Efficient adsorption to hexavalent chromium by iron oxalate modified D301:Characterization,performance and mechanisms

Chromium is a common harmful pollutant with high toxicity and low bearing capacity of soil and water. Excellent salinity resistance, a wide p H range, and high regeneration capacity were essential for qualified adsorbents used in removing hexavalent chromium(Cr(VI)) from polluted water. Herein, iron oxalate modified weak basic resin(IO@D301) for the removal of Cr(VI) was prepared by the impregnation method. The IO@D301 was characterized by scanning electron microscope(SEM), Fourier transform infrared spectroscopy(FTIR), X-Ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS). Owing to abundant amine, carboxyl groups and iron ions existing on the surface, IO@D301 possesses high adsorption and salinity resistance capacity for Cr(VI). The maximum adsorption capacity of IO301 towards Cr(VI) reached 201.30 mg·g~(-1) at 293 K and a p H of 5. The adsorption equilibrium was well fitted by the Freundlich model, and the adsorption process was described by the pseudofirst-order kinetics model as spontaneous and exothermic. The mechanism may be identified as electrostatic attraction, coordination, and reduction, which was confirmed by FT-IR and X-ray photoelectron spectroscopy.     

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.     

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.     

Facile fabrication of graphene oxide-polyethylenimine composite and its application for the Cr(VI) removal

A binary composite consisting of graphene oxide (GO) and polyethylenimine (PEI) was fabricated by a facile physical mixing. Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), thermo-gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Zeta potential were used to characterize the prepared graphene oxide-polyethylenimine composite (GOPC). A series of experiments were carried out to investigate the effects of some important parameters, such as molecular weight of PEI, pH, time and temperature, on the adsorption efficiency of GOPC. Due to the high amine density of GOPC, its adsorption for Cr(VI) occurred more easily at lower pH mainly via electrostatic interaction. The adsorption process matched well with the Langmuir isotherm model and the pseudo-second-order kinetic model. The maximum adsorption capacity from the Langmuir model was 370.37 mg/g at pH 2.0 and 45°C for GOPC. Thermodynamic parameters revealed spontaneous and endothermic nature of the Cr(VI) adsorption onto GOPC. The main adsorption mechanism of GOPC toward Cr(VI) was electrostatic interaction. The adsorption-desorption experiments suggested GOPC was easily recycled and its stable adsorption capacity endowed it great potential as an adsorbent of Cr(VI) from wastewater.     

Metal ion adsorption behavior of lignocellulosic fiber–ethylene vinyl acetate composites

This study describes the applicability of lignocellulosic fiber dispersed in ethylene vinyl acetate (EVA) to adsorb Pb(II), Cr(III), and Cr(VI) ions in aqueous solutions. Water absorption studies revealed that metal‐ion uptake does not only take place on the surface of the adsorbent but ions can also diffuse into the composite. The adsorption of the metal ions under different experimental conditions was studied. Solute concentration, pH, and contact time were used to assess the adsorption capacity and efficiency. The amount of metal adsorbed increased to 7 mg/g with an increase in solute concentration but compromising the efficiency. Adsorption equilibrium was reached after 3 h, when the maximum lead adsorption was above 80%. The optimum pH for the adsorption of Pb(II) and Cr(III) was 6.5, and pH 2.5 was used for the adsorption of Cr(VI). Competitive adsorption revealed the order of adsorption to be: Pb(II) > Cr(VI) > Cr(III). POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

A high Cr (VI) absorption efficiency and easy recovery adsorbent: Electrospun polyethersulfone/polydopamine nanofibers

Cr (VI) is a highly toxic pollutant to humans, to achieve high adsorption capacity, easy recovery, and good reusability, polyethersulfone/polydopamine (PES/PDA) ultrafine fibers were prepared successfully. A series of preparing effect factors were investigated systematically and the optimum one is 8.5 pH value at room temperature and 2 g/L dopamine concentration. And then they were used as an adsorbent for the removal of Cr (VI) ions from wastewater. The effect factors pH, the adsorbent dosage, and time were discussed on Cr (VI) adsorption process and the Cr (VI) adsorption behavior was investigated. It is found that the maximum Cr (VI) adsorption capacity is 115.2 ± 4.8 mg/g at pH = 3 using 0.06 g PES/PDA with 80 mins. The Cr (VI) adsorption process followed the pseudo-second-order model (r² ≥ 0.99) and adsorption isotherms were fitted to the Langmuir model (R² ≥ 0.999). Furthermore, the Cr (VI) adsorption mechanism was supposed according to the X-ray photoelectron spectroscopic results. Finally, PES/PDA ultrafine fibers were considered to be a promising adsorbent with good stability (decomposing temperature, 356°C), high adsorption efficiency (112.1 ± 2.5 mg/g), and good reusability (three times) on the coexistence of anions and the actual industry wastewater environment.     

Removal of Cu(II), Cr(III), and Cr(VI) from Aqueous Solution using a Novel Agricultural Waste Adsorbent

A novel adsorbent, chufa corm peels (CCP), is used for removing Cu(II), Cr(III), and Cr(VI) from aqueous solutions. The adsorption ability and characteristics of the CCP are thoroughly investigated. The adsorption capability for three heavy metal ions is in the order of Cu(II) > Cr(III) > Cr(VI). The morphology and elemental distribution on the biomass of CCP were evaluated by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Fourier-transform infrared spectroscopy (FTIR) analysis revealed that oxygen-containing functional groups, especially carboxylic and hydroxyl groups were responsible for chemical coordination between ionizable functional groups and metal ions. The adsorption features were evaluated based on the batch biosorption experiment. The results showed that the adsorption well meets the Freundlich adsorption isotherm models and pseudo-second-order kinetics model. In summary, this work demonstrated that CCP is an attractive, efficient, and low-cost adsorbent biomaterial that can be used for the removal of heavy metals from environmental contaminations.     

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 ℃. 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^-, SO₄^2- and PO₄^3- 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.     

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.     

Adsorption Characteristics of Chromium(VI) Ions onto Fe(III)-Coordinated Amino-Functionalized Poly(glycidylmethacrylate)-Grafted TiO2-Densified Cellulose

An investigation was conducted with a newly developed adsorbent, iron(III)- coordinated amino-functionalized poly(glycidylmethacrylate)-grafted TiO₂-densified cellulose (Fe(III)-AM-PGDC) on the removal of chromium(VI) from aqueous solution. Batch experiments were performed under various conditions of time, pH, concentration, dose, ionic strength, and temperature. Adsorption of Cr(VI) on Fe(III)-AM-PGDC was dominated by ion exchange or outer-sphere complexation. The maximum adsorption capacity was found to be 109.76 mg g^?1. Thermodynamic study showed that adsorption of Cr(VI) onto Fe(III)-AM-PGDC is more favored. The complete removal of Cr(VI) from electroplating wastewater was achieved by the adsorbent. The adsorbent did not lose its adsorption capacity even after the fourth regeneration.     

Cationic polymer chain tethered on the pore-wall of 3-D ordered macroporous resin for the removal of hexavalent chromium from aqueous solution

A novel 3-D ordered macroporous (3DOM) adsorbent with a cationic polymer chain (poly(N,N-dimethylaminoethyl methacrylate), PDMAEMA) tethered on the pore wall was prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) for the removal of toxic Cr(VI) ions from aqueous solution. In comparison with recently reported adsorbents, the adsorbent remarkably stands out owing to large adsorption capacity, relatively fast kinetics, and high stability in the regeneration process. The adsorption capacity significantly depended on the solution pH and there was a wide working pH range that is much convenient in practical application. Kinetics of Cr(VI) adsorption by the 3DOM adsorbent was studied in batch experiments, in the temperature range 298–318 K. The equilibriums were arrived within 120–130 min and a pseudo-second order model can be described well. In the adsorption isotherm study, experimental data followed the Langmuir adsorption model. The maximum adsorption capacity increased with the increase of temperature, and reached the high value of 431.0 mg/g at 308 K. Thermodynamic parameters revealed spontaneous and endothermic adsorption processes. Furthermore, the 3DOM adsorbent remained high adsorption capacity (above 90% of the original Cr(VI) loading capacity) after 15 adsorption–desorption cycles by simply using sodium hydroxide solution as the desorption liquid, which ensured the reusability of 3DOM adsorbent.     

聚丙烯酸复合铝改性膨润土制备及其对Cr(VI)的吸附

为改善膨润土对Cr(VI)的吸附性能,用铝、丙烯酸聚合及十六烷基三甲基溴化铵改性合成聚丙烯酸复合铝改性膨润土。采用X射线衍射、红外光谱和扫描电子显微镜对天然膨润土和改性膨润土进行表征。结果表明,在25℃、溶液pH=5~6时,0.5 g吸附剂对200 mL浓度为20 mg/L Cr(VI)的平衡吸附量为1.996 mg/g,平衡吸附时间为130 min,且固液分离容易。吸附过程较好地符合Lagergren二级吸附动力学方程和Freundlich等温吸附方程,颗粒状吸附剂对Cr(VI)的吸附以络合吸附为主。     

Synthesis of functionalized PET fibers by grafting and modification and their application for Cr(VI) ion removal

A new fiber adsorbent for removing Cr(VI) ions from aqueous solution was prepared by grafting and modification. The grafted fiber and modified fiber were characterized by SEM, FTIR, and TGA. FTIR analysis indicated that acrylonitrile monomer was grafted onto the PET surface and that new groups were present on the surface after the modification. Scanning electron microscopy showed that the PET fiber was wider after grafting and especially modification. The TGA results showed that the degradation steps and the thermal behavior of the PET fiber changed after modification. The effects of the pH, ion concentration, and temperature on the amount of Cr(VI) adsorbed were investigated. The fiber showed its maximum adsorption capacity in acidic medium. Isotherm studies indicated that the experimental results were best fitted to the Langmuir isotherm. The adsorption capacity of the modified fiber was found to be 25.77, 38.17, and 44.84 mg/g fiber at 25, 35, and 45 °C, respectively. Kinetic results indicated that the adsorption of Cr(VI) onto the modified fiber followed a pseudo-second-order kinetic model. Calculated thermodynamic parameters demonstrated that the adsorption of Cr(VI) ions on the modified fiber is an endothermic, feasible, and spontaneous process.     

Removal of toxic metal Cr(VI) from aqueous solutions using sawdust as adsorbent: Equilibrium, kinetics and regeneration studies

In the present study, a low-cost adsorbent is developed from the naturally and abundantly available sawdust which is biodegradable. The removal capacity of Cr(VI) from aqueous solutions and from the synthetically prepared industrial effluent of electroplating and tannery industries is obtained. The batch experiments are carried out to investigate the effect of the significant process parameters such as initial pH, change in pH during adsorption, contact time, adsorbent amount, and the initial Cr(VI) concentration. The maximum adsorption of Cr(VI) on sawdust is obtained at an initial pH value of 1. The value of pH increases with increase in contact time and initial Cr(VI) concentration. The equilibrium data for the adsorption of Cr(VI) on sawdust is tested with various adsorption isotherm models such as Langmuir, Freundlich, Redlich–Peterson, Koble–Corrigan, Tempkin, Dubinin–Radushkevich and Generalized equation. The Langmuir isotherm model is found to be the most suitable one for the Cr(VI) adsorption using sawdust and the maximum adsorption capacity obtained is 41.5 mg g⁻¹ at a pH value of 1. The adsorption process follows the second-order kinetics and the corresponding rate constants are obtained. Desorption of Cr(VI) from sawdust using acid and base treatment exhibited a higher desorption efficiency by more than 95%. A feasible solution is proposed, for the disposal of the contaminant (acid and base solutions) containing high concentration of Cr(VI) obtained during the desorption process. The interference of other ions which are generally present in the electroplating and tannery industrial effluent streams on the Cr(VI) removal is investigated.     

Removal of hexavalent chromium from aqueous solution using novel dye-based adsorbent prepared by flocculation

In this paper, the dye sludge which was prepared from Congo red solution by flocculation method was further modified by catechol and 1, 6-hexanediamine before usage to remove Cr(VI) ions. This particles were characterized by multiple testing means and the effects of removal, such as contact time, pH value, initial concentration, and temperature, were studied by batch mode. The maximum adsorption capacity of Cr(VI) was 282.48 mg/g and the whole process was spontaneous and endothermic. Hopefully, with the advantages of facile preparation and high adsorption capacity, the dye-based adsorbent has broad application prospects in the field of wastewater treatment.     

Experimental design and batch experiments for optimization of Cr(VI) removal from aqueous solutions by hydrous cerium oxide nanoparticles

Hydrous cerium oxide (HCO) was synthesized by intercalation of solutions of cerium(III) nitrate and sodium hydroxide and evaluated as an adsorbent for the removal of hexavalent chromium from aqueous solutions. Simple batch experiments and a 2⁵ factorial experimental design were employed to screen the variables affecting Cr(VI) removal efficiency. The effects of the process variables; solution pH, initial Cr(VI) concentration, temperature, adsorbent dose and ionic strength were examined. Using the experimental results, a linear mathematical model representing the influence of the different variables and their interactions was obtained. Analysis of variance (ANOVA) demonstrated that Cr(VI) adsorption significantly increases with decreased solution pH, initial concentration and amount of adsorbent used (dose), but slightly decreased with an increase in temperature and ionic strength. The optimization study indicates 99% as the maximum removal at pH 2, 20 °C, 1.923 mM of metal concentration and a sorbent dose of 4 g/dm³. At these optimal conditions, Langmuir, Freundlich and Redlich–Peterson isotherm models were obtained. The maximum adsorption capacity of Cr(VI) adsorbed by HCO was 0.828 mmol/g, calculated by the Langmuir isotherm model. Desorption of chromium indicated that the HCO adsorbent can be regenerated using NaOH solution 0.1 M (up to 85%). The adsorption interactions between the surface sites of HCO and the Cr(VI) ions were found to be a combined effect of both anion exchange and surface complexation with the formation of an inner-sphere complex.     

Adsorptive Characteristics of Chromium(VI) Ions from Aqueous Phase by Iron(III) Coordinated Amino-Functionalized Poly(glycidyl methacrylate)-Grafted Cellulose: Equilibrium Kinetics and Thermodynamic Study

A novel sorbent, Iron(III)-coordinated amino-functionalized poly(glycidyl methacrylate)-grafted cellulose (Fe(III)-AM-PGMACell), was prepared through graft copolymerization of glycidyl methacrylate (GMA) onto cellulose (Cell) in the presence of N,N′-methylenebisacrylamide (MBA) as a cross linker using benzoyl peroxide initiator, followed by treatment with ethylenediamine and ferric chloride in the presence of HCl. The surface features of the adsorbent were characterized using FTIR, XRD, and SEM, N₂ adsorption, and potentiometric titration. The contact time to attain equilibrium and the pH value for maximum adsorption were found to be 90 min and 4.0, respectively. A two-step pseudo-first-order kinetic model agreed well with the dynamic behavior for the adsorption process. Equilibrium data were fitted with the Langmuir, Freundlich, and Sips isotherm equations with the latter giving the best fit to the experimental data with maximum adsorption capacity of 72.05 mg/g at 30°C. A simulated industry wastewater sample was treated by the Fe(III)-AM-PGMACell to demonstrate its efficiency in removing Cr(VI) from wastewater. The adsorbed Cr(VI) ions were desorbed effectively by 0.1 M NaCl solution and hence can be reused through many cycles of water treatment and regeneration without any loss in the adsorption capacity.     

Kinetic,isotherm, and thermodynamic studies of Cr(VI) removal from aqueous solution using mesoporous silica materials prepared by fly ash

A series of mesoporous silica materials (FMD, FMT, and FMC were synthesized with DTAB, TTAB, and CTAB as template, respectively) have been prepared using fly ash as a silica resource. The as-synthesized materials were characterized by BET, XRF, FTIR, and XPS. The results confirmed the mesoporous structure and nitrogen content to act as potential adsorbents. The adsorption properties of these materials were also investigated by batch adsorption experiments. The FMC exhibited the highest effective removal of Cr(VI) (99%). The Cr(VI) adsorption process over FMC follows the pseudo-second-order kinetic and Langmuir model. Thermodynamic studies revealed that the Cr(VI) adsorption by FMC was spontaneous and endothermic. The study of the adsorption mechanism showed that the removal of Cr (VI) by FMC is through electrostatic attraction and chemical reduction. The coexisting ions experiment showed that FMC had high selectivity for Cr(VI). After three regeneration cycles, the Cr(VI) removal rate of FMC adsorbent still remained about 80%. Thus, this inexpensive adsorbent (FMC) is suitable for removing Cr(VI) from discharged industrial water.     

Removal of Hexavalent Chromium by Different Modified Spruce Bark Adsorbents

In this work, spruce bark was used as a raw material to remove Cr(VI) ions from aqueous solutions. Three kinds of chemically modified bark adsorbents were prepared by treatment with formaldehyde (FB), dilute sulfuric acid (AB), and concentrated sulfuric acid (CB), respectively. The chemical modifications mainly changed the relative lignin content in the bark. Lower pH facilitated the adsorption of Cr(VI) ions because reduction of Cr(VI) ions to Cr(III) ions occurred during the adsorption process which consumed a large amount of H⁺ ions. Higher temperature accelerated the adsorption process, owing to the endothermic nature of the redox reaction. At initial solution pH around 1, the adsorption capacities of Cr(VI) ions on FB, AB, and CB were as high as 423, 503, and 759 mg/g, respectively, which were much higher than the reported adsorption capacities by other agricultural and forest biosorbents in the literatures. XPS analysis revealed the adsorption mechanism was adsorption-coupled reduction involving the electron-donor groups of lignin moieties.     

Sorption equilibrium of Cr(VI) ions on oak wood charcoal (Carbo Ligni) and charcoal ash as low-cost adsorbents

The aim of this study is to demonstrate the potential of oak wood charcoal (WC) and oak wood charcoal ash (WCA) as a low-cost adsorbent for environmental protection applications of Cr(VI) ion. The influence of contact time, solution pH, initial metal concentration, amount of adsorbent and ionic strength on the removal of Cr(VI) ion was studied. The adsorption of Cr(VI) with (WC) and (WCA) was investigated in a batch arrangement. The Cr(VI) ions sorbed onto the adsorbents were determined by a UV-Visible Spectrophotometer. The sorption of Cr(VI) on the adsorbent surface depends strongly on the pH and Cr(VI) ion-sorption increased with a decreasing pH until pH 2 and increase in the concentration of this metal in solution phase. The adsorption of Cr(VI) was higher between pH 2.0 and 2.5 for both adsorbents. The Freundlich adsorption isotherm was used to describe observed sorption phenomena. The maximum adsorption capacity of 30.10 mg of Cr(VI)/g for (WC) and 46.17 mg of Cr(VI)/g for (WCA) was obtained at pH of 2 and 2.5 respectively.