Synthesis of crosslinked oxidized starch and its adsorption behavior for calcium ion

Cornstarch, after crosslinking with epichlorohydrin (4%, v/w, dry basis of the starch), was oxidized with hydrogen peroxide over the catalyst Cu(II). The newly synthesized products were applied to examine the calcium ion removal activity from water, under various conditions. Removal efficiency of calcium ion from aqueous solution increased proportionally with carboxyl content and the dose of crosslinked oxidized starch in the solution. Ionization of carboxyl groups in starch was necessary for the effective calcium removal. When the pH of the solution was adjusted below 4.0, the starch was no longer an effective calcium‐sequestering agent. Adsorption isotherm models were developed, wherein the best fit was obtained in the Langmuir model. Thermodynamic study indicated that the adsorption process was exothermic, and the enthalpy change (ΔH^θ), the entropy change (ΔS^θ), and free energy change (ΔG^θ) of the adsorption process were calculated with adsorption isotherm data and basic thermodynamic relations. It was assessed that adsorption occurred by strong electrostatic interactions with the negative adsorption enthalpy (ΔH^θ). The regeneration and reusability of oxidized starch were also assessed and were found to retain the adsorption capacity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1539–1546, 2006     

Novel hexamethylene diamine‐functionalized macroporous copolymer for chromium removal from aqueous solutions

Macroporous copolymers of poly[(glycidyl methacrylate)‐co ‐(ethylene glycol dimethacrylate)] (PGME ) with various crosslinker (ethylene glycol dimethacrylate) concentrations and porosity parameters and additionally functionalized with hexamethylene diamine (PGME‐HD ) were tested as potential Cr(VI ) oxyanion sorbents from aqueous solutions. Kinetics of Cr(VI ) sorption was investigated in the temperature range 298–343 K and the results were fitted to chemical reaction and particle diffusion models. The Cr(VI ) sorption obeys the pseudo‐second‐order model with definite influence of pore diffusion. A temperature rise promotes chromium removal, with a maximum experimental uptake capacity of 4.21 mmol g^?1 at 343 K for the sample with the highest amino group concentration. Equilibrium data were analysed with Langmuir, Freundlich and Temkin adsorption isotherm models. Thermodynamic parameters, i.e. Gibbs free energy (ΔG ⁰), enthalpy (ΔH ⁰) and entropy change (ΔS ⁰) and activation energy of sorption (E _a), were calculated. The Cr(VI) adsorption onto PGME‐HD was found to be spontaneous and endothermic, with increased randomness in the system. Desorption experiments show that chromium anion sorption was reversible and the PGME‐HD sample GMA 60 HD was easily regenerated with 0.1 mol L^?1 NaOH up to 90% recovery in the fourth sorption/desorption cycle. In the fifth cycle, a substantial sorption loss of 37% was observed. © 2016 Society of Chemical Industry     

Adsorption of Cu(II) and Cr(VI) onto Treated Shorea dasyphylla Bark: Isotherm,Kinetics, and Thermodynamic Studies

The efficacy of treated Shorea dasyphylla bark for Cu(II) and Cr(VI) adsorption was assessed in a batch adsorption system as a function of pH, agitation period, and initial metal concentration. The equilibrium nature of Cu(II) and Cr(VI) adsorption was described by the Freundlich, Langmuir, and Dubinin-Radushkevich isotherms. The maximum monolayer capacities of treated Shorea dasyphylla bark, estimated from the Langmuir equation were 184.66 and 42.72 mg/g for Cu(II) and Cr(VI), respectively. The experimental results were fitted using pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models; the pseudo-second order showed the best conformity to the kinetic data. Thermodynamic parameters such as enthalpy change (ΔH°), free energy change (ΔG°) and entropy change (ΔS°) were determined by applying the Van't Hoff equation. The adsorption of Cu(II) and Cr(VI) onto treated Shorea dasyphylla bark was found to be spontaneous and exothermic. The adsorption mechanism was confirmed by means of Fourier transform infrared (FTIR) and Energy dispersive X-ray (EDX) spectroscopy. The dimensionless constant separation factor (R _L), indicated that treated Shorea dasyphylla bark was favorable for Cu(II) and Cr(VI) adsorption.     

Removal of Cr (VI) from aqueous solution by newspapers

The potential to remove Cr (VI) ions from aqueous solution using newspapers was investigated in the present study. The effects of relevant parameters such as solution pH, adsorbent concentration, and reaction temperature on Cr (VI) adsorption were examined. The adsorption of Cr (VI) ions onto newspapers was found to be highly pH-dependent and the highest uptake occurred at pH 1.0. The sorption equilibrium data were correlated to the Langmuir, Freundlich, Redlich-Peterson and Dubinin-Radushkevich equations. Five different non-linear error functions were examined and the result indicated that the Freundlich and Redlich-Peterson equations better fitted the equilibrium data than Langmuir isotherm. The maximum sorption capacity was found to be 55.06 mg/g at pH 1.0, adsorbent concentration 4 g/L and reaction temperature of 30 °C. Different thermodynamic parameters viz., changes in standard free energy (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) were also evaluated and the results show that the sorption process was spontaneous and endothermic in nature. The kinetic experimental data were well fitted by the pseudo-second order, external film diffusion and diffusion models allowing the corresponding parameters to be evaluated. The sorption capacity increased with the decrease of adsorbent concentration.     

Removal of Cr(VI) From Aqueous Solution by Turkish Vermiculite: Equilibrium,Thermodynamic and Kinetic Studies

Abstract

The adsorption of Cr(VI) from aqueous solution by Turkish vermiculite were investigated in terms of equilibrium, kinetics, and thermodynamics. Experimental parameters affecting the removal process such as pH of solution, adsorbent dosage, contact time, and temperature were studied. Equilibrium adsorption data were evaluated by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. Langmuir model fitted the equilibrium data better than the Freundlich model. The monolayer adsorption capacity of Turkish vermiculite for Cr(VI) was found to be 87.7 mg/g at pH 1.5, 10 g/L adsorbent dosage and 20°C. The mean free energy of adsorption (5.9 kJ/mol) obtained from the D–R isotherm indicated that the type of sorption was essentially physical. The calculated thermodynamic parameters (ΔG ^o , ΔH ^o and ΔS ^o ) showed that the removal of Cr(VI) ions from aqueous solution by the vermiculite was feasible, spontaneous and exothermic at 20–50°C. Equilibrium data were also tested using the adsorption kinetic models and the results showed that the adsorption processes of Cr(VI) onto Turkish vermiculite followed well pseudo-second order kinetics.     

Fabrication of a copolymer flocculant and application for Cr(VI) removal

A copolymer flocculant (CATCS) derived from starch and chitosan was fabricated and used as eco‐friendly adsorbent for removal of Cr(VI) from aqueous solution. The CATCS flocculant was characterized by scanning electron microscope, thermogravimetic analysis, and Fourier transform infrared spectroscopy. The effects of CATCS dosage, initial Cr(VI) concentration, pH, and reaction time on removal of Cr(VI) were discussed. The results showed CATCS removed Cr(VI) effectively and the adsorption isotherm agreed well with the Freundlich isotherm and R–P isotherm models. The enthalpy change (ΔH) of the process was 16.75 kJ/mol suggesting the existence of chemisorption and the reaction was endothermic. Moreover, the negative free energy change (ΔG) indicated the adsorption process was feasible and spontaneous. The positive entropy change (ΔS) showed there was an increase of disorder in the system during the adsorption process. The adsorption kinetics results showed that the adsorption could be described by the pseudo‐second‐order kinetics mechanism. The activation energy (E_a) of the adsorption reaction was 29.16 kJ/mol. POLYM. ENG. SCI., 56:1213–1220, 2016. © 2016 Society of Plastics Engineers     

Fe2+-modified Vermiculite for the Removal of Chromium (VI) from Aqueous Solution

A novel adsorbent: Fe²⁺-modified vermiculite was prepared in a two-step reaction. Adsorption experiments were carried out as a function of pH, contact time, and concentration of Cr(VI). It was found that Fe²⁺-modified vermiculite was particularly effective for the removal of Cr(VI) at pH 1.0. The adsorption of Cr(VI) reached equilibrium within 60 min, and the pseudo-second-order kinetic model best described the adsorption kinetics. The adsorption data follow the Langmuir model more than the Freundlich model. At pH 1.0, the maximum Cr(VI) sorption capacity (Q _max ) was 87.72 mg · g^?1. Desorption of Cr(VI) from Fe²⁺-modified vermiculite using NaOH treatment exhibited a higher desorption efficiency by more than 80%. The sorption mechanisms including electrostatic interaction and reduction were involved in the Cr (VI) removal. The results showed that Fe²⁺-modified vermiculite can be used as a new adsorbent for Cr(VI) removal which has a higher adsorption capacity and a faster adsorption rate.     

Equilibrium kinetic and thermodynamic studies of Cr(VI) adsorption onto a novel adsorbent of <Emphasis Type="Italic">Eucalyptus camaldulensis</Emphasis> waste: Batch and column reactors

Cr(VI) adsorption onto Eucalyptus camaldulensis sawdust (ECS) waste was investigated in batch and column reactors. Various parameters, including the adsorbent dose, pH, initial concentration, particle size, contact time and temperature were optimized. The maximum adsorption capacity (35.58mg g^-1, 71.16%) was achieved at pH 2.0. Data fitted well to Freundlich and Halsey’s models (R²=0.992), indicating the multilayer adsorption of Cr(VI). It obeys the pseudo-second order kinetics. Endothermic and non-spontaneous nature of Cr(VI) adsorption was observed with positive values of changes in enthalpy (9.83 kJ mol^-1), and Gibbs-free energy (1.52, 1.38, 1.24, 1.10 and 0.97 kJ mol^-1), respectively. In this column study, the breakthrough curve time increased from 670 to 1,270min by increasing the bed height from 5 to 15 cm, respectively. Column data was found well fitted to bed depth service time model. Adsorption capacity at 60% breakthrough was 2,443.636mg L^-1. The study indicates that ECS waste can be a promising adsorbent for Cr(VI) remediation from industrial effluents.     

Enhanced adsorptive removal of Cr(VI) in aqueous solution by polyethyleneimine modified palygorskite

Polyethyleneimine (PEI) modified palygorskite (Pal) was used for the adsorption of Cr(VI) in aqueous solution. The absorbent was characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). Characterized results confirmed that the Pal has been successfully modified by PEI. The modification of PEI increased the Cr(VI) adsorption performance of the Pal by the adsorption combined reduction mechanism, and amino groups of the adsorbent play the main role in the enhanced Cr(VI) adsorption. The maximum adsorption capacity was 51.10 mg·g⁻¹ at pH 4.0 and 25 °C. The adsorption kinetics of Cr(VI) on the adsorbent conforms to the Langmuir isotherm model. The maximum adsorption occurs at pH 3, and then the adsorption capacity of PEI-Pal was decreased with the increase of pH values. The adsorption kinetics of Cr(VI) on PEI-Pal was modeled with pseudo-second-order model. The addition of Cl⁻, SO₄²⁻ and PO₄³⁻ reduced the Cr(VI) adsorption by competition with Cr(VI) for the active sites of PEI-Pal. The Cr(VI) saturated PEI-Pal can be regenerated in alkaline solution, and the adsorption capacity can still be maintained at 30.44 mg·g⁻¹ after 4 cycles. The results demonstrate that PEI-Pal can be used as a potential adsorbent of Cr(VI) in aqueous solutions.     

Removal of Chromium(VI) and Chromium(III) from Aqueous Solution by Grainless Stalk of Corn

Abstract

Grainless stalk of corn (GLSC) was tested for removal of Cr(VI) and Cr(III) from aqueous solution at different pH, contact time, temperature, and chromium/adsorbent ratio. The results show that the optimum pH for removal of Cr(VI) is 0.84, while the optimum pH for removal of Cr(III) is 4.6. The adsorption processes of both Cr(VI) and Cr(III) onto GLSC were found to follow first-order kinetics. Values of k _ads of 0.037 and 0.018 min^?1 were obtained for Cr(VI) and Cr(III), respectively. The adsorption capacity of GLSC was calculated from the Langmuir isotherm as 7.1 mg g^?1 at pH 0.84 for Cr(VI), and as 7.3 mg g^?1 at pH 4.6 for Cr(III), at 20°C. At the optimum pH for Cr(VI) removal, Cr(VI) reduces to Cr(III). EPR spectroscopy shows the presence of Cr(V) + Cr(III)-bound-GLSC at short contact times and adsorbed Cr(III) as the final oxidation state of Cr(VI)-treated GLSC. The results indicate that, at pH ≈ 1, GLSC can completely remove Cr(VI) from aqueous solution through an adsorption-coupled reduction mechanism to yield adsorbed Cr(III) and the less toxic aqueous Cr(III), which can be further removed at pH 4.6.     

Study of stability and thermodynamic properties for polychlorinated dihydrophezines by density functional theory

The thermodynamic properties of 76 polychlorinated dihydrophezines (PCDPs) in the gaseous state at 298.15 K and 101.325 kPa, have been calculated using the density functional theory (the BHANDHLYP/6‐31G*) with Gaussian 03 program. Based on these data, the isodesmic reactions were designed to calculate the standard formation heat (Δ_fH^θ), standard Gibbs free energy of formation (Δ_fG^θ) of PCDPs in the gaseous state. The relations of these thermodynamic parameters with the number and position of chlorine substituents (N_PCS) were discussed, and it was found that there exist good correlation between thermodynamic parameters, including heat capacity at constant volume , entropy (S^θ), enthalpy (H^θ), free energy (G^θ), Δ_fH^θ, Δ_fG^θ, and N_PCS. The relative stability order of PCDP congeners was theoretically proposed based on the relative magnitude of their Δ_fG^θ. In addition, the values of molar heat capacity at constant pressure (C_p,m) for PCDP congeners have been calculated.     

Removal of hexavalent chromium in wastewater by polyacrylamide modified iron oxide nanoparticle

Iron oxide nanoparticle has been successfully modified by polyacrylamide and the polyacrylamide modified magnetic nanoparticles (PMMNs) were applied to remove Cr(VI) in wastewater. The vibrating sample magnetometer (VSM) spectra indicated the large saturation magnetization and superparamagnetic property of the PMMNs. This made the polyacrylamide modified iron oxide easily separate with liquid phase. Scanning electron microscope (SEM) results showed that both the synthesized iron oxide and the PMMNs were nanoscale. Batch adsorption studies had been carried out to determine the effect of pH, contact time, Cr(VI) initial concentration, and coexisting salts on the adsorption of Cr(VI). Maximum removal (98.30%) was observed from an initial concentration of 100 mg L^?1 Cr(VI) at pH 3.0, 30°C. This process followed pseudo‐second‐order kinetics model and the equilibrium time was 40 min. The experimental data fitted the Langmuir isotherm better than Freundlich. Maximum adsorption amount of Cr(VI) by PMMN was 35.186 mg g^?1. The effect of coexisting salts on Cr(VI) removal was not apparent even the concentration of salt was 10 times as big as the low concentration, 0.01M. It had been proposed that the mechanism of Cr(VI) uptake onto PMMN was adsorption‐coupled reduction. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40945.     

Effect of pre‐treatments on the biosorption of Chromium (VI) ions by the dead biomass of Rhizopus arrhizus

BACKGROUND: This work fulfils the need to develop an eco‐friendly biosorbent, elucidating the mechanism of biosorption. Removal of Cr(VI) by Rhizopus arrhizus was investigated in batch mode. Enhancement in the performance of the biosorbent was attempted by pre‐treating the biomass with inorganic and organic acids, chelating agent, cross‐linker and an organic solvent followed by autoclaving. The surface characterization of the biomass was carried out by potentiometric titration, surface area analysis, infrared spectroscopy, chemical modification of the biomass and scanning electron microscopy. RESULTS: All the physico‐chemical treatments of the biosorbent improved Cr(VI) uptake compared with the native biomass (21.72 mg g^?1). The highest biosorption capacity (31.52 mg g^?1) was achieved after pre‐treating the biomass with 0.5 mol L^?1 HNO₃ followed by autoclaving. Surface characterization of the biomass using pH_zpc, potentiometry and Fourier transform infrared (FTIR) analysis revealed the role of amino and carboxyl groups in Cr(VI) removal by electrostatic attraction. Chemical modification of amino and carboxyl groups significantly decreased Cr(VI) uptake capacity confirming their role in biosorption. SEM analysis showed adsorption of Cr(VI) on the biosorbent surface. CONCLUSION: Rhizopus arrhizus biomass proved to be an effective and low cost alternative biosorbent for removal of Cr(VI) from aqueous solutions. Copyright © 2011 Society of Chemical Industry     

Fly ash as a sorbent for boron removal from aqueous solutions: Equilibrium and thermodynamic studies

ABSTRACT

This study presents the application of fly ash from brown coal and biomass burning power plant as a sorbent for the removal of boron ions from an aqueous solution. The adsorption process efficiency depended on the parameters, such as adsorbent dosage, pH, temperature, agitation time and initial boron concentration. The experimental data fitted well with the Freundlich isotherm model and the maximum capacity was found to be 16.14 mg g^?1. The adsorption kinetics followed the pseudo-second-order model. Also, the intra-particle diffusion model parameters were calculated. Thermodynamic parameters such as change in free energy (ΔG°), enthalpy (ΔH°), entropy (ΔS°) revealed on exothermic nature of boron adsorption onto the fly ash.     

Extraction of Uranium(VI) and Thorium(IV) from Nitric Acid Solution by N,N,N′,N′ – Tetraoctylglutaricamide

Synthesis and characterization of N,N,N′,N′-tetraoctylglutaricamide (TOGA) was carried out and used for extraction of U(VI) and Th(IV) from nitric acid solutions. The processes of extraction were determined by the slope analysis and by analyzing a function that allows the simultaneous treatment of all the experimental points obtained in different conditions. The different factors affecting the extraction distribution ratio(D) of U(VI) and Th(IV) (extraction concentration, concentrations of nitric acid, salting-out agent NaNO₃ concentration, equilibration time, temperature, and types of diluents) were investigated. The results obtained indicated that the extraction species of U(VI) and Th(IV) are mainly extracted as UO₂(NO₃)₂·1.0TOGA and Th(NO₃)₄·1.5TOGA. The apparent equilibrium constant of U(VI) and Th(IV) extraction determined are 3.35 ± 0.03 L³/mol³ and 1.87 ± 0.01 L⁵/mol⁵ at 298 ± 1 K. Thermodynamic parameters such as the free energy(ΔG), enthalpy(ΔH), and entropy(ΔS) changes associated with the extraction processes could be evaluated. Back-extraction of U(VI) and Th(IV) from organic phases was also studied.     

Adsorption of hexavalent chromium by chitosan‐based polymeric surfactants

Chitosan‐based polymeric surfactants (CBPSs) were prepared by the partial N‐acylation of amine groups on chitosan with acid anhydrides. To apply the CBPSs for the removal of Cr(VI) commonly found in wastewater, a batch test was conducted to evaluate the adsorption capacity. The removal efficiency of Cr(VI) by the CBPS depended on several factors, including the solution pH, CBPS dose, and ionic strength. Our results show that the CBPSs exhibited a greater adsorption capacity for Cr(VI) than have other modified chitosans reported in the literature. The maximum adsorption capacity of Cr(VI) was 180 mg/g of CBPS at a final pH of 5.3. From the results of dynamic light scattering, we propose that the removal mechanism of Cr(VI) by the CBPSs was mainly through the adsorption of negatively charged chromium ions by positively charged amine groups on the CBPSs followed by colloidal precipitation because of its lower solubility. Conclusively, we found that the CBPS was significantly effective for the removal of Cr(VI). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 44–50, 2005     

EQUILIBRIUM,KINETICS, AND BREAKTHROUGH STUDIES FOR ADSORPTION OF Cr(VI) ON CHITOSAN

Wastewater containing low levels of pollutants can be effectively treated by the adsorption technique. In the present work, an adsorption study was carried out using chitosan as adsorbent in a fixed-bed column for the removal of Cr(VI) from wastewater solutions. The column performance of Cr(VI) adsorption onto chitosan was studied at different bed heights (3–9 cm), flow rates (50–200 mL/min), initial metal concentrations (2–10 mg/L), pH values (2–7), and temperatures (30°–60°C). The equilibrium data for the batch adsorption of Cr(VI) on chitosan were tested using the Langmuir, Freundlich, and BET isotherm models. The Langmuir model was found to be the most suitable, with a maximum adsorption capacity of 35.7 mg/g and a correlation coefficient (R ²) = 0.952. The experimental data were found to fit well with the pseudo-second-order kinetic model, with R ² = 0.999. The dynamics of the adsorption process was modeled using the Adams-Bohart, Thomas, and mass transfer models. The models were used to predict the breakthrough curves of adsorption systems and to determine the characteristic design parameters of the column. The adsorption data were observed to fit well with all three models. The model parameters were derived using MATLAB software. In order to compare quantitatively the applicability of adsorption dynamic models in fitting to experimental data, the percentage relative deviation (P) was calculated and found to be less than 5, confirming that the fit is good for all three models.     

Adsorption of fulvic acids from aqueous solutions by carbon nanotubes

Carbon nanotubes (CNTs) were used as adsorbent to remove fulvic acids (FA) from aqueous solutions. The adsorption capacity of CNTs for FA can reach 24 mg g^?1 at 5 °C and equilibrium concentration of 18 mg dm^?3. The kinetic and thermodynamic parameters, such as rate of adsorption, standard free energy changes (ΔG⁰), standard enthalpy change (ΔH⁰) and standard entropy change (ΔS⁰), have been obtained. Acidic conditions (pH = 2–5) favor FA removal. An increase in the ionic strength or the addition of divalent cations increase the adsorption of FA dramatically (FA = 60 mg dm^?3). An increase in the maximum adsorbed amount of FA was observed when treating FA in synthetic seawater. Desorption studies reveal that FA can be easily and quickly removed from CNTs by altering the pH values of the solution. Good adsorption capacity and quick desorption indicate that CNTs are a promising adsorbent to remove FA from aqueous solutions. Copyright © 2007 Society of Chemical Industry     

Equilibrium modeling,kinetic and thermodynamic studies on the adsorption of Cr(VI) using activated carbon derived from matured tea leaves

A new porous carbon with high surface area of 1,313.41 m² g^?1 with pore volume 1.359 cm³ g^?1 has been synthesized from matured tea leaves by chemical activation method using phosphoric acid. The carbon was found to be highly efficient for removal of Cr(VI) from aqueous solution. The effects of various parameters such as contact time, initial metal ion concentration, pH, temperature and amount of adsorbent on the extent of adsorption were studied. Langmuir, Freundlich and Temkin adsorption models were used to interpret the experimental data. The adsorption data were best fitted with Langmuir isotherm model. The adsorption capacity of Cr(VI) onto the activated carbon calculated from Langmuir isotherm was found to be 30.8 mg g^?1 at pH 4.8 and temperature 303 K. The adsorption capacity increases from 25.36 to 32.04 mg g^?1 with an increase in temperature from 303 to 323 K at initial Cr(VI) concentration of 60 mg L^?1. The adsorption process followed a pseudo second order kinetic model. Thermodynamic parameters ΔH⁰ (28.6 KJ mol^?1), ΔG⁰ at three different temperatures [(?0.145, ?1.09, ?2.04) KJ mol^?1] and ΔS⁰ (94.87 J mol^?1 K^?1) were calculated. These values confirm the adsorption process to be endothermic and spontaneous in nature.