Removal of cadmium from dilute aqueous solutions with a rotating cylinder electrode of expanded metal

The removal of cadmium from dilute solutions using a continuous undivided electrochemical reactor with a rotating cylinder cathode of expanded metal is analysed. The effects of cathodic applied potential, size and orientation of expanded metal meshes and inlet cadmium concentration were ascertained. The results show that cadmium can be removed from dilute solutions (inlet concentration range 5–50 mg dm⁻³) with a high fractional conversion of between 35 and 40% depending on the operating conditions. Thus a minimal residual cadmium concentration of 3 mg dm⁻³ was achieved. The specific energy consumption increases from 0.6 to 2 kWh mol⁻¹ as the cadmium concentration decreases. Copyright © 2003 Society of Chemical Industry     

Electrochemical removal of cadmium using a batch undivided reactor with a rotating cylinder electrode

The performance of an undivided electrochemical batch reactor with a rotating cylinder electrode under potentiostatic control is examined for the removal of cadmium from a sodium sulfate solution containing 500 ppm Cd(II) at pH ? 7. The effect of hydrogen evolution as a side cathodic reaction on the figures of merit of the reactor is analysed. The best results were obtained for a cathode potential of ?0.9 V against the saturated calomel electrode. With an angular velocity of 1500 rpm the space time yield and the normalized space velocity were 0.66 mol m^?3 s^?1 and 3.9 h^?1 respectively, while the fractional conversion was 67.3% with a current efficiency of 66.7%. The surface morphology of the deposits as a function of the applied potential is also reported. © 2001 Society of Chemical Industry     

Removal of cadmium and production of cadmium powder using a continuous undivided electrochemical reactor with a rotating cylinder electrode

The behaviour of a continuous undivided electrochemical reactor with a rotating cylinder electrode under potentiostatic control is examined for the abatement of cadmium from synthetic sodium sulfate solutions with Cd(II) concentrations lower than 500 mg dm^?3 at a reactor inlet pH ? 7. The process was designed to convert the metal ions in solution to metal powder, which settles to the conical of the reactor and may be removed at intervals as a sludge by opening a drop valve. The effect of applied potential, inlet cadmium concentration, rotation speed and hydrogen evolution as side cathodic reaction on the ‘figures of merit’ of the reactor are analysed. The best results were obtained for cathode potentials in the range from ?0.9 V to ?1.0 V against the saturated calomel electrode. Therefore, when the rotation speed was 1000 rpm the space time yield and the normalized space velocity were 0.64 ×10^?2 mol m^?3 s^?1 and 0.89 h^?1 respectively, while the fractional conversion per pass was 35% with a current efficiency higher than 74%. The surface morphology of the deposits as a function of the process variables is also reported. © 2002 Society of Chemical Industry     

Effect of particles on Polarization during Electrocodeposition using a Rotating Cylinder Electrode

The influence of suspended submicrometric diameter alumina particles on polarization during electrocodeposition with copper at a rotating cylinder electrode was investigated. Cathodic polarization and mass transfer experiments were conducted as a function of electrode rotational speed and particle loading.     

Electrochemical removal of cadmium from dilute aqueous solutions using a rotating cylinder electrode of wedge wire screens

Rates of mass transfer at rotating cylinder electrodes of wedge wire screens were studied by measuring the limiting current for the cathodic reduction of ferricyanide as test reaction. The experimental data are well correlated by an empirical expression between the Sherwood number and the Reynolds number, both in terms of the internal slot opening as characteristic length, and including two additional dimensionless parameters in order to characterize the geometry of the screens. The performance of an undivided electrochemical batch reactor with a rotating cylinder cathode of wedge wire screens was tested analyzing the cadmium removal from dilute solutions. The effect of cathodic applied potential and size of the screen is studied. Taking into account the residual cadmium concentration the best results were obtained for a cathode potential of −1.1 V vs. SCE at 700 rpm, where the cadmium concentration decreased from 54 to 0.9 mg l⁻¹ after 30 min of electrolysis with a specific energy consumption of 10.7 kWh kg⁻¹ and a normalized space velocity of 3.54 h⁻¹.     

Mass transfer studies at rotating cylinder electrodes of expanded metal

Mass transfer has been studied at rotating cylinder electrodes of expanded metal using the reduction of ferricyanide as test reaction. The experimental data are well correlated by an empirical expression between the Sherwood number and the Reynolds number, both in terms of the hydraulic diameter as characteristic length, and including two additional dimensionless parameters in order to characterize the geometry of the expanded metal. Comparisons of the mass-transfer performance of the expanded metal electrodes with other three-dimensional structures are made.     

Electro-Oxidation of Carbonate in Aqueous Solution on a Platinum Rotating Ring Disk Electrode

The kinetics of electro-oxidation of carbonate aqueous solution on a platinum electrode were examined by a rotating ring (platinum) – disk (platinum) electrode in aqueous sodium carbonate/bicarbonate solutions (25 °C, pH = 10.75) with the peroxide stabilizing additives sodium silicate, magnesium sulphate and sodium DTPA such as are used in brightening mechanical wood pulp. A theoretical model based on the experimental data is proposed to describe this electro-oxidation process. The model shows consistency between the experimental results and the expectation from the proposed reaction sequence. The first-order rate constants at 25 °C, pH = 10.75 in 1.13 M (Na₂CO₃ + NaHCO₃) for carbonate electro-oxidation to percarbonate (a.k.a. peroxidicarbonate C₂O₆^2-), percarbonate hydrolysis to hydrogen peroxide and hydrogen peroxide electro-oxidation to oxygen are estimated from the experimental data, respectively, as (1.43±0.1) × 10⁻¹¹cm s⁻¹ (extrapolated to the equilibrium electrode potential which is estimated as ca. 0.21 (vs SCE)), (1.1 ± 0.2) × 10⁻² s⁻¹ and (5.6±0.5) × 10⁻⁸cm s⁻¹ (extrapolated to the equilibrium electrode potential of −0.019 V (vs SCE)).     

Removal of Cu2+ Ions from Aqueous Solutions by Starch-Graft-Acrylic Acid Hydrogels

Gelatinized starch was prepared by constantly stirring a mixture of starch and water at 95°C for 1 hour. Starch-graft-acrylic acid (S-g-AA) hydrogels were prepared by grafting acrylic acid (AA) [monomer/starch (w/w) 0.5–1.5] onto gelatinized starch with ceric ammonium nitrate as initiator under nitrogen atmosphere. The surface morphology of samples was studied using a scanning electron microscope (SEM). The hydrogels were evaluated for the removal of Cu²⁺ ion from aqueous solutions at different pH. The concentration of Cu²⁺ ion in aqueous solution was kept constant at 4 mmol/L. The metal ion removal capacities changed depending on treatment time, initial pH of the solution, and monomer/starch (w/w) ratio of the S-g-AA hydrogels. Cu²⁺ ion removal capacities were determined by atomic absorption spectrometer (AAS).     

Study of mass transfer in a vertically moving particle bed electrode

A study was made of the influence of process parameters on the mass-transfer coefficient in a flow-through cell with a cascade of rotating drums partially filled with conductive particles (called the vertically moving particle bed). Copper deposition from an acidic sodium sulphate solution was used as the model reaction. To evaluate the experimental data a macrohomogeneous mathematical model of potential and current density distribution inside the cell was developed. The electrolyte flow distribution between the empty space above the particle bed and through the bed was evaluated. On the basis of these results the following correlation is proposed:

Ion-Exchange Characteristics of a Layered Metal Sulfide for Removal of Sr2+ from Aqueous Solutions

Strontium-90 (⁹⁰Sr) is the most abundant radionuclide in radioactive wastes, and is typically isolated by treatment with an inorganic ion-exchange material. Most inorganic ion-exchange materials contain oxygen. The ion-exchange chemistry of layered metal sulfides is relatively poorly explored compared with that of oxide ion-exchange materials. Here, a layered metal sulfide (UCR-28), constructed from [ZnGe₃S₉(H₂O)]^4? supertetrahedral clusters, was prepared under hydrothermal conditions and used for the removal of Sr²⁺ ions from aqueous solution. Batch experiments showed that UCR-28 had affinity for Sr²⁺ ions at pH values ranging from 1 to 10 and the maximum ion-exchange capacity of UCR-28 (50.1 mg/g) was achieved at pH 7. Thermodynamic parameters for the ion-exchange process were evaluated, and the enthalpy and Gibbs free energy results suggested the Sr²⁺ ion-exchange process was endothermic and spontaneous. The ion-exchange data were a good fit to the Langmuir model. In addition, the metal sulfide reported here had a relatively high thermal stability. The results of this study provide insight into the largely unknown ion-exchange chemistry of metal sulfides, and could be used for design of new chalcogenide frameworks with improved ion-exchange properties.     

Effluent treatment using a bipolar electrochemical reactor with rotating cylinder electrodes of woven wire meshes

BACKGROUND: The behaviour of a bipolar electrochemical reactor consisting of one or more rotating cylinder electrodes of woven wire meshes is reported using copper and cadmium deposition from dilute solutions as test reactions. RESULTS: The best performance related to electrode number was determined for copper deposition and was achieved by an arrangement with two bipolar electrodes, for which the conversion in a single pass was approximately 47%. The specific energy consumption was 3.27 kWh kg^?1 with a normalised space velocity of 23.05 h^?1. The copper powder obtained showed a nodular and dendritic surface morphology. This reactor configuration was also analysed for cadmium deposition, in which hydrogen evolution takes place simultaneously as a side cathodic reaction, considering the effect of flow rate and total current. The maximum conversion per pass for cadmium removal was 38.91%. In this case the reactor with two bipolar electrodes showed a performance similar to that of a monopolar reactor operated at a rotation speed three times higher. CONCLUSION: A continuous electrochemical reactor with two rotating bipolar electrodes of woven wire meshes presents a good performance for copper or cadmium removal from dilute solutions. Copyright © 2009 Society of Chemical Industry     

Removal of cupric ions from acidic sulfate solution using reticulated vitreous carbon rotating cylinder electrodes

The potentiostatic deposition of copper from acid sulfate solutions (0.50 mol dm^?3 Na₂SO₄ at pH 2 and 298 K) was studied at four porosity grades (10, 30, 60 and 100 pores per linear inch, ppi) of reticulated vitreous carbon (RVC) rotating cylinder electrode (RCE). The rate of removal of cupric ions from a 200 cm³ volume of electrolyte was examined as a function of the grade of RVC foam, the electrode potential and the initial cupric ion concentration. For the 100 ppi material, the product of the mass transport coefficient and the electroactive area per unit volume of electrode (k_mA_e) was equal to 0.28 s^?1 at a potential of ?500 mV vs SCE for an initial cupric ion concentration of 0.85 mmol dm^?3 and a constant rotation speed of 1500 rev min^?1. Under the experimental conditions, an initial dissolved copper concentration of 63.5 ppm could be reduced to <0.1 ppm in approximately 60 min using a 100 ppi RVC RCE. SEM studies showed some non‐uniform deposition of metal due to heterogeneous nucleation of copper together with the development of rough deposits. Copyright © 2004 Society of Chemical Industry     

Electrochemical Removal of Copper Ions from Aqueous Solutions Using a Modulated Current Method

The use of porous electrodes to remove toxic metals from industrial effluents has been recognized over the years due to its high mass transfer rates resulting in high current efficiencies (CE) and low energy consumption (EC), even at very low metal concentrations. This work addresses the effects of flow velocity and electric current on current efficiency and energy consumption of copper electrodeposition using reticulated vitreous carbon, aiming to optimize the CE and EC by using a modulated current method. First, it was found that a flow velocity of 0.246 m s^?1 maximizes the mass transfer coefficient (k_m). Applying this flow velocity and a modulated current, the electrodeposition process was investigated and compared with that carried out under galvanostatic mode. The results showed that using a current control there is a reduction of average EC due to the improvement of the average CE, but the operational time also increases when compared to that obtained using the galvanostatic mode.     

Electrochemical assessment of calcium carbonate deposition using a rotating disc electrode (RDE)

An electrochemically-based technique, which uses assessment of the oxygen reduction reaction at a rotating disc electrode, has been devised which shows promise as a method for studying nucleation and growth of mineral scale at a solid surface. In this paper the background and development of the technique are described for the study of deposition of CaCO3 from a supersaturated solution. Results are presented which illustrate the good correlation between the surface coverage predicted by electrochemical analysis and the actual coverage quantified by image analysis. The potential of this technique for mechanistic studies of surface scaling and for assessment of inhibitors is discussed.     

Adsorptive Removal of Cobalt from Aqueous Solutions by Utilizing Industrial Waste and its Cement Fixation

Abstract

In the present study, the adsorption potential of battery industry waste as adsorbent has been investigated for the removal of cobalt from aqueous solutions. The results have shown that the prepared adsorbent adsorbs cobalt to a sufficient extent (35 mg/g). The adsorption of cobalt has been studied on this battery industry waste as a function of contact time, concentration, and temperature by the batch method. The adsorption has been found to be endothermic and the data conform to the Langmuir equation. The analysis of kinetic data indicates that adsorption is a first order process and pore‐diffusion controlled.

Further, the metal‐laden adsorbent was immobilized into cement for ultimate disposal and no significant leaching was observed from the stabilized products. Thus, the present study clearly reveals that battery industry waste can be fruitfully employed in treating industrial effluents containing toxic metal ions. The proposed technology (utilization of industrial wastes for effluent treatment and then ultimate disposal of adsorbents laden with pollutants in cementitious materials by fixation) provides a twofold aim of wastewater treatment and solid waste management.     

Removal of Heavy Metals from Aqueous Solutions by Precipitation-Filtration Using Novel Organo-Phosphorus Ligands

Abstract

An organophosphorus mixture of sodium mono- and di-(n-hexa-decyl) phosphinate was synthesized and purified, and then used as a ligand to remove heavy metals by precipitation from aqueous nitrate, chloride, and sulfate solutions. The new ligand offers more advantages over the previously studied sodium dioctyl and dodecyl phosphinates. The sodium form of the mono- and di-(n-hexa-decyl) phosphinate has a much lower solubility in water, which contributed to much lower back contamination and much lower loss of the reagent, even when excess amount of ligand was employed. Moreover, an excess amount of the ligand did not alter the filtration characteristics of the resultant precipitate. The heavy metals: lead, cadmium, mercury, cobalt, and nickel were precipitated with the sodium mono- and di-(n-hexa-decyl) phosphinate, NaL, in the form of Pb L _2(s), Cd L _2(s), Hg L _2(s), Co L _2(s), and Ni L _2(s). In the absence of free acid in the feed, a maximum removal of each metal corresponded to the stoichiometric ratio. The residual concentrations of each of the metals at the optimum conditions were measured for the different media and found to be lower than 10 ppb, lower than the acceptable levels for most regions. Lead, as a model heavy metal, was studied in more detail. Adding an acid to the feed solution reduced the removal of lead as some of the phosphinate ligand was converted to the acid form. The presence of chloride and sulfate in the feed solution; up to mole ratios to lead of 5000, and of calcium in the feed solution; up to mole ratio to lead of 200, had no effect on the removal of lead. The ligand was more selective to lead than the other four metals, and the selectivity was in the order Pb > Cd > Co & Ni > Hg. The ligand was regenerated up to 99.99% and the metals were recovered in 100 times more concentrated aqueous solutions.     

Adsorptive Removal of Pb(II) and Cu(II) Ions from Aqueous Solutions by Cross-Linked Chitosan-Polyphosphate-Epichlorohydrin Beads

In this study, the cross-linked chitosan-polyphosphate-epichlorohydrin (CCPE) beads were prepared by cross-linking chitosan with both polyphosphate and epichlorohydrin and used as bioadsorbent for the removal of Pb(II) and Cu(II) ions from aqueous solutions. The effects of the dosage of CCPE beads, solution pH, initial metal ion concentration, contact time, and temperature were investigated. Then, three important factors were selected to optimize the removal processes by the orthogonal test. The results show that CCPE beads can effectively remove the Pb(II) and Cu(II) ions from aqueous solutions, and the maximum percentage removals for Pb(II) and Cu(II) ions are 99.7% and 91.2%, respectively. The data show also that the removal processes for both Pb(II) and Cu(II) ions fit best the pseudo-second order kinetic model. Moreover, the decrease of the adsorption ability of CCPE beads is less than 10% after reuse for 9 times, which suggests that CCPE beads have good reusability.     

Removal of Hexavalent Chromium from Aqueous Solutions by Sodium Dodecyl Sulfate Stabilized Nano Zero-Valent Iron: A Kinetics,Equilibrium, Thermodynamics Study

Sodium dodecyl sulfate stable nanoscale zero-valent iron (SDS-nZVI) was synthesized by the sodium borohydride reduction method, characterized with SEM and XRD. SDS-nZVI was used for the removal of Cr (VI) from aqueous solutions at different conditions in a batch process. XRD analysis indicated the presence of iron oxide and iron-chromium hydroxide coprecipitation on the surface of SDS-nZVI after reaction some time. The reaction kinetics, mechanism, isotherms, and thermodynamics for Cr (VI) removal of aqueous solution via SDS-nZVI were investigated. The pseudo-second-order model was relatively suitable for describing the reaction process. Intraparticle diffusion model was used to analysis the mechanism, the results indicated that there were two processes (bulk diffusion and surface diffusion) controlling the reaction rate, while only one was rate limiting in any particular time range. The fitted Temkin and D-R model satisfactorily explanted the experimental data in the range of 303–343 K. The maximum removal capacity of SDS-nZVI for Cr (VI) was obtained for 336.7 mg g^?1 at 303 K. The overall removal process was endothermic. These results demonstrated that SDS-nZVI could potentially be used as an effective material for environmental remediation.     

Polymer-Enhanced Crossflow Filtration for Removal of Fe(III), Cu(II), and Cd(II) Ions from Dilute Aqueous Solutions

Abstract

The removal of Fe(III), Cu(II), and Cd(II) ions from aqueous solutions was studied by polymer-enhanced crossflow filtration technique. Alginic acid polymer was used as complexing agents to enhance the retention. Alginic acid/cellulose composite membranes were used in the filtration. In the filtration of metal ion solutions the effects of alginic acid content of the membranes and pH on the percent retention and the permeate flux were examined. The maximum percent retention was found as 98% for 1 × 10^?4 M Fe(III) solution at the flow velocity of 100 mL/min, pH of 3.0, pressure of 60 kPa in the presence of alginic acid as complexing agent by using 0.25 (w/v)% alginic acid/cellulose composite membranes. For 1 × 10^?4 M Cu(II) and Cd(II) solutions the maximum percent retentions were found as 71% and 80% respectively using 0.50 (w/v)% Alginic acid/cellulose composite membranes when the filtration was carried out in the presence of alginic acid at pressure of 10 kPa, flow velocity of 100 mL/min and pH of 7.0.