Mixed Acid Medium Research Articles

Highly sensitive determination of trace antimony in water samples by cobalt ion enhanced photochemical vapor generation coupled with atomic fluorescence spectrometry or ICP-MS

A method for highly sensitive determination of trace antimony was proposed by using cobalt ion enhanced photochemical vapor generation (PCVG) for sample introduction into atomic fluorescence spectrometry (AFS) or inductively coupled plasma-mass spectrometry (ICP-MS) for elemental detection. During the PCVG process, the sample introduction efficiency of Sb could be significantly improved by addition of 5 mg L−1 Co2+ in the mixed acid medium of 10% (v/v) formic acid and 20% (v/v) acetic acid, with a final 12-fold and 133-fold enhancement of AFS and ICP-MS intensity, respectively. The experimental conditions including enhancement ions, acid medium, UV irradiation, working gas as well as potential interference were investigated in detail. Under the optimal experimental conditions, the limit of detection (LOD) for Sb was 0.05 and 0.001 μg L−1 by using AFS and ICP-MS determination, respectively. The method was successfully used for analysis of real water samples, with satisfactory recoveries of 92–94%.

Effects of mixed acid solution on bromide epoxy vinyl ester and its glass fiber reinforced composites

Abstract As fiber reinforced plastics (FRP) have been increasingly widely used, they may sometimes come into contact with several corrosive media simultaneously, for example, the condensate in the smokestack liners of coal-fired power FGD systems. To study the long-term performance and degradation mechanism of FRP in these complicated environments, an accelerated aging test of bromide epoxy vinyl ester (Br-VE) and its glass fiber reinforced composites (GF/VE) in a mixed acid solution(H2SO4, HNO3, HF and HCl) at three different temperatures(25, 55 and 80 °C) for 180 days was carried out. Weight changes, flexural properties, Fourier transforming infrared spectra (FTIR), dynamic thermal mechanical (DMA), macroscopic and microscopic morphology were investigated. Results showed that immersion temperature has important effects on the corrosion behavior of specimens. The long-term weight change behavior of GF/VE at normal temperature was in accordance with Fick’s second law, but deviated at higher temperature. Flexural properties of GF/VE declined more drastically than those of Br-VE at elevated temperatures. The Tg of GF/VE decreased with rising temperatures. Results also indicted that Br-VE and GF/VE manifested varied degradation mechanisms when subject to the same mixed acid medium immersion. The degradation of GF/VE mainly involved plasticization, embrittlement, the hydrolysis of resin, an ion exchange between HF, H+ and Si-O-Si or alkali metal of the fiber as well as the debonding of the resin/fiber interface.

Cobalt ion-enhanced photochemical vapor generation in a mixed acid medium for sensitive detection of tellurium(iv) by atomic fluorescence spectrometry

Cobalt ion-assisted enhancement of photochemical vapor generation in a mixed acid medium was used for sensitive determination of tellurium(iv) by atomic fluorescence spectrometry.

A two-dimensional model of the vanadium–cerium redox flow battery

Redox flow batteries (RFB) provide efficient storage of renewable energy facilitating sustainable energy supply. Among various RFB, the vanadium cerium battery is distinguished with large storage potential and without phase transition during the redox reactions. Herein, a two-dimensional model of a slice of the cell in a vanadium cerium redox flow battery is developed for the first time. Electrochemical characterization of both the V(II)/V(III) and Ce(III)/Ce(IV) electrochemical systems in mixed acid media is conducted to obtain the key parameters of the model. The data obtained from the simulations is then validated against the results of real flow battery experiments exhibiting a good agreement. With the perspective of state-of-the-art design in RFB system management for future large-scale systems, state of charge deviation and flow efficiency, are introduced as innovative measures of lifetime and energy density of the battery. The illustrated effect of several parameters involved in the proposed model provides direction toward optimum design of RFB systems.

Separation of tungsten and cobalt from WC-Co hard metal wastes using ion-exchange and solvent extraction with ionic liquid

Recently, the development of a process to separate W and Co from tungsten carbide-cobalt (WC-Co) hard metal wastes has become important. In this study, we proposed a novel hydrometallurgical process involving the following steps: pretreatment, leaching, ion exchange, and two-step solvent extraction (I) and (II) using ionic liquids (ILs). First, an AlCrN film coating was completely removed from a WC-Co hard metal sample by leaching in a H2SO4–H3PO4 mixed acid medium at 423 K for 120 h. Then, the sample was oxidized at 1173 K for 10 h and XRD analysis showed that WO3 and CoWO4 were generated during this oxidization. After the oxidization, the leaching reaction WO3 + 2LiOH → WO42− + 2Li+ + H2O smoothly proceeded in leaching solution of 0.1 mol/L LiOH at 343 K for 19 h and the stoichiometry of WO3:LiOH was 1:2, which was consistent with that of the leaching reaction. Further, after the leaching step was completed, it was beneficial to exchange H+ and Li+ in the leaching solution using a cation exchange resin.Solvent extraction was performed using triethyl-n-pentyl phosphonium bis(trifluoromethylsulfonyl)amide as the IL, and tri-n-octylamine was employed as the extractant for the selective separation of W(VI) for solvent extraction (I). The extraction percentages (E) of W(VI) and Co(II) were >95% and <2.5% at pH = 1.0, respectively, and the selective extraction of W(VI) was confirmed in this study. The extraction mechanism of W(VI) was based on the ion association reaction n[R3N]org + [HxWyOzn−]aq + n[H+]aq ⇔ [(R3NH)nHxWyOz]org. In solvent extraction (II), a PC-88A/[P2225][NTf2] system was used for the effective extraction of Co(II) at pH > 4.3. The slope analysis results showed that the extraction mechanism was governed by the cation exchange reaction [Co2+]aq + 2[(HL)2]org ⇔ [CoL2·2HL]org + 2[H+]aq. A series of novel hydrometallurgical process using IL enabled us to demonstrate that W(VI) and Co(II) were efficiently recovered from WC-Co hard metal wastes.

Nitric acid decomposition kinetics in mixed acid and their use in the modeling of aromatic nitration

Nitric acid decomposition in mixed acid (an aqueous mixture of nitric and sulfuric acids) was studied from a chemical and a kinetic point of view. The study was focused on the behavior of the reactive mixture in an open system in which the gas formed through the decomposition process can leave the vessel. The reaction network, through which the system could develop, depending on the chemical composition of the mixture and on the temperature, was completely characterized. The data collected indicate that water evaporation can significantly influence the system behavior. Isothermal experiments were carried out to estimate the unknown kinetic parameters through the adoption of a mathematical model able to predict the system behavior at varying process conditions. The proposed model and the estimated parameters were validated through the use of the results collected in a set of experimental runs performed during the nitration of methyl m-nitrobenzoate (3NMB) in mixed acid media.

Study of the Ce3+/Ce4+ Redox Couple in Mixed-Acid Media (CH3SO3H and H2SO4) for Redox Flow Battery Application

The present paper first reports a kind of supporting electrolyte, mixed-acid media (CH3SO3H and H2SO4), used in redox flow battery (RFB) technology. Experimental work is performed with the aim of evaluating the Ce3+/Ce4+ redox couple in mixed-acid electrolyte for use in RFB technology. The mixed-acid media have their special advantages: (i) the Ce3+/Ce4+ electrode reaction appears to be more reversible in mixed-acid solution; the peak splittings in mixed acid are significantly less than in sulfuric acid; the diffusion coeffcient in mixed acid is larger than in single acid (CH3SO3H or H2SO4); the exchange current density and standard rate constant of the Ce3+/Ce4+ redox reaction in mixed-acid media on graphite electrode are 8.05 × 10–3 A cm–2 and 4.17 × 10–4 cm s–1; (ii) the solubility of cerium salt in mixed acid is larger than in sulfuric acid; a solution of 1 mol dm–3 cerium containing 2 mol dm–3 MSA and 0.5 mol dm–3 H2SO4 is sufficiently stable for more than 1 month at temperatures up to 313 K; (iii) Coulombic and energy efficiencies of the test cell using mixed-acid electrolyte are both higher than that using single CH3SO3H electrolyte; the average Coulombic and energy efficiencies of the cell using mixed acid are 87.1 and 73.5%, respectively, which are comparable to that of the all-vanadium RFB.

TiO2 nanorod arrays grown from a mixed acid medium for efficient dye-sensitized solar cells

A series of oriented rutile TiO2 nanorod-array films are in-situ grown on fluorine-doped tin oxide (FTO) coated glass substrates from a mixed acid solution containing titanium tetraisopropoxide (TTIP), hydrochloric acid (HCl), acetic acid (HOAc), and water (H2O) by means of hydrothermal reaction at 150 °C. The effect of HOAc in the titania growth solution on the structure and micro-morphology of TiO2 nanorod array films, as well as the photoelectric conversion properties in dye-sensitized solar cells (DSSCs) has been fully investigated. It is found that HOAc can facilitate the formation of uniform, dense, and vertically oriented TiO2 nanorods and hence improves the dye adsorption, electron diffusion coefficient, and the photovoltaic performance of DSSCs, typically in short-circuit photocurrent and power conversion efficiency. A power conversion efficiency of 4.03% has been achieved on a DSSC based on a 2.3 µm-long nanorod array film obtained from a mixed acid solution with the TTIP:HCl:HOAc:H2O ratio of 0.8:4:8:8 by volume.

Kinetics modeling of inhibition and utilization of mixed volatile fatty acids in the formation of polyhydroxyalkanoates by Ralstonia eutropha

Acetic, propionic and butyric acids are the major fermentation acids produced on acidogenesis of organic wastes such as food scraps. They can be utilized by Ralstonia eutropha as sole carbon sources for cell growth and polyhydroxyalkanoate (PHA) synthesis. The acids, however, are inhibitory and toxic to the bacterium depending on the medium pH and the total acid concentration. The inhibition and utilization kinetics of the total acids and individual acids in mixed acid media were investigated in flask batch cultures, and simulated by modified Michaelis–Menten models based on variable cell activity. Cell activity, a function of the total acid concentration, is defined as the active fraction of the measurable residual biomass (RBM) under specific culture conditions, which might be as low as 20% at high acid concentrations. The overall production rate of PHA is contributed from the utilization rates of individual acids as well as the interaction of two acids such as acetate and propionate, depending on the predominant acids in the medium. R. eutropha preferred propionic acid for cell mass synthesis and butyric acid for polymer synthesis, the latter giving the highest polymer yield (0.39 g/g) among the three acids. In mixtures of predominant acetic and butyric acids, a high PHA formation rate (60 mg/g RBM per h) was achieved, compared with the relatively low PHA formation rate (35 mg/g RBM per h) in the mixtures of predominant acetic and propionic acids. Acetic acid in acid mixtures reduced the metabolism of propionic acid, which resulted in a high rate ratio (up to 0.8) of hydroxyvalerate (HV) formation to the overall PHA formation.

NEW XANTHIC ACID DERIVATIVES AS POTENTIAL REAGENTS IN THE SOLVENT EXTRACTION OF PRECIOUS METAL IONS: EXTRACTION OF PALLADIUM(II) WITH 13-BIS(0-BUTYLXANTHATO)PROPANE

ABSTRACT Two series of new xanthic acid derivatives namely, the bis (O-butylxanthato) alkanes ( abbreviated as BBXAs or simply as bis-xanthates in this paper) have been synthesized in connection with the solvent extraction of precious metal ions. From an aqueous medium containing 0.1 M NaC104 (1 M=l mol dm-3), these compounds exhibited high selectivity for extraction of Pd(II) and Ag(I) in dichloroethane, over most of the base metals as well as Pt(IV) and Au(III) ions. Towards Pd(II) and Ag(I) ions, the bis compounds act as SS chelating agents where the stabilities of the extractable complexes are determined by the length of the alkylene chain existing between the donor atoms. Pd(II) extraction has been studied in detail taking 13-bis(O-n-butylxanthato)propane (BnBXP) as the representative member of the series of bis-xanthates synthesized in this work. The extraction of palladium(II) was found to be quite slow in pure chloride medium. But, a mixed acid medium containing H2SO4 or HNO3 in the presence of sm...

Thin-layer chromatographic behaviour of metals on deae-cellulose in oxalic acid and mixed oxalic acid-hydrochloric acid media

The adsorption behaviour of 46 metals on layers of DEAE-cellulose has been examined in aqueous oxalic acid media. R F values are given as a function of oxalic acid concentration over the range 0.010–0.30 M and are compared with those obtained in a similar manner with Avicel SF. R F data are also presented for 48 metals in oxalic acid-hydrochloric acid mixtures, where the oxalic acid concentration was kept constant at either 0.030 or 0.25 M and that of hydrochloric acid was varied from 0.010 to 3.0 M. Pronounced ion exchange takes place in oxalic acid media for many metals, but a limited number of metals are adsorbed on DEAE-cellulose from the mixed acid media. The versatility of the chromatographic system investigated is demonstrated by many multi-component separations conducted without marked tailing.

Anion-exchange separation of gold on deae-cellulose in acetic acid-hydrochloric acid media

Gold(III) is strongly retained on DEAE-cellulose columns from acetic acid-hydrochloric acid mixtures. The distribution coefficients of gold(III) on DEAE-cellulose are given as functions of both acetic acid and hydrochloric acid concentrations. The adsorption becomes enhanced to a great extent in the mixed acid media as compared with those in aqueous hydrochloric acid media, reaching a distribution coefficient of 500 in acetic acid−0.5 M hydrochloric acid (9:1). The ion-exchange system allows separation of gold(III) from large quantities of many other metals on a short column. Results of the separation and determination of gold in an anode slime consisting of a complicated matrix are included.

The determination of arsenic by non-dispersive atomic fluorescence spectrometry with a gas sampling technique

Non-dispersive atomic fluorescence measurements of arsenic with a gas sampling technique have been investigated. Arsenic is converted to arsine in a mixed acid medium containing iodide, tin(II) and zinc powder, and is atomized in a hydrogen-argon-entrained air flame. A microwave-excited (2450 MHz) electrodeless arsenic discharge lamp, a solar-blind photomultiplier, and a lock-in amplifier are used. The detection limit of arsenic is 2 ng and the linear working range covers nearly three decades of concentration.

Titrimetric determination of indigo sulphonate with potassium iodate

Conditions have been established for the direct titration of indigo sulphonate with potassium iodate at room temperature. The titration can be carried out in a medium which is 6–8 N with respect to hydrochloric acid. The blue colour of the indigo disappears sharply at the end-point, giving a clear yellow solution. It has been observed that 1 g mole of indigo consumes very nearly 1 g mole of potassium iodate. The reaction of indigo sulphonate with potassium iodate is very slow, but is markedly accelerated by chloride ion. Direct titration of indigo sulphonate has also been found possible in mixed acid media containing sulphuric and hydrochloric acids at suitable concentrations. The stoichiometry observed in these titrations is in striking contrast with the reported deviations in the titrations of indigo sulphonate with potassium permanganate and cerium IV sulphate. Evidence has also been obtained for the formation of a new type of iodo derivative of isatin sulphonate in the reaction between indigo sulphonate and potassium iodate. The new iodo-isatin sulphonate is capable of liberating iodine from potassium iodide quantitatively.