Secondary zinc

Electrolytic and distillation processes are used to produce primary slab zinc at smelters from ores and concentrates, whereas redistillation is used to recover zinc from secondary zinc materials at both primary and secondary smelters (see Table 13) (64,65). In 1965, neady 60% of the primary slab zinc was manufactured by the distillation process. However, in 1975, electrolytic slab zinc became dominant and by 1996 its share increased to 78%. 

The production of secondary zinc requires only 20-25% of the energy required for primary zinc production. Only one-fourth of the total zinc produced is the secondary metal. The reason for such limited recycling is that the major application of zinc is in castings rather than in parts. 

The zinc industry employs 2200 workers at mines and mills and 1400 at primary smelters.14 The four primary zinc smelters in the U.S. are located in Illinois, Oklahoma, Tennessee, and Pennsylvania. There are ten secondary zinc recovery plants in the U.S.17... 

The material inputs and pollution outputs resulting from primary and secondary zinc processing are presented in Table 3.7. 

Secondary zinc Zinc scrap, electric arc Particulates... 

Secondary zinc Medium-grade zinc drosses, Zinc oxide fumes... 

D—Leclanche Zinc anode Carbon, silver chloride, and air Primary and secondary Zinc—air batteries, carbon—zinc batteries, and silver chloride-zinc batteries... 

The secondary zinc carbenoid 52 is trapped immediately by the organocopper before it can undergo a rearrangement of the type described in Section I.B.3. This methodology gives 1,1,3-trisubstituted allenes 51 in high yields as shown in Table 525. 

By contrast, when the first electrophile was an aldehyde as illustrated for the reaction of 276 with benzaldehyde, the resulting alkenylmetal presumably became part of a six-membered ring alkoxide 279 and hence so poorly reactive that it did not even react with iodine. However, treatment with Me3SiCl resulted in the silylation of the secondary zinc alkoxide and allowed iodinolysis to subsequently proceed, affording the (Z)-alkenyl iodide 280 (equation 132)165. Unfortunately, this protocol was not efficient for tertiary alkoxides generated by initial reaction of 276 with ketones. 

Raw Materials. In the early days, the raw materials were mainly zinc ores or concentrates for the direct process, or metal from zinc producers for the indirect process. Nowadays, zinc oxide manufacturers mainly use residues and secondary zinc. This fact, combined with the demand for chemical purity imposed by the users, means that processes have had to be modified and a number of purification techniques are used. 

Tribofilms Zinc di-isopropyl- dithiophosphate (primary) Zinc di-isobutyl- dithiophosphate (secondary) Zinc di-(p-tert- octyl)-phenyl- dithiophosphate... 

The remaining unreacted (RJ-20 can be trapped with an aldehyde such as pivalaldehyde giving the chiral homopro-pargylic alcohol in 87.5% ee.74 This kinetic resolution has been used to prepare anti/inti-vicinal amino diols in > 95% ee and dr > 40 l.75 In general, diorganozincs are more easily prepared in optically pure form. On another hand, secondary zinc reagents prepared by the direct zinc insertion to secondary alkyl iodides are obtained without stereoselectivity (Scheme 4).76... 

Zinc dust is produced from primary or secondary zinc metal by evaporation. The generated zinc vapor is condensed under controlled conditions under exclusion of air followed by sieving processes in order to obtain different particle size fractions [5.105]. The particle sizes of zinc dust are normally in the range 2 to 8 pm [5.105]. A product classed as fine quality shows a typical particle size of 3 pm whereas standard quality has particle size 8 pm [5.105]. 

Scheme 7-46 Carbocyclization from a secondary zinc reagent.

It is likely that some of the clinical features of cirrhosis of the liver such as loss of body hair, testicular hypofunction, poor appetite, mental lethargy, diflSculty in woimd healing, and night blindness may indeed be related to the secondary zinc-deficient state in this disease. In the future, careful clinical trials with zinc supplementation must be carried out to determine whether or not zinc is beneficial to patients with chronic liver disease. 

Where filter dust is sent to a secondary zinc processing plant, this increase is a very valuable benefit. The steel plant is charged for dust treatment by the zinc processor on a sliding scale which decreases as the zinc content increases. Therefore, for... 

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