Sulfur dioxide, sulfided iron oxide

Oxidation. The furnace is allowed to cool to ca. 500 °C when air is admitted in controlled amounts. The oxygen reacts with excess sulfur to form sulfur dioxide, which exothermically oxidizes the di- and triatomic polysulfide ions to S and S, free radicals, leaving sodium sulfoxides and sulfur as byproducts. When oxidation is complete, the furnace cools and is unloaded - a full kiln cycle can take several weeks. The raw ultramarine product typically contains 75 wt % blue ultramarine, 23wt% sodium sulfoxides, and 2wt% free (uncombined) sulfur with some iron sulfide. 

Figure 6. Effect of temperature on the weight loss of sulfided iron oxide sorbents in sulfur dioxide atmosphere.

Sulfur dioxide is also produced by roasting sulfidic ores. Pyrites is, for example, converted into sulfur dioxide and iron(III) oxide (calcine) according to the following equation ... 

Hydrogen sulfide Iron oxide Sulfur dioxide Potassium carbonate... 

A fascinating little company in Canada was producing pyrites to recover sulfur from coal gas. In 1882, the Vesey Chemical Company of Montreal commenced burning spent oxide from the city s gasworks into sulfur dioxide. The spent oxide was iron ore that had been used to remove hydrogen sulfide from coal gas. The plant was purchased by Nichols Chemical in 1902 and shut down. 

A sulfide of iron, containing 36.5% S by mass, is heated in 02(g), and the products are sulfur dioxide and an oxide of iron containing 27.6% O, by mass. Write a balanced chemical equation for this reaction. 

Hydrochloric acid reacts with sulfur only in the presence of iron to form hydrogen sulfide. Sulfur dioxide forms when sulfur is heated with concentrated sulfuric acid at 200°C. Dilute nitric acid up to 40% concentration has Htde effect, but sulfur is oxidized by concentrated nitric acid in the presence of bromine with a strongly exothermic reaction (19). 

Zinc does not react with nitrogen, even at elevated temperatures but zinc nitride, Zn N2, forms with ammonia at red heat. Zinc sulfide, the most common form of zinc in nature, is not reduced direcdy in commercial practice because of reactions of the zinc vapor during condensation. Rather, the sulfide is burned (roasted) to the oxide plus sulfur dioxide before reduction. However, zinc can be reduced to the metal at ca 1300°C with carbon or iron. 

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. 

Sulfur is widely distributed as sulfide ores, which include galena, PbS cinnabar, HgS iron pyrite, FeS, and sphalerite, ZnS (Fig. 15.11). Because these ores are so common, sulfur is a by-product of the extraction of a number of metals, especially copper. Sulfur is also found as deposits of the native element (called brimstone), which are formed by bacterial action on H,S. The low melting point of sulfur (115°C) is utilized in the Frasch process, in which superheated water is used to melt solid sulfur underground and compressed air pushes the resulting slurry to the surface. Sulfur is also commonly found in petroleum, and extracting it chemically has been made inexpensive and safe by the use of heterogeneous catalysts, particularly zeolites (see Section 13.14). One method used to remove sulfur in the form of H2S from petroleum and natural gas is the Claus process, in which some of the H2S is first oxidized to sulfur dioxide ... 

Roasting pyrite, an iron ore composed of iron sulfide, results in the oxidation and decomposition of this compound to volatile sulfur dioxide and the formation of iron oxide, which can be smelted with relative ease into iron ... 

Claus A process for removing hydrogen sulfide from gas streams by the catalyzed reaction with sulfur dioxide, producing elementary sulfur. The process has two stages in the first, one third of the hydrogen sulfide is oxidized with air to produce sulfur dioxide in the second, this sulfur dioxide stream is blended with the remainder of the hydrogen sulfide stream and passed over an iron oxide catalyst at approximately 300°C. The resulting sulfur vapor is condensed to liquid sulfur. 

Iron Sponge Also called Dry box. An obsolete process for removing hydrogen sulfide from gas streams by reaction with iron oxide monohydrate. The ferric sulfide that is formed is periodically re-oxidized to regenerate ferric oxide and elemental sulfur. When this process becomes inefficient because of pore-blockage, the sulfur is either oxidized to sulfur dioxide for conversion to sulfuric acid, or is extracted with carbon disulfide. 

A picture of the last step, the casting, can be seen in Figure 5.1. The processing steps are done under strictly controlled temperatures (up to roughly 1220 °C). During these, several chemical reactions take place and these enable the separation of copper from other materials. A typical reaction during the conversion is to remove the ferrous sulfides (FeS) by oxidization to iron oxides (FeO), which react with silica and can be thereafter removed as slag that is collected on the top of a ladle. As a side product, sulfur dioxide is formed and it is quite common to reuse it in a combined sulfuric acid plant. These two reactions are shown in (A) and (B) ... 

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