For coinage, most frequently alloyed with copper or gold; for manufacture of tableware, mirrors, jewelry, ornaments; for electroplating; for making vessels and apparatus used in manufacture of medicinal chemicals, in processing foods and beverages, in handling organic acids; as catalyst in hydrogenation and oxidation processes; as ingredient of dental alloys. Has been used for purification of drinking water because of toxicity to bacteria and lower forms of life. Some salts used in photography.
Dust is flammable.
Silver and its alloys and compounds have numerous applications. As a precious metal, silver is used in jewelry. Also, one of its alloys, sterling silver, containing 92.5 weight % silver and 7.5 weight % copper, is a jewelry item and is used in tableware and decorative pieces. The metal and its copper alloys are used in coins. Silver-copper brazing alloys and solders have many applications. They are used in automotive radiators, heat exchangers, electrical contacts, steam tubes, coins, and musical instruments.
Some other uses of silver metal include its applications as electrodes, catalysts, mirrors, and dental amalgam. Silver is used as a catalyst in oxidation-reductions involving conversions of alcohol to aldehydes, ethylene to ethylene oxide, and ethylene glycol to glyoxal.
Silver is one of the oldest metals, known since ancient times. It is a precious metal worldwide, used in ornaments, coins, and utensils. The symbol Ag for this element is derived from the Latin word, argentum. Silver occurs in nature in native form, commonly associated with gold. It is found in most lead and copper ores. The principal mineral of silver is argentite, Ag2S [1332-04-3]. Some other silver minerals include pyrargyrite, Ag3SbS3 [15123-77-0]; proustite, Ag3AsS3 [15152-58-4]; polybasite, Ag16Sb2S11 [53810-31-4]; cerargyrite, AgCl [14358-96-4]; stephanite, Ag5SbS4 [1302-12-1]; and tetrahedrite, Cu3(AsSb)S3. Abundance of silver in the earth’s crust is estimated to be 0.075 mg/kg and its average concentration in sea water is 0.014 µg/L.
For purification by electrolysis, see Craig et al. [J Res Nat Bur Stand 64A 381 1960]. For purification of crude, or silver residues to pure silver see Glemser & Sauer in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 1028-1030 1963, and for the preparation of colloidal silver see ibid (Ed. Brauer) p 1034.
Silver reacts violently with chlorine trifluoride (in the presence of carbon) [Mellor 2 Supp. 1 1956]. Bromoazide explodes on contact with Silver foil. Acetylene forms an insoluble acetylide with Silver [Von Schwartz 1918 p. 142 ]. When Silver is treated with nitric acid in the presence of ethyl alcohol, Silver fulminate, which can detonated may be formed. Ethyleneimine forms explosive compounds with Silver, hence Silver solder should not be used to fabricate equipment for handling ethyleneimine. Finely divided Silver and strong solutions of hydrogen peroxide may explode [Mellor 1:936 1946-47)]. Incompatible with oxalic acid and tartaric acid [Nav Aer. 09-01-505 1956]. Silver can form explosive salts with azidrine. ("Ethyleneimine" Brocure 125-521-65, Midland (Mich.), Dow Chemical Co., 1965). Ammonia forms explosive compounds with gold, mercury, or Silver. (Eggeman, Tim. "Ammonia" Kirk-Othmer Encyclopedia of Chemical Technology. John Wiley & Sons, Inc. 2001.). Acetylene and ammonia can form explosive Silver salts in contact with Ag. (Renner, Hermann, Gunther Schlamp. “Silver, Silver Compounds, and Silver Alloys." Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag GmbH & Co. KGaA. 2001.)
lustrous soft white metal;silvery metallic solid; insoluble in water.
Many processes are known for recovery of silver from its ores. These depend mostly on the nature of the mineral, its silver content, and recovery of other metals present in the ore. A few processes are briefly outlined below.
Silver is usually extracted from high-grade ores by three common processes that have been known for many years. These are amalgamation, leaching, and cyanidation. In one amalgamation process, ore is crushed and mixed with sodium chloride, copper sulfate, sulfuric acid, and mercury, and roasted in cast iron pots. The amalgam is separated and washed. Silver is separated from its amalgam by distillation of mercury.
In the cyanidation process the ore is crushed and roasted with sodium chloride and then treated with a solution of sodium cyanide. Silver forms a stable silver cyanide complex, [Ag(CN)2]–. Adding metallic zinc to this complex solution precipitates silver. Several leaching processes are known. One such process, known as the Patera process, developed in the mid 19th century, involves roasting ore with sodium chloride followed by leaching with sodium thiosulfate solution. Silver 834 SILVERis precipitated as silver sulfide, Ag2S, by adding sodium sulfide to the leachate. In the Clandot process, leaching is done with ferric chloride solution. Addition of zinc iodide precipitates silver iodide, AgI. AgI is reduced with zinc to obtain silver.
The above processes are applied for extraction of silver from high-grade ores. However, with depletion of these ores, many processes were developed subsequently to extract silver from low-grade ores, especially lead, copper, and zinc ores that contain very small quantities of silver.
Low grade ores are concentrated by floatation. The concentrates are fed into smelters (copper, lead, and zinc smelters). The concentrates are subjected to various treatments before and after smelting including sintering, calcination, and leaching. Copper concentrates are calcined for removal of sulfur and smelted in a reverberatory furnace to convert into blister copper containing 99 wt% Cu. The blister copper is fire-refined and cast into anodes. The anodes are electrolytically refined in the presence of cathodes containing 99.9% copper. Insoluble anode sludges from electrolytic refining contain silver, gold, and platinum metals. Silver is recovered from the mud by treatment with sulfuric acid. Base metals dissolve in sulfuric acid leaving silver mixed with any gold present in the mud. Silver is separated from gold by electrolysis.
Lead and zinc concentrates can be treated in more or less the same manner as copper concentrates. Sintering lead concentrates removes sulfur and following that smelting with coke and flux in a blast furnace forms impure lead bullion. The lead bullion is drossed with air and sulfur and softened with molten bullion in the presence of air to remove most impurities other than silver and gold. Copper is recovered from the dross and zinc converts to its oxide and is recovered from blast furnace slag. The softened lead obtained above also contains some silver. The silver is recovered by the Parkes Process. The Parkes process involves adding zinc to molten lead to dissolve silver at temperatures above the melting point of zinc. On cooling, zinc-silver alloy solidifies, separating from the lead and rising to the top. The alloy is lifted off and zinc is separated from silver by distillation leaving behind metallic silver.
The unsoftened lead obtained after the softening operation contains silver in small but significant quantities. Such unsoftened lead is cast into anode and subjected to electrolytic refining. The anode mud that is formed adhering to these anodes is removed by scraping. It contains bismuth, silver, gold, and other impurity metals. Silver is obtained from this anode mud by methods similar to the extraction of anode mud from the copper refining process discussed earlier.
If the low–grade ore is a zinc mineral, then zinc concentrate obtained from the flotation process is calcined and leached with water to remove zinc. Silver and lead are left in leach residues. Residues are treated like lead concentrates and fed into lead smelters. Silver is recovered from this lead concentrate by various processes described above.