Removal of chromium (VI) from aqueous solutions using poly(4‐vinyl pyridine) beads

Sorption of hexavalent chromium ions from aqueous solution by poly 4‐vinyl pyridine [Poly(4‐VP)] was studied. The batch method was applied for adsorption processes. The effects of initial ion concentration, time, pH and temperature on adsorption were investigated. A treatment time of 60 min was found to be sufficient to reach equilibrium. pH 3.0 was found as the optimum pH value for the process. The maximum adsorption performance was achieved at 86.7 mg g^?1 using 500 mg L^?1 Cr (VI) solutions. The process of adsorption of Cr (VI) was explained by Langmuir isotherm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2865–2870, 2006     

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.     

A Study in the Adsorption Behaviors of Cr (VI) on Crosslinked Cationic Starches

The adsorption behaviors between Cr (VI) and crosslinked cationic starch with quaternary ammonium group were investigated in various conditions. The adsorption processes are found to be dependent on the initial pH of the solution, the dose of the absorbents, initial concentration of Cr (VI), and adsorption temperature. The adsorption reaches equilibrium in a short time, and follows the Langmuir isotherm. The adsorption capacity increases with the increasing cationic groups. The adsorption thermodynamics study shows that adsorption processes are exothermic, and lower temperature is favorable to the adsorption of Cr (VI).     

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.     

Removal of Cr(VI) from aqueous solution by London plane leaves

The effect of initial metal concentration, contact time and solution temperature on the removal of Cr(VI) from solution by waste London plane leaves, generated by the pruning of street trees, was investigated in batch mode conditions. The removal of Cr(VI) was highly concentration‐dependent and mainly governed by physico‐chemical adsorption under the weak acidic conditions studied. The equilibrium data fit well in the Langmuir isotherm model. The Langmuir constants were calculated at different temperatures and both the adsorption capacity and adsorption intensity increased with rising temperature. The endothermic nature of the Cr(VI) adsorption was confirmed by the thermodynamic parameters. The study has shown that the waste leaves can be used as an effective adsorbent for removal of Cr(VI) from wastewater. Copyright © 2003 Society of Chemical Industry     

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.     

Hexavalent chromium adsorption on superparamagnetic multi-wall carbon nanotubes and activated carbon composites

Hexavalent chromium (Cr(VI)) adsorption from aqueous solutions on magnetically modified multi-wall carbon nanotubes (M-MWCNT) and activated carbon (M-AC) was investigated. M-MWCNT and M-AC were prepared by co-precipitation method with Fe²⁺:Fe³⁺ salts as precursors. The magnetic adsorbents were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The effects of amount of adsorbents, contact time, initial pH, temperature and the initial concentration of Cr(VI) solution were determined. The adsorption equilibrium, kinetics, thermodynamics and desorption of Cr(VI) were investigated. Equilibrium data fitted well with the Langmuir isotherm for both of the adsorbents. The theoretical adsorption capacities are 14.28 mg/g of M-MWCNT and 2.84 mg/g of M-AC. Cr(VI) adsorption kinetics was modeled with pseudo-second order model, intra-particle diffusion model and Bangham model. Thermodynamic parameters were calculated and ΔG°, ΔH° and ΔS° indicate that the adsorption of Cr(VI) onto M-MWCNT and M-AC was exothermic and spontaneous in nature. Results revealed that M-MWCNT is an easily separated effective adsorbent for Cr(VI) adsorption from aqueous solution.     

Ion-crosslinked carboxymethyl cellulose/polyaniline bio-conducting interpenetrated polymer network: preparation,characterization and application for an efficient removal of Cr(VI) from aqueous solution

A simple, cheap, and environmentally friendly bio-conducting interpenetrated polymer blend network was prepared and introduced as a highly efficient system with suitable physical and mechanical properties for industrial removal of toxic Cr(VI) ions from aqueous solution. Carboxymethyl cellulose/polyaniline (CMC/PANI) interpenetrated network (IPN) blend was prepared by simple simultaneous ion-cross-linking of CMC and PANI chains using Al³⁺ cations. The CMC/PANI bio-conducting nanocomposite was characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy equipped with an "energy dispersive X-ray spectroscopy" (SEM–EDX) technique. The CMC/PANI blend, ion-cross-linked by Al³⁺ cations, showed good stability and high surface area, proper for the removal of toxic Cr(VI) ions of the aqueous solution. Batch removal experiments were accomplished and the impression of effective variables including solution pH, initial concentration of Cr(VI) ions, contact time, and adsorbent dosage were checked and optimized. The outcome of our findings revealed that the removal of Cr(VI) ions by CMC/PANI nanocomposite IPN strongly depends on solution pH. The removal information was matched with the Langmuir adsorption isotherm model and the utmost monolayer adsorption capacity at pH 2 was 136.98 mg/g at 25 °C. The pseudo-second-order kinetics were operated and the thermodynamic parameters suggested spontaneous and exothermic nature of the adsorption process. Consequences indicated that CMC/PANI nanocomposite IPN could be an affective eco/environmentally friendly adsorbent for the removal of Cr(VI) ions from aqueous solutions.

     

Removal of Cr(VI) from Aqueous Solution: Electrocoagulation vs Chemical Coagulation

Abstract

Hydrolyzed products of Al(III) have affinity below pH_zpc for oppositely charged mono and bi‐nuclear species of hexavalent chromium. This study investigates the comparative performance of electrocoagulation (EC) and chemical coagulation (CC) for the removal of Cr(VI) from aqueous solution. The highest removal of Cr(VI) achieved with EC was about 42% with 4.36 mA/cm² current density. Cathodic adsorption of chromium boosted up Cr(VI) removal during EC. Simultaneous electro‐ and chemical‐dissolution lead to high current efficiency of about 178%. Both the pH and the coagulant dosage have a significant impact on Cr(VI) removal in the pH ranges from 4.9 to 7.0. CC with alum and aluminum sulfate (AS) removed about 11% and 12% of Cr(VI). Co‐adsorption of divalent SO₄ ^2? ions with Cr(VI) is responsible for the lower removal observed with chemical coagulants. About 0.061 and 0.099 mole of SO₄ ^2? was adsorbed per mole Al in the precipitate in the pH range 4.9 to 7.0 with AS and alum. A higher coagulant dosage increases the removal of Cr(VI) but adversely affects the removal efficiency (Cr(VI) removed per unit of Al dosing). Cell current density (CD) has shown little effect on Cr(VI) removal and the pH elevation at the same charge density. Higher initial Cr(VI) concentration improves the removal efficiency as the species of Cr(VI) is acidic in solution and decreases the pH elevation rate.     

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.     

3D flower like δ-MnO2/MXene Nano-hybrids for the removal of hexavalent Cr from wastewater

Herein, 3D flower-like δ-MnO₂, MXene and δ-MnO₂/MXene in-situ hybrid (IH) composites were prepared (via hydrothermal and solution treatment methods) for the effective removal of Cr (VI) from the contaminated water. The effect of various experimental parameters including contact time, pH levels and initial Cr (VI) ions concentration was determined and compared under static conditions. The kinetics of Cr (VI) adsorption onto δ-MnO₂, MXene, and IH confirmed the existence of a pseudo-second-order model. The obtained results reveal that the removal of Cr (VI) largely depends on the pH of the solution. The adsorption isotherm data fits best for Freundlich model, illustrating a multi-site adsorption mechanism of Cr (VI) ion on these adsorbents. The maximum Cr (VI) adsorption capacities onto δ-MnO₂, MXene and IH are 235.65 mg g⁻¹, 273.1 mg g⁻¹ and 353.87 mg g⁻¹, respectively. The study reveals that hetero-engineered approach of synthesizing transition metal oxides with MXenes provides abundant opportunities to remove contaminants from water with better efficiency due to reduction and electrostatic interaction.     

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.     

Studies of adsorption behavior of crosslinked chitosan for Cr(VI), Se(VI)

In this work, it was found that crosslinked chitosan (CCTS) had strong adsorption ability for some anions under certain conditions. Cr(VI) and Se(VI) existed in anion forms in aqueous solution, and their adsorption rates by CCTS were 97% for Cr(VI) at pH 3.0 and 95% for Se(VI) at pH 4.0. In addition, the adsorption balance time and isotherm of CCTS for Cr(VI) and Se (VI) were discussed and adsorption mechanism was explained. This research will be useful for designing CCTS‐based adsorption for metallic toxin removal and preconcentrating Cr(VI) and Se(VI) in their trace analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3216–3219, 2000     

Fabrication of copper coated polymer foam and their application for hexavalent chromium removal

The polymer foam coated with zero-valent copper (Cu⁰) was designed and prepared for the removal of hexavalent chromium (Cr(VI)) in water. Firstly, porous poly(tert-butyl acrylate) was fabricated by concentrated emulsion polymerization and then acrylic acid groups were generated on the surface of foam by hydrolysis reaction. Secondly, with the help of the large amount reactive carboxylic acid groups, polyethyleneimine (PEI) were chemically grafted onto the surface by the reaction between amine group and acrylic acid group. Finally, zero-valent copper was reduced by sodium borohydride (NaBH₄) and coated on the surface of polymer foam. Thus the copper functionalized porous adsorbent (Cu⁰–PEI–PAA) was constructed, and then applied for removing Cr(VI) from aqueous solution. The removal mechanism of Cr(VI) involved redox reaction by zero-valent copper and adsorption by amine groups, simultaneously. As a result, 99.5% of Cr(VI) could be removed within 2 h, and the maximum removal capacity for Cr(VI) of Cu⁰–PEI(1800)–PAA was 9.16 mg/g. Furthermore, the effect of initial concentration of Cr(VI), pH value, and temperature on the Cr(VI) removal was investigated. Therefore, the as-prepared zero-valent copper-loaded polymer foam could be an efficient and promising remediation material to remove Cr(VI) from wastewater.     

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.     

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     

Bacterial cellulose/PANi mat for Cr(VI) removal at acidic pH

Remediation of hexavalent chromium - Cr(VI) at acidic pH using polyaniline coated bacterial cellulose porous mat (BC/PANi) is presented and the possible mechanism is discussed. The efficacy of BC/PANi mats in remediation of Cr(VI) was studied by varying pH (pH 1, 2, 3, and 5) and initial Cr(VI) concentrations (250–1000 ppm) of the solution. The BC/PANi (50 mg) mat was able to completely reduce 2000 ppm Cr(VI) into Cr(III) in a 20 ml solution at pH ~ 1 in 24 h. An increasing chromium removal efficiency was observed with decreasing solution pH; reaching a maximum removal capacity of ~920 mg/g at pH 1. The proposed mechanism of negatively charged Cr(VI) ions removal by BC/PANi mat is adsorption and simultaneous reduction into Cr(III), followed by desorption of Cr(III) from the mat. The role of temperature and co-existing anions like sulphate, nitrate and chloride found in industrial sludge were also investigated for removal efficiency of Cr(VI) at acidic pH ~ 1. The adsorption kinetics of Cr(VI) on polyaniline surface followed a pseudo-second-order model with reduction of Cr(VI) into Cr(III) as rate-limiting step. The reduced Cr(III) from the media was further recovered by neutralizing the pH of the solution.     

Kinetics, thermodynamic and equilibrium study of Cr(VI) adsorption from aqueous solutions by NCL coal dust

The waste material NCL coal dust was used as adsorbent for removal of Cr(VI) from aqueous solutions under batch adsorption experiments. The maximum removal of 99.97% was recorded at pH 2. The time required to attain equilibrium was found to be 60 min. Adsorption kinetics was described by the Lagergren equation. The value of the rate constant of adsorption was found to be 0.0615 min^?1 at 16 mg dm^?3 initial concentration and 298 K. The applicability of the Langmuir and Freundlich equations for the present system was also tested at different temperatures: 298, 313, and 328 K. Both thermodynamic parameters and temperature dependence indicated the endothermic nature of Cr(VI) adsorption on coal dust. The results showed that NCL coal dust is a promising adsorbent for the removal of Cr(VI) from aqueous solutions.     

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.