Silver bullion

Silver chloride is a common source and intermediate product in many extractive metallurgical processes, for example it occurs in the anode slimes from copper refineries, the residues of leaching processes for base metals, as a product of the chlorination of impure gold—silver bullion, and in photographic waste. A novel process for the leaching and purification of silver chloride, which was devised by Parker et a/.,26 is based on the observation that silver chloride is very soluble in some dipolar aprotic solvents containing chloride ion but is much less soluble when water is present. The very different behaviour of the equilibrium... 

Most modem silver mined has been used to make photographic film emulsions, in plating, and in alloys for tableware, jewelry, and electrical equipment. Sterling silver is an expression of purity, being at least 92.5% silver. This is expressed either with the word sterling, 0.925 (the is often omitted), or the Lion Passant hallmark. Fine silver is 99.9% pure, but is too soft for most applications. This is the standard purity for silver bullion, as a commodity. 

The ore is crushed and ground in.ball mills to pass through a 30-mesh sieve. It is mixed with suitable fluxes (limestone and quartz) and smelted in small blast-furnaces having a capacity of 25 to 30 tons per twenty-four hours. The products obtained are (i) flue dust, which is returned to the furnaces, and crude arsenious oxide, which is resublimed and sold (ii) a silicate slag, which is thrown away unless it contains more than 10 ounces of silver per ton (iii) crude silver bullion, which is mechanically detached and cupelled to a fineness of 994 before it is sold to silver refiners and (iv) a speiss of cobalt, nickel, iron, and copper arsenides, containing considerable amounts of silver. The crude silver bullion contains about three-fourths of the silver present in the ore. 

Ordinary silver bullion processed in air may contain ca 200 ppm oxygen. Commercial silver bullion prepared under nitrogen may contain as Htde as 25 ppm oxygen. During casting some oxygen may be introduced to convert base metal impurities into oxides. Because these oxides do not enter into the soHd solution, they have no effect on the annealing and recrystaUization temperature of the silver critical to the silversmith. 

Commodity exchanges require good delivery silver bullion to be 999 parts per 1000 fine silver. Samples of specifications for silver are given in Table 6. 

Specifications for silver bullion, brazing alloys, electrical contact alloys, etc, are published by ASTM, the American Welding Society, Japanese Industrial Standards, SAE (Aerospace Materials Specifications), and the U.S. Department of Defense. ... 

The cost of various silver compounds is a function of the silver market price. In 1980, the estimated usage of silver in the United States was 3730 metric tons (120 X 10 troy oz) (23). This silver is derived from silver mined within the United States silver recycled or reclaimed from secondary sources, eg, coinage, flatware, jewelry, and photographic materials and imported silver. In 1980, Canada, Mexico, and Pern, the principal exporters of silver to the United States, shipped 1670 tons (53.8 x 10 troy oz) as silver bullion and silver compounds. U.S. imported 2799 t and exported 9641 in 1988 (23). 

Metallurgical process plant dryers, smelters, roasters, and refining on nonferrous plants (e.g., copper, lead, nickel, and zinc) gold and silver bullion refining operations. 

Economists distinguish among currency (or hand-to-hand circulating media, which includes coins and bank notes), money equivalents (such as demand bank deposits and treasury notes), and commodities used as money (such as gold or silver bullion or consumables such as tobacco). In modern industrial societies, coins and paper money form only a small part of a nation s total money supply, money equivalents accounting for the larger portion of it. 

The separation of silver by the Pattinson process used fractional crystallisation, in which molten lead was cooled and partly solidified in a pan while being briskly stirred. The solid lead crystals were relatively pure, leaving silver in the remaining liquid. A row of about nine pans were used, each heated by a fire from below. Crude bullion from the smelter was fed to the middle pan, from which solid crystals were transferred to the first pan on one side and the remaining liquid to the first pan on the other side. This process was repeated from one pan to the next up and down the line to give a purified lead with low silver content at one end and a residual liquid of around 9 kg of silver per tonne at the other end. The silver rich lead was subjected to cupellation to recover a silver bullion. Today, precious metals are separated from lead bullion using the Parkes Process, following the removal of copper, arsenic and antimony. In this process, zinc is added and the lead bulUon is cooled to precipitate a zinc-silver alloy, which is removed and separately treated. 

Betts Electrolytic Process. The Betts process starts with lead bullion, which may carry tin, silver, gold, bismuth, copper, antimony, arsenic, selenium, teUurium, and other impurities, but should contain at least 90% lead (6,7). If more than 0.01% tin is present, it is usually removed from the bullion first by means of a tin-drossing operation (see Tin AND TIN ALLOYS, detinning). The lead bullion is cast as plates or anodes, and numerous anodes are set in parallel in each electrolytic ceU. Between the anodes, thin sheets of pure lead are hung from conductor bars to form the cathodes. Several ceUs are connected in series. 

The flake cyanide is dissolved and added to suspensions of finely ground ore under agitation and ia the presence of air. The dissolved gold and silver are precipitated by the addition of 2iac dust and the cmde precipitate is refined to produce bullion. 

Bulk solids, dispersion in a liquid, 24 157 Bulk superconducting joints, 23 844 Bulk superconductors, 23 870 Bulk viscosity, 22 717-718 Bulk weigher, 26 247 Bulky rayon, 22 261-262 Bullion, silver, 22 643, 644-645, 647, 649-650... 

London Bullion Market Association, silver specifications by, 22 649 London coherence length, 23 806 London equations, 23 806 London-Norris equations, 23 845 London penetration depth, 23 805, 806 London s forces, 12 4 15 213 21 602-604 ... 

In his High Price of Bullion, Ricardo wrote, Gold and silver, like other commodities, have an intrinsic value, which is not arbitrary, but is dependent on their scarcity, the quantity of labor bestowed in procuring them, and the value of the capital employed in the mines which produce them (cited in Marcuzzo and Rosselli 42). This is somewhat different from the... 

All the ores are concentrated in complex mills by selective froth flotation lu produce individual copper, zinc, lead, and, infrequently, silver concentrates. The copper and lead concentrates are smelted to produce lead and copper bullions from which silver is recovered by electrolytic or fine refining. The silver bearing zinc concentrates are commonly processed by leaching and electrolytic methods. Silver is ultimately recovered as a byproduct from zinc plant residues. Canada is a leading silver mining country. Other important sources of silver are Mexico, die United States, Peru, the former U.S.S.R., and Australia. See also Mineralogy. 

The largest decrease in imported silver was from the United Kingdom and Switzerland. For these two countries import levels fell by 18.1 million ounces, primarily in the form of refined bullion. A total of 125.4 million troy ounces of refined silver were imported in 1986 with only 9.5 million troy ounces accounted for in other forms. 

The Male Intellect is evidently not equal to the contest with feminine rivals in the class rooms and in examinations. Miss Wren annexes three out of four silver medals which the Pharmaceutical Society contributes annually. .. and at the same time establishes her claim to the Periera medal. Miss Neve supplements this demonstration of the superiority of the sex by scooping in exactly the same proportion of the bronze medals awarded in the Minor course. This appropriation of the Society s bullion by two very young ladies. .. leaves but a scanty distribution of honours. .. among the masculine... 

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