Initial Fe Concentration Research Articles

Cyanobacteria-ferrihydrite aggregates, BIF sedimentation and implications for Archaean- Palaeoproterozoic seawater geochemistry

Abstract Precambrian banded iron formations (BIFs) are iron- and silica-rich (bio)chemical sediments that are widely believed to have been precipitated by microbial oxidation of dissolved Fe(II). The by-product of these metabolisms – insoluble ferric iron – would have settled through the water column, often as aggregates with the cell biomass. While the mineralogy, composition and physical properties of cell-iron mineral aggregates formed by anaerobic Fe(II)-oxidising photoferrotrophic bacteria have been extensively studied, there are limited studies that characterise cyanobacteria-iron mineral aggregates that formed during oxygenic photosynthesis. This gap in knowledge is important because it impacts sedimentation velocities and the Fe(III) to organic carbon (Corg) ratios in the marine sediment pile. Here, we used a recently introduced approach to precisely measure the sedimentation velocity of cyanobacteria-ferrihydrite aggregates and the Fe(III):Corg ratios of the cyanobacteria-ferrihydrite aggregates over a wide range of pH and initial Fe(II) concentrations under predicted Palaeoproterozoic atmospheric conditions. Our results indicate that it was highly unlikely BIFs formed at pH <7 via chemical oxidation due to the insufficient sedimentation velocity, even at the maximum predicted Fe(II) concentration of 1800 μM with excess oxygen. Instead, large Banded Iron Formation (BIF) deposits, such as those associated with the ca. 2.47 Ga Kuruman Formation in South Africa, would only had been deposited at minimum Fe(II) concentrations of 500 μM at pH 7 or 250 μM at pH 8. The Fe:Corg ratios in cyanobacteria-ferrihydrite sediments formed during initially anoxic Fe(II) oxidation experiments represent the maximum values under each condition because we specifically extracted samples after all Fe(II) was oxidised. The Fe(III) to organic carbon ratio was consistently below 4, which is also the ratio required for dissimilatory Fe(III) reduction (DIR). This result indicates that biomass in this case was in excess, which contradicts the low organic carbon content seen in most BIFs. Thus, we suggest that biomass was either physically separated from ferrihydrite aggregates during sedimentation under the influence of ocean currents and waves, or it was degraded prior to DIR. The mineralogical and geochemical evidences of both oxide and carbonate facies from the Kuruman Iron Formation (IF) suggest that ferrihydrite was most likely the precursor along with a significant initial organic carbon input, supporting the proposed cyanobacterially-mediated BIF depositional model and experimental results.

Treatment of Coking Wastewater Using Hydrodynamic Cavitation Coupled with Fenton Oxidation Process.

Effective and economical processes for the advanced treatment of coking wastewater were urgently needed to reduce the persistent organic pollutants of external drainage. In the present work, we investigated the degradation of organic pollutants in coking wastewater through IHC/FO (imping stream hydrodynamic cavitation (IHC) coupled with the Fenton oxidation (FO) process) and IHC alone for their feasibility in the advanced treatment of coking wastewater. To select the optimum parameters, attention was paid to the effects of main operation conditions including inlet fluid pressure, medium temperature, initial pH, reaction time, and initial Fe(II) and initial H2O2 concentrations. The results showed that the effects of conditions that need energy to be maintained (such as initial pH and inlet pressure) on the organic pollutant removal efficiency through IHC/FO were less pronounced than those through IHC alone. Moreover, the application of IHC/FO could remove more organic pollutants from coking wastewater than IHC even at an energy-efficient condition. For example, the highest COD removal efficiency of 12.5% was achieved in the IHC treatment at 0.4 MPa, pH 3, and 60 min for the reaction time. In the case of IHC/FO, the maximum COD removal of 33.2% was obtained at pH 7, 0.1 MPa, 12 mmol/L H2O2, and 3 mmol/L Fe2+ after reacting for 15 min. The ultraviolet and visible spectrophotometry (UV-Vis) absorption spectra and gas chromatography and mass spectrometry (GC-MS) analysis further revealed that the kinds and amounts of pollutants (especially those that had benzenes) remaining in water treated through IHC/FO were much fewer and smaller than in water treated through IHC alone. The better performances of IHC/FO than IHC alone were likely related to the more hydroxyl radicals produced through IHC/FO. Taken together, our findings indicate that IHC/FO has great application potential in the advanced treatment of coking wastewater.

Chitosan/Alginate nanocomposites containing magnetic nanoparticles and multi-wall carbon nanotubes for efficient iron sorption

The widespread presence of iron pollution in groundwater is a major global worry, as increased levels can lead to severe health hazards. To tackle this urgent problem, we engaged in a synthesis procedure where magnetic nanoparticles (MNPs) and multi-wall carbon nanotubes (CNTs) were combined with a mixture of chitosan (CS) and sodium alginate (Alg) to produce a magnetic composite material. This novel composite, known as CS/Alg/MNPs/CNTs, was crafted with the primary aim of effectively removing iron from groundwater through adsorption. A thorough physicochemical analysis using FTIR, SEM, PSA, XRD, DSC, and TGA confirmed the composition's characteristics. The study delved into the influence of parameters such as retention time, sorbent dose, initial Fe concentration, pH, agitation rate, and temperature on the adsorption process. The Langmuir isotherm model fittingly represented the adsorption data, indicating a monolayer coverage of 12.43 mg/g and aligning with the pseudo-second-order kinetic model. Additionally, the adsorption of iron ions by the composite material was identified as a endothermic process. Furthermore, the study highlights the sorption process's inherent spontaneity and survivability, as demonstrated by the negative ΔG value. In conclusion, the results of this study indicate that the magnetic composite adsorbent (CS/Alg/MNPs/CNTs) holds considerable promise for effectively removing iron ions from groundwater, making it a viable and attractive choice for use in water purification applications.

Effective removal of As from a high arsenic-bearing ZnSO4 solution by ultrasonic enhanced ozonation in a one-pot method

Currently, removing arsenic (As) from ZnSO4 solution using lime presents several drawbacks, including high wet precipitate content, long reaction time, and the introduction of new impurities. In this study, we propose a novel ultrasonic (US) ozone one-pot method for effectively removing As from a high-arsenic ZnSO4 solution. In this method, as in ZnSO4 solution was removed by ultrasound enhanced ozone oxidation combined with zinc roasting dust (ZRD). No secondary pollution will occur with the addition of ZRD and ozone, as neither introduces new impurities. The experimental results show that under the conditions of initial As and Fe concentrations of 1640 mg/L and 2963 mg/L, US power of 480 W, frequency of 20 kHz, reaction temperature of 60 °C, reaction time of 1 h, ZRD dose of 12 g/L and gas flow rate of 900 mL/min, the removal rate of As can reach 99.4%. The introduction of US can further enhance the oxidation effect of ozone on As(III) and Fe2+ by increasing the solubility of ozone and promoting the production of OH radicals. Additionally, US cavitation and mechanical action increase the probability of contact between various reactants in the solution, facilitating the occurrence of reactions. US also reduces the aggregation of arsenic-containing precipitates and the encapsulation of ZRD by arsenic containing precipitates, thereby decreasing the amount of arsenic-containing precipitates. In comparison to the traditional lime method, this approach results in a significant reduction in the amount of arsenic-containing precipitate by 54.5% and a 60% decrease in the total reaction time. The As removal mechanism of our method encompasses ZRD neutralization, US-enhanced ozone mass transfer and decomposition, oxidation of As(III) and Fe2+, and adsorption and coprecipitation. Consequently, the proposed method provides a cost-effective, fast, safe and environmentally friendly alternative for treating arsenic-contaminated ZnSO4 solutions.

Experimental study on the performance of the dielectric barrier discharge technique in the treatment of simulated groundwater with high iron and manganese content

Abstract Groundwater with high concentrations of iron and manganese is harmful to the human body and modern industries. Conventional methods of treating iron and manganese have the disadvantage of high costs and complex control processes. A dielectric barrier discharge (DBD) water treatment system was built to remove iron and manganese from groundwater in this paper. Single-factor experiments were used to analyze the effect of discharge power, initial iron and manganese concentrations, gas flow rate, liquid flow rate, initial pH, flocculant and capture agent process parameters on iron and manganese removal rates. It was found that Fe2+ removal rates can reach 97.31% and Mn2+ removal rates can reach 81.42% when the initial concentrations of Fe2+ and Mn2+ are 6 and 3 mg/L, respectively. The use of 10 mg/L NaHCO3 or 5 mg/L Ca(OH)2 increased the removal rate of Fe2+ to 99% but had no effect on the removal rate of Mn2+. It was found that the optimum treatment time for Mn2+ was different for different process parameters, mainly in the range of 9–15 min, which needs to be noted in future production applications. This work shows that DBD can effectively remove iron and manganese ions from groundwater and analyzes the removal mechanism.

Fe(II)-Catalyzed Transformation of Ferrihydrite with Different Degrees of Crystallinity.

Natural occurring ferrihydrite (Fh) nanoparticles have varying degrees of crystallinity, but how Fh crystallinity affects its transformation behavior remains elusive. Here, we investigated the Fe(II)-catalyzed transformation of Fh with different degrees of crystallinity (i.e., Fh-2h, Fh-12h, and Fh-85C). X-ray diffraction patterns of Fh-2h, Fh-12h, and Fh-85C exhibited two, five, and six diffraction peaks, respectively, indicating the order of crystallinity: Fh-2h < Fh-12h < Fh-85C. Fh with the lower crystallinity has a higher redox potential, corresponding to the faster Fe(II)-Fh interfacial electron transfer and Fe(III)labile production. With the increase of initial Fe(II) concentration ([Fe(II)aq]int.) from 0.2 to 5.0 mM, the transformation pathways of Fh-2h and Fh-12h change from Fh → lepidocrocite (Lp) → goethite (Gt) to Fh → Gt, but that of Fh-85C switches from Fh → Gt to Fh → magnetite (Mt). The changes are rationalized using a computational model that quantitatively describes the relationship between the free energies of formation for starting Fh and nucleation barriers of competing product phases. Gt particles from the Fh-2h transformation exhibit a broader width distribution than those from Fh-12h and Fh-85C. Uncommon hexagonal Mt nanoplates are formed from the Fh-85C transformation at [Fe(II)aq]int.= 5.0 mM. The findings are crucial to comprehensively understand the environmental behavior of Fh and other associated elements.

A Feasibility Study on the Recall of Metallophilic Fungi from Fe(III)-Contaminated Soil and Evaluating Their Mycoremediation Capacity: Experimental and Theoretical Study

Mycoremediation is one of the most attractive, eco-friendly, and sustainable methods to mitigate the toxic effects of heavy metals. This study aimed to determine the mycoremediation capacity of metallophilic fungi isolated from heavy-metal-contaminated soil containing a high Fe(III) concentration (118.40 mg/kg). Four common fungal strains were isolated, including Curvularia lunata, Fusarium equiseti, Penicillium pinophilum, and Trichoderma harzianum. These fungal strains were exposed to gradually increasing concentrations of Fe(III) of 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 mg/L. Sophisticated techniques and tests were employed to investigate the mycoremediation capability, including tolerance index (TI), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and adsorption isotherm. Furthermore, the impacts of initial concentration, pH, and temperature on the Fe(III) removal (%) and uptake capacity (mg/g) of the studied samples were investigated. The results were validated by statistical analysis using one-way ANOVA. It was found that the Fe(III) uptake with different ratios triggered alterations in the Fe(III) tolerance (TI) morphological (SEM), chemical (FTIR), and adsorption capacity properties. The highest Fe(III) tolerance for all studied fungal strains was achieved at 100 mg/L. Moreover, the optimum conditions of Fe(III) removal (%) for all studied fungal strains were within pH 7 and 28 °C, with similar performance at the initial Fe(III) concentration ranging from 50-200 mg/L. At the same time, the maximum Fe(III) uptake was achieved at pH 7, 20 °C, and 200 mg/L. Compared to other strains, the Fe(III) tolerance of T. harzianum was rise in the Fe(III) concentration. The Fe(III) uptake reaction was corroborated by best fitting with the Langmuir model, achieving optimum adsorption capacities of 61.34, 62.90, 63.30, and 72.46 mg/g for C.lunata, F. equiseti, P. pinophilum, T. harzianum, respectively. It can be deduced that the addressed fungi species can be applied in mycoremediation according to the utilized Fe(III) concentrations with more superiority for live T. harzianum.

Adsorption of iron(III) from aqueous solution onto activated carbon of a natural source: Bombax ceiba fruit shell

Under this study, the extent of Fe(III) adsorption from aqueous solution onto activated charcoal prepared from a natural source, Bombax ceiba fruit shell was investigated. The fruit shell was carbonized and then activated using zinc chloride (ZnCl2) as an activating agent. The prepared activated carbon was characterized using Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) and Point Zero Charge (PZC). Some important parameters influencing the adsorption rate namely adsorbent dosage, initial metal ion concentration, contact time and solution pH were optimized through batch adsorption study. The optimum adsorption was found to be at pH 3.5, adsorbent dosage 0.05 g, contact time 25 min and initial Fe(III) concentration 75 mg/L. Langmuir, Freundlich and Temkin isotherm models were investigated. Where, Temkin model was found to be more suitable compared to other two describing the adsorption of Fe(III). The maximum iron(III) removal efficiency was commenced to be 99.10 % and the adsorption capacity of the prepared activated carbon was initiated as 37.16 mg/g.

A detailed electronic-scale DFT simulation and a response surface methodology for the removal of Fe (III) ions from aqueous solutions

At significant concentrations, Fe (III) is toxic and may cause industrial and human health problems. Iron ions and compounds reacting with oxygen can be critical in producing oxygen radicals and peroxides that can damage DNA. Adsorption is a critical chemical process that is widely used to remove heavy metals. In this study, the Hummers method was used to prepare graphene oxide, which was then used as an adsorbent in the adsorption process of iron ions. Graphene oxide was characterized using IR, SEM, and AFM. The most important parameters influencing the adsorption of Fe (III) ions (adsorbent mass, contact time, and pH) were investigated. The process optimization was performed using the Box–Behnken Design under response surface methodology by Minitab Version 19. According to response surface analysis, the experimental data fit the quadratic model perfectly. The experimental results indicated that GO has significant potential as an adsorbent for removing Fe (III). With a pH of 3.0, an adsorbent weight of 0.15 g, and a contact time of 90.0 minutes for an initial Fe (III) concentration of 20 mg/L, the predicted maximum removal ratio of Fe (III) ions was 100% during process optimization. Furthermore, kinetic and isotherm studies were conducted. Apart from the experiments, detailed density functional theory simulations were successfully used to investigate the interactions and possible adsorption of water-solvated Fe (III) cation onto model GO adsorbents. The simulated results demonstrated that cationic Fe (III)/water complexes have a high affinity for adsorption and binding to the GO surface.

Coupling and environmental implications of in situ formed biogenic Fe–Mn minerals induced by indigenous bacteria and oxygen perturbations for As(III) immobilization in groundwater

Iron (Fe)–manganese (Mn) minerals formed in situ can be used for the natural remediation of the primary poor-quality groundwater with coexistence of arsenite [As(III)], Mn(II), and Fe(II) (PGAMF). However, the underlying mechanisms of immobilization and coupling of As, Mn, and Fe during in-situ formation of Fe–Mn minerals in PGAMF remains unclear. The simultaneous immobilization and coupling of arsenic (As), Mn, and Fe in PGAMF during in-situ formation of biogenic Fe–Mn minerals induced by O2 perturbations and indigenous bacteria (Comamonas sp. RM6) were investigated at the different molar ratios of Fe(II):Mn(II) (1:1, 2:1, and 3:1). Compared with systems without Fe(II) in the presence of Mn(II), the coexisted Fe(II) significantly enhanced Mn(II) bio-oxidation and mineral precipitation, resulting in As immobilization increased by 5, 7, and 7 times at initial Fe(II) concentration of 0.3, 0.6, and 0.9 mM, respectively. Moreover, the As(III) immobilization efficiencies in Mn(II) and Fe(II) mixed system at initial Fe(II) concentration of 0.3, 0.6, and 0.9 mM were 73%, 91%, and 92%, respectively, that were significantly higher than those of single Fe(II) system (30%, 59%, and 74%) and those of single Mn(II) system (12%), indicating that Fe(II) and Mn(II) oxidation synergically enhanced As(III) immobilization. This was mainly attributed to the formation and As adsorption capacity of biogenic Fe–Mn minerals (BFMM). The formed BFMM significantly facilitated simultaneous immobilization of Fe, Mn, and As in PGAMF by oxidation, adsorption, and precipitation/coprecipitation, a coupling of biological, physical, and chemical processes. Fe component was mainly responsible for As fixation, and Mn component dominated As(III) oxidation. Based on the results from this work, biostimulation and bioaugmentation techniques can be developed for in-situ purification and remediation of PGAMF. This work provides insights into the simultaneous immobilization of pollutants in PGAMF, as well as promising strategies for in-situ purification and remediation of PGAMF.

Effect of As(III) on kinetics of Fe2+ bio-oxidation

Fe2+ bio-oxidation influenced by toxic metal ions released from the dissolution of arsenic-bearing gold ores was investigated. Fe2+ bio-oxidation by moderately thermophilic microorganisms was studied under different initial concentrations of Fe2+ and As(III), and Monod equation was used to fit the Fe2+ bio-oxidation under different conditions. Results showed that the Fe2+ bio-oxidation rate increased as the initial Fe2+ concentration increased until it reached 12 g/L. As(III) severely inhibited Fe2+ bio-oxidation. When the As(III) concentration was 8 g/L, 9 g/L Fe2+ was more than 200 h. The Monod equation fitted the Fe2+ bio-oxidation well. In the absence of As(III), the maximum specific growth rate of the culture and the substrate affinity constant were 0.142 h-1 and 0.053 g/L, respectively. As(III) inhibited Fe2+ bio-oxidation via competitive inhibition, and the inhibition constant was 0.0035 g/L.

Fenton Process for Treating Acrylic Manufacturing Wastewater: Parameter Optimization, Performance Evaluation, Degradation Mechanism

Acrylic manufacturing wastewater is characterized by high toxicity, poor biodegradability, high chemical oxygen demand (COD) and ammonia nitrogen. Herein, we exploited traditional Fenton technology to treat acrylic fiber manufacturing wastewater. The impacts of key operating variables including the initial concentration of H2O2 (CH2O2), the initial concentration of Fe2+ (DFe2+), and solution pH (pH) on the COD removal rate (RCOD) were explored and the treatment process was optimized by Response Surface Methodology (RSM). The results indicated that the optimum parameters are determined as pH 3.0, 7.44 mmol/L of Fe2+ and 60.90 mmol/L of H2O2 during Fenton process. For the actual acrylic manufacturing wastewater treatment shows that the removal rates for COD, TOC, NH4+-N and TN are 61.45%~66.51%, 67.82%~70.99%, 55.67%~60.97% and 56.45%~61.03%, respectively. It can meet the textile dyeing and finishing industry water pollutant discharge standard (GB4287-2012). During the Fenton reaction, the effective degradation and removal of organic matter is mainly achieved by HO• oxidation, supplemented by flocculation and sedimentation of Fe3+ complexes. This study will provide useful implications in the process parameters for the practical application of Fenton method in acrylic acid production wastewater.

Iron(II)-activated phase transformation of Cd-bearing ferrihydrite: Implications for cadmium mobility and fate under anaerobic conditions

The factors and mechanisms affecting the fate of the associated Cd during the Fe(II)-activated Cd-bearing ferrihydrite transformation remain poorly understood. Herein we have conducted a series of batch reactions containing ferrihydrite with diverse pH values and initial Fe(II) and Cd concentrations coupled with chemical analyses and spectroscopic examination on the transformation products to probe the mechanisms of the Cd partitioning and the processes of Fe(II)-activated Cd-bearing ferrihydrite transformation under anaerobic conditions. Chemical analyses, Fourier transform infrared spectroscopy (FTIR), and powder X-ray diffraction (PXRD) results show that the initial Fe(II) and Cd concentrations as well as pH values all have significant effects on the rates and pathways of ferrihydrite transformation. Increasing Cd loading enhances the inhibition of the Fe(II)-activated ferrihydrite transformation rates. High Cd loading alters the Fe(II)-activated ferrihydrite transformation pathways by hindering the recrystallization of both ferrihydrite to more stable iron minerals and the newly formed lepidocrocite to goethite. Chemical analyses show that the release of Cd to solutions during ferrihydrite transformation is accompanied by a reduction in the 0.4 M HCl extractable Cd fraction and that a significant amount of the released Cd is transformed to a 0.4 M HCl unextractable form. Moreover, enhanced Cd release during the Fe(II)-activated ferrihydrite transformation is observed by reducing the pH value or increasing the initial Cd concentration. Results from synchrotron X-ray absorption spectroscopy (XAS) confirm that the majority of the 0.4 M HCl unextractable Cd form is associated with structural incorporation into the recrystallized iron (hydr)oxides via isomorphous substitution for Fe(III). These findings not only provide molecular-level understanding on the behavior of Cd under natural anoxic environments, but also are useful in predicting the geochemical cycling of Cd and developing long-term Cd contaminant management strategies.

Iron and Manganese Removal from Wastewater by Constructed Wetlands Planted with Caladium bicolor

Constructed wetlands (CWs) have been applied to treat various wastewater types including domestic wastewater, livestock wastewater, industrial wastewater and acid mine drainage with the advantages of low cost, environmentally-friendly technology and high treatment efficiency. Mining wastewater with the high content of heavy metals often causes negative impacts on the ecosystems and human health. In this study, the capacity of using limestone, hydrolyzed rice husk as filter materials and the CWs planted with Caladium bicolor to treat iron and manganese in artifical wastewater treatment are evaluated. The wetland model has the size of length x width x height of 50 cm x 15 cm x 20 cm. 10 liters of the synthetic wastewater were used and initial Fe and Mn concentrations varied from 5, 10, 15, 20 and 25 mg/L. The results showed that limestone and hydrolyzed rice husk with the weight ratio of 5 : 2.5 (kg) had good ability to remove Fe and Mn with treatment efficiencies of approximately 99.8% after 144 hours. During a 24-hour retention time, the Fe and Mn concentrations ​​in the wastewater decreased rapidly in CWs and the initial Fe and Mn concentrations affected treatment performance. When the initial Fe and Mn concentrations were below 20 mg/L, treatment efficiencies of Fe and Mn reached about 99% after 144 hours in the CWs and Fe and Mn concentrations met the national regulation QCVN 40: 2011/BTNMT, column B. The study highlights the potential applications of C. bicolor in CWs with the use of natural limestone and hydrolyzed rice husk as substrates in treatment of iron and manganese-contaminated wastewater.&#x0D; Keywords: Constructed wetlands, Caladium bicolor, limestone, rice husk, iron, manganese.

Effects of Fe(II) concentration on the biosynthesis of schwertmannite by Acidithiobacillus ferrooxidans and the As(III) removal capacity of schwertmannite

ABSTRACT The effect of Fe(II) concentrations on schwertmannite bio­synthesis and the As(III) removal capacity of schwertmannite were investigated in this study. Acidithiobalillus ferrooxidans (A. ferrooxidans) were inoculated into five FeSO4 systems with initial concentrations of 50, 100, 200, 300, and 400 mmol/L, respectively, to bio-synthesize schwertmannite. The Fe(II) of the systems were almost completely oxidised at 48, 72, 120, 168, and 192 h, respectively, and the bio­schwertmannite yield was 1.99, 3.81, 9.36, 12.42, and 21.60 g/L. The results of this study indicate that all minerals harvested from the different systems are schwertmannite. As the initial Fe(II) concentration increases, the effect of the minerals removing As(III) decreases; moreover, the structure and extracellular polymeric substance (EPS) of schwertmannite may regulate the As(III) removal process. The EPS generated by the A. ferrooxidans can absorb As(III). The outcomes of this study provide fresh insights into the bio­synthetic regulation of schwertmannite and play a significant role in treating As­containing groundwater.

Interfacial Reinitiation of Free Radicals Enables the Regeneration of Broken Polymeric Hydrogel Actuators

Interfacial Reinitiation of Free Radicals Enables the Regeneration of Broken Polymeric Hydrogel Actuators

Release Kinetics of Iron (Fe) from Soil and Growing Media Mixtures: An Incubation Study

ABSTRACT An incubation study was conducted to examine the time dependent release of iron from the soil and growing media mixtures of Cocopeat (CP), Vermicompost (VC), Farm Yard Manure (FYM), Pressmud (PM), Vermiculite (VL), and Composted cocopeat (CCP) with various levels of ferrous sulfate (FeSO4) application for 60 days. Higher Fe release was recorded in the growing media comprising soil + composted cocopeat (1:1) followed by Cocopeat + Vermicompost + Press mud (1:1:1). Fitting of various kinetic equations for better understanding of iron release satisfactorily accounted (R2, 0.867 to 0.998, at p ≤.05) by the zero-order kinetic equation. Higher half-life time for Fe release (t1/2) as well as initial Fe concentration (q0) was noticed in Soil + Composted cocopeat and Cocopeat + Vermicompost + Pressmud. A significant negative correlation between pH, C/N ratio with Fe availability as well as higher organic carbon content prompted iron release. Based on the released amount of iron and principal component analysis with hierarchical clustering, Cocopeat + Vermicompost + Press mud (1:1:1) and Soil + Composted cocopeat (1:1) were grouped as best growing media mixtures. Higher initial Fe availability, release rate, and half-life time for iron release was observed in Soil + Composted cocopeat and Cocopeat + Vermicompost + Pressmud growing media which makes them more efficient as those can sustain the Fe supply for a longer period of time with higher availability to crops.

Coprecipitation of humic acid and phosphate with Fe(III) enhances the sequestration of carbon and phosphorus in sediments

The coprecipitation of dissolved organic matter (DOM) and phosphate with Fe(III) at the sediment-water interface plays an important role in the biogeochemical cycle of organic carbon (OC) and phosphorus (P) in aquatic ecosystems. However, studies remain limited towards understanding the strength of ternary DOM-phosphate-Fe(III) coprecipitation in sequestering OC and P. Here, we investigated the behaviors of humic acid (HA) and phosphate during their coprecipitation with Fe(III) and compared the coprecipitation behaviors with those during the adsorption process. The results showed that the coprecipitation of HA and phosphate with Fe(III) enhanced as pH decreased or initial Fe(III) concentrations increased. The presence of phosphate had a moderate inhibition effect on HA coprecipitation, leading to 3%–37% of reduction in precipitated HA. Changes in optical properties of DOM (i.e., SUVA254, E2/E3, and fluorescent components) showed that macromolecular, aromatic molecules preferentially coprecipitated, and this selectivity pattern was not influenced by the presence of phosphate. Compared to the adsorption of HA and phosphate to goethite, coprecipitation with Fe(III) displayed stronger binding ability, sequestering more than10 times of HA and phosphate, and was more efficient in sequestering protein-like compounds. The inhibitory effect of phosphate on HA sequestration was weaker during coprecipitation than during adsorption. Moreover, coprecipitation led to a lower degree of compositional fractionation of HA than adsorption, which may be explained by that inclusion, an important pathway for coprecipitation, has low selectivity for chemical compositions. Collectively, our results demonstrate that coprecipitation plays a crucial role in sequestering both OC and P in aquatic systems, arguing that the formation of ternary OC-Fe-P coprecipitates may be an important pathway for sequestering OC and P over a long term and reducing the internal loading of P in eutrophic lakes.

Enhanced degradation of organic contaminants by Fe(III)/peroxymonosulfate process with l-cysteine

The difficulty in Fe(III)/Fe(II) conversion in the Fe(III)/peroxymonosulfate (PMS) process limits its efficiency and application. Herein, l-cysteine (Cys), a green natural organic ligand with reducing capability, was innovatively introduced into Fe(III)/PMS to construct an excellent Cys/Fe(III)/PMS process. The Cys/Fe(III)/PMS process, at room temperature, can degrade a variety of organic contaminants, including dyes, phenolic compounds, and pharmaceuticals. In subsequent experiments with acid orange 7 (AO7), the AO7 degradation efficiency followed pseudo-first-order kinetic which exhibited an initial “fast stage” and a second “slow stage”. The rate constant values ranged depending on the initial Cys, Fe(III), PMS, and AO7 concentrations, reaction temperature, and pH values. In addition, the presence of Cl−, NO3−, and SO42− had negligible impact while HCO3− and humic acid inhibited the degradation of AO7. Furthermore, radical scavenger experiments and methyl phenyl sulfoxide (PMSO) transformation assay indicated that sulfate radical, hydroxyl radical, and ferryl ion (Fe(IV)) were the dominant reactive species involved in the Cys/Fe(III)/PMS process. Finally, based on the results of gas chromatography-mass spectrometry, several AO7 degradation pathways, including N=N cleavage, hydroxylation, and ring opening were proposed. This study provided a new insight to improve the efficiency of Fe(III)/PMS process by accelerating Fe(III)/Fe(II) cycle with Cys.

Titanium-pillared montmorillonite composite as an efficient catalyst for 2-nitrophenol reductive transformation by Fe(II): The effects of aqueous chemistry and mechanistic insights

The abiotic reduction of 2-nitrophenol (2-NP) to 2-aminophenol is the major remediation strategy used to remove 2-NP from contaminated aquifers and groundwaters. In the present study, both the aqueous chemistry and surface nature of a titanium-pillared montmorillonite (TPMnt) catalyst were investigated in-depth, to obtain comprehensive insight into the reductive transformation mechanisms of 2-NP in a Fe(II)/TPMnt reaction system. The results show that almost all the 2-NP disappeared within 0.5 h in the Fe(II)/TPMnt3 reduction system in stark contrast to just 26% of 2-NP removal within 4.0 h in a Fe(II) solution, and 85% of 2-NP removal within 4.0 h in a Mnt system. These results demonstrate that the specially adsorbed Fe(II) species bound to the mineral surface is one key species crucial for achieving the 2-NP transformation. Among the aqueous chemistry, i.e., the ratio of [Ti]/Mnt, the solution pH, the initial Fe(II) concentration, the dose of TPMnt, the solution pH, and the initial Fe(II) concentration significantly influenced the 2-NP transformation. High effectiveness was achieved under these conditions: TPMnt3 with a content of 20.0 mmol/g TiO2, pH of 7, an initial Fe(II) concentration of 10.0 mmol/L, and a dose of TPMnt at 2 g/L. There was a positive correlation between the constant k values of the reduction rate and the amounts of adsorbed Fe(II) species on the TPMnt surface. Further, the TPMnt was shown to possess good recyclability, and the catalytic activity of TPMnt3 for the 2-NP reduction remained mostly unchanged when reused four times. Our results for cyclic voltammograms and electrochemical impedances confirmed that the enhanced performance of the 2-NP reduction can be attributed to a negative shift of the oxidation potentials of Fe(II) along with decreased impedance values (RCT) of the Fe(II)/Fe(III) coupling on the GC electrodes. The intercalated TiO2 in TPMnt functionalized as an ideal promoter for the efficient transformation of 2-NP by Fe(II). Taken together, these results suggest the TPMnt surface-mediated 2-NP reduction by Fe(II) is a promising application for the remediation of 2-NP-contaminated aquifers and groundwaters.