Cr(VI) ion removal from artificial waste water using supported liquid membrane

In this study, a novel flat-type synergic-supported liquid membrane was evaluated with a mixture of N-methyl-N,N,N-trioctylammonium chloride (Aliquat 336) and tributyl phosphate (TBP) as the carrier and kerosene as the diluent to remove Cr(VI) from synthetic waste water. The main parameters involved in the process were identified and optimised. The parameters were divided into two groups, those that were independent and those having an interaction. The parameters of the carrier/kerosene volumetric proportion and stirring rate were optimised individually due to their nature. The optimal values of these parameters were 0.5 and 500 min^?1, respectively, for a constant carrier/kerosene ratio and stirring rate in the designed experiments using the response surface method (RSM). The four parameters of TBP/Aliquat 336, chromium concentration in the feed phase, feed and product pH were optimised using RSM; it was observed that the TBP/Aliquat 336 ratio, feed pH, pH of the stripping phase and interaction of this parameter with feed concentration have the most important effects on the removal of Cr(VI). The optimal levels of these parameters were 0.61, 71.75 mg L^?1, 3.5 and 12.66 for the ratio of TBP/Aliquat 336, feed chromium concentration, pH of the feed and pH of the product, respectively. An experimental removal rate of 94.63 % at the optimized levels was obtained.     

The removal of uranium(VI) from aqueous solutions onto activated carbon: kinetic and thermodynamic investigations

The adsorption of uranium(VI) from aqueous solutions onto activated carbon has been studied using a batch adsorber. The parameters that affect the uranium(VI) adsorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated and optimized conditions determined (contact time 240 min; pH 3.0+/-0.1; initial uranium concentration 100 mg/L; temperature 293.15 K). The experimental data were analyzed using sorption kinetic models (pseudo-first- and pseudo-second-order equations) to determine the equation that fits best our experimental results. Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of activated carbon and experimental results showed this to be 28.30 mg/g. The Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models have been applied and the data correlate well with Freundlich model and that the sorption is physical in nature (the activation energy Ea=7.91 kJ/mol). Thermodynamic parameters (DeltaHads0=-50.53 kJ/mol, DeltaSads0=-98.76 J/mol K, DeltaGads(293.15 K)0=-21.61 kJ/mol) showed the exothermic heat of adsorption and the feasibility of the process.     

Enhanced removal of U(VI) from aqueous solution by chitosan-modified zeolite

Journal of Radioanalytical and Nuclear Chemistry - A typical type of natural zeolite(Z) modified with chitosan was applied to remove U(VI) from aqueous solution. Batch experiments were performed to...     

Adsorption of51Cr(VI) on manganese dioxide from aqueous solution

Sorption of⁵¹Cr(VI) by MnO₂ has been studied as a function of pH and ionic concentration in the presence of certain added cations and anions. The findings are explained in the light of deprotonation/hydroxyl ion association reaction on oxide surface and its subsequent interaction with the tracer. Infrared spectroscopy has shown the chemical interaction of Cr(VI) on the surface of MnO₂. The influence of certain interfering ions has been shown on the sorption of⁵¹Cr(VI) on MnO₂ surface. An attempt has been made to concentrate traces of⁵¹Cr under optimum experimental conditions. The experimental observation shows that the activity sorbed under specified conditions can be recovered appreciably by leaching the pre-adsorbed carrier.     

Investigation of the Cr(VI) removal from aqueous solutions by stabilized iron-nanoparticles using 51Cr-tracer

Stabilized iron-nanoparticles were used for the Cr(VI)-removal from acidic and neutral aqueous solutions (pH 1, 3, 5 and 7). The chromium interaction with the iron-nanoparticles was studied by a batch technique under different experimental conditions (e.g. pH, temperature, contact time, solid to liquid ratio) using ⁵¹Cr as radiotracer and gamma-ray spectroscopy. The results showed that the Cr-removal was fast and the interaction kinetics could be described by a pseudo-second order rate equation. The maximum Cr-removal was observed from solutions of initial pH 3. The sorption showed a positive temperature and solid to liquid ratio dependence. The experimental results were modeled using the Langmuir, Freundlich and Dubinin–Radushkevich isotherm equations and compared with literature data obtained using other sorbents. X-ray photoelectron spectroscopy (XPS) measurements were performed in order to obtain information about the mechanism of the Cr-removal by the iron-nanoparticles. It was demonstrated that the dominated process based on the Cr(VI) reduction followed by the simultaneous oxidation of iron.     

Adsorption of low level51Cr(VI) from aqueous solution by bismuth trioxide: Kinetic and IR study

Radiotracer technique has been used for the investigation of adsorption of chromium (VI) traces on bismuth trioxide from aqueous solution. The effect of pH (2–10), concentration of chromate solution (10^–6–10^–2M) and temperature (303–323 K) has been thoroughly investigated. The influence of certain foreign ions has also been studied. The calculated kinetic and thermodynamic parameters indicate the first order rate law, spontaneity and exothermic nature of the adsorption process. Further, IR studies have established the chemical interaction between the sorbate and sorbent and a possible mechanism of the sorption process based on ligand exchange has been proposed.     

Removal of Cr(VI) from water by cork waste

The biosorption by cork powder is considered as a promising method for heavy metal removal from industrial waste waters such as chromium tanning factories. The aim of this study is to evaluate the efficiency extent of this method using cork powder as a biosorbent for Cr(VI). The Fourier Transform Infrared spectroscopy (FTIR) analysis permits to distinguish the type of functional groups likely to participate in metal binding. A linear form of BET isotherms for all the three used temperatures (i.e., 25, 35 and 45 °C) and a pseudo-second-order equation of adsorption kinetics are obtained. Other experimental results highlight the meaningful influence of parameters such as contact time, pH, concentration of Cr(VI) and the adsorbent particle size on Cr(VI) adsorption. 97% of Cr(VI) has been removed under definite conditions particularly a particle size of diameter d < 0.08 mm and pH of 2–3 values.     

Highly efficient adsorption of Cr(VI) from aqueous solution by Fe3+ impregnated biochar

Biochar (BC) has been widely used as a low-cost adsorbent for the removal of contaminants from water and soil. However, the adsorption ability of BC towards heavy metal oxyanions (e.g., Cr(VI)) is relatively low due to the negatively charged surface of BC. In this study, pristine BC was impregnated with Fe³⁺ to improve its Cr(VI) adsorption capability. Fe³⁺-impregnated BC (Fe³⁺-BC) was successfully synthesized by a simple impregnation method and used for the removal of Cr(VI) from aqueous solution. Various factors affecting the adsorption, such as impregnation ratio, pH, adsorbent dosage, contact time, temperature, and the presence of humic acid, were investigated in detail. Results showed that Fe³⁺-BC had strong adsorption ability to Cr(VI) with a maximum adsorption capacity of 197.80 mg/g, which were not only significantly higher than that of the pristine BC, but also were superior to many previously reported adsorbents. It was favorable for Cr(VI) adsorption under the condition of acidic and high temperature. The adsorption data obeyed Sips and Langmuir isotherms and the kinetic data were well described by the pseudo-first-order kinetic model. The results herein revealed that the Fe³⁺-impregnated BC had a good potential as a highly efficient material for adsorption of Cr(VI) from aqueous solution.     

Removal of uranium(VI) and thorium(IV) ions from aqueous solutions by functionalized silica: kinetic and thermodynamic studies

Adsorption behavior of uranyl and thorium ions from synthetic radioactive solutions onto functionalized silica as sorbent has been investigated. The effect of contact time, initial concentration of radioactive solutions, sorbent mass, pH value and temperature on the adsorption capacity of the sorbent was investigated. Negative values of Gibbs free energy of adsorption suggested the spontaneity of the adsorption process on both functionalized silica with –NH₂ groups and with –SH groups. Positive values obtained for ΔH° indicates that the adsorption is an endothermic process. The adsorption isotherms were better fitted by Freundlich model and the adsorption kinetic was well described by the pseudo-second order equation. Desorption studies indicated that the most favorable desorptive reagents for UO₂ ²⁺ is HNO₃ 1 M and for Th⁴⁺ is EDTA 1 M solutions.     

Adsorption of uranium (VI) from aqueous solution by tetraphenylimidodiphosphinate

The adsorption of uranium (VI) using tetraphenylimidodiphosphinate (Htpip) was studied. Factors of affecting sorption efficiency have been investigated and results showed the adsorption of uranium (VI) was equilibrium at pH 4.5, time 20 min, adsorbent dosage 0.005 g and initial concentration 50 mg L^?1 reaching 99.86 mg g^?1 of adsorption capacity and 99.86% of removal efficiency. Additionally, the interfering ions studies showed that the adsorbent possessed excellent adsorption selectivity of uranium (VI). The surface morphology of Htpip was investigated by SEM. The adsorption process of uranium (VI) onto Htpip fit the pseudo-second-order kinetic model and the Freundlich isotherm model very well.     

Adsorptive removal of U(VI) from aqueous solution by hydrothermal carbon spheres with phosphate group

The phosphorylated hydrothermal carbon spheres (HCS-PO₄) were developed by functionalizing hydrothermal carbon spheres (HCS) with o-phosphoethanolamine, and the structure and textural property were characterized by SEM and FT-IR. The parameters that affect the uranium(VI) sorption, such as solution pH, initial U(VI) concentration, contact time, and temperature, had been investigated. The HCS-PO₄ showed the highest uranium sorption capacity at initial pH 6.0 and contact time of 120 min. The adsorption kinetics was better described by the pseudo-second-order model, and the adsorption process could be well defined by the Langmuir isotherm and the maximum monolayer adsorption capacity increased from 80.00 to 434.78 mg/g after phosphorylation. The thermodynamic parameters, ?G° (298 K), ?H° and ?S°, demonstrated shown that the sorption process of U(VI) onto HCS-PO₄ was feasible, spontaneous and endothermic in nature. The spent HCS-PO₄ could be effectively regenerated by 0.1 mol/L EDTA solution for the removal and recovery of U(VI) and reused for ten cycles at least. Selective adsorption studies showed that the HCS-PO₄ could selectively remove U(VI), and the selectivity coefficients of HCS in the presence of co-existing ions, Mg(II), Na(I), Zn(II), Mn(II),Co(II), Ni(II), Sr(II), Cs(I) and Hg(II) improved after functionalization.     

Application of NKF-6 zeolite for the removal of U(VI) from aqueous solution

To better understand the application of NKF-6 zeolite as an adsorbent for the removal of U(VI) from radionuclides and heavy metal ions polluted water, herein, NKF-6 zeolite was employed to remove U(VI) at different experimental conditions. The influence of solid/liquid ratio, contact time, pH, ionic strength, humic substances and temperature on sorption of U(VI) to NKF-6 zeolite was investigated using batch technique under ambient conditions. The experimental results demonstrated that the sorption of U(VI) on NKF-6 zeolite was strongly dependent on pH. The sorption property of U(VI) was influenced by ionic strength at pH < 7.0, whereas was independent of ionic strength at pH > 7.0. The presence of fulvic acid or humic acid promoted the sorption of U(VI) on NKF-6 zeolite at low pH values while restrained the sorption at high pH values. The thermodynamic parameters (i.e., ΔS ⁰, ΔH ⁰, and ΔG ⁰) calculated from the temperature-dependent sorption isotherms demonstrated that the sorption process of U(VI) on NKF-6 zeolite was endothermic and spontaneous. At low pH values, the sorption of U(VI) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on NKF-6 zeolite surfaces, while inner-sphere surface complexation was the main sorption mechanism at high pH values. From the experimental results, one can conclude that NKF-6 zeolite can be used as a potential adsorbent for the preconcentration and solidification of U(VI) from large volumes of aqueous solutions.     

Removal of Cr (VI) from aqueous solution using magnetic biochar synthesized by a single step method

Magnetic biochar, as an adsorbent, was synthesized by a single step method, where iron salt was directly mixed with pinewood sawdust by chemical co-precipitation and subsequently pyrolyzed at 700°C for Cr (VI) removal from aqueous solution. The effects of some important parameters including adsorbent dosage (0.4–2.8?g/L), pH (1–10) of the solution, contact time (0–1440 minutes), initial concentration (30–120?mg/L), and temperature (20–40°C) were investigated in batch experiments. Both pre- and post-adsorbents were characterized by SEM-EDX and XPS to investigate the adsorption mechanism. The maximum adsorption capacity of the tested magnetic biochar under the certain experimental conditions determined as optimal was 42.7?mg/g for Cr (VI). The adsorption data were proved to be suitable for the pseudo-second order model for kinetics and the Langmuir model for isotherms with correlation R²?=?0.9996 andR²?>?0.9980, respectively, after fitting with four kinetic models (pseudo-first order, pseudo-second order, W-M model, and Elovich) and three isotherm models (Langmuir, Freundlich, and Temkin). The characteristic analyses further verified that the efficient particle was a mixture of iron oxides in essence, and it had a strong effect on the spontaneous and endothermic adsorption process.     

On the use of a natural peat for the removal of Cr(VI) from aqueous solutions

A natural peat has been used as an adsorbent for the removal of hexavalent chromium from aqueous solution. The peat was firstly characterized in terms of particle size and chemical composition (ash content, pH of the point of zero charge, FT-IR and thermal analysis). Next, the kinetic and equilibrium aspects of the adsorption of Cr(VI) by this adsorbent were studied. The kinetic data were satisfactorily fitted to a kinetic law of partial order in C equal to one. The specific adsorption rates are around 10(-4)s(-1), increasing as temperature does. A noticeable influence of diffusion on the global adsorption process has been demonstrated. Finally, the equilibrium isotherms were satisfactorily fitted to a previously proposed model. The adsorption capacity of Cr(VI) was similar to some other previously reported and the affinity of Cr(VI) towards the active sites of the adsorbent increases as temperature rises.     

Equilibrium and kinetics study of uranium(VI) from aqueous solution by Citrus limetta peels

The potential of the biowaste Citrus limetta peels (CLP) was assessed for adsorption of uranium(VI) from uranyl nitrate solution. Maximum adsorption capacity of 75.33 mg g^?1 was achieved at pH 4, showing drastic falls thereafter. This was attributed to the presence of UO₂ ²⁺, UO₂OH⁺, (UO₂)₃(OH)⁵⁺ and (UO₂)₂(OH) ₂ ²⁺ ions. The peels were characterized for elucidating the role of functional groups and morphology on the sorption capacity. The isotherm studies revealed that Langmuir, Freundlich as well as Sips models give the best fit for the experimental data observing pseudo second order kinetics. The equilibrium was achieved in 90 min. The adsorption shows complex mechanism, took place by both physical and ion-exchange mechanism.     

Low-cost reed straw-derived biochar prepared by hydrothermal carbonization for the removal of uranium(VI) from aqueous solution

Journal of Radioanalytical and Nuclear Chemistry - Uranium is the important nuclear fuel and its effective adsorption using low-cost materials is meaningful to environmental protection and...     

Application of Brazilian kaolinite clay as adsorbent to removal of U(VI) from aqueous solution: Kinetic and thermodynamic of cation-basic interactions

The compound N¹-[3-(trimethoxysilyl)propyl]diethylenetriamine was anchored onto Amazon kaolinite surface by heterogeneous route. The modified and natural kaolinite samples were characterized by transmission electron microscopy, scanning electron microscopic, X-ray diffraction, and nuclear magnetic nuclei of ²⁹Si and ¹³C. The well-defined peaks obtained in the ¹³C NMR spectrum in the 5.0-62.1 ppm region confirmed the attachment of organic functional groups as pendant chains bonded into the porous clay. The ability of these materials to remove U(VI) from aqueous solution was followed by a series of adsorption isotherms adjusted to a Sips equation at room temperature and pH 4.0. The kinetic parameters analyzed by the Lagergren and Elovich models gave a good fit for a pseudo-second order reaction with k₂ values 16.0 and 25.1 mmol g⁻¹ min⁻¹ ranges for natural and modified kaolinite clays, respectively. The energetic effects caused by metal ion adsorption were determined through calorimetric titrations.     

Adsorptive removal of Cr(III) from aqueous solution using tripolyphosphate cross-linked chitosan beads

Chitosan tripolyphosphate (CTPP) beads were prepared at two different cross-linking densities and adsorption of Cr(III) onto it were studied as a function of different operational parameters such as solution pH, equilibration time and initial Cr(III) ion concentration. Higher cross-linked beads were found to have more adsorption capacity at all the experimental pH employed (pH = 3–5), whereas adsorption capacity is found to increase with increase in pH. Adsorption data were analyzed using Langmuir and Freundlich isotherm models. Langmuir model is found be more suitable to explain the experimental results with a monolayer adsorption capacity of 469.5 mg/g. Among the kinetic models used, pseudo-second order kinetic model could best describe the adsorption process. Competition experiments done in presence of Na(I), Mg(II), Ca(II), Al(III) and Fe(III) revealed that, except in the case of Al(III), adsorption of Cr(III) is not significantly affected by the presence of foreign cations. NaCl is found to be a suitable leaching agent for the desorption of adsorbed Cr(III) from CTPP beads. FTIR spectroscopic investigations confirmed that phosphate groups are the principal binding site responsible for the sorption of Cr(III) onto CTPP beads.     

Ultrasound facilitates and improves removal of triphenylmethane (crystal violet) dye from aqueous solution by activated charcoal: A kinetic study

This work was aimed at removing crystal violet (CV) from an aqueous solution via an ultrasound-aided sorption process. Different operational parameters, such as contact time, ultrasonic power, and the sorbent dosage, were investigated. The results indicated that the sorption process was more rapid compared with the previously stated process; a sorption equilibrium was obtained after 1.5 h. The increase in the dose from 0.02 to 5.0 g/L increased the adsorption efficiency by 100%. The decolorization of the CV pigment occurred very rapidly at the highest sound power, 200 W, and it reached ～85%. The kinetics study indicated that the sorption process fitted the pseudo-second-order model with the chemisorption mechanism. The sorption isotherm data were also interpreted by the mass-transfer model, which established the intraparticle diffusion. Additionally, to estimate the rate-limiting step mechanisms, the intraparticle diffusion was not considered as the sole rate-controlling step. The maximum sorption capacity (q_max) increased from 19.0 to 24 mg/g during the ultrasound and indicated the positive synergistic effect of the ultrasound. The proposed sonosorption technique is a low cost-effective method for purifying water and wastewater from organic pollutants.