellent stability relying on the introduction of oxygen functional groups on the anode, and their electrolysis energy consumption was significantly lower than that of EP-Pt system. The three degradation pathways of IBP were proposed, and the toxicity of intermediates were evaluated. In general, carbon anodes have a good application prospect in the removal of ROCs in EP systems. [Display omitted] • GF and ACF anodes exhibited the excellent performance for the IBP removal in EP system. • O ⋅ H was dominant reactive species, contributing 80.9% to IBP removal in EP-ACF system. • O ⋅ H and DET separately contributed 54.0% and 33.0% to IBP removal in EP-GF system. • EP-GF system showed the superior stability due to the introduced OGs on GF anode. [ABSTRACT FROM AUTHOR]

A novel approach of ball milling and oxalic acid was employed to modify sludge-based biochar (BOSBC) to boost its activation performance for peroxymonosulfate (PMS) towards efficient degradation of sulfamethoxazole (SMX). 98.6% of SMX was eliminated by PMS/BOSBC system within 60 min. Furthermore, PMS/BOSBC system was capable of maintaining high removal rates for SMX (>88.8%) in a wide pH range from 3 to 9, and displayed a high tolerance to background electrolytes including inorganic ions and humic acid (HA). Quenching experiments, electron paramagnetic resonance (EPR) analysis, in-situ Raman characterization and PMS decomposition experiments confirmed that the non-radicals of 1O 2 and surface-bound radicals were the main contributors to SMX degradation by PMS/BOSBC system. The results of ecotoxicity assessment illustrated that all transformed products (TPs) generated in PMS/BOSBC system were less toxic than that of SMX. After five reuse cycles, PMS/BOSBC system still maintained a high removal rate for SMX (77.8%). Additionally, PMS/BOSBC system exhibited excellent degradation performance for SMX in various real waters (Yangtze River water (76.5%), lake water (74.1%), tap water (86.5%), and drinking water (98.1%)). Overall, this study provided novel insights on non-metal modification for sludge-based biochar and non-radical mechanism, and offered a feasible approach for municipal sludge disposal. [Display omitted] • A novel carbon material (BOSBC) with high PMS activation ability was synthesized. • 1O 2 and surface-bound radicals played dominant roles in SMX degradation. • PMS/BOSBC system performed high tolerance to background electrolytes. • PMS/BOSBC system showed high degradation rates for SMX in various real waters. • BOSBC exhibited stable catalytic performance in the reuse cycles. [ABSTRACT FROM AUTHOR]

Spent petroleum refining catalyst is regarded as the important secondary resource for valuable metals. However, common recycling strategies, including soda roasting, acid and alkaline solutions leaching and chemically precipitation, produced large quantities of high salinity wastewater. This study proposed an efficient method to recovery of Mo and Ni from the spent hydrodesulfurization (HDS) catalyst via O 2 -rich roasting and organic acid leaching with the advantage of less salinity wastewater production. The transformation of Mo(IV) into soluble Mo(VI) was enhanced by O 2 -rich atmosphere roasting, and 98.64% of Mo(IV) was oxidized at 650 ℃ for 2 h in atmosphere containing 30% of O 2. The oxidation process of Mo(IV) was agreed with the shrinkage pore model, and regulated by surface reaction and internal diffusion. 97.97% of Mo(VI) was leached from roasted product by oxalic acid, separated with complexation extraction agent of Ala-TBP and recovered as (NH 4) 8 Mo 10 O 34 and (NH 4) 2 Mo 3 O 10 by evaporative crystallization. Ni was leached out from spent catalyst with 1 mol/L acetic acid, and precipitated as NiC 2 O 4 with oxalic acid. 95.92% of Mo and 96.77% of Ni were recovered from spent HDS catalyst with this recycling route. This study provided a high-efficient and eco-friendly method to recovery of valuable metals from spent catalyst. [Display omitted] • MoS 2 oxidation was improved during roasting in O 2 -rich atmosphere. • MoS 2 oxidation process was agreed with shrinkage pore model. • O 2 dissociative adsorption occurred on the MoS 2 and O charge was transferred to S. • Mo(VI) was extracted and enriched with complexation extraction agents Ala-TBP. [ABSTRACT FROM AUTHOR]

Based on the efficiency of the catalytic ozonation techniques (HDWS+O 3 and MnFe 2 O 4 @SBC+O 3) in enhancing the sludge dewaterability, the effectiveness in synchronized abatement antibiotics and antibiotic resistance genes (ARGs) was conducted to determine. The results revealed that catalytic ozonation conditioning altered the distribution of target antibiotics (tetracycline (TC), oxytetracycline (OTC), norfloxacin (NOR), ofloxacin (OFL)) in the dewatered filtrate, the dewatered sludge cake and the extra-microcolony/cellular polymers (EMPS/ECPS) layers, achieving the redistribution from solid-phase adsorption to liquid-phase dissolution. The total degradation rate was over 90% for TC and OTC, 72–78% for NOR and OFL; the abatement efficiency of eleven ARGs reached 1.47–3.01 log and 1.64–3.59 log, respectively, and more than four eARGs were eliminated. The effective abatement of the absolute abundance of Mobile genetic elements (MGEs) (0.91–1.89 log) demonstrated that catalytic ozonation conditioning could also significantly inhibit horizontal gene transfer (HGT). The abundance of resistant bacteria was greatly reduced and the signal transduction of the typical ARGs host bacteria was inhibited. The highly reactive oxidation species (ROS) generated were responsible for the abatement of antibiotics and ARGs. These findings provided new insights into the sludge conditioning for ideal and synchronized reduction in volume and hazardousness by catalytic ozonation processes in sludge treatment. [Display omitted] • Catalytic ozonation conditioning WAS achieved synchronized volume and harm reduction. • The total degradation rate was over 90% for TC and OTC, and 72–78% for NOR and OFL. • ARGs abatement rate reached 1.47–3.59 log and more than four eARGs were eliminated. • MGEs abatement rate reached 0.91–1.89 log, HGT was blocked and hosts were reduced. • The generated ·OH, O 2 ·- and 1O 2 were contributed to antibiotics and ARGs abatement. [ABSTRACT FROM AUTHOR]

• Diffusion coefficients estimation of Cr-OABL (Organic acid-based ligands) complexes. • The maximum Cr removal efficiency of OABL was slightly less than inorganic acids. • Soil ecotoxicity improved significantly with nutrient enrichment before treatment. We assessed whether soil with high Cr contamination could be reclaimed by alkali, mineral, and organic acid-based ligands (OABLs) washing. We tested HNO 3 , H 2 SO 4 , HCl, NaOH, H 2 O 2 , lactic acid (LA), malic acid (MA), oxalic acid (OA), and citric acid (CA), together with EDTA, obtaining the highest efficiencies in presence of 1 M sulfuric acid (98%). Nonetheless we noted that using OABLs, we obtained a Cr(III) removal efficiency similar to the one obtained using mineral acids. Indeed 1 M of LA and MA and 0.8 M of OA allowed obtaining, respectively, 88%, 75%, and 67% removal percentage. The extraction process with OABLs was strongly dependent on intraparticle diffusion of Cr-LA, Cr-MA, and Cr-OA complexes. We also determined the apparent diffusion coefficients. Residual toxicity of treated soils was tested with the nematode, Caenorhabditis elegans. The OABL washing generally allowed getting a soil without Cr and with reduced toxicity. However, the washing process also removed other cations that acted as nutrients. Consequently, we conducted toxicity tests on enriched soil and found that the mortality index improved. In some cases (LA and MA), mortality was comparable to that observed with uncontaminated control samples. In contrast, when contaminated soils were washed with sulfuric acid, in all conditions, we observed significant ecotoxicity. Therefore, we concluded that only the OABL treatment provided a non-toxic soil that could be reused for anthropic activities. [ABSTRACT FROM AUTHOR]

• Cu-OMS x -T nanorods were prepared by the hydrothermal-calcination method. • First report on Cu incorporated into OMS-2 as highly efficient ozonation catalysts. • Cu-OMS 0.5 -140 exhibited the highest catalytic activity, stability and reusability. • Cu incorporation promoted the formation of multivalent metals and oxygen vacancies. • The plausible generation mechanism of ⋅OH and O 2 ⋅-was elucidated. A series of copper doped manganese oxide octahedral molecular sieves (Cu-OMS x -T) with different Cu/Mn ratios and hydrothermal temperatures were successfully synthesized and used for catalytic ozonation towards oxalic acid (OA) degradation. The as-prepared Cu-OMS x -T composites were comprehensively investigated by BET, FT-IR, XPS and etc. characterizations. The results indicated that the Cu doping would increase the specific surface area, change chemical bonds, and promote the transformation of multivalent metals and the generation of oxygen vacancies. It was noteworthy that the hydrothermal temperature played an important role in the morphology of Cu-OMS x -T composites and the Cu/Mn molar ratios greatly influenced the catalytic activities. Amongst, the Cu-OMS 0.5 -140 achieved the optimum catalytic activity with 97.3% of OA degradation efficiency and 98.8% of mineralization rate in 30 min at pH 6.0. Moreover, hydroxyl radical and superoxide radical were identified as the major reactive radicals and the catalytic mechanism for OA degradation enhancement was also elucidated. In addition, the Cu-OMS 0.5 -140 exhibited great stability and reusability with high OA mineralization rate (>90%) and low metal release after five times recycle. Overall, the results indicated that the synthesized Cu-OMS 0.5 -140 is an efficient, stable, and recyclable ozonation catalyst, and could be a promising alternative material for water purification. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Biochar and root exudates synergistically promoted high-ring PAH dissipation. • Biochar and root exudates enhanced microbial biomass and activity. • Biochar and root exudates synergistically affected microbial community structures. • Biochar and root exudates enhanced the genera associated with PAH degradation. • Biochar and root exudates enhanced the genes associated with PAH degradation. Abstract Whether the rhizodegradation of organic contaminants occurs in biochar- amended soil and its potential mechanisms have rarely been reported. Therefore, a study was conducted to investigate the combined effects of root exudates and biochar on the dissipation of polycyclic aromatic hydrocarbons (PAHs) and on the microbial community structures in soil. As a major component of the root exudates of ryegrass, oxalic acid (OA) significantly enhanced the dissipation of high- and low-ring PAHs in the studied soil with or without maize straw biochar amendment (p < 0.05). However, biochar alone enhanced only the dissipation of high-ring PAHs. The activities of three enzymes (urease, polyphenol oxidase and dehydrogenase) were the highest in soil amended with both maize straw biochar and 0.5 mg kg−1 of OA. Moreover, soil microbial biomass and the abundances of genera and genes associated with PAH degradation were significantly enhanced with the tandem application of biochar and OA (p < 0.05). These changes led to a synergetic effect of biochar and OA on the shifts in microbial community structures and on the dissipation of PAHs, especially for high-ring PAHs. The results in this study suggested that a combined biochar-rhizosphere approach should be a feasible remediation strategy for PAH-contaminated soil. [ABSTRACT FROM AUTHOR]

Biochar-based materials have been widely used to remove Cr(VI). However, current strategies mainly focus on slow adsorption through electrostatic and functional group properties, ignoring the confinement catalytic fast kinetics caused by inherent porous properties. Herein, we designed a confinement strategy to achieve high-efficiency Cr(VI) reduction by encapsulating the catalytic reaction of Cr(VI) and oxalic acid (OA) in the micropore of PCRN-3–10–2–800. The results showed that the removal rate constant of the PCRN-3–10–2–800/OA system was 14.3 and 146.8 times higher than that of the BC-800/OA system (low porosity) and PCRN-3–10–2–800 alone (adsorption), which was highest removal rate constant in the current reported materials under the same system. The structure-activity relationship indicated that the catalytic activity of Cr(VI) depended on the micropore characteristics of the catalyst. Density functional theory calculations confirmed that nanoscale space could enhance Cr(VI) adsorption and reduce the energy barrier of the rate-determining step. The electron paramagnetic resonance spectrum demonstrated the rapid conversion of Cr(VI) to Cr(III). Furthermore, the PCRN-3–10–2–800/OA system showed good applicability and high efficiency for Cr(VI) removal (nearly 100% in 5 min) in industrial electroplating wastewater treatment. This work first proposes a nanoconfinement-induced heavy metal reduction strategy and guides biochar's universality design in wastewater treatment. [Display omitted] • Biochar-based microporous nanosheets were prepared by one-step calcination. • The micropore and OA assembled confinement system achieved rapid Cr(VI) reduction. • The designed method showed potential for actual wastewater removal and water reuse. • Micropore confinement can reduce the energy barrier of the rate-determining step. • The EPR result proved the fast conversion of Cr(VI) to Cr(III) during the reaction. [ABSTRACT FROM AUTHOR]

Low-molecular-weight organic acids (LMWOAs) interact with potentially toxic elements (PTEs) and affect their mobility; however, the effect of different amendments on PTEs release from soils when added along with LMWOAs is still unclear. In this study, two soils (a clay loam and a sandy loam) amended with sugar beet bagasse ash (SBBA), poultry manure (PM), sewage sludge (SS) from Kermanshah city (SSK), and SS from Toyserkan city (SST) at a rate of 5 %. In these treatments we studied release of Cd, Cu, Fe, Mn, Ni, Pb, and Zn with citric, oxalic, and malic acids added at 10 different rates each, i.e., 0.1, 1, 2.5, 5, 10, 30, 40, 50, 70, and 100 mmol L−1. We found that the percentage of PTEs release was higher for citric, followed by oxalic and malic acids. The highest amount of PTEs released in both soils decreased in the following order: SST > SBBA > SSK > PM. The percentage of PTEs complexed with LMWOAs and the log activity of PTEs species mostly increased with decreasing pH. It could be concluded that the application of PM is more environmentally friendly than that of the other amendments. Since Cd had the highest percentage of release in all treated soils and LMWOAs, more consideration should be given to Cd to prevent environmental pollution. [Display omitted] • Sugar beet bagasse ash, poultry manure, and sewage sludge were used as amendments. • Cd, Cu, Fe, Mn, Ni, Pb, and Zn release was studied in citric, oxalic, and malic acids. • Elements were released more in poultry manure and less in sewage sludge. • Clay loam soil released more elements compared to the sandy loam. [ABSTRACT FROM AUTHOR]

Marine plastic pollution, with annual emissions into the marine over 53 million metric tons, has been a major worldwide concern. Many of so-called "biodegradable" polymers degrade very slowly in seawater. Oxalate have attracted attention because the electron-withdrawing effect of adjacent ester bonds promotes their natural hydrolysis, particularly in the ocean. However, the low boiling point and poor thermal stability of oxalic acids severely limits their applications. The successful synthesis of light-colored poly(butylene oxalate-co-succinate) (PBOS), with weight average molecular weight higher than 1 × 105 g/mol, displays the breakthroughs in the melt polycondensation of oxalic acid-based copolyesters. The copolymerization of oxalic acid retains the crystallization rate of PBS, with minimum half-crystallization times from 16 s (PBO 10 S) to 48 s (PBO 30 S). PBO 10 S-PBO 40 S exhibit good mechanical properties with elastic modulus of 218–454 MPa, and tensile strength between 12 and 29 MPa, better than packaging materials such as biodegradable PBAT and non-degradable LLDPE. PBOS achieve rapid degradation in the marine environment, with a mass loss 8%− 45% after 35 days. The characterization of structural changes demonstrate that the introduced oxalic acid plays a key role in the process of seawater degradation. This new class of polymers therefore provide highly promising materials for sustainable packaging with unique seawater degradation properties. [Display omitted] • Curbing the marine plastic pollutions requires really marine degradable materials. • High molecular weight and light-colored oxalic acid polyesters were synthesized. • Influence of oxalic acid on key properties of polymers. • Oxalic acid gives the ability to degrade in seawater within 35 days. • Oxalic acid as a universal "breaking point" for the seawater-degradable packaging. [ABSTRACT FROM AUTHOR]

To extract As bound to amorphous and crystalline iron oxides, this study proposed simultaneous application of oxalic acid and dithionite, which was observed to induce synergistic effect and accomplish effective extraction of As bound to both iron oxides. However, the formation of arsenic sulfide decreased overall removal of As because the insoluble precipitate form of As remained as a residual fraction of As in soil. Therefore, stepwise addition of dithionite in the simultaneous application was applied to minimize the formation of secondary minerals and maximize the As extraction. As a result, 74% of As bound to amorphous iron oxides and 65% of As bound to crystalline iron oxides were removed. More importantly, the stepwise application of oxalic acid and dithionite was effective to reduce the bioaccessible concentration of As in the treated soil. Therefore, the proposed application could reduce the potential risk of contaminated soil to human health by extraction-based remedial action. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate that Mn 2+ can greatly promote the Cr(VI) reduction by oxalic acid at pH < 5 via an induction period and a subsequent auto-acceleration process. The Cr(VI) reduction rate constant during the late auto-acceleration process was about 10 times that of the initial induction period. Characterization results revealed that this interesting two-step Cr(VI) reduction phenomenon was attributed to the in-situ generated Mn 3+ by the oxidation of Mn 2+ with Cr(VI) in the presence of oxalic acid during the induction period. The in-situ generated Mn 3+ might complex with oxalate and Cr(VI) to produce a ternary complex, thus facilitating the electron transfer from oxalate to Cr(VI) to automatically accelerate the Cr(VI) reduction process. These findings shed insight into the possible roles of widely existed Mn ions (Mn 2+ and Mn 3+ ) and oxalic acid in the transformation of Cr(VI) in natural aquatic environment, and also provided an efficient way to remediate Cr(VI)-containing acid wastewater. [ABSTRACT FROM AUTHOR]

The microbially- and chemically-mediated redox process is critical in controlling the fate of vanadium (V) in tailing environment. Although the microbial reduction of V has been widely studied, the coupled biotic reduction mediated by beneficiation reagents and the underlying mechanism remain unclear. Herein, the reduction and redistribution of V in V-containing tailings and Fe/Mn oxide aggregates mediated by Shewanella oneidensis MR-1 and oxalic acid were explored. The dissolution of Fe-(hydr)oxides by oxalic acid promoted the microbe-mediated V release from solid-phase. After 48-day of reaction, the dissolved V concentrations in the bio-oxalic acid treatment reached maximum values of 1.72 ± 0.36 mg L–1 and 0.42 ± 0.15 mg L–1 in the tailing system and the aggregate system, respectively, significantly higher than those in control (0.63 ± 0.14 mg L–1 and 0.08 ± 0.02 mg L–1). As the electron donor, oxalic acid enhanced the electron transfer process of S. oneidensis MR-1 for V(V) reduction. The mineralogical characterization of final products indicates that S. oneidensis MR-1 and oxalic acid promoted solid-state conversion from V 2 O 5 to NaV 6 O 15. Collectively, this study demonstrates that microbe-mediated V release and redistribution in solid-phase were promoted by oxalic acid, suggesting that the role of organic agents for the V biogeochemical cycle in natural systems deserves greater attention. [Display omitted] • Dissolved V increased in biotic incubations compared to abiotic controls. • Oxalic acid could stimulate microbial reduction process and V release. • V mobilization resulted from reductive dissolution of Fe-(hydr)oxides in tailings. • The reduced V(IV) was immobilized in the newly formed mineral NaV 6 O 15. [ABSTRACT FROM AUTHOR]

This article describes the detoxification of pure chrysotile (Chr) asbestos by following an acid leaching treatment with oxalic acid dihydrate (Oxac) (H 2 C 2 O 4 ·2H 2 O). Oxac was chosen due to its low environmental impact (or toxicity) and cost. We demonstrate the effectiveness of different concentrations of Oxac as proposed formulations. The results from FTIR, XRD and optical microscopy analyses indicated that all the applied treatments destructed the Chr structure while a new biomaterial, Glushinskite (Gls) was formed by the reaction between Oxac with the outer Brucite (Brc) (MgO 2 ) layer surface of Chr. Oxac 0.05 M was selected as the optimal concentration for an eight-day treatment for the detoxification. The heating of the supernatant of the above-treated solution at 480 °C, yielded MgO in a considerable concentration (8.29% w/w). According to the energy consumption study the whole applied procedure is viable with an economic profit up to 4.3% and a low cost method of detoxification on the operation of a potential asbestos waste management site. [ABSTRACT FROM AUTHOR]

The toxicity of metals to microorganisms is highly correlated with the type of metal used. However, the differences in the resistance mechanisms of filamentous fungi to multiple metals remain unclear. In this study, we investigated the responses of Aspergillus niger to three toxic metals, i.e., Pb2+, Cd2+, and Cu2+. Fungal growth and metabolism indices showed that A. niger had a higher tolerance to Pb2+ (>1000 mg L−1) than to Cu2+ (300 mg L−1) and Cd2+ (50 mg L−1). An appropriate Pb2+ concentration (<500 mg L−1) stimulated fungal growth and metabolic activity, whereas Cd2+ and Cu2+ stress showed continuously negative influences on fungal physiological parameters, such as biomass and secretion of oxalic acid. A. niger responded to Pb stress by constructing a new border layer around its cell wall. This pathway was also confirmed using RNA-seq analysis, i.e., the gene encoding cell wall α-1,3-glucan synthase was upregulated. This upregulation subsequently promoted the production of polysaccharides, which are the main components that support fungal cell walls. In contrast, the expression of genes encoding both AAA family ATPase and efflux pump antibiotic resistance proteins for Cd2+ and Cu2+ was significantly downregulated. Therefore, these findings elucidated the relatively complete fungal responses to different metal stresses. [Display omitted] • A. niger showed higher tolerance to Pb2+ than Cd2+ and Cu2+. • Pb2+ stress induced the significant morphological alternation on cell wall of A. niger. • Up-regulation of α-1,3-glucan synthase strengthened cell wall structure under Pb stress. • The expression of genes encoding α-1,3-glucan synthase showed no significant differences under Cd/Cu stress. • The high toxicity of Cd/Cu was related with reduced efflux function. [ABSTRACT FROM AUTHOR]

Bioleaching is a promising route for electrolytic manganese (Mn) residue (EMR) reutilization due to being eco-friendly and cost-effective. However, microbes with high bioleaching efficiency are scarce. This work aimed to isolate, screen, and characterize a novel fungal strain with high Mn-bioleaching efficiency from EMR, and study the kinetics and mechanism. The novel Penicillium oxalicum strain Z6-5-1 was found to selectively bioleach Mn from EMR. A maximum Mn2+ recovery of 93.3 % was achieved after 7 days and was mainly dependent upon acidolysis of the bio-organic acids, specifically gluconic acid and oxalic acid, as well as mycelial biosorption. This efficiency was the highest reported in the literature for a fungus over such a short time. EMR strongly induced P. oxalicum to produce gluconic acid and oxalic acid. The novel transcription factor PoxCxrE of P. oxalicum controlled the production of bio-organic acids by regulating the expression of rate-limiting enzyme genes involved in the biosynthesis of bio-organic acids. Scanning electron microscopy, laser particle size analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were employed to analyze EMR changes after bioleaching. This study provides an alternative fungal resource for Mn-bioleaching of EMR, and a novel target for metabiotic engineering to improve bio-organic acid production. [Display omitted] • P. oxalicum is reported to efficiently bioleach Mn from EMR for the first time. • A novel P. oxalicum Z6-5-1 was isolated with a maximum Mn2+ recovery of 93.3 %. • Gluconic acid and oxalic acid mainly contributed to Mn-bioleaching by P. oxalicum. • Mycelial adsorption is required for Mn-bioleaching by P. oxalicum. • A novel TF PoxCxrE is found to control Mn-bioleaching by P. oxalicum. [ABSTRACT FROM AUTHOR]

Manganese incorporated fibrous silica nanosphere (MnO x -0.013/KCC-1) was synthesized by one step hydrothermal method for the first time and its catalytic activity for ozonation of oxalic acid was studied. For comparison, manganese loaded MCM-41 (MnO x -0.013/MCM-41) was prepared by impregnation method. Various characterizations showed that the morphological, structural and textural properties of MnO x -0.013/KCC-1 were well preserved. Ozonation and catalytic ozonation by MnO x -0.013/KCC-1 and MnO x -0.013/MCM-41 led to 4, 85 and 60% reduction in TOC respectively. Furthermore, 0.05 and 1.2 mg L −1 leaching of Mn was detected from MnO x -0.013/KCC-1 and MnO x -0.013/MCM-41, which are approximately 2.0 and 42.0% of the total Mn present in MnO x -0.013/KCC-1 and MnO x -0.013/MCM-41 respectively. The high catalytic activity was attributed to the generation of hydroxyl radical. Surface hydroxyl groups investigated by using phosphates and ATR-FTIR were believed to be the active sites. Our proposed method of synthesis can be generalized for the synthesis of other metal oxides incorporated fibrous silica for environmental catalysis and other catalytic reactions. [ABSTRACT FROM AUTHOR]

Oxalic acid enhances arsenic (As) mobilization by dissolving As host minerals and competing for sorption sites. Oxalic acid amendments thus could potentially improve the efficiency of widely used pump-and-treat (P&T) remediation. This study investigates the effectiveness of oxalic acid on As mobilization from contaminated sediments with different As input sources and redox conditions, and examines whether residual sediment As after oxalic acid treatment can still be reductively mobilized. Batch extraction, column, and microcosm experiments were performed in the laboratory using sediments from the Dover Municipal Landfill and the Vineland Chemical Company Superfund sites. Oxalic acid mobilized As from both Dover and Vineland sediments, although the efficiency rates were different. The residual As in both Dover and Vineland sediments after oxalic acid treatment was less vulnerable to microbial reduction than before the treatment. Oxalic acid could thus improve the efficiency of P&T. X-ray absorption spectroscopy analysis indicated that the Vineland sediment samples still contained reactive Fe(III) minerals after oxalic acid treatment, and thus released more As into solution under reducing conditions than the treated Dover samples. Therefore, the efficacy of enhanced P&T must consider sediment Fe mineralogy when evaluating its overall potential for remediating groundwater As. [ABSTRACT FROM AUTHOR]

This study was primarily imposed by the ever increasing need for detoxification of asbestos and asbestos containing materials (ACM), with potential application onsite. The present work investigates potential detoxification of pure chrysotile (Chr) asbestos via a combined treatment of oxalic acid dihydrate (Oxac) (Η 2 C 2 Ο 4 ·2Η 2 Ο) with silicates, such as tetraethoxysilane (TEOS) (SiH 20 C 8 O 4 ) and pure water glass (WG) (potassium silicate) (K 2 SiO 3 ). These reagents used in the experimental procedure, do not cause adverse effects on the environment and are cost effective. The results of FTIR, XRD, optical and scanning microscopy coupled with EDS analyses indicated that all of the applied treatments destructed the Chr structure and yielded silica of amorphous phase and the biomaterial glushinskite from the Oxac reacted with brucite [Mg(OH) 2 ] layer. Each of the proposed formulations can be applied for the detoxification of asbestos, according to priorities related to the specific products of the recovery treatment. Therefore, Oxac acid leaching followed by the TEOS addition is preferred in cases of glushinskite recovery; TEOS treatment of asbestos with subsequent Oxac addition produced amorphous silica production; finally Oxac acid leaching followed by WG encapsulated the asbestos fibers and can be used in cases of onsite asbestos and ACM detoxification. [ABSTRACT FROM AUTHOR]

Over the past few decades, reduction of hexavalent chromium (Cr(VI)) has been studied in many physicochemical contexts. In this research, we reveal the mechanism underlying the favorable effect of Mn(II) observed during Cr(VI) reduction by oxalic acid using liquid chromatography with spectrophotometric diode array detector (HPLC–DAD), nitrogen microwave plasma atomic emission spectrometry (HPLC–MP-AES), and high resolution mass spectrometry (ESI–QTOFMS). Both reaction mixtures contained potassium dichromate (0.67 mM Cr(VI)) and oxalic acid (13.3 mM), pH 3, one reaction mixture contained manganese sulfate (0.33 mM Mn(II)). In the absence of Mn(II) only trace amounts of reaction intermediates were generated, most likely in the following pathways: (1) Cr(VI) → Cr(IV) and (2) Cr(VI) + Cr(IV) → 2Cr(V). In the presence of Mn(II), the active reducing species appeared to be Mn(II) bis-oxalato complex (J); the proposed reaction mechanism involves a one-electron transfer from J to any chromium compound containing Cr O bond, which is reduced to Cr OH, and the generation of Mn(III) bis-oxalato complex (K ) . Conversion of K to J was observed, confirming the catalytic role of Mn(II). Since no additional acidification was required, the results obtained in this study may be helpful in designing a new, environmentally friendly strategy for the remediation of environments contaminated with Cr(VI). [ABSTRACT FROM AUTHOR]

With the booming of consumer electronics (CE) and electric vehicle (EV), a large number of spent lithium-ion battery (LIBs) have been generated worldwide. Resource depletion and environmental concern driven from the sustainable industry of CE and EV have motivated spent LIBs should be recovered urgently. However, the conventional process combined with leaching, precipitating, and filtering was quite complicated to recover cobalt and lithium from spent LIBs. In this work, we developed a novel recovery process, only combined with oxalic acid leaching and filtering. When the optimal parameters for leaching process is controlled at 150 min retention time, 95 °C heating temperature, 15 g L −1 solid–liquid ratio, and 400 rpm rotation rate, the recovery rate of lithium and cobalt from spent LIBs can reach about 98% and 97%, respectively. Additionally, we also tentatively discovered the leaching mechanism of lithium cobalt oxide (LiCoO 2 ) using oxalic acid, and the leaching order of the sampling LiCoO 2 of spent LIBs. All the obtained results can contribute to a short-cut and high-efficiency process of spent LIBs recycling toward a sound closed-loop cycle. [ABSTRACT FROM AUTHOR]

Complete mineralization of phenolic compounds into CO 2 and H 2 O is desirable for removing them in wastewater, but it is challenging due to the generated recalcitrant intermediates, which requires highly effective advanced oxidation process with proper catalysts. Herein, we found that single-crystal WO 3 nanosheets (NSs)-based photocatalytic ozonation (PCO) can realize complete mineralization of phenols (phenol and 2-chlorophenol) under visible light irradiation. Almost 100% mineralization ratio of phenols was achieved through WO 3 NSs-based PCO system within short time. By comparing their performances with those of polycrystalline WO 3 nanoparticles, detecting and analyzing the intermediates, identifying the dominant radicals and conducting some electrochemical characterizations, the origin of superior catalytic activity of WO 3 NSs was uncovered, the mineralization pathways and the overall mechanism were proposed. The excellent PCO performance of WO 3 NSs was contributed to their nanosheet morphology with single-crystal microstructure and good dispersion, which can provide continuous interior channels for the photogenerated charge transport from the bulk to surface of WO 3 NSs and enough active sites for the surface reactions triggered by these charges. This work puts forwards new ideas to design highly active photocatalysts for PCO and helps deepen understanding of the catalytic mechanism of PCO. [Display omitted] • WO 3 nanosheets (NSs) showed superior catalytic activity in photocatalytic ozonation (PCO). • Complete mineralization of phenols can be achieved with WO 3 NSs-based PCO. • The superior catalytic activity of WO 3 NSs was ascribed to their single-crystal structure. • Oxalic acid was confirmed as the key intermediate of phenol degradation. • The mechanism of WO 3 NSs-based PCO for mineralizing phenol was thoroughly investigated. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C 3 N 4 ) was employed as the active photocatalyst in the photocatalytic ozonation coupling system in the present study. g-C 3 N 4 was prepared by directly heating thiourea in air at 550 °C. XRD, FT-IR, UV–vis was used to characterize the structure and optical property. Oxalic acid and bisphenol A were selected as model substances for photocatalytic ozonation reactions to evaluate the catalytic ability of g-C 3 N 4 (g-C 3 N 4 /Vis/O 3 ). The results showed that the degradation ratio of oxalic acid with g-C 3 N 4 /Vis/O 3 was 65.2% higher than the sum of ratio when it was individually decomposed by g-C 3 N 4 /Vis and O 3 . The TOC removal of biphenol A with g-C 3 N 4 /Vis/O 3 was 2.17 times as great as the sum of the ratio when using g-C 3 N 4 /Vis and O 3 . This improvement was attributed to the enhanced synergistic effect between photocatalysis and ozonation by g-C 3 N 4 . Under visible light irradiation, the photo-generated electrons produced on g-C 3 N 4 facilitated the electrons transfer owing to the more negative conduction band potential (−1.3 V versus NHE). It meant that the photo-generated electrons could be trapped by ozone and reaction with it more easily. Subsequently, the yield of hydroxyl radicals was improved so as to enhance the organics degradation efficiency. This work indicated that metal-free g-C 3 N 4 could be an excellent catalyst for mineralization of organic compounds in waste control. [ABSTRACT FROM AUTHOR]

Metals recovery from spent automotive catalytic converters (SACCs) has gained great attention due to high metal content of SACCs and their potential to pollute the environment. This study presented a novel green strategy for treating SACCs using oxalic acid-enriched spent culture medium from Aspergillus niger cultivations. To enhance oxalic acid production, the Central Composite Design (CCD) was applied, which demonstrated that glucose (27.06 g/L), NaNO 3 (0.9 g/L), disodium oxalate (7.7 g/L), MnSO 4 ·H 2 O (0.28 g/L), and ethanol (0.65%(v/v)) were the optimum values leading to production of 15.3 g/L oxalic acid. The results of metals biorecovery with the fungal metabolites showed that pulp density of 15 g/L, temperature of 60 °C, and leaching time of 6 h resulted in the highest extraction of 99.1% Al, 99.3% Si, 82.2% Mn, 91.9% Zn, 17.6% Ba, 99.5% Fe, 92.2% Sr, 35.7% Ti, 60.9% Pt, and 73.7% Pd, as well as maximum enrichment of rare earth elements (REEs) in the residual powder. The EDX-mapping analysis indicated that the concentration of ∑REEs was nearly 8% in the initial waste powder, while it reached around 81% in the residual powder after bioleaching. The bioleaching mechanism was further analyzed by characterizing the bioleaching residues through XRD, FTIR, and FESEM analyses. [Display omitted] • The spent automotive catalyst was treated by the indirect fungal leaching method. • Optimization of medium composition led to producing 15.3 g/L oxalic acid by A. niger. • Bioleaching of metals was much better at a pulp density of 15 g/L, 60 °C, and 6 h. • The enrichment of REEs in the residual powder was successfully achieved. [ABSTRACT FROM AUTHOR]

A selective separation-recovery process based on tuning organic acid was proposed to the resource recycling of spent lithium-ion batteries (LIBs) for the first time. The low-cost preparation of CoFe 2 O 4 , reuse of waste acid and recovery of Li can be realized in this process, simultaneously. Li and Co in spent LIBs can be leached efficiently using citric acid as a leaching agent, and separated effectively from leaching solution by tuning oxalic acid content. The results from the characterizations of the prepared CoFe 2 O 4 (CoFe 2 O 4 -LIBs) show that it possesses higher ratio of Co(II)/Co(III) and Fe(II)/Fe(III), larger surface specific area and more number of acid sites in comparison with pure CoFe 2 O 4. Besides, CoFe 2 O 4 -LIBs was used to activate peroxymonosulfate (PMS) for the degradation of bisphenol A (BPA). Interestingly, its degradation performance is superior to that of pure CoFe 2 O 4 and the related Co-based catalysts. The excellent degradation performance can be maintained in presence of inorganic ions (e.g., C l − , HC O 3 − , H 2 P O 4 − and N O 3 − ) with high concentration or humic acid. Moreover, surface-bound S O 4 ∙ − is considered as the main reactive species for the degradation of BPA. More importantly, CoFe 2 O 4 -LIBs can be readily recycled by using an external magnet and own superior ability of regeneration. [Display omitted] • A green process was proposed to recover spent lithium-ion batteries. • The efficient separation of Li from other metals was realized in this process. • Magnetic CoFe 2 O 4 -LIBs was successfully prepared to activate PMS for BPA removal. • CoFe 2 O 4 -LIBs/PMS had excellent removal efficiency under high salinity condition. • The mechanism of PMS activation by CoFe 2 O 4 -LIBs was investigated in detail. [ABSTRACT FROM AUTHOR]

Highlights: [•] Oxalic, malic, lactic, and acetic acids were detected as intermediates in the MOP. [•] Oxalic acid is the dominant organic acid formed in treatment of leachate by MOP. [•] Lactic acid was generated from decomposition of malic acid. [•] Acetic acid formed and soon decomposed as a short-life intermediate. [•] Lower or higher persulfate doses yielded little or no lactic acid in the MOP. [ABSTRACT FROM AUTHOR]

Abstract: Sewage derived sludge is produced with an annual amount increase of 2% all over the world and it is an urgent issue to be addressed by human being. In the present study, sludge was converted into sludge-based catalyst (SBC) with ZnCl2 as activation agent and characterized by several methods (e.g., scanning electron microscope, X-ray photoelectron spectroscope and Fourier transform infrared spectroscope). Then it was used as a catalyst to enhance the removal of refractory organic matter, oxalic acid, and to control the formation of bromate (BrO3 −) in bench semi-continuous ozonation experiments. The effects of various operating parameters on the control of BrO3 − formation were investigated. Furthermore, the mechanism for the enhancement of organic matter removal and the control of BrO3 − formation was discussed as well. Results indicate that the combination of SBC with ozone shows a strong synergistic effect, resulting in a notable improvement on oxalic acid removal. A crucial surface reaction mechanism for the enhancement of organic matter removal is proposed on the basis of negative effect of higher pH and no inhibition effect of tert-butanol. The control for BrO3 − formation was demonstrated and the reason for its control in the process of O3/SBC is the combined effect of SBC reductive properties, ozone exposure decrease and hydrogen peroxide concentration increase. [Copyright &y& Elsevier]

Abstract: Polyacrylonitrile(PAN)/manganese acetate(Mn(CH3COO)2) composite nanofibers have been fabricated by electrospinning, a simple and effective technology. The obtained composite nanofibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectrometer (FT-IR). The composite nanofibers are amorphous in structure, continuous, even and smooth. At the same time, the reduction performance of Cr(VI) by oxalic acid in the presence of the composite nanofibers is also investigated. The results indicate that the composite nanofibers have exhibited excellent catalysis performance for Cr(VI) reduction from a Cr2O7 2−-containing solution by oxalic acid. And the critical parameters, such as the catalyst dosage, oxalic acid content, chromium concentration, the pH value of the reaction solution and light have important impact on the reduction process. Under the simulated solar light irradiation, after only 60min, 1.2mM initial Cr(VI) solution was reduced absolutely in the presence of PAN/Mn(CH3COO)2 composite nanofibers containing 17.5wt.% Mn(CH3COO)2 by 0.3mL 0.5M oxalic acid. In light, the reduction of Cr(VI) by oxalic acid is markedly accelerated. [Copyright &y& Elsevier]

Abstract: Manganese oxide and manganese oxide–carbon composites were prepared and tested as catalysts for the removal of oxalic acid by ozonation. Their performances were compared with the parent carbon material (activated carbon or carbon xerogel) used to prepare the composites. Oxalic acid degradation by carbon materials is slower than that attained with manganese oxide or manganese oxide–carbon composites. A complete degradation after 90 and 45min of reaction was obtained for carbon materials and for the catalysts containing manganese, respectively. The ozonation in the presence of the prepared composites are supposed to occur mainly by surface reactions, following a direct oxidation mechanism by molecular ozone and/or surface oxygenated radicals. [Copyright &y& Elsevier]

Abstract: The main goal of this study was to find a novel impregnated resin as an alternative for the conventional resin (KY-2 and AN-31) used for low and intermediate level liquid radioactive waste treatment. Novel impregnated ion exchangers namely, poly (acrylamide-acrylic acid-acrylonitril)-N,N’-methylenedi-acrylamide-4,4’(5′)di-t-butylbenzo 18 crown 6 [P(AM-AA-AN)-DAM/DtBB18C6], poly (acrylamide-acrylic acid-acrylonitril)-N,N’-methylenediacrylamide-dibenzo 18 crown 6 [P(AM-AA-AN)-DAM/DB18C6], and poly (acrylamide-acrylic acid-acrylonitril)-N,N’-methylenediacrylamide-18 crown 6 [P(AM-AA-AN)-DAM/18C6] were prepared and their removal efficiency of some radionuclides was investigated. Preliminary batch experiments were performed in order to study the influence of the different derivatives of 18 crown 6 on the characteristic removal performance. Separation of 134Cs, 60Co, 65Zn and (152+154)Eu radionuclides from low level liquid radioactive waste was investigated by using column chromatography with P(AM-AA-AN)-DAM/DtBB18C6 and metal salt solutions traced with the corresponding radionuclides. Breakthrough data was obtained in a fixed bed column at room temperature (298K) using different bed heights and flow rates. The breakthrough capacities were found to be 94.7, 83.3, 58.7, 43.1 (mg/g) for 60Co, 65Zn, 134Cs, and (152+154)Eu, respectively. Pre-concentration and separation of all radionuclides under study have been carried out using different concentration of nitric and/or oxalic acids. [Copyright &y& Elsevier]

Abstract: Heterogeneous photocatalytic decomposition of perfluoroocatanoic acid (PFOA) by TiO2 under 254nm UV light was investigated. Adding oxalic acid as a hole-scavenger significantly accelerated PFOA decomposition under nitrogen atmosphere. Fluoride ion, formic acid and six shorter-chain perfluorinated carboxylic acids (PFCAs) bearing C2–C7 were identified as intermediates. When using perchloric acid (HClO4) as a replacement of oxalic acid to maintain the same pH of the reaction solution, PFOA did not decomposition efficiently. Compared with oxalic acid, potassium iodide (KI, another hole-scavenger) also led to a slower PFOA decomposition, while the addition of an electron acceptor (potassium persulfate, K2S2O8) obviously inhibited PFOA decomposition. This suggested that oxalic acid played more than one role in PFOA decomposition rather than simply providing acidity and acting as a hole-scavenger. The electron paramagnetic resonance (EPR) measurements confirmed the existence of carboxyl anion radicals (CO2 −) in the photocatalytic process, which was a result of the reaction between oxalic acid and photogenerated hole. These findings indicated that PFOA decomposition was primarily induced by CO2 − radicals, although photogenerated electron was also conducive to PFOA decomposition. A possible mechanism for PFOA decomposition was proposed. [Copyright &y& Elsevier]

Abstract: The photocatalytic activity of a brick grain-supported iron oxide (denoted as B1) was tested for its activity to degrade Reactive Black 5 (RB5) in the presence of oxalic acid. B1 was obtained as a solid waste from a wastewater treatment plant, and characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD) and N2 adsorption/desorption isotherm analyses. The decolorization experiments were performed in a fluidized bed reactor with aeration under UV-A irradiation (λ =365nm). The effects of various factors such as solution pH, concentration of oxalic acid and dissolved oxygen on the decolorization of RB5 were evaluated considering the contributions of adsorption and photo-catalytic degradation. The role of dissolved iron in the removal of RB5 and the stability of B1 were also examined. In addition, the removal of TOC during the photo-catalytic reaction was monitored. [Copyright &y& Elsevier]

Abstract: In this study, two electrochemical oxidation processes were utilized to mineralize oxalic acid which was a major intermediate compound in the oxidation of phenols and other aromatic compounds. The anode rod and cathode net were made of a titanium coated with RuO2/IrO2 (Ti-DSA) and stainless steel (S.S. net, SUS304), respectively. First, the Fered-Fenton process, which used H2O2 and Fe2+ as additive reagents, achieved 85% of TOC removal. It proceeded with ligand-to-metal charge-transfer (LMCT), which was evidenced by the accumulation of metallic foil on the selected cathode. However, in the absence of H2O2/Fe2+, it showed a higher TOC removal efficiency while using Cl− only as an additive reagent due to the formation of hypochlorite on the anode. It was also found that the mineralization of oxalic acid by electrolysis generated hypochlorite better than the dosage of commercial hypochlorite without electricity. Also, pH value was a major factor that affected the mineralization efficiency of the oxalic acid due to the chlorine chemistry. 99% TOC removal could be obtained by Cl− electrolysis in an acidic environment. [Copyright &y& Elsevier]

Abstract: The kinetics of molybdenum, nickel, vanadium and aluminium leaching from a spent hydrodesulphurization catalyst in a solution containing oxalic acid and hydrogen peroxide was investigated. The effects of temperature and particle size were examined. In addition, the reaction mechanism for the dissolution of the spent catalyst was discussed. The results of the kinetic analysis for various experimental conditions indicated that the reaction rate of leaching process is controlled by chemical reaction at the particle surface. The values of the activation energies of 31±2, 36±4, 30±4 and 57±3kJmol−1 for Mo, Ni, V and Al, respectively, are characteristic for mechanism controlled by chemical reaction. [Copyright &y& Elsevier]