Cork stoppers as an effective sorbent for water treatment: the removal of mercury at environmentally relevant concentrations and conditions

Use of Biopowders as Adsorbents of Potentially Toxic Elements Present in Aqueous Solutions

This study examines the adsorption and desorption behaviors of phosphorus (P), arsenic (As), fluoride (F), and chromium (Cr) in aqueous solutions on green materials such as cork bark (CB) and pine bark (PB). These materials are characterized by active functional groups and net negative charges on their surfaces and porous structures. The evaluation considers variations in contaminant concentrations (0.01-10 mM) and pH (3.5-12). Cork bark exhibited higher adsorption capacity for As and F, while PB was more effective for P and Cr. Adsorption isotherms followed the Freundlich and Langmuir models, indicating surface heterogeneity and multilayer adsorption for most potentially toxic elements (PTEs). Desorption tests demonstrated low rates, with CB retaining up to 99% of F and 85% of As, and PB achieving up to 86% retention for Cr and 70% for P. The influence of pH was minimal for As, P, and F, but acidic conditions significantly enhanced Cr adsorption, showing similar behavior for both biopowders. These findings suggest that CB and PB biopowders are promising, environmentally friendly biosorbents for the removal of PTEs from aqueous solutions. Their effectiveness varies depending on the specific contaminant. This study highlights the potential of these natural materials for sustainable applications in water treatment and soil remediation.

Effectiveness of cork and pine bark powders as biosorbents for potentially toxic elements present in aqueous solution

Cork oak and pine bark, two of the most prolific byproducts of the European forestry sector, were assessed as biosorbents for eliminating potentially toxic elements (PTEs) from water-based solutions. Our research suggests that bioadsorption stands out as a viable and environmental eco-friendly technology, presenting a sustainable method for the extraction of PTEs from polluted water sources. This study aimed to evaluate and compare the efficiency of cork powder and pine bark powder as biosorbents. Specifically, the adsorption of Fe, Cu, Zn, Cd, Ni, Pb and Sn at equilibrium were studied through batch experiments by varying PTEs concentrations, pH, and ionic strength. Results from adsorption-desorption experiments demonstrate the remarkable capacity of both materials to retain the studied PTE. Cork powder and pine bark powder exhibited the maximum retention capacity for Fe and Cd, while they performed poorly for Pb and Sn, respectively. Nevertheless, pine bark showed a slightly lower retention capacity than cork. Increasing the pH resulted in cork showing the highest adsorption for Zn and the lowest for Sn, while for pine bark, Cd was the most adsorbed, and Sn was the least adsorbed, respectively. The highest adsorption of both materials occurred at pH 3.5-5, depending on the PTE tested. The ionic strength also influenced the adsorption of the various PTEs for both materials, with decreased adsorption as ionic strength increased. The findings suggest that both materials could be effective for capturing and eliminating the examined PTEs, albeit with different efficiencies. Remarkably, pine bark demonstrated superior adsorption capabilities, which were observed to vary based on the specific element and the experimental conditions. These findings contribute to elucidating the bio-adsorption potential of these natural materials, specifically their suitability in mitigating PTEs pollution, and favoring the recycling and revalorization of byproducts that might otherwise be considered residue.

Evaluation of novel biomass-derived materials as binding layers for determining labile mercury in water by diffusive gradient in thin-films technique

In this work, several binding gels were successfully prepared in Diffusive Gradient in Thin-film (DGT) that targeted the inclusion of novel biomass-derived materials for the determination of the labile fraction of mercury (Hg) in water. First, five biomass-derived materials were tested and the descending order as a function of the average percentage of Hg removal in solution was feathers > biochar > cork > canola meal > rice husk. The best two materials were treated and pulverized into powder to be embedded in a hydrogel; and so, feathers were pyrolyzed preserving the sulfur contained in their keratin structure (FBC), and biochar (BC) was modified and pyrolyzed with sublimated sulfur (SBC) to increase the Hg sorption sites in its structure. Analysis by Energy Dispersive X-ray fluorescence (EDXRF) spectrometry confirmed that the different pyrolysis procedures increased sulfur absorption successfully. The efficiency of the new gels (BC, SBC and FBC) in agarose was evaluated by comparative Hg uptake tests, showing a larger efficacy in the following order: SBC > BC > FBC. To assess the suitability of their application in freshwater environments, novel DGT devices were also evaluated to determine their diffusion coefficients (D). This test was conducted under controlled laboratory conditions, with particular focus on the potential competence of trace elements (Mn, Cu, Zn, Ni, Pb, Cd and As), which are commonly present in natural waters affected by mining. A stronger linear relationship between the Hg uptake by binding layers and the deployment time were obtained for the DGT devices with SBC (R2 = 0.948) vs. BC (R2 = 0.885). Therefore, the D obtained for Hg were 8.94 × 10-6 cm2 s-1 for DGT-SBC and 5.12 × 10-6 cm2 s-1 for DGT-BC devices at 25 °C, both within the same order of magnitude reported by previous studies. The good performance obtained by DGT-SBC devices is a promising result and indicates the potential for valorization of waste materials in the DGT technique.

Recovery of palladium from a low grade palladium solution by anionic-ion exchange: kinetics, equilibrium, and metal competition

Petroleum spent catalysts may contain a significant amount of palladium (Pd) together with other major [aluminum (Al), nickel (Ni), and molybdenum (Mo)] and minor [iron (Fe), lead (Pb), and vanadium (V)] elements. Due to the high intrinsic value of Pd and its scarcity in natural ores, its recovery is highly desired. For this purpose, the ability of a strong basic anionic- resin, Purogold™ A194 resin, to remove Pd from the solution was assessed. Data from kinetic and equilibrium studies, performed under batch mode in 1 mol/L of NaCl and 1 mol/L of HNO₃ at (21 ± 1) °C, revealed that the removal of Pd fits well a pseudo-second-order kinetic model [constant rate value, k₂, of (0.062 ± 0.010) g/(mmol.min)] and a Langmuir isotherm [maximum sorption capacity of (0.80 ± 0.02) mmol/g with an affinity of resin binding sites towards Pd, K_L, of (0.18 ± 0.02) L/mmol], respectively. The sorption of other metals (Al, Fe, Pb, Mo, Ni, and V) that may be present in spent catalyst leachates was tested under similar experimental conditions [C_M = 2.5 mmol/L, 1 mol/L of NaCl and 1 mol/L of HNO₃ at (21 ± 1) °C)] and the resin showed little affinity towards each one of these metals. Also, simultaneous multi-element batch experiments with Pd and the major components (M = Al, Ni, and Mo ions) ([M]/[Pd] molar ratios between 3.4 and 52 were used) pointed out that the resin is highly selective towards Pd suggesting that the resin can be used in the selective recovery of Pd from petroleum spent catalyst leachates.

Bioaccumulation processes for mercury removal from saline waters by green, brown and red living marine macroalgae

Mercury is a very toxic metal that persists and accumulates in the living organisms present in the aquatic systems and its elimination is an urgent need. Two green (Ulva intestinalis and Ulva lactuca), brown (Fucus spiralis and Fucus vesiculosus), and red (Gracilaria sp. and Osmundea pinnatifida) marine macroalgae were tested for mercury removal from saline waters. The ability of each species was evaluated to the initial mercury concentrations of 50, 200, and 500 μg dm^-3 along 72 h. In general, all species exhibited good performances, removing 80.9-99.9% from solutions with 50 μg dm^-3, 79.3-98.6% from solutions with 200 μg dm^-3, and 69.8-97.7% from solutions containing 500 μg dm^-3 of mercury. Among the macroalgae, Ulva intestinalis showed the highest affinity to mercury and it presented an uptake ability up to 1888 μg g^-1 of Hg(II) and bioconcentration factors up to 3823, which proved its promising potential on Hg removal.

EFECTO DEL pH EN LAS TASAS DE BIOACUMULACIÓN DE METALES PESADOS EN LA MACROALGA Bostrychia calliptera (Rhodomelaceae, Ceramiales)

Uno de los factores que más influye las características químicas de un metal en solución es el nivel de acidez. El pH por lo tanto, afecta la reactividad del ion y por ende, su interacción con los puntos de unión de la pared celular de la planta. Este estudio evaluó el efecto del pH en la capacidad de bioacumulación de metales pesados en el alga roja Bostrychia calliptera (Rhodophyta, Rhodomelaceae), expuesta a diferentes rangos de pH. Se sometieron talos del alga a diferentes concentraciones de mercurio (Hg) y Plomo (Pb) a concentraciones desde: 0,1 hasta 10 mg l-1, para Hg y desde 0,1 hasta 15 mg l-1 para Pb, durante periodos exposición de 0, 12, 24 y 96 horas para cada ion, bajo diferentes niveles de pH. Las concentraciones de metal fueron determinadas por espectrofotometría de absorción atómica de acuerdo a los métodos estándar APHA. Las mayores tasas de acumulación se encontraron cuando el alga estaba expuesta a pH 7.8 (tanto para Hg como para Pb) el cual es un nivel de pH muy cercano al medido en el área de estudio. La concentración de metal en el alga se incrementó de manera lineal hasta las 48 hrs, tiempo donde se evidenció una mayor eficiencia de acumulación durante el primer intervalo del periodo del bioensayo.

Mercury Removal from Aqueous Solution Using ETS-4 in the Presence of Cations of Distinct Sizes

The removal of the hazardous Hg²⁺ from aqueous solutions was studied by ion exchange using titanosilicate in sodium form (Na-ETS-4). Isothermal batch experiments at fixed pH were performed to measure equilibrium and kinetic data, considering two very distinct situations to assess the influence of competition effects: (i) the counter ions initially in solution are Na⁺ and Hg²⁺ (both are exchangeable); (ii) the initial counter ions in solution are tetrapropylammonium (TPA⁺) and Hg²⁺ (only Hg²⁺ is exchangeable, since TPA⁺ is larger than the ETS-4 micropores). The results confirmed that ETS-4 is highly selective for Hg²⁺, with more than 90% of the mercury being exchanged from the fluid phase. The final equilibrium attained under the presence of TPA⁺ or Na⁺ in solution was very similar, however, the Hg²⁺/Na⁺/ETS-4 system in the presence of Na⁺ required more 100 h to reach equilibrium than in the presence of TPA⁺. The Hg²⁺/Na⁺/ETS-4 system was modelled and analyzed in terms of equilibrium (mass action law) and mass transfer (Maxwell–Stefan (MS) formalism). Concerning equilibrium, no major deviations from ideality were found in the range of studied concentrations. On the other hand, the MS based model described successfully (average deviation of 5.81%) all kinetic curves of mercury removal.

Green Graphene-Chitosan Sorbent Materials for Mercury Water Remediation

The development of new graphene-based nanocomposites able to provide synergistic effects for the adsorption of toxic heavy metals in realistic conditions (environment) is of higher demand for future applications. This work explores the preparation of a green nanocomposite based on the self-assembly of graphene oxide (GO) with chitosan (CH) for the remediation of Hg(II) in different water matrices, including ultrapure and natural waters (tap water, river water, and seawater). Starting at a concentration of 50 μg L^-1, the results showed that GO-CH nanocomposite has an excellent adsorption capacity of Hg (II) using very small doses (10 mg L^-1) in ultrapure water with a removal percentage (% R) of 97 % R after only two hours of contact time. In the case of tap water, the % R was 81.4% after four hours of contact time. In the case of river and seawater, the GO-CH nanocomposite showed a limited performance due the high complexity of the water matrices, leading to a residual removal of Hg(II). The obtained removal of Hg(II) at equilibrium in river and seawater for GO-CH was 13% R and 7% R, respectively. Our studies conducted with different mimicked sea waters revealed that the removal of mercury is not affected by the presence of NO₃^- and Na⁺ (>90% R of Hg(II)); however, in the presence of Cl^-, the mercury removal was virtually nonexistent (1% R of Hg(II)), most likely because of the formation of very stable chloro-complexes of Hg(II) with less affinity towards GO-CH.

Preparation and Modification of Mullite Whiskers/Cordierite Porous Ceramics for Cu2+ Adsorption and Removing

In this paper, mullite whiskers were prepared by a molten salt reaction method based on a porous cordierite ceramic substrate (MC), and the modified mullite whiskers/cordierite ceramic sample (MCK) was obtained via the silane coupling reaction with γ-aminopropyl triethoxysilane (KH550). The structural morphology and phase compositions of the MC were characterized by X-ray diffraction and scanning electron microscopy. The surface functional groups of MCK were characterized using Fourier transform infrared spectroscopy, and the result showed that the amino group (-NH₂) was successfully grafted onto the surface of cordierite ceramic. X-ray photoelectron spectroscopy analysis successfully showed inclusion of the amino and Cu²⁺ adsorption mechanism onto MCK. The adsorption properties of MCK were investigated using Cu²⁺ as the target pollutant by varying the experimental conditions such as pH, time, temperature, and initial Cu²⁺ concentration. The adsorption was found to be spontaneous, endothermic, and feasible, as indicated by the study of thermodynamic parameters. The adsorption kinetic analysis suggested that the pseudo-second-order kinetic model was best fitted for Cu²⁺ adsorption. The adsorption isotherm studies showed that the results of the Freundlich model are more suitable for experimental adsorption data than the Langmuir model. The adsorption-desorption cycle indicated that MCK had good reusability and stability. A novel porous ceramic-based adsorbent with high Cu²⁺ adsorption and removal efficiency was fabricated and has potential applications for the metal ion removing field.

Valuation of banana peels as an effective biosorbent for mercury removal under low environmental concentrations

The use of banana peels as biosorbent for mercury sorption from different aqueous solutions was investigated in this work. The impact of the operating conditions, such as biosorbent dosage, contact time and ionic strength was evaluated for realistic initial Hg(II) concentrations of 50 μg dm^-3. Biosorbent dosage and contact time showed more influence on Hg(II) removal than ionic strength, and their increase led to improve Hg(II) uptake achieving final concentrations with drinking water quality. The kinetic behaviour of the sorption process was assessed through the reaction-based models of pseudo-first order, pseudo-second order and Elovich, being the last two more appropriated to describe the process. The equilibrium study showed that Freundlich isotherm provided the best fit to the experimental results (R² = 0.991), which may suggest a multilayer mechanism at biosorbent surface, and the sorption capacity of banana peels obtained from Langmuir isotherm was 0.75 mg g^-1. The ability of banana peels to sorb Hg(II) was also examined under real waters, like seawater and a wastewater, which confirmed the feasibility of the biosorbent. Additionally, a counter-current two-stages unit has been proposed for the application of banana peels as biosorbent in water treatments for mercury removal.

Can contaminated waters or wastewater be alternative sources for technology-critical elements? The case of removal and recovery of lanthanides

Technology critical elements (TCE) are considered the vitamins of nowadays technology. Factors such as high demand, limited sources and geopolitical pressures, mining exploitation and its negative impact, point these elements as new emerging contaminants and highlight the importance for removal and recycling TCE from contaminated waters. This paper reports the synthesis, characterization and application of hybrid nanostructures to remove and recover lanthanides from water, promoting the recycling of these high value elements. The nanocomposite combines the interesting properties of graphite nanoplatelets, with the magnetic properties of magnetite, and exhibits good sorption properties towards La(III), Eu(III) and Tb(III). The sorption process was very sensitive to solution pH, evidencing that electrostatic interactions are the main binding mechanism involved. Removal efficiencies up to 80% were achieved at pH 8, using only 50 mg/L of nanocomposite. In ternary solution, occurred a preferential removal of Eu(III) and Tb(III). The equilibrium evidenced a rare but interesting behaviour, and as a proof-of-concept the recoveries and reutilization rates, at consecutive cycles, highlight the recyclability of the composite without loss of efficiency. This study evidences that surface charge and the number of active sites of the composite controls the removal process, providing new insights on the interactions between lanthanoids and magnetic-graphite-nanoplatelets.

Functionalized magnetic mesoporous silica/poly(m-aminothiophenol) nanocomposite for Hg(II) rapid uptake and high catalytic activity of spent Hg(II) adsorbent

Currently, magnetic mesoporous silica nanospheres have been employed widely as adsorbents due to their large surface area and easy recovery. Herein, the functionalized magnetic mesoporous silica/organic polymers nanocomposite (MMSP) was fabricated by the grafted poly(m-aminothiophenol) embedded the aminated magnetic mesoporous silica nanocomposite based on Fe₃O₄ magnetic core, which was shelled by mesoporous silica and further modified by (3-aminopropyl) triethoxysilane. The adsorption properties of as-developed MMSP were systematically explored by altering the experimental parameters. The results indicated that the adsorption capacity and removal percentage of the MMSP could reach 243.83 mg/g and 97.53% within only 10 min at pH 4.0, and the coexisting ions had no significant effect on the selective Hg(II) ions removal from aqueous solutions, meanwhile, the adsorbent recovered by a magnet still exhibited good adsorption performance after recycled 5 times. In addition, by analyzing experimental data, the adsorption process of Hg(II) ions belonged to spontaneous exothermic adsorption, and the possible adsorption mechanisms were proposed based on the pseudo-second-order model and Langmuir model. After adsorption study, the waste material adsorbed Hg(II) was developed as an efficient catalyst for transformation of phenylacetylene to acetophenone with yield of 97.06%. In this study, we designed an efficient and selective material for Hg(II) ions remove and provided a treatment of the post-adsorbed mercury adsorbent by converting the waste into an excellent catalyst, which reduced the economic and environmental impact from conventional adsorption techniques.

Treatment of a textile effluent by adsorption with cork granules and titanium dioxide nanomaterial

This study aimed to explore the efficiency of two adsorbents, cork granules with different granulometry and titanium dioxide nanomaterial, in the removal of chemical oxygen demand (COD), colour and toxicity from a textile effluent. The adsorption assays with cork were unsatisfactory in the removal of chemical parameters however they eliminated the acute toxicity of the raw effluent to Daphnia magna. The assay with TiO₂ NM did not prove to be efficient in the removal of colour and COD even after 240 min of contact; nevertheless it also reduced the raw effluent toxicity. The best approach for complete remediation of the textile effluent has not yet been found however promising findings were achieved, which may be an asset in future adsorption assays.

Towards a better understanding on mercury adsorption by magnetic bio-adsorbents with γ-Fe2O3 from pinewood sawdust derived hydrochar: Influence of atmosphere in heat treatment

Pyrolysis under protective atmosphere was regarded as an indispensable process for the preparation of biomass-based adsorbents to achieve higher surface areas. In this paper, magnetic carbon composites (MCC) that fabricated under air atmosphere showed an adsorption capacity of 167.22 mg/g in 200 ppm Hg(II), which was significantly higher than magnetic biochar (MBC, 31.80 mg/g) that fabricated under traditional nitrogen protection, and this remarkable performance of MCC was consistent in a wide range of pHs. Based on BET, XRD, FTIR, SEM and Boehm titration, MCC was demonstrated with limited surface area (43.29 m²/g) but large amount of surface functional groups comparing with MBC. Additionally, γ-Fe₂O₃ with a high degree of crystallization was generated in MCC, which led to a better magnetic property and recyclability. Moreover, characterizations, Langmuir isotherm and pseudo-second-order kinetics demonstrated the chemisorption was dominant for MCC in mercury capture, and surface complexation co-precipitate of Hg₄Fe₈O₁₆C₅₆H₄₀ were also formed.

A macroalgae-based biotechnology for water remediation: Simultaneous removal of Cd, Pb and Hg by living Ulva lactuca

Metal uptake from contaminated waters by living Ulva lactuca was studied during 6 days, under different relevant contamination scenarios. In mono-metallic solutions, with concentrations ranging from 10 to 100 μg L^-1 for Hg, 10-200 μg L^-1 for Cd, and 50-1000 μg L^-1 for Pb, macroalgae (500 mg L^-1, d.w.) were able to remove, in most cases 93-99% of metal, allowing to achieve water quality criteria regarding both surface and drinking waters. In multi-metallic solutions, comprising simultaneously the three metals, living macroalgae still performed well, with Hg removal (c.a. 99%) not being significantly affected by the presence of Cd and Pb, even when those metals were in higher concentrations. Removal efficiencies for Cd and Pb varied between 57 and 96%, and 34-97%, respectively, revealing an affinity of U. lactuca toward metals: Hg > Cd > Pb. Chemical quantification in macroalgae, after bioaccumulation assays demonstrated that all Cd and Hg removed from solution was really bound in macroalgae biomass, while only half of Pb showed to be sorbed on the biomass. Overall, U. lactuca accumulated up to 209 μg g^-1 of Hg, up to 347 μg g^-1 of Cd and up to 1641 μg g^-1 of Pb, which correspond to bioconcentration factors ranging from 500 to 2200, in a dose-dependent accumulation. Pseudo-first order, pseudo-second order and Elovich models showed a good performance in describing the kinetics of bioaccumulation, in the whole period of time. In the range of experimental conditions used, no mortality was observed and U. lactuca relative growth rate was not significantly affected by the presence of metals. Results represent an important contribution for developing a macroalgae-based biotechnology, applied for contaminated saline water remediation, more "green" and cost-effective than conventional treatment methods.

Bioaccumulation of Hg, Cd and Pb by Fucus vesiculosus in single and multi-metal contamination scenarios and its effect on growth rate

Results of 7-days exposure to metals, using environmentally realistic conditions, evidenced the high potential of living Fucus vesiculosus to remove Pb, Hg and Cd from contaminated salt waters. For different contamination scenarios (single- and multi-contamination), ca 450 mg L-1 (dry weight), enable to reduce the concentrations of Pb in 65%, of Hg in 95% and of Cd between 25 and 76%. Overall, bioconcentration factors ranged from 600 to 2300. Elovich kinetic model described very well the bioaccumulation of Pb and Cd over time, while pseudo-second-order model adjusted better to experimental data regarding Hg. F. vesiculosus showed different affinity toward studied metals, following the sequence order: Hg > Pb > Cd. Analysis of metal content in the macroalgae after bioaccumulation, proved that all metal removed from solution was bound to the biomass. Depuration experiments reveled no significant loss of metal back to solution. Exposure to contaminants only adversely affected the organism's growth for the highest concentrations of Cd and Pb. Findings are an important contribute for the development of remediation biotechnologies for confined saline waters contaminated with trace metal contaminants, more efficient and with lower costs than the traditional treatment methods.

Reducing hazardous heavy metal ions using mangium bark waste

The objective of this study was to evaluate the characteristics of mangium bark and its biosorbent ability to reduce heavy metal ions in standard solutions and wastewater and to assess changes in bark characteristics after heavy metal absorption. The experiments were conducted to determine heavy metal absorption from solutions of heavy metals alone and in mixtures as well as from wastewater. The results show that mangium bark can absorb heavy metals. Absorption percentages and capacities from single heavy metal solutions showed that Cu(2+) > Ni(2+) > Pb(2+) > Hg(2+), while those from mixture solutions showed that Hg(2+) > Cu(2+) > Pb(2+) > Ni(2+). Wastewater from gold mining only contained Cu, with an absorption percentage and capacity of 42.87 % and 0.75 mg/g, respectively. The highest absorption percentage and capacity of 92.77 % and 5.18 mg/g, respectively, were found for Hg(2+) in a mixture solution and Cu(2+) in single-metal solution. The Cu(2+) absorption process in a single-metal solution changed the biosorbent characteristics of the mangium bark, yielding a decreased crystalline fraction; changed transmittance on hydroxyl, carboxyl, and carbonyl groups; and increased the presence of Cu. In conclusion, mangium bark biosorbent can reduce hazardous heavy metal ions in both standard solutions and wastewater.

Remediation of mercury contaminated saltwater with functionalized silica coated magnetite nanoparticles

The study aimed to evaluate the efficiency of dithiocarbamate functionalized silica coated magnetite nanoparticles (NPs) for Hg decontamination of saltwater either contaminated with Hg alone or with As and Cd. For this, the residual levels of Hg in seawater were assessed and Hg-contaminated or Hg+As+Cd-contaminated seawater toxicity to aquatic biota, before and after the sorption process, was compared. The results showed that under highly competitive conditions (water salts, Cd and As), the removal of Hg from seawater, by using these magnetic NPs, for the lowest concentration (50μg/L) was superior to 98% and for the highest concentration (500μg/L) ranged between 61% to 67%. Despite the great affinity of the magnetic NPs for Hg, they were not effective at removing As and Cd from seawater. In relation to the ecotoxicity endpoints after remediation, the mixture with lower Hg concentration exhibited no toxicity to rotifer Brachionus plicatilis and bacteria Vibrio fischeri ; however, the mixture with higher concentration revealed toxicity. In addition, the toxicity of bacteria V. fischeri, rotifer B. plicatilis and algae Phaeodactylum tricornutum, whose responses where inhibited during its exposure to the non-remediate sample was considerably reduced after treatment with NPs. Furthermore, microalgae P. tricornutum appears to be most sensitive species while Artemia franciscana showed no toxic effects to the tested solutions. Both chemical and ecotoxicological approaches revealed a high efficiency for the remediation of Hg-contaminated saltwater.

Comparative study on metal biosorption by two macroalgae in saline waters: single and ternary systems

The biosorption capability of two marine macroalgae (green Ulva lactuca and brown Fucus vesiculosus) was evaluated in the removal of toxic metals (Hg, Cd and Pb) from saline waters, under realistic conditions. Results showed that, independently of the contamination scenario tested, both macroalgae have a remarkable capacity to biosorb Hg and Pb. In single-contaminant systems, by using only c.a. 500 mg of non-pre-treated algae biomass (size <200 μm) per litter, it was possible to achieve removal efficiencies between 96 and 99 % for Hg and up to 86 % for Pb. Despite the higher removal of Hg, equilibrium was reached more quickly for Pb (after 8 h). In multi-contaminant systems, macroalgae exhibited a similar selectivity toward the target metals: Hg > Pb> > Cd, although Pb removal by U. lactuca was more inhibited than that achieved by F. vesiculosus. Under the experimental conditions used, none of the macroalgae was effective to remove Cd (maximum removal of 20 %). In all cases, the kinetics of biosorption was mathematically described with success. Globally, it became clear that the studied macroalgae may be part of simple, efficient, and cost-effective water treatment technologies. Nevertheless, Fucus vesiculosus has greater potential, since it always presented higher initial sorption rates and higher removal efficiencies.

Removal of mercury by adsorption: a review

Due to natural and production activities, mercury contamination has become one of the major environmental problems over the world. Mercury contamination is a serious threat to human health. Among the existing technologies available for mercury pollution control, the adsorption process can get excellent separation effects and has been further studied. This review is attempted to cover a wide range of adsorbents that were developed for the removal of mercury from the year 2011. Various adsorbents, including the latest adsorbents, are presented along with highlighting and discussing the key advancements on their preparation, modification technologies, and strategies. By comparing their adsorption capacities, it is evident from the literature survey that some adsorbents have shown excellent potential for the removal of mercury. However, there is still a need to develop novel, efficient adsorbents with low cost, high stability, and easy production and manufacture for practical utility.

Optimized graphene oxide foam with enhanced performance and high selectivity for mercury removal from water

This work explores the preparation of three-dimensional graphene oxide macroscopic structures, shaped by self-assembling single graphene oxide (3DGO) sheets with control of its surface chemistry by combining with nitrogen functional groups (3DGON), or with nitrogen and sulphur functional groups (3DGOSN), and their application in the removal of mercury (Hg(II)) from aqueous solutions. The chemical structure of the materials was assessed by using different characterization techniques: SEM, XPS and BET. Adsorption studies conducted in Hg(II) contaminated ultra-pure water reveal the enhanced ability of 3DGON for the adsorption of this metal, when compared to the other GO foams. A small dose of 3DGON (10 mg L(-1)) allows to remove up to 96% of Hg(II) after 24 h of contact time, leading to a residual concentration in solution close to the guideline value for drinking water (1 μg L(-1)). The ability of this material to adsorb Hg (II) was evaluated relatively to different experimental parameters such as pH, sorbent dose, time and effect on different competing metal ions. Real application was also evaluated by testing its performance in two different natural matrices, river and sea water, with very promising results.

A multidisciplinary approach to evaluate the efficiency of a clean-up technology to remove mercury from water

A microporous material denoted ETS-4 was used as the decontaminant agent to treat water with a low level of Hg contamination. The effectiveness of the treatment was evaluated by assessment of the efficiency of Hg removal and ecotoxicological responses. The results showed that under highly competitive conditions the removal of Hg ranged between 58 % and 73 % depending upon the initial Hg concentration, and that Hg removal was reflected in decreased toxicity to some organisms. The ecotoxicological data indicated that the bacterium Vibrio fischeri was the least sensitive organism tested, as no toxicity was observed in either pre- or post-treatment waters. Daphnia magna was highly sensitive to Hg. Mercury removal by ETS-4 was not sufficient to completely remove the toxicity of Hg to D. magna. However, it was effective in the complete reduction of toxicity for the green alga, Pseudokirchneriella subcapitata.