A new approach to modification of natural adsorbent for heavy metal adsorption

This paper describes modification of a natural adsorbent with Fenton reagent and determines the removal of Cd(II) ions from aqueous solution. Changes of the surface properties of adsorbent materials were determined by the FT-IR analysis after the modification of pine bark. The effect of Fe2+/H2O2 ratio, ORP, pH, and contact time were determined. Different adsorption isotherms were also obtained using concentrations of Cd(II) ions ranging from 0.1 to 100 mg L(-1). The adsorption process follows pseudo-first-order reaction kinetics and follows the Langmuir adsorption isotherm. The paper discusses thermodynamic parameters, including changes in Gibbs free energy, entropy, and enthalpy, for the adsorption of Cd(II) on modified bark, and revealed that the adsorption process was spontaneous and exothermic under natural conditions. The maximum removal efficiency obtained was 97% at pH 7 and with a 90-min contact time (for 35 mg L(-1) initial concentration and a 2.5 g L(-1) solid-to-liquid ratio).     

Utility of Eucalyptus tereticornis (Smith) bark and Desulfotomaculum nigrificans for the remediation of acid mine drainage

The efficacy of the bark of Eucalyptus tereticornis (Smith) as an adsorbent for the removal of metal ions and sulphate from acid mine water was assessed. About 96% of Fe, 75% of Zn, 92% of Cu and 41% of sulphate removal was achieved from the acid mine water of pH 2.3 with a concomitant increase in pH value by about two units after interaction with the tree bark, under appropriate conditions. The adsorption isotherms adhered to Freundlich and Langmuir relationships and were exothermic in nature. The free energy of the adsorption process was found to be negative attesting to the feasibility of the reaction. The adsorption kinetics followed the first-order Lagergren rate equation. The filtrate obtained after treatment with E. tereticornis (Sm) bark was found to contain essential elements like potassium, magnesium, calcium, sodium and phosphate apart from carbon which served as a successful growth medium for the sulphate reducing bacteria (SRB) namely Desulfotomaculum nigrificans. Bacterial growth studies showed that about 57% and 72% of sulphate reduction could be achieved at initial pH values of 4.1 and 5.5 respectively of the acid mine water. Pretreatment of the acid mine water with tree bark followed by bioremoval using Dsm. nigrificans resulted in about 75% and 84% respectively of sulphate reduction at pH 4.1 and 5.5, cumulatively by biosorption and bioreduction. The mechanisms of metal ion removal using tree bark and sulphate reduction using Dsm. nigrificans are discussed.     

Activation of pine cone using Fenton oxidation for Cd(II) and Pb(II) removal

This paper describes activation of pine cone with Fenton reagent and determines the removal of Cd(II) and Pb(II) ions from aqueous solution. Changes of the surface properties of adsorbent materials were determined by the FT-IR and SEM analysis after activation of pine cone. The effect of Fe(2+)/H(2)O(2) ratio, ORP, pH and contact time were determined. Different adsorption isotherms were also obtained using concentrations of heavy metal ions ranging from 0.1 to 150mgL(-1). The adsorption process follows pseudo-first-order reaction kinetics and follows the Langmuir adsorption isotherm. The study discusses thermodynamic parameters, including changes in Gibbs free energy, entropy, and enthalpy, for the adsorption of Cd(II) and Pb(II) on activated cone, and revealed that the adsorption process was spontaneous and exothermic under natural conditions. The maximum removal efficiencies were obtained as 91% and 89% at pH 7 with 90 and 105-min contact time for Cd(II) and Pb(II), respectively.     

Kinetic modeling and equilibrium studies during cadmium biosorption by dead Sargassum sp. biomass

A basic investigation on the removal of cadmium(II) ions from aqueous solutions by dead Sargassum sp. was conducted in batch conditions. The influence of different experimental parameters; initial pH, shaking rate, sorption time, temperature and initial concentrations of cadmium ions on cadmium uptake was evaluated. Results indicated that cadmium uptake could be described by the Langmuir adsorption model, being the monolayer capacity negatively affected with an increase in temperature. Analogously, the adsorption equilibrium constant decreased with increasing temperature. The kinetics of the adsorption process followed a second-order adsorption, with characteristic constants increasing with increasing temperature. Activation energy of biosorption could be calculated as equal to 10 kcal/mol. The biomass used proved to be suitable for removal of cadmium from dilute solutions. Its maximum uptake capacity was 120 mg/g. It can be considered an optimal result when compared to conventional adsorbing materials. Thus Sargassum sp. has great potential for removing cadmium ions especially when concentration of this metal is low in samples such as wastewater streams.     

Copper removal from wastewater using spent-grain as biosorbent

The removal of Cu(II) ions from aqueous solutions using spent-grain was studied. The experimental data fitted the Langmuir isotherm and the maximum adsorption capacity of spent-grain was determined to be 10.47 mg g(-1) dry weight (pH 4.2). Kinetic studies showed the adsorption process followed pseudo second-order rate model. Column studies with synthetic Cu(II) solutions were used to investigate the effects of Cu(II) ion concentration, initial pH, flow rate and the presence of EDTA on the Cu(II) removal performance. When treating the spent-lees, the wastewater from the whisky distilling industry, the reduction of Cu(II) uptake capacity to 77.7% (solution pH adjusted to 4.5 with 1N NaOH) and 31.6% (pH 3.8 without adjustment) was observed compared to Cu(II) uptake capacity when treating synthetic Cu(II) solution. On the basis of the results and that spent-grain is an abundant and by-product from the whisky distilling industry we suggest that it can be economically and effectively applied as a biosorbent for the removal of Cu(II) ions from distilling wastewaters.     

Adsorptive Removal and Recovery of U(VI), Cu(II), Zn(II), and Co(II) from Water and Industry Effluents

Tamarind fruit shell (TFS) was converted to a cation exchanger (PGTFS-SP-COOH) having a carboxylate functional group at the chain end by grafting poly(hydroxyethylmethacrylate) onto TFS (a lignocellulosic residue) using potassium peroxydisulfate-sodium thiosulfate redox initiator, and in the presence of N, N ′-methylenebisacrylamide as a cross-linking agent, followed by functionalization. The chemical modification was investigated using Fourier transform infrared (FTIR), X-ray diffraction (XRD), and potentiometric titrations. The feasibility of PGTFS-SP-COOH for the removal of heavy metals such as U(VI), Cu(II), Zn(II), and Co(II) ions from aqueous solutions was investigated by batch process. The optimum pH range for the removal of meal ions was found to be 6.0. For all the metal ions, equilibrium was attained within 2 h. The kinetic and isotherm data, obtained at optimum pH value 6.0, could be fitted with pseudo-second-order equation and Sips isotherm model, respectively. The Sips maximum adsorption capacity for U(VI), Cu(II), Zn(II), and Co(II) ions at 30°C was found to be 100.79, 65.69, 65.97, and 58. 81 mg/g, respectively. Increase of ionic strength decreased the metal ion adsorption. Different wastewater samples were treated with PGTFS-SP-COOH to demonstrate its efficiency in removing metal ions from wastewater. The adsorbed metal ions on PGTFS-SP-COOH can be recovered by treating with 1.0 M NaCl + 0.5 M HCl for U(VI) ions and 0.2 M HCl for Cu(II), Co(II), and Zn(II) ions. Four adsorption/desorption cycles were performed without significant decrease in removal capacity. The results showed that PGTFS-SP-COOH developed in this study exhibited considerable adsorption potential for the removal of U(VI), Cu(II), Zn(II), and Co(II) ions from water and wastewaters.     

Biosorption and Desorption of Lead(II) by Hydrilla verticillata

The potential of nonliving biomass of Hydrilla verticillata to adsorb Pb(II) from an aqueous solution containing very low concentrations of Pb(II) was determined in this study. Effects of shaking time, contact time, biosorbent dosage, pH of the medium, and initial Pb(II) concentration on metal-biosorbent interactions were studied through batch adsorption experiments. Maximum Pb(II) removal was obtained after 2 h of shaking. Adsorption capacity at the equilibrium increased with increasing initial Pb(II) concentration, whereas it decreased with increasing biosorbent dosage. The optimum pH of the biosorption was 4.0. Surface titrations showed that the surface of the biosorbent was positively charged at low pH and negatively charged at pH higher than 3.6. Fourier transform infrared (FT-IR) spectra of the biosorbent confirmed the involvement of hydroxyl and C?O of acylamide functional groups on the biosorbent surface in the Pb(II) binding process. Kinetic and equilibrium data showed that the adsorption process followed the pseudo-second-order kinetic model and both Langmuir and Freundlich isothermal models. The mean adsorption energy showed that the adsorption of Pb(II) was physical in nature. The monolayer adsorption capacity of Pb(II) was 125 mg g^?1. The desorption of Pb(II) from the biosorbent by selected desorbing solutions were HNO₃ > Na₂CO₃ > NaOH > NaNO₃.     

Enhancement of Lead(II) Biosorption by Microalgal Biomass Immobilized onto Loofa (Luffa cylindrica) Sponge

A unicellular green microalga, Chlorella sorokiniana, was immobilized on loofa (Luffa cylindrica) sponge and successfully used as a new biosorption system for the removal of lead(II) ions from aqueous solutions. The biosorption of lead(II) ions on both free and immobilized biomass of C. sorokiniana was investigated using aqueous solutions in the concentration range of 10–300 mg/L. The biosorption of lead(II) ions by C. sorokiniana biomass increased as the initial concentration of lead(II) ions increased in the medium. The maximum biosorption capacity for free and immobilized biomass of C. sorokiniana was found to be 108.04 and 123.67 mg lead(II)/g biomass, respectively. The biosorption kinetics were found to be fast, with 96 % of adsorption within the first 5 min and equilibrium reached at 15 min. The adsorption of lead(II) both by free and immobilized C. sorokiniana biomass followed the Langmuir isotherm. The biosorption capacities were detected to be dependent on the pH of the solution; and the maximum adsorption was obtained at a solution pH of about 5. The effect of light metal ions on lead(II) uptake was also studied and it was shown that the presence of light metal ions did not significantly affect lead(II) uptake. The loofa sponge‐immobilized C. sorokiniana biomass could be regenerated using 0.1 M HCl, with up to 99 % recovery. The desorbed biomass was used in five biosorption‐desorption cycles, and no noticeable loss in the biosorption capacity was observed. In addition, fixed bed breakthrough curves for lead(II) removal were presented. These studies demonstrated that loofa sponge‐immobilized biomass of C. sorokiniana could be used as an efficient biosorbent for the treatment of lead(II) containing wastewater.     

Adsorption behaviour of Fe(II) and Fe(III) ions in aqueous solution on chitosan and cross-linked chitosan beads

A batch adsorption system was applied to study the adsorption of Fe(II) and Fe(III) ions from aqueous solution by chitosan and cross-linked chitosan beads. The adsorption capacities and rates of Fe(II) and Fe(III) ions onto chitosan and cross-linked chitosan beads were evaluated. Chitosan beads were cross-linked with glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) in order to enhance the chemical resistance and mechanical strength of chitosan beads. Experiments were carried out as function of pH, agitation period, agitation rate and concentration of Fe(II) and Fe(III) ions. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. The kinetic experimental data correlated well with the second-order kinetic model, indicating that the chemical sorption was the rate-limiting step. Results also showed that chitosan and cross-linked chitosan beads were favourable adsorbers.     

The adsorption of copper(II) ions on to dehydrated wheat bran (DWB): determination of the equilibrium and thermodynamic parameters

The adsorption of copper(II) ions on to dehydrated wheat bran (DWB), a by-product of the flour process, was investigated as a function of initial pH, temperature, initial metal ion concentration and adsorbent dosage. The optimum adsorption conditions were initial pH 5.0, initial copper concentration 100 mg l⁻¹, temperature 60 °C and adsorbent dosage 0.1 g. The adsorption equilibrium was described well by the Langmuir isotherm model with maximum adsorption capacity of 51.5 mg g⁻¹ of copper(II) ions on DWB. The observation of an increase in adsorption with increasing temperature leads to the result that the adsorption of copper(II) ions on DWB is endothermic in nature. The thermodynamic parameters such as enthalpy, free energy and entropy changes were calculated and these values show that the copper(II)-DWB adsorption process was favoured at high temperatures.     

Adsorption of toxic mercury(II) by an extracellular biopolymer poly(gamma-glutamic acid)

Adsorption of mercury(II) by an extracellular biopolymer, poly(gamma-glutamic acid) (gamma-PGA), was studied as a function of pH, temperature, agitation time, ionic strength, light and heavy metal ions. An appreciable adsorption occurred at pH>3 and reached a maximum at pH 6. Isotherms were well predicted by Redlich-Peterson model with a dominating Freundlich behavior, implying the heterogeneous nature of mercury(II) adsorption. The adsorption followed an exothermic and spontaneous process with increased orderliness at solid/solution interface. The adsorption was rapid with 90% being attained within 5 min for a 80 mg/L mercury(II) solution, and the kinetic data were precisely described by pseudo second order model. Ionic strength due to added sodium salts reduced the mercury(II) binding with the coordinating ligands following the order: Cl(-) >SO(4)(2-) >NO(3)(-). Both light and heavy metal ions decreased mercury(II) binding by gamma-PGA, with calcium(II) ions showing a more pronounced effect than monovalent sodium and potassium ions, while the interfering heavy metal ions followed the order: Cu(2+) > Cd(2+) > Zn(2+). Distilled water adjusted to pH 2 using hydrochloric acid recovered 98.8% of mercury(II), and gamma-PGA reuse for five cycles of operation showed a loss of only 6.5%. IR spectra of gamma-PGA and Hg(II)-gamma-PGA revealed binding of mercury(II) with carboxylate and amide groups on gamma-PGA.     

Esterified coir pith as an adsorbent for the removal of Co(II) from aqueous solution

Coir pith was chemically modified for the adsorption of cobalt(II) ions from aqueous solution. Chemical modification was done by esterification using succinic anhydride followed by activation with NaHCO(3) in order to improve the adsorption of Co(II). Adsorptive removal of Co(II) from aqueous solution onto modified coir pith was evaluated in batch studies under varying conditions of agitation time and metal ion concentration to assess the kinetic and equilibrium parameters. A pseudo-second-order kinetic model fitted well for the sorption of Co(II) onto modified coir pith. Sorption kinetics showed that the loading of Co(II) by this material was quite fast under ambient conditions. The Langmuir and Freundlich equilibrium isotherm models provided excellent fits for the adsorption data, with R(2) of 0.99 and 0.98, respectively. After esterification, the maximum Co(II) sorption loading Q(0); was greatly improved. It is evident that chemically modified adsorbent exhibits better Co(II) removal capability than raw adsorbent suggesting that surface modification of the adsorbent generates more adsorption sites on its solid surface for metal adsorption. A complete recovery of the adsorbed metal ions from the spent adsorbent was achieved by using 1.0N HCl.     

Determination of the biosorption heats of heavy metal ions on Zoogloea ramigera and Rhizopus arrhizus

The biosorption of Fe(III), Cr(VI), Pb(II), Cu(II) and Ni(II) ions on Zoogloea ramigera (activated sludge bacterium) and Rhizopus arrhizus (filamentous fungus) has been studied as a function of initial metal ion concentration and temperature. The applicability of the Langmuir model for each metal-microorganism system has been tested at different temperatures. The enthalpy change for the biosorption process has been evaluated by using the Langmuir constant b, related to the energy of adsorption. Thermodynamic parameters indicate the exothermic nature of Cu(II) and Ni(II) biosorption on both microorganisms. Fe(III), Cr(VI) and Pb(II) biosorption is determined to be an endothermic process since increased binding occurs as the temperature is increased in the range 15-45 degrees C.     

Construction a hybrid biosorbent using Scenedesmus quadricauda and Ca-alginate for biosorption of Cu(II), Zn(II) and Ni(II): kinetics and equilibrium studies

The potential use of the immobilized fresh water algae (in Ca-alginate) of Scenedesmus quadricauda to remove Cu(II), Zn(II) and Ni(II) ions from aqueous solutions was evaluated using Ca-alginate beads as a control system. Ca-alginate beads containing immobilized algae were incubated for the uniform growth at 22 degrees C for 5d ays. Adsorption of Cu(II), Zn(II) and Ni(II) ions on the immobilized algae showed highest values at around pH 5.0. Adsorption of Cu(II), Zn(II) and Ni(II) ions on the immobilized algae increased as the initial concentration of metal ions increased in the medium. The maximum adsorption capacities of the immobilized algal biosorbents for Cu(II), Zn(II) and Ni(II) were 75.6, 55.2 and 30.4 mg/g (or 1.155, 0.933 and 0.465 mmol/g) biosorbent, respectively. When the heavy metal ions were in competition, the amounts of adsorbed metal ions were found to be 0.84 mol/g for Cu(II), 0.59 mol/g for Ni(II) and 0.08 mol/g for Zn(II), the immobilised algal biomass was significantly selective for Cu(II) ions. The adsorption-equilibrium was also represented with Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms. The adsorption of Cu(II), Zn(II) and Ni(II) ions on the immobilized algae followed second-order kinetic.     

Highly enhanced adsorption for decontamination of lead ions from battery wastewaters using chitosan functionalized with xanthate

Decontamination of lead ions from aqueous media has been investigated using cross linked xanthated chitosan (CMC) as an adsorbent. Various physico-chemical parameters such as contact time, amount of adsorbent, concentration of adsorbate were optimized to simulate the best conditions which can be used to decontaminate lead from aqueous media using CMC as an adsorbent. The atomic absorption spectrometric technique was used to determine the distribution of lead. Maximum adsorption was observed at both pH 4 and 5. The adsorption data followed both Freundlich and Langmuir isotherms. Langmuir isotherm gave a saturated capacity of 322.6+/-1.2mg/g at pH 4. From the FTIR spectra analysis, it was concluded that xanthate and amino group participate in the adsorption process. The developed procedure was successfully applied for the removal of lead ions from real battery wastewater samples.     

Kinetic,isotherm and thermodynamic investigations on adsorption of trace elements and pigments from soybean oil using high voltage electric field-assisted bleaching: A comparative study

In this study, the amounts of trace elements (Fe (II) and Cu (II)) and pigments (chlorophyll and carotenoid) in soybean oil were evaluated under high voltage electric field (HVEF) bleaching method at different voltage (10 and 20 kV), temperature (35–65 °C), time (0−30 min) and clay percentage (0.5–2 %) and then were compared to the industrial bleaching method (IBM). The kinetic data of ions and pigments adsorbed on activated bentonite clay under IBM and HVEF at two voltages of 10 and 20 kV followed the mechanism of the pseudo-first-order model (PFOM). The carotenoid and chlorophyll equilibrium data followed a Freundlich isotherm type model, which demonstrated multilayer adsorption under HVEF. The thermodynamic parameters (ΔG°, ΔH°, and ΔS°) displayed that the adsorption of trace metal ions and pigments on bentonite clay under IBM and HVEF were feasible, endothermic and spontaneous between 35 and 65 °C. The results indicated that the HVEF, especially at higher voltage, has a high remarkable capability to remove metal ions and pigments from soybean oil than the IBM. The highest removal capacity for metal and pigments of soybean oil bleaching were obtained in the order of HVEF-20 kV > HVEF-10 kV > IBM.     

Cadmium(II) sorption from water samples by powdered marble wastes

Abstract

A series of batch adsorption experiments were carried out, with the aim of removing cadmium ions from aqueous solutions and water samples using powdered marble wastes (PMW) as an effective inorganic sorbent. PMW is inexpensive, widespread, and may be considered as environmental problem. The main parameters (i.e. solution pH, sorbent and cadmium concentrations, stirring time, and temperature) influencing the sorption process were investigated. The results obtained for sorption of cadmium ions onto PMW are well described by the Freundlich and Langmuir models. The Dubinin-Radushkevick (D–R) isotherm model was applied to describe the nature of the adsorption of the metal ion; it was found that the adsorption process was chemical in nature. The thermodynamic parameters were also calculated from the Gibbs free energy change (ΔG°), enthalpy (AH°) and entropy (ΔS°). These parameters indicated that the adsorption process of cadmium(II) ions on PMW was spontaneous and endothermic in nature. Under the optimum experimental conditions employed the removal of ca ~100% of Cd²⁺ ions was attained. The procedure was successfully applied to removal of the cadmium ions from aqueous and various natural water samples. The adsorption mechanism is discussed.     

Biosorptive removal of cadmium from contaminated groundwater and industrial effluents

The cadmium removing capacity of a biosorbent Calotropis procera, a perennial wild plant, is reported here. The biomass was found to possess high uptake capacity of Cd(II). Adsorption was pH dependent and the maximum removal was obtained at two different pH i.e. pH 5.0 and 8.0. Maximum biosorption capacity in batch and column mode was found to be 40 and 50.5 mg/g. The adsorption equilibrium (> or =90% removal) was attained within 5 min irrespective of the cadmium ion concentration. Interfering ions viz. Zn(II), As(III), Fe(II), Ni(II) interfered only when their concentration was higher than the equimolar ratio. The Freundlich isotherm best explained the adsorption, yet the monolayer adsorption was also noted at lower concentrations of Cd(II). The FTIR analysis indicates the involvement of hydroxyl (-OH), alkanes (-CH), nitrite (-NO(2)), and carboxyl group (-COO) chelates in metal binding. The complete desorption of the cadmium was achieved by 0.1M H(2)SO(4) and 0.1M HCl. The C. procera based Cd(II) removal technology appears feasible.     

A new approach for Fe(III)EDTA reduction in NOx scrubber solution using bio-electro reactor

A new process for the removal of NO_x by a combined Fe(II)EDTA absorption and microbial reduction has been demonstrated, in which part of the Fe(II)EDTA will be oxidized by oxygen in the flue gas to form Fe(III)EDTA. In former studies, strain FR-2 has been found to reduce Fe(III)EDTA efficiently. Otherwise, it has been reported that bio-electro reactor could efficiently provide a chance for simultaneous denitrification and metal ion removal. Therefore, a use of bio-electro reactor is suggested to promote the reduction of Fe(III)EDTA by strain FR-2 in this paper. The results showed that the concentration of Fe(III)EDTA decreased rapidly when electric current was applied, and that as the current density rose, the Fe(III)EDTA reduction rate increased while followed by a decrease afterward. The formation of the biofilm on the electrode was observed by ESEM (Environmental Scan Electro-Microscope). In addition, the Fe(III)EDTA reduction rate obviously decreased with the existence of NaNO₂.     

The removal of Cu(II) from aqueous solutions by Ulothrix zonata

In this work, adsorption of copper(II) ions on alga has been studied by using batch adsorption techniques. The equilibrium biosorption level was determined as a function of contact time at several initial metal ion concentrations. The effect of adsorbent concentration on the amount adsorbed was also investigated. The experimental adsorption data were fitted to the Langmuir adsorption model. The free energy change (deltaG0) for the adsorption process was found to be -12.60 kJ/mol. The results indicated that the biomass of Ulothrix zonata is a suitable biosorbent for both the removal and recovery of heavy metals from wastewater.