Iron Sludge Research Articles

The possibility of recycling iron sludge in the steel industry

Abstract The steel industry strives to achieve quality steel with improved mechanical properties. In order to meet these market requirements, steel manufacturers need to streamline technological operations, increase process efficiency and productivity, and improve product quality control. Old iron and scrap metal used in the production of steel come from various sources and special attention should be paid to their quality, in particular, to the content of elements harmful to steel. The paper presents the results of the research undertaken on the use as raw material of the steel-making aggregates, in addition to the classic assortments of old iron of by-products obtained from the processing of iron slats in the form of briquettes. The influence of the quality of waste used was assessed by expanding the raw material base in the context of sustainable development, on steel blanks by investigating the effect on the chemical composition as well as the possibility of recovery of alloying element.

A photocatalysis-self-Fenton system based on NCDs@ZnIn2S4 composites at neutral pH and low amount of Fe2+ for the effective degradation of antibiotics

Photocatalysis-self-Fenton combining photocatalytic production of H2O2 with Fenton reaction has been a hotspot, but the pH limitation and iron sludge production problems remain unsolved. Herein, we proposed a self-fenton system based on N-doped carbon dots modified ZnIn2S4 (NCDs@ZnIn2S4) composites that exhibits effective degradation of antibiotics under neutral pH using low amounts of Fe2+. The decoration of ZnIn2S4 with NCDs significantly increased the surface area, visible light absorption, charge transfer ability and oxygen adsorption ability. NCDs@ZnIn2S4 composites exhibited a high H2O2 production rate (1528 μM g−1•h−1) under visible light, which was 1.9 and 5.3 times higher than ZnIn2S4 and NCDs, respectively. Meanwhile, the Fe2+/NCDs@ZnIn2S4 system with a low concentration of Fe2+(1 mg/L) could remove over 95% levofloxacin and oxytetracycline within 30 min. Interestingly, the highest degradation efficiency occurred under neutral pH. Quenching experiments and analytical measurements indicated that the high catalytic performance under pH = 7 with low amounts of Fe2+ stemmed from the higher amount of inner-generate H2O2 under neutral pH and easy regeneration of Fe2+ by photoinduced electrons for high •OH yields. Additionally, the Fe2+/NCDs@ZnIn2S4 system exhibited high degradation performance under different water matrix and ultrahigh degradation efficiency towards levofloxacin under real sunlight irradiation. The work shows the prospects of photocatalysis-self-Fenton systems for overcoming the pH limitation and the difficulty of iron sludge separation in the purification of effluents.

Degradation of phenol by metal-free electro-fenton using a carbonyl-modified activated carbon cathode: Promoting simultaneous H2O2 generation and activation

The low yield of hydrogen peroxide, narrow pH application range, and secondary pollution due to iron sludge precipitation are the major drawbacks of the electro-Fenton (EF) process. Metal-free electro-Fenton technology based on carbonaceous materials is a promising green pollutant degradation technology. Activated carbon cathodes enriched with carbonyl functional groups were prepared using a two-step annealing method for the degradation of phenol pollutants. The •OH in the activation process of H2O2 were identified using the EPR test technique. The action mechanism of carbonyl groups on H2O2 activation was investigated in conjunction with density functional theory (DFT) calculations. The EPR tests demonstrated that the modified activated carbon could promote the in-situ activation of H2O2 to •OH. And the results of material analysis and DFT showed that C=O could facilitate the activation of hydrogen peroxide through the electron transfer mechanism as an electron-donating group. Electrochemical tests showed that both the oxygen reduction activity and 2e−ORR selectivity of the modified activated carbons were significantly improved. Compared with the original activated carbon cathode and EF, the degradation efficiency of phenol in the ACNH-1000/GF cathode was increased by 58.10% and 45.61%, respectively. Compared with EF, ACNH-1000/GF metal-free electro-Fenton effectively expands the pH application range, and is proven to be less affected by solution initial pH, while avoiding secondary pollution. The metal-free electro-Fenton system can save more than a quarter of the cost of EF system. This study has a deep understanding of the reaction mechanism of the carbonyl modified activated carbon, and provides valuable insights for the design of metal-free catalysts, so as to promote its application in the degradation of organic pollutants.

Key role of Phyllanthus emblica L. fruit extract promotes ZVI/H2O2 process: rich titratable acid, suitable chelating ability, and antioxidant capacity.

Phyllanthus emblica L. fruit extract (PFE) was introduced to improve ZVI/H2O2 technology, and the efficiency and mechanism of PFE promoting ZVI/H2O2 technology were explored. With the introduction of PFE, the Norfloxacin (NOR) removal rate and kobs of the process were improved by 41.17% and 5.08 times, respectively. In the ZVI/H2O2/PFE process, the degradation of NOR by the attack of ROS is the main pathway for decontamination and is dominated by the heterogeneous reaction on the catalyst surface. PFE contains 13.92 g/L titratable acid and has good complexing ability and antioxidant ability. The mechanism of PFE promoting ZVI/H2O2 technology was based on lowering the pH, complemented by chelation and antioxidant capacity. With the introduction of PFE, the utilization rate of the reagent was significantly increased (7.56 times for ZVI and 3.21 times for H2O2), the applicable pH range was widened (6-9) and the iron sludge was reduced (32.80%). Meanwhile, the concept of UPR is proposed for the first time. The result is the key role to the selection of green promoters in the ZVI/H2O2 process depends on the abundance of titratable acid, followed by a certain chelating ability and antioxidant capacity.

Using flow-through reactor to enhance ferric ions electrochemical regeneration in electro-fenton for wastewater treatment

Electrochemical regeneration of ferric ions catches more and more attention since it could decrease iron sludge to avoid the sludge problem while it could simultaneously obtain similar robust removal efficiency to refractory organic contaminants in wastewater treatment as the normal Fenton agent method. However, the electrochemical regeneration of ferric ions in aqueous solution was very slow. In this paper, the mass transfer limit of ferric ions in electro-Fenton reaction was evaluated. Koutecky-Levich equation reveals an extremely low diffusion coefficient (D0) value of ferric ions since its complex coordination of [Fe(HO)x(H2O)6-x]3-x. The D0 value was only 2.70 × 10−6 cm2·s−1. Flow-through reactor was therefore introduced in which the ferric ions was designed to penetrate through the 73.1 μm porous holes in the graphite fiber electrode. The μm-scaled confinement of ferric ions diffusion inside the holes was proved to successfully enhance the reduction current of ferric ions by more than 200 % since the diffusion distance of the ferric ions was significantly decreased in the flow-through reactor. However, besides the benefit of the flow-through reactor, the ferric ions reduction electro-Fenton (FeRR electro-Fenton) in flow-through still faces both the pH limit and H2O2 decomposition problems. Hydrogen evolution reaction (HER) could also cause the decrease of pH which exceeded the optimal pH window for Fenton and therefore destroyed the electro-Fenton reaction consequently although the electrochemical reaction of FeRR was 770 mV prior to HER reaction. The regeneration of Fe (II) process simultaneous destruction of H2O2 since H2O2 e-reduction was 120 mV prior to FeRR reaction, which resulted in only very low H2O2 concentration suitable for FeRR electro-Fenton. Even using stepwise addition of H2O2 in electro-Fenton, the decomposition of H2O2 still could not be avoided. Although the decomposition of H2O2 quite limited the application of FeRR electro-Fenton in real application, FeRR electro-Fenton still supports the enhancement removal efficiency of the refractory organic contaminants under low organic contaminants application.

Overlooked pyrite-mediated heterogeneous Fenton processes: Mechanisms of surface hydroxyl radical generation and associated decontamination performance

Pyrite-based Fenton-like processes have been extensively studied for wastewater decontamination; however, most relevant studies placed excessive emphasis on the homogeneous Fenton reaction mediated by aqueous Fe2+, resulting in the proposed technologies facing issues such as additional acid requirements for pH adjustment and excessive iron sludge production. Herein, through in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), custom dual-chamber reactor experiments, and a series of control experiments, significant hydroxyl radical generation was identified during the pyrite/H2O2 process, while the dominant reactive iron species was verified to the structural Fe sites on the pyrite surface, rather than structural Fe(II) in secondary iron minerals and surface adsorbed Fe2+. Consequently, even with significant suppression of the homogeneous Fenton pathway, the pyrite/H2O2 process exhibited significant degradation efficiency for sulfamethoxazole (SMX) at pH 4. Moreover, the pyrite/H2O2 process was found to selectively remove 50 μM of pollutants with high affinity for pyrite (bisphenol A, carbamazepine, nitrobenzene, and SMX), even in the presence of 50–100 mM methanol. Compared to the typical iron-based reductive catalyst (zero-valent iron, ZVI), pyrite mediated a Fenton process with greater potential for practical applications at pH 4, achieving a 43.75-fold reduction in iron sludge production and almost doubling the H2O2 utilization efficiency. Additionally, in contrast to ZVI, minimal iron oxide formed on the pyrite surface during the oxidation process. Thus, after seven cycles of degradation experiments, the decontamination efficiency of the pyrite/H2O2 process remained stable. These findings are crucial for understanding the complex environmental behavior of pyrite in both natural and engineering processes and provide a new perspective for the efficient utilization of pyrite resources as well.

Activated hydrogen-promoted self-generation of H2O2 and reduction of Fe(III) mediated by Pd-based catalysts: A green Fenton-like process

The traditional Fenton process has two issues that hinder its further application and promotion. One is the generation of large amounts of iron sludge. The other is the safe storage and transport of explosive H2O2. The problems could be solved by accelerating to regenerate Fe(II) and realizing to self-generate H2O2. The key to the solution lies in the use of reducing active hydrogen [H] to supply electrons. The effect of different loading methods of Pd0 nanoparticles (NPs), active centres for [H] generation, on the catalytic performance is unknown. Herein, the Pd/UiO-66(Zr) (Pd0 NPs loaded on the surface of UiO-66(Zr)) and Pd@UiO-66(Zr) (Pd0 NPs confined into the pores of UiO-66(Zr)) were synthesized. It confirmed that the [H] could be used to promote to regenerate Fe(II) and self-generate H2O2. Using only a trace amount of ferrous (25 μM) and without H2O2, the trimethoprim (20 mg·L−1) could be thoroughly removed within 90 min. Moreover, the stability of Pd@UiO-66(Zr) was slightly superior to that of Pd/UiO-66(Zr) because of the confinement effect of pore wall on Pd0 NPs, as well as the interception effect on the intermediate products that can be complexed with Pd0 NPs.

Recyclable carbon nitride composite catalyst for degradation of tetracycline under natural light in a novel iron-free photo-Fenton system

Fenton technology has great advantages in treating antibiotic pollution, but the generation and treatment of iron sludge has always restricted the development and application of traditional Fenton technology. In this work, an iron-free photo-Fenton (IF-PF) system with MoS2/TCNCl-S(P) as the core catalyst was established to achieve efficient degradation of antibiotics. We investigated the efficiency and stability of MoS2/TCNCl-S(P) in degrading tetracycline (TC) in IF-PF system. The cyclic mass transfer between photogenerated carrier and H2O2 in the IF-PF system was explained, and the transformation mechanism of H2O2 into strong oxidizing free radicals under the action of photogenerated carrier was revealed, and it was used for the degradation of antibiotics under natural light. The experimental results show that the efficient degradation of TC by IF-PF (MoS2/TCNCl-S(P)) system under natural light is mainly due to the abundant formation of radO2– and radOH. This finding offers a promising research direction for the photocatalytic degradation of organic pollutants in natural light conditions.

Simultaneous removal of tetracycline hydrochloride and hexavalent chromium by heterogeneous Fenton in a photocatalytic fuel cell system

In this work, a novel double-chamber system (PFC-Fenton), combined photocatalytic fuel cell (PFC) with Fenton, was constructed for tetracycline hydrochloride (TCH) and hexavalent chromium (Cr(VI)) removal and electricity production. Therein, Zn5(OH)6(CO3)2/Fe2O3/BiVO4/fluorine-doped SnO2 (ZIO/BiVO4/FTO) and carboxylated carbon nanotubes/polypyrrole/graphite felt (CCNTs/Ppy/GF) were served as photoanode and cathode, respectively. Under light irradiation, the removal efficiencies of TCH and Cr(VI) with the addition of H2O2 (2 mL) could reach 93.1% and 80.4%, respectively. Moreover, the first-order kinetic constants (7.37 × 10−3 min−1 of TCH and 3.94 × 10−3 min−1 of Cr(VI)) were 5.26 and 5.57 times as much as the absence of H2O2. Simultaneously, the maximum power density could be obtained 0.022 mW/cm2 at a current density of 0.353 mA/cm2. Therein, the main contribution of TCH degradation was ·OH and holes in anode chamber. The synergistic effect of photoelectrons, generated ·O2−, and H2O2 played a crucial role in the reduction of Cr(VI) in cathode chamber. The high-performance liquid chromatography-mass spectrometry indicated that TCH could be partially mineralized into CO2 and H2O. X-ray photoelectron spectroscope and X-ray absorption near-edge structure spectra showed that Cr(VI) could be reduced to Cr(III). After 5 times of cycling, the removal efficiencies of TCH and Cr(VI) were still greater than 70%, indicating the remarkable stability of the PFC-Fenton system. Overall, this system could remove TCH/Cr(VI) and generate power simultaneously without iron sludge formation, demonstrating a promising method to further develop PFC-Fenton technology.

Fe-Ce based metal-organic framework as a novel heterogeneous catalyst accelerating redox cycle for efficient degradation of sulfamethoxazole in wide pH ranges

The electro-Fenton (EF) technology holds immense potential for wastewater treatment. However, there persist certain factors that affect its degradation efficiency, such as the restricted pH range, production of iron sludge and sluggish conversion rate between Fe2+ and Fe3+. Herein, 2,3,6,7,10,11-hexahydroxytriphenyl (HHTP) was introduced as the organic ligand to synthesize a series of efficient iron-based MOF catalysts (FexCe1-HHTP (x = 1, 2, 3, 4)) with different molar ratios for sulfamethoxazole (SMX) degradation in heterogeneous EF system. HHTP with electron-rich functional groups is beneficial to enhance performance of oxygen evolution reaction. Among these catalysts, Fe3Ce1-HHTP catalyst achieved 97.3 % degradation efficiency in 30 min and mineralization rate was 89.7 % at 1 h. The introduction of Ce promoted the transition of Fe3+ and Fe2+ in heterogeneous EF reaction. The synergistic effects between Fe3+/Fe2+ and Ce4+/Ce3+ further catalyzed the generation of hydroxyl radicals and it was proved as the main active species. The heterogeneous catalyst showed good performance in wide pH range, good stability, and high degradation efficiency to other pollutants. Three possible SMX degradation routes are suggested on basis of intermediates detected by mass spectrum analysis and theoretical calculations. The toxicity of these intermediates was assessed using Toxicity Estimation Software Tool (T.E.S.T.). This work provides valuable guidance for the design of highly efficient and stable heterogeneous EF catalyst for antibiotic degradation and expand the application potential in wastewater treatment of organic pollutants.

Hydrogen-promoted oxygen reduction Fenton reaction system constructed by Pd/UiO-66(Zr) to efficiently degradate trimethoprim

As a representative antibiotic, trimethoprim (TMP), the emerging pollutant has been frequently detected in water bodies, and its potential harm has aroused the attention of society. Although the emerging pollutant could be efficiently degraded by the advanced oxidation process (AOP) represented by the Fenton reaction, both the problem of iron sludge disposal and the safe use of H2O2 have plagued the further promotion of this technology. The H2 (precursor of the active hydrogen [H]) and catalyst Pd/UiO-66(Zr) were introduced into the Fenton reaction in this paper. It was found that the process of reducing Fe(III) and self-generating H2O2 could be facilitated due to the reduction of [H]. Under certain reaction conditions (initial pH 3, trace total iron 25 μM, H2 30 mL·min−1, catalyst 2 g·L−1) and without H2O2, a Fenton-like system was constructed, named MHORF-UiO-66(Zr). While achieving zero iron sludge discharge, 100 % of 20 mg·L−1 TMP was rapidly degraded within 1 h. It was found that the degradation of TMP could be attributed to the attack of singlet oxygen and hydroxyl radical. Furthermore, the performance changes of catalyst before and after six rounds of reactions were studied and it was found that Pd/UiO-66(Zr) had excellent and stable catalytic performance.

Degradation of tetracycline under a wide pH range in a heterogeneous photo bio-electro-fenton system using FeMn-LDH/g-C3N4 cathode: Performance and mechanism

The widespread use of antibiotics and the inefficiency of traditional degradation treatments pose threats to the environment and human health. Previous studies have reported the potential of bio-electro-Fenton (BEF) processes for antibiotic removal. However, some drawbacks, such as a strict pH range of 2–3 and iron sludge generation, limit their large-scale application. Thus, to overcome the narrow pH range of traditional BEF processes, a photo-BEF (PBEF) system was established using a novel FeMn-layered double hydroxide (LDH)/graphitic carbon nitride (g-C3N4) (FM/CN) composite cathode. The performance of the PBEF system was investigated by degrading tetracycline (TC) under low-power LED lamp irradiation. The results indicated that the pH range of the PBEF system could be expanded to 3–11 using an FM/CN cathode, which exhibited a TC removal efficiency of 63.0%–75.9%. The highest TC removal efficiency was achieved at pH 7. The efficient mineralization of TC by the PBEF system can be high, up to 67.6%. In addition, the TC removal mechanism was discussed in terms of reactive oxygen species, TC degradation intermediate analyses, and density functional theory (DFT) calculations. Strong oxidative hydroxyl radicals (·OH) were the dominant reactive oxidizing species in the PBEF system, followed by ·O2− and h+. Three pathways of TC degradation were proposed based on the analysis of intermediates, and the reactive sites attacked by electrophilic reagents were explored using DFT modeling. In addition, the overall toxicity of TC degradation intermediates effectively decreased in the PBEF system. This work offers deep insights into the TC removal mechanisms and performance of the PBEF system over a wide pH range of 3–11.

Application of sulfidated nano zero-valent iron to enhance fluoranthene degradation by Fe(III) activated sodium percarbonate process in aqueous and soil media

Iron sludge generation poses a challenge to the application of Fenton/Fenton-like processes in wastewater treatment. In this study, sulfidated nano zero-valent iron (S-nZVI) was introduced to enhance the activation of sodium percarbonate (SPC) by Fe(III), mitigating the generation of iron sludge by promoting the Fe(III)/Fe(II) cycle. The proposed technique efficiently removed 94.3 % fluoranthene (FLT) in which HO• acted as the major reactive oxygen species responsible for FLT degradation. Toxicity analysis revealed phthalic acid and 1-phenylnaphthalene as FLT degradation intermediates which finally converted to CO2 and H2O. Similarly, the luminous bacteria experiment also showed that the FLT degradation process was environmentally benign. The support of S-nZVI to the Fe(III)/Fe(II) cycle was determined by analyzing the morphology and characterization of S-nZVI. The removal of FLT reached more than 80 % at pH ranging from 3.0 to 10.0, and the detrimental effects of low concentrations of Cl− were mitigated. SPC/S-nZVI/Fe(III) process showed good removal of FLT (90 %) in both real groundwater and river simulation experiments. Furthermore, SPC/S-nZVI/Fe(III) process was successfully applied in soil slurry media with around 90 % FLT degradation in 12 h. The influence of the soil/water ratio on FLT removal was found to be negligible. SPC/S-nZVI/Fe(III) process was superior for the removal of mixed FLT, naphthalene, and phenanthrene contamination. In conclusion, the SPC/S-nZVI/Fe(III) system exhibits enormous potential in the remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated sites.

A Highly Synergistic Dual-Cathode Electro-Fenton Process with Self-Regulation of pH and Coating Stability for the Effective Degradation of Refractory Pollutants

As a result of issues related to pH control and the competition between H2O2 production and activation at the same sites, the applications of electro-Fenton (EF) pollutant remediation systems are limited. This work designed a synergistic dual-cathode EF system that exhibits self-adjustment of pH and stable electrode coatings. This system is based on using biomass as the active cathode material for H2O2 generation and the interaction between a stainless-steel mesh and FeOCl to reduce Fe3+ ions. The synergistic factor for this dual-cathode system was calculated to be 85.2%. Significantly, the production and activation of H2O2 in this composite system are unaffected by pH and the pH value can be adjusted between 9.67 and 3.7 without adding any acidic reagents. This process allows for the degradation of recalcitrant organic pollutants over the pH range of 3 to 9 without pre-acidification or challenges related to iron sludge and effluent chromaticity. Various organic pollutants, including antibiotics and organic dyes, can be effectively decomposed using this technology, which also exhibits good stability throughout 22 continuous trials over 1400 min. This work demonstrates a novel yet viable approach to highly efficient, inexpensive pollutant treatment with good reusability, a wide pH range and no iron leaching.

Facile Preparation of Magnetic Chitosan Carbon Based on Recycling of Iron Sludge for Sb(III) Removal

In this study, following the concept of “treating waste with waste”, magnetic chitosan carbon (MCC) was developed through the pyrolysis of chitosan/iron sludge (CHS) beads created using an embedding method in a closed environment for antimony removal. The results indicate MCC has a good magnetic recovery rate and that its magnetic saturation strength can reach 33.243 emu/g. The iron proportion and acid resistance of MCC were all better than those of CHS, and at 25 °C, its adsorption saturation capacity improved from 24.956 mg/g to 38.234 mg/g. MCC has a quick adsorption equilibrium time, and in about 20 min, 90% of the final equilibrium capacity can be achieved. The primary mechanism of Sb adsorption by MCC is the formation of an inner sphere complex between Fe-O and Sb, while surface complexation, hydrogen bonding, and interaction also play a function. Thus, MCC, a lower-cost and greener adsorbent for Sb removal, has been made using iron sludge. This enabled it to utilize iron sludge as a resource and served as a reference for the sustainable management of water treatment residuals.

CuS assisted Fe(III)-induced peracetic acid activation for bisphenol A degradation: significance of synergetic roles of copper and sulfur in enhanced Fenton-like process

Peracetic acid (PAA), as a promising synthetic organic acid disinfectant, is widely used in advanced oxidation processes to produce radicals for micropollutant abatement. While PAA activation driven by common Fenton-like processes suffers from the slow iron cyclic conversion and production of ferric sludge. This study introduces a metal sulfide, i.e., CuS, to assist the Fe(III)-induced PAA activation via multiple pathways, including the direct PAA activation and Fe(II)/Fe(III) cyclic conversion acceleration, termed as the CuS/Fe(III)/PAA process, to produce •OH, O2•−, Fe(IV), CH3C(O)O•, and CH3C(O)OO•, capable of degrading bisphenol A (BPA), one of representative endocrine disruptors in wastewater, thus overcoming the limitation of conventional Fenton-like processes. Cu(I), S22−, and S2− are determined to be catalytic sites of CuS responsible for the promotion of PAA activation. The CuS/Fe(III)/PAA process exhibits excellent degradation performances under acid conditions and performed high reactivities toward the degradation of various contaminants. The introduction of metal sulfide into the Fe(III)/PAA process improves the PAA activation and micropollutant degradation and reduces accumulation of iron sludge. Of particular significance is that water matrices performed limited effects on the BPA degradation, suggesting the potential of CuS/Fe(III)/PAA process to degrade micropollutants in real water treatment.

A comprehensive study of As(V) removal by starch-coated magnetite nano-adsorbent based on waste iron sludge

Combining natural polymer starch with magnetite nanoparticles (MNPs) can reduce the aggregation of MNPs and enhance their adsorption capacity and stability. Iron sludge from a de‑ironing water plant and starch were employed as basic ingredients in this study. Bare magnetite nanoparticles (MNPs) and starch-coated magnetite nanocomposites (ST2-MNPs) were synthesized by a “green” co-precipitation method for the removal of low-concentration As(V) solutions. TEM, XPS, FTIR, XRD, VSM, BET, and TGA techniques were used to examine the physicochemical properties of the synthesized ST2-MNPs. TEM verified that the magnetite nanoparticles in the composites were evenly distributed. The ST2-MNPs (5.26 nm) possessed a smaller average particle size than MNPs (6.24 nm). And VSM confirmed their remarkable magnetic properties. The starch-to‑iron-sludge ratio was optimized and the influence of adsorbent dosage, pH, and co-existing anions on As(V) adsorption were studied. The acquired arsenate adsorption data were found to be consistent with the Langmuir isotherm model, with maximum adsorption capacities of 23.04 mg/g for MNPs and 42.88 mg/g for ST2-MNPs. This shows that the active sites on MNPs and ST2-MNPs are energetically homogenous, and that the addition of starch coating significantly increases magnetite's adsorption capacity for As(V). The adsorption kinetics follow a Pseudo-second-order kinetic model, indicating chemisorption between As(V) and ST2-MNPs. In addition, the adsorption mechanism of As(V) by ST2-MNPs including chemical adsorption and electrostatic attraction was determined through in-depth discussion of characterization methods and adsorption experiments. This study offers references for the removal of As(V) and the resourceful application of backwash iron sludge.

Study on the co-catalytic performance and mechanism of MoO2 in oil-contaminated wastewater treated by Fenton system

BackgroundIn the treatment of organic wastewater, Fenton technology often produces iron sludge due to iron circulation obstruction, which inhibits the treatment efficiency and causes secondary pollution to the actual water. MethodsIn this study, MoO2 was used as a cocatalyst to promote the effective cycling of Fe2+/Fe3+ in the Fe2+/H2O2 system, thus efficiently degrading total petroleum hydrocarbons (TPHs). The superiority of MoO2 as co-catalyst was verified under different reaction conditions, and its mechanism was discussed. FindingsThe degradation rate of TPHs in the Fe2+/H2O2/MoO2 system (0.069 min−1) was about 14 times that of Fe2+/H2O2 system (0.005 min−1). Compared with the Fe2+/H2O2 system, the Fe2+/H2O2/MoO2 system not only had a wider pH adaptation range, but also could effectively remove TPHs under the interference of co-existing organic and inorganic anions. MoO2 did not change the types of reactive species in Fenton system, but it enhanced the production of reactive oxygen species (ROS) by promoting the Fe2+/Fe3+ cycling in the reaction system, and ·OH was the main reactive species of TPHs degradation.

Surfactant enhanced persulfate system for the synergistic oxidation and reduction of mixed chlorinated hydrocarbons

Surfactant-enhanced in-situ chemical oxidation (S-ISCO) is widely applied in soil and groundwater remediation. However, the role of surfactants in the reactive species (RSs) transformation remains inadequately explored. This work introduced nonionic surfactant Tween-80 (TW-80) into a nano zero-valent iron (nZVI) activated persulfate (PS) system. The findings indicate that PS/nZVI/TW-80 system can realize the concurrent removal of trichloroethylene (TCE), tetrachloroethene (PCE), and carbon tetrachloride (CT), whereas CT cannot be eliminated without TW-80 presence. Further analysis unveiled that hydroxyl (HO•) and sulfate radicals (SO4－•) were the primary species for TCE and PCE degradation, while CT was reductively eliminated by surfactant radicals generated from TW-80. Moreover, the surfactant radicals were found to accelerate Fe(III)/Fe(II) cycle, reduce the production of iron sludge, and increase PS decomposition. The possible degradation routes of mixed chlorinated hydrocarbons (CHCs) and the decomposition pathways of TW-80 were proposed through the density function theory (DFT) calculation and intermediates analysis. Additionally, the effects of other nonionic surfactants on the simultaneous removal of TCE, PCE, and CT, and the practical applications using the actual contaminated groundwater were also evaluated. This study provides theoretical support for the simultaneous removal of CHCs, particularly those containing perchlorinated contaminants, using the S-ISCO techniques.

Design of a new ZnO photocatalytic Fenton-like system for enhancing the removal of methylene blue at neutral pH

Although doping, nanostructuration, metallization, and binary/ternary oxide systems are widely used to improve the degradation kinetics in photocatalytic processes, rapid electron _ hole recombination remains one of its major limitations. On the other hand, homogeneous photo-Fenton-like processes suffer from the slow regeneration of Fe3+/Fe2+ catalysts and the formation of iron sludge at pH > 3. In this work, a new catalytic system is designed based on the coupling of nanostructured ZnO thin films photocatalysts with Fe3+/H2O2 (Fenton-Like) for the degradation of methylene blue (MB) molecules under UVA irradiation, at near-neutral pH (7.5). This coupled process promotes the formation of additional reactive oxygen species and reduces the formation of sludge by accelerating the regeneration of the iron catalysts in the medium. Furthermore, it exhibits a single kinetic regime of degradation with a rate constant of 0.0049 min−1 exceeding the sum of both individual processes and allowing therefore the removal of 94 % of MB after 480 min.