High-efficiency HFSLM for silver-ion pertraction from pharmaceutical wastewater and mass-transport models

Hollow fiber supported liquid membrane (HFSLM) is a favorable technique for the pertraction of metal ions, especially at very low metal concentration. In this work, the pertraction of silver ions from acidic pharmaceutical wastewater via HFSLM was investigated. Pharmaceutical wastewater containing 30 mg/dm³ of silver ions and 120 mg/dm³ of ferric ions was subjected to HFSLM as a feed solution. LIX 84-I dissolved in organic solvent together with Na₂S₂O₃·5H₂O solution was selected for use as a liquid membrane and a receiving solution, respectively. The influence of ferric ions on the pertraction of silver ions was studied firstly using wastewater with normal ferric ion concentration and secondly using wastewater with ferric ion precipitation by phosphoric acid solution. The highest pertraction of silver ions was achieved by using 0.1 M of LIX 84-I and 0.5 M of Na₂S₂O₃·5H₂O solution at pH of feed and receiving solutions of 3.5 and 2. The flow rates of feed and receiving solutions were 0.2 dm³/min. 0.6 mg/dm³ of silver ions that remained in the wastewater was below the mandatory discharge limit. No effect of normal ferric ion concentration in the wastewater on silver ion pertraction was observed. The crucial parameters were defined to confirm the efficiency and reliability of the system. Finally, the controlling transport regime of silver ion pertraction across HFSLM was determined by the diffusion flux and reaction flux models.     

Effect of sulphuric acid and copper sulphate concentrations on the morphology of silver deposit in the cementation process

The silver ion cementation on copper was investigated in the presence or absence of oxygen in solutions containing 1.85 × 10⁻⁴ M Ag⁺ at 25 °C. The influence of sulphuric acid and copper sulphate concentration (0.005-0.5 M) on the silver cement morphology was studied in details and results were linked with the previously determined kinetics data of the process. The morphology of silver deposit was found to be independent of the presence of oxygen in the system as well as the sulphuric acid concentration. Contrary, the concentration of copper sulphate strongly influenced the morphology of silver deposit. At the beginning of the cementation process silver covers uniformly the copper surface. Afterwards, a growth of dendrites is initiated on preferential parts of the surface. The growing dendrite behaves as cathodic sites, with relatively huge surface area and promotes the creation of anodic sites in a close neighbourhood. Finally, the anodic site encloses the dendrite island and develops its area inward the copper material. Copper ions at low concentration modified slightly silver dendrites but the increase in concentration up to 0.5 M Cu²⁺ leads to completely disappearance of dendrites from the surface. The lack of dendrites on the surface is a result of the competitive process that consumes additional silver ions, occurring in the bulk of the solution. The morphology of silver deposit cemented in the deoxygenated solution containing 0.5 M H₂SO₄ + 0.5 M CuSO₄ depends strongly on the mechanism of the process.     

Effect of hydroxyl ions on chloride penetration depth measurement using the colorimetric method

In this paper, the effect of hydroxyl ions on chloride penetration depth measurement using the colorimetric method was studied. Equivalent silver nitrate solution (i.e. Ag⁺ = Cl⁻) was added to the NaCl + NaOH solution with different concentrations, then the amount of precipitated silver chloride and silver oxide were determined by chemical methods, and the color of the precipitated products was examined. Results show that the amount of silver chloride formed decreases linearly as OH⁻ to Cl⁻ ratio (r) increases. Thus, the chloride concentration at color change boundary changes with the pH value of the concrete. AgCl has a white color, while Ag₂O has a dark brown color. When the value of r exceeds 4, the color of the mixture looks brown, and color change boundary cannot be easily distinguished.     

In situ preparation,electrospinning, and characterization of polyacrylonitrile nanofibers containing silver nanoparticles

Silver nanoparticles were prepared from a polyacrylonitrile (PAN)/N,N‐dimethylformamide solution of silver nitrate (0.05–0.5 wt %) with light treatment (xenon arc) to reduce Ag⁺ ions into Ag⁰. The formation of silver nanoparticles in the PAN solution and the effect of treatment time on the numbers of silver nanoparticles, their average diameter and size distribution were investigated by UV–visible spectroscopy. In addition, the average size of silver nanoparticles and their shapes in colloidal solution were determined by transmission electron microscopy images and found to be on the order of 10 nm. The resulting solution was electrospun into PAN nanofibers. An increase in the salt concentration led to decreases in the nanofiber diameter and bead numbers (determined by scanning electron microscopy images) and an increase in the crystallinity (confirmed by X‐ray diffraction patterns). A continuous rate of silver release from the nanofiber web was monitored by the atomic absorption technique. These nanofibers showed strong antibacterial activity against Pseudomonas aeruginosa. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electrochemical behavior of pyrite in sulfuric acid solutions containing silver ions

A systematic electrochemical study of pyrite in H₂SO₄ solutions containing dissolved silver was undertaken to gain more information about the transfer of silver ions to pyrite and their role in enhancing the direct oxidation of pyrite. The results of cyclic voltammetry experiments provide additional evidence of the formation of metallic silver on the FeS₂ surface under open-circuit conditions. A pyrite electrode held at the open-circuit potential for 2 h in the presence of 10^–3 m Ag⁺ exhibits a large and sharp anodic peak at about 0.7V. The current associated with this peak is the result of the dissolution of metallic silver deposited during the initial conditioning period. There is no evidence of silver deposition without preconditioning until the potential drops below about 0.6V for Ag⁺ concentrations ranging from 10^–4 to 10^–2 m. However, subsequent silver deposition appears to be very sensitive to the dissolved silver concentration in this range. There is also evidence that the state of the pyrite surface has a pronounced influence on its interaction with silver ions. Agitation has also been found to have a significant effect on the electrochemistry of the Ag–FeS₂ system.     

Functionalized hectorite clay mineral for Ag(I) ions extraction from wastewater and preparation of silver nanoparticles supported clay

A novel clay mineral-based adsorbent for Ag(I) ions extraction was obtained by modifying hectorite with 2-(3-(2-aminoethylthio)propylthio)ethanamine (AEPE-hectorite). The modified hectorite was used to recover Ag(I) ions from wastewater for further preparation of silver nanoparticles supported hectorite. The parameters affecting silver ions extraction by AEPE-hectorite were investigated. The adsorbent could extract Ag(I) ions from solution in a wide pH range (1–8) and high extraction efficiencies were achieved in the solution pH ranged from 4 to 9. AEPE-hectorite showed a good selectivity toward Ag(I) ions over Co(II), Ni(II) and Cd(II) ions and the solution ionic strength had no significant effect on extraction efficiency. The adsorption of Ag(I) ions onto AEPE-hectorite followed the Freundlich isotherm model with maximum adsorption capacity observed in the experiment of 49.5 mg g^− 1. The adsorbent was successfully used to recover silver ions from a wastewater containing high concentration of silver and silver nanoparticles supported hectorite was obtained after reducing with NaBH₄. These results show an alternative in the preparation of silver nanoparticles supported clay.     

Electrochemical recovery of silver from cyanide leaching solutions

In the hydrometallurgy industry cyanide solutions are the most common leaching baths used during the extraction of metals such as silver and gold. After extraction, the solution containing various cyanide species, and usually copper cyanide, has a higher concentration than the gold and silver complexes. Higher concentration of copper species may interfere during the selective recovery of precious metals. This work presents a study of the selective recovery of silver from leaching solutions mimicking those used in industry. Chemical speciation and cyclic voltammetry studies showed that copper reduction occurs at more negative potentials than silver in the cyanide leaching solutions. The cyclic voltammetry of cyanide solutions on a vitreous carbon electrode showed that copper cyanide ions modify the interface properties, lowering the overpotential required for silver reduction. A macroelectrolysis study of a simulated leaching solution (10^–4 M Ag(I), 0.1 M Cu(I) in 0.5 M CN^– at pH 10), was carried out in a filter press electrochemical reactor (ElectroCell AB) with a reticulated vitreous carbon electrode (RVC), nominally having 45 pores per inch and a flow rate of 5 cm³ s^–1 at 25 °C. The study showed that the high copper concentration does not interfere in the selective deposition of silver.     

Removal of Ag(l), Cu(II) and Zn(ll) ions with a supported liquid membrane containing cryptands as carriers

The interface behaviour in the facilitated co-transport of Ag(I), Cu(II) and Zn(II) ions through supported liquid membranes (SLMs) made of a flat-sheet polypropylene membrane support containing cryptands (2.2.2 or 2.2.1) as carriers was studied. The liquid-liquid extraction tests showed a maximum distribution coefficient when the carrier concentration was greaterthan 10⁻⁴M. In transport experiments the transmembrane flux increased with increasing carrier concentration reaching a limiting value at greater than 10⁻³M concentration. The calculation ofthe diffusion coefficients in membranes showed ahigherdiffusivityof2.2.2-metal complexes with respect to 2.2.1-metal complexes for silver ions. A sequence of diffusivity D(Ag+)>D(Cu²⁺)>D(Zn²⁺) was obtained, but carrier 2.2.1 showed a higher selectivity through copper ions. A sequence of diffusivity D(Cu²⁺)>D(Zn²⁺)>D(Ag⁺) was obtained. The diffusivity was significantly higher when using Celgard 2500 support compared to Celgard 2400 or 2402. Variable metal ion concentrations in the feed phase fluxes almost zero, at less than 10⁻² M concentration, were obtained. In the transient state of the transport through the SLM, different molar flow rates at the feed-membrane and membrane-strip interfaces were observed. The selectivity of the interfaces containing 2.2.2 in the separation binary mixtures of ions showed the following separation factors: SF_AgZn = 2.50, SF_AgCu = 1.64, SF_cuZn = 1.42.     

Electrolytic oxidation of cuprocyanide electroplating waste waters under different pH conditions

The main purpose of this work was to investigate the electrolytic oxidation of cuprocyanide solution with various total cyanide to copper molar ratios ranging from 2.8 to 20 and under different pH conditions. In strong alkaline solution (pH12), cuprocyanide ions Cu(CN) _n ^/(n–1)– , wheren=2, 3 or 4, are directly electroxidized, and copper oxide precipitates on the anode. Cyanate ions, as well as nitrogen gas, were detected as the products and 0.30–0.43 g mol of total cyanide was destroyed per Faraday. For less alkaline solutions (pH<12), cuprocyanide ions first dissociated to free cyanide ions and then electroxidized. At a pH of 10.5–11.7, cyanate ion and brown azulmin polymer were produced in the anolyte. In the neutral solution (pH=7.0–8.6), carbonate and ammonium ions and azulmin were formed and 0.52–0.56 g mol of total cyanide was destroyed per Faraday. In weak acidic solution (pH=5.2–6.8), oxalate and ammonium ions and white oxamide were produced and 1.01–1.18 g mol of total cyanide were destroyed per Faraday.Nomenclature C _CN molar concentration of total cyanide (kmol m^–3) - C _Cu molar concentration of total copper (kmol m^–3) - C _d equivalent concentration of cyanide destroyed due to the formation of cupric oxide (kg m^–3) - C _f concentration of cyanide destroyed by dissociation of complex ion to free cyanide ion and then electroxidized (kg m^–3) - C _i initial concentration of total cyanide (kg m^–3) - C _t change of total cyanide concentration during electrolysis (kg m^–3) - F Faraday constant (96 487 C mol^–1) - K ₁,K ₂,K ₃ formation constant of dicyanocuprate, tricyanocuprate and tetracyanocuprate ions - R molar ratio of total cyanide concentration to total copper concentration (i.e.C _CN/C _Cu) - W weight of precipitates on electrodes or in anolyte (kg) - angle of incidence     

Removal behavior and mechanism of silver from low concentration wastewater using cellulose aerogel modified by thiosemicarbazide

Due to the low concentration of silver in water, most of the cellulose adsorbents exhibited low removal efficiency, which greatly limited their practical applications. Herein, a cellulose aerogel modified by thiosemicarbamide (CAT) was fabricated for reducing and adsorbing silver ions from low concentration wastewater. The characterization results concluded that CAT owned a three-dimensional spongy structure with many circular microspheres and a better specific surface area (19.37 m² g⁻¹), as well as the functional groups of ─C═N⁺─H and ─(C═S)─N. The static batch adsorption experiments demonstrated that CAT could reached the maximum removal percentage of 94.94% and adsorption capacity of 42.12 mg g⁻¹ under the initial concentration of Ag(I) was 15 mg L⁻¹ and the pH value was 7. Meanwhile, the adsorption of Ag(I) on CAT was second-order reaction, and the Langmuir model could better fit the adsorption process. In addition, CAT exhibited wide pH values (1–9) adaptability and excellent adsorption performance for silver through electrostatic interaction, chelation, and reduction. This study probably provides a new method as well as important experimental data and theoretical reference for the removal of silver ions and other metals.     

Silver‐loaded lyocell fibers modified by tempo‐mediated oxidation

The purpose of this research was to accomplish antimicrobial properties in lyocell fibers by Ag⁺ ions sorption from aqueous silver nitrate solution. Sorption properties of lyocell fibers were improved by the selective TEMPO‐mediated oxidation, i.e. oxidation with sodium hypochlorite and catalytic amount of sodium bromide and 2,2,6,6‐tetramethylpiperidine‐1‐oxy radical (TEMPO). The most suitable experimental conditions for the selective TEMPO‐mediated oxidation were determined by changing oxidation conditions: concentration of sodium hypochlorite, as well as duration of sorption. The obtained results showed that the maximum sorption capacity (0.809 mmol of Ag⁺ ions per gram of fibers) of modified lyocell fibers was obtained for the sample modified with 4.84 mmol NaClO per gram of cellulose, during 1 h. The antifungal activity of the TEMPO‐oxidized lyocell fibers with silver ions against fungi from the Candida family, Candida albicans (ATCC 24433), and antibacterial activity against two strains: Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) were confirmed in vitro. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Activity of antibacterial compounds immobilised on montmorillonite

The activities of antibacterial compounds, such as cetylpyridinium (CP), cetyltrimethylammonium (CTA), silver ions and metallic silver, immobilised on montmorillonite (MMT), were tested in Escherichia coli and Enterococcus faecium bacteria. The results of bacterial growth tests were confirmed by determination of the minimum inhibition concentrations (MICs). Unlike CP and CTA, the intercalated silver ions were easily released from MMT by ion-exchange with Na⁺ and acted as very effective antibacterial substances in the long term. Their bactericidal and bacteriostatic effects were determined. Generally, antibacterial compounds are effective when they are released from an inorganic carrier. Metallic silver was prepared by reduction of intercalated Ag⁺ with sodium borohydride. Antibacterial effects of metallic silver were not observed.     

Adsorption characteristics of metal ions by CO2-fixing Chlorella sp. HA-1

Single and binary metal systems were employed to investigate the removal characteristics of Pb²⁺, Cu²⁺, Cd²⁺, and Zn²⁺ by Chlorella sp. HA-1 that were isolated from a CO₂ fixation process. Adsorption test of single metal systems showed that the maximum metal uptakes were 0.767 mmol Pb²⁺, 0.450 mmol Cd²⁺, 0.334 mmol Cu²⁺ and 0.389 mmol Zn²⁺ per gram of dry cell. In the binary metal systems, the metal ions on Chlorella sp. HA-1 were adsorbed selectively according to their adsorption characteristics. Pb²⁺ ions significantly inhibited the adsorption of Cu²⁺, Zn²⁺, and Cd²⁺ ions, while Cu²⁺ ions decreased remarkably the metal uptake of Cd²⁺ and Zn²⁺ ions. The relative adsorption between Cd²⁺ and Zn²⁺ ions was reduced similarly by the presence of the other metal ions.     

Preparation, separation, and confirmation of the eight geometrical cis/trans conjugated linoleic acid isomers 8,10-through 11,13–18∶2

Conjugated linoleic acid (CLA) mixtures were isomerized with p-toluenesulfinic acid or I₂ catalyst. The resultant mixtures of the eight cis/trans geometric isomers of 8,10-, 9,11-, 10,12-, and 11,13-octadecadienoic (18∶2) acid methyl esters were separated by silver ion-high-performance liquid chromatography (Ag⁺-HPLC) and gas chromatography (GC). Ag⁺-HPLC allowed the separation of all positional CLA isomers and geometric cis/trans CLA isomers except 10,12–18∶2. However, one of the 8,10 isomers (8cis, 10trans-18∶2) coeluted with the 9trans,11cis18∶2 isomer. There were differences in the elution order of the pairs of geometric CLA isomers resolved by Ag⁺-HPLC. For the 8,10 and 9,11 CLA isomers, cis,trans eluted before trans,cis, whereas the opposite elution pattern was observed for the 11,13–18∶2 geometric isomers (trans,cis before cis,trans). All eight cis/trans CLA isomers were separated by GC on long polar capillary columns only when their relative concentrations were about equal. Large differences in the relative concentration of the CLA isomers found in natural products obscured the resolution and identification of a number of minor CLA isomers. In such cases, GC-mass spectrometry of the dimethyloxazoline derivatives was used to identify and confirm coeluting CLA isomers. For the same positional isomer, the cis,trans consistently eluted before the trans,cis CLA isomers by GC. High resolution mass spectrometry (MS) selected ion recording (SIR) of the molecular ions of the 18∶1 18∶2, and 18∶3 fatty acid methyl esters served as an independent and highly sensitive method to confirm CLA methyl ester peak assignments in GC chromatograms obtained from food samples by flame-ionization detection. The high-resolution MS data were used to correct for the nonselectivity of the flame-ionization detector.     

Effect of potassium and silver ion-exchange on the strengthening effect and properties of aluminosilicate glass

In this work, the aluminosilicate glass was subjected to ion-exchange using the KNO₃-AgCl mixed molten salt in order to strengthen the glass while imparting antimicrobial properties. The concentration distribution of K⁺ ions and Ag⁺ ions of the ion-exchanged glasses was characterized by EDS, the effects of ion-exchange temperature (460-500 °C), ion-exchange time (0.5-3 h) and AgCl concentration (0–2.5 wt%) in the mixed molten salt on the strengthening effect and properties of the glass were investigated. The results showed that Ag⁺-Na⁺ ion-exchange, K⁺-Na⁺ ion-exchange existed simultaneously, and Ag⁺-Na⁺ ion-exchange occurred preferentially. Due to the presence of metallic silver, the appearance of the Ag⁺ ion-exchanged glass was light yellow and its transmittance showed a decrease. The surface compressive stress trended up and then down with increasing temperature and time because of the stress relaxation effect. The Vickers hardness of ion-exchanged glass increased by 15%, and the densities and chemical stability were also increased. Ions leaching experiments showed that the Ag⁺ ions release concentration of silver-loaded glass in aqueous environment can reach the bactericidal level. It has been shown that ion-exchange of glass in KNO₃-AgCl mixed molten salts allowed the glass to be strengthened and incorporated with antimicrobial active ions, its chemical stability was improved, too.     

Fluoride ion reactions in the acetonitrile-10%(mole) water medium. pF scale and potential-pF diagrams relative to the silver, copper and hydrogen redox systems

Ag⁺, Cu⁺, Cu²⁺, Co²⁺, UO²⁺₂, La³⁺, Fe³⁺, Al³⁺ precipitation by fluoride ions and their reaction with H⁺ ion have been studied in the acetonitrile-10%(mole) water medium. The pF⁻ buffers are positioned on a pF⁻ scale extending over about 14 unities. The potential-pF⁻ diagrams relative to the silver, copper and hydrogen systems, established in the same medium, give evidence that in contrast with water, their redox properties depend largely on the fluoride ion concentration.     

Studies with chromium ferricyanide epoxy resin-based membranes

The solid membrane of chromium ferricyanide in epoxy resin has been used as a silver sensitive electrode. The electrode response to silver ions is non-Nernstian, but a linear plot has been obtained in the concentration range 10^?1-10^?3M with a slope of 46 mV per decade of activity. The response time of the electrode is a few seconds and potentials generated are reproducible. The electrode is not specific to silver ions but can nevertheless be used in presence of Hg²⁺, Zn²⁺ and Cd²⁺. Anions show no interference. Silver can be estimated even in the presence of interfering ions by potentiometric titration using the membrane as an end point indicator electrode.     

Separation of Toluene and n‐Heptane through Emulsion Liquid Membranes Containing Ag+ as Carrier

Using silver ions as carrier in oil/water/oil‐type emulsion liquid membranes, batch wise extraction experiments were carried out to separate toluene from a mixture of toluene and n‐heptane. The separation performances, represented by the permeation rate, emulsion stability, and separation factor, were analyzed systematically by varying the operating parameters, viz., contact time, concentration of Ag⁺, emulsification time, surfactant concentration, membrane stabilizer concentration, relative amount of solvent, and initial feed phase concentration. The emulsion liquid membranes thus formed are stable, and Ag⁺ and surfactant concentrations strongly affect the permeation behavior of toluene.     

A potentiometric and voltammetric sensor based on polypyrrole film with electrochemically induced recognition sites for detection of silver ion

Conducting polypyrrole membranes were deposited on glassy carbon electrodes by electropolymerizing pyrrole in the presence of Eriochrome Blue-Black B (EBB) as the counter anion. The electrodes were then subjected to several oxidation/reduction potential steps in pure silver nitrate solution for successive accumulation/stripping of silver species. This electrochemically mediated doping/templating generated selective recognition elements in the EBB/PPy film for silver ions. The resulting sensor exhibited a considerable enhancement in the potentiometric and voltammetric response characteristics: extending the linear dynamic range and lowering the detection limit. In the potentiometric mode, the sensor showed highly reproducible response with a Nernstian slope of 58.5 ± 0.3 mV per decade of Ag⁺ activity over a linear range spanning seven orders of magnitude (1 × 10⁻⁸ to 1 × 10⁻¹ M Ag⁺), with a detection limit of ∼6 × 10⁻⁹ M. The electrodes demonstrated high selectivity over a large number of cations including alkali, alkaline earth and several transition and heavy metal ions, and could be used over a wide pH range of 1-8.5. The EBB/PPy modified electrode was also used for preconcentration and differential pulse anodic stripping voltammetric (DPASV) measurements. The DPASV peak current was dependent on the concentration of Ag⁺ over the range 3 × 10⁻¹⁰ to 1 × 10⁻⁴ M. The presence of 1000-fold excess of Cd²⁺, Cu²⁺, Cr³⁺, Co²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Ni²⁺ and Pb²⁺ can be tolerated in the determination of silver ion.     

Morphology,physical properties,silver release,and antimicrobial capacity of ionic silver‐loaded poly(l‐lactide) films of interest in food‐coating applications

In the present study, silver ions were incorporated into a poly‐(l ‐lactide) (PLA) matrix by a solvent casting technique using different solvents and glycerol as plasticizer. The effect of the different formulations on the morphology, thermal, mechanical and color properties were first evaluated. Additionally, a thorough study of the silver ions release to an aqueous environment was also monitored over time by anodic stripping voltammetry and correlated with the antimicrobial performance against S. enterica. The incorporation of silver contents of up to 1 wt % did not affect morphology, thermal or mechanical properties of the films. A sustainable, antibacterial effectiveness was found for the films in liquid medium and a breakpoint of 10–20 μg L^?1 silver was established under the stated conditions, evincing silver ion releasing technologies may be applied to liquid environments while complying with current legislation. This study provides insight into the structure properties relationship of these antibacterial polylactide materials of significant potential in coating applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41001.