Removal of Zinc

Changes in fluid compositions include the reduction and removal of zinc from hydrauHc fluids. Zinc-free antiwear hydrauHc fluids, which may be ashless and free of phenol, were developed to meet wastewater treatment regulations for industrial sites by reducing the discharge of heavy metals and phenol into waterways. 

The removal of zinc chloride involves an extremely lengthy procedure. The plied sheets are passed through a series of progressively more dilute zinc chloride solutions and finally pure water in order to leach out the gelatinising agent. This may take several months. The sheets are then dried and consolidated under light pressure. 

In contrast, the selective dissolution or leaching-out by corrosion of one component of a single-phase alloy is of considerable practical importance. The most common example of this phenomenon, which is also referred to as parting , is dezincification, i.e. the selective removal of zinc from brass (see Section 1.6). Similar phenomena are observed in other binary copper-base alloys, notably Cu-Al, as well as in other alloy systems. 

In certain alloys and under certain environmental conditions selective removal of one metal (the most electrochemically active) can occur resulting in either localised attack, with the consequent possibility of perforation (plug type), or in a more uniform attack (layer type) that results in a weakening of the strength of the component. Although the selective removal of metals such as Al, Fe, Co, Ni and Cr from their alloys is known, the most prevalent form of de-alloying is the selective removal of zinc from the brasses —a phenomenon that is known as dezincification. 

The treatment with sulfuric acid produces a noticeable decrease in contact angle (i.e., improved wettability) due to the removal of zinc stearate and the formation of polar moieties on the mbber, mainly the creation of highly conjugated C=C bonds and the sulfonation of the butadiene units (Figure 27.1), i.e., the hydrogen of C—H bond is removed and replaced by a SO3 molecule, which is then hydrogenated to form a sulfonic acid at the site of attachment. The treatment is not restricted to the surface but also produces a bulk modification of the mbber. 

Transporting the dust to an offsite processor for thermal treatment and removal of zinc, chemical fixation, glassification, or fertilizer manufacture... 

The results of the study are summarized in part in Table 2 and demonstrate two useful consequences. The first result was an effective removal of nuisance transition metal ions 98% removal of zinc ion, 93% removal of nickel(II), 73% removal of copper(II) species. The second result, as a consequence, was the ability to reduce the fresh water intake by recycling reducing water usage by 67%. 

In zinc metalloenzymes. zinc is a selective stoichiometric constituent and is essential for catalytic activity. It is frequently present in numerical correspondence with the number of active enzymatic sites, coenzyme binding sites, or enzyme subunits Removal of zinc results in loss of activity. Inhibition by metal complexing agents is a characteristic feature of zinc metalloenzymes. However, no direct relationship holds between the inhibitory effectiveness of these agents and their affinity for ionic zinc. Although zinc is the only constituent of zinc metalloenzymes in vivo, it can be replaced by other metals m vitro, such as cobalt, nickel, iron, manganese, cadmium, mercury, and lead, as m the case of carboxy-peprida.ses. 

Initial cyclizadons were effected by the addition of an enamine to an imidate ester, both groups being suitably located by ligand coordination.263 An analogous process can be carried out on a thioimidate but a sulfide is formed and removal of sulfur with consequent ring contraction yields the corrin (100).264 These two complementary routes can be effected with different metal ions, nickel(II), palladium(II) and cobalt(III) in the first route, zinc(II) in the second. Removal of zinc ions easily provides the free corrin macrocycle. These two routes are summarized in Scheme 64. The sulfide contraction route was used in the Eschenmoser-Woodward total synthesis of vitamin Bn-265... 

About one third of the zinc in venous plasma is bound to a2-macroglobulin, and the remainder to albumin, with the exception of trace amounts bound to histidine and cysteine.1145 However, transferrin has been implicated in the uptake of zinc from the intestinal membrane, while albumin is involved in the removal of zinc from intestinal mucosal cells and its transport to the liver. Other ligands proposed for various transport processes for zinc are citric acid and picolinic acid.1146... 

Dezincification. Copper-Zinc alloys containing more than 15% zinc are susceptible to dezincification. In the dezincification of brass, selective removal of zinc leaves a relatively porous and weak layer of copper and copper oxide. Corrosion of a similar nature continues beneath the primary corrosion layer, resulting in gradual replacement of sound brass by weak, porous copper. Uniform dealloying in admiralty brass is shown in Figure 6.25.5,7,53,54... 

Hypersilyl lithium 1 and sodium 2 can be easily synthesized by the reaction of an excess of molten sodium or lithium powder with bis(hypersilyl)zinc in boiling nheptane (Eq. 1). After removal of zinc and sodium by filtration and cooling down the reaction mixtures to room temperature, the less soluble sodium derivative 2 precipitates nearly quantitatively in colorless crystals. A similar procedure has been utilized... 

Complete removal of zinc and thus inactivation of the enzyme can be accomplished in these systems at low D-PEN concentrations if a secondary scavenger chelator is added to the system. Such chelators bind metal that has been released from the enzyme but do not participate in the release.In the case of carboxypeptidase A, aM thionein (apo-metallothionen see Metallothioneins) inhibits catalysis by only about 10% over a 15-min period consistent with its action as a secondary chelator. However, in the presence of 250 aM D-PEN and aM thionein total inhibition is achieved in less than 15 min. D-PEN accelerates zinc equilibration between carboxypeptidase A and thionein (Scheme 1). This is accomplished by D-PEN catalyzing the release of Zn from the enzyme. Since D-PEN is in vast excess over both the enzyme and thionein, the enzyme-released zinc would be expected to bind to D-PEN first. However, since thionein binds zinc more tightly than D-penicillamine and can accept 7 moles of zinc per mole of thionein, it should be the ultimate acceptor of the released zinc. 

Removal of zinc by dialysis against 1,10-phenanthroline (Table IV) abolishes activity in proportion to the zinc content 18). On readdition of zinc to two gram atoms per subunit, activity is regained completely. Other metals such as Mn Ca Mg, and Cu are ineflFective in this regard. However, Mg and Mn have an activating effect on the zinc-containing enzyme. 

The circular dichroic spectrum of the zinc azoenzyme in solution contains one positive and two negative ellipticity bands at 420, 335, and 510 nm, respectively (Figure 3). On removal of zinc, almost the entire visible CD spectrum is abolished. It is completely restored on the addition of one gram atom of zinc per mole of enzyme. This eflFect of zinc on both the absorption and CD spectra suggests that the red color of the enzyme in solution may be caused by the formation of a zinc-azophenol coordination complex. Closely similar color changes can be observed by adding zinc to a typical azophenol compound, tetrazolyl-N-benzyloxycar-... 

ZnSO, 6H2O + H2O = ZnSO. 7H2O is associated with the current, since the removal of zinc sulphate from the solution in B, so long as saturation lasts, results in the dissolving, and therefore disappearance, of ZnSO. 6H2 0 while the taking up of zinc sulphate by the solution in a necessarily makes ZnSO. 7H2O separate out. 

Wastewater heatment, e.g., removal of zinc, removal of radioactive materials and nuclear wastes, recovery of nickel from plahng wastes, and phenol removal. 

Clinical management is supportive. Gastric decontamination should be considered only in the case of massive ingestions. Normal zinc levels in the blood are between 68 and 136pgdl . Chelating agents such as BAL (British Antilewisite 2,3-dimercapto-propanol) or calcium EDTA will enhance removal of zinc, but are not likely indicated unless the unusual case of massive chronic exposure. Hemodialysis and other methods of extracorporeal elimination are not necessary. 

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