Single- and multi-component adsorption of cadmium and zinc using activated carbon derived from bagasse--an agricultural waste

Clinoptilolite and palygorskite as sorbents of neutral emerging organic contaminants in treated wastewater: Sorption-desorption studies

Water reuse for aquifer recharge could be an important route for the introduction of emerging organic contaminants (EOCs) into the environment. The installation of a Horizontal Permeable Reactive Barrier (H-PRB) could constitute a tertiary treatment process to remove EOCs from treated domestic wastewater prior to recharge activities. The sorption-desorption behaviour of six neutral EOCs present in treated domestic wastewater (acetaminophen, caffeine, carbamazepine, cotinine, 4-acetamidoantipyrine (4-AAA) and 4-formylaminoantipyrine (4-FAA)) has been evaluated. Clinoptilolite and palygorskite have been studied as sorbents to be installed in the H-PRB. Batch tests were carried out using an EOC initial concentration ranging from 5 to 100 μg L^-1. Apart from acetaminophen and caffeine, both materials showed a limited sorption capacity of neutral EOCs (K_d = 0.63-5.42 L kg^-1). In general, the experimental results show that EOCs exhibit a higher sorption affinity for clinoptilolite than for palygorskite. With the exception of carbamazepine, the sorption of the compounds occurs mainly by interactions with mineral surfaces as indicated by the comparison of the partition coefficients into organic matter and into mineral surfaces. According to the molecular geometry of the compounds and the sorption sequences observed, it appears that the dimensions of the organic molecules play a key role in the sorption process. All the studied EOCs exhibit irreversible sorption and sorption-desorption hysteresis.

Removal of Zn2+ and SO42- from aqueous solutions on acidic and chelating dehydrated carbon

The agricultural waste, date palm leaflets, was carbonized chemically using sulfuric acid treatment. Produced dehydrated carbon (DC) was subjected to surface functionalization using ethylene diamine producing chelating dehydrated carbon (CDC). In the process, ∼80 % of the carboxylic content on DC was converted to amide successfully. DC acts as a cation exchanger because of the high content of carboxylic groups on its surface showing acidic nature. However, CDC possesses amine and amide groups showing basic nature. Both amine and amide groups are capable of chelating Zn²⁺ at high pH; however, at low pH, the amine group becomes protonated acting as anion exchanger. Sorption of Zn²⁺ and SO₄^2- was investigated in terms of contact time, initial pH, concentration, and carbon reuse. Zn²⁺ shows maximum sorption at initial pH 5; however, maximum sorption of SO₄^2- takes place at initial pH 2. Kinetic and equilibrium studies were carried out at initial 5 and 2 for Zn²⁺and SO₄^2-, respectively. Sorption kinetics data follow well the pseudo second-order model. The equilibrium sorption data follow the Langmuir isotherm more than the Freundlich isotherm. CDC shows better sorption performance for Zn²⁺ and SO₄^2- than DC. DC and CDC show combined equimolar removal of both Zn²⁺ and SO₄^2- at initial pH 2.3 and 2.6, respectively, with efficient recycle properties. Combined removal of Zn²⁺ and SO₄^2- from spiked municipal wastewater shows less uptake on both carbons than from deionized water.

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.

Cadmium Removal from Aqueous Solution by a Deionization Supercapacitor with a Birnessite Electrode

Birnessite is widely used as an excellent adsorbent for heavy metal ions and as active electrode materials for supercapacitors. The occurrence of redox reactions of manganese oxides is usually accompanied by the intercalation-deintercalation of cations during the charge-discharge processes of supercapacitors. In this study, based on the charge-discharge principle of the supercapacitor and excellent adsorption properties of birnessite, a birnessite-based electrode was used to remove Cd²⁺ from aqueous solutions. The Cd²⁺ removal mechanism and the influences of birnessite loading and pH on the removal performance were investigated. The results showed that Cd²⁺ was adsorbed on the surfaces and interlayers of birnessite, and the maximum electrosorption capacity of birnessite for Cd²⁺ was about 900.7 mg g^-1 (8.01 mmol g^-1), which was significantly higher than the adsorption isotherm capacity of birnessite (125.8 mg g^-1). The electrosorption specific capacity of birnessite for Cd²⁺ increased with an increase in initial Cd²⁺ concentration and decreased with an increase in the loading of active birnessite. In the pH range of 3.0-6.0, the electrosorption capacity increased at first with an increase in pH and then reached equilibrium above pH 4.0. This work provides a new method for the highly efficient adsorption of Cd²⁺ from polluted wastewater.

Role of Bioadsorbents in Reducing Toxic Metals

Industrialization and urbanization have led to the release of increasing amounts of heavy metals into the environment. Metal ion contamination of drinking water and waste water is a serious ongoing problem especially with high toxic metals such as lead and cadmium and less toxic metals such as copper and zinc. Several biological materials have attracted many researchers and scientists as they offer both cheap and effective removal of heavy metals from waste water. Therefore it is urgent to study and explore all possible sources of agrobased inexpensive adsorbents for their feasibility in the removal of heavy metals. The objective was to study inexpensive adsorbents like various agricultural wastes such as sugarcane bagasse, rice husk, oil palm shell, coconut shell, and coconut husk in eliminating heavy metals from waste water and their utilization possibilities based on our research and literature survey. It also shows the significance of developing and evaluating new potential biosorbents in the near future with higher adsorption capacity and greater reusable options.

Noncompetitive and Competitive Adsorption of Heavy Metals in Sulfur-Functionalized Ordered Mesoporous Carbon

In this work, sulfur-functionalized ordered mesoporous carbons were synthesized by activating the soft-templated mesoporous carbons with sulfur bearing salts that simultaneously enhanced the surface area and introduced sulfur functionalities onto the parent carbon surface. XPS analysis showed that sulfur content within the mesoporous carbons were between 8.2% and 12.9%. The sulfur functionalities include C-S, C═S, -COS, and SO_x. SEM images confirmed the ordered mesoporosity within the material. The BET surface areas of the sulfur-functionalized ordered mesoporous carbons range from 837 to 2865 m²/g with total pore volume of 0.71-2.3 cm³/g. The carbon with highest sulfur functionality was examined for aqueous phase adsorption of mercury (as HgCl₂), lead (as Pb(NO₃)₂), cadmium (as CdCl₂), and nickel (as NiCl₂) ions in both noncompetitive and competitive mode. Under noncompetitive mode and at a pH greater than 7.0 the affinity of sulfur-functionalized carbons toward heavy metals were in the order of Hg > Pb > Cd > Ni. At lower pH, the adsorbent switched its affinity between Pb and Cd. In the noncompetitive mode, Hg and Pb adsorption showed a strong pH dependency whereas Cd and Ni adsorption did not demonstrate a significant influence of pH. The distribution coefficient for noncompetitive adsorption was in the range of 2448-4000 mL/g for Hg, 290-1990 mL/g for Pb, 550-560 mL/g for Cd, and 115-147 for Ni. The kinetics of adsorption suggested a pseudo-second-order model fits better than other models for all the metals. XPS analysis of metal-adsorption carbons suggested that 7-8% of the adsorbed Hg was converted to HgSO₄, 14% and 2% of Pb was converted to PbSO₄ and PbS/PbO, respectively, and 5% Cd was converted to CdSO₄. Ni was below the detection limit for XPS. Overall results suggested these carbon materials might be useful for the separation of heavy metals.

Sorption of Lead Ions from Aqueous Solution by Chickpea Leaves, Stems and Fruit Peelings

Leaves, stems and fruit peelings of chickpea (Cicer arientinum L.) were successfully utilized for the accumulation of lead ions from aqueous solutions onto their surfaces. The rate and extent of accumulation were affected by pH, particle size, contact time and the initial concentration of Pb(II) ions, respectively. The sorption capacities of leaves, stems and fruit peelings towards Pb(II) ions were found to be 81.30, 80.10 and 53.26%, respectively, at an initial Pb(II) ion concentration of 200 mg/dm3, optimum pH conditions of 6.0, a particle size of 0.354 mm and a contact time of 120 min. Most of the sorption occurred within the first 15 min and attained a maximum value after 120 min. The Bangham equation was used to express the adsorption mechanism. The adsorption rates of Pb(II) ions were found to decrease in the order: leaves > stems > fruit peelings. Possible cell–metal ion interactions may be due to the involvement of –COOH, –OH and –NH groups in the sorption process. The obtained sorption data were well fitted by the Freundlich and Langmuir adsorption isotherms, respectively. The results showed that chickpea leaves and stems behave as good adsorbents for the removal of Pb(II) ions from aqueous solution.

Kinetics and Equilibrium Study of Cadmium Ion Sorption onto Date Pits — An Agricultural Waste

Activated carbons derived from date pits obtained as a surplus agricultural solid waste and natural date pits were used for the adsorption of cadmium ions from water. The effect of contact time, pH, temperature, cadmium ion concentration, sorbent dose, salinity, as well as the activation temperature on the removal of cadmium ions by date pits was studied. The maximum adsorption capacity of date pits for cadmium ions was obtained using the linear Langmuir isotherm model and used as a basis for comparative purposes. Three sorption kinetic models were used for explaining the probable mechanisms of cadmium ion uptake. The kinetic data for the adsorption process obeyed a second-order rate equation.

Sorption of zinc onto elemental selenium nanoparticles immobilized in Phanerochaete chrysosporium pellets

The use of a novel hybrid biosorbent, elemental selenium nanoparticles (nSe⁰) immobilized in pellets of Phanerochaete chrysosporium, to remove Zn from aqueous solutions was investigated. Fungal pellets containing nSe⁰ (nSe⁰-pellets) showed to be better biosorbents as they removed more Zn (88.1 ± 5.3 %) compared to Se-free fungal pellets (56.2 ± 2.8 %) at pH 4.5 and an initial Zn concentration of 10 mg L^-1. The enhanced sorption capacity of nSe⁰-pellets was attributed to a higher concentration of sorption sites resulting in a more negative surface charge density, as determined by analysis of the potentiometric titration data. Fourier transform infrared spectroscopy (FT-IR) analysis of fungal pellets prior to and after being loaded with Zn showed the functional groups, including hydroxyl and carboxyl groups, involved in the sorption process. The experimental data indicated that the sorption rate of the nSe⁰-pellets fitted well to the pseudo-second order kinetic model (R ²  = 0.99), and the sorption isotherm was best represented by the Sips model (Langmuir-Freundlich) with heterogeneous factor n = 1 (R ²  = 0.99), which is equivalent to the Langmuir model. Operational advantages of fungal pelleted reactors and the Zn removal efficiencies achieved by nSe⁰-pellets under mild acidic conditions make nSe⁰-pellet based bioreactors an efficient biosorption process.

Sorption of chlorophenols on microporous minerals: mechanism and influence of metal cations, solution pH, and humic acid

Sorption of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) on a range of dealuminated zeolites were investigated to understand the mechanism of their sorption on microporous minerals, while the influence of common metal cations, solution pH, and humic acid was also studied. Sorption of chlorophenols was found to increase with the hydrophobicity of the sorbates and that of the microporous minerals, indicating the important role of hydrophobic interactions, while sorption was also stronger in the micropores of narrower sizes because of greater enhancement of the dispersion interactions. The presence of metal cations could enhance chlorophenol sorption due to the additional electrostatic attraction between metal cations exchanged into the mineral micropores and the chlorophenolates, and this effect was apparent on the mineral sorbent with a high density of surface cations (2.62 sites/nm(2)) in its micropores. Under circum-neutral or acidic conditions, neutral chlorophenol molecules adsorbed into the hydrophobic micropores through displacing the "loosely bound" water molecules, while their sorption was negligible under moderately alkaline conditions due to electrostatic repulsion between the negatively charged zeolite framework and anionic chlorophenolates. The influence of humic acid on sorption of chlorophenols on dealuminated Y zeolites suggests that its molecules did not block the micropores but created a secondary sorption sites by forming a "coating layer" on the external surface of the zeolites. These mechanistic insights could help better understand the interactions of ionizable chlorophenols and metal cations in mineral micropores and guide the selection and design of reusable microporous mineral sorbents for sorptive removal of chlorophenols from aqueous stream.

Evaluation of CNTs/MnO2 composite for adsorption of 60Co(II), 65Zn(II) and Cd(II) ions from aqueous solutions

CNTs/MnO2 composite was synthesized by a co-precipitation method after preparation of carbon nanotubes (CNTs) using a chemical oxidation method and was characterized using Fourier transformer infrared (FT-IR), X-ray diffraction (XRD) and scanning electron microscope (SEM). The synthesized CNTs/MnO2 composite was used as a sorbent for the removal of some radionuclides (60Co and 65Zn-radioisotopes) and Cd (II) ions from aqueous solutions. Different parameters affecting the removal process including pH, contact time and metal ion concentration were investigated. Isotherm and kinetic models were studied. Adsorption data was interpreted in terms of both Freundlich and Langmuir isotherms and indicated that the CNTs/MnO2 composite complied well with both Langmuir and Freundlich models for 60Co and Cd(II) ions and with the Freundlich model only for the 65Zn radioisotope. A pseudo-second-order model was effectively employed to describe the adsorption behavior of 60Co, 65Zn and Cd(II) ions. Desorption of 60Co and 65Zn and Cd(II) ions from loaded samples was studied using different eluents.

Improvement of oxygen-containing functional groups on olive stones activated carbon by ozone and nitric acid for heavy metals removal from aqueous phase

Recently, modification of surface structure of activated carbons in order to improve their adsorption performance toward especial pollutants has gained great interest. Oxygen-containing functional groups have been devoted as the main responsible for heavy metal binding on the activated carbon surface; their introduction or enhancement needs specific modification and impregnation methods. In the present work, olive stones activated carbon (COSAC) undergoes surface modifications in gaseous phase using ozone (O3) and in liquid phase using nitric acid (HNO3). The activated carbon samples were characterized using N2 adsorption-desorption isotherm, SEM, pHpzc, FTIR, and Boehm titration. The activated carbon parent (COSAC) has a high surface area of 1194 m(2)/g and shows a predominantly microporous structure. Oxidation treatments with nitric acid and ozone show a decrease in both specific surface area and micropore volumes, whereas these acidic treatments have led to a fixation of high amount of surface oxygen functional groups, thus making the carbon surface more hydrophilic. Activated carbon samples were used as an adsorbent matrix for the removal of Co(II), Ni(II), and Cu(II) heavy metal ions from aqueous solutions. Adsorption isotherms were obtained at 30 °C, and the data are well fitted to the Redlich-Peterson and Langmuir equation. Results show that oxidized COSACs, especially COSAC(HNO3), are capable to remove more Co(II), Cu(II), and Ni(II) from aqueous solution. Nitric acid-oxidized olive stones activated carbon was tested in its ability to remove metal ions from binary systems and results show an important maximum adsorbed amount as compared to single systems.

Cost effective biochar gels with super capabilities for heavy metal removal

A novel KGM based biochar with super heavy metal removal capacities can be prepared conveniently.

Valorization of Wasted Black Tea as a Low-Cost Adsorbent for Nickel and Zinc Removal from Aqueous Solution

Characteristics and efficiency of wasted black tea (WBT) were investigated as a low-cost sorbent in removal of Ni2+and Zn2+ions from aqueous solution. Initial findings showed WBT potential to be applied as an effective sorbent due to high concentrations of carbon and calcium and high porosity and availability of functional groups. Sorption dynamics were studied with varying pH, contact time, and adsorbent dose. Maximum percentages of metal ions removal were recorded at pH 5, contact time 250 min, and 20 g/L of adsorbent concentration. Binary metal sorption studies showed that Ni2+and Zn2+do not compete with each other for available sorption sites, so the adsorption trend in binary system appears similar to monocomponent metal adsorption. Evaluation of the isotherms confirmed that WBT has high value of adsorption capacity. Sorption data fitted well with both Freundlich and Langmuir models. In the optimum conditions, maximum capacity of WBT could reach up to 90.91 mg-Ni/g adsorbent and 166.67 mg-Zn/g adsorbent. This experiment demonstrated the ability of tea waste as an effective, sustainable, and low-cost adsorbent for removal of the heavy metal ions.

Enhanced adsorption of Cu(ii) ions on chitosan microspheres functionalized with polyethylenimine-conjugated poly(glycidyl methacrylate) brushes

Crosslinked chitosan microspheres were tethered with branched polyethylenimine-conjugated poly(glycidyl methacrylate) brushes via surface-initiated ATRP and were further utilized as novel adsorbent to purify Cu(ii)-contaminated aqueous solution​.

Removal of barium and strontium from aqueous solution using zeolite 4A

The adsorption efficiency of Sr(2+) and Ba(2+) from aqueous solutions by zeolite 4A was investigated. Adsorption studies were carried out both in single and binary component systems. The single ion equilibrium adsorption data were fitted to three isotherm models: Langmuir, Freundlich and Dubinin-Radushkevich. The Langmuir model represents the equilibrium data better than the Freundlich model in the studied initial metal concentration (0.3-25 mmol L(-1)) in both the single and binary component systems. The obtained RL (separation factor or Langmuir parameter) values were in the range of 0-1 indicating that Sr(2+) and Ba(2+) sorption were favorable. The obtained mean free energy value for adsorption of Ba(2+) and Sr(2+) was 8.45 kJ mol(-1) and 9.12 kJ mol(-1), respectively, indicating that both ions were uptaken through an ion exchange process. The maximum adsorption capacities (Qmax) were 2.25 mmol g(-1) and 2.34 mmol g(-1) for Ba(2+) and Sr(2+) ions, respectively. Also, the study of the competitive sorption of ions in the binary system showed that zeolite 4A preferentially adsorbs cations in the following order: Ba(2+) < Sr(2+).

Enhancing adsorptive removal of sulfate by metal layered double hydroxide functionalized Quartz-Albitophire iron ore waste: preparation, characterization and properties

In this study, the seemingly worthless Quartz-Albitophire iron ore mineral waste has been modified with metal double hydroxides (Mg–Al, Ni–Fe, Ni–Al and Mg–Fe) and utilized as a sulfate adsorbent which is characterized by XRD, XRF, FTIR and SEM analysis.

Preparation and characterization of a series of porous anion-exchanger chelating fibers and their adsorption behavior with respect to removal of cadmium(ii)

The aim of the present study was to investigate a series of porous anion-exchanger chelating fibers (PP-g-AA-Am), prepared using polypropylene (PP) for the removal of Cd(ii) in non-salt systems and in high-salt complex systems.

Mass Transfer Studies on Adsorption of Phenol from Wastewater UsingLantana camara, Forest Waste

Adsorption is one of the important treatment methods for the removal of pollutants from wastewater. The determination of rate controlling step in the process is important in the design of the process. Therefore, in the present work, mass transfer studies were done to evaluate the rate-limiting step in the adsorption of phenol from aqueous solution ontoLantana camara. Different mass transfer models were used to find the rate-limiting step and also to find the values of external mass transfer coefficient and diffusion coefficient. The Biot number was found to investigate the importance of external mass transfer to intraparticle diffusion. From the various models studied and the Biot numbers obtained, it was found that the adsorption onLantana camarawas controlled by film diffusion. The sensitivity analysis was performed to study the significance of the model parameters on the adsorption process.

Alleviating the toxicity of heavy metals by combined amendments in cultivated bag of Pleurotus cornucopiae

The substrate of mushroom can be polluted with heavy metals and subsequently contaminate mushroom, which requires alternative solutions to reduce associated environmental and human health risks. The effects of amendment application on alleviating Cu and Cd toxicities to Pleurotus cornucopiae were investigated in a cultivated bag experiment conducted with the naturally contaminated substrate. Addition of combined amendments (sodium bentonite, silicon fertilizer, activated carbon, and potassium dihydrogen phosphate) increased the P. cornucopiae biomass and substrate pH. Cu and Cd concentration in P. cornucopiae as well as the available Cu and Cd in substrate reduced for the presence of amendments, and the silicon fertilizer had the biggest inhibition on metal uptake. The smallest amount of Cu and Cd in P. cornucopiae was only 30.8 and 5.51% of control, respectively. Moreover, application of amendments also decreased malondialdehyde (MDA) and hydrogen peroxide (H2O2) level in metal-stressed mushroom by 4.38-53.74 and 8.90-58.42% relative to control, respectively. The decreased oxidative stress could well contribute to the growth of P. cornucopiae, and the elevated substrate pH might lead to the lower metal availability, thus resulting in the reduction of metal accumulation in mushroom. These above results suggest that application of combined amendments in mushroom substrate could be implemented in a general scheme aiming at controlling metal content in P. cornucopiae.