Metal concentrations

More concentrated metals are sometimes used despite declining metal efficiency. These catalysts are used to decrease loss of valuable products by absorption on the carrier, to minimize the amount of catalyst to be filtered, to aid in settling of the catalyst, and to facilitate difficult reductions. 

Base metals are much less active and are generally used in much higher metal concentration ranges up to 100%. 

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Table 8. Trace Metal Concentrations in Ash from Agricultural Biofuels and Wood-Fired Boilers, mg/kg...

Divalent copper, cobalt, nickel, and vanadyl ions promote chemiluminescence from the luminol—hydrogen peroxide reaction, which can be used to determine these metals to concentrations of 1—10 ppb (272,273). The light intensity is generally linear with metal concentration of 10 to 10 M range (272). Manganese(II) can also be determined when an amine is added to increase its reduction potential by stabili2ing Mn (ITT) (272). Since all of these ions are active, ion exchange must be used for deterrnination of a particular metal in mixtures (274). 

Flow Sheets. AH minerals processing operations function on the basis of a flow sheet depicting the flow of soHds and Hquids in the entire plant (6,13,14). The complexity of a flow sheet depends on the nature of the ore treated and the specifications for the final product. The basic operations in a flow sheet are size reduction (qv) (comminution) and/or size separation (see Separation, size), minerals separation, soHd—Hquid separation, and materials handling. The overaH flow sheet depends on whether the specification for the final mineral product is size, chemical composition, ie, grade, or both. Products from a quarry, for example, may have a size specification only, whereas metal concentrates have a grade specification. 

PGM Concentration. The ore mined from the Merensky Reef in South Africa has a maximum PGM content of 8.1 g/1, of which 50—60% is platinum, and 20—25% palladium. The PGMs are in the form of a ferroplatinum alloy, or as their sulfides, arsenides, or teUurides. The aim of the concentration process is to separate from the ore a cmde metal concentrate, having a PGM content of 60%. The majority of other metals, such as nickel and copper, are separated out at this stage for further refining. 

The raw precious metal concentrate is totally dissolved in hydrochloric acid—chlorine solution to form the soluble chloride ions of each of the metals. Silver remains as insoluble silver chloride and can be filtered off. Gold, in the form of [AuClJ, is extracted with, eg, tributyl phosphite or methyl isobutyl ketone. Base metals are also extracted in this step, and are removed from the organic phase by scmbbing with dilute hydrochloric acid (HCl). Iron powder is then used to reduce the gold species and recover them from the organic phase. 

New chelating ion-exchange resins are able to selectively remove many heavy metals in the presence of high concentrations of univalent and divalent cations such as sodium and calcium. The heavy metals are held as weaMy acidic chelating complexes. The order of selectivity is Cu > Ni > Zn > Co > Cd > Fe + > Mn > Ca. This process is suitable for end-of-pipe polishing and for metal concentration and recovery. 

The stabihty of zirconium sulfate solutions to spontaneous precipitation when heated to 70°C for 2 h was studied as a function of S02 Zr02 ratio and metal concentrations (209). The zirconium solutions were considered unstable at metal concentrations below 0.64 M or at S02 Zr02 ratios <1.2. 

The equivalent nickel content of the feed to the FCCU can vary from <0.05 ppm for a weU-hydrotreated VGO to >20 ppm for a feed containing a high resid content. The nickel and vanadium deposit essentially quantitatively on the cracking catalyst and, depending on catalyst addition rates to the FCCU, result in total metals concentrations on the equiUbrium catalyst from 100 to 10,000 ppm. 

The second important class of sorbents on CMSG basis for noble metal concentration are anion-exchangers, that is predetermined by their presence as acidocomplexes in hydrochloric acid solutions. 

The use of CO is complicated by the fact that two forms of adsorption—linear and bridged—have been shown by infrared (IR) spectroscopy to occur on most metal surfaces. For both forms, the molecule usually remains intact (i.e., no dissociation occurs). In the linear form the carbon end is attached to one metal atom, while in the bridged form it is attached to two metal atoms. Hence, if independent IR studies on an identical catalyst, identically reduced, show that all of the CO is either in the linear or the bricked form, then the measurement of CO isotherms can be used to determine metal dispersions. A metal for which CO cannot be used is nickel, due to the rapid formation of nickel carbonyl on clean nickel surfaces. Although CO has a relatively low boiling point, at vet) low metal concentrations (e.g., 0.1% Rh) the amount of CO adsorbed on the support can be as much as 25% of that on the metal a procedure has been developed to accurately correct for this. Also, CO dissociates on some metal surfaces (e.g., W and Mo), on which the method cannot be used. 

Parameter studies have shown that single-layer nanotubes can be produced by the arc method under a wide range of conditions, with large variations in variables such as the buffer gas pressure (100-500 Torr), gas flow rate, and metal concentration in the... 

Armoryde, n.pl. (Lead) skimmings. armselig, a. poor, wretched, paltry, armtreiben, v.t. (Metal.) concentrate. 

Konzentrattriibe,/. (Metal.) concentrate pulp, konzentrieren, v.t. concentrate, konzentriert. p.a. concentrated. — konzen-trierter Alaun, concentrated alum (aluminum sulfate). 

Figure 12 Effect of polymer concentration on the residual metal concentration [M] for p(AM-AANa). = Mg, O = Cu2-.

The influence of pH on the residual metal concentration [M] was studied at a constant polymer concentration of 10 mg/1 and copper sulphate concentration of 10 gm/1, results are shown in Table 4. It is clear that [M] decreases with increasing pH value. Results are given in Table 4, which shows that the concentration of Cu decreases with an increase in the pH value for each polymer used. This is attributed to the effect of the pH value on the active groups, which are distributed along the polymer chains. At a low pH value the amide groups... 

Internal stress of copper deposits may vary between —3.4MN/m (compressive) and -1- l(X)MN/m (tensile). In general, tensile stress is considerably lower in deposits from the sulphate bath than in those from cyanide solutions " , while pyrophosphate copper deposits give intermediate values. In cyanide solutions, tensile stress increases with metal concentration and temperature decreases if the free cyanide concentration is raised. P.r. current significantly lowers tensile stress. With some exceptions, inorganic impurities tend to increase tensile stress . Thiocyanate may produce compressive stress in cyanide baths . 

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