Simultaneous stabilization of Pb and improvement of soil strength using nZVI

Cd2+ Sorption Alterations in Ultisol Soils Triggered by Different Engineered Nanoparticles and Incubation Times

The progressive influx of engineered nanoparticles (ENPs) into the soil matrix catalyses a fundamental transformation in the equilibrium dynamics between the soil and the edaphic solution. This all-encompassing investigation is geared towards unravelling the implications of an array of ENP types, diverse dosages and varying incubation durations on the kinetics governing Cd2+ sorption within Ultisol soils. These soils have been subjected to detailed characterizations probing their textural and physicochemical attributes in conjunction with an exhaustive exploration of ENP composition, structure and morphology. To decipher the intricate nuances of kinetics, discrete segments of Ultisol soils were subjected to isolated systems involving ENP dosages of 20 and 500 mg ENPs·kg-1 (AgNPs, CuNPs and FeNPs) across intervals of 1, 3 and 6 months. The comprehensive kinetic parameters were unveiled by applying the pseudo-first-order and pseudo-second-order models. At the same time, the underlying sorption mechanisms were studied via the intra-particle diffusion model. This study underscores the substantial impact of this substrate on the kinetic behaviours of contaminants such as Cd, emphasizing the need for its consideration in soil-linked economic activities and regulatory frameworks to optimize resource management.

Metabolomic profiles reveals the dose-dependent effects of rice grain yield and nutritional quality upon exposure zero-valent iron nanoparticles

Zero-valent iron nanoparticles (nZVI) were widely used material in environmental remediation, which has attracted increasing concern for their safety. Previous studies have shown that the addition of nZVI could inhibit rice seedling growth. However, the effect of nZVI on the soil-rice system during the entire life cycle was not reported. Furthermore, the effect of nZVI on the quality of rice grain has also not been studied. Therefore, we investigated the effects of rice grain yield and nutritional quality upon exposure nZVI. The results showed that the soil pH value, redox potential and Fe (II) content in the nZVI-treated group were decreased in a dose-dependent manner. Interestingly, 2500 mg/kg nZVI significantly decreased the relative abundance of several functional microbial communities (10.52-73.53 %) associated with carbon and nitrogen cycles in response to plants compared to the control. Meanwhile, the nZVI treatment clearly reduced grain yield (8.71-18.21 %). Furthermore, the content of protein (51.72-57.79 %) and several essential nutrients (Zn, Cu, Mn and Mo) in the nZVI-treated grains was also decreased in a dose-dependent manner. The results of grain metabolomics indicated that nZVI could interfere with the relative expression of lysine and glutathione by regulating the metabolic pathways of antioxidant and protein synthesis in rice.

Remediation methods of heavy metal contaminated soils from environmental and geotechnical standpoints

Heavy metal contaminated soil (HMCS) threatens world health and sustainable growth, owing to which numerous remediation methods have been devised. Meanwhile, environmental sustainability and geotechnical serviceability of remediated HMCS are important considerations for reusing such soils and achieving sustainable development goals; therefore, these considerations are critically reviewed in this article. For this purpose, different onsite and offsite remediation methods are evaluated from environmental and geotechnical standpoints. It was found that each remediation method has its own merits and limitations in terms of environmental sustainability and geotechnical serviceability; generally, sustainable green remediation (SGR) and cementation are regarded as effective solutions for the problems related to the former and latter, respectively. Overall, the impact of remediation techniques on the environment and geotechnical serviceability is a developing area of study that calls for increased efforts to improve the serviceability, sustainability, reusability and environmental friendliness of the remediated HMCS.

Simultaneous stabilization of Pb, Cd, and As in soil by rhamnolipid coated sulfidated nano zero-valent iron: Effects and mechanisms

Sulfidation effectively improves the electron transfer efficiency of nanoscale zero-valent iron (nZVI), but decreases the specific surface area of nZVI. In this study, sulfidated nZVI (S-nZVI) coated with rhamnolipid (RL-S-nZVI) was synthesized and used to stabilize Pb, Cd, and As in combined polluted soil. The stabilization efficiency of 0.3% (wt) RL-S-nZVI to water soluble Pb, Cd, and As in soil reached 88.76%, 72%, and 63%, respectively. Rhamnolipid coating inhibited the reduction of specific surface area and successfully encapsulated nZVI, thus reducing the oxidation of Fe⁰. The types of iron oxides in RL-S-nZVI were reduced compared to S-nZVI, but the content and strength of Fe⁰ iron were obviously enhanced. Furthermore, rhamnolipid functional groups (-COOH and -COO^-) were also involved in the stabilization process. In addition, the stabilization efficiency of RL-S-nZVI to the bioavailable Pb, Cd, and As in soil increased by 41%, 41%, and 50%, respectively, compared with nZVI. The presence of organic acids, especially citric acid, improved the stabilization efficiency of RL-S-nZVI to the three metals. The result of BCR sequential extraction indicated that RL-S-nZVI increased the residual state of Pb, Cd, and As and reduced the acid-soluble and reducible state after 28 days of soil incubation. XRD and XPS analyses showed that the stabilization mechanisms of RL-S-nZVI on heavy metals involved in ion exchange, surface complexation, adsorption, co-precipitation, chemisorption, and redox.

Exogenous iron alters uptake and translocation of CuO nanoparticles in soil-rice system: A life cycle study

The abundant iron in farmland soil may affect the environmental fate of metal-based nanoparticles (MNPs). In this study, the effect of FeSO4 and nano-zero-valent iron (nZVI) as exogenous iron on the uptake and translocation of CuO nanoparticles (NPs) in soil-rice system was performed in a life cycle study. The results show that exogenous iron basically elevated the soil pH and electrical conductivity but lowered the redox potential. Moreover, the Cu bioavailability in soil was significantly increased by 86-269% with exogenous iron at the tillering stage, while was reduced by 15-45% with medium and high concentrations of Fe(II) at the maturation stage. Meanwhile, the addition of exogenous iron resolved the unfilling of grains caused by CuO NPs. Notably, except for highest Fe(II) treatment, both Fe(II) and nZVI reduced Cu accumulation from 31% to 84% in roots and leaves due to more iron plaque. Especially, medium Fe(II) level markedly decreased the Cu content in the brown rice. μ-XRF analysis suggests that high intensity of Cu was primarily located in the rice hull and embryo under Fe(II) treatment. The reduction of CuO NPs to Cu2O caused by Fe(II) can explain the positive effect of exogenous iron on controlling the environmental risk of MNPs.

Zero valent iron or Fe3O4-loaded biochar for remediation of Pb contaminated sandy soil: Sequential extraction, magnetic separation, XAFS and ryegrass growth

In this study, the feasibility of using zero-valent iron (ZVI) and Fe₃O₄-loaded biochar for Pb immobilization in contaminated sandy soil was investigated. A 180-day incubation study, combined with dry magnetic separation, chemical extraction, mineralogical characterization, and model plant (ryegrass, namely the Lilium perenne L.) growth experiment was conducted to verify the performance of these two materials. The results showed that both amendments significantly transferred the available Pb (the exchangeable and carbonates fraction) into more stable fractions (mainly Fe/Mn oxides-bound Pb), and ZVI alone showed a better performance than the magnetic biochar alone. The magnetic separation and extended X-ray absorption fine structure (EXAFS) analysis proved that Fe (oxyhydr)oxides on aged ZVI particles were the major scavengers of Pb in ZVI-amended soils. In comparison, the reduced Pb availability in magnetic biochar-amended soil could be explained by the association of Pb with Fe/Mn (oxyhydr)oxides in aged magnetic biochar, also the possible precipitation of soil Pb with soluble anions (e.g. OH^-, PO₄^3-, and SO₄^2-) released from magnetic biochar. ZVI increased ryegrass production while Fe₃O₄-loaded biochar had a negative effect on the ryegrass growth. Moreover, both markedly decreased the Pb accumulation in aboveground and root tissues. The simple dry magnetic separation presents opportunities for the removal of Pb from soils, even though the efficiencies were not high (17.5% and 12.9% of total Pb from ZVI and biochar-treated soils, respectively). However, it should be noted that the ageing process easily result in the loss of magnetism of ZVI while the magnetic biochar tends to be more stable and has high retrievability during the dry magnetic separation application.

Stabilization of lead and cadmium in soil by sulfur-iron functionalized biochar: Performance, mechanisms and microbial community evolution

Sulfur-iron functionalized biochar (BC-Fe-S) was designed by simultaneously supporting Fe₂O₃ nanoparticles and grafting sulfur-containing functional groups onto biochar to stabilize Pb and Cd in soil. The BC-Fe-S exhibited excellent stabilization performance for Pb and Cd with fast kinetic equilibrium within 5 days associating with pseudo-second-order model. The bioavailable-Pb and -Cd contents decreased by 59.22% and 70.28% with 3% BC-Fe-S treatment after 20 days of remediation. Speciation transformation analysis revealed that the increase of stabilization time and BC-Fe-S dosage with appropriate soil moisture and pH promoted toxicities decrease of Pb and Cd with transformation of labile fractions to more steady fractions. The labile fractions of Pb and Cd decreased by 12.22% and 16.21% with 3% BC-Fe-S treatment, and transformed to the residual speciation. Meanwhile, wetting-drying and freezing-thawing aging did not markedly alter the bioavailability of Pb and Cd, proving that the BC-Fe-S holds promise for stabilization of Pb and Cd in varying environmental conditions. 16S rRNA sequencing analysis demonstrated that the BC-Fe-S significantly improved diversity and composition of microbial community, especially increasing the relative abundance of heavy metal-resistant bacteria. Overall, these results suggested BC-Fe-S as a high-performance and environmental-friendly amendment with stability to remediate heavy metals polluted soil.

A plasma thermal slag-derived from hazardous waste has a born hydrothermal stability

Hydrothermal instability restricts performances of silica-based catalysts, which have wide applications in both industry and environment. For the first time, plasma-thermal slag was revealed to be a catalyst with a born hydrothermal stability in selective catalytic reduction of nitric oxide. The slag catalyst removed 98.5 % of NO with a high N₂ selectivity (> 95 %) at 200 °C. After a hydrothermal treatment at 900 °C, the activity of the slag only decreased to 84.0 %. According to characterizations of XRD, HTREM, XPS, and EPR, active metals existed in coordination states in the slag at first. Under hydrothermal conditions, these species transformed to short-range single crystals, which were hindered from sintering by surrounded Si-O bands. At the same time, in-situ DRIFT indicated that more Brønsted and Lewis acid sites were formed. Hence, enough active sties were reserved for effective catalytic reduction of nitric oxide. The main result of this work helps us to understand hydrothermal stability of a catalyst. What's more, the high-value-added utilization of plasma-thermal slag is in favor of the development of hazardous-waste treatment.

A new insight on enhanced Pb(II) removal by sludge biochar catalyst coupling with ultrasound irradiation and its synergism with phenol removal

The applicability of sludge biochar catalyst (SBC) coupling with ultrasound (US) irradiation for the simultaneous removal of Pb(II) and phenol was firstly investigated in this study. Results indicate that Pb(II) removal of SBC/US process was superior to that of SBC without US. The inhibitory order of the coexisting anions on Pb(II) removal was PO43- > HCO3- > NO3- > F- > SO42- > Cl-. Also, several coexisting metals ions inculding Cr(VI), Ni(II) and Cu(II) could be removed in a simultaneous manner with Pb(II). A high removal performance of Pb(II) by SBC/US process and its synergism with phenol oxidation had been successfully achieved. The simultaneous removal efficiencies of Pb(II) and phenol were high up to 95% within 60 min at optimum reaction conditions. Four kinds of Pb species inculding Pb0, PbCO3, PbO and Pb(OH)2 were formed during the reaction, whereas five kinds of transformation compounds of phenol such as 1,4-benzoquinone, acetic acid, formic acid, maleic acid and propionic acid were detected. Both HO and O2- contributed to the oxidation of phenol by SBC/US process, but HO was dominant radical. A reaction mechanism for the synergistic removal of Pb(II) and phenol by SBC/US process involving in four stages-namely adsorption, precipitation, reduction and Fenton-like oxidation processes was proposed. This study demonstrates that SBC/US process could be considered as a potential candidate for the remediation of real wastewaters containing Pb(II) and phenol.

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.

Uptake of vegetable and soft drink affected transformation and bioaccessibility of lead in gastrointestinal track exposed to lead-contaminated soil particles

Accidental ingestion of Pb-contaminated soil particles by direct hand-to-mouth activity or by swallowing airborne dust particles is important pathway of human exposure to Pb. Appropriate evaluation of Pb risk to human is important in determining whether the soil needs remediation or not, however, there is paucity of data about the dietary influences on Pb bioaccessibility (Pb-BA) and transformation in humans. This study chose two typical foods, spinach and cola, representing vegetable and soft drink, respectively, and investigated their effects on Pb species in gastrointestinal tract using the physiologically based extraction test. Results showed that ingestion of spinach and cola decreased the Pb-BA by 52%-94% in the gastric phase and by 38%-95% in the intestinal phase, respectively. The reduction of Pb-BA by spinach was attributed to the precipitation of Pb with phosphorus in spinach and the sorption of Pb by the generated hydrolysate and un-hydrolysate from spinach in gastrointestinal tract. Cola decreased Pb-BA mainly via formation of insoluble Pb phosphates precipitates. Analysis of X-ray diffraction and MINTEQ modeling demonstrated that the dissolved Pb was transformed to precipitated or sorbed Pb with intake of cola or spinach. Our findings suggest that dietary habit greatly influence the speciation and subsequent Pb-BA in the gastrointestinal tract, which should be incorporated into human health risk assessment of Pb-contaminated soil.

Remediation of Cr(VI)-Contaminated Soil by Nano-Zero-Valent Iron in Combination with Biochar or Humic Acid and the Consequences for Plant Performance

Nano-scale zero-valent iron (nZVI) is among the most common nanoparticles widely used for the treatment of various environmental contaminants. However, little is known about the combined effects of nano-zero-valent iron (nZVI) and other soil amendments on soil remediation and plant performance. For the first time, we studied the remediation of Cr(VI)-contaminated soil using bare nZVI (B-nZVI) and starch-supported nZVI (S-nZVI) in combination with either biochar (BC) or humic acid (HA), and the consequent effects on plant growth and Cr accumulation. Both S-nZVI and B-nZVI decreased the contents of Cr(VI) and available Cr in soil, but increased available Fe content, with S-nZVI generally showing more pronounced effects at a higher dose (1000 mg/kg). B-nZVI exerted no inhibition and even stimulation on plant growth, but 1000 mg/kg S-nZVI produced significant phytotoxicity, resulting in decreased plant growth, low chlorophyll content in leaves, and excessive accumulation of Fe in roots. Each nZVI decreased shoot and root Cr concentrations. BC and HA produced synergistic effects with nZVI on Cr(VI) removal from soil, but HA decreased soil pH and increased the availability of Cr and Fe, implying a potential environmental risk. Addition of BC or HA did not alter the effects of either nZVI on plant growth. In conclusion, combined application of 100 mg/kg nZVI and BC could be an ideal strategy for the remediation of soil contaminated with Cr(VI), whereas high-dose S-nZVI and HA are not recommended in the remediation of agricultural soils for crop production or in the phytostabilization of Cr(VI).

Preparation of Biomass Activated Carbon Supported Nanoscale Zero-Valent Iron (Nzvi) and Its Application in Decolorization of Methyl Orange from Aqueous Solution

The nanoscale zero-valent iron (nZVI) has great potential to degrade organic polluted wastewater. In this study, the nZVI particles were obtained by the pulse electrodeposition and were loaded on the biomass activated carbon (BC) for synthesizing the composite material of BC-nZVI. The composite material was characterized by SEM-EDS and XRD and was also used for the decolorization of methyl orange (MO) test. The results showed that the 97.94% removal percentage demonstrated its promise in the remediation of dye wastewater for 60 min. The rate of MO matched well with the pseudo-second-order model, and the rate-limiting step may be a chemical sorption between the MO and BC-nZVI. The removal percentage of MO can be effectively improved with higher temperature, larger BC-nZVI dosage, and lower initial concentration of MO at the pH of 7 condition.

Comparison of reactive magnesia, quick lime, and ordinary Portland cement for stabilization/solidification of heavy metal-contaminated soils

Stabilization/solidification (S/S) is commonly applied to treat heavy metal-contaminated soils through the use of lime and ordinary Portland cement (OPC). Recently, reactive magnesia (MgO) has emerged as a novel binder for S/S of heavy metal-contaminated soils; however, a comprehensive comparison between MgO, lime (CaO), and OPC for S/S application is still missing. This study compares the S/S efficiency of MgO, CaO, and OPC for soils contaminated by six individual heavy metals (Pb, Cu, Zn, Ni, Cd, and Mn) through unconfined compressive strength (UCS) test, one stage batch leaching test, and microstructural analysis. The addition of binders can transform soluble heavy metal salts to insoluble hydroxides and their complexes, and hence the leachability of heavy metals decreases. However, the level, to which the leachability can be reduced, is highly pH dependent. Contaminated soils treated with MgO have pH of 9-10.5, at which the leachability of Pb and Zn is much lower than that of OPC- or CaO-treated soils with pH of 10.5-13; for example, the leached Pb and Zn from MgO-treated soils are only 0.1%-3.3% and 0.1%-9.4% of those from OPC-treated soils, respectively. On the other hand, the leached Cd and Mn from OPC-treated soils are 0.1%-28.5% and 0.1-10.7% of those from MgO-treated soils, respectively, due to the high pH and the formation of calcium silicate hydrate (CSH) in OPC-treated soils. OPC and CaO are more effective than MgO in decreasing the Ni leachability at high original concentrations, but less effective at low original concentrations. For all soils except those contaminated by Zn, the OPC generally produces a much higher UCS, up to two orders of magnitude, than the CaO and MgO. The results of study indicate that no single binder can treat all types of heavy metal-contaminated soils perfectly, and the selection of binder is a site-specific problem.

Geoenvironmental characteristics of bisphenol A contaminated soil after persulfate treatment with different activation/enhancement methods

Persulfate (PSF) is a strong oxidant that has been used extensively in the In-Situ Chemical Oxidation (ISCO) technology. The geoenvironmental impact of PSF treatment is barely investigated. This situation should be carefully considered as it may affect the reutilization of contaminated soil as engineering materials. This paper studied the removal of bisphenol A (BPA) by PSF with Nano Zero-Valent Iron (nZVI) and percarbonate (SPC) activated/enhanced and their subsequent impacts on the engineering properties of soil. The physicochemical and geotechnical properties of soils before and after treatment were evaluated using batch experiments. The results indicate that the introduced pristine PSF can be activated by some naturally occurring matters and subsequently lead to the mineralization of BPA. Both non-activated PSF and activated/enhanced PSF treatment led to the soil improvement in the undrained shear strength at different degrees. The primary mechanism of soil improvement is ascribed to the heterogeneous sulfate and/or carbonate precipitation. Meanwhile, Ca²⁺ in the pore fluid played a significant role in the enhancement of the soil strength. A conclusion was drawn that the treatment of both non-activated PSF, nZVI- and SPC-activated PSF treatment can achieve removal of BPA and soil improvement in the short-term simultaneously. This study can improve the PSF-involved remediation of brownfields and dredged sediments for a sustainable and low-carbon society.