Concentrated Sulphuric Acid Solutions Research Articles

Moisture Sorption Studies using the GAB Model of a Beef Based Dambun Nama (A Ground Meat Product) Stored over a Period of Six Months

Water adsorption isotherms of Dambun Nama, a ground beef product, were determined over a storage period of six months, at an average ambient temperature of 33.8oC and an accelerated temperature of 50oC, using the static gravimetric method. The study was aimed at establishing the moisture sorption profile of a traditional meat product Dambun Nama common in Northern Nigeria, produced from beef and stored over a period of six months. The sample was produced using a standardized method; it was sterilized, packaged in six airtight glass containers and stored at ambient temperature as the sample stock for the analyses over a period of six months. Data was generated from the sorption studies based on the isopiestic transfer method using concentrated sulphuric acid solutions. The isotherms are generally shaped like the type 4 isotherms for food products. Between 33.8oC and 50oC adsorption, the monolayer moisture content ranged from 0.036 to 0.048 gH2O/g solids, and between 0.037 to 0.049 gH2O/g solids for desorption. There was a general increase in the GAB constants K and C. The correlation coefficient (R) values obtained for adsorption ranged from 0.941 to 0.959, and for desorption, the values ranged from 0.940 to 0.957, indicating that the GAB model was suitable in describing the moisture sorption profile of Dambun Nama within the prescribed water activity ranges and storage period.

Nitrogen-doped carbon quantum dots for effective corrosion inhibition of Q235 steel in concentrated sulphuric acid solution

In recent years, steel corrosion, an issue affecting a trillion-dollar industry, is being addressed with nanotechnology technologies. Small clusters and nanoparticles, as well as numerous molecules, are viable solutions, with carbon quantum dots (CQDs) being among the best and most promising. However, the complexity and duration of the CQDs purification process, as well as a few other issues, limit their practical applications as corrosion inhibitors. Therefore, in this study, a new type of nitrogen-doped CQDs (N-CQDs) with an average size of 2.5 ± 0.8 nm were synthesized via hydrothermal reaction of amino-guanidine and citric acid using a robust purification process. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques were used to evaluate the new inhibitor's corrosion mitigation effect on Q235 steel in 0.5 M H2SO4 solution. X-ray photoelectronic spectroscopy (XPS) and FTIR analyses were employed for the chemical composition investigation of as-prepared N-CQDs and surface characterization of Q235 steel samples. The analysis of the impedance module and the current density of Q235 steel in the corrosive solution validates the effective protective performance of the inhibitor. The results showed that the maximum inhibition efficiency of 95.3% was achieved at the concentration of 200 mg/L. Moreover, it was found that the formation of the protective layer on the steel samples results from the Physico-chemical adsorption of the inhibitor on the steel surface and follows the Langmuir adsorption isotherm that was also confirmed via XPS. The quantum chemical calculations show that CQD nitrogen doping has an effect on corrosion inhibition performance. Overall, the corrosion inhibition efficiency of the carbon dots inhibitor is higher at the same concentration than that of most other similar inhibitor types.

Studies on high performance alkali activated slag concrete mixes subjected to aggressive environments and sustained elevated temperatures

In contemporary constructions, there is a continuous drive for enhancing the performances of concrete mixes, both green and as well as on hardened state. Again there are simultaneous efforts to take full advantage of all the various fast-track, state-of-art construction technologies, leading to early completion of efficient, economical and eco-friendly infrastructure projects. The present authors have developed a new class of high performance self-compacting, alkali activated slag concrete mixes (HPAASC) using three industrial by-products, all obtained from iron and steel industry and have evaluated them for their strength properties. While these HPAASC mixes have higher compressive strengths (about 70–90 MPa) and reasonable split-tensile and flexural strengths, they are also self-compacting in nature. In the present paper, the durability performance of this class of mixes on long-term exposure to aggressive environments like acids, sulphates and chlorides is discussed. Strength deteriorations of the standard test specimens subjected to 5% concentrated sulphuric acid solution and so also in 10% magnesium sulphate solution were monitored for a period of one year. The impermeability of the mixes against chloride-ions was evaluated using both Bulk diffusion test (BDT) and the Rapid chloride penetration test (RCPT). Further these mixes were also evaluated for their performance on exposure to sustained elevated temperatures in the range of 200–800 °C. All the specimens were further analysed for their microstructural studies. Results in the present study indicate that, all the HPAASC mixes exhibit better resistances to aggressive environments and sustained elevated temperatures as compared to the OPC-based reference concrete mix.

Experimental Study of Sulphate Attack on Steel Embedded in Reinforced Concrete

Corrosion in reinforced concrete structure is a serious problem that leads to unexpected premature deterioration of reinforced concrete structure. One of the causes of the steel corrosion is due to ingress of sulphide ions at the surface of reinforcing bars in concrete. This study is an attempt to estimate corrosion effect of sulphuric acid solution through the parameters such as corrosion current density, corrosion rate and weight loss. This experimental study is carried out with the help of three-electrode electrochemical system. The study involves 12 mm o and 8 mm o steel bars embedded in cylindrical concrete specimen kept in sulphuric acid solution. Formation of a brown ring and cracks is observed near the bottom. The corrosion rate is found to be very high, when the specimens are immersed in concentrated sulphuric acid solution. The effect of diameter of bar to corrosion rate is observed to be negligible. Rusting is more in that portion of bar which is near the top; this may be due to its proximity to counter electrode and no provision of cover at this portion.

Leaching of yttrium, europium and accompanying elements from phosphor coatings

The aim of this work was to study and describe leaching behaviour of Y, Eu and accompanying elements (Zn, Cd) from the phosphors of waste cathode ray tube (CRT) screens in low concentrated sulphuric acid solutions under both non-oxidizing and oxidizing conditions (H2O2). Thermodynamic study showed that non-oxidizing acid leaching leads to elemental sulphur and hydrogen generation followed by formation of H2S(g). In the presence of oxidant in the leaching system SO2(g) or H2SO4 formation is possible. PbSO4 was formed during leaching independently from the presence of the oxidant. Y, Eu and Zn dissolution without using H2O2 in 0.4M H2SO4 at 80°C attained 6, 9 and 8% respectively. The appropriate content of H2O2 in leaching solution was determined as 3.9v/v %. The highest leaching efficiency of Y and Eu (around 90–95% after 20min) was achieved by using the leaching solution (400ml 0.4M H2SO4, 60ml 30v/v % H2O2) at 80°C and L/S ratio 23. Under these conditions Zn extraction was relatively low (20%) in comparison with Cd extraction (80%). The study also reveals that high leaching efficiency of both Y and Eu (around 90%) was achieved with even more diluted leaching solution (400ml 0.05M H2SO4, 60ml of 30v/v % H2O2) at 60°C, L/S ratio 23 after 20min of leaching. Zn and Cd extractions reached 20% and 55% respectively. Activation energy values calculated for Y and Eu leaching in the solution (400ml 0.4M H2SO4 with 60ml of 30v/v % H2O2) refer to diffusion mechanism in the range 40–80°C (Ea=14.85kJ/mol and 16.47kJ/mol respectively). In contrast, Ea values for Y and Eu leaching in the solution (400ml 1M H2SO4, 60ml of 30v/v % H2O2) suggest a mechanism change at the temperature around 40°C. The leaching of Y as well as Eu up to 40°C is controlled by diffusion and at higher temperatures by chemical reaction.

Selective recovery of Copper from waste mobile phone printed circuit boards using Sulphuric acid leaching

In the present study, the leaching of Cu(II) from the waste mobile phone printed circuit board (WM-PCB) was investigated using concentrated sulphuric acid solution. Cu(II)) uptake efficiency was determined at varying pH (pH 2.0 – pH 8.0), temperatures (40 oC-80 oC) and treatment time (15 - 90 min). It was observed that the copper uptake increased with increasing temperature and acid concentration. The highest Cu(II) uptake was found to be 190 mg/g at pH 6.0 and 80°C within 60 min. Results indicate that sulphuric acid has the potential to recover the heavy metals from WM-PCB.

Impact of magnetic field gradients on the free corrosion of iron

Abstract The influence of magnetic fields oriented parallel and perpendicular to the electrode surface on the corrosion behaviour of differently shaped iron samples in low concentrated sulphuric acid solutions has been studied. It is demonstrated, that the relative sample-to-magnet configuration, which determines the magnetic flux density distribution in front of the electrode surface, is decisive for the free corrosion activity. In a configuration generating low magnetic flux density gradients the Lorentz force driven micro-convection leads to an anodic shift of the free corrosion potential. In contrast, a configuration yielding high magnetic flux density gradients causes a cathodic potential shift and leads to a suppression of the corrosion reaction. These effects are discussed on the basis of the Lorentz force and the magnetic field gradient force acting on the partial reaction steps during the corrosion process.

The corrosion inhibition of Ti-alloy (VT-9) in mixture of H2SO4-NaF by organic compounds

This investigation deals with corrosion behavior of high strength titanium alloy in concentrated sulphuric acid solution containing different concentrations (500, 1000, 1500 ppm) of fluoride ion (F−) using various organic compounds (MPA, L-OH, NFP) as inhibitor, potentiodynamically. The open circuit potential values noted before and after each experiment, varied appreciably. These values were negative before polarization but after completion of the experiment turned positive and remained stable over long period of time. It is observed that cathodic current density values increase with increasing cathodic potential (more negative) and fluoride ion. The values of cathodic Tafel slopes derived from the curves (∼110 − 140 mV/dec I) indicate hydrogen evolution reaction (h.e.r). The corrosion potential (Ecorr) varied slightly with addition of inhibitors. The corrosion current densities (Icorr) increased with increasing fluoride ion concentration, but these values decreased appreciably when inhibitor (MPA) was used. SEM micrograph reveals reduction of pits in the presence of inhibitor (MPA). So this concludes that organic compound was used in this case acts as a good inhibitor.

On the corrosion inhibition of low carbon steel in concentrated sulphuric acid solutions. Part I: Chemical and electrochemical (AC and DC) studies

The influence of the concentration of adenine (AD), as a safe inhibitor, on the corrosion of low carbon steel (LCS) in aerated 4.0 M H 2SO 4 solutions was studied. The investigations involved weight loss, potentiodynamic polarization, impedance and electrochemical frequency modulation (EFM) methods. Variations of open-circuit potential (OCP) as a function of time till steady-state potentials were also studied. Measurements were conducted under the influence of various experimental conditions complemented with ex situ EDX examinations of the electrode surface. By using EFM measurements, corrosion current density was determined without prior knowledge of Tafel slopes. Results obtained revealed that together with iodide ion, AD is an effective corrosion inhibitor for LCS corrosion in H 2SO 4 solutions. Synergism between iodide ion and AD was proposed. Potentiodynamic polarization studies showed that AD alone and the mixture of AD and iodide ions act as mixed-type inhibitors for the corrosion of LCS in 4.0 M H 2SO 4 solution. The inhibition mechanism involves the electrostatic adsorption of protonated AD molecules on the LCS surface charged with a negative layer of chemisorbed I − ions. An adherent layer of inhibitor is postulated to account for the protective effect. EDX examinations of the electrode surface confirmed the existence of such adherent layer on the electrode surface. The inhibition efficiency increases with increase in the concentration of AD and immersion time. The potential of zero charge (PZC) of the LCS electrode was determined in 4.0 M H 2SO 4 solutions in the absence and presence of 0.001 M KI, and the mechanism of adsorption was discussed. The results obtained from chemical and electrochemical measurements were in good agreement.

The removal of polonium-210 and lead-210 from copper process streams by molybdenum-doped sodium tungstate

SummaryA molybdenum-doped sodium tungstate phase (Mo-HTB) and a porous, granular polyacrylonitrile composite variant (PAN-Mo-HTB) have been shown to effectively remove polonium-210 and lead-210 from concentrated sulphuric acid solutions (1–8 M) and a copper electrowinning electrolyte. Both forms of the exchanger were characterised by high polonium-210 and lead-210 distribution coefficients and very good selectivity for polonium-210 and lead-210 over divalent copper and iron.

Elaboration of mixed tantalum and niobium carbides from tantalite mineral (Fe,Mn)(Ta1−xNbx)2O6

This paper presents an original method of synthesis of mixed tantalum and niobium carbides from an oxalic precursor elaborated from the tantalite mineral (Fe,Mn)(Ta1−xNb x )2O6. The process of elaboration consists initially in melting the ore with potassium pyrosulphate, then performing a lixiviation with a concentrated hydrochloric acid solution. During the latter reaction, iron and manganese oxides are converted into water-soluble chlorides while the fused mass containing potassium, niobium and tantalum is not dissolved. Traces of chlorides are eliminated by filtration with boiling aqueous solution. Then, the solid is dissolved slowly in hot concentrated sulphuric acid solution. Adding ammonium hydroxide up to a pH of 8 completes the precipitation of niobium and tantalum hydroxides. The precipitate (Ta1−xNb x )(OH)5 is washed and submitted to a reaction of complexation with oxalate ions in an aqueous environment. This reaction involves the formation of a water-soluble oxalic complex containing tantalum and niobium. The excess of water is eliminated by evaporation at 333 K. The tantalum and niobium carbides are obtained by submitting the oxalic complex of chemical formula (NH4)3(Ta1−xNb x )O(C2O4)3·nH2O to a gas-solid reaction in a methane-hydrogen atmosphere at 1273 K. The oxalic precursor and their resultant mixed carbides are characterized by atomic absorption and Infra-Red spectroscopies, thermogravimetric-differential thermal analysis coupled, laser granulometry, X-ray diffraction and transmission electronic microscopy.

Microphysics and chemistry of sulphate aerosols at warm stratospheric temperatures

Observations of high NOx/NOy ratios (overall 40% larger than modelled values) during the Polar Ozone Loss in the Arctic Region in Summer campaign have led us to re‐examine the heterogeneous chemistry of stratospheric aerosol particles during the polar summer period, using the Integrated MicroPhysics and Aerosol Chemistry on Trajectories model. The warm summer temperatures (up to 235 K) imply very concentrated sulphuric acid solutions (80 wt %). On the one hand, these solutions are more likely to freeze, into sulphuric acid monohydrate (SAM), reducing the efficiency of the N2O5 hydrolysis reaction. Including this freezing process increases NOx/NOy ratios but does not improve model/measurement agreement: in polar spring, SAM formation causes the NOx/NOy ratio to be overpredicted whereas freezing has a much smaller effect on nitrogen chemistry during the continuous solar exposure of polar summer. On the other hand, if sulphate aerosols remain liquid, the high acidity may promote acid‐catalysed reactions. The most important reaction is CH2O + HNO3, which effectively increases NOx/NOy ratios across a wide range of conditions, improving agreement with measurements. Furthermore, the production of HONO can either enhance gas‐phase OH concentrations or promote secondary liquid reactions, including HONO + HNO3 and HONO + HCl. Primary uncertainties include the uptake coefficient of CH2O relevant to reaction with HNO3, the amount of HONO available for secondary reaction, and the relative rates of HONO reaction with HNO3 and HCl. The fate of the formic acid product, whose presence in the stratosphere may be an indicator for the CH2O reaction, and the impact on the stratospheric hydrogen budget are also discussed.

Supported liquid membranes modification with sulphonated poly(ether ether ketone): Permeability, selectivity and stability

The development of a new type of composite membrane consisting of a microfiltration support membrane, an immobilised liquid membrane phase and a hydrophilic, charged polymer layer and its function as a supported liquid membrane (SLM) for copper selective transport are described. The ion-exchange layers function as stabilisation layers to improve the membrane lifetime and consist of sulphonated poly(ether ether ketone) (SPEEK). This polymer shows a high permeability for copper ions due to the presence of fixed negative charges and to its swelling capacity in an aqueous phase. A method was developed to prepare composite membranes composed of the support membranes Celgard with one stabilisation layer on either the feed or strip side of the membrane or on both sides. Good adhesion of homogeneous, negatively charged, hydrophilic SPEEK layers to the hydrophobic macroporous support membranes could only be established when the support membranes were first hydrophilised with a concentrated sulphuric acid solution containing 5 wt% free SO 3. The lifetime of the SLMs is significantly improved when one stabilisation layer is applied at the strip side or two layers at both sides of the SLM. A second advantage of this composite SLM is the increase in copper flux caused by a decrease in thickness of liquid membrane phase. However, when SPEEK penetrates entirely through some pores of the support membrane, ions diffuse non-specifically through the SPEEK matrix resulting in an undesired selectivity loss. This phenomenon occurs only when thin Celgard membranes are used as support membranes.

Direct observation of anodic films formed on tantalum in concentrated phosphoric and sulphuric acid solutions

The anodic films formed at 1 mA cm −2 on tantalum in concentrated H 3PO 4 (85%) and H 2SO 4 (95%) solutions at 25°C have been examined directly in the transmission electron microscope employing ultramicrotomed sections. In the former electrolyte, duplex films comprising an outer PO 4 [3]− -doped layer, constituting about 70% of the film thickness, and an inner relatively pure Ta 2O 5 layer are developed, contrasting with the uniformly SO 4 [2]− -doped films developed during anodizing in concentrated H 2SO 4. The doped layers contain high concentrations of PO 4 [3]− and SO 4 [2]− ions, with compositions represented by Ta 2O 5(1−x)(PO 4) 10×\\3 and Ta 2O 5(1−x)(SO 4) 5x, where x = 0.27 and 0.30 respectively. The increased incorporation of electrolyte species relative to films formed in dilute electrolytes significantly enhances the resistivity of the film material with an associated reduction in the dielectric constant.

A Thiophene-Based Liquid Crystalline Aromatic Polyamide

We have synthesized a liquid crystalline, aromatic polyamide from p-phenylene diamine (PPD) and 2, 5-thiophene dicarboxylic acid (Th). The new polymer, poly( p-phenylene thiophenylamide), abbreviated PPD-Th, like its terephthalic acid precursor, poly( p-phenylene terepthalamide) (PPD-T), exhibits a lyotropic mesophase in concentrated sulphuric acid solutions. Polarizing optical microscopy and deuterium NMR show that concentrated PPD-Th solutions exhibit nematic-to-isotropic phase transitions at a much lower temperature than comparable PPD-T solutions. More importantly, unlike PPD-T, lyotropic PPD-Th solutions do not form a crystallo-solvate complex gel phase at room temperature, i.e. the fluid PPD-Th mesophase persists below 300 K enabling the spinning of PPD-Th fibres from a lyotropic dope at ambient temperatures. Thermogravimetric analysis shows that the 2, 5-thiophene heterocycle in the PPDTh backbone does not significantly diminish its thermal stability relative to that of PPD-T. Preliminary x-ray diffraction results show that PPD-Th crystallizes in a tentative two-chain, orthorhombic unit cell with dimensions a = 3.73 Å, b = 5.04 Å and c = 25.20 Å (fibre axis). The fibre repeat corresponds to two chemical repeats related by a twofold screw axis. Mechanical properties (tensile strength, modulus and elongation to break) are presented for as-spun and heat-treated PPD-Th fibres.

Photochemistry of N-benzylideneanilinium cations in concentrated sulphuric acid solutions

The photoreversible EZ isomerization of a series of protonated N-benzylideneanilines (X-C 6H 5CH=NC 6H 5-Y; X ≡ H, N(CH 3) 2; Y ≡ H, NO 2) was investigated in concentrated sulphuric acid solution. The UV absorption spectra of the E isomers are practically independent of substituents on benzene rings and suggest a planar conformation for protonated N-benzylideneanilines. The UV spectra of Z isomers were obtained from photostationary state conditions at two wavelengths. Also the quantum yields of E → Z and Z → E photoisomerization are not markedly affected by the ring substituents and are compatible with a photoreversible process occurring through a common excited state.

Protonation of fully aromatic betacarbolines in highly concentrated sulphuric acid media

AbstractThe monocation–dication equilibria of 6‐nitro and 6‐sulphonic acid derivatives of betacarboline (9H‐pyrido[3,4‐b]indole) were investigated mostly by UV‐visible absorption spectroscopy. Dications are formed in very highly concentrated sulphuric acid solutions (>15 M). Ionization constants, pKa values and solvation parameters obtained from the excess acidity method are reported. The unusually high m* parameters are discussed and compared with other related data.

Influence of temperature on electroreduction of anodically formed passive films on lead electrodes in H2SO4 Solutions Part II: Electroreduction of PbO layers

Combined voltammetry and potentiostatic current transient techniques have been employed to study the electroreduction of anodically formed lead oxide layers, which build up beneath the initially grown PbSO4 crystal, on polycrystalline lead electrodes in concentrated sulphuric acid solution in the 0 to 50° C temperature range. Current transient analysis of the PbO electroreduction performed by using parametric identification procedures and nonlinear fit routines has demonstrated that kinetic data can be mainly interpreted in terms of a progressive nucleation and three-dimensional growth mechanism under charge transfer control, whereas in the initial short time range a process under H+ ion diffusion control has been detected. The phenomenological explanation of the temperature effect on electrode processes is based on the Arrhenius behaviour of kinetic operational parameters.

Development of the Polish wasteless technology of apatite phosphogypsum utilization with recovery of rare earths

The most promising source of rare earth elements in Poland is apatite phosphogypsum, a waste product obtained in the process of phosphoric acid production from Kola apatite. Depending on the technology used, as the hydration ratio of calcium sulphate is changed from hemihydrate to dihydrate, the content of rare earths varies from 0.6% to 0.3% Ln 2O 3 respectively. Technological flow charts for recovering the rare earths as a byproduct have been developed. The basic process used in the technology consists of three steps: apatite phosphogypsum leaching with dilute sulphuric acid solution; separation of rare earth concentrates from leaching sulphuric acid by preconcentration via evaporization, liquid-liquid extraction or precipitation method; anhydrite production from purified phosphogypsum by recrystallization in concentrated sulphuric acid solution.

Characterization of passive layers formed on lead by electrochemical impedance spectroscopy

The corrosion process and characteristics of the surface layer formed on lead in concentrated sulphuric acid solutions were studied using electrochemical impedance spectroscopy (EIS) and rotating-disc electrodes. Data obtained under a wide variety of experimental conditions show that the surface films generated in the passive potential range consist of various Pb(II)-containing species. The inner barrier PbO layer, which builds up progressively beneath the initially grown PbSO 4 porous layer, behaves as a p-type semiconductor. The influence of its formation potential on the semiconducting properties and diffusion processes is discussed from impedance spectra by application of transfer-function analysis using non-linear fitting routines.