Use of hop (Humulus lupulus) agricultural by-products for the reduction of aqueous lead(II) environmental health hazards

The agricultural by-products of the hop plant (Humulus lupulus L.) were investigated to determine their potential for use in the removal of heavy lead(II) ions from contaminated aqueous solutions. Separate batch laboratory experiments were performed to establish the optimal binding pH, time exposures, and capacity of the metal adsorption for lead(II) ions by dried and ground hop leaves and stems biomass. Results from these studies have shown a pH dependent binding trend from pH 2-6, with optimum binding occurring around pH 5.0. Time dependency experiments showed a rapid adsorption of lead(II) ions within the first 5 min of contact. Binding capacity experiments demonstrated that 74.2mg of lead(II) were bound per gram of leaf biomass. Similarly overall capacity was seen for the leaves and stems. Desorption of 99% of the bound lead(II) ions was achieved by exposing the metal laden biomass to 0.5M sodium citrate. Further experiments were performed with silica-immobilized hop tissues to determine the lead(II) binding ability under flow conditions. Comparison studies were performed with ion-exchange resins to evaluate the binding ability and to gain further insight into the metal binding mechanism. X-ray absorption spectroscopy experiments were also utilized to gain further insight into the possible lead(II) binding mechanism by the hop plant tissue. Results from these studies indicate that carboxyl ligands are involved in the binding of lead(II) from aqueous solution. These findings show that the use of hop agricultural waste products may be a viable alternative, for the removal and recovery of aqueous lead(II) ions from contaminated waters.     

Surface adsorption of poisonous Pb(II) ions from water using chitosan functionalised magnetic nanoparticles

In this study, chitosan functionalised magnetic nano‐particles (CMNP) was synthesised and utilised as an effective adsorbent for the removal of Pb(II) ions from aqueous solution. The experimental studies reveal that adsorbent material has finer adsorption capacity for the removal of heavy metal ions. Parameters affecting the adsorption of Pb(II) ions on CMNP, such as initial Pb(II) ion concentration, contact time, solution pH, adsorbent dosage and temperature were studied. The adsorption equilibrium study showed that present adsorption system followed a Freundlich isotherm model. The experimental kinetic studies on the adsorption of Pb(II) ions exhibited that present adsorption process best obeyed with pseudo‐first order kinetics. The maximum monolayer adsorption capacity of CMNP for the removal of Pb(II) ions was found to be 498.6 mg g⁻¹. The characterisation of present adsorbent material was done by FTIR, energy disperse X‐ray analysis and vibrating sample magnetometer studies. Thermodynamic parameters such as Gibbs free energy (ΔG °), enthalpy (ΔH °) and entropy (ΔS °) have declared that the adsorption process was feasible, exothermic and spontaneous in nature. Sticking probability reported that adsorption of Pb(II) ions on CMNP was favourable at lower temperature and sticking capacity of Pb(II) ions was very high.Inspec keywords: adsorption, lead, wastewater treatment, monolayers, Fourier transform infrared spectra, X‐ray chemical analysis, magnetometers, pHOther keywords: poisonous Pb(II) ions surface adsorption, chitosan functionalised magnetic nanoparticle, CMNP, Pb(II) ions removal, aqueous solution, finer adsorption capacity, heavy metal ion removal, contact time, solution pH, adsorbent dosage, adsorption equilibrium, Freundlich isotherm model, pseudofirst order kinetics, monolayer adsorption capacity, FTIR, energy disperse X‐ray analysis, vibrating sample magnetometer study, thermodynamic parameter, sticking probability, Pb(II) ions sticking capacity, initial Pb(II) ion concentration     

Electrochemical properties of carbon nanotube (CNT) film electrodes prepared by controllable adsorption of CNTs onto an alkanethiol monolayer self-assembled on gold electrodes

This paper describes electrochemical properties, such as electrode reactivity, electrode dimensions, and interfacial capacitance, of multiwalled carbon nanotube (MWNT) film electrodes prepared by controllable adsorption of the MWNTs onto the self-assembled monolayer (SAM) of n-octadecyl mercaptan (C18H37SH) deposited onto Au electrodes. The adsorption of the MWNTs onto the SAM-modified Au electrode substantially restores heterogeneous electron transfer between bare Au electrode and redox species in solution phase that is almost totally blocked by the SAM of C18H37SH, and as a result, the prepared MWNT/SAM-modified electrode possesses good electrode reactivity without a remarkable barrier to heterogeneous electron transfer. In addition, the surface coverage of the MWNTs is readily controlled by adjusting the immersion time for the adsorption of the MWNTs onto the SAM of C18H37SH, which essentially endows the prepared MWNT/SAM-modified electrodes with tunable electrode dimensions ranging from a nanoelectrode array to a macro-sized conventional electrode. On the other hand, the MWNT/SAM-modified electrode is found to possess a largely reduced interfacial capacitance, as compared with the MWNT film electrodes prepared with existing methods by directly confining the MWNTs onto electrode surface. This demonstration offers a new approach to fabrication of stable MWNT film electrodes with excellent electrochemical properties that are believed to be very attractive for electrochemical studies and electroanalytical applications.     

Removal of Pb(II) ions from aqueous solutions by sulphuric acid-treated wheat bran

Sulphuric acid-treated wheat bran (STWB) was used as an adsorbent to remove Pb(II) ions from aqueous solution. It was observed that the adsorption yield of Pb(II) ions was found to be pH dependent. The equilibrium time for the process was determined as 2h. STWB gave the highest adsorption yield at around pH 6.0. At this pH, adsorption percentage for an initial Pb(II) ions concentration of 100mg/L was found to be 82.8 at 25 degrees C for contact time of 2h. The equilibrium data obtained at different temperatures fitted to the non-linear form of Langmuir, Freundlich and Redlich-Peterson and linear form of Langmuir and Freundlich models. Isotherm constants were calculated and compared for the models used. The maximum adsorption capacity (q(max)) which was obtained linear form of Langmuir model increased from 55.56 to 79.37mg/g with increasing temperature from 25 to 60 degrees C. Similar trend was observed for other isotherm constants related to the adsorption capacity. Linear form of Langmuir isotherm data was evaluated to determine the thermodynamic parameters for the process. Thermodynamic parameters show that adsorption process of Pb(II) ions is an endothermic and more effective process at high temperatures. The pseudo nth order kinetic model was successfully applied to the kinetic data and the order (n) of adsorption reaction was calculated at the range from 1.711 to 1.929. The values of k(ad) were found to be 5.82x10(-4) and 21.81x10(-4)(min(-1))(mg/g)(1-n) at 25 and 60 degrees C, respectively. Activation energy was determined as 29.65kJ/mol for the process. This suggest that the adsorption Pb(II) ions by STWB is chemically controlled.     

Speciation of organometallic compounds in environmental samples by gas chromatography after flow preconcentration on fullerenes and nanotubes

The development of a simple speciation method for the determination of lead (trimethyllead(I), dimethyllead(II), triethyllead(I), and diethyllead(II)), mercury (methylmercury(I), ethylmercury(I), mercury(II)), and tin (n-butyltin(III), di-n-butyltin(II), tri-n-butyltin(I), tin(IV)) compounds in environmental samples was described. The potential of C70 fullerenes and multiwalled carbon nanotubes (MWNTs) as sorbents was investigated for the first time; this study revealed that there are no significant differences between them in terms of sensitivity, selectivity, precision, and reusability. Comparative studies showed that MWNTs and C60 and C70 fullerenes were superior to graphitized carbon black and RP-C18 for the extraction of the 11 compounds studied. The accuracy of the MWNT method was evaluated from recovery values with two standard reference coastal sediments, and good concordance in the results were obtained. Detection limits of 0.5-2 pg/mL were obtained when using a sorbent column containing 160 mg of MWNTs (sample breakthrough, 50 mL of water). The method was successfully applied to the determination of lead, mercury, and tin compounds in water and coastal sediment samples with satisfactory results.     

Effects of chemical competition for multi-metal binding by Medicago sativa (alfalfa).

Alfalfa shoot biomass has demonstrated the ability to bind an appreciable amount of cadmium(II), chromium(III), copper(II), lead(II), nickel(II), and zinc(II) separately from aqueous solutions. Since most heavy metal contaminated waters contain more than one heavy metal ion, it was necessary to determine the binding abilities of the alfalfa biomass with multi-metal solutions. Batch laboratory experiments were performed with a solution containing 0.1 mM of each of the following metal ions: cadmium(II), chromium(III), copper(II), lead(II), nickel(II), and zinc(II). We determined the pH profile, time dependency, and binding capacity by the alfalfa biomass of each metal ion under multi-elemental conditions. For all the metal ions studied, the alfalfa biomass showed to have a high affinity for metal binding around pH 5.0 within a time period of approximately 5 min. The binding capacity experiments showed that there was a preferential binding of the metal ions from the multi-elemental solution with the following amounts of metal ion bound per gram of biomass: 368.5 micromol/g for copper(II), 215.4 micromol/g for chromium(III), 168.0 micromol/g for lead(II), 56.9 micromol/g for zinc(II), 49.2 micromol/g for nickel(II), and 40.3 micromol/g for cadmium(II). Reacting the biomass from the capacity experiments with 0.1 M HCl resulted in 90% or greater recovery of bound cadmium, copper, lead, nickel, and zinc. However, only 44% of the bound chromium was recovered. These experiments show the ability of Medicago sativa (alfalfa) to bind several metal ions under multi-contaminant conditions. Similar results were obtained when the experiments were performed under flow conditions using silica-immobilized alfalfa biomass. Chromium bound on the silica-immobilized biomass was also difficult to be desorbed with 0. 1 M HCl. The information obtained will be useful for the future development of an innovative technology to remove heavy metal contaminants from polluted ground waters.     

Sorption and desorption of lead (II) from wastewater by green algae Cladophora fascicularis

Biosorption is an effective method to remove heavy metals from wastewater. In this work, adsorption features of Cladophora fascicularis were investigated as a function of time, initial pH, initial Pb(II) concentrations, temperature and co-existing ions. Kinetics and equilibria were obtained from batch experiments. The biosorption kinetics followed the pseudo-second order model. Adsorption equilibria were well described by the Langmuir and Freundlich isotherm models. The maximum adsorption capacity was 198.5 mg/g at 298K and pH 5.0. The adsorption processes were endothermic and the biosorption heat was 29.6 kJ/mol. Desorption experiments indicated that 0.01 mol/L Na(2)EDTA was an efficient desorbent for the recovery of Pb(II) from biomass. IR spectrum analysis suggested amido or hydroxy, CO and C-O could combine intensively with Pb(II).     

Lead removal from aqueous solutions by a Tunisian smectitic clay

The adsorption of Pb(2+) ions onto Tunisian smectite-rich clay in aqueous solution was studied in a batch system. Four samples of clay (AYD, AYDh, AYDs, AYDc) were used. The raw AYD clay was sampled in the Coniacian-Early Campanian of Jebel A?doudi in El Hamma area (South of Tunisia). AYDh and AYDs corresponds to AYD activated by 2.5 mol/l hydrochloric acid and 2.5 mol/l sulphuric acid, respectively. AYDc corresponds to AYD calcined at different temperatures (100, 200, 300, 400, 500 and 600 degrees C). The raw AYD clay was characterized by X-ray diffraction, chemical analysis, infrared spectroscopy and coupled DTA-TGA. Specific surface area of all the clay samples was determined from nitrogen adsorption isotherms. Preliminary adsorption tests showed that sulphuric acid and hydrochloric acid activation of raw AYD clay enhanced its adsorption capacity for Pb(2+) ions. However, the uptake of Pb(2+) by AYDs was very high compared to that by AYDh. This fact was attributed to the greater solubility of clay minerals in sulphuric acid compared to hydrochloric acid. Thermic activation of AYD clay reduced the Pb(2+) uptake as soon as calcination temperature reaches 200 degrees C. All these preliminary results were well correlated to the variation of the specific surface area of the clay samples. The ability of AYDs sample to remove Pb(2+) from aqueous solutions has been studied at different operating conditions: contact time, adsorbent amount, metal ion concentration and pH. Kinetic experiments showed that the sorption of lead ions on AYDs was very fast and the equilibrium was practically reached after only 20 min. The results revealed also that the adsorption of lead increases with an increase in the solution pH from 1 to 4.5 and then decreases, slightly between pH 4.5 and 6, and rapidly at pH 6.5 due to the precipitation of some Pb(2+) ions. The equilibrium data were analysed using Langmuir isotherm model. The maximum adsorption capacity (Q(0)) increased from 25 to 25.44 mg/g with increasing temperature from 25 to 40 degrees C. Comparative study between sulphuric acid activated clay (AYDs) and powder activated carbon (PAC) for the adsorption of lead was also conducted. The results showed that sulphuric acid activated clay is more efficient than PAC.     

Biosorption of copper(II) and lead(II) from aqueous solution by chaff in a fixed-bed column

In this article, the ability of chaff to adsorb heavy metal ions from aqueous solution was investigated in a fixed-bed column. The effect of important parameters, such as the value of pH, the flow rate, the influent concentration of solution and the effect of coexistence ions, was studied. Also the adsorption/desorption recycles of chaff were shown, and the results indicated that chaff could be recycled to remove heavy metal ions. The Thomas model was applied to adsorption of copper and lead at different flow rate and different influent concentration to predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design. The model was found suitable for describing the biosorption process of the dynamic behavior of the chaff column. All the results suggested that chaff as adsorbent to removal heavy metal ions from solution prove efficient, and the rate of biosorption process is speedy. Furthermore, the efficiency of adsorption is high. When the flow rate was 3.6 ml min(-1) and the influent concentration of copper and lead was 14.82 mg l(-1) and 50.12 mg l(-1) respectively, the equilibrium adsorption biomass reached 1.98 mg g(-1) and 6.72 mg g(-1), respectively. The competitive adsorption for lead and copper was studied. Moreover the total adsorbing capability of chaff did not decrease when there were both copper(II) and lead(II) in solution.     

Adsorption of lead(II) ions onto 8-hydroxy quinoline-immobilized bentonite

In this study, the immobilization of 8-hydroxy quinoline onto bentonite was carried out and it was then used to investigate the adsorption behavior of lead(II) ions from aqueous solutions. The changes of the parameters of pH, contact time, initial lead(II) ions concentration and temperature were tested in the adsorption experiments. The XRD, FTIR, elemental and thermal analyses were done to observe the immobilization of 8-hydroxy quinoline onto natural bentonite. The adsorption was well described by the Langmuir adsorption isotherm model at all studied temperatures. The maximum adsorption capacity was 142.94mgg(-1) from the Langmuir isotherm model at 50 degrees C. The thermodynamic parameters implied that the adsorption process is spontaneous and endothermic. The kinetic data indicate that the adsorption fits well with the pseudo-second-order kinetic model. 8-Hydroxy quinoline-immobilized bentonite can be used as well respective adsorbent for the removal of the heavy metal pollutants according to the results.     

Grape bagasse as an alternative natural adsorbent of cadmium and lead for effluent treatment

This work investigated the utilization of grape bagasse as an alternative natural adsorbent to remove Cd(II) and Pb(II) ions from laboratory effluent. X-ray diffractometry, Fourier transform infrared spectroscopy, scanning electron microscopy, nuclear magnetic resonance, thermogravimetric analyses, surface analysis, porosity and porous size were used for characterization of the material. Batch experiments were carried out to evaluate the adsorption capacity of the material. Parameters such as adsorption pH and contact time were optimized for the maximum accumulation onto the solid surface. The pH values found were 7 and 3 for Cd(II) and Pb(II), respectively, and contact time was 5 min for both metals. Adsorption capacity for metals were calculated from adsorption isotherms by applying the Langmüir model and found to be 0.774 and 0.428 mmol g(-1) for Cd(II) and Pb(II), respectively. The competition between metals for the same adsorption sites on grape bagasse was also evaluated, showing an increasing affinity for Pb(II) over Cd(II) when only these metals are present. The potential of this material was demonstrated by efficient metal removal from laboratory effluent using a glass column. The results indicate that the referred material could be employed as adsorbent for effluent treatment, especially due to its easy acquisition and low cost as well as the fast adsorption involved.     

Adsorption of copper (II), chromium (III), nickel (II) and lead (II) ions from aqueous solutions by meranti sawdust

The present study proposed the use of meranti sawdust in the removal of Cu(II), Cr(III), Ni(II) and Pb(II) ions from synthetic aqueous solutions. Batch adsorption studies showed that meranti sawdust was able to adsorb Cu(II), Cr(III), Ni(II) and Pb(II) ions from aqueous solutions in the concentration range 1–200 mg/L. The adsorption was favoured with maximum adsorption at pH 6, whereas the adsorption starts at pH 1 for all metal ions. The effects of contact time, initial concentration of metal ions, adsorbent dosage and temperature have been reported. The applicability of Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherm was tried for the system to completely understand the adsorption isotherm processes. The adsorption kinetics tested with pseudo-first-order and pseudo-second-order models yielded high R² values from 0.850 to 0.932 and from 0.991 to 0.999, respectively. The meranti sawdust was found to be cost effective and has good efficiency to remove these toxic metal ions from aqueous solution.     

Tartrazine modified activated carbon for the removal of Pb(II), Cd(II) and Cr(III)

A two in one attempt for the removal of tartrazine and metal ions on activated carbon has been developed. The method was based on the modification of activated carbon with tartrazine then its application for the removal of Pb(II), Cd(II) and Cr(III) ions at different pH values. Tartrazine adsorption data were modelled using both Langmuir and Freundlich classical adsorption isotherms. The adsorption capacities qm were 121.3, 67 and 56.7mgg(-1) at initial pH values of 1.0, 6.0 and 10, respectively. The adsorption of tartrazine onto activated carbon followed second-order kinetic model. The equilibrium time was found to be 240min at pH 1.0 and 120min at pH 10 for 500mgL(-1) tartrazine concentration. A maximum removal of 85% was obtained after 1h of contact time. The presence of tartrazine as modifier enhances attractive electrostatic interactions between metal ions and carbon surface. The adsorption capacity for Pb(II), Cd(II) and Cr(III) ions has been improved with respect to non-modified carbon reaching a maximum of 140%. The adsorption capacity was found to be a pH dependent for both modified and non-modified carbon with a greater adsorption at higher pH values except for Cr(III). The enhancement percent of Pb(II), Cd(II) and Cr(III) at different pH values was varied from 28% to 140% with respect to non-modified carbon. The amount of metal ions adsorbed using static regime was 11-40% higher than that with dynamic mode. The difference between adsorption capacities could be attributed to the applied flow rate.     

Removal of nickel ions from water by multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were produced by chemical vapor decomposition using acetylene gas in the presence of Ferrocene catalyst at 800 degrees C, and then oxidized with concentrated nitric acid at 150 degrees C. Both (as-produced and oxidized) CNTs were characterized by TEM, Boehm titration, N2-BET and cation exchange capacity techniques. The adsorption capacity for nickel ions from aqueous solutions increased significantly onto the surface of the oxidized CNTs compared to that on the as-produced CNTs. The effects of adsorption time, solution pH and initial nickel ions concentrations on the adsorption uptake of Ni2+ for both the as-produced and oxidized CNTs were investigated at room temperature. Both Langmuir and Freundlich isotherm models match the experimental data very well. According to the Langmuir model the maximum nickel ions adsorption uptake onto the as-produced and oxidized CNTs were determined as 18.083 and 49.261 mg/g, respectively. Our results showed that CNTs can be used as an effective Ni2+ adsorbent due to the high adsorption capacity as well as the short adsorption time needed to achieve equilibrium.     

Proposal of a sequential treatment methodology for the safe reuse of oil sludge-contaminated soil

In this study sequential steps were used to treat and immobilize oil constituents of an oil sludge-contaminated soil. Initially, the contaminated soil was oxidized by a Fenton type reaction (13 wt% for H(2)O(2); 10mM for Fe(2+)). The oxidative treatment period of 80 h was carried out under three different pH conditions: 20 h at pH 6.5, 20 h at pH 4.5, and 40 h at pH 3.0. The oxidized contaminated sample (3 kg) was stabilized and solidified for 2h with clay (1 kg) and lime (2 kg). Finally, this mixture was solidified by sand (2 kg) and Portland cement (4 kg). In order to evaluate the efficiency of different processes to treat and immobilize oil contaminants of the oil sludge-contaminated soil, leachability and solubility tests were performed and extracts were analyzed according to the current Brazilian waste regulations. Results showed that the Fenton oxidative process was partially efficient in degrading the oil contaminants in the soil, since residual concentrations were found for the PAH and BTEX compounds. Leachability tests showed that clay-lime stabilization/solidification followed by Portland cement stabilization/solidification was efficient in immobilizing the recalcitrant and hazardous constituents of the contaminated soil. These two steps stabilization/solidification processes are necessary to enhance environmental protection (minimal leachability) and to render final product economically profitable. The treated waste is safe enough to be used on environmental applications, like roadbeds blocks.     

The effects of synthesis procedures on the morphology and photocatalytic activity of multi-walled carbon nanotubes/TiO(2) nanocomposites

This study investigates the microstructures of multi-walled carbon nanotubes (MWNTs)/TiO(2) nanocomposites, obtained by sol-gel and hydrothermal processes. The synthesized nanocomposite materials were characterized by x-ray diffractometry (XRD), Brunauer-Emmett-Teller (BET) adsorption analysis, transmittance electron microscopy (TEM), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, and x-ray photoelectron spectroscopy (XPS). The effects of the synthetic procedures and MWNTs on the morphology and photocatalytic activity of the nanocomposites were studied. The photocatalytic activity of the MWNTs/TiO(2) nanocomposite was elucidated based on the photooxidation of NO(x) under UV light illumination. A fleck-like and well dispersed TiO(2) microstructure on the surface of the MWNTs was observed in the sol-gel system, while compact and large aggregated particles were found in the hydrothermal procedure. The nanocomposite prepared by the sol-gel system exhibits better photocatalytic activity for NO oxidation (from 20.52 to 32.14%) than that prepared by the hydrothermal method (from 22.58 to 26.51%) with the same MWNT loading (from 0 to 8?wt%), respectively. The optimal MWNT content in the nanocomposite was considered at 8?wt%. Additionally, results confirm that the introduction of MWNTs will cause the NO(2) to be more consumed than NO in the photocatalytic experiments, leading to more complete NO(x) photooxidation. These observations indicate that the different TiO(2) distributions on the MWNT surfaces and MWNT contents in the materials would determine the morphology, the physicochemical and photocatalytic characteristics for the nanocomposite materials.     

Determination of kinetic and equilibrium parameters of the batch adsorption of Ni(II) from aqueous solutions by Na-mordenite

The potential to remove nickel(II) ions from aqueous solutions using Na-mordenite, a common zeolite mineral, was thoroughly investigated. The effects of relevant parameters solution pH, adsorbent dose, ionic strength, and temperature on nickel(II) adsorption capacity were examined. The sorption data followed the Langmuir, Freundlich, Langmuir-Freundlich and Dubinin-Radushkevich (D-R) isotherms. The maximum sorption capacity was found to be 5.324 mg/g at pH 6, initial concentration of 40 mg/L and temperature of 20 degrees C. Thermodynamic parameters, viz. changes in standard free energy (DeltaG degrees ), enthalpy (DeltaH degrees ) and entropy (DeltaS degrees ) have also been evaluated and the results show that the sorption process was spontaneous and endothermic in nature. Dynamics of the sorption process were studied and the values of rate constant of adsorption, rate constant of intraparticle diffusion were calculated. The activation energy (E(a)) was found to be 12.465 kJ/mol in the present study, indicating a chemical sorption process involving weak interactions between sorbent and sorbate. The sorption capacity increased with the increase of solution pH and the decrease of ionic strength and adsorbent dose. The nickel(II) ions sorption by the Na-mordenite is not completely attributable to ion exchange. Compared to the other adsorbents, the nickel(II) ions show a lower affinity towards the clay mineral adsorbents.     

Sorption of U(VI) from aqueous solutions with carbon sorbents

The sorption characteristics of ordinary and oxidized sorts of synthetic (SKN) and kernel (KAU) carbons and also carbon fabric oxidized with HNO₃ (AUTo) with respect to U(VI) were studied. The influence of solution pH on the sorption capacity of carbon materials with respect to uranium was elucidated. The influence of chlorine and sulfate anions on the sorption rate and sorption capacity was studied. Based on kinetic curves and sorption isotherms of uranyl ions and their derivatives, possible mechanisms of uranium adsorption with carbon sorbents were considered. It was shown that carbon sorbents can be used for treatment of aqueous media, among them drinking water, to remove U(VI) compounds.     

The adsorption of Cd(II) ions on sulphuric acid-treated wheat bran

The adsorption of Cd(II) ions which is one of the most important toxic metals by using sulphuric acid-treated wheat bran (STWB) was investigated. The effects of solution pH and temperature, contact time and initial Cd(II) concentration on the adsorption yield were studied. The equilibrium time for the adsorption process was determined as 4 h. The adsorbent used in this study gave the highest adsorption capacity at around pH 5.4. At this pH, adsorption capacity for an initial Cd(II) ions concentration of 100 mg/L was found to be 43.1 mg/g at 25 degrees C for contact time of 4 h. The equilibrium data were analysed using Langmuir and Freundlich isotherm models to calculate isotherm constants. The maximum adsorption capacity (qmax) which is a Langmuir constant decreased from 101.0 to 62.5 mg/g with increasing temperature from 25 to 70 degrees C. Langmuir isotherm data were evaluated to determine the thermodynamic parameters for the adsorption process. The enthalpy change (deltaH(o)) for the process was found to be exothermic. The free energy change (deltaG(o)) showed that the process was feasible. The kinetic results indicated that the adsorption process of Cd(II) ions by STWB followed first-order rate expression and adsorption rate constant was calculated as 0.0081 l/min at 25 degrees C. It was observed that the desorption yield of Cd(II) was highly pH dependent.     

Adsorption of Ni(II) on oxidized multi-walled carbon nanotubes: Effect of contact time,pH, foreign ions and PAA

The adsorption of Ni(II) on oxidized multi-walled carbon nanotubes (MWCNTs) as a function of contact time, pH and foreign ions in the absence and presence of polyacrylic acid (PAA) was studied using batch technique. The results indicated that adsorption of Ni(II) on oxidized MWCNTs increased from zero to ∼99% at pH 2–9, and then maintained the high level with increasing pH. Kinetic data showed that the adsorption process achieved equilibrium within 2 h and experimental data were fitted well by the pseudo-second-order equation. A positive effect of PAA on Ni(II) adsorption was found at pH < 8, whereas a negative effect was observed at pH > 8. The effect of addition sequences of PAA/Ni(II) on the adsorption of Ni(II) to PAA–MWCNT hybrids were also studied. The results indicated that the adsorption of Ni(II) was influenced by addition sequences obviously. The adsorption of Ni(II) on oxidized MWCNTs may be mainly attributed to surface complexation and ion exchange. Oxidized MWCNTs are suitable material in the solidification and pre-concentration of Ni(II) from aqueous solutions.