Application of nitroso-R-salt in modification of strongly basic anion-exchangers Amberlite IRA-402 and Amberlite IRA-958

The batch method was applied in order to determine the influence of phase contact time, solution pH and temperature as well as HCl concentration on nitroso-R-salt (NRS) deposition on the strongly basic anion-exchangers Amberlite IRA-402 and Amberlite IRA-958. The equilibrium sorption of NRS from 1 × 10^− 4 mol/dm³ solution was achieved after 60 min. The amount of NRS adsorbed decreased with increasing hydrochloric acid concentration. A significant increase of NRS uptake is observed with the increase of initial solution pH up to 3 for Amberlite IRA-402. Amberlite IRA-402 and Amberlite IRA-958 in chloride form as well as modified by means of NRS were used for recovery of Pd(II) ions from 0.1, 0.5 and 1.0 mol/dm³ HCl solutions.The studied anion-exchangers in NRS form as far as their application in removal of Pd(II) chlorocomplexes is concerned can be presented in the order: Amberlite IRA-402 > Amberlite IRA-958.     

Activated carbon adsorption of cyanide complexes and thiocyanate ion from petrochemical wastewaters

Experimental isotherms indicate that thiocyanate and nickel cyanide complex (tetracyanonicklate (II)) adsorb to an equal extent from synthetic and actual waste solutions at loadings below 10 mg/g carbon. Loading of nickel hexammine complex is an order of magnitude less. Adsorption of the divalent nickel cation is strongly pH dependent and is believed to be a chemisorption by precipitation or reaction on the carbon surface. In pure solution, ferrocyanide (hexacyanoferrate (II)) adsorption was comparable to that of thiocyanate or nickelocyanide, but adsorption from the waste liquor tested was negligible. This difference may be due to solvation of ferrocyanide with methanol in the wastewater to form a species with entirely different adsorption characteristics. Chemical oxygen demand (COD) values were obtained for several of the pure materials (SCN^?, 1.1; Fe(CN)₆^?4, 0.5; Ni(CN)₄^?2, 0.4 mg $\text{COD}\text{mg}$ ion) and the wastewater to monitor adsorption of organic background materials.     

Ion flotation and solvent sublation of cobalt cyanide complexes

An experimental investigation into the batch ion flotation of cobalt complex anions with the cationic surfactant, cetylpyridinium chloride is described. The concentration ratio of cetyl-pyridinium: cobalt in the foam was determined and found to be 2.0–2.7 for CoCl₂ plus KCN solution and 3.0–3.3 for K₃[Co(CN)₆] solution. Spectroscopic measurements of the former anion show that mainly [Co(CN)₅H₂O]²- anions were floated. The [Co(CN)₆]^3- flotation was established in the presence of Cl^?, Br^?, I^?, CN^?, NO₃^? and SO₄^2- anions. The accelerating influence of the ion flotation produced by the presence of Cl^?, Br^?, I^?, CN^?, NO₃^? and SO₄^2- increased as their partial molal volume increased. The solvent sublation of [Co(CN)₆]^3- anions was established in the presence of these anions.     

TEMPERATURE EFFECT ON ION EXCHANGE SORPTION OF PHOSPHATE

Phosphate sorption on the strong basic anion exchanger Amberlite IRA-400 (Cl^? form) is studied as a function of temperature ( 25^°C–50^°C), at two initial pH values (5 and 9 ) in the concentration range 120–190 ppm. Chloride released/phosphate sorbed ratios increase with the increase both in temperature and pH and decrease with the increase in the concentration of solution. It is suggested that phosphate sorption takes place initially as HPO₄ ^2? followed by H₂PO₄ ^?. The data is explained with the help of a modified Langmuir and mass law action equations. Various thermodynamic parameters (ΔG^°,ΔH^° and ΔS^°) are presented. The differential isosteric heat of adsorption, is computed at different temperatures, showing the sorption of phosphate to be endothermic on the anion exchanger Amberlite IRA-400.     

Selectivity Coefficients for Zn(CN)4 2-, Cd(CN)4 2-, and Hg(CN)4 2- from Continuous Foam Fractionation with a Quaternary Ammonium Surfactant

Abstract

An experimental study is presented on the continuous flow, foam fractionation of cyanide complex anions. Zn(CN)₄ ^2-, Cd(CN)₄ ^2-, and Hg(CN)₄ ^2- form 7.5 × 10^?6 to 1.5 × 10^?5 M aqueous solutions with the quaternary ammonium surfactant, hexadecyltrimethylammonium iodide. The selectivity coefficients were determined for Zn(CN)₄ ^2- vs I^? equal to 8.86. for Cd(CN)₄ ^2- vs I^? equal to 21.79 and for Hg(CN)₄ ^2- vs I^? equal to 25.12. The surfactant ion-exchange reaction with the studied complex ions was also suggested.     

Chromogenic anionic chemosensors based on protonated merocyanine solvatochromic dyes: Influence of the medium on the quantitative and naked-eye selective detection of anionic species

Three merocyanine solvatochromic dyes, Brooker's merocyanine, Reichardt's dye and 4-(2,4,6-triphenylpyridinium-1-yl)phenolate were solubilized in acetonitrile. Although solutions of each of the compounds are colored, the color disappears after protonation. Addition of various anions to solutions of the protonated dyes revealed that only CN^?, F^?, and H₂PO₄^? led to the reappearance of the original color of protonated Reichardt's dye, and only CN^? and F^? ions caused the original color of the solutions containing the other two protonated dyes to reappear. Addition of small amounts of water to solutions containing the protonated compounds made them useful only for detecting CN^? among all the other anions. A model was used to explain the experimental results, which considers proton transfer from the protonated dye to the anion through three dye:anion stoichiometries, namely 1:1, 1:2, and 1:3.     

Removal of Congo Red dye from aqueous solution using Amberlite IRA-400 in batch and fixed bed reactors

Removal of Congo Red (CR) azo dye by adsorption process using Amberlite IRA-400 resin was evaluated in both batch and fixed bed system. From the batch adsorption results, maximum loading efficiency (99.99%) of CR dye was obtained at the conditions pH 4.5, temp. 303?K, contact time 180?min., Amberlite IRA-400 dose 0.5?g. The isotherm study ascertained on favorability of adsorption process as the value of separation factor (K_L?=?0.88) and Freundlich constant (1/n?=?0.96?R²?=?0.99) than Freundlich model (R²?=?0.97). The kinetic data studied at three different CR dye concentration (50, 75, 100?mg) and results were fitted with both pseudo-first-order and second-order model equations. The values of R² obtained are of 0.95 and 0.99 for former and later one, respectively, ensuring on best fitting of pseudo-second-order kinetics and also suggesting about the chemisorptions type of adsorption. The bed depth service model was applied for competitive analysis of the CR dye adsorption in column variables indicating mass transfer from aqueous solution to Amberlite IRA-400 phase. Fourier transform infrared analysis of CR-loaded resin Amberlite IRA-400 showed a band shifted from 1057 to 1130?cm^?1 confirming CR adsorption with Amberlite IRA-400. Scanning electron microscope analysis of resin before and after adsorption was well evident from the phase patterns. Selective separation of CR dye from waste effluent of a textile industry bearing CR dye along with other trace heavy metal was achieved.     

Investigation on conductivity of mixed surfactants reverse microemulsion

P-octyl polyethylene glycol phenyl ether (Triton X-100) and cetyltrimethylammonium bromide (CTAB) were mixed to be used as surfactant for preparing reverse microemulsion with n-hexane, n-hexanol and water. Effects of weight ratio of the two surfactants, temperature, concentrations of water and cosurfactant on the conductivity were studied. The results indicate that the conductivity of the mixed surfactants reverse microemulsion is greatly higher than that of the single surfactant system. The reverse microemulsion has been modified to be with good conductivity. The weight ratio of the two surfactants, temperature, concentrations of water and cosurfactant have obvious effects on the conductivity of the reverse microemulsion. Furthermore, the electrochemical behavior of potassium ferricyanide [K₃Fe(CN)₆] in the mixed surfactants reverse microemulsion was investigated by cyclic voltammetry. The result shows that the redox processes of \textFe( \textCN ) ₆ ^3- / \textFe( \textCN ) ₆ ^4- {{\text{Fe}}\left( {\text{CN}} \right)_{ 6}}^{ 3- } / {{\text{Fe}}\left( {\text{CN}} \right)_{ 6}}^{ 4-} present good reversibility and are controlled by diffusion in the system.     

Copper Solvent Extraction from Waste Cyanide Solution with LIX 7820

The use of a solvent mixture of a quaternary amine and nonylphenol (LIX 7820) to extract copper cyanide from waste cyanide solution has been studied. Copper extraction is favorable at low pH, whereas a high cyanide‐to‐copper ratio tends to suppress copper loading. The preferential extraction of Cu(CN)₃ ^2? over Cu(CN)₄ ^3? and CN^? has been confirmed by the examination of both the extraction of copper and cyanide by the solvent mixture under different experimental conditions. The solvent mixture also strongly extracted zinc and nickel from the cyanide solution, but it exhibits weak affinity for iron cyanide complex and free cyanide. The important findings suggested the potential application of the solvent mixture for the recovery of copper and cyanide from waste cyanide solutions, by which copper can be extracted and concentrated into a small volume of solution and the barren cyanide solution recycled to the cyanidation process.     

Redox copolymer with N-bromosulfonamide groups for the decomposition of cyanide ions in dilute aqueous solutions

A redox copolymer, macroporous poly(styrene-co-divinylbenzene) (S/DVB) resin having N-bromosulfonamide groups, was used for removal of cyanide ions from aqueous solutions. This resin contains active bromine in functional groups (1.86 mmol g^?1, i. e. 3.72 meq g^?1) and shows oxidative properties. It was employed in static and flow system for oxidation of cyanide ions to non-toxic compounds. The reactions were carried out in aqueous media containing 26–2600 mg L^?1 CN^? at different pH values. The data showed that the resin having active bromine easily oxidized cyanides, forming cyanates being 1000-times less toxic than cyanides. In contact with the resin the concentration of cyanides in tested solutions dropped below 0.05 mg L^?1 CN^?. During the oxidation processes the ? SO₂NBrNa groups transform to ? SO₂NH₂ groups. They can be reactivated by use of sodium hypochlorite and bromide solutions. As an alternative to oxidation of cyanides by N-bromosulfonamide resin, the oxidation of these ions by N-chlorosulfonamide resin with addition of a small amount of bromides was examined.     

Voltammetric study of the cyanide complexes of osmium—II. The behaviour of lower oxidation state cyanide complexes of osmium on a platinum rde

It was found that the product of the reduction of the cyanide complex of hexavalent osmium, OsO₂(OH)₂(CN)^2?₂ is the Os(OH)₄(CN)^3?₄ complex and the product of the reduction of the OsO₂(CN)^2?₄ complex is the Os(OH)₂(CN)^2?₂ complex. Further reduction of the Os(OH)₄(CN)^3?₄ complex of trivalent osmium is complicated by a follow-up chemical reaction and the stable reduction product is a complex of divalent osmium, Os(OH)₂(CN)^4?₄ which forms a reversible redox system with the Os(OH)₂(CN)^3?₂ complex with a formal redox protential (1 M KOH, 0.1 M KCN) of ?760 mV/sce. The Os(OH)₄(CN)^3?₂ and Os(OH)₂(CN)^4?₄ complexes are stable only in solutions with at least a ten-fold excess of OH^? ions over the concentration of CN^t- ions. At greater cyanide concentrations, the chemical reactioins, Os(OH)₄(CN)^3?₂ → Os(OH)₂(CN)^3?₄ and Os(OH)₂(CN)^4?₄ → Os(CN)^4?₆, occur. The reaction rate for the latter reaction was found to be ?₄ = 1.87 × 10^t-4 l mol^?1 s^?1 in solutions with pH = 11.8. The characteristics of the individual forms of the cyanide complexes of osmium are also discussed.     

FIXATION MECHANISMS OF CESIUM ON NICKEL AND ZINC FERROCYANIDES

The retention of cesium on rhomboedric M^{1 2}Zn³/Fe(CN)⁶/2, xH₂O, trigonal Zn₂Fe(CN)₆, 2H₂O and cubic M¹ ₂Ni-2, Fe(CN)₄ ferrocyanides (M¹ = H₁, Na₁, K) was studied. The influence of the ferrocyanide composition and structure, the retention kinetics and capacity and the changes in the solid phase at each step of the ion fixation were studied by several different methods i radioactive tracers, atomic absorption, infra-red spectroscopy, X-ray diffraction and potentiometric measurements. All the ferrocyanides examined can remove radioactive cesium from aqueous solutions with high efficiency. The main mechanism is the substitution of cations in the ferrocyanide by cesium leading to nixed cesium ferrocyanides. The kinetics are very fast on nixed ferrocyanides containing both alkali and divalent metal ions, but much slower (requiring several hours to reach equilibrium) on simple zinc ferrocyanide. In the first case, the fixation is the result of monovalent ion exchange with no structural change. In the second case, some zinc ions are released and the fixation is a complex phenomenon involving a structural change. A new preparation process (slow growth on solid alkaline ferrocyanide placed in a concentrated nickel or zinc solution) makes it possible to recommend these materials for the treatment of radioactive waste solutions using column chromatography.     

Photo‐oxidation of cyanide in aqueous solution by the UV/H2O2 process

Photo‐oxidation of cyanide was studied in aqueous solution using a low‐pressure ultra‐violet (UV) lamp along with H₂O₂ as an oxidant. It was observed that by UV alone, cyanide degradation was slow but when H₂O₂ was used with UV, the degradation rate became faster and complete degradation occurred in 40 min. The rate of degradation increased as the lamp wattage was increased. It was also observed that cyanide oxidation is dependent on initial H₂O₂ concentration and the optimum dose of H₂O₂ was found to be 35.3 mmol dm^?3. Photo‐oxidation reactions were carried out at alkaline pH values (10–11) as at acidic pH values, cyanide ions form highly toxic HCN gas which is volatile and difficult to oxidise. By the UV/H₂O₂ process, using a 25 W low‐pressure UV lamp and at alkaline pH of 10.5 with an H₂O₂ dose of 35.3 mmol dm^?3, cyanide (100 mg dm^?3) was completely degraded in 40 min when air was bubbled through the reactor, but when pure oxygen was bubbled the time reduced to 25 min. The cyanide degradation reaction pathway has been established. It was found that cyanide was first oxidised to cyanate and later the cyanate was oxidised to carbon dioxide and nitrogen. The kinetics of cyanide oxidation were found to be pseudo‐first order and the rate constant estimated to be 9.9 × 10^?2min^?1 at 40 °C. The power required for complete degradation of 1 kg of cyanide was found to be 167 kWh (kilowatt hour). Copyright © 2004 Society of Chemical Industry     

Piperazine Functionalized Resins for Au(III), Pt(IV), and Pd(II) Sorption

The result of synthesis of anion exchangers bearing piperazine functionalities is presented in this paper. A series of new ion exchange resins was synthesized by modification of VBC/DVB copolymer with 1(2-aminoethyl)piperazine (resin 1P), 1-amino-4-methylpiperazine (resin 2P), and 1-methylpiperazine (resin 3P). Adsorption studies of gold, platinum, and palladium were conducted with batch and dynamic method from multicomponent solutions containing AuCl₄^?, PtCl₆^2?, and PdCl₄^2? in the concentration range 10 mg/dm³ to 919 mg/dm³. The resins revealed excellent sorption ability towards these metals. The greatest total sorption capacities were determined as 331 mg/g Au for 2P resin, 405 mg/g Pt for 3P resin, and 150 mg/g Pd for 1P resin. The examined 3P resin showed the best total sorption capacity 796 mg/g. Affinity studies were also conducted. The examined resin 1P revealed the greatest affinity to platinum and palladium (lgK 4.5-5) whereas resin 2P revealed the best affinity to gold where lgK were ca. 4.9.     

The Uptake of Gold(I) from Ammonia Leaching Solution by Imidazole Containing Polymeric Resins

Abstract

The polymeric resins containing guanylthiourea, 1-methylimidazole, 2-mercapto-1-methylimidazole ligands have been synthesized from vinylbenzyl chloride-divinylbenzene copolymers and used in the removal of Au(I) from ammonium buffer and ammoniacal thiosulphate solutions. The best gold sorption from ammonium buffer that contains 100 g/dm³ NH₃ · H₂O and 5 g/dm³ (NH₄)₂SO₄, is reached in the case of 1-methylimidazole resin (2) (27.9 mg/g) and all three resins do not have a measurable sorption of copper(II) ammine complexes. The resins display a higher affinity towards gold(I) from ammoniacal thiosulphate solutions than from the ammonium buffer solution. The XPS analysis of gold loaded resins suggests the presence of gold at Au(I) oxidation state, most likely in the form of ionic pair Au(NH₃)₂ ⁺OH^? or neutral complex AuNH₃OH and as highly-dispersed metallic gold. The degree of gold desorption is about 50% using 1% potassium cyanide solution in 0.3% hydrogen peroxide solution. Resins retain their capacity towards gold in five consecutive sorption/desorption cycles.     

Use of three types of magnetic biochar in the removal of copper(II) ions from wastewaters

Three types of magnetic biochars (MBC1, MBC2, and MBC3) were synthesized from biochar using NaBH₄ as a reducing agent of Fe(II) to Fe(0) to remove copper(II) ions from different wastewaters. Based on the research it was found that removal of copper(II) ions by MBC1 occurs with a yield of 99.8% for the concentration 50 mg/dm³ and decreases to 71.7% at 200 mg/dm³. The maximum pH sorption was found at pH 5. The highest correlation coefficient values (65.55 mg/g) were obtained for the Langmuir isotherm model. Application of 0.5 mol/dm³ HNO₃ as a desorbing agent gives the highest desorption percentage 98.92%.     

A study of ion exchange at the poly(butyl viologen)-electrolyte interface by SECM

In this work, the ion exchange characteristics of poly(butyl viologen) (PBV) thin films on a platinum electrode has been investigated by cyclic voltammetric (CV) scans. Since ferrocyanide anions (Fe(CN)₆⁴⁻) were added during the polymerization of the PBV thin-film for its stability, Fe(CN)₆⁴⁻ could form charge transfer complex with monomer and co-deposited with polymer. Scanning electrochemical microscopy (SECM) was used to probe the released Fe(CN)₆⁴⁻ ions from PBV film with Os(bpy)₃Cl₂ as a mediator for the approaching process in 0.5 M KCl medium. Mass changes during the redox process of the film were also monitored in-situ by electrochemical quartz crystal microbalance (EQCM). The ion exchange and transport behavior was observed during CV cycling of the film of the SECM and EQCM. The insertion and extraction of anions were found to be potential-dependence. Moreover, the decrease in tip current of released Fe(CN)₆⁴⁻ with increasing cycle number accounted for the ion exchange between Fe(CN)₆⁴⁻ and Cl⁻ in the KCl electrolyte. However, the Fe(CN)₆⁴⁻/Fe(CN)₆³⁻ redox couple was found to be highly stable between 0.0 and 0.5 V (vs. Ag/AgCl/saturated KCl) in the phosphate buffer solution. Therefore, the electrochemical property of Fe(CN)₆⁴⁻/Fe(CN)₆³⁻ redox couple was studied at different scan rates using CV technique. The peak currents were directly proportional to the scan rate as predicted for a surface confined diffusionless system. The surface coverage (Γ) and the concentration of Fe(CN)₆⁴⁻ were determined to be 1.88 × 10⁻⁸ mol/cm² and 0.641 mol/dm³, respectively. By neglecting cations incorporation during redox reaction of the PBV film and also based on the results obtained from energy-dispersive X-ray spectroscopy for the films of as-deposited, reduced and oxidized states, an ion exchange mechanism was proposed.     

Voltammetric study of the cyanide complexes of osmium—I. The reduction of the cyanide complex of Os(VI) on a platinum rde

Two forms of cyanide complexes of hexavalent osmium were found in alkaline KCN solutions. The initially formed complex, OsO₂(OH)₂(CN)^2?₂, is stable only in solutions with at least a ten-fold excess of OH^? ions over CN^? ions. At higher cyanide concentrations it is converted into the OsO₂(CN)^2?₄ complex. Both these complexes are reduced to tervalent osmium. A more detailed study of complex OsO₂(OH)₂(CN)^2?₂ has shown that it is reduced electrochemically according to the scheme of a consecutive electrochemical reaction.OsO₂(OH)₂(CN)^2?₂ + 2e(k₁,α₁) → Os(IV) + e(k₂,α₂) → Os(OH)₄(CN)^3?₂The values α₁ = 0.65 and α₂ = 0.40 and the potential dependences of constants k₁ and k₂ were determined.     

Kinetic study of Hg(II)-promoted substitution of cyanide from hexacyanoferrate(II) in an anionic surfactant medium by 2,2′-bipyridine

The kinetic investigation of Hg(II)-promoted reaction between [Fe(CN)₆]⁴⁻ and 2,2′-bipyridine (Bipy) has been performed in anionic sodium dodecyl sulfate (SDS) micellar medium by recording the surge in absorbance at 400 nm, corresponding to ultimate reaction product [Fe(CN)₄ Bipy]²⁻ using UV–visible spectrophotometer. Pseudo-first-order condition has been used to examine the progress of reaction as a function of temperature, [Fe(CN)₆⁴⁻], ionic strength, [SDS], pH, [Hg²⁺], and [Bipy] by changing one parameter at a time. The results exhibit that [Hg²⁺], [SDS], and pH are the decisive parameter showing maximum reaction rate at 1.5 × 10⁻⁴ mol dm⁻³, 6.0 × 10⁻³ mol dm⁻³, and 3.8, respectively. [Fe(CN)₆]⁴⁻ does not show any appreciable effect on the critical micellar concentration (CMC) of SDS as the polar head of SDS and [Fe(CN)₆]⁴⁻ both are negatively charged. Variable order kinetics was observed for [Fe(CN)₆]⁴⁻ and Bipy in their examined concentration range. The reverse response observed in the reaction rate with [KNO₃] shows a negative salt effect. The K⁺ provided by K₄[Fe(CN)₆] and KNO₃ decreases the repulsion between the negatively charged heads of the surfactant molecules thereby decreasing the CMC of SDS. The negative value for the entropy of activation also supports the interchange dissociative (I_d) mechanism recommended by us.     

Faradaic impedance titration and control of electron transfer of 1-(12-mercaptododecyl)imidazole monolayer on a gold electrode

In this work, we studied interfacial proton transfer of the self-assembled monolayer (SAM) of 1-(12-mercaptododecyl)imidazole on a gold electrode by faradaic impedance titration method with Fe(CN)₆³⁻ as an anionic redox probe molecule. The surface pK_1/2 was found to be 7.3, which was nearly the same as that of 1-alkylimidazole in solution. We also investigated the electrochemical properties of the SAM-modified electrode by cyclic voltammetry. Cyclic voltammetry was performed (1) in the solution containing Fe(CN)₆³⁻ with repeated alternation of pH values to investigate the electrostatic interaction of the protonated or deprotonated imidazole with Fe(CN)₆³⁻ and (2) in the acidic or basic electrolyte containing Ru(NH₃)₆³⁺ as a cationic redox probe to verify the effect of the polarity of a redox probe. We observed the reversible adsorption/desorption of Fe(CN)₆³⁻ and concluded that the adsorbed Fe(CN)₆³⁻ catalyzed the electron transfer of both Fe(CN)₆³⁻ itself and cationic Ru(NH₃)₆³⁺.