Sulfur precipitation

At the anode, a chemical oxidation reaction is bound to take place. In normal fixers, sulfite (SOj ) is oxidized and acid (H ) is released as a consequence of this oxidation. Due to the decrease of the sulfite concentration and the decrease in the pH, the fixing solution becomes unstable and sulfur precipitation starts to occur when the pH of the fixer decreases below 4.0. In the case of hardening fixers, there is also an upper limit to the pH, since aluminum-hydroxides starts to precipitate when the pH exceeds 5.0. 

The decomposition of dithionite in aqueous solution is accelerated by thiosulfate, polysulfide, and acids. The addition of mineral acid to a dithionite solution produces first a red color which turns yellow on standing subsequentiy, sulfur precipitates and evolution of sulfur dioxide takes place (346). Sodium dithionite is stabilized by sodium polyphosphate, sodium carbonate, and sodium salts of organic acids (347). 

The reaction involves two electrons per thionyl chloride [7719-09-7] molecule (40). Also, one of the products, SO2, is a Hquid under the internal pressure of the cell, facihtating a more complete use of the reactant. Finally, no cosolvent is required for the solution, because thionyl chloride is a Hquid having only a modest vapor pressure at room temperature. The electrolyte salt most commonly used is lithium aluminum chloride [14024-11-4] LiAlCl. Initially, the sulfur product is also soluble in the electrolyte, but as the composition changes to a higher SO2 concentration and sulfur [7704-34-9] huA.ds up, a saturation point is reached and the sulfur precipitates. 

The iron, now in a reduced ferrous form, is not consumed instead, it is continuously regenerated by bubbling air through the solution. The sulfur precipitates out of the solution and is removed from the reactor with a portion of the reagent. The sulfur slurry is pumped to a melter requiring a small amount of heat and then to a sulfur separator where the reagent in the vapor phase is recovered, condensed, and recycled back to the reactor. 

Schwefel-natrium, -natron, n. sodium sulfide, -nickel, m. nickel sulfide, -niederschlag, m. precipitate of sulfur, precipitated sulfur, -ofen, m. sulfur burner, -oxyd, n. (any) sulfur oxide, -phosphor, m. (any) phosphorus sulfide, -probe, /. sulfur sample mercury sulfide, -quelle, /. sulfur spring, -rducherung, /. sulfur fumigation, -rubin, m. ruby sulfur, realgar, -salz, n. sulfur salt, thio salt, sulfo salt sulfate. 

A thin layer of a mix of natural rubber, sulfur, precipitated silica, water, and some additives, such as carbon black and vulcanizing agents, is extruded on a paper support belt, calendered, and vulcanized as a roll in an autoclave under elevated pressure and temperature ( 180 °C). A modi-... 

Elemental sulfur precipitates and is recovered. Copper powder is produced by electrolyzing the resulting solution. Developed by G. E. Atwood and C. H. Curtis of Duval Corporation at Tucson, AZ. See also Cymet. 

Lacy-Keller A process for removing hydrogen sulfide and mercaptans from natural gas by absorption in a proprietary solution. Elemental sulfur precipitates as a colloid and is separated from the solution by means of an electrolytic flotation cell. The process does not remove carbon dioxide. 

The colloid is prepared by rapidly mixing dilute solutions of sodium thiosulfate and hydrochloric acid so that the final concentration of each is about 0.002 M. The following reaction then occurs so slowly that the sulfur precipitates only on those particles that nucleate first ... 

A combination of the various processes (formation of polysulfides and elemental sulfur, precipitation of FeS, and adsorption of Fe2+) leads to the... 

If the crude product is held at 50-55° for 6-8 hours, approximately 70% of the theoretical amount of free sulfur precipitates and may be separated by decantation and filtration. The remaining 30% of the theoretical quantity of sulfur remains in solution in the diethylthiocarbamyl chloride. 

The cell potential for such a process is shown in Fig. 15.28 (Dandapani, 1987). In fact, at about 80 °C and pH 14, polysulfides are first produced, but pure sulfur precipitates on cooling. The process has been developed to an engineering stage (Petrov and Srinivasan, 1996). It is necessary to protect the cathode against catalytic inactivation by polysulfide (i.e., a membrane must be used). For continuous use, the pH must be controlled. The cooling and production of S may be best carried out outside the cell. 

This method of preparing sodium polysulfides can be used to purify sulfur to high degree. When hydrochloric acid is added to the mixture, pure sulfur precipitates. 

If the immersion medium is strongly alkaline, the anions will remain in solution, but if it is weakly alkaline or neutral, dissociation of a polysulfide will occur as it departs the concrete, and sulfur will precipitate either on the concrete surface or in the surrounding liquid. In either case the concrete should be leached of sulfur, but the process is much slower with neutral media, possibly because diffusion of leachate and polysulfide is slowed as sulfur precipitates near the surface. 

Summary Sulfur nitride is conveniently prepared by passing dry anhydrous ammonia gas into a benzene or toluene solution of sulfur chloride. During the reaction, ammonium chloride and sulfur precipitates, and towards the end of the reaction, red fumes will develop. When red fumes evolve, the reaction is complete. Thereafter, the reaction mixture is filtered, and then evaporated to yield dry crystals. These crystals are then recrystallized from toluene to yield high purity sulfur nitride. 

The degree to which a pollutant is taken up, which also determines its potential toxicity, is determined by its bioavailability. Bioavailability refers to the ability of a chemical to move from the environment into a living organism. Bioavailability depends upon the ionization state and speciation of a chemical. Because certain organic compounds and clays can strongly bind various hydrocarbon chemicals and metals, the amount of organic carbon and clay in the soil, sediment, and water determines the bioavailability of these compounds. Bioavailability of metals is also dependent on the amount of sulfur precipitates of other metals in soils and sediments. 

In the bottom of wells where pressure and temperature are high, sulfur is soluble in the gas, but at the top, where pressure and temperature decrease, the sulfur precipitates in the piping, thus plugging the flow of gas. Catalyzed DMDS, known as SulfaHitec , a product made by Arkema, can be injected batchwise to unplug sour gas wells and to keep pipes and formations free of precipitated sulfur. 

Effect of 02 in the feed Formation of degradation products None Sulfur precipitation at low temperature... 

When thiosulfate is treated with dilute acid, the reaction is reversed. The sulfite ion is reformed and elemental sulfur precipitates ... 

If this sequence is started with elemental sulfur enriched with the radioactive sulfur-35 isotope, the isotope acts as a label for S atoms. All the labels are found in the sulfur precipitate in Equation (23.2) none of them appears in the final sulfite ions. Clearly, then, the two atoms of sulfur in 8203 are not structurally equivalent, as would be the case if the structure were... 

Otherwise, the radioactive isotope would be present in both the elemental sulfur precipitate and the sulfite ion. Based on spectroscopic studies, we now know that the structure of the thiosulfate ion is... 

As the bisulfite concentration approaches zero, the polythionate concentration levels off and sulfur precipitation begins. Then as the polythionate reacts with hydrogen sulfide, its concentration begins to decrease while the thiosulfate and sulfur concentrations continue to increase. Under the mild conditions used, there was no apparent reaction of thiosulfate or of the trithionate portion of the polythionates to form sulfur. 

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