Thiocyanate Media Research Articles

Oxidation of mercury microelectrodes in complexing media in the presence and absence of supporting electrolyte:: Formation of thiocyanate complexes

Normal pulse- and staircase-voltammetric oxidation of a mercury microelectrode in thiocyanate media both with and without supporting electrolyte was investigated. An equation describing the normal pulse voltammetric limiting currents flowing through a nearly spherical segment microelectrode was developed theoretically and verified experimentally. The diffusion coefficients of mercury(II) complexes containing different numbers of the thiocyanate anions were determined. A general time-dependent digital simulation scheme was developed for calculating the current for the oxidation of mercury(0) in the presence of ligands and excess supporting electrolyte and for any pulse voltammetric technique. The time-dependent mass balance equation recently developed for a system, in which diffusion coefficients of reactant and products are different, was applied. A brief review was given on the standard potentials of various mercury systems available in the literature. A general procedure for the evaluation of the stability constants of metal complexes based on the shape of the voltammograms was described and applied to the case of thiocyanato complexes of Hg(II). The stability constant results agreed well with those of Nyman and Alberts [Anal. Chem. 32 (1960) 207]. Also discussed was the determination of the formation constant β 1 for Hg(SCN) +.

EXTRACTION OF U(VI) FROM NITRATE AND THIOCYANATE MEDIA WITH MONOAMIDES

ABSTRACT The extraction of UO2 2+ from nitrate and thiocyanate media at pH 2.0 has been carried out using N,N-methylbutyldecanamide (MBDA), N,N-dibutyldecanamide (DBDA), and N,N-dihexyldecanamide (DHDA) in dodecane, chlorobenzene, o-dichlorobenzene, and xylene. Thermodynamic parameters for the extraction of UO2 2+ in the system NO3 −/SCN−–DHDA in dodecane have been calculated from the temperature dependence of the log K ex values. UO2 2+–SCN–amide complexes have been synthesized, characterized, and compared with the species extracted in the organic phase from such systems.

Voltammetry of immobilised microparticles: a powerful analytical technique to study the physical and chemical composition of brass

Voltammetry of immobilised microparticles with a square wave potential scan (SQW) is used to study the phases composition of brass. Several electrolytes are considered in order to obtain peaks representing all the brass phases as well as to achieve the best resolution between peaks. Cyclic voltammetry was also used to characterise the electrode processes and the results obtained were in agreement with those from SQW voltammetry. The position and shape of the peaks changed with the media and concentration used to perform the experiment. Thiocyanate medium offered the richest information.

NITROGEN REAGENTS IN METAL ION SEPARATION. XI. THE SYNTHESIS AND EXTRACTION BEHAVIOR OF A NEW NS IMIDAZOLE DERIVATIVE

A new extractant with an NS donor chromophore viz. 2-(1-ethylthiomethyl)-1-decyl imidazole (ETDIMZ) has been synthesized. Its extraction behavior towards each of Co2+, Ni2+, Cu2+, and Zn2+ in each of perchlorate, chloride and thiocyanate media in dilute acid media have been studied. Its behavior was compared with a similar pyridine derivative, viz. 2-(octylthiomethyl)-pyridine (OTMP) under comparable conditions. These behaviors have been interpreted in terms of the coordination chemistry of the metal ions. It was shown how formation constants of simple ligands, symmetry of the complex species and phase transferability can influence extraction behavior and how the above parameters can assist in the development of metal ion specific extractants.

Solvent extraction of uranium(VI) using dibenzo-18-crown-6 in nitrobenzene from ammonium thiocyanate medium

Solvent extraction of uranium(VI) from aqueous solutions of ammoniumthiocyanate has been investigated in the presence of dibenzo-18-crown-6. Uranium(VI)was quantitatively extracted from 1.0M ammonium thiocyanate using 0.01M dibenzo-18-crown-6in nitrobenzene. Back extraction of U(VI) was quantitative with various strippingagents. Separation of U(VI) from other elements was achieved from binary aswell as multicomponent mixtures. Uranium was determined in monazite sand andsyenite rock samples. The method is very simple, rapid and highly reproducible(approximately ±2%).

Separation of trace amounts of palladium (II) with crown ether from hydrochloric acid and potassium thiocyanate media.

A new method for the separation of trace amounts of palladium from hydrochloric acid and potassium thiocyanate media has been established based on the formation of an ion-pair complex of palladium thiocyanate anion Pd(SCN)4(2-) and the cationic potassium complex of dicyclohexyl- 18-crown-6 (DC18C6) in chloroform. The effect of various factors (solvent, crown ether, potassium thiocyanate, hydrochloric acid, reagent concentration, shaking time, phase volume ratio, composition of the extracted species, foreign ions, etc.) on the extraction and back-extraction of palladium has been investigated. The method can be combined with subsequent FAAS determination of palladium. The procedure was applied to determine palladium traces in chloroplatinic acid and rhodium chloride.

Analysis of the Electrode Kinetics of Ni(II) Reduction in Thiocyanate Media on the Dropping Mercury Electrode

A study of two prewaves of the Ni(II)-SCN- system was carried out under the experimental conditions when the influence of electroreduction of SCN- is negligible. Kinetics of Ni(II) reduction in thiocyanate media on the dropping mercury electrode was studied by DC Tast Polarography (DCTP) via determination of Koutecký's parameter χ; the influence of different variables was analyzed. The study of prewaves was performed using various polarographic techniques. Values of χ depend on the SCN- concentration, pH, ionic strength (Ψ-effect) and on the nature of the supporting electrolyte. The number of electrons n, the transfer coefficient α, the stoichiometric number ν, ∆H≠, and ∆S≠ were determined (compensation effect). The first prewave has character of a reaction in the solution, the second prewave is a surface process. Main features of both mechanisms are common: catalytic nature, one-electron step discharge and the rate-determining process between species of opposite charges.

Radiometric determination of trace amounts of zinc using liquid scintillation counting

A sensitive and selective radiometric method of substoichiometric isotope dilution analysis for the determination of trace amounts of zinc is described. The activity of 65Zn used as a tracer in this method was measured by liquid scintillation counting and its counting efficiency was found to be 76±2.7%. The method is based on the extraction of the ion-association complex of zinc from thiocyanate medium at pH 7.9 using substoichiometric amount of Aliquat-336 in toluene. The method is sensitive to 20 ng of Zn(II) in an aqueous phase volume of up to 15 ml and its reliability was tested by applying it to a certified reference material—magnesium alloy and pharmaceutical samples.

Extractive Separation of Selenium and Tellurium Using 2,3,5-Triphenyltetrazolium Chloride

Abstract A simple and selective solvent-extraction method has been devised for the separation of SeIV and TeIV, not only from each other, but also from the other accompanying elements. 2,3,5-Triphenyltetrazolium chloride has been used as an extractant for the quantitative extraction of TeIV and SeIV from bromide and thiocyanate medium, respectively. The formed ion-pair complex of TeIV and SeIV can be quantitatively extracted into a dichloromethane and 1 : 1 cyclohexanol–toluene solvent mixture, respectively. The optimum conditions have been evaluated based on a critical study of the acid concentration, extractant concentration, period of equilibration, effect of dilution and effect of the solvent. Water was used for the stripping of tellurium, while a fresh solution of sodium hypobromite was used for selenium. This separation procedure in conjunction with the developed methods was applied to an analysis of the selenium and tellurium content of copper concentrate, incineration ash and In–Sb alloy samples.

Selective determination of cobalt using polyurethane foam and 2-(2-benzothiazolylazo)-2-p-cresol as a spectrophotometric reagent

The present work describes a selective, rapid and economical method for the determination of cobalt using the 2-(2-benzothiazolylazo)- p-cresol (BTAC) as a spectrophotometric reagent associated with a solid extraction on polyurethane foam. The BTAC reacts with Co(II) in the presence of Triton-X100 surfactant forming a green complex with maximum absorption at 615 nm. The reaction is used for cobalt determination within a pH range of 6.50–7.50, with an apparent molar absorptivity of 1.62 × 10 4 L mol −1 cm −1. Beer's Law is obeyed for a concentration of at least 1.60 μg ml −1. A selective procedure is proposed for cobalt determination in the presence of Fe(II), Hg(II), Zn(II) and Cu(II) up to milligram levels using masking agents. Polyurethane foam is used for the preconcentration and separation of cobalt from thiocyanate media and this procedure is applied to its determination in nickel salts and steel alloys.

Cl(-)-dependent NH4+ transport mechanisms in medullary thick ascending limb cells.

To characterize Cl(-)-dependent NH4+ transport mechanisms in renal medullary thick ascending limb (MTAL), intracellular pH (pHi) and membrane potential (PD) were monitored with use of 2',7'-bis(carboxyethyl)- 5(6)-carboxyfluorescein and 3,3'-dipropylthiadicarbocyanine, respectively, in suspensions of rat MTAL tubules in CO2-free media. Exposure of MTAL cells to 4 mM NH4Br caused, after an initial cell alkalinization due to NH3 entry, an NH4(+)-induced fall in pHi that was approximately 67% less pronounced in Cl(-)-free than in Cl(-)-containing media. The following experiments were performed in the presence of 1 microM amiloride to block the MTAL NH4+ conductance. When cells were preincubated in a Cl(-)-free gluconate medium in which K+ and Cl- conductances are greatly reduced, abrupt addition of 100 mN N-methyl-D-glucamine (NMDG)-Cl had no effect on cell PD and pHi in the absence of ammonia, but acutely acidified the cells by approximately 0.2 pH units in the presence of 4 mM NH4Br, which thus indicated nonelectrogenic (NMDG-Cl)-dependent NH4+ influx. The latter also occurred in a Cl(-)-free thiocyanate medium in which the Cl- conductance was blocked by 0.1 mM diphenylamine-2-carboxylate (DPC). An NMDG-Cl- dependent NH4(+)-induced fall in pHi was reduced approximately 33% by 10 mM Ba+, approximately 84% by 0.1 mM bumetanide, and 100% by 1.5 mM furosemide, whereas 1 mM hydrochlorothiazide had no effect; inhibition by Ba+ was observed even in the presence of 0.1 mM verapamil added to block both K+ channels and K+/NH4+ antiport.(ABSTRACT TRUNCATED AT 250 WORDS)

Extraction, Separation, and Determination of Nickel and Bismuth with 1-(2-Pyridylazo)-2-naphthol in Aqueous Thiocyanate Media

Abstract Nickel(II) and bismuth(III) are quantitatively extracted from aqueous thiocyanate solutions, adjusted to pH 4.0–9.0 and 3.5–5.0, respectively, using solutions of 1-(2-pyridylazo)-2-naphthol (PAN) in tri-n-butyl phosphate (TBP). The extracted species of nickel and bismuth have the formulas [Ni(PAN)SCN]·4TBP and [Bi(PAN)SCN]X·TBP, respectively. Polyurethane foam treated with TBP solution containing PAN is used successfully for the quantitative retention and recovery of nickel and bismuth from aqueous thiocyanate solutions in the column extraction mode. The preconcentration of small amounts (10 mg) of nickel and bismuth from dilute aqueous solutions (1 L) is also possible, with a recovery of 95–97%. The feasibility of using PAN-foam for selective detection and semiquantitative determination of nickel and bismuth in aqueous thiocyanate media is examined. The detection limits of nickel and bismuth by the foam batch method are 0.05 and 0.50 ppm, respectively. Lower concentrations of these metal ions ar...

Solvent extraction of Er(III) and Lu(III) with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester in presence of some reagents

The extraction of Er(III) and Lu(III) from thiocyanate media with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHEHPA) and also with mixtures of EHEHPA and thenoltrifluoroacetone (HTTA) or tri-n-octylphosphine oxide (TOPO) or bis 2-ethylhexyl sulfoxide (B2EHSO) in benzene has been studied systematically. Synergistic effects have been observed with mixtures of EHEHPA+HTTA or TOPO. On the other hand, antagonistic effects have been observed with mixtures of EHEHPA+B2EHSO. These extraction data have been analyzed theoretically with the aid of a computer by taking into account complexation of the metal in the aqueous phase by SCN− and plausible complexation in the organic phase. The extraction constants of the various product species have been deduced by non-linear regression analysis. The stability constants for the thiocyanate complexes of the metal ions have also been determined.

Modulation of the mitochondrial cyclosporin A-sensitive permeability transition pore by matrix pH. Evidence that the pore open-closed probability is regulated by reversible histidine protonation

Energized mitochondria in sucrose medium take up a Ca2+ pulse but do not show opening of the permeability transition pore (MTP) upon membrane depolarization by uncoupler. This is due to locking of the pore in the closed conformation by matrix acidification and fast Ca2+ efflux following membrane depolarization (Petronilli, V., Cola, C., & Bernardi P. (1993) J. Biol. Chem. 268, 1011-1016). Here we show that addition of diethyl pyrocarbonate (DPC) prior to membrane depolarization restores the ability of uncoupler to induce MTP opening. Since DPC does not modify the rate and extent of matrix acidification and the rate and extent of Ca2+ release following addition of uncoupler, its effects on pore opening appear to be due to modification of histidyl residues regulating the pore open-closed probability. This hypothesis was confirmed in studies with deenergized mitochondria incubated in potassium thiocyanate medium. While at acidic pH values pore opening is otherwise prevented, DPC allows Ca2(+)-dependent pore opening at pH 6.5 in a process that maintains full sensitivity to cyclosporin A. Pore induction by DPC can be completely prevented and partially reversed by hydroxylamine, indicating that the effect of DPC can be specifically traced to carbethoxylation of histidyl residue(s) rather than to reaction with tyrosyl or sulfhydryl groups, while the possible involvement of lysyl residues cannot be excluded. Since DPC increases the pore open probability even at matrix pH values between 7.0 and 7.7, we propose that reversible protonation of one or more histidyl residues on the matrix side of the MTP plays a role in the physiological modulation of pore opening.

A thermodynamic study of the dissolution of gold in an acidic aqueous thiocyanate medium using iron (III) sulphate as an oxidant

Species distribution and pH-potential diagrams have been constructed for the gold/iron/thiocyanate/sulphate/water system in the pH and concentration ranges expected in the practical leaching process. Apart from elucidating the complex chemistry of such a system, these diagrams were used to predict: the feasibility of; the optimum experimental conditions for; and the significant factors affecting the leaching of gold with acidic thiocyanate solutions in the presence of iron (III) sulphate.

Liquid-liquid extraction of cerium(III) from thiocyanate media with mixtures of organophosphorus extractants.

The extraction of Ce(III) from thiocyanate solutions with mixtures of 2-ethylbexylphosphonic acid mono-2-ethylhexyl ester (EHPNA) and di(2-ethylhexyl)-phosphoric acid (DEHPA) or tri-n-butyl phosphate (TBP) in benzene has been studied systematically over a wide range of conditions. A relatively small synergistic enhancement has been observed with mixtures of acidic organophosphorus extractants (EHPNA + DEHPA) and also with mixtures of acidic and neutral organophosphorus extractants (EHPNA + TBP). These extraction data have been analysed theoretically, taking into account complexation of the metal in the aqueous phase by inorganic ligands and plausible complexation in the organic phase.

Extraction and separation of Zr, Nb and Hf by Aliquat 336 and its mixtures with TOPO from acidic thiocyanate media

Presence of thiocyanate ions results in appreciable extraction of Zr(IV) by Aliquat 336 from low aqueous HCl acidities, i.e., 0.1 to 4.5M. The variation of concentrations of HCl, thiocyanate and Aliquat 336 greatly influences the extent of extraction. Mixtures of Aliquat 336 and TOPO result in synergistic extraction of Zr and Hf from acidic thiocyanate media, the extracted species being the disolvate with TOPO. By controlled adjustment of HCl, SCN− and Aliquat 336 concentrations, separation of Zr, Nb and Hf is possible. A maximum separation factor (DNb/DZr) of 3675 has been achieved under certain conditions.

Organophosphorus reagents as extractants—part 3. Synergic effect of triphenyl phosphine oxide and bis(diphenyl phosphinyl) alkanes on extraction of iron(III) from thiocyanate medium with 2,4-pentdione

The extraction of iron(III) from thiocyanate medium was carried out with a synergic combination of 2,4-pentdione (Hacac) and either triphenyl phosphine oxide (Ph 3 PO) or bis (diphenylphosphinyl) alkanes, Ph 2P(O)(CH 2) n ·P(O)PH 2 [ligand abbreviation, n: dpeO 2, 2; dpbO 2, 4]. Iron(III) was quantitatively separated from its binary mixture with chromium(III), manganese(III), cobalt(II), nickel(II), zinc(II), cadmium(II), mercury(II), lead(II), magnesium(II) and from steel samples. Copper(II) and silver(I) however, interfered. The percentage extraction was 99.0%. The respective extraction constants, K HA, K L or K syn, for the extracted species, [Fe(NCS)(acac) 2(H 2O)] (HA  Hacac), Fe(NCS) 3L 2 [L b Ph 3PO, dpeO 2 or dpbO 2], or Fe(NCS)(acac) 2L were found to be: K HA, 1.48 × 10 3, K L, 1.80 × 10 2 (L  Ph 3PO), 2.02 × 10 2 (L  dpeO 2 or dpbO 2) and K syn, 1.87 × 10 6 (L  Ph 3PO), 2.56 × 10 6 [L  dpeO 2 or dpbO 2].

THE EXTRACTION OF COBALT(II) FROM A THIOCYANATE MEDIUM BY SOME DIAMINE AND MONOAMINE EXTRACTANTS DISSOLVED IN 5% ISODECANOL - BENZENE

Abstract The tertiary amine extractants N,N,N’,N’-tetra-n-octylethylenediamine, N,N-di-n-octyl-2-(aminomethyl)pyridine and Alamine 336 were used to extract cobalt(II) from a thiocyanate medium. The extraction equilibria were identified and the extraction constants for these equilibria are presented. Thiocyanic and sulphuric acid extraction was investigated. The protonation constants of the tertiary amines with these acids are reported. The potential of the chelate mode, displayed by tertiary diamine extractants, was evaluated. The extraction properties of tertiary diamine extractants were demonstrated to be superior to a tertiary monoamine extractant, Alamine 336.

Synergistic Extraction Studies of Thiocyanate Complexes of Gadolinium, Dysprosium and Erbium with Mixture of Tributyl Phosphate and Tricaprylmonomethylammonium Chloride

The synergistic extraction behavior of thiocyanate complexes of gadolinium, dysprosium and erbium has been studied for a mixed system: M3+/NH4SCN/tributyl phosphate (TBP)+tricaprylmonomethylammonium chloride (Aliquat-336)+ xylene. The percentage extraction and distribution ratios were measured as a function of the pH as well as the NH4SCN, Aliquat-336 and TBP concentrations, respectively. The percentage extraction of gadolinium, dysprosium and erbium increases with increase in pH. It was significant in the pH range 4 to 6 in a thiocyanate media. The composition of a binary synergistic extracted complex of lanthanides into the organic phase is probably M(SCN)52-(L+)2•2TBPo under the conditions studied. The synergistic extraction sequence as a function of the atomic number of lanthanide elements is given.