Kinetic and equilibrium study for the sorption of cadmium(II) ions from aqueous phase by eucalyptus bark

The efficiency of eucalyptus bark as a low cost sorbent for removing cadmium ions from aqueous solution has been investigated in batch mode. The equilibrium data could be well described by the Langmuir isotherm but a worse fit was obtained by the Freundlich model. The five linearized forms of the Langmuir equation as well as the non-linear curve fitting analysis method were discussed. Results show that the non-linear method may be a better way to obtain the Langmuir parameters. Maximum cadmium uptake obtained at a temperature of 20 degrees C was 14.53mgg(-1). The influence of temperature on the sorption isotherms of cadmium has been also studied. The monolayer sorption capacity increased from 14.53 to 16.47 when the temperature was raised from 20 to 50 degrees C. The DeltaG degrees values were negative, which indicates that the sorption was spontaneous in nature. The effect of experimental parameters such as contact time, cadmium initial concentration, sorbent dose, temperature, solution initial pH, agitation speed, and ionic strength on the sorption kinetics of cadmium was investigated. Pseudo-second-order model was evaluated using the six linear forms as well as the non-linear curve fitting analysis method. Modeling of kinetic results shows that sorption process is best described by the pseudo-second-order model using the non-linear method. The pseudo-second-order model parameters were function of the initial concentration, the sorbent dose, the solution pH, the agitation speed, the temperature, and the ionic strength.     

Application of dolochar in the removal of cadmium and hexavalent chromium ions from aqueous solutions

Dolochar, a waste material generated in sponge iron industry, is processed and put to test as an adsorbent for removal of Cd(II) and Cr(VI) ions from aqueous solutions. The dolochar samples were characterised to determine the different phases and their distribution by reflection microscopy. The analysis indicated that the sample consists of metallic iron, fused carbon, and Ca-Mg bearing phases (Ca-Mg-silicate-oxide) along with lots of voids and pores. The fixed carbon (FC) content of the material is 13.8% with a Langmuir surface area of 81.6 m²/g and micropore area of 34.1 m²/g. Batch adsorption experiments have been conducted to study the sorption behaviour of Cd(II) and Cr(VI) ions on dolochar as a function of particle size, contact time, adsorbent dosages, pH and temperature. It is observed that higher pH and temperature enhances sorption of Cd(II) ions. In contrast, the adsorption for Cr(VI) is found to be better in acidic pH in comparison to alkaline media. The equilibrium adsorption isotherm data are tested by applying both Langmuir and Freundlich isotherm models. It is observed that Langmuir isotherm model fitted better compared to the Freundlich model indicating monolayer adsorption. The thermodynamic parameters such as ΔG°, ΔH° and ΔS° indicate the effectiveness of dolochar to remove Cd(II) and Cr(VI) ions from aqueous solution. The kinetics of adsorption is found to better fit to pseudo second order reaction.     

Studies on sorption of some geomaterials for fluoride removal from aqueous solutions

In the present study the defluoridation capacities of some of the naturally occurring materials like low and high iron containing lateritic ores, overburden from chromite mines of Orissa Mining Corporation (OMC) and Tata Steel have been estimated. The various experimental parameters studied for fluoride sorption from aqueous solutions were: time, pH, initial fluoride concentration, sorbent dose and temperature. The three geomaterials, namely chromite overburden from Orissa Mining Corporation, both low and high iron containing lateritic ores sorbed fluoride effectively. The sorption kinetics for these samples was found to follow first order rate expression and the experimental equilibrium sorption data fitted reasonably well to both Langmuir and Freundlich models. The negative values of ΔG° suggest the sorption of fluoride onto three samples to be spontaneous and the exothermic nature of sorption is confirmed by the −ΔH° values. The negative ΔS° values for these sorbents point towards decreased randomness at the solid/solution interface. The sorption studies were also carried out at natural pH conditions for fluoride removal from ground water samples and the fluoride level could be reduced from 10.25 to <1.0 mg L⁻¹ by multistage adsorption process using OMC and NH samples.     

Sawdust--a green and economical sorbent for the removal of cadmium (II) ions

The ability of sawdust (treated and untreated) waste, a waste material derived from the commercial processing of cedrus deodar wood for furniture production, to remove/preconcentrate Cd(II) ions from aqueous solution was determined. Sorption was found to be rapid (approximately 97% within 8 min). The binding of metal ions was found to be pH dependent, optimal sorption accruing at around pH 4-8. Potentiometric titrations of sawdust revealed two distinct pK(a) values, the first having the value similar to carboxylic groups (3.3-4.8) and second comparable with that of amines (8.53-10.2) with the densities 1.99 x 10(-4) and 7.94 x 10(-5), respectively. Retained Cd(II) ions were eluted with 5 ml of 0.1 mol l(-1) HCl. Detection limit of 0.016 microg ml(-1) was achieved with enrichment factors of 120. Recovery was quantitative using sample volume of 600 ml. The Langmuir and D-R isotherm equations were used to describe partitioning behavior for the system at different temperatures. Kinetic and thermodynamic behavior of sawdust for Cd(II) ions removal was also studied.     

Adsorption characteristics of heavy metal ions onto a low cost biopolymeric sorbent from aqueous solutions

In this study, the adsorption conditions of Cu(II), Pb(II) and Cd(II) metal ions onto sporopollenin have been studied. The different variables effecting the sorption capacity such as pH of the solution, adsorption time, initial metal ion concentration and temperature have been investigated. Adsorption isotherms correlated well with the Freundlich type adsorption isotherm and adsorption capacities were found to be 0.0195, 0.0411 and 0.0146 mmol g(-1) for Cu(II), Pb(II) and Cd(II) metal ions, respectively. Experimental data were also evaluated to find out kinetic characteristics of the adsorption process. Adsorption processes for three target heavy metal ions were found to follow pseudo-second order type adsorption kinetics. Intraparticle diffusion was found to take part in adsorption processes but it could not be accepted as the primary rate-determining step. The mean free energies of adsorption (E) were found to be between 8 and 16 kJ mol(-1) for the metal ions studied and therefore adsorption mechanism for the adsorbent was explained as an ion-exchange process. But it was observed that chelating effect is also playing an important role in the adsorption of metal ions onto sporopollenin. Thermodynamic parameters, DeltaH degrees , DeltaS degrees and DeltaG degrees were also calculated from graphical interpretation of the experimental data. Standard heats of adsorption (DeltaH degrees ) were found to be endothermic and DeltaS degrees values were calculated to be positive for the adsorption of Cu(II), Pb(II) and Cd(II) ions onto the adsorbent. Negative DeltaG degrees values indicated that adsorption process for these three metal ions onto sporopollenin is spontaneous.     

Isotherms and thermodynamics for the sorption of heavy metal ions onto functionalized sporopollenin

In this study, sporopollenin of Lycopodium clavatum spores was used for the sorption experiment. Glutaraldehyde (GA) immobilized sporopollenin (Sp), is employed as a sorbent in sorption of selected heavy metal ions. The sorbent prepared by sequential treatment of sporopollenin by silanazing compound and glutaraldehyde is suggested for sorption of Cu(II), Zn(II) and Co(II) from aqueous solutions. Experimental conditions for effective sorption of heavy metal ions were optimized with respect to different experimental parameters using batch method in detail. Optimum pH range of Cu(II) has occurred at pH ≥ 5.5 and Zn(II), Co(II) at pH ≥ 5.0, for the batch method. All of the metal ions can be desorbed with 10 cm³ of 0.5 mol dm⁻³ of ethylenediaminetetraacetic acid (EDTA) solution. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm equations were applied to the experimental data. Thermodynamic parameters such as free energy (ΔG^o), entropy (ΔS^o) and enthalpy (ΔH^o) were also calculated from the sorption results used to explain the mechanism of the sorption. The results indicated that this sorbent is successfully employed in the separation of trace Cu(II), Zn(II) and Co(II) from the aqueous solutions.     

Selective removal of cesium ions from aqueous solutions using different inorganic metal hexacyanoferrate-prepared sorbents

Mg-Fe–hexacyanoferrate (MgFeCF) and Ni-Fe–hexacyanoferrate (NiFeCF) were prepared and characterized using X-ray diffraction, Fourier-transform infrared spectroscopy spectra, and thermal analysis. The isotherm study showed that the sorption data fit with the Langmuir and Freundlich isotherms at 25?±?1°C. The sorption capacities of the prepared sorbents for MgFeCF and NiFeCF were found to be 154.32 and 180.83?mg?g^?1, respectively. The adsorption of cesium by MgFeCF and NiFeCF is exothermic and spontaneous processes. Kinetic study indicated that the adsorption of cesium on MgFeCF and NiFeCF fits with the pseudo-second-order kinetic model. Desorption tests indicated that the sorption process is relatively stable. The new sorbents are promising efficient materials for cesium removal from aqueous solutions and sea water. The possibility of reusing the sorbents after stripping the metal ions was studied using 0.5?M HCl, and its efficiency for cesium removal was found to be 98% after five runs.     

Adsorption of copper and zinc from aqueous solutions by using natural clay

In this study, removal of copper (Cu(2+)) and zinc (Zn(2+)) from aqueous solutions is investigated using Cankiri bentonite, a natural clay. During the removal process, batch technique is used, and the effects of pH, clay amount, heavy metal concentration and agitation time on adsorption efficiency are studied. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms are applied in order to determine the efficiency of natural clay used as an adsorbent. Results show that all isotherms are linear. It is determined that adsorption of Cu(2+) and Zn(2+) is well-fitted by the second order reaction kinetic. In addition, calculated and experimental heavy metal amounts adsorbed by the unit clay mass are too close to each other. It is concluded that natural clay can be used as an effective adsorbent for removing Cu(2+) and Zn(2+) from aqueous solutions.     

Chemically modified olive stone: a low-cost sorbent for heavy metals and basic dyes removal from aqueous solutions

In the present work, we have investigated the sorption efficiency of treated olive stones (TOS) towards cadmium and safranine removal from their respective aqueous solutions. TOS material was prepared by treatment of olive stones with concentrated sulfuric acid at room temperature followed up by a subsequent neutralization with 0.1 M NaOH aqueous solution. The resulting material has been thoroughly characterized by SEM, energy-dispersive X-ray (EDX), MAS (13)C NMR, FTIR and physicochemical parameters were calculated. The sorption study of TOS at the solid-liquid interface was investigated using kinetics, sorption isotherms, pH effect and thermodynamic parameters. The preliminary results indicate that TOS exhibit a better efficiency in terms of sorption capacities toward the two pollutants (128.2 and 526.3 mg/g for cadmium and safranine, respectively) than those reported so far in the literature. Moreover, the sorption process is ascertained to occur fast enough so that the equilibrium is reached in less than 15 min of contact time. The results found in the course of this study suggest that ion exchange mechanism is the most appropriate mechanism involved in cadmium and safranine removal. Finally, the sorption efficiency of TOS is compared to those of other low-cost sorbents materials yet described in the literature.     

Comparison of various error functions in predicting the optimum isotherm by linear and non-linear regression analysis for the sorption of basic red 9 by activated carbon

A comparison of linear and non-linear regression method in selecting the optimum isotherm was made to the experimental equilibrium data of basic red 9 sorption by activated carbon. The r(2) was used to select the best fit linear theoretical isotherm. In the case of non-linear regression method, six error functions namely coefficient of determination (r(2)), hybrid fractional error function (HYBRID), Marquardt's percent standard deviation (MPSD), the average relative error (ARE), sum of the errors squared (ERRSQ) and sum of the absolute errors (EABS) were used to predict the parameters involved in the two and three parameter isotherms and also to predict the optimum isotherm. Non-linear regression was found to be a better way to obtain the parameters involved in the isotherms and also the optimum isotherm. For two parameter isotherm, MPSD was found to be the best error function in minimizing the error distribution between the experimental equilibrium data and predicted isotherms. In the case of three parameter isotherm, r(2) was found to be the best error function to minimize the error distribution structure between experimental equilibrium data and theoretical isotherms. The present study showed that the size of the error function alone is not a deciding factor to choose the optimum isotherm. In addition to the size of error function, the theory behind the predicted isotherm should be verified with the help of experimental data while selecting the optimum isotherm. A coefficient of non-determination, K(2) was explained and was found to be very useful in identifying the best error function while selecting the optimum isotherm.     

Effects of dissolved organic matter from the rhizosphere of the hyperaccumulator Sedum alfredii on sorption of zinc and cadmium by different soils

Pot experiments were conducted to investigate the changes of the dissolved organic matter (DOM) in the rhizosphere of hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of Sedum alfredii and its effects on Zn and Cd sorption by soils. After planted with HE, soil pH in the rhizosphere reduced by 0.5-0.6 units which is consistent with the increase of DOM. The hydrophilic fractions (51%) in DOM from the rhizosphere of HE (HE-DOM) was much greater than NHE-DOM (35%). In the presence of HE-DOM, Zn and Cd sorption capacity decreased markedly in the following order: calcareous clay loam > neutral clay loam > acidic silty clay. The sorption isotherms could be well described by the Freundlich equation (R² > 0.95), and the partition coefficient (K) in the presence of HE-DOM was decreased by 30.7-68.8% for Zn and 20.3-59.2% for Cd, as compared to NHE-DOM. An increase in HE-DOM concentration significantly reduced the sorption and increased the desorption of Zn and Cd by three soils. DOM derived from the rhizosphere of the hyperaccumulating ecotype of S. alfredii could significantly reduce metal sorption and increase its mobility through the formation of soluble DOM-metal complexes.     

Sono-sorption as a new method for the removal of lead ion from aqueous solution

Sorption of Pb(II) as a toxic heavy metal ion, onto styrene-divinylbenzene co-polymer resin in the presence of ultrasound (sono-sorption) and in its absence (classical method) is presented in this work. Batch experiments were conducted to study the effect of the main parameters such as the amount of sorbent, concentration of sorbate, contact time, intensity of ultrasound and temperature on this sorption process. The equilibrium between liquid and solid phase was described by Langmuir model better than the Freundlich model. The time to reach equilibrium especially in the presence of ultrasound was very fast. This indicates that the resin mentioned has a high potential for the sorption of this pollutant ion. The isotherm constants were obtained under several different conditions. These constants were used in the calculation of the thermodynamic parameters of sorption. According to the results, the kinetics of sorption was in agreement with both pseudo-first-order and first-order reversible models.     

The study of adsorption characteristics Cu and Pb ions onto PHEMA and P(MMA-HEMA) surfaces from aqueous single solution

The adsorption characteristics of Cu²⁺ and Pb²⁺ ions onto poly2-hydroxyethyl methacrylate (PHEMA) and copolymer 2-hydroxyethyl methacrylate with monomer methyl methacrylate P(MMA-HEMA) adsorbent surfaces from aqueous single solution were investigated with respect to the changes in the pH of solution, adsorbent composition (changes in the weight percentage of MMA copolymerized with HEMA monomer), contact time and the temperature in the individual aqueous solutions. The linear correlation coefficients of Langmuir and Freundlich isotherms were obtained. The results revealed that the Langmuir isotherm fitted the experimental results better than the Freundlich isotherm. Using the Langmuir model equation, the monolayer adsorption capacity of PHEMA surface was found to be 0.840 and 3.037 mg/g for Cu²⁺ and Pb²⁺ ions and adsorption capacity of (PMMA-HEMA) was found to be 31.153 and 31.447 mg/g for Cu²⁺ and Pb²⁺ ions, respectively. Changes in the standard Gibbs free energy (ΔG⁰), standard enthalpy (ΔH⁰) and standard entropy (ΔS⁰) show that the adsorption of mentioned ions onto PHEMA and P(MMA-HEMA) are spontaneous and exothermic at 293–323 K.     

Removal of cadmium from aqueous solutions using clinoptilolite: influence of pretreatment and regeneration

In this study, Cd removal from aqueous solutions via clinoptilolite was investigated in terms of the effect of pretreatment and regeneration. Four different chemicals (NaCl, KCl, CaCl₂ and HCl) were tested for this purpose. Samples treated by a total of 20 bed volume (BV) of 1 M NaCl solution prepared in tap water with no pH adjustment were found to perform satisfactorily. Five exhaustion and regeneration cycles were then carried out, revealing an increasing Cd removal capacity, coupled with constant Cd elution efficiency in progressing cycles. Furthermore, the change of pH and the presence of exchangeable (Na, K, Ca and Mg) and framework cations (Si and Al) in the aqueous phase were investigated. Subsequently, these were discussed in terms of progressive conversion of clinoptilolite to its homoionic Na-form, and the presence of different Cd removal mechanisms in the system. This study emphasizes the potential of clinoptilolite to be a part of sustainable wastewater treatment technologies, enabling the recovery of both the sorbent and the metal, via demonstration of effective Cd removal and clinoptilolite recovery, besides successful concentration of metal in the regenerant solution.     

Preparation and characterization of zeolite from waste Linz-Donawitz (LD) process slag of steel industry for removal of Fe3+ from drinking water

Cubical-shaped zeolite A was synthesized from the Linz-Donawitz (LD) process slag of the Steel Industry, utilizing conventional fusion-assisted hydrothermal treatment. Morphological and Physico-chemical characterizations were performed by various characterization techniques. A weight ratio of 1:1.2 (LD-slag: NaOH) was maintained during fusion, which provides a better binding effect with better mechanical stability to the zeolite framework. Fe³⁺ adsorption studies were performed at 273, 298, 303, and 308 K, respectively, within the range of 10–40 mg L⁻¹ Fe³⁺ ion concentration for kinetic and isotherm studies. A maximum adsorption capacity of 27.55 mg g⁻¹ was obtained at a 1.4 g L⁻¹ adsorbent dosage, with 99.99% Fe³⁺ ion removal. Moreover, the Fe³⁺ adsorption study obeyed the pseudo-second-order kinetic model, whereas multistage diffusion controlled the adsorption process. Langmuir isotherm model best fitted the equilibrium data suggesting the highly negative charge over the adsorbent surface played a vital role in the electrostatic attraction of Fe³⁺ ions. Isomorphic replacement of silicon by aluminum ion imparted a highly negative charge over the zeolite surface in the primary structure unit. For real-life sample drinking water, the Fe³⁺ ion removal efficiency increases to 97.7%.     

Kinetic and equilibrium studies on the removal of acid dyes from aqueous solutions by adsorption onto activated carbon cloth

Removal of acid dyes Acid Blue 45, Acid Blue 92, Acid Blue 120 and Acid Blue 129 from aqueous solutions by adsorption onto high area activated carbon cloth (ACC) was investigated. Kinetics of adsorption was followed by in situ UV-spectroscopy and the data were treated according to pseudo-first-order, pseudo-second-order and intraparticle diffusion models. It was found that the adsorption process of these dyes onto ACC follows the pseudo-second-order model. Adsorption isotherms were derived at 25 degrees C on the basis of batch analysis. Isotherm data were treated according to Langmuir and Freundlich models. The fits of experimental data to these equations were examined.     

Chitosan selectivity for removing cadmium (II), copper (II), and lead (II) from aqueous phase: pH and organic matter effect

The aim of this study was to investigate the selectivity of chitosan for cadmium, copper and lead in the presence and absence of natural organic matter (NOM) in different pH solutions. Adsorption isotherms of one and three adsorbates at initial concentration of 5-100mg/L were carried out in batch reactors at pH 4, 5, or 7 and 25 degrees C in reactive and clarified water. The chitosan employed had a MW of 107.8 x 10(3)g/mol and degree of acetylation (DA) of 33.7%. The chitosan adsorption capacity at pH 4 in reactive water was 0.036, 0.016, 0.010mmol/g for Pb(2+), Cd(2+), and Cu(2+), respectively, and it decreased for Pb(2+) and Cd(2+) in clarified water. Conversely, experiments carried out in clarified water showed that the cadmium adsorption capacity of chitosan was enhanced about three times by the presence of NOM at pH 7: an adsorption mechanism was proposed. Furthermore, it was found that the biosorbent selectivity, in both reactive and clarified water at pH 4, was as follows Cu(2+)>Cd(2+)>Pb(2+). Finally, the preliminary desorption experiments of Cd(2+) conducted at pH 2 and 3 reported 68 and 44.8% of metal desorbed, which indicated that the adsorption mechanism occurred by electrostatic interactions and covalent bonds.     

Removal of mercury(II) from aqueous media using eucalyptus bark: Kinetic and equilibrium studies

In this study, eucalyptus camaldulensis bark, a forest solid waste, is proposed as a novel material for the removal of mercury(II) from aqueous phase. The operating variables studied were sorbent dosage, ionic strength, stirring speed, temperature, solution pH, contact time, and initial metal concentration. Sorption experiments indicated that the sorption capacity was dependent on operating variables and the process was strongly pH-dependent. Kinetic measurements showed that the process was uniform and rapid. In order to investigate the mechanism of sorption, kinetic data were modeled using the pseudo-first-order and pseudo-second-order kinetic equations, and intraparticle diffusion model. Among the kinetic models studied, the pseudo-second-order equation was the best applicable model to describe the sorption process. Equilibrium isotherm data were analyzed using the Langmuir and the Freundlich isotherms. The Langmuir model yields a much better fit than the Freundlich model. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy, and entropy of sorption. The maximum sorption capacity was 33.11 mg g⁻¹ at 20 °C and the negative value of free energy change indicated the spontaneous nature of sorption. These results demonstrate that eucalyptus bark is very effective in the removal of Hg(II) from aqueous solutions.