Dilute Sulfuric Acid Solution Research Articles

Removal of Gold Particles From Chromium Oxynitride Surface With Dilute Sulfuric Acid Solutions

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Modeling sucrose hydrolysis in dilute sulfuric acid solutions at pretreatment conditions for lignocellulosic biomass

Agricultural and herbaceous feedstocks may contain appreciable levels of sucrose. The goal of this study was to evaluate the survivability of sucrose and its hydrolysis products, fructose and glucose, during dilute sulfuric acid processing at conditions typically used to pretreat lignocellulose biomass. Solutions containing 25g/l sucrose with 0.1–2.0% (w/w) sulfuric acid concentrations were treated at temperatures of 160–200°C for 3–12min. Sucrose was observed to completely hydrolyze at all treatment conditions. However, appreciable concentrations of fructose and glucose were detected and glucose was found to be significantly more stable than fructose. Different mathematical approaches were used to fit the kinetic parameters for acid-catalyzed thermal degradation of these sugars. Since both sugars may survive dilute acid pretreatment, they could provide an additional carbon source for production of ethanol and other bio-based products.

Analysis of membraneless microfuel cell using decomposition of hydrogen peroxide in a Y-shaped microchannel

A theoretical analysis has been performed in this study for a novel design of membraneless microfuel cell utilizing a Y-shaped microchannel. Hydrogen peroxide is employed both as fuel and oxidant and dissolved in dilute sodium hydroxide and sulfuric acid solutions, respectively. The anode and cathode liquid streams enter the Y-shaped microchannel separately at different inlets and then flow in parallel through the microchannel without occurrence of turbulent mixing on the contact interface of both streams. The decomposition of hydrogen peroxide in both streams will generate electric power. Such a novel design eliminates the need of a membrane to partition the two liquid streams. The cell performance was investigated in detail by examining the important system parameters such as the concentration of reactant, volumetric flow rate, thickness of catalytic layer, length of microchannel, and geometric design of electrodes. Results provide physical insights for the effects of these parameters on the cell performance and benefit the optimal design of this type of microfuel cell as well as the fulfillment of its application in portable power sources.

Leaching Kinetics of Cadmium from Scallop Waste by Dilute Sulfuric Acid Solution

The leaching kinetics of cadmium from scallop waste in dilute sulfuric acid was investigated by examining the effect of temperature (293–333 K), pH (1.5–2.5), and particle size on the leaching rate. The kinetics of the cadmium extraction process with intraparticle diffusion was reasonably interpreted according to the shrinking core model as a rate-determining step in accordance with the value of the activation energy, 15.9 kJ/mol. Increasing temperature, and decreasing pH and particle size positively influence the extraction of cadmium from the uro.

Analysis of membraneless formic acid microfuel cell using a planar microchannel

A novel design of membraneless microfuel cell employing a planar microchannel has been investigated theoretically in this study. The fuel and oxidant are, respectively, formic acid and oxygen and both dissolved in dilute sulfuric acid solutions. Both liquid streams enter the planar microchannel and flow in parallel without the need of a membrane to separate them. A theoretical model is developed to simulate the species transport in both anode and cathode streams and the cell performance is analyzed accordingly by examining the effects of flow rate, concentration, and the geometric size of the system. The results show that the cell performance is mainly restricted by the high transport resistance in the cathode stream. It is found that the transport of oxygen to the cathode electrode can be improved significantly by using a higher flow rate or oxygen concentration, or a thicker cathode catalyst layer. However, the effectiveness of the flow rate and thickness of catalyst layer diminishes gradually which indicates that there exist optimal conditions of these parameters. The influences of thickness and length of the microchannel on cell performance are also examined in detail.

Reaction of dolomite with dilute solutions of sulfuric acid and Iron(II), Copper (II), and Zinc(II) sulfates

We study how the composition of dolomite changes in its reaction with 0.1 N solutions of H2SO4, FeSO4, CuSO4, and ZnSO4, using X-ray diffraction and differential thermal analysis (DTA). The MgCO3 concentration in the mineral decreases; the maximal decrease is observed in the reaction of dolomite with aqueous sulfuric acid.

Extraction and separation of Cd and Te from cadmium telluride photovoltaic manufacturing scrap

The extraction and separation of cadmium, tellurium, and copper from CdTe PV module scrap was investigated. Several leaching technologies were assessed and the extraction of CdTe from samples of PV modules was optimized for maximum efficiency and minimum cost. A dilute aqueous solution of hydrogen peroxide and sulfuric acid was sufficient to completely leach out cadmium and tellurium from these samples. The same method successfully removed cadmium and tellurium from actual manufacturing scrap; copper was partially extracted. Subsequently, cation-exchange resins were used to separate cadmium and copper from tellurium. Complete separation (i.e., 99·99%) of Cd from Te was accomplished. The estimated costs of these processes for 10 MW/year processing are about 2 cents per W. Copyright © 2006 John Wiley & Sons, Ltd.

A rotating ring–disk study of the initial stages of the anodic dissolution of chalcopyrite in acidic solutions

The initial stages of the dissolution of chalcopyrite have been studied using rotating ring–disk electrode techniques in dilute sulfuric acid solutions at 60 °C. It has been confirmed that the mineral undergoes a dissolution process under freely dissolving conditions in the absence of an oxidant. This process involves the formation of soluble copper(II) ions and a soluble sulfur species which is presumably H2S. By the use of an anodic stripping technique on the ring electrode, it has been possible to determine that the dissolution of chalcopyrite under oxidative conditions involves a soluble sulfur species such as thiosulfate. Collection efficiency measurements involving the detection of both iron(II) and copper(II) on the ring have been used to identify possible anodic reactions in the potential region relevant to the oxidative leaching of the mineral.

Copper Electrodeposition Dynamics at a Porous Flow-through Electrode

The dynamics of the copper electrodeposition out of a dilute sulfuric acid solution of copper sulfate (straight-through regime, solution supplied from the rear at a velocity of ∼1 cm s−1) onto preliminarily metallized carbonaceous felt of the VINN-250 brand is studied. The profile, which describes the final deposit distribution, qualitatively conforms to predictions made in terms of a dynamic model for a porous electrode described previously, as does the nonmonotonic variation of the gain in the copper weight and the current efficiency for copper with time in the first half of the deposition process. At later stages of the process, along with the enhancement of the tendency towards the forcing of the copper electrodeposition process towards the front end of the electrode, there appears a new factor, which is not taken into account by the method. This factor is the deposition of a loose rough copper layer outside the porous electrode at its front side.

Effects of dissolved oxygen on passive behavior of stainless alloys

A potential-control circuit has been devised to measure passive-current (corrosion rate) on stainless alloys in conditions simulating the usual noble drift of the open-circuit corrosion potential in the presence of passivating dissolved oxidizers. Open-circuit corrosion potential and passive-current decay were measured with and without dissolved oxygen in dilute sulfuric acid solutions as a function of time on austenitic stainless steel and a Ni-base Cr–Mo–W alloy. The results confirm the long-standing assumption that constant-potential potentiostatic tests give a good approximation of passive-film growth kinetics in the presence of passivating dissolved oxidizers. Mott–Schottky measurements showed that passive films on each alloy have similar semiconducting properties whether formed potentiostatically or by dissolved oxygen. In both cases, the passive film on stainless steel seems to be composed of an inner n-type barrier layer covered with an outer p-type layer. The passive film on the nickel-base alloy is primarily n-type with only weak evidence of p-type behavior in an outer layer. Results are in general agreement with predictions of the point-defect passive-film model proposed by Macdonald and coworkers.

A kinetic study of trace element leachability from abandoned-mine-polluted soil treated with SS-MSW compost and red mud. Comparison with results from sequential extraction

The effect of adding treated red mud, a by-product of alumina production, to soil polluted by an abandoned mine and characterised by high concentrations of heavy metals, relatively low reaction grade, and low organic carbon content, was investigated. Also studied was addition of both red mud and compost (produced from source-separated municipal solid waste)--the synergistic action of red mud and compost could be exploited to achieve both metal trapping and an increase in organic carbon content. Leaching batch tests were performed on four different systems: soil, soil and treated red mud, soil and compost, soil and compost plus treated red mud. Dilute sulfuric acid and EDTA solution (liquid/solid ratio 10:1) were used in the tests--sulfuric acid to "mimic" acid rain and EDTA in accordance with general methods for estimating "plant-available" metals. Sequential extraction was also applied to the same samples. The use of relatively non-specific extractant reagents in the leaching tests led to a kinetic approach (already proposed in literature), because measurements of trace elements extracted at equilibrium cannot be related to their speciation. Comparison of information obtainable by the kinetic approach to evaluation of data from leaching tests with results from sequential extraction enabled evaluation whether the "kinetic fractionation method", a relatively rapid and simple procedure, furnishes adequate information about the mobility and bioavailability of trace elements. Especially interesting results were obtained for Mn, Zn, and Ni, present in large amounts in the soil studied--their leachability was significantly reduced by addition of red mud and compost, suggesting interesting perspectives in soil-remediation activity.

Use of the Eurachem guide on method validation for determination of uranium in environmental samples

Three analytical methods for determination of uranium in environmental samples by a fluorescence technique have been validated and compared in accordance with the Eurachem Guide on method validation. The first method depends on uranium separation from iron using the mercury anode technique; in the other two methods uranium is separated from iron on an anion exchange column by use of either a solution of hydrochloric acid containing ascorbic acid and hydrazine hydrate or a dilute sulfuric acid solution. Detection limits, repeatability, reproducibility, and recovery coefficient were the main validation characteristics. The results showed that better statistical values can be achieved by using the third method. Control charts for in-house control samples and international intercomparison samples have also shown that the third method is more statistically stable with time. In addition, uncertainties of measurement were estimated and compared for the three methods. It was found that the Eurachem Guide and comparison of quality statistical validation data can be good tools for selection of the appropriate method for an application.

Oxygen Solubility in Industrial Process Development

Oxygen solubility in pure water and in dilute sulfuric acid solution has been studied as a part of atmospheric direct zinc leaching process development. The experimental results were compared with reference data and the Gibbs energy model. The dissolution dynamics of oxygen was further combined with the Gibbs energy minimization method. Together the experimental and model results give useful information and methodology for the developers of industrial processes related to gas solubility. The dynamic Gibbs energy calculation approach presented in this work extends the possibilities of evaluating changes in different process chemistries needed in process design.

The corrosion and passivation of SS304 stainless steel under square wave electric field

Atomic force microscopy (AFM), a powerful, high-resolution imaging technique for determining the structure of surface, was used to examine the growth of the oxide film formed on 304 stainless steel in dilute sulfuric acid solution by using alternating voltage (AV) passivation. Transmission electron microscopy (TEM) was also used to investigate the growth of the film. It was pointed out that there were pores in the film during AV passivation, causing the oxide to grow rapidly. The site of pores changes continuously with the change of the morphology of the substrate caused by active dissolution under lower potential part of square wave electric field ( E L), this make the substrate dissolved to a polishing interface during AV passivation.

The Effect of Protic Doping Level on the Anticorrosion Characteristics of Polyaniline in Sulfuric Acid Solutions

In a previous paper we investigated the mechanism by which fully protically doped (emeraldine-salt form) polyaniline (PANI) protects stainless steel surfaces from corrosion in 1 M sulfuric acid solution. A mechanism was proposed, based on prior work by Deng et al. , whereby passivation is achieved because the emeraldine-salt form holds the potential of the underlying stainless steel electrode in the passive region. This paper describes investigations of PANI-coated stainless steel surfaces exposed to more dilute sulfuric acid solutions. This is an interesting issue because while the solution becomes less corrosive as the concentration of the decreases, the concomitant change in pH also changes the protic doping level of the PANI film. UV-visible spectroscopy indicated that partially protic films are obtained upon exposure of PANI to solutions with concentrations in the range from 500 to 1.0 mM. Exposure to 0.1 mM yielded the protically undoped emeraldine-base material. We have found that both the partially protically doped PANI films and the totally undoped emeraldine-base films also hold the potential of the substrate stainless steel electrode in the passive region. Hence, the mechanism by which PANI protects the underlying metal surface from corrosion is independent of doping level. © 2002 The Electrochemical Society. All rights reserved.

Highly selective transport of a uranyl ion through a liquid membrane containing a lipophilic ion-associate of methyltrioctylammonium and hydroxycalix[n]arene-p-sulfonates (n = 6, 8) as metal carriers.

Uranyl ion, UO2(2+), in an aqueous sodium hydrogen carbonate solution of pH 4-8 (source phase) was simultaneously and selectively transported into a dilute sulfuric acid solution (receiving phase) through a membrane (chloroform, bulk) containing a lipophilic ion-associate of methyltrioctylammonium ion and hydroxycalix[n]arene-p-sulfonate ion, 2n (n = 6, 8), MTA+-2n, as a metal carrier. The rate of transport increased in proportion to the concentrations of UO2(2+) in the source phase and carrier in the membrane and along with an increase in the temperature of the system. The rate was also increased along with an increase in the pH of the source phase. None of the other metal ions were transported, or obstructed the transport of UO2(2+), while the presence of large amounts of sodium hydrogencarbonate and sodium chloride in the source phase interfered with the transport by causing a delay in the start of transport.

Cadmium recovery and recycling from chemical bath deposition of CdS thin layers

AbstractCadmium sulfide thin layers for polycrystalline solar cells are produced by chemical bath deposition (CBD). This process generates wastes containing mainly ammonia and cadmium. We have implemented and described in a previous paper a process to recover 90% of ammonia and to confine cadmium as a cake which is a mixture of cadmium sulfide and cadmium cyanamide. The present paper concerns cadmium recycling to the CBD step. The cake is first dissolved in a moderate sulfuric acid solution 0.2–0.5 mol/l mixed with hydrogen peroxide (about 1 mol/l). This last component must be used in large excess (molar ratio H2O2/Cd ≥ 5) and must be completely removed from the solution before recycling or cadmium electrowinning. Hydrogen peroxide decomposition is electrochemically catalyzed by platinized platinum immersed into the solution. The resulting solution contains cadmium sulfate 0.2 mol/l, sodium and ammonium sulfate. One can either recycle it as a chemical bath, or recover the cadmium content by electrowinning; in this case the residual concentration of hydrogen peroxide is electrochemically reduced at the beginning of cadmium electrolysis. The raffinate solution is recycled into the stripping reactor. The pure cadmium metal recovered may be dissolved in a dilute sulfuric acid solution by means of internal electrolysis with two electrodes: a platinized platinum grid as cathode and the cadmium metal as anode. According to the mass of cadmium dissolved it is possible to obtain a concentrated solution of pure cadmium sulfate. The global process recovers at least 99.999% of cadmium and generates only solid sulfur and a liquid effluent containing traces of cadmium (< 10 μg/l). Copyright © 2002 John Wiley & Sons, Ltd.

Direct polymerization of sulfonated poly(arylene ether sulfone) random (statistical) copolymers: candidates for new proton exchange membranes

Novel biphenol-based wholly aromatic poly(arylene ether sulfone)s containing up to two pendant sulfonate groups per repeat unit were prepared by potassium carbonate mediated direct aromatic nucleophilic substitution polycondensation of disodium 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (SDCDPS), 4,4′-dichlorodiphenylsulfone (DCDPS) and 4,4′-biphenol. Copolymerization proceeded quantitatively to high molecular weight in N-methyl-2-pyrrolidinone at 190 °C. Tough membranes with a SDCDPS/DCDPS mole ratio up to 60:40 were successfully cast using N, N-dimethylactamide. An increase of sulfonate groups in the copolymer resulted in increased glass transition temperature, enhanced membrane hydrophilicity, and intrinsic viscosity; the 100% SDCDPS homopolymer was water soluble. The acid form membranes were successfully obtained by treating the sodium form of the membranes with dilute sulfuric acid solution. Thermogravimetric analysis shows that the sodium form materials have enhanced thermal stability relative to the acid form, as expected. Atomic force microscopy (AFM) phase images of the acid form membranes clearly show the hydrophilic domains, with sizes increasing from 10 to 25 nm as a function of the degree of sulfonation. A phase inversion could be observed for the 60% SCSDPS copolymer, which was consistent with a rapid increase in water absorption. Short-term aging (30 min) indicates that the desired acid form membranes are stable to 220 °C in air and conductivity values at 30 °C of 0.11 S/cm (SDCDPS/DCDPS=0.4) and 0.17 S/cm (SDCDPS/DCDPS=0.6) were measured, which are comparable to or higher than the state-of-the-art fluorinated copolymer Nafion 1135 control (0.12 S/cm). The conductivity is greatly influenced by ion exchange capacity, temperature, and water activity. The new copolymers, which contain ion conductivity sites on the deactivated positions of the aryl backbone rings, are candidates as new polymeric electrolyte materials for proton exchange membrane (PEM) fuel cells.

Ion-Exchange Procedure Developed for Isolation of Element 106 (Seaborgium) and Study of Its Chemistry in H2SO4 and H2SO4/HF Solutions, with W as Imitator

Ion-exchange behavior of W, Hf, Sr (homologs of elements 106, 104, and 102, respectively), U (pseudohomolog of element 106), Cm, and Eu in H2SO4 and H2SO4/HF solutions was studied. The static and dynamic ion-exchange properties of these elements were determined as influenced by the solution composition and the nature of the ion exchanger. The best conditions were found for separating element 106 (seaborgium) from daughter elements (Rf, No, and Fm) and its pseudohomolog, U, on a single cation-exchange column with the purification coefficients of ≥105-106. A possibility of using the anion exchanger for concentrating element 106 and separating it from the long-lived decay products was demonstrated. The speciation of these elements in dilute sulfuric acid solutions and in solution containing strong complexing agents was discussed.

Morphological aspects of sulfate-induced reconstruction of Cu(1 1 1) in sulfuric acid solution: in situ STM study

Using in situ STM the atomic structure and the morphology of a Cu(1 1 1) surface exposed to a dilute sulfuric acid solution have been studied depending on the applied electrode potential. At anodic potentials near the onset of copper dissolution the electrode surface is reconstructed (expanded) caused by the specific adsorption of sulfate anions. The extent of the surface reconstruction strongly depends on the sulfate adsorption rate. Fast sulfate adsorption results in a mainly disordered sulfate adlayer on an unreconstructed copper surface. Conversely, slow sulfate adsorption produces a mainly reconstructed copper surface with a highly ordered sulfate/water coadsorption layer. This adsorbate structure shows an additional long-range Moiré modulation, due to a misfit between the first reconstructed and the second unreconstructed copper layer. This is verified by spectroscopy-like STM experiments, which allow the imaging not only of the adsorbate overlayer, but also of the underlying reconstructed substrate. This type of adsorbate-induced reconstruction is characterized by an expansion of the topmost copper layer. The kinetically slow process of reconstruction can be easily followed by dynamic STM measurements revealing a mass transport out of the topmost copper layer during the slow sulfate adlayer formation. Characteristically, new copper islands nucleate and grow, while the sulfate Moiré adlayer expands over the electrode surface. At cathodic electrode potentials the desorption of the sulfate adlayer is accompanied by the lifting of the surface reconstruction and the massive formation of surface defects, such as small pits and vacancy islands. A continuous cycling of the electrode potential leads to an enormous roughening of the surface morphology.