Binary component sorption of Cu(II) and Pb(II) with activated carbon from Eucalyptus camaldulensis Dehn bark

Recent Progress on the Adsorption of Heavy Metal Ions Pb(II) and Cu(II) from Wastewater

With the processes of industrialization and urbanization, heavy metal ion pollution has become a thorny problem in water systems. Among the various technologies developed for the removal of heavy metal ions, the adsorption method is widely studied by researchers and various nanomaterials with good adsorption performances have been prepared during the past decades. In this paper, a variety of novel nanomaterials with excellent adsorption performances for Pb(II) and Cu(II) reported in recent years are reviewed, such as carbon-based materials, clay mineral materials, zero-valent iron and their derivatives, MOFs, nanocomposites, etc. The novel nanomaterials with extremely high adsorption capacity, selectivity and particular nanostructures are summarized and introduced, along with their advantages and disadvantages. And, some future research priorities for the treatment of wastewater are also prospected.

An integrated experimental and theoretical approach to probe Cr(vi) uptake using decorated halloysite nanotubes for efficient water treatment

Halloysite nanotubes (HNTs) were surface functionalized using four distinct chemical moieties (amidoxime, hydrazone, ethylenediamine (EDA), and diethylenetriamine (DETA)), producing modified HNTs (H1-H4) capable of binding with Cr(vi) ions. Advanced techniques like FTIR, XRD, SEM, and EDX provided evidence of the successful functionalization of these HNTs. Notably, the functionalization occurred on the surface of HNTs, rather than within the interlayer or lumen. These decorated HNTs were effective in capturing Cr(vi) ions at optimized sorption parameters, with adsorption rates ranging between 58-94%, as confirmed by atomic absorption spectroscopy (AAS). The mechanism of adsorption was further scrutinized through the Freundlich and Langmuir isotherms. Langmuir isotherms revealed the nearest fit to the data suggesting the monolayer adsorption of Cr(vi) ions onto the nanotubes, indicating a favorable adsorption process. It was hypothesized that Cr(vi) ions are primarily attracted to the amine groups on the modified nanotubes. Quantum chemical calculations further revealed that HNTs functionalized with hydrazone structures (H2) demonstrated a higher affinity (interaction energy -26.33 kcal mol-1) for the Cr(vi) ions. This can be explained by the formation of stronger hydrogen bonds with the NH moieties of the hydrazone moiety, than those established by the OH of oxime (H1) and longer amine chains (H3 and H4), respectively. Overall, the findings suggest that these decorated HNTs could serve as an effective and cost-efficient solution for treating water pollution.

Orange peels magnetic activate carbon (MG-OPAC) composite formation for toxic chromium absorption from wastewater

This work prepared a composite of orange peels magnetic activated carbon (MG-OPAC). The prepared composite was categorized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), Energy-dispersive X-ray spectroscopy (EDX), Scanning Electron Microscopy (SEM) and vibrating-sample magnetometer (VSM) analyses. The MG-OPAC composite showed the surface area (155.09 m²/g), the total volume of pores (0.1768 cm³/g), and the mean diameter of pores (4.5604 nm). The saturation magnetization (Ms = 17.283 emu/g), remanence (Mr = 0.28999 emu/g) and coercivity (Hc = 13.714 G) were reported for the prepared MG-OPAC. Likewise, at room temperature, the MG-OPAC was in a super-paramagnetic state, which could be collected within 5 S (< 5 S) with an outside magnetic field. Influence of time of contact, absorbent dose, starting concentration of Cr⁶⁺ ions, and pH were tested to adjust the absorption process. The absorption behavior of MG-OPAC for hexavalent chromium was investigated by Langmuir (LIM), Freundlich (FIM) and Temkin (TIM) isotherm models (IMs). Applicability of LIM specifies that Cr⁶⁺ ions absorption procedure may be monolayer absorption. The maximum monolayer capacity (Q_m) premeditated by LIM was 277.8 mg/g. Similarly, the absorption process was tested with different kinetic models like intraparticle diffusion (IPDM), pseudo-first-order (PFOM), Elovich (EM), pseudo-second-order (PSOM), and Film diffusion (FDM). The PSOM was best fitted to the experimental results of Cr⁶⁺ ions absorption with R² ranging between 0.992 and 1.

Strontium-doped hydroxyapatite as adsorbent effectively to remove lead ions from water

In this study, a strontium-doped hydroxyapatite (Sr-HAP) was synthesized by the solgel method, which was used as adsorbent to remove lead ions (Pb²⁺) from water. The results showed that the adsorption capacities of the Sr-HAP were obviously higher than those of the HAP, the adsorption capacities of which for Pb²⁺ reached 651.175 mg/g. The proper increasement in the dosage of adsorbent was beneficial to the removal of Pb²⁺ by Sr-HAP. Meanwhile Sr-HAP had a wide applicable pH range for Pb²⁺. And the increasement in temperature could increase the adsorption capacity of Sr-HAP for Pb²⁺ to a certain extent. The Langmuir model was used to fit the isotherm adsorption process of Sr-HAP to Pb²⁺ in water. Compared with HAP, the specific surface area of Sr-HAP has increased by 11.1%, and the pore size distribution of Sr-HAP tended to be smaller and more uniform. Hence, Sr-HAP could be used as an ideal adsorbent to remove Pb²⁺ in wastewater.

Treatment of electroplating industry wastewater: a review on the various techniques

Water pollution by recalcitrant compounds is an increasingly important problem due to the continuous introduction of new chemicals into the environment. Choosing appropriate measures and developing successful strategies for eliminating hazardous wastewater contaminants from industrial processes is currently a primary goal. Electroplating industry wastewater involves highly toxic cyanide (CN), heavy metal ions, oils and greases, organic solvents, and the complicated composition of effluents and may also contain biological oxygen demand (BOD), chemical oxygen demand (COD), SS, DS, TS, and turbidity. The availability of these metal ions in electroplating industry wastewater makes the water so toxic and corrosive. Because these heavy metals are harmful to living things, they must be removed to prevent them from being absorbed by plants, animals, and humans. As a result, exposure to electroplating wastewater can induce necrosis and nephritis in humans and lung cancer, digestive system cancer, anemia, hepatitis, and maxillary sinus cancer with prolonged exposure. For the safe discharge of electroplating industry effluents, appropriate wastewater treatment has to be provided. This article examines and assesses new approaches such as coagulation and flocculation, chemical precipitation, ion exchange, membrane filtration, adsorption, electrochemical treatment, and advanced oxidation process (AOP) for treating the electroplating industry wastewater. On the other hand, these physicochemical approaches have significant drawbacks, including a high initial investment and operating cost due to costly chemical reagents, the production of metal complexes sludge that needs additional treatment, and a long recovery process. At the same time, advanced techniques such as electrochemical treatment can remove various kinds of organic and inorganic contaminants such as BOD, COD, and heavy metals. The electrochemical treatment process has several advantages over traditional technologies, including complete removal of persistent organic pollutants, environmental friendliness, ease of integration with other conventional technologies, less sludge production, high separation, and shorter residence time. The effectiveness of the electrochemical treatment process depends on various parameters, including pH, electrode material, operation time, electrode gap, and current density. This review mainly emphasizes the removal of heavy metals and another pollutant such as CN from electroplating discharge. This paper will be helpful in the selection of efficient techniques for treatment based on the quantity and characteristics of the effluent produced.

Activated Biocarbons Obtained from Plant Biomass as Adsorbents of Heavy Metal Ions

This paper deals with the adsorption of heavy metal ions on the surface of carbonaceous materials obtained via the chemical activation of biomass. Waste plum stones, pine sawdust and horsetail herb were used as the precursors of carbonaceous adsorbents. The effect of the precursor type and preparation procedure on the physicochemical properties of activated biocarbons and their sorption abilities towards Pb(II) and Cu(II) ions have been checked. The obtained micro-mesoporous activated biocarbons were characterized by determination of elemental composition and ash content, the number of surface functional groups and pH of water extracts as well as textural study based on low temperature nitrogen adsorption/desorption and scanning electron microscopy. Additionally, the electrokinetic studies including solid surface charge density and zeta potential determination were performed. Moreover, the adsorption data modelling (equilibrium and kinetics), XPS results analysis and comparison of parameters characterizing electrical double layer formed at the solid-liquid interface enabled the specification of the mechanism of heavy metals binding with the activated biocarbons surface. The maximum adsorption capacity towards copper and lead ions (177.5 and 178.1 mg/g, respectively) was found for plum stone-based activated biocarbon. For all carbonaceous materials, better fit to the experimental data was achieved with a Langmuir isotherm than a Freundlich one. In turn, a better fit of the kinetics data was obtained using the pseudo-second order model.

Utilization of Waste Amine-Oxime (WAO) Resin to Generate Carbon by Microwave and Its Removal of Pb(II) in Water

Utilising waste amine-oxime (WAO) resin through microwave semi-carbonization, a carbon adsorbent (CA) was obtained to remove Pb(II). After microwave treatment, the pore size of the skeleton structure, three-dimensional porous network, and lamellar pore structure of WAO was improved. The distribution coefficient (Kd) of Pb(II) onto CA is 620 mL/g, and the maximum adsorption capacity of Pb(II) is 82.67 mg/g after 20 min of WAO microwave treatment. The adsorption kinetics and adsorption isotherms conform to the quasi-second-order kinetic equation and Langmuir adsorption isotherm model, respectively. The surface of MT-WAO is negatively charged and the adsorption mechanism is mainly electrostatic interaction. Pb(II) elution in hydrochloric acid solution is more than 98%, and its recovery is high at 318 K and for 1 h.

Biochars and activated carbons as adsorbents of inorganic and organic compounds from multicomponent systems - A review

Biochars are obtained by biomass pyrolysis, whereas activated carbon is a biochar that has undergone chemical or physical activation. Owing to the large surface area and easy surface modification both solids are widely applied as adsorbents. They are low-costs materials, they could be regenerated and their disposal is not troublesome. Adsorption of heavy metals, dyes, pharmaceuticals on the surface of biochars and activated carbons, from simple systems of adsorbate containing only one compound, are described extensively in the literature. The present paper provides an overview of reports on adsorption of inorganic and organic compounds onto these two types of adsorbents from the mixed adsorbate systems. The described adsorbate systems have been divided into those consisting of: two or more inorganic ions, two or more organic compounds and both of them (inorganic and organic ones). The research of this type is carried out much less frequently due to the more complicated description of interactions in the mixed adsorbate systems.

A review on sources of heavy metals, their toxicity and removal technique using physico-chemical processes from wastewater

The world is facing environmental pollution and is in an alarming situation due to industrialization and urbanization. Especially, industrial wastewater discharge is causing serious pollution in the environment (water, soil, and air) and has become a challenge for researchers and scientists. Wastewater contains heavy metals like Cu, Ni, Cr, Pb, and Ar and causes toxicity in living beings and the environment. In this review, the sources of heavy metals and their toxicological effects on the environment have been reviewed. Various remediation techniques such as reverse osmosis, chemical precipitation, and ultrafiltration are being used for the treatment of wastewater, but still are limited in their efficiencies, residues, cost, and versatility. In this study, the most promising wastewater treatment technique, the physic-chemical technique, has been reviewed along with its working mechanism and efficiency. Further, the pros and cons of this technique and sub-techniques have also been reviewed to provide a basic understanding to beginners and a pathway to experts in the selection of better techniques.

Heavy metal biosorption by Extracellular Polymeric Substances (EPS) recovered from anammox granular sludge

The recovery and conversion of Extracellular Polymeric Substances (EPS) from sewage sludge into bio-based commodities might improve the economics and environmental sustainability of wastewater treatment. This contribution explores the application of EPS from anammox granular waste sludge as biosorbent for the removal of heavy metals, specifically lead, copper, nickel, and zinc. Adsorption capacities equivalent or higher than well-established adsorbent media emerged from single-metal biosorption studies (up to 84.9, 52.8, 21.7 and 7.4 mg/gTS_EPS for Pb²⁺, Cu²⁺, Ni²⁺ and Zn²⁺, respectively). Combining spectroscopic techniques, a mechanistic hypothesis for metal biosorption, based on a combination of electrostatic interaction, ion exchange, complexation, and precipitation, was proposed. The adsorption mechanisms of extracted EPS and non-extracted EPS in the native biomass were indirectly compared by means of single-metal biosorption studies performed with pristine granules (adsorbing up to 103.7, 36.1, 48.2 and 49.8 mg/gTSgranules of Pb²⁺, Cu²⁺, Ni²⁺, and Zn²⁺, respectively). In comparison with pristine anammox granules, EPS showed lower adsorption capacities except for copper and different adsorption pathways as postulated based on the adsorption data interpretation via theoretical models. The multi-metal biosorption tests excluded significant competitions among different heavy metals for the EPS binding sites, thus opening further scenarios for the treatment of complex wastewaters.

Characterization of Waste Amidoxime Chelating Resin and Its Reutilization Performance in Adsorption of Pb(II), Cu(II), Cd(II) and Zn(II) Ions

The continuous expansion of the market demand and scale of commercial amidoxime chelating resins has caused large amounts of resin to be discarded around the world. In this study, the waste amidoxime chelating resin was reutilized as an adsorbent for the removal and recovery of Pb(II), Cu(II), Cd(II) and Zn(II) ions from aqueous solutions. The physical morphology and chemical composition of the waste amidoxime chelating resin (WAC-resin) from the factory was characterized by the elemental analyzer, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. The influence of the initial metal ions concentration, contact time, temperature and the solution pH on the adsorption performance of the metal ions was explored by batch experiments. It was shown that the optimal pH was 4. Kinetic studies revealed that adsorption process corresponded with the pseudo-second-order kinetic model and the adsorption isotherm was consistent with the Langmuir model. At room temperature, the adsorption capacities of WAC-resin for Pb2+, Cu2+, Zn2+ and Cd2+ reached 114.6, 93.4, 24.4 and 20.7 mg/g, respectively.

Synthesis of Magnetic Adsorbents Based Carbon Highly Efficient and Stable for Use in the Removal of Pb(II) and Cd(II) in Aqueous Solution

In this study, two alternative synthesis routes for magnetic adsorbents were evaluated to remove Pb(II) and Cd(II) in an aqueous solution. First, activated carbon was prepared from argan shells (C). One portion was doped with magnetite (Fe₃O₄+C) and the other with cobalt ferrite (CoFe₂O₄+C). Characterization studies showed that C has a high surface area (1635 m² g⁻¹) due to the development of microporosity. For Fe₃O₄+C the magnetic particles were nano-sized and penetrated the material’s texture, saturating the micropores. In contrast, CoFe₂O₄+C conserves the mesoporosity developed because most of the cobalt ferrite particles adhered to the exposed surface of the material. The adsorption capacity for Pb(II) was 389 mg g⁻¹ (1.88 mmol g⁻¹) and 249 mg g⁻¹ (1.20 mmol g⁻¹); while for Cd(II) was 269 mg g⁻¹ (2.39 mmol g⁻¹) and 264 mg g⁻¹ (2.35 mmol g⁻¹) for the Fe₃O₄+C and CoFe₂O₄+C, respectively. The predominant adsorption mechanism is the interaction between -FeOH groups with the cations in the solution, which are the main reason these adsorption capacities remain high in repeated adsorption cycles after regeneration with HNO₃. The results obtained are superior to studies previously reported in the literature, making these new materials a promising alternative for large-scale wastewater treatment processes using batch-type reactors.

Synthesis of highly fluorescent and water soluble graphene quantum dots for detection of heavy metal ions in aqueous media

Fluorescent graphene quantum dots (GQDs) are nanomaterials which possess unique properties that show great potential in different applications. In this work, GQDs were synthesized using graphene oxide (GO) as precursor via thermal treatment at high temperature. The obtained GQDs were highly fluorescent and were suitable for the determination of heavy metal ions. X-ray diffraction, FTIR spectroscopy, and UV visible spectroscopy confirm the formation of GQDs. TEM images show that formed GQDs have size ranging from 2 to 10 nm. Emission profile of aqueous GQDs was taken by exciting GQDs at different wavelength. The intensity of GQDs remains the same for 4-5 months. Furthermore, as prepared, GQDs were used for selective recognition of Fe³⁺, Pb⁺², and Cr³⁺ from the bunch of different metal ions in aqueous media. Lower limit of detection obtained for Fe³⁺, Cr³⁺ and Pb²⁺ using GQDs were 50, 100 and 100 nM, respectively, which indicates that the GQDs can be utilized as a promising material for sensing of the heavy metal ions. Graphical abstract.

Pyrolysis of waste biomass and plastics for production of biochar and its use for removal of heavy metals from aqueous solution

The aim of this work was to study the pyrolysis of waste biomass and plastics and use the produced biochar for the removal of heavy metals from aqueous solution. The batch experiments of Fe, Ni, Cu, Cr, Cd and Pb with biochars and plastic chars were carried for determining the effects of various experimental parameters (feedstock, contact time, adsorbent dose, pH and pyrolysis temperature). The isothermal sorption models demonstrated that the sorption capacities of biochars are higher in comparison to the plastic chars. The maximum removal efficiency shown by biochars and plastic chars at pH 4 was 99.86% and 99.93%, respectively. Both the carbon materials are thereby recognized as an environment-friendly and efficient pollutant control material at various studied parameters.

Structural design and environmental applications of electrospun nanofibers

Nanofibers have attracted extensive attention and been applied in various fields due to their high aspect ratio, high specific surface area, flexibility, structural abundance, etc. The electrospinning method is one of the most promising and effective ways to produce nanofibers. The electrospun nanofibers-based films and membranes have already been demonstrated to possess small pore sizes, larges specific surface area, and can be grafted with different functionalities to adapt to various purposes. The environmental applications of nanofibers are one of the essential application fields, and great achievements have been made in this field. To well summarize the development of nanofibers and their environmental applications, we review the nanofiber fabrication methods, advanced fiber structures, and their applications in the field of air filtration, heavy metal removal, and self-cleaning surface. We hope this review and summary can provide readers a comprehensive understanding of the structural design and environmental applications of electrospun nanofibers.

A nature-inspired hydrogen-bonded supramolecular complex for selective copper ion removal from water

Herein, we present a scalable approach for the synthesis of a hydrogen-bonded organic–inorganic framework via coordination-driven supramolecular chemistry, for efficient remediation of trace heavy metal ions from water. In particular, using copper as our model ion of interest and inspired by nature’s use of histidine residues within the active sites of various copper binding proteins, we design a framework featuring pendant imidazole rings and copper-chelating salicylaldoxime, known as zinc imidazole salicylaldoxime supramolecule. This material is water-stable and exhibits unprecedented adsorption kinetics, up to 50 times faster than state-of-the-art materials for selective copper ion capture from water. Furthermore, selective copper removal is achieved using this material in a pH range that was proven ineffective with previously reported metal–organic frameworks. Molecular dynamics simulations show that this supramolecule can reversibly breathe water through lattice expansion and contraction, and that water is initially transported into the lattice through hopping between hydrogen-bond sites.

Heavy metals and metalloids pose major threats to health and environmental ecosystems, thus systems for low-cost remediation are needed. Here the authors report the scalable design of a hydrogen-bonded organic–inorganic framework for selective removal of trace heavy metal ions from water.

Biosorption Mechanism of Aqueous Pb2+, Cd2+, and Ni2+ Ions on Extracellular Polymeric Substances (EPS)

Heavy metal pollution has been a focus with increasing attention, especially Pb²⁺, Cd²⁺, and Ni²⁺ in an aqueous environment. The adsorption capacity and mechanism of extracellular polymeric substances (EPS) from Agrobacterium tumefaciens F2 for three heavy metals were investigated in this study. The adsorption efficiency of 94.67%, 94.41%, and 77.95% were achieved for Pb²⁺, Cd²⁺, and Ni²⁺ adsorption on EPS, respectively. The experimental data of adsorption could be well fitted by Langmuir, Freundlich, Dubinin–Radushkevich isotherm models, and pseudo-second-order kinetic model. Model parameters analysis demonstrated the great adsorption efficiency of EPS, especially for Pb²⁺, and chemisorption was the rate-limiting step during the adsorption process. The functional groups of C=O of carboxyl and C-O-C from sugar derivatives in EPS played the major role in the adsorption process judged by FTIR. In addition, 3D-EEM spectra indicated that tyrosine also assisted EPS adsorption for three heavy metals. But EPS from strain F2 used the almost identical adsorption mechanism for three kinds of divalent ions of heavy metals, so the adsorption efficiency difference of Pb²⁺, Cd²⁺, and Ni²⁺ on EPS could be correlated to the inherent characteristics of each heavy metal. This study gave the evidence that EPS has a great application potential as a bioadsorbent in the treatment of heavy metals pollution.

Nacre-inspired hydroxyapatite/chitosan layered composites effectively remove lead ions in continuous-flow wastewater

Design and fabrication of novel adsorbents to remove heavy metal ions in continuous-flow wastewater remained a great challenge. Inspired by the hierarchical architecture and biomineralization process of nacre, we firstly constructed hydroxyapatite/chitosan (HA/CH) layered composites. The brick-and-mortar characteristics of HA/CH layered composites improved their flexure strengths up to 3.08 MPa so that the hierarchical architectures could not be destroyed even under high-pressure drop. HA/CH layered composites had the hierarchical microstructures analogous to plate towers, facilitating the separation of adsorbents from water. The interlaminar macropores in the layered composites contributed to the transfer of continuous-flow wastewater. The Pb(II), Cd(II) and Hg(II) ions in wastewater showed similar adsorption trends, and their adsorption amounts arrived at 295.96, 192.37 and 127.38 mg g^-1 after 6 days, respectively. Among the above heavy metal ions, the HA/CH layered composites possessed the best Pb(II) adsorption ability due to forming lead hydroxyapatite rods and CH-Pb complexes. The Pb(II) adsorption performances of HA/CH layered composites matched well with Elovich equation, pseudo-first-order and pseudo-second-order kinetics models, revealing the heterogeneous chemisorption mechanism at adsorbent/wastewater interfaces. Therefore, the nacre-like HA/CH layered composites with appropriate mechanical property and excellent adsorption capacity are a novel platform for heavy metal removal in continuous-flow wastewater.

Carbon Nanomaterials for the Treatment of Heavy Metal-Contaminated Water and Environmental Remediation

Nanotechnology is an advanced field of science having the ability to solve the variety of environmental challenges by controlling the size and shape of the materials at a nanoscale. Carbon nanomaterials are unique because of their nontoxic nature, high surface area, easier biodegradation, and particularly useful environmental remediation. Heavy metal contamination in water is a major problem and poses a great risk to human health. Carbon nanomaterials are getting more and more attention due to their superior physicochemical properties that can be exploited for advanced treatment of heavy metal-contaminated water. Carbon nanomaterials namely carbon nanotubes, fullerenes, graphene, graphene oxide, and activated carbon have great potential for removal of heavy metals from water because of their large surface area, nanoscale size, and availability of different functionalities and they are easier to be chemically modified and recycled. In this article, we have reviewed the recent advancements in the applications of these carbon nanomaterials in the treatment of heavy metal-contaminated water and have also highlighted their application in environmental remediation. Toxicological aspects of carbon-based nanomaterials have also been discussed.

Synthesis of super hydrophilic cellulose-alpha zirconium phosphate ion exchange membrane via surface coating for the removal of heavy metals from wastewater

In this study, commercial cellulose membranes were surface coated with alpha‑zirconium phosphate nanoparticles (α-ZrP-n) to study their impact on the overall removal efficiency of heavy metals from synthetic metal mixture wastewater solution. A total of four homogeneous solutions (0.25, 0.50, 0.75, and 1.00 wt%) of α-ZrP-n were prepared by sonicating the nanoparticles in deionized water. These solutions were used to surface coat the commercial cellulose membranes. The Scanning Electron Microscopy (SEM) along with Energy Dispersive Spectroscopy (EDS) were used to confirm the attachment of α-ZrP-n on the cellulose membrane surface. Furthermore, the structural characteristics of the α-ZrP-n modified cellulose membranes were also studied. The water contact angle results showed that all coated membranes remained super-hydrophilic. The porosity of the membranes decreased to 48% with the addition of 1.00 wt% α-ZrP-n compared to 65% for the pristine membrane. The mechanical strength has improved from 3.4 MPa for the pristine membrane to about 4 MPa for the 1.00 wt% α-ZrP-n membrane. Similarly, the thermal stability was found to be slightly enhanced as evidenced by the increase in decomposition temperature to 280 and 285 °C in the 0.75 and 1.00 wt% α-ZrP-n membranes, respectively. Furthermore, a removal efficiency of 97.0 ± 0.6, 98.0 ± 0.5, 99.5 ± 0.2, and 91.5 ± 2.0% for Cu (II), Zn (II), Ni (II), and Pb (II), respectively, was observed with the 0.50 wt% α-ZrP-n membrane. This removal was achieved at a flux of 41.85 ± 0.87 × 10³ LMH. Increasing the α-ZrP-n concentration further did not show any improvement in the overall removal efficiency. However, it led to 46% flux reduction in the 1.00 wt% α-ZrP-n membrane. The mechanism of removal of the heavy metal ions was postulated to be a combination of ion exchange and electrostatic attraction of the strong negatively charged α-ZrP-n membranes and the free metal ions in the wastewater solution.

Immobilization of Zn(II) ions from contaminated biomass using ceramic matrices

This article describes the adsorption of zinc ions from synthetic solutions using residual pine sawdust as an adsorbent and, subsequently, the use of clay ceramic pieces and contaminated biomass as metal immobilizers. The process of adsorption was carried out with a synthetic solution of ZnCl₂ in contact with sawdust for a fixed time of 24 h. The mixture was stirred continually. The mixture was then filtered, and the metal ions not adsorbed by the biomass and present in the liquid phase were quantified. The physicochemical characteristics of the sawdust were determined by thermogravimetric and differential thermal analysis, infrared Fourier transform spectroscopy, fluorescence and X-ray diffraction, among others. The adsorption kinetics shows that the equilibrium was reached at 24 h. The most efficient ratio of the amount of biomass and the concentration of Zn(II) was 10 g/L of sawdust and 6.5 × 10⁴ mg/L of metal, which was used to analyse the capacity of metal immobilization in the designed bricks. The values obtained for the apparent porosity, the loss of weight by ignition, the mechanical properties and the efficiency of retention, indicate that these bricks are suitable for use in civil construction.

Efficient DBT removal from diesel oil by CVD synthesized N-doped graphene as a nanoadsorbent: Equilibrium, kinetic and DFT study

Adsorptive Dibenzothiophene (DBT) removal from diesel oil stream on nitrogen doped graphene (N-doped graphene) was considered. The N-doped graphene was synthesized by chemical vapor deposition (CVD) method at 1000 °C using camphor and urea. The adsorbent was characterized by Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and Nitrogen adsorption/desorption technique. Adsorption parameters such as temperature, time, concentration and mass loaded were optimized by experimental design method. Experimental kinetic data was fitted to Pseudo second order model successfully. Frendulich model was recommended for experimental isotherm data. However, Tempkin model was presented because of the importance of interaction between pyridinic nitrogen and DBT aromatic structure. The results indicate that not only the pore volume and surface area but also types of surface functionalities have an important role for DBT adsorption process, especially for the adsorbates with aromatic structures. The adsorption capacity was calculated up to 73.4 mg/g which is 1.25 times higher than the adsorption capacity of pristine. Thermal regeneration stability, fast adsorption kinetics and high adsorption capacity make N-G4 a potential promising adsorbent for DBT removal. Besides, density functional theory calculations revealed that an increase in the number of doped N atoms as well as the presence of a mono or divacancy defect in N-doped graphene can enhance the adsorption energy of DBT.

Synthesis of multifunctional activated carbon nanocomposite comprising biocompatible flake nano hydroxyapatite and natural turmeric extract for the removal of bacteria and lead ions from aqueous solution

Clean water, which is free from pathogens and toxic chemicals, is vital to human health. The blue planet is encountering remarkable challenges in meeting the ever-increasing demands of clean water. The intention of this research study was to develop a water filter material that is capable of removing bacterial contaminants and heavy metals from fresh water using cost effective and easily fabricated biocompatible filter material. For this purpose, granular activated carbon (GAC) was coated with both hydroxyapatite (HAP) nanoflakes and turmeric extract (TE) (HAP/TE/GAC) which had been extracted from natural turmeric powder. In addition, GAC was coated only with HAP nanoflakes to synthesize HAP coated GAC (HAP/GAC) composite. Prepared HAP/GAC and HAP/TE/GAC were characterized using Fourier-transform infrared spectroscopy, X-ray diffractometry, scanning electron microscopy and UV–visible spectrophotometry. Antibacterial effect of the prepared nanocomposites, HAP/GAC and HAP/TE/GAC was compared with neat GAC using Gram-negative bacteria Escherichia coli. Results showed that antibacterial studies of the synthesized nanocomposites exhibit effective antibacterial activity against E. coli compared with neat GAC alone. However, the composite HAP/TE/GAC revealed better activity than HAP/GAC. Heavy metal adsorption ability of the synthesized composites was carried out using Pb²⁺ ions at room temperature at different time intervals and different pH levels. The equilibrium adsorption data were assessed via Langmuir and Freundlich adsorption isotherm models for neat GAC, HAP/GAC and HAP/TE/GAC at pH 6. The equilibrium adsorption data for GAC, HAP/GAC and HAP/TE/GAC were well fitted with both Freundlich and Langmuir isotherm models in the given Pb²⁺ concentrations. The HAP/TE/GAC composite is capable of maintaining the natural function of GAC in addition to removal of bacterial contaminants and heavy metals, which can be used as a point-of-use water filter material.

Adsorption of heavy metals on conventional and nanostructured materials for wastewater treatment purposes: A review

The problem of water pollution is of a great concern. Adsorption is one of the most efficient techniques for removing noxious heavy metals from the solvent phase. This paper presents a detailed information and review on the adsorption of noxious heavy metal ions from wastewater effluents using various adsorbents - i.e., conventional (activated carbons, zeolites, clays, biosorbents, and industrial by-products) and nanostructured (fullerenes, carbon nanotubes, graphenes). In addition to this, the efficiency of developed materials for adsorption of the heavy metals is discussed in detail along with the comparison of their maximum adsorption capacity in tabular form. A special focus is made on the perspectives of further wider applications of nanostructured adsorbents (especially, carbon nanotubes and graphenes) in wastewater treatment.

Effect of competitive adsorption on zinc removal from aqueous solution and zinc smelting effluent by eucalyptus leaf-based magnetic biosorbent

The objectives of this study were to investigate the competitive sorption behaviors and mechanisms of heavy metals onto ELMB, a novel eucalyptus-leaf-based magnetic biosorbent, and to study the potential application of ELMB in the treatment of actual zinc smelting effluent after a necessary pretreatment process. ELMB and ELMB-metals systems were characterized using several techniques. Competitive sorption of Zn²⁺ with Pb²⁺, Cu²⁺ and Cd²⁺ onto ELMB was studied by batch experiments and the used sorbent was separated under a magnetic field. The results show that the ELMB can be considered as paramagnetic material with various functional groups on its surface. The presence of Pb²⁺, Cu²⁺ and Cd²⁺ significantly decreases the sorption of Zn²⁺ in either the binary system or multimetal systems. The order of adsorption preference is Pb²⁺ > Cu²⁺ > Cd²⁺ > Zn²⁺ in multimetal systems and the sequence of competitive ability to zinc is: Pb²⁺ > Cu²⁺ > Cd²⁺. Non-competitive Langmuir multicomponent isotherm model fits to the adsorption data of Pb²⁺ and Cu²⁺ well in aqueous solution. The co-existent Ca²⁺ and SO₄^2- decrease the removal efficiencies of heavy metals while the presence of Na⁺ and Cl^- shows little effect in the multimetal solution. In the case of actual zinc smelting effluent, "pretreatment + ELMB sorption" is successfully applied to remove heavy metals and the contents of Zn²⁺ and its associated metals are well below discharge limits.

Adsorption of Cd(II) and Pb(II) by in situ oxidized Fe3O4 membrane grafted on 316L porous stainless steel filter tube and its potential application for drinking water treatment

Removing heavy metal ions from aqueous solutions is one of the most challenging separations. In situ oxidized Fe₃O₄ membranes using 316L porous stainless steel filter tube have shown great potential for removing anion Cr(VI). Here we report the performances of the in situ oxidized Fe₃O₄ membranes for removing two toxic cations Cd(II) and Pb(II) commonly existing in water and their potential applications for drinking water purification. The membranes exhibited high removal efficiency: 97% at pH 9.0 for Cd(II) of 1.0 mg/L initial concentration and 100% at pH 5.0-6.0 for Pb(II) of 5.0 mg/L initial concentration. The maximum adsorption capabilities were estimated at 0.800 mg/g and 2.251 mg/g respectively for Cd(II) and Pb(II) at 318 K by the Langmuir model. Results of batch tests revealed the existence of electrostatic attraction and chemisorption. XRD and FT-IR analyses indicated that the chemisorption might be the insertion of Cd(II) and Pb(II) into the Fe₃O₄ crystal faces of 311 and 511 to form mononuclear or binuclear coordination with O atoms of Fe-O₆ groups. Competitive adsorption of Cd(II) and Pb(II) in binary solutions revealed a preferential adsorption for Pb(II). Na₂EDTA solution was used to regenerate the membranes, and the maximum desorption ratio was 90.29% and 99.75% respectively for Cd(II) and Pb(II). The membranes were able to efficiently lower Cd(II) and Pb(II) concentrations to meet the drinking water standards recommended by the World Health Organization and are promising for engineering applications aimed at drinking water purification.

Physicochemical effect of activation temperature on the sorption properties of pine shell activated carbon

Activated carbons produced from a variety of raw materials are normally selective towards a narrow range of pollutants present in wastewater. This study focuses on shifting the selectivity of activated carbon from inorganic to organic pollutants using activation temperature as a variable. The material produced from carbonization of pine shells substrate was activated at 250°C and 850°C. Both adsorbents were compared with commercial activated carbon for the sorption of lead, cadmium, methylene blue, methyl blue, xylenol orange, and crystal violet. It was observed that carbon activated at 250°C was selective for lead and cadmium whereas the one activated at 850°C was selective for the organic dyes. The Fourier transform infrared spectroscopy study revealed that AC850 had less surface functional groups as compared to AC250. Point of zero charge and point of zero salt effect showed that AC250 had acidic groups at its surface. Scanning electron microscopy depicted that increase in activation temperature resulted in an increase in pore size of activated carbon. Both AC250 and AC850 followed pseudo-second-order kinetics. Temkin isotherm model was a best fit for empirical data obtained at equilibrium. The model also showed that sorption process for both AC250 and AC850 was physisorption.

Bioturbation effects on heavy metals fluxes from sediment treated with activated carbon

Adding activated carbon (AC) to sediment has been proposed as an in situ sediment remediation technique. To date, it is not clear whether this technique is effective in the treatment of heavy metal-contaminated sediment in the presence of bioturbators. In the present study, we compare the ability of granular-activated carbon (GAC) and powder-activated carbon (PAC) to reduce Cu, Zn, and Pb pore water concentrations at environmentally relevant concentrations in the absence and presence of Chironomid larvae. Compared to untreated sediment, PAC and GAC addition in the absence of Chironomid larvae resulted in reductions of free Cu concentrations of 78 and 66 % just below the sediment-water interface after 28 days, respectively. While for Pb and Zn these concentration reductions were only 40 and 38, 19 and 25 %, respectively. The presence of Chironomid larvae in untreated, and GAC sediment generally increased the free heavy metals concentrations in pore water, especially in the deeper layers. In comparison with untreated sediment, the coexistence of AC enhanced the accumulation of heavy metals, especially for PAC. This increased bioaccumulation may decrease the survival of Chironomid larvae. The result indicated that ACs may not be suitable for the remediation of heavy metal-contaminated sediments.

Facile preparation of highly hydrophilic, recyclable high-performance polyimide adsorbents for the removal of heavy metal ions

To obtain high-performance adsorbents that combine excellent adsorption ability, thermal stability, service life and recycling ability, polyimide (PI)/silica powders were prepared via a facile one-pot coprecipitation process. A benzimidazole unit was introduced into the PI backbone as the adsorption site. The benzimidazole unit induced more hydroxyls onto the silica, which provided hydrophilic sites for access by heavy metal ions. By comprehensively analyzing the effect of hydrophilcity, agglomeration, silica polycondensation, specific surface area and PI crystallinity, 10% was demonstrated to be the most proper feed silica content. The equilibrium adsorption amount (Qe) for Cu(2+) of PI/silica adsorbents was 77 times higher than that of pure PI. Hydrogen chloride (HCl) was used as a desorbent for heavy metal ions and could be decomplexed with benzimidazole unit at around 300°C, which was lower than the glass transition temperature of PI. The complexation and decomplexation process of HCl made PI/silica adsorbents recyclable, and the adsorption ability remained steady for more than 50 recycling processes. As PI/silica adsorbents possess excellent thermal stability, chemical resistance and radiation resistance and hydrophilicity, they have potential as superior recyclable adsorbents for collecting heavy metal ions from waste water in extreme environments.

Influence of operating parameters on the performance of magnetic seeding flocculation

In the present study, magnetic seeding flocculation was applied to remove copper (200 mg/L) and turbidity (180 mg/L) from simulated microetch copper waste. Fe3O4 particles (40 to 1600 mesh) were used as magnetic seeds. Poly-aluminum chloride (PAC) and anionic polyacrylamide (PAM) were added as coagulant and flocculant, respectively. The effect of operating factors, such as the dosages of the coagulant and flocculant, initial pH of the wastewater, and dosage and size of the magnetic seeds, on copper and turbidity removal was systematically investigated. In addition, settling speed, floc-size distribution, and volume of sludge were measured with and without the addition of magnetic seeds to compare the efficiency of magnetic seeding to that of traditional flocculation. The results indicated that the highest settling speed, the largest floc size, and the smallest volume of sludge were obtained simultaneously when the dosage and size of magnetic seeds were 2.0 g/L and 300–400 mesh, respectively. High removal efficiencies of 98.53 and 94.72 % for copper and turbidity, respectively, were also achieved under this condition; values that are 4.11 and 0.61 % higher, respectively, than those found in traditional flocculation. The high performance might be attributed to efficient collision of particles and slightly moderate vortex centrifugal force of inertia among the magnetic seeds, which could produce larger magnetic flocs with lower moisture.

Competitive adsorption of metals on cabbage waste from multi-metal solutions

This study assessed the adsorption capacity of the agro-waste 'cabbage' as a biosorbent in single, binary, ternary and quaternary sorption systems with Cu(II), Pb(II), Zn(II) and Cd(II) ions. Dried and ground powder of cabbage waste (CW) was used for the sorption of metals ions. Carboxylic, hydroxyl, and amine groups in cabbage waste were found to be the key functional groups for metal sorption. The adsorption isotherms obtained could be well fitted to both the mono- and multi-metal models. In the competitive adsorption systems, cabbage waste adsorbed larger amount of Pb(II) than the other three metals. However, the presence of the competing ions suppressed the sorption of the target metal ions. Except the case of binary system of Cd(II)-Zn(II) and Cd(II)-Cu(II), there was a linear inverse dependency between the sorption capacities and number of different types of competitive metal ions.

Comparative study of adsorption of Pb(II) on native garlic peel and mercerized garlic peel

A comparative study using native garlic peel and mercerized garlic peel as adsorbents for the removal of Pb(2+) has been proposed. Under the optimized pH, contact time, and adsorbent dosage, the adsorption capacity of garlic peel after mercerization was increased 2.1 times and up to 109.05 mg g(-1). The equilibrium sorption data for both garlic peels fitted well with Langmuir adsorption isotherm, and the adsorbent-adsorbate kinetics followed pseudo-second-order model. These both garlic peels were characterized by elemental analysis, Fourier transform infrared spectrometry (FT-IR), and scanning electron microscopy, and the results indicated that mercerized garlic peel offers more little pores acted as adsorption sites than native garlic peel and has lower polymerization and crystalline and more accessible functional hydroxyl groups, which resulted in higher adsorption capacity than native garlic peel. The FT-IR and X-ray photoelectron spectroscopy analyses of both garlic peels before and after loaded with Pb(2+) further illustrated that lead was adsorbed on the through chelation between Pb(2+) and O atom existed on the surface of garlic peels. These results described above showed that garlic peel after mercerization can be a more attractive adsorbent due to its faster sorption uptake and higher capacity.

Waste biomass adsorbents for copper removal from industrial wastewater--a review

Copper (Cu(2+)) containing wastewaters are extensively released from different industries and its excessive entry into food chains results in serious health impairments, carcinogenicity and mutagenesis in various living systems. An array of technologies is in use to remediate Cu(2+) from wastewaters. Adsorption is the most attractive option due to the availability of cost effective, sustainable and eco-friendly bioadsorbents. The current review is dedicated to presenting state of the art knowledge on various bioadsorbents and physico-chemical conditions used to remediate Cu(2+) from waste streams. The advantages and constraints of various adsorbents were also discussed. The literature revealed the maximum Cu adsorption capacities of various bioadsorbents in the order of algae>agricultural and forest>fungal>bacterial>activated carbon>yeast. However, based on the average Cu adsorption capacity, the arrangement can be: activated carbon>algal>bacterial>agriculture and forest-derived>fungal>yeast biomass. The data of Cu removal using these bioadsorbents were found best fit both Freundlich and Langmuir models. Agriculture and forest derived bioadsorbents have greater potential for Cu removal because of higher uptake, cheaper nature, bulk availability and mono to multilayer adsorption behavior. Higher costs at the biomass transformation stage and decreasing efficiency with desorption cycles are the major constraints to implement this technology.

Removal of heavy metal ions from wastewaters: a review

Heavy metal pollution has become one of the most serious environmental problems today. The treatment of heavy metals is of special concern due to their recalcitrance and persistence in the environment. In recent years, various methods for heavy metal removal from wastewater have been extensively studied. This paper reviews the current methods that have been used to treat heavy metal wastewater and evaluates these techniques. These technologies include chemical precipitation, ion-exchange, adsorption, membrane filtration, coagulation-flocculation, flotation and electrochemical methods. About 185 published studies (1988-2010) are reviewed in this paper. It is evident from the literature survey articles that ion-exchange, adsorption and membrane filtration are the most frequently studied for the treatment of heavy metal wastewater.