Preparation of a novel hydrogel of sodium alginate using rural waste bone meal for efficient adsorption of heavy metals cadmium ion

Study on the adsorption performance of carbon-magnetic modified sepiolite nanocomposite for Sb(V), Cd(II), Pb(II), and Zn(II): Optimal conditions, mechanisms, and practical applications in mining areas

A carbon-magnetic modified sepiolite nanocomposite (γ-Fe2O3/SiO2-Mg(OH)2@BC) was synthesized using a hydrothermal method, consisting of γ-Fe2O3, activated sludge biochar (BC), and alkali-modified sepiolite. Its ability to remove heavy metals such as Sb(V), Pb(II), Cd(II), and Zn(II) was investigated through adsorption experiments. Using response surface optimization, the optimal adsorption conditions were determined: adsorption time = 3.78 h, pH = 2.63, initial concentration = 15.78 mg/L, temperature = 35.14°C, and adsorbent dosage = 100.71 mg. Characterization results revealed that the main adsorption mechanisms included complexation, π-π interactions, and electrostatic attraction. Kinetic and isotherm model analyses indicated that the adsorption process of γ-Fe2O3/SiO2-Mg(OH)2@BC adhered to the pseudo-second-order kinetic model and the Freundlich isotherm model, primarily involving multilayer chemical adsorption. The application of this composite material in complex aquatic environments in antimony mining areas demonstrated promising practical results, as well as excellent regeneration performance. This study provides technical and theoretical support for the treatment of complex heavy metal wastewater in antimony mining areas and lays a foundation for the development of novel carbon-magnetic modified nanocomposite adsorbents.

N-functionalized calcium alginate encapsulated with microalgae for efficient Pb removal: Mechanisms and performance in batch and column operations

In this study, a novel adsorbent called Ca@SP was developed by immobilizing microalgae protein (Spirulina platensis, SP) in an alginate matrix for enhanced Pb²⁺ removal from aqueous solutions. Synthesized via in situ crosslinking, Ca@SP leverages the synergistic effects of alginate's gel-forming ability and SP's N-rich biomass. Characterization of Ca@SP revealed a green spherical hydrogel with a BET specific surface area of 159.5 m²/g. The composite exhibited pH-dependent and highly selective adsorption for Pb²⁺ over other divalent metal ions, which can be explained by the relatively lower hydrated Gibbs free energy of Pb²⁺. The main adsorption mechanisms were identified as physical adsorption, electrostatic interaction, complexation, and ion exchange. Column experiments demonstrated Ca@SP's effectiveness under various operational conditions, including flow rate, influent concentration, and column heights. RSM was employed to optimize the adsorption process, with initial pH emerging as a critical parameter influencing Pb²⁺ removal efficiency. Desorption experiments showed that acidic solvents had higher desorption efficiency than alkaline solvents, and the potential for reusability was confirmed. These results suggest that Ca@SP has potential as an effective and sustainable adsorbent for Pb²⁺ removal from aqueous environments.

Fixation behavior of oceanic manganese nodule-sodium alginate composite microspheres for heavy metal release during manganese nodule mining

Research on the environmental impact of deep-sea mining is crucial, particularly for fragile deep-sea ecosystems. This research focuses on the issue of heavy metal release during mining activities. Through simulation experiments, we investigated the release of Cu2+, Co2+, and Ni2+ from sediments under disturbance conditions and the fixation behavior during the deployment of ocean manganese nodule-sodium alginate composite microspheres (OMN@SA). The experimental results revealed that mining disturbances cause the release of 0.291% of Cu2+, 7.34% of Co2+, and 4.13% of Ni2+ from sediments into the water, primarily in the form of exchangeable metals. Compared with the bottom adsorption, OMN@SA has a faster adsorption rate in the slow settling process. The removal rates of Cu2+, Co2+ and Ni2+ reached 54.0%, 78.3% and 61.8% for 5 h adsorption, and the bottom adsorption removal rates reached 96.4%, 97.8% and 95.1% for 30 d adsorption, which has a good removal effect. In addition, OMN@SA can effectively block the diffusion of Cu2+, Co2+, and Ni2+ from interstitial water to overlying water, and reduce the influence of interstitial water on overlying water. SEM-EDS, FTIR, and XRD analyses revealed that OMN@SA adsorbs heavy metal ions through its abundant -OH groups and incorporates Cu2+, Co2+, and Ni2+ into the crystal lattices of vernadite and todorokite via substitution or intercalation. This study provides guidance for the remediation of heavy metal release from deep-sea mining using adsorption methods and demonstrates the promising application prospects of OMN@SA.

New insights into sustainable in-situ fixation of heavy metals in disturbed seafloor sediments

To address the issues of plume formation and heavy metal ion release during deep-sea mining operations, this study employed multi-sourced mineral composite roasting materials (MMCCM) of varying sizes. An in-situ capping technique was applied within a simulated system to immobilize heavy metals in contaminated sediments. The results demonstrated that capping with MMCCM of different sizes significantly suppressed the upward migration of Cu, Co, and Ni from sediments into the overlying seawater following disturbance. Ion diffusion was identified as a key mechanism driving heavy metal migration. By calculating the release rates of heavy metals during both the disturbed and undisturbed phases, it was found that the application of MMCCM induced a negative diffusion of heavy metals, indicating that the MMCCM-sediment layer functioned as a "sink" for heavy metals. FTIR and XPS analysis showed that the primary mechanisms for heavy metal removal by MMCCM were electrostatic attraction and complexation-precipitation. Additionally, capping with MMCCM facilitated the transition of heavy metals from labile to stable forms within the sediments. Through comprehensive evaluation, the long-term effectiveness of the fixed effects was demonstrated as follows: large MMCCM (L@MCM) > medium MMCCM (M@MCM) > small MMCCM (S@MCM) > powder MMCCM (P @ MCM). Finally, we proposed future research directions and introduced the DQSE framework for the sustainable application of MMCCM. Based on the above findings, this study provides new insights and research references for the in-situ immobilization of heavy metals and plume reduction during future deep-sea mining processes.

Insight into the impact of environmental factors on heavy metal adsorption by sodium alginate hydrogel: Inspiration on applicable scenarios

Sodium alginate (SA) emerges as a promising adsorbent for the remediation of heavy metal-polluted wastewater. However, the systematic investigations on how and the extent to which the various compositions in real water matrices impact its performance were essential but rare when considering its use. Here, we explored the effect of common environmental factors on Cu(II) adsorption by an as-synthesized SA-based hydrogel (SAH). The result showed that high concentration of organics (above 10 mg L-1) had a negative influence on heavy metal removal (decreased by 9.45 % at least), while inorganic ion, turbidity and antibiotics at relatively low concentrations exhibited a negligible even promoting effect (increased by 9.8 % with the presence of 5 mg L-1 Nor). Based on above results and corresponding mechanism analyses, the possible applicable and unsuitable scenarios of SAH can be predicted. SAH could be a great candidate for treating heavy metal-polluted water such as river and lake water, while it is not a good option for electroplating or livestock wastewater which contains high concentration of organic matters. Besides, the operating conditions including pH (5.0 for Cu(II), 6.0 for Ni(II)), contact time (24 h), temperature (298 K) et al. were also determined. Overall, this work provides theoretical guidance and operational strategies for promoting the practical application of SA adsorbent in water treatment.

Eco-Friendly Hydrogel Beads from Seashell Waste for Efficient Removal of Heavy Metals from Water

The objective of this study is to develop a calcium carbonate-based adsorbent derived from Cellana Tramoscrica seashells, incorporated into a sodium alginate matrix (Na-Alg@CTs) to form hydrogel beads, for the efficient removal of Cu (II) and Zn (II) heavy metals from aqueous solutions. XRD, SEM/EDS, and FTIR analysis confirm the successful synthesis and characterization of the fabricated adsorbent. The adsorption study of Cu (II) and Zn (II) onto Na-Alg@CTs hydrogel beads revealed that the Langmuir model was the most suitable for characterizing the adsorption isotherms, suggesting monolayer coverage. Na-Alg@CTs exhibited a maximum Langmuir adsorption capacity of 368.58 mg/g and 1075.67 mg/g for Cu (II) and Zn (II), respectively. Additionally, the kinetics followed the pseudo-second-order model, indicating that the adsorption process is primarily governed by chemisorption. The thermodynamic study suggests that the uptake of metal ions on Na-Alg@CTs hydrogel beads is spontaneous and endothermic. The exceptional adsorption capacity, eco-friendly nature, and low-cost characteristics of Na-Alg@CTs hydrogel beads make them an ideal adsorbent for the removal of Cu (II) and Zn (II) from wastewater.

A Natural Carbon Encapsulated in Gellan-Based Hydrogel Particles Designed for Environmental Challenges

This article reports the obtention of a new gellan-based hydrogel linked with Fe3+ and loaded with a natural micro/nanostructured carbon designed as a contaminant's removal from wastewater. Hydrogels are known for their water-retaining properties, high binding capacity, and eco-friendly features. The new material is expected to behave as one cost-effective and efficient sorbent, including natural carbon structures with various functional groups. The encapsulation efficiency ranges between 89% and 95%. The obtained hydrogel particles were characterized using FT-IR spectroscopy and scanning electron microscopy techniques. The hydrogel particles' water stability was evaluated by measuring the transmittance for 10 days, and the capacity to retain water was assessed by determining the swelling degree (Q%). The results showed that hydrogel particles are stable (the transmittance value is higher than 97.8% after 10 days), and their properties are influenced by the cross-linking degree, the amount of the carbon particles encapsulated, and the concentration of gellan. For example, the Q% values and encapsulation efficiency increased when the cross-linking degree, the carbon microstructure quantity, and the gellan concentration decreased. The new hybrid material can retain Pb(II) ions and diclofenac molecules, and could be used in different adsorption-desorption cycles.

Enhancing the effect of novel cd mobilization bacteria on phytoremediation and microecology of cadmium contaminated soil

The efficacy of phytoextraction for remediating heavy-metal contaminated soil depends on the bioavailability of the heavy metals and plant growth. In this study, we employed a synergistic system comprising water-soluble chitosan and the novel Cd mobilization bacteria, Serratia sp. K6 (hereafter K6), to enhance cadmium (Cd) extraction by Lolium perenne L. (ryegrass). The application of chitosan and K6 resulted in an increase in the biomass of ryegrass by 11.81% and Cd accumulation by 73.99% and effective-state Cd by 43.69% and pH decreased by 4.67%, compared to the control group. Microbiome and metabolomics analyses revealed significant alterations in the inter-root microbial ommunity, with rhizobacteria such as Sphingomonas, Nocardioides, and Bacillus likely contributing to enhanced plant growth and Cd accumulation in response to chitosan and K6 addition. Additionally, the contents of various organic acids, amino acids, lipids, and other metabolites exhibited significant changes under different additive treatments, suggesting that ryegrass can regulate its own metabolites to resist Cd stress. This study provides valuable insights into the effects of additives on phytoextraction efficiency and the soil bacterial community, offering a promising approach for phytoremediation of Cd-contaminated soils.

Design, characterization and implementation of cost-effective sodium alginate/water hyacinth microspheres for remediation of lead and cadmium from wastewater

The aquatic plant water hyacinth was dried then cross-linked with sodium alginate to produce ionic cross-linked microspheres. The mechanism of controlling cadmium (Cd) and lead (Pb) in wastewater was tested by DFT at B3LYP level using LANL2DZ basis set. Modeling results indicated that the hydrated metals could interact with sodium alginate (SA)/water hyacinth (WH) microspheres through hydrogen bonding. Adsorption energies showed comparable results while total dipole moment and HOMO/LUMO band gap energy showed slight selectivity towards the remediation of Pb. FTIR spectra of cross-linked microspheres indicated that WH is forming a composite with SA to change its structure into a microsphere to remove Cd and Pb from water. Raman mapping revealed that the active sites along the surface of the microspheres enable for possible adsorption of metals through its surface. This finding is supported by molecular electrostatic potential and optical confocal microscopy. Atomic absorption spectroscopy results confirmed that the microspheres are more selective for Pb than Cd. It could be concluded that WH cross-linked with SA showed the potential to remove heavy metals through its unique active surface as confirmed by both molecular modeling and experimental findings.

Integration of metal organic framework nanoparticles into sodium alginate biopolymer-based three-dimensional membrane capsules for the efficient removal of toxic metal cations from water and real sewage

Sodium alginate (SA) biopolymer has been recognized as an efficient adsorbent material owing to their unique characteristics, including biodegradability, non-toxic nature, and presence of abundant hydrophilic functional groups. Accordingly, in the current research work, UiO-66-OH and UiO-66-(OH)2 metal organic framework (MOF) nanoparticles (NPs) have been integrated into SA biopolymer-based three-dimensional (3-D) membrane capsules (MCs) via a simple and facile approach to remove toxic metal cations (Cu2+ and Cd2+) from water and real sewage. The newly configured capsules were characterized by FTIR, SEM, XRD, EDX and XPS analyses techniques. Exceptional sorption properties of the as-developed capsules were ensured by evaluation of the pertinent operational parameters, i.e., contents of MOF-NPs (1-100 wt%), adsorbent dosage (0.001-0.05 g), content time (0-360 h), pH (1-8), initial concentration of metal cations (5-1000 mg/L) and reaction temperature (298.15-333.15 K) on the eradication of Cu2+ and Cd2+ metal cations. It was found that hydrophilic functional groups (-OH and -COOH) have performed an imperative role in the smooth loading of MOF-NPs into 3-D membrane capsules via intra/inter-molecular hydrogen bonding and van der waals potencies. The maximum monolayer uptake capacities (as calculated by the Langmuir isotherm model) of Cd2+ and Cu2+ by 3-D SGMMCs-OH were 940 and 1150 mg/g, respectively, and by 3-D SGMMCs-(OH)2 were 1375 and 1575 mg/g, respectively, under optimum conditions. The as-developed capsules have demonstrated superior selectivity against targeted metal cations under designated pH and maintained >80 % removal efficiency up to six consecutive treatment cycles. Removal mechanisms of metal cations by the 3-D SGMMCs-OH/(OH)2 was proposed, and electrostatic interaction, ion-exchange, inner-sphere coordination bonds/interactions, and aromatic ligands exchange were observed to be the key removal mechanisms. Notably, FTIR and XPS analysis indicated that hydroxyl groups of Zr-OH and BDC-OH/(OH)2 aromatic linkers played vital roles in Cu2+ and Cd2+ adsorption by participating in inner-sphere coordination interactions and aromatic ligands exchange mechanisms. The as-prepared capsules indicated >70 % removal efficiency of Cu2+ from real electroplating wastewater in the manifestation of other competitive metal ions and pollutants under selected experimental conditions. Thus, it was observed that newly configured 3-D SGMMCs-OH/(OH)2 have offered a valuable discernment into the development of MOFs-based water decontamination 3-D capsules for industrial applications.

On the performance of Sargassum-derived calcium alginate ion exchange resins for Pb2+ adsorption: batch and packed bed applications

Driven by climate change and human activity, Sargassum blooming rates have intensified, producing copious amount of the invasive, pelagic seaweed across the Caribbean and Latin America. Battery recycling and lead-smelter wastes have heavily polluted the environment and resulted in acute lead poisoning in children through widespread heavy metal contamination particular in East Trinidad. Our study details a comprehensive investigation into the use of Sargassum (S. natans), as a potential resource-circular feedstock for the synthesis of calcium alginate beads utilized in heavy metal adsorption, both in batch and column experiments. Here, ionic cross-linking of extracted sodium alginate with calcium chloride was utilized to create functional ion-exchange beads. Given the low quality of alginates extracted from Sargassum which produce poor morphological beads, composite beads in conjunction with graphene oxide and acrylamide were used to improve fabrication. Stand-alone calcium alginate beads exhibited superior Pb2+ adsorption, with a capacity of 213 mg g-1 at 20 °C and pH 3.5, surpassing composite and commercial resins. Additives like acrylamide and graphene oxide in composite alginate resins led to a 21-40% decrease in Pb2+ adsorption due to reduced active sites. Column operations confirmed Alginate systems' practicality, with 20-24% longer operating times, 15 times lower adsorbent mass on scale-up and 206% smaller column diameters compared to commercial counterparts. Ultimately, this study advocates for Sargassum-based Alginate ion-exchange beads as a bio-based alternative in Trinidad and developing nations for dealing with heavy metal ion waste, offering superior heavy metal adsorption performance and supporting resource circularity.

Highly selective detection and removal of mercury ions in the aquatic environment based on magnetic ZIF-71 multifunctional composites with sufficient chlorine functional groups

The development of both detection and removal technologies for heavy metal ions is of great importance. Most of the existing adsorbents that contain oxygen, nitrogen or sulfur functional groups can remove heavy metals, but achieving both selective detection and removal of a single metal ion is difficult because they bind to a wide range of heavy metal ions. Herein, we selected zeolite imidazolium hydrochloride framework-71 (ZIF-71) with sufficient chlorine functional groups to fabricate magnetic ZIF-71 multifunctional composites (M-ZIF-71). M-ZIF-71 had a large specific surface area, excellent water stability, and good magnetic properties, which made M-ZIF-71 conducive to the separation and recovery of adsorbents and the assembly of electrodes. M-ZIF-71 exhibited high selectivity, wide linear range (1-500 μg/L), and low detection limit (0.32 μg/L) for electrochemical detection of mercury ions (Hg2+). Meanwhile, M-ZIF-71 demonstrated rapid Hg2+ adsorption with a high capacity of 571.2 mg/g and excellent recyclability. The high selectivity for Hg2+ was attributed to the powerful affinity of highly electronegative chlorine and Hg2+. Moreover, XPS spectra demonstrated the interaction between chlorine and Hg2+. This work provides a new inspiration for applications in the targeted monitoring and removal of heavy metal pollution.

Molecular engineering of a new method for effective removal of cadmium from water

Cadmium (Cd) is a widespread and highly toxic environmental pollutant, seriously threatening animal and plant growth. Therefore, monitoring and employing robust tools to enrich and remove Cd from the environment is a major challenge. In this work, by conjugating a fluorescent indicator (CCP) with a functionalized glass slide, a special composite material (CCPB) was constructed to enrich, remove, and monitor Cd2+ in water rapidly. Then Cd2+ could be effectively eluted by immersing the Cd-enriched CCPB in an ethylenediaminetetraacetic acid (EDTA) solution. With this, the CCPB was continuously reused. Its recovery of Cd2+was above and below 100 % after multiple uses by flame atomic absorption spectrometry (FAAS), which was excellent for practical use in enriching and removing Cd2+ in real aqueous samples. Therefore, CCPB is an ideal material for monitoring, enriching, and removing Cd2+ in wastewater, providing a robust tool for future practical applications of Cd enrichment and removal in the environment.

A state-of-the-art review on plant-derived cellulose-based green hydrogels and their multifunctional role in advanced biomedical applications

The most prevalent carbohydrate on Earth is cellulose, a polysaccharide composed of glucose units that may be found in diverse sources, such as cell walls of wood and plants and some bacterial and algal species. The inherent availability of this versatile material provides a natural pathway for exploring and identifying novel uses. This study comprehensively analyzes cellulose and its derivatives, exploring their structural and biochemical features and assessing their wide-ranging applications in tissue fabrication, surgical dressings, and pharmaceutical delivery systems. The use of diverse cellulose particles as fundamental components gives rise to materials with distinct microstructures and characteristics, fulfilling the requirements of various biological applications. Although cellulose boasts substantial potential across various sectors, its exploration has predominantly unfolded within industrial realms, leaving the biomedical domain somewhat overlooked in its initial stages. This investigation, therefore, endeavors to shed light on the contemporary strides made in synthesizing cellulose and its derivatives. These innovative techniques give rise to distinctive attributes, presenting a treasure trove of advantages for their compelling integration into the intricate tapestry of biomedical applications.

Efficient adsorptive removal of used drugs during the COVID-19 pandemic from contaminated water by magnetic graphene oxide/MIL-88 metal-organic framework/alginate hydrogel beads

Currently, the presence of drugs used in the COVID-19 pandemic in water bodies is worrisome due to their high toxicity, which necessitates their critical removal by developing highly efficient adsorbents. Hence, in this study, alginate hydrogel beads of magnetic graphene oxide@MIL-88 metal-organic framework (GO@Fe3O4@MIL-88@Alg) were prepared for the first time and then utilized as a new absorption system for the removal of COVID-19 drugs such as doxycycline (DOX), hydroxychloroquine (HCQ), naproxen (NAP), and dipyrone (DIP) from aqueous solutions by batch adsorption manner. The effects of different experimental factors, such as adsorbent dosage, contact time, pH, drug concentration, temperature, ionic strength, presence of an external magnetic field (EMF), and magnet distance from the adsorption flask were optimized for the removal of COVID-19 drugs. The adsorption equilibrium isotherm proved that the adsorption process of DOX, HCQ, NAP, and DIP drugs on GO@Fe3O4@MIL-88@Alg hydrogel beads conformed to the Langmuir model and followed the pseudo-second-order adsorption kinetics. The maximum adsorption capacities of DOX, HCQ, NAP, and DIP drugs obtained for GO@Fe3O4@MIL-88@Alg hydrogel beads with the Langmuir model were 131.57, 79.92, 55.55, and 49.26 mg/g at 298 K, respectively. The thermodynamic study suggested a spontaneous endothermic adsorption process. Also, the conclusion from this study confirmed the validity of GO@Fe3O4@MIL-88@Alg hydrogel beads for excellent removal of COVID-19 drugs from water samples. It was also found that the GO@Fe3O4@MIL-88@Alg hydrogel beads could be reused with satisfactory removal efficiency in six cycles. Based on the study, the GO@Fe3O4@MIL-88@Alg hydrogel beads could be considered a sustainable, simple, economical, environmentally friendly absorption system for the removal of pharmaceutical contaminants from water.

Adsorption of metal ions by oceanic manganese nodule and deep-sea sediment: Behaviour, mechanism and evaluation

Deep-sea mining disturbs the sediment on the seabed to form plumose flows, carrying metal ions that are transmitted through the food chain, posing a serious threat to marine ecosystems and human health. In this study, two types of marine raw materials were screened: Oceanic Manganese Nodules (OMN) and Deep-sea Sediments (DSS), and prepared the spherical regenerative adsorption materials OMN@SA, DSS@SA and OMN&DSS@SA using sodium alginate (SA) by sol-gel method. Preliminary investigations on the adsorption effect of metal ions were carried out. OMN@SA exhibited the best adsorption capacity, with the adsorption quantities for Cu2+, Co2+ and Ni2+ reaching 31.12, 21.11 and 16.66 mg/g, respectively. The adsorption behaviour is consistent with the Langmuir, pseudo-second-order kinetics and particle diffusion model, indicating that the adsorption process is mainly spontaneous, monolayer chemical adsorption, and the adsorption rate is mainly controlled by internal particle diffusion. SEM-EDS, XRD, FTIR and XPS analyses suggest that the adsorption mechanism includes surface physical adsorption, ion exchange, functional group complexation, electrostatic attraction and precipitation. The fixed bed column experiment shows that OMN@SA can effectively remove metal ions Cu2+, demonstrating excellent stability, safety and good regenerability. This study paves a new direction for the design of efficient and sustainable materials for heavy metal adsorption. More importantly, as marine primordial materials, OMN and DSS have strong technical and economic feasibility for future use in in-situ fixation of metal ions in seafloor sediments and restoration of the original seabed environment.

Drought-resistant and water-retaining tobermorite/starch composite hydrogel for the remediation of cadmium-contaminated soil

The objective of this work is utilizing fly ash to synthesize tobermorite (TOB) with a higher specific surface area and layered structure, and incorporating it into the starch/acrylic acid network to boost the drought resistance, water retention and heavy metal adsorption properties. The water absorption and water retention performance and cadmium adsorption characteristics of tobermorite/leftover rice-based composite hydrogel (TOB@LR-CH) were evaluated by water absorption swelling test, soil evaporation test and batch adsorption experiment. By adjusting the addition of TOB and other synthesized conditions, the swelling property (from 114.80 g/g to 322.64 g/g), water retention (71.80 %, 144 h) and Cd2+ adsorption characteristics (up to 591.36 mg/g) were significantly enhanced. Adding a moderate amount of TOB (2 wt%) provided the most uniform tobermorite dispersion during synthesis, and TOB2@LR-CH exhibited the most stable three-dimensional network and highest proportion of effective TOB. The adsorption behavior of cadmium on TOB2@LR-CH was more consistent with the pseudo-second-order kinetics and Langmuir isotherm models. Additionally, the regeneration test results displayed that the adsorption removal rate of cadmium by TOB2@LR-CH adsorbent remained stable after 5 cycles. This study demonstrates that TOB@LR-CH has good water absorption and water retention potential in arid and semi-arid soils, and also has potential application prospects in remediating Cd(II)-contaminated soil.

Immobilization of cadmium in river sediments by different modified nanoscale zero-valent iron: performance, mechanisms, and Fe dissolution

Modified nanoscale zero-valent iron (NZVI) exhibited great potential for the remediation of heavy metal contaminated river sediments, but its mechanisms and environmental risks are still unclear. This study systematically discussed the performance and the mechanisms of modified NZVI materials, i.e., sodium alginate-coated NZVI (SNZVI), rhamnolipid-coated NZVI (RNZVI), and graphene oxide-loaded NZVI (GNZVI), for the stabilization of Cd in sediment, with the exploration of their stability to Cd at various pH values and Fe dissolution rate. Compared with the control, the toxicity characteristic leaching procedure (TCLP) leachable Cd decreased by 52.66-96.28%, and the physiologically based extraction test (PBET) extractable Cd decreased by 44.68-70.21% after 56 days of incubation with the immobilization efficiency varying according to GNZVI > RNZVI > SNZVI > NZVI. Besides, the adsorption behavior of Cd on materials was fitted with the Freundlich model and classified as an endothermic, spontaneous, and chemical adsorption process. SEM-EDX, XRD, and FTIR results verified that the stabilization mechanisms of Cd were principally based on the adsorption, complexation of Cd2+ with secondary Fe minerals (including Fe2O3, γ-Fe2O3, and γ-FeOOH) and precipitation (Cd(OH)2). From the risk assessment results, it was observed that the materials were favorable for Cd stabilization at a pH range from 7 to 11, meanwhile, the leaching concentration of Fe in the overlying water was detected below the limit value. These findings pave the way to developing an effective strategy to remediate Cd contaminated river sediments.

Use of thermally activated Fenton sludge for Cd removal in zinc smelter wastewater: Mechanism and feasibility of Cd removal

Fenton sludge is a byproduct of the Fenton process that contains large amounts of Fe and Ca. Because of the secondary contamination generated during the disposal of this byproduct, ecofriendly treatment methods are needed. In this study, we used Fenton sludge to remove the Cd discharged from a zinc smelter factory, using thermal activation to enhance the Cd adsorption capacity. Among the various temperatures considered (300-900 °C), the Fenton sludge that was thermally activated at 900 °C (TA-FS-900) adsorbed the highest amount of Cd because of its high specific surface area and high Fe content. Cd was adsorbed onto TA-FS-900 via complexation with C-OH, C-COOH, FeO-, and FeOH and cation exchange with Ca2+. The maximum adsorption of TA-FS-900 was 260.2 mg/g, indicating that TA-FS-900 is an efficient adsorbent, comparable to those reported in the literature. The initial Cd concentration in the zinc smelter wastewater discharged was 105.7 mg/L, 98.4% of which was removed by applying TA-FS-900, suggesting the applicability of TA-FS-900 for real wastewater containing high concentrations of various cations and anions. The leaching of heavy metals from TA-FS-900 was within the EPA standard limits. We concluded that the environmental impact of Fenton sludge disposal can be reduced, and the use of Fenton sludge can add value to the treatment of industrial wastewater in terms of the circular economy and environment.

Graphitic N-doped biochar for superefficient uranium recycling from nuclear wastewater

N-doped biochar (AL-N/BC) prepared by pyrolyzing lignin in various temperatures manifested superefficient performance for uranium (U) recycling from nuclear wastewater. The optimist AL-N/BC-700 showed higher adsorption capacity of 25,000 mg/g and faster kinetics of 4100 g·min^-1·mg^-1 than the most of reported adsorbents, and excellent adsorption-desorption capability (adsorption rate > 90 % and desorption rate > 70 % after 12 cycles). Moreover, the high applicability of AL-N/BC-700 was verified by its superefficient U(VI) adsorption performance in a broad working pH range, various water matrices, and high irradiation stability. Furthermore, the adsorption mechanism discloses the significant role of graphitic N, rather than pyridinic N or pyrrolic N, for U(VI) adsorption. Overall, this work not only presents an applicable approach to alleviate the increasingly serious energy crisis via recycling U(VI) from nuclear wastewater, but also enriches the method of synthesizing N-doped materials for U(VI) adsorption.

A Comprehensive Review of Polysaccharide-Based Hydrogels as Promising Biomaterials

Polysaccharides have emerged as a promising material for hydrogel preparation due to their biocompatibility, biodegradability, and low cost. This review focuses on polysaccharide-based hydrogels' synthesis, characterization, and applications. The various synthetic methods used to prepare polysaccharide-based hydrogels are discussed. The characterization techniques are also highlighted to evaluate the physical and chemical properties of polysaccharide-based hydrogels. Finally, the applications of SAPs in various fields are discussed, along with their potential benefits and limitations. Due to environmental concerns, this review shows a growing interest in developing bio-sourced hydrogels made from natural materials such as polysaccharides. SAPs have many beneficial properties, including good mechanical and morphological properties, thermal stability, biocompatibility, biodegradability, non-toxicity, abundance, economic viability, and good swelling ability. However, some challenges remain to be overcome, such as limiting the formulation complexity of some SAPs and establishing a general protocol for calculating their water absorption and retention capacity. Furthermore, the development of SAPs requires a multidisciplinary approach and research should focus on improving their synthesis, modification, and characterization as well as exploring their potential applications. Biocompatibility, biodegradation, and the regulatory approval pathway of SAPs should be carefully evaluated to ensure their safety and efficacy.

Repurposing of steel rolling sludge: Solvent-free preparation of α-Fe2O3 nanoparticles and its application for As(III/V)-containing wastewater treatment

Steel rolling sludge (SRS) is the by-product of metallurgical industry with abundant iron content, which needs to be utilized for producing high value-added products. Herein, cost-effective and highly adsorbent α-Fe₂O₃ nanoparticles were prepared from SRS via a novel solvent-free method and applied to treat As(III/V)-containing wastewater. The structure of the prepared nanoparticles was observed to be spherical with a small crystal size (12.58 nm) and high specific surface area (145.03 m²/g). The nucleation mechanism of α-Fe₂O₃ nanoparticles and the effect of crystal water were investigated. More importantly, compared with the traditional methods of preparation cost and yield, this study was found to have excellent economic benefits. The adsorption results indicated that the adsorbent could effectively remove arsenic over a wide pH range, and the optimal performance of nano adsorbent for As(III) and As(V) removal was observed at pH 4.0-9.0 and 2.0-4.0, respectively. The adsorption process was consistent with pseudo-second-order kinetic and Langmuir isothermal model. The maximum adsorption capacity (q_m) of adsorbent for As(III) and As(V) was 75.67 mg/g and 56.07 mg/g, respectively. Furthermore, α-Fe₂O₃ nanoparticles exhibited great stability, and q_m remained at 64.43 mg/g and 42.39 mg/g after five cycles. Particularly, the As(III) was removed by forming inner-sphere complexes with the adsorbent, and it partially oxidized to As(V) during this process. In contrast, the As(V) was removed by electrostatic adsorption and reaction with -OH on the adsorbent surface. Overall, resource utilization of SRS and the treatment of As(III)/(V)-containing wastewater in this study are in line with the current developments in the environmental and waste-to-value research.