Sulphuric Acid Concentration Research Articles

Alteration of cameroonian clays under acid treatment. Comparison with industrial adsorbents

In view to evaluate an alternative local cheaper source for vegetable oil refiners, three cameroonian clays containing swelling (smectites) and non-swelling (kaolinite) clay minerals were treated with sulphuric acid solutions at concentrations of 1, 2, 4 and 8 N at 80 °C for 2 h. Their alteration and resulting products were characterized by XRD, FT-IR-spectroscopy, chemical analyses, along with TEM-EDS, nitrogen adsorption isotherms at 77 K, and compared with industrial bleaching earths. Acid treatment of Cameroonian clays leads to the classically observed cristallochemical and textural modifications. The plot of TEM-EDS data in Al 2O 3/SiO 2 and Fe 2O 3/Al 2O 3 diagrams indicate that upon acid treatment, clay particles principally move towards the SiO 2 pole, consistent with the formation of an amorphous compound mainly siliceous as the result of acid activation. Concomitantly, a progressive decrease in cation exchange capacity (CEC) was observed with increasing sulphuric acid concentrations while both specific surface area and mesoporosity of the studied materials increase. Elemental analyses, X-ray and spectroscopy data reveal that acid activation affects both the octahedral and the tetrahedral sheets. The analysis of their reactivity shows that clays with high amounts of smectite are more sensitive to acid leaching than those with relative large kaolinite contents. Further, upon acid treatment, most trace and rare earth elements are leached, and the amount of toxic elements (e.g. Cd, Pb, Ni, Cu, As, Zn) in the by-products is low (< 50 mg/kg). Mineralogy, chemical analyses and textural properties of the activated products match the specifications of industrial adsorbents. Therefore, activated Cameroonian clays are expected to perform well in respect with decolorization of vegetable oils.

The role of relative humidity in continental new particle formation

[1] Relative humidity (RH) has been observed to be anticorrelated with continental new particle formation. Several reasons have been proposed for this rather surprising finding, but no firm conclusions have been drawn so far. Here we study several of the proposed reasons: Enhanced coagulational scavenging of sub-3 nm clusters at high RH, diminished solar radiation at high RH leading to diminished gas phase oxidation chemistry, and increased condensation sink (CS) of condensable gases due to hygroscopic growth of the preexisting particles. Our theoretical calculations indicate that the increase of coagulational scavenging plays a relatively small role in the inhibition of nucleation at high RH. On the other hand, field data show that the maximum observed gas phase sulphuric acid concentrations are limited to RHs below 60%. The field data also indicate that this is likely due to low OH concentrations at high RH. This finding is also supported by aerosol dynamics model simulations. The model was used to find out whether this is mainly due to decreased source (solar radiation) or increased sink (CS) terms at the elevated RH. The simulation results show that the decreased source term at high RH limits H2SO4 levels in the air, and therefore high new particle formation rates (above ∼1 cm−3 s−1) rarely occur above 80% RH.

SOSA – a new model to simulate the concentrations of organic vapours and sulphuric acid inside the ABL – Part 1: Model description and initial evaluation

Abstract. Chemistry in the atmospheric boundary layer (ABL) is controlled by complex processes of surface fluxes, flow, turbulent transport, and chemical reactions. We present a new model SOSA (model to simulate the concentration of organic vapours and sulphuric acid) and attempt to reconstruct the emissions, transport and chemistry in the ABL in and above a vegetation canopy using tower measurements from the SMEAR II at Hyytiälä, Finland and available soundings data from neighbouring meteorological stations. Using the sounding data for upper boundary condition and nudging the model to tower measurements in the surface layer we were able to get a reasonable description of turbulence and other quantities through the ABL. As a first application of the model, we present vertical profiles of organic compounds and discuss their relation to newly formed particles.

A new flexible multicomponent model for the study of aerosol dynamics in the marine boundary layer

A new sectional aerosol dynamics model, MAFOR, was developed with the focus to study nucleation in the marine boundary layer. Novel aspects of the model are (1) flexibility in the treatment of gas phase chemistry, (2) treatment of liquid phase chemistry, which can be extended according to needs and (3) simultaneous calculation of number and mass concentration distributions of a multicomponent aerosol as functions of time. Comparison with well-documented aerosol models (MONO32 and AEROFOR), a comprehensive data set on gas phase compounds, aerosol size distribution and chemical composition obtained during theA OE-96 (Arctic Ocean Expedition, 1996)was used to evaluate the model. Dimethyl sulphide decay during advection of an air parcel over the Arctic pack ice was well captured by the applied models and predicted concentrations of gaseous sulphuric acid and methane sulphonic acid range up to 1.0 × 106 cm−3 and 1.8 × 106 cm−3, respectively. Different nucleation schemes were implemented in MAFOR which allow the simulation of new particle formation. Modelled nucleation rates from sulphuric acid nucleation via cluster activation were up to 0.21 cm−3 s−1 while those from ion-mediated nucleationwere below 10−2 cm−3 s−1. Classical homogeneous binary and ternary nucleation theories failed to predict nucleation over the central Arctic Ocean in summer.

Characterization of Plasmid pPO1 from the HyperacidophilePicrophilus oshimae

Picrophilus oshimae and Picrophilus torridus are free-living, moderately thermophilic and acidophilic organisms from the lineage of Euryarchaeota. With a pH optimum of growth at pH 0.7 and the ability to even withstand molar concentrations of sulphuric acid, these organisms represent the most extreme acidophiles known. So far, nothing is known about plasmid biology in these hyperacidophiles. Also, there are no genetic tools available for this genus. We have mobilized the 7.6 Kbp plasmid from P. oshimae in E. coli by introducing origin-containing transposons and described the plasmid in terms of its nucleotide sequence, copy number in the native host, mode of replication, and transcriptional start sites of the encoded ORFs. Plasmid pPO1 may encode a restriction/modification system in addition to its replication functions. The information gained from the pPO1 plasmid may prove useful in developing a cloning system for this group of extreme acidophiles.

Phosphine and Thiophene Cyclopalladated Complexes: Hydrolysis Reactions in Strong Acidic Media

The mechanisms for the hydrolysis of organopalladium complexes [Pd(CNN)R]BF(4) (R=P(OPh)(3), PPh(3), and SC(4)H(8)) were investigated at 25 °C by using UV/Vis absorbance measurements in 10 % v/v ethanol/water mixtures containing different sulphuric acid concentrations in the 1.3-11.7 M range. In all cases, a biphasic behavior was observed with rate constants k(1obs), which corresponds to the initial step of the hydrolysis reaction, and k(2obs), where k(1obs)>k(2obs). The plots of k(1obs) and k(2obs) versus sulfuric acid concentration suggest a change in the reaction mechanism. The change with respect to the k(1obs) value corresponds to 35 %, 2 %, and 99 % of the protonated complexes for R=PPh(3), P(OPh)(3), and SC(4)H(8), respectively. Regarding k(2obs), the change occurred in all cases at about 6.5 M H(2)SO(4) and matched up with the results reported for the hydrolysis of the 2-acetylpyridinephenylhydrazone (CNN) ligand. By using the excess acidity method, the mechanisms were elucidated by carefully looking at the variation of k(i),(obs) (i=1,2) versus cH+. The rate-determining constants, k(0,A-1), k(0,A-2), and k(0,A-SE2) were evaluated in all cases. The R=P(OPh)(3) complex was most reactive due to its π-acid character, which favors the rupture of the trans nitrogen-palladium bond in the A-2 mechanism and also that of the pyridine nitrogen-palladium bond in the A-1 mechanism. The organometallic bond exerts no effect on the relative basicity of the complexes, which are strongly reliant on the substituent.

On the roles of sulphuric acid and low-volatility organic vapours in the initial steps of atmospheric new particle formation

Abstract. Sulphuric acid and organic vapours have been identified as the key components in the ubiquitous secondary new particle formation in the atmosphere. In order to assess their relative contribution and spatial variability, we analysed altogether 36 new particle formation events observed at four European measurement sites during EUCAARI campaigns in 2007–2009. We tested models of several different nucleation mechanisms coupling the formation rate of neutral particles (J) with the concentration of sulphuric acid ([H2SO4]) or low-volatility organic vapours ([org]) condensing on sub-4 nm particles, or with a combination of both concentrations. Furthermore, we determined the related nucleation coefficients connecting the neutral nucleation rate J with the vapour concentrations in each mechanism. The main goal of the study was to identify the mechanism of new particle formation and subsequent growth that minimizes the difference between the modelled and measured nucleation rates. At three out of four measurement sites – Hyytiälä (Finland), Melpitz (Germany) and San Pietro Capofiume (Italy) – the nucleation rate was closely connected to squared sulphuric acid concentration, whereas in Hohenpeissenberg (Germany) the low-volatility organic vapours were observed to be dominant. However, the nucleation rate at the sulphuric acid dominant sites could not be described with sulphuric acid concentration and a single value of the nucleation coefficient, as K in J=K [H2SO4]2, but the median coefficients for different sites varied over an order of magnitude. This inter-site variation was substantially smaller when the heteromolecular homogenous nucleation between H2SO4 and organic vapours was assumed to take place in addition to homogenous nucleation of H2SO4 alone, i.e., J=KSA1[H2SO4]2+KSA2[H2SO4][org]. By adding in this equation a term describing homomolecular organic vapour nucleation, Ks3[org]2, equally good results were achieved. In general, our results suggest that organic vapours do play a role, not only in the condensational growth of the particles, but also in the nucleation process, with a site-specific degree.

Dissolution behaviour of a Turkish lateritic nickel ore

The atmospheric pressure sulphuric acid leaching characteristics of Adatepe (Eskişehir, Turkey) laterite ore that has recently been put into operation was investigated. The effects of sulphuric acid concentration (5–95%), temperature (20–95 °C) and time (30–240 min) on leaching were determined by nickel, iron and arsenic analyses. The amounts of Ni, Fe and As in solution were observed to increase with increase of temperature from 20 °C to 70 °C for sulphuric acid concentrations between 5% and 95%. Further increase of temperature to 95 °C showed that the dissolution of Ni, Fe and As were increased until 60% sulphuric acid concentration and over 60% a decrease in the dissolution percentages was observed due to the probable formation of nickel and silicon containing ferric sulphate type compounds that cause nickel loss from the leach solution. Experimental results showed that maximum nickel dissolution of 99.2% at 95 °C could be reached in 120 min of leaching time for a sulphuric acid concentration of 60%. The congruency of Ni dissolution with respect to Fe was found to be congruent over about 25% Ni and 15% Fe dissolution values. XRD analyses on the residues obtained after leaching showed that it was not required to dissolve all goethite phase to reach maximum dissolution of nickel contained in the sample. An activation energy of 30.36 kJ/mole was determined for Ni dissolution showing that leaching is controlled by external diffusion and chemical reactions.

The characterisation of a genipin-gelatin gel dosimeter

Genipin cross links gelatin to slowly form a blue colour that bleaches upon irradiation. Spectrophotometric measurements of the absorbance change following irradiation to doses up to 100 Gy gives a linear dose response for certain concentrations of the gel ingredients; genipin, gelatin and sulphuric acid. Dose sensitivity increases with increasing concentrations of sulphuric acid and genipin and is also strongly dependent on the time allowed for the genipin-gelatin cross linking reaction (referred to here as blending) to take place. The optimum formulation of this gel was found for genipin concentration between 0.3 – 0.5 mM and blending time of at least 4 h.

Development of a radiochromic ferric oligomer hydrogel

Ferrous gelatin hydrogels were prepared by using sulphuric acid concentrations lower than required to maintain radiation induced ferric ions fully hydrated. The ferric hydroxyl species that are produced following irradiation exhibit a radiochromic response that can be probed with blue light. The dose distribution shapes were stable in time, indicating no long term diffusion. An over response to dose gradients was observed both in one centimeter cuvette samples and litre volumes probed with optical cone beam CT. This ferrous hydrogel may represent a model system for studying iron radiochemistry in biological systems.

Corrosion inhibition of 6061 Al–15 vol. pct. SiC(p) composite and its base alloy in a mixture of sulphuric acid and hydrochloric acid by 4-(N,N-dimethyl amino) benzaldehyde thiosemicarbazone

The corrosion inhibition characteristics of 4-(N,N-dimethylamino) benzaldehyde thiosemicarbazone (DMABT) on the corrosion behavior of 6061 Al–15 vol. pct. SiC(p) composite and its base alloy were studied at different temperatures in acid mixture medium containing varying concentrations of hydrochloric acid and sulphuric acid using Tafel extrapolation technique and ac impedance spectroscopy (EIS). The effect of inhibitor concentration, temperature and concentration of the acid mixture media on the inhibitor action was investigated. It was found that inhibition efficiencies increase with the increase in inhibitor concentration, but decrease with the increase in temperature and with the increase in concentration of the acid media. Thermodynamic parameters for dissolution process were determined. The adsorption of DMABT on both the composite and base alloy was found to be through physisorption obeying Freundlich adsorption isotherm.

Sub-10 nm particle growth by vapor condensation – effects of vapor molecule size and particle thermal speed

Abstract. The growth of freshly formed nanoparticles has been investigated. A new analytical expression based on a recently developed exact solution for the condensational growth rate has been derived. Based on the new growth rate, a new approximate but accurate analytical expression for growth time has been derived. The expression includes transition regime effects on growth, molecule size effects on the collision cross section and particle thermal speed effects on the relative collisional speeds – the last two of which are typically neglected, but may have significant effects when dealing with the growth of freshly nucleated particles. To demonstrate the use of the derived expressions, the contribution of sulphuric acid and organic compounds on sub 3 nm and sub 10 nm particle growth rates has been studied. For sulphuric acid also the effect of hydration as function of relative humidity has been taken into account. According to the new expression the sulphuric acid concentration needed for 1 nm/h growth in sub 3 nm range is ca. 1.5×107 cm−3, which is a factor of 1.5 smaller than values typically used in aerosol physics based on standard model in kinetic regime.

Xylitol production from olive-pruning debris by sulphuric acid hydrolysis and fermentation with Candida tropicalis

AbstractThe debris of olive pruning is a renewable, low-cost and widely available agricultural waste. Its biochemical conversion by hydrolysis and fermentation was undertaken in the present study. Diluted acid hydrolysis was conducted in a heterogeneous stirred tank reactor at 90°C and at a low sulphuric acid concentration (0.0–1.0 N) for 300 min. To increase thed-xylose/d-glucose ratio into the hydrolysate, in another experiment amorphous cellulose and extracts were removed by means of a pretreatment in an extruder with 1 N H2SO4at 70°C before the acid hydrolysis. The fermentation of hydrolysates was performed under microaerobic conditions in a batch bioreactor at 30°C and pH 5 withCandida tropicalisNBRC 0618. The controlled fermentation parameters included maximum specific growth rate, biomass productivity, rate of the specific substrate uptake, rates of specific ethanol and xylitol production, and overall yield of ethanol and xylitol. In the presence of 1.0 N H2SO4, the fermentation of the pretreated hydrolysate led to specific xylitol production rates and overall xylitol yield (0.1 g g-1 h for t=25 h; 0.49 g g-1, respectively) higher than those achieved without pretreatment (0.03 g g-1 h for t=25 h; 0.39 g g-1, respectively). Under these conditions, 53 g xylitol kg-1of dry olive-pruning debris was obtained from the pretreated culture, whereas without pretreatment 70 g ethanol and 34 g xylitol were recovered.

Kinetics of indium dissolution from sphalerite concentrate in pressure acid leaching

The mineralogical analysis of a sphalerite concentrate by electron-microprobe shows that the main indium-bearing minerals are pyrite, zinckenite, galena, cassiterite, jamesonite. The kinetics of indium dissolution from sphalerite concentrate in the sulphuric acid–oxygen system indicated that the particle size, temperature and sulphuric acid concentration significantly influenced the leaching efficiencies of indium. The experimental data indicated that under the conditions employed up to 92% indium extraction were achieved. The empirical kinetic model, − ln(1 − x) = kt was used to describe the dissolution kinetics of indium in sulphuric acid solutions, and the results showed that indium dissolution process was controlled by chemical reaction with the activation energies calculated to be 47 kJ/mol and the reaction order with respect to sulphuric acid concentration closed to 1.

Erratum to: “Statistical Modeling of Electrochemical Reactivation Conditions for Detecting Sensitization to IGC of Austenitic Stainless Steel Type 316L”

The aim of this study was to determine the optimum conditions of the DL EPR test in order to evaluate the highest values of the degree of sensitization (DOS) of a forged austenitic stainless steel type 316L evaluated by the ratio Ir/Ia or Qr/Qa in %. The criteria of sensitization to the IGC corresponds toIr/Ia > 1% and Qr/Qa > 1%. A model using a full factorial design has been established, and the selected factors were the sweep rate (dE/dt), sulphuric acid concentration (H2SO4), ammonium thiocyanate concentration (NH4SCN), and temperature in °C. A first order model is obtained by using a 24 full factorial design. An experimental test carried out using a 24 factorial design indicated that all the factors and their interactions have a positive effect on the response Ir/Ia. Furthermore, the highest value detected ofIr/Ia was found to be 65.6%. On the other hand, a microstructural study based on an optical microscope and a scanning transmission electron microscope (STEM) has been carried out for annealed and aged samples (550°C-80000 h). The profiles of the chromium, nickel, and molybdenum concentration established by X-ray microanalysis in STEM confirm a decrease of the content of these elements leading to the formation of Cr-depleted zones responsible for the sensitization to the IGC.

A simulation tool for aerosol formation during sulphuric acid absorption in a gas cleaning process

A simulation tool has been developed to predict sulphuric acid aerosol formation in typical industrial absorption processes for gas cleaning. The underlying model comprises homogeneous nucleation and the growth of a polydisperse droplet collective under the special circumstances of a gas–liquid contact device where heat and mass transfer processes between the bulk phases take place simultaneously. The model is applied to a hot flue gas (200 °C) with sulphuric acid concentrations between 5 and 100 mg m −3 (STP) (STP: standard temperature and pressure ). The simulation yields high droplet number concentrations up to 10 16 m −3 especially for low gas inlet concentrations of sulphuric acid (5 mg m −3 (STP)), and very small droplet sizes in the range 20–100 nm. The droplet number concentrations decrease and the droplet sizes increase with increasing sulphuric acid inlet concentrations. It is shown that small droplets (<20 nm) need relatively high supersaturation for growing. If the saturation in the absorption equipment is not high enough the droplets partially re-evaporate but do not vanish due to the extremely low vapor pressure of concentrated sulphuric acid. The resulting size distributions of the aerosol droplets are not very sensitive with respect to the nucleation model used. This is demonstrated by comparing nucleation models with and without hydrate formation. The new simulation tool allows an estimate of the true sulphuric acid removal efficiency of absorption processes which is often not more than 50% due to aerosol formation. In general, the simulation results enable a deeper insight in the mechanisms of aerosol formation and behavior in absorption processes.

AC impedance–emission spectroscopy for determining the electrochemical behaviour of anodised aluminium in aqueous solutions

In the present investigation, holographic interferometry was utilised for the first time to determine the rate change of the alternating current (AC) impedance of aluminium samples during the initial stage of anodisation processes in aqueous solution without any physical contact. In fact, because the AC impedance values in this investigation were obtained by holographic interferometry, electromagnetic method rather than electronic method, the abrupt rate change of the AC impedance was called AC impedance–emission spectroscopy. The anodisation process (oxidation) of the aluminium samples was carried out chemically in different sulphuric acid concentrations (0.5–3.125% H2SO4) at room temperature. In the mean time, the real time holographic interferometry was used to determine the difference in the AC impedance of two subsequent values, dZ, as a function of the elapsed time of the experiment for the aluminium samples in 0. 5, 1.0, 1.5 and 3.125% H2SO4 solutions. The AC impedance–emission spectra of the present investigation represent a detailed picture of not only the rate change of the AC impedance throughout the anodisation processes but also the spectra represent the rate change of the growth of the oxide films on the aluminium samples in different solutions. Consequently, holographic interferometry is found to be very useful for surface finish industries, especially for monitoring the early stage of anodisation processes of metals, in which the rate change of AC impedance of the aluminium samples can be determined in situ.

ChemInform Abstract: Anodic Voltammetry of Hydroxylamine at Rotating Disc Electrode of Platinum.

Hydroxylamine has been examined by anodic voltammetry at platinum electrode in sulphuric acid media. Obedience to Levich relationship was shown at platinum electrode in 0.01 M sulphuric acid concentration in the range 2.0×10−4 to 1.0×10−3 M, (M=mol dm−3). Electrode kinetics parameters have been evaluated and a possibility of the reaction mechanism path is suggested.

Evaluation of Acid Leaching of Low Grade Chalcopyrite Using Ozone by Statistical Analysis

Several attempts have been made to optimize the process and reduce operating costs of the acid leaching of low grade sulphide copper ores. In this study, we conducted acidic leaching of low-grade chalcopyrite by using ferric ion and ozone as oxidants, at 25°C. In particular, we used a Taguchi L9 experimental design (four factors, three levels) to determine the effects of particle size, ferric ion and sulphuric acid concentrations ([Fe+3] and [H2SO4]) and ozone (O3) mass flow rate, on the amount of copper extracted. Statistical analysis showed that [Fe+3] had the greatest effect on the amount of copper extracted followed by particle size and O3 mass flow rate. [H2SO4] had no statistical significance. The highest copper leaching yield was obtained for [Fe+3] = 0.5 M, O3 flow rate = 0.5 g/h, [H2SO4] = 0.1 M and particle size=398 μm.RésuméOn a fait plusieurs essais d'optimisation du procédé et de réduction des coûts d'opération de la lixiviation acide de minerais de sulfure de cuivre à faible teneur. Au cours de cette étude, nous avons effectué des essais de lixiviation acide de chalcopyrite à faible teneur en utilisant l'ion ferrique et de l'ozone comme oxydants, à 25°C. En particulier, nous avons utilisé un plan expérimental de Taguchi L9 (quatre facteurs, trois niveaux) pour déterminer l'effet de la taille de particule, des concentrations de l'ion ferrique et d'acide sulfurique ([Fe+3] et [H2SO4]) et du débit massique de l'ozone (O3), sur la quantité extraite du cuivre. L'analyse statistique a montré que [Fe+3] avait le plus grand effet sur la quantité extraite du cuivre, suivi par la taille de particule et par le débit massique d'O3. [H2SO4] n'avait aucune importance statistique. On a obtenu la production de cuivre la plus élevée par lixiviation avec [Fe+3] = 0.5M, débit d'O3 = 0.5 g/h, [H2SO4] = 0.1M et une taille de particule = 398 μm.

Kinetics of vanadium dissolution from black shale in pressure acid leaching

The leaching kinetics of vanadium from black shale in the sulphuric acid–oxygen system is presented. The effects of agitation speed, leaching temperature in the range of 110–150 °C, sulphuric acid concentration, oxygen partial pressure and particle size on the rate of vanadium leaching were determined. The results indicate that the rate is nearly independent of agitation above 200 rpm and increases with increasing temperature, sulphuric acid concentration and oxygen partial pressure. As leaching occurs, there is a progressive dissolution of a vanadium-bearing alumino-silicate phase, while the inert quartz phase assembles onto the mineral surface and remains as an “ash” layer. The leaching kinetics was analyzed by using a new variant of the shrinking core model (SCM) in which both the interfacial transfer and diffusion across the product layer affect the leaching rate. The determined activation energy was found to be 40.14 kJ/mol and the reaction orders with respect to sulphuric acid concentration and oxygen partial pressure were 0.61 and 1.67, respectively. A semi-empirical rate equation was derived to describe the process.