Metallic, from

Fig. xn-2. Comparison of actual contact areas for (a) metal-on-metal and (b) plastic-on-metal. (From Ref. 2.)... 

Fig. XVin-24. TVimover frequencies for methanation using silica-supported metals. (From Ref. 270.)...

Anta J A, Jesson B J and Madden P A 1998 Ion-electron correlations In liquid metals from orbital-free ab initio molecular dynamics Phys. Rev. B 58 6124-32... 

What are the principal differences in physical and chemical properties between any one metal from Group I and any one metal from Group IV and any one transition metal How far can you explain these differences in terms of their different atomic structures ... 

Give an account of the principles underlying the extraction of metals from their oxides, illustrating your answer by specific examples. 

Using the electron transfer definition, many more reactions can be identified as redox (reduction-oxidation) reactions. An example is the displacement of a metal from its salt by a more reactive metal. Consider the reaction between zinc and a solution of copper(If) sulphate, which can be represented by the equation... 

Fig. 5.37 Comparison of the calculated phonon dispersion curve for Al with the experimental values measured using neutron diffraction. (Figure redrawn from Michin Y, D Farkas, M ] Mehl and D A Papaconstantopoulos 1999. Interatomic Potentials for Monomatomic Metals from Experimental Data and ab initio Calculations. Physical Review 359 3393-3407.)...

It is also used as a reducing agent in the production of pure uranium and other metals from their salts. The hydroxide (milk of magnesia), chloride, sulfate (Epsom salts), and citrate are used in medicine. Dead-burned magnesite is employed for refractory purposes such as brick and liners in furnaces and converters. 

Selenium is found in a few rare minerals such as crooksite and clausthalite. In years past it has been obtained from flue dusts remaining from processing copper sulfide ores, but the anode metal from electrolytic copper refineries now provide the source of most of the world s selenium. Selenium is recovered by roasting the muds with soda or sulfuric acid, or by smelting them with soda and niter. 

NaB(CgHg)4 (aqueous) metals from dilute HNO3 or HOAc solution (pH 2), or pH 6.5 in presence of EDTA. ... 

Obtain a sample of a metal from your instructor, and determine its density by one or both of the following methods ... 

The fundamental Ziegler-Natta recipe consists of two components the halide or some other compound of a transition metal from among the group IVB to VIIIB elements and an organometallic compound of a representative metal from groups lA to IIIA. Some of the transition metal compounds that have been... 

Microbial leaching of metals from ores is a promising adjunct to more aggressive metal recovery technologies (77), but is generally achieved by oxidative processes that generate very acidic waters. It seems unlikely that similar approaches will be of much value in removing contaminant metals and metalloids from soils. 

Soil. The first reported field trial of the use of hyperaccumulating plants to remove metals from a soil contaminated by sludge appHcations has been reported (103). The results were positive, but the rates of metal uptake suggest a time scale of decades for complete cleanup. Trials with higher biomass plants, such as B.juncea, are underway at several chromium and lead contaminated sites (88), but data are not yet available. 

When processing municipal solid wastes, an eddy current separation unit is often used to separate aluminum and other nonferrous metals from the waste stream. This is done after removal of the ferrous metals (see Fig. 1). The eddy current separator produces an electromagnetic field through which the waste passes. The nonferrous metals produce currents having a magnetic moment that is phased to repel the moment of the appHed magnetic field. This repulsion causes the nonferrous metals to be thrown out of the process stream away from nonmetallic objects (13). 

The depressed prices of most metals in world markets in the 1980s and early 1990s have slowed the development of new metal extraction processes, although the search for improved extractants continues. There is a growing interest in the use of extraction for recovery of metals from effluent streams, for example the wastes from pickling plants and electroplating (qv) plants (276). Recovery of metals from Hquid effluent has been reviewed (277), and an AM-MAR concept for metal waste recovery has recentiy been reported (278). Possible appHcations exist in this area for Hquid membrane extraction (88) as weU as conventional extraction. Other schemes proposed for effluent treatment are a wetted fiber extraction process (279) and the use of two-phase aqueous extraction (280). 

The overall extraction process is sometimes subdivided into two general categories according to the main mechanisms responsible for the dissolution stage (/) those operations that occur because of the solubiHty of the solute in or its miscibility with the solvent, eg, oilseed extraction, and (2) extractions where the solvent must react with a constituent of the soHd material in order to produce a compound soluble in the solvent, eg, the extraction of metals from metalliferous ores. In the former case the rate of extraction is most likely to be controUed by diffusion phenomena, but in the latter the kinetics of the reaction producing the solute may play a dominant role. 

Fluoroboric acid is used as a stripping solution for the removal of solder and plated metals from less active substrates. A number of fluoroborate plating baths (27) require pH adjustment with fluoroboric acid (see Electroplating). 

Liquid—Liquid Extraction. Among the various extractants available for the recovery of metals from aqueous streams, only 8-hydroxyquinoline derivatives are effective for the recovery of galHum from Bayer Hquor. A process has been developed and patented (7—12). Production began in 1980 in Salindres, France, foUowed in 1989 in Pinjarra, western AustraHa. 

The melt drag process drags molten metal from an orifice onto a cooled dmm (Fig. 4d) (45). Ribbons in excess of 20 cm can be produced having thicknesses from 25 to 1000 p.m (46). Gravity is used to force the molten Hquid from the orifice so that it touches the rotating dmm. The partially solidified alloy is then dragged onto the dmm forming wine or ribbons. 

In addition to oxidation itself, gas diffusion into the base metal can be more damaging than the actual loss of metal from the surface. Thus the loss in mechanical properties owing to diffusion of oxygen into niobium makes it more difficult to protect niobium against oxidation damage than molybdenum, even though molybdenum has less resistance to normal oxidation effects than niobium. 

Uses. The principal uses of NaBH are ia synthesis of pharmaceuticals (qv) and fine organic chemicals removal of trace impurities from bulk organic chemicals wood-pulp bleaching, clay leaching, and vat-dye reductions and removal and recovery of trace metals from plant effluents. 

Miscellaneous. Hydrochloric acid is used for the recovery of semiprecious metals from used catalysts, as a catalyst in synthesis, for catalyst regeneration (see Catalysts, regeneration), and for pH control (see Hydrogen-ION activity), regeneration of ion-exchange (qv) resins used in wastewater treatment, electric utiUties, and for neutralization of alkaline products or waste materials. In addition, hydrochloric acid is also utilized in many production processes for organic and inorganic chemicals. 

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