Heavy metals in Iberian soils: Removal by current adsorbents/amendments and prospective for aerogels

Novel sustainable extraction of vegetable oils with simultaneous heavy metal and anti-nutrient removal capability

The accumulation of heavy metals (HMs) in oilseeds presents a serious risk to food safety, emphasizing the necessity of developing effective methods for producing safe vegetable oils and oilseed meals. This study proposed a biphasic system consisting of methanol, water, and additives as the polar phase and n-hexane as the nonpolar phase to simultaneously extract vegetable oils while removing HMs and anti-nutrients from oilseeds. Results indicated that the optimal oil extraction time for the four oilseeds was 180 min. The highest HMs removal rate of 64.3 % was achieved using 0.5 % HCl as an additive. The extracted vegetable oils met both Chinese and international standards for HMs content and adhered to Chinese standards for fatty acid composition ratios. The biphasic system decreased surface functional groups in the oilseed meal by 58.8-75.0 %. The oilseed meal retained all its proteins, while glucosinolate and phytic acid contents decreased by 86.8 % and 81.2 %, respectively. The flocculation and precipitation method successfully recovered 95.9 %-99.6 % of HMs and 44.2 %-92.8 % of anions, ensuring that the treated polar phase complied with China's surface water quality standards. Consequently, 82.7 % of the polar phase and 66.7 % of the nonpolar phase were efficiently recovered and reused, significantly reducing operational costs. The biphasic system maintained high efficiency in oil extraction and HMs removal during the second cycle. Collectively, the biphasic system provided a sustainable and innovative approach for the simultaneous safe production of vegetable oils and oilseed meals.

Advances in Soil Amendments for Remediation of Heavy Metal-Contaminated Soils: Mechanisms, Impact, and Future Prospects

Heavy metal contamination is a critical factor contributing to soil degradation and poses significant environmental threats with profound implications for ecosystems and human health. Soil amendments have become an effective strategy to address these challenges by reducing heavy metal hazards and remediating contaminated soils. This review offers a comprehensive analysis of recent advancements in soil amendments for heavy metal-contaminated soils, with a focus on natural, synthetic, natural-synthetic copolymer, and biological amendments. By thoroughly examining and contrasting their remediation mechanisms and effects, this study provides a detailed evaluation of their influence on soil physicochemical properties, leachable heavy metal content, and microbial communities. Through bibliometric analysis, current research priorities and trends are highlighted, offering a multidimensional comparison of these amendments and clarifying their varying applicability and limitations. Furthermore, this review explores future prospects and the inherent challenges in soil amendments for heavy metal contamination, aiming to offer valuable insights and theoretical references for the development and selection of novel, efficient, multifunctional, environmentally friendly amendments.

Removal of environmental pollutants using biochar: current status and emerging opportunities

In recent times, biochar has emerged as a novel approach for environmental remediation due to its exceptional adsorption capacity, attributed to its porous structure formed by the pyrolysis of biomass at elevated temperatures in oxygen-restricted conditions. This characteristic has driven its widespread use in environmental remediation to remove pollutants. When biochar is introduced into ecosystems, it usually changes the makeup of microbial communities by offering a favorable habitat. Its porous structure creates a protective environment that shields them from external pressures. Consequently, microorganisms adhering to biochar surfaces exhibit increased resilience to environmental conditions, thereby enhancing their capacity to degrade pollutants. During this process, pollutants are broken down into smaller molecules through the collaborative efforts of biochar surface groups and microorganisms. Biochar is also often used in conjunction with composting techniques to enhance compost quality by improving aeration and serving as a carrier for slow-release fertilizers. The utilization of biochar to support sustainable agricultural practices and combat environmental contamination is a prominent area of current research. This study aims to examine the beneficial impacts of biochar application on the absorption and breakdown of contaminants in environmental and agricultural settings, offering insights into its optimization for enhanced efficacy.

An Updated Overview of Silica Aerogel-Based Nanomaterials

Silica aerogels have gained much interest due to their unique properties, such as being the lightest solid material, having small pore sizes, high porosity, and ultralow thermal conductivity. Also, the advancements in synthesis methods have enabled the creation of silica aerogel-based composites in combination with different materials, for example, polymers, metals, and carbon-based structures. These new silica-based materials combine the properties of silica with the other materials to create a new and reinforced architecture with significantly valuable uses in different fields. Therefore, the importance of silica aerogels has been emphasized by presenting their properties, synthesis process, composites, and numerous applications, offering an updated background for further research in this interdisciplinary domain.

Fluorescent composite beads: An advanced tool for environmental monitoring and harmful pollutants removal from water

The quality and safety of water sources have been significantly impacted by various pollutants, including trace elements. To address this concern, this study utilized composite beads made of alginate and carbon quantum dots (CDs) for detecting and removing As(III) and Se(IV) ions in tap water. Fluorescent CDs were hydrothermally synthesized and incorporated into an alginate-Ca2+ matrix through a straightforward procedure. Characterization analyses revealed distinct properties of the composite beads, containing varying amounts of CDs, compared to the pristine beads. Optimal adsorption parameters (30 mg of adsorbent, 10 mg/L of initial pollutant concentration, 35 °C, and 180 min of contact time) for the beads containing 30 w/w-% of CDs (Alg@CDs30) were determined through a fractional factorial design. These composite beads exhibited the highest adsorption capacity for both metals, achieving a removal rate of 94.5% for As(III) and 98.0% for Se(IV) in tap water. Kinetic and isothermal analyses indicated that the adsorption of both metals on Alg@CDs30 involves a combination of chemisorption and diffusion processes. Recycling experiments demonstrated that the composite beads could be reused up to 20 times without a noticeable loss of adsorption efficiency. Regarding the sensing property, our experiments revealed a significant reduction in the fluorescence emission intensity of Alg@CDs30 upon interaction with As(III) and Se(IV), confirming its ability to detect both ions in tap water, with limits of detection (LOD) of 2.6 ± 0.5 μg/L for As(III) and 1.1 ± 0.2 μg/L for Se(IV). The alginate-Ca2+ matrix s contributed to the stability of the CDs' fluorescence. These results confirm the potential of Alg@CDs beads as effective tools for the simultaneous monitoring and removal of hazardous metal ions from real water samples.

Cyclodextrin-based nanosponges as promising carriers for active pharmaceutical ingredient

Effective drug distribution at the intended or particular location is a critical issue that researchers are now dealing. Nanosponges have significantly increased in importance in medication delivery using nanotechnology in recent years. An important step toward solving these problems has been the development of nanosponges. Recently created and proposed for use in drug delivery, nanosponge is a unique type of hyper-crosslinked polymer-based colloidal structures made up of solid nanoparticles with colloidal carriers. Nanosponges are solid porous particles that may hold pharmaceuticals and other actives in their nanocavities. They can be made into dosage forms for oral, parenteral, topical, or inhalation use. The targeted distribution of drugs in a regulated manner is greatly aided by nanosponge. The utilization of nanosponges, their benefits, their production processes, the polymers they are made of, and their characterization have all been covered in this review article.

Carbon quantum dots-containing poly(β-cyclodextrin) for simultaneous removal and detection of metal ions from water

This study investigates the synthesis and characterization of supramolecular composites composed of poly(β-cyclodextrin-co-citric acid) and carbon quantum dots (QDs). These composites serve a dual purpose as adsorbents and photoluminescent probes for divalent metal ions, including Ni(II), Cu(II), Cd(II), and Pb(II), which can have detrimental effects on the environment. Various characterization techniques were employed to confirm the successful synthesis of the composites and the interaction between cyclodextrins and QDs. By using mathematical tools, optimal conditions for metal adsorption were determined, resulting in the composites exhibiting high adsorption capacities, reaching 220 mg/g, and impressive removal efficiencies exceeding 90 % for Ni(II) and Cu(II). The supramolecular composites also exhibit selective adsorption of metal ions with small ionic radio and can be reused with minimal loss of efficiency. In addition to their adsorption capabilities, these composites display luminescence quenching upon the adsorption of metal ions, which can be utilized for sensing applications. Spectroscopic evaluation reveals Stern-Volmer quenching constants for the accessible fraction of QDs in the range of 3777 to 13,359 M-1. The high stability of QDs on the composites allows for long-term storage. In summary, this original supramolecular composite shows promise for simultaneously monitoring and treating water and wastewater, making it a valuable tool in environmental applications.

Incorporation of Cellulose-Based Aerogels into Textile Structures

Given their exceptional attributes, aerogels are viewed as a material with immense potential. Being a natural polymer, cellulose offers the advantage of being both replenishable and capable of breaking down naturally. Cellulose-derived aerogels encompass the replenish ability, biocompatible nature, and ability to degrade naturally inherent in cellulose, along with additional benefits like minimal weight, extensive porosity, and expansive specific surface area. Even with increasing appreciation and acceptance, the undiscovered possibilities of aerogels within the textiles sphere continue to be predominantly uninvestigated. In this context, we outline the latest advancements in the study of cellulose aerogels' formulation and their diverse impacts on textile formations. Drawing from the latest studies, we reviewed the materials used for the creation of various kinds of cellulose-focused aerogels and their properties, analytical techniques, and multiple functionalities in relation to textiles. This comprehensive analysis extensively covers the diverse strategies employed to enhance the multifunctionality of cellulose-based aerogels in the textiles industry. Additionally, we focused on the global market size of bio-derivative aerogels, companies in the industry producing goods, and prospects moving forward.

Reduced Chitosan as a Strategy for Removing Copper Ions from Water

Toxic heavy metals are priority pollutants in wastewater, commonly present in dangerous concentrations in many places across the globe. Although in trace quantities copper is a heavy metal essential to human life, in excess it causes various diseases, whereby its removal from wastewater is a necessity. Among several reported materials, chitosan is a highly abundant, non-toxic, low-cost, biodegradable polymer, comprising free hydroxyl and amino groups, that has been directly applied as an adsorbent or chemically modified to increase its performance. Taking this into account, reduced chitosan derivatives (RCDs 1-4) were synthesised by chitosan modification with salicylaldehyde, followed by imine reduction, characterised by RMN, FTIR-ATR, TGA and SEM, and used to adsorb Cu(II) from water. A reduced chitosan (RCD3), with a moderate modification percentage (43%) and a high imine reduction percentage (98%), proved to be more efficient than the remainder RCDs and even chitosan, especially at low concentrations under the best adsorption conditions (pH 4, R_S/L = 2.5 mg mL^-1). RCD3 adsorption data were better described by the Langmuir-Freundlich isotherm and the pseudo-second-order kinetic models. The interaction mechanism was assessed by molecular dynamics simulations, showing that RCDs favour Cu(II) capture from water compared to chitosan, due to a greater Cu(II) interaction with the oxygen of the glucosamine ring and the neighbouring hydroxyl groups.

Triazine-Based Porous Organic Polymers: Synthesis and Application in Dye Adsorption and Catalysis

The scientific community has been developing promising materials to increase the sustainability and efficiency of production processes and pollutant environmental remediation strategies. Porous organic polymers (POPs) are of special interest, as they are insoluble custom-built materials at the molecular level, endowed with low densities and high stability, surface areas, and porosity. This paper describes the synthesis, characterization, and performance of three triazine-based POPs (T-POPs) in dye adsorption and Henry reaction catalysis. T-POPs were prepared by a polycondensation reaction between melamine and a dialdehyde (terephthalaldehyde (T-POP1) or isophthalaldehyde derivatives with a hydroxyl group (T-POP2) or both a hydroxyl and a carboxyl group (T-POP3)). The crosslinked and mesoporous polyaminal structures, with surface areas between 139.2 and 287.4 m² g^-1, positive charge, and high thermal stability, proved to be excellent methyl orange adsorbents, removing the anionic dye with an efficiency >99% in just 15-20 min. The POPs were also effective for methylene blue cationic dye removal from water, reaching efficiencies up to ca. 99.4%, possibly due to favorable interactions via deprotonation of T-POP3 carboxyl groups. The modification of the most basic polymers, T-POP1 and T-POP2, with copper(II) allowed the best efficiencies in Henry reactions catalysis, leading to excellent conversions (97%) and selectivities (99.9%).

Exploring key physicochemical sediment properties influencing bioleaching of heavy metals

Bioleaching is a promising technology to remediate sediments contaminated by heavy metals. However, the complex heterogeneities of the sediments can reduce the acidification efficiency and the heavy metal removal rate, thus hindering the practical application of sediment bioleaching. This experiment conducted comparative bioleaching experiments between the inoculated group (average leaching percentages: Cu 67.64%; Zn 54.44%; Ni 29.59%) and the non-inoculated control group (Cu 37.10%; Zn 41.04%; Ni 19.89%) on 28 sediments characterized by different physicochemical properties to explore the key factors influencing bioleaching. The results indicated that the bioleaching process was predominated by the indigenous bioleaching bacteria and the bioleaching inoculum, respectively. The ACC_pH=4 (acid-consuming capacity), TOC (total organic carbon), and TN (total nitrogen) of the sediments played an essential role in influencing the microbial community structure and bioleaching performance: the ACC_pH=4, as the inhibitive factor, could influence the succession growth of the indigenous bioleaching bacteria and the inoculum during the bioleaching process, while the TOC and TN, as the contributing factor, could influence the metabolism of the indigenous bioleaching bacteria. Based on these results, the bioleaching process was improved with the classification and pretreatments of sediment to realize successful bioleaching of all types of the sediments examined in this research.

Carbon Nanostructures-Silica Aerogel Composites for Adsorption of Organic Pollutants

Silica aerogels are a class of materials that can be tailored in terms of their final properties and surface chemistry. They can be synthesized with specific features to be used as adsorbents, resulting in improved performance for wastewater pollutants' removal. The purpose of this research was to investigate the effect of amino functionalization and the addition of carbon nanostructures to silica aerogels made from methyltrimethoxysilane (MTMS) on their removal capacities for various contaminants in aqueous solutions. The MTMS-based aerogels successfully removed various organic compounds and drugs, achieving adsorption capacities of 170 mg⋅g^-1 for toluene and 200 mg⋅g^-1 for xylene. For initial concentrations up to 50 mg⋅L^-1, removals greater than 71% were obtained for amoxicillin, and superior to 96% for naproxen. The addition of a co-precursor containing amine groups and/or carbon nanomaterials was proven to be a valuable tool in the development of new adsorbents by altering the aerogels' properties and enhancing their adsorption capacities. Therefore, this work demonstrates the potential of these materials as an alternative to industrial sorbents due to their high and fast removal efficiency, less than 60 min for the organic compounds, towards different types of pollutants.

Molecular Sieve, Halloysite, Sepiolite and Expanded Clay as a Tool in Reducing the Content of Trace Elements in Helianthus annuus L. on Copper-Contaminated Soil

The aim of this study was to determine the effect of copper soil contamination on the trace element content of sunflower aerial parts and in roots. Another aim was to assess whether the introduction of selected neutralizing substances (molecular sieve, halloysite, sepiolite and expanded clay) into the soil could reduce the impact of copper on the chemical composition of sunflower plants. Copper soil contamination with 150 mg Cu²⁺ kg^-1 of soil and 10 g of each adsorbent per kg of soil were used. Soil contamination with copper caused a significant increase in the content of this element in the aerial parts (by 37%) and roots (by 144%) of sunflower. Enriching the soil with the mineral substances reduced the amount of copper in the aerial parts of sunflower. Halloysite had the greatest effect (35%), while expanded clay had the smallest effect (10%). An opposite relationship was found in the roots of this plant. In copper-contaminated objects, a decrease in the content of cadmium and iron and an increase in the concentrations of nickel, lead and cobalt in the aerial parts and roots of sunflower were observed. The applied materials reduced the content of the remaining trace elements more strongly in the aerial organs than in the roots of sunflower. Molecular sieve had the greatest reducing effect on the content of trace elements in sunflower aerial organs, followed by sepiolite, while expanded clay had the least impact. The molecular sieve also reduced the content of iron, nickel, cadmium, chromium, zinc and, especially, manganese, whereas sepiolite reduced the content of zinc, iron, cobalt, manganese and chromium in sunflower aerial parts. Molecular sieve contributed to a slight increase in the content of cobalt, while sepiolite had the same effect on the content of nickel, lead and cadmium in the aerial parts of sunflower. All materials decreased the content of chromium in sunflower roots, molecular sieve-zinc, halloysite-manganese, and sepiolite-manganese and nickel. The materials used in the experiment, especially the molecular sieve and to a lesser extent sepiolite, can be used effectively to reduce the content of copper and some other trace elements, particularly in the aerial parts of sunflower.

Superinsulating nanocellulose aerogels: Effect of density and nanofiber alignment

Cellulose aerogels are potential alternatives to silica aerogels with advantages in cost, sustainability and mechanical properties. However, the density dependence of thermal conductivity (λ) for cellulose aerogels remains controversial. Cellulose aerogels were produced by gas-phase pH induced gelation of TEMPO-oxidized cellulose nanofibers (CNF) and supercritical drying. Their properties are evaluated by varying the CNF concentration (5-33 mg·cm^-3) and by uniaxial compression (9-115 mg·cm^-3). The aerogels are transparent with specific surface areas of ~400 m²·g^-1, mesopore volumes of ~2 cm³·g^-1 and a power-law dependence of the E-modulus (α ~ 1.53, and the highest reported E of ~1 MPa). The dataset confirms that λ displays a traditional U-shaped density dependence with a minimum of 18 mW·m^-1·K^-1 at 0.065 g·cm^-3. For a given density, λ is ~5 mW·m^-1·K^-1 lower for compressed aerogels due to the alignment of nanofibers, confirmed by small angle X-ray scattering (SAXS).

A back propagation neural network model for accurately predicting the removal efficiency of ammonia nitrogen in wastewater treatment plants using different biological processes

Accurately predicting the water quality of treated water from a water treatment plant (WWTP) based on the obtained operating database is of great significance. However, it is difficult for common mechanistic models to work well. In this study, a back propagation artificial neural network (BPANN) model with high accuracy was developed to predict the denitrification efficiency based on a 1-year operating database. Standardized principal component analysis (PCA) methods were used to address the data, and the PCA processed data exhibited the best accuracy. In three WWTPs adopting the anaerobic/anoxic/oxic (A²O) process, the ammonia nitrogen removal efficiency of WWTPs was successfully predicted by using five variables: inlet flow rate, pH value, original ammonia nitrogen concentration, Chemical oxygen demand (COD) concentration, and total phosphorus concentration. Importantly, the obtained BPANN model can be effectively used for other widely used treatment processes, such as oxidation ditch (OD), sequencing batch reactor activated sludge process (SBR), membrane bioreactor (MBR), and cyclic activated sludge technology (CAST), by simply optimizing the training data ratios between 50/50 and 90/10. This is the first trial to set up a universal model for predicting the denitrification efficiency of WWTPs adopting common biological processes. The model could be used to choose the optimum treatment process in the new WWTP design or take action in advance to avoid the risk of excessive emissions when the already built WWTPs are subjected to sudden shocks.

β-Ketoenamine Covalent Organic Frameworks—Effects of Functionalization on Pollutant Adsorption

Water pollution due to global economic activity is one of the greatest environmental concerns, and many efforts are currently being made toward developing materials capable of selectively and efficiently removing pollutants and contaminants. A series of β-ketoenamine covalent organic frameworks (COFs) have been synthesized, by reacting 1,3,5-triformylphloroglucinol (TFP) with different C2-functionalized and nonfunctionalized diamines, in order to evaluate the influence of wall functionalization and pore size on the adsorption capacity toward dye and heavy metal pollutants. The obtained COFs were characterized by different techniques. The adsorption of methylene blue (MB), which was used as a model for the adsorption of pharmaceuticals and dyes, was initially evaluated. Adsorption studies showed that –NO₂ and –SO₃H functional groups were favorable for MB adsorption, with TpBd(SO₃H)₂-COF [100%], prepared between TFP and 4,4′-diamine- [1,1′-biphenyl]-2,2′-disulfonic acid, achieving the highest adsorption capacity (166 ± 13 mg g⁻¹). The adsorption of anionic pollutants was less effective and decreased, in general, with the increase in –SO₃H and –NO₂ group content. The effect of ionic interactions on the COF performance was further assessed by carrying out adsorption experiments involving metal ions. Isotherms showed that nonfunctionalized and functionalized COFs were better described by the Langmuir and Freundlich sorption models, respectively, confirming the influence of functionalization on surface heterogeneity. Sorption kinetics experiments were better adjusted according to a second-order rate equation, confirming the existence of surface chemical interactions in the adsorption process. These results confirm the influence of selective COF functionalization on adsorption processes and the role of functional groups on the adsorption selectivity, thus clearly demonstrating the potential of this new class of materials in the efficient and selective capture and removal of pollutants in aqueous solutions.

Advances in the application of immobilized enzyme for the remediation of hazardous pollutant: A review

Nowadays, ecofriendly, low-cost, and sustainable alternatives techniques have been focused on the effective removal of hazardous pollutants from the water streams. In this context, enzyme immobilization seems to be of specific interest to several researchers to develop novel, effective, greener, and hybrid strategies for the removal of toxic contaminants. Immobilization is a biotechnological tool, anchoring the enzymes on support material to enhance the stability and retain the structural conformation of enzymes for catalysis. Recyclability and reusability are the main merits of immobilized enzymes over free enzymes. Studies showed that immobilized enzyme laccase can be used up to 7 cycles with 66% efficiency, peroxidase can be recycled to 2 cycles with 50% efficiency, and also cellulase to 3 cycles with 91% efficiency. In this review, basic concepts of immobilization, different immobilization techniques, and carriers used for immobilization are summarized. In addition to that, the potential of immobilized enzymes as the bioremediation agents for the effective degradation of pollutants from the contaminated zone and the impact of different operating parameters are summarized in-depth. Further, this review provides future trends and challenges that have to be solved shortly for enhancing the potential of immobilized systems for large-scale industrial wastewater treatment.

Ultrasensitive detection of mercury(II) ions on a hybrid film of a graphene and gold nanoparticle-modified electrode

Aggravated by human and industrial activities, heavy metal pollution has become a severe problem, causing widespread concern in society, and cannot be ignored. Herein, a graphene/gold nanoparticle-hybrid (AuNPs/ERGO) was proposed and synthesized by electrochemical methods. Based on the AuNPs/ERGO hybrid, a novel electrochemical sensing platform was established and successfully applied for the selective, quantitative detection of Hg²⁺, taking advantage of the well-established anodic stripping voltammetry (ASV). This hybrid material not only increases the surface area and charge transfer rate but also provides more active sites for Hg deposition due to the formation of homogeneous, high density and monodispersed AuNPs on the ERGO film. The prepared AuNPs/ERGO hybrid was modified on a glassy carbon electrode (GCE) to detect Hg²⁺ with a linear range from 0.5 to 20 μg L^-1 and a low limit of detection (LOD) of 0.06 μg L^-1. The selectivity and stability of the as-prepared electrode were investigated and showed promising results. In addition, a screen-printed carbon electrode (SPCE) was also employed to verify the practical application ability of our assay with an excellent performance, which presents a bright application prospect for in situ Hg²⁺ detection.

Biochar Alleviates Phytotoxicity by Minimizing Bioavailability and Oxidative Stress in Foxtail Millet (Setaria italica L.) Cultivated in Cd- and Zn-Contaminated Soil

Soil contamination with multiple heavy metals is a global environmental issue that poses a serious threat to public health and ecological safety. Biochar passivation is an efficient and economical technology to prevent heavy metal contamination of Cd; however, its effects on compound-contaminated and weakly alkaline soil remain unclear. Further, the mechanisms mediating the immobilization effects of biochar have not been evaluated. In this study, three biochar treated at different pyrolytic temperatures [300°C (BC300), 400°C (BC400), and 500°C (BC500)] were applied to Cd-/Zn-contaminated soils, and their effects on plant growth, photosynthetic characteristics, Cd/Zn accumulation and distribution in foxtail millet were evaluated. Further, the effect of biochar application on the soil physicochemical characteristics, as well as the diversity and composition of the soil microbiota were investigated. Biochar significantly alleviated the phytotoxicity of Cd and Zn. DTPA (diethylenetriamine pentaacetic acid)-Cd and DTPA-Zn content was significantly reduced following biochar treatment via the transformation of exchangeable components to stable forms. BC500 had a lower DTPA-Cd content than BC300 and BC400 by 42.87% and 39.29%, respectively. The BC500 passivation ratio of Cd was significantly higher than that of Zn. Biochar application also promoted the growth of foxtail millet, alleviated oxidative stress, and reduced heavy metal bioaccumulation in shoots, and transport of Cd from the roots to the shoots in the foxtail millet. The plant height, stem diameter, biomass, and photosynthetic rates of the foxtail millet were the highest in BC500, whereas the Cd and Zn content in each organ and malondialdehyde and hydrogen peroxide content in the leaves were the lowest. Moreover, biochar application significantly increased the abundance of soil bacteria and fungi, as well as increasing the fungal species richness compared to no-biochar treatment. Overall, biochar was an effective agent for the remediation of heavy metal-contaminated soil. The passivation effect of biochar exerted on heavy metals in soil was affected by the biochar pyrolysis temperature, with BC500 showing the best passivation effect.

Cyclodextrin-Based Nanosponges: Overview and Opportunities

Nanosponges are solid cross-linked polymeric nano-sized porous structures. This broad concept involves, among others, metal organic frameworks and hydrogels. The focus of this manuscript is on cyclodextrin-based nanosponges. Cyclodextrins are cyclic oligomers of glucose derived from starch. The combined external hydrophilicity with the internal hydrophobic surface constitute a unique "microenvironment", that confers cyclodextrins the peculiar ability to form inclusion host‒guest complexes with many hydrophobic substances. These complexes may impart beneficial modifications of the properties of guest molecules such as solubility enhancement and stabilization of labile guests. These properties complemented with the possibility of using different crosslinkers and high polymeric surface, make these sponges highly suitable for a large range of applications. Despite that, in the last 2 decades, cyclodextrin-based nanosponges have been developed for pharmaceutical and biomedical applications, taking advantage of the nontoxicity of cyclodextrins towards humans. This paper provides a critical and timely compilation of the contributions involving cyclodextrins nanosponges for those areas, but also paves the way for other important applications, including water and soil remediation and catalysis.

Enhanced desorption of cationic and anionic metals/metalloids from co-contaminated soil by tetrapolyphosphate washing and followed by ferrous sulfide treatment

In this study, a novel approach was employed for the remediation of cationic and anionic metals/metalloids co-contaminated soil by tetrapolyphosphate enhanced soil washing coupled with ferrous sulfide treatment. Tetrapolyphosphate could simultaneously enhance the desorption of cationic metals (Pb and Zn) and anionic metal/metalloid (Cr and As) from the contaminated soil in the whole tested pH range of 2-10. With addition of 0.15 mol/L tetrapolyphosphate at pH 7.0, the removal ratio of Pb, Zn, As and Cr could achieve 83.1%, 70.4%, 75.7% and 66.4% respectively. The fractionation analysis of heavy metals/metalloids demonstrated the release of exchangeable and Fe/Mn bound forms contributed to most desorption of Pb and Zn. The decreases of non-specifically sorbed form and amorphous and poorly-crystalline hydrous oxides of Fe and Al bound form were responsible for most removal of As. The comparison with other common washing agents (EDTA, oxalate and phosphate) under their respective optimal dosage could confirm that tetrapolyphosphate was superior to simultaneously desorb the cationic and anionic metals/metalloids with higher efficiency. After 12 h, applying 150 mg/L FeS at pH 3.5 could totally remove Pb, Zn, As and Cr from the washing effluent by sulfide precipitation, reduction and adsorption processes. Higher pH would inhibit the removal of As and Cr by FeS. Meanwhile, the residual of tetrapolyphosphate could be totally recovered from the washing effluent by employing anion exchange resin. This study suggests tetrapolyphosphate enhanced soil washing coupled with ferrous sulfide treatment is a promising approach for remediation of cationic and anionic metals/metalloids co-contaminated soil in view of its high efficiency and simple operation.

Heavy Metals and As in Ground Water, Surface Water, and Sediments of Dexing Giant Cu-Polymetallic Ore Cluster, East China

Heavy metals and As (HMs) pollution in mining areas are a widespread environmental concern. In this study, ground water, surface water, and sediment samples around the Dexing area, one of the largest Cu-polymetallic ore clusters in China, were collected to examine the concentrations and distributions of As, Cd, Cr, Cu, Hg, Pb, and Zn. Pollution indices, geo-accumulation index, and potential ecological risk index were used to estimate the pollution characteristics and ecological risk of HMs. The results show that the major pollutants in the surface water were Cd, Cu, Zn, and Pb, while the dominant ecological risk of HMs in the sediments originated from Cu, As, Hg, and Cd. Moreover, HMs in the surface water and sediments exhibited substantial spatial heterogeneity in the study area, indicating a severely disturbed environment due to mining activities. The proportions of HM pollutions were higher in the Dexing River and its tributaries than in the Le’an River and its tributaries. The surface water pollution was predominant at the tributaries closest to the mine area, while the sediment contamination has been expanded several kilometers downstream of the major rivers. Overall, the ecological risk of HMs was higher in the sediments than in the surface water.

Microplastics and environmental pollutants: Key interaction and toxicology in aquatic and soil environments

Nowadays, a growing number of microplastics are released into the environment due to the extensive use and inappropriate management of plastic products. With the increasing body of evidence about the pollution and hazards of microplastics, microplastics have drawn major attention from governments and the scientific community. As a kind of emerging and persistent environmental pollutants, microplastics have recently been detected on a variety of substrates in the world. Therefore, this paper reviews the recent progress in identifying the sources of microplastics in soil, water, and atmosphere and describing the transport and fate of microplastics in the terrestrial, aquatic and atmospheric ecosystems for revealing the circulation of microplastics in the ecosystem. In addition, considering the persistence of microplastics, this study elucidates the interactions of microplastics with other pollutants in the environment (i.e., organic pollutants, heavy metals) with emphasis on toxicity and accumulation, providing a novel insight into the ecological risks of microplastics in the environment. The negative impacts of microplastics on organisms and environmental health are also reviewed to reveal the environmental hazards of microplastics. The knowledge gaps and key research priorities of microplastics are identified to better understand and mitigate the environmental risks of microplastics.

Effect of Sorbent Additives to Copper-Contaminated Soils on Seed Germination and Early Growth of Grass Seedlings

Heavy metal and metalloid-contaminated soil is a serious barrier to colonization for many plant species. The problem of the elimination of toxic waste accumulated in technogenous soils in many highly transformed regions is extremely important. Hence, another attempt was made to analyze the effect of the addition of sorbents (BCH-biochar, B-bentonite, ChM-chicken manure, OS-organo-zeolitic substrate) to contaminated copper soil on the germination and early growth of Eurasian common grass species (Agrostis capillaris, A. stolonifera, Festuca rubra and Poa pratensis), which could potentially be used in recultivation. This experiment was based on the laboratory sandwich method. Standard germination indexes, morphometry and biomass analysis were used. The percentage of germinating seeds was lower in each of the soil variants and sorbents used compared to the control. Dry mass was positively stimulated by all sorbents. The response to the addition of sorbents, expressed as the electrolyte leakage of seedlings, was different depending on the species and type of sorbent. Among all sorbents, the most positive effects on germination and growth were observed in the case of OS. Overall, the response to the addition of sorbents was different in the studied species, depending on their stage of development.

Underestimated heavy metal pollution of the Minjiang River, SE China: Evidence from spatial and seasonal monitoring of suspended-load sediments

Previous assessments on rivers in SE China with highly developed economy and enormous population indicate diverse and relatively low particulate heavy metal pollution levels. However, the controlling mechanisms for heavy metal enrichment and transport remain enigmatic. Here, we target a mesoscale mountainous river, the Minjiang River, and obtain grain size, mineralogical and heavy metal concentration (Pb, Cd, Cr, Mn, Mo, Zn, V, Co, Ni, Cu) data from seasonal suspended particulate matter (SPM) near the river mouth, riverbed sediments and SPM samples from mainstream and major tributaries of the river. The results indicate that SPM samples have higher particulate heavy metal concentrations than riverbed sediments collected in pairs. Heavy metal concentrations of Cd, Zn, Cr, V, Co, Ni and Cu are higher in upstream SPM samples than those in downstream regions, whereas Pb, Mn and Mo concentrations don't show this spatial variation. Most heavy metals (e.g., Pb and Zn) show high concentrations in flood seasons and relatively low concentrations in dry seasons, revealing a hydrologic control. However, Cr and Mn show high concentrations in some dry season samples, suggesting incidental anthropogenic input events. The SPM-based pollution assessments using enrichment factor, geoaccumulation index and potential ecological risk index demonstrate that the Minjiang River is moderately to strongly polluted by particulate Pb, Cd, Mo and Zn contaminations and most particulate heavy metals have moderate to considerable potential ecological risks. We contend that transport and discharge of particulate heavy metals by the Minjiang River are controlled by both natural and anthropogenic forcings and the pollution levels are worse than previously known. Our findings suggest that particulate heavy metal discharge by subtropical mountainous rivers is related to sediment types and hydrologic characteristics. Therefore, high-spatiotemporal-resolution investigations on river SPM samples are highly recommended to better evaluate particulate heavy metal pollution levels and aquatic environmental conditions.

Ligands as copper and nickel ionophores: Applications and implications on wastewater treatment

Modern society depends on many finite natural resources, from which metals are of great importance. Copper and nickel's relevance is due to their vast applications, resulting in high market value and demand. As such, their polluting emissions are also significant and their removal from wastewaters is imperative. Moreover, effluent treatment techniques can be used to recover the metallic cations, via selective processes. In this review, copper and nickel selective ligands in the literature are surveyed. These are most commonly Schiff bases, along with crown ethers and porphyrins. They are usually employed in ion sensing (colorimetric chemosensors or electrodes) with great success - the disruption in response of colorimetric sensors is up to 7% and binding constants are usually at least one order of magnitude greater with the desired cation than with interferents. However, modified adsorbents are also reported. The possibilities of using ionophores in wastewater cleaning, allowing the treatment of effluents and the selective recovery of valuable materials, and their implications on new green policies is discussed.

Simultaneous leaching of multiple heavy metals from a soil column by extracellular polymeric substances of Aspergillus tubingensis F12

The use of the biological agents for leaching heavy metals from contaminated soils is a very promising method that is both efficient and eco-friendly. In this study, a fungus Aspergillus tubingensis F12 was reported to possess a strong adsorption capacity for various heavy metal ions and shown to adsorb 90.8% Pb, 68.4% Zn, 64.5% Cr, 13.1% Cu, 12.9% Ni, and 6.9% Cd in aqueous solution. As extracellular polymeric substance (EPS) was found to play a leading role in the adsorption of metal ions, we applied EPS as a leaching agent to simultaneously remove six metals from soil in a column leaching experiment. The flow rate, initial solution pH, initial EPS concentration, and ionic strength were investigated using response surface methodology. The minimum and maximum metal leaching capacities were determined to be 0.089 mg/g and 3.703 mg/g, respectively. Verified by Fourier transform infrared spectroscopy, scanning electron microscope energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, we made the preliminary deductions that ion exchange determines the leaching capacity limit and that biosorption plays a large role in reaching that limit. Additionally, the redox behaviour of Cu produced more carboxyl groups, which increased the adsorption of heavy metals. The ecological impact of this method was also examined; we found that the influences of leaching with EPS on soil properties and microbial community structure were slight. Therefore, the reported leaching process might have application prospects for metal removal from soil.

An overview on alumina-silica-based aerogels

Silica aerogels are remarkable materials with excellent physicochemical properties, such as high porosity and surface area, along with low density and thermal conductivity. In addition to their outstanding properties, these materials are quite interesting due to the possibility to change their chemistry according to intended applications. However, they also show some disadvantages, like low mechanical strength and poor dimensional stability under high temperatures (above 600 °C). Although these aerogels are frequently used as thermal insulators, for high temperature environments some of their properties need to be improved. The mixing with other ceramic thermally resistant phases is a viable approach. Thus, this work presents an overview on alumina-silica-based aerogels, describing their synthesis, processing and properties. The improvement on their properties will be discussed as a function of the amount of refractory phase (alumina) in the silica matrix. The introduction of the alumina phase makes them stable until 1200-1400 °C, maintaining low values of thermal conductivity at very high temperature (below 81 mW m^-1 K^-1). Finally, a brief survey on the most promising applications of these materials is presented, with several examples. In catalysis, alumina-silica aerogels have shown equivalent performance when compared to reference catalysts. In the field of thermal insulation, these materials show great potential, especially in high temperatures environments, due to their thermal dimensional stability and inherent low thermal conductivity. As adsorbents, higher stability and adsorption capacity were obtained with the incorporation of the alumina phase in silica aerogels, and these materials can be reused for repeated adsorption/desorption cycles. Indeed, a significant improvement of the aerogel performance by the synergetic effect of combining silica and alumina phases is usually obtained, supporting the expectation of the extension of their fields of application.

Naturally available diatomite and their surface modification for the removal of hazardous dye and metal ions: A review

The presence of toxic pollutants such as dyes and metal ions at higher concentrations in water is very harmful to the environment. Removal of these pollutants using diatomaceous earth or diatomite (DE) and surface-modified DE has been extensively explored due to their excellent physio-chemical properties and low cost. Therefore, naturally available DE being inexpensive, their surface modified adsorbents could be one of the potential candidates for the wastewater treatment in the future. In this context, the current review has been summarized for the removal of both pollutants i.e., dyes and metal ions by surface-modified DE using the facile adsorption process. In addition, this review is prominently focused on the various modification process of DE, their cost-effectiveness; the physio-chemical characteristics and their maximum adsorption capacity. Further, real-time scenarios of reported adsorbents were tabulated based on the cost of the process along with the adsorption capacity of these adsorbents.

Silica Aerogels/Xerogels Modified with Nitrogen-Containing Groups for Heavy Metal Adsorption

Heavy metals are common inorganic pollutants found in the environment that have to be removed from wastewaters and drinking waters. In this work, silica-derived aerogels and xerogels were modified via a co-precursor method to obtain functional adsorbents for metal cations. A total of six formulations based upon four different functional precursors were prepared. The materials′ structural characterization revealed a decreased porosity and surface area on modified samples, more prominent in xerogel counterparts. Preliminary tests were conducted, and the prepared samples were also compared to activated carbon. Three samples were selected for in-depth studies. Isotherm studies revealed that the pre-selected samples remove well copper, lead, cadmium and nickel, and with similar types of interactions, following a Langmuir trend. The adsorption kinetics starts very fast and either equilibrium is reached quickly or slowly, in a two-stage process attributed to the existence of different types of active sites. Based on the previous tests, the best sample, prepared by mixing different functional co-precursors, was selected and its behavior was studied under different temperatures. For this material, the adsorption performance at 20 °C is dependent on the cation, ranging from 56 mg·g⁻¹ for copper to 172 mg·g⁻¹ for lead.

2-Hydroxymelatonin mitigates cadmium stress in cucumis sativus seedlings: Modulation of antioxidant enzymes and polyamines

Cadmium level is continuously increasing in agricultural soils mainly due to anthropogenic activities. Cadmium is one of the most phytotoxic metals in the soils. The present study investigates the possible role of 2-hydroxymelatonin (2-OHMT) in assuagement of Cd-toxicity in cucumber (Cucumis sativus L.) plants. 2-OHMT is an important metabolite produced through interaction of melatonin with oxygenated compounds. Cadmium stress decreased the activity of antioxidant enzymes and polyamines. However, exogenously applied 2-OHMT enhanced plant growth attributes including photosynthetic rate, intercellular CO2 concentration, stomatal conductance and transpiration rate in treated plants. In addition, 2-OHMT induced enhancement of the activity of PAs biosynthesizing enzymes (putrescine, spermidine and spermine) in conjunction with reduction in activity of polyamine oxidase (PAO). 2-OHMT mitigated Cd stress through up-regulation in expression of stress related CS-ERS gene along with the amplified activity of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) in treated seedlings. The improved activity of antioxidant scavengers played central role in reduction of hydrogen peroxide (H2O2), electrolyte leakage (EL) and malondialdehyde (MDA) in plants under Cd stress. Recent findings also advocate the positive correlation between PAs and ethylene, as both possess common precursor. The current study reveals that priming seeds with 2-OHMT reduces Cd-toxicity and makes it possible to cultivate cucumber in Cd-contaminated areas. Future experiments will perhaps help in elucidation of 2-OHMT intervened stress mitigation procedure in C. sativus crop. Furthermore, research with reference to potential of 2-OHMT for stress alleviation in other horticultural and agronomic crops will assist in enhancement of crop productivity.

Geo- and nano-materials affect the mono-metal and competitive sorption of Cd, Cu, Ni, and Zn in a sewage sludge-treated alkaline soil

We evaluated the effect of geomaterials (modified zeolite and bentonite using CaCl₂) and nanoparticles (ZnO and MgO) on the mono-metal and competitive sorption of cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) in an alkaline soil treated with three sewage sludges (SSs) collected from Isfahan, Rasht and Shiraz, Iran. The three SSs increased Cu sorption compared to the control. Sorption of Cd and Zn increased by the addition of Isfahan SS, but decreased by that of Rasht SS. Isfahan SS increased significantly the distribution coefficient of Cd, Cu, and Zn by 1.9, 1.2 and 1.5 times, respectively, compared to the control. The geomaterials and nanoparticles increased metal sorption in the SS-amended soil. Zeolite and MgO were the best sorbents for Cu in Rasht and Shiraz SS-treated soil, while ZnO and MgO were better in Isfahan SS-treated soil. Bentonite showed the highest Cd sorption capacity in Isfahan SS-treated soil, and MgO in the Shiraz SS-treated soil. ZnO showed the highest sorption capacity for Ni among the three SSs treatments. The nanoparticles showed higher sorption capacity for Zn than the geomaterials. We conclude that zeolite, bentonite, ZnO and MgO could be suitable immobilizing agents for Cd, Cu, Ni, and Zn in SS-amended alkaline soils.

Amine Modification of Silica Aerogels/Xerogels for Removal of Relevant Environmental Pollutants

Serious environmental and health problems arise from the everyday release of industrial wastewater effluents. A wide range of pollutants, such as volatile organic compounds, heavy metals or textile dyes, may be efficiently removed by silica materials advanced solutions such as aerogels. This option is related to their exceptional characteristics that favors the adsorption of different contaminants. The aerogels performance can be selectively tuned by an appropriate chemical or physical modification of the aerogel's surface. Therefore, the introduction of amine groups enhances the affinity between different organic and inorganic contaminants and the silica aerogels. In this work, different case studies are reported to investigate and better understand the role of these functional groups in the adsorption process, since the properties of the synthesized aerogels were significantly affected, regarding their microstructure and surface area. In general, an improvement of the removal efficiency after functionalization of aerogels with amine groups was found, with removal efficiencies higher than 90% for lead and Rubi Levafix CA. To explain the adsorption mechanism, both Langmuir and Freundlich models were applied; chemisorption is most likely the sorption type taking place in the studied cases.

Assessment of heavy metal pollution from anthropogenic activities and remediation strategies: A review

Heavy metal pollution is a nefarious issue with implications for life. Heavy metals are natural occurring elements, having both natural and anthropogenic sources. The latter are however the most significant, releasing greater amounts of these pollutants in more toxic and mobile forms. Their chemistry and dynamics in the ecosystems are presented, and the relation to the pollution problematic thereof is discussed. The concentration of heavy metals in several sites, assessed in water, soil and sediment samples, affected by different pollution sources are reviewed. These evidence how human activities impact natural media and how the pollution spreads. The pollution in each media is assessed by the concentration relative to drinking and irrigation water guidelines, and by the geoaccumulation index of soils and sediments. It is found that ore extraction and processing and metallurgical industries stand atop the most polluting sources. Given the dynamics of heavy metal cations and that, most of these are released in liquid effluents, wastewater treatment techniques for the removal of heavy metals are also surveyed and critically discussed. Economic viability at a large municipal scale and the ability to comply with strict regulations are the determining factors in the selection of these techniques. A critical discussion on the viability of such techniques is made, reviewing some literature studies and commenting on their applicability on the previously found polluted media.

Use of an Environmental Pollutant From Hexavalent Chromium Removal as a Green Catalyst in The Fenton Process

The present study refers to the use of an environmental pollutant generated during the removal of hexavalent chromium from aqueous media. This pollutant is a material with catalytic properties suitable for application in the oxidative degradation of problematic organic compounds. The material, initially used as an adsorbent, is a composite prepared by modifying the crystalline phases of iron oxides together with the chitosan (CT-FeCr). Chemical and morphological characterizations of the materials were performed using SEM analysis coupled with EDS, XRD and DSC. The CT-FeCr beads were used in the degradation of methylene blue dye (MB) and showed excellent degradation potential (93.6%). The presence of Cr on the surface of the catalyst was responsible for the increase in catalytic activity compared to the CT-Fe and pure magnetite materials. The product of the effluent treatment and the presence of the catalyst itself in the environment do not pose toxic effects. In addition, the CT-FeCr beads showed catalytic stability for several consecutive reaction cycles with possible technical and economic viability. The concept of "industrial symbiosis" may be applied to this technology, with that term relating to the reuse of a byproduct generated in one particular industrial sector by another as a raw material.

Removal of Heavy Metal Water Pollutants (Co2+ and Ni2+) Using Polyacrylamide/Sodium Montmorillonite (PAM/Na-MMT) Nanocomposites

Nanocomposites composed of polyacrylamide and nanoclay were synthesized via free-radical cross-linking polymerization and used to adsorb Co²⁺ and Ni²⁺ ions from water. The polyacrylamide (PAM)/sodium montmorillonite (Na-MMT) nanocomposites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy to confirm the interaction between montmorillonite and the polymer matrix. The effects of pH and heavy metal ion concentration on the adsorption capacity of PAM/Na-MMT were evaluated to determine suitable operating conditions for further experiments. Batch adsorption experimental data were fitted to Langmuir and Freundlich models, which provided information about the adsorption mechanism and the adsorbent surface. The highest Ni²⁺ removal yield was found to be 99.3% using the 2:1 (w/w) nanocomposite at pH 6 in 100 ppm of Ni²⁺ solution. The Co²⁺ removal yield was 98.7% at pH 6 in 60 ppm of Co²⁺ solution using the 4:1 (w/w) nanocomposite. These results were higher than those obtained by polyacrylamide and nanoclay under the same conditions (removal yield between 87.40 and 94.50%), indicating that PAM/Na-MMT nanocomposites remove heavy metal water pollutants more efficiently and can be used as a novel adsorbent for further industrial applications.

Lead removal by phosphate solubilizing bacteria isolated from soil through biomineralization

Microorganisms with the function of biological mineralization were isolated from a soil. The bacteria were identified by 16S rRNA as Bacillus sp and possessed a significant lead removal ability. Lead removal experiment indicated that the mathematical model of η=η_max-η_ce^t/k fit the variation of removal rate with time well. Different from the previous studies, this work discovered that the culture medium had the ability to remove aqueous lead (Pb²⁺). At the same dosage, the removal rates of Pb²⁺ followed the order of: cells < culture medium < metabolites < bacterial suspension. The lead removal mechanism was further explored using the techniques of XRD, FTIR, and SEM. The results showed that during the fermentation, the bacteria decomposed phosphate-containing organic compounds in the culture medium to generate a large amount of phosphate groups on the surface of the bacterial cells. Pb²⁺ was precipitated in the form of Pb₃(PO₄)₂ stable minerals.

An Opinion Paper on Aerogels for Biomedical and Environmental Applications

Aerogels are a special class of nanostructured materials with very high porosity and tunable physicochemical properties. Although a few types of aerogels have already reached the market in construction materials, textiles and aerospace engineering, the full potential of aerogels is still to be assessed for other technology sectors. Based on current efforts to address the material supply chain by a circular economy approach and longevity as well as quality of life with biotechnological methods, environmental and life science applications are two emerging market opportunities where the use of aerogels needs to be further explored and evaluated in a multidisciplinary approach. In this opinion paper, the relevance of the topic is put into context and the corresponding current research efforts on aerogel technology are outlined. Furthermore, key challenges to be solved in order to create materials by design, reproducible process technology and society-centered solutions specifically for the two abovementioned technology sectors are analyzed. Overall, advances in aerogel technology can yield innovative and integrated solutions for environmental and life sciences which in turn can help improve both the welfare of population and to move towards cleaner and smarter supply chain solutions.

Immobilization of Lead and Nickel Ions from Polluted Yam Peels Biomass Using Cement-Based Solidification/Stabilization Technique

Nowadays, biomass has been employed to prepare biosorbents for heavy metals uptake; however, further disposal of polluted material has limited its application. In this work, nickel and lead removal was performed using yam peels and the resulting polluted biomass was mixed with concrete to produce bricks. The biomass was characterized by FT-IR analysis for testing functional groups diversification before and after adsorption process. The effect of adsorbent dosage, temperature, and initial solution concentration was evaluated to select suitable values of these parameters. Adsorption results were adjusted to kinetic and isotherm models to determine adsorption mechanism. Desorption experiments were also performed to determine the appropriate desorbing agent as well as its concentration. Immobilization technique of cement-based solidification/stabilization was applied and the polluted biomass was incorporated to concrete bricks at 5 and 10%. Mechanical resistance and leaching tests were carried out to analyze the suitability of heavy metals immobilization. The suitable values for dosage, temperature, and initial solution concentration were 0.5 g/L, 40°C and 100 ppm, respectively. The kinetic model that best fitted experimental results was pseudo-second order indicating a dominant physicochemical interaction between the two phases. The highest desorption yields were found in 52.47 and 74.84% for nickel and lead ions. The concrete bricks exhibited compression resistance above 5 MPa and all the leachate reported concentrations below the environmental limit. These results suggested that nickel and lead immobilization using concrete bricks is a good alternative to meet disposal problems of contaminated biomass.

Efficient adsorption of multiple heavy metals with tailored silica aerogel-like materials

Recently developed tailored adsorbents for heavy metal uptake are studied in batch tests with Cu, Pb, Cd, Ni, Cr and Zn, in order to decontaminate polluted environments where these heavy metals are found in solution - water courses and groundwater. The adsorbents feature mercapto or amine-mercapto groups that are capable of complexating the cations. Through the use of equilibrium tests it is found that a remarkably high heavy metal uptake is obtained for all metals (ranging from 84 to 140 mg/g). These uptake values are quite impressive when compared to other adsorbents reported in the literature, which is also due to the double functionalization present in one of the adsorbents. For the best adsorbent, adsorption capacities followed the order Cu(II) > Pb(II) > Zn(II) > Cr(III) > Cd(II) > Ni(II). With these adsorbents, the removal process was fast with most of the metals being removed in less than 1 h. Competitive sorption tests were performed in tertiary mixtures that were based on real world polluted sites. It was found that although competitive sorption occurs, affecting the individual removal of each metal, all the cations in solution still interact with the adsorbent, achieving removal values that make this type of material very interesting for its proposed application.

Bioavailability and leaching of Cd and Pb from contaminated soil amended with different sizes of biochar

Biochars have been successfully used to reduce bioavailability and leaching of heavy metals in contaminated soils. The efficiency of biochar to immobilize heavy metals can be increased by reducing the particle size, which can increase the surface area and the cation exchange capacity (CEC). In this study, the empty fruit bunch biochar (EFBB) of oil palm was separated into two particle sizes, namely, fine (F-EFBB < 50 µm) and coarse (C-EFBB > 2 mm), to treat the contaminated soil with Cd and Pb. Results revealed that the addition of C-EFBB and F-EFBB increased the pH, electrical conductivity and CEC of the contaminated soil. The amounts of synthetic rainwater extractable and leachable Cd and Pb significantly decreased with the EFBB application. The lowest extractable and leachable Cd and Pb were observed from 1% F-EFBB-treated soil. The amount of extractable and leachable Cd and Pb decreased with increasing incubation times and leaching cycles. The application of F-EFBB to Cd and Pb-contaminated soil can immobilize the heavy metals more than that of C-EFBB. Therefore, the EFBB can be recommended for the remediation of heavy metal-contaminated soils, and a finer particle size can be applied at a lower application rate than the coarser biochar to achieve these goals.

Cellulose Aerogels: Synthesis, Applications, and Prospects

Due to its excellent performance, aerogel is considered to be an especially promising new material. Cellulose is a renewable and biodegradable natural polymer. Aerogel prepared using cellulose has the renewability, biocompatibility, and biodegradability of cellulose, while also having other advantages, such as low density, high porosity, and a large specific surface area. Thus, it can be applied for many purposes in the areas of adsorption and oil/water separation, thermal insulation, and biomedical applications, as well as many other fields. There are three types of cellulose aerogels: natural cellulose aerogels (nanocellulose aerogels and bacterial cellulose aerogels), regenerated cellulose aerogels, and aerogels made from cellulose derivatives. In this paper, more than 200 articles were reviewed to summarize the properties of these three types of cellulose aerogels, as well as the technologies used in their preparation, such as the sol⁻gel process and gel drying. In addition, the applications of different types of cellulose aerogels were also introduced.

Assessing the efficacy over time of the addition of industrial by-products to remediate contaminated soils at a pilot-plant scale

The effect of the addition of industrial by-products (gypsum and calcite) on the leaching of As and metals (Cu, Zn, Ni, Pb and Cd) in a soil contaminated by pyritic minerals was monitored over a period of 6 months at a two-pit pilot plant. The contaminated soil was placed in one pit (non-remediated soil), whereas a mixture of the contaminated soil (80% w/w) with gypsum (10% w/w) and calcite (10% w/w) was placed in the other pit (remediated soil). Soil samples and leachates of the two pits were collected at different times. Moreover, the leaching pattern of major and trace elements in the soil samples was assessed at laboratory level through the application of the pH_stat leaching test. Addition of the by-products led to an increase in initial soil pH from around 2.0 to 7.5, and it also provoked that the concentration of trace elements in soil extracts obtained from the pH_stat leaching test decreased to values lower than quantification limits of inductively coupled plasma optical emission spectrometry and lower than the hazardous waste threshold for soil management. The trace element concentration in the pilot-plant leachates decreased over time in the non-remediated soil, probably due to the formation of more insoluble secondary minerals containing sulphur, but especially decreased in pit of the remediated soil, in agreement with laboratory data. The pH in the remediated soil remained constant over the 6-month period, and the X-ray diffraction analyses confirmed that the phases did not vary over time, thus indicating the efficacy of the addition of the by-products. This finding suggests that soil remediation may be a feasible option for the re-use of non-hazardous industrial by-products.