Liquid-Liquid Extraction Studies of Trivalent Yttrium from Phosphoric Acid Solutions Using TOPS 99 as an Extractant

Liquid-liquid extraction studies of trivalent yttrium (Y) from phosphoric acid solutions have been carried out with commercial organophosphoric acid based extractant TOPS 99 (Talcher Organo phosphorus solvent, an equivalent of di-2-ethylhexyl phosphoric acid). The parameters studied include equilibration time, acid concentration, extractant concentration, diluent, metal concentration, temperature, stripping, and regeneration of the extractant. Increase of phosphoric acid concentration in the range from 0.01 to 0.5 M on the extraction of trivalent Y with 6 × 10^?3 M TOPS 99 (Talcher Organo phosphorus solvent) decreases the percentage extraction, indicating the transfer of metal follows ion exchange type reaction. The plot of log D vs. equilibrium pH gave a straight line with a slope of 3.1 indicating the exchange of three moles of hydrogen ions for every mole of trivalent Y extracted into the organic phase. Stripping of metal from the loaded organic with mineral acids indicate sulphuric acid as the best stripping agent. The extraction behavior of associated elements clearly follows their ionic radii with a maximum separation factor of 414 for Lu-Tb.     

Variations in the Composition of Bromine Water During Oxidation Reactions

A cubic equation has been derived that permits calculation of the composition of aqueous bromine solutions in terms of HOBr, BrO^?, Br₂, Br^?₃ and Br^? as a continuous function of the pH, the initial oxidant concentration and the mole fraction of oxidant consumed. The calculations were performed by computer for the pH range 0–14 at bromine concentrations (c₀) of 10^?1 to 10^?7 M. Throughout the course of an oxidation at pH 0 and c₀= 10^?4, bromine water is pure Br₂. No Br^?₃ exists at c₀ < 10^?3. In the pH range 4–6, dilute bromine solutions are pure HOBr (+ equimolar Br^?). For pH > 10, bromine water is pure BrO^?, while at pH < 7, no BrO^? is present. These conditions are unchanged during oxidant consumption.     

Platinum-Graphite Biamperometric Indication for the Low Concentration Determination of Antimony,Arsenic and Tin

The application of a bi-electrode system for the determination of Sb (III), As (III) and Sn (II) in dilute solutions is described. The electrode system consists of a platinum microelectrode and a wax-impregnated graphite electrode. Iodine is used as oxidant. The determinations are quite accurate even in 10^?3–10^?4M concentration range.     

Removal of tin from dilute solutions

The fluidised bed cell of inert glass beads is an electrolytic reactor which is designed to provide higher ion‐transfer conditions during electrolysis, thus enabling metals to be removed efficiently from dilute solutions. The effectiveness of the method as a means of removing metals from effluent to meet discharge consent levels is studied for the in situ removal of tin from dilute solution (concentration range 0.25–1.00 gdm⁻³). The results show that the combination of high mass transport conditions and a moderately high electrode surface area per unit electrode volume provides a system for continuous removal of metal from dilute solutions. The effects of acid concentration, tin concentration, current density, fluidised bed agitation, electrode spacing, type of electrode and lead impurities on the removal of tin are reported and expressed in terms of the percentage removal of tin (α_Sn), the efficiency of tin deposition (ϕ_Sn), and the energy consumption (W_Sn) for 1 kg of tin deposited. The results show that tin can, under optimised conditions, be removed from dilute solutions to a residual concentration of 0.001 gdm⁻³. © 2001 Society of Chemical Industry     

Inhibiting effect of citric acid on the pitting corrosion of tin

Potentiostatic and potentiodynamic studies were carried out to establish the inhibiting effects of citric acid on the pitting corrosion of tin. The critical potential (Ecrit), which leads to pitting or general corrosion, was determined in sodium perchlorate solution in the pH range 1.0 to 4.0. Pit nucleation and growth, at pH4.0, can be described by instantaneous nucleation followed by progressive nucleation. The results show that the minimum acid concentration needed to inhibit pitting of tin is 10–2m. Pitting occurrence by direct interaction between metal and perchlorate anions was observed.     

Construction and performance characteristics of a metformin electrode based on the metformin phosphotungstate ion-associate

A new metformin (Mf) ion selective PVC membrane electrode based on the ion-associate of Mf with phosphotungstic acid was prepared. The electrode exhibited a mean calibration graph slope of 58 mV Mf concentration decade^?1, at 25°C, within the concentration range 2·0 × 10^?5?1·0 × 10^?2 M MfCl. The change of pH within the range 4·0–11·0 did not affect the electrode performance. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode (0.000352 V°C^?1). The electrode showed a very good selectivity for Mf with respect to a large number of inorganic and organic cations. The standard addition method and potentiometric titration were applied to determine Mf in pure solutions and in metformin-containing tablets.     

The corrosion of iron in sulphate solutions at pH = 0–2

The effects of pH and stirring rate on the kinetics and mechanism of pure iron corrosion in deaerated, argon saturated solutions at 25°C have been studied. The entire concentration of sulphate ions in the tested solutions was 2.0 M. The increase of pH in the tested range causes the change of the anodic process mechanism, which is manifested in the decrease of the Tafel anodic straight line slope from 0.06 V (pH ～ 0) through 0.04 V (pH ～ 1) to 0.03 V (pH ～ 2) and the increase of the order of reaction with respect to OH^? ion, which is 0, 1 and 2 respectively. At adequately low potentials there occurs a change (to a small degree dependent on pH) of the anodic process mechanism which corresponds to the anodic straight line slope being 0.12 V. For the hydrogen evolution reaction the cathodic Tafel slope has been found to be ?0.12 V and the order of reaction with respect to OH^? ion to be ?1. Stirring of the solution has no practical effect on either the corrosion rate or the run of the polarization curves above pH = 1. For lower pH values, at the decrease of the stirring rate there occurs the increase of the corrosion rate and the increase of the anodic and cathodic process rate which is clearly visible below the corrosion potential. The cause of this phenomenon may be the catalyzing of both electrode processes by small quantities (～ 10^?7 Ml^?1) of the H₂SO₄ reduction products. The effect of pH on the corrosion potential and current has also been found.     

Separation of Carrier-Free 90Y from 90Sr by SLM Technique Using D2EHPA in N-Dodecane as Carrier

Solvent extraction studies on Sr²⁺ and Y³⁺ are carried out from varying concentrations (0.01–6.0 M) of nitric acid using di-(2-ethylhexyl)phosphoric acid (D2EHPA) as extractant. Extraction of yttrium is observed to be higher than that of strontium at all the acidities and is found to increase substantially with decreasing concentration of nitric acid. Practically negligible extraction (D < 10^?3) of Sr²⁺ is observed from feed solutions containing nitric acid in the range of 1.0 to 4.0 M. These solvent extraction data are used to optimize the transport of ⁹⁰Sr and ⁹⁰Y across the supported liquid membrane (SLM) individually as well as from their mixture (due to insitue growth) under different experimental conditions. Selective separation of ⁹⁰Y (>90%) from ⁹⁰Sr is obtained in 6 h, when the concentration of nitric acid in feed is kept at 1.0 M and that of receiving phase is maintained at 4.0 M. 20% D2EHPA in n-dodecane is found to be the optimum carrier concentration for the efficient transport of ⁹⁰Y in SLM mode. Under these conditions transport of strontium is found to be negligible. Radiochemical purity of the product ⁹⁰Y is checked by following its decay as well as by extraction paper chromatography. The contamination of ⁹⁰Sr in ⁹⁰Y product is found to be < 0.001%. Based on the experimental results, a single stage SLM system for the generation of carrier-free ⁹⁰Y from ⁹⁰Sr source is described. The system is amenable for automation and scale up.     

Potentiometric Determination of Alkyl Dimethyl Hydroxyethyl Ammonium Surfactant by a New Chemically Modified Carbon Past Electrode

This paper introduces the development a new chemically modified carbon paste electrode (CMCPE) for the determination of a cationic surfactant. The paste is based on alkyl dimethyl hydroxyethyl ammonium chloride (ADHACl) with phosphomolybdic acid as an ion‐exchanger (ADHA‐PM). The electrode exhibits a Nernstian slope of 59.1 ± 0.5 mV/decade for ADHA ions in the concentration range 1.0 × 10^?6–1.0 × 10^?3 M with the limit of detection of 8.2 × 10^?7 M. The proposed electrode has a fast and stable response time of 5–8 s, a good reproducibility and it can be used in the pH range of 2.2–9.0. Selectivity coefficients, determined by a matched potential method and separate solution method, showed high selectivity for ADHA over a large number of inorganic cations and organic cations. These characteristics of the electrode enable it to be used successfully for determination of ADHA in shampoo and liquid detergents solutions by standard addition and the calibration curve methods. In addition, the modified electrode was applied as an indicator electrode in potentiometric titration and successfully used to determine ADHA in water samples with satisfactory results.     

Poly(acridine orange)-modified glassy carbon electrodes: electrosynthesis,characterisation and sensor application with uric acid

Poly(acridine orange) was electropolymerised on glassy carbon electrodes by potential cycling in phosphate buffer solution at pH 5.5, 6.0, 7.0 and 8.0. Electrochemical behaviour of the modified electrodes was studied by cyclic voltammetry in phosphate buffer solution at various pHs and found that the best polymer film formation was obtained at pH 5.5. Quantitative determination of uric acid was achieved by cyclic voltammetry, differential pulse voltammetry (DPV) and fixed-potential amperometry in phosphate buffer solution at pH 5.5. Anodic peak currents were linearly proportional to concentration of uric acid in the range 1–75 µM for cyclic voltammetry, 0.4–75 µM for DPV and 0.04–5.3 µM for amperometry. Detection limits were 3.7 × 10^?1, 9.7 × 10^?2 and 9.5 × 10^?3 µM for cyclic voltammetry, DPV and amperometry, respectively. The modified electrodes exhibited good sensitivity, wide linear range and good stability. There is no interference from substances commonly present in natural samples.     

Corrosion rates of lead based anodes for zinc electrowinning at high current densities

The corrosion rates of anodes made from various lead/silver alloys have been determined during electrolysis in sulphuric acid solution, pure and containing additives, using current densities in the range 2500 to 10 000 A m^–2. An increase in acid concentration, and in some cases temperature, caused an increase in the corrosion rate. In the absence of manganese in the bath, the corrosion rate was effectively independent of current density in the range studied, whereas in the presence of manganese, the corrosion rate decreased with decreasing current density. The corrosion rates of various calcium, tin and thallium alloys of lead were also determined. The presence of chloride ions in the electrolyte increases the corrosion rate, whereas potassium ions and strontium carbonate have a negligible effect. Pre-treating silver/lead anodes with a solution of acidic potassium fluoride at 500 A m^–2 prior to testing markedly decreased the corrosion rate in the presence of manganese, but increased the corrosion rate with manganese absent. The effect of zinc on the corrosion rate in synthetic electrolyte solutions, with and without manganese present, has also been determined for silver/lead alloys at 10 000 A m^–2. At zinc levels over 1 M, the corrosion rate increased with and without added manganese. As the work has been undertaken in an attempt to improve the electrowinning of zinc, an electrolyte based on acidified industrial solution has also been tested. The rates observed were similar to those obtained for synthetic zinc-containing solutions.     

EXTRACTION STUDIES ON THE SYSTEM BETWEEN BIS(2-ETHYLHEXYL) PHOSPHORIC ACID AND CHROMIUM(III) IN SEVERAL AQUEOUS SOLUTIONS

The extraction of chromium(III) by carboxylic acids and acidic organophosphorus compounds has been investigated. In general, chromium(III) was not extracted by carboxylic acids but the organophosphorus compound, di-2-ethylhexyl phosphoric acid, was found to be particularly adequate for the extraction. The partition of chromium(III) in nitrate medium and solutions of di-2-ethylhexyl phosphoric acid in Shellsol-T was studied using a tracer of 51cr. Distribution measurements of the metal ion in a wide range of pH and organophosphoric acid concentrations have been performed. The experimental data treated by a graphical method have been explained assuming the presence in the organic phase of the species Cr(DEHP)₃(H₂O)²(HDEHP). Equilibrium constants for the different extraction reactions are given. The extraction of the monomeric species was found to be independent of Ac^?or SO⁼ ₄ions presence.     

Synthesis,Corrosion Inhibition Performance and Biodegradability of Novel Alkyl Hydroxyethyl Imidazoline Salts

New alkyl hydroxyethyl imidazoline salts were synthesized via a high pressure process with imidazoline and dimethyl carbonate, and their chemical structure were confirmed using mass spectral fragmentation and FTIR spectroscopic analysis. In addition, several quaternary ammonium salts with new counterions (formic acid, acetic acid and lactic acid) were also synthesized by ion exchange reaction of methyl carbonate quaternary ammoniums with the corresponding acids. These new compounds reduced the surface tension of water to a minimum value of approximately 27 mN m^?1 at a concentration of 8.72 × 10^?5 mol L^?1. They also show efficient corrosion inhibition performances and could significantly inhibit the corrosion of mild steel in acid solutions. It was also found that the biological degradation of these imidazoline surfactants was greater than 98 % after 7 days.     

Precipitate flotation. IV. Flotation of silver,uranium and gold

The conditions for the flotation of silver using α-nitroso-β-naphthol and β-nitroso-α-naphthol, that of uranium using α-nitroso-β-naphthol and benzoylacetone, and that of gold using phenyl-α-pyridylketoxime were examined. Recoveries of over 90% were possible from 5 × 10^?5 M solutions of silver, 10^?4 M solutions of uranium (VI) and 3 × 10^?4 M solutions of gold (III). Extractions were best in the pH range 7–9, 6–9 and 3–5 respectively. Silver could be separated from 10-fold molar excesses of copper, zinc and lead; uranium from 10-fold molar excesses of gold and iron and 100-fold molar excesses of sulphate and manganese: gold from a 10-fold molar excess of uranium. Methods are suggested whereby redispersion in precipitate flotation of the second kind can be avoided. The efficiency of this kind of flotation is considered.     

Control of polyaniline conductivity and contact angles by partial protonation

Many studies require a specific value of conductivity when investigating conducting polymers. The conductivity of polyaniline can efficiently be controlled by partial protonation of the polyaniline base. Although this is a simple task in principle, practical guidelines are missing. In the present study, the changes in the conductivity of polyaniline base after immersion in aqueous solutions of various acids are reported. Polyaniline base has been reprotonated in aqueous solutions of picric, camphorsulfonic and phosphoric acids. The conductivity of partially reprotonated polyaniline varied between 10⁻⁹ and 10⁰ S cm⁻¹. The relation between the pH of a phosphoric acid solution, which was in equilibrium with polyaniline, and the conductivity σ is pH = 0.77 − 0.64 log(σ [S cm⁻¹]). The wettability, i.e. water contact angles, can similarly be set by partial protonation to between 78° for polyaniline base and 44° for polyaniline reprotonated in 1 mol L⁻¹ phosphoric acid. In solutions of picric acid, the transition from the non‐conducting to the conducting state occurs over a narrow range of acid concentrations, and the tuning of conductivity is consequently difficult. Phosphoric acid is well suited for the control of conductivity of polyaniline because of the moderate dependence of the conductivity on the acid concentration or pH. Copyright © 2007 Society of Chemical Industry     

SOLVENT EXTRACTION ENHANCED MICROFILTRATION OF STRONTIUM AND TECHNETIUM WITH DI-2-ETHYLHEXYLPHOSPHORIC ACID AND QUATERNARY AMMONIUM SALTS

ABSTRACT

Application of extractants in form of microphase (micelles or microdrops) separated from aqueous matrix by microfiltration, “solvent extraction enhanced microfiltration (SEEMF)” is closely related to micellar enhanced ultrafiltration (MEUF) technique.

Uptake of strontium from aqueous solutions with microphase di-2-ethylhexylphosphoric acid (DEHPA) and pertechnetate with quaternary ammoniumsalts (QAS): trioctylmethylammonium chloride, benzyldodecyl-dimethylammonium bromide, and n-(α-carbethoxypenthadecyl)trimetyl-ammonium chloride was investigated as a function of microphase concentration and composition, pH and salinity of aqueous phase. Recovery of microfiltration on cellulose acetate 200 nm filters reached 95% for strontium with 4×10^?3 M DEHPA and 99% for technetium with 10^?4 M trioctyl-methylammonium chloride. A substantial part of 88-99% retention of technetium with investigated quaternary ammonium salts on microfilter may be caused by the filter wetting or sorption phenomena.     

Extraction of aconitic acid from mixtures of organic acids and cane molasses solutions using supported liquid membranes

This paper details experimental trials of aconitic acid transport from defined mixtures of organic acids (trans‐aconitic, oxalic, malic and citric) and from cane molasses solutions using a supported liquid membrane (SLM) apparatus. The SLM was impregnated with tributyl phosphate extractant combined with Shellsol 2046 diluent. The transport rates of the organic acids, bulk impurities and glucose were measured. The conditions varied were: extractant to diluent ratio (1:3–3:1), organic acid concentration (2.5–40 mg cm^?3 organic acid), pH of departure phase (1–5.5) and temperature (22–80 °C). Results for the organic acid mixtures showed that aconitic acid and oxalic acid were transported at much greater rates than malic and citric acids. Aconitic acid was transported to a significant degree with recovery of 400 g kg^?1 over a 24 h period. Operation at temperatures higher than 22 °C caused instability of the membrane and bulk leakage across the membrane. With molasses, the purity of the aconitic acid recovered ranged between 400 and 600 g kg^?1 (dry basis) with aconitic acid transport rates of 0.17–0.25 g m^?2 min^?1. The extraction of other acids (oxalic, malic and citric) and impurities was significantly less, hence a process to produce high purity aconitic acid based on this method is technically feasible. © 2002 Society of Chemical Industry     

Passivation and pitting corrosion of tin in gluconate solutions and the effect of halide ions

The passivation and pitting corrosion of tin in sodium gluconate (SG) solutions was studied by using potentiodynamic and cyclic voltammetric techniques. Some samples were examined by X-ray and SEM. The effect of the concentration of gluconate ion, pH, potential scanning rate, successive cyclic voltammetry, switching potential and progressive additions of halide ions on the passivation and pitting corrosion of a tin anode was discussed. The data obtained show that low concentrations of SG have an inhibition effect on the pitting corrosion of tin in neutral media. The pitting corrosion of tin increases with increasing SG concentrations due to the formation of soluble tin-gluconate complex. The critical pitting potential depends on the gluconate ion concentration, pH and scan rate. Two cathodic peaks are observed in the cathodic polarization curve, corresponding to the reduction of the dissolved pitting corrosion products. The critical pitting potential shifts progressively to more negative values with increasing halide ion concentration. In all experiments, the aggressive action of halides decreased in the order Cl^–>Br^–>I^–.     

Cobalt removal from waste‐water by means of supported liquid membranes

BACKGROUND: Supported liquid membranes (SLM) are an alternative technique to remove and recover metals from diluted process solutions and waste‐water. In the present work, the removal of Co(II) from a synthetic CoSO₄ solution containing initial amounts of cobalt(II) in the range 100–200 ppm (0.1–0.2 g dm^?3) has been studied on a pilot scale. By performing batch equilibrium experiments, the optimal settings, i.e. the composition of the organic phase, the pH of the feed, the type and concentration of the stripping agent were determined. RESULTS: It is shown that the equilibrium characteristics of a synergistic extractant mixture containing di‐2‐ethyl‐hexylphosphoric acid (D2EHPA) and 5‐dodecylsalicylaldoxime (LIX 860‐I) are superior to D2EHPA. Both hydrochloric acid and sulfuric acid have been evaluated as stripping solutions in liquid–liquid extraction tests and as the receiving phase in a SLM configuration. Although equilibrium tests showed no difference in stripping characteristics between both chemicals, it was observed that in a SLM configuration the stability of the system when hydrochloric acid is used is poor. With a commercially available SLM module (Liqui‐Cel Extra‐Flow 4 × 28) having a surface area of 19 m², a steady Co(II) flux of 0.140 gm^?2h^?1 has been obtained at influent concentrations of cobalt between 100 and 200 ppm with 3 mol dm^?3 sulfuric acid as stripping phase. CONCLUSIONS: The results obtained show that a supported liquid membrane containing a synergistic mixture of LIX 860‐I and D2EHPA gives the possibility of recovering cobalt from dilute solutions. Copyright © 2008 Society of Chemical Industry     

Electrochemical dissolution of tin in methanesulphonic acid solutions

High-rate electroplating of tin on a moving steel strip is generally carried out in cells with dimensionally stable anodes. To obtain a matt tin deposit a concentrated acidic tin methanesulphonate solution containing a small concentration of sulphuric acid is used. The concentrated tin methanesulphonate solution is prepared by dissolution of tin particles with oxygen in a special column. To describe this dissolution process electrode reactions (namely, reduction of oxygen, hydrogen peroxide and hydrogen ions on a tin electrode and oxidation of tin) were studied using electrochemical techniques. It was concluded that on tin, oxygen is almost entirely reduced to water and that H₂O₂ cannot corrode tin directly, but its decomposition products, for instance oxygen, can. The exchange current density and the charge transfer coefficient for the investigated electrode reactions are estimated. The dissolution of tin by oxygen is determined by the kinetic parameters of the oxygen reduction reaction and by the mass transfer of (i) dissolved oxygen to and (ii) Sn²⁺ ions from the tin electrode surface. Hydrogen evolution can be neglected during the dissolution of tin in the presence of oxygen. Moreover, it was found that the rate of tin corrosion increases with (i) increasing H⁺ concentration, (ii) oxygen concentration, (iii) convection intensity and (iv) temperature. It is likely that the tin surface is not covered with oxygen during corrosion in pure methanesulphonic acid solutions, but an oxide layer may be present on the tin surface during oxygen corrosion in pure sulphuric acid solutions. This oxide layer may hinder the oxygen corrosion of tin.