Pervaporation of benzene/cyclohexane mixtures using ion-exchange membrane containing copper ions

The sorption, diffusion, and pervaporation (PV) properties of benzene/cyclohexane (Bz/Cx) mixtures on cation-exchange membranes containing copper ions (Cu(II)) were investigated. The equilibrium sorption isotherms of pure vapors in the membranes and the partial solubility of binary solutions in the membranes were described using the UNIQUAC model. The τ_iM and τ_Mi values were 0.978 and 0.591 for Bz, and 0.922 and 0.475 for Cx. The transient regimes of vapor sorption were employed to calculate the concentration-dependent diffusion coefficients. Long’s model sufficiently explained the diffusivity of Bz and Cx in the membranes. The pre-exponential factors were 3×10⁻¹³ m²/s and the plasticization factors were 3.0 and 3.6 for Bz and Cx, respectively. Excellent agreement was found with the experimental results applying the solubility and diffusivity data to simulate the pervaporation performance (flux and selectivity) using the modified Maxwell–Stefan equation. The membrane containing Cu(II) demonstrates better facilitating capability for Bz transport than that with Na(I), mainly due to its preferential sorption property toward Bz. Replacing Na(I) with Cu(II) into a Neosepta membrane resulted in better separation efficiency and higher Bz flux throughout the entire Bz concentration range.     

Chelating ion-exchange resin membrane sensor for nickel(II) ions

A chelating ion-exchange resin (1-hydroxy-2-naphthaldoxime-formaldehyde polymer) containing nitrogen and oxygen donor atoms was prepared and characterized. The resin behaves as a selective chelating ion exchanger for some metal ions. The poly(vinyl chloride)-based membrane electrode of the resin shows a Nernstian response for Ni(2+) over a wide concentration range (2.94 x 10(3)-5.87 x 10(3) mg dm(-3)) between pH 3.0 and 7.5. The electrode is found to possess adequate stability and specific selectivity with a response time of 10 s. The sensor can also be used in a partially non-aqueous medium having a 35% (v/v) non-aqueous content.     

Sorption of cesium ions by nanostructured calcium aluminosilicates

Data on the sorption properties of synthetic calcium aluminosilicates (CASes) with Al: Si ratios of 2: 2, 2: 6, and 2: 10, fabricated within the multicomponent system CaCl₂–AlCl₃–KОН–SiO₂–H₂O, are presented. Isotherms of the sorption of Cs⁺ ions from aqueous solutions with Cs⁺ concentrations of 0.2 to 6.0 mmol L^–1 are analyzed. The CAS maximum sorption capacity and the Langmuir constants are determined. Kinetic data are obtained, and the energy of cation-exchange activation upon the sorption of Cs⁺ ions is determined. The effect of a salt background (1% KCl + 6% NaCl) has on the values of distribution coefficient (K_d) and the degree of Cs⁺ ion removal is established.     

Uptake of cesium and strontium by crystalline silicotitanates from radioactive wastes

Crystalline silicotitanate inorganic ion exchanger, with a sitinakite structure is candidate material for remediation of aqueous nuclear waste streams. The syntheses of crystalline silicotitanate (CST) and Nb-substituted crystalline silcotitanate (Nb-CST) were carried out under hydrothermal conditions and the products were characterized using techniques viz., XRD, SEM/EDS, DTA/TGA, surface area respectively. Batch experiments were carried out to study the kinetics of uptake of ¹³⁷Cs and ⁹⁰Sr, to estimate the decontamination factor (DF) values and distribution coefficients (K _d) for the above synthesized CST and Nb-CST samples from actual radioactive waste solutions. The DF values for uptake of Cs and Sr by Nb-CST after 24 h of equilibration was 355 and 136 whereas for CST it was found to be 40 and 176 respectively. The K _d values for uptake of Cs and Sr for Nb-CST after 24 h of equilibration was found to be 35,490 and 13,500 mL/g respectively whereas the K _d values for uptake of Cs and Sr for CST was found to be 4,025 and 17,525 mL/g respectively. The ion exchange capacity of Nb-CST towards ⁹⁰Sr and ¹³⁷Cs was estimated to be 11.8 and 3.2 meq/g respectively whereas the ion exchange capacity of CST towards ⁹⁰Sr and ¹³⁷Cs was estimated to be 14.6 and 4.4 meq/g respectively.     

Decontamination of spent ion-exchange resins contaminated with cesium radionuclides

Possible causes of the occurrence of radioactive contamination irremovable by acid–base regeneration of ion-exchange resins used in treatment of process media and liquid radioactive waste have been studied. It has been found that most of the irremovable cesium radionuclides are bound to inorganic deposits on the surface and in the bulk of ion-exchange resin granules. The nature of inorganic inclusions has been investigated on real and model spent ion-exchange resins (SIER). A method has been proposed for decontaminating SIER using resorcinol–formaldehyde resins selective to cesium radionuclides. Such an approach has been shown to be promising for deep decontamination of SIER.     

Treatment of low level radioactive liquid wastes using composite ion-exchange resins based on polyurethane foam

Composite ion-exchange resins were prepared by coating copper-ferrocyanide (CFC) and hydrous manganese oxide (HMO) powders on polyurethane (PU) foam. Polyvinyl acetate/Acetone was used as a binder. The foam was loaded with about five times its weight with CFC and HMO powders. The distribution coefficients of CFC-PU foam and HMO-PU foam for cesium and strontium respectively were estimated. Under similar conditions the HMO-PU foam showed higher capacity as well as better kinetics for removal of strontium than CFC-PU foam for Cs. The pilot plant scale studies were conducted using a mixed composite ion-exchange resin bed. About 1000 bed volumes could be passed before attaining a DF of 10 from an initial value of 60–80. The spent resin was digested in alkaline KMnO₄ and the digested liquid was fixed in cement matrix. The matrices were characterized with respect to compressive strength and leach resistance.     

Studies with an inorganic ion-exchange membrane exhibiting selectivity for Pb(II) ions

A solid membrane electrode made with titanium arsenate as membrane material and "Araldite" as binder has been used to measure the activity of lead in the concentration range from 0.1 M to 5 x 10(-6)M. The electrode is unaffected by many cations, nitrate and acetate. The response time is 40-60 sec over the whole concentration range (in a static system) and the electrode has a working life of at least four months. The electrode can work in the pH range 2-5 and is tolerant of ethanol up to a content of 30% v v . It has been successfully used for end-point indication in potentiometric titration of lead. A membrane treated with cationic surfactant exhibits better selectivity.     

Adsorption of copper(II) ions from aqueous solutions on alumina industrial wastes

Equilibrium adsorption of copper(II) ions on red mud (alumina industrial wastes) modified by various methods was studied. The effect exerted by the nature the modifier (NaHSO₄, NaCl + HCl, and H₂SO₄) on the sorption activity of red mud was determined.     

Kinetics of liquid-solid ion-exchange reactions of transition metal ions in tin(IV) phosphate

A simple approach to liquid-solid ion exchange kinetics of Cu²⁺, Zn²⁺, Cd²⁺, Co²⁺ ions in tin(IV) phosphate under different conditions of temperature, exchange ion concentration, and the particle size of the exchanger has been reported. The kinetics were controlled by particle diffusion and the $\text{t}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ law operated to about 65–75% of exchange. The diffusion coefficients and activation energies were calculated. The activation energies of Cu²⁺ and Co²⁺ ions were found to be low when compared with Zn²⁺ and Cd²⁺ ions due to Jahn-Teller distortion.     

A novel electrochemical method to detect mercury (II) ions

A novel and sensitive electrochemical method for determination of mercury (II) ions (Hg²⁺) based on the formation of thymine–Hg²⁺–thymine complexes and gold nanoparticle-mediated signal amplification is reported. Two 5′ end thiolated complementary oligonucleotides containing six strategically placed thymine–thymine mistakes were introduced in this work. One of the two oligonucleotides was immobilized on a gold electrode and the other one on gold nanoparticles (AuNPs). Due to six thymine–thymine mistakes the two oligonucleotides were not able to be hybridized, so AuNPs could not be immobilized onto the electrode surface after the electrode was immersed in the DNA–AuNPs solution. However, if Hg²⁺ existed, T–Hg²⁺–T complexes could be formed and AuNPs could be immobilized onto the electrode surface. Meanwhile, large numbers of [Ru(NH₃)₆]³⁺ molecules as electrochemical species could be localized onto the electrode surface. The Hg²⁺ detection limit of this assay could be as low as 10 nM, which is the US Environmental Protection Agency (EPA) limit of Hg²⁺ for drinkable water. This method is proven to be simple, convenient, high sensitive and selective.     

Stability of chromate electrolytes containing ions of Cr(III)

The reason for the unstable influence of Cr(III) on the maximum rate of incomplete reduction of chromic acid is studied by a method of cyclic voltammetry and analytical investigations of the electrolyte composition. It is established that the decrease in the maximum rate of electrochemical reaction Cr(VI) → Cr(III) is due to the drop of concentration of free sulfate ions in the electrolyte. The drop of the concentration of free sulfate ions increases with the content of electrochemically synthesized ions of Cr(III) in the solution. The decrease in the concentration of sulfate ions is assumed to stem from the formation of unstable complexes of Cr(III) with sulfate ions. Sulfate ions regain their initial concentration with time and upon heating solution to 50–70°C, which facilitates dissociation of unstable sulfate complexes of Cr(III). It is shown that the concentration of sulfate ions in the solution remains invariant during chemical reduction of Cr(VI) to Cr(III), which points to the formation of inert complexes of Cr(III) that make no impact on the rate of incomplete reduction of chromic acid.     

A rod-like polymer containing (Ru(terpy)2) units prepared by electrochemical coupling of pendant thienyl moieties

A new rod-like coordination polymer consisting of (Ru-(terpy)2) motifs bridged by bithiophene units has been prepared by electrochemical polymerisation in acidic organic medium.     

Effects of chloride ions on electrochemical reactions of manganese(III) complexes

Electrochemical reactions of manganese(III) complexes, Mn^III(L)X (L; salen, salpn, 5-NO₂–salen or 5-NO₂–salpn, X; Cl, Br or NO₂) and Mn^III(L’)₂X (L’; N-Bu-sal, N-Oct–sal, N-Oct–5-Br–sal or N-Oct–5-NO₂–sal, X; Cl or Br), were investigated by voltammetry at a glassy carbon electrode in the absence/presence of Cl⁻ in acetonitrile solution. By the addition of Cl⁻, oxidation processes of Mn^III(L)X and Mn^III(L’)₂X have been found to be improved from quasi-reversible to reversible, and their oxidation products, [Mn^IV(L)X]⁺ and [Mn^IV(L’)₂X]⁺, were stabilized by the combination with Cl⁻ resulting in [Mn^IV(L)Cl₂] and [Mn^IV(L’)₂Cl₂], respectively. On the other hand, the reduction processes of Mn^III(L)X and Mn^III(L’)₂Cl were not so significantly affected by Cl⁻ as those observed for their oxidation. Other types of manganese(III) complexes and iron(III) complex were also investigated. The present study may clarify the role of Cl⁻ being involved in OEC (oxygen-evolving center) in photosystem II.     

Preparation and electrochemical study of manganese(II) macrocycles containing terpyridine

The macrocycle, L, prepared by template condensation of bis-6,6-(-methylhydrazino)-4-phenyl-2,2:6,2-terpyridine with glyoxal, forms a stable crystalline Mn^II complex, [Mn(L)(H₂O)₂][PF₆]₂, which has been used as a starting material for electrochemical studies on a series of seven coordinate Mn^II complexes [Mn(L)X₂]²⁺ (X = pyridine, 4-cyanopyridine, 4-aminopyridine, 4-dimethylaminopyridine, pyrazine, imidazole 1-methylimidazole, 2-dimethylimidazole or Ph₃P). Cyclic voltammetry of the complexes in MeCN shows a reversible one electron reduction wave in the range –1.32 to –1.42 V versus the Ag/AgBF₄ reference electrode.     

Separation and concentration of molybdenum(VI) and tungsten(VI) with chelating ion-exchange resins containing sulphur ligands

Three chelating ion-exchange resins based on macroreticular polyacrylonitrile-divinylbenzene copolymers with thioglycollic acid and cysteine as functional groups have been tested for separation of molybdenum(VI) and tungsten(VI). On a short column of the thioglycollic acid resin, molybdenum(VI) and tungsten(VI) can be selectively sorbed from pH-4.3 acetate buffer and eluted with 2M hydrochloric acid and a mixture of 0.1M sodium hydroxide and 0.1M sodium chloride, respectively, with quantitative recovery even at very low concentrations. Simulated sea-water samples have been analysed.     

Adsorption characteristics of radiotoxic cesium and iodine from low-level liquid wastes

In order to remove the radiotoxic nuclides, Cs⁺ and I^–, from low-level liquid wastes, the adsorption characteristics have been studied using a mixed adsorbent of chabazite zeolite and activated carbon. The equilibrium data of each nuclide were well correlated with the DA equation in the wide range of equilibrium concentrations. The SEM-EDAX analysis provided precise understanding of the adsorption mechanism of each nuclide. A surface diffusion model was applied to estimate the intraparticle mass transfer and provided prediction results acceptable for practical implementation in the liquid waste treatment.     

Poly (phenylmethylsilane) obtained by electrochemical reduction in a divided cell containing a polymeric membrane

The electrochemical synthesis of poly(phenylmethylsilane) was carried out in a divided cell using a polymeric anion-exchange membrane. The solution contained phenylmethydichlorosilane (PhMeSiCl₂), mixed solvent tetrahydrofuran + hexamethylphosphoramide, with tetrabutylammonium perchlorate as support electrolyte. The electrodes were stainless steel as the cathode, stainless steel as the sacrificial anode or platinum as the resistant anode. Poly(phenylmethylsilane) was obtained in yields from 1.5 to 4.5 % from phenylmethyldichlorosilane concentrations equal or higher than 1 M. The number-average molecular mass M_n of poly(phenylmethylsilane) was in the range from 5600 to 9500. A monomodal molecular weight distribution was obtained with a polydipersity Index of 2. The spectra of ¹H, ¹³C, ²⁹Si MMR and IR were determined. From the ²⁹Si NMR analysis, the poly(phenylmethylsilane) showed a clear difference in the tacticity related to the chemical synthesis of the same polymer. The UV spectra showed a strong absorption in a 331 to 335 nm characteristic for the poly(phenylmethylsilane).