Adsorption of Ni(II), Zn(II) and Fe(II) on modified coir fibres

Adsorbents for water decontamination: A recycling alternative for fiber precursors and textile fiber wastes

The exponential growth in textile fiber production and commensurate release of textile waste-based effluents into the environment has significant impacts on human wellbeing and the long-term planetary health. To abate these negative impacts and promote resource circularity, efforts are being made to recycle these waste materials via conversion into adsorbents for water decontamination. This review critically examines plant- and regenerated cellulose-based fibers for removing water pollutants such as heavy metals, dyes, pharmaceutical and petrochemical wastes. The review reveals that chemical modification reactions such as grafting, sulfonation, carboxymethylation, amination, amidoximation, xanthation, carbon activation, and surface coating are normally employed, and the adsorption mechanisms often involve Van der Waals attraction, electrostatic interaction, complexation, chelation, ion exchange, and precipitation. Furthermore, the adsorption processes and thus the adsorption mechanisms are influenced by factors such as surface properties of adsorbents, pollutant characteristics including composition, porosity/pore size distribution, specific surface area, hydrophobicity/hydrophobicity, and molecular interactions. Besides, feasibility of the approaches in terms of handling and reuse, environmental fate, and economic impact was evaluated, in addition to the performances of the adsorbents, the prospects, and challenges. As current cost analysis is non-exhaustive, it is recommended that researchers focus on extensive cost analysis to fully appreciate the true cost effectiveness of employing these waste materials. In addition, more attention must be paid to potential chemical leaching, post-adsorption handling, and disposal. Based on the review, fiber precursors and textile fiber wastes are viable alternative adsorbents for sustainable water treatment and environmental management, and government entities must leverage on these locally accessible materials to promote recyclability and circularity.

Potential of using Alfa grass fibers (Stipa Tenacissima L.) to remove Pb2+, Cu2+, and Zn2+ from an aqueous solution

This study used alfa grass fibres as a natural low-cost adsorbent to remove lead, copper, and zinc ions from aqueous solutions. The adsorbent was characterized by FTIR, SEM, BET surface area, ATG, and XRD techniques. The effects of pH, contact time, initial metal concentration, and adsorbent dosage on the adsorption efficiency were evaluated in batch experiments. The results showed that the adsorption of all metals was fast, and optimal removal efficiency was achieved within 25 min of contact time using 5000 mg/L of Alfa fibres at pH 6.3. The adsorption selectivity order was Pb2+ > Cu2+ > Zn2+ with Pb2+ removal efficiencies up to 97.6%. The adsorption kinetics were best explained by a pseudo-second-order kinetic model. The experimental adsorption data fitted very well with the Langmuir isotherm model, and less well with the Freundlich and Temkin isotherm models. The maximum adsorption capacities were respectively 14.492, 11.904, and 8.695 mg/g for Pb2+, Cu2+, and Zn2+. The results of this study indicated that Alfa fibres could be used as effective adsorbent for the removal of Pb2+, Cu2+, and Zn2+ from aqueous solutions.

Sustainable grafted chitosan-dialdehyde cellulose with high adsorption capacity of heavy metal

A novel adsorbent was prepared using a backbone comprising chemically hybridized dialdehyde cellulose (DAC) with chitosan via Schiff base reaction, followed by graft copolymerization of acrylic acid. Fourier transform infrared spectroscopy (FTIR) confirmed the hybridization while scanning electron microscopy (SEM) revealed intensive covering of chitosan onto the surface of DAC. At the same time, energy dispersive X-ray (EDX) proved the emergence of nitrogen derived from chitosan. The X-ray diffraction (XRD) indicated that the crystallinity of the backbone and graft copolymer structures was neither affected post the hybridization nor the grafting polymerization. The adsorbent showed high swelling capacity (872%) and highly efficient removal and selectivity of Ni2+ in the presence of other disturbing ions such as Pb2+ or Cu2+. The kinetic study found that the second-order kinetic model could better describe the adsorption process of (Cu2+, Ni2+) on the graft copolymer. In contrast, the first-order kinetic model prevails for the binary mixture (Pb2+, Ni2+). Moreover, the correlation coefficient values for the adsorption process of these binary elements using Langmuir and Freundlich isotherms confirmed that the developed grafted DAC/chitosan exhibits a good fit with both isotherm models, which indicates its broadened and complicated structure. Furthermore, the grafted DAC/chitosan exhibited high efficient regeneration and high adsorption capacity for Pb2+, Cu2+ and Ni2+.

Valorization of Fibrous Plant-Based Food Waste as Biosorbents for Remediation of Heavy Metals from Wastewater-A Review

Mobilization of heavy metals in the environment has been a matter of concern for several decades due to their toxicity for humans, environments, and other living organisms. In recent years, use of inexpensive and abundantly available biosorbents generated from fibrous plant-based food-waste materials to remove heavy metals has garnered considerable research attention. The aim of this review is to investigate the applicability of using fibrous plant-based food waste, which comprises different components such as pectin, hemicellulose, cellulose, and lignin, to remove heavy metals from wastewater. This contribution confirms that plant-fiber-based food waste has the potential to bind heavy metals from wastewater and aqueous solutions. The binding capacities of these biosorbents vary depending on the source, chemical structure, type of metal, modification technology applied, and process conditions used to improve functionalities. This review concludes with a discussion of arguments and prospects, as well as future research directions, to support valorization of fibrous plant-based food waste as an efficient and promising strategy for water purification.

Insights into the Applications of Natural Fibers to Metal Separation from Aqueous Solutions

There is a wide range of renewable materials with attractive prospects for the development of green technologies for the removal and recovery of metals from aqueous streams. A special category among them are natural fibers of biological origin, which combine remarkable biosorption properties with the adaptability of useful forms for cleanup and recycling purposes. To support the efficient exploitation of these advantages, this article reviews the current state of research on the potential and real applications of natural cellulosic and protein fibers as biosorbents for the sequestration of metals from aqueous solutions. The discussion on the scientific literature reports is made in sections that consider the classification and characterization of natural fibers and the analysis of performances of lignocellulosic biofibers and wool, silk, and human hair waste fibers to the metal uptake from diluted aqueous solutions. Finally, future research directions are recommended. Compared to other reviews, this work debates, systematizes, and correlates the available data on the metal biosorption on plant and protein biofibers, under non-competitive and competitive conditions, from synthetic, simulated, and real solutions, providing a deep insight into the biosorbents based on both types of eco-friendly fibers.

Removal of toxic metals from wastewater environment by graphene-based composites: A review on isotherm and kinetic models, recent trends, challenges and future directions

Access to clean water has reduced in recent years due to pollution and man-made activities. Wastewater treatment regimens are many such as electrocoagulation, adsorption, ozonation, membrane and advanced oxidation processes. Owing to economical, resource availability and ease of operation adsorption has upper hand over all other methods employed in wastewater treatment. Graphene based adsorbents attracted researchers due to their ability to play dual role as adsorbent and photo-catalysts. When it comes to removal of heavy metals and dyes graphene-based aerogels are successful. Graphene composites were predominantly synthesized by top-down and bottom-up approach methods. Graphene composites are mesoporous and have microporous structure on surface. Graphene has copper desorption efficiency of 90 % upon 10th consecutive cycle. Graphene based adsorbents have adsorption efficiency of 367, 246 and 106.3 mg^-1 for lead, zinc and cadmium respectively. Though graphene possesses numerous applications, this review was devoted towards heavy metals removal from aqueous environment. In detail, the synthesis routes and interaction mechanism were explained and also the adsorption isotherms, kinetics were added. This review will serve as support for future research directions on removal of wastewater contaminants (heavy metals).

Selective removal of some heavy metals from Lanthanide solution by graphene oxide functionalized with sodium citrate

Lanthanides are widely used in several advanced technologies, and the presence of heavy metal ions as traces reduce their efficiencies. Hence, adsorption of some heavy metals from Lanthanides aqueous solution using previously prepared graphene oxide-citrate (GO-C) composite was reported. In this regard, the GO-C was applied to remove various heavy metal ions (Fe, Ni, Mn) through the batch technique. The GO-C after the adsorption process was characterized by various advanced techniques. The results obtained from the experimental investigations revealed that the GO-C showed a rapid equilibrium adsorption time (1.0 min) for all the studied heavy metal ions. Moreover, the adsorption isotherm data for Fe3+, Mn2+, and Ni2+ was fit by the Langmuir isotherm model with excellent adsorption capacity for Fe3+ (535.0 mg/g), Mn2+ (223.22 mg/g), and Ni2+ (174.65 mg/g). Furthermore, the GO-C can be reused over five times to enhance the removal efficiency. Interestingly, the GO-C adsorbent achieved removal performance reached 95.0% for the Fe3+ and ≥ 35.0% for Ni, Mn, Co, and Cu compared to < 1% for lanthanides metal ions.

Removal of inorganic toxic contaminants from wastewater using sustainable biomass: A review

Lignocellulosic biomass is most abundant, ecofriendly and sustainable material on this green planet which has received great attention due to exhaustion of petroleum reserves and various environmental complications. Due to its abundance and sustainability, it has been opted in number of advanced applications i.e. synthesis of green chemicals, biofuels, paper, packaging, biocomposite and for discharge of toxic contaminants from wastewaters. Utilization of sustainable biomass for removal of toxic pollutants from wastewater is robust technique due to its low-cost and easy availability. In this review, we have summarized removal of inorganic pollutants by sustainable lignocellulosic biomass in their natural as well as in chemically functionalized form. Various techniques for modification of sustainable biomass have been discussed and it was found that modified biomass showed better biosorption ability as compared to natural biomass. We conclude that modified biomass biosorbents are useful for removal of toxic inorganic pollutants to deficient levels. Several modification strategies can improve the qualities of biosorbent, however grafting is the most successful among them, as demonstrated in this work. The numerous grafting methods using a free radical grafting process are also summarized in this review article. This review also gathers studies comparing sorption capabilities with and without modification using modified and unmodified biosorbents. Chemically modified cellulosic biomass is favoured over untreated biomass because it has a higher adsorption efficiency, which is favoured by a large number of reactive binding sites, improved ion-exchange characteristics, and more functional groups available after modification.

Evaluation of Original and Enzyme-Modified Fique Fibers as an Azo Dye Biosorbent Material

As natural fibers, low-cost biosorbents have proven to be an effective and clean tool to remove textile dyes from wastewater. In this research, the Reactive Black 5 removal ability of original and enzyme-modified natural fibers were assessed. A fiber extracted from a Colombian fique plant (Furcraea sp.) was employed. The effects of fique fiber protonation with different solvents and dye solution pH on RB5 removal were evaluated. The biosorbent chemical composition was modified using the commercial enzymes pectinase, ligninase, and xylanase. The point of zero charge (PZC) of the original and modified material was measured, and the dye removal capacity of the three enzyme-modified fibers was determined. Fiber protonation with 0.1 M HCl and a dye solution with pH of 2.4 increased the RB5 elimination to 49.1%. The change in the fiber chemical composition led to a reduction in the PZC from 5.5 to a 4.7–4.9 range. Pectinase-pretreated fique fibers presented the highest dye removal of 66.29%, representing a 36% increase in RB5 dye removal. Although the original fique fiber showed RB5 dye removal ability, its enzymatic modification changed the charge distribution on the fiber surface, improving the capture of dye molecules. Enzyme modification can be applied to obtain new functionalities for plant fibers as biosorbent materials.

A critical review on the electrospun nanofibrous membranes for the adsorption of heavy metals in water treatment

Electrospun nanofibrous membranes (ENFMs) have many superior advantages, such as large specific surface area, high porosity, easy modification, good flexibility, and easy separation for recycling, which are consider as excellent adsorbents. In this paper, the research progress in the adsorption of heavy metals in water treatment by ENFMs is reviewed. Three types of ENFMs, including organic polymer ENFMs, organic polymer/inorganic material composite ENFMs and inorganic ENFMs are summarized, and their adsorption capacities for heavy metals in water are compared. The adsorption selectivity and capacity of ENFMs for heavy metals are depended largely on the type and number of functional groups on the surface of membranes, and usually the more the functional groups, the higher the adsorption capacity. The adsorption mechanisms of ENFMs are also mainly determined by the type of functional groups on the membrane. At present, the main challenge is to achieve the mass production of high-quality nanofibers and their actual application in the treatment of heavy metal-containing wastewater. Therefore, more consideration should be focused on the improvement of stability, mechanical strength and reusability of ENFMs. This review may provide an insight for the development of ENFMs-based adsorbents for heavy metals separation and water purification in the future.

Enhanced adsorption performance of oxidised coconut coir for removal of Cd(II) ions by multi-column arrangement in series

Biosorption potential of oxidised coconut coir (OCC) for removal of Cd(II) was evaluated by multi-column arrangement by connecting three columns in series. Effect of flow rate at 5, 10 and 15 mL/min was studied at 30 mg/L initial Cd(II) concentration. The dynamic capacity of the system was found to be 321, 206 and 83 mg/L for 5, 10 and 15 mL/min flow rates, respectively, by applying the bed depth service time model. Biosorbent usage rates for single-column and multi-column systems were compared. Better utilisation of biosorbent was observed when the columns are connected in series at similar operating parameters. A simple acid-base regeneration procedure was found to be effective in desorbing/regenerating the cadmium bound biosorbent. Adsorption efficiency was found to decrease from 76.3% for the first cycle to 72.2% and 70.6% in the second and third cycles, respectively. Regeneration efficiencies were more than 94% up to 3 cycles. The study highlights the effectiveness of the multi-column system in biosorption against the conventional single-column system.

Adsorptive Removal of Iron Using SiO2 Nanoparticles Extracted from Rice Husk Ash

In this work, SiO₂ nanoparticles were prepared by the sol-gel method after sodium silicate was extracted from rice husk ash (RHA) under various experimental conditions such as types of acids, NaOH concentration, dissolved time, and temperature and used for removal of Fe²⁺ ions from aqueous solutions. The extracted SiO₂ was morphologically and chemically characterized and showed a surface area of 78 m²/g and uniform pores of 2.71 nm, offering high adsorption capacity for Fe²⁺ ions. The influence of pH, contact time, and amount of adsorbent was studied in order to establish the best conditions for the Fe²⁺ adsorption and removal. Furthermore, the adsorption data were fitted with an exponential shape curve for all the three variable parameters that affect the adsorption process. The best results were obtained for pH 5, 20 min contact time, and 0.5 g adsorbent dose. The loading adsorption capacity was 9 mg of Fe²⁺ ions/g SiO₂ in the concentration range 0.1-1.0 mgL^-1. In addition, the synthesized SiO₂ with the size of around 50 nm can be used for specific heavy metal removal and drug delivery, after modification of the SiO₂ surface with various functional groups.

Coconut endocarp and mesocarp as both biosorbents of dissolved hydrocarbons in fuel spills and as a power source when exhausted

Health and environmental problems associated with the presence of toxic aromatic compounds in water from oil spills have motivated research to develop effective and economically viable strategies to remove these pollutants. In this work, coconut shell (endocarp), coconut fiber (mesocarp) and coconut shell with fiber (endocarp and mesocarp) obtained from coconut (Cocos nucifera) waste were evaluated as biosorbents of benzene, toluene and naphthalene from water, considering the effect of the solution pH (6-9) and the presence of dissolved organic matter (DOM) in natural water (14 mg/L). In addition, the heat capacity of saturated biosorbents was determined to evaluate their potential as an alternative power source to conventional fossil fuels. Tests of N₂ physisorption, SEM, elemental and fiber analysis, ATR-FTIR and acid-based titrations were performed in order to understand the materials' characteristics, and to elucidate the biosorbents' hydrocarbon adsorption mechanism. Coconut fiber showed the highest adsorption capacities (222, 96 and 5.85 mg/g for benzene, toluene and naphthalene, respectively), which was attributed to its morphologic characteristics and to its high concentration of phenolic groups, associated with the lignin structure. The pH of the solution did not have a significant influence on the removal of the contaminants, and the presence of DOM improved the adsorption capacities of aromatic hydrocarbons. The adsorption studies showed biphasic isotherms, which highlighted the strong affinity between the molecules adsorbed on the biosorbents and the aromatic compounds remaining in the solution. Finally, combustion heat analysis of coconut waste saturated with soluble hydrocarbons showed that the heat capacity increased from 4407.79 cal/g to 5064.43 ± 11.6 cal/g, which is comparable with that of woody biomass (3400-4000 cal/g): this waste biomass with added value could be a promising biofuel.

Heavy metals in handloom-dyeing effluents and their biosorption by agricultural byproducts

The Madhabdi municipality in the Narsingdi district of Bangladesh is a well-known area for textile, handloom weaving, and dyeing industries. These textile industries produce a considerable amount of effluents, sewage sludge, and solid waste materials every day that they directly discharge into surrounding water bodies and agricultural fields. This disposal poses a serious threat to the overall epidemic and socio-economic pattern of the locality. This research entailed the collection of 34 handloom-dyeing effluent samples from different handloom-dyeing industries of Madhabdi, which were then analyzed to determine the contents of the heavy metals iron (Fe), zinc (Zn), copper (Cu), chromium (Cr), manganese (Mn), lead (Pb), and cadmium (Cd). Average concentrations of Fe, Cr, Cu, Pb, Mn, and Zn were 3.81, 1.35, 1.70, 0.17, 0.75, and 0.73 mg L^-1, respectively, whereas Cd content was below the detectable limit of the atomic adsorption spectrophotometer. The concentrations of Fe, Cr, Cu, Pb, and Mn exceed the industrial effluent discharge standards (IEDS) for inland surface water and irrigation water guideline values. A biosorption experiment of the heavy metals (Fe, Cr, Cu, Mn, and Zn) was conducted without controlling for any experimental parameters (e.g., pH, temperature, or other compounds present in the effluent samples) by using four agricultural wastes or byproducts, namely rice husk, sawdust, lemon peel, and eggshell. Twenty grams of each biosorbent was added to 1 L of effluent samples and stored for 7 days. The biosorption capacity of each biosorbent is ranked as follows: eggshell, sawdust, rice husk, and lemon peel. Furthermore, the biosorption affinity of each metal ion was found in the following order: Cu and Cr (both had similar biosorption affinity), Zn, Fe, Mn. The effluents should not be discharged before treatment, and efficient treatment of effluents is possible with eggshell powder or sawdust at a rate of 20 g of biosorbent per liter of effluents.

Polyethyleneimine-bacterial cellulose bioadsorbent for effective removal of copper and lead ions from aqueous solution

Bacterial cellulose (BC) is a green biopolymer suitable for heavy metal ion removal from aqueous solution due to its nano-porous microstructure. Polyethyleneimine-bacterial cellulose (PEI-BC) was prepared by reductive amination of dialdehyde BC with polyethyleneimine. The capacity of PEI-BC in Cu(II) and Pb(II) adsorption from aqueous solution was investigated. The adsorption kinetics could be well expressed by pseudo-second-order model and the adsorption isotherm data were well fitted with Freundlich model. Adsorption processes of Cu(II) and Pb(II) by PEI-BC reached equilibrium very rapid in 30 and 60min, respectively. The maximum adsorption capacity of PEI-BC on Cu(II) and Pb(II) was found to be 148 and 141mg/g, respectively, which was higher than that of unmodified BC and other modified BC reported. PEI-BC also showed good reusability in the adsorption of Cu(II) and Pb(II). This study demonstrates that polyethyleneimine modification makes BC a potential bioadsorbent for heavy metal ion removal in waste water.

Synthesis of monodisperse core shell PVA@P(AMPS-co-NIPAm) nanogels structured for pre-concentration of Fe(III) ions

Core shell-structured poly(vinyl alcohol) @ poly(2-acrylamido-2-methyl-1-propane-sulfonic acid-co-N-isopropylacrylamide) PVA@P(AMPS-co-NIPAm) spheres are synthesized. The well-defined PVA@P(AMPS-co-NIPAm) core shell nanogels with diameter nearly 30 nm enriches Fe(III), and the nanogels are characterized by FT-IR, TEM, SEM and X-ray diffraction (XRD). The many factors affecting adsorption were successfully investigated. The maximum capacity of Fe(III) ions was 320 (mg/g) for PVA@P(90AMPS-co-10NIPAm) (wt.: wt%). The equilibrium data matching well with the Langmuir model and the pseudo-second-order form described the adsorption process better than the pseudo-first-order model. Findings of the present study highlight using a simple synthesis of PVA@P(AMPS-co-NIPAm) nanogels as superior and recyclable nanoadsorbents.

Potassium fulvate-functionalized graft copolymer of polyacrylic acid from cellulose as a promising selective chelating sorbent

(Cell-g-PAA)/KF is a promising selective chelating graft copolymer for heavy metal ions from aqueous solutions.

Biosorptive uptake of Fe(2+), Cu(2+) and As(5+) by activated biochar derived from Colocasia esculenta: Isotherm, kinetics, thermodynamics, and cost estimation

The adsorptive capability of superheated steam activated biochar (SSAB) produced from Colocasia esculenta was investigated for removal of Cu(2+), Fe(2+) and As(5+) from simulated coal mine wastewater. SSAB was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and Brunauer-Emmett-Teller analyser. Adsorption isotherm indicated monolayer adsorption which fitted best in Langmuir isotherm model. Thermodynamic study suggested the removal process to be exothermic, feasible and spontaneous in nature. Adsorption of Fe(2+), Cu(2+) and As(5+) on to SSAB was found to be governed by pseudo-second order kinetic model. Efficacy of SSAB in terms of metal desorption, regeneration and reusability for multiple cycles was studied. Regeneration of metal desorbed SSAB with 1 N sodium hydroxide maintained its effectiveness towards multiple metal adsorption cycles. Cost estimation of SSAB production substantiated its cost effectiveness as compared to commercially available activated carbon. Hence, SSAB could be a promising adsorbent for metal ions removal from aqueous solution.

Evaluation of adsorption properties of sulphurised activated carbon for the effective and economically viable removal of Zn(II) from aqueous solutions

The prospective application of sulphurised activated carbon (SAC) as an ecofriendly and cost-effective adsorbent for Zinc(II) removal from aqueous phase is evaluated, with an emphasis on kinetic and isotherm aspects. SAC was prepared from sugarcane bagasse pith obtained from local juice shops in Sree Bhadrakali Devi Temple located at Ooruttukala, Neyyattinkara, Trivandrum, India during annual festive seasons. Activated carbon modified with sulphur containing ligands was opted as the adsorbent to leverage on the affinity of Zn(II) for sulphur. We report batch-adsorption experiments for parameter optimisations aiming at maximum removal of Zn(II) from liquid-phase using SAC. Adsorption of Zn(II) onto SAC was maximum at pH 6.5. For initial concentrations of 25 and 100mgL(-1), maximum of 12.3mgg(-1) (98.2%) and 23.7mgg(-1) (94.8%) of Zn(II) was adsorbed onto SAC at pH 6.5. Kinetic and equilibrium data were best described by pseudo-second-order and Langmuir models, respectively. A maximum adsorption capacity of 147mgg(-1) was obtained for the adsorption of Zn(II) onto SAC from aqueous solutions. The reusability of the spent adsorbent was also determined.

Utilization of maize husk (Zea mays L.) as low-cost adsorbent in removal of iron from aqueous solution

Adsorption of iron from aqueous solution by using maize husk (Zea mays L.) as a low-cost adsorbent was studied. Batch experiments were carried out at ambient temperature, 0.075-0.250 mm of particle size and 100 rpm of agitation speed to determine the influence of initial pH, adsorbent dose, initial concentration and contact time on the removal of iron. Langmuir and Freundlich models were applied to describe the adsorption isotherm of iron by maize husk. The results showed that optimum condition of iron removal were 4 of pH solution, 20 g/L of adsorbent dose, 10 mg/L of Fe concentration and 15 min of contact time of adsorption with 0.499 mg Fe/g maize husk of adsorption capacity. Experimental data fitted well to Langmuir's adsorption equilibrium isotherm within the concentration range studied. This study demonstrated that maize husk, which is an agricultural waste, has potential for iron removal from groundwater or other polluted waters.

Biosorption of Fe(II) and Mn(II) ions from aqueous solution by rice husk ash

Rice husk ash (RHA), an agricultural waste, was used as biosorbent for the removal of Iron(II) and Manganese(II) ions from aqueous solutions. The structural and morphological characteristics of RHA and its elemental compositions before and after adsorption of Fe(II) and Mn(II) were determined by scanning electron microscopic (SEM) and X-ray fluorescence (XRF) analyses. Batch experiments were carried out to determine the influence of initial pH, contact time, adsorbent dosage, and initial concentration on the removal of Fe(II) and Mn(II) ions. Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) models were applied to describe the biosorption isotherm of the metal ions by RHA. The correlation coefficient (R²) of Langmuir and Freundlich isotherm models equals 0.995 and 0.901 for Fe(II), 0.9862 and 0.8924 for Mn(II), respectively, so the Langmuir model fitted the equilibrium data better than the Freundlich isotherm model. The mean free energy values evaluated from the D-R model indicated that the biosorption of Fe(II) and Mn(II) onto RHA was physical in nature. Experimental data also showed that the biosorption processes of both metal ions complied with the pseudo-second-order kinetics.

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.

Arsenic removal from aqueous solutions by adsorption onto iron oxide/activated carbon magnetic composite

In this work the adsorption features of activated carbon and the magnetic properties of iron oxides were combined in a composite to produce magnetic adsorbent. Batch experiments were conducted to study the adsorption behavior of arsenate onto the synthetic magnetic adsorbent. The effects of initial solution pH, contact time, adsorbent dosage and co-existing anionic component on the adsorption of arsenate were investigated. The results showed that the removal percentage of arsenate could be over 95% in the conditions of adsorbent dosage 5.0 g/L, initial solution pH 3.0-8.0, and contact time 1 h. Under the experimental conditions, phosphate and silicate caused greater decrease in arsenate removal percentage among the anions, and sulfate had almost no effect on the adsorption of arsenate. Kinetics study showed that the overall adsorption rate of arsenate was illustrated by the pseudo-second-order kinetic model. The applicability of the Langmuir and Freundlich models for the arsenate adsorption data was tested. Both the models adequately describe the experimental data. Moreover, the magnetic composite adsorbent could be easily recovered from the medium by an external magnetic field. It can therefore be potentially applied for the treatment of water contaminated by arsenate.

Potential of biological materials for removing heavy metals from wastewater

Agricultural products/by-products are natural sorbent materials that possess capacity for removing contaminants including heavy metals from wastewaters and hence can be exploited as replacement of costly methods for wastewater treatment. The sorption of heavy metals onto these biomaterials is attributed to constituent's proteins, carbohydrates, and phenolic compounds that contain functional groups such as carboxylate, hydroxyl, and amine. Natural efficiency of these materials for removing heavy metals can be enhanced by treating them with chemicals. The present review emphasizes their use in developing eco-friendly technology for a large-scale treatment of wastewater.

Recovery of Ga(III) by Raw and Alkali Treated Citrus limetta Peels

Alkali treated Citrus limetta peels were used for recovery of Ga(III) from its aqueous solution. The raw and alkali treated peels were characterized for functional groups. The efficiency of adsorption increased from 47.62 mg/g for raw peels to 83.33 mg/g for alkali treated peels. Between pH 1 and 3, the adsorption increased and thereafter decreased drastically. The adsorption followed pseudosecond order kinetics and Langmuir isotherm gave the best fit for the experimental data. Desorption studies showed 95.28% desorption after 3 cycles for raw peels while it was 89.51% for alkali treated peels. Simulated Bayer liquor showed 39.57% adsorption for gallium ions on raw peels which was enhanced to 41.13% for alkali treated peels.

Biosorption of Cr(VI) and Zn(II) ions from aqueous solution onto the solid biodiesel waste residue: mechanistic, kinetic and thermodynamic studies

In this present study, the biosorption of Cr(VI) and Zn(II) ions from synthetic aqueous solution on defatted J atropha oil cake (DJOC) was investigated. The effect of various process parameters such as the initial pH, adsorbent dosage, initial metal ion concentration and contact time has been studied in batch-stirred experiments. Maximum removal of Cr(VI) and Zn(II) ions in aqueous solution was observed at pH 2.0 and pH. 5.0, respectively. The removal efficiency of Cr(VI) and Zn(II) ions from the aqueous solution was found to be 72.56 and 79.81%, respectively, for initial metal ion concentration of 500 mg/L at 6 g/L dosage concentration. The biosorbent was characterized by Fourier transform infrared, scanning electron microscopy and zero point charge. Equilibrium data were fitted to the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models and the best fit is found to be with the Freundlich isotherm for both Cr(VI) and Zn(II) metal ions. The kinetic data obtained at different metal ion concentration have been analysed using the pseudo-first-order, pseudo-second-order and intraparticle diffusion models and were found to follow the pseudo-second-order kinetic model. The values of mass transfer diffusion coefficients (De) were determined by Boyd model and compared with literature values. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, were analysed using the equilibrium constant values (Ke) obtained from experimental data at different temperatures. The results showed that biosorption of Cr(VI) and Zn(II) ions onto the DJOC system is more spontaneous and exothermic in nature. The results indicate that DJOC was shown to be a promising adsorbent for the removal of Cr(VI) and Zn(II) ions from aqueous solution.