Calcined tetrabutylammonium kaolinite and montmorillonite and adsorption of Fe(II), Co(II) and Ni(II) from solution

Kaolinite and montmorillonite were modified with tetrabutylammonium (TBA) bromide, followed by calcination. The structural changes were monitored with XRD, FTIR, surface area and cation exchange capacity measurements. The modified clay minerals were used for adsorption of Fe(III), Co(II) and Ni(II) ions from aqueous solution under different conditions of pH, time and temperature. The uptake of the metal ions took place by a second order kinetics. The modified montmorillonite had a higher adsorption capacity than the corresponding kaolinite. The Langmuir monolayer capacities for the modified kaolinite and montmorillonite were Fe(III): 9.3 mg g^− 1 and 22.6 mg g^− 1; Co(II): 9.0 mg g^− 1 and 22.3 mg g^− 1; and Ni(II): 8.4 mg g^− 1 and 19.7 mg g^− 1. The modified kaolinite interacted with Co(II) in an endothermic manner, but all the other interactions were exothermic. The decrease of the Gibbs energy in all the cases indicated spontaneous adsorption.     

Reductive transformation of 2-nitrophenol by Fe(II) species in γ-aluminum oxide suspension

Fe(II) adsorption onto γ-Al₂O₃ surfaces was studied in view of its high reactivity towards the aqueous reductive transformation of 2-NP. Kinetic measurements demonstrated that rates of 2-NP reduction were highly sensitive to pH, Fe(II) concentration and reaction temperature. An increase in pH, Fe(II) concentration or reaction temperature gave rise to an elevated density of Fe(II) adsorbed to mineral surfaces, which further resulted in an enhanced reaction rate of 2-NP reduction. By using the diffuse double layer (DDL) surface complexation model, the dominant Fe(II) surface complex that was responsible for the high reactivity was predicted to be the strongly bound ≡ SOFe⁺ functional group (represented by ≡ Al_stOFe⁺) onto γ-Al₂O₃ surfaces. In addition, cyclic voltammetry tests showed that the enhanced activity of Fe(II) species was attributed to the negative shift of the redox potential of Fe(III)/Fe(II) couple, resulted from the enhanced concentration of ≡ Al_stOFe⁺ complex.     

Capacity of Cr(VI) reduction in an aqueous solution using different sources of zerovalent irons

Zerovalent iron (ZVI) has drawn intense interest as an effective and inexpensive tool to enhance degradation of various environmental contaminants. Reduction of Cr(VI) to Cr(III) by ZVI merits environmental concern as a hazardous species is transformed into a non-hazardous one. Objectives of this research were to assess kinetics and capacity of Cr(VI) reduction by different sources of ZVIs, of which chemical parameters can base in situ application of ZVI to treat Cr(VI) contaminated water. Reduction kinetics were first-order and rapid showing that 50% of the initial Cr(VI) was reduced within 7.0 to 347 min depending on Cr(VI) concentration, temperature and ZVI source. The reduction rates were increased with decreasing the initial Cr(VI) concentrations and increasing the reaction temperatures. The J ZVI (Shinyo Pure Chemical Co., Japan) was more effective in Cr(VI) reduction than PU (Peerless Metal Powders, USA). The maximum reduction capacities of J and PU ZVIs at 25°C were 0.045 and 0.042 mmol g⁻¹ Fe⁰, respectively. A relatively higher value of the net reaction energy (E _a ) indicated that Cr(VI) reduction by ZVI was temperature dependent and controlled by surface properties of ZVI. Chemical parameters involved in the Cr(VI) reduction by ZVI such as temperature quotient, kinetic rates, and stoichiometry indicated that the ZVI might be effective for in situ treatment of the Cr(VI) containing wastewater.     

Reduction of Fe(II)EDTA‐NO using Paracoccus denitrificans and changes of Fe(II)EDTA in the system

BACKGROUND: In the BioDeNO_X technology for NO_X removal from flue gas, bioreduction of Fe(II)EDTA‐NO and Fe(III)EDTA are core processes. In this study, a newly isolated strain, Paracoccus denitrificans, was used to reduce Fe(II)EDTA‐NO with glucose and Fe(II)EDTA as donor electrons. To better understand the change law of Fe(II)EDTA, the process of Fe(II)EDTA‐NO reduction by P. denitrificans with glucose and Fe(II)EDTA as electron donors was investigated, and the factors that might affect Fe(II)EDTA concentration were studied. RESULTS: For the bioreduction process of Fe(II)EDTA‐NO, P. denitrificans could use glucose and Fe(II)EDTA as electron donors. At different stages, primary electron donors were different, thereby affecting the concentration of Fe(II)EDTA in the system. It was also proved that this strain not only reduced Fe(III)EDTA with glucose as the electron donor but also secreted several substances that reacted with Fe(III)EDTA, resulting in increased Fe(II)EDTA concentration in the solution. CONCLUSIONS: This work has shown that P. denitrificans can reduce Fe(II)EDTA‐NO and Fe(III)EDTA simultaneously to regenerate NO_X absorption solution. © 2012 Society of Chemical Industry     

Removal process and mechanism of hexavalent chromium by adsorption-coupled reduction with marine-derived Aspergillus niger mycelial pellets

In order to remove hexavalent chromium(Cr(Ⅵ)) from solutions efficiently, the mycelial pellets with a marine-derived fungus Aspergillus niger as a biosorbent were prepared. The effects of removal process parameters such as solution pH, initial Cr(Ⅵ) concentration and biomass concentration on Cr(Ⅵ) removal process were investigated. The results showed that Cr(Ⅵ) removal rate up to 100% could be achieved under optimized conditions, which indicated the excellent Cr(Ⅵ) removal performance of the Asp...     

Effect of the chelating agents on bio-sorption of hexavalent chromium using Agave sisalana fibers

The current work is focused on the study of the bio-sorption of hexavalent chromium from aqueous solution using sisal natural fiber(Agave sisalana) treated by various chelating agents(ligands) such as urea(UR),thiocarbamide(TC), ethylenediaminetetraacetic acid(EDTA), and diphenyl carbazide(DCZ). The fiber treatments were investigated using Fourier Transform Infrared Spectroscopy(FTIR) and Scanning electron microscope(SEM). The kinetics of chromium bio-sorption was studied in batch presses under the effect of some physicochemical factors such as the nature of chelating agent(F@UR, F@TC, F@DCZ, and F@EDTA),adsorbent dose(2–10 g·L~(-1)), chromium initial concentration(100–500 mg·L~(-1)), solution pH(1–6), and batch temperature(20 ℃–50 ℃). This study resulted in an optimum adsorption at a chromium initial concentration of 100 mg·L~(-1), at pH 2, and at 20 ℃. The obtained results showed clearly that the treatment with chelating agent boosts the adsorptive capacity of A. sisalana fibers Cr(VI) 10.9 mg·g~(-1) to 58.6 mg·g~(-1). The modeling study showed that the adsorption kinetics obey the pseudo-second-order model, with an R2 in the range of 0.991 and 0.999. The bio-sorption isotherms followed the Langmuir model; the maximum uptake capacity of(F@N, F@UR,F@TC, F@DCZ, and F@EDTA) was found to be respectively, 12.3 mg·g~(-1), 25.33 mg·g~(-1), 28.73 mg·g~(-1),42.54 mg·g~(-1), and 61.45 mg·g~(-1). The determined adsorption thermodynamics parameters such as enthalpy,free energy, and entropy showed that the adsorption process is exothermic, spontaneous, and has a stable configuration.     

Advances in electrochemical Fe(VI) synthesis and analysis

Hexavalent iron species (Fe(VI)) have been known for over a century, and have long-time been investigated as the oxidant for water purification, as the catalysts in organic synthesis and more recently as cathodic charge storage materials. Conventional Fe(VI) syntheses include solution phase oxidation (by hyphchlorite) of Fe(III), and the synthesis of less soluble super-irons by dissolution of FeO₄ ²⁻, and precipitation with alternate cations. This paper reviews a new electrochemical Fe(VI) synthesis route including both in situ and ex situ syntheses of Fe(VI) salts. The optimized electrolysis conditions for electrochemical Fe(VI) synthesis are summarized. Direct electrochemical synthesis of Fe(VI) compounds has several advantages of shorter synthesis time, simplicity, reduced costs (no chemical oxidant is required) and providing a possible pathway towards more electro-active and thermal stable Fe(VI) compounds. Fe(VI) analytical methodologies summarized in this paper are a range of electrochemical techniques. Fe(VI) compounds have been explored as energy storage cathode materials in both aqueous and non-aqueous phase in “super-iron” battery configurations. In this paper, electrochemical synthesis of reversible Fe(VI/III) thin film towards a rechargeable super-iron cathode is also summarized.     

Chelation of Cu(II), Zn(II), and Fe(II) by Tannin Constituents of Selected Edible Nuts

The tannin fractions isolated from hazelnuts, walnuts and almonds were characterised by colorimetric assays and by an SE-HPLC technique. The complexation of Cu(II) and Zn(II) was determined by the reaction with tetramethylmurexide, whereas for Fe(II), ferrozine was employed. The walnut tannins exhibited a significantly weaker reaction with the vanillin/HCl reagent than hazelnut and almond tannins, but the protein precipitation capacity of the walnut fraction was high. The SE-HPLC chromatogram of the tannin fraction from hazelnuts revealed the presence of oligomers with higher molecular weights compared to that of almonds. Copper ions were most effectively chelated by the constituents of the tannin fractions of hazelnuts, walnuts and almonds. At a 0.2 mg/assay addition level, the walnut tannins complexed almost 100% Cu(II). The Fe(II) complexation capacities of the tannin fractions of walnuts and hazelnuts were weaker in comparison to that of the almond tannin fraction, which at a 2.5 mg/assay addition level, bound Fe(II) by ~90%. The capacity to chelate Zn(II) was quite varied for the different nut tannin fractions: almond tannins bound as much as 84% Zn(II), whereas the value for walnut tannins was only 8.7%; and for hazelnut tannins, no Zn(II) chelation took place at the levels tested.     

Removal of chromium (III) and cadmium (II) from aqueous solutions

Chromium and cadmium are toxic heavy metals present in wastewaters from a variety of industries. A strong cationexchange resin, Amberlite IR 120, was used for the removal of chromium and cadmium. The resin was prepared in two different cationic forms, as Na⁺ and H⁺. The optimum conditions were concentration, pH, stirring time and resin amount. The concentration range was between 2–50 mg/L, pH range between 2–10, stirring time between 5–60 min, and the amount of resin was from 50–1000 mg. Exchange capacities, moisture content and optimum conditions of this resin were determined in a batch system. The stirring speed was 2000 rpm during all of the batch experiments. The initial and final chromium and cadmium amounts were determined by atomic absorption spectrophotometry. The optimum conditions were found to be a concentration of 20 mg/L, pH of 5.5, stirring time of 20 min and 100 mg of resin. The results obtained show that the Amberlite IR 120 strong cation-exchange resin performed well for the removal and recovery of chromium and cadmium.     

INDIVIDUAL AND SIMULTANEOUS BIOSORPTION OF CHROMIUM (VI) AND NICKEL (II) ONTO DRIED ACTIVATED SLUDGE

The biosorption of chromium(VI) and nickel(II) ions, both singly and in combination, by dried activated sludge was investigated in a batch system as a function of initial pH and single- and dual-metal ion concentrations. The working pH value for single chromium(VI) and nickel(II) biosorption was determined as 1.0 and 4.5, respectively, due to the selective uptake of biomass. Multi component biosorption studies were performed at these two initial pH values. It was observed that the biosorption kinetics and equilibrium uptakes of chromium(VI) and nickel(II) ions in binary mixtures changed due to the initial biosorption pH and the presence of the other component.     

A simple mathematical analysis on the effect of sand in Cr(VI) reduction using zero valent iron

A simple mathematical model was proposed to analyze the enhancement of Cr(VI) reduction when sand materials are added to the zero valent iron (ZVI). Natural decay of Cr(VI) in a control experiment was analyzed by using a zero-order decay reaction. Adsorption kinetics of Cr(VI) to sand was modeled as a first-order reversible process, and the reduction rate by ZVI was treated as a first-order reaction. Natural decay of Cr(VI) was also included in other experiments, i.e., the adsorption to sand, the reduction by ZVI, and both adsorption and reduction when sand and ZVI are present together. The model parameters were estimated by fitting the solution of each model to the corresponding experimental data. To observe the effect of sand addition to ZVI, both adsorption and reduction rate models were considered simultaneously including the natural decay. The solution of the combined model was fitted to the experimental data to determine the first-order adsorption and reduction rate constants when sand as well as ZVI is present. The first-order reduction rate constant in the presence of sand was about 35 times higher than that with ZVI only.     

Adsorption of chromium(VI) and nickel(II) ions on acid- and heat-activated deoiled spent bleaching clay

De-oiled spent bleaching clay was activated either by acid treatment followed by heat activation or by heat activation alone at temperatures between 200 and 800°C. The surface area of the heat-activated clay attained a maximal value of ≈120 m² g⁻¹ at temperatures between 400 and 500°C while the acid-heat-treated clay attained maximal surface area of ≈140 m² g⁻¹. The adsorption capacities of chromium [Cr(VI)] for both series studied increased as the activation temperature increased until 300°C and decreased again at higher temperatures. At lower pH, more than 95% of the Cr(VI) was absorbed in a solution with initial concentration of 1 mg L⁻¹ per gram of adsorbent activated at 300°C. The adsorption patterns followed Freudlich's isotherms. Two maximal values of adsorption capacities of nickel [Ni(II)] were observed at activation temperatures of 200 and 500°C for acid-treated samples, whereas these were at 200 and 700°C for the nonacid-treated samples. The amount of Ni(II) adsorbed increased with the pH of the solution for all samples studied. The maximal adsorption capacities of the adsorbents in solution containing initial Ni(II) concentration of 5 mg L⁻¹ per 0.5 g of adsorbent and at pH 6 were found to be 44 and 42%, respectively, for the acid-treated sample activated at 500°C and for the nonacid-treated sample activated at 700°C. They all obeyed both the Langmuir's and Freundlich's isotherms.     

Removal behavior of Cu(II) during Cr(VI) reduction by cast iron powder in absence and presence of ultrasound

ABSTRACT

Cu(II) is an important and typical heavy metal ion in the wastewater containing Cr(VI), and its removal during Cr(VI) reduction by zero valent iron (ZVI) may make it separately be recovered as a kind of copper resource. In this study, the removal behavior of Cu(II) during Cr(VI) reduction by cast iron powder in absence and presence of ultrasound was investigated by atomic absorption spectrometry (AAS), X-ray powder diffractometer (XRD), scanning electron microscope-energy dispersion spectrum (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The AAS tests indicated that the ultrasound could not only obviously enhance the removal of Cu(II) but also improve the reduction rate of Cr(VI). The XRD and SEM-EDS analyses showed that Cu(II) in the solution was reduced to metallic copper and then was deposited at the surface of ZVI. The ultrasound could remove the Fe-Cr oxides and hydroxides at the ZVI surfaces, resulting in the active surfaces of iron increased. The XPS analyses demonstrated that the surface of metallic copper would be transformed into the film of copper oxide (CuO) in the ultrasound system. The obtained metallic copper and copper oxide could be recovered alone by traditional method of the acid pickling.     

氰根桥联Fe（II）自旋交叉配位化合物材料的研究进展

自选交叉是有些配合物的一种奇特现象,这种材料能够用于信息储存技术。在温度、压力、磁场、光等的作用下发生高低自旋的转换,本文主要介绍Real组的研究成果。     

Determination of hexavalent chromium in South African cements and cement-related materials with electrothermal atomic absorption spectrometry

The selective extraction of Cr(VI) in a cement matrix, based on treatment with 0.1 M Na₂CO₃ solution and subsequent determination of chromium by electrothermal atomic absorption spectrometry has been proposed. The proposed method has been applied to South African cement clinkers, natural gypsum, limestone and certified reference materials. The limit of detection of chromium determination in cement samples was found to be 0.14 μg g⁻¹. Between 30% and 80% of the total chromium in South African cement clinkers are Cr(VI) compounds and 8-26% of the total amount of Cr(VI) species is water soluble. The analytical performance of the proposed method has been verified by the analysis of BCS-CRM, a sulphate-resisting Portland cement, and the results obtained were in good agreement with the certified values.     

Solvent extraction of hexavalent chromium with tetrabutyl ammonium bromide from aqueous solution

The extraction of hexavalent chromium (Cr) from aqueous solutions by tetrabutyl ammonium bromide (TBAB) salt in dichloromethane was investigated. The results indicated that the maximum extraction efficiency of Cr(VI) was at pH 1±0.1. The strippant 0.1 M sodium hydroxide, completely stripped Cr(VI) from the loaded solvent. The stripped solvent can be reused for extracting Cr(VI). After five extraction cycles, the dichloromethane showed no significant loss in volume and retains the same extracting ability. The solvent extraction method was applied for the removal and recovery of Cr(VI) from real chromeplating wastewater and found to be satisfactory.     

Separation and concentration processes of solutions of Co(II), Ni(II), Cr(III), Fe(III) and Mn(II) by extraction with toluene-dissolved rosin

The extraction and stripping of Co(II), Ni(II), Cr(III) and Fe(III) from aqueous solutions by rosin dissolved in toluene has been investigated. Results obtained show that rosin is better extractant than abietic or n-lauric acids under comparable conditions. From these results, and the data of Mn(II) solvent extraction studied previously under the same conditions, a separation and concentration process for these five cations in aqueous solutions has been designed. Saturated solutions of Fe(III), Cr(III), Mn(II) and finally Co(II) and Ni(II) have been obtained successively by extraction and stripping, by addition of ammonium hydroxide to obtain the appropriate pH value, and by modifying adequately the organic phase/aqueous phase volume ratio.     

Reaction rate and electrochemical stability of conducting polymer films used for the reduction of hexavalent chromium

The reduction of toxic hexavalent chromium to its trivalent state at conducting polymers films was studied. The process is based on the capacity of conducting polymers to spontaneously donate electrons to the Cr(VI) species. Electrodes of polyaniline and polypyrrole, deposited as films on reticulated vitreous carbon (RVC), were prepared. The process of Cr(VI) reduction was studied under open and closed circuit conditions. It was observed that polyaniline was only suitable for use only under closed circuit conditions, whereas polypyrrole did not perform well under either open or closed circuit conditions. The electrocatalytic power of polyaniline for Cr(VI) reduction was demonstrated when the reaction rates for bare RVC and RVC/PANI were compared.     

Homogeneous catalysts for ethylene polymerization based on bis(imino)pyridine complexes of iron, cobalt, vanadium and chromium

Results of a comparative study of ethylene polymerization activity and the structure of polyethylene (PE) produced over homogeneous catalysts based on bis(imino)pyridine complexes with close ligand frameworks and different transition metal centers (Fe(II), Co(II), Cr(III) and V(III)) are reported. The effects of the activator nature and polymerization conditions on the activity of these complexes and the resulting PE structure (molecular weight, molecular weight distribution, content of methyl and vinyl groups) have been studied. The experimental data obtained under comparable conditions demonstrate a pronounced effect of transition metal center on the catalytic properties of bis(imino)pyridine complexes (polymerization activity, copolymerization reactivity, thermal stability, PE structure, composition of optimal activator, formation of single-site or multiple-site catalytic system).     

Arsenic adsorption using copper (II) oxide nanoparticles

Arsenic poisoning is a major problem in today's life. To reduce its concentration in drinking water, different metal based compounds were explored as arsenic adsorbents. In the present study, copper (II) oxide nanoparticles were prepared by thermal refluxing technique and used as an adsorbent for arsenic removal from water. Characterization of the adsorbent using TEM, BET, XRD and FTIR implied that the prepared adsorbent was in nano size and had excellent adsorption behavior with surface area of 52.11 m²/g. Systematic adsorption experiments were carried out with different process parameters such as contact time, adsorbent mass, pH, temperature and stirring speed and found that copper (II) oxide had very good efficiency towards arsenic adsorption. Thermodynamic parameters and adsorption kinetics were studied in detailed to know the nature and mechanism of adsorption. Results showed that the adsorption process followed pseudo second order kinetic and endothermic behavior. Adsorption equilibrium was studied with Langmuir and Freundlich isotherm models. The adsorption process followed Langmuir isotherm with an adsorption capacity of 1086.2 μg/g. A regeneration study was proposed in order to reuse the adsorbent for better economy of the process. Finally, a process design calculation is reported to know the amount of adsorbent required for efficient removal of arsenic from aqueous medium.