Refined lead

While simulations reach into larger time spans, the inaccuracies of force fields become more apparent on the one hand properties based on free energies, which were never used for parametrization, are computed more accurately and discrepancies show up on the other hand longer simulations, particularly of proteins, show more subtle discrepancies that only appear after nanoseconds. Thus force fields are under constant revision as far as their parameters are concerned, and this process will continue. Unfortunately the form of the potentials is hardly considered and the refinement leads to an increasing number of distinct atom types with a proliferating number of parameters and a severe detoriation of transferability. The increased use of quantum mechanics to derive potentials will not really improve this situation ab initio quantum mechanics is not reliable enough on the level of kT, and on-the-fly use of quantum methods to derive forces, as in the Car-Parrinello method, is not likely to be applicable to very large systems in the foreseeable future. 

The most important ores are bismuthinite or bismuth glance and bismite. Peru, Japan, Mexico, Bolivia, and Canada are major bismuth producers. Much of the bismuth produced in the U.S. is obtained as a by-product in refining lead, copper, tin, silver, and gold ores. 

Lead [7439-92-17, Pb, is an essential commodity ia the modem iadusttial world, ranking fifth ia tonnage consumed after iron (qv), copper (qv), aluminum (see Aluminumand aluminum alloys), and 2iac (see Zinc and zinc alloys). In 1993, the United States accounted for 30% of the 4,450,000 metric tons of refined lead consumed by the Western world. Slightly over half of the lead produced ia the world now comes from recycled sources (see Recycling, NONFERROUS LffiTALS). 

Bismuth concentrates in the dorn until the last stages of cupeUation, when it is oxidized and removed with the Htharge. After the last Htharge has been removed, it is often necessary to add bars of refined lead to provide more Htharge to carry off the last traces of bismuth. The dorn metal is then cast into bars for marketing. 

The lead contains residual calcium and magnesium that must be removed by chlorination or treatment with caustic and niter. The molten lead is pumped or laundered to the casting kettles in which it is again treated with caustic and niter prior to mol ding, After a final drossing, the refined lead is cast into 45-kg pigs or 1- and 2-t blocks. 

A world production summary of primary and refined lead is given in Table 5. U.S. consumption for the same period is given in Table 6. 

Table 5. World Mine and Refined Lead Production, 1(P t...

A conservative estimate of the total value of the products from the mineral industry is ca 3.9 trillion ia terms of 1992 dollars (4). This estimate does not include the value of products derived from secondary sources such as recycling (qv) or reclamation. Secondary recovery is significant for certain commodities. For example, in 1992 ca 30% of the world steel (qv) production, 46% of the world refined lead output, 15% of the world refined copper (qv) production, and ca 30% of the aluminum (see Aluminumand ALUMINUM alloys) output from the Western world were clearly identified as being derived from scrap. The value of the world mineral commodity export trade in 1992 was ca 616,698 million ia 1992 dollars. This accounted for ca 18% of all commodities exported (4). 

Arm-binde, m. sling, -blei, n. refined lead (from which the silver has been removed). 

Frisch-blei, n. refined lead, -dampf, m. live steam, -eisen, n. refined iron, frischen, v.t. fine, refine revive (litharge) ... 

Weichblei, n. soft lead, refined lead, weichbleibend, p.a. remaining soft, non-hardening. 

Marchandise H, Vandendriessche S (1985) The Certification of the Impurity Contents (Ag, As, Bi, Cd, Ni, Sb, Se, Sn, Te, T1 and Zn) in Three Grades of Lead, Electrolytically Refined Lead BCR No 286, Thermally Refined Lead BCR No 287, Lead with Added Impurities BCR No 288. European Commission Report EUR 9665 EN. Community Bmeau of Reference, Brussels. Merry f (1995) Reference materials for monitoring nutrients in sea water environment, approach, preparation, certification and their use in environmental laboratories. Fresenius J Anal Chem 352 148-151. 

The problem of the separation of zinc and lead from each other is encountered not only in the refining of zinc but also in the refining of lead. When lead is subjected to refining by the Parkes process, a certain amount of zinc, which is not insignificant, is introduced into the refined lead bullion. This zinc impurity may be removed by distillation. 

The U.S. is the world s largest recycler of lead scrap and is able to meet about 72% of its total refined lead production needs from scrap recycling. The secondary lead industry consists of 16 companies that operate 23 battery breakers-smelters with capacities of between 10,000 and 120,000 t/yr five smaller operations with capacities between 6000 and 10,000 t/yr and 15 smaller plants that produce mainly specialty alloys for solders, brass and bronze ingots, and miscellaneous uses. 

Betts An electrolytic process for refining lead and recovering silver and gold from it. The electrolyte is a solution of lead fluosilicate and hydiofluosilicic acid. The other metals collect as a slime on the anode and are retained there. Developed by A.G. Betts in 1901, first operated at Trail, British Columbia, in 1903, and now widely used in locations having cheap electric power. 

The complexes A2CrI6 (A = T1 or In) contain isolated [Crl6]4" units in the a phase there is a random distribution of Jahn-Teller distorted octahedra, which are elongated perpendicular to the c axis, and below 77 K the j8-phase forms in which die directions of elongation are ordered (Table 36). Refinement leading to axially compressed octahedra in the [Crl6]4- units [Cr—I, 3.046 A (4 x), 2.738 A (2 x J]280 is said2 to be due to an inadequate model. 

A refinement of the statistical theory can be made by repeating the calculation with use of the bond numbers given by the preceding calculation as probabilities, until a self-consistent set is obtained. This refinement leads to small changes only in the bond numbers. 

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