The general knowledge of silver

image_pdfimage_print

Silver, a kind of beautiful white metal, has the best electrical conductivity, thermal conductivity and reflectivity to visible light among all the metals. It also has good ductility and plasticity. It is easily to be polished and modeled and it also can form alloys or pseudo – alloy with many metals. Silver also has strong corrosion resistance and the ability of resistant to organic acid and alkali. It will not be easily oxidized in normal temperature and humidity. The chemical property of silver is most active among the precious metals and the silver compound which is of the most industrial value is silver nitrate and silver halides.

Silver is widely distributed in nature. There is a little silver in elementary substance state and it is mostly associated with other non-ferrous metal ores in the state of sulfides. Currently the known silver mineral and minerals containing silver are more than 200 species, but the minerals which are of important economic value and serve as the main raw materials for the silver production are 12 species: native silver (Ag), electrum (AgAu), argentite (Ag2S), pyrargyrite (Ag3SbS3), chlorargyrite AgCe), stephanite (Ag2SbS3), dyscrasite (Ag3Sb), naumannite (Ag3Se), hessite (Ag2Te), polyargyrite (5Ag2Sb2S3) and polybasite (8 (AgCu) SSb2S3). Silver mostly forms a symbiotic relationship with heavy metals sulphide mine such as copper, lead, zinc and so on.

The extraction method of silver is to enrich it into the heavy metals sulphide concentrate through ore dressing and extract it in the process of smelting these heavy metals. The silver which is symbiotic with gold can be recycled in the gold cyanidation process. The coarse particles of silver and silver-gold ore are disposed by amalgamation or gravity-amalgamation process. Argentite and   chlorargyrite can be enriched in the method of gravity separation and they can also be directly cyanide. As the mineral content of silver is higher than gold and as silver and silver sulphide are more difficult to cyanide than gold, it should use high concentrations of cyanide solution to extract silver in common and to extend the leaching time, improve the stirring intensity and increase the aeration. As silver chloride is easier to cyanide than silver sulfide, the silver sulfide ore often goes through chloridizing roasting before cyaniding. To extract silver from pyrolusite, we should restore and roast the pyrolusite to reduce high-manganese oxide into manganese oxide before cyaniding so as to reduce the consumption of cyanide agents. The extraction of silver from anode slime is an important means of modern production of silver.

For a long time, a lot of high purity silver is used to make coins and decorations. With the development of science and technology, silver has been gradually transferred to the industrial applications from the traditional consumer of currency and jewelry crafts. At present, silver has been widely used in the industries of electronics, computers, telecommunications, military, aerospace, televisions, photographic and so on.

Due to the special light sensitive characteristics of silver halide salts (silver bromide, silver chloride and silver iodide) and silver nitrate in the industries of television and photography, they can be used as the black-white and color film, negative, picture development and photographic paper for making movies, TV and photography, the photographic film for graphic arts, x light film for medical and industrial inspection and various special photosensitive material used in the aerial mapping, astronomical universe exploration and defense science research, etc.

In electromechanical and electrical industry, silver is mainly used as the electric contact material, resistance material, soldering material, thermometrical material and thick film ink in the form of pure metal and silver alloy. For example, the electrical contact made by the alloys of silver copper, silver cadmium and silver nickel can eliminate the consumption deformation, contact resistance and splice of general metals and other problems. The low voltage power switch, crane switch, the relay and electric contact material of heavy load made by the alloys of silver tungsten, silver molybdenum and silver iron can be widely used in the advanced industrial of traffic metallurgical automation and aviation space. In the process of achieving breakover by contacting with the semiconductors, silver powder which is used as the padding of electrocondution slurry plays a role that other metals cannot achieve, except for its special properties. In addition, the alloys of silver gold, silver argental mercury and silver tin are the important dental materials for the health care industry.