Zero-valent iron nanoparticles in treatment of acid mine water from in situ uranium leaching

Corrosion behaviors and kinetics of nanoscale zero-valent iron in water: A review

Knowledge on corrosion behaviors and kinetics of nanoscale zero-valent iron (nZVI) in aquatic environment is particularly significant for understanding the reactivity, longevity and stability of nZVI, as well as providing theoretical guidance for developing a cost-effective nZVI-based technology and designing large-scale applications. Herein, this review gives a holistic overview on the corrosion behaviors and kinetics of nZVI in water. Firstly, Eh-pH diagram is introduced to predict the thermodynamics trend of iron corrosion. The morphological, structural, and compositional evolution of (modified-) nZVI under different environmental conditions, assisted with microscopic and spectroscopic evidence, is then summarized. Afterwards, common analytical methods and characterization technologies are categorized to establish time-resolved corrosion kinetics of nZVI in water. Specifically, stable models for calculating the corrosion rate constant of nZVI as well as electrochemical methods for monitoring the redox reaction are discussed, emphasizing their capabilities in studying the dynamic iron corrosion processes. Finally, in the future, more efforts are encouraged to study the corrosion behaviors of nZVI in long-term practical application and further build nanoparticles with precisely tailored properties. We expect that our work can deepen the understanding of the nZVI chemistry in aquatic environment.

Synergistic effects of hydrogen peroxide and phosphate on uranium(VI) immobilization: implications for the remediation of groundwater at decommissioned in situ leaching uranium mine

The processes of acid in situ leaching (ISL) uranium (U) mines cause the pollution of groundwater. Phosphate (PO43-) has the potential to immobilize U in groundwater through forming highly insoluble phosphate minerals, but the performance is highly restricted by low pH and high sulfate concentration. In this study, hydrogen peroxide (H2O2) and PO43- were synergistically used for immobilizing U based on the specific properties of groundwater from a decommissioned acid ISL U mine. The removal mechanisms of U and the stability of U on the formed minerals were elucidated by employing X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and kinetic experiments. Our results indicated that the removal of U by simultaneously adding H2O2 and PO43- was significantly higher than the removal of U by individually adding H2O2 or PO43-. The removal of U increased with increasing PO43- concentration from 20 to 200 mg L-1 while decreased with increasing H2O2 concentration from 0.003 to 0.3%. Specifically, the removal efficiency of U from groundwater reached 98% after the application of 0.003% H2O2 and 200 mg L-1 PO43-. Amorphous iron phosphate that preferentially formed at low H2O2 and high PO43- concentrations played a dominant role in U removal, while the formations of schwertmannite and crystalline iron phosphates may be also contributed to the removal of U. This was significantly different from the immobilization mechanism of U through the formation of uranyl phosphate minerals after adding phosphate. The kinetic experimental results suggested that the immobilized U had a good stability. Our research may provide a promising method for in situ remediating U-contaminated groundwater at the decommissioned acid ISL U mines.

Sustainable removal of uranium from acidic wastewater using various mineral raw materials

Various types of plutonic and volcanic rocks and their alteration products from Greece (serpentinite, magnesite and andesite), have been used for sustainable removal of Uranium (U) from the acidic drainage of Kirki mine, as well as for the pH increase of the polluted solutions. In this light, this study aims at the further understanding and improvement of the ecofriendly reuse of sterile, natural raw materials (including those remaining through industrial processing and engineering testing of aggregate rocks), for remediation of acid mine drainage. The selected rocks constitute such residues of sterile materials were used as filters in experimental continuous flow devices in the form of batch-type columns, in order to investigate acidic remediation properties with special focus on U removal. The initial pH of the wastewater was 2.90 and increased after seven (7) days of experimental application and more specifically from the fourth day onwards. Uranium removal became quantitatively significant once pH reached the value of 5.09. The volcanic rocks appeared to be more effective for U removal than the plutonic ones because of microtextural differences. However, optimum U removal was mainly achieved by serpentinite: while the raw materials rich in Mg strongly reacted and remediated the pH of the drainage water waste. Furthermore, the increase of pH values due to the presence of mineral raw materials, provided increased oxidation potential which deactivated the toxic load of metals, particularly U. Consequently, batch-type serpentinite reaction with the tailing fluid caused a drop in U concentration from an initial value of 254 ppb to the one of 8 ppb, which corresponds to 97% of removal. Andesite presented the second best reactant for experimental remediation, especially when it was mixed with magnetically separated mineral fractions. Despite the fact that the proposed methodology is currently at a relatively low Technology Readiness Level (TRL), it carries the potential to become an extremely effective and low-cost alternative to conventional environmental restoration technologies.

Occurrence characteristics of uranium mineral-related substances in various environmental media in China: A critical review

The high demand and extensive exploitation of uranium resources resulted in the ubiquity and high detection levels of uranium mineral-related substances in various environment media in China. The potential adverse effects of uranium mineral-related substances on environment and human health have received extensive attention. Therefore, we reviewed the occurrence and spatial distribution of uranium mineral-related substances in various basins and environmental media in China to obtain an overall understanding. We collected information from over 70 papers reporting the occurrence and distribution of uranium mineral-related substances in multiple environments and 183 articles on the genesis of uranium deposits in China from 2001 to 2021. Then the occurrence of uranium mineral-related substances and corresponding correlation in different basins, environmental media and depth ranges were compared in detail. And this review assessed the uranium mineral-related pollution in China based on various environmental quality standards of China, EPA and WHO, and proposed the priority uranium mineral-related heavy metals and radioactive substances based on cluster analysis. This review showed that there were obvious differences in the occurrence characteristics of various uranium mineral-related substances in different environmental media, especially in the surrounding environment of sandstone type and hard rock type uranium deposits. These results will guide us to tackle the challenge of uranium mineral-related pollution in China. The correlation analysis of uranium mineral-related pollutants in different environmental media and the identification of priority pollutants will also provide instructions for us to control uranium mineral-related pollution. Finally, we put forward a series of urgent and practical suggestions on risk management and control of uranium mining according to the current situation of uranium mining environment in China, which is of guiding significance for the realization of "green uranium mining".

A high-efficient and recyclable aged nanoscale zero-valent iron compound for V5+ removal from wastewater: Characterization, performance and mechanism

An effective complex of nanoscale zero-valent iron (NZVI) supported on zirconium 1,4-dicarboxybenzene metals-organic frameworks (UIO-66) with strong oxidation resistance was synthesized (NZVI@UIO-66) for V⁵⁺ removal from wastewater. The results demonstrated that NZVI was successfully loaded on UIO-66 with a uniform dispersion, and then the composite was aged in the air which was named A-NZVI@UIO-66. V⁵⁺ could be removed quickly and completely using A-NZVI@UIO-66 in a wider pH range except for the pH = 1 condition. The reaction between A-NZVI@UIO-66 and V⁵⁺ was an endothermic process. Freundlich model with a better-fitted value showed the adsorption of V⁵⁺ on A-NZVI@UIO-66 was multi-layer heterogeneous adsorption and the adsorbed amount of V⁵⁺ was 397.23 mg V/g NZVI. Nitrate had a competitive inhibition on V⁵⁺ removal by A-NZVI@UIO-66. Mechanisms of vanadium elimination from the aqueous phase by A-NZVI@UIO-66 included physical adsorption, reduction, and complex co-precipitation, particularly the reduction dominated. The subsistent Zr-O bond in A-NZVI@UIO-66 provided a possible double reaction path by playing an electron donor, storage, or conductor role. After acid leaching, A-NZVI@UIO-66 represented good reusability in the removal of V⁵⁺ from the practical mine sewage.

Experimental and Numerical Investigations of Using Nanoparticles in Groundwater Remediation

The efficiency of using zeolite nano-clay and silica sand in removing iron from groundwater is investigated experimentally as an application of in situ remediation technique using permeable reactive barrier (PRB). In the first stage of the study batch experiments were conducted on coarse silica sand and fine silica gravel to determine their iron removal efficiency from contaminated water. The results showed that the removal efficiency was about 51.90% for coarse silica sand while fine silica gravel failed to reduce the iron concentration in water. A mix of zeolite nano-clay and coarse silica sand with a ratio of 1:30 was tested. It was found that iron removal efficiency significantly increases to about 99.70%. The linear adsorption isotherm was found to be the most representative for the adsorption of iron onto coarse silica sand and the mix of nano-clay and coarse silica sand with distribution coefficients equal 0.0009 and 0.001, respectively. In the second stage a glass sand tank with coarse silica sand and a mix of zeolite nano-clay and coarse silica PRBs was constructed. The sand tank was used to investigate the effect of sampling time, head difference, iron concentration, nano-clay dosage, and thickness of permeable reactive barrier on the iron removal efficiency. The results indicated that increasing iron concentration and head difference decreases iron removal efficiency. The mix of zeolite nano-clay and coarse silica sand improves iron removal efficiency. Furthermore, increasing nano-clay dosage slightly increases the removal efficiency. However, increasing the thickness of filter layer (i.e., PRB) significantly improves the removal efficiency. Finally, the experimental model data were used to test the capability of a numerical contaminant transport model to predict the removal efficiency. The MT3DMS numerical model included within the Groundwater Modeling System (GMS) was used along with the different experimental data to obtain reaction rate values as calibration parameters for linear isotherm. Reaction rates that yield modeling results matching experimental data were obtained.

Covalent and Non-covalent Functionalized Nanomaterials for Environmental Restoration

Nanotechnology has emerged as an extraordinary and rapidly developing discipline of science. It has remolded the fate of the whole world by providing diverse horizons in different fields. Nanomaterials are appealing because of their incredibly small size and large surface area. Apart from the naturally occurring nanomaterials, synthetic nanomaterials are being prepared on large scales with different sizes and properties. Such nanomaterials are being utilized as an innovative and green approach in multiple fields. To expand the applications and enhance the properties of the nanomaterials, their functionalization and engineering are being performed on a massive scale. The functionalization helps to add to the existing useful properties of the nanomaterials, hence broadening the scope of their utilization. A large class of covalent and non-covalent functionalized nanomaterials (FNMs) including carbons, metal oxides, quantum dots, and composites of these materials with other organic or inorganic materials are being synthesized and used for environmental remediation applications including wastewater treatment. This review summarizes recent advances in the synthesis, reporting techniques, and applications of FNMs in adsorptive and photocatalytic removal of pollutants from wastewater. Future prospects are also examined, along with suggestions for attaining massive benefits in the areas of FNMs.

Enhanced Nitrate Ions Remediation Using Fe0 Nanoparticles from Underground Water: Synthesis, Characterizations, and Performance under Optimizing Conditions

The presence of nitrates in water in large amounts is one of the most dangerous health issues. The greatest risk posed by nitrates is hemoglobin oxidation, which results in Methemoglobin in the human body, resulting in Methemoglobinemia. There are many ways to eliminate nitrates from underground water. One of the most effective and selective methods is using zero-valent iron (ZVI) nanoparticles. ZVI nanoparticles can be easily synthesized by reducing ferric or ferrous ions using sodium borohydride. The prepared ZVI nanoparticles were examined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), electron microscopy (TEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, and zeta potential. We aim to eliminate or reduce the nitrates in water to be at the acceptable range, according to the world health organization (WHO), of 10.0 mg/L. Nitrate concentration in water after and before treatment is measured using the UV scanning method at 220 nm wavelength for the synthetic contaminated water and electrochemical method for the naturally contaminated water. The conditions were optimized for obtaining an efficient removing process. The removal efficiency reaches about 91% at the optimized conditions.

Acid mine drainage treatment using zero-valent iron nanoparticles in biochemical passive reactors

Acid mine drainage (AMD) is the major effluent generated from metal and coal mines, causing serious ecological risks and degradation of aquatic habitats and surrounding soil quality. Biochemical passive reactors (BPRs) are an option for improving AMD affected water. This study investigates the effect of the size and concentration of zerovalent iron nanoparticles (nZVI) on the efficiency of batch BPRs during AMD remediation. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were also used as complementary techniques for the investigation of the changes in microbial cells and nZVI properties after the AMD remediation. The results from the batch experiment showed that the concentration of nZVI increases the pH and decreases ORP during AMD treatment, thus favouring the removal of metals. The results also suggest that metal sulfide precipitation occurred in all the batch with reactive mixture but was greater in reactors amended with nZVI of larger size. This study revealed that the presence of nZVI in the BPR leads to metal removal as well as the inhibition of sulfate-reducing bacteria (SRB) activity. Microscopy study indicated that the addition of nZVI creates a morphological change on certain microorganisms in which the cellular membrane was fully covered with nZVI, inducing cell lysis process. These results show that nZVI is a promising reactive material for the treatment of AMD in BPR systems.

Removal of Organoselenium from Aqueous Solution by Nanoscale Zerovalent Iron Supported on Granular Activated Carbon

Nanoscale zerovalent iron particles (nZVI) immobilized on coconut shell-based granular activated carbon (GAC) were studied to remove organoselenium from wastewater. A chemical reduction technique that involves the application of sodium borohydride was adopted for the adsorbent preparation. The texture, morphology and chemical composition of the synthesized adsorbents were analyzed with a scanning electron microscope (SEM), nitrogen adsorption–desorption isotherms and X-ray diffraction (XRD). Batch experiment with various pHs and contact times were conducted to evaluate nZVI/GAC adsorption performance. The results showed that nZVI/GAC has a strong affinity to adsorb selenomethionine (SeMet) and selenocysteine (SeCys) from wastewaters. The maximum removal efficiency for the composite (nZVI/GAC) was 99.9% for SeCys and 78.2% for SeMet removal, which was significantly higher than that of nZVI (SeCy, 59.2%; SeMet, 10.8%). The adsorption kinetics were studied by pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models. Amongst the two, PSO seemed to have a better fit (SeCy, R2 > 0.998; SeMet, R2 > 0.999). The adsorption process was investigated using Langmuir and Freundlich isotherm models. Electrostatic attraction played a significant role in the removal of organoselenium by nZVI/GAC adsorption. Overall, the results indicated that GAC-supported nZVI can be considered a promising and efficient technology for removing organoselenium from wastewater.

Nanotechnology in the Restoration of Polluted Soil

The advancements in nanoparticles (NPs) may be lighting the sustainable and eco-friendly path to accelerate the removal of toxic compounds from contaminated soils. Many efforts have been made to increase the efficiency of phytoremediation, such as the inclusion of chemical additives, the application of rhizobacteria, genetic engineering, etc. In this context, the integration of nanotechnology with bioremediation has introduced new dimensions for revamping the remediation methods. Hence, advanced remediation approaches combine nanotechnological and biological remediation methods in which the nanoscale process regulation supports the adsorption and deterioration of pollutants. Nanoparticles absorb/adsorb a large variety of contaminants and also catalyze reactions by lowering the energy required to break them down, owing to their unique surface properties. As a result, this remediation process reduces the accumulation of pollutants while limiting their spread from one medium to another. Therefore, this review article deals with all possibilities for the application of NPs for the remediation of contaminated soils and associated environmental concerns.

Field-scale investigation of nanoscale zero-valent iron (NZVI) injection parameters for enhanced delivery of NZVI particles to groundwater

The effects of the injection parameters on delivery of nanoscale zero-valent iron (NZVI) to contaminated groundwater were investigated. The first two NZVI injections (gravity injection at low flow rates) resulted in NZVI being poorly mobile and gave total cumulative mass recoveries at the monitoring wells of 1.07%-2.43%. NZVI reached some wells (KDMW-3, MW-2, MW-4, and MW-7) earlier than the bromide tracer. The dominant travel directions for NZVI and the bromide tracer were very different. The NZVI transport characteristics suggested that targeted NZVI delivery requires preferential groundwater flow paths and local heterogeneity to be considered. In the gravity injection tests, the maximum NZVI concentrations and cumulative NZVI mass recoveries in the wells decreased markedly as the injected NZVI concentration and dose increased. In the third and fourth tests, in which NZVI was injected under pressure at high flow rates, NZVI was effectively delivered to the wells despite the injected NZVI concentration and dose being high. Relatively high cumulative mass recoveries of 26.0% and 74.5% were found for the third and fourth injections, respectively. Controlling the flow rate (pressure) and NZVI concentration and dose simply and effectively controlled NZVI mobility in the groundwater. The colloidal and electrostatic characteristics of the NZVI particles were monitored and modeled, and the results indicated that NZVI particles without Derjaguin-Landau-Verwey-Overbeek energy barriers were successfully delivered to the target zone and that decreased magnetic attractive forces between NZVI particles caused by iron corrosion probably decreased the degree of NZVI particle aggregation and therefore contributed to NZVI being delivered to the target zone.

Sulfidated nano-scale zerovalent iron is able to effectively reduce in situ hexavalent chromium in a contaminated aquifer

In a number of laboratory studies, sulfidated nanoscale zero-valent iron (S-nZVI) particles showed increased reactivity, reducing capacity, and electron selectivity for Cr(VI) removal from contaminated waters. In our study, core-shell S-nZVI particles were successfully injected into an aquifer contaminated with Cr(VI) at a former chrome plating facility. S-nZVI migrated towards monitoring wells, resulting in a rapid decrease in Cr(VI) and Cr_tot concentrations and a long-term decrease in groundwater redox potential observed even 35 m downstream the nearest injection well. Characterization of materials recovered from the injection and monitoring wells confirmed the presence of nZVI particles, together with iron corrosion products. Chromium was identified on the surface of the recovered iron particles as Cr(III), and its occurrence was linked to the formation of insoluble chromium-iron (oxyhydr)oxides such as Cr_xFe_(1-x)(OH)_3(s). Injected S-nZVI particles formed aggregates, which were slowly transformed into iron (oxyhydr)oxides and carbonate green rust. Elevated contents of Fe⁰ were detected even several months after injection, indicating good S-nZVI longevity. The sulfide shell was gradually disintegrated and/or dissolved. Geochemical modelling confirmed the overall stability of the resulting Cr(III) phase at field conditions. This study demonstrates the applicability of S-nZVI for the remediation of a Cr(VI)-contaminated aquifer.

Impact of Zero-Valent Iron on Freshwater Bacterioplankton Metabolism as Predicted from 16S rRNA Gene Sequence Libraries

The application of zero-valent iron particles (ZVI) for the treatment of heavily polluted environment and its biological effects have been studied for at least two decades. Still, information on the impact on bacterial metabolic pathways is lacking. This study describes the effect of microscale and nanoscale ZVI (mZVI and nZVI) on the abundance of different metabolic pathways in freshwater bacterial communities. The metabolic pathways were inferred from metabolism modelling based on 16S rRNA gene sequence data using paprica pipeline. The nZVI changed the abundance of numerous metabolic pathways compared to a less influencing mZVI. We identified the 50 most affected pathways, where 31 were related to degradation, 17 to biosynthesis, and 2 to detoxification. The linkage between pathways was two times higher in nZVI samples compared to mZVI, and was specifically higher considering the arsenate detoxification II pathway. Limnohabitans and Roseiflexus were linked to the same pathways in both nZVI and mZVI. The prediction of metabolic pathways increases our knowledge of the impacts of nZVI and mZVI on freshwater bacterioplankton.

Applications of Nanomaterials for Heavy Metal Removal from Water and Soil: A Review

Heavy metals are toxic and non-biodegradable environmental contaminants that seriously threaten human health. The remediation of heavy metal-contaminated water and soil is an urgent issue from both environmental and biological points of view. Recently, nanomaterials with excellent adsorption capacities, great chemical reactivity, active atomicity, and environmentally friendly performance have attracted widespread interest as potential adsorbents for heavy metal removal. This review first introduces the application of nanomaterials for removing heavy metal ions from the environment. Then, the environmental factors affecting the adsorption of nanomaterials, their toxicity, and environmental risks are discussed. Finally, the challenges and opportunities of applying nanomaterials in environmental remediation are discussed, which can provide perspectives for future in-depth studies and applications.

Natural and anthropogenic radionuclides in water and wastewater: Sources, treatments and recoveries

Water-energy nexus in the context of changing climate amplifies the importance of comprehending the transport, fate and recovery of radioisotope. While countries have been more interested for zero/low greenhouse gas emission technologies, energy production from nuclear power plant (NPP) can be a prominent solution. Moreover, radioisotopes are also used for other benefits such as in medical science, industrial activities and many more. These radionuclides are blended accidently or intentionally with water or wastewater because of inefficacious management of the nuclear waste; and therefore, it is an imperative task to manage nuclear waste so that the harmful consequences of the waste on environment, ecology and human health can be dispelled. Due to generation of significant amount of waste throughout its utilization, a noticeable number of physical, chemical and biological processes has been introduced as remediation processes although mechanisms of optimum removal process are still under investigation. Removal mechanisms and influencing factors for radionuclide removal are elucidated in this review so that, further, operation and process development can be promoted. Again, resource recovery, opportunities and challenges are also discussed for elevating the removal rates and minimizing the knowledge gaps existing in development and applications of novel decontamination processes.

Effectiveness of nanoscale zero-valent iron for the immobilization of Cu and/or Ni in water and soil samples

In the last few years, the effectiveness of nanoscale zero-valent iron (nZVI) as a treatment for polluted waters and soils has been widely studied. However, little data are available on its efficacy for metal immobilization at low and moderate doses. In this study, the effectiveness of two doses of commercial nZVI (1 and 5%) to immobilize Cu and/or Ni in water and acidic soil samples was evaluated. The influence of the nanoremediation technology on iron availability, physico-chemical soil properties and soil phytotoxicity was also assessed. The results show that the effectiveness of nZVI to immobilize Cu and Ni in water and soil samples was determined by the dose of the nanomaterial and the presence of both metals. Nickel immobilization was significantly decreased by the presence of Cu but the opposite effect was not observed. nZVI showed better immobilization capacity in water than in soil samples. In water, the dose of 5% completely removed both metals, whereas at a lower dose (1%) the percentage of immobilized metal decreased, especially for Ni in Cu + Ni samples. In soil samples, 5% nZVI was more effective in immobilizing Ni than Cu, with a 54% and 21% reduction of leachability, respectively, in single contaminated samples. In Cu + Ni soil samples, nZVI treatment led to a significant decrease in Ni immobilization, similar to that observed in water samples. The application of nZVI induced a dose-dependent increase in available Fe—a relevant effect in the context of soil rehabilitation. Germination assays of Medicago sativa and Vicia sativa seeds revealed that treatment with nZVI did not induce phytotoxicity under the experimental conditions tested, and that the phytotoxicity induced by Ni decreased significantly after the treatment. Thus, the use of nZVI emerges as an interesting option for Cu and/or Ni immobilization in water samples. The effectiveness of nZVI to remove Cu from acidic soil samples was moderate, while for Ni it was strongly dependent on the presence of Cu. These observations therefore indicate that the results in water samples cannot be extrapolated to soil samples.

Remediation of heavy metals polluted environment using Fe-based nanoparticles: Mechanisms, influencing factors, and environmental implications

Environmental pollution by heavy metals (HMs) has raised considerable attention due to their toxic impacts on plants, animals and human beings. Thus, the environmental cleanup of these toxic (HMs) is extremely urgent both from the environmental and biological point of view. To remediate HMs-polluted environment, several nanoparticles (NPs) such as metals and its oxides, carbon materials, zeolites, and bimetallic NPs have been documented. Among these, Fe-based NPs have emerged as an effective choice for remediating environmental contamination, due to infinite size, high reactivity, and adsorption properties. This review summarizes the utilization of various Fe-based NPs such as nano zero-valent iron (NZVI), modified-NZVI, supported-NZVI, doped-NZVI, and Fe oxides and hydroxides in remediating the HMs-polluted environment. It presents a comprehensive elaboration on the possible reaction mechanisms between the Fe-based NPs and heavy metals, including adsorption, oxidation/reduction, and precipitation. Subsequently, the environmental factors (e.g., pH, organic matter, and redox) affecting the reactivity of the Fe-based NPs with heavy metals are also highlighted in the current study. Research shows that Fe-based NPs can be toxic to living organisms. In this context, this review points out the environmental hazards associated with the application of Fe-based NPs and proposes future recommendations for the utilization of these NPs.

Core-Shell Fe/FeS Nanoparticles with Controlled Shell Thickness for Enhanced Trichloroethylene Removal

Zero-valent iron nanoparticles (nZVI) treated by reduced sulfur compounds (i.e., sulfidated nZVI, S-nZVI) have attracted increased attention as promising materials for environmental remediation. While the preparation of S-nZVI and its reactions with various groundwater contaminants such as trichloroethylene (TCE) were already a subject of several studies, nanoparticle synthesis procedures investigated so far were suited mainly for laboratory-scale preparation with only a limited possibility of easy and cost-effective large-scale production and FeS shell property control. This study presents a novel approach for synthesizing S-nZVI using commercially available nZVI particles that are treated with sodium sulfide in a concentrated slurry. This leads to S-nZVI particles that do not contain hazardous boron residues and can be easily prepared off-site. The resulting S-nZVI exhibits a core-shell structure where zero-valent iron is the dominant phase in the core, while the shell contains mostly amorphous iron sulfides. The average FeS shell thickness can be controlled by the applied sulfide concentration. Up to a 12-fold increase in the TCE removal and a 7-fold increase in the electron efficiency were observed upon amending nZVI with sulfide. Although the FeS shell thickness correlated with surface-area-normalized TCE removal rates, sulfidation negatively impacted the particle surface area, resulting in an optimal FeS shell thickness of approximately 7.3 nm. This corresponded to a particle S/Fe mass ratio of 0.0195. At all sulfide doses, the TCE degradation products were only fully dechlorinated hydrocarbons. Moreover, a nearly 100% chlorine balance was found at the end of the experiments, further confirming complete TCE degradation and the absence of chlorinated transformation products. The newly synthesized S-nZVI particles thus represent a promising remedial agent applicable at sites contaminated with TCE.

Sustainable Synthesis of Nanoscale Zerovalent Iron Particles for Environmental Remediation

Nanoscale zerovalent iron (nZVI) particles represent an important material for diverse environmental applications because of their exceptional electron-donating properties, which can be exploited for applications such as reduction, catalysis, adsorption, and degradation of a broad range of pollutants. The synthesis and assembly of nZVI by using biological and natural sustainable resources is an attractive option for alleviating environmental contamination worldwide. In this Review, various green synthesis pathways for generating nZVI particles are summarized and compared with conventional chemical and physical methods. In addition to describing the latest environmentally benign methods for the synthesis of nZVI, their properties and interactions with diverse biomolecules are discussed, especially in the context of environmental remediation and catalysis. Future prospects in the field are also considered.

Zero valent iron and goethite nanoparticles as new promising remediation techniques for As-polluted soils

The capacity of two iron-based nanomaterials, namely goethite nanospheres (nGoethite) and zero valent iron nanoparticles (nZVI), to immobilize As in a polluted soil was evaluated and compared. The composition and morphology of the products were studied by energy dispersive X-ray analysis and transmission electron microscopy, while zeta potential and average sizes were determined by dynamic light scattering. To assess As immobilization, soil subsamples were treated with nGoethite or nZVI at a range of Fe doses (0.5%, 2%, 5% and 10%) and then studied by the TCLP test and the Tessier sequential extraction procedure. The influence of both nanoparticles on As speciation was determined, as was impact on soil pH, electrical conductivity, Fe availability and phytotoxicity (watercress germination). For nZVI, notable results were achieved at a dose of 2% (89.5% decrease in As, TCLP test), and no negative effects on soil parameters were detected. Indeed, even soil phytotoxicity was reduced and only at the highest dose was a slight increase in As³⁺ detected. In contrast, excellent results were obtained for nGoethite at the lowest dose (0.2%) (82.5% decrease in As, TCLP test); however, soil phytotoxicity was increased at higher doses, probably due to a marked enhancement of electrical conductivity. For both types of nanoparticle, slight increases in Fe availability were observed. Thus, our results show that both nZVI and nGoethite have the capacity to effectively immobilize As in this brownfield. The use of lower doses of nGoethite emerges as a promising soil remediation strategy for soils affected by As pollution.

Polymeric ion exchanger supported ferric oxide nanoparticles as adsorbents for toxic metal ions from aqueous solutions and acid mine drainage

BACKGROUND

Acid mine drainage (AMD) is a worldwide industrial pollution of grave concern. AMD pollutes both water sources and the environment at large with dissolved toxic metals which are detrimental to human health. This paper reports on the preparation of polymeric ion exchange resins decorated with hydrated iron oxides and their application for the ecological removal of toxic metals ions from AMD.

METHODS

The hydrated iron oxide particles were incorporated within commercial chelating ion exchange resins using the precipitation method. The synthesised hybrid resins were then characterized using appropriate spectroscopic and solid-state techniques. The metal ion levels were measured using the inductively coupled plasma-optical emission spectrometer (ICP-OES). The optimization of contact time, pH, and adsorbent dosage were conducted to enhance the efficiency of adsorption of toxic metals onto the hybrid organic/inorganic nanosorbents. Kinetics and adsorption isotherms were constructed to study the adsorption mechanisms of the adsorbents.

RESULTS

The results showed that the dispersed Fe-O is hydrated and amorphous within the hybrid materials. The adsorption kinetics followed the pseudo-second-order shown by the high R² values. The hybrid adsorbents were finally tested on environmental AMD samples and were able to remove toxic metals Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn at various removal degrees.

CONCLUSION

Solution pH played a crucial role in the adsorption of toxic metals on hybrid iron oxide adsorbents. The hybrid TP-260 HFO had higher affinity for toxic metals than other prepared adsorbents thus has a potential for acidic mine water pollution remediation. The adsorbed Al(III) can be recovered using NaCl-NaOH binary solution from the loaded resins.

Removal efficiency of hexavalent chromium from wastewater using starch-stabilized nanoscale zero-valent iron

In this study, starch-stabilized nanoscale zero-valent iron (S-nZVI) was produced using the liquid-phase reduction method. It was used to remove chromium from wastewater, and compared to a commercial nanoscale zero-valent iron (C-nZVI). Both nZVIs were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The characterization results showed that S-nZVI had smaller particles and a more uniform particle size distribution than C-nZVI. Both nZVIs showed a core-shell structure with the Fe⁰ core prominently surrounded by less iron oxides of Fe²⁺ and Fe³⁺. The optimal application methods to remove Cr(VI) from wastewater were also explored. The results showed that both the removal efficiencies of total Cr and Cr(VI) increased with increases in the addition of nZVIs, while the removal efficiencies of total Cr and Cr(VI) by S-nZVI were clearly higher than that of C-nZVI, especially in a low pH range (pH = 1.0-6.0). This research indicated that starch-stabilized nanoscale zero-valent iron is a valuable material to remove heavy metals from wastewater due to its stability and high reactivity.

Effect of multiple iron-based nanoparticles on availability of lead and iron, and micro-ecology in lead contaminated soil

Although iron nanoparticles (NPs) have been used for environmental remediation of heavy metal, their potential to remediate lead (Pb) contaminated soil and effect on soil micro-ecology is unclear. The purpose of this study was to investigate the potential of nanoscale zerovalent iron (nZVI), nanoscale zerovalent iron supported by biochar (nZVI@BC), ferrous sulfide (FeS-NPs), ferrous sulfide supported by biochar (FeS-NPs@BC), ferriferrous oxide (Fe₃O₄-NPs) and ferriferrous oxide supported by biochar (Fe₃O₄-NPs@BC) to remediate Pb contaminated soil and the influences for soil micro-ecology. The results showed that biochar (BC) could improve the crystal shape and superficial area of iron-based nanoparticles. Soil pH values was significantly decreased by FeS-NPs and FeS-NPs@BC, but increased by other iron-nanoparticles. The ability to reduce available Pb concentration showed significant difference among these iron-nanoparticles, that is, the immobilized rate were nZVI by 45.80%, nZVI@BC by 54.68%, FeS-NPs by 2.70%, FeS-NPs@BC by 5.13%, Fe₃O₄-NPs by 47.47%, Fe₃O₄-NPs@BC by 30.51% at day 90. Almost all soil enzyme activities in Fe₃O₄-NPs and Fe₃O₄-NPs@BC groups were increased, but the majority of the enzyme activities were inhibited in other iron-based nanoparticles groups, while the maximum bacterial number was determined in FeS-NPs group. Furthermore, microbial diversity analysis showed that FeS-NPs has significantly changed microbial community richness and diversity, followed by nZVI and Fe₃O₄-NPs. Accordingly, our results suggested that nZVI@BC had the best immobilization effect on Pb in high-concentration Pb-contaminated alkaline soil, but the toxic effect of Fe₃O₄-NPs on soil micro-ecology was relatively minimal.

Nanoremediation and long-term monitoring of brownfield soil highly polluted with As and Hg

In the last decade, several laboratory-scale experiments have shown the use of nanoscale zero-valent iron (nZVI) to be effective in reducing metal(loid) availability in polluted soils. The present study evaluates the capacity of nZVI for reducing the availability of As and Hg in brownfield soils at a pilot scale, and monitors the stability of the immobilization of these contaminants over a 32 month period. To the best of our knowledge, this is the first study to apply nZVI to metal(loid)-polluted soils under field conditions. Two sub-areas (A and B) that differed in pollution load were selected, and a 5 m² plot was treated with 2.5% nZVI (by weight) in each case (Nanofer 25S, NanoIron). In sub-area A, which had a greater degree of pollution, a second application was performed eight months after the first application. Overall, the treatment significantly reduced the availability of both As and Hg, after only 72 h, although the effectiveness of the treatment was highly dependent on the degree of initial contamination. Sub-area B (with a lower level of pollution) showed the best and most stable immobilization results, with As and Hg in toxicity characteristics leaching procedure (TCLP) extracts decreasing by 70% and 80%, respectively. In comparison, the concentrations of As and Hg in sub-area A decreased by 65% and 50%, respectively. Based on our findings, the use of nZVI at a dose of 2.5% appears to be an effective approach for the remediation of soils at this brownfield site, especially in sub-area B. For sub-area A, a higher dose of nZVI-or its use in combination with other remediation strategies-should be tested.

Electric-field enhanced reactivity and migration of iron nanoparticles with implications for groundwater treatment technologies: Proof of concept

The extensive use of nanoscale zero-valent iron (nZVI) particles for groundwater treatment has been limited, in part, because of their non-selective reactivity and low mobility in aquatic environments. Herein, we describe and explore progressive changes in the reactivity and migration of aqueous dispersed nZVI particles under an applied DC electric field. Due to the applied electric field with an intensity of about 1 V cm^-1, the solution oxidation-reduction potential (ORP) remained as low as -200 mV for at least 32 days, which was in agreement with the persistence of the reduced iron species (mainly Fe(II)), and led to substantially prolonged reactivity of the original nZVI. The treatment of chlorinated ethenes (DCE > PCE > TCE) was markedly faster, individual CHC compounds were eliminated with the same kinetics and no lesser-chlorinated intermediates were accumulated, following thus the direct dechlorination scheme. When nZVI-dispersion flows towards the anode through vertical laboratory columns filled with quartz sand, significant enhancement of nZVI migration was recorded because of lower extent of nanoparticle aggregation and increased repulsion forces between the nanoparticles and the surface of silica dioxide. The results of this study have significant consequences for groundwater remediation, mainly for the treatment of slowly degradable DCE in real CHC contaminated groundwater, where it could improve the reactivity, the longevity and the migration of nZVI particles.

Efficient novel amphiphilic double shells layer coupled with nanoscale zero-valent composite for the degradation of trichloroethylene

An efficient novel amphiphilic material composed of core-double shells nanocomposite (CDSN) with nanoscale zero-valent iron (NZVI) as the core and PS₁₀₀-b-PAA₁₆ as inner shell and chitosan as outmost shell has been synthesized successfully. Its application to remove the trichloroethylene (TCE) in stimulated TCE solution with 7.3 ± 0.3 mg/L dissolved oxygen was investigated. The results showed that CDSN after exposure to air for a month could still remove 92.6% of TCE as compared to 61.5% removal rate of NZVI in 360 min (the gram ratio of material: TCE equals to 10:1), exhibiting the great oxidation resistance performance. Specifically, dynamic research of the total removal divided into adsorption by shell layer and degradation by reducibility of NZVI at a predetermined interval was engaged to understand the complete mass transfer process of TCE. The results revealed that CDSN adsorbed 1.5 to 2 folds time TCE as compared to NZVI in the same initial pH = 8.5 aqueous solution. Importantly, CDSN could sustain fixed reactivity to remove about 94.8% of TCE from the start to end. NZVI exhibited greater removal capacity in first 180 min, but later it lost the reducibility and finial removal rate was 89%. The selective adsorption to protonated CDSN was strengthened to increase the removal of TCE at pH 3.5 while NZVI had a worse removal in pH 3.5 performance than pH 8.5.

Advances in Surface Passivation of Nanoscale Zerovalent Iron: A Critical Review

Nanoscale zerovalent iron (NZVI) is one of the most extensively studied nanomaterials in the fields of wastewater treatment and remediation of soil and groundwater. However, rapid oxidative transformations of NZVI can result in reduced NZVI reactivity. Indeed, the surface passivation of NZVI is considered one of the most challenging aspects in successfully applying NZVI to contaminant degradation. The oxidation of NZVI can lead to the formation of Fe^II-bearing phases (e.g., Fe^IIO, Fe^II(OH)₂, Fe^IIFe^III₂O₄) on the NZVI surface or complete oxidation to ferric (oxyhydr)oxides (e.g., Fe^IIIOOH). This corrosion phenomenon is dependent upon various factors including the composition of NZVI itself, the type and concentration of aqueous species, reaction time and oxic/anoxic environments. As such, the coexistence of different Fe oxidation states on NZVI surfaces may also, in some instances, provide a unique reactive microenvironment to promote the adsorption of contaminants and their subsequent transformation via redox reactions. Thus, an understanding of passivation chemistry, and its related mechanisms, is essential not only for effective NZVI application but also for accurately assessing the positive and negative effects of NZVI surface passivation. The aim of this review is to discuss the nature of the passivation processes that occur and the passivation byproducts that form in various environments. In particular, the review presents: (i) the strengths and limitations of state-of-the-art techniques (e.g., electron microscopies and X-ray-based spectroscopies) to identify passivation byproducts; (ii) the passivation mechanisms proposed to occur in anoxic and oxic environments; and (iii) the effects arising from synthesis procedures and the presence of inorganics/organics on the nature of the passivation byproducts that form. In addition, several depassivation strategies that may assist in increasing and/or maintaining the reactivity of NZVI are considered, thereby enhancing the effectiveness of NZVI in contaminant degradation.

Characterization and evaluation of surface modified materials based on porous biochar and its adsorption properties for 2,4-dichlorophenoxyacetic acid

In this study, the effect of surface modification on the properties of porous biochar was studied, and these modification techniques were synthetically evaluated by principal component analysis. The results showed that surface modification significantly affected the surface and adsorption properties of porous biochar. Potassium carbonate activated porous biochar (KBC) was modified by surface oxidation, surface amination, loading nano-zero valent iron (nZVI) and loading nano-iron oxyhydroxide (nHIO). The surface modification affected the pore structure, especially the micropores. Surface modification influenced the oxygen-containing functional groups, amino, and metal-O significantly. It also changed the diffusion of 2,4-dichlorophenoxyacetic acid (2,4-D) on the biochar surface. The specific surface area was not the only factor determining the adsorption capacity. Surfaces rich in oxygen-containing functional groups would favor the adsorption of 2,4-D by biochar. The adsorption of biochars on 2,4-D were determined by π-π interaction, chemisorption and hydrogen bonding. The synthetic properties of modified biochar were evaluated by principal component analysis, and the comprehensive performance was in order of NKBC > OKBC > KBC > BC > nHIO@KBC > nZVI@KBC. Structural activation, surface amination and surface oxidation can improve the comprehensive properties of biochar.

Efficient U(VI) Reduction and Sequestration by Ti2CT x MXene

Although reduction of highly mobile U(VI) to less soluble U(IV) has been long considered an effective approach to in situ environmental remediation of uranium, candidate reducing agents are largely limited to Fe-based materials and microbials. The importance of titanium-containing compounds in natural uranium ore deposits suggests a role for titanium in uranium migration. Herein, for the first time, a two-dimensional transition metal carbide, Ti₂CT _x, is shown to efficiently remove uranium via a sorption-reduction strategy. Batch experiments demonstrate that TiC₂T _x exhibits excellent U(VI) removal over a wide pH range, with an uptake capacity of 470 mg g^-1 at pH 3.0. The mechanism for U(VI) to U(IV) reduction by Ti₂CT _x was deciphered by X-ray absorption spectroscopy and diffraction and photoelectron spectroscopy. The reduced U(IV) species at low pH is identified as mononuclear with bidendate binding to the MXene substrate. At near-neutral pH, nanoparticles of the UO_{2+ x} phase adsorb to the substrate with some Ti₂CT _x transformed to amorphous TiO₂. A subsequent in-depth study suggests Ti₂CT _x materials may be potential candidates for permeable reactive barriers in the treatment of wastewaters from uranium mining. This work highlights reduction-induced immobilization of U(VI) by Ti₂CT _x MXene including a pH-dependent reduction mechanism that might promote applications of titanium-based materials in the elimination of other oxidized contaminants.

Effect of bicarbonate on aging and reactivity of nanoscale zerovalent iron (nZVI) toward uranium removal

Bicarbonate, ubiquitous in natural and waste waters is an important factor regulating the rate and efficiency of pollutant separation and transformation. For example, it can form complexes with U(VI) in the aqueous phase and at the solid-water interface. In this work, we investigated the effect of bicarbonate on the aging of nanoscale zero-valent (nZVI) in the context of U(VI) reduction and removal from wastewater. For fresh nZVI, over 99% aqueous uranium was separated in less than 10 min, of which 83% was reduced from U(VI) to U(IV). When nZVI was aged in water, its activity for U(VI) sequestration and reduction was significantly reduced. Batch experiments showed that for nZVI aged in the presence of 10 mM bicarbonate, only 20.3% uranium was reduced to U(IV) after 6 h reactions. Characterizations of the iron nanoparticles with spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) suggest that in fresh nZVI, uranium was concentrated at the nanoparticle center; whereas in nZVI aged in bicarbonate, uranium was largely deposited on the outer surface of the nanoparticles. Furthermore, aged nZVI without bicarbonate contained more lepidocrocite (γ-FeOOH) while aged nZVI in the presence of bicarbonate had more magnetite/maghemite (Fe₃O₄/γ-Fe₂O₃). This could be attributed to the formation of carbonate green rust and pH buffer effect of . Primary mechanisms for U(VI) removal with nZVI include reduction, sorption and/or precipitation. Results demonstrate that bicarbonate alter the aging products of nZVI, and reduces the separation efficiency and reduction capability for uranium removal.

Selective formation of copper nanoparticles from acid mine drainage using nanoscale zerovalent iron particles

Nanoscale zerovalent iron (nZVI) has been investigated for the selective formation of Cu nanoparticles from acid mine drainage (AMD) taken from a legacy mine site in the UK. Batch experiments were conducted containing unbuffered (pH 2.67 at t = 0) and pH buffered (pH < 3.1) AMD which were exposed to nZVI at 0.1-2.0 g/L. Results demonstrate that nZVI is selective for Cu, Cd and Al removal (>99.9% removal of all metals within 1 h when nZVI ≥ 1.0 g/L) from unbuffered AMD despite the coexistent of numerous other metals in the AMD, namely: Na, Ca, Mg, K, Mn and Zn. An acidic pH buffer enabled similarly high Cu removal but maximum removal of only <1.5% and <0.5% Cd and Al respectively. HRTEM-EDS confirmed the formation of discrete spherical nanoparticles comprised of up to 68% wt. Cu, with a relatively narrow size distribution (typically 20-100 nm diameter). XPS confirmed such nanoparticles as containing Cu°, with the Cu removal mechanism therefore likely via cementation with Fe°. Overall the results demonstrate nZVI as effective for the one-pot and selective formation of Cu°-bearing nanoparticles from acidic wastewater, with the technique therefore potentially highly useful for the selective upcycling of dissolved Cu in wastewater into high value nanomaterials.

Advances in Sulfidation of Zerovalent Iron for Water Decontamination

Sulfidation has gained increasing interest in recent years for improving the sequestration of contaminants by zerovalent iron (ZVI). In view of the bright prospects of the sulfidated ZVI (S-ZVI), this review comprehensively summarized the latest developments in sulfidation of ZVI, particularly that of nanoscale ZVI (S-nZVI). The milestones in development of S-ZVI technology including its background, enlightenment, synthesis, characterization, water remediation and treatment, etc., are summarized. Under most circumstances, sulfidation can enhance the sequestration of various organic compounds and metal(loid)s by ZVI to various extents. In particular, the reactivity of S-ZVI toward contaminants is strongly dependent on S/Fe molar ratio, sulfidation method, and solution chemistry. Additionally, sulfidation can improve the selectivity of ZVI toward targeted contaminant over water under anaerobic conditions. The mechanisms of sulfidation-induced improvement in contaminants sequestration by ZVI are also summarized. Finally, this review identifies the current knowledge gaps and future research needs of S-ZVI for environmental application.

New hybrid nanocomposite of copper terephthalate MOF-graphene oxide: synthesis, characterization and application as adsorbents for toxic metal ion removal from Sungun acid mine drainage

The application of a hybrid Cu(tpa).GO (Cu(tpa) copper terephthalate metal organic framework, GO graphene oxide) composite as a new adsorbent for the removal of toxic metal ions was reported. New hybrid nanocomposite with excellent dispersibility and stability was successfully fabricated by the simple and effective ultrasonication method. The synthesized composite was characterized by scanning electron microscopy (SEM), UV-Vis and Fourier-transform infrared (FT-IR) techniques. The characterization results concluded that the binding mechanism of the Cu(tpa) and GO was related to both π-π packing and hydrogen bonding. For scrutinizing the sorption activity, the prepared adsorbents were assessed for the removal of Mn²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and Fe³⁺ metal ions from aqueous synthetic solution and also acid mine drainage (AMD) wastewater. The sorption experiments demonstrated that the removal efficiency was significantly improved by modified hybrid Cu(tpa).GO composite, owing to the significant number of active binding sites and unique structure formed based on π-conjugated networks. Also, it was shown that the adsorption reaction was mainly attributed to the chemical interactions between metal ions and the surface functional groups. Moreover, kinetic and adsorption studies clarified that the adsorption process onto the Cu(tpa).GO follows a pseudo-second-order kinetics and fits the Langmuir and Freundlich adsorption models. Holistically, the results of this research represent that applying Cu(tpa).GO can be remarked as an effective adsorbent with high possibility at conventional water treatment.

The application of illite supported nanoscale zero valent iron for the treatment of uranium contaminated groundwater

In this study, nanoscale zero valent iron I-NZVI was investigated as a remediation strategy for uranium contaminated groundwater from the former Cimarron Fuel Fabrication Site in Oklahoma, USA. The 1 L batch-treatment system was applied in the study. The result shows that 99.9% of uranium in groundwater was removed by I-NZVI within 2 h. Uranium concentration in the groundwater stayed around 27 μg/L, and there was no sign of uranium release into groundwater after seven days of reaction time. Meanwhile the release of iron was significantly decreased compared to NZVI which can reduce the treatment impact on the water environment. To study the influence of background pH of the treatment system on removal efficiency of uranium, the groundwater was adjusted from pH 2-10 before the addition of I-NZVI. The pH of the groundwater was from 2.1 to 10.7 after treatment. The removal efficiency of uranium achieved a maximum in neutral pH of groundwater. The desorption of uranium on the residual solid phase after treatment was investigated in order to discuss the stability of uranium on residual solids. After 2 h of leaching, 0.07% of the total uranium on residual solid phase was leached out in a HNO₃ leaching solution with a pH of 4.03. The concentration of uranium in the acid leachate was under 3.2 μg/L which is below the EPA's maximum contaminant level of 30 μg/L. Otherwise, the concentration of uranium was negligible in distilled water leaching solution (pH = 6.44) and NaOH leaching solution (pH = 8.52). A desorption study shows that an acceptable amount of uranium on the residuals can be released into water system under strong acid conditions in short terms. For long term disposal management of the residual solids, the leachate needs to be monitored and treated before discharge into a hazardous landfill or the water system. For the first time, I-NZVI was applied for the treatment of uranium contaminated groundwater. These results provide proof that I-NZVI has improved performance compared to NZVI and is a promising technology for the restoration of complex uranium contaminated water resources.

Magnetite and cobalt ferrite nanoparticles used as seeds for acid mine drainage treatment

In this study, magnetite and cobalt ferrite nanoparticles were used as seeds for acid mine drainage (AMD) treatment at pH of 7.05±0.35. Duplicate samples of AMD, one without heating and another with heating at 60°C was treated under continuous stirring for 1h. The filtrate analysis results from ICP-OES have shown complete removal of Al, Mg, and Mn, while for Fe, Ni and Zn over 90% removals were recorded. Particularly, settling time has significant effect on the removal of Mg, Ca and Na. The results from SQUID have shown superparamagnetic properties of the synthesised magnetic nanoparticles and ferrite sludge. The recovered nanoparticles from AMD are economically important and reduce the cost of waste disposal.

Removal of U(VI) from aqueous solution using TiO2 modified β-zeolite

β-Zeolite was synthesized and modified with TiO2. The synthesized materials were characterized and used for removal of U(VI) from aqueous solutions. The influences of pH, contact time and temperature on U(VI) adsorption onto modified β-zeolite by TiO2 were studied by batch technique, and XPS was employed to analysed the experimental data. The dynamic process showed that the adsorption of U(VI) onto TiO2/β-zeolite matched the pseudo-second-order kinetics model, and the adsorption of U(VI) were significantly dependent on pH values. Through simulating the adsorption isotherms by Langmuir, Freundlich and Dubini–Radushkevich (D–R) models, it could be seen, respectively that the adsorption patterns of U(VI) onto TiO2/β-zeolite were mainly controlled by surface complexation, and the adsorption processes were endothermic and spontaneous. The modification of β-zeolite by TiO2 it shows a novel material for the removing of U(VI) from water environment for industrialized application.

Comparing different commercial zero valent iron nanoparticles to immobilize As and Hg in brownfield soil

Nanoscale zero valent iron (nZVI) particles obtained by different methods differ in their structure, which lead to different reactivity, and therefore a likely difference in the remediation efficiency. The present study compares the effectiveness of three commercial ZVI nanoparticles to immobilize As and Hg in two soils (A and B) collected from a brownfield highly contaminated by mining and metallurgy activities. Scarce data are available on the effectiveness of nZVI for Hg immobilization in soil. Two commercial nZVI slurries from Toda (RNIP and RNIP-D) and one from Nano Iron (25S) were used at different doses (1, 5 and 10%). The metal(loid) availability and mobility was evaluated with the TCLP test and Tessier extraction procedure. The influence of nZVI application on As and Hg speciation was also evaluated as well as its impact on soil pH, electrical conductivity and soil phytotoxicity to vetch germination. The three commercial nZVI particles significantly reduced As and Hg availability in the two soils studied, which led to a decrease in soil phytotoxicity. At the dose of 5% of nZVI a decrease of exchangeable-As higher than 70% was observed for both soils, whereas in the case of Hg, a higher dose of nZVI (10%) was necessary to achieve reductions of exchangeable-Hg between 63 and 90% depending on the type of nZVI and soil. No impact on soil pH and electrical conductivity was observed. The effectiveness of metal(loid) immobilization depended on type of nZVI, soil properties and metal(loid) characteristics. Nanoparticles from Nano Iron showed better results for As immobilization whereas RNIP nanoparticles were more effective for Hg. Overall, 25S at the dose of 5% resulted more effective than RNIP nanoparticles for the reduction of exchangeable-As (in the range of 6-14%), whereas RNIP and RNIP-D were 10 and 13% more effective, respectively, for the reduction of exchangeable-Hg at the dose of 10% in soil B. Thus, nZVI can be used for the remediation of highly As and Hg polluted soils, although previous experiments at lab scale are necessary to determine the most viable type of nZVI and its dose.