Ammonia solutions sulfur dioxide removal with

Ammonium bisulfite can be used in place of the sulfur dioxide. The solution is treated with activated carbon and filtered to remove traces of sulfur. Excess ammonia is added and the solution evaporated if the anhydrous crystalline form is desired. The crystals ate dried at low temperature in the presence of ammonia to prevent decomposition (61—63). 

There has also been concern over the potential air pollution problem that can be caused by the ammonia present in the off-gas. However, it has been reported (12) that the ammonia concentration in the off-gas from a stripping tower seldom exceeds 10 mg/m even before its dispersion in the surrounding air. The threshold for odor is about 35 mg/m therefore, there is little likelihood for the ammonia-stripping operation to cause an odor problem. However, small concentrations of ammonia in air may react with sulfur dioxide to form aerosols or fog. Under such a situation, ammonia can be removed from the offgas by a scrubber of by bubbling it through a dilute sulfuric acid solution. 

I. From molybdenite, the extraction may be made in several ways, (a) The mineral is roasted as long as sulfur dioxide is given off. The residue which contains MoOs is leached with dilute ammonia and the solution evaporated until the ammonium molybdate crystallizes. Japanese patent 37420 (1920) extracts the roasted ore with Na2COj solution, then precipitates calcium molybdate by adding CaCb. (6) The finely ground ore is heated with nitric acid and the MoOj dissolved in ammonia, (c) A current of chlorine is passed over the dry pulverized ore at a temperature of 208°. The molybdenum chloride distills over and may be separated from sulfur and other chlorides by fractional condensation.2 (d) A British patent describes the extraction with an alkaline sulfide or polysulfide solution which removes the molybdenum from the ore as the soluble thio-molybdates. These may be converted to the molybdates by acidification or by contact with more ore. 

Some of the advanced techniques used in postcombustion cleaning—such as the use of granular calcium oxide or sodium sulfite solutions—have already been described above. In the SNOX process, cooled flue gases are mixed with ammonia gas to remove the nitric oxide by catalytically reducing it to molecular nitrogen. The resulting gas is reheated and sulfur dioxide is oxidized catalytically to sulfur trioxide, which is subsequently hydrated by water to sulfuric acid, condensed, and removed. 

The amount of an evolved gas can be determined by a continuous titration method. A carrier gas removes the evolved gas from the furnace chamber and transports it to an aqueous-absorbing solution where it is continuously titrated. The titrant used will depend on the type of evolved gas to be determined. For example, ammonia is titrated with dilute hydrochloric acid, whereas water is determined by the Karl Fischer method. Compounds that can be determined include water, hydrogen chloride, ammonia, sulfur dioxide, carbon dioxide, and chlorine (80). 

Recovery systems in which sulfur dioxide or elemental sulfur is removed from the spent sorbing material, which is recycled, are much more desirable from an environmental and sustainability viewpoint than are throwaway systems. Many kinds of recovery processes have been investigated, including those that involve scrubbing with magnesium oxide slurry, sodium sulfite solution, ammonia solution, or sodium citrate solution. One type of recovery system uses a solution of sodium sulfite to react with sulfur dioxide in the flue gas... 

Derivation (pure oxide) Powdered uranium ore is digested with hot nitric-sulfuric acid mixture and filtered to remove the insoluble portion. Sulfate is precipitated from the solution with barium carbonate, and uranyl nitrate is extracted with ether. After re-extraction into water, it is heated to drive off nitric acid, leaving uranium trioxide. The latter is reduced with hydrogen to the dioxide. Can be prepared from uranium hexafluoride by treating with ammonia and subsequent heating of the ammonium diuranate. It is also recovered from phosphoric acid. 

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