Adsorption of Cr(VI) on Stipa tenacissima L (Alfa): Characteristics,kinetics and thermodynamic studies

This study aims to remove ionic Cr(IV) from aqueous solution using Stipa tenacissima L as a biomass source. The Arabic name for the plant Stipa tenacissima L is HALFA (ALFA) ; it belongs to the category of biosorbents agro-industrial origin. Stipa tenacissima L is from the center of the province of Djelfa Algeria. This biomass was characterized by various analytical techniques such as scanning electron microscopy, energy dispersive spectroscopy and Fourier-transform infrared spectroscopy. In order to optimize the operating conditions for the determination of ions of Cr(VI), the initial concentration of Cr(VI) ions, temperature, pH of the solution and the solid/liquid ratio were individually studied. According to the results, a fix rate of about 90% was recorded. Optimum biosorption conditions were found to be pH ~1, C_o = 50 mg/L, R = 5 g/L and T = 296 K. It was found that biosorption of Cr(VI) ions onto biomass of Stipa tenacissima L was better suitable to Langmuir model. The correlation coefficients for the second-order kinetic model obtained were found to be 0.996 for all concentrations. These indicate that the biosorption system studied belongs to the second-order kinetic model. Thermodynamics parameters as enthalpy, entropy of system and free energy were evaluated, which confirms the feasibility of the process. An empirical modeling was performed by using a 2⁴ full factorial design, and the regression equation for adsorption chromium (VI) was determined from the data. The initial metal ion concentration has the most positive pronounced effect in increasing the chromium (VI) adsorption, whereas the pH and adsorbent dosage have the most negative effect on the process.     

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.     

Removal of Chromium (VI) from Aqueous Solution by Cellulose Modified with D-Glucose

Cellulose powder was grafted with the vinyl monomer glycidyl methacrylate using ceric ammonium nitrate as initiator and was further derived with D-Glucose (D-Glu) to build a adsorbent (Cell-g-GMA-D-Glu). Epoxy cellulose, which was made up of Cell-g-GMA and Cell-hydro-g-GMA, was found to contain 5.48 mmol g^?1 epoxy groups. The adsorption process of the adsorbent was described by the Langmuir model of adsorption well and the maximum adsorption capacity of chromium (VI) reached to 54.59 mg g^?1. The adsorption-desorption tests of the Cell-g-GMA-D-Glu exhibited that the reproducibility of the absorbent was well and the adsorbent could be reused six times at least.     

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.     

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.     

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.     

BIOSORPTION STUDIES ON NACL-MODIFIED CERATOPHYLLUM DEMERSUM: REMOVAL OF TOXIC CHROMIUM FROM AQUEOUS SOLUTION

The present research provides information on the Cr(VI) removal potential of NaCl-modified Ceratophyllum demersum, an aquatic plant biomass. The effects of various parameters including pH, biomass dosage, contact time, and initial concentration on Cr(VI) biosorption were investigated. The best conditions for Cr(VI) biosorption in the present study were: pH of 2, biosorbent dose of 8 g/L, and contact time of 60 min. Under these conditions, maximum adsorption capacity of modified C. demersum for Cr(VI) was 10.20 mg/g. The experimental biosorption data were modeled by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The biosorption process followed the Langmuir isotherm model with a high coefficient of determination (R² > 0.99). The biosorption process followed pseudo-second-order kinetics. Further, the biosorbent was characterized by Fourier transform-infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The results showed that biosorption of Cr(VI) on NaCl-modified C. demersum occurred through chemical sorption.     

Adsorption of Cr (VI) Oxyanions onto Modified Wood Pulp

A new adsorbent was prepared from wood pulp (WP) after reaction with epichlorohydrin and dimethylamine in the presence of pyridine and N,N-dimethylformamide (DMF). The adsorption of Cr (VI) from aqueous solutions by the so-prepared wood pulp adsorbent (WP-A) was investigated. Various factors affecting adsorption, such as pH, adsorbent concentration (1–5 g/L), agitation time (5–60 min), and Cr (VI) concentration (50–700), were taken into consideration. The adsorption of Cr (VI) onto (WP-A) was found to be pH-dependent and maximum adsorption was obtained at pH 3. The adsorption data obeyed Langmuir and Freundlich adsorption isotherms. The Langmuir adsorption capacity (Q_max) was found to be 588.24 mg/g. Freundlich constants, K_F and n, were found to be 55.03 and 2.835, respectively.     

Study on adsorption of Cu(II)–Cr(VI) binary system by carbonized Eupatorium adenophorum

We first report a mechanism study on the adsorption of Cu(II)-Cr(VI) binary mixture by a novel low-cost adsorbent, carbonized Eupatorium adenophorum. The influences by pH value, dosage, initial concentration, temperature, and adsorption time on its performance to absorb copper and chromium were investigated. The experimental data were fitted according to the Langmuir and Freundlich adsorption isotherm models, the pseudo-first-order kinetics, the pseudo-second-order kinetics, and the intra-particle diffusion model. The results indicated that when the reaction system was with its pH = 5, the dosage of carbonized Eupatorium adenophorum was 0.1 g, the adsorption time was 30 min, and the temperature was 25°C; the adsorption capacities for Cu(II) and Cr(VI) reached 27.62 mg/g and 9.68 mg/g, respectively. The process of carbonized Eupatorium adenophorum to absorb Cr(VI) is also accompanied by redox reactions. The Langmuir model and the pseudo-second-order model can better ?t the experimental data. Observation by fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) found no significant change of functional groups before and after the adsorption by carbonized Eupatorium adenophorum, and this adsorption process is mainly a physical adsorption.     

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 copper,cadmium, and chromium from wastewater by modified wheat bran using Box–Behnken design: Kinetics and isotherm

In this work, copper, cadmium, and chromium were removed using hydrochloric acid-treated wheat bran as an adsorbent. Experiments were carried out in batch adsorption mode. Box–Behnken design of response surface methodology was used to determine the effect of initial metal concentration, pH, temperature, and adsorbent dose on removal efficiency of copper, cadmium, and chromium. Analysis of variance results are shown for all the three heavy metal, and the effect of the parameters is discussed. The optimum initial metal concentration, pH, temperature, and adsorbent dose were found to be 90.58 mg/L, 6, 35.9°C, and 2.39 g, respectively. Pseudo-second-order kinetic model was found to be the best suitable model for adsorption rate. The isotherms of adsorption data were analysed using various adsorption isotherm models such as Langmuir, Freundlich, Dubinin–Radushkevich, and Temkin isotherms. It was found that Langmuir and Temkin isotherms represent the equilibrium data for these heavy metal removals.     

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.     

Re‐use of Exhausted Ground Coffee Waste for Cr(VI) Sorption

Abstract

Exhausted ground coffee waste has been investigated as metal biosorbent for Cr(VI) from aqueous solution. Maximum metal sorption was found to occur at initial pH 3.0. Kinetic studies revealed that the initial uptake was quite rapid; nevertheless, it took five days to reach equilibrium. The value of the Langmuir maximum uptake was found to be 10.2 mg Cr(VI)/g waste. The sorbent is able to reduce hexavalent chromium to its trivalent form. A solution of 1 M NaOH was the most effective desorption agent and after 24 hours contact 42% of total chromium was desorbed in both hexavalent and trivalent oxidation states.     

Kinetics and thermodynamic studies of Cr(VI) adsorption using environmental friendly multifunctional zeolites synthesized from coal fly ash under mild conditions

Abstract

The Na-P1 zeolite was produced from coal fly ash and modified with different environmental friendly surfactants. The potential of these green modified zeolites was investigated as adsorbents for Cr(VI) ions in a batch system. XRD, SEM, XRF, and ICP-AES analyses were used for the characterization of raw materials and zeolite samples. The environmental friendly modified zeolites successfully immobilized different toxic elements in their framework inhibiting the transfer of these toxic elements to the surrounding liquid phase. The effects of various operational parameters on Cr(VI) removal were studied. The Hexamethylenediamine (HDTMA) and Ammonyx KP (KP) modified zeolites had larger chromium removal potential than the other samples at all temperatures. The effectiveness of Cr(VI) ions elimination became greater as the pH decreased and the adsorbent dose increased. The Freundlich, Langmuir, and Dubinin–Radushkevich isotherms were fitted to the equilibrium data. The Dubinin–Radushkevich and Langmuir models gave a better fitness to equilibrium data of HDTMA-Na-P1 and KP-Na-P1, respectively. The positive and high ΔH° values showed the endothermic nature of the total Cr(VI) sorption procedure and indicated that Cr(VI) adsorption onto HDTMA-Na-P1 and KP-Na-P1 is a chemisorption. The negative ΔS° values also showed that chromium ions were stable on the surface of adsorbents. The adsorption potential of the developed eco-friendly KP-Na-P1 was higher than those of other adsorbents reported in the literature.     

Use of polyethylene films photografted with 2‐(dimethylamino)ethyl methacrylate as a potential adsorbent for removal of chromium (VI) from aqueous medium

A new polymeric adsorbent material based on polyethylene (PE) was prepared by photografting of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) as a positively chargeable monomer to a PE film. The effects of the experimental parameters, such as the pH value, temperature, and grafted amount on adsorption of chromium(VI) (Cr(VI)) ions were investigated for the DMAEMA‐grafted PE (PE‐g‐PDAMEMA) films. The maximum adsorption capacity was obtained at the initial pH value of 3.0 for a PE‐g‐PDMAEMA film with 1.8 mmol/g and the maximum adsorption capacity obtained was higher than or compatible to those of many of the other polymeric adsorbents prepared for Cr(VI) ions. The adsorption kinetics obeyed the mechanism of the pseudo‐second order kinetic model and adsorption of Cr(VI) ions on PE‐g‐PDMAEMA films was well expressed by the Langmuir isotherm model. A high Langmuir adsorption constant suggests that the adsorption of Cr(VI) ions occurs between protonated dimethylamino groups and ions mainly through the electrostatic interaction. Cr(VI) ions adsorbed were successfully desorbed from a PE‐g‐PDMAEMA film in solutions of NaCl, NH₄Cl, NH₄Cl containing NaOH, and NaOH and a PE‐g‐PDMAEMA film was regenerated and repeatedly used for adsorption of Cr(VI) ions without appreciable loss in the adsorption capacity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43360.     

Application of multicomponent adsorption isotherms to simultaneous biosorption of iron(iii) and chromium(vi) on C. vulgaris

Although the biosorption of single metal ions to various microorganisms has been extensively studied and adsorption isotherms have been developed for single metal ion situations, very little attention has been given to the bioremoval and the expression of the adsorption isotherms of multi-metal ions systems. In this study, the competitive biosorption of iron(III) and chromium(VI) to Chlorella vulgaris from a binary metal mixture was studied and compared with the single metal ion situation in a batch stirred system. The effects of pH and single and dual metal ion concentrations on the biosorption rates and equilibrium uptakes were investigated. The optimum biosorption pH for both metal ions was determined as 2·0. Multi-metal ion biosorption studies were also performed at this pH value. It was observed that the biosorption rates and yields and equilibrium uptakes of iron(III) or chromium(VI) ions were reduced by the presence of increasing concentrations of the other metal ion. Adsorption isotherms developed for both single and dual metal ion systems at the optimum pH were expressed by the non-competitive and competitive Langmuir and Freundlich adsorption models, and model parameters were determined by computer. It was seen that the adsorption equilibrium data fitted very well to both of the models in the concentration ranges studied. ©1997 SCI     

Removal of chromium(VI) from aqueous solutions using polypyrrole-based magnetic composites

PPy/Fe₃O₄/AgCl composites were prepared via in situ polymerization for the removal of highly toxic Cr(VI). The structure and morphology of the prepared composites were characterized by the XRD, SEM, TEM, and VSM examinations. Up to 100 % removal was found with 1000 mg/L Cr(VI) aqueous solution at pH 2.0. The process of Cr(VI) ions’ adsorption was easy to reach equilibrium at higher temperatures. Adsorption results showed that Cr(VI) removal efficiency by the composites decreased with an increase in pH. Adsorption kinetics was described by the pseudo-second-order rate model. Isotherm data fitted well to the Langmuir isotherm model. Desorption experiment showed that the regenerated adsorption of PPy/Fe₃O₄/AgCl can be reused successfully for three times successive adsorption–desorption cycles without appreciable loss of its original capacity.     

Selective Adsorption of Mo(VI) From Re(VII) Containing Effluent on Orange Waste Gel Modified by Ethylenediamine,Diethylamine, and Triethylamine

New adsorption gels were prepared by chemically immobilizing functional groups of ethylenediamine, diethylamine and/or triethylamine on orange waste, named OW-en, OW-DEA, and OW-TEA, respectively. By comparing with the adsorption of other coexisting metals, such as Re(VII), Pb(II), Fe(III), Zn(II), Mn(VII), Ca(II), and Cu(II), the novel gels exhibited selectivity only for Mo(VI) and the adsorption behavior obeys the Langmuir model. The maximum adsorption capacity for molybdenum was in the order, OW-en (2.17 mol/kg) > OW-TEA (1.26 mol/kg) > OW-DEA (0.88 mol/kg). A kinetic study for the adsorption of molybdenum at various temperatures confirmed that the endothermic adsorption process followed pseudo-second order kinetics. In addition, its excellent adsorption characteristics for Mo(VI) were confirmed by the adsorption and elution tests using a column packed with the OW-en gel, especially by separation of Mo(VI) from Mo-Re containing industrial effluent.     

Removal of hexavalent chromium in soil by lignin-based weakly acidic cation exchange resin

The adsorption of Cr(VI) from soil onto lignin-based weakly acidic cation exchange resin (LBR) has been investigated. Lignin is a three-dimensional amorphous polymer composed of methoxylated phenylpropane units. The unique structure and chemical properties render the lignin suitable for the remediation of hexavalent chromium in the soil. Soil column leaching experiments were conducted to optimize the adsorption conditions. The effects of contact time, pH, adsorbent dosage and temperature on the adsorption of Cr(VI) onto the LBR have been investigated. Experiment data were then correlated with Freundlich and Langmuir isotherms. The Langmuir isotherm model fits the experimental data better than the Freundlich isotherm. It was found that the LBR has a high adsorption capability for Cr(VI) (3.95 mg·g^-1) with a removal rate of 91.9%. Thus, LBR can serve as a good absorbent for the reduction of the concentration of Cr(VI) in soil.     

Uptake of Cr (VI) by Sphingomonas paucimobilis Biomass from Aqueous Solutions

The Sphingomonas paucimobilis biomass has been successfully utilized to degrade several persistent organic pollutants (POPs). However, few studies have been conducted to use it to remove heavy metals from aqueous solutions. In the present study, biosorption experiments for Cr (VI) were investigated using nonliving biomass of S. paucimobilis isolated from activated sludge, Lianyungang Dapu sewage treatment plant, China. The effects of several parameters including solution pH, contact time, and ionic strength, etc. on Cr (VI) uptake were studied. The biomass was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) and Fourier transform infrared spectrometer (FTIR). The applicability of the Langmuir and Freundlich models was tested. The correlation coefficients (R) of both models were greater than 0.95. The maximum adsorption capacities were found to be 28.5 mg/g for Cr (VI) at 20°C. The adsorption process was quick and found to follow the pseudo-second-order equation. The optimum adsorption was achieved at pH 2. The adsorption was also NaCl concentrations dependent.