Oxidation of dissolved sulfur dioxide

Finally, atmospheric chemical transformations are classified in terms of whether they occur as a gas (homogeneous), on a surface, or in a liquid droplet (heterogeneous). An example of the last is the oxidation of dissolved sulfur dioxide in a liquid droplet. Thus, chemical transformations can occur in the gas phase, forming secondary products such as NO2 and O3 in the liquid phase, such as SO2 oxidation in liquid droplets or water films and as gas-to-particle conversion, in which the oxidized product condenses to form an aerosol. 

Hoffmann, M. R., and D. J. Jacob, Kinetics and Mechanisms of Catalytic Oxidation of Dissolved Sulfur Dioxide in Aqueous Solution An Application to Nighttime Fog Water Chemistry, in SO2, NO, and N02 Oxidation Mechanisms Atmospheric Considerations, Acid Precipitation Series, Vol. 3, pp. 101-172 (J. I. Teasley, Series Ed.), Butterworth, Stoneham, MA, 1984. 

Figure 11.4 Voltammetric oxidation of dissolved sulfur dioxide at a gold electrode in 0.1 M H2S04 cyclic scans.

The alternative process, wet deposition, deposits the sulfur in rain or other forms of precipitation. Here it is largely as sulfate, which has been incorporated from aerosols or through oxidation of dissolved sulfur dioxide. Sulfate particles can also be dry deposited to the Earth s surface. 

Hoffmann, M. R., and Jacob, D. J. (1984) Kinetics and mechanisms of the catalytic oxidation of dissolved sulfur dioxide in aqueous solution an application to nighttime fog water chemistry, in 50, NO, and NO2 Oxidation Mechanisms Atmospheric Considerations, edited by J. G. Calvert. Butterworth, Stoneham, MA, pp. 63-100. 

Card, J. C., Foral, M. J., Langer, S. H. (1988). Electrogenerative oxidation of dissolved sulfur dioxide with packed-bed anodes. Envionmental Science Technology, 22, 1499—1505. http //dx.doi.org/10.1021/es00177a018. 

Sulfur oxides (SO,) are compounds of sulfur and oxygen molecules. Sulfur dioxide (SO2) is the predominant form found in the lower atmosphere. It is a colorless gas that can be detected by taste and smell in the range of 1, (X)0 to 3,000 uglm. At concentrations of 10,000 uglm , it has a pungent, unpleasant odor. Sulfur dioxide dissolves readily in water present in the atmosphere to form sulfurous acid (H SOj). About 30% of the sulfur dioxide in the atmosphere is converted to sulfate aerosol (acid aerosol), which is removed through wet or dry deposition processes. Sulfur trioxide (SO3), another oxide of sulfur, is either emitted directly into the atmosphere or produced from sulfur dioxide and is readily converted to sulfuric acid (H2SO4). 

The throw-away processes with aqueous slurries of lime or limestone as the scrubbing media are the most extensively installed processes. These processes create a waste sludge containing calcium sulfite, calcium sulfate, fly ash, unreacted alkali, and other minor dissolved species in the free water contained in the sludge. Since flue gas contains oxygen, some of the dissolved sulfur dioxide is oxidized, and calcium sulfate is formed. 

Twenty-five grains of potassium dichromate (or lTg of chromium (VI) oxide) are dissolved in 500ml of water. Sulfur dioxide is bubbled into the solution until reduction to the trivalent state is complete, as indicated by the pure green color of the liquid with no trace of yellow. The solution is then boiled to remove excess sulfur dioxide. 

Many of the ancient authors sing praises to the utility of vitriol. Basil Valentine called it The True Mineral Salt which contains the Red and the White spirits. If vitriol alone is distilled, there will first come over a clear liquid (the White spirit) with a strong sulfur dioxide odor. Keep this tightly sealed and the choking odor will disappear as the dissolved sulfur dioxide oxidizes to form a mild solution of sulfuric acid. As the heat is increased quite high, there will finally ascend a more viscous, reddish liquid which is a concentrated sulfuric acid filled with martial essence (the Red spirit). 

Card et al. [108] oxidized dissolved sulfur dioxide gas to sulfuric acid, at room temperature, using packed bed anodes. The corresponding cathodic reaction was oxygen reduction to water. A variety of electrodes and electrode systems were studied,... 

The dissolved sulfur dioxide will react in alkaline solution to form either lithium bisulfite LiHSOs or lithium sulfite Li2S03, both of which will be readily oxidized to sulfate. 

More than 80% of the sulfur dioxide was oxidized in the first reaction vessel. Reaction was rapid and the surface of the liquid was violently agitated. A consequence of this mixing was that as sulfuric acid was produced the gaseous nitrogen oxide catalyst dissolved to form more nitrous vitriol. 

Tin does not react directly with nitrogen, hydrogen, carbon dioxide, or gaseous ammonia. Sulfur dioxide, when moist, attacks tin. Chlorine, bromine, and iodine readily react with tin with fluorine, the action is slow at room temperature. The halogen acids attack tin, particularly when hot and concentrated. Hot sulfuric acid dissolves tin, especially in the presence of oxidizers. Although cold nitric acid attacks tin only slowly, hot concentrated nitric acid converts it to an insoluble hydrated stannic oxide. Sulfurous, chlorosulfuric, and pyrosulfiiric acids react rapidly with tin. Phosphoric acid dissolves tin less readily than the other mineral acids. Organic acids such as lactic, citric, tartaric, and oxaUc attack tin slowly in the presence of air or oxidizing substances. 

Titanium Sulfates. Solutions of titanous sulfate [10343-61-0] ate readily made by reduction of titanium(IV) sulfate ia sulfuric acid solutioa by electrolytic or chemical means, eg, by reduction with ziac, ziac amalgam, or chromium (IT) chloride. The reaction is the basis of the most used titrimetric procedure for the determination of titanium. Titanous sulfate solutions are violet and, unless protected, can slowly oxidize ia coatact with the atmosphere. If all the titanium has been reduced to the trivalent form and the solution is then evaporated, crystals of an acid sulfate 3 Ti2(S0 2 [10343-61-0] ate produced. This purple salt, stable ia air at aormal temperatures, dissolves ia water to give a stable violet solutioa. Whea heated ia air, it decomposes to Ti02, water, sulfuric acid, and sulfur dioxide. 

Vanadium(IV) Oxide. Vanadium(IV) oxide (vanadium dioxide, VO2) is a blue-black solid, having a distorted mtile (Ti02) stmcture. It can be prepared from the reaction of V20 at the melting point with sulfur or carbonaceous reductants such as sugar or oxaUc acid. The dioxide slowly oxidizes in air. Vanadium dioxide dissolves in acids to give the stable (VO) " ions and in hot alkaUes to yield vanadate(IV) species, eg, (HV20 ) . 

The sihca dux combines with iron(II) sulfide and iron(II) oxide to form slag. The duidity of the slag, in which unwanted impurities dissolve, is controlled by the addition of limestone. Reverberatory furnaces have been largely replaced by more advanced smelting furnaces, which require lower energy input, have higher capacity, and produce higher sulfur dioxide content off-gas. 

The confinement of the cracks to a specific area of the cooler suggests that condensate from atmospheric moisture initially formed in this area and dissolved a corrodent from the atmosphere such as ammonia, sulfur dioxide, or oxides of nitrogen. Since the previous cooler had been in service for 20 years, it is conjectured that the rapid failure of this exchanger was due principally to very high bending stresses, which may have been induced during construction of the cooler. 

Health effects attributed to sulfur oxides are likely due to exposure to sulfur dioxide, sulfate aerosols, and sulfur dioxide adsorbed onto particulate matter. Alone, sulfur dioxide will dissolve in the watery fluids of the upper respiratory system and be absorbed into the bloodstream. Sulfur dioxide reacts with other substances in the atmosphere to form sulfate aerosols. Since most sulfate aerosols are part of PMj 5, they may have an important role in the health impacts associated with fine particulates. However, sulfate aerosols can be transported long distances through the atmosphere before deposition actually occurs. Average sulfate aerosol concentrations are about 40% of average fine particulate levels in regions where fuels with high sulfur content are commonly used. Sulfur dioxide adsorbed on particles can be carried deep into the pulmonary system. Therefore, reducing concentrations of particulate matter may also reduce the health impacts of sulfur dioxide. Acid aerosols affect respiratory and sensory functions. 

The deleterious effect of sulfur dioxide and sulfites in domestic water is increased corrosivity owing to the lowered pH. However, oxidation of sulfite to sulfate in aqueous solutions uses dissolved oxygen, and lliis may retard corrosion. While llte oxichition of sulfite and sulfiirous acid to sulfate and sulfuric acid in the atmosphere is an environmental concern, this reaction is too... 

Rainwater is naturally slightly acidic due to the dissolved carbon dioxide. Acid rain results when acidic sulfur and nitrogen oxides produced during the combustion of coal and oil react with rainwater (see Box 10.1). 

Acid rain. Natural (unpolluted) precipitation is naturally acidic with a pH often in the range of 5 to 6 caused by carbonic acid from dissolved carbon dioxide and sulfurous and sulfuric acids from natural emissions of SO and H2S. Human activity can reduce the pH very significantly down to the range 2 to 4 in extreme cases, mainly caused by emissions of oxides of sulfur. Because atmospheric pollution and clouds travel over long distances, acid rain is not a local problem. The problem may manifest itself a long way from the source. Problems associated with acid rain include ... 

The purify of the water changes constantly during the water cycle. As rain falls through the air, for example, the water dissolves some atmospheric gases such as oxygen, carbon dioxide, and in industrial regions also such air pollutants as sulfur dioxide and oxides of nitrogen. Still more carbon dioxide... 

Sulfur Dioxide. Sulfur dioxide and nitrogen oxides, which are produced in modern society when coal, gas, and oil are burned in cars, power plants, and factories, react with water vapor in the air to form acids that negatively affect organic materials and even metals and stone when dissolved in airborne rainwater, the oxides of sulfur and nitrogen are the main cause of the formation of acid rain (see below). 

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