Assessment of schwertmannite, jarosite and goethite as adsorbents for efficient adsorption of phenanthrene in water and the regeneration of spent adsorbents by heterogeneous fenton-like reaction

Polycyclic aromatic hydrocarbons in water environments: Impact, legislation, depollution processes and challenges, and magnetic iron oxide/graphene-based nanocomposites as promising adsorbent solutions

Environmental pollution is a big challenge of today's world, as population continues to grow, and industrialisation and urbanisation increase. Out of the different micropollutants in the atmosphere and aquatic environments, polycyclic aromatic hydrocarbons are of particular importance because they have known severe associated health risks to human life and they have high stability, leading to their persistence in the environment. They are generally present in the environment in low concentrations, but, even at these levels, they pose threats. This review thus focuses on this family of pollutants, on their occurrence and consequences, as well as the current methodologies employed to remove them from water environments and the challenges that remain. This work then focuses on the potential of magnetic iron oxide/graphene nanocomposites for the adsorption of PAHs, extensively discussing past and undergoing works, as well as the interactions between these adsorbents and PAHs.

Uptake, desorption, and hysteresis of heavy metals and PAHs with environmental concerns onto quick clays: effects of salinity and temperature

This study investigated the sorption, desorption, and trapping of 9,10 dimethylated anthracene (DMA), copper (Cu), and cadmium (Cd) onto quick clay (QC), focusing on the effects of temperature, salinity, and their environmental relevance. Sorption isotherms were generated at different temperatures (4, 10, and 20 °C) and salinities (1 and 25 g·L-1). Thermodynamic parameters were calculated to elucidate the underlying mechanisms. Isosteric heat of adsorption (ΔHX) was determined to assess the heterogeneity of adsorption sites. Isotherms results were processed using the Freundlich model to assess sorption and hysteresis parameters of QC. Kinetic studies revealed a rapid initial uptake of DMA followed by a slower logarithmic phase, reaching equilibrium within 1440 min. The presence of the methyl group in DMA compared to non-methylated PAHs from other studies likely influences its adsorption rate. Temperature and salinity significantly impacted both the adsorption and desorption processes. Notably, Cd adsorption was nearly made ineffective with increasing salinity. Interestingly, Cu hysteresis index (HI) decreased from 1.57 to - 0.08 with increasing salinity, suggesting a shift from inner-sphere complexation at low salinity to outer-sphere complexation at high salinity. Conversely, DMA adsorption increased by 1.83-fold with increasing salinity, likely due to the salting-out effect. Thermodynamic analysis indicated a spontaneous and endothermic adsorption process driven by a positive entropy change (ΔS0). The ΔHX values supported physical adsorption as the dominant mechanism. The observed homogeneity in ΔHX values for DMA and Cd suggests consistent interaction with the clay surface, while the heterogeneity observed for Cu signifies a variation in adsorption site energies.

Influence of goethite on the fate of antibiotic (tetracycline) in the aqueous environment: Effect of cationic and anionic surfactants

Over the last decades, the release and occurrence of organic pollutants in aquatic systems have become a major global concern due to their bioaccumulation, toxicity, and adverse effects on the ecosystem. Tetracycline (TC), a widely used antibiotic, is often found at high concentrations in the aqueous environment and tends to bind with the natural colloids. Post-COVID-19 pandemic, the release of surfactants in the environment has increased due to the excessive use of washing and cleaning products. This study systematically investigated the interaction of goethite with TC in the absence and presence of anionic (sodium dodecyl sulfate, SDS) and cationic (cetyltrimethylammonium bromide, CTAB) surfactants. The impact of various environmental parameters like pH, ionic strength, temperature, and organic matter was also studied. It was observed that SDS has drastically increased TC sorption onto goethite from 11 mg/g to 19 mg/g, while CTAB had the opposite effect. To delineate the goethite-TC interaction mechanisms, FTIR with two-dimensional correlation analysis (2D-COS) was performed. The pH of the solution was crucial in the presence of SDS, while ionic strength did not affect the interaction process. The sorption process was endothermic, as evidenced by the increase in sorption capacity with the rise in the temperature. The presence of organic matter hinders the sorption of TC onto goethite, which is also observed in river water where the organic content is very high. Overall, our study helps to predict the fate of organic pollutants like antibiotics in aqueous environments in the coexistence of surfactants and iron oxyhydroxides.

Cutting-edge regeneration technologies for saturated adsorbents: a systematic review on pathways to circular wastewater treatment system

Adsorption seemed like an excellent physicochemical process employed for wastewater treatment. In the last few decades, significant improvements have been made in efficiency and economy to remove contaminants from wastewater using several adsorbents. However, less attention was paid to the regeneration of used adsorbents. Aside from the adsorbent's high adsorption performance, the disposal of spent adsorbents is an environmental concern. Regeneration is an important aspect to stimulate the adsorption efficiency of the spent adsorbent for wastewater treatment. This article reviews the various regeneration techniques like electrochemical regeneration, biological regeneration, thermal regeneration, ultrasound regeneration, and chemical regeneration in detail that have been performed for the renewal of saturated adsorbents. In the ultrasonic regeneration technique, Fe3O4-loaded coffee waste hydrochar adsorbent showed 100% regeneration efficiency (RE) after 1.3 h at the power consumption of 300 W/L. Electrochemical regeneration of granular activated carbon, Nyex, graphene and titanium dioxide composite, and Nyex 1000 showed 100% RE after 3, 0.16, 0.12, and 1.5 h, respectively, with electrolyte Na2SO4 and NaCl. In the regeneration technique, powdered activated carbon showed 90% RE after 48-72 h. Immobilized fungal biomass (Rhizopus nigricans) adsorbent showed 111-115% RE with base (0.01 N NaOH, NaHCO3, and Na2CO3) solvent. The present study addresses issues including waste generation, adsorbent potential and efficiency, eco-friendly techniques, and the release of adsorbed pollutants in regenerating saturated adsorbents. The mechanisms of adsorbent regeneration were thoroughly examined, highlighting the significance of the regeneration process in adsorption. Furthermore, this review discusses the advantages of hybrid regeneration techniques like microwave-activated ultraviolet-advanced oxidation, electro-peroxide approach, electrochemical and electrothermal methods, and the secondary use of spent adsorbents as catalysts, fertilizer, cementitious materials, secondary adsorbent bio-fuels, etc. Using saturated adsorbents is a practical technology for sustainable wastewater treatment that has the potential to minimize pollution and promote a circular economy. This review concludes with a discussion of the present challenges in the regeneration of the used adsorbents, as well as future directions for ensuring the system's feasibility from an economic and environmental standpoint for use on an industrial scale.

Simulation, prediction and optimization for synthesis and heavy metals adsorption of schwertmannite by machine learning

Due to its sea urchin-like structure, Schwertmannite is commonly applied for heavy metals (HMs) pollutant adsorption. The adsorption influence parameters of Schwertmannite are numerous, the traditional experimental enumeration is powerless. In recent years, machine learning (ML) has been gradually employed for adsorbent materials, but there is no comprehensive research on the Schwertmannite adsorbent. In this paper, 27 features and 814 groups of experimental data were used to systematically analyze the adsorption modeling of Schwertmannite first time. The results indicated that the adsorption capacity of Schwertmannite was better predicted by the Random Forest (RF) model (the R2 was 0.874). Then, the RF model was used to analyze the features importance that affects the adsorption of HMs by Schwertmannite. And the importance of Schwertmannite synthesis conditions, Schwertmannite characteristics, adsorption environment, and HMs properties were 11.88%, 30.01%, 48.26%, and 8.19% respectively. Moreover, the synthesis and adsorption conditions of Schwertmannite were predicted and optimized based on RF model, it was predicted that the better synthesis method of Schwertmannite was biological oxidation > Fe2+ oxidation > Fe3+ hydrolysis. Finally, a predictive Graphical User Interface Web Page for Schwertmannite-HMs was developed. We hope that this paper can promote the integration of machine learning and Schwertmannite.

Effective selenate removal using pH modulated synthesis of biogenic jarosite: Comparative insight with non-biogenic jarosite and biogenic schwertmannite

Selenium, a crucial trace element for many organisms, including prokaryotes and humans, is toxic at high concentrations, necessitating its removal from wastewater. This study investigates the use of jarosite, a naturally occurring iron sulfate mineral with excellent heavy metal attenuation properties, for selenate (Se(VI)) removal for the first time. Biogenic jarosite was synthesized through Fe(II) oxidation by Acidithiobacillus ferrooxidans at an initial pH ranging from 1.5 to 4.0 (J-1.5 to J-4.0). This resulted in the formation of morphologically diverse particles of biogenic jarosite owing to varying Fe(II) oxidation and precipitation rates. For comparative analysis, non-biogenic jarosite (J-90C) and biogenic schwertmannite (S-2.5) were also synthesized. At 0.2 mM initial Se(VI) concentration, J-2.5 demonstrated superior Se(VI) removal compared to J-3.5 and J-90C. At 2.0 mM Se(VI), J-2.5 still outperformed J-3.5 and J-90C although its overall removal efficiency decreased. Notably, at 0.2 mM concentration, Se(VI) removal by J-2.5 was 63 %, which is comparable to 77 % removal by S-2.5. Furthermore, sulfate release from J-2.5 was significantly lower than that from S-2.5 in both Se-free and Se-containing solutions. This study provides critical insights into the synthesis and application of biogenic jarosite as a replacement for metastable schwertmannite, emphasizing its potential as an excellent Se sink for wastewater treatment.

Highly efficient degradation of tetracycline in groundwater by nanoscale zero-valent iron-copper bimetallic biochar: active [H] attack and direct electron transfer mechanism

Development of carbon materials with high activity was important for rapid degradation of emerging pollutants. In this paper, a novel nanoscale zero-valent iron-copper bimetallic biochar (nZVIC-BC) was synthesized by carbothermal reduction of waste pine wood and copper-iron layered double hydroxides (LDHs). Characterization and analysis of its structural, elemental, crystalline, and compositional aspects using XRD, FT-IR, SEM, and TEM confirmed the successful preparation of nZVIC-BC and the high dispersion of Fe-Cu nanoparticles in an ordered carbon matrix. The experimental results showed that the catalytic activity of nZVIC-BC (Kobs of 0.0219 min-1) in the degradation of tetracycline (TC) in anoxic water environment was much higher than that of Fe-BC and Cu-BC; the effective degradation rate reached 85%. It was worth noting that the negative effects of Ca2+, Mg2+, and H2PO4- on TC degradation at ionic strengths greater than 15 mg/L were due to competition for active sites. Good stability and reusability were demonstrated in five consecutive cycle tests for low leaching of iron and copper. Combined with free radical quenching experiments and XPS analyses, the degradation of TC under air conditions was only 62%, with hydroxyl radicals (·OH) playing a dominant role. The synergistic interaction between Fe2+/Fe3+ and Cu0/Cu+/Cu2+ under nitrogen atmosphere enhances the redox cycling process; π-π adsorption, electron transfer processes, and active [H] were crucial for the degradation of TC; and possible degradation pathways of TC were deduced by LC-MS, which identified seven major aromatic degradation by-products. This study will provide new ideas and materials for the treatment of TC.

Influence mechanism of organic matter and low-molecular-weight organic acids on the interaction between minerals and PAHs

Investigate the effect of soil organic matter (SOM) and low molecular weight organic acids (LMWOAs) on minerals adsorption of PAHs. Batch adsorption experiments have been carried out to study the adsorption of PAHs (Naphthalene (NaP), Phenanthrene (Phe) and Pyrene (Pyr)) by minerals (Montmorillonite (Mnt), kaolinite (Kln) and calcite (Cal)). This research found that compared with Kln and Cal, Mnt showed the maximum adsorption capability for PAHs. And the order of PAHs adsorption by Mnt was: Pyr > Phe > Nap, which corresponds to the octanol-water partition coefficient (K_ow) of different PAHs. The adsorption kinetic and isotherm were well fitted by Pseudo-second-order kinetic model, Freundlich and Linear isotherm model. Furthermore, inorganic ions (Ca²⁺) impacted PAHs adsorption by competitive adsorption and cation-π interactive. Cal has the maximum desorption of PAHs among three minerals, and there was desorption hysteresis phenomenon. Field emission-scanning electron microscope (Fe-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) analysis indicated that SOM enhanced the sorption of PAHs by van der Waals, hydrogen bonding, π-π interactions, and chemical bonding. LMWOAs significantly inhibited PAHs adsorption and promote PAHs desorption from the minerals. As a result, LMWOAs increased of PAHs bioavailability, which provide a new strategy to improve PAHs cleanup efficiency.

Toxic mechanism on phenanthrene-triggered cell apoptosis, genotoxicity, immunotoxicity and activity changes of immunity protein in Eisenia fetida: Combined analysis at cellular and molecular levels

Phenanthrene (PHE) is a harmful organic contaminant and exists extensively in the soil environment. The accumulation of PHE would potentially threaten soil invertebrates, including earthworms, and the toxicity is also high. Currently, the possible mechanisms underlying apoptotic pathways induced by PHE and its immunotoxicity and genotoxicity in earthworms remain unclear. Thus, Eisenia fetida coelomocytes and immunity protein lysozyme (LYZ) were chosen as targeted receptors to reveal the apoptotic pathways, genotoxicity, and immunotoxicity triggered by PHE and its binding mechanism with LYZ, using cellular, biochemical, and molecular methods. Results indicated that PHE exposure can cause cell membrane damage, increase cell membrane permeability, and ultimately trigger mitochondria-mediated apoptosis. Increased 8-hydroxy-2-deoxyguanosine (8-OHdG) levels indicated PHE had triggered DNA oxidative damage in cells after PHE exposure. Occurrence of detrimental effects on the immune system in E. fetida coelomocytes due to decreased phagocytic efficacy and destroyed the lysosomal membrane. The LYZ activity in coelomocytes after PHE exposure was consistent with the molecular results, in which the LYZ activity was inhibited. After PHE binding, the protein structure (secondary structure and protein skeleton) and protein environment (the micro-environment of aromatic amino acids) of LYZ were destroyed, forming a larger particle size of the PHE-LYZ complex, and causing a significant sensitization effect on LYZ fluorescence. Molecular simulation indicated the key residues Glu 35, Asp 52, and Trp 62 for protein function located in the binding pocket, suggesting PHE preferentially binds to the active center of LYZ. Additionally, the primary driving forces for the binding interaction between PHE and LYZ molecule are hydrophobicity forces and hydrogen bonds. Taken together, PHE exposure can induce apoptosis by mitochondria-mediated pathway, destroy the normal immune system, and trigger DNA oxidative damage in earthworms. Besides, this study provides a comprehensive evaluation of phenanthrene toxicity to earthworms on molecular and cellular level.

Regeneration and reuse of salt-tolerant zwitterionic polymer fluids by simple salt/water system

Highly-efficient separation of adsorbent and pollutant from chemical sludge is urgent for the recycled materials and chemical resources and minimization of sludge production in industry. Herein, an effortless and cost-efficient salt/water system is developed for efficient zwitterionic polymer/dye separation from chemical sludge. To achieve this aim, a novel salt-tolerant zwitterionic polymer (STZP) is synthesized through etherifying 2-chloro-4,6-bis(4-carboxyphenyl amino)-1,3,5-triazine onto corn starch. It is found that "all-surface-area" adsorption of dye can be achieved by in-situ sol-gel transition of STZP. Spent polymer fluid and solid-state dye can be easily regenerated and separated from sewage sludge by a simple salt/water system. At a high NaCl concentration (225 g/L), the separation factor between zwitterionic polymer and dye is up to 50.4, which is 50 times larger than that of salt-free solution. More importantly, the regenerated polymer fluids exhibit an outstanding reusability ability and can maintain over 92.8% decoloration efficiency for dyeing effluent after multiple adsorption-desorption cycles. This study thus provides a technically feasible and economically acceptable strategy for the recycling and reuse of polymer from hazardous textile sludge waste, greatly promising to achieve zero emissions toward conventional adsorption units.

Microplastics lag the leaching of phenanthrene in soil and reduce its bioavailability to wheat

Microplastics wildly occur in soil and they can become the carriers of persistent contaminants. However, the influence of microplastics on polycyclic aromatic hydrocarbons vertical translocation in the soil system after rainfall is limitedly understood. Here, experiments were conducted to study the influence of polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC) microplastics on the leaching behavior and bioavailability of phenanthrene (Phe). The adsorption capacity of phenanthrene on the microplastics followed the order of PS > PE > PVC. The Phe concentrations in the top soil layer after 15 days of leaching with water were 30.25, 28.32 and 27.25 mg kg^-1 for the treatments of Phe-PS, Phe-PE and Phe-PVC respectively, which is consistent with the adsorption capacities of microplastics. The concentrations of Phe were correlated with the microplastic adsorption capacities at soil depths of 5-45 cm. Under long-term leaching, Phe could reach the deeper soil layer. Phe concentrations significantly decreased in the leachate over time. Phe concentrations in wheat had a positive correlation with that in leachate/leached top soil layer. Our findings are beneficial to accurately evaluate the ecological risk of the combined contamination of PAHs and microplastics, and improve the understanding of the environmental behaviors of different microplastics.

Comparison of Cr(VI) Adsorption Using Synthetic Schwertmannite Obtained by Fe3+ Hydrolysis and Fe2+ Oxidation: Kinetics, Isotherms and Adsorption Mechanism

Good sorption properties and simple synthesis route make schwertmannite an increasingly popular adsorbent. In this work, the adsorption properties of synthetic schwertmannite towards Cr(VI) were investigated. This study aimed to compare the properties and sorption performance of adsorbents obtained by two methods: Fe3+ hydrolysis (SCHA) and Fe2+ oxidation (SCHB). To characterise the sorbents before and after Cr(VI) adsorption, specific surface area, particle size distribution, density, and zeta potential were determined. Additionally, optical micrographs, SEM, and FTIR analyses were performed. Adsorption experiments were performed in varying process conditions: pH, adsorbent dosage, contact time, and initial concentration. Adsorption isotherms were fitted by Freundlich, Langmuir, and Temkin models. Pseudo-first-order, pseudo-second-order, intraparticle diffusion, and liquid film diffusion models were used to fit the kinetics data. Linear regression was used to estimate the parameters of isotherm and kinetic models. The maximum adsorption capacity resulting from the fitted Langmuir isotherm is 42.97 and 17.54 mg·g-1 for SCHA and SCHB. Results show that the adsorption kinetics follows the pseudo-second-order kinetic model. Both iron-based adsorbents are suitable for removing Cr(VI) ions from aqueous solutions. Characterisation of the adsorbents after adsorption suggests that Cr(VI) adsorption can be mainly attributed to ion exchange with SO42- groups.

Co-adsorption of As(III) and phenanthrene by schwertmannite and Fenton-like regeneration of spent schwertmannite to realize phenanthrene degradation and As(III) oxidation

Co-contamination of arsenic and polycyclic aromatic hydrocarbons (PAHs) in groundwater is frequently reported, and it is thus necessary to develop efficient techniques to tackle this problem. Here, we evaluated the feasibility of utilizing schwertmannite to co-adsorb As(III) and phenanthrene from water solution and regenerating spent schwertmannite via a heterogeneous Fenton-like reaction to degrade adsorbed phenanthrene and meanwhile oxidize adsorbed As(III). The results suggested that schwertmannite with a hedgehog-like morphology was superior to that with a smooth surface for the adsorption removal of As(III) or phenanthrene because of the much higher BET surface area and hydroxyl proportion of the former one, and schwertmannite formed at 72 h incubation effectively co-adsorbed As(III) and phenanthrene from water solution. The adsorption of As(III) and phenanthrene on schwertmannite did not interfere with each other, while the acidic initial solution pH delayed the adsorption of As(III) on schwertmannite but enhanced the adsorption capacity for phenanthrene. The adsorption of As(III) on schwertmannite mainly involved its exchange with SO₄^2- (outer-sphere or inner-sphere) and its complexation with iron hydroxyl surface groups, and phenanthrene adsorption mainly occurred through cation-π bonding and OH-π interaction. During the adsorption-regeneration processes, schwertmannite adsorbed As(III) and phenanthrene firstly, and then it can be successfully regenerated via Fenton-like reaction catalyzed by itself to effectively degrade the adsorbed phenanthrene and meanwhile oxidize the adsorbed As(III) to As(V). Therefore, schwertmanite is an outstanding environmental adsorbent to decontaminate As(III) and phenanthrene co-existing in groundwater.

Preparation of Monoclinic Pyrrhotite by Thermal Decomposition of Jarosite Residues and Its Heavy Metal Removal Performance

Jarosite residues produced by zinc hydrometallurgical processing are hazardous solid wastes. In this study, monoclinic pyrrhotite (M-Po) was prepared by the pyrolysis of jarosite residues in H2S atmosphere. The influence of gas speed, reaction temperature, and time was considered. The mineral phase, microstructure, and elemental valence of the solids before and after pyrolysis were analyzed using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, respectively. The performances of the prepared M-Po on the removal of Zn and Pb from aqueous solution were evaluated. The results show M-Po to be the sole product at the reaction temperatures of 550 to 575 °C. Most of the M-Po particles are at the nanometer scale and display xenomorphic morphology. The phase evolution process during pyrolysis is suggested as jarosite → hematite/magnetite → pyrite → pyrite+M-Po → M-Po+hexagonal pyrrhotite (H-Po) → H-Po. The formation rate, crystallinity, and surface microtexture of M-Po are controlled by reaction temperature and time. Incomplete sulfidation may produce coarse particles with core–shell (where the core is oxide and the shell is sulfide) and triple-layer (where the core is sulfate, the interlayer is oxide, and the shell is sulfide) structures. M-Po produced at 575 °C exhibits an excellent heavy metal removal ability, which has adsorption capacities of 25 mg/g for Zn and 100 mg/g for Pb at 25 °C and pH ranges from 5 to 6. This study indicates that high-temperature sulfidation is a novel and efficient method for the treatment and utilization of jarosite residues.