Packed bed electrodes. I. The electrochemical extraction of copper ions from dilute aqueous solutions

A study has been made of the cathodic deposition of copper ions from flowing dilute aqueous solutions onto a packed bed of graphite. The electrodeposition reaction is mass transfer controlled and expressions are presented for the cathodic current as a function of time, solution flow rate and bed characteristics. These have been verified from potentiostatic experiments. The cathode current efficiency is shown to approach 100% and packed bed electrodes are shown to be an effective means of extracting or removing metal ions from dilute solutions.     

The removal of radioactive caesium contaminants from simple aqueous solutions

Cs ions can be removed from aqueous solutions by forming a precipitate of copper ferrocyanide which, having occluded the Cs ions, can in turn be floated by means of an anionic collector. Collection was achieved with either α-sulphopalmitic acid or sodium dodecyl sulphate depending on what interfering ions were initially present in the solution. Recoveries of 98–99% were obtained on batch scale experiments and 97.5–98.5% on continuous scale operation. The investigations of the flotation parameters of pH, gas-rate, concentrations of precipitating reagents and collector, as well as the interference effects of other ions are discussed. Using data obtained in batch scale tests, continuous scale experiments were designed and operated.     

电化学界面处离子分布、静电势和ξ势的研究

Density functional theory is applied to predicting the structures and electrostatic potentials of planar electrochemical surfaces within the framework of the restricted primitive model where small ions are represented by charged hard spheres of equal diameter and the solvent is assumed to be a continuous dielectric medium. The hard-sphere contribution to the excess Helmholtz energy functional is evaluated using the modified fundamentalmeasure theory and the electrostatic contribution is obtained from the quadratic functional Taylor expansion using the second-order direct correlation function from the mean-spherical approximation. Numerical results for the ionic density profiles and the mean electrostatic potentials near a planar surface of various charge densities are in excellent agreement with molecular simulations. In contrast to the modified Gouy-Chapman theory, the present density functional theory correctly predicts the second layer formation and charge inversion of charged surfaces as observed in simulations and in experiments. The theory has also been tested with the zeta potentials of positively charged polystyrene particles in aqueous solutions of KBr. Good agreement is achieved between the calculated and experimental results.     

电化学界面处离子分布、静电势和ζ势的研究

Density functional theory is applied to predicting the structures and electrostatic potentials of planar electrochemical surfaces within the framework of the restricted primitive model where small ions are represented by charged hard spheres of equal diameter and the solvent is assumed to be a continuous dielectric medium. The hard-sphere contribution to the excess Helmholtz energy functional is evaluated using the modified fundamental-measure theory and the electrostatic contribution is obtained from the quadratic functional Taylor expansion using the second-order direct correlation function from the mean-spherical approximation. Numerical results for the ionic density profiles and the mean electrostatic potentials near a planar surface of various charge densities are in excellent     

Elucidation of the ion binding mechanism in heterogeneous carbon-composite adsorbents

A two-stage analysis of the mechanism of metal ion binding by a heterogeneous adsorbent was developed. In the first stage, a continuous proton affinity distribution was calculated from potentiometric titration data using the CONTIN method with a Langmuir kernel. Electrostatic effects were accounted for using a diffuse layer model. In the second stage, the parameters obtained from the continuous distribution function (i.e. the number of different types of surface sites, site densities and their protonation constants) were utilized in a discrete distribution to represent the adsorbent in surface complexation and double layer models using the GRFIT speciation code. This information on the surface groups was applied to metal ion potentiometric titration experiments to calculate the surface complexation equilibrium constants of the metal ions and hence elucidate the mechanism of ion binding to these sites. The proposed method was applied successfully to the adsorption of Sr and Cu ions on carbon-composite adsorbents, KAU-mod and SCN-mod. The continuous distribution method (CONTIN) revealed three types of surface sites within these carbon-composite adsorbents with pK values ranging between 3.5–4.1, 5.3–6.3 and 7.7–8.2. The analysis of the metal ion adsorption data using the GRFIT speciation code showed that only the first two surface sites were capable of forming surface complexes with the Sr ions, and that only the first site governed the adsorption of the Cu ions.     

Bipolar Membranes Made of a Single Polyolephine Sheet

The preparation of bipolar membranes from a single sheet of polyolephine by sulphochlorination is described in detail. Rectification experiments between salt solutions and between HCl and NaOH solutions respectively are described. The transference of salt ions relative to each other and relative to the ions of water have been determined. Some analytical data on the concentration of mobile ions in the membranes during current transport are given. The mechanism of rectification is explained and used to clarify the experimental results. Problems concerning conduction in bipolar membranes are enumerated and some experiments are proposed which may assist in solving them.     

Adsorptions of Some Heavy Metal Ions in Aqueous Solutions by Acrylamide/Maleic Acid Hydrogels

Abstract

In this study, acrylamide—maleic acid (AAm/MA) hydrogels in the form of rod have been prepared by γ-radiation. They have been used for adsorption of some heavy metal ions such as uranium, iron, and copper. For the hydrogel containing 40 mg of maleic acid and irradiated at 3.73 kGy, maximum and minimum swellings in the aqueous solutions of the heavy metal ions have been observed with water (1480%) and the aqueous solution of iron(III) nitrate (410%), respectively. Diffusions of water and heavy metal ions onto hydrogels have been found to be of the non-Fickian type of diffusion. In experiments of uranyl ions adsorption, Type II adsorption has been found. One gram of AAm/MA hydrogels sorbed 14–86 mg uranyl ions from solutions of uranyl acetate, 14–90 mg uranyl ions from solutions of uranyl nitrate, 16–39 mg iron ions from solutions of iron(IV) nitrate, and 28–81 mg copper ions from solutions of copper acetate, while acrylamide hydrogel did not sorb any heavy metals ions.     

Cation Exchange Equilibria with Chromium (III) Species by Strong Acid Ion Exchangers

The exchange of hydrogen ions for trivalent chromium species with strongly acidic exchange resins has been investigated. The experiments comprised of systems with chromium chloride and basic chromium sulphate which are applied in leather tanning. Exchange equilibria at ambient temperature were investigated as a function of pH and total chromium concentration. Exchange strongly depends on the speciation in each system. As can be expected, with chromium chloride solutions a strong preference of chromium species occurs. However, a complete pattern is found for systems with basic chromium sulphate where chromium species are not fully preferred.     

Biodegradation of phenol in the presence of heavy metals

A microbial growth model was presented for estimating the dynamic behavior of cell growth and substrate consumption in the biodegradation of phenol containing a heavy metal, such as zinc or copper ions. The application of the model for experiments in a batch culture and a continuous culture was examined. The values calculated according to the model corresponded satisfactorily with experimental data, such as the optical density of cells and the concentration of phenol. Using the model, the stability of steady states in a continuous culture was analytically evaluated based on the eigenvalues. The steady states were separated into three categories: (i) a stable steady state where phenol was consumed, (ii) an unstable steady state where phenol was consumed, and (iii) a washout state where phenol was not consumed. The number, kind, and stability of steady states varied significantly with operational conditions such as dilution rate, feed concentration of phenol, and feed concentration of heavy metal ions. The operational conditions required to obtain the stable steady state where phenol was consumed are shown graphically. © 2000 Society of Chemical Industry     

Separation of Radionuclides from Liquid Waste Using a Mineral Mixture

Abstract

The use of a naturally available mineral mixture (MM) for decontamination of low-level radioactive liquid waste has been investigated. Adsorption of ¹³⁷Cs and ⁹⁰Sr radionuclides on MM from aqueous solutions is reported by describing the effect of equilibration time, hydrogen ions, and adsorbent and adsorbate concentrations. Optimum physicochemical conditions have been identified. The data suggest the effective use of MM for on-line isolation of the radionuclides from the effluent of a nuclear industry/laboratory and subsequent storing for a long time in reduced solid form.     

Transient response of three-phase slurry reactors

Analytical time domain solutions are provided for the transient response of three-phase slurry reactors, with diffusion and first-order irreversible ch input of the reactant in the inlet gas stream; and (b) when the catalyst particles are suddenly introduced into the reactor which has otherwise reached obtained for the general case of continuous slurry reactors but can be easily reduced for application to semi-batch slurry reactors in which there is n and are expected to be useful for evaluating the rate and equilibrium constants from dynamic response experiments.Asymptotic solutions have also been obtained for the case of large Thiele parameter (φ ≥ 3) and some other simpler expressions have been derived as only for gaseous reactants of moderate or high solubility in the liquid phase and are not applicable to those with low solubility.     

嗜酸氧化亚铁硫杆菌在沥青铀矿石浸出中的作用

为了研究沥青铀矿石的细菌浸出机理,设计了有菌有铁、有菌无铁及无菌无铁3种矿粉浸出试验及有菌无铁、无菌无铁两种试块浸出试验,检测了矿粉浸出体系中细菌的浓度、pH值、Eh、亚铁离子浓度、总铁离子浓度及铀浓度的变化,分析了浸出尾渣中O、Mg、K、P、S、Fe、U等元素的含量,观测了浸出前后试块表面形貌的变化。结果表明,在沥青铀矿石浸出过程中,嗜酸氧化亚铁硫杆菌可以高效氧化浸出体系中的亚铁、还原态硫及元素硫,使得浸出体系中的Eh升高和pH值降低;有菌有铁浸出体系中,高浓度的细菌、高浓度的铁、低pH值和高Eh可加速铀矿石的浸出和提高铀矿石的浸出率;有菌无铁浸出体系中,即使总铁离子浓度很低,但由于有细菌的存在,同样可以加速铀矿石的浸出和提高铀矿石的浸出率。有菌无铁的试块浸出中,试块表面出现了许多溶蚀坑,这表明细菌对铀矿石具有直接氧化作用。     

Study of ternary-component bismuth molybdate catalysts by 18O2 tracer in the oxidation of propylene to acrolein

Participation of lattice oxide ions of ternary-component bismuth molybdate catalysts MBiMo O (M = Ni, Co, Mg, Mn, Ca, Sr, Ba, and Pb) was investigated using the ¹⁸O₂ tracer in the selective oxidation of propylene to acrolein. The participation of the lattice oxide ions in the oxidation is prominent on every catalyst but the extent of the participation varies significantly depending on the structure of the catalyst. Only lattice oxide ions in the bismuth molybdate phase are incorporated into the oxidized products on the catalysts (M = Ni, Co, Mg, and Mn) where M have smaller ionic radius than Bi³⁺; catalyst particles are composed of a shell of bismuth molybdates and a core of MMoO₄. On the other hand, whole oxide ions in the active particles are involved in the oxidation on catalysts having a scheelite-type structure (M = Ca, Sr, Ba, and Pb) where M has a comparable ionic radius to Bi³⁺.     

Dual-Temperature Ion-Exchange Separation of Copper and Zinc by Different Techniques

Abstract

Separation of copper from zinc-containing acidic solutions has been advanced by different techniques of dual-temperature ionexchange fractionation on iminodiacetic resin Amberlite IRC 718. Cycling-zone adsorption and parametric pumping (using single-column as well as double-column set-ups) experiments have been carried out in fixed-bed ion-exchange column. Measurement of equilibrium characteristics of the resin-solution system has shown that separation results from the variation of the ions sorbability with temperature. It has been found that temperature variation leads to reverse of selectivity between copper and hydrogen ions. Cycling-zone adsorption technique has allowed the copper content to be decreased up to 4 times in the resin phase and increased up to 1.7 times in the effluent when carrying out the process at 80 and 20 °C, respectively. The copper concentration has been decreased 4.4 fold after 9 treatment cycles of solution aliquot (15 BV) by single-column mode of the parametric pumping method. Two steps of the fractionation process (loading and elution) have been performed by continuous mode of operation in two counter-current columns. Continuous separation is preferred over fixed-bed column techniques. The steady-state sorption fronts have been formed on both stages of the process due to the reverse of selectivity mentioned above.     

Electroextraction of Pb ions from diluted solutions by a process combining ion-exchange textiles and membranes

The extraction of Pb²⁺ ions from diluted solutions was achieved using a hybrid process combining cation exchange textiles, ion-exchange membranes and electric current. Two methods were investigated: an electroextraction process in two steps where the fixation of Pb²⁺ ions was followed by electroregeneration of the cation-exchange textiles; the second one a continuous electroextraction process where the ion exchange and regeneration take place simultaneously. For these electroextraction processes, the cation-exchange textile is introduced into an electrodialysis cell and compressed between two cation-exchange membranes. Under an applied current, the Pb²⁺ ions are substituted by regenerating ions coming from the anodic compartment and are transferred into a receiver compartment at the cathodic side where they are concentrated. Cation-exchange textiles having strong or weak acid functional groups, sulfonic (SCET) and carboxylic (CCET), respectively, were used. Different regenerating ions, H⁺, Na⁺, K⁺ and NH₄⁺ were investigated under various current densities. Electroregeneration ratios between 85% and 100% were obtained with sulfonic and carboxylic textiles previously loaded with Pb²⁺ ions. In the continuous electroextraction, removal efficiencies higher than 95% were obtained with a 10 ppm Pb²⁺ feed solution giving an outlet concentration of less than 1 ppm. The efficiency of the two textiles was compared in terms of mass transfer and energy consumption.     

Effects of A1/A2‐Sites Occupancy upon Ferroelectric Transition in (SrxBa1−x)Nb2O6 Tungsten Bronze Ceramics

The dielectric and ferroelectric characteristics of (Sr_xBa_1?x)Nb₂O₆ unfilled tungsten bronze ceramics have been investigated together with the structure. The dielectric and ferroelectric characteristics of the present ceramics vary significantly with x, and the A1/A2‐sites occupancy has been determined as the primary parameter governing this variation tendency. Ba ions tend to occupy A2‐sites, Sr ions tend to occupy A1‐sites, and one A1‐site is empty. When the ratio of Sr/Ba is close to 1:4 (where four A2‐sites are just occupied by Ba ions, and one A1‐site is occupied by Sr ion while another A1‐site is empty), the normal ferroelectric transition is observed with one anomaly in the tanδ–T curve (x = 0.25). When the ratio of Sr/Ba is far away from 1:4, the typical relaxor behavior is indicated together with three anomalies in the tanδ–T curve (x = 0.75). The incommensurate oxygen octahedral tilting and A‐site random distribution are considered to be the structure origins for the relaxor ferroelectricity and low temperature dielectric relaxations.     

EXTRACTION KINETICS OF COPPER BY TRILAURYLAMMONIUM CHLORIDE IN TOLUENE FROM AQUEOUS CHLORIDE MEDIA

Abstract

The rate of extraction of copper(II) from aqueous chloride solutions by tri-n-laurylammonium chloride (TLAHC1) dissolved in toluene has been investigated. The extraction rate was evaluated as function of the chemical composition of the system. The experiments were performed by using a stirred cell with constant inter-facial area. The experiments were performed at a stirring rate of the two phases where the influence of film diffusion is minimized. The data have been interpreted by a mechanism which assumes interfacial chemical reactions between the bulk species containing copper(II) and the molecules of TLAHC1 absorbed at the interface as rate determining.     

Influence of the operating conditions on the electrochemical disinfection process of natural waters at BDD electrodes

Results are reported of an investigation of the oxidation products formed during electrolyses of aqueous solutions of NaCl, in which the initial concentration of chloride ions was maintained at levels normally present in natural waters. The Design of Experiments (DOE) technique has been used effectively to plan a framework of experiments, in which the main operative parameters: current density, electrolyte stirring rate, and cell geometry, were varied at two levels. Their effects, as well as their possible interactions have been evaluated on the yield of chloride oxidation and on the selectivity of the reaction towards the formation of hypochlorite.     

Strontium Separation with Ultrafiltration Membranes from Dilute Aqueous Solutions

Abstract

The separation of Sr²⁺ from dilute and trace solutions of low activity by means of hollow fiber Amicon ultrafiltration membranes is studied. The cation is absorbed on colloidal particles of titanium oxide formed directly in solution, and the colloidal dispersion is filtrated. The method has been studied under several different operative conditions (pH, Ti/Sr ratio, the presence of interfering ions, colloid formation time) with the aim of determining the optimum conditions to develop a separation process.     

Industrial wastewater desalination using electrodialysis: evaluation and plant design

Industrial processes usually generate streams enriched with high organic and inorganic components. Due to the complexity of these streams sometimes it is not quite straightforward to predict the performance of desalination technologies. Some technologies are available for the selective removal of salts from aqueous stream, but in general these technologies are applied in high value applications where salts are either the product or limit further purification of the final product is required. These technologies are, however, not widely used in low value applications like wastewater treatment. The aim of this article is to review, improve and perform the design of electrodialysis processes for relevant industrial wastewater applications. It is focused on the determination of the critical design parameters like membrane resistance, current efficiency and limiting current density through lab scale experiments and its further use for industrial scale first approximation design. In this article, the basic equations for design are reviewed and a practical approach to obtain the number of stacks required for a certain separation is introduced. An industrial wastewater stream has been used for lab batch experiment and its following continuous plant design. The results show that it is possible to separate monovalent ions in a high rate (more than 70 %) and divalent ions were less separated (less than 50 %). The energy required for the particular case was evaluated in a range from 6 to 11 kWh/m³ of feed stream depending on the water reclamation rate.