Sorption of lead from aqueous solution by chemically modified carbon adsorbents

Application of Noug (Guizotia abyssinica cass.) stalk activated carbon for the removal of lead (II) ions from aqueous solutions

Due to the rise of industries worldwide, huge amounts of pollutants including heavy metals are released into the surroundings. Disposal of effluents containing heavy metals in higher concentrations without proper treatment is common in industries; lead is one of them. This study aims to determine and optimize the efficiency of Noug (Guizotia abyssinica Cass.) stalk porous carbon (NSAC) for the elimination of lead (II) from aqueous solutions. For studying the adsorption characteristics of Noug stalk activated carbon (NSAC) an adsorbate of lead (II) ions was used. The interaction and effect of the following parameters on Pb(II) adsorption were investigated using Design Expert version 7.0 software (central composite design) to determine the optimum adsorption condition: pH, initial concentration of Pb(II) ion, adsorbent dose, and contact time. The optimized condition for the elimination of lead (II) using Noug stalk porous carbon (98.77 %) was achieved at pH [4.87], initial concentration of Pb(II) [84.66 mg/L], adsorbent dose [18.43 g/L], and contact time [2.04 h]. The pseudo-second-order kinetics and the Langmuir isotherm model which had a maximum adsorption capacity of 89.25 mg/g, provided the best-fit models for Pb(II) adsorption, with R2 values of 0.99 and 0.98, respectively. Efficient elimination of Pb(II) from wastewater can be performed through the use of NSAC. Future research should delve more into column adsorption under continuous wastewater flow.

Efficient removal of PAHs from peanut oil using coconut shell-based activated charcoal decorated by cationic (CTAB), anionic (SDS), non-ionic surfactant (Triton X-100)

The coconut shell-based activated charcoal was decorated by three different electronegativities of surfactants (CTAB, SDS, and Triton X-100) through the impregnation method, and the decorated activated charcoal adsorbents were used for the removal of PAHs from peanut oil, respectively. The influence of surfactant decoration on the adsorption and detoxification effect of coconut shell-based activated charcoal was discussed. The thermodynamic and kinetic behaviors of PAHs adsorption on the surfactant-modified activated charcoal were investigated, and the adsorption mechanism was analyzed in-depth. Notably, the prepared modified coconut shell activated charcoal could not only remove more than 90% of PAHs from the peanut oil but also keep the cytotoxicity of the treated peanut oil low. Meanwhile, the detoxification procedure has little effect on the nutritional quality and flavor of the peanut oil. The results of this fundamental study demonstrate that the low-cost surfactant-modified coconut shell-based activated charcoal was effective and feasible.

An efficient biosorbent for the removal of arsenic from a typical urban-generated wastewater

The arousal of environmental concerns due to spike in environmental degradation has necessitated proper waste management and disposal. Arsenic, a potentially toxic element in cassava wastewater, requires treatment prior to the wastewater disposal to minimize environmental pollution and associated health implications. The present study thus addressed the treatment of As⁵⁺ heavy metal in cassava wastewater using an efficient biosorbent from chemically pretreated unshelled Moringa oleifera seeds. The effect of various factors influencing the biosorption process for arsenate removal was studied including pH, contact time, biosorbent dosage, and biosorbent pretreatment concentration. The results of Fourier transform infrared spectroscopy clearly suggested that additional functional groups attributed to esters were formed in the pretreated biosorbent, which is responsible for improvement in biosorption. It was found that contact time, biosorbent dosage, and biosorbent pretreatment concentration had statistically significant effect (p values < 0.05) on arsenate removal. A maximum percentage removal of 99.9% was achieved in the synthetic solution at pH 4.0, contact time of 30 min, and dosage of 2 g for biosorbent pretreated with 1 M of chemical solution. Furthermore, through isotherm and kinetics studies, it was discovered that the biosorption process for untreated biosorbent is by ion exchange, while that for treated biosorbents indicated a multifarious adsorption mechanism. Moreover, the biosorption process was exothermic and spontaneous. Also, it is noted that the sorption capability of the biosorbent increases with pretreatment concentration. A statistical model has been developed with prediction R² of 0.898, which incorporates the effect of treatment concentration on the percentage removal of As⁵⁺ from cassava wastewater.

Utilization of Phyllanthus emblica fruit stone as a Potential Biomaterial for Sustainable Remediation of Lead and Cadmium Ions from Aqueous Solutions

In the present work, an effort has been made to utilize Phyllanthus emblica (PE) fruit stone as a potential biomaterial for the sustainable remediation of noxious heavy metals viz. Pb(II) and Cd(II) from the aqueous solution using adsorption methodology. Further, to elucidate the adsorption potential of Phyllanthus emblica fruit stone (PEFS), effective parameters, such as contact time, initial metal concentration, temperature, etc., were investigated and optimized using a simple batch adsorption method. It was observed that 80% removal for both the heavy metal ions was carried out within 60 min of contact time at an optimized pH 6. Moreover, the thermodynamic parameters results indicated that the adsorption process in the present study was endothermic, spontaneous, and feasible in nature. The positive value of entropy further reflects the high adsorbent-adsorbate interaction. Thus, based on the findings obtained, it can be concluded that the biosorbent may be considered a potential material for the remediation of these noxious impurities and can further be applied or extrapolated to other impurities.

Simultaneous removal of heavy metals and dyes in water using a MgO-coated Fe3O4 nanocomposite: Role of micro-mixing effect induced by bubble generation

This study focused on the development of a nano-adsorbent for contaminant removal without the use of any external energy. An eco-friendly Fe₃O₄@MgO core-shell nanocomposite was synthesized and tested for the removal of a heavy metal, lead (Pb²⁺) and a dye, rhodamine B (RhB). The addition of H₂O₂ into the system enabled the self-mixing of the aqueous solution containing Fe₃O₄@MgO through the generation of bubbles. This system showed an excellent removal efficiency of 99% in just 15 min for Pb²⁺ and 120 min for RhB, which is far better than the control experiment (without H₂O₂). The cation exchange mechanism dominated in the removal of heavy metals, while the adsorptive removal of dye proceeded through the H-bonding between Mg(OH)₂ and dye molecules. The removal efficiency increased exponentially with the increase of H₂O₂ at the optimal concentration of 5% and it was effective over a wide pH range. Moreover, the performance of the Fe₃O₄@MgO-H₂O₂ system was verified for other heavy metals such as Cd, Ni, Zn, Co, and Cu, demonstrating that the Fe₃O₄@MgO-H₂O₂ system can be widely implemented in the treatment of real water matrices contaminated with heavy metals and organic dyes.

Waste biomass based potential bioadsorbent for lead removal from simulated wastewater

Present study deals with the lead removal from simulated wastewater using cost effective bio-adsorbent of mango seeds cover with kernel (M), and jamun seeds cover with kernel (JP). Lead removal optimization of adsorption parameters has been analyzed by using Response surface methodology (RSM). The optimum adsorption was attained at speed of 500 rpm, 60 mg, pH 6.5 and contact time of 120 min. The adsorption capacities are around 39.15 mg/g of M and 20.28 mg/g of JP bio-adsorbent, and also the maximum Pb removal were observed ̴ 94.85% and 92.78%, respectively. The regression coefficient was best fitted for both bio-adsorbents are Freundlich model and pseudo-first order reaction kinetic.

Treatment and Recovery of High-Value Elements from Produced Water

Oil and gas production wells generate large volumes of water mixed with hydrocarbons (dispersed and dissolved), salts (ions), and solids. This ‘produced water’ (PW) is a waste stream that must be disposed of appropriately. The presence of toxic hydrocarbons and ions in PW makes it unsuitable for surface discharge or disposal in groundwater resources. Thus, PW is often injected into deep geological formations as a disposal method. However, the supply of global water sources is diminishing, and the demand for water in industrial, domestic, and agricultural use in water-stressed regions makes PW a potentially attractive resource. PW also contains valuable elements like lithium and rare earth elements, which are increasing in global demand. This review article provides an overview of constituents present in PW, current technologies available to remove and recover valuable elements, and a case study highlighting the costs and economic benefits of recovering these valuable elements. PW contains a promising source of valuable elements. Developing technologies, such as ceramic membranes with selective sorption chemistry could make elemental recovery economically feasible and turn PW from a waste stream into a multi-faceted resource.

Adsorption capacity of composite bio-modified geopolymer for multi-component heavy metal system: optimisation, equilibrium and kinetics study

Industrialisation and urbanisation contribute greatly to the deposition of toxic waste and metalloids to the environment. Therefore, the use of efficient and eco-friendly materials such as geopolymers and biopolymers is essential for the adsorption of the toxic metals. The implementation of these low-cost sorbents has fascinated a great deal of interest owing to effectiveness, ease of operation, less environmental impact, etc. In this study, biocomposites were synthesised from bio-treatment of geopolymer (kaolin and palm oil fuel ash) using an anionic biopolymer. The biocomposites were utilised as biosorbent for removal of Cu, Fe and Zn in a multi-component system, with the process parameters optimised. FTIR and SEM/EDX outcomes clearly denoted the microporous framework of geopolymer structures and the presence of bio-molecules from the biopolymer. XRD and XRF techniques on the precursors described suitability for geopolymerisation due to the rich aluminate-silicate content. Based on response surface methodology, the adsorption capacities for Cu, Fe and Zn are 35.01 mg/g, 45.175 mg/g and 44.630 mg/g at optimal conditions of pH (7.5), time (40.5 min), metal ion concentration (80 mg/l), biosorbent dosage (0.2 g) and biopolymer concentration (0.75 g in 50 ml). The multi-component system was apt with the modified competitive Langmuir isotherm which described the homogeneity of the prominent sites of the biocomposites. Based on the adsorption kinetics, Cu was only dominated by the pseudo-first-order reaction (PFOR) while Fe and Zn were influenced by both PFOR and intra-particle diffusion processes. The result obtained from the synthesised biocomposites recommends application to actual wastewater systems.

Sustainable removal of arsenic from simulated wastewater using solid waste seed pods biosorbents of Cassia fistula L

The present investigation is focused to develop a new type of solid waste based biosorbent, derived from the Cassia fistula pod biomass. The prepared biosorbent has been characterized through different techniques including field emission scanning electron microscopy, fourier transform infrared spectroscope and X-ray diffraction to investigate the physiochemical properties which are potential for the bioadsorbent application. The experiments have been performed considering four parameters namely; pH, biosorbent dose, initial concentration of As⁺³ and duration in the batch reactor. The experimental results have been analyzed using the design-expert software for the optimization of different parameters. The maximum removal of arsenic could be achieved ∼91% whereas monolayer adsorption capacity is found to be 1.13 mg g^-1 in 80 min at pH 6.0 and 30 °C by using 60 mg dose of bioadsorbent. The arsenic adsorption behavior of the bio-adsorbent has been well interpreted in terms of pseudo-first order and Freundlich model.

Sustainable Chromium Recovery From Wastewater Using Mango and Jackfruit Seed Kernel Bio-Adsorbents

Wastewater is a rich source of valuable chemicals of industrial importance. However, their economic recovery is crucial for sustainability. The objective of the present work is to recover hexavalent chromium (Cr VI) as a value-added transition metal from wastewater cost-effectively; the biosorbent derived from seed kernels of mango (M) and jackfruit (JF) were applied for removing the metal from simulated wastewater. The functional groups of the biomass were analysed with the help of Fourier transform infrared (FTIR) spectroscopy, micrographs were generated using a scanning electron microscope, and crystallinity was determined by an x-ray diffractometer (XRD). The concentration of Cr VI in wastewater was analysed by an inductively coupled plasma optical emission spectrometer (ICP-OES). Process parameters (pH, dose, contact time, temperature, and initial concentration) were optimized for efficient Cr VI adsorption using a response surface methodology-based Box-Behnken design (BBD) employing Design-software 6.0.8. The batch experiment at room temperature at pH 4.8 and Cr VI removal ∼94% (M) and ∼92% (JF) was achieved by using a 60-mg dose and an initial Cr (VI) concentration of 2 ppm in 120 min. The equilibrium Cr binding on the biosorbent was well explained using Freundlich isotherm (R ² = 0.97), which indicated the indirect interactions between Cr (VI) and the biosorbent. Biosorption of Cr (VI) followed the pseudo-order and intra-particle diffusion models. The maximum adsorption capacity of the M and JF bio-adsorbent is 517.24 and 207.6 g/mg, respectively. These efficient, cost-effective, and eco-friendly biosorbents could be potentially applied for removing toxic Cr (VI) from polluted water.

Java plum and amaltash seed biomass based bio-adsorbents for synthetic wastewater treatment

Biomass of Java plum (JP) and amaltash (AT) seeds were employed to remove arsenic from synthetic wastewater, cost effectively. The prepared biomasses were characterized by FE-SEM, EDX, FTIR, XRD, and ICP techniques. Experimentation the optimization study has been carried out by using Design-software 6.0.8. Response surface methodology has been applied to design the experiments where we have used three factors and three levels Box-Behnken design (BBD). Arsenic removal ability of bio-sorbents was evaluated and optimized by varying pH, adsorbent dose concentration of arsenic in synthetic wastewater. For 2.5 mg/L arsenic concentration and 80 mg adsorbent dose at pH 8.8 Java plum seeds (JP) based bio-adsorbent removed ∼93% and amaltash seeds (AT) based bio-adsorbent removed ∼91% arsenic from synthetic wastewater. The adsorption behaviour better explained following Freundlich model (R² = 0.99) compared to Temkin model (R² = 0.986) for As (III) ions. The adsorption capacity was 1.45 mg g^-1 and 1.42 mg g^-1 for JP and AT, respectively after 80 min under optimal set of condition. The adsorption kinetics was explained by either pseudo-first order model or Elovich model.

Study on Cost-Efficient Carbon Aerogel to Remove Antibiotics from Water Resources

Because of pharmaceutical-emerging contaminants in water resources, there has been a significant increase in the antibiotic resistance in bacteria. Therefore, the removal of antibiotics from water resources is essential. Various antibiotics have been greatly studied using many different carbon-based materials including graphene-based hydrogels and aerogels. In this study, carbon aerogels (CAs) were synthesized from waste paper sources and their adsorption behaviors toward three antibiotics (hygromycin B, gentamicin, and vancomycin) were investigated, for which there exist a limited number of reports in the literature. The prepared CAs were characterized with scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and micro-computerized tomography (μ-CT). According to the μ-CT results, total porosity and open porosity were calculated as 90.80 and 90.76%, respectively. The surface area and surface-to-volume ratio were found as 795.15 mm² and 16.79 mm^-1, respectively. The specific surface area of the CAs was found as 104.2 m²/g. A detailed adsorption study was carried out based on different pH values, times, and analyte concentrations. The adsorption capacities were found as 104.16, 81.30, and 107.52 mg/g for Hyg B, Gen, and Van, respectively. For all three antibiotics, the adsorption behavior fits the Langmuir model. The kinetic studies showed that the system fits the pseudo-second-order kinetic model. The production of CAs, within the scope of this study, is safe, facile, and cost-efficient, which makes these green adsorbents a good candidate for the removal of antibiotics from water resources. This study represents the first antibiotic adsorption study based on CAs obtained from waste paper.

Adsorption of Cu(II) by phosphogypsum modified with sodium dodecyl benzene sulfonate

Phosphogypsum (PG) is a solid waste generated during the wet production of phosphoric acid, and stockpiling PG causes serious pollution to the environment. Therefore, we prepared an adsorption material modified with sodium dodecyl benzene sulfonate (SDBS) based on PG (SDBS@PG). SDBS@PG can be regenerated and used in several adsorption-desorption cycles. The optimum conditions for Cu(II) removal are as follows: the Cu(II) concentration is 10 mg/L, the amount of adsorbent is 1.6 g/L, the pH is 6, and the contact time is 60 min. Under these conditions, the removal rate is 99.23 %. The kinetic data of adsorption conform to the pseudo-second-order model. The equilibrium isotherm results are consistent with the Langmuir isotherm equation. Furthermore, plausible mechanisms were proposed: PG was modified with SDBS, which greatly improved the adsorption of Cu(II) onto PG. The main reason is that SDBS is adsorbed on the surface of PG by chemical action in the form of micelles and then Cu(II) is adsorbed on the anionic SDBS micelles of SDBS@PG due to chemical and electrostatic interactions. This work indicates that SDBS@PG can be used for the removal of Cu(II) and is qualified for practical application.

Amyloid Fibrils Aerogel for Sustainable Removal of Organic Contaminants from Water

Water contamination by organic pollutants is ubiquitous and hence a global concern due to detrimental effects on the environment and human health. Here, it is demonstrated that amyloid fibrils aerogels are ideal adsorbers for removing organic pollutants from water. To this end, amyloid fibrils prepared from β-lactoglobulin, the major constituent of milk whey protein, are used as building blocks for the fabrication of the aerogels. The adsorption of Bentazone, Bisphenol A, and Ibuprofen, as model pollutants, is evaluated under quasi-static conditions, without use of energy or pressure. Through adsorption by amyloid fibrils aerogel, excellent removal efficiencies of 92%, 78%, and 98% are demonstrated for Bentazone, Bisphenol A, and Ibuprofen, respectively. Furthermore, the maximum adsorption capacity of amyloid fibrils aerogel for Bentazone, Bisphenol A, and Ibuprofen is 54.2, 50.6, and 69.6 mg g^-1 , respectively. To shed light on the adsorption equilibrium process, adsorption isotherms, binding constants, saturation limits, and the effect of pH are evaluated. Finally, the regeneration of the aerogel over three consecutive cycles is studied, exhibiting high reusability with no significant changes in its removal performance. These results point at amyloid fibrils aerogels as a sustainable, efficient, and inexpensive technology for alleviating the ubiquitous water contamination by organic pollutants.

Facile and efficient removal of Pb(II) from aqueous solution by chitosan-lead ion imprinted polymer network

A new chitosan based imprinted polymer was prepared by copolymerization of 4-Vinylpyridine (VP) as a functional monomer and N,N'-Methylenebisacrylamide (MBA) as a crosslinker in the presence of Potassium peroxodisulfate (KPS) as an initiator to eliminate Pb(II) from aqueous solutions. The template ions were removed from ion imprinted polymer (IIPs) particles by leaching with 0.1 M nitric acid (HNO₃) that leaves cavities in the particles with the capability of selective extraction of the Pb(II) ions. Some properties of the bioadsorbent were further identified using Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and Thermal Gravimetric Analysis (TGA). In addition, the equilibrium adsorption data were examined through Langmuir and Freundlich isotherm models and it was found that adsorption data fit well with the Freundlich isotherm. The competitive adsorption studies clearly showed that the Pb(II)-IP has a much higher adsorption capacity for Pb(II) than the non-imprinted polymer (NIP) with the same chemical composition; furthermore, it has excellent selectivity for the targeted ion. In addition, the studies regarding the regeneration and reuse studies revealed that the Pb(II)-IP beads showed no significant decrease in their adsorption capacities.

Amido-amine derivative of alginic acid (AmAA) for enhanced adsorption of Pb(II) from aqueous solution

The present work reports the alternate synthesis of amido-amine derivative of alginic acid (AmAA) with high degree of functionalization. The AmAA have been characterized for percentage functionalization, functional group change, surface morphology and thermal decomposition behavior. The results indicate that the amido-amine derivatisation of alginic acid (AA) with >95% functionalization, significantly improves its Pb(II) adsorption efficiency (395.72 mg/g to 535.87 mg/g) over the AA. The equilibrium and kinetic studies showed that Langmuir and Freundlich adsorption isotherm models fitted well to the experimental data, and these followed pseudo-second order kinetic model. The FTIR (Fourier transform infrared spectroscopy) and ¹³C CP-MAS NMR (Cross-polarization magic angle spinning carbon-13 solid state nuclear magnetic resonance spectroscopy) analysis revealed that Pb(II) binds to the carboxyl group in case of AA and to the carbonyl & amine group in case of AmAA, which leads to increase in its adsorption efficiency. The study concludes that the functionalization of amido-amine on AA improves its adsorptive efficiency for Pb(II) from aqueous medium.

Biological, nutritional, and therapeutic significance of Moringa oleifera Lam

The genus Moringa Adans. comprises 13 species, of which Moringa oleifera Lam. native to India and cultivated across the world owing to its drought and frost resistance habit is widely used in traditional phytomedicine and as rich source of essential nutrients. Wide spectrum of phytochemical ingredients among leaf, flower, fruit, seed, seed oil, bark, and root depend on cultivar, season, and locality. The scientific studies provide insights on the use of M. oleifera with different aqueous, hydroalcoholic, alcoholic, and other organic solvent preparations of different parts for therapeutic activities, that is, antibiocidal, antitumor, antioxidant, anti-inflammatory, cardio-protective, hepato-protective, neuro-protective, tissue-protective, and other biological activities with a high degree of safety. A wide variety of alkaloid and sterol, polyphenols and phenolic acids, fatty acids, flavanoids and flavanol glycosides, glucosinolate and isothiocyanate, terpene, anthocyanins etc. are believed to be responsible for the pragmatic effects. Seeds are used with a view of low-cost biosorbent and coagulant agent for the removal of metals and microbial contamination from waste water. Thus, the present review explores the use of M. oleifera across disciplines for its prominent bioactive ingredients, nutraceutical, therapeutic uses and deals with agricultural, veterinarian, biosorbent, coagulation, biodiesel, and other industrial properties of this "Miracle Tree."

Thermodynamic study of adsorption of nickel ions onto carbon aerogels

In this work, 8 samples of carbon aerogels with different ratios of catalyst versus resorcinol (R/C) from 25 to 1500 were used. The textural properties were evaluated from N₂ adsorption isotherms in 77 K, as well as the chemical ones, where the surface chemistry was evaluated through the Boehm titrations. The results were analyzed and related to the adsorption of the nickel (II) ion from aqueous solution. The experimental results show that the aerogel samples can be divided into two series with different properties: Series I, mainly microporous (low ratio R/C) and Series II (high ratio R/C) mainly microporous but with a contribution of mesoporosity. The specific surface area varied between 64 and 990 m² g^-1. The experimental results show that prepared aerogels have an adequate adsorption capacity towards nickel (II) ions. The behavior of the kinetics of Ni(II) adsorption on carbon aerogels adjusts in a better way the kinetic model of pseudo-second order since it is the one that presents the value of the highest R² correlation coefficient. The calorimetric data shows that the greater the area developed in carbons aerogels the enthalpy increases.

A comparative study for removal of cadmium(II) ions using unmodified and NTA-modified Dendrocalamus strictus charcoal powder

Release of cadmium, a non-essential and highly toxic heavy metal, into aquatic ecosystem through discharge of effluents from various industries such as electroplating, photographic, steel/iron production and tanneries, is of considerable environmental conern at global level. Hence, it is essential to develop economic methods to remove cadmium from industrial effluents before their discharge into water bodies. The aim of present study was to explore the efficiency of Nitrilotriacetic acid (NTA) for the surface modification of Dendrocalamus strictus charcoal powder (DCP) and application of both unmodified DCP and NTA modified DCP (NTA-MDCP) as adsorbents to remove cadmium (II) ions from aqueous solution. Isotherms, thermodynamic and kinetic studies were carried out to describe the adsorption behavior of both adsorbents for the removal of Cd(II) ions. Maximum adsorption capacity calculated from Langmuir isotherm was found to be higher for NTA-MDCP (166.66 mg/g) as compared to DCP (142.85 mg/g) which may be attributed to the complex formation (1:1 & 2:1) between NTA on the surface of adsorbent and Cd(II) ions in the solution at optimum conditions: pH = 6, temperature = 25 °C, adsorbent dose = 2 g/l and contact time = 2 h. Thermodynamic studies confirmed endothermic as well as spontaneous nature of adsorption process and kinetic investigation revealed that the adsorption process followed pseudo second-order for both DCP and NTA-MDCP. Physical characterization of both adsorbents before and after adsorption was studied using Scanning Electron Microscope, Brunauer-Emmett-Teller surface analyzer, Energy Dispersion X-ray Spectrometer, CHNS analyzer and X-Ray diffractometer which confirmed the adsorption of cadmium(II) ions. Further, the desorption studies for regeneration of adsorbents were successfully carried out using two eluents viz., 1 M sulfuric acid and 0.5% calcium chloride. The present study revealed that NTA-MDCP could be used as an effective adsorbent for the removal of cadmium(II) ions from aqueous solution.

Adsorption of Rhodamine B dye from aqueous solution onto acid treated banana peel: Response surface methodology, kinetics and isotherm studies

The adsorption of rhodamine B (RhB) using acid modified banana peels has been examined. Chemical characteristics of the adsorbents were observed in order to determine active functional groups. The major functional groups on the surface were OH, C = O, C = C and C-O-C. Interactions between operational parameters were studied using the central composite design (CCD) of response surface methodology (RSM). The predictions of the model output indicated that operational factors influenced responses at a confidence level of 95% (P<0.05). The optimum conditions for adsorption were pH 2 at a 0.2 g/L dose within 60 minutes of contact time. Isotherm studies were carried out using the optimized process variables. The data revealed that RhB adsorption fitted the Langmuir isotherm equation while the reduction of COD followed the Freundlich isotherm. Kinetic experiments fitted the pseudo second order model for RhB removal and COD reduction. The adsorption mechanism was not the only rate controlling step. Diffusion through the boundary layer described the pattern of adsorption.

A novel route for preparation of chemically activated carbon from pistachio wood for highly efficient Pb(II) sorption

Pistachio wood-derived activated carbon prepared by a two-stage process (PWAC-2), conducting two consecutive chemical activation processes with NH₄NO₃ and NaOH, respectively. The results showed that explosive characteristic of NH₄NO₃ can primarily be employed to produce a char, with a large surface area and a highly-ordered pore structure, which can be subjected to a second activation process with NaOH to prepare a more suitable activated carbon, with a highly porous structure and useful functional groups, for removal of lead ions from aqueous media. An L₂₅ Taguchi experimental design was used by varying impregnation ratio, activation time and temperature in both pre- and post-activation stages, and the results showed that, in both stages, a small activating agent/precursor and a proportional low activation time suffice for preparation of an advantageous activated carbon for Pb(II) adsorption. A comprehensive study was performed on the equilibrium, kinetic and thermodynamic aspects of Pb(II) adsorption by the new activated carbon. The results exhibited that, having had a high lead adsorption capacity (190.2 mg g^-1), a high adsorption rapidness, and thermodynamic favorability, PWAC-2 is a beneficial alternative for utilization in full-scale plants of lead removal from waters and wastewaters.

Feasibility study of cadmium adsorption by palm oil fuel ash (POFA)-based low-cost hollow fibre zeolitic membrane

Palm oil fuel ash (POFA) is an agricultural waste which was employed in this study to produce novel adsorptive ceramic hollow fibre membranes. The membranes were fabricated using phase inversion-based extrusion technique and sintered at 1150 °C. The membranes were then evaluated on their ability to adsorb cadmium (Cd(II)). These membranes were characterised using (nitrogen) N₂ adsorption-desorption analysis, field emission scanning electron microscopy-energy-dispersive X-ray spectroscopy (FESEM-EDX) mapping, X-ray fluorescence (XRF), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses while adsorptivity activity was examined by batch adsorption studies. The adsorption test results show that the quantity of hollow fibre used and water pH level significantly affected the adsorption performance with the 3-fibre membrane yielding 96.4% Cd(II) removal in 30 min equilibrium time at pH 7. These results are comparable to those reported by other studies, and hence demonstrate a promising alternative of low-cost hollow fibre adsorbent membrane. Graphical abstract Figure of FESEM image of the hollow fibre, proposed mechanism and the graph of percentage removal of Cd(II) using POFA.

Super high removal capacities of heavy metals (Pb2+ and Cu2+) using CNT dendrimer

This research demonstrates the capability of carbon nanotubes (CNT) modified with four generations of poly-amidoamine dendrimer (PAMAM, G4) to remove Cu²⁺ and Pb²⁺ heavy metals from aqueous solution in single and binary component systems. Uniquely high adsorption capacities for copper and lead, which are 3333 and 4870mg/g respectively, were achieved. FTIR, H¹ NMR, Zeta potential, SEM and TEM techniques were employed for characterizing the synthetic nanocomposite and indicated that the dendrimer functionalized CNTs have been synthesized. The effects of several parameters including initial metal ion concentration, solution pH and the nanocomposite dosage were studied. The experimental data were analyzed by the Langmuir and Freundlich isotherms and the pseudo-first order and pseudo-second order kinetics models. The maximum adsorption occurred at pH=7. The adsorption process for Cu²⁺ and Pb²⁺ in single and binary component systems fit the Langmuir and extended Langmuir models respectively. This study also tested the kinetic sorption of the metals on PAMAM/CNT in single and binary component metal systems at various metal ions concentrations. The results showed that PAMAM/CNT nanocomposite was a super-adsorbent, able to uptake uniquely large quantities of heavy metal from single and binary component liquid phase.

Removal of cadmium (II) from aqueous solution: A comparative study of raw attapulgite clay and a reusable waste-struvite/attapulgite obtained from nutrient-rich wastewater

In this study, raw attapulgite (APT) and a novel adsorbent, struvite/attapulgite (MAP/APT) obtained from nutrient-rich wastewater treated by MgO modified APT, were applied as the absorbent for Cd(II) ion removal from aqueous solution. The two adsorbents were characterized by BET, SEM-EDS, XRD, FT-IR. Raw APT and MAP/APT separately presented the maximum Cd(II) adsorption capacities of 10.38mg/g and 121.14mg/g at pH of 5.45. The Cd(II) adsorption on raw APT and MAP/APT could be well fitted by Freundlich isotherm and Langmuir isotherm, respectively. Pseudo-second order equation was able to properly describe the kinetics of Cd(II) adsorption by raw APT and MAP/APT. The calculated thermodynamic parameters indicated that Cd(II) adsorption onto raw APT and MAP/APT were spontaneous and endothermic. An economic evaluation revealed that the treatment costs of the adsorption process by raw APT and MPA/APT were 0.013 $ per 1000mg Cd and 0.004 $ per 1000mg Cd, respectively.

Characterization and lead(II) ions removal of modified Punica granatum L. peels

The aim of the present study was to enhance the biosorption capacity of a waste biomass of Punica granatum L. peels (PGL) using various chemical modification agents. Among these agents, hexamethylenediamine (HMDA) indicated the best performance with regard to the improvement of lead(II) ions removal from aqueous solution. The characterization of HMDA-modified P. granatum L. peels (HMDA-PGL) was achieved by using elemental analysis, FT-IR, thermogravimetric (TG) analysis and zeta potential measurement techniques. Based on FT-IR study, the chemical modification of P. granatum L. peels take place with its carboxyl, carbonyl, hydroxyl, etc. groups and these groups are responsible for the biosorption of lead(II) ions onto modified biomass. Biosorption equilibrium and kinetic data fitted well the Langmuir isotherm and the pseudo-second-order kinetic models, respectively. The highest biosorption capacity obtained from Langmuir isotherm model was 371.36 mg g^-1. Biosorption process was spontaneous and endothermic in nature according to the thermodynamic results and it quickly reached the equilibrium within 60 minutes. The validity of kinetic models used in this study can be quantitatively tested by using a normalized standard deviation Δq(%).

Application of Deep Eutectic Solvent Modified Cotton as a Sorbent for Online Solid-Phase Extraction and Determination of Trace Amounts of Copper and Nickel in Water and Biological Samples

Deep eutectic solvent (DES) was used as the extractant to improve the extraction properties of cotton. DES of choline chloride-urea (ChCl-urea) was prepared and immobilized on the surface of cotton fibers. The resulting sorbent was packed on a microcolumn, and a flow injection flame atomic absorption spectrometry was designed for the online separation and determination of trace amounts of copper and nickel. Various parameters affecting the extraction recovery of analytes such as pH, sample volume, sample loading rate, nature, volume, concentration, and flow rate of eluent were investigated and optimized. Under the optimum conditions, the method showed good linearity in the concentration range of 0.25-50.0 and 4.0-125.0 μg L^-1 with the coefficient of determination (r ²) of 0.9991 and 0.9990 for copper and nickel, respectively. The method was very sensitive with the detection limits (defined as 3S_b/m) of 0.05 and 0.60 μg L^-1 for Cu and Ni, respectively. It was successfully applied for the determination of Cu and Ni in water and biological samples. The accuracy of the method was evaluated through the recovery experiments and independent analysis by electrothermal atomic absorption spectrometry.

Use ofMoringa oleifera(Moringa) Seed Pods andSclerocarya birrea(Morula) Nut Shells for Removal of Heavy Metals from Wastewater and Borehole Water

Use of nonedible seed pods ofMoringa oleifera(Moringa) tree and nutshells ofSclerocarya birrea(Morula) tree for removal of selected metal ions (lead, cadmium, copper, manganese, iron, zinc, and magnesium) from wastewater and borehole water samples was investigated. Removal parameters such as contact time, pH, temperature, particle size, sorbent dose, and initial metal concentration were optimized. Determination of residual metal ions after employing sorbent was done using flame atomic absorption spectroscopy (FAAS). Using 200 ng synthetic metal ion mixture in 50 mL of water sample, the optimized parameters for Moringa seed pods were 60 min contact time, 1.0 g of sorbent dose, pH 8, 100 μm sorbent particle size, and extraction temp 35°C. While using Morula nutshells, the optimized conditions were 120 min contact time, 2.0 g sorbent dose, pH 8, 100 μm sorbent particle size, and extraction temp of 35°C. The removal efficiency of acid treated sorbents was compared to that of untreated sorbents and it was found to be higher for acid treated sorbents. These nonedible plant parts for Morula and Moringa plants are proposed as a cheap, simple, and an effective alternative for purification of water contaminated with heavy metals.

Preparation of Enteromorpha prolifera-based cetyl trimethyl ammonium bromide-doped activated carbon and its application for nickel(II) removal

Activated carbon was prepared from Enteromorpha prolifera (EP) by H3PO4 activation in the presence of doped cetyl trimethyl ammonium bromide (CTAB), producing EPAC-CTAB. The thermal decomposition process of the activated carbon substrate was identified by thermo-gravimetric analysis. Scanning electron microscope (SEM), N2 adsorption/desorption, Fourier transform infrared spectroscopy (FTIR), Boehm titration, and X-ray Photoelectron Spectroscopy (XPS) were employed to characterize the physicochemical properties of native EPAC and EPAC-CTAB. EPAC-CTAB exhibited smaller surface area (689.0m(2)/g) and lower total pore volume (0.361cm(3)/g) than those of EPAC (1045.8m(2)/g and 1.048cm(3)/g), while the number of acidic groups, oxygen and nitrogen groups on the surface of EPAC-CTAB increased through CTAB doping. The batch kinetics and isotherm adsorption studies of nickel(II) onto the adsorbents were examined and agreed well with the pseudo-second-order model and the Langmuir model. The maximum adsorption capacity determined from the Langmuir model was 16.9mg/g for EPAC and 49.8mg/g for EPAC-CTAB. Under acidic condition, the adsorption of nickel(II) onto EPAC and EPAC-CTAB was hindered due to ion competition and electrostatic repulsion. The results indicated that using CTAB as a dopant for EPAC modification could markedly enhance the nickel(II) removal.

Feasibility of constructed wetland planted with Leersia hexandra Swartz for removing Cr, Cu and Ni from electroplating wastewater

As a low-cost treatment technology for effluent, the constructed wetlands can be applied to remove the heavy metals from wastewater. Leersia hexandra Swartz is a metal-accumulating hygrophyte with great potential to remove heavy metal from water. In this study, two pilot-scale constructed wetlands planted with L. hexandra (CWL) were set up in greenhouse to treat electroplating wastewater containing Cr, Cu and Ni. The treatment performance of CWL under different hydraulic loading rates (HLR) and initial metal concentrations were also evaluated. The results showed that CWL significantly reduced the concentrations of Cr, Cu and Ni in wastewater by 84.4%, 97.1% and 94.3%, respectively. High HLR decreased the removal efficiencies of Cr, Cu and Ni; however, the heavy metal concentrations in effluent met Emission Standard of Pollutants for Electroplating in China (ESPE) at HLR less than 0.3 m3/m2 d. For the influent of 5 mg/L Cr, 10 mg/L Cu and 8 mg/L Ni, effluent concentrations were below maximum allowable concentrations in ESPE, indicating that the removal of Cr, Cu and Ni by CWL was feasible at considerably high influent metal concentrations. Mass balance showed that the primary sink for the retention of contaminants within the constructed wetland system was the sediment, which accounted for 59.5%, 83.5%, and 73.9% of the Cr, Cu and Ni, respectively. The data from the pilot wetlands support the view that CWL could be used to successfully remove Cr, Cu and Ni from electroplating wastewater.

Thermodynamic and kinetic studies of As(V) removal from water by zirconium oxide-coated marine sand

Arsenic contamination of groundwater is a major threat to human beings globally. Among various methods available for arsenic removal, adsorption is fast, inexpensive, selective, accurate, reproducible and eco-friendly in nature. The present paper describes removal of arsenate from water on zirconium oxide-coated sand (novel adsorbent). In the present work, zirconium oxide-coated sand was prepared and characterised by infrared and X-ray diffraction techniques. Batch experiments were performed to optimise different adsorption parameters such as initial arsenate concentration (100-1,000 μg/L), dose (1-8 g/L), pH of the solution (2-14), contact time (15-150 min.), and temperature (20, 30, 35 and 40 °C). The experimental data were analysed by Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. Furthermore, thermodynamic and kinetic parameters were evaluated to know the mode of adsorption between ZrOCMS and As(V). The maximum removal of arsenic, 97 %, was achieved at initial arsenic concentration of 200 μg/L, after 75 min at dosage of 5.0 g/L, pH 7.0 and 27 ± 2 °C. For 600 μg/L concentration, the maximum Langmuir monolayer adsorption capacity was found to be 270 μg/g at 35 °C. Kinetic modelling data indicated that adsorption process followed pseudo-second-order kinetics. The mechanism is controlled by liquid film diffusion model. Thermodynamic parameter, ΔH°, was -57.782, while the values of ΔG° were -9.460, -12.183, -13.343 and -13.905 kJ/mol at 20, 30, 35 and 40 °C, respectively, suggesting exothermic and spontaneous nature of the process. The change in entropy, ΔS°= -0.23 kJ/mol indicated that the entropy decreased due to adsorption of arsenate ion onto the solid adsorbent. The results indicated that the reported zirconium oxide-coated marine sand (ZrOCMS) was good adsorbent with 97 % removal capacity at 200 μg/L concentration. It is interesting to note that the permissible limit of arsenic as per World Health Organization is 10 μg/L, and in real situation, this low concentration can be achieved through this adsorbent. Besides, the adsorption capacity showed that this adsorbent may be used for the removal of arsenic from any natural water resource.