Removal and Recovery of Chromium(VI) from Industrial Waste Water

Carbon slurry, generated as a waste material in a naphtha-based ammonia plant of the Fertilizer Corporation of India, Gorakhpur, has been used as an adsorbent for the removal of Cr(VI) from aqueous solution at different experimental conditions. The removal was favoured at low pH, with maximum removal at pH 2·5. The effects of concentration and temperature have also been reported. Batch adsorption kinetics have been described by the Lagergren equation. The applicability of the Langmuir isotherm for the present system has been tested at different temperatures. Thermodynamic parameters indicate the endothermic nature of Cr(VI) adsorption on carbon slurry. Recovery of adsorbed chromium for reuse has also been reported in the present study. © 1997 SCI.     

Preparation and characterization of higher degree‐deacetylated chitosan‐coated magnetic adsorbent for the removal of chromium(VI) from its aqueous mixture

Chitosan (90% deacetylated) coated magnetic adsorbent prepared by coprecipitation method to remove Cr(VI) from its aqueous solution. The experimental studies depicts that the predominant option for removal of Chromium by adsorption from its aqueous phase using Magnetic‐Chitosan (MC). The subsequent physical, chemical, and magnetic properties of MC were characterized by X‐ray powder diffraction, scanning electron microscopy, Fourier transform infrared spectrometer, vibrating sample magnetometer. The influence of batch process parameters such as contact time, initial concentration, pH, and coexisting anions were investigated. The Box‐Behnken experimental design in response surface methodology was performed to design the experiment optimal operating conditions. The maximum percentage reduction of Cr(VI) is 96.3 that was obtained by magnetic chitosan with the optimal operating conditions of 149.53 mg/L at pH of 5.32 at the contact time of 80 min and at the temperature of 303 K. The average diameter of the magnetic chitosan was calculated from X‐ray diffractometer analysis as 24.5 nm. The equilibrium adsorption isotherm models such as Langmuir and Freundlich and the adsorption kinetics such as pseudo first order, pseudo second order and intra‐particle diffusion kinetic model were analyzed. The experimental data's suited for the best fit with the Langmuir isotherm model and pseudo first order kinetic model. It also revealed that Cr(VI) adsorption on MC is intrinsically exothermic and spontaneous. The magnetic chitosan was also used to investigate for the removal of Cr(VI) from the real water sources such as surface, underground, and tannery wastewater. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45878.     

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.     

Multiwalled CNTs for Cr(VI) removal from industrial wastewater: An advanced study on adsorption,kinetics, thermodynamics for the comparison between the embedded and non‐embedded carboxyl group

The adsorption capabilities of multiwalled carbon nanotubes (MWCNTs) with and without the embedded carboxyl group for the removal of parts per million levels of hexavalent chromium were examined as a function of several parameters, namely contact time, pH of initial solution, initial concentration of Cr(VI), adsorbent dosage as well as temperature of solution. Adsorption isotherms have been utilized to explain the adsorption mechanism. Ion exchange, intra‐particle diffusion, and electrostatic interactions are found to be the fundamental mechanisms describing the adsorption of Cr(VI). The maximum adsorption capacities of Cr(VI) ion by raw MWCNTs and functionalized MWCNTs were found to be 84.75 and 78.13 mg · g^?1, respectively, as calculated by the Langmuir adsorption isotherm model. This is with regard to the electron‐rich atoms inside the functional group which repels the negatively charged dichromate ions. Kinetic studies were performed, and the data was found in good agreement with the pseudo‐second‐order.     

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.     

Adsorption of chromium(VI) from aqueous solution by Artist’s Bracket fungi

The objective of this study was to investigate Artist’s Bracket (AB) fungi for the removal of Cr(VI) from aqueous solutions. The effects of pH, adsorbent dosage, temperature, contact time and initial concentration of Cr(VI) were evaluated. The optimal pH value for the removal of Cr(VI) was at pH 2. Moreover, the results showed that the adsorption of Cr(VI) decreased by increasing the initial Cr(VI) concentration and pH. The absorption of Cr(VI) on AB can be described by both Freundlich and Langmuir isotherm models. In addition, both pseudo-first-order and pseudo-second-order kinetic model well described the adsorption of Cr(VI) onto AB.     

Characterizations and Cr (VI) adsorption properties of polyaniline/filter‐paper composite

Polyaniline/filter‐paper (PANI/FP) composite was prepared by in situ polymerization of polyaniline onto FP and subsequently evaluated for the removal of Cr (VI) from aqueous solution. Scanning electron microscopy and Fourier‐transform infrared were used to investigate the morphology and physicochemical property of PANI/FP composite. Batch experimental results showed that pH value and temperature could affect the removal capability of PANI/FP composite. Langmuir and Freundlich models were used to analysis the equilibrium adsorption, and both of the two models showed the similar correlation coefficients (about R² = 0.9383). Although the removal capability was still limited, the PANI/FP composite showed the great potential that can be used as an effective adsorbent for removing Cr (VI) from industrial waste‐water. POLYM. COMPOS., 35:993–998, 2014. © 2013 Society of Plastics Engineers     

钢渣颗粒对水中Cr(VI)的吸附与还原作用

以钢渣颗粒为水处理剂,分析了其组成和结构,研究了钢渣颗粒直接吸附去除水中Cr(VI)的工艺过程及机理. 结果表明,钢渣颗粒在适当的粒度与用量下,经10 min搅拌处理,水中Cr(VI)浓度由200 mg/L降低到0.5 mg/L,达到《污水综合排放标准》(GB8978-1996)的要求. 钢渣颗粒对水中Cr(VI)的吸附符合Langmuir等温吸附过程,对Cr(VI)的饱和吸附量达6.878 mg/g. 化学分析和XPS分析均表明,钢渣颗粒对水中Cr(VI)具有吸附与还原的联合作用,吸附后钢渣颗粒中Cr(III)含量由0.0985%提高到0.39%,而FeO含量由9.20%下降到8.35%. 吸附后钢渣颗粒表面形成了Cr(OH)3,说明钢渣颗粒中FeO充当了还原剂,将水中Cr(VI)吸附于钢渣颗粒表面并还原成了低毒的Cr(OH)3随钢渣颗粒沉降直接从水中去除.     

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.     

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).     

Artificial neural network (ANN) approach for modeling of Cr(VI) adsorption from aqueous solution by zeolite prepared from raw fly ash (ZFA)

In this present work, artificial neural networks (ANN) are applied for prediction of percentage adsorption efficiency for the removal of Cr(VI) ions from aqueous solution by zeolite (ZFA) prepared from raw fly ash (RFA). The off operational parameters such as initial pH, adsorbent dosage, contact time and temperature is studied to optimize the conditions for maximum removal of Cr(VI) ions. Three equations, i.e. Morris–Weber, Lagergren, and pseudo second order have been tested to track the kinetics of removal process. The Langmuir, Freundlich, Redlich–Peterson, Temkin, and D-R are subjected to sorption data to estimate sorption capacity. Thermodynamic parameters showed that the adsorption of Cr(VI) onto ZFA was feasible, spontaneous and endothermic. Artificial neural networks are effective in modeling and simulation of highly non-liner multivariable relationships. The comparison of the removal efficiencies of Cr(VI) using ANN model and experimental results showed that ANN model can estimate the behavior of the Cr(VI) removal process under different conditions.     

Synthesis of polyaniline nanocomposite and its application for chromium removal from aqueous solution

The aim of this research was to investigate the sorption characteristics of polyaniline coated on sawdust (PAn/SD) for the removal of Cr(VI) ions from aqueous solutions. The sorption of Cr(VI) ions was carried out by the batch method. Characterization of PAn/SD was done by FTIR and SEM. The optimum conditions of sorption were found to be a PAn/SD dose of 0.6 g in 100 mL of Cr(VI) solution (50 mg/L), a contact time of 20 min, pH 2, and a temperature of 20°C, Increased temperature had a negative effect on the removal efficiency. Three equations, that is Morris–Weber, Lagergren, and pseudo‐second‐order, were tested to track the kinetics of the removal process. The kinetic data indicated that the adsorption process was described by the Morris–Weber equation. The Langmuir, Freundlich, and Dubinin–Radushkevick models were used with sorption data to estimate sorption capacity, intensity, and energy. The data were fitted with the Freundlich model. The thermodynamic parameters ΔH, ΔS, and ΔG were evaluated. They showed that the adsorption of Cr(VI) onto PAn/SD was feasible, spontaneous, and exothermic under the studied conditions. For desorption of Cr(VI) adsorbed onto PAn/SD, aqueous NaOH was used; with it, 85% of the adsorbed Cr(VI) could be desorbed. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

改性板栗苞对Cr(Ⅵ)的吸附性能研究

以板栗苞为原料,经过磷酸改性后制备改性板栗苞吸附材料,并用于重金属Cr（Ⅵ）的吸附研究。研究了pH值、吸附时间、吸附剂用量和温度对改性板栗苞吸附Cr（Ⅵ）活性的影响,采用Freundlich和Langmuir等温吸附方程对等温吸附过程进行拟合。结果表明：Cr（Ⅵ）的质量浓度为10mg/L时,改性板栗苞的最佳吸附条件为pH值4,吸附时间2h,改性板栗苞用量0.2g,温度45℃,在此条件下,改性板栗苞对Cr（Ⅵ）的吸附率可达99.33%。等温吸附过程符合Langmuir方程,说明改性板栗苞对Cr（Ⅵ）的吸附为单分子层吸附。通过FT-IR表征可以发现：吸附后的改性板栗苞的基团没有发生变化,说明改性板栗苞对Cr（Ⅵ）的吸附主要是物理吸附。通过SEM表征发现：改性板栗苞比未改性板栗苞的表面更光滑、空间更大,说明磷酸使得改性板栗苞附着的杂质被去除,褶皱铺展开,孔隙结构更发达,有利于对Cr（Ⅵ）的吸附。     

Adsorption of Cr(VI) ions onto poly(ethylene glycol dimethacrylate‐1‐vinyl‐1,2,4‐triazole)

Poly(ethylene glycol dimethacrylate‐1‐vinyl‐1,2,4‐triazole) [poly(EGDMA‐VTAZ)] beads (average diameter = 150–200 μm) were prepared by copolymerizing ethylene glycol dimethacrylate (EGDMA) with 1‐vinyl‐1,2,4‐triazole (VTAZ). Poly(EGDMA‐VTAZ) beads were characterized by swelling studies and scanning electron microscope (SEM). The adsorption of Cr(VI) from solutions was carried at different contact times, Cr(VI) concentrations, pH, and temperatures. High adsorption rates were achieved in about 240 min. The amount of Cr(VI) adsorbed increased with increasing concentration and decreasing pH and temperature. The intraparticle diffusion rate constants at various temperatures were calculated. Adsorption isotherms of Cr(VI) onto poly(EGDMA‐VTAZ) have been determined and correlated with common isotherm equations such as Langmuir and Freundlich isotherm models. The Langmuir isotherm model appeared to fit the isotherm data better than the Freundlich isotherm model. The pseudo first‐order kinetic model was used to describe the kinetic data. The study of temperature effect was quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy changes. The dimensionless separation factor (R_L) showed that the adsorption of metal ions onto poly(EGDMA‐VTAZ) was favorable. It was seen that values of distribution coefficient (K_D) decreasing with Cr(VI) concentration in solution at equilibrium (C_e) indicated that the occupation of activate surface sites of adsorbent increased with Cr(VI). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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.     

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 fast and efficient method for the removal of hexavalent chromium from aqueous solutions

In this study, removal of chromium (VI) from aqueous solution by as-synthesized MCM-48 adsorbent was studied. Cetyltrimethylammonium bromide (CTAB) was used as a cationic template for the synthesis of MCM-48. The extent of adsorption was investigated as a function of solution pH, agitation speed, contact time, adsorbent and adsorbate concentrations, reaction temperature and supporting electrolyte (sodium chloride). Langmuir and Freundlich isotherms were used to model the adsorption equilibrium data. The adsorption of Cr (VI) is found to be maximum at pH values in the range of 1–3. The yielded maximum adsorption capacity of 153.8 mg/g at initial concentration of 800 (mg/L) is well predicted by of the Langmuir isotherm. Compared to the various adsorbents reported in the literature, the surfactant-containing material prepared in this study showed promise for practical applications.     

交联薯渣黄原酸酯对废水中Cr(Ⅵ)的吸附研究

交联薯渣黄原酸酯(CCX)废水中Cr(Ⅵ)离子的吸附,探讨了pH值、温度、吸附时间、CCX含硫量、Cr(Ⅵ)初始浓度等因素对其吸附效果的影响。结果表明,当CCX加入量为理论加入量的3.0倍时,pH为2.5,在45℃下搅拌反应50 min,对Cr(Ⅵ)的吸附容量为37.76 mg/g,去除率达到99.69%,处理后的废水中Cr(Ⅵ)浓度为0.15 mg/L,低于国标排放标准(0.5 mg/L)。并通过红外光谱和热重分析,对CCX吸附Cr(Ⅵ)的机理进行了探讨。