Adsorption of Cr(VI) using activated neem leaves: kinetic studies

In the present study, adsorbent is prepared from neem leaves and used for Cr(VI) removal from aqueous solutions. Neem leaves are activated by giving heat treatment and with the use of concentrated hydrochloric acid (36.5 wt%). The activated neem leaves are further treated with 100 mmol of copper solution. Batch adsorption studies demonstrate that the adsorbent prepared from neem leaves has a significant capacity for adsorption of Cr(VI) from aqueous solution. The parameters investigated in this study include pH, contact time, initial Cr(VI) concentration and adsorbent dosage. The adsorption of Cr(VI) is found to be maximum (99%) at low values of pH in the range of 1-3. A small amount of the neem leaves adsorbent (10 g/l) could remove as much as 99% of Cr(VI) from a solution of initial concentration 50 mg/l. The adsorption process of Cr(VI) is tested with Langmuir isotherm model. Application of the Langmuir isotherm to the system yielded maximum adsorption capacity of 62.97 mg/g. The dimensionless equilibrium parameter, R _L, signifies a favorable adsorption of Cr(VI) on neem leaves adsorbent and is found to be between 0.0155 and 0.888 (0<R _L<1). The adsorption process follows second order kinetics and the corresponding rate constant is found to be 0.00137 g/(mg) (min).     

Use of immobilized tannin adsorbent for removal of Cr(VI) from water

PIXE studies on pure metal targets surrounded by insulating material produced enhanced X-ray yields at comparatively low proton energies. Specially prepared metal discs of selected transition elements were embedded in Macor target holders and irradiated with 700 keV protons. Improved X-ray yields of up to more than 300% were observed. It was found that the enhanced yields were affected by the incident beam current due to a “leakage” effect. The recorded time-dependent spectra showed similar charge build-up and discharge patterns as those originally obtained for non-conducting samples. A possible mechanism for the enhancement is discussed.     

Facial Synthesis of Adsorbent from Hemicelluloses for Cr(VI) Adsorption

It is challenging work to develop a low-cost, efficient, and environmentally friendly Cr(VI) adsorbent for waste water treatment. In this paper, we used hemicelluloses from chemical fiber factory waste as the raw material, and prepared two kinds of carbon materials by the green hydrothermal method as adsorbent for Cr(VI). The results showed that hemicelluloses hydrothermally treated with citric acid (HTC) presented spherical shapes, and hemicelluloses hydrothermally treated with ammonia solution (HTC-NH₂) provided spongy structures. The adsorption capacity of the samples can be obtained by the Langmuir model, and the adsorption kinetics could be described by the pseudo-second-order model at pH 1.0. The maximum adsorption capacity of HTC-NH₂ in the Langmuir model is 74.60 mg/g, much higher than that of HTC (61.25 mg/g). The green hydrothermal treatment of biomass with ammonia solution will provide a simple and feasible way to prepare adsorbent for Cr(VI) in waste water treatment.     

Perfluorinated polymer film with functional group prepared by radiation-induced grafting

A perfluorinated vinyl ether monomer, 2-bromotetrafluoroethyl trifluorovinyl ether (BrTFF) was grafted into crosslinked poly(tetrafluoroethylene) (cPTFE) films by γ-rays irradiation under different conditions. The irradiation with absorbed doses more than 550 kGy gave the poly(BrTFF) grafted cPTFE membranes with grafting yields of more than 20%. FTIR spectra and SEM-EDS testified that BrTFF was successfully grafted into cPTFE films homogeneously in the film perpendicular direction. TGA analysis of the grafted films indicated that the perfluorinated poly(BrTFF) grafts were phase-separated from the PTFE region due to the crosslinked structure of the cPTFE based film, but the grafted films still had high thermal stability (above 300 °C). DSC measurements showed the decrease of melting temperature, but the increase of both heat of fusion and degree of crystallinity in cPTFE film after grafting. The grafted film, a new kind of perfluorinated polymer with bromine active groups and good mechanical properties, is expected to be modified for new applications.     

Adsorption Studies of Cr(III) & Cr(VI) on Lead Sulphide,Copper Sulphide & Zinc Sulphide-Determination Cr(III) in the Presence of Cr(VI)

Abstract

The adsorption studies of Cr(VI) in presence of Cr(III) on the sulphide of Lead, Zinc and Copper has been studied. It has been found that in case of lead sulphide 100% adsorption of Cr(VI) took place at pH 4.0 and of Cr(III) at pH 7.0. While in case of zinc sulphide the 100% adsorption of Cr(VI) took place at pH 4.5 and of Cr(III) at pH 6.5. In case of copper sulphide 100% adsorption of Cr(VI) took place at pH 5.0 and of Cr(III) at pH 7.0. This difference in adsorption at different pH values forms the basis for the determination of these ions. The method is accurate.     

Speciation of Cr(III) and Cr(VI) by reversed phase high-performance liquid chromatography using UV-detection

Summary A method for the simultaneous determination of Cr(III) and Cr(VI) in water samples is described. The different reaction products of Cr(III) and Cr(VI) species with ammonium pyrrolidinedithiocarbamate (APDC) are extracted with ethyl acetate and determined by reversed phase HPLC using UV-detection. The procedure is optimized and its detection limit accordingly improved as compared to literature data. The detection limits achieved are 2.4 g/l for Cr(III) and 2.1 g/l for Cr(VI) and the calibration curves are linear between 5 g/l and 5000 g/l. For the speciation of Cr, APDC was demonstrated to be more suitable as chelating agent than sodium diethyldithiocarbamate (NaDDC). The procedure was applied to the determination of both Cr species in galvanic waste waters and its accuracy was approved by comparing the results (at the 100 g/l level) with those of a photometric determination of Cr(VI) species.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Effect of Temperature on Interfacial Adsorption of Cr(VI) on Wollastonite

An extensive study on the effect of temperature on interfacial adsorption of Cr(VI) on wollastonite has been carried out. Adsorption on the wollastonite surface increased from 69.5 to 91.7% by increasing the temperature from 30 to 50 degrees C under optimum conditions. Kinetic modeling of the process of adsorption of Cr(VI) was done and various parameters were determined. The process follows a first-order kinetic equation and the rate of uptake was found to be 2.40x10(-2) min(-1) at 30 degrees C, 2.5 pH, 0.5x10(-4) M Cr(VI) concentration, and 0.01 M NaClO(4) ionic strength. Kinetic and equilibrium modeling of the process of adsorption was undertaken and the equilibrium parameters were determined. The process of adsorption follows pore diffusion and the value of the rate constant of pore diffusion was found to be 5.00x10(-3) mg g(-1) min(-1/2) at 30 degrees C and optimum conditions. The values of the coefficient of mass transfer, beta(L), were determined at different temperatures. Thermodynamic studies of the removal process were performed. The study suggests that the process is a typical example of endothermic adsorption. Copyright 2001 Academic Press.     

Cell culture on polymers prepared by radiation-induced grafting of various monomers

The adhesion and growth of tissue cells on polymers prepared by radiation grafting was investigated. The apparent rates of initial attachment and growth of Chang liver and C₆ cells were promoted on surfaces with increased wettability and with a heterogeneous structure for grafted polyvinyl fluoride film. The degree of cell attachment and growth on surfaces having a dense microblock structure, formed by grafting of methyl methacrylate in acetone solvent, was greater than that caused by other factors, such as wettability.     

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.     

Optimization of Parameters for Cr(VI) Adsorption on Used Black Tea Leaves

Dynamic characteristics of Cr(VI) sorption on used black tea leaves (UBTLs) as a low-cost adsorbent are studied. Batch experiments were conducted to evaluate the effects of Cr(VI) concentration, solution pH and temperature on the removal process. Both of adsorption and reduction, involved in the process, are affected by the processing parameters. The adsorption kinetics is described successfully using pseudo-second order rate equation and the rate constant decreases with increasing the initial concentration of Cr(VI) up to 150 mg/L (for 0.1 g/L UBTLs) then becomes slow. Experimental and calculated kinetic data for equilibrium are well expressed by Langmuir isotherm. The solution pH has a profound effect on the adsorption rate. The rate constant increases linearly with an increase in temperature, and the low value of activation energy of adsorption, 16.3 kJ/mol, indicates that Cr(VI) is easily adsorbed on UBTLs. The maximum Cr(VI) adsorptive conditions, with a minimum reduction, were achieved from the dynamics of operational parameters: the initial Cr(VI) concentration < 150 mg/L (for 0.1 g/L UBTLs); the initial solution pH = 1.54–2.00 and the processing temperature < 50 ^∘C, for the possibility of its practical application.     

聚苯胺/凹凸棒石纳米纤维复合材料对溶液中痕量Cr(VI)的吸附性能

采用原位聚合法合成了盐酸掺杂聚苯胺/凹凸棒石黏土(PANI/ATP)纳米纤维复合材料。 研究了它对含痕量Cr(Ⅵ)废水的吸附,考察了物料配比、投料质量、吸附时间、吸附温度和pH值对其吸附性能的影响。 结果表明,复合材料中的物料配比为m(An)∶m(ATP)=2∶1,用量为0.4 g,50 min时对Cr(Ⅵ)的吸附量达到99.8%,符合Langmuir等温吸附方程。 该复合材料充分发挥了有机和无机吸附材料的协同作用,具有成本低、再生性能良好的特点。     

Adsorption of Cr(VI) on ureolytic mixed culture from biocatalytic calcification reactor

Ca-rich water and wastewater have caused problems in water use, wastewater reuse and the operations of reactors treating Ca-rich wastewater. Nowadays, reuse of wastewaters is fast gaining importance as water sources have been polluted. Therefore, the concept of biocatalytic calcification reactors (BCR) based on urea hydrolysis, pH increase and calcite production has been studied to remove Ca from wastewaters. This biological process produces significant amounts of waste sludge. In the present study, Cr(VI) adsorption on the ureolytic mixed culture (UMC) waste by-product from BCR was investigated to evaluate its potential for metal removal. The biosorption process was investigated using equilibrium batch tests and the data were fit to the Langmuir, Freundlich and Temkin isotherm models. The Cr(VI) ion concentration dependence of sorption (1-100 mg/L) could be fit to the Langmuir isotherm model. Monolayer adsorption capacity, qm (mg/g), of the adsorbent was 8.67 and the Langmuir constant b (L/mg) was 0.881. Based on the obtained results, the waste UMC appears to be a potential biosorbent for the removal of Cr(VI) from wastewater, although its adsorptive capacity is lower than those of other biosorbents.     

Removal of Cr(VI) from wastewater using rice bran

The novel biosorbent rice bran has been successfully utilized for the removal of Cr(VI) from wastewater. The maximum removal of Cr(VI) was found to be 99.4% at pH 2.0, initial Cr(VI) concentration of 200 mg l(-1), and temperature 20 degrees C. The effect of different parameters such as contact time, adsorbate concentration, pH of the medium, and temperature was investigated. The adsorption kinetics was tested for first-order reversible, pseudo-first-order, and pseudo-second-order; reaction and the rate constants of kinetic models were calculated. Mass transfer of Cr(VI) from the bulk to the solid phase (rice bran) was studied at different temperatures. Different thermodynamic parameters, viz., changes in standard free energy, enthalpy, and entropy, have also been evaluated and it has been found that the reaction was spontaneous and endothermic in nature. The Langmuir and Freundlich equations for describing adsorption equilibrium were applied to data. The constants and correlation coefficients of these isotherm models were calculated and compared. Desorption studies was also carried out and found that complete desorption of Cr(VI) took place at pH of 9.5. The data were also subjected to multiple regression analysis and a model was developed to predict the removal of Cr(VI) from wastewater.     

Preconcentration and separation of Cr(III) and Cr(VI) using sawdust as a sorbent

A simple, inexpensive method based on solid-phase extraction (SPE) on sawdust from Cedrus deodera has been developed for speciation of Cr(III) and Cr(VI) in environmental water samples. Because different exchange capacities were observed for the two forms of chromium at different pH—Cr(III) was selectively retained at pH 3 to 4 whereas Cr(VI) was retained at pH 1—complete separation of the two forms of chromium is possible. Retained species were eluted with 2.5 mL 0.1 mol L⁻¹ HCl and 0.1 mol L⁻¹ NaOH. Detection limits of 0.05 and 0.04 μg mL⁻¹ were achieved for Cr(III) and Cr(VI), respectively, with enrichment factors of 100 and 80. Recovery was quantitative using 250 mL sample volume for Cr(III) and 200 mL for Cr(VI). Different kinetic and thermodynamic properties that affect sorption of the chromium species on the sawdust were also determined. Metal ion concentration was measured as the Cr(VI)–diphenylcarbazide complex by UV–visible spectroscopy. The method was successfully applied for speciation of chromium in environmental and industrial water samples.     

功能化有序介孔碳对重金属离子Cu(II)、Cr(VI)的选择性吸附行为

以三嵌段共聚物F127为模板剂, 酚醛树脂为碳源, 正硅酸乙酯为硅源, 三组分共组装合成介孔碳?氧化 硅纳米复合物, 再经HF去除氧化硅, 得到有序介孔碳(OMC). X射线衍射(XRD)、透射电子显微镜(TEM)、低温 N2吸脱附(BET)等测试表明, 所得样品具有高度有序的介孔结构, 比表面积和孔容分别为1330 m²·g^-1和2.13 cm³·g^-1, 平均孔径6.4 nm. 对其先氧化、后氯化、再胺化, 得到不同胺基接枝量的胺化介孔碳(C-NH₂(m), m为加入的乙二胺的质量(g)). 傅里叶变换红外(FT-IR)光谱表征结果证实, 胺基官能团成功接枝到有序介孔碳表面.TEM测试表明介孔碳的有序孔道结构得到了较好的保持. 以有序介孔碳、胺化介孔碳作吸附剂对Cu(II)、Cr(VI)进行选择性吸附研究. 结果表明: 功能化修饰前, 样品对Cu(II)、Cr(VI)饱和吸附量分别为213.33、241.55 mg·g^-1; 修饰后饱和吸附量可分别达到495.05、68.21 mg·g^-1. 功能化介孔碳表现了较强的选择性吸附Cu(II)的能力.     

Amperometric Determination of Cr(III) and Cr(VI) by Flow Injection Analysis

Speciation of Cr(III) and Cr(VI) can be attained by flow injection analysis with amperometric detection. Cr(VI) is reduced in an acidic medium to Cr(III) with a glassy carbon electrode at —0.1 V vs. Ag/AgCl and the current is recorded. Cr(III) is oxidised on-line to Cr(VI) with alkaline hydrogen peroxide solution. From the difference of the total chromium and Cr(VI), the amount of Cr(III) was obtained. A linear calibration curve for Cr(VI) was obtained for the concentration ranges 0.01-5.0ppm of Cr(VI) and we have calculated the limit of determination to be about 0.5ppb. We have studied the degree of reproducibility obtained using the solid electrodes under various conditions. The influence of flow rate, coil length, interfenences and the extent of reaction were studied.     

可再生甲壳素吸附铬（Ⅵ）的特性研究

可再生甲壳素吸附铬（Ⅵ）的特性研究陈炳稔＊汤又文李国明万春华（华南师范大学化学系广州５１０６３１）关键词可再生甲壳素，制备，铬（Ⅵ），吸附１９９７－０８－１９收稿，１９９７－１２－２３修回广东省科委及高教厅资助课题利用甲壳素作为铬（Ⅵ）的捕集剂已有报...