Silver manufacturing

An additional resource is industrially used silver that is recycled. Most important are scrapped photographic film and paper as well as used photographic baths. Reclamation of scrap from the electronics industry and catalysts from chemical industry contribute to modern silver manufacturing and dental scrap, silver amalgam, is also important. 

Silver Manufacture - Metallurgical and Chemical l35 Table 6.1 World mine production of silver by country in 2000... 

CH rCHCH NHCSNH. Colourless crystalline solid with a faint garlic-like odour m.p. 74 C. Manufactured by treating propenyl isothiocyanate with a solution of ammonia in alcohol. It has been given by injection in the treatment of conditions associated with the formation of excessive fibrous tissue. Toxic side reactions may occur. Propenyl thiourea is a chemical sensitizer for photographic silver halide emulsions. 

Na COj and Na2S with SO2 or from Na2S03 plus sulphur. Forms many hydrates. Used-in photography ( hypo ) because it dissolves silver halides. Also used in tanning, preparation of mordants, as a fermentation preventative in dyeing and in chemical manufacture. 

Bromine is used in the manufacture of many important organic compounds including 1,2-dibromoethane (ethylene dibromide), added to petrol to prevent lead deposition which occurs by decomposition of the anti-knock —lead tetraethyl bromomethane (methyl bromide), a fumigating agent, and several compounds used to reduce flammability of polyester plastics and epoxide resins. Silver(I) bromide is used extensively in the photographic industry... 

Obtainable from Parr Instrument Co., Moline, Illinois, U.S.A. An equivalent apparatus is manufactured by American Instrument Co., Silver Springs, Maryland, U.S.A-, and by C. W. Cook and Sons Ltd., 97, Walsall Road, Birmingham, 22B, England. 

Most of the world s commercial formaldehyde is manufactured from methanol and air either by a process using a silver catalyst or one using a metal oxide catalyst. Reactor feed to the former is on the methanol-rich side of a flammable mixture and virtually complete reaction of oxygen is obtained conversely, feed to the metal oxide catalyst is lean in methanol and almost complete conversion of methanol is achieved. 

Aqueous formaldehyde is corrosive to carbon steel, but formaldehyde in the vapor phase is not. AH parts of the manufacturing equipment exposed to hot formaldehyde solutions must be a corrosion-resistant alloy such as type-316 stainless steel. Theoretically, the reactor and upstream equipment can be carbon steel, but in practice alloys are required in this part of the plant to protect the sensitive silver catalyst from metal contamination. 

Salts. Rochelle salt is used in the silvering of mirrors. Its properties of piezoelectricity make it valuable in electric oscillators. Medicinally, it is an ingredient of mild saline cathartic preparations, eg, compound effervescing powder. In food, it can be used as an emulsifying agent in the manufacture of process cheese. 

The manufacture of silver nitrate for the preparation of photographic emulsions requires silver of very high purity. At the Eastman Kodak Company, the principal U.S. producer of silver nitrate, 99.95% pure silver bars are dissolved in 67% nitric acid in three tanks coimected in parallel. Excess nitric acid is removed from the resulting solution, which contains 60—65% silver nitrate, and the solution is filtered. This solution is evaporated until its silver nitrate concentration is 84%. It is then cooled to prepare the first crop of crystals. The mother Hquor is purified by the addition of silver oxide and returned to the initial stages of the process. The cmde silver nitrate is centrifuged and recrystallized from hot, demineralized water. Equipment used in this process is made of ANSI 310 stainless steel (16). 

Typical equipment made from tantalum includes heat exchangers, reaction vessels liners, thermowells, and heating elements or heat shields for high temperature vacuum sintering furnaces. Tantalum fabricated parts are found in the manufacturing of pharmaceuticals, explosives, insecticides, dyes, acidic baskets for silver cyanide barrel platers, and in hydrochloric and hydrobromic acid condensers. 

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