Transport of chromium through cation-exchange membranesby Donnan dialysis in the presence of some metals of different valences

The transport of a trivalent chromium ion through charged polysulfonated cation-exchange membranes in the presence of metals of different valences under Donnan dialysis conditions was studied as a function of pH gradient at 25°C. The recovery factor (RF) values of chromium ion were obtained, and it was found that the RIF values decreased with the increasing of the metal valence. The transport of chromium ions through membranes was correlated with the flux data, which depended on the metal valences as well as the structure of the membrane. It was observed that the transport was influenced with H⁺ ion concentration in the receiver phase.     

The removal of sodium,cadmium and chromium ions from dilute aqueous solutions using foam fractionation

Cationic metallic ions such as sodium, cadmium and chromium were flotated from aqueous solution by using foam separation or foam fractionation technique in a continuous flow system. Experimental results showed a considerable difference between mono- or divalent and trivalent metallic ions in their affinity to neutralize the negatively charged surface layer formed at the gas-liquid interface. This was verified by use of the Gouy-Chapman diffuse double-layer theory, except for the case of high concentration of the co-existing collector which formed miscellaneous metal-collector complexes.     

Kinetics and mechanism of chromium electrodeposition from formate and oxalate solutions of Cr(III) compounds

Kinetics of multistep reaction of Cr(III) ions discharge to metal was studied on a stationary electrode and on a rotating disk electrode from the solutions containing formic acid or oxalic acid. The electroreduction of Cr(III) complex ions in aqueous solutions is shown to proceed via the formation of relatively stable intermediates—Cr(II) compounds which are partially removed into bulk solution. The effect of pH, organic ligand concentration and disk rotation velocity on the partial current density of chromium electroplating was demonstrated. The kinetic equations of the studied process were derived and compared with the experimental data. Kinetic parameters for the discharge of Cr(II) ions were calculated. The mechanism of chromium electrodeposition reaction was proposed. The electrodeposition of chromium from formate bath is suggested to proceed with the participation of hydroxocomplexes of bivalent chromium. The oxalate complexes of bivalent chromium directly discharge in the electrolytes containing oxalic acid. The partial polarization curves of chromium electrodeposition exhibit a current peak which may be caused by blocking the electrode surface with poorly soluble Cr(III) hydroxide.     

Removal of Cr(VI) from Aqueous Solution: Electrocoagulation vs Chemical Coagulation

Abstract

Hydrolyzed products of Al(III) have affinity below pH_zpc for oppositely charged mono and bi‐nuclear species of hexavalent chromium. This study investigates the comparative performance of electrocoagulation (EC) and chemical coagulation (CC) for the removal of Cr(VI) from aqueous solution. The highest removal of Cr(VI) achieved with EC was about 42% with 4.36 mA/cm² current density. Cathodic adsorption of chromium boosted up Cr(VI) removal during EC. Simultaneous electro‐ and chemical‐dissolution lead to high current efficiency of about 178%. Both the pH and the coagulant dosage have a significant impact on Cr(VI) removal in the pH ranges from 4.9 to 7.0. CC with alum and aluminum sulfate (AS) removed about 11% and 12% of Cr(VI). Co‐adsorption of divalent SO₄ ^2? ions with Cr(VI) is responsible for the lower removal observed with chemical coagulants. About 0.061 and 0.099 mole of SO₄ ^2? was adsorbed per mole Al in the precipitate in the pH range 4.9 to 7.0 with AS and alum. A higher coagulant dosage increases the removal of Cr(VI) but adversely affects the removal efficiency (Cr(VI) removed per unit of Al dosing). Cell current density (CD) has shown little effect on Cr(VI) removal and the pH elevation at the same charge density. Higher initial Cr(VI) concentration improves the removal efficiency as the species of Cr(VI) is acidic in solution and decreases the pH elevation rate.     

Preparation and characterization of P2FAn/PVDF composite cation-exchange membranes for the removal of Cr(III) and Cu(II) by Donnan dialysis

In this work, poly(2-fluoroaniline) (P2FAn) was chemically synthesized with different dopant anions such as p-toluenesulfonate (PTS), 1,3 (6 or 7)-naphthalene trisulfonic acid (NSA), o-aminobenzen sulfonic acid (ABS), sodium dodecyl sulfate (SDS). The P2FAn/PVDF composite cation-exchange membranes were obtained from prepared poly(2-fluoroaniline) by casting method. These membranes were used for the removal of chromium (III) and copper (II) ions from aqueous solution with Donnan dialysis (DD) experiments. The change of surface morphologies of the P2FAn/PVDF composite cation-exchange membranes were investigated by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The membrane thickness and their ion-exchange capacities were also measured. The flux values (J) and recovery factor (RF) of chromium (III) and copper (II) were obtained. The flux value of Cu(II) ion was higher than Cr(III) for all of composite membranes because of the hydration volume.     

电解制备焦磷酸锰（Ⅲ）盐工艺条件及动力学研究

首次采取二极室在焦磷酸介质中电解制备可溶性三价锰盐。分别研究了电流密度、焦磷酸浓度、电解温度等因素对电极反应制备可溶性三价锰盐浓度和电流效率的影响。通过单因素条件实验进行了工艺参数的优化,对工艺的影响因素进行了具体的解释分析,并对焦磷酸介质下锰（Ⅲ）/锰（Ⅱ）在石墨电极上的动力学参数进行了计算。最佳工艺条件:电解时间为5 h左右,电流密度为10.87 mA/cm²,电解温度为0 ℃,电解液为0.3 mol/L磷酸二氢锰+3 mol/L焦磷酸。在最佳工艺条件下电解制备可溶性三价锰的浓度最高,而且电流效率也较高。通过电化学测试的参数进行动力学计算,锰（Ⅲ）/锰（Ⅱ）在0.3 mol/L磷酸二氢锰+3 mol/L焦磷酸电解液中为准可逆过程,过程的条件电极电位为1.315 V vs.NHE,二价锰离子在这个体系中的扩散系数为8.347×10^-6 cm²/s。     

电沉积纳米晶镍-铁-铬合金

采用直流和脉冲电沉积方式从三价铬的氯化物镀液中沉积出镍-铁-铬纳米合金镀层，利用扫描电镜分析镀层形貌及晶粒尺寸，研究了沉积速率，电流效率，三价铬浓度及pH值随沉积时间的变化关系，结果表明，脉冲电沉积所得镀层的结构和性能均优于直流电沉积，这是由于脉冲电沉积存在断电时间，使得电极表面扩散层中金属离子的浓度得到及时恢复。     

Development of thin‐film composite membranes for carbon dioxide and methane separation using sulfonated poly(phenylene oxide)

Novel membranes based on sulfonated poly (phenylene oxide) (SPPO) was developed. SPPO membranes in the hydrogen form were converted to metal ion forms. The effect of exchange with metal ions including monovalent (Li⁺, Na⁺, K⁺), divalent (Mg²⁺, Ba²⁺, Ca²⁺) and trivalent (Al³⁺) ions was investigated in terms of permeation rate and permeation rate ratios for CO₂ and CH₄ gases. Both dense homogeneous membranes and thin‐film composite (TFC) membranes were studied for their gas separation characteristics. The effect of membrane preparation conditions and operating parameters on the membrane performance were also investigated. The selectivity of the TFC membrane increased as the cationic charge density increased as a result of electrostatic cross‐linking. TFC membrane of very high selectivity was achieved by coating a thin layer of SPPO‐Mg on a PES substrate. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 735–742, 2000     

Modification of poly(vinyl chloride) films by aliphatic amines to prepare anion-exchange membranes for Cr (VI) removal

ABSTRACT

A method for the synthesis of anion-exchange membranes by the grafting of ethylenediamine (EDA), diethylenetriamine (DETA) or pentaethylenehexamine (PEHA) onto poly(vinyl chloride) (PVC) film has been presented. The chemical structure was determined by means of Fourier Transform Infrared Spectroscopy (FTIR) and the membranes were characterized by ion-exchange capacity, chloride and nitrogen contents, water regain and surface energetics. The obtained membranes were evaluated in the Donnan dialysis (DD) of hexavalent chromium solutions. Among the membranes, those modified with EDA and DETA showed the best separation features: high flux and high recovery factor (RF). The highest degree of recovery was observed for membranes prepared by the casting of PVC solution in (THF), followed by grafting EDA.     

Separation of Cr(VI) from Water by Green Reduction Reaction and Adsorptive Removal on Gelatin-Grafted-Yeast Biosorbent

A green chemical method was explored and described for separation and extraction of the toxic hexavalent chromium from aqueous solutions and real water samples. A green reduction reaction for the transformation of toxic hexavalent chromium into the nontoxic trivalent chromium ion was performed by using hydrogen peroxide. The produced Cr(III) was then extracted by biosorption on the surface of a novel and eco-friendly gelatin-grafted-baker’s yeast (Gelatin-Yeast) biosorbent. The investigated biosorbent was characterized by high capacity value of the reduced trivalent chromium species in pH 6.0 as 1.120 mmol g^?1. The biosorption processes were examined, monitored, and optimized in different experimental and controlling parameters. The potential applications of Gelatin-Yeast for separation and removal of Cr(VI) from real industrial and sea water samples were also studied.     

Re‐use of Exhausted Ground Coffee Waste for Cr(VI) Sorption

Abstract

Exhausted ground coffee waste has been investigated as metal biosorbent for Cr(VI) from aqueous solution. Maximum metal sorption was found to occur at initial pH 3.0. Kinetic studies revealed that the initial uptake was quite rapid; nevertheless, it took five days to reach equilibrium. The value of the Langmuir maximum uptake was found to be 10.2 mg Cr(VI)/g waste. The sorbent is able to reduce hexavalent chromium to its trivalent form. A solution of 1 M NaOH was the most effective desorption agent and after 24 hours contact 42% of total chromium was desorbed in both hexavalent and trivalent oxidation states.     

Microstructure and electrochemical characterization of trivalent chromium based conversion coating on zinc

A trivalent chromium based conversion coating (CCC), based on chromium nitrate solution with Co(II) ions, was developed on Zn substrate. The corrosion resistance of the trivalent CCC, measured in deaerated pH 8.0 borate buffer + 0.01 M NaCl solution using anodic polarization and electrochemical impedance spectroscopy (EIS), was very sensitive to both immersion time and bath pH. Micro-cracks were found on the surface of the CCC. Besides, the density of micro-crack and the coating thickness also depended on immersion time and bath pH. With increasing the coating thickness its pitting potential increased and passive current density decreased. The trivalent CCC formed on Zn for 40 s in pH 1.7 bath showed the best corrosion resistance, and the pitting potential increased significantly from −355 mV_SCE for Zn to 975 mV_SCE for the trivalent CCC on Zn. To explain the corrosion behavior of the trivalent CCC using EIS analysis, a modified equivalent circuit, which considered the micro-cracks in the coating and chromium corrosion product (CCP) deposited in the micro-cracks, was designed and the variation of each electrical parameter was examined. Especially, its corrosion behavior was well described by the variation of the resistance of CCP (R_ccp).     

Electrokinetic Properties of Acid-Activated Montmorillonite Dispersions

In this study, the influence of pH, electrolyte concentration, and type of ionic species on the electrokinetic properties (zeta potential and electrokinetic charge density) of the acid-activated montmorillonite mineral have been investigated using the microelectrophoresis method. The electrokinetic properties of acid-activated montmorillonite dispersions have been determined in aqueous solutions of mono-, di-, and trivalent salts and divalent heavy metal salts. Zeta potential experiments have been performed to determine the point of zero charge (pzc) and potential determining ions (pdi). The zeta potential values of the acid-activated montmorillonite particles were negative and did not vary significantly within the pH range studied. Acid-activated montmorillonite dispersions do not have point of zero charge (pzc). The valence of the electrolytes has a great influence on the electrokinetic behavior of the suspension. A gradual decrease in the zeta potential (from ?25 mV to ?5 mV) occurs with the monovalent electrolytes when concentration increased. Divalent and heavy metal electrolytes have less negative z-potentials due to the higher valence of ions. A sign reversal of z-potential has been observed at AlCl₃, FeCl₃, and CrCl₃ electrolytes (potential determining ions) and zeta potential values have had a positive sign at high electrolyte concentrations.

The electrokinetic charge density of acid-activated montmorillonite has shown similar trends for variation in mono- and divalent electrolyte solutions. Up to concentrations of ca. 10^?3 M, it has remained practically constant at approximately 0.5 × 10^?3 C m^?2 For higher concentrations of monovalent electrolytes more negative values (?16 × 10^?3 C m^?2) were observed. It has less negative values in divalent electrolyte concentrations according to monovalent electrolytes (?5 × 10^?3 C m^?2). For low concentrations of trivalent electrolytes, the electrokinetic charge density of montmorillonite particles is constant, but at certain concentrations it rapidly increased and changed its sign to positive.     

黄原胶-丙烯酰胺接枝共聚物对Cr~(3+)的吸附性能

研究了黄原胶-丙烯酰胺接枝共聚物(XG-g-AM)对Cr3+的静态吸附行为,考察了pH(1.0~8.0)、吸附温度(298~318 K)、吸附时间(0~12 h)和Cr3+初始浓度(0.01~0.20 mol/L)等因素对XG-g-AM吸附Cr3+性能的影响。利用傅立叶变换红外光谱仪(FT-IR)和X射线衍射仪(XRD)对吸附产物进行了结构表征,探讨了吸附机理。在pH=6.0,Cr3+初始浓度为0.20 mol/L,常温吸附12 h的条件下,XG-g-AM对Cr3+的吸附量达205.40 mg/g。XG-g-AM对Cr3+吸附行为符合Freundlich吸附等温方程,XG-g-AM通过静电作用、配位吸附方式吸附Cr3+,吸附Cr3+破坏了XG-g-AM的结晶结构,使其结晶度下降。Cr3+以非结晶态形式在XG-g-AM上聚集存在。     

Cr(VI) transport through ceramic ion-exchange membranes for treatment of industrial wastewaters

This work is devoted to assessment of the possibility of using ceramic membranes, which contain an ion-exchange component, such as hydrated zirconium dioxide (HZD), for Cr(VI) removal from dilute solutions by electrodialysis. Transport properties of the membranes were investigated. HZD-containing membranes were found to be permeable to anions in acidic media while they demonstrate cation-exchange properties in alkaline media. Cr(VI) anion transport through HZD membranes was studied. It was shown that an increase in the amount of ion-exchanger in the membrane results in a rise in electrodialysis efficiency. The transport number of Cr(VI) species was found to range from 0.33 to 0.63 for currents below the limiting current. It was also shown that increasing the concentration of H⁺ or Cr(VI) ions in the solution to be purified allows higher rate of Cr(VI) ion transport through the membrane.     

Cr (VI) adsorption from aqueous solutions on grafted chitosan

Chitosan was grafted on the surface of a cotton gauze (20, 50, and 100 mg chitosan g⁻¹ cotton) to improve its stability in aqueous solutions. The adsorption of hexavalent chromium ions from water on the grafted chitosan was evaluated to determine, by means of linear and nonlinear models, the kinetic and isotherm adsorption of the process. The kinetics of pseudo second-order, pseudo first-order, and adsorption isotherms type II were obtained, that is, a monolayer adsorption on nonporous adsorbents with physical adsorption was present. The most probable energy of adsorption corresponded to a physisorption with hydrogen bond interactions between chromium ions and ammonium groups. Moreover, three different cross-sectional areas of hexavalent chromium ions were calculated and used to estimate the specific surface area employed by active sites to adsorb metal ions in terms of chitosan or cotton mass. Finally, the percentage of the area occupied by chromium ions on the surface was estimated by dividing the resulting specific surface area in terms of cotton mass by the specific surface area of cotton reported in literature. As a result, it was determined that the occupied area is between 6% (for 20 mg chitosan g⁻¹ cotton)-24% (for 100 mg chitosan g⁻¹ cotton) from the total area of cotton.     

三价铬镀铬资讯

Cr(Ⅵ)对环境和人体健康有严重的危害,因此,促进了三价铬镀铬研究的发展.三价铬镀铬与Cr(Ⅵ)镀铬相比,具有很多优点.但是,三价铬镀铬要广泛应用,仍需要解决一些问题如镀液成分复杂、工艺难以维护和控制、阳极选择困难、镀层难以增厚及镀层色泽不够理想等.简要回顾了三价铬镀铬的发展历程,介绍了目前三价铬镀铬存在的问题,并着重论述了解决问题的途径和未来的发展方向.     

Substitution Model of Monovalent (Li, Na, and K), Divalent (Mg), and Trivalent (Al) Metal Ions for β-Tricalcium Phosphate

The maximum substitution of monovalent, divalent, and trivalent metal ions for β-tricalcium phosphate (β-TCP) was investigated, and a substitution model of these metal ions for β-TCP was proposed. Monovalent metal ions (M^I) could replace Ca(4) site and vacancy ( V _Ca(4)) in β-TCP as 2M^I=Ca²⁺+ V _Ca(4) and the maximum substitution was about 9.1 mol%. In the case of divalent metal ions (M^II), Ca(4) and Ca(5) sites were replaced by divalent metal ions as M^II=Ca²⁺, and the maximum substitution was about 13.6 mol%. Trivalent metal ions (M^III) could be substituted for Ca(4) site and vacancy as 3M^III=2Ca²⁺+ V _Ca(4), and the maximum substitution was about 9.1 mol%.     

硫酸盐体系三价铬镀铬工艺及镀层性能的研究

采用硫酸盐体系进行三价铬镀铬,获得了光亮银白色镀层。分别研究了镀液的pH值、镀液温度、电流密度、热处理温度等对镀层硬度的影响;分别用X射线衍射法、扫描电镜法等研究了镀层的性质。当溶液的pH值为2.4,镀液温度为45℃,电流密度为45 A/dm2时,镀层的硬度和摩擦系数分别为7 740 MPa和0.816。镀层分别在25℃,200℃,250℃,300℃和350℃下进行热处理,镀层的硬度分别为7 740 MPa,8 750 MPa,9 010 MPa,9 250 MPa,9 450 MPa,镀层的硬度增加的原因可能是镀层由非晶态向晶态转化所致。     

Polypropylene membranes modified with interpenetrating polymer networks for the removal of chromium ions

Polypropylene (PP) membranes incorporating poly[(ar‐vinylbenzyl) trimethylammonium chloride] P(ClVBTA), and poly[sodium (styrene sulfonate)] P(SSNa) were modified via an “in situ” radical polymerization synthesis. Two methods were used for impregnation of the reactive solution: pressure injection and plasma superficial activation with argon gas. The following conditions were varied: the monomer concentrations, number of injections, and cross‐linked concentration. The modified polypropylene membranes were then characterized using scanning electron microscopy/energy dispersive X‐ray spectroscopy, Fourier transform‐infrared spectroscopy, electrokinetic potential, and Donnan dialysis for the chromium ions transport. The modified membranes exhibited a hydrophilic character with a water uptake capacity between 15% and 20% and a percent modification between 2.5% and 4.0%. This was compared with the results of an unmodified polypropylene membrane as the blank and the mentioned polypropylene membrane has not the capacity to uptake water because this kind of material is highly hydrophobic. Hexavalent chromium ions were efficiently transported by the modified membranes containing P(ClVBTA) via a plasma method and it achieved 59.2% extraction at pH 9.0 using a 1‐mol L^?1 NaCl extraction agent. Therefore, unmodified polypropylene membrane shows an extraction percentage close to 10% from the hexavalent chromium ions at pH 9.0. In the same way, the trivalent chromium transport using membranes modified with P(SSNa) achieved 49.0% extraction at pH 2.0 using 1 × 10^?1 mol L^?1 HNO₃ and 1 mol L^?1 NaCl as the extraction agents. Moreover, the unmodified polypropylene membrane reached a value close to 10% from the trivalent chromium ions using 1 × 10^?1 mol L^?1 HNO₃ and 1 mol L^?1 NaCl. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41953.