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 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.     

Comparison of Cr(VI) Adsorption Using Synthetic Schwertmannite Obtained by Fe3+ Hydrolysis and Fe2+ Oxidation: Kinetics,Isotherms and Adsorption Mechanism

Good sorption properties and simple synthesis route make schwertmannite an increasingly popular adsorbent. In this work, the adsorption properties of synthetic schwertmannite towards Cr(VI) were investigated. This study aimed to compare the properties and sorption performance of adsorbents obtained by two methods: Fe³⁺ hydrolysis (SCH_A) and Fe²⁺ oxidation (SCH_B). To characterise the sorbents before and after Cr(VI) adsorption, specific surface area, particle size distribution, density, and zeta potential were determined. Additionally, optical micrographs, SEM, and FTIR analyses were performed. Adsorption experiments were performed in varying process conditions: pH, adsorbent dosage, contact time, and initial concentration. Adsorption isotherms were fitted by Freundlich, Langmuir, and Temkin models. Pseudo-first-order, pseudo-second-order, intraparticle diffusion, and liquid film diffusion models were used to fit the kinetics data. Linear regression was used to estimate the parameters of isotherm and kinetic models. The maximum adsorption capacity resulting from the fitted Langmuir isotherm is 42.97 and 17.54 mg·g⁻¹ for SCH_A and SCH_B. Results show that the adsorption kinetics follows the pseudo-second-order kinetic model. Both iron-based adsorbents are suitable for removing Cr(VI) ions from aqueous solutions. Characterisation of the adsorbents after adsorption suggests that Cr(VI) adsorption can be mainly attributed to ion exchange with SO₄²⁻ groups.     

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

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

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.     

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.     

Removal of chromium (VI) from dilute aqueous solutions by activated carbon developed from Terminalia arjuna nuts activated with zinc chloride

Different structured activated carbons were prepared from Terminalia arjuna nuts, an agricultural waste, by chemical activation with zinc chloride for the adsorption of Cr(VI) from dilute aqueous solutions. The most important parameter in chemical activation was found to be the chemical ratio (activating agent/precursor, g/g). Carbonization temperature and time are the other two important variables, which had significant effect on the pore structure of carbon. A high surface area of was obtained at a chemical ratio of 300%, carbonization time and temperature of 1 h and 500 °C, respectively. The activated carbon developed shows substantial capability to adsorb Cr(VI) from dilute aqueous solutions. The parameters studied include pH, adsorbent dosage, contact time, and initial concentrations. The kinetic data were best fitted to the Lagergren pseudo-first-order model. The isotherm equilibrium data were well fitted by the Langmuir and Freundlich models. The maximum removal of chromium was obtained at pH 1.0 (about 99% for adsorbent dose of 2 g/l and 10 mg/l initial concentration).     

Removal of Neutral Red from aqueous solution by using modified hectorite

The object of this work was to study the modified hectorite as effective adsorbent for Neutral Red (NR) from aqueous solution. The adsorbent capacity of modified hectorite was discussed. The effects of surfactant content, adsorbent content, pH and adsorption temperature on the sorption of NR on modified hectorite were studied. Experimental results showed that the equilibrium adsorption data fitted well with Langmuir isotherm and the adsorption capacity was 393.70 mg/g for the modified cetylpyridinium bromide hectorite (CPB-Hect). Kinetic studies showed that the dynamical data fitted well with the pseudo-second-order kinetic model. For thermodynamic studies, parameters such as the Gibbs free energy (ΔG⁰), the enthalpy (ΔH⁰) and the entropy (ΔS⁰) indicated that the adsorption process was spontaneous and endothermic in nature.     

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.     

The use of exhausted olive cake ash (EOCA) as a low cost adsorbent for the removal of toxic metal ions from aqueous solutions

The removal characteristics of cadmium (Cd(II)) and nickel (Ni(II)) ions from aqueous solution by exhausted olive cake ash (EOCA) were investigated under various conditions of contact time, pH, initial metal concentration and temperature. Batch kinetic studies showed that an equilibrium time of 2 h was required for the adsorption of Ni(II) and Cd(II) onto EOCA. Equilibrium adsorption is affected by the initial pH (pH₀) of the solution. The pH₀ 6.0 is found to be the optimum for the individual removal of Cd(II) and Ni(II) ions by EOCA. The adsorption test of applying EOCA into synthetic wastewater revealed that the adsorption data of this material for nickel and cadmium ions were better fitted to the Langmuir isotherm since the correlation coefficients for the Langmuir isotherm were higher than that for the Freundlich isotherm. The estimated maximum capacities of nickel and cadmium ions adsorbed by EOCA were 8.38 and 7.32 mg g⁻¹, respectively. The thermodynamic parameters for the adsorption process data were evaluated using Langmuir isotherm. The free energy change (ΔG°) and the enthalpy change (ΔH°) showed that the process was feasible and endothermic respectively. As the exhausted olive cake is discarded as waste from olive processing, the adsorbent derived from this material is expected to be an economical product for metal ion remediation from water and wastewater.     

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.     

Removal of basic dyes from aqueous solution by low-cost adsorbent: Wood apple shell (Feronia acidissima)

The adsorption of two basic dyes, methylene blue (MB) and crystal violet (CV) on wood apple shell (WAS) were investigated using a batch adsorption technique. A series of experiments were undertaken in an agitated batch adsorber to assess the effect of the system variables such as solution pH, dye concentration and temperature. Removal of dyes was observed to be most effective at higher pH. Freundlich and Langmuir isotherm models were applied to the equilibrium data. The results showed that Langmuir equation fits better than the Freundlich equation. It was observed that the WAS adsorbent showed higher adsorption capacity for crystal violet (130 mg/g) than methylene blue (95.2 mg/g). The FTIR studies indicate that the interaction of dye and WAS surface is via the nitrogen atoms of the adsorbate and oxygen groups of the adsorbent. The adsorption of dyes onto WAS proceeds according to a pseudo-second-order model. Thermodynamic parameters such as free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were also calculated. The studies show that WAS, a lignocellulosic inexpensive material, can be an alternative to other expensive adsorbents used for dye removal in wastewater treatment.     

Kinetic and equilibrium studies of Pb(II) and Cd(II) removal from aqueous solution onto colemanite ore waste

The adsorption characteristics of Pb(II) and Cd(II) onto colemanite ore waste (CW) from aqueous solution were investigated as a function of pH, adsorbent dosage, contact time, and temperature. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models were applied to describe the adsorption isotherms. Langmuir model fitted the equilibrium data better than the Freundlich isotherm. The adsorption capacity of CW was found to be 33.6 mg/g and 29.7 mg/g for Pb(II) and Cd(II) ions, respectively. Analyte ions were desorbed from CW using both 1 M HCl and 1 M HNO₃. The recovery for both metal ions was found to be higher than 95%. The mean adsorption energies evaluated using the D-R model indicated that the adsorption of Pb(II) and Cd(II) onto CW were taken place by chemisorption. The thermodynamic parameters (ΔG^o, ΔH^o and ΔS^o) showed that the adsorption of both metal ions was feasible, spontaneous and exothermic at 20-50 °C. Adsorption mechanisms were also investigated using the pseudo-first-order and pseudo-second-order kinetic models. The kinetic results showed that the adsorption of Pb(II) and Cd(II) onto CW followed well pseudo-second order kinetics.     

Physico-chemical study of dew melon peel biochar for chromium attenuation from simulated and actual wastewaters

This work introduces a biochar as novel adsorbent prepared from the dew melon peel by pyrolysis method, and demonstrates its potential for eliminating Cr(VI) from simulated and actual wastewaters. The dew melon peel biochar (DPB) was characterized by several techniques and methodologies such as, BET, SEM, FTIR, Boehm titration, ultimate analysis, and pHzpc. DPB is a microporous material with the BET specific surface area of 196 m²/g. The effects of different parameters including pH, amount of adsorbent, Cr(VI) concentration, and mixing time on the removal of Cr(VI) from wastewater were studied. Maximum adsorption (98.6%) was observed at pH 6 and 100 mg/L metal concentration. The equilibrium adsorption was analyzed by Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms. Kinetic data were evaluated by pseudo-first order, pseudo-second order, intraparticle diffusion, film diffusion (Boyd), Elovich, and Avrami models. The kinetic data were best fitted to the pseudo-second order model. The Langmuir isotherm model gives the better correlation to predict the adsorption equilibrium, with a maximum adsorption capacity of 198.7 mg/g. The thermodynamic parameters showed that the adsorption of Cr(VI) was endothermic and spontaneous. Competition between the co-existing ions of Cl^?, NO ₃ ^? , SO ₄ ^2? , PO ₄ ^3? , and HCO ₃ ^? on the adsorption process was studied. The efficacy of DPB was successfully examined by analyzing the removal of Cr(VI) from two industrial wastewaters. The results indicate that DPB is promising as an effective and economical adsorbent for Cr(VI) ions removal and could be repeatedly used with no significant loss of adsorption efficiency.     

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.     

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.     

Removal of Copper (II) Ions from Aqueous Solutions using Na‐mordenite

Abstract

The potential to remove copper (II) ions from aqueous solutions using Na‐mordenite, a common zeolite mineral, was thoroughly investigated. The effects of relevant parameters solution pH, adsorbent dose, ionic strength, and temperature on copper (II) adsorption capacity were examined. The sorption data followed the Langmuir, Freundlich, and Dubinin‐Radushkevich (D‐R) isotherms. The maximum sorption capacity was found to be 10.69 mg/g at pH 6, initial concentration of 40 mg/dm³, and temperature of 40°C. Different thermodynamic parameters viz., changes in standard free energy (ΔG⁰), enthalpy (ΔH⁰), and entropy (ΔS⁰) have also been evaluated and the results show that the sorption process was spontaneous and endothermic in nature. The dynamics of the sorption process were studied and the values of rate constant of adsorption, rate constant of intraparticle diffusion were calculated. The activation energy (E_a) was found to be 11.25 kJ/mol in the present study, indicating a chemical sorption process involving weak interactions between sorbent and sorbate. The interaction between copper (II) ions and Na‐mordenite is mainly attributable to ion exchange. The sorption capacity increased with the increase of solution pH and the decrease of ionic strength and adsorbent dose. The Na‐mordenite can be used to separate copper (II) ions from aqueous solutions.     

Sodic and Acidic Crystalline Lamellar Magadiite Adsorbents for the Removal of Methylene Blue from Aqueous Solutions: Kinetic and Equilibrium Studies

The present study reports the feasibility of two synthetic crystalline lamellar nano-silicates, sodic magadiite (Na-mag) and its converted acidic form (H-mag), as alternative adsorbents for the removal of the dye methylene blue (MB) from aqueous solutions. The ability of these adsorbents for removing the dye was explored through the batch adsorption procedure. Effects such as the pH and the adsorbent dosage on the adsorption capacities were explored. Four kinetic models were applied, the adsorption being best fitted to a fractionary-order kinetic model. The kinetic data were also adjusted to an intra-particle diffusion model to give two linear regions, indicating that the kinetics of adsorption follows multiple sorption rates. The equilibrium data were fitted to Langmuir, Freundlich, Sips, and Redlich-Peterson isotherm models. The maxima adsorption capacities for MB of Na-mag and H-mag were 331 and 173 mg g^?1, respectively.     

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.