Aqueous SO2 Research Articles

Apparent molar heat capacities of aqueous solutions of phosphoric acid and sulfur dioxide from 303 to 623 K and a pressure of 28 MPa

Heat capacities of aqueous solutions of phosphoric acid from 0.1 to 0.8 mol- kg-1 and sulfur dioxide from 0.2 to 0.9 mol-kg-1 have been measured with a flow heat-capacity calorimeter from 303 to 623 K and a pressure of 28 MPa. At the lowest molality single-solute solutions as well as mixtures of either H3PO4 or SO2 with HC1 were measured to repress dissociation. Calculated apparent molar heat capacities were corrected for dissociation reactions and the chemical relaxation effect. Experimental results for mixtures were analyzed using Young’s rule. Standard state partial molar heat capacities of H3PO4(aq) and SO2(aq) were obtained by extrapolation to infinite dilution. A few measurements of the densities of aqueous H3PO4 and SO2 were made at 25°C and a pressure of 28 MPa.

Electrochemical behaviour of aqueous SO2 at Pt electrodes in acidic medium. A voltammetric and in situ Fourier transform IR study Part I. Oxidation of SO2 on Pt electrodes with sulphur-oxygen adsorbed species

The electrochemical oxidation of aqueous SO 2 at platinum electrodes has been studied in an acidic medium by means of cyclic voltammetry and in situ Fourier transform IR (FTIR) spectroscopy. In the potential zone ranging from 0.55 to 1.50 V (vs.RHE), the oxidation reaction of SO 2 takes place at a Pt surface initially covered by a sulphur-oxygen adsorbate. In situ FTIR spectroscopy yields a band at 1271 cm −1 , which could be assigned to adsorbed SO 2 . However, (bi)sulphate is detected as the only SO 2 oxidation product. The generation of S(VI) species occurs during both the forward and the reverse sweeps. The different voltammetric responses obtained in each case are attributed to the oxidation of SO 2 on a Pt electrode with different surface states.

A three‐dimensional numerical model of cloud dynamics, microphysics, and chemistry: 4. Cloud chemistry and precipitation chemistry

A study of the cloud chemistry and precipitation chemistry of the three‐dimensional cloud chemical modeling of a severe local storm case (Wang and Chang, this issue) is discussed in this paper. In our simulation the microphysical processes, especially those related to the ice phase, were found to have significant effects on influencing both the rhythm of time evolution and the amount of quantitative variation of pollutants. Most chemical species in the ice phase particles were transformed from liquid phase droplets by the riming process. The ratio of the transfer of chemical species from aqueous phase to ice phase induced by riming to that induced by freezing was about 55 to 1 for N(V) and 8 to 1 for S(VI). The average equivalent pH value had a linear correlation with the logarithm of total water content and with the logarithm of [S(VI)] + [N(V)] in the cloud. The average equivalent pH value for the whole cloud changed from 5.1 at 28 min to 4.4 at 55 min. Most low pH values appeared in the less convective region. For this particular case study, aerosol scavenging was the major source of S(VI) production, which provided a total amount 50 times that provided by sulfur oxidation in the cloud. The major contributor of sulfur oxidation changed during the lifetime of the modeled storm. The peaks of acid deposition did not correspond to the peaks of precipitation. The sub cloud dissolution and microphysics‐related transformation played an important role in the acid production and deposition. The nitric acid production total in the sub cloud area doubled that in the cloud. Most of the S(VI) produced by the aqueous phase SO2 oxidation was also found to be due to sub cloud processes.

Leaching of Cu2O with aqueous solution of sulfur dioxide

Leaching of Cu2O with aqueous SO2 solution is significant, since during the dissolution process, precipitation of copper as Chevreul’s salt also takes place under appropriate conditions. The dissolution is controlled by surface reactions and proceeds through both aqueous SO2 and acid dissolution paths. An overall rate equation based on the above premise has been found to agree well with the experimental data. At pH values higher than 1.8, precipitation of copper as Chevreul’s salt takes place after about 10 minutes of leaching. The extent of the precipitation depends upon the pH, SO2 concentration, initial Cu2+ concentration, and sulfate concentration in the leaching solution.

Surface chemistry of carbon: activation of molecular oxygen

Three different industrial carbon blacks were characterized in their surface chemistry with respect to their relative abilities to activate molecular oxygen. A variety of techniques was used including x-ray diffraction, gasification experiments, electron spectroscopy as XPS and UPS, helium ion scattering spectroscopy, thermal desorption spectroscopy and the catalytic oxidation of aqueous SO2 as a “chemical probe” for activated oxygen. The activation properties for molecular oxygen at high temperatures were probed by analysing the gasification characteristics in 5 vol % oxygen-inert gas mixtures; at low temperatures the activity in the oxidation of SO2 to sulfuric acid with molecular oxygen was taken as indicator. For this reaction the carbons had to be activated by ammonia treatment at elevated temperatures. Thermal desorption spectroscopy and valence band photoemission provided data for the identification of reaction intermediates in the activation process of oxygen. The important role of surface chemica...

Leaching of nickel from supported nickel waste catalyst using aqueous sulfur dioxide solution

Waste nickel catalyst is an important secondary source for recovery of nickel. Nickel from the waste has been leached out using aqueous SO2 solution. The initial leaching kinetics is controlled by reaction at the surface involving the adsorption of SO2 and H+ resulting in the formation of product species. A kinetic model based on the above scheme has been presented. The X-ray photoelectron spectroscopy (XPS) studies indicate that easily soluble Ni(OH)2 or NiO is initially leached out, leaving behind the other nickel species which dissolves at a slower rate.

Heat Stability of Sunflower‐Hull Anthocyanin Pigment

ABSTRACTAnthocyanin pigment was extracted from hulls of a sunflower genotype, Neagra de Cluj, using aqueous SO2 solutions of varying concentrations. Thermal stability of the pigment was studied between 65–95°C, and pH 1.0–5.0. Thermal degradation of the pigment followed first order kinetics. Calculated activation energy was 23.1 ± 2.2 kcal/ mole. Extraction of hulls with 1000 ppm SO2 solution gave highest anthocyanin content and best thermal stability. The pigment was most stable at pH 3.0.

Studies of latex paint films exposed to aqueous SO2: pH effects

AbstractLatex paint films containing the acid‐soluble extender calcium carbonate have been exposed to aqueous SO2 and other acidic solutions to evaluate the effects of acidic deposition at different pH values on the coatings. CaCO3 is completely removed from these films upon immersion in acidic solutions. The leaching process was monitored with weight loss and infrared measurements. The removal rate was found to be strongly dependent on pH, decreasing with increasing pH. Removal of CaCO3 occurs even for distilled water which has been allowed to equilibrate with atmospheric CO2 (pH 5.6). The removal rate seems to depend only on [H+]; the identity of the acidic anion is apparently insignificant. An empirical relation between the rate of removal and pH was formulated from the weight loss data. The analyses of the results from both weight loss and infrared methods suggested that the mechanism of removal at pH 2.0 is diffusion controlled, whereas a chemical reaction involving H+ becomes more important at higher pH values.

Infrared attenuated total reflectance study of latex paint films exposed to aqueous sulfur dioxide

AbstractFourier‐transform infrared/attenuated total reflectance (FTIR–ATR) has been used to investigate the effects of acidic deposition on latex paint films with and without a calcium carbonate extender additive. Paint films approximately 5 mils thick were exposed to aqueous SO2(pH 2.0) for various times by simple immersion. Rapid and complete removal of CaCO3 from the paint film was found to occur, and the kinetics of the removal process were monitored using both weight loss and FTIR–ATR measurements. Both methods revealed Fickian diffusion, with an apparent diffusion coefficient D = 1.84 × 10−9 cm2/s. Good agreement was obtained between D measured via FTIR–ATR and from the weight lost data. The mechanism of removal of CaCO3 from the latex paint films appears to be controlled by the rate at which water and other components of the aqueous SO2 solution can diffuse into the film.

ChemInform Abstract: Oxidation of Aqueous SO2 by Peroxymonosulfate

Abstractis studied because recent model calculations suggest that HSO5‐ may constitute a significant fraction of the total sulfur in remote tropospheric water droplets such as cloud, fog, and rain.

Winter cloud water and air composition in central Ontario

Time histories of surface air composition and cloud water composition in winter in Central Ontario are compared in order to establish a winter data set for this region, and to identify dominant processes responsible for the incorporation of sulfate, nitrate, and acidity into cloud water. Cloud water comparisons are restricted to low‐level collections (median altitude 625 m above ground) within the boundary layer. Surface level measurements during the 6‐week period show a variety of conditions, including several episodes of elevated concentrations of SO2, NO3−, HNO3, aerosol SO4=, and occasionally aerosol NO3−. Nitric acid comprised the majority of soluble acidity at ground level more than half the time, and was relatively more important during the periods of elevated SO4 = and NO3− concentrations. Examination of cloud water composition indicated that HNO3 was also the dominant contributor to cloud water acidity on the majority of days sampled. Comparisons of air and cloud water absolute concentrations and concentration ratios suggest that aqueous SO2 oxidation was of minor importance in determining cloud composition. The conclusion is supported by measurements of hydrogen peroxide in cloud water samples. Cloud water NO3−/SO4 = ratios were found to exceed (HNO3 + aerosol NO3−)/SO4= ratios in air at the surface in most cases, and in a few instances cloud water NO3− concentrations were higher than expected based on the surface air composition data; several possible causes for this observation are discussed. It is concluded that in this region in winter, the composition of low‐level clouds can be estimated to within a factor of 2 by measurements of air composition at the surface, and that dissolution of soluble aerosol and gaseous species is primarily responsible for cloud composition. In‐cloud SO2 oxidation is found to be of minor significance, but the data may indicate in‐cloud production of HNO3 in some cases.

Beneficiation of Florida Dolomite Phosphate Ores

The Bureau of Mines, US Department of the Interior, conducted studies to recover phosphate from four dolomitic southern Florida deposits not currently mined. The samples contained 5.8–10.2% P2O5 and 1.7–4.8% MgO. Chemical analyses of sized fractions indicated that no pebble concentrate, +1.2 mm (+ 14 mesh) could be produced from these samples. A scheme was developed that consisted of desliming, grinding, scrubbing, and redesliming the ore to produce a flotation feed. Conventional one-step fatty acid-fuel oil batch flotation tests on the samples resuited in concentrates containing 29.0–31.3% P2O5 at flotation recoveries ranging from 72.4 to 96.1% of the flotation feed. The MgO content of the concentrates ranged from 0.47 to 1.36%. Continuous flotation of the Manatee No. 2 sample indicated that commercial-grade phosphate concentrates analyzing 31.3% P2O5 and 0.55% MgO could be produced with a flotation recovery of 89.9%. The MgO content of concentrates obtained from the Manatee No. 1 and Hardee samples was 1.20–1.36%, respectively. Leaching with aqueous SO2 reduced the MgO content of these phosphate concentrates to 0.5 and 0.8%, but with a concomitant loss in phosphate recovery of about 10%.

Thermodynamics of aqueous carbon dioxide and sulfur dioxide: heat capacities, volumes, and the temperature dependence of ionization

A flow microcalorimeter and vibrating tube densimeter were used at 25 °C to obtain apparent molar heat capacities and volumes of aqueous NaHCO3, KHCO3, NaHSO3, and KHSO3, from 0.1 to 1.0 mol kg−1, aqueous CO2 from 0.01 to 0.10 mol kg−1 and aqueous SO2 from 0.045 to 2.0 mol kg−1. The contribution of "chemical relaxation" (changes in equilibrium state and enthalpy due to change in temperature) to the experimental heat capacities of aqueous SO2 required special attention, leading to the derivation of a new equation for calculating this effect. Standard state values for the heat capacities and volumes of aqueous CO2, SO2, HCO3−, and HSO3− were obtained from the apparent molar properties by extrapolation to infinite dilution. Combining these results with other thermodynamic data from the literature gave estimates of log K1b the equilibrium constant for the first neutralization of CO2 and SO2, at high temperatures. The results for CO2 reproduce very accurate literature values to within 0.2 at 200 °C. The expression for the reaction [Formula: see text] log K1b = 22.771 + 2776.0/T–8.058 log T, is consistent with the sparse and limited experimental data.

Diffusion with hydrolysis equilibria: transport coefficients of aqueous SO2, NH3, and Na2CO3

Practical equations are derived for estimating diffusion coefficients and Onsager transport coefficients of aqueous solutes subject to hydrolysis. The derivation is based on the Nernst–Hartley method which is extended to include chemical reaction of solute with solvent. The derived equations and existing mobility data are used to estimate transport coefficients of aqueous SO2 (20 °C), NH3 (15 °C), and Na2CO3 (25 °C). In dilute solution where hydrolysis is extensive, rates of diffusion of SO2 and NH3 are increased by about 50% and 25%, respectively, relative to unhydrolyzed solute. Because of the carbonate–bicarbonate equilibrium, diffusion in aqueous Na2CO3 is a ternary process characterized by coupled transport of NaOH. In dilute solution the NaOH flux may exceed the flux of Na2CO3.

SO2-Induced changes in the polyribosomal profiles of the gametophyte of the moss tortula ruralis

Aqueous SO2 (0.5-2.0 mM), in short-term exposure experiments (30-120 min.), causes a rapid loss of integrity of the polyribosomes in the moss Tortula ruralis. This effect is concentration- and exposure time-dependent and appears to be unattributable to an SO2-induced pH change.

THE ROLE OF METAL-ION BINDING IN MODIFYING THE TOXIC EFFECTS OF SULPHUR DIOXIDE ON THE LICHEN UMBILICARIA MUHLENBERGII: I. POTASSIUM EFFLUX STUDIES.

K+ efflux from Umbilicaria muhlenbergii was not affected following the uptake of known amounts (< 20 μmol g-1 ) of Ca2+ , Mg2+ , Sr2+ and Zn2+ , but was increased in the cases of Cu2+ and Pb2+ . In a number of samples that had taken up increasing amounts of Cu2+ , a discontinuity in K+ release during metal incubation correlated with a decrease in subsequent 14 C fixation. Some of the binding sites associated with the first phase of Cu2+ uptake (up to 12 μmol g-1 ) are interpreted to occur near, on or within the algal cells. The larger K+ loss associated with higher Cu2+ uptake levels indicated that a component of the second Cu2+ uptake phase involved binding at or penetration of the fungal membranes. The uptake of Sr2+ , Ni2+ and Zn2+ conferred some protection to samples subsequently exposed to 75 p.p.m. aqueous SO2 for 1 h, while Mg2+ , and Ca2+ had no effect. The combined effects of Cu2+ uptake and SOS exposure (and also Pb2+ and SO8 ) were approximately cumulative. Finally, the results are explained by reference to a classification that separates metal ions into three chemically and biologically significant categories. It is concluded that class A metal ions (those with a preference for ionic interactions) and borderline metal ions with class A character tend to protect lichens against SO2 damage, while borderline metal ions with class B character (a preference for covalent interactions) have the opposite effect.

Calculated sulfur dioxide equilibria at low concentrations between air and water

Low concentration equilibria of SO2 between air and water have been calculated for temperatures in the range 0 to 60°C and air concentrations of 2 ppb to 100 ppm incorporating the best currently available theory to define this process. The data showed negative, non-regular deviations of from less than 1 to about 12% lower than the limited experimental aqueous concentration data available at these levels. Log-log plots of these equilibrium data were linear over a four decade concentration span in air and provided a format which may be readily interpolated for data access. Linear plots of the fraction of the total aqueous SO2 present as unreacted SO2 presented here for the first time, show a more marked rise with concentration than was expected, which is used to qualitatively explain biological and corrosion activity of dilute solutions of SO2.

THE EFFECT OF TIME OF EXPOSURE TO SULPHUR DIOXIDE ON POTASSIUM LOSS FROM AND PHOTOSYNTHESIS IN THE LICHEN, CLADINA RANGIFERINA (L.) HARM.

SummarySamples of the lichen, Cladina rangiferina, were exposed to various concentrations of aqueous SO4 for 10 min, and 0.5, 1, 3, 6 and 12 h. K+‐efflux curves (K+ release versus ppm SO2(wt/wt, aqueous)) were constructed for each exposure period. In separate experiments, the photosynthetic 14C fixation rates were measured after the SO2 exposures. Plots of % total 14C fixation v. ppm SO2 (wt/wt, aqueous) were found to be linear for the 3 h and 6 h exposure periods, while plots of log (% total 14C fixation) v. ppm SO2 (wt/wt, aqueous) were linear for shorter exposures (10 min, 0.5 and 1 h). Threshold SO2 concentrations for each exposure time were evaluated by extrapolating the K+‐efflux curves, or their linear transformations, to zero K+ release. Similarly, the threshold SO2 concentrations that did not cause a reduction in 14C fixation (relative to control samples not exposed to SO2) were determined by extrapolation of the linear relationships mentioned. The threshold values obtained from the K+‐efflux data were in good agreement with those evaluated from fixation rates. Aqueous threshold SO2 concentrations were converted to gaseous threshold values by an experimentally verified relationship. The resulting gaseous SO2 threshold concentrations, (SO2)g** in units of ppm(v/v) in air, were related to the exposure time in hours, t, through the following rectangular hyperbolic function: (SO2)g**=1.5 t−0.62. Notwithstanding the uncertainties involved, extrapolation of this expression to exposure times considerably longer than the experimental range yielded threshold values for 6 months and 1 year in good agreement with mean SO2 levels known from mapping studies to affect detrimentally sensitive lichen species.

POTASSIUM EFFLUX BY LICHEN THALLI FOLLOWING EXPOSURE TO AQUEOUS SULPHUR DIOXIDE*

SummaryPotassium efflux is a useful experimental quantity for assessing damage to lichens exposed to SO2. This SO2‐induced K+ efflux is biphasic in response to increasing concentrations of aqueous SO2. The first phase can be extrapolated to identify the SO2 concentration at which no K+ release occurred above the control values. This threshold concentration was used to determine the relative sensitivities of various lichen species. Good agreement was observed between the total K+ lost and the reduction in the total photosynthetic 14C‐fixation rates. The magnitude of the SO2‐induced K+ efflux indicated that release occurred from intra‐cellular sources. The kinetics of the release process and the effects of SO2 on membrane integrity are discussed.

EFFECTS OF AQUEOUS SULPHUR DIOXIDE ON CHLOROPHYLL DESTRUCTION IN PINUS CONTORTA

SUMMARYThe effects of aqueous SO2 on chlorophyll breakdown in lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) were determined under laboratory conditions. Aqueous SO2 concentrations ranging from 100 to 500 ppm resulted in a sharp decrease in total chlorophyll content. Chlorophyll a was more sensitive to SO2 than chlorophyll b. Quantitative determinations of various pigments suggested that's SO2 causes the conversion of chlorophyll a into phaeophytin a (100–500 ppm SO2) and chlorophyll b into chlorophyllide b (10–50 ppm SO2). The suggested conversion of chlorophyll into chlorophyllide induced by SO2 was supported by increased activity of pine needle chlorophyllase at low aqueous SO2 concentrations (10–50 ppm). The breakdown of chlorophyll molecules by SO2 as measured by loss of Mg++ and total chlorophyll was accompanied by a decreased ability of pine needles to photosynthesize H14CO3. The effect of SO2 on pigment breakdown and rate of photosynthesis was due mostly to the specific direct actions of SO2 and was not a function of increased acidity.