Associations of phosphorus concentrations with medial arterial calcification in lower-extremity arteries and diabetic foot in people with diabetes: a retrospective cross-sectional study.

BACKGROUND: The aim of this study was to investigate the associations of blood phosphorus levels with the risk of developing medial arterial calcification (MAC) in lower-limb arteries and diabetic foot (DF) in diabetes patients. We sought to enhance the understanding of the pathophysiology of diabetic complications and develop strategies to mitigate diabetes-related risks. METHODS: We conducted a retrospective analysis of 701 diabetic patients from the Department of Endocrinology at Sun Yat-Sen Memorial Hospital (2019-2023). We utilized multimodel-adjusted logistic regression to investigate the associations of serum phosphorus levels and the risk of developing MAC and DF. Restricted cubic spline plots were employed to model the relationships, and threshold analysis was used to identify inflection points. Subgroup analyses were performed to explore variations across different demographics. The diagnostic utility of phosphorus concentrations was assessed via the C index, net reclassification improvement (NRI), and integrated discrimination improvement (IDI). RESULTS: Of the 701 patients (mean age 63.9 years; 401 (57.20%) were male), 333 (47.50%) had MAC, and 329 (46.93%) had DF. After controlling for numerous confounding variables, each one-unit increase in phosphorus concentrations was associated with an increased risk of developing MAC (OR 2.65, 95% CI 1.97-3.57, p < 0.001) and DF (OR 1.54, 95% CI 1.09-2.18, p = 0.014). Phosphorus levels demonstrated a linear risk association, with risk not being uniform on either side of the inflection point, which was approximately 3.28 mg/dL for MAC and varied for DF (3.26 to 3.81 mg/dL). Adding the phosphorus as an independent component to the diagnostic model for MAC and DF increased the C index, NRI, and IDI to varying degrees. CONCLUSIONS: Elevated serum phosphorus levels are significantly associated with an increased risk of developing MAC and DF among diabetic people. These findings suggest that phosphorus management could be integrated into routine diagnostic processes to improve the identification and management of lower-extremity diabetic complications.

Selective recovery of Cu(II) from strongly acidic wastewater by zinc dimethyldithiocarbamate: Affecting factors, efficiency and mechanism.

The selective recovery of copper from strongly acidic wastewater containing mixed metal ions remains a significant challenge. In this study, a novel reagent zinc dimethyldithiocarbamate (Zn(DMDC)2) was developed for the selective removal of Cu(II). The removal efficiency of Cu(II) reached 99.6% after 120 min reaction at 30°C when the mole ratio Zn(DMDC)2/Cu(II) was 1:1. The mechanism investigation indicates that the Cu(DMDC)2 products formed as a result of the displacement of Zn(II) from the added Zn(DMDC)2 by Cu(II) in wastewater, due to the formation of stronger coordination bonds between Cu(II) and the dithiocarbamate groups of Zn(DMDC)2. Subsequently, we put forward an innovative process of resource recovery for strongly acidic wastewater. Firstly, the selective removal of Cu(II) from actual wastewater using Zn(DMDC)2, with a removal efficiency of 99.7%. Secondly, high-value CuO was recovered by calcining the Cu(DMDC)2 at 800°C, with a copper recovery efficiency of 98.3%. Moreover, the residual As(III) and Cd(II) were removed by introducing H2S gas, and the purified acidic wastewater was used to dissolve ZnO for preparation of valuable ZnSO4·H2O. The total economic benefit of resource recovery is estimated to be 11.54 $/m3. Accordingly, this study provides a new route for the resource recovery of the treatment of copper-containing acidic wastewater.

Reductive Removal and Recovery of As(V) and As(III) from Strongly Acidic Wastewater by a UV/Formic Acid Process.

The removal of arsenic (As(V) and As(III)) from strongly acidic wastewater using traditional neutralization or sulfuration precipitation methods produces a large amount of arsenic-containing hazardous wastes, which poses a potential threat to the environment. In this study, an ultraviolet/formic acid (UV/HCOOH) process was proposed to reductively remove and recover arsenic from strongly acidic wastewater in the form of valuable elemental arsenic (As(0)) products to avoid the generation of hazardous wastes. We found that more than 99% of As(V) and As(III) in wastewater was reduced to highly pure solid As(0) (>99.5 wt %) by HCOOH under UV irradiation. As(V) can be efficiently reduced to As(IV) (H2AsO3 or H4AsO4) by hydrogen radicals (H•) generated from the photolysis of HCOOH through dehydroxylation or hydrogenation. Then, As(IV) is reduced to As(III) by H• or through its disproportionation. The reduction of As(V) to H4AsO4 by H• and the disproportionation of H4AsO4 are the main reaction processes. Subsequently, As(III) is reduced to As(0) not only by H• through stepwise dehydroxylation but also through the disproportionation of intermediate arsenic species As(II) and As(I). With additional density functional theory calculations, this study provides a theoretical foundation for the reductive removal of arsenic from acidic wastewater.

Clean and effective removal of Cl(-I) from strongly acidic wastewater by PbO2.

Recycling strongly acidic wastewater as diluted H2SO4 after contaminants contained being removed was previously proposed, however, Cl(-I), a kind of contaminant contained in strongly acidic wastewater, is difficult to remove, which severely degrades the quality of recycled H2SO4. In this study, the removal of Cl(-I) using PbO2 was investigated and the involved mechanisms were explored. The removal efficiency of Cl(-I) reached 93.38% at 50℃ when PbO2/Cl(-I) mole ratio reached 2:1. The identification of reaction products shows that Cl(-I) was oxidized to Cl2, and PbO2 was reduced to PbSO4. Cl2 was absorbed by NaOH to form NaClO, which was used for the regeneration of PbO2 from the generated PbSO4. Cl(-I) was removed through two pathways, i.e., surface oxidation and •OH radical oxidation. •OH generated by the reaction of PbO2 and OH- plays an important role in Cl(-I) removal. The regenerated PbO2 had excellent performance to remove Cl(-I) after six-time regeneration. This study provided an in-depth understanding on the effective removal of Cl(-I) by the oxidation method.

Removal of Ni(II) from strongly acidic wastewater by chelating precipitation and recovery of NiO from the precipitates.

Strongly acidic wastewater produced in nonferrous metal smelting industries often contains high concentrations of Ni(II), which is a valuable metal. In this study, the precipitation of Ni(II) from strongly acidic wastewater using sodium dimethyldithiocarbamate (DDTC) as the precipitant was evaluated. The effects of various factors on precipitation were investigated, and the precipitation mechanism was also identified. Finally, the nickel in the precipitates was recovered following a pyrometallurgical method. The results show that, under optimised conditions (DDTC:Ni(II) molar ratio = 4:1; temperature = 25 °C), the Ni(II) removal efficiency reached 99.3% after 10 min. In strongly acidic wastewater, the dithiocarbamate group of DDTC can react with Ni(II) to form DDTCNi precipitates. Further recovery experiments revealed that high-purity NiO can be obtained by the calcination of DDTCNi precipitates, with the nickel recovery efficiency reaching 98.2%. The gas released during the calcination process was composed of NO2, CS2, H2O, CO2, and SO2. These results provide a basis for an effective Ni(II) recovery method from strongly acidic wastewater.

Specific H2S Release from Thiosulfate Promoted by UV Irradiation for Removal of Arsenic and Heavy Metals from Strongly Acidic Wastewater.

The removal of arsenic and heavy metals (HMs) from strongly acidic wastewater by hydrogen sulfide (H2S) is an efficient method. However, traditional sulfuration reagents (Na2S, FeS, CaS, etc.) rapidly release H2S under acidic conditions via spontaneous hydrolysis, leading to serious H2S pollution. Herein, a H2S release process employing thiosulfate as a sulfuration reagent was proposed to eliminate H2S pollution. We found that thiosulfate can release H2S with specificity both in the dark and under ultraviolet (UV) irradiation under acidic conditions. In the absence of arsenic/HMs, H2S is not released because the formed H2S is consumed by a thiosulfate decomposition product, sulfite, or by its photolysis. In the presence of arsenic/HMs, H2S is released because the formed H2S immediately reacts with arsenic/HMs to generate sulfide precipitates rather than being consumed. The efficiency of transforming thiosulfate to H2S under UV irradiation is 2.5-fold the efficiency in the dark, because UV irradiation promotes the transformation of "effective sulfur" in thiosulfate molecules to form H2S through the transformation of HS· and S2O3• - radicals. Moreover, more than 99.9% of arsenic/HMs were removed from strongly acidic wastewater without producing H2S pollution under UV irradiation. This thiosulfate-based H2S-specific release process solves the problem of H2S pollution under acidic conditions.

UV-Improved Removal of Chloride Ions from Strongly Acidic Wastewater Using Bi2O3: Efficiency Enhancement and Mechanisms.

Strongly acidic wastewater generated from nonferrous metal smelting industries can be recycled as sulfuric acid after the contaminants have been removed, and among which, Cl- is rather difficult to remove. Although previous studies showed that Cl- can be removed from acidic Zn electrolyte by Bi2O3, this method still suffers from low efficiency when being employed for strongly acidic wastewater recycling. Otherwise, very high Bi2O3 dosage and H2SO4 concentration are required, leading to the need for improvement. In this study, UV irradiation was employed to improve the removal, and it was found that Cl- removal efficiency was substantially enhanced from 63.9 to 98.3%, the optimum Bi2O3/Cl- mole ratio was lowered from 1.5:1 to 0.5:1, and to achieve the maximum removal efficiency, the required H2SO4 concentration was lowered from 70 to 40 g/L. The mechanisms were also elaborated. First, Bi2O3 dissolves under the function of UV and H+, and the produced Bi3+ combines with H2O and Cl- to form BiOCl. Then, Bi2O3/BiOCl transforms into BiOCl(h+)/Bi2O3(e-) under UV irradiation, and the generated h+ oxidizes Cl- to Cl•. Finally, Cl• reacts with Bi2O3/e- to produce BiOCl. This study offered a theoretical foundation for the improvement of Cl- removal from strongly acidic wastewater.

Removal of Chloride Ions from Strongly Acidic Wastewater Using Cu(0)/Cu(II): Efficiency Enhancement by UV Irradiation and the Mechanism for Chloride Ions Removal.

Strongly acidic wastewater, which is usually generated from nonferrous metal smelting industries, has the ability to be recycled as sulfuric acid. Before this wastewater is recycled, the removal of chloride ions is necessary to improve the quality of the recycled sulfuric acid. At present, the widely used method to remove chloride ions from acidic wastewater in the form of CuCl precipitate has several disadvantages, including low removal efficiency, high temperature, long treatment time, and high dosage of Cu(II). This study proposed an improved new method of removing Cl(-I) using Cu(0)/Cu(II) under UV irradiation, and the mechanism was investigated. The Cl(-I) concentration was lowered to below 50 mg/L at a Cu(II) dosage of 1200 mg/L. Under UV irradiation, ligand-to-metal charge transfer takes place, thereby resulting in the formation of Cl•. Next, CuCl precipitates form through the reaction between Cu(0) and Cl• and produce h+/•OH under UV irradiation, which can oxidize Cl(-I) to Cl•. Simultaneously, Cl2 gas also forms directly from Cl•. This study offered a theoretical foundation for the application of UV irradiation for the enhanced removal of chloride ions from strongly acidic wastewater.

Mechanism for Photopromoted Release of Vanadium from Vanadium Titano-Magnetite.

The release of V from vanadium titano-magnetite, a predominant natural source of V, was studied under light irradiation. The release rate of V from vanadium titano-magnetite was accelerated by light irradiation, and the oxidation of V was detected. The essence of the photopromoted release of V is that the immobile low valence V is transformed to the mobile V(V) by photoinduced active species generated from the photocatalysis process of magnetite. Among the photoinduced active species, •OH and H2O2 were recognized as the most important oxidizing agents. Not only can they directly convert the immobile low-valence V to the mobile V(V) but also initiate the Fenton reaction, which produces more •OH and then further promotes the oxidation of low-valence V. In addition, a conceptual model of the photo promoted release of V was proposed. This study, as part of a broader study of the release behavior of V, can improve the understanding of the pollution problem about V, as well as the fate and environmental geochemistry cycling of V in the natural environment.

Removal of Arsenic from Strongly Acidic Wastewater Using Phosphorus Pentasulfide As Precipitant: UV-Light Promoted Sulfuration Reaction and Particle Aggregation.

Strongly acidic wastewater (H2SO4) with a high arsenic concentration is produced by many industries. The removal of arsenic by traditional sulfide (e.g., Na2S, FeS) from strongly acidic wastewater introduces cations (Na+ and Fe2+) to the solution, which may prevent the recycle of acid. In this study, a new sulfuration agent, phosphorus pentasulfide (P2S5) was employed, and its feasibility in arsenic removal from strongly acidic wastewater was investigated. In the dark, As(III) was efficiently removed, but the removal rate of As(V) was rather slow, which was the crucial defect for this method. We found that this defect can be efficiently overcome by UV irradiation through accelerating the formation and transformation of an intermediate species, monothioarsenate (H3AsO3S) in the As(V) removal process. In addition, the hydrolysis of P2S5 was enhanced under UV irradiation, which resulted in the increase of the arsenic removal efficiencies. Besides, the aggregation of the formed particles was also promoted. Different from FeS and Na2S, P2S5 introduces H3PO4 instead of cations to the solution, which can facilitate the recycle and reuse of arsenic and acid in strongly acidic wastewater.

UV-Light-Induced Aggregation of Arsenic and Metal Sulfide Particles in Acidic Wastewater: The Role of Free Radicals.

The removal of arsenic and metals by sulfide (S(-II)) from acidic wastewater is an efficient method. However, the small sulfide particles formed in such a process make solid-liquid separation difficult, which greatly hinders its application. This study investigated the aggregation behavior of different sulfide particles (As2S3, CuS and CdS) under ultraviolet (UV) irradiation. In the dark, the aggregation rate of the arsenic sulfide (As2S3) particles was extremely slow. However, under UV irradiation, the growth of the As2S3 particles was significantly enhanced. A possible mechanism of UV-light-induced aggregation of As2S3 particles was proposed. The HS· and ·OH radicals formed by a series of photochemical reactions can efficiently attack the S(-II) in the As2S3 particle, leading to the formation of an intermediate species, [As2S2-S·]+. Then, two [As2S2-S·]+ species combine to form [As2S2-S-S-S2As2]2+. The formation of [As2S2-S-S-S2As2]2+ results in the attenuation of the electronegativity and the rapid aggregation of the sulfide particles. In addition, the small S0 particles generated in irradiated As2S3 system can efficiently coalesce into As2S3 particles. The CuS and CdS particles should have similar aggregation mechanisms. This study proposed a potential method for sulfide particle aggregation and provided a theoretical foundation for the development and application of UV-light-induced sulfide particle aggregation technology.

Release kinetics of vanadium from vanadium titano-magnetite: The effects of pH, dissolved oxygen, temperature and foreign ions.

As part of a broader study of the environmental geochemistry behavior of vanadium (V), the release kinetics of V from the dissolution of natural vanadium titano-magnetite under environmentally relevant conditions was investigated. In both the acidic and basic domains, the V release rate was found to be proportional to fractional powers of hydrogen ion and dissolved oxygen activities. The dependence of the rate on dissolved oxygen can also be described in terms of the Langmuir adsorption model. The empirical rate equation is given by: r [Formula: see text] where, α=0.099-0.265, k'=3.2×10-6-1.7×10-5, K=2.7×104-3.9×104mol/L in acid solution (pH4.1), and α=-0.494-(-0.527), k'=2.0×104-2.5×10-11, and K=4.1×103-6.5×103mol/L in basic solution (pH8.8) at 20°C. Based on the effect of temperature on the release rate of V, the activation energies of minerals at pH8.8 were determined to be 148-235kJ/mol, suggesting that the dissolution of vanadium titano-magnetite is a surface-controlled process. The presence of Na+, Ca2+, Mg2+, K+, NO3-, Cl-, SO42- and CO32- was found to accelerate the V release rates. This study improves the understanding of both the V pollution risk in some mine areas and the fate of V in the environment.

Release kinetics of vanadium from vanadium (III, IV and V) oxides: Effect of pH, temperature and oxide dose.

Batch experiments were performed to derive the rate laws for the proton-promoted dissolution of the main vanadium (III, IV and V) oxides at pH 3.1-10.0. The release rates of vanadium are closely related to the aqueous pH, and several obvious differences were observed in the release behavior of vanadium from the dissolution of V2O5 and vanadium(III, IV) oxides. In the first 2hr, the release rates of vanadium from V2O3 were r=1.14·([H+])0.269 at pH 3.0-6.0 and r=0.016·([H+])-0.048 at pH 6.0-10.0; the release rates from VO2 were r=0.362·([H+])0.129 at pH 3.0-6.0 and r=0.017·([H+])-0.097 at pH 6.0-10.0; and the release rates from V2O5 were r=0.131·([H+])-0.104 at pH 3.1-10.0. The release rates of vanadium from the three oxides increased with increasing temperature, and the effect of temperature was different at pH 3.8, pH 6.0 and pH 7.7. The activation energies of vanadium (III, IV and V) oxides (33.4-87.5kJ/mol) were determined at pH 3.8, pH6.0 and pH 7.7, showing that the release of vanadium from dissolution of vanadium oxides follows a surface-controlled reaction mechanism. The release rates of vanadium increased with increasing vanadium oxides dose, albeit not proportionally. This study, as part of a broader study of the release behavior of vanadium, can help to elucidate the pollution problem of vanadium and to clarify the fate of vanadium in the environment.

Mechanisms of UV-Light Promoted Removal of As(V) by Sulfide from Strongly Acidic Wastewater.

Strongly acidic wastewater with a high arsenic concentration is produced by a number of industries. The removal of As(V) (H3AsO4) by sulfide from strongly acidic wastewater remains a difficult issue. This study proposed a UV-assisted method to efficiently remove As(V) by sulfide, and the involved mechanisms were systematically investigated. In the dark, the low removal efficiency of As(V) by sulfide was attributed to the slow formation and transformation of an intermediate species, i.e., monothioarsenate (H3AsO3S), in the As(V) sulfuration reaction, which were the rate-controlling steps in this process. However, UV irradiation significantly promoted the removal efficiency of As(V) not only by promoting the formation of H3AsO3S through light-induced HS• and •H radicals but also by enhancing the transformation of H3AsO3S through a charge-transfer process between S(-II) and As(V) in the H3AsO3S complex, leading to the reduction of As(V) to As(III) and the oxidation of S(-II) to S(0). The formed As(III) species immediately precipitated as As2S3 under excess S(-II). Kinetic modeling offered a quantitative explanation of the results and verified the proposed mechanisms. This study provides a theoretical foundation for the application of light-promoted As(V) sulfuration removal, which may facilitate the recycling and reuse of arsenic and acid in strongly acidic wastewater.

Organic ligand-induced dissolution kinetics of antimony trioxide.

The influence of low-molecular-weight dissolved organic matter (LMWDOM) on the dissolution rate of Sb2O3 was investigated. Some representative LMWDOMs with carboxyl, hydroxyl, hydrosulfuryl and amidogen groups occurring naturally in the solution were chosen, namely oxalic acid, citric acid, tartaric acid, EDTA, salicylic acid, phthalandione, glycine, thiolactic acid, xylitol, glucose and catechol. These LMWDOMs were dissolved in inert buffers at pH=3.7, 6.6 and 8.6 and added to powdered Sb2O3 in a stirred, thermostatted reactor (25°C). The addition of EDTA, tartaric acid, thiolactic acid, citric acid and oxalic acid solutions at pH3.7 and catechol at pH8.6 increased the rate of release of antimony. In the 10mmol/L thiolactic acid solution, up to 97% by mass of the antimony was released after 120min reaction. There was no effect on the dissolution of Sb2O3 for the other ligands. A weak correlation between dissolution rate with the dissociation constant of ligands and the stability of the dissolved complex was also found. All the results showed that the extent of the promoting effect of ligands on the dissolution of Sb2O3 was not determined by the stability of the dissolved complex, but by the dissociation constant of ligands and detachment rate of surface chelates from the mineral surface. This study can not only help in further understanding the effect of individual low-molecular-weight organic ligands, but also provides a reference to deduce the effect of natural organic matters with oxygen-bearing functional groups on the dissolution of antimony oxide minerals.

pH-dependent release characteristics of antimony and arsenic from typical antimony-bearing ores.

The pH-dependent leaching of antimony (Sb) and arsenic (As) from three typical Sb-bearing ores (Banxi, Muli and Tongkeng Antimony Mine) in China was assessed using a pH-static leaching experiment. The pH changes of the leached solutions and pH-dependent leaching of Sb and As occurred in different ways. For the Banxi and Muli Sb ores, alkaline conditions were more favorable for the release of Sb compared to neutral and acidic conditions, but the reverse was true for the pH-dependent release of As. For the Tongkeng Sb ore, unlike the previous two Sb-bearing ores, acidic conditions were more favorable for Sb release than neutral and alkaline conditions. The ores with lower Sb and As contents released higher percentages of their Sb and As after 16day leaching, suggesting that they are the largest potential sources of pollution. This work may provide key information on the geochemistry of Sb and As in the weathering zone.

Mechanisms of Sb(III) oxidation by pyrite-induced hydroxyl radicals and hydrogen peroxide.

Antimony (Sb) is an element of growing interest, and its toxicity and mobility are strongly influenced by redox processes. Sb(III) oxidation mechanisms in pyrite suspensions were comprehensively investigated by kinetic measurements in oxic and anoxic conditions and simulated sunlight. Sb(III) was oxidized to Sb(V) in both solution and on pyrite surfaces in oxic conditions; the oxidation efficiency of Sb(III) was gradually enhanced with the increase of pH. The pyrite-induced hydroxyl radical (·OH) and hydrogen peroxide (H2O2) are the oxidants for Sb(III) oxidation. ·OH is the oxidant for Sb(III) oxidation in acidic solutions, and H2O2 becomes the main oxidant in neutral and alkaline solutions. ·OH and H2O2 can be generated by the reaction of previously existing FeIII(pyrite) and H2O on pyrite in anoxic conditions. The oxygen molecule is the crucial factor in continuously producing ·OH and H2O2 for Sb(III) oxidation. The efficiency of Sb(III) oxidation was enhanced in surface-oxidized pyrite (SOP) suspension, more ·OH formed through Fenton reaction in acidic solutions, but Fe(IV) and H2O2 were formed in neutral and alkaline solutions. Under the illumination of simulated sunlight, more ·OH and H2O2 were produced in the pyrite suspension, and the oxidation efficiency of Sb(III) was remarkably enhanced. In conclusion, Sb(III) can be oxidized to Sb(V) in the presence of pyrite, which will greatly influence the fate of Sb(III) in the environment.

Antimony leaching release from brake pads: Effect of pH, temperature and organic acids.

Metals from automotive brake pads pollute water, soils and the ambient air. The environmental effect on water of antimony (Sb) contained in brake pads has been largely untested. The content of Sb in one abandoned brake pad reached up to 1.62×10(4) mg/kg. Effects of initial pH, temperature and four organic acids (acetic acid, oxalic acid, citric acid and humic acid) on Sb release from brake pads were studied using batch reactors. Approximately 30% (97 mg/L) of the total Sb contained in the brake pads was released in alkaline aqueous solution and at higher temperature after 30 days of leaching. The organic acids tested restrained Sb release, especially acetic acid and oxalic acid. The pH-dependent concentration change of Sb in aqueous solution was best fitted by a logarithmic function. In addition, Sb contained in topsoil from land where brake pads were discarded (average 9×10(3) mg/kg) was 3000 times that in uncontaminated soils (2.7±1 mg/kg) in the same areas. Because potentially high amounts of Sb may be released from brake pads, it is important that producers and environmental authorities take precautions.

Kinetics and mechanism of photopromoted oxidative dissolution of antimony trioxide.

Light (sunlight, ultraviolet, simulated sunlight) irradiation was used to initiate the dissolution of antimony trioxide (Sb2O3). Dissolution rate of Sb2O3 was accelerated and dissolved trivalent antimony (Sb(III)) was oxidized in the irradiation of light. The photopromoted oxidative dissolution mechanism of Sb2O3 was studied through experiments investigating the effects of pH, free radicals scavengers, dissolved oxygen removal and Sb2O3 dosage on the release rate of antimony from Sb2O3 under simulated sunlight irradiation. The key oxidative components were hydroxyl free radicals, photogenerated holes and superoxide free radicals; their contribution ratios were roughly estimated. In addition, a conceptual model of the photocatalytic oxidation dissolution of Sb2O3 was proposed. The overall pH-dependent dissolution rate of Sb2O3 and the oxidation of Sb(III) under light irradiation were expressed by r = 0.08 ·[OH(-)](0.63) and rox = 0.10 ·[OH(-)](0.79). The present study on the mechanism of the photo-oxidation dissolution of Sb2O3 could help clarify the geochemical cycle and fate of Sb in the environment.

UV irradiation induced simultaneous reduction of Cu(II) and degradation of EDTA in Cu(II)-EDTA in wastewater containing Cu(II)-EDTA.

Decomplexation of Cu(II)-EDTA followed by chemical precipitation of free Cu(II) ions can effectively degrade EDTA in Cu(II)-EDTA and remove Cu(II), but requires large precipitant dosage and inevitably produces a large amount of copper-containing sludge that is difficult to deal with. Herein, we demonstrated that simultaneous reduction of Cu(II) and degradation of EDTA in Cu(II)-EDTA can be achieved by UV irradiation of wastewater containing Cu(II)-EDTA without adding reagent. 93.65% of Cu(II) was reduced to Cu(0) with a high purity of 99.93 wt%, which can be recycled, thus avoiding the generation of copper-containing sludge. 96.67% of EDTA in Cu(II)-EDTA was degraded, and the final products were HCHO, NH4+, NO3- and low-molecular acids. In depth, the dominant degradation mechanism of EDTA in Cu(II)-EDTA was photo-induced successive decarboxylation through homolysis of C-O and C-C bond of -CH2-COOH group, followed by ligand to metal charge transfer (LMCT) and hydrolysis reactions. The minor degradation mechanism of EDTA in Cu(II)-EDTA was successive decarboxylation by •OH radicals. Simultaneously, Cu(II) was reduced to Cu(0) by H• and eaq- produced by UV irradiation of Cu(II)-EDTA. This study provided an approach of simultaneous removal of heavy metals and degradation of EDTA in Cu(II)-EDTA in wastewater containing heavy metal-EDTA complex.